Daily explosions, incandescent block avalanches, lava flows, and ash plumes during September 2022-February 2023

Eruptions recorded since 1628 CE from Sangay, the southernmost of Ecuador’s volcanoes, have been characterized by pyroclastic flows, lava flows, ash plumes, and lahars. The current eruption began in March 2019 and has more recently consisted of daily explosions, avalanches, ash plumes, and crater incandescence (BGVN 47:09). This report covers activity during September 2022 through February 2023 and describes similar events of daily explosions, incandescent avalanches, lava flows, and ash plumes, based on information from Ecuador's Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Servicio Nacional de Gestión de Riesgos y Emergencias (SNGRE), the Washington Volcanic Ash Advisory Center (VAAC), and various satellite data.

During September 2022 through February 2023, IG-EPN reported daily explosions, gas-and-steam and ash plumes that rose as high as 8.3 km above the crater, and frequent crater incandescence, often accompanied by incandescent block avalanches of material descending the flanks of the volcano. The highest ash plume occurred on 4 November and drifted NW, W, and SW. Explosions occurred nearly every day, ranging from 3-2,040, the most of which occurred on 4 October (figure 143). The average number of explosions was 563, the highest average number of explosions was 950, which occurred during December 2022 (table 12).

Figure 143. Graph showing the number of daily explosions at Sangay during September 2022 through February 2023. The number of explosions markedly decreased during early January 2023 and remained relatively low through February 2023. Data courtesy of IG-EPN (September 2022-February 2023 daily reports).

Table 12. Monthly summary of explosions and plume heights recorded at Sangay during September 2022 through February 2023. Data courtesy of IG-EPN (September 2022-February 2023 daily reports).

During September, activity consisted of 146-1,152 daily explosions and gas-and-ash emissions that rose as high as 2 km above the summit crater during 12-13, 18-24, and 29-30 September and drifted SW, W, WNW, NW, N, and NE. Seismicity consisted of near-daily long-period (LP) and emission tremor (TRE) events. According to the Washington VAAC, ash emissions rose 500-2,700 m above the crater rim and drifted SW, WSW, W, NW, S, and N. During 1-2 September crater incandescence was visible, accompanied by blocks that rolled down the E flank. During the afternoon and night of 14-15 September incandescent ejecta was observed. Strombolian activity and crater incandescence was visible during the night and early morning during 17-18 September (figure 144). Continuous gas-and-ash emissions rose 1.5 km above the summit and drifted W in the morning. Light ashfall was reported in Cebadas, and stronger ashfall was detected in Rayoloma during 18-19 September; both towns are located to the NW of the volcano. During 22-23 September ash emissions rose 1 km above the crater rim and drifted W, resulting in ashfall in Chauzán in the Chimborazo province.

Figure 144. Webcam image showing incandescent material ejected above Sangay’s crater at 0059 on 18 September 2022. Courtesy of IG-EPN Daily report.

Activity persisted during October, with 154-2,040 daily explosions, occasional crater incandescence, and gas-and-ash emissions rising as high as 2.5 km above the crater during 26-27 October that drifted W, N, NW, SW, and SE. The Washington VAAC reported that ash emissions rose 570-2,370 m above the crater rim and drifted W, SW, NW, SE, N, SSW, NE, and E. During 2-5 October several explosions were accompanied by incandescent blocks descending the SE flank. Nighttime incandescence was intermittently visible in the upper part of the volcano. During 11-17, 19-21, and 24-27 October incandescent material descended the SE flank. A collapse of the lava flow front generated a small pyroclastic flow that descended the upper part of the SE drainage during 12-13 October. According to GOES-16 satellite images, an ash cloud was detected during the early morning of 14 October that rose 2,370 m above the crater and drifted W. There was a report of ashfall in Guamote as a result. During the night of 18-19 October summit crater incandescence was visible and a lava flow traveled down the SE flank. A lava flow was reported descending the SE flank during 22-23 October. During the night of 25 October strong incandescence was visible in the crater accompanying a lava flow on the SE flank. In the early morning, reports of loud noises were reported in Salitre and Naranjito, which IG noted was likely associated with the explosive activity. Early morning crater incandescence on 29 October was accompanied by a continuous ash emission that rose 1 km above the crater rim and drifted NW. Slight ashfall was observed in Huamboya Canton in the Morona Santiago province.

There were 80-1,380 daily explosions detected during November, in addition to LP and TRE-type events, gas-and-ash emissions that rose as high as 8.3 km above the crater and drifted generally W and NW, and nighttime crater incandescence. According to the Washington VAAC, gas-and-ash emissions rose 570-3,000 m above the crater and drifted in multiple directions. During 31 October to 1 November crater incandescence was accompanied by incandescent avalanches of material along the SE flank and some ashfall in nearby towns. According to a GOES-16 satellite image, an ash cloud was visible starting at 0520 on 4 November, and around 0700 pyroclastic flows descended the Volcán drainage on the SE flank (figure 131). By 0840 the ash plumes had intensified, rising to a height of 8.3 km above the crater and drifting NW, W, and SW. Light-to-moderate ashfall was recorded in the cities of Riobamba, Guamote, Colta, Alausí, Pallatanga, Chambo, and Chunchi during 3-4 November. During 4-5 November pyroclastic flows traveled along the Volcán drainage (figure 145). An ash plume rose 3 km above the crater and drifted NW, resulting in moderate ashfall in Chimborazo, Bolivar, and Los Rios.

Figure 145. Webcam image showing pyroclastic flows descending the SE flank of Sangay during the morning of 4 November 2022. Courtesy of IG-EPN Daily report.

SNGRE reported that on 9 November a moderate amount of ash fell in Zuñac, in the province of Morona Santiago. During the night and early morning of 9-10 November when the volcano cleared for short periods, gas-and-ash emissions, explosions, and crater incandescence were observed, accompanied by an incandescent avalanche of material descending the SE flank. Crater incandescence and an avalanche of material were also visible during clear weather, moving down the SE flank during 10-14, 17-23, and 26-29 November. On 16 November at 0200 the seismic station recorded seismic signals that corresponded to lahars, though cloudy weather obscured views of the volcano. Heavy rain was reported during 17-18 November which resulted in small mud and debris flows down the SE flank. During the night of 21 November crater incandescence was observed in addition to a lava flow that traveled down the SE flank. On 24 November incandescence was recorded in the upper part of the volcano in the early morning, accompanied by pyroclastic flows. An active lava flow was reported on the SE flank during the night and early morning of 25-26 November. Nighttime crater incandescence and pyroclastic flows on the E flank on 29 November.

Activity during December consisted of 34-1,320 daily explosions, gas-and-ash emissions that rose as high as 2.5 km above the crater during 30 November-1 December and 3-4 December and drifted SE, NNE, NE, W, SW, and NW and seismicity consisting of LP and TRE-type events. According to the Washington VAAC, satellite-based images showed gas-and-ash emissions rising to 570-2,700 m altitude and drifting in different directions. Nighttime and early morning crater incandescence was often visible in clear weather, sometimes accompanied by incandescent block avalanches. During 30 November-1 December, 12-15, and 17-18 December an active lava flow was detected on the SE flank of the volcano. During 1-2 and 5-8 December a pyroclastic flow was observed descending the SE flank. During 28-29 December light ashfall was reported in Cebadas.

During January 2023 activity was often obscured due to cloud cover and the number of daily explosions notably decreased; there were 25-824 daily explosions recorded. Gas-and-ash emissions rose as high as 2.5 km above the crater during 16-17 January and drifted in multiple directions (figure 146). The Washington VAAC reported that gas-and-ash emissions rose 570-1,770 m above the crater and drifted SW, WNW, N, NW, W, SE, S, and NE. Crater incandescence was intermittently visible on clear weather days. During the night and early morning of 9-11 January, a lava flow was observed on the SE flank. An incandescent avalanche of material was visible on the SE flank during 21-22 January.

Figure 146. Webcam image of a white gas-and-ash plume rising 2.5 km above the crater of Sangay on 16 January 2023. The dark spots on the image is material on the camera lens. Courtesy of IG-EPN Daily report.

Low activity continued during February, consisting of 3-333 daily explosions. TRE events continued to be detected throughout the month. The Washington VAAC reported that ash emissions rose 500-1,800 m above the crater and drifted NE, S, N, NW, W, SW, and SE. During 14-15 February crater incandescence was visible and an active lava flow traveled 500 m below the summit on the SE flank. During 18-19 November incandescent material rolled down the SE flank. During the night of 21-22 February crater incandescence was accompanied by a lava flow on the S flank. Gas-and-ash emissions rose 1.2 km above the crater and drifted S and NW, based on satellite images during 21-24 February. During 26-28 February continuous ash emissions rose 1.5-2 km above the crater and drifted SW and W.

Satellite data. Thermal activity was consistently strong throughout the reporting period due to crater incandescence, block avalanches, and lava flows primarily affecting the SE flank. This activity was detected by the MIROVA hotspot detection system (figure 147) and the MODVOLC Thermal Alerts system, which detected 108 hotspots. Sentinel-2 infrared satellite imagery showed incandescence block avalanches and lava flows descending the SE flank and crater incandescence (figure 148). Frequent, strong sulfur dioxide plumes were captured by the TROPOMI instrument on the Sentinel-5P satellite; many of these plumes exceeded 2 Dobson Units (DUs) and drifted in different directions (figure 149).

Figure 147. Thermal activity at Sangay was relatively strong throughout the reporting period of September 2022-February 2023 due to frequent crater incandescence, incandescent block avalanches, and lava flows on the flanks. Courtesy of MIROVA.

Figure 148. Strong thermal activity was visible in these Sentinel-2 infrared satellite images of Sangay on 18 September 2022 (top left), 27 December 2022 (top right), 31 January 2023 (bottom left), and 25 February 2023 (bottom right). Incandescent block avalanches and lava flows primarily descended the SE flank, as shown here. Images use “Atmospheric penetration” rendering (bands 12, 22, 8A). Courtesy of Sentinel Hub Playground.

Figure 149. Strong sulfur dioxide plumes from Sangay were frequent throughout the reporting period, as shown here on 13 September 2022 (top left), 26 October 2022 (top middle), 17 November 2022 (top right), 29 December 2022 (bottom left), 4 January 2023 (bottom middle), and 17 February 2023 (bottom right). Each of these plumes exceeded 2 Dobson Units (DUs) and drifted in different directions. Sangay is located toward the bottom of the satellite images with sulfur dioxide plumes; Colombia’s Nevado del Ruiz is the topmost symbol that also frequently emits sulfur dioxide. Data is from the TROPOMI instrument on the Sentinel-5P satellite. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Servicio Nacional de Gestion de Riesgos y Emergencias (SNGRE), Samborondón, Ecuador (URL: https://www.gestionderiesgos.gob.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard MD 20771, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Information is preliminary and subject to change. All times are local (unless otherwise noted)

January 1974 (CSLP 09-74)

Continuing eruptive activity with frequent explosions

Card 1774 (11 January 1974) Continuing eruptive activity with frequent explosions

"Continual quiet eruption. Much explosive activity. Smoke plume leaves crater every 20-30 minutes. No data about flows or ejecta."

Information Contacts: Minard Hall, Escuela Politécnica Nacional, Quito.

July 1975 (CSLP 50-75)

Continued activity; block lava flows and ash emissions

Card 2214 (08 July 1975) Continued activity; block lava flows and ash emissions

The following represents a brief description of the continuing volcanic activity of the almost unknown and inaccesible volcano El Sangay. A scientific group visited the volcano during the week of 24 May to 1 June 1975.

New blocky lava flows, that began before February 1975, continue advancing down the west side of this composite cone. The flows apparently originate in the summit crater (5,160 m) as suggested by the brilliant red glows seen in the crater at night and by occasional small explosions and blasts of dark gray smoke that are quickly dispersed by the high winds. The flows descend to about 3,800 m where they have fanned out and probably cover ~2 km² in total area. The flow rock appears to be a basaltic andesite with olivine phenocrysts; milky white quartz xenocrysts are notably abundant to the total exclusion of all other types of inclusions.

The summit crater appears to be formed by at least two vents, one of which is emitting white clouds of vapor and sulfurous fumes almost continuously and another which emits infrequent blasts of dark gray clouds. The crater rim was continually being sandblasted by fine volcanic sand and ash, coming from the vents below, but no larger ejecta were observed. The strength of the fumes and the lack of visibility precluded a reconnaissance of the summit vents.

The west side (leeward side) of the volcano is covered by an approximate 70-m-thick sequence of thinly-bedded ashes, which probably corresponds to the renovation of activity in the 1940's after a 15 year dormancy. Since the 1940's the activity has been more Strombolian, marked by very muld but continuous ash eruptions and occasional lava flows. Evidence of past lahar activity is everywhere. The recent activity of El Sangay presents no danger to man.

Information Contacts: Minard Hall, Escuela Politécnica Nacional, Quito.

July 1976 (NSEB 01:10) Cite this Report

Explosions, lava flows, and ashfall; two deaths following 10 August explosion

A recent expedition, 28 July-9 August, to the stratovolcano Sangay reports the following activity.

Mild explosive activity occurred at intervals of 6-12 hours with the expulsion of white, vapor-rich, sulfurous plumes that rose approximately 100 m. Very acidic rains were falling W of the cone. The NW side of the cone was covered by still-hot lava flows (basaltic andesite) from the last few years. A new lava flow was leaving the S crater and has descended W several hundred meters. A light coating of ash covered the snow on the SW side of the cone. No other activity was observed on the other sides of the volcano. It appeared that this activity has continued steadily from last year. A small parasitic cone of approximately 50 m height was recently discovered on the lower E flank. It is not presently active.

On 10 August an independent British team, which apparently included no geologist, reached the 3,700 m basecamp level on the volcano. Two days later six members ascended to within 300 m of the summit. At 1230 an explosion produced a black mushroom cloud that reached an estimated 300 m above the volcano and dropped ejecta (to 35 cm) on the group. Later, search parties found three injured, one dead, and another had not been found 5 days after the accident. Helicopter rescue attempts were abandoned on 18 August after two days of heavy snowfall.

Information Contacts: M. Hall, Escuela Politécnica Nacional, Quito; J. Aucott, British Embassy, Quito.

July 1983 (SEAN 08:07) Cite this Report

Eruption continues with ash emission every 10 minutes

. . . During overflights on 4 and 6 August, Maurice Krafft observed frequent ash emission from 1 of 4 WSW-ENE-trending vents in the summit area. The westernmost vent was filled by a blocky lava dome 15-20 m in diameter, partially covered by ash. ENE of the dome, explosions at least every 10 minutes from a 15-m-diameter crater produced thick black cauliflower-shaped ash columns 100-300 m high. Winds blew ash from these explosions to the SW, toward the dome. Each explosion also triggered small ash avalanches from deposits on the upper W and SW flanks. The largest of the four vents, ENE of the active crater, was 80-100 m across and contained two fumaroles that were emitting vapor. The fourth vent, 20-30 m in diameter and slightly N of the trend of the other 3 vents, was not active during the overflights.

Minard Hall reported that activity was generally similar when he visited the volcano in 1976. Although lava was oozing from the westernmost vent at that time, it had not yet built a dome.

Information Contacts: M. Krafft, Cernay, France; M. Hall, Escuela Politécnica, Quito.

August 1988 (SEAN 13:08) Cite this Report

Explosions, lava flow

Geologists from GEVA visited the volcano in June and August. Throughout June, only summit fumarolic activity was noted, but in early August, explosions every 5 minutes ejected small ash clouds. A warning was issued to aircraft flying in the vicinity of Sangay on 4 August at 2249. On 11 August, a new lava flow extended from the summit ~ 200 m below the crater rim. Blocks from the crumbling flow front rolled down the W and SW flanks to 4,400 m altitude. Larger avalanches from the flow front were observed on 12 August between 1400 and 1500. At 0005 on 13 August, explosions from a S-flank vent covered the volcano's S slope with red-hot lava blocks up to 1 m in diameter. Explosions ejecting blocks and ash continued until 0900. By 1600, the flow had moved to ~ 400 m below the crater rim and numerous blocks fell from the two lobes of the flow front.

Information Contacts: J. Durieux, GEVA, Lyon, France; G. Heiken, LANL, Los Alamos.

March 1996 (BGVN 21:03) Cite this Report

Phreatic explosions, blue gas plumes, crater glow, and dome rockfalls

From 24 November to 12 December 1995, the first detailed study of Sangay volcano (figures 1 and 2) was carried out by an Instituto Geofísico/ORSTOM team (Escuela Politécnica Nacional, Quito), with helicopter support from the Ecuadorian Army and the assistance of five local guides from Alao. During this time, activity was characterized by continuous fumarolic steaming, frequent phreatic explosions, occasional crater glow, and dome rockfalls. Previous reports from August 1976, August 1983, and June-August 1988 (SEAN 01:10, 08:07, and 13:08) identified four summit vents aligned WSW-ENE, which are here numbered from 1 to 4 going from W to E.

Figure 1. Present cone of Sangay in December 1995 viewed from the base camp 4.3 km SW. The recent pyroclastic-flow deposit on which the campsite is located is in the foreground, among the badlands corresponding to an older edifice. At the summit can be seen the W lava dome (Vent 1) and its now inactive lava tongues. Photo by M. Monzier, courtesy of ORSTOM.

Figure 2. View of the Sangay summit in December 1995 looking NE from the base camp showing the lava dome and associated lava flows from Vent 1. Behind this dome, a steam plume rises from the main crater (Vent 3). Photo by M. Monzier, courtesy of ORSTOM.

In 1976, Vent 1 consisted of a fracture from which lava was slowly issuing, but by August 1983 it had built a lava dome. This small dome was apparently more active in August 1988, and sent a lava flow 400 m down the W flank, where it split into two lobes. In late 1995 this dome was possibly still growing, and was the source of some fumarolic activity and many rockfalls, making the W and SW slopes of the cone dangerous to cross. Apparently there have been no new lava flows from this vent since August 1988. Vent 2, a small 15-m-diameter crater immediately ENE of Vent 1 has frequently been the site of explosive activity (1976 and 1983), but apparently was less active in 1988 and was quiet during the 1995 visit. The ENE crater (Vent 4) remained inactive but with occasional fumarolic activity.

Vent 3, at 80-100 m across, is the largest and deepest crater. In 1976 and 1983 only fumarolic activity was observed from this crater, but lava was reported in 1988. During the 1995 visit it was the site of frequent phreatic explosions, some separated by hours, others coming as often as every 26 minutes. Several explosions were followed by a rhythmic, pulsating roar that lasted for up to 50 oscillations. White vapor plumes, ejected with the audible explosions, rose several hundred meters above the summit. Light blue gas plumes and occasional red glow at night immediately above this crater implied the presence of lava. Frequent rockfalls from the upper S flank of the cone suggested that some lava may be escaping, breaking off, and rolling down the S slopes.

During the visit a portable MEQ-800 Sprengnether seismograph with a vertical, 1-Hz L4C geophone was operated at the La Playa base camp, 4.3 km SW of the main crater at 3,600 m elevation. A preliminary study of the smoked-paper seismograms showed three types of seismic signals, frequently associated with observed explosions in the crater (figures 3 and 4): tremor, long-period, and hybrid events. Tremor events had a monochromatic signature with a period of 1 second and lasted < 60 seconds. The long-period events had emergent arrivals and a constant period of ~0.7 seconds; they were often associated with observed explosions. Hybrid events began with a long-period event (0.7 seconds) and were followed by a signal similar to that of the tremor (1 second). Some hybrid events were associated with audible and observed explosions followed by a roar like pulsating, rhythmic exhalations. No local high-frequency events were detected.

Figure 3. Types of volcanic earthquakes at Sangay recorded by the seismic station 4.3 km SW in December 1995. Courtesy of ORSTOM.

Figure 4. Volcanic seismicity recorded at Sangay, 26 November-10 December 1995. Courtesy of ORSTOM.

Recent lavas and pyroclastic-flow, debris-flow, and lahar deposits are ubiquitous around the cone and testify to Sangay's nearly continuous activity. The site of the La Playa camp (figure 5) is on an andesitic pyroclastic-flow deposit containing bombs up to 4 m in diameter which was emplaced between 1956 and 1965. An accident with two fatalities happened in August 1976 (SEAN 01:10). A previously unreported accident occurred in December 1993 when the main crater exploded just as two mountaineers looked over its rim. Both were blinded by the heat and fragment impacts and remained lost in the jungle on the cone's lower slopes until rescued three days later.

Figure 5. Preliminary geological/structural map of Sangay volcano based on fieldwork, aerial photographs, and 1:50,000 topographic maps from the Instituto Geografico Militar, Quito. Key: M = metamorphic formations; I, II, III = successive volcanic edifices; C1 and C2 = avalanche calderas; AD = avalanche deposits. Campsites are shown as black dots (La Playa = basecamp, Z = Zumbacocha and D = Duende are secondary camps).

In addition to the present cone (Sangay III), two previous edifices were identified and sampled, both of which had been destroyed by collapse. The remnant calderas are found on the E side of the present cone and are breached E toward the Amazon plain. Their probable avalanche deposits lie at the E foot of the cone. A preliminary geologic map of Sangay (figure 5) shows the three successive edifices and the two associated calderas. Edifice I is mainly built of lava, whereas edifices II and III contain both lava and pyroclastic deposits. The products of edifices I and II appear to be more varied in composition (greater differentiation) than those of Sangay III, where mafic andesites seem to predominate.

This isolated stratovolcano E of the Andean crest is one of Ecuador's most active volcanoes having been in frequent eruption for the past several centuries. The steep-sided glacier-covered volcano towers above the tropical jungle on the E side; on the other sides heavy rains have caused plains of ash to be sculpted into steep-walled canyons up to 600 m deep. The first historical eruption was reported in 1628, and more or less continuous eruptions took place from 1728 until 1916, and again from 1934 to the present.

Information Contacts: M. Monzier and C. Robin, ORSTOM, A.P. 17-11-6596, Quito, Ecuador; M. Hall, P. Mothes, and P. Samaniego, Instituto Geofísico, Escuela Politécnica Nacional, A.P. 17-01-2759, Quito, Ecuador.

April 2006 (BGVN 31:04) Cite this Report

Some conspicuous plumes during 2004-2005; climber's photos from January 2006

Our previous report was in 1996 (BGVN 21:03); this report covers the time interval January 2004 to January 2006. According to a 2004 annual summary on the Instituto Geofísico (IG) website, Sangay was one of the most active volcanoes in Ecuador, and has been in eruption for ~ 80 years. Its isolated location (figure 6) has meant it has been thought of as a relatively small hazard risk. For this reason, monitoring has been less than for other Ecuadorian volcanoes. Thermal, visual, and satellite monitoring during 2002-2004 confirmed the central crater as the source of frequent explosions and continuing steam-and-gas emissions.

Figure 6. Satellite imagery showing the region around the city of Riobamba (center) in Ecuador), including Sangay (lower right), Chimborazo (upper left), Tungurahua (upper right), and Licto (center) volcanoes. An eruption plume can be discerned coming from Tungurahua, but the date of the image is unknown. The city of Riobamba is about 50 km NW of Sangay. Courtesy of Google Earth.

During 2004 observers did not see lava flows or pyroclastic flows. An abnormally large eruption cloud was detected on 14 January 2004; it contained dominantly steam and gases, with minor ash content. Although only clearly detected and reported then, such events are thought to occur with considerable frequency.

Ramon and others (2006) summarized Sangay's activity as continuously erupting since 1934. Thermal images taken during the last three years showed that only one of the three summit craters was active and documented a lack of new, visible lava flows.

On 14 January 2004 a plume from Sangay was observed around 0500. The plume extended about 45 km E and most likely contained ash. During this time a hotspot was also visible on the satellite imagery. On 27 January 2004 a narrow ash plume emitted by Sangay rose to 6 km altitude and drifted SW.

On 1 May 2004, based on a pilot's report, the Washington VAAC noted that ash from an eruption at Sangay produced a plume to a height of ~ 6 km altitude at 1750. Ash was not visible on satellite imagery.

On 28 December 2004 around 0715 a plume from Sangay, most likely composed of steam with little ash, was detected. The plume was E of the volcano's summit at a height of ~ 6.4 km altitude. A hotspot was prominent on satellite imagery, but ash was more difficult to distinguish.

On 16 October 2005 around 0645 Sangay emitted an ash plume. The plume moved SSW very slowly, corresponding to a possible height of ~ 6.7 km altitude. By 0900 the plume was too thin to be visible on satellite imagery and thunderstorms developed in the area, further obscuring the ash cloud. Based on information from the IG, on 26 October 2005 the Washington VAAC noted that ash was seen over Sangay at 0758. No ash was visible on satellite imagery.

Climber's photo journal. Climbers Thorsten Boeckel and Martin Rietze created a website briefly describing a trek to Sangay's summit during 4-12 January 2006. Several of their posted photos from that trip appear here (figures 7-10; unfortunately, the photos, which are strikingly beautiful, were generally presented without much geographic context). The team included at least one local guide and was aided by horses. Settlements on the approach and return included the mountain village St. Eduardo, which they described as ~ 50 km S of Riobamba.

Figure 7. A vista of Sangay at nightfall in early January 2006. Direction of view is approximately WNW. Photo credit to Boeckel and Rietze.

Figure 8. Photograph documenting the climbers tent camp high on the snowbound slopes of Sangay during their descent. Exact location on Sangay unknown; this was labeled "day 4/5," and should correspond to 7 or 8 January 2006. Photo credit to Boeckel and Rietze.

Figure 9. A topographic high forming part of the Sangay structure, gently steaming, apparently seen from the summit. This corresponds to 7 or 8 January 2006. Photo credit to Boeckel and Rietze.

Figure 10. A crater on Sangay as seen by the climbers from the summit or upper flanks, described by them as the "snow covered east crater." This photo corresponds to 7 or 8 January 2006. Photo credit to Boeckel and Rietze.

Except for some degassing, the group saw no other activity. Although local residents indicated that the last eruption had occurred about 2 months prior to their visit, intermittent eruptions pose hazards to climbers; in 1976 two climbers were killed by explosions from Sangay (SEAN 01:10).

Reference. Ramón, P., Rivero, D., Böker, F., and Yepes, H., 2006, Thermal monitoring using a portable IR camera: results on Ecuadorian volcanoes in "Cities on Volcanoes IV"; 23-27 January 2006.

Information Contacts: P. Ramón, Instituto Geofísico-Departamento de Geofísica (IG), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador; Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Thorsten Boeckel and Martin Rietze, c/o Kermarstr.10, Germerswang, D-82216, Germany (URL: http://www.tboeckel.de/).

March 2008 (BGVN 33:03) Cite this Report

Conspicuous ash plumes, October 2006-December 2007

Our previous report on Sangay (BGVN 21:03) described occasional, but sometimes conspicuous, steam and/or ash plumes between January 2004 and January 2006. The current report continues coverage of plume emissions through December 2007.

Sangay has continued to erupt, sending ash plumes up to an altitude of about 11 km. A summary of plume activity is indicated in table 1. The information is from the Washington Volcanic Ash Advisory Center (VAAC), and is based on reports from the Guayaquil Meteorologic Watch Office, pilot reports, satellite imagery, and the Instituto Geofísico-Departamento de Geofísica (Escuela Politécnica Nacional). We did not receive any report of activity during the period February 2006 through September 2006, or during the first three months of 2008.

Table 1. Ash plume advisories about Sangay activity, October 2006 through December 2007. Courtesy of the Washington VAAC.

According to a report from the Instituto Geofísico, activity at Sangay increased at the end of 2006 through the beginning of 2007. They reported that a thermal anomaly was detected by satellite imagery during several days in December 2006. During that time, mountain guides near the volcano observed the fall of incandescent rocks down the volcano's flanks at night and a recent deposit of ash that was sufficiently deep to affect birds, rabbits, and other small animals. The report indicated that the Instituto Geofísico has not installed monitoring instrumentation near Sangay because of a significant logistics problem in maintaining them in this inhospitable area, and also because the area is uninhabited and thus poses no direct human risk. However, the report notes that because ash emissions from Sangay may pose problems for aircraft in the S, SE, and SW parts of the country, the Instituto maintains contact with the civil aviation authority.

Information Contacts: Washington Volcanic Ash Advisory Center, Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); P. Ramón, Instituto Geofísico-Departamento de Geofísica (IG), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador.

January 2009 (BGVN 34:01) Cite this Report

Thermal anomalies and a minor ash plume during 2008

Ash plumes were reported between October 2006 and December 2007 (BGVN 33:03). Thermal anomalies have been detected between 27 March and 4 December 2008 (table 2). A minor ash plume was seen on satellite imagery and by pilots drifting WNW on 24 September 2008.

Table 2. Thermal anomalies at Sangay based on MODIS-MODVOLC imaging during 1 January to 19 October 2008 (continued from the list in BGVN 33:03). No thermal anomalies were noted in 2008 prior to 27 March. Courtesy of Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System.

Information Contacts: Washington Volcanic Ash Advisory Center, Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

June 2009 (BGVN 34:06) Cite this Report

Occasional ash plume activity continues

Our most recent reports on Sangay noted occasional steam and/or ash plumes between 11 October 2006 and 28 December 2007 (BGVN 33:03) and thermal anomalies between 27 March and 4 December 2008 (BGVN 34:01). The current report continues to tabulate this persistently erupting volcano's plumes from 28 December 2007 to 31 July 2009 (table 3), and thermal anomalies from 4 December 2008 to 10 August 2009 (table 4).

Table 3. Sangay ash plume activity, reported for 29 December 2008 to July 2009. NR signifies not reported and no plumes were observed 29-31 December 2008. TA is thermal anomaly. Courtesy of the Washington Volcanic Ash Advisory Center.

Table 4. Thermal anomalies at Sangay based on MODIS-MODVOLC data during 4 December 2008 to 10 August 2009 (continued from the list in BGVN 34:01). Courtesy HIGP Thermal Alerts System.

Information Contacts: Washington Volcanic Ash Advisory Center, Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

January 2010 (BGVN 35:01) Cite this Report

Occasional ash plumes and thermal anomalies continue into at least February 2010

Sangay, which has been in near constant eruption for centuries, continued its eruptive activity into 2010. Previous reports on Sangay (BGVN 33:03, 34:01, and 34:06) had documented occasional ash plumes through 31 July and thermal anomalies through 10 August 2009. After almost two months with no indications of observed by satellite, both plumes and thermal anomalies resumed on 4 October 2009 (tables 5 and 6). Intermittent observations of plumes and MODVOLC thermal alerts were made every month afterwards through February 2010.

Table 5. Sangay ash plumes recorded during August 2009-February 2010. TA indicates a thermal anomaly noted by a VAAC analyst. No plumes were observed during 24 July-3 October 2009. Courtesy of the Washington Volcanic Ash Advisory Center (VAAC).

Table 6. Thermal alerts issued for Sangay by the MODVOLC system during August 2009-February 2010 (continued from the list in BGVN 34:06). Courtesy HIGP Thermal Alerts System.

Information Contacts: Washington Volcanic Ash Advisory Center, Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

February 2011 (BGVN 36:01) Cite this Report

Many plumes seen by pilots during past year ending February 2011

The last report discussed observations of ash plumes and MODVOLC thermal alerts at Sangay through February 2010 (BGVN 35:01). Intermittent reporting indicated that similar activity continued through at least February 2011, with plumes reaching up to 7.6 km altitude (table 7). Clouds obscured the view at times, and plumes were reported primarily by pilots and were sometimes visible on satellite imagery.

Table 7. Plumes reported at Sangay during April 2010-February 2011. No plumes were noted during March 2011. Courtesy of the Washington VAAC.

On 5 December 2010, the Washington Volcanic Ash Advisory Center (VAAC) stated that Instituto Geofisico reported elevated seismicity.

The MODVOLC alert system issued thermal alerts for Sangay monthly during March 2010 through early October 2010. Then, alerts were absent until 11 January 2011 (table 8).

Table 8. Thermal alerts issued for Sangay by the MODVOLC system during March 2010-20 March 2011 (continued from the list in BGVN 35:01). The system uses the MODIS instrument on the Terra and Aqua satellites. Courtesy MODVOLC Thermal Alerts System.

Information Contacts: Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP) MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

July 2013 (BGVN 38:07) Cite this Report

Ongoing thermal anomalies, ash fall and plumes continued through May 2013

Previously reported activity from Sangay volcano (figure 11) included ash plumes and elevated temperatures (BGVN 36:01). In this report, we note that similar activity persisted during August 2011-May 2013. We highlight low-level unrest that was primarily detected with remote sensing instruments and pilot reports.

Figure 11. This Google Earth image of Sangay includes an inset (below) from Landsat 7 acquired on 16 September 2001. The exaggerated blue color distinguishes the snow-and-ice covered summit from regional clouds (white with magenta in locations where the cloud is thinning). Note the gray area in the SE sector, an eruptive event had recently occurred that covered (or potentially melted) the typically symmetrical snowcover. The scale bar is approximate. Courtesy of GoogleEarth and USGS/NASA.

Ash plumes during 2011-2013. Notices from the Washington Volcanic Ash Advisory Center (VAAC) during this reporting period were primarily based on pilot reports and a weather station located in Guayaquil (MWO). There were seven significant plumes visible with satellite images; those plumes reached altitudes of altitudes 6-8 km a.s.l. (table 9). Ash plumes drifted to a maximum distance of 20 km from the summit.

A 25 January 2012 report from Instituto Geofísico-Escuela Politécnica Nacional (IG) (Special Report No. 01-2012) stated that activity at Sangay had intensified since 23 January. Pilot reports on 23 January were noted by the Washington VAAC with observations of ash moving SSE. Satellite images from 24 January noted thermal anomalies.

Table 9. Washington VAAC reports for Sangay during August 2011-May 2013. The following abbreviations are used: volcanic ash (VA) and meteorological watch observatory (MWO). No VAAC reports were released during June-August 2013, the remaining duration of this report. Courtesy of VAAC.

Elevated temperatures from the summit. Modvolc detected hotspots from February 2010 to early May 2013 (table 10). The elevated temperatures were detected around the summit area with as many as 3 pixels but typically one pixel per observation (figure 12). Hotspots were no longer visible after 4 May through August 2013.

Table 10. Hotspots from the region of Sangay were detected consistently during February 2010 through early May 2013. The Modvolc system uses the MODIS instrument on the Terra and Aqua satellites. Courtesy MODVOLC Thermal Alerts System.

Figure 12. From 4 May 2013 to 4 May 2012, Modvolc detected 11 hotspots in the region of Sangay. These elevated temperatures were centered on and located within 3 km of the summit area. Courtesy of HIGP.

Satellite images during 2012-2013. Significant cloudcover in the region of Sangay prohibited clear satellite views of volcanic activity. In Figure 13, four images were chosen for relatively unobstructed views, however, due to technical problems with a sensor onboard Landsat 7, black bands interfere with the images. Despite these challenges, bright snow is easily distinguished from the summit area and the disruptions of the typically white (altered to blue for higher contrast) summit suggest processes such as ashfall, lahars, or melting causing new exposures of underlying rock. Ash events were frequently documented as late as 23 May 2013 and it is clear in the 8 August 2013 image that the summit snow was no longer significantly disturbed.

Figure 13. Satellite images from Landsat 7 (12 July 2012, 10 April 2013, and 26 April 2013) and Landsat 8 (8 August 2013) captured views of the changing conditions at Sangay. Snow and ice at the summit appears as bright blue while cloudcover is typically white with some magenta fringes; recent ashfall, lahars, or melting events have disrupted the symmetrical snow region in these images except for the image from 8 August 2013. Courtesy of USGS/NASA.

References. NASA Landsat Program, 2001, Landsat ETM scene L71010061_06120010916, SLC-Off, USGS, Sioux Falls, Sept. 16, 2001.

NASA Landsat Program, 2012, Landsat ETM scene LE70100612012194ASN00, SLC-Off, USGS, Sioux Falls, July 12, 2012.

NASA Landsat Program, 2013, Landsat ETM scene LE70100612013100EDC00, SLC-Off, USGS, Sioux Falls, April 10, 2013.

NASA Landsat Program, 2013, Landsat ETM LE70100612013116EDC00, SLC-Off, USGS, Sioux Falls, April 26, 2013.

NASA Landsat Program, 2013, Landsat ETM scene LC80100612013220LGN00, SLC-Off, USGS, Sioux Falls, August 8, 2013.

Information Contacts: Instituto Geofísico-Escuela Politécnica Nacional (IG), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); and Hawai'i Institute of Geophysics and Planetology (HIGP) MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

February 2014 (BGVN 39:02) Cite this Report

Absence of evidence for ongoing eruption; new hazard maps

Previously reported activity from Sangay volcano (figure 14) included ash plumes as late as 23 May 2013 and satellite infrared thermal alerts ending in early May 2013 (BGVN 36:01). In that previous report, satellite thermal alerts from the MODVOLC system were noted to have persisted and as late as 4 May 2013. That lack of alerts continued as late as 16 July 2013 when the MODVOLC website was last checked. Since that reporting, there have been no new updates regarding Sangay on the website of the Instituto Geofisico (IG), the aviation reports have not mentioned Sangay, and other news of Sangay behavior has also been generally lacking.

Figure 14. (Inset at bottom) A regional map showing Sangay with respect to large rivers and other features surrounding Sangay. Orange line is the PanAmerican highway, which passes near Río Bamba on the map's N. Major rivers (blue) are primary routes of lahars. (Main map) A hazards map for Sangay made with hazards focus and compiling the results of multiple kinds of modeling. Key (in Spanish) notes that the upper three colors were based on slope angle (H/L) with text noting gradation of hazards in those regions from pyroclastic flows, lava flows, ash falls, volcanic bombs, rock falls, and proximal lahars. The lower three colors on the key represent inferred gradations of lahar hazard at distance from the volcano. Dashed envelopes in red refer to boundaries for small and moderate sizes of ash falls. White line shows inferred boundary for an E directed debris avalanche. Base map is from the Instituto Geografico Militar (IGM). Taken from an online poster by Ordóñez and others, 2014).

Absence of MODVOLC and aviation alerts does not necessarily translate to a lack of eruptions. The MODVOLC system imposes a reasonably high threshold to the infrared data acquired from space. Factors such as weather conditions, snow pack, and geometry of the vent area may play a role. Emissions of spatter, ash fall, and small pyroclastic flows could easily be missed. Assessments are generally best made in conjunction with information at the volcano. The current eruption began on 8 August 1934 and is thus far confirmed only through 23 May 2013.

Hazard modeling and products. In late 2013 to early 2014 IG released a poster discussing Sangay hazards (Ordóñez and others, 2014), some of the results of which we reprint here (figures 14, 15, and 16). Figure 14 contains IGEPN's recently published a map of volcanic hazards associated with Sangay, which resides in the Cordillera Real between the cities of Río Bamba and Macas. The IG and others have generally considered Sangay one of the most active volcanoes in South America. The poster noted historical records of its eruptive activity dating back to 1628 (Hall, 1977) and in the last century some important periods of activity were recorded during 1903, 1934-1937, 1941-1942, 1975-1976, and 1995 to the present (Monzier et al.. 1999). Observations of surface activity carried out in the past 40 years allowed scientists to recognize some important morphological changes at the summit of the volcano, including the emergence of new craters, dome growth, extrusion of lava flows, local explosions and ash emissions, and relatively small pyroclastic flows.

Figure 15. Modeled ash fall blanket from a hypothetical eruption at Sangay of moderate size. The key (in Spanish) refers to the colors in the key and on the isopach map, with thicknesses in millimeters. Taken from an online poster by Ordóñez and others (2014).

Figure 16. Modeled ash fall blanket from a hypothetical eruption at Sangay of large size. The key (in Spanish) refers to the colors in the key and on the isopach map, with thicknesses in millimeters. Taken from an online poster by Ordóñez and others (2014).

A larger suite of volcanic hazards models is not shown here but includes results VolcFlow. Ash3D, Tephra2, and LAHARZ. The data used for the simulations were obtained from the few geological studies in this volcano (Hall, 1977; Monzier et al, 1999; Johnson et al, 2003). Sangay is judged in some ways analogous to Tungurahua volcano, because of its chemical composition, and it similar lava rheology and eruptive style of volcanic flows.

During August-September 2013, IG installed seismic monitoring instruments (broad band and infrasound ) and for the measurement of sulfur dioxide (SO₂) in the southwestern flank of the volcano Sangay. These tools facilitate the monitoring of internal and surface activity of the volcano which will give an early warning of a potential hazards.

With regard to monitoring, during August-September 2013 IG personnel installed ~4 km southwest of Sangay volcano, permanent telemetered monitoring system consisting of a broadband seismic sensor, infrasound, and gas monitoring.

Figures 15 and 16 show the respective modeled results for a moderate and large eruption. To define the zones affected by ash fall, the modeling used the following computer routines based on assumptions and approaches discussed in the literature: Ash3d (Mastin and others, 2012) and Tephra2 (Banadonna and others, 2005). Some input data came from inferences and interpretations of descriptions by Monzier and others (1999) and from analogy with recent eruptions at Tungurahua. Plume heights were assumed to reach 10-15 km in altitude and the magma volumes in the plumes were assumed to be on the order of 0.001-0.005 km³ (dense-rock equivalent, DRE). Wind field data came from the Global Forecast System (NOAA, US National Weather Service, Environment Modeling Center). LAHARZ (Schilling, 1998), a modeling approach, was also taken to estimate the extent and coverage of lahars seen in figure 14. (The poster includes other maps on this topic as well.)

References. Bonadonna, C, Connor CB, Houghton BF, Byrne M, Laing A, Hincks T., 2005, Probabilistic modeling of tephra dispersal: Hazard assessment of a multi-phase eruption at Tarawera, New Zealand; J. Geophys. Res., 110, B03203.

Hall M. (1977). El Volcanismo en Ecuador. Publicación del Instituto Panamericano de Geografía e Historia, Sección nacional del Ecuador, Quito. 120pp.

Mastin, L, Schwaiger H, Denlinger R., 2012, User's Guide to Ash3d: A 3-D Eulerian Atmospheric Tephra Transportation and Dispersion Model, U.S. Geological Survey Open File Report.

Monzier M, Robin C, Samaniego P, Hall M, Cotten J, Mothes P, Arnaud N., 1999, J. Volcanol. Geotherm. Res. 90, 49-79.

Ordóñez J., Vallejo S., Bustillos J., Hall M., Andrade D., Hidalgo S., and Samaniego P., (Document created, December 2013; Accessed online July 2014), Volcan Sangay---Peligros Volcanicos Potenciales, Instituto Geofísico, Escuela Politécnica Nacional (IG-ESPN) (URL: http://www.igepn.edu.ec/volcan-sangay/mapa-de-peligros.html ).

Schilling S. (1998). LAHARZ: GIS programs for automated mapping of lahar-inundation hazard zones. US Geological Survey Open-File Report 98-638; 79 pp.

Information Contacts: Instituto Geofísico-Escuela Politécnica Nacional (IG), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); and Hawai'i Institute of Geophysics and Planetology (HIGP) MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

August 2017 (BGVN 42:08) Cite this Report

Intermittent ash emissions and thermal anomalies, January 2015-July 2017

Ecuador's Sangay, isolated on the east side of the Andean crest, has exhibited frequent eruptive activity over the last 400 years. Its remoteness has made ground observations difficult until recent times, and thus most information has come from aviation reports from the Washington Volcanic Ash Advisory Center (VAAC) and MODIS (Moderate Resolution Imaging Spectroradiometer) satellite-based data. Thermal anomaly information is reported by the University of Hawaii's MODVOLC system and the Italian MIROVA Volcano HotSpot Detection System. Ecuador's Instituto Geofísico (IG) issues periodic Special Reports of activity. This report summarizes the intermittent nature of the eruptions from 2011-2013, and covers renewed activity during January 2015 through July 2017.

Summary of activity during 2011-2013. Activity during 2011 (figure 17) began with a continuation of the intermittent ash emissions and thermal anomalies that persisted throughout 2010 (BGVN 36:01). Ash plumes during January and February 2011 were reported at typical altitudes between 6 and 8 km; thermal alerts appeared once each during January and March. No activity was reported after 2 March until a new series of thermal alerts began more than 3 months later on 6 June 2011; they were intermittent from then through 19 September 2012, with reports occurring during 1-4 days of all but three months. Ash emissions were also intermittent during this time, with VAAC reports issued during eight of the months from 2 August 2011-28 July 2012 for plumes reported at altitudes of 6-8 km. They also generally occurred during 1-4 days of the month. A four-month break in activity followed until ash plumes were reported on 25 January 2013; they were intermittent until 24 May 2013. MODVOLC thermal anomalies were also reported during this time, on 2 February, 25 March, and 3-4 May.

Figure 17. Summary chart of ash emissions and thermal anomalies reported from Sangay during January 2010 to early August 2017. Red bars show eruptive periods where there are reports of either ash plumes or thermal anomalies without a lack of observed activity for more than 3 months. Rows with pink cells indicate dates with thermal anomalies (MODVOLC or MIROVA). Rows with blue cells indicate dates with ash emissions as reported by the Washington VAAC. A range of dates means that activity occurred at least on those two dates, but may not have been continuous. Data courtesy of Washington VAAC, HIGP MODVOLC Thermal Alerts System, and MIROVA.

Summary of activity during January 2015-July 2017. After 19 months of quiet from June 2013 through December 2014, an ash plume reported on 19 January 2015 marked the beginning of a new eruptive episode that included ash plumes, lava flows, and block avalanches between 19 January and 7 April 2015. The next reported activity included both ash emissions and thermal anomalies observed almost a year later on 25 March 2016, although IG had reported increases in seismicity during the previous two weeks. Ash emissions and thermal anomalies were intermittent through 16 July 2016. There was a single thermal anomaly seen in MIROVA data on about 10 October and a brief ash emission occurred during 16-17 November 2016, after which Sangay was quiet until a new episode started on 20 July 2017 that was ongoing into August.

Activity during January-April 2015. After a 19-month period of no reported activity (since May 2013), ash emissions were again seen beginning on 18 January 2015 when an ash plume rose to 6.4 km altitude and drifted SW. Additional plumes on 25 January and 4 February rose to 7.3 km and 6.7 km, respectively, and drifted less than 20 km SW (figure 18). Ash plumes primarily observed by pilots between 27 February and 16 March were generally not visible in satellite images due to weather clouds. During this episode, MODVOLC thermal alerts were reported on 26 January; 7, 21, 23 and 27 February; 2,4,18, and 27 March; and 1, 3, and 7 April.

Figure 18. Ash emission at Sangay sometime during 19-26 January 2015. The ash plume eventually reached about 2 km above the 5,286-m-high summit crater. Photo by Gustavo Cruz, courtesy of IG (Informe Especial del Volcan Sangay No 1, 16 March 2015).

In a March 2015 report, IG noted that new lava flows and block-avalanche deposits had been emplaced during January and February 2015. The lava flows descended the SE flank about 900 m (figure 19). Two areas of deposits from block avalanches and ashfall extended 2.5 km ESE from the lava front, and 1.5 km down the S flank. According to IG, there were 21 thermal anomalies identified in MIROVA during 31 January-25 February 2015.

Figure 19. Locations of lava flows and block-avalanche deposits at Sangay that were emplaced during January and February 2015. The new lava flows are shown in red. The ash and block-avalanche deposits are shown in stippled yellow/green. Courtesy of IG (Informe Especial del Volcan Sangay No 1, 16 March 2015).

Activity during March-November 2016. IG reported an increase in seismicity on 5 March 2016, after ten months of no reported activity. An explosion signal was followed by harmonic tremor on 9 March, and IG noted that both a thermal anomaly and an emission drifting S were identified in NOAA satellite images. They inferred that increased seismic "explosion" signals on 14 March were indicative of ash-and-gas emissions, although weather clouds prohibited visual confirmation. Ash emissions rising to 6.1 km altitude were first reported by the Guayaquil MWO on 25 March 2016; they noted two more emissions on 27 and 28 March rising to similar altitudes (7.6 and 6.4 km, respectively), but cloudy weather prevented satellite confirmation. Plumes reported on nine days during April rose to similar altitudes (ranging from 5.5-7 km) and extended 18-30 km N or NW from the summit. A series of daily emissions occurred from 30 April-7 May. The emissions included a plume on 2 May that extended 120 km NW, and one on 6 May that rose to 8.2 km altitude and extended approximately 55 km SW before dissipating. Ash-bearing plumes were reported on 10 more days during the rest of May.

Although no more ash plumes were reported until 16 July 2016, MODVOLC thermal alerts were persistent every month beginning on 25 March and lasting through 5 July (see figure 17 above). The MIROVA data for this period also clearly show persistent thermal anomalies (figure 20). A short-lived eruption event during 16-17 November 2016 consisted of an ash emission that rose to 6.1 km altitude and drifted as far as 290 km SE.

Figure 20. Thermal anomaly data from MIROVA for the year ending on 18 January 2017 at Sangay, showing the eruptive episode of March-July 2016, and a brief anomaly on about 10 October 2016; late October-November anomalies are more than 20 kilometers from the summit and unrelated to volcanism. Courtesy of MIROVA.

Activity beginning July 2017. A new eruptive episode began on 20 July 2017, after eight months without major surface activity. Low-energy ash emissions rising to 3 km above the crater, incandescent block avalanches on the ESE flank (figure 21), and a possible new lava flow were reported by IG. The Washington VAAC reported an ash emission on 20 July rising to 8.2 km altitude and drifting about 80 km W. A plume was reported on 1 August by the Guyaquil MWO but obscured by clouds in satellite images, and a plume on 2 August was seen in webcam images (figure 22).

Figure 21. Incandescent blocks roll down the ESE flank of Sangay during the early morning of 1 August 2017. Courtesy of IG (Informe Especial del Volcán Sangay-2017-No 1, 3 August 2017).

Figure 22. Ash emission at Sangay on 2 August 2017, with the plume rising about 400 m above the summit crater drifting SW. Courtesy of IG (Informe Especial del Volcán Sangay-2017-No 1, 3 August 2017).

Information Contacts: Instituto Geofísico (IG), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

March 2018 (BGVN 43:03) Cite this Report

Eruptive episode of ash-bearing explosions and lava on SE flank, 20 July-26 October 2017

Periodic eruptive activity at Ecuador's remote Sangay has included frequent explosions with ash emissions and occasional andesitic block lava flows. Eruptive activity from late March to mid-November 2016 included multiple ash emissions and persistent thermal signals through July 2016 (BGVN 42:08). A new episode of ash emissions and thermal anomalies, that began on 20 July 2017 (BGVN 42:08) and lasted through late October 2017, is covered in this report. Subsequent activity through February 2018 included a single ash-emission event near the end of the month. Information is provided by Ecuador's Instituto Geofísico (IG) and the Washington Volcanic Ash Advisory Center (VAAC); thermal data from the MODIS satellite instrument is recorded by the University of Hawaii's MODVOLC system and the Italian MIROVA project.

The first ash plume of the latest eruptive episode at Sangay was reported on 20 July 2017. VAAC reports were issued on 20 and 21 July, eleven days in August, six days in September, and on 13 October. Thermal activity first appeared in a MIROVA plot during the last week of July and continued through 26 October. Multiple MODVOLC thermal alerts were issued between 2 August and 19 October. IG reported that low-energy ash emissions rising 1 km or less above the summit crater were typical throughout the period. They also repeatedly noted two distinct thermal hot spots in satellite data. A single ash emission on 25 February 2018 was the only additional activity through the end of February 2018.

Activity during July-October 2017. The Washington VAAC reported an ash emission on 20 July 2017 that rose to 8.2 km altitude and drifted about 80 km W. A plume was reported on 1 August by the Guyaquil MWO near the summit at about 5.3 km altitude, but was obscured by clouds in satellite imagery. The following day an ash plume was observed at 7.6 km altitude centered about 15 km NW of the summit. An ash emission was reported on 6 August, but was not visible in satellite imagery. The MWO reported an ash emission on 12 August at 6.4 km altitude moving SW, but no ash was detected in satellite imagery under partly cloudy conditions. The Washington VAAC observed an ash plume on 13 August extending around 50 km SW at 6.1 km altitude and a well-defined hotpot. IG reported an ash emission drifting W on 16 August, but clouds obscured satellite views of the plume. Hotspots continued to be observed in shortwave infrared (SWIR) imagery. The Washington VAAC reported an ash plume at 8.2 km altitude on 17 August. The imagery showed an initial puff moving NW followed by several smaller puffs. On 19 August, the Guayaquil MWO reported an ash plume at 5.8 km altitude drifting SW. The next day, another explosion was reported with ash rising again to 5.8 km and drifting W, and a hotspot was observed in satellite imagery.

The Washington VAAC reported a possible ash plume extending 30 km SW of the summit at 7 km altitude on 22 August. It had dissipated the next day, but they noted that a hotspot was visible in SWIR imagery. The next ash plume was reported by the MWO on 1 September at 5.2 km altitude but was not observed in satellite imagery. The next day, the Washington VAAC observed an ash plume at 6.1 km altitude extending 15 km NW of the summit. The Guayaquil MWO reported an ash plume to 7.3 km altitude on 6 September. On 20 September, a possible ash plume could be seen in GOES-16 imagery extending about 150 km W from the summit at 6.1 km altitude. Another plume extended 15 km SW from the summit later in the day at the same altitude. By the end of the day, continuous ash emissions were reported drifting W at 5.8 km altitude. The following day, occasional ash emissions were still reported drifting W and dissipating within 35 km of the summit. A new emission late on 21 September sent an ash plume 25 km W of the summit at 6.1 km altitude. Possible ongoing emissions were reported on 22 September, but not visible in satellite imagery. After three weeks of quiet, the Washington VAAC reported an ash emission on 13 October drifting S at 6.1 km altitude along with a bright hot spot visible for part of the day. This was the last report of ash emissions for 2017.

The eruption that began on 20 July 2017 was characterized by explosions from the central crater and lava emissions from the Ñuñurco dome on the E side of the summit. IG reported two areas of hot spots visible in thermal images during August and September. Around 65 seismic explosions and 25 long-period events were recorded daily during most of this time, along with a few harmonic tremors. Low-energy ash emissions rising 1 km or less above the summit crater were typical. Ashfall was reported to the SW and NW in Culebrillas (75 km SW), and Licto (35 km NW). New lava flows were interpreted to be on the ESE flank by IG based on the repeated hot spots visible in satellite imagery and darkened areas in the snow in the webcam images (figure 23).

Figure 23. A dark streak in the snow near the summit (left side, arrow) of Sangay indicates recent ejecta of blocks or flows on the upper ESE flank of the cone on 1 October 2017. View is from the ECU911 webcam located in Huamboya, 40 km E. Courtesy of IG-EPN (Informe Especial del Volcán Sangay, 2017-2, Continúa la erupción, se observan dos ventos, 4 de octubre del 2017).

Thermal activity measured from satellite instruments support the interpretation of significant lava emissions as blocks or flows at Sangay during late July-October 2017. The MODVOLC system reported 11 thermal alerts beginning on 14 August, 15 during September, and 13 between 3 and 19 October. A similar signal of thermal activity was recorded by the MIROVA system during the same period (figure 24).

Figure 24. The MIROVA project graph of thermal anomalies in MODIS data from Sangay for the year ending on 17 November 2017 (lower graph) clearly shows the period of increased heat flow between late July and late October. The last anomaly appeared on 26 October 2017 (upper graph). Courtesy of MIROVA.

Activity on 25 February 2018. The Washington VAAC reported an ash plume rising to 6.1 km altitude and drifting NE from the summit on 25 February 2018. The plume was visible 170 km NE before dissipating by the end of the day.

Information Contacts: Instituto Geofísico (IG), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec ); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

January 2019 (BGVN 44:01) Cite this Report

Eruption produced ash plumes, lava flows, and rockfalls during August-December 2018

Sangay is the southernmost active volcano in Ecuador and has displayed frequent eruptive activity since 1628, producing pyroclastic flows, lava flows, ash plumes, and lahars. An eruption from July through October 2017 produced ash plumes and lava flows on the ESE flank. After nine months of quiescence an eruption occurred from 8 August to 7 December 2018, with four months of continuous activity producing ash plumes, lava flows, and rockfalls. This report covers March through December 2018 and summarizes reports issued by the Instituto Geofisico, the Washington Volcano Ash Advisory Center (VAAC), and satellite data.

There was no reported activity from March through July. After nine months of inactivity a new eruptive phase began on 8 August 2018. On this day the Washington VAAC reported a possible ash plume that rose approximately 500 m above the vent and drifted 28 km WSW. An ash plume on 11 August reached a height of 2.3 km above the crater and moved towards the WSW. Prior to these two events, the last ash plume was detected on 13 October 2017.

The NASA Fire Information for Resource Management System (FIRMS) thermal alert and the first thermal anomaly alert issued by the MODVOLC near-real-time thermal monitoring algorithm for this eruptive episode was on 14 August. The eruption onset was confirmed visually on 14 August when an incandescent lava flow was seen on the upper SE flank on a webcam image (figure 25). Sentinel-2 detected elevated temperatures at the summit and lava effusion on the ESE flank (figure 26).

Figure 25. Visual confirmation of eruptive activity with incandescence on the upper SE flank of Sangay volcano on 14 August. Webcam image by ECU911 from the city of Macas, courtesy of Instituto Geofisico (14 August 2018 report).

Figure 26. Sentinel-2 thermal satellite image showing the active central crater, Ñuñurco dome, and a lava flow (bright orange/yellow) on the ESE flank of Sangay on 25 August 2018. The bright blue indicates snow on the volcano and the white/light blue areas are meteoric clouds. Sentinel-2 false color (Urban) image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

During 28 August to 3 September ash emissions reached altitudes of 5.8-6.7 km and traveled various directions out to 45 km. Ash plumes on 11, 13, 15, and 17 September reached altitudes of 5.8-6.4 km and drifted to the SW and W. Light ashfall occurred in the city of Guayaquil on 18 September, 170 km W. Ash plumes reached 5.8 to 6.1 km altitude on 19 and 20 September and drifted 37 km to the WNW and W.

Activity continued through October with lava emission. A Sentinel-2 thermal satellite image acquired on 24 October shows the lava flow on the ESE flank, with elevated thermal energy at the central crater and the Ñuñurco dome (figure 27). The final MODVOLC thermal alert was on 30 November 2018. During this time, lava flows were emitted and flowed down the ESE flank, and ash plumes were often produced and traveled to the W and NW (figure 28). From 2 December there was a substantial decrease in seismicity, ten times less than the previous months (figure 29). No further activity was noted in December.

Figure 27. False color Sentinel-2 Satellite image of Sangay acquired on 24 October 2018 showing the active crater, the Ñuñurco dome, and a hot lava flow (bright orange/yellow) that has traveled more than 1.83 km. Sentinel-2 false color (Urban) image (bands 12, 11, 4) courtesy of Sentinel Hub Playground, figure labels and description courtesy of Instituto Geofisico (17 December 2018 report).

Figure 28. The activity of Sangay during September, August, and November 2018. Small explosive events occurred at the main crater throughout the eruptive episode. The red outlines the active lava flow on the ESE flank and the yellow indicates the area impacted by rockfalls and possible collapse of the lava flow front. Annotated images courtesy of Instituto Geofisico (21 November 2018 report), webcam images taken by ECU-911 from the city of Macas.

Figure 29. Chart showing the number of seismic events during the November-December 2018 activity at Sangay. The tremor was related to the lava flow activity, VT (volcano-tectonic) events are related to rock fracturing, LP (long-period) events are related to fluid movement, and explosions are the number of detected explosions. Between 25 and 88 explosions were detected per day prior to a decrease in seismicity on 2 December. Courtesy of Instituto Geofisico (17 December 2018 report).

Elevated temperatures on the volcano were detected from 14 August to 30 November (figure 30). During this period the Washington Volcanic Ash Advisory Center (VAAC) issued 164 alerts for ash plumes. The ash plumes occasionally exceeded 2 km above the crater but were typically below 1.4 km, drifting in different directions through time (figures 31 and 32). The continuous emission of lava produced flows that traveled 1-2 km from the vent. Rockfalls and possible small pyroclastic flows produced at the lava flow fronts reached a distance of 7 km from the crater. Due to a decrease in thermal activity, ash plumes, and seismicity, Instituto Geofisico declared the eruption over on 7 December, after 121 days of activity.

Figure 30. Plot of MODIS (Moderate Resolution Imaging Spectroradiometer) thermal infrared satellite data analyzed by MIROVA from February 2018 to 2019. Top: the log radiative power of thermal anomalies showing through the eruptive episode. Bottom: The locations of the crater, dome, and lava flow as indicated by thermal anomalies, measured as the distance of the thermal anomalies from the vent in kilometers. Courtesy of MIROVA.

Figure 31. The ash plume heights in meters above the Sangay crater during the 2018 August to December eruption period (top) with detected thermal energy (bottom). Ash plume heights were given by the Washington VAAC and thermal anomalies were calculated by the MODVOLC satellite algorithm. Courtesy of Instituto Geofisico (17 December 2018 report).

Figure 32. A summary of ash plumes from Sangay during the August-December 2018 eruptive episode. A) The ash plume heights as reported by the Washington VAAC. The red line gives the average value for that month while the box represents the standard deviation. The maximum heights are indicated by the circles. B) The ash plume extents overlain over an image of Ecuador. Courtesy of Instituto Geofisico (21 November 2018 report).

Information Contacts: Instituto Geofísico (IG-EPN), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec); ECU911 - Integrated Security Service ECU 911, ulio Endara street s/n. Sector Parque Itchimbía Quito – Ecuador (URL: http://www.ecu911.gob.ec/servicio-integrado-de-seguridad-ecu-911/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

July 2019 (BGVN 44:07) Cite this Report

Explosion on 26 March 2019; activity from 10 May through June produced ash plumes, lava flows, and pyroclastic flows

Sangay is the southernmost active volcano in Ecuador, with confirmed historical eruptions going back to 1628. The previous eruption occurred during August and December and was characterized by ash plumes reaching 2,500 m above the crater. Lava flows and pyroclastic flows descended the eastern and southern flanks. This report summarizes activity during January through July 2019 and is based on reports by Instituto Geofísico (IG-EPN), Washington Volcanic Ash Advisory Center (VAAC), and various satellite data.

After the December 2018 eruption there was a larger reduction in seismicity, down to one event per day. During January, February, and most of March there was no recorded activity and low seismicity until the Washington VAAC reported an ash plume at 0615 on 26 March. The ash plume rose to a height of around 1 km and dispersed to the SW as seen in GOES 16 satellite imagery as a dark plume within white meteorological clouds. There was no seismic data available due to technical problems with the station.

More persistent eruptive activity began on 10 May with thermal alerts (figure 33) and an ash plume at 0700 that dispersed to the W. An explosion was recorded at 1938 on 11 May, producing an ash plume and incandescent material down the flank (figure 34). Two M 2 earthquakes were detected between 3.5 and 9 km below the crater on 10 May, possibly corresponding to explosive activity. By 17 May there were two active eruptive centers, the central crater and the Ñuñurcu dome (figure 35).

Figure 33. MIROVA log radiative power plot of MODIS thermal infrared at Sangay for the year ending June 2019. The plot shows the August to December 2018 eruption, a break in activity, and resumed activity in May 2019. Courtesy of MIROVA.

Figure 34. An explosion at Sangay on 10 May 2019 sent ballistic projectiles up to 650 m above the crater at a velocity of over 400 km/hour, an ash plume that rose to over 600 m, and incandescent blocks that traveled over 1.5 km from the crater at velocities of around 150 km/hour. Screenshots are from video by IG-EPN.

Figure 35. A photograph of the southern flank of Sangay on 17 May 2019 with the corresponding thermal infrared image in the top right corner. The letters correspond to: a) a fissure to the W of the lava flow; b) an active lava flow from the Ñuñurcu dome; c) the central crater producing a volcanic gas plume; d) a pyroclastic flow deposit produced by collapsing material from the front of the lava flow. Prepared by M. Almeida; courtesy of IG-EPN (special report No. 3 – 2019).

Activity at the central crater by 21 May was characterized by sporadic explosive eruptions that ejected hot ballistic ejecta (blocks) with velocities over 400 km/hour; after landing on the flanks the blocks travelled out to 2.5 km from the crater. Ash plumes reached heights between 0.9-2.3 km above the crater and dispersed mainly to the W and NW; gas plumes also dispersed to the W. The Ñuñurcu dome is located around 190 m SSE of the central crater and by 21 May had produced a lava flow over 470 m long with a maximum width of 175 m and an estimated minimum volume of 300,000 to 600,000 m³. Small pyroclastic flows and rockfalls resulted from collapse of the lava flow front, depositing material over a broad area on the E-SE flanks (figure 36). One pyroclastic flow reached 340 m and covered an area of 14,300 m². During the 17 May observation flight the lava flow surface reached 277°C.

Figure 36. A view of the ESE flanks of Sangay on 17 May 2019. The area within the black dotted line is the main area of pyroclastic flow deposition from the Ñuñurco Dome. Photo by M. Almeida; courtesy of IG-EPN (special report No. 4 – 2019).

At the end of June activity was continuing at the central crater and Ñuñurco Dome. At least three lava flows had been generated from the dome down the SE flank and pyroclastic flows continued to form from the flow fronts (figure 37). Pyroclastic material had been washed into the Upano river and steam was observed in the Volcán River possibly due to the presence of hot rocks. Ash plumes continued through June reaching heights of 800 m above the crater (figure 38), but no ashfall had been reported in nearby communities.

Figure 37. Sentinel-2 natural color (left) and thermal (center) images (bands 12, 11, 4), and 1:50 000 scale maps (right) of Sangay with interpretation on the background of a 30 m numerical terrain model (WGS84; Zone 17S) (Prepared by B. Bernard). The dates from top to bottom are 17 May, 22 May, 27 May, 16 June, and 26 June 2019. Prepared by B. Bernard; courtesy IG-EPN (special report No. 4 – 2019).

Figure 38. Plots giving the heights and dispersal direction of ash plumes at Sangay during May and June 2019. Top: Ash plume heights measures in meters above the crater. Bottom: A plot showing that the dominant dispersal direction of ash plumes is to the W during this time. Courtesy of IG-EPN (special report No. 4 – 2019).

Information Contacts: Instituto Geofísico (IG-EPN), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

January 2020 (BGVN 45:01) Cite this Report

Continuing ash emissions, lava flows, pyroclastic flows, and lahars through December 2019

Frequent activity at Ecuador's Sangay has included pyroclastic flows, lava flows, ash plumes, and lahars since 1628. Its remoteness on the east side of the Andean crest has made ground observations difficult until recent times. The current eruption began in March 2019; this report covers ongoing activity from July through December 2019. Information is provided by Ecuador's Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), and a number of sources of remote data including the Washington Volcanic Ash Advisory Center (VAAC), the Italian MIROVA Volcano HotSpot Detection System, and Sentinel-2 satellite imagery.

The eruption that began in March 2019 continued during July-December 2019 with activity focused on two eruptive centers at the summit, the Cráter Central and the Ñuñurco (southeast) vent. The Cráter Central produced explosive activity which generated small ash emissions that rose up to 3.2 km above the crater and were frequently directed towards the W and SW. Associated with these emissions in early November, ashfall was reported in Chimborazo province and elsewhere, and ejecta from explosions was deposited on all the upper flanks. At the Ñuñurcu vent, effusive activity resulted in an almost continuous emission of material down the SE flank. Small rockfalls and pyroclastic flows along the fronts and sides of the flows reached the basin and upper channel of the Volcán river which flows into the Upano river. These deposits were remobilized by rainfall and formed mud and debris flows (lahars) in the Volcán river, which caused damming at the confluence with the Upano river downstream. Increased thermal activity was recorded by the MIROVA system from mid-May 2019 through the end of the year, corresponding to the ongoing lava flow and explosive activity (figure 39).

Figure 39. Increased heat flow at Sangay was recorded beginning in mid-May 2019 and continued steadily through the end of the year as seen in this graph of Log Radiative Power produced by the MIROVA project. Courtesy of MIROVA.

Activity during July-September 2019. Several ash emissions were reported by the Washington VAAC during the first part of July 2019. On 1 July a plume rose to 6.7 km altitude and extended 45 km WSW from the summit. During 3-4 July a plume rose 6.4 km and drifted WNW; it included occasional discrete emissions that extended approximately 35 km from summit. The VAAC recorded a bright hotspot in SWIR imagery on 4 July. On 11 July a 7.3-km-altitude ash plume detached from the summit and extended from immediately W of the summit S past Segu. Webcam and satellite imagery on 11 July demonstrated the continuing thermal activity of the lava flow on the SE flank and ash emissions drifting W (figure 40). On 29 July a plume rose to 7.6 km altitude and drifted 65 km WSW. Later in the day continuous emissions were drifting SW from the summit at 5.8 km altitude before dissipating. The first satellite images of 30 July showed a plume extending 110 km WSW from the summit at 7 km altitude. Activity decreased later in the day and the plume extended W about 45 km from the summit at 6.4 km altitude. Composite satellite imagery on 31 July showed almost constant ash emissions extending over 150 km W of the summit (figure 41).

Figure 40. The local webcam at Sangay (left) and Sentinel satellite imagery (right, bands 12, 11, and 8A) both confirmed the high heat output from the active lava flow on the SE flank on 11 July 2019. The flow is about 2 km long. A plume of steam and ash also drifted W from the summit (right). Courtesy of IG-EPN (left) and Sentinel Hub Playground (right).

Figure 41. An ash emission from Sangay on 29 July 2019 drifted tens of km WSW as seen in the webcam (left). Two days later on 31 July a small dark ash plume was visible above the dense cloud cover in Sentinel satellite imagery; the VAAC reported ash drifting W throughout the day. Courtesy of IG-EPN (left) and Sentinel Hub Playground (right).

During an overflight on 6 August 2019 scientists from IG-EPN observed ash emissions from the Cráter Central, and the lava flow continuing from the Vento Ñuñurco in a similar location to where it was in May 2019 (figure 42). Light-colored sediments filled much of the upper basin of the Volcán river. Thermal images of the area also showed that some of the deposits were elevated in temperature, even in the riverbed (figure 43).

Figure 42. The E and SE flanks of Sangay showed continuing activity during August 2019 (right) that was similar to activity going on during May (left). In May, steam issued from the Cráter Central and a lava flow descended the SE flank from Vento Ñuñurco (photo by M. Almeida, IG-EPN). In August, diffuse ash and steam issued from the Crater Central, and a new flow descended from the same area of the Vento Ñuñurco seen in May (photo by P. Ramón , IG-EPN). Courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2019 - No 5, Quito, 13 de noviembre del 2019).

Figure 43. The upper Volcán River basin was filled with deposits of pyroclastic material associated with the most recent activity at Sangay when observed during an overflight on 6 August 2019 (left). Thermal analysis of the drainage indicated that several of the deposits were still hot, as was the active flow (right). Left photo by P. Ramón, thermal image by Silvia Vallejo; courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2019 - No 5, Quito, 13 de noviembre del 2019).

Frequent ash emissions continued during August 2019. Diffuse ash was seen moving W from the summit at 5.8 km altitude on 1 August. Another short-lived plume was observed extending 15 km WSW the next day at 5.8-6.1 km altitude. Continuous ash emissions were visible in satellite imagery extending 35 km SW from the summit at 6.1 km altitude on 5 August. During the next two days, the emissions extended 45 km WSW and a prominent hot spot was visible through the meteoric clouds. The ash plume altitude rose to 6.7 km on 8 August and a larger ash emission extended more than 100 km WSW. A new emission the next day drifted 25-35 km W at 6.1 km altitude. A well-defined hotspot seen in shortwave imagery on 10 August accompanied an ash emission that extended 35 km WSW from the summit at 6.7 km altitude. On 12 August a plume drifted 65 km due W at 6.4 km altitude; emissions continued the next day in the same direction at 6.1 km altitude. An ash plume extended 100 km WNW of the summit at 5.8 km altitude on 18 August. A very bright hotspot was observed in infrared imagery the next day. The ash emissions continued to be visible in satellite imagery through 20 August.

An ash plume extending 10 km N from the summit on 25 August coincided with the appearance of a vivid hot spot, according to the Washington VAAC. The plume was initially reported at 7.6 km altitude and later in the day was at 6.7 km altitude. The leading edge of an ash emission reported on 31 August was 350 km W of the summit late that day moving at 5.8 km altitude, and over 950 km WSW before it dissipated on 1 September. Fewer ash emissions were reported during September 2019. The leading edge of a plume extended about 160 km W from the summit on 2 September at 7.6 km altitude; a second emission that day moved NE at 6.4 km altitude. On 4 September a small emission rose to 6.4 km altitude and drifted SW; on 9 September a plume was observed moving W at 5.5 km. A new emission on 19 September was seen in satellite imagery moving in many different directions (N, NE, E, and SE) at 6.7 km altitude. The lava flow on the SE flank produced a strong thermal signature that appeared unchanged from late August through late September (figure 44).

Figure 44. The thermal signature from the lava flow on the SE flank of Sangay appeared unchanged from late August (top left) to late September 2019 (bottom right) in Sentinel-2 imagery (bands 12, 11, and 8A); an ash emission drifted in multiple directions on 19 September 2019. Courtesy of Sentinel Hub Playground and IG-EPN.

Activity during October-December 2019. Pulses of ash were reported during 1, 9-11, 14, 26, and 31 October 2019 by the Washington VAAC. On 1 October the plume rose to 5.8 km altitude and drifted NE. A narrow plume on 9 October extending 55 km NW corresponded with a bright hotspot at its source. Concentrated emissions the next day rose to 7.3 km altitude and extended over 200 km WNW. Later in the day on 10 October emissions were reported at 5.8 km drifting W. A substantial thermal anomaly and a constant plume of diffuse ash appeared in satellite imagery on 14 October at 6.1 km altitude drifting 15 km W. Diffuse emissions on 26 October appeared 35 km NW of the summit at 5.8 km altitude. The intensity of the thermal anomaly from the lava flow on the SE flank remained strong during the month, and emissions of steam and ash were also visible in satellite images (figure 45). In a site visit on 19 October 2019, IG-EPN scientists measured a recent lahar deposited near the confluence of the Volcán and Upano rivers. It was full of sand-sized particles and approximately 30 cm thick at the river’s edge (figure 46).

Figure 45. The thermal anomaly from the lava flow on the SE flank of Sangay remained strong during October 2019, and both ash and steam emissions were seen in Sentinel-2 satellite images (bands 12, 11, and 8A). The lava flow is about 2 km long. Courtesy of Sentinel Hub Playground.

Figure 46. A lahar deposit at the confluence of Río Volcán and Río Upano at Sangay was about 30 cm thick on 19 October 2019. Photograph by Francisco Vasconez, courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2019 - No 5, Quito, 13 de noviembre del 2019).

Ash emissions during 10-26 November 2019 were reported daily by the Washington VAAC, each lasting for less than 24 hours before dissipating. The first report of ash detected in satellite imagery on 10 November indicated that the plume extended 25 km WSW at 6.7 km altitude. On the subsequent days, the plumes drifted in many different directions at altitudes of 5.8-7.3 km, usually around 6.4 km. The plumes generally drifted 25-45 km from the summit, although some were still visible over 100 km away, depending on weather conditions. The highest plume reached 7.3 km altitude on 18 November and drifted W. The plume on 26 November rose to 6.4 km altitude and was last seen 140 km SW of the summit before it dissipated. Pyroclastic flows were witnessed on 20 November 2019 (figure 47). The last plume of the month, on 29 November, rose to 6.4 km altitude and drifted 65 km W, dissipating quickly, and was accompanied by a very bright thermal anomaly.

Figure 47. Ash plumes from Sangay rose to 5.8 km altitude on 20 November 2019 and drifted 25 km NE before dissipating, according to the Washington VAAC. Pyroclastic flows appeared on the flank that day. Courtesy of Walter Calle C.

Ashfall was reported during November in the provinces of Chimborazo (Alao, 20 km NW, Cebadas, 35 km NW, and Guaguallá), Morona Santiago (Macas, 40 km SE), and Azuay (120 km SW). Samples of ash collected from two locations indicated that the amount of material was very small (less than10 g/m²) with a high content of extremely fine ash (between 40 and 60% ash less 63 μm in diameter). The larger fraction over 63 μm was mainly composed of juvenile magma (80%) and a small fraction of free crystals (10% plagioclase and pyroxenes), oxidized fragments (5%), and gray lithics (5%) (figure 48).

Figure 48. Photos from a binocular microscope of the greater than 63 μm fraction of ash from Sangay collected in Macas and at the SAGA station during November 2019. See text for details. Courtesy of IG (Informe Especial del Volcán Sangay - 2019 - No 6, 4 de diciembre del 2019).

In a report issued in early December 2019 the IG-EPN noted that eruptive activity which increased in May 2019 was continuing (figure 49); a small amount of inflation was observed during November. Explosive activity continued at the Cráter Central with ash plumes reaching 2 km above the summit, and plumes drifting frequently towards the NE causing small amounts of ash to fall in the Chimborazo, Morona Santiago, and Azuay provinces. Effusive activity from the Ñuñurco vent produced almost continuous lava that flowed down the SE flank. Small pyroclastic flows around the margins of the lava flows reached the basin and the upper channel of the Volcán river, causing temporary dams that turned to mudflows during rain events.

Figure 49. IG-EPN published this multi-parameter chart of activity of the Sangay volcano from May to 1 December 2019. a: seismic activity (number of events per day) detected at the PUYO station (source: IG-EPN); b: SO2 emissions (tons per day) detected by the Sentinel-5P satellite sensor (source: MOUNTS); c: height of ash clouds (m above crater level) detected by the GOES-16 satellite sensor (source: Washington VAAC); d: thermal emission power (megawatt) detected by the MODIS satellite sensor (source: MODVOLC) and estimated accumulated lava volume (million m3, dotted lines represent the error range). Courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2019 - No 6, 4 de diciembre del 2019).

During an overflight on 3 December 2019 a strong smell of sulfur was noted 1 km above the summit. The Ñuñurco vent continued to emit lava with a maximum apparent temperature of 100 to 210°C (figure 50). IG-EPN scientists concluded that approximately 58 ± 29 million m³ of lava had been emitted through 3 December.

Figure 50. Views of the SE flank of Sangay on 3 December 2019 with visible (left) and thermal (right) imagery. Photograph by C. Viracucha, thermal analysis by F. Naranjo; courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2019 - No 6, 4 de diciembre del 2019).

Recurring lahars in the Río Volcán during the period occasionally reached the Rio Upano (figure 51). By late November, they had partially dammed the Upano river (figure 52). On 26 November 2019 when IG-EPN and Sangay National Park officials inspected the area, they recorded deposits more than 2 m thick at the confluence of the two rivers (figure 53). During an overflight the next day, additional deposits were identified along 16 km upstream. The total volume of the lahar deposits was estimated at 5 million m³ to date.

Figure 51. Inferred lahar deposits at Sangay along the Río Volcán from the foot of the volcano up to its confluence with Río Upano shown in red. Courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2019 - No 6, 4 de diciembre del 2019).

Figure 52. Lahar deposits at Sangay filled Río Volcán and dammed part of the confluence where it joins río Upano when photographed during an overflight on 26 November 2019. Photographs by Pedro Espín; courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2019 - No 6, 4 de diciembre del 2019).

Figure 53. Lahar deposits from Sangay exceeded 2 m in thickness at the confluence of the Upano and Volcán rivers on 26 November 2019. Photography by Pedro Espín; courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2019 - No 6, 4 de diciembre del 2019).

Another extended period of ash emissions began on 4 December 2019 and continued daily through 19 December. The Washington VAAC reported that an ash plume was initially at 6.7 km altitude drifting S on 4 December. Continuous emissions were observed at 4.6 km altitude later in the day and were visible in satellite images located 25 km S at 5.8 km altitude that evening. The drift directions were initially mostly SW in early December, but migrated to mostly SE during 10-16 December, then back to SW. Plume altitudes ranged from 5.8 to 7.3 km and satellite images revealed ash as far as 160 km away; most plumes were visible to about 25 km before dissipating or disappearing into meteoric clouds. IG-EPN reported steam and gas emissions with small amounts of ash on 13 December that drifted SE (figure 54). Small block avalanches from the active flow were also observed on the SE flank. The next day, ash and gas emissions rose to 1,170 m above the summit and drifted NE while the lava flow appeared incandescent on the SE flank.

Figure 54. Numerous explosions produced ash emissions from Sangay during 4-30 December 2019, shown here on days 13, 14, 16, and 25. Courtesy of IG-EPN (Informe Diario del Estado del Volcán Sangay No. 2019-1, 13 Diciembre; No. 2019-2, 14 Diciembre; No. 2019-5, 17 Diciembre; No. 2019-13, 25 Diciembre 2019).

During the night of 14-15 December ashfall was reported in San Isidro in the Province of Morona Santiago (30 km SE). Ash plumes rose 870 m above the summit on 15 December and 1,470 m high the next day. Ashfall was reported in the Guasuntos (60 km SW) and Llagos (80 km SW) areas of the Chimborazo province on the morning of 16 December. The next day plumes drifted SE and SW, and minor ashfall was reported that night (16-17 December) in Macas (40 km SE), Morona Santiago province. Satellite images captured gas and ash emissions on 25 December, and ashfall was reported in Alausí (60 km SW) in the province of Chimborazo. An explosion on 29 December produced an ash plume that rose to 6.1 km and first drifted WNW then in an arc to the SW almost 185 km to the coast. Multiple plumes at 5.8-6.7 km drifted westerly for tens of kilometers that day and the next. Prominent thermal anomalies were noted in satellite imagery on 8, 15, 17, and 30 December.

By late December 2019, the lahar deposits in Rio Volcán had backed up noticeably further into the Upano river from a month earlier (figure 55). Sulfur dioxide emissions were not recorded during July through August 2019, but small, pulsing plumes were captured in satellite images during September, October and November, gradually increasing in density. Several plumes were detected hundreds of kilometers from the volcano before dissipating; by December, larger, more frequent pulses of SO₂ were measured during many days when ash emissions were reported (figure 56).

Figure 55. Lahar deposits from Sangay in the Rio Volcán (right) continued to dam up the Rio Upano into late December 2019. Compare with figure 49 taken one month earlier. Photo by WJ Hernandes, courtesy of Edgar Chulde, posted online 21 December 2019.

Figure 56. Sulfur dioxide emissions from Sangay were weak but persistent during September-November 2019 (top row), often drifting in narrow plumes with distinct pulses. During December, the density of the SO2 emissions increased noticeably (bottom row). Colombia’s Nevado del Ruiz was also producing plumes of SO2 at the same time. Courtesy of NASA Goddard Space Flight Center.

Information Contacts: Instituto Geofísico (IG-EPN), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Walter Calle C., Macas, Ecuador (Twitter: @walterc333; URL: https://twitter.com/walterc333/status/1197273200822046720); Edgar Chulde, Quito, Ecuador (Twitter: @EdgarChulde2; URL: https://twitter.com/EdgarChulde2/status/1208547471024173056).

July 2020 (BGVN 45:07) Cite this Report

Daily ash plumes and frequent pyroclastic flows produce ashfall and lahars, January-June 2020

Frequent activity at Ecuador's Sangay has included pyroclastic flows, lava flows, ash plumes, and lahars reported since 1628. Its remoteness on the east side of the Andean crest make ground observations difficult; remote cameras and satellites provide important information on activity. The current eruption began in March 2019 and continued through December 2019 with activity focused on the Cráter Central and the Ñuñurco (southeast) vent; they produced explosions with ash plumes, lava flows, and pyroclastic flows and block avalanches. In addition, volcanic debris was remobilized in the Volcan river causing significant damming downstream. This report covers ongoing similar activity from January through June 2020. Information is provided by Ecuador's Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), and a number of sources of remote data including the Washington Volcanic Ash Advisory Center (VAAC), the Italian MIROVA Volcano HotSpot Detection System, and Sentinel-2 satellite imagery. Visitors also provided excellent ground and drone-based images and information.

Throughout January-June 2020, multiple daily reports from the Washington Volcanic Ash Advisory Center (VAAC) indicated ash plumes rising from the summit, generally 500-1,100 m. Each month one or more plumes rose over 2,000 m. The plumes usually drifted SW or W, and ashfall was reported in communities 25-90 km away several times during January-March and again in June. In addition to explosions with ash plumes, pyroclastic flows and incandescent blocks frequently descended a large, deep ravine on the SE flank. Ash from the pyroclastic flows rose a few hundred meters and drifted away from the volcano. Incandescence was visible on clear nights at the summit and in the ravine. The MIROVA log radiative power graph showed continued moderate and high levels of thermal energy throughout the period (figure 57). Sangay also had small but persistent daily SO₂ signatures during January-June 2020 with larger pulses one or more days each month (figure 58). IG-EPN published data in June 2020 about the overall activity since May 2019, indicating increases throughout the period in seismic event frequency, SO₂ emissions, ash plume frequency, and thermal energy (figure 59).

Figure 57. This graph of log radiative power at Sangay for 18 Aug 2018 through June 2020 shows the moderate levels of thermal energy through the end of the previous eruption in late 2018 and the beginning of the current one in early 2019. Data is from Sentinel-2, courtesy of MIROVA.

Figure 58. Small but persistent daily SO2 signatures were typical of Sangay during January-June 2020. A few times each month the plume was the same or larger than the plume from Colombia’s Nevado del Ruiz, located over 800 km NE. Image dates are shown in the header over each image. Courtesy of NASA’s Global Sulfur Dioxide Monitoring Page.

Figure 59. A multi-parameter graph of activity at Sangay from May 2019 to 12 June 2020 showed increases in many types of activity. a) seismic activity (number of events per day) detected at the PUYO station (source: IG-EPN). b) SO2 emissions (tons per day) detected by the Sentinel-5P satellite sensor (TROPOMI: red squares; source: MOUNTS) and by the IG-EPN (DOAS: green bars). c) height of the ash plumes (meters above crater) detected by the GOES-16 satellite sensor (source: Washington VAAC). d) thermal emission power (megawatt) detected by the MODIS satellite sensor (source: MODVOLC) and estimate of the accumulated lava volume (million M3, thin lines represent the error range). Courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2020 - N°3, “Actualización de la actividad eruptiva”, Quito, 12 de junio del 2020).

Activity during January-March 2020. IG-EPN and the Washington VAAC reported multiple daily ash emissions throughout January 2020. Gas and ash emissions generally rose 500-1,500 m above the summit, most often drifting W or SW. Ashfall was reported on 8 January in the communities of Sevilla (90 km SSW), Pumallacta and Achupallas (60 km SW) and Cebadas (35 km WNW). On 16 January ash fell in the Chimborazo province in the communities of Atillo, Ichobamba, and Palmira (45 km W). Ash on 28 January drifted NW, with minor ashfall reported in Púngala (25 km NW) and other nearby communities. The town of Alao (20 km NW) reported on 30 January that all of the vegetation in the region was covered with fine white ash; Cebadas and Palmira also noted minor ashfall (figure 60).

Figure 60. Daily ash plumes and repeated ashfall were reported from Sangay during January 2020. Top left: 1 January 2020 (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-2, JUEVES, 2 ENERO 2020). Top right: 20 January 2020 (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-21, MARTES, 21 ENERO 2020). Bottom left: 26 January-1 February 2020 expedition (Martes, 18 Febrero 2020 12:21, EXPEDICIÓN AL VOLCÁN SANGAY). Bottom right: 30 January 2020, minor ashfall was reported in the Province of Chimborazo (#IGAlInstante Informativo VOLCÁN SANGAY No. 006, JUEVES, 30 ENERO 2020). Courtesy of IG-EPN.

A major ravine on the SE flank has been the site of ongoing block avalanches and pyroclastic flows since the latest eruption began in March 2019. The pyroclastic flows down the ravine appeared incandescent at night; during the day they created ash clouds that drifted SW. Satellite imagery recorded incandescence and dense ash from pyroclastic flows in the ravine on 7 January (figure 61). They were also reported by IG on the 9th, 13th, 26th, and 28th. Incandescent blocks were reported in the ravine several times during the month. The webcam captured images on 31 January of large incandescent blocks descending the entire length of the ravine to the base of the mountain (figure 62). Large amounts of ash and debris were remobilized as lahars during heavy rains on the 25th and 28th.

Figure 61. Sentinel-2 satellite imagery of Sangay from 7 January 2020 clearly showed a dense ash plume drifting W and ash and incandescent material from pyroclastic flows descending the SE-flank ravine. Left image uses natural color (bands 4, 3, 2) rendering and right images uses atmospheric penetration (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Figure 62. Pyroclastic flows at Sangay produced large trails of ash down the SE ravine many times during January 2020 that rose and drifted SW. Top left: 9 January (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-9, JUEVES, 9 ENERO 2020). Top right: 13 January (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-14, MARTES, 14 ENERO 2020). On clear nights, incandescent blocks of lava and pyroclastic flows were visible in the ravine. Bottom left: 16 January (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-17, VIERNES, 17 ENERO 2020). Bottom right: 31 January (#IGAlInstante Informativo VOLCÁN SANGAY No. 007, VIERNES, 31 ENERO 2020). Courtesy of IG-EPN.

Observations by visitors to the volcano during 9-17 January 2020 included pyroclastic flows, ash emissions, and incandescent debris descending the SE flank ravine during the brief periods when skies were not completely overcast (figure 63 and 64). More often there was ash-filled rain and explosions heard as far as 16 km from the volcano, along with the sounds of lahars generated from the frequent rainfall mobilizing debris from the pyroclastic flows. The confluence of the Rio Upano and Rio Volcan is 23 km SE of the summit and debris from the lahars has created a natural dam on the Rio Upano that periodically backs up water and inundates the adjacent forest (figure 65). A different expedition to Sangay during 26 January-1 February 2020 by IG personnel to repair and maintain the remote monitoring station and collect samples was successful, after which the station was once again transmitting data to IG-EPN in Quito (figure 66).

Figure 63. Hikers near Sangay during 9-17 January 2020 witnessed pyroclastic flows and incandescent explosions and debris descending the SE ravine. Left: The view from 40 km SE near Macas showed ash rising from pyroclastic flows in the SE ravine. Right: Even though the summit was shrouded with a cap cloud, incandescence from the summit crater and from pyroclastic flows on the SE flank were visible on clear nights. Courtesy of Arnold Binas, used with permission.

Figure 64. The steep ravine on the SE flank of Sangay was hundreds of meters deep in January 2020 when these drone images were taken by members of a hiking trip during 9-17 January 2020 (left). Pyroclastic flows descended the ravine often (right), coating the sides of the ravine with fine, white ash and sending ash billowing up from the surface of the flow which resulted in ashfall in adjacent communities several times. Courtesy of Arnold Binas, used with permission.

Figure 65. Debris from pyroclastic flows that descended the SE Ravine at Sangay was carried down the Volcan River (left) during frequent rains and caused repeated damming at the confluence with the Rio Upano (right), located 23 km SE of the summit. These images show the conditions along the riverbeds during 9-17 January 2020. Courtesy of Arnold Binas, used with permission.

Figure 66. An expedition by scientists from IG-EPN to one of the remote monitoring stations at Sangay during 26 January-1 February 2020 was successful in restoring communication to Quito. The remote location and constant volcanic activity makes access and maintenance a challenge. Courtesy of IG-EPN (Martes, 18 Febrero 2020 12:21, EXPEDICIÓN AL VOLCÁN SANGAY).

During February 2020, multiple daily VAAC reports of ash emissions continued (figure 67). Plumes generally rose 500-1,100 m above the summit and drifted W, although on 26 February emissions were reported to 1,770 m. Ashfall was reported in Macas (40 km SE) on 1 February, and in the communities of Pistishi (65 km SW), Chunchi (70 km SW), Pumallacta (60 k. SW), Alausí (60 km SW), Guamote (40 km WNW) and adjacent areas of the Chimborazo province on 5 February. The Ecuadorian Red Cross reported ash from Sangay in the provinces of Cañar and Azuay (60-100 km SW) on 25 February. Cebadas and Guamote reported moderate ashfall the following day. The communities of Cacha (50 km NW) and Punín (45 km NW) reported trace amounts of ashfall on 29 February. Incandescent blocks were seen on the SE flank multiples times throughout the month. A pyroclastic flow was recorded on the SE flank early on 6 February; additional pyroclastic flows were observed later that day on the SW flank. On 23 February a seismic station on the flank recorded a high-frequency signal typical of lahars.

Figure 67. Steam and ash could be seen drifting SW from the summit of Sangay on 11 February 2020 even though the summit was hidden by a large cap cloud. Ash was also visible in the ravine on the SE flank. Courtesy of Sentinel Hub Playground, natural color (bands 4, 3, 2) rendering.

A significant ash emission on 1 March 2020 was reported about 2 km above the summit, drifting SW. Multiple ash emissions continued daily during the month, generally rising 570-1,170 m high. An emission on 12 March also rose 2 km above the summit. Trace ashfall was reported in Cebadas (35 km WNW) on 12 March. The community of Huamboya, located 40 km ENE of Sangay in the province of Morona-Santiago reported ashfall on 17 March. On 19 and 21 March ashfall was seen on the surface of cars in Macas to the SE. (figure 68). Ash was also reported on the 21st in de Santa María De Tunants (Sinaí) located E of Sangay. Ash fell again in Macas on 23 March and was also reported in General Proaño (40 km SE). The wind changed direction the next day and caused ashfall on 24 March to the SW in Cuenca and Azogues (100 km SW).

Figure 68. Ashfall from Sangay was reported on cars in Huamboya on 17 March 2020 (left) and in Macas on 19 March (right). Courtesy IG-EPN, (#IGAlInstante Informativo VOLCÁN SANGAY No. 024, MARTES, 17 MARZO 2020 and #IGAlInstante Informativo VOLCÁN SANGAY No. 025, JUEVES, 19 MARZO 2020).

Incandescence from the dome at the crater and on the SE flank was noted by IG on 3, 4, and 13 March. Remobilized ash from a pyroclastic flow was reported drifting SW on 13 March. The incandescent path of the flow was still visible that evening. Numerous lahars were recorded seismically during the month, including on days 5, 6, 8, 11, 15, 30 and 31. Images from the Rio Upano on 11 March confirmed an increase from the normal flow rate (figure 69) inferred to be from volcanic debris. Morona-Santiago province officials reported on 14 March that a new dam had formed at the confluence of the Upano and Volcano rivers that decreased the flow downstream; by 16 March it had given way and flow had returned to normal levels.

Figure 69. Images from the Rio Upano on 11 March 2020 (left) confirmed an increase from the normal flow rate related to lahars from Sangay descending the Rio Volcan. By 16 March (right), the flow rate had returned to normal, although the large blocks in the river were evidence of substantial activity in the past. Courtesy of IG (#IGAlInstante Informativo VOLCÁN SANGAY No. 018, MIÉRCOLES, 11 MARZO 2020 and #IGAlInstante Informativo VOLCÁN SANGAY No. 023, LUNES, 16 MARZO 2020).

Activity during April-June 2020. Lahar activity continued during April 2020; they were reported seven times on 2, 5, 7, 11, 12, 19, and 30 April. A significant reduction in the flow of the Upano River at the entrance bridge to the city of Macas was reported 9 April, likely due to a new dam on the river upstream from where the Volcan river joins it caused by lahars related to ash emissions and pyroclastic flows (figure 70). The flow rate returned to normal the following day. Ash emissions were reported most days of the month, commonly rising 500-1,100 m above the summit and drifting W. Incandescent blocks or flows were visible on the SE flank on 4, 10, 12, 15-16, and 20-23 April (figure 71).

Figure 70. A significant reduction in the flow of the Upano River at the entrance bridge to the city of Macas was reported on 9 April 2020, likely due to a new dam upstream from lahars related to ash emissions and pyroclastic flows from Sangay. Courtesy of IG-EPN (#IGAlInstante Informativo VOLCÁN SANGAY No. 032, JUEVES, 9 ABRIL 2020).

Figure 71. Incandescent blocks rolled down the SE ravine at Sangay multiple times during April 2020, including on 4 April (left). Pyroclastic flows left two continuous incandescent trails in the ravine on 23 April (right). Courtesy of IG-EPN (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-95, SÁBADO, 4 ABRIL 2020 and INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-114, JUEVES, 23 ABRIL 2020).

Activity during May 2020 included multiple daily ash emissions that drifted W and numerous lahars from plentiful rain carrying ash and debris downstream. Although there were only a few visible observations of ash plumes due to clouds, the Washington VAAC reported plumes visible in satellite imagery throughout the month. Plumes rose 570-1,170 m above the summit most days; the highest reported rose to 2,000 m above the summit on 14 May. Two lahars occurred in the early morning on 1 May and one the next day. A lahar signal lasted for three hours on 4 May. Two lahar signals were recorded on the 7th, and three on the 9th. Lahars were also recorded on 16-17, 20-22, 26-27, and 30 May. Incandescence on the SE flank was only noted three times, but it was cloudy nearly every day.

An increase in thermal and overall eruptive activity was reported during June 2020. On 1 and 2 June the webcam captured lava flows and remobilization of the deposits on the SE flank in the early morning and late at night. Incandescence was visible multiple days each week. Lahars were reported on 4 and 5 June. The frequent daily ash emissions during June generally rose to 570-1,200 m above the summit and drifted usually SW or W. The number of explosions and ash emissions increased during the evening of 7 June. IG interpreted the seismic signals from the explosions as an indication of the rise of a new pulse of magma (figure 72). The infrasound sensor log from 8 June also recorded longer duration tremor signals that were interpreted as resulting from the descent of pyroclastic flows in the SE ravine.

Figure 72. Seismic and infrasound signals indicated increased explosive and pyroclastic flow activity at Sangay on 7-8 June 2020. Left: SAGA station (seismic component) of 7 and 8 June. The signals correspond to explosions without VT or tremor signals, suggesting the rise of a new magma pulse. Right: SAGA station infrasound sensor log from 8 June. The sharp explosion signals are followed a few minutes later (examples highlighted in red) by emergent signals of longer duration, possibly associated with the descent of pyroclastic material in the SE flank ravine. Courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2020 - N°3, “Actualización de la actividad eruptiva”, Quito, 12 de junio del 2020).

On the evening of 8 June ashfall was reported in the parish of Cebadas and in the Alausí Canton to the W and SW of Sangay. There were several reports of gas and ash emissions to 1,770 m above the summit the next morning on 9 June, followed by reports of ashfall in the provinces of Guayas, Santa Elena, Los Ríos, Morona Santiago, and Chimborazo. Ashfall continued in the afternoon and was reported in Alausí, Chunchi, Guamote, and Chillanes. That night, which was clear, the webcam captured images of pyroclastic flows down the SE-flank ravine; IG attributed the increase in activity to the collapse of one or more lava fronts. On the evening of 10 June additional ashfall was reported in the towns of Alausí, Chunchi, and Guamote (figure 73); satellite imagery indicated an ash plume drifting W and incandescence from pyroclastic flows in the SE-flank ravine the same day (figure 74).

Figure 73. Ashfall from Sangay was reported in Alausí (top left), Chunchi (top right) and Guamote (bottom) on 10 June 2020. Courtesy of IG-EPN (#IGAlInstante Informativo VOLCÁN SANGAY No. 049, MIÉRCOLES, 10 JUNIO 2020).

Figure 74. Incandescent pyroclastic flows (left) and ash plumes that drifted W (right) were recorded on 10 June 2020 at Sangay in Sentinel-2 satellite imagery. Courtesy of Sentinel Hub Playground.

Ashfall continued on 11 June and was reported in Guayaquil, Guamote, Chunchi, Riobamba, Guaranda, Chimbo, Echandía, and Chillanes. The highest ash plume of the report period rose to 2,800 m above the summit that day and drifted SW. That evening the SNGRE (Servicio Nacional de Gestion de Riesgos y Emergencias) reported ash fall in the Alausí canton. IG noted the increase in intensity of activity and reported that the ash plume of 11 June drifted more than 600 km W (figure 75). Ash emissions on 12 and 13 June drifted SW and NW and resulted in ashfall in the provinces of Chimborazo, Cotopaxi, Tungurahua, and Bolívar. On 14 June, the accumulation of ash interfered with the transmission of information from the seismic station. Lahars were reported each day during 15-17 and 19-21 June. Trace amounts of ashfall were reported in Macas to the SE on 25 June.

Figure 75. The ash plume at Sangay reported on 11 June 2020 rose 2.8 km above the summit and drifted W according to the Washington VAAC and IG (left). Explosions and high levels of incandescence on the SE flank were captured by the Don Bosco webcam (right). Courtesy of IG-EPN (#IGAlInstante Informativo VOLCÁN SANGAY No. 055, JUEVES, 11 JUNIO 2020 and INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-164, VIERNES, 12 JUNIO 2020).

During an overflight of Sangay on 24 June IG personnel observed that activity was characterized by small explosions from the summit vent and pyroclastic flows down the SE-flank ravine. The explosions produced small gas plumes with a high ash content that did not rise more than 500 m above the summit and drifted W (figure 76). The pyroclastic flows were restricted to the ravine on the SE flank, although the ash from the flows rose rapidly and reached about 200 m above the surface of the ravine and also drifted W (figure 77).

Figure 76. A dense ash plume rose 500 m from the summit of Sangay on 24 June 2020 and drifted W during an overflight by IG-EPN personnel. The aerial photograph is taken from the SE; snow-covered Chimborazo is visible behind and to the right of Sangay. Photo by M Almeida, courtesy of IG EPN (Jueves, 02 Julio 2020 10:29, INFORME DEL SOBREVUELO AL VOLCÁN SANGAY EL 24 DE JUNIO DE 2020).

Figure 77. Pyroclastic flows descended the SE flank ravine at Sangay during an overflight by IG-EPN personnel on 24 June 2020. Ash from the pyroclastic flow rose 200 m and drifted W, and infrared imagery identified the thermal signature of the pyroclastic flow in the ravine. Photo by M Almeida, IR Image by S Vallejo, courtesy of IG EPN (Jueves, 25 Junio 2020 12:24, SOBREVUELO AL VOLCÁN SANGAY).

Infrared imagery taken during the overflight on 24 June identified three significant thermal anomalies in the large ravine on the SE flank (figure 78). Analysis by IG scientists suggested that the upper anomaly 1 (125°C) was associated with explosive activity that was observed during the flight. Anomaly 2 (147°C), a short distance below Anomaly 1, was possibly related to effusive activity of a small flow, and Anomaly 3 (165°C) near the base of the ravine that was associated with pyroclastic flow deposits. The extent of the changes at the summit of Sangay and along the SE flank since the beginning of the eruption that started in March 2019 were clearly visible when images from May 2019 were compared with images from the 24 June 2020 overflight (figure 79). The upper part of the ravine was nearly 400 m wide by the end of June.

Figure 78. A thermal image of the SE flank of Sangay taken on 24 June 2020 indicated three thermal anomalies. Anomaly 1 was associated with explosive activity, Anomaly 2 was associated with effusive activity, and Anomaly 3 was related to pyroclastic-flow deposits. Image prepared by S Vallejo Vargas, courtesy of IG EPN (Jueves, 02 Julio 2020 10:29, INFORME DEL SOBREVUELO AL VOLCÁN SANGAY EL 24 DE JUNIO DE 2020).

Figure 79. Aerial and thermal photographs of the southern flank of the Sangay volcano on 17 May 2019 (left: visible image) and 24 June 2020 (middle: visible image, right: visible-thermal overlay) show the morphological changes on the SE flank, associated with the formation of a deep ravine and the modification of the summit. Photos and thermal image by M Almeida, courtesy of IG EPN (Jueves, 02 Julio 2020 10:29, INFORME DEL SOBREVUELO AL VOLCÁN SANGAY EL 24 DE JUNIO DE 2020).

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Arnold Binas (URL: https://www.doroadventures.com).

January 2021 (BGVN 46:01) Cite this Report

Ash plumes, lava flows, pyroclastic flows, and lahars during July-December 2020; larger explosions in September

Sangay is one of the most active volcanoes in Ecuador with the current eruptive period continuing since 26 March 2019. Activity at the summit crater has been frequent since August 1934, with short quiet periods between events. Recent activity has included frequent ash plumes, lava flows, pyroclastic flows, and lahars. This report summarizes activity during July through December 2020, based on reports by Ecuador's Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), ash advisories issued by the Washington Volcanic Ash Advisory Center (VAAC), webcam images taken by Servicio Integrado de Seguridad ECU911, and various satellite data.

Overall activity remained elevated during the report period. Recorded explosions were variable during July through December, ranging from no explosions to 294 reported on 4 December (figure 80), and dispersing mostly to the W and SW. SO₂ was frequently detected using satellite data (figure 81) and was reported several times to be emitting between about 770 and 2,850 tons/day. Elevated temperatures at the crater and down the SE flank were frequently observed in satellite data (figure 82), and less frequently by visual observation of incandescence. Seismic monitoring detected lahars associated with rainfall events remobilizing deposits emplaced on the flanks throughout this period.

Figure 80. A graph showing the daily number of explosions at Sangay recorded during July through December 2020. Several dates had no recorded explosions due to lack of seismic data. Data courtesy of IG-EPN (daily reports).

Figure 81. Examples of stronger SO2 plumes from Sangay detected by the Sentinel 5P/TROPOMI instrument, with plumes from Nevado del Ruiz detected to the north. The image dates from left to right are 31 August 2020, 17 September 2020, 1 October 2020 (top row), 22 November 2020, 3 December 2020, 14 December 2020 (bottom row). Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Figure 82. This log radiative power MIROVA plot shows thermal output at Sangay during February through December 2020. Activity was relatively constant with increases and decreases in both energy output and the frequency of thermal anomalies detected. Courtesy of MIROVA.

Activity during July-August 2020. During July activity continued with frequent ash and gas emission recorded through observations when clouds weren’t obstructing the view of the summit, and Washington VAAC alerts. There were between one and five VAAC alerts issued most days, with ash plumes reaching 570 to 1,770 m above the crater and dispersing mostly W and SE, and NW on two days (figure 83). Lahar seismic signals were recorded on the 1st, 7th, three on the 13th, and one on the 19th.

Figure 83. Gas and ash plumes at Sangay during July 2020, at 0717 on the 17th, at 1754 on the 18th, and at 0612 on the 25th. Bottom picture taken from the Macas ECU 911 webcam. All images courtesy of IG-EPN daily reports.

During August there were between one and five VAAC alerts issued most days, with ash plumes reaching 600 to 2,070 m above the crater and predominantly dispersing W, SW, and occasionally to the NE, S, and SE (figure 84). There were reports of ashfall in the Alausí sector on the 24th. Using seismic data analysis, lahar signals were identified after rainfall on 1, 7, 11-14, and 21 August. A lava flow was seen moving down the eastern flank on the night of the 15th, resulting in a high number of thermal alerts. A pyroclastic flow was reported descending the SE flank at 0631 on the 27th (figure 85).

Figure 84. This 25 August 2020 PlanetScope satellite image of Sangay in Ecuador shows an example of a weak gas and ash plume dispersing to the SW. Courtesy of Planet Labs.

Figure 85. A pyroclastic flow descends the Sangay SE flank at 0631 on 27 August 2020. Webcam by ECU911, courtesy of courtesy of IG-EPN (27 August 2020 report).

Activity during September-October 2020. Elevated activity continued through September with two significant increases on the 20th and 22nd (more information on these events below). Other than these two events, VAAC reports of ash plumes varied between 1 and 5 issued most days, with plume heights reaching between 600 and 1,500 m above the crater. Dominant ash dispersal directions were W, with some plumes traveling SE, S, SE, NE, and NW. Lahar seismic signals were recorded after rainfall on 1, 2, 5, 8-10, 21, 24, 25, 27, and 30 September. Pyroclastic flows were reported on the 19th (figure 86), and incandescent material was seen descending the SE ravine on the 29th. There was a significant increase in thermal alerts reported throughout the month compared to the July-August period, and Sentinel-2 thermal satellite images showed a lava flow down the SE flank (figure 87).

Figure 86. Pyroclastic flows descended the flank of Sangay on 19 (top) and 20 (bottom) September 2020. Webcam images by ECU911 from the city of Macas, courtesy of IG-EPN (14 August 2018 report).

Figure 87. The thermal signature of a lava flow is seen on SW flank of Sangay in this 8 September 2020 Sentinel-2 thermal satellite image, indicated by the white arrow. False color (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Starting at 0420 on the morning of 20 September there was an increase in explosions and emissions recorded through seismicity, much more energetic than the activity of previous months. At 0440 satellite images show an ash plume with an estimated height of around 7 km above the crater. The top part of the plume dispersed to the E and the rest of the plume went W. Pyroclastic flows were observed descending the SE flank around 1822 (figure 88). Ash from remobilization of deposits was reported on the 21st in the Bolívar, Chimborazo, Los Ríos, Guayas and Santa Elena provinces. Ash and gas emission continued, with plumes reaching up to 1 km above the crater. There were seven VAAC reports as well as thermal alerts issued during the day.

Figure 88. An eruption of Sangay on 22 September 2020 produced a pyroclastic flow down the SE flank and an ash plume that dispersed to the SW. PlanetScope satellite image courtesy of Planet Labs.

Ash plumes observed on 22 September reached around 1 km above the crater and dispersed W to NW. Pyroclastic flows were seen descending the SE flank (figure 89) also producing an ash plume. A BBC article reported the government saying 800 km² of farmland had experienced ashfall, with Chimborazo and Bolívar being the worst affected areas (figure 90). Locals described the sky going dark, and the Guayaquil airport was temporarily closed. Ash plume heights during the 20-22 were the highest for the year so far (figure 91). Ash emission continued throughout the rest of the month with another increase in explosions on the 27th, producing observed ash plume heights reaching 1.5 km above the crater. Ashfall was reported in San Nicolas in the Chimborazo Province in the afternoon of the 30th.

Figure 89. A pyroclastic flow descending the flank of Sangay on 22 September 2020. Webcam image by ECU911 from the city of Macas, courtesy of IG-EPN (Sangay Volcano Special Report - 2020 - No 5, 22 September 2020).

Figure 90. Ashfall from an eruption at Sangay on 22 September 2020 affected 800 km2 of farmland and nearby communities. Images courtesy of EPA and the Police of Ecuador via Reuters (top-right), all via the BBC.

Figure 91. Ash plume heights (left graph) at Sangay from January through to late September, with the larger ash plumes during 20-22 September indicated by the red arrow. The dominant ash dispersal direction is to the W (right plot) and the average speed is 10 m/s. Courtesy of IG-EPN (Sangay Volcano Special Report - 2020 - No 5, 22 September 2020).

Thermal alerts increased again through October, with a lava flow and/or incandescent material descending the SE flank sighted throughout the month (figure 92). Pyroclastic flows were seen traveling down the SE flank during an observation flight on the 6th (figure 93). Seismicity indicative of lahars was reported on 1, 12, 17, 19, 21, 23, 24, and 28 October associated with rainfall remobilizing deposits. The Washington VAAC released one to five ash advisories most days, noting plume heights of 570-3,000 m above the crater; prevailing winds dispersed most plumes to the W, with some plumes drifting NW, N, E to SE, and SW. Ashfall was reported in Alausí (Chimborazo Province) on the 1st and in Chunchi canton on the 10th. SO₂ was recorded towards the end of the month using satellite data, varying between about 770 and 2,850 tons on the 24th, 27th, and 29th.

Figure 92. A lava flow descends the SE flank of Sangay on 2 October 2020. Webcam images courtesy of ECU 911.

Figure 93. A pyroclastic flow descends the Sangay SE flank was seen during an IG-EPN overflight on 6 October 2020. Photo courtesy of S. Vallejo, IG-EPN.

Activity during November-December 2020. Frequent ash emission continued through November with between one and five Washington VAAC advisories issued most days (figure 94). Reported ash and gas plume heights varied between 570 and 2,700 m above the crater, with winds dispersing plumes in all directions. Thermal anomalies were detected most days, and incandescent material from explosions was seen on the 26th. Seismicity indicating lahars was registered on nine days between 15 and 30 November, associated with rainfall events.

Figure 94. Examples of gas and ash plumes at Sangay during November 2020. Webcam images were published in IG-EPN daily activity reports.

Lahar signals associated with rain events continued to be detected on ten out of the first 18 days of November. Ash emissions continued through December with one to five VAAC alerts issued most days. Ash plume heights varied from 600 to 1,400 m above the crater, with the prevailing wind direction dispersing most plumes W and SW (figure 95). Thermal anomalies were frequently detected and incandescent material was observed down the SE flank on the 3rd, 14th, and 30th, interpreted as a lava flow and hot material rolling down the flank. A webcam image showed a pyroclastic flow traveling down the SE flank on the 2nd (figure 96). Ashfall was reported on the 10th in Capzol, Palmira, and Cebadas parishes, and in the Chunchi and Guamote cantons.

Figure 95. Examples of ash plumes at Sangay during ongoing persistent activity on 9, 10, and 23 December 2020. Webcam images courtesy of ECU 911.

Figure 96. A nighttime webcam image shows a pyroclastic flow descending the SE flank of Sangay at 2308 on 2 December 2020. Image courtesy of ECU 911.

Information Contacts: Instituto Geofísico (IG-EPN), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec); ECU911, Servicio Integrado de Seguridad ECU911, Calle Julio Endara s / n. Itchimbía Park Sector Quito – Ecuador. (URL: https://www.ecu911.gob.ec/; Twitter URL: https://twitter.com/Ecu911Macas/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Planet Labs, Inc. (URL: https://www.planet.com/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); BBC News “In pictures: Ash covers Ecuador farming land” Published 22 September 2020 (URL: https://www.bbc.com/news/world-latin-america-54247797).

July 2021 (BGVN 46:07) Cite this Report

Multiple explosions send ash over 3 km above the summit during March-May 2021

Frequent activity at Ecuador's Sangay has included pyroclastic flows, lava flows, ash plumes, and lahars reported since 1628. Its remoteness on the east side of the Andean crest makes ground observations difficult; web cameras and satellites provide important information on activity. The current eruption began in March 2019 and has continued into 2021. Ongoing activity from January-June 2021 covered in this report includes explosions with ash plumes, large SO₂ plumes, incandescent ejecta, lava flows, and numerous lahars. Information is provided by Ecuador's Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), and multiple sources of remote data including the Washington Volcanic Ash Advisory Center (VAAC), the Italian MIROVA Volcano HotSpot Detection System, and Sentinel-2 satellite imagery.

Throughout January-June 2021, multiple daily reports from the Washington VAAC indicated ash plumes rising generally 500-2,100 m above the summit. During March-May plumes rose over 3 km above the summit multiple times and they usually drifted SW or W with ashfall reported in communities 25-90 km away after most of the larger explosive events. Incandescent ejecta and blocks descended a large, deep ravine on the SE flank a few times each month. The MIROVA log radiative power graph showed continued moderate and high levels of thermal anomalies into March; they decreased somewhat in frequency and intensity after that through June (figure 97). Small and moderate-size SO₂ plumes were detected with satellite instruments daily during January and February. During March and April very large SO₂ plumes accompanied the large explosions and ash plumes. Some of the large explosions during May were also accompanied by significant SO₂ emissions.

Figure 97. Moderate and high levels of intensity of thermal anomalies were recorded by the MIROVA project for Sangay from 13 August 2020 through mid-March 2021. Thermal activity decreased somewhat in frequency and intensity after March through June 2021. Courtesy of MIROVA.

Activity during January-March 2021. Three to five daily volcanic ash advisories were issued by the Washington VAAC during January 2021. Ash emissions were observed in satellite images rising 500-2,400 m above the summit, drifting W or SW on most days. On 11 January the Washington VAAC reported ash plumes visible in satellite imagery drifting W at 7.6 km altitude (2,300 m above the summit) 100-150 km from the summit. Extensive cloud cover made webcam observations infrequent, but plumes of gas and ash were observed rising 2,000 m above the summit and drifting NW on 12 January. The Volcan Sangay webcam also captured ash emissions on 16 and 21 January, and Sentinel infrared satellite images showed hot material on the SE flank and ash emissions on those same days as well (figure 98). Ashfall was reported in Chimborazo and Guayas on 24 January. Seismic signals indicating mud and debris flows from the near-daily rain were recorded during 11-14 and 22-26 January; no damage was reported.

Figure 98. Webcam images on 16 and 21 January 2021 recorded ash emissions from the summit of Sangay (top row). Sentinel-2 satellite images on those same days also recorded evidence of activity. On 16 January (bottom left) strong thermal signals from the ravine on the SE flank indicated some type of hot material moving. A dense ash plume drifted NW from the summit on 21 January above the meteoric cloud cover (bottom right). Satellite images use Atmospheric penetration rendering (bands 12, 11, 8a). Top images courtesy of IG daily reports, bottom images courtesy of Sentinel Hub Playground.

Multiple daily ash emissions reported by the Washington VAAC during February 2021 indicated that plumes generally rose 600-1,800 m above the summit with drift directions primarily SW or W. Cloudy weather conditions prohibited webcam observations on many days, however gas and ash emissions were observed drifting SW at 1,500 m above the summit on 4 February, SW at 800-1,000 m above the summit during 9-11 February, and drifting N and W at 500-1,500 m high during 15-18 February. Incandescent material descended the SE flank overnight during 2-3 and 10 February (figure 99), and ashfall was reported N and W of Macas on 10 February. Seismic vibrations indicating lahars were recorded on 2, 3, 7, 11, 12, 16, and 25 February; no damage was reported.

Figure 99. Incandescent hot material descended the SE flank of Sangay on 2 and 10 February 2021. Top image is from IG webcam, bottom is Sentinel-2 satellite thermal imagery with Atmospheric penetration rendering (bands 12, 11, 8a). Left image courtesy of IG-EPN; right image courtesy of Sentinel Hub Playground.

Daily explosions with ash plumes continued during March 2021; emissions generally rose 600-2,000 m above the summit. Two episodes of larger explosive events that resulted in substantial ashfall were recorded during 6-7 and 11 March. The Washington VAAC initially reported an ash plume drifting W 50 km from the summit at 9.1 km altitude (3.8 km above the summit) early on 6 March. It fanned out from the NW to the SW up to 170 km at that altitude and additional ash was drifting E from the summit below 5.8 km altitude. This was followed later in the day by a second explosion with a large ash plume that drifted in three directions: E at 6.1 km altitude, SW at 7.3 km altitude, and W at 10.7 km altitude. Several hours later the leading edge of the ash plume was located 300 km W of the summit at 12.2 km altitude while another part of the plume extended 130 km WSW at 8.2 km altitude (figure 100). This resulted in significant ashfall in numerous communities. Ashfall was reported on 6 March in Cumandá, and on 6 and 7 March in Bolívar, Milagro, San Jacinto de Yaguachi, El Triunfo, Daule, Samboróndon, Coronel Marceliño Maridueña, Durán, Naranjito, Alfredo Baquerizo Moreno, Playas, Guamote, Alausí, Pallatanga, Chunchí and Colta. Traces of ashfall were still reported on 8 March in Guamote and Alausí.

Figure 100. A dense ash plume above meteoric clouds extends several kilometers NW from Sangay after a large explosion on 7 March 2021; hot material is also visible on the SE flank. The summit itself is obscured by clouds. Sentinel-2 image uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

A large explosion on 11 March initially rose to 12.5 km altitude and spread out 45 km in all directions with additional ash extending 100 km W. A little over an hour later it was still expanding in all directions and moving mostly W at 13.7 km altitude about 100 km from the summit. It dissipated rapidly and was no longer detectible in satellite imagery 8 hours later. Significant ashfall from the explosion was recorded that day in the Canton of Guamote, moderate ashfall was reported in the Cantons of Chambo, Riobamba, Penipe, and Guano, and traces of ash were reported in Colta, Alausí and Macas (figure 101). Very large SO₂ plumes detected by satellite instruments from the explosions on 6-7 and 11-12 March drifted hundreds of kilometers before dissipating (figure 102). Steam and gas emissions with low ash content were observed in a webcam on 14 March rising to 600 m above the summit and drifting E and NE (figure 103). Vibrations from mudflows and lahars were measured on 16 days during March. On 12 March the Macas authorities reported an overflow of the Upano River dam by mud and debris flows. On 24 March the rains generated signals associated with mud and debris flows that lasted for three hours.

Figure 101. Crops, livestock, and people were affected by significant ashfall in multiple provinces after large explosions from Sangay on 11 March 2021. Courtesy of Fundación Maquita.

Figure 102. Very large SO2 plumes were detected by the TROPOMI instrument on the Sentinel-5P satellite from Sangay during 6-7 (top) and 11-12 (bottom) March 2021. Colombia’s Nevado del Ruiz also had small and moderate SO2 emissions throughout the month of March. Explosions produced ash plumes that rose to 12.2 km altitude on 6-7 March and 13.7 km altitude on 11 March, dispersing SO2 over a large area of the upper atmosphere. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Figure 103. Steam and gas with low ash content drifted N and NE from Sangay in the early morning on 14 March 2021. Courtesy of IG-EPN.

Activity during April-June 2021. A notable increase in the flow of the Upano River was reported on 4 April 2021 after heavy rains, and vibrations from lahars were recorded 13 times throughout the month. Multiple daily VAAC reports continued throughout April, similar to previous months. The daily ash emissions generally rose 600-2,100 m above the summit and drifted W, SW, and NW. An incandescent flow was observed descending the upper part of the SE flank overnight on 4-5 April (figure 104). Incandescence at the summit was also visible overnight during 19-20 April.

Figure 104. An incandescent flow was observed descending the upper part of the SE flank of Sangay late on 4 April 2021. Courtesy of IG Daily Reports.

The Washington VAAC reported a large eruptive event on 13 April 2021 that started shortly after midnight (UTC) and sent an ash cloud to 8.2 km altitude that drifted 50 km WNW but also fanned out in all directions. Less than three hours later the cloud was reported at 12.2 km altitude continuing to drift about 100 km WNW. A large plume of SO₂ was also detected by satellite instruments from this event (figure 105). Ashfall was reported in the Provinces of Chimborazo, Bolivar, Los Rios, and Guayas. Significant amounts of ash fell in the Cantons of Guamote and Chillanes, moderate amounts fell in Riobamba, Guaranda, San Miguel and Chimbo, and trace amounts were reported in Colta, Chunchi, Babahoyo, Montalvo, Vinces, Guayaquil, Durán, Samborondón, Alfredo Baquerizo Moreno, Salitre, and San Jacinto de Yaguach. Ash plumes on 17 and 18 April drifted W and caused ashfall in Guamote located in the Chimborazo Province (figure 106).

Figure 105. A large explosion at Sangay on 13 April 2021 sent ash to over 12 km altitude. By later in the day, steam and gas emissions were drifting away from the summit at low altitude (left). The event produced a large SO2 plume that was detected by the TROPOMI instrument on the Sentinel-5P satellite (right). Courtesy of IG-EPN Daily Information Report (left) and NASA Global Sulfur Dioxide Monitoring Page (right).

Figure 106. A dense ash plume rose from Sangay on 17 April 2021 and was responsible for ashfall in Guamote located in the Chimborazo Province. Courtesy of IG Daily Information Report.

The Washington VAAC reported ash emissions that rose as high as 7.6 km altitude on 20 April 2021; they were drifting NW 15 km from the summit in addition to continuing emissions from earlier events that were drifting WSW at 6.1 km altitude 75 km from the volcano (figure 107). IG reported another strong eruptive pulse from Sangay on 28 April that produced an ash plume that rose to 5-7 km above the summit and drifted NNE and SSW. The Washington VAAC reported three different directions of drift from the explosion at different altitudes; the lower-level ash was moving NNW at 5.8 km altitude, the mid-level ash was moving W at 7.0 km altitude, and the higher-level ash was moving SW at 9.7 km altitude. The plume dissipated after a few hours and no ashfall was reported.

Figure 107. Ash emissions drifted up to 75 km W from Sangay on 20 April 2021. Courtesy of IG-EPN Daily Information Report.

Abundant rain during May 2021 resulted in eighteen days with reports of lahars; an increase in the flow of Rio Upano was reported on 16 May. Explosive activity increased in intensity during May 2021. There were six days when emissions were reported rising over 3 km above the summit in addition to daily plumes that rose 200-2,000 m high and usually drifted W, NW, or SW. Overnight on 7-8 May the Washington VAAC reported an ash plume that extended 100 km WSW from the summit at 7.6 km altitude and NW at 10.6 km altitude. The webcam captured incandescent lava descending the SE flank that evening (figure 108). Large SO₂ plumes were detected by satellite instruments on both days. Significant ashfall from the event was recorded in multiple provinces including Chimborazo in the Cebadas and Palmira parishes of Guamote canton and in the Pungalá and Flores parishes of the Riobamba canton. Moderate ashfall was reported in Punín and Colta parishes in the Riobamba canton. Trace ashfall was reported in the parishes of Tixán and the high part of Licto in the Alusi canton. On the morning of 8 May trace amounts of ash were reported in the province of Guayas, in the cantons of Salitre, Alfredo Baquerizo Moreno (Jujan), Samborondón, Dúran, and Daule.

Figure 108. Incandescent ejecta and lava flows were observed in the webcams at Sangay overnight on 7-8, 20-21, and 30-31 May 2021. Courtesy of IG-EPN Daily Information Report.

An eruption on 16 May 2021 produced an ash plume that rose to 11.3 km altitude and drifted 140 km N. A lower-level plume was also drifting WSW 80 km from the summit at 6.4 km altitude. Traces of ashfall were reported in Ishupamba-Chimborazo. The ash plume was discernible in Sentinel-2 satellite imagery above a dense meteoric cloud layer (figure 109). An explosion on 20 May produced an ash plume reported by the Washington VAAC extending over 100 km SW from the summit at 9.5 km altitude and also fanning out 75-100 km SE and S of the summit at 7.6 km altitude. Ashfall from this event was reported in the regions of Guamote and Ichupamba in the Chimborazo province. Incandescent ejecta was noted overnight on 21-22 May (figure 110) and a substantial ash plume seen in satellite imagery produced ashfall in Ichupamba, San Nicolas, Guamote, Alausi, Cumandá, Tixan, Sibambe, and Achupallas in the province of Chimborazo and in General Elizalde in Guayas Province. The Washington VAAC reported the ash plume moving E at 9.1 km altitude and W at 7.6 km altitude.

Figure 109. An explosion at Sangay on 16 May 2021 produced an ash plume that was visible drifting WSW from the summit above a dense cloud layer. Image uses Natural color rendering (bands 4, 3, 2), the contrast has been enhanced. Courtesy of Sentinel Hub Playground.

Figure 110. Eruptive activity at Sangay overnight on 21-22 May 2021 produced incandescent ejecta and a dense ash plume Courtesy of IG Daily Information Report.

High-level ash emissions continued during 25-27 May 2021, although no ashfall was reported. The Washington VAAC reported a large eruption on 25 May that sent ash plumes in three different directions; ash was moving W at 5.2 km altitude, E at 6.7 km altitude, and S at 9.8 km altitude. During the next two days additional emissions produced plumes that drifted SE and SW at 7.6-8.2 km altitude. Incandescent explosions produced incandescent material that descended the flanks overnight on 30-31 May. Reports were received from communities near the volcano of loud noises and vibrations rattling windows. The Washington VAAC reported ash emissions that rose to 7.9 km altitude and drifted 100 km SW. The SNGRE (Servicio Nacional de Gestión de Riesgos y Emergencias) reported ash fall in the Alausí, Guamote and Chunchi cantons of the Chimborazo province. Emissions continued the next day, 1 June (figure 111), and ashfall was again reported in Alausí and Chunchi.

Figure 111. Ash emissions continued at Sangay on 1 June 2021 after incandescent explosions and ashfall occurred the day before. Courtesy of IG Daily Information Report.

No ashfall was reported during June 2021 after the 1st, though daily ash emissions continued, rising 400-1,500 m above the summit and usually drifting W, SW, or NW. Continuous ash clouds drifting 40 km NW were observed on 10 June by the Washington VAAC; they were also visible that day in Sentinel-2 satellite imagery along with a thermal anomaly from the summit crater (figure 112). Incandescence appeared at the summit crater and blocks rolled down the SE flank overnight on 27-28 June. Lahar signals were reported on 19 days during the month.

Figure 112. Ash emissions drifting WNW and a thermal anomaly at the summit of Sangay appeared in Sentinel-2 satellite imagery on 10 June 2021. Image uses Atmospheric penetration rendering of bands 12, 11, and 8a. Courtesy of Sentinel Hub Playground.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Fundación Maquita (URL: https://twitter.com/Maquita_Cjusto/status/1370047448316542977).

February 2022 (BGVN 47:02) Cite this Report

Large explosion on 2 December 2021 with ash plumes to 15 km altitude and new flow on N flank

Frequent activity at Ecuador's Sangay has included pyroclastic flows, lava flows, ash plumes, and lahars reported since 1628. The current eruption began in March 2019 and has continued throughout 2021. Ongoing activity from July-December 2021 covered in this report includes explosions with ash plumes, incandescent ejecta, lava flows, and lahars. Information is provided by Ecuador's Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), and multiple sources of remote data including the Washington Volcanic Ash Advisory Center (VAAC), the Italian MIROVA Volcano HotSpot Detection System, and Sentinel-2 satellite imagery.

Gas and ash emissions rose 500-1,500 m above the summit of Sangay on most days during July-December 2021. Pulses of activity that produced emissions higher than 2 km above the summit occurred at least once almost every month. Ashfall in Chimborazo Province was reported on 14 and 19 July; a plume on the 19th rose to over 10 km altitude. A new vent appeared on the W side of the summit on 24 November, a new lava flow began on the N flank on 2 December, and lava remained intermittently active in the SE flank ravine throughout the period. Steady levels of thermal energy were present in the MIROVA data from July through early December, with a marked increase in frequency at the middle of the month that corresponded with increased observations of incandescence on the N and W flanks (figure 113). A major explosive event on 2 December produced an ash plume that rose to 15.2 km altitude.

Figure 113. MIROVA Log Radiative Power graph of MODIS data for Sangay from 22 March through December 2021 showed relatively low levels of activity into July followed by increased thermal activity through November. After an explosive event in early December, multiple active vents at the summit produced incandescent material, significantly increasing the thermal activity that was recorded. Courtesy of MIROVA.

Multiple daily VAAC reports during July 2021 indicated frequent ash emissions that rose 100-2,400 m above the summit (5.4-7.7 km altitude) and most often drifted W or SW (figure 114). A larger explosion on 19 July produced a plume that rose to 10.7 km altitude and drifted SE while another part of the plume moved NE at 8.5 km altitude. A few hours later a plume was drifting W at 6.4 km altitude. Ashfall was observed on 14 July in the Guamote and Cebadas sectors from one of the 12 explosions reported that day, and on 19 July in the canton of Guamote in the Chimborazo province. Noises were reported to the W and SW after explosions on 19 and 25 July. Incandescence at the crater accompanied ash emissions on 15 July (figure 115). MODVOLC thermal alerts were recorded on 8, 14, 24, and 31 July. Rains were strong enough to produce lahar signals at the seismic stations on 1-3, 9-13, 16, 18-22, 27, and 29-31 July but no damages were reported.

Figure 114. An ash plume drifted W from the summit of Sangay on 5 July 2021 while a significant thermal anomaly was present at the summit. Similar ash emissions were reported almost every day of the month. Sentinel-2 satellite image uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Figure 115. Incandescence at the summit of Sangay was visible from the ECU 911 webcam on 15 July 2021. Courtesy of IG-EPN Daily report.

Gas and ash emissions drifted SW to NW at 500-1,500 m above the summit during most days in August 2021, although activity was more intermittent than during July, with no emissions reported during 15-18 and 26-31 August. The tallest plume reported by IG-EPN rose 2 km above the summit and drifted SW, W, and NW on 21 August, but no ashfall was reported. A pulse of thermal activity on 4 August that was recorded in satellite imagery (figure 116) led IG-EPN to identify a new flow on the SE flank. Incandescence and ash emissions were both visible in webcams on 5 August, confirming that the flow was confined to the upper flank of the volcano. Explosions produced incandescent blocks that rolled down the SE flank ravine overnight on 13-14 and 19-20 August (figure 117). The next night the lava was also visible in the ravine. MODVOLC thermal alerts were issued on 4, 20, 23, and 24 August. Lahar signals were recorded on 2, 11-13, 16-20, 23, and 26 August.

Figure 116. A new lava flow at Sangay produced a strong thermal anomaly on the SE flank on 4 August 2021 (left). The summit anomaly was also very strong on 24 August (right). Sentinel-2 satellite imagery uses Atmospheric penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Figure 117. Explosions at Sangay on 14 (left) and 19 (right) August 2021 sent incandescent blocks down the SE flank ravine. Courtesy of IG-EPN daily reports.

Steam, gas, and ash emissions from the summit continued throughout September 2021, drifting SW, W, or NW on most days. Plumes were usually reported at 600-1,200 m above the summit; they rose as high as 2,000 m on 8 and 20 September. Incandescence was visible at the crater on the morning of 15 September. Overnight on 23-24 September, Strombolian activity at the summit sent incandescent ejecta down the SE flank ravine (figure 118). MODVOLC thermal alerts on 5, 14, 15, 24, 28, and 30 September indicated continued pulses of thermal activity. Heavy rain produced lahar signals at seismic stations on 1-4, 6, 7, 9, and 11-13 September.

Figure 118. Strombolian activity at Sangay overnight on 23-24 September 2021 sent incandescent ejecta down the SE flank ravine that was recorded by the ECU 911 webcam. Courtesy of IG-EPN daily report.

A single MODVOLC thermal alert was issued on 1 October; multiple alerts were issued each day on 9, 14, and 18 October. Webcam images of a lava flow near the summit were seen overnight on 3-4 October. Incandescent blocks were visible on the SE flank overnight on 5-6 October. On 10 October the ECU 911 webcam showed an active flow on the SE flank. Sentinel satellite images showed strong thermal anomalies at the summit and on the SE flank on 8, 13, and 18 October (figure 119). Satellite images from 13 October indicated continued slow growth of the ravine on the SE flank. When last measured in March 2021 it was 600 (± 40 m) wide; as of 13 October is was 650 (± 40 m) wide. Overnight on 16-17 October incandescent blocks were seen rolling down the SE flank ravine. The Washington VAAC issued multiple ash advisories each day during October 2021. Plumes were reported rising 500-1,200 m above the summit on most days; although on 13, 18-19 (figure 120), and 30 October gas and ash plumes rose 1,200-1,500 m high from multiple emission events. A narrow plume of steam and ash drifted tens of kilometers WSW from the summit on 28 October and corresponded to an increase in seismic tremor signals, according to IG-EPN. Small lahars were recorded as high-frequency seismic signals during 29-31 October.

Figure 119. Strong thermal anomalies on the SE flank and at the summit of Sangay on 8 (top) and 13 (bottom) were accompanied by ash or steam emissions drifting NW in Sentinel-2 satellite imagery. Images uses Atmospheric penetration rendering (bands 12, 22, 8A). Courtesy of Sentinel Hub Playground.

Figure 120. The ECU 911 webcam at Sangay captured a dense ash and steam plume rising 1,500 m from the summit and drifting W on 18 October 2021. Courtesy if IG-EPN daily reports.

A pulse of increased emissions activity on 1 and 2 November 2021 produced plumes that rose higher than 2,000 m above the summit and drifted SW, W, and NW; incandescence was also observed in the webcams at the summit overnight. Ash plumes on most days of the month rose 600-1,200 m above the summit and drifted in multiple directions. Incandescent blocks were observed descending the SE flank ravine overnight on 6-7 November (figure 121). On 8 November trace amounts of ashfall were reported in Guamote and Flores, with moderate ashfall in Pungala and Cebadas. Overnight the ash plumes reached as high as 2,400 m above the summit. Additional pulses of ash emissions that rose as high as 2,000 m above the summit were reported on 12, 14-15, 24, and 28-29 November.

Figure 121. Ash emissions or incandescent activity was recorded daily at Sangay throughout November 2021. Strombolian activity and incandescent material descended the SE flank ravine and were recorded in the ECU-911 webcam on 6 November (left). Overnight on 8-9 November (right), ash emissions that rose as high as 2,400 m above the summit resulted in ashfall reported in several parishes in the Chimborazo province. Courtesy of IG-EPN daily reports.

In a special report issued on 24 November IG-EPN noted that there had been an increase in the rate of explosions since the evening of 17 November, reaching an average of two per minute; most of them were small. They also noted that the slight inflation recorded on most flanks since June 2021 had grown more pronounced in recent weeks. Strombolian activity and a lava flow in the SE flank ravine were recorded in the ECU-911 webcam on 24 November. Also, IG-EPN reported a possible new vent on the upper W flank that day. Steam and ash emissions were visible in Sentinel-2 satellite imagery along with a summit thermal anomaly on 27 November. A single MODVOLC thermal alert was recorded on 4 November, and multiple alerts were recorded each day on 15, 17, 22, and 26-28 November. Two lahar signals were measured each day on 12 and 26 November, and one each on 18 and 19 November.

A seismic swarm that began on the afternoon of 1 December 2021 was detected by the SAGA station located 6 km SW of the summit. The frequency of the events increased from 32 per hour to 60 per hour by the following morning. A major explosive event during the early morning of 2 December produced an ash plume that rose to 15.2 km altitude and drifted W according to the Washington VAAC (figure 122). The plume dissipated quickly and was seen 45 km WSW of the summit about an hour later at 6.1 km altitude. The higher part of the plume was moving S and E at 13.7 km altitude and dissipating more slowly. A second emission a few hours later rose to 7 km altitude and drifted NW. There were no reports of ashfall that day. Multiple VAAC reports were issued daily for the remainder of the month; steam, gas, and ash plumes rose 500-1,500 m above the summit and drifted mostly W and SW (figure 123).

Figure 122. A seismic swarm at Sangay began during the afternoon of 1 December 2021 (local time), shown by the red arrow on the left side in the seismograph from the SAGA station located 6 km SW of the summit. The frequency and amplitude of the seismic events increased until the following morning, as indicated by the yellow arrow on the right side. A major explosion shortly after 0900 UTC (0400 local time) is shown in purple identified by the red arrow labeled ‘Primera explosion’ at the bottom left of the image. Courtesy of IG-EPN (Informe Volcánico Especial – Sangay – 2021 – Number 03, Nuevo pulso de actividad en el volcán Sangay, Quito, 3 de diciembre de 2021).

Figure 123. A dense steam plume at Sangay drifted SW adjacent to multiple small pulses of dark ash emerging from the summit, also drifting SW on 7 December 2021. Sentinel-2 satellite image uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

A new lava flow on the N flank was first reported after the explosions of 2 December; it was observed in Sentinel-2 satellite imagery on 12 December (figure 124). During the second week of December IG technicians installed five new infrasound sensors and a new high-resolution seismic station in the Domono area, northwest of Macas, 34 km from the summit. Between 15 and 17 December they also installed new ash sampling meters W of the volcano in the Guamote Canton, including the communities of Piscinas de Atillo, Punto Cero-Atillo, Cashapamba, Palmira, and Guamote. Webcam images from overnight on 20-21 December showed incandescent blocks rolling down the SE flank ravine (figure 125).

Figure 124. After the major explosion on 2 December 2021 at Sangay a new lava flow was reported on the N flank; its thermal anomaly first appeared in a Sentinel-2 satellite image on 12 December. Also apparent in this image is the new vent on the W side of the summit first reported in late November. Image uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Figure 125. Strombolian explosions at Sangay on 21 December 2021 sent incandescent blocks down the SE flank ravine as seen in the ECU 911 webcam. Courtesy of IG-EPN Daily Report.

Members of the volcanic observers network in Macas (in the Morona Santiago Province) reported loud noises from Sangay on 25 December. Seismic data showed a slight increase in the intensity of the explosions. A lava flow was visible in the SE flank ravine overnight on 27-28 December along with incandescence at the crater. Pulses of gas and ash emissions rose to 1,000-1,500 m altitude and drifted NE, NW, S, and SW on both days (figure 126). On 31 December, IG-EPN reported three active emissions from the summit: the lava flow in the SE flank ravine, pyroclastic ejecta at the western vent first observed in late November, and lava flows from a N-flank vent, all resulting in a significant increase in thermal energy. All three were visible in Sentinel-2 satellite imagery taken on 27 December (figure 126). More multiple per day MODVOLC thermal alerts were recorded in December than previous months, confirming the increase in thermal activity witnessed in the webcams. Alerts were issued on 3, 8, 10, 12, 15, 19, 21, 22, 24, 26, 28, and 31 December. Lahar seismic signals were recorded on 14, 16, and 18-19 December. Sulfur dioxide emissions were generally low throughout the period, though increases in activity during December coincided with more frequent plumes of SO₂ as measured with satellite instruments (figure 127).

Figure 126. Activity increased at the summit of Sangay at the end of December 2021. In a Sentinel-2 image from 27 December (left), three emission sites were producing thermal anomalies; the N vent produced a flow on the N flank, the W vent sent pyroclastic ejecta down the W flank, and the SE vent produced lava that descended the ravine on that flank. Pulses of ash emissions (right) were visible through dense meteoric clouds on 28 December. Sentinel image uses Atmospheric penetration rending (bands 12, 11, 8a). Left image courtesy of Sentinel Hub Playground; right image courtesy of IG-EPN Daily Report.

Figure 127. Strong sulfur dioxide plumes originated from Sangay during December 2021, as seen here in images from 1, 6, 12, and 27 December. Sangay is the triangle at the bottom of the image and Columbia’s Nevado del Ruiz it the topmost symbol, also with frequent SO2 emissions. Data is from the TROPOMI instrument on the Sentinel-5P satellite. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard MD 20771, USA (URL: https://so2.gsfc.nasa.gov/).

September 2022 (BGVN 47:09) Cite this Report

Daily explosions, avalanches, ash plumes, and crater incandescence during January-August 2022

Sangay is located east of the Andean crest and is the southernmost of Ecuador’s volcanoes. Frequent activity has included pyroclastic flows, lava flows, ash plumes, and lahars, which date back to 1628. The current eruption began in March 2019 and has more recently consisted of explosions, incandescent lava flows, and ash plumes (BGVN 47:02). This report covers activity during January through August 2022 and describes similar events of daily explosions, incandescent avalanches, ash plumes, and thermal activity, based on information from Ecuador's Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Servicio Nacional de Gestión de Riesgos y Emergencias (SNGRE), the Washington Volcanic Ash Advisory Center (VAAC), and various satellite data.

During January through August 2022, IG-EPN reported daily explosions, gas-and-steam and ash plumes that rose 1.4-7 km above the crater, and frequent crater incandescence, often accompanied by incandescent block avalanches of material descending the flanks of the volcano. The highest ash plume occurred on 8 February that drifted NW and resulted in ashfall in several towns. Explosions occurred nearly every day, ranging from 0 to 959, the most of which occurred on 26 July; according to IG-EPN late July into August experienced the greatest number of daily explosions compared to previous months (figure 128). The average number of explosions was 103, with the highest average number of explosions occurring during July (table 11).

Figure 128. Graph showing the number of daily explosions at Sangay during January through August 2022. Data courtesy of IG-EPN (January-August 2022 daily reports).

Table 11. Monthly summary of explosions and plume heights recorded at Sangay during January through August 2022. Data courtesy of IG-EPN (January-August 2022 daily reports).

Activity during January consisted of daily explosions, from 8-207 per day and gas-and-steam emissions containing a small amount of ash that rose as high as 2,000 m above the volcano on 8 January and drifted W and NW. According to the Washington VAAC, several satellite-based images showed ash emissions rising 570-2,070 m above the crater and drifting in several directions, the higher of which occurred on 20 January. Near daily long-period (LP) and tremor events were also reported. During the morning of 8 January crater incandescence was visible. IG reported that on 15 January at 1615 the SAGA seismic station recorded two lahars. Crater incandescence and material was captured in a webcam image on the morning of 18 January (figure 129). On 30 January an ash plume rose 1.5 km above the crater and drifted ESE (figure 130). As a result, according to SNGRE, ash fall was detected in the city of Macas (40 km SE), Morona, and Sucúa (50 km SE), all of which is in the Morona-Santiago province. Slight ashfall was reported in San Isidro the next day on 31 January.

Figure 129. Summit incandescence and material descending the flank of Sangay was visible from the ECU 911 webcam at 0546 on 18 January 2022. Courtesy of IG-EPN Daily report.

Figure 130. A gas-and-ash plume rising above the summit crater of Sangay at 0710 on 30 January 2022. The plume drifted ESE and rose as high as 1.5 km above the crater. Courtesy of IG-EPN Daily report.

Similar activity continued during February, with 0-174 daily explosions and gas-and-ash plumes rising 570-7 km above the crater, the latter of which occurred on 8 February. The area around the volcano was often cloudy, making surface activity difficult to see. LP and tremor events also persisted nearly every day. Satellite surveillance from the Washington VAAC reported that ash emissions rose as high as 4 km above the crater and drifted NW on 8 February. During the early morning of 4 February minor ashfall was reported in Cebadas (35 km NW) and Palmira (45 km W). According to a VAAC alert on 5 February an ash emission was visible at the summit crater accompanied by blocks on the S flank. On 8 February at 0430, a GOES-16 satellite image showed an ash cloud reaching more than 7 km above the crater and drifting NW (figure 131). Reports from the SNGRE and Volcano Observers Network of Ecuador confirmed ashfall in the Chimborazo province (80 km NW), including Riobama, Colta, Guamote, Bolívar, Las Naves, Los Ríos, and Mocache. During the night of 8 February explosions were reported, which resulted in an incandescent avalanche of material. Two lahars were detected during 11 February, one during 13 February, and one during 14 February. Light ashfall was reported by SNGRE in Guamote (40 km W), though the volcano was obscured by clouds on 11 February. A webcam video near Macas showed that there was an incandescent lava flows visible at night on 13 February as a result of explosions at the summit crater. Ten volcano-tectonic events were reported during 22 February.

Figure 131. GOES-16 satellite image showing a strong ash emissions drifting NW from Sangay on 8 February 2022. Sangay is highlighted by the red box and the ash plume is the darker orange color. Courtesy of IG-EPN Daily report.

During March, 4-128 explosions were dectected per day, and gas-and-ash plumes rose as high as 1.4 km above the crater. Frequent LP and tremor events were also detected frequently throughout the month. The weather was often cloudy, which prevented clear views of the summit crater. According to the Washington VAAC, ash emissions rose 570-1,170 m above the summit crater and drifted in different directions. The Sentinel-5P satellite using TROPOMI data occasionally reported sulfur dioxide data throughout the month, ranging from 34.7 tons/day to 2,465 tons/day. During the night of 8 and 15 March crater incandescence was visible in webcam images (figure 132). There was a lahar detected on 14 March that lasted 1 hour and 30 minutes. One lahar was detected on 20 March, two occurred on 22 March, two on 25 March, one on 27 March, and one on 29 March. An explosion and crater incandescence were visible on 30 March and an accompanying ash plume rose as high as 870 m and drifted W and SW (figure 133).

Figure 132. Webcam image of Sangay showing an incandescent explosion during the night of 15 March 2022. Incandescent material was deposited on the flank of the volcano, accompanied by an ash plume. Courtesy of IG-EPN Daily report.

Figure 133. Webcam image showing an incandescent explosion and accompanying ash plume rising above Sangay on 30 March 2022 using the ECU 911 webcam. Courtesy of IG-EPN Daily report.

During April, there were 1-66 daily explosions. Gas-and-ash emissions rose 700-2,000 m above the crater. According to data from the Washington VAAC, gas-and-ash emissions rose 570-2,070 m above the crater and drifted in various directions. Sulfur dioxide based on TROPOMI data ranged from 15.5 tons/day to 2,169 tons/day. During 31 March to 1 April several explosions were detected with incandescent blocks rolling down the flanks of the volcano (figure 134). Frequent LP and tremor events occurred throughout the month. During the night of 1 and 5 April minor ashfall was reported in Guamote and Palmira, respectively by ROVE (Volcano Observers Network). A lahar was detected on 9, 10, 13, 14, 19, 21, 27, 28, 29 April, based on seismic signals that IG recorded; two lahars were detected on 15 April and three lahars occurred on 30 April. During the early morning of 11 April Strombolian explosions were observed. Light ashfall was observed in Chauzán (40 km W), according to ROVE on 13 April; in addition, crater incandescence was visible at the volcano.

Figure 134. Image from the ECU 911 webcam showing several incandescent explosions at Sangay during the night of 31 March 2023. Incandescent blocks of material descended the flanks as a result. Courtesy of IG-EPN Daily report.

Activity continued during May. The number of daily explosions increased to 3-503 per day compared to the previous month. Gas-and-ash emissions rose 500-1,500 m above the crater, though cloudy weather often obscured clear views of the summit. The largest number of explosions occurred on 3 May (503). Occasional LP and tremor-type events were also reported during the month. According to data from the Washington VAAC, gas-and-ash emissions rose 570-2,370 m above the crater and drifted in different directions. Sulfur dioxide measurements from TROPOMI data ranged from 19 tons/day to 430 tons/day. A total of two lahars were detected at 2315 on 3 May and 1030 on 4 May. Another lahar occurred at 1100 on 5 May and on 12 May. Two lahars were reported on 13, 17, 26, 27 May and one on 14, 15, 16, 18, 29 May. Three reports of ashfall were issued, starting at 0754 on 25 May, based on observations in Chauzan and Ichubamba.

In June, daily explosions ranged from 4-101 per day. Gas-and-ash plumes rose 300-1,500 m above the crater and drifted in different directions, though clouds often obscured the view of the summit. The Washington VAAC reported that gas-and-ash emissions rose 570-2,370 m above the crater. The Sentinel-5P satellite using TROPOMI data recorded 17 tons/day to 413 tons/day of sulfur dioxide. Lahars were generated on 8, 9, 11, 12, 23, 26 June based on seismic station signals. During 15-16 June a thin ash cloud rose 1.4 km above the crater and drifted WSW. As a result, there were reports of ashfall in Retén Ichubamba (35 km NW). On 21 June a lahar was observed, in addition to a gas-and-ash plume that rose 1 km above the crater that drifted W. A volcano-tectonic earthquake was also detected that day, along with 97 LP-type events and 83 emission tremor-type events. During 26-27 June a gas-and-ash plume rose 1.4 km above the crater and drifted W and SW, according to IG (figure 135).

Figure 135. Photo of Sangay with a gas-and-ash plume rising 1.4 km above the crater at 0910 at 27 June 2022. Courtesy of Luis Castillo, IG-EPN Daily report.

A high number of daily explosions occurred during July, with 27-959 per day. Gas-and-ash plumes rose 700-2,000 m above the crater, though clouds often prevented clear views of the summit. The Washington VAAC issued volcanic ash notices each day that reported ash emissions rising 570-2,400 m above the summit. TROPOMI data recorded 87 tons/day to 302 tons/day of sulfur dioxide. Frequent LP and emission tremor events continued to be recorded. Lahars were recorded on 3, 5, 8, 9, 11, and 20 July, according to the SAGA seismic station. On 7 July there were 480 explosions detected, and ash emissions rose 870-1,170 m above the crater and drifted W. A volcano-tectonic-type event was also detected. During the night of 7 July, a webcam image showed an explosion and incandescent material on the SE flank of the volcano (figure 136). On 16 July gas-and-ash emissions rose 1 km above the crater and drifted NW. Though the summit was mostly cloudy throughout the day, ECU 911 webcam images showed a Strombolian explosion and incandescent material descending the SE flank (figure 137). No reports of ashfall were made.

Figure 136. Incandescent material was observed on the SE flank of Sangay at 2214 on 7 July, based on the ECU 911 webcam. Courtesy of IG-EPN Daily report.

Figure 137. ECU 911 webcam image showing a Strombolian explosions and incandescent material descending the SE flank of Sangay at 0538 on 16 July. Courtesy of IG-EPN Daily report.

On 18 July there were 689 explosions detected, though weather made it difficult to observe any surface activity. During 19 July the Washington VAAC reported that ash emissions rose 570-870 m above the summit and drifted W. As a result, light ashfall was reported in Alausí, according to SNGRE and ROVE. During the night of 21 July the ECU 911 webcam showed continuous incandescent explosive activity, in addition to an avalanche of incandescent material on the SE flank. There were 959 explosions detected on 26 July, accompanied by gas-and-ash emissions that rose 500 m above the crater and drifted W. According to IG, there were 23 lahars detected during 26 and 27 July. During the morning of 29 July an incandescent avalanche of material was visible on the SE flank. There were reports of explosion-like noises and window vibrations during the morning of 31 July from residents in the towns of Nabón, San Fernando, Guayaquil, Samborondón, and Salitre. Additionally, SNGRE reported that ashfall was detected in Guayaquil, Samborondon, Duran, Salitre, and Daule.

Strong-to-moderate activity continued into August, with 4-680 daily explosions and gas-and-ash plumes that rose 500-3,500 m above the crater, though the summit was often obscured by clouds. The Washington VAAC reported ash emissions as high as 870-2,060 m above the crater. Sulfur dioxide measurements ranged from 17 tons/day to 1,730 tons/day. Occasional LP and emission events occurred throughout the month. On 3 August there were reports of noises coming from the volcano according to residents in Molleturo. Lahars were detected in seismic signals on 5, 9-10, 20, and 29 August. During the evening of 9 August crater incandescence was visible, accompanied by blocks rolling down the flanks of the volcano (figure 138). Ashfall was observed over the SAGA station 5 km SW of the volcano.

Figure 138. Image from the ECU 911 webcam showing crater incandescence at Sangay at 2327 on 8 August 2022. Courtesy of IG-EPN Daily report.

Surface activity increased on 12 August, which consisted of low altitude ash emissions (less than 2 km above the crater), and an ash cloud that extended W and SW across Chimborazo, Bolivar, Cañar, Azuay, and Guayas. There were reports of ashfall in the provinces of Chimborazo (Cebadas, Palmira, Chunchi, and Alausí) and Guayas (Guayaquil, Milagro, and Samborondón). A new lava flow was observed on the SE flank, which was visible in ECU 911 webcam and satellite images. Sounds were audible in several places in the Guayas province, and it was possible to see incandescence from Macas. A strong ash plume rose more than 3.5 km above the crater on 14 August that drifted SW (figure 139). Ashfall was also reported on 14 August in Chauzán San Alfonso in the province of Chimborazo.

Figure 139. Photo of an ash plume rising more than 3.5 km above the crater of Sangay at 1730 on 14 August 2022. Courtesy of IG-EPN Daily report.

On 16 August several continuous gas-and-steam and ash emissions rose higher than 2 km above the crater and drifted mainly W. Ashfall was reported by ROVE in Pancun Ichubamba, Guamote, and Chimborazo. Similar activity occurred into the next day, with ashfall confirmed in Cebadas, Palmira, Sibambe, Tixán, Multitud, Chauzan, and Atapo Santa Cruz in the province of Chimborazo. During the night of 17 August SNGRE reported light ashfall in Alausí (Achupallas, Multitud, Sibambe and Tixán) and Guamote (Cebadas and Palmira). During the early morning of 19 August SNGRE reported light ashfall in Guamote (Cebadas and Palmira). During the night of 23 August crater incandescence was visible with blocks descending the E flank. On 26 August there were 680 explosions detected, which was accompanied by ash emissions that rose 870 m above the crater, according to the Washington VAAC.

Beginning around August 2021, the Sentinel-2 MODIS Thermal Volcanic Activity graph provided by the MIROVA system showed persistent strong thermal signatures in and near the summit area through November 2022 (figure 140). According to the MODVOLC Thermal Alerts system, there were 375 hotspots detected during the reporting period: 81 in January, 61 in February, 72 in March, 21 in April, 56 in May, 35 in June, 27 in July, and 22 in August. These were likely due to frequent incandescence block avalanches that affected the flanks of the volcano, which were occasionally visible in Sentinel-2 infrared satellite imagery, which were seen affecting the N flank during January through June 2022 (figure 141). Frequent, strong sulfur dioxide plumes were also captured by the TROPOMI instrument on the Sentinel-5P satellite; many of these plumes exceeded 2 Dobson Units (DUs) and drifted in different directions (figure 142).

Figure 140. Thermal activity at Sangay was relatively strong due to intermittent incandescent block avalanches on the flanks. Strong thermal activity (red dots) persisted from August 2021 through November 2022, as recorded by the Sentinel-2 MODIS Thermal Volcanic Activity data (bands 12, 11, 8A). Courtesy of MIROVA.

Figure 141. Strong thermal activity was reflected in these Sentinel-2 infrared satellite images of Sangay on 11 January 2022 (top left), 11 April (top right), 21 May (bottom left), and 15 June (bottom right). Incandescent block avalanches shown here mainly descended the N flanks of the volcano. Images use Atmospheric penetration rendering (bands 12, 22, 8A). Courtesy of Sentinel Hub Playground.

Figure 142. Strong sulfur dioxide plumes originated from Sangay throughout the reporting period, as shown here on 2 January 2022 (top left), 6 February (top middle), 17 March (top right), 5 April (bottom left), 21 June (bottom middle), and 29 July (bottom right). Each of these plumes exceed 2 Dobson Units (DUs) and drift in different directions. Sangay is located toward the bottom of the satellite images with sulfur dioxide plumes; Colombia’s Nevado del Ruiz is the topmost symbol that also frequently emits sulfur dioxide. Data is from the TROPOMI instrument on the Sentinel-5P satellite. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Servicio Nacional de Gestion de Riesgos y Emergencias (SNGRE), Samborondón, Ecuador (URL: https://www.gestionderiesgos.gob.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard MD 20771, USA (URL: https://so2.gsfc.nasa.gov/).

March 2023 (BGVN 48:03) Cite this Report

Daily explosions, incandescent block avalanches, lava flows, and ash plumes during September 2022-February 2023

Eruptions recorded since 1628 CE from Sangay, the southernmost of Ecuador’s volcanoes, have been characterized by pyroclastic flows, lava flows, ash plumes, and lahars. The current eruption began in March 2019 and has more recently consisted of daily explosions, avalanches, ash plumes, and crater incandescence (BGVN 47:09). This report covers activity during September 2022 through February 2023 and describes similar events of daily explosions, incandescent avalanches, lava flows, and ash plumes, based on information from Ecuador's Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Servicio Nacional de Gestión de Riesgos y Emergencias (SNGRE), the Washington Volcanic Ash Advisory Center (VAAC), and various satellite data.

During September 2022 through February 2023, IG-EPN reported daily explosions, gas-and-steam and ash plumes that rose as high as 8.3 km above the crater, and frequent crater incandescence, often accompanied by incandescent block avalanches of material descending the flanks of the volcano. The highest ash plume occurred on 4 November and drifted NW, W, and SW. Explosions occurred nearly every day, ranging from 3-2,040, the most of which occurred on 4 October (figure 143). The average number of explosions was 563, the highest average number of explosions was 950, which occurred during December 2022 (table 12).

Figure 143. Graph showing the number of daily explosions at Sangay during September 2022 through February 2023. The number of explosions markedly decreased during early January 2023 and remained relatively low through February 2023. Data courtesy of IG-EPN (September 2022-February 2023 daily reports).

Table 12. Monthly summary of explosions and plume heights recorded at Sangay during September 2022 through February 2023. Data courtesy of IG-EPN (September 2022-February 2023 daily reports).

During September, activity consisted of 146-1,152 daily explosions and gas-and-ash emissions that rose as high as 2 km above the summit crater during 12-13, 18-24, and 29-30 September and drifted SW, W, WNW, NW, N, and NE. Seismicity consisted of near-daily long-period (LP) and emission tremor (TRE) events. According to the Washington VAAC, ash emissions rose 500-2,700 m above the crater rim and drifted SW, WSW, W, NW, S, and N. During 1-2 September crater incandescence was visible, accompanied by blocks that rolled down the E flank. During the afternoon and night of 14-15 September incandescent ejecta was observed. Strombolian activity and crater incandescence was visible during the night and early morning during 17-18 September (figure 144). Continuous gas-and-ash emissions rose 1.5 km above the summit and drifted W in the morning. Light ashfall was reported in Cebadas, and stronger ashfall was detected in Rayoloma during 18-19 September; both towns are located to the NW of the volcano. During 22-23 September ash emissions rose 1 km above the crater rim and drifted W, resulting in ashfall in Chauzán in the Chimborazo province.

Figure 144. Webcam image showing incandescent material ejected above Sangay’s crater at 0059 on 18 September 2022. Courtesy of IG-EPN Daily report.

Activity persisted during October, with 154-2,040 daily explosions, occasional crater incandescence, and gas-and-ash emissions rising as high as 2.5 km above the crater during 26-27 October that drifted W, N, NW, SW, and SE. The Washington VAAC reported that ash emissions rose 570-2,370 m above the crater rim and drifted W, SW, NW, SE, N, SSW, NE, and E. During 2-5 October several explosions were accompanied by incandescent blocks descending the SE flank. Nighttime incandescence was intermittently visible in the upper part of the volcano. During 11-17, 19-21, and 24-27 October incandescent material descended the SE flank. A collapse of the lava flow front generated a small pyroclastic flow that descended the upper part of the SE drainage during 12-13 October. According to GOES-16 satellite images, an ash cloud was detected during the early morning of 14 October that rose 2,370 m above the crater and drifted W. There was a report of ashfall in Guamote as a result. During the night of 18-19 October summit crater incandescence was visible and a lava flow traveled down the SE flank. A lava flow was reported descending the SE flank during 22-23 October. During the night of 25 October strong incandescence was visible in the crater accompanying a lava flow on the SE flank. In the early morning, reports of loud noises were reported in Salitre and Naranjito, which IG noted was likely associated with the explosive activity. Early morning crater incandescence on 29 October was accompanied by a continuous ash emission that rose 1 km above the crater rim and drifted NW. Slight ashfall was observed in Huamboya Canton in the Morona Santiago province.

There were 80-1,380 daily explosions detected during November, in addition to LP and TRE-type events, gas-and-ash emissions that rose as high as 8.3 km above the crater and drifted generally W and NW, and nighttime crater incandescence. According to the Washington VAAC, gas-and-ash emissions rose 570-3,000 m above the crater and drifted in multiple directions. During 31 October to 1 November crater incandescence was accompanied by incandescent avalanches of material along the SE flank and some ashfall in nearby towns. According to a GOES-16 satellite image, an ash cloud was visible starting at 0520 on 4 November, and around 0700 pyroclastic flows descended the Volcán drainage on the SE flank (figure 131). By 0840 the ash plumes had intensified, rising to a height of 8.3 km above the crater and drifting NW, W, and SW. Light-to-moderate ashfall was recorded in the cities of Riobamba, Guamote, Colta, Alausí, Pallatanga, Chambo, and Chunchi during 3-4 November. During 4-5 November pyroclastic flows traveled along the Volcán drainage (figure 145). An ash plume rose 3 km above the crater and drifted NW, resulting in moderate ashfall in Chimborazo, Bolivar, and Los Rios.

Figure 145. Webcam image showing pyroclastic flows descending the SE flank of Sangay during the morning of 4 November 2022. Courtesy of IG-EPN Daily report.

SNGRE reported that on 9 November a moderate amount of ash fell in Zuñac, in the province of Morona Santiago. During the night and early morning of 9-10 November when the volcano cleared for short periods, gas-and-ash emissions, explosions, and crater incandescence were observed, accompanied by an incandescent avalanche of material descending the SE flank. Crater incandescence and an avalanche of material were also visible during clear weather, moving down the SE flank during 10-14, 17-23, and 26-29 November. On 16 November at 0200 the seismic station recorded seismic signals that corresponded to lahars, though cloudy weather obscured views of the volcano. Heavy rain was reported during 17-18 November which resulted in small mud and debris flows down the SE flank. During the night of 21 November crater incandescence was observed in addition to a lava flow that traveled down the SE flank. On 24 November incandescence was recorded in the upper part of the volcano in the early morning, accompanied by pyroclastic flows. An active lava flow was reported on the SE flank during the night and early morning of 25-26 November. Nighttime crater incandescence and pyroclastic flows on the E flank on 29 November.

Activity during December consisted of 34-1,320 daily explosions, gas-and-ash emissions that rose as high as 2.5 km above the crater during 30 November-1 December and 3-4 December and drifted SE, NNE, NE, W, SW, and NW and seismicity consisting of LP and TRE-type events. According to the Washington VAAC, satellite-based images showed gas-and-ash emissions rising to 570-2,700 m altitude and drifting in different directions. Nighttime and early morning crater incandescence was often visible in clear weather, sometimes accompanied by incandescent block avalanches. During 30 November-1 December, 12-15, and 17-18 December an active lava flow was detected on the SE flank of the volcano. During 1-2 and 5-8 December a pyroclastic flow was observed descending the SE flank. During 28-29 December light ashfall was reported in Cebadas.

During January 2023 activity was often obscured due to cloud cover and the number of daily explosions notably decreased; there were 25-824 daily explosions recorded. Gas-and-ash emissions rose as high as 2.5 km above the crater during 16-17 January and drifted in multiple directions (figure 146). The Washington VAAC reported that gas-and-ash emissions rose 570-1,770 m above the crater and drifted SW, WNW, N, NW, W, SE, S, and NE. Crater incandescence was intermittently visible on clear weather days. During the night and early morning of 9-11 January, a lava flow was observed on the SE flank. An incandescent avalanche of material was visible on the SE flank during 21-22 January.

Figure 146. Webcam image of a white gas-and-ash plume rising 2.5 km above the crater of Sangay on 16 January 2023. The dark spots on the image is material on the camera lens. Courtesy of IG-EPN Daily report.

Low activity continued during February, consisting of 3-333 daily explosions. TRE events continued to be detected throughout the month. The Washington VAAC reported that ash emissions rose 500-1,800 m above the crater and drifted NE, S, N, NW, W, SW, and SE. During 14-15 February crater incandescence was visible and an active lava flow traveled 500 m below the summit on the SE flank. During 18-19 November incandescent material rolled down the SE flank. During the night of 21-22 February crater incandescence was accompanied by a lava flow on the S flank. Gas-and-ash emissions rose 1.2 km above the crater and drifted S and NW, based on satellite images during 21-24 February. During 26-28 February continuous ash emissions rose 1.5-2 km above the crater and drifted SW and W.

Satellite data. Thermal activity was consistently strong throughout the reporting period due to crater incandescence, block avalanches, and lava flows primarily affecting the SE flank. This activity was detected by the MIROVA hotspot detection system (figure 147) and the MODVOLC Thermal Alerts system, which detected 108 hotspots. Sentinel-2 infrared satellite imagery showed incandescence block avalanches and lava flows descending the SE flank and crater incandescence (figure 148). Frequent, strong sulfur dioxide plumes were captured by the TROPOMI instrument on the Sentinel-5P satellite; many of these plumes exceeded 2 Dobson Units (DUs) and drifted in different directions (figure 149).

Figure 147. Thermal activity at Sangay was relatively strong throughout the reporting period of September 2022-February 2023 due to frequent crater incandescence, incandescent block avalanches, and lava flows on the flanks. Courtesy of MIROVA.

Figure 148. Strong thermal activity was visible in these Sentinel-2 infrared satellite images of Sangay on 18 September 2022 (top left), 27 December 2022 (top right), 31 January 2023 (bottom left), and 25 February 2023 (bottom right). Incandescent block avalanches and lava flows primarily descended the SE flank, as shown here. Images use “Atmospheric penetration” rendering (bands 12, 22, 8A). Courtesy of Sentinel Hub Playground.

Figure 149. Strong sulfur dioxide plumes from Sangay were frequent throughout the reporting period, as shown here on 13 September 2022 (top left), 26 October 2022 (top middle), 17 November 2022 (top right), 29 December 2022 (bottom left), 4 January 2023 (bottom middle), and 17 February 2023 (bottom right). Each of these plumes exceeded 2 Dobson Units (DUs) and drifted in different directions. Sangay is located toward the bottom of the satellite images with sulfur dioxide plumes; Colombia’s Nevado del Ruiz is the topmost symbol that also frequently emits sulfur dioxide. Data is from the TROPOMI instrument on the Sentinel-5P satellite. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Servicio Nacional de Gestion de Riesgos y Emergencias (SNGRE), Samborondón, Ecuador (URL: https://www.gestionderiesgos.gob.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard MD 20771, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).