Explosions, ash plumes, and block avalanches during June-September 2021

Sinabung in north Sumatra, Indonesia had its first confirmed Holocene eruption during August and September 2010. Dome growth, block avalanches, multiple explosions with ash plumes, and pyroclastic flows are common events that occur. The continuing eruption that began in August 2020 has recently consisted of ash plumes, pyroclastic flows, hundreds of block avalanches, and explosions (BGVN 46:08). This report covers intermittent explosions, ash plumes, and block avalanches from June through September 2021 with information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, and the Darwin Volcanic Ash Advisory Centre (VAAC).

White gas-and-steam emissions dominantly occurred throughout the reporting period; during June, they rose 50-500 m above the summit and drifted E, SE, SW, W, and NW (figure 102). An eruption occurred at 2004 on 3 June, though it was not visually confirmed due to cloud cover. Another event at 2335 on 6 June consisted of ash plumes and pyroclastic flows, though weather again obscured views. A Darwin VAAC notice reported an ash plume visible in satellite images, with the multi-level plume rising to 4.3 km altitude (N), 6.1 km altitude (WNW), 7.3 km altitude (W), and 9.1 km altitude (drifted W and WSW). During 11-13 June block avalanches from the summit lava dome were occasionally recorded, but not visually observed due to weather conditions. Occasional deep volcanic earthquakes occurred through September.

Figure 102. Image of a white gas-and-steam plume rising above Sinabung on 30 June 2021. Courtesy of PVMBG and MAGMA Indonesia.

During July, white gas-and-steam emissions continued to rise 100-500 m above the summit and drift in multiple directions. On 1 July at 1151 a gray plume rose 800 m above the summit and drifted SW and W. An ash plume rose 500 m above the summit and drifted ESE at 0925 on 13 July due to an eruptive or collapse event. Video taken on 13 July showed new vents on the upper W flank that generated gas-and-ash emissions. An eruptive event at 1850 on 19 July produced an ash plume that rose 1 km above the summit and extended ESE; the activity lasted about 11 minutes. A strong explosion on 28 July at 1320 produced an ash plume that rose 4.5 km above the summit and drifted E and S (figure 103) and pyroclastic flows traveled as far as 1 km down the E and SE flanks, prompting PVMBG to raise the Aviation Color Code (ACC) to Red. Ashfall was reported in areas to the E, including the subdistricts of Namanteran, Merdeka, Berastagi, and Simpang Empat; the event lasted for about 12.5 minutes. In addition, a small sulfur dioxide plume that exceeded two Dobson Units (DU) was detected above the volcano, based on data from the TROPOMI instrument on the Sentinel-5P satellite (figure 104).

Figure 103. Image of the resulting ash plume that rose 4.5 km above Sinabung from the strong explosion on 28 July 2021. Courtesy of PVMBG.

Figure 104. The explosion at Sinabung on 28 July 2021 produced a distinct sulfur dioxide plume that exceeded 2 Dobson Units (DU), based on data from the TROPOMI Instrument on the Sentinel-5P satellite. The accompanying ash plume rose 4.5 km above the summit. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Persistent white gas-and-steam emissions rose 50-500 m above the summit and drifted in different directions during August. An avalanche of incandescent material was observed descending 500-700 m to the E and SE during 4-7 August. Another block avalanche descended 700 m on 25 August. Activity decreased during September and October and mostly consisted of white gas-and-steam emissions that rose 50-800 m above the summit and drifted multiple directions. On 23 September infrared Sentinel-2 satellite imagery showed a small thermal anomaly in the summit crater (figure 105).

Figure 105. A small thermal anomaly at Sinabung was recorded in Sentinel-2 infrared satellite imagery on 23 September 2021. Image uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Firdaus Surbakti (URL: https://www.facebook.com/firdaus.surbakti).

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

July 2010 (BGVN 35:07) Cite this Report

First Holocene eruption; ash explosions during August-September 2010

This report documents the first confirmed Holocene eruption at Sinabung, beginning on 27 August 2010 (figure 1). Sinabung is an elongated stratovolcano in the Karo plateau of northern Sumatra, Indonesia, ~80 km NNW of Toba. By 23 September the Center of Volcanology and Geological Hazard Mitigation (CVGHM) had reported six distinct eruptions (table 1), with another two (12 and 14 September) described by analysts at the Darwin Volcanic Ash Advisory Center (VAAC).

Figure 1. [Photos of the Sinabung eruption during 30 August-3 September 2010.] (top) Plume [on the evening of 3 September deflected by winds down the E flank], but spreading and rising at distance. (bottom) Dual plumes discharging [on 30 August, viewed from the NE], the one at left dropping minor ash in the near-source region. Note portions of antenna, presumably from the instrument telemetry system. The emission of dual plumes appears in photos and videos on the internet. Photo credit to Rahmanto (CVGHM).

Table 1. Date and time of Sinabung explosive eruptions reported by CVGHM as of 22 September 2010.

Although widespread press reports indicated that the last eruption occurred in 1600, this statement is incorrect. CVGHM reported that Sinabung had no radiocarbon dates documented after 1600, but that solfataric activity was observed at the summit in 1912.

An initial phreatic eruption reported by CVGHM occurred on 27 August 2010 following heavy rainfall. Later activity ejected juvenile material and was clearly magmatic. Ash and scoria fell to the E and SE, covering the villages of Sukameriah, Gangpitu, Sigarang-Garang, Sukadebi, and Susuk. On 28 August, only a cloud of sparse white smoke was observed, rising to a height of 20 m.

On 29 August observers heard a rumbling noise. The hazard status was changed to Alert Level 4 (on a scale of 1-4), resulting in authorities relocating people living within a 6 km radius of the volcano. At 1000 on 29 August a continuous eruptive signal was recorded, with amplitudes ranging from 0.5 to 1.5 mm. During the following night of 29-30 August activity became visible, and plumes reached 1,500 m above the crater rim. An explosion several hours later produced a white to medium dark plume. Subsequent explosions sent plumes to heights of ~ 100 m.

Footage of the eruption on 29 August showed two closely spaced ash plumes from vents near the summit. The ash plumes caused domestic flights to be diverted and the local Medan airport was closed. The next day (30 August) a second, more powerful, explosion generated an ash plume that rose 2 km above the crater. Media sources reported that 20,000-30,000 residents had evacuated as ash fell in nearby areas and a strong sulfur odor was reported. Nighttime video showed incandescent material descending an undisclosed flank of the volcano. One news report described six hours of activity on 30 August as "... raining ash and debris across several miles and killing two villagers who suffered respiratory and cardiac problems." Although these fatalities were commonly noted in press reports, the cause of these fatalities (and whether linked to the eruption or coincidental) remained uncertain.

The Darwin VAAC, based on information from CVGHM, reported a large explosion on 3 September. News reports stated that the explosion caused vibrations of homes and trees on the flanks, and generated a 3-km-high ash plume. According to news articles, during 31 August-7 September about 6,000 evacuees had been able to return home because activity had decreased.

CVGHM described the 7 September explosion as the largest of the eruptive episode. It produced a gray-to-black ash plume that rose to a nominal ~ 5 km above the crater and drifted SE. Strong vibrations caused by the explosion were detected as far away as ~ 8 km SE. Andrew Tupper (Darwin VAAC) noted that the plume rose soon after midnight on the 7th and presented huge difficulties for both visual and satellite observations. The 5-km plume altitude estimate came from ground observers (time of observation unknown), but a pilot report noted the altitude as ~ 8 km altitude (FL250, 25,000 feet, over the M300 route). A Volcanic Ash Advisory noted those values and traced the report to CVGHM and observations around 0530 on the 7th (local time and date).

Monitoring campaign. Although there is no continuous monitoring at Sinabung, there is a hazard map to provide guidance to local officials (figure 2). CVGHM installed a near-real-time video monitoring system (see Information Contacts) to assess the volcano's behavior during this active episode. Monitoring included four seismic stations high on the mountain with data telemetered to the observation post. Other monitoring included tilt (from a station at 1,200 m elevation), deformation (electronic distance measuring surveying three reflectors measured from Sukanalu Teran village, 4 km from the summit), and sulfur-dioxide emissions (mini-DOAS, and environmental monitoring using a Drager X-am 7000 in residential areas).

Figure 2. Hazard map of Sinabung showing two zones, an inner "danger zone" and an outer "alert zone." Courtesy of CVGHM.

Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://vsi.esdm.go.id/); Camera: http://merapi.bgl.esdm.go.id/aktivitas_merapi.php?page=aktivitas-merapi&subpage=kamera-g-sinabung); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Associated Press; Daily Mail; Jakarta Post; CNN.

March 2011 (BGVN 36:03) Cite this Report

Decreased activity following August-September 2010 eruption

Sinabung, which sits 80 km NNW of Toba caldera, produced its first confirmed historical eruption in August 2010 (BGVN 35:07). We present clarifications on our previous report, some seismic data from the interval 2-4 September 2010 that included large local tectonic earthquakes, episodes of continuous volcanic tremor, and the return of calm after mid-September 2010.

Clarifications. Kus Hendratno (of the Center of Volcanology and Geological Hazard Mitigation, CVGHM) provided additional information about the first figure in our last Sinabung report (BGVN 35:07), which we had captioned as undated. The upper photo, taken from the SW, showed the second eruption on 3 September (in the evening) and shows a plume he considered to be deflected down the E flank by strong winds blowing down-slope. The lower photo was taken on 30 August from the NE. Hedratno did not know the date that the eruption ended. In addition, we described the 27 August 2010 eruption as the "first Holocene eruption" in BGVN 35:07. There was an unconfirmed historical eruption in 1881, and there may yet emerge evidence for other Holocene eruptions. Thus, we now prefer to refer to the 27 August eruption as the first confirmed historical eruption.

Additional information about 2-4 September 2010 activity. Table 2 presents some basic data on 2 to 4 September seismicity. These data are but a portion of a 4 September report by Agus Budianto (head of a geophysical team that responded to the crisis). The seismic data reflect both the presence of volcanic earthquakes, earthquakes interpreted as associated with emissions, far tectonic earthquakes, and tremor. The latter continued in all but one 6-hour time slot on the table, and in two cases, 1800-2400 on the 3rd and 0000-0600 on the 4th, tremor reached dominant amplitudes of 50 mm.

Table 2. Details about seismicity observed at Sinabung during 2-4 September 2010. Terminology as follows: "12@3-63 mm" refers to 12 earthquakes with amplitudes of 3-63 mm; "5-15 s," to duration times. Courtesy of Agus Budianto (affiliation listed in Information contacts).

During 2-4 September, fog often obscured the view. An eruption at 0438 on 3 September was accompanied by a roaring sounds and vibrations that were felt up to 8 km SE. A thick black plume erupted up to 3 km above the crater and drifted E. An eruption on the same day during the hours 1759 to 1801 also caused a roaring sound and weak vibrations that were felt up to 8 km away. Visual observations showed several periods of the eruption; early in the eruption, a black plume soared as high as 1 km above the crater and drifted E. Then, a plume that appeared "clotted" moved approximately 2 km down the E slopes, with most of the ash falling on the E slope. Finally, a plume rose vertically and took the shape of a mushroom. Electronic distance measurements after the eruption at 1759 on 3 September 2010 showed deflation (up to 4.5 mm). On 4 September, the weather was clear, and a thick white plume was visible reaching up to 50 m above the crater and drifting as far as 100 m down the E slope.

Activity during mid- to late-September 2010. CVGHM reported a few noteworthy eruptions, emissions, and changes occurred after early September. During 8-11 September observers saw white-to-gray plumes rising 30-100 m above the crater and generally drifting E. Deformation measurements during 8-14 September showed a slow rate of inflation. Based on analyses of satellite imagery and the CVGHM web camera, the Darwin VAAC reported that on 12 and 14 September ash plumes rose to altitudes of 4.3-4.6 km altitude.

During 15 September-21 September 2010, based on information from CVGHM and views through a web camera, the Darwin VAAC reported ash plumes rising to an altitude of 4.3 km and drifting W. CVGHM reported a slow rate of inflation during 15-18 September followed by deflation during 19-21 September. Fog mostly prevented visual observations. On 20 September diffuse white plumes rose 30 m above the crater and drifted NE.

On 22 September a white plume rose as high as 100 m above the crater. The decrease in activity based on visual observations, seismicity, deformation, and SO₂ concentration prompted CVGHM to lower the Alert Level to 3 (on a scale of 1-4) on 23 September, where it remained through at least mid-March 2011.

Information Contacts: Kus Hendratno, Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://vsi.esdm.go.id/); Camera URL: http://merapi.bgl.esdm.go.id/aktivitas_merapi.php?page=aktivitas-merapi&subpage=kamera-g-sinabung); Agus Budianto, Kementerian Energi Dan Sumber Daya Mineral, Republik Indonesia, Badan Geologi, Jalan Diponegoro No. 57 Bandung 40122 Indonesia.

April 2013 (BGVN 38:04) Cite this Report

Two simultaneous ash plumes from adjacent vents on 30 August 2010

Our previous report on Sinabung (BGVN 36:03) discussed the decreased activity following the 27 August-September 2010 eruption (BGVN 35:07). That was Sinabung's first confirmed Holocene eruption (although there was an unconfirmed eruption in 1881). The decrease in activity since that event prompted Center of Volcanology and Geological Hazard Mitigation (CVGHM) to lower the Alert Level to 3 (on a scale of 1-4) on 23 September, where it remained through at least mid-March 2011. Sinabung is the highest mountain in North Sumatra and sits 80 km NNW of the Toba caldera.

This report includes a more recently available post eruption photo (figure 3). That photo was taken from an aircraft on 13 May 2011 and posted by Johnny Siahaan on Flickr (Siahaan, 2010).

Figure 3. Aerial photo taken 13 May 2011 showing summit area craters and deeply incised upper flanks at Sinabung, as seen in the aftermath of the late 2010 eruption. A thin white plume rises from the summit area. Photo posted by Johnny Siahaan.

This report also includes aspects of the eruption (Siahaan, 2010) during August-September 2010 (BGVN 35:07), including video of the Mt. Sinabung. Johnny Siahaan's video of 30 August 2010 shows a scene with two separate ash plumes rising together (figure 4). The larger plume emitted laterally (almost horizontally) but convection of the hot ash and gasses bent it into the vertical well out over the flank of the volcano. The other plume was initially smaller, escaping from an adjacent but distinct area of the summit, and rising nearly vertically. The two plumes appear to merge at altitude and then bend in the wind. What looks like an older plume in the distance near the beginning of the video rose and was strongly sheared in the wind. The "look direction" of the video was not stated.

Figure 4. Two separate ash plumes rising from two vents at Sinabung. Photo courtesy of Johnny Siahaan's Youtube video, 30 August 2010.

References: Siahaan, J, Image 1414, Sinabung Flickr (URL: http://www.flickr.com/photos/johnnysiahaan/5735509397/)

Siahaan, J, 30 August 2010, Mount Sinabung Eruption, YouTube video (URL: http://www.youtube.com/watch?v=dMSkvYRxLwA )

Siahaan, J, 30 August 2010, Gunung Sinabung Meletus, YouTube video (URL: http://www.youtube.com/watch?v=dMSkvYRxLwA )

Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://vsi.esdm.go.id/).

September 2013 (BGVN 38:09) Cite this Report

17,000 evacuees as mid- to late-2013 eruption emits pyroclastic flows

In several issues of the Bulletin (BGVN 35:07, 36:03, and 38:04) we described the first confirmed eruption at Sinabung volcano (figure 1), which began 27 August 2010. This report notes ongoing eruptions along with more evacuations, more pyroclastic flows, and plumes as tall as 10 km.

Figure 5. A map centered on Indonesia, showing the location of Sinabung volcano on Sumatra Island near the NW end of the long line of active volcanoes (black triangles) in that country. Sinabung lies 35 km NNW from the nearest margin of the crater lake of Toba, the largest identified volcanic caldera on Earth. Courtesy of U.S. Geological Survey.

The Indonesian Center of Volcanology and Geological Hazard Mitigation (CVGHM) reported that seismicity at Sinabung fluctuated during 2012 and through September 2013. During early September 2013, dense white plumes rose 100-150 m above the crater, and, on 14 September, incandescence from the crater was observed. Although this and several other instances of incandescence from the volcano's crater were reported during this eruption period, no MODVOLC thermal alerts were measured.

An estimated 16,000 people live within 10 km of the Sinabung volcano. Many photos of the volcano during this eruption can be found in an article from The Atlantic (Taylor, 2013). Some of the photos disclosed plumes otherwise little documented.

According to news articles, an eruption at 0245 on 15 September produced an ash plume and ashfalls in the towns of Sukameriah (50 km NE), Kutarayat (location uncertain), Kutagugung (16 km SW), and Berastagi (14 km E). About 6,000 people were evacuated from areas within a 3-km radius of the volcano, and several flights at Medan's airport (55 km NW) were canceled. CVGHM raised the Alert Level to III.

An eruption at 1203 on 17 September 2013 ejected tephra and a dense ash plume that rose higher than the plume seen on 15 September. According to the Darwin VAAC, on 17 September, a pilot observed an ash plume that rose to an altitude of 6.1 km and drifted 55 km SE. On 18 September a low-level ash plume rose to an altitude of 3 km and drifted SE, dissipating later that day. The VAAC also noted that CVGHM had confirmed that Sinabung was degassing but not emitting any ash. The evacuees started to return home on 22 September.

Seismicity at Sinabung declined but continued to fluctuate through 22 October. White plumes were seen rising 100-300 m from the crater. On 29 September 2013, the Alert Level was lowered to II.

On 22 October grayish plumes rose 250 m. Vents appeared on the N flank and produced dense white plumes that rose 70 m. On 23 October landslides at two locations were observed, and explosions occurred at 1619 and 1651 hours. Plumes rose from the summit crater and from a fracture formed on 15 October near Lau Kawar, a lake at the foot of Sinabung. Fog prevented observations for a period after the explosions; once the fog cleared dense gray plumes were observed. A third explosion occurred at 2100 hours. On 24 October at 0550 and 0612 explosions s generated ash plumes, and at least one rose 3 km and deposited ashfall in areas S. Based on information from the Indonesian Meteorological Office, the Darwin VAAC reported that an eruption at 1737 on 26 October 2013 generated an ash plume that rose to an altitude of 4.9 km. At 0700 and 1200 hours on 27 October a webcam showed an ash plume rising to an altitude of 3.7 km and drifting over 35 km NE.

CVGHM reported elevated seismicity including continuous tremor ongoing since 29 October 2013. Relatively small ash explosions were also reported prior to the larger events on 3 November. During 29 October-2 November plumes rose to 200-2,000 m above the volcano's summit. Gas measurements conducted by CVGHM during 31 October and on 1-2 November showed a sulfur dioxide (SO₂) flux of 226-426 tons per day; this was a general decrease in emissions compared to those measured routinely during the year In addition, remote sensing data suggested the formation of a new vent sometime between 29 October and 2 November 2013 near the NE summit crater.

During 31 October ashfall was noted on the SE flank up to 1 km from the summit. CVGHM reported that explosions occurred on 3 November at 0126 and 1615, both generating ash plumes up to altitudes of 7 km that drifting W. These triggered evacuations from communities within 3 km of the volcano (~1,681 residents). Rumbling sounds that lasted up to 10 min were noted by staff at the Sinabung Observation Post (~8.5 km from the volcano). News agencies reported that this was the second largest eruption since the 24 October event that displaced more than 3,300 people. The Alert Level was increased from Level II (Watch) to Level III (Alert) at 0300 on the 31st.

Another eruption was reported by CVGHM at 1423 hours on 5 November 2013. This event lasted for 20 minutes and generated an ash plume up to 3,000 m above the crater that drifted SW. Pyroclastic flows were observed at 1431 hours on 5 November that extended 1 km down the SE flank. No casualties were reported.

Based on information from the Jakarta Meteorological Watch Office, webcam data, wind data, and satellite images, the Darwin VAAC reported that on 6 November 2013 an ash plume from Sinabung rose to an altitude of 3 km (figure 2). In addition, a glowing spot was seen near Sinabung's summit.

Figure 6. Sinabung erupts and emits a pyroclastic flow on 6 November 2013. Glowing material appears just below the summit. Hundreds of residents were evacuated to safer areas as the volcano erupted anew following the earlier September 2013 eruptions. Courtesy of Atar/AFP/Getty Images; appeared in Taylor (2013).

The next day an ash plume rose to the same altitude but was not observed in satellite images because of meteorological cloud cover. Webcam images showed an eruption on 8 November that produced a low-level ash plume. The Jakarta Meteorological Watch Office, the webcam, and satellite data detecting SO₂ indicated two explosions on 10 November. The first one, at 0720, generated an ash plume that rose to an altitude of 3.7 km. The altitude of the second plume, from an explosion at 1600, was unknown.

An ash plume on 11 November rose to an altitude of 3 km and drifted less than 20 km SW (figure 3). The next day an ash plume rose to an altitude of 3.7 km and drifted almost 40 km NW.

Figure 7. A press photo taken at Sinabung on 11 November 2013. A larger pyroclastic flow seems poised to descend from the summit area behind two smaller, adjacent pyroclastic flows. A narrow columnar cloud hangs over the summit. Courtesy of AP Photo/Dedy Zulkifli; appeared in Taylor (2013).

Based on webcam data and satellite images, the Darwin VAAC reported that during 13-14 November an ash plume from Sinabung rose to an altitude of 3.7 km and drifted almost 150 km NW and W. A pyroclastic flow traveled 1.2 km down the SE flank on 14 November, prompting more evacuations from villages near the base of the volcano.

An explosion observed with the webcam on 18 November 2013 produced an ash plume that rose to an altitude of 7.6 km. About 30 minutes later an ash plume also visible in satellite images rose to an altitude of 11.3 km and drifted 65 km W. Four hours later satellite images showed fresh ash plumes at an altitude of 9.1 km to the W of Sinabung and at an altitude of 4.6 km over the crater. On 19 November the webcam recorded an ash plume that rose to an altitude of 4.6 km over the crater. A news article stated that later that night that an ash plume rose to an altitude of 10 km.

A news article from 20 November noted that volcanologists updated the previous hazard map for Sinabung (see figure in BGVN 35:07). The second-tier disaster-prone area, previously defined as a radius of 2-3 km from Sinabung's crater, was expanded to 4-5 km.

CVGHM reported three explosions from Sinabung on 17 November 2013. The first explosion, at 2024, generated an ash plume that rose 500 m and drifted SW, and a pyroclastic flow that traveled 500 m down the SE flank.

At 2152 hours that day a dense ash plume from an explosion rose 500 m and drifted SW. Incandescent material was ejected 50 m away from the crater. At 2252 an ash plume rose 1 km and drifted SW. At 0704 on 18 November an explosion generated an ash plume that rose 8 km and drifted SW. A pyroclastic flow also traveled 800 m down the SE flank.

On 19 November at 2155 a dense ash plume rose 10 km, drifted SW, and exhibited lightning. Pyroclastic flows again traveled 500 m SE. Multiple explosions on 20 November (at 0240, 0405, 0529, 0619, and 0641) generated ash plumes that rose to heights between 1 and 3.5 km. An explosion at 1716 was detected by the seismic network but cloud cover prevented observations of possible plumes. White plumes rose 100 m on 21 and 23 November, but misty conditions prevented visual observations on 22 November. On 23 November scoria fell in the Sigarang-garang and Desa Kuta villages in the NNE. Two explosions on 24 November, at 0043 and 0232 hours, were detected but not visually observed. Ash plumes rose 8 km and drifted NNE at 0727, rose 1 km at 0812, and rose 3 km at 0855. Since Sinabung's activity continued to increase, CVGHM raised the Alert Level to IV on 24 November. CVGHM noted that residents and tourists were advised not to approach the crater within a 5-km radius. Remaining residents in 17 villages around the volcano were to be evacuated.

News reported that on the morning of 25 November 2013 six new eruptive events sent "lava and searing gas" up to 1.5 km down the slopes, causing villagers to evacuate; this description apparently refers to pyroclastic flows. Volcanic material erupted as high as 2 km above the crater. The Indonesian National Agency for Disaster Management (BNPB) reported that 17,713 people, out of the 20,270 residents had been evacuated to 31 shelters.

Based on webcam data and wind data, the Darwin VAAC reported that during 28-31 November and 2 December ash plumes from Sinabung rose to altitudes of 3-5.5 km. Ash plumes drifted 150 km W during 30-31 November and 55 km W on 2 December. On 3 December ash plumes rose to an altitude of 8.2 km and drifted W. According to a news report on 2 December, landslides triggered by torrential rain buried houses and killed nine people in Gundaling village, 12 km E. On 4 December an ash plume from Sinabung rose to an altitude of 8.2 km and drifted N. Later that day and during 5-6 December ash plumes rose to altitudes of 3-3.7 km and drifted NW. CVGHM reported that observers in Ndokum Siroga, about 8.5 km away from the volcano, noted gray plumes rising 1 km above Sinabung on 6 December. They also saw grayish-white and dense white plumes as high as 400 m on 7 and 8 December, respectively. Dense grayish-to-white plumes rose 70-200 m on 9 December. White plumes rose 100-150 m above the crater during 10-13 December. Tremor during 6-13 December was recorded continuously, with varying amplitude. The number of low-frequency earthquakes significantly increased on 7 December, and the number of hybrid earthquakes increased the next day. RSAM (real-time seismic amplitude measurement) values of energy steadily increased since 28 November. The Alert Level remained at IV.

In conclusion, seismicity and images of ash plumes and pyroclastic flows suggest that the current eruption of Sinabung volcano began around 14-15 September 2013 and has continued through at least 11 December 2013.

Reference: Taylor, A., 18 November 2013, In Focus: The Eruptions of Mount Sinabung, The Atlantic (URL: http://www.theatlantic.com/infocus/2013/11/the-eruptions-of-mount-sinabung/100630/).

Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM) (also known as Pusat Vulkanologi dan Mitigasi Bencana Geologi-PVMBG), National Agency for Disaster Management (Badan Nacional Penanggulangan Bencana-BNPB), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); CBC.CA News, Toronto, Canada (URL: http://www.cbc.ca/); The Atlantic (URL: http://www.theatlantic.com); ReliefWeb (a specialized digital service of the United Nations Office for the Coordination of Humanitarian Affairs-OCHA) (URL: reliefweb.int); and Volcano Discovery (URL: http://www.volcanodiscovery.com).

January 2014 (BGVN 39:01) Cite this Report

Dome eruption continues; fatal pyroclastic flow on 1 February 2014

The latest eruption of Sinabung volcano began mid-September 2013; activity through early December 2013 was reported in BGVN 38:09. This report describes the continuing eruption from December 2013 through April 2014, primarily drawn from reports issued by the Indonesian Center of Volcanology and Geological Hazard Mitigation (CVGHM) and reports from the Darwin Volcanic Ash Advisory Centre (VAAC). Many videos and photographs also emerged online, some of outstanding information content.

Badan Nacional Penanggulangan Bencana (BNPB — the Indonesian National Agency for Disaster Management) produced a map in 2013 showing disaster-prone areas near Sinabung (figure 8 and table 3). Orange shading shows the highest hazard area, Area III. The S and SE extensions of Area III project downslope, delineating regions and villages with high exposure to pyroclastic- and lava-flow hazards.

Figure 8. Sinabung 2013 hazard map of Sinabung showing villages within hazard-prone zones, including locations such as the village of Sukameriah located S of the summit (labeled 'Ds. Suka Meriah'). Table 3 translates critical portions of the map key. Courtesy of BNPB; from Carl (2014).

Table 3. Sinabung hazard-prone areas (KRB) map's legend translated into English (refer to figure 1). Courtesy of BNPB and Google Translate.

December 2013-January 2014. Based on webcam images, the Darwin VAAC reported that on 22 December an ash plume from Sinabung rose to an altitude of 3.7 km and drifted 55 km W. During 23-24 December ash plumes recorded by the webcam rose to an altitude of 3 km.

PVMBG reported that seismicity at Sinabung increased during 21-26 December and indicated rising magma and lava-dome growth. Observers in Ndokum Siroga, about 8.5 km away, noted dense white plumes rising 70-1,200 m above the crater. Roaring was also periodically heard. A lava dome in the North Crater, visible on 24 December, was 56 m high and 210 m wide. During 25-26 December plumes were white and gray, and rose 300-400 m above the crater. On 26 December the lava-dome volume was estimated to be over 1 million cubic meters, with a growth rate of 3.5 cubic meters per second. The Alert Level remained at 4 (on a scale of 1-4). Visitors and tourists were prohibited from approaching the crater within a radius of 5 km.

On 30 December Badan Nacional Penanggulangan Bencana (BNPB) reported that the number of displaced people reached 19,126 (5,979 families). They also noted that activity at Sinabung had increased. Collapsing parts of the lava dome generated block-and-ash flows as well as pyroclastic flows which traveled as far as 3.5 km down the SE flank. Explosions and pyroclastic flows generated ash plumes that rose at least 6 km above the crater.

BNPB reported vigorous eruptions during 30-31 December 2013. Ash plumes rose as high as 7 km above the summit lava dome, pyroclastic flows traveled as far as 3.5 km SE, and incandescent lava and ash traveled 1.5 km SE. Dome growth and vigorous related dynamics in January were documented on the Photovolcanica (2014) web site. Lightning, lava-dome growth, pyroclastic flows, and ash whirls ("twisters", shown below) were observed during Sinabung's eruptions.

On 3 January 2014 lava-dome collapses generated more than 100 pyroclastic flows that traveled 2-4 km SE. Two villages evacuated, Jerawa (Ds. Jeraya) and Desa Pintu Besi (Ds. Pintu Besi) (figure 8). On 4 January pyroclastic flows were larger and more frequent; they traveled up to 5 km SE and 3.5 km SSE. Ash plumes rose 2-4 km (figure 9). Roaring was periodically heard and burned trees on the S flank were noted. Seismicity remained high, with constant tremor, hybrid earthquakes indicating a growing lava dome, and volcanic earthquakes. The number of low-frequency earthquakes dropped dramatically, however.

Figure 9. A woman carrying her daughter in an agricultural plot near Sinabung as an ash plume rose and pyroclastic flows descended the flanks on 4 January 2014. Photo by Ifansasti (2014).

At 1600 (UTC) (2300 local) on 4 January 2014, MODVOLC satellite thermal alerts were measured over Sinabung for the first time in at least the last 10 years. (The MODVOLC system was described in the 1980's and an online version started during 2000-2001, although some similar thermal databases now span on the order of 4 decades (Ramsey and Harris, 2011; Wright and others, 2004)). Lava effusion was high, resulting in thermal alerts during much of January 2014. From the time of that first alert, nearly daily to weekly alerts were measured through May 2014.

During 4-5 January pyroclastic flows were recorded 426 times. On 5 January the number of hybrid earthquakes increased, indicating lava-dome growth, and pyroclastic flows traveled 1.5-4.5 km SE. On 7 January ash plumes rose 1-6 km and drifted SW, and pyroclastic flows continued to travel 1.5-4.5 km SE. The village of Payang, ~4.6 km S of Sinabung's summit, was blanketed by ash on 7 January 2014 (figure 10).

Figure 10. The village of Payung (~4.6 km S of Sinabung's summit) as ash falls during the eruption of Sinabung on 7 January 2014. Image courtesy of Martin (2014); photography by Ulet Ifansasti/Getty Images.

A pyroclastic flow photographed on 10 January appears in figure 11. BNPB reported that the number of hybrid earthquakes decreased on 11 January and volcanic earthquakes increased. Amid these January eruptions aAsh plumes rose 1-5 km and drifted W, and pyroclastic flows traveled 1-4.5 km SE and 1 km E. Several villages in the Namanteran district reported ashfall. On 16 January, satellite imagery showed a white ash plume underlain by previous deposits of gray pyroclastic flows (figure 12). Around this time, the number of refugees reached over 22,000 persons.

Figure 11. Pyroclastic flows traveling down Sinabung's S flank during an eruption on 10 January 2014. This photo was taken from Berastepu village in Karo district (~4 km SE of volcano summit). Courtesy of Bracken (2014), with caption information from REUTERS/Beawiharta.

Figure 12. The Advanced Land Imager (ALI) on the Earth Observing-1 (EO-1) satellite collected this natural-color image of an ash plume from Sinabung on 16 January 2014. Frequent collapses from the unstable lava dome at the volcano's summit created pyroclastic flows that have traveled at least 4.5 km down the volcano's flanks. The SE margin of these flows are just visible to the lower right of the plume. Courtesy of NASA Earth Observatory. Image by Jesse Allen and Robert Simmon, using EO-1 ALI data from the NASA EO-1 team. Caption by Robert Simmon.

A number of images of the eruption of Sinabung volcano during the second week of January 2014 are available on the Photovolcanica website (Roscoe, 2014). James Reynolds captured some remarkable videos of pyroclastic flows at Sinabung on 21 January 2014 (Earth Uncut TV, 2014; Vervaeck, 2014). Those videos showed explosions that often initiated the pyroclastic flows. As the flows moved downslope, they rapidly formed turbulent, ash-laden currents comprising the bulk of the flow volume (see Figure 3). An image of the S flank of Sinabung taken on 14 January shows lava flows erupting from the summit (figure 13).

Figure 13. Sinabung volcano on 14 January 2014 as it erupts a small plume and a lava flow that traveled down the volcano's S flank, as seen from Kuta Tengah village. Note the sinuous gulley (shaded depression) running downslope just to the right (E) of the lava flows; this is also a prominent landmark in figure 9. Courtesy of India Times (2014).

On 31 January 2014 Sinabung continued to effusively erupt viscous lava, further contributing to both the growth of the lava dome and the lava flow that descended the SE flank. The depression on the SE side of the volcano was mostly been filled by the lava flow, prompting concerns that pyroclastic flows lacked confinement and might take other paths to the S or E.

February 2014. On the morning of 1 February 2014 the lava dome collapsed and created one or two pyroclastic flows. As a result, 17 people (mostly students) died. All known fatalities occurred in Sukameriah village ('Ds. Suka Meriah,' figure 1). That village sits just over 3 km S of the summit, thus well within the 5-km-exclusionary zone. The resulting expanse of hot deposit generated a series of narrow spinning vortices ('twisters') of rising air and ash, that with height joined a rising plume (figure 14).

Figure 14. Twisters generated from pyroclastic flows at Sinabung on 1 February 2014. Courtesy of Plait (2014) (photo from video on Photovolcanica website).

Waning trend. According to CVGHM, during 2-4 February 2014 no significant explosions or pyroclastic flows seemed to have occurred. Activity showed an overall decreasing trend. The number of seismic events related to the rise of new magma (hybrid earthquakes and tremor) had generally decreased over the preceding weeks. This corresponded to what was observed visually (when weather permitted clear views). Occasional medium-sized explosions and dome collapses produced pyroclastic flows that reached up to 3 km in length at 1350 on 3 February and at 0750 on 4 February.

Based on webcam images, Indonesian Met office notices, wind data, and ground reports, the Darwin VAAC reported that during 12-13 and 15-18 February ash plumes from Sinabung rose to an altitude of 3.7 km (12,000 ft) a.s.l. and drifted 25-95 km N, NE, and E.

During 15-23 February 2014 the eruption continued without significant changes, but with progressively decreasing activity. CVGHM noted the slow extrusion and gradual enlargement of the lava effusing from the summit vent and onto the S slope. Occasional rockfalls, ash emissions, and minor pyroclastic flows occurred as well. The erupted lava was determined to be andesite, typical of many stratovolcanoes in subduction settings.

March 2014. Based on wind data, webcam images, and satellite images, the Darwin VAAC reported that during 25 February-1 March and 3-4 March ash plumes from Sinabung rose to altitudes of 3-4 km a.s.l. and drifted 25-55 km E, NE, N, NW, W, and SW. Darwin VAAC also reported that during 4-7 and 9-11 March ash plumes from Sinabung rose to 3.7-4 km a.s.l. and drifted W and SW. During 6 and 9-11 March ash plumes drifted 35-165 km SW and W.

PVMBG described activity at Sinabung during 8-15 March based on observations from a post in the Ndokum Siroga village, 8.5 km away. Dense white plumes rose from the lava dome daily, as high as 1 km on most days; plumes rose 2 km on 12 March. Incandescent material originating from various parts of the lava dome traveled up to 2 km S and SE. Tremor and volcanic earthquakes were detected, and signals representing avalanches from the unstable and still-growing dome increased. Sulfur dioxide emissions varied between 300 and 598 tons per day. Observations on 13 March showed that lava from the dome had flowed 2.4 km downslope.

On 15 March 2014, Sinabung was still at Alert Level 4 (the highest level). During 15-22 March 2014, there was a declining trend in the RSAM (real-time seismic amplitude measurement).

The volcano continued to be active on 18 March 2014 with no significant changes, but an overall decreasing trend. Lava effusion fed the S-flank lava lobe which had been mainly growing along its E side. No significant pyroclastic flows occurred, only frequent smaller rockfalls. Small ash plumes continued to be regularly visible on satellite imagery. The 18 March report indicated that seismicity decreased overall and hybrid earthquakes had disappeared. This suggested to the authors that pressure and magma supply rate had dropped significantly and that the eruption could be ending in the near future.

Based on webcam images, the Darwin VAAC reported that on 29 March an ash plume from Sinabung rose to an altitude of 4.3 km. Meteorological cloud cover prevented satellite views.

On 30 March 2014, CVGHM reported a slowly decreasing trend in activity, with little variation over the preceding weeks. The viscous lava lobe remained weakly sustained and continued to grow very slowly. An intermittent steam and an occasional ash plume often rose to ~4.2 km a.s.l. No new pyroclastic flows occurred. During 23 March-8 April dense white plumes rose at most 1.2 km above the lava dome. Lava had traveled 2.5 km down the flanks as of 6 April and was incandescent at various locations. Incandescent material originating from the edges of the lava dome and flow traveled up to 2 km S and 500 m SE. Tremor and volcanic earthquakes were detected, and signals representing avalanches from the unstable and still-growing dome decreased. Sulfur dioxide emissions varied but were relatively insignificant. Based on decreasing seismicity, deformation, and SO₂ gas flux, CVGHM lowered the Sinabung Alert Level from 4 to 3 on 8 April 2014.

Flow paths into April 2014. Figure 15 shows two satellite images of Sinabung, the upper taken on 7 June 2013 (before the eruption) and the lower taken on 6 February 2014 (during the current eruption). The path of the pyroclastic and lava flows on the SE flank shows the extent of the devastated area and the orientation of other images (figures 13 and 16). Ashfall coated nearby villages and the flanks, as well as the coffee, chili pepper, and other types of plantations clustered at the foot of the volcano.

Figure 15. (Top) Pre-eruption Sinabung image acquired by Landsat on 7 June 2013; much of the surrounding landscape was covered by dark green forests. (Bottom) An image acquired on 6 February 2014 by the Advanced Land Imager (ALI) on the Earth Observing-1 (EO-1) satellite. This is a natural-color image of an ash plume, a light gray apron of pyroclastic flow deposits, and broad scale ash fall coating much of the region. Frequent collapses from the unstable lava dome near Sinabung's summit created pyroclastic flows that traveled at least 4.5 km from the summit. NASA Earth Observatory images by Jesse Allen, using EO-1 ALI data provided courtesy of the NASA EO-1 team and Landsat data from the U.S. Geological Survey. Caption by Robert Simmon and Adam Voiland.

CVGHM prepared an image (figure 16) of the path along which lava and pyroclastic flows traversed down the S side of Sinabung, delineating the extent of the lava flows at various dates from 31 January through 6 April 2014. On 6 April 2014 the lava flow was 2.5 km from the volcano summit. The image of 6 February 2014 (figure 15) revealed that pyroclastic flows had gone ~4 km from the summit of Sinabung. Some of those pyroclastic-flow deposits appear outboard and below the lavas at the bottom of figure 9.

Figure 16. This 6 April 2014 photograph of the S flank of Sinabung was annotated with dates by CVGHM (in Indonesian) to mark the advance of lava during 31 January-6 April 2014. The annotations include such features as flow margins and fronts ('lidah lava' means lava tongue). Taken from the CVGHM weekly report of 8 April 2014.

A report from CVGHM dated 10 April 2014 indicated that lava had recently extruded slowly, feeding a thick lobe on the S flank. The effusion rate had declined, hybrid earthquakes disappeared, and rockfall-induced seismicity decreased. Owing to these recent decreases in the intensity of activity, on 10 April authorities decreased the alert status from the Level 4 to 3 (on a scale of 1-4). People from some of the evacuated areas (to the E and NE) were allowed to return to their homes where they began the process of cleaning up the ash (of unstated thickness). Only the areas remaining off limits were within 3 km radius (eg., Sukameriah) and the SE sector village Berastapu (figure 8).

The lava lobe descending from the summit was considered by CVGHM to represent a large unstable mass draped onto the steep slope of the volcano. They acknowledged the risk of a sudden failure that could potentially result in a devastating pyroclastic flow. A pyroclastic flow did occur on 17 April 2014 at 1740, triggered by a partial collapse of the steep lava tongue. The flow was relatively small and only reached the then depopulated area at the base of the volcano.

Based on webcam images, satellite images, and wind data, the Darwin VAAC reported that on 22 April an ash plume rose to an altitude of 3.7 km and drifted almost 40 km W. MODVOLC thermal alerts were measured on 21 April 2014 at 1540 UTC and on 26 April 2014 at 1855 UTC.

Geophysical and geochemical plots. Figures 17 and 18 summarize measurements made and provided by CVGHM; figure 17 plots seismic signals measured from 7 November 2013 to 8 April 2014, and figure 18 plots various geochemical fluxes from1 September 2013 to 8 April 2014.

Figure 17. Plots showing on the y-axis the daily number ('jumlah') of various seismic events measured at Sinabung volcano for the period 7 November 2013 (07/11/2013) to 6 April 2014 (06/04/2014). The common x-axis values depict time, with dates shown for 10-day intervals, using the format 'dd/mm/yyyy'. The seismic types include: 'letusan'-seismically-detected eruptions; 'guguran'-avalanche signals, which correlated with the instability of the lava dome; 'hybrid' earthquakes—associated with growth of the lava dome; and 'VA'-deep volcanic earthquakes, indicating the persistence of a relatively small pressure due to intrusion of magma. Although not shown, CVGHM also measured low-frequency and shallow-volcanic earthquakes and tremor. Courtesy of CVGHM.

The deep volcanic ('VA') and hybrid earthquakes were among the earliest to show clear escalation, with the latter the most sustained. As seen on figure 17, all seismic data, except that associated with avalanches, decreased dramatically after mid-February 2014.

Figure 18 shows in the upper panel, the same seismic peak ('Letusan,' seismically detected eruptions) seen in the previous figure, an interval of high values measured in late December and especially prominent during early to mid-January. In the 2nd panel from the top, SO₂ flux, there is a gap in data during the time of the eruption, due at least in part to the challenge of obtaining meaningful measurements in ash-choked plumes. Pronounced peaks occurred in available SO₂ flux measurements during the periods 11-18 January and ~mid to late February 2014, with data gaps in their midst, probably for the same reasons just mentioned. Later and earlier measurements yielded much lower fluxes.

The 3rd panel down plots hot-spring-water temperatures ('suhu air panas'), which showed but gradual changes on the order of 0.5°C increase overall. The 4th and 5th panels down plot CO₂ and H₂S, respectively (in percent by volume) for the same area. Both those measurements display similar patterns. They lack data from January, around the time the eruption, thwarting direct comparisons to the eruption. In addition, CVGHM measured and reported deformation nearby Sinabung from tiltmeters and electronic distance measurement (EDM) equipment (not shown here). They also employ a webcam to monitor the volcano in clear weather.

Figure 18. Daily number of explosion earthquake ('Letusan') and various geochemical fluxes and concentrations measured at Sinabung volcano on a common x-axis scale for the period from 1 September 2013 to 8 April 2014 (in figure as 01/09/2013 to 08/04/2014; i.e., dates in the format 'dd/mm/yyyy'). The measurements indicated by the heading labels for each graph include: 'letusan' — eruption earthquakes per day; SO2 flux in tons/day; 'suhu air panas'—water temperature of the hot springs area in District Payung at the S foot of Sinabung in °C; and hot spring CO2 and H2S there in percent by volume. Courtesy of CVGHM.

References. BNPB, 2014, Disaster Map of Mount Sinabung (URL: http://geospasial.bnpb.go.id/2014/04/09/peta-penurunan-status-gunung-sinabung/ ).

Bracken, M., 2014 (10 January), Eruptions at Mount Sinabung in Indonesia displace residents, Baltimore Sun Darkroom, (URL: http://darkroom.baltimoresun.com/2014/01/eruptions-at-mount-sinabung-in-indonesia-displace-residents/##2).

Carl, 2014 (6 January), The Road to Sinabung, VolcanoCafe (URL: http://volcanocafe.wordpress.com/2014/01/06/the-road-to-sinabung/).

Earth Uncut TV — You Tube, 2014 (16 February), (URL: http://www.youtube.com/watch?v=8nGoRPeZMjo&list=UULKYsEXfI0PGXeKYL1KV7qA ).

Ifansasti, U., 2014 (4 January), Villagers Evacuated As Mount Sinabung Eruptions Continue, Getty Images (URL: http://www.google.com/hostednews/getty/article/ALeqM5i60aXEMfqnd64Q0ILmbE2qrbV98A?docId=460700117&hl=en).

India Times, 2014 (14 January), Mount Sinabung volcano spews ash as seen from Kuta Tengah village in Karo district 14 Jan, 2014, Economic Times (URL: http://economictimes.indiatimes.com/slideshows/day-in-pics/january-14-2014/mount-sinabung-volcano-spews-ash-as-seen-from-kuta-tengah-village-in-karo-district/slideshow/28800393.cms).

Martin, M., 2014 (7 January), Indonesia's Mt. Sinabung continues to spew ash, Los Angeles Times Photography website (URL: http://framework.latimes.com/2014/01/07/mount-sinabung/##/9).

NASA Earth Observatory, 2014 (16 January), Roiling Ash Plume above Sinabung Volcano, (URL: http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=82872).

NASA Earth Observatory, 2014 (12 February), Changed landscape around Sinabung (URL: http://earthobservatory.nasa.gov/IOTD/view.php?id=83080&eocn=image&eoci=related_image).

Plait, P, 2014 (7 February), Like Volcanoes Aren't Scary Enough, Now They're Spawning Twisters, Slate (URL: http://www.slate.com/blogs/bad_astronomy/2014/02/07/volcano_twisters_ash_devils_spawned_from_sinabung.html).

Ramsey, M.S., Harris, A.JL., 2012, Volcanology 2020: How will thermal remote sensing of volcanic surface activity evolve over the next decade? J. Volcanol. Geotherm. Res., doi: 10.1016/j.jvolgeores.2012.05.01.

Roscoe, R, 2014, Sinabung Volcano (Gunung Sinabung), Photovolcanica website (URL: http://www.photovolcanica.com/VolcanoInfo/Sinabung/Sinabung.html).

Wright, R., Flynn, L.P., Garbeil, H., Harris, A., Pilger, E., 2004.MODVOLC: near-real-time thermal monitoring of global volcanism. J. Volcanol. Geotherm. Res. 135 (1-2), 29-49; DOI: 10.1016/j.jvolgeores.2003.12.008

Information Contacts: Indonesian Center of Volcanology and Geological Hazard Mitigation (CVGHM) (also known as Pusat Vulkanologi dan Mitigasi Bencana Geologi-PVMBG), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://vsi.esdm.go.id/); Indonesian National Agency for Disaster Management (Badan Nacional Penanggulangan Bencana-BNPB), Gedung Graha 55 Jl. Tanah Abang II No. 57, 10120, Jakarta Pusat (URL: http://www.bnpb.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); CBC.CA News (URL: http://www.cbc.ca/news/world/); Volcano Discovery (URL: http://www.volcanodiscovery.com); MODVOLC, 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/); and NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/NaturalHazards).

October 2014 (BGVN 39:10) Cite this Report

Frequent eruptions, pyroclastic flows, and advancing lava-flow lobe during May-October 2014

On the basis of ash-plume reports from the aviation community around the time of this reporting, Sinabung ranked as the most active volcano in Indonesia, the world's fourth-most populated country. The volcano is located in the Karo Regency of N Sumatra (figure 19). The latest eruption began mid-September 2013; activity through April 2014 was reported in BGVN 39:01. This report describes the continuing volcanic activity from May 2014 through October 2014, primarily drawn from reports issued by the Indonesian Center of Volcanology and Geological Hazard Mitigation (CVGHM) and reports from the Darwin Volcanic Ash Advisory Centre (VAAC). During this reporting interval, many photographs of Sinabung emerged online, some with outstanding information content, but far too numerous to either catalog or feature here.

Figure 19. Sinabung is located in Karo Regency on the island of Sumatra in the Indonesian archipelago. Sinabung resides NE of the closest margin of Toba caldera, the largest volcano of this type known on Earth. The elongate caldera contains a lake 100 km long. The central portion of the lake is occupied by a prominent island (a classic resurgent dome). Taken from Darwin VAAC.

The Darwin VAAC describes their jurisdiction as covering ~150 active volcanoes located in the South Pacific region from the Philippines to the Solomon Islands, including Indonesia. They issued 1,511 Volcanic Ash Advisories (VAAs) during the 12-month period, 1 July 2013 to 30 June 2014 (their fiscal year 13/14; Darwin VAAC, 2014). During the next 7-month interval (ending 31 January 2015) the VAAC issued 742 reports (Darwin VAAC, 2015). These VAAs are part of their mission to create materials for warning and guidance to the aviation community, including aviation meteorologists, air traffic control offices, and airlines (e.g. dispatchers and pilots).

One way to assess the production of noteworthy ash plumes at volcanoes is to consider the number of VAAs issued, an assessment found in their Management Reports (Darwin VAAC, 2014; 2015). The Darwin VAAC issued Management Reports that both cover and extend beyond (i.e., both earlier and later than) this reporting interval (May to October 2014). Specifically, their reports cover 1 July 2013-30 June 2014 and 1 July 2014-31 January 2015. In both those intervals the largest number of VAAs issued for any single volcano in their region went to Sinabung. In the earlier interval this consisted of 537 out of 1,511 total regional reports; in the later interval, 321 out of 742 total regional reports.

The table in the section "Data compilation" at the bottom of this report also highlights a case at 12:32 UTC on 22 May 2014 of a rapidly growing cloud around Sinabung plausibly associated with an eruption there. The cloud reached ~15.2 km altitude and was initially assessed as eruptive and ash bearing. At the time forecasters felt there was sufficient evidence the cloud contained ash to warrant an advisory. A more detailed assessment made later determined the cloud to probably have been a cumulonimbus cloud (abbreviated Cb; a towering vertical dense cloud often associated with thunderstorms and atmospheric instability). The case illustrates the challenge of creating VAAs rapidly with limited information and time for analysis, balanced against the desire for high accuracy (with low rates of false positives and false negatives). Darwin VAAC (2015) also described the region as one with "...moist tropical convection that makes remote sensing difficult for much of the year."

During the reporting interval, Sinabung was the scene of both lava flows and vigorous dome-building eruptions that discharged significant ash plumes and pyroclastic flows (PFs). Lava flows constructed a several kilometer long tongue or lobe of lava on the flank to the S-SE. These events accompanied elevated seismicity.

During the reporting interval the Aviation Colour Code (ACC) issued by the VAAC was generally Orange; however, during the week of 15-21 October, the ACC was Red.

The ACC is a four-color scale used to inform the needs of the aviation community. The four colors denoting increasing risk are Green, Yellow, Orange, and Red. According to the World Organization of Volcano Observatories' website, Orange connotes "Volcano is exhibiting heightened unrest with increased likelihood of eruption." Red connotes "Eruption is forecast to be imminent with significant emission of ash into the atmosphere likely."

The CVGHM uses a separate volcanic hazard status code to warn people in the region. The Darwin VAAC Weekly report issued for 29 October-4 November 2014 gave this overview of the eruption and the variation in CVGHM's volcanic hazard status: "On 14 September 2013, a new eruptive phase began. By mid-October the volcano was degassing almost daily with small phreatic eruptions. Seismic and visual activity continued to build into November. After nine powerful explosions in a 24 hour period, the Centre for Volcanology and Geological Hazard Mitigation (CVGHM) raised the Alert level to Level IV on 24 November 2013, the highest volcano rating. The status was decreased to Alert Level III on 8 April 2014."

During this reporting interval, lava flows advanced in the sector S- SE from the summit (figure 20). In accord with that lobe or tongue of lava, incandescent zones were at various times noted in different parts of the flows. As reported by CVGHM, avalanches from the front of the advancing lava flows occurred often. Scientists associated this process with a distinct seismic signal called an avalanche earthquake. CVGHM repeatedly warned residents that the lava flows and their associated avalanches could threaten areas to the S and SE within 5 km of the summit. Measurements of the length of this flow are included in the table at the bottom of this report. A previous map with clearer labels of the earlier flows appears as figure 16 in BGVN 39:01.

Figure 20. Annotated photo showing the S-SE flank of Sinabung covered by an advancing lava flow (often referred to as lava tongue, 'lidah lava' in Indonesian). On 6 September 2014, the day of this photo, the lava flow was reported as measuring 2.915 km long from distal end to the vent area at or adjacent the summit lava dome. Although the upper slopes on the E (right) side are too cloudy to see, CVGHM had recorded the locations of the various dated flow margins there. Note the area on the upper flanks where some lava branched off the main lobe to create a series of small finger-shaped areas trending more to the W. Courtesy of CVGHM.

Seismicity at Sinabung included avalanche earthquakes, low-frequency earthquakes, tectonic earthquakes, volcanic earthquakes and ongoing tremor. Totals and measured averages of these seismic events are included when available (see table at bottom). CVGHM reported that the dominating seismic signals, avalanche earthquakes and intervals of constant tremor, were associated with the instability of the growing lava dome and lava flows.

During this reporting interval, numerous eruptions took place, often generating ash plumes and in some cases pyroclastic flow. During the eruptions, some ash plumes were detected by satellite imagery. Ground-based observations were also important. For example, CVGHM often detected Sinabung eruptions, PFs, and plumes via webcam. Darwin VAAC also benefited from the CVGHM webcam data in several of their VAAs. The VAAC has also begun to use social media to both dispense and retrieve operationally relevant information (Darwin VAAC, 2015). This has aided VAAC forecaster's understanding of, for example, whether residents have noticed ashfall during times when ash is not discernable due to meteorological clouds (Darwin VAAC, 2015).

During May and October 2014, PFs had runout distances up to 4.5 km and ash plumes rose up to 5.2 km altitude. White or slightly discolored plumes were the most common type reported by CVGHM. These plumes sometimes rose to as high as on the order of 1 km over the summit.

Figure 21 is a map of Sinabung and towns surrounding the volcano.

Figure 21. Relief map of Sinabung volcano and surrounding towns, some of which are named in reporting. The base map was made prior to the current eruption and the lava tongue descending the S-SE flank is not shown. For scale, the distance is ~3 km from the summit area N to the closest (S) margin of Kawar lake. Map found online at Pixshark.com and edited by Bulletin editors.

Photographs. The following are photos documenting events at Sinabung during this reporting interval. Ancillary information pertaining to each photo can be found in a table at the bottom of this report.

Figure 22. Photo of a pyroclastic flow (PF) descending Sinabung on 14 August 2014. Two PFs occurred that day, at 0728 UTC and 0750 UTC. The time that this photo was captured is unknown. Photographer unknown; photo posted on Facebook by CVGHM and taken from the 13-19 August 2014 Darwin VAAC weekly activity report.

Figure 23. A pyroclastic flow (PF) captured at 0940 UTC on 2 September 2014. This PF traveled 1.5 km to the SE. Taken from the 27 August-2 September 2014 Darwin VAAC weekly activity report.

Figure 24. Sinabung in a low-light photo allegedly taken at 1444 UTC on 7 September 2014, which would make it about 46 minutes after Darwin VAAC reported an eruption. The ash plume rose 2 km above the summit and blew S. A rivulet of red glowing material descends an area of the flank. Bulletin editors interpret the rivulet as a lava flow (or possibly a glowing avalanche or both) traveling down the lava tongue on the S-SE flank. Copyrighted photo taken by Endro Lewa, posted on Facebook by CVGHM, and taken from the 3-9 September 2014 Darwin VAAC weekly activity report.

Figure 25. Eruption at Sinabung on 8 October 2014. This time and the location of this photo were unstated. Photo by the news agency AFP and taken from the 8-14 October 2014 Darwin VAAC weekly activity report.

Figure 26. (A) Ground-based photo of a Sinabung eruption column looking approximately NE on 19 October 2014. Photo was captured at 0731 UTC. The eruption column is obscured by weather clouds but is visible again above them in a small area. Photo was taken by Ricky Febriand, posted on Facebook by CVGHM, and taken from the 15-21 October 2014 Darwin VAAC weekly activity report. B. Aerial photo of Sinabung's eruption column on 20 October 2014. Photo was captured at 0736 UTC. Height of eruption column and position photo was taken are unknown. Photo taken by Ricky Febriand, posted on Facebook by CVGHM and taken from the 15-21 October 2014 Darwin VAAC weekly activity report.

Data compilation. Table 4 summarizes activity at Sinabung from May-October 2014. Data sources include reporting by CVGHM (often the original source), the Darwin VAAC (their Volcanic Ash Advisories (VAAs), Weekly Activity Reports; and other reports), the Indonesian National Agency for Disaster Management (Badan Nacional Penanggulangan Bencana-BNPB), occasional news articles; and the Smithsonian-USGS Weekly Volcanic Activity Reports.

Table 4. A synthesis of Sinabung's reported activity from May-October 2014. The bulk of this table came from CVGHM and Darwin VAAC reporting unless otherwise stated. Dates and times are in some cases ambiguous as to local time (LT) or UTC (LT = UTC + 7). Abbreviations: pyroclastic flow, PF; Aviation Color Code, ACC; earthquake(s), EQ(s); maximum amplitude, max. amp.; and altitude, alt.

References. Associated Press, 2014, Volcano in Western Indonesia erupts again, accessed on 28 September 2014, (URL: http://abcnews.go.com/International/wireStory/volcano-western-indonesia-erupts-25720623 )

Darwin VAAC, (6 August) 2014, VAAC Darwin Management Report [discussing 1 July 2013 to the 30 June 2014], International Civil Aviation Organization (ICAO); Eighteenth Meeting of the Meteorology Sub-Group (Met Sg/18) Of Apanpirg; ICAO Regional Sub-Office, Beijing, China; 18–21 August 2014 [Agenda Item 7.4: Research, development and implementation issues in the MET field, [7.4] Advisories and warnings, MET SG/18 - IP/17; Agenda Item 7.4; 6 August 2014; (Presented by Australia)]; 5 pp. (URL: http://www.icao.int/APAC/Meetings/2014 METSG18/IP17_AUS AI.7.4 - VAAC Darwin Management.pdf )

Darwin VAAC, (18 February) 2015, Darwin VAAC Management Report [discussing 1 July 2014-31 January 2015], International Civil Aviation Organization (ICAO), Fifth Meeting of Meteorological Hazards Task Force (MET/H TF/5), Seoul, Republic of Korea, 18 March 2015 [Thirteenth Meeting of the Asia/Pacific Regional Opmet Bulletin Exchange Working Group (Robex Wg/13), ROBEX WG/13 & MET/H TF/5 – WP/C6; Agenda Item (conjoint session) 2 (Presented by Australia)] (URL: http://www.icao.int/APAC/Meetings/2015 ROBEXWG13/WP-C6 - AI.2 - AUS - Darwin VAAC Management Report.pdf )

Indonesian National Agency for Disaster Management (Badan Nacional Penanggulangan Bencana-BNPB), 2014, Four time Sinabung, Normal Community Activity, accessed on 6 October 2014, (URL: http://bnpb.go.id/berita/2211/empat-kali-sinabung-meletus-masyarakat-beraktivitas-normal)

The Jakarta Post/Asia News Network, 2014, Mount Sinabung erupts again, accessed on 6 October 2014, (URL: http://news.asiaone.com/news/asia/mount-sinabung-erupts-again)

Okezone.com, 2014, accessed on 28 September 2014, (URL: http://news.okezone.com/read/2014/10/01/340/1046715/hujan-abu-gunung-sinabung-guyur-karo-petani-menderita )

Pixshark.com, accessed on 7 April 2015 (URL: http://pixshark.com/peta-gunung-sinabung.htm)

World Organizations of Volcano Observatories (WOVO), Aviation Colour Codes, accessed on 8 April 2015, (URL: http://www.wovo.org/aviation-colour-codes.html)

Xinhua News Agency, 2014, 2nd LD Writethru: Mount Sinabung in Indonesia erupts, triggering massive evacuation, accessed on 29 June 2014, (URL: http://www.globalpost.com/article/6190943/2014/06/29/2nd-ld-writethru-mount-sinabung-indonesia-erupts-triggering-massive)

Xinhua News Agency, 2014, Mount Sinabung erupts in Sumatra, Indonesia, accessed on 28 September 2014, (URL: http://english.cntv.cn/2014/09/24/ARTI1411549583755731.shtml).

Information Contacts: Indonesian Center of Volcanology and Geological Hazard Mitigation (CVGHM) (also known as Pusat Vulkanologi dan Mitigasi Bencana Geologi-PVMBG), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://vsi.esdm.go.id/); Indonesian National Agency for Disaster Management (Badan Nacional Penanggulangan Bencana-BNPB), Gedung Graha 55 Jl. Tanah Abang II No. 57, 10120, Jakarta Pusat (URL: http://www.bnpb.go.id/); and Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/).

October 2015 (BGVN 40:10) Cite this Report

Eruption continues during November 2014-April 2015

The latest eruption of Sinabung began in mid-September 2013 (BGVN 38:09) and was previously described through October 2014 (BGVN 39:01 and 39:10). This report describes the continuing eruption from November 2014 through April 2015. Data were primarily drawn from reports issued by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Center for Volcanology and Geological Hazard Mitigation) and the Darwin Volcanic Ash Advisory Centre (VAAC).

The Alert Level remained at 3 (on a scale of 1-4) throughout the reporting period. Visitors and tourists were prohibited from approaching the crater within a radius of 5 km on the S and SE flanks, and 3 km in the other directions. According to the Badan Nacional Penanggulangan Bencana (National Disaster Management Authority, BNPB), by the middle of November, activity had displaced 2,086 people from 956 households.

Activity fluctuated during the reporting period, with frequent explosions, intermittent pyroclastic flows, and lava flows. Explosions generated ash plumes that generally rose to altitudes of 3-4.6 km. According to PVMBG, a new lava dome began to develop in October 2014 on the W side of the SSE-flank lava flow.

On 14 November there were 79 avalanches reported, with three of them generating pyroclastic flows that traveled 4 km S. PVMBG reported that 53 pyroclastic flows occurred during 8-16 December 2014 and they traveled as far as 4.5 km S and 1 km SE; ash plumes rose as high as 5 km. By 15 December the dome was 215 m long and the main lava flow was about 3 km long.

BNPB reported that an explosion in the evening of 3 January 2015 was larger than previous, almost daily, explosions. Pyroclastic flows traveled 2-4 km down the flanks and ash plumes rose as high as 3 km. Ashfall was reported in Payung (5 km SSW), Tiganderket (7 km W), Selandi (5 km SSW), Juhar (20 km SW), and Laubaleng (35 km WSW).

On 18 January BNPB reported that activity remained high, with low-frequency earthquakes and constant tremor being recorded. A pyroclastic flow traveled 2 km S and ash plumes rose 700 m. The number of displaced people had increased to 2,443 (795 families).

Elevated activity continued through February and March 2015. Plumes on 20 February and 5 March 2015 rose to altitudes as high as 13.7 km and 9.1 km, respectively. Based on PVMBG notices, BNPB reported that activity increased on 1 April. Seismicity increased and pyroclastic flows traveled 3.5 km S and produced ash plumes that rose 2 km. Avalanches were detected and incandescent lava was observed at night. On 2 April pyroclastic flows traveled 4 km S and 1 km SE, and avalanches continued.

PVMBG reported that seismicity declined during 6-12 April, compared to 30 March-6 April. However, lava was incandescent as far as 1.5 km S and SE of the lava dome. The main lava flow remained 2.9 km long. After pyroclastic flows descended the flanks on 2 April, a new lava flow from the growing dome formed near the crater and traveled 170 m SSE. Seismicity consisted of avalanche signals, low-frequency and hybrid events, local and distant tectonic events, and volcanic earthquakes. Tilt and EDM (Electronic Distance Measurement) data fluctuated but showed overall deflation.

Thermal anomalies, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, were observed an average of 3-5 days per month during the reporting period. Four pixels were observed 8 and 15 December 2014, 5 March 2015, and 2 April 2015, and five pixels were observed on 13 December 2015.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Badan Nacional Penanggulangan Bencana (National Disaster Management Authority, BNPB) (URL: http://www.bnpb.go.id/); 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/)

March 2016 (BGVN 41:03) Cite this Report

Eruption that began in September 2013 continued during May-October 2015

The eruption of Sinabung which began in mid-September 2013 (BGVN 38:09 continued during May-October 2015. Data were primarily drawn from reports issued by the Indonesian Center of Volcanology and Geological Hazard Mitigation (PVMBG, CVGHM) and the Badan Nacional Penanggulangan Bencana (National Disaster Management Authority, BNPB).

During the reporting period, activity remained at high levels, but fluctuated over time, with frequent explosions, intermittent pyroclastic flows, and lava flows. PVMBG reported that fog and other inclement weather often prevented visual observations.

The Alert Level remained at 3 (on a scale of 1-4) through May, but on 2 June it was raised to 4, signifying that people within 7 km in the SSE sector and 6 km in the ESE sector should evacuate. According to BNPB, this increase was a result of a sharp rise in activity during the previous several days, including an increase in the lava dome volume to more than 3 million cubic meters and greater dome instability. The higher Alert Level prompted the evacuation of 2,727 people (677 families) from the S and SE flanks. BNPB noted that by 29 June a total of 10,645 people (3,150 families) had been displaced.

White and white-gray plumes frequently rose 200-1,000 m above the crater. Ash plumes were common, some caused by explosions and others generated by pyroclastic flows. The ash plumes generally rose up to 4.3 km in altitude, but several rose to 6-7 km and one rose to 7.6 km on 30-31 October. During 9-15 September, explosions caused thick ashfall deposits in Berastagi, Kabanjahe, and surrounding areas.

Pyroclastic flows from the lava dome were common, ranging from 0 to 8 per day. The flows traveled up to 4 km down the S, SE, ESE, and SSE flanks, often generating ash plumes that rose as high as 3.5 km above the crater. Lava from the dome traveled down the S and SE flanks during late May to late June, and down the E, ESE, SSE, and SE flanks during September and October. The lava was incandescent 1.5-3 km down the flanks.

Seismicity consisted of avalanche signals, low-frequency and hybrid events, tremor, tectonic events, and volcanic earthquakes. During mid-May seismicity declined, but at the end of May, avalanche signals increased. Elevated numbers of avalanche signals were also reported during 24-30 June and 12-18 August. During 27 May-2 June, deformation data trended toward inflation. The trend continued until 16-22 September, when deflation was observed.

Thermal anomalies based on MODIS satellite instruments analyzed using the MODVOLC algorithm, were observed each month during June-October 2015. None were reported in May, while the highest number, ten, occurred in June. The number of days with anomalies during other months ranged from 3-8. In September, five alert pixels were present on the 4th, and four on the 20th.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nacional Penanggulangan Bencana (National Disaster Management Authority, BNPB)(URL: http://www.bnpb.go.id/); 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/).

September 2016 (BGVN 41:09) Cite this Report

Eruption that began in September 2013 continues during November 2015-April 2016

The latest eruption of Sinabung began mid-September 2013 (BGVN 38:09). Since then, activity was persistent through October 2015 (BGVN 39:01, 39:10, 40:10, and 41:01). This report describes the continuing eruption from November 2015 through April 2016. Data were primarily drawn from reports issued by the Indonesian Center of Volcanology and Geological Hazard Mitigation (PVMBG, CVGHM), the Darwin Volcanic Ash Advisory Centre (VAAC), and the Badan Nacional Penanggulangan Bencana (National Disaster Management Authority, BNPB).

Inclement weather sometimes prevented visual observations, including the growing lava dome in the summit crater. Throughout the reporting period, the Alert Level remained at 4 (on a scale of 1-4), indicating that people within 7 km of the volcano on the SSE sector, and within 6 km in the ESE sector, should evacuate.

According to Darwin VAAC and PVMBG reports, a number of ash plumes were observed each month (table 5). They generally rose to altitudes of 3-4.5 km, although a few rose as high as 5.5 km; the summit is about 2.5 km. A pyroclastic flow on 8 November 2015 generated an ash plume, but clouds obscured its altitude.

Table 5. Ash plumes with altitudes and drift directions reported at Sinabung from November 2015 to April 2016. Weather clouds often prevented observations. Courtesy of PVMBG, Darwin VAAC, and BNPB.

PVMBG reported that, during 21-28 December 2015, as many as 21 hot avalanches and pyroclastic flows traveled 0.7-1.5 km ESE, producing ash plumes that rose 1 km. Ash plumes from explosions rose as high as 3 km and drifted E and SW. Seismicity consisted of avalanche and pyroclastic-flow signals, low-frequency and hybrid events, tremor, tectonic events, and volcanic earthquakes. Seismicity fluctuated at high levels, although it had declined compared to the previous week, and indicated lava-dome growth.

According to PVMBG, during 4-14 January 2016, as many as 192 hot avalanches and 12 pyroclastic flows traveled 0.5-3 km ESE (figure 27). Ash plumes from a total of 40 events rose as high as 3 km. Consistent with the previous month, seismicity fluctuated at high levels, although it had declined compared to the previous week.

Figure 27. Photo showing a pyroclastic flow from Sinabung on 10 January 2016 as viewed from Berastepu Village (SE flank). Courtesy of Y.T Haryono/Anadolu Agency/Getty Images; from an Eruptions Blog article by Erik Klemetti in Wired.

On 10 April 2016, BNPB reported that activity remained high, characterized by almost daily lava extrusion and pyroclastic flows, and high levels of seismicity. BNPB noted that 9,322 people (2,592 families) remained in 10 evacuation centers. Many families awaited relocation; 1,212 people had already been permanently relocated to new homes.

Thermal anomalies, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, were observed seven days every month during November 2015-April 2016, except for six days in December and 12 days in January. Three pixels were observed on 25 December, 30 January, and 2 February; four pixels were observed on 12 November and 19 January; five pixels were observed on 23 January. The Mirova (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, also based on analysis of MODIS data, detected numerous hotspots every month during the reporting period.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); 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/, 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/); Eruptions Blog, Wired Magazine (URL: https://www.wired.com/category/science/science-blogs/eruptions/).

February 2017 (BGVN 42:02) Cite this Report

Eruption continues during May-October 2016; multiple fatalities from pyroclastic flows and lahars

The latest eruption of Sinabung that began mid-September 2013 (BGVN 38:09) had persisted through April 2016 (BGVN 41:09). This report describes the continuing activity from May-October 2016, and unfortunately included a fatality. Data were primarily drawn from reports issued by the Indonesian Center of Volcanology and Geological Hazard Mitigation (PVMBG, CVGHM), the Darwin Volcanic Ash Advisory Centre (VAAC), and the Badan Nacional Penanggulangan Bencana (National Disaster Management Authority, BNPB).

Inclement weather sometimes prevented visual observations. Throughout the reporting period, the Alert Level remained at 4 (on a scale of 1-4), indicating that the public should remain outside of a 3-km radius; those within 7 km of the volcano on the SSE sector, and within 6 km in the ESE sector, and 4 km in the NNE sector should evacuate.

According to the Darwin VAAC and PVMBG reports, a number of ash plumes were observed each month (table 6). They generally rose to altitudes of 3.3-5.5, although one rose as high as 5.9 km.

Table 6. Ash plumes with altitudes and drift directions reported at Sinabung from May 2016 to October 2016. Weather clouds often prevented observations. Courtesy of PVMBG, Darwin VAAC, and BNPB.

According to BNPB, a lahar passed through Kutambaru village, 20 km NW of Sinabung and near the Lau Barus River, at 1545 on 9 May 2016, killing a boy and injuring four more. One person was missing. A news article (Okezone News) noted that three houses were also damaged.

BNPB reported that a pyroclastic flow descended the flanks at 1648 on 21 May, killing six people and critically injuring three more. A later CBS news account on 22 May indicated that seven people had died, with two in critical condition. The victims were gardening in the village of Gamber, 4 km SE from the summit crater, in the restricted zone. The report noted that activity remained high; four pyroclastic flows descended the flanks on 21 May.

On 3 July, BNPB reported that the eruption continued at a very high level. Lava was incandescent as far as 1 km down the SE and E flanks, and multiple avalanches were detected. An explosion at 1829 generated an ash plume that rose 1.5 km and drifted E and SE, causing ashfall in Medan (55 km NE). There were 2,592 families (9,319 people) displaced to nine shelters, and an additional 1,683 families in temporary shelters waiting for relocation.

According to BNPB, on 24 August, observers at the PVMBG Sinabung observation post noted a marked increase in seismicity and counted 19 pyroclastic flows and 137 avalanches from the early morning until the late afternoon. Foggy conditions obscured visual observations through most of the day, although incandescent lava as far as 500 m SSE and 1 km ESE was noted in the morning, and a pyroclastic flow was seen traveling 3.5 km ESE at 1546. The lava dome had grown to a volume of 2.6 million cubic meters. Activity remained very high on 25 August; pyroclastic flows continuously descended the flanks, traveling as far as 2.5 km E and SE, and 84 avalanches occurred during the first part of the day.

Thermal anomalies. During the reporting period, thermal anomalies, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, occurred during one to five days every month. Only three days had more than one pixel (1, 3 May, 8 October). The Mirova (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, also based on analysis of MODIS data, detected thermal anomalies every month during the reporting period within 5 km of the volcano, with the heaviest concentration in May and fewest in September and October.

Information Contacts: Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/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/); 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/); Okezone News (URL: http://news.okezone.com/); CBS News (URL: http://www.cbsnews.com/).

December 2017 (BGVN 42:12) Cite this Report

Constant activity through September 2017, with ash plumes, block avalanches, and pyroclastic flows

Indonesia's Sinabung volcano, located on North Sumatra, had its first confirmed Holocene eruption between 27 August and 18 September 2010; ash plumes rose up to 2 km above the summit, and falling ash and tephra caused fatalities and thousands of evacuations (BGVN 35:07). It remained quiet after the initial eruption until 15 September 2013, when a new eruption began that has continued for over three years. Details of events during October 2016-September 2017 are covered in this report. Information is provided by, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), referred to by some agencies as CVGHM, the Indonesian Center of Volcanology and Geological Hazard Mitigation (CVGHM), the Darwin Volcanic Ash Advisory Centre (VAAC), and the Badan Nacional Penanggulangan Bencana (National Disaster Management Authority, BNPB).

Summary of activity during November 2013-September 2016. Thousands of evacuations took place during November and December 2013 when ash plumes reached heights between 6 and 11 km altitude multiple times. Ashfall from hundreds of pyroclastic flows in January 2014 covered communities in the region. Lava flows emerged from the summit in mid-January 2014 and traveled down the S flank. Pyroclastic flows on 1 February 2014 killed 17 people in the village of Sukameriah, located 3 km S of the summit (BGVN 39:01). The lava flow had advanced 2.5 km from the summit by 6 April 2014. Lava flows, ash plumes, and pyroclastic flows persisted throughout 2014 and 2015. Ash plumes generally rose up to about 5 km altitude, and pyroclastic flows traveled up to 4.5 km from the summit throughout this period (BGVN 39:10). Repeated lava dome growth and destruction was also reported by PVMBG during this time (BGVN 40:10).

Increases in lava dome volume and instability during June 2015 again led to evacuations of thousands living within 7 km of the volcano. Ash deposits were common in the communities up to 10-15 km away. Similar activity continued into 2016, with tens of pyroclastic flows affecting nearby communities during many months. In April 2016, over 9,000 people remained in evacuation centers. Ash plumes were reported 3-8 times each month by the Darwin VAAC between April and October 2016, with plume altitudes ranging generally from 3-5.5 km. Several fatalities were reported during May 2016 (BGVN 42:02). A lahar passed through Kutambaru village, 20 km NW of Sinabung, on 9 May and killed one and injured four people. A pyroclastic flow on 21 May 2016 killed 7 people in the village of Gamber, 4 km SE from the summit. Ashfall was reported during July 2016 more than 50 km NE, and incandescent lava was visible up to a kilometer from the summit. Continuous pyroclastic flows were reported on 25 August 2016, with an ash plume observed at 6.1 km altitude the following day.

Summary of activity during October 2016-September 2017. Ash plumes, block avalanches, and pyroclastic flows were all nearly constant at Sinabung throughout this period (table 7). The number of explosions recorded every month ranged from 37 (March 2017) to 105 (June 2017). The number of Volcanic Observatory Notices to Airmen (VONAs) each month ranged from 34 (September 2017) to 93 (June 2017). The Darwin VAAC reported ash plumes on 17 or more days every month of 2017 through September. Thermal anomaly signals also persisted throughout, likely caused primarily by dome growth and incandescent block avalanches.

Table 7. Ash plumes and explosions reported for Sinabung, October 2016-September 2017. Data from Darwin VAAC and PVMBG reports.

Activity during October 2016-September 2017. The visiting head of PVMGB observed an ash plume from an explosion on 28 September 2016. Ash emissions continued at Sinabung, with multiple aviation advisories issued by the Darwin VAAC through the end of 2016. Explosions generated ash plumes that rose to altitudes of 3.0-6.1 km, and drifted in multiple directions during the last quarter of 2016 (table 7). Pyroclastic flows were observed several times during November (figure 28), and a hotspot was visible in satellite imagery on 30 December.

Figure 28. A large pyroclastic flow descended the E flank of Sinabung on 29 November 2016 in this view taken a few kilometers SE of the volcano. . Courtesy of Sadrah Peranginangin.

Activity during January 2017 was dominated by incandescent block avalanches (figure 29). PVMBG reported 101 ash-bearing explosions with plumes rising up to 1 km above the summit, and pyroclastic flows that traveled up to 3 km ESE and 500 m S. A You Tube video captured a pyroclastic flow and ash plume on 17 January 2017. Ash plumes were reported by the Darwin VAAC on 21 days during the month with plume heights ranging from 3.4-5.5 km altitude.

Figure 29. Block avalanches descended the E flank of Sinabung many times during January 2017, including at 0134 local time on 17 January, as seen looking to the WSW. Courtesy of Endro Lewa.

Near-daily ash plumes from 88 explosive events during February 2017 rose to heights of 500-5,000 m above the summit (3.0-7.5 km altitude), and pyroclastic flows traveled 3.5 km E and 1 km S. The Darwin VAAC reported ash emissions on all but three days of the month. A large explosion on 4 February sent an ash plume to 7.4 km altitude that then drifted SE (figure 30), and on 9 February a large ash plume drifted WSW at 6.7 km altitude.

Figure 30. Photo of an ash plume at Sinabung on 4 February 2017 that rose more than 5 km above the summit and slowly drifted SE. Photo taken from Kabanjahe, about 13 km SE. Courtesy of Sadrah Peranginangin.

Block avalanches continued to travel 500-2,000 m down the ESE flank during March 2017. Ash plume heights ranged from 500 to 3,000 m above the summit (3.0-5.5 km altitude) during the 37 explosion events reported by PVMBG (figure 31). Pyroclastic flows traveled 2.5 km down the S flank. The highest plumes of the month were recorded on 17 and 18 March; they rose to 5.5 km altitude and drifted W and WSW. The Darwin VAAC reported ash plumes during 21 days of the month.

Figure 31. Photo of an ash plume at Sinabung on 29 March 2017 at 1548 local time, in this view looking W. Courtesy of Igan S. Sutawijaya.

During April 2017, block avalanches were observed traveling between 800 and 3,500 m down the SSE flank (figure 32), and 104 explosions were recorded by PVMBG. Ash plumes from these explosions rose to heights of 800 to 3,500 m above the summit. Pyroclastic flows descended 2.8 km down the S flank. A large explosion on 9 April reported in a VONA by a ground observer sent an ash plume to 8.4 km altitude, drifting SE. Pyroclastic flows were also observed on the SE flank. The Darwin VAAC reported ash plumes on 22 days of the month.

Figure 32. Pyroclastic flows descended the S flank (left) and block avalanches descended the E flank of Sinabung near midnight on 4 April 2017, while a small explosion took place at the summit. Image taken from a small village a few kilometers from the base of the SE flank. Courtesy of Sadrah Peranginangin.

Ash plumes rose between 500 and 6,000 m above the summit during May 2017. Eighty-seven explosive events were recorded (figure 33), and block avalanches were observed traveling 500-1,500 m down the S and SE flanks. The Darwin VAAC reported ash plumes on 26 days during the month. A series of large explosions during 17-20 May resulted in several plumes that rose to altitudes between 6.1 and 8.8 km, in addition to numerous others at lower altitudes between 3.7 and 5.8 km. As of late May, over 9,000 people were still displaced from the volcano, living in either shelters or evacuation camps, according to BNPB.

Figure 33. Strombolian activity at the summit of Sinabung on 1 May 2017. Courtesy of Sadrah Peranginangin.

Incandescent block avalanches and pyroclastic flows were persistent during June 2017. They moved down the SE and S flanks up to 2,500 m. PVMBG reported 105 explosive events with plume heights ranging from 500-4,000 m above the summit (figure 34). The largest explosions of the month, on 17 June, generated ash plumes that rose to 6.4 km altitude and drifted 15 km SW. The Darwin VAAC reported ash emissions every day except for 28 June.

Figure 34. Ash plume rose from Sinabung on 26 June 2017. The view is from a small village about 7 kilometers ENE of the summit. Courtesy of Endro Lewa.

PVMBG reported 91 explosive events during July 2017 that produced ash plumes that rose 500-3,500 m above the summit. They also noted four pyroclastic flows that traveled 1-3 km down the S and SE flanks. Block avalanches continued on the S and E flanks, traveling as far as 3 km. The Darwin VAAC issued reports on 24 days during July. The largest explosions occurred on 20 and 23 July when ash plumes rose to 5.8 and 6.1 km altitude and drifted WSW, ENE, and SE (figure 35).

Figure 35. A large ash plume from Sinabung rose more than 5 km above the summit on 20 July 2017. The view is from a small village about 7 kilometers ENE of the summit. Courtesy of Endro Lewa.

Although fewer explosive events (61) were reported during August, block avalanches continued to travel 500-2,300 m down the SE flank. Ash plumes rose 500-2,000 m above the summit; 22 pyroclastic flows traveled up to 4.5 km down the SE flank. The Darwin VAAC issued reports of ash emissions on 17 days of the month.

A large explosion on 2 August sent ash emissions to 5.5-6.4 km altitude (figure 36). The S-drifting plume brought ashfall to the communities of the Ndokum Siroga District (SE), Simpang (7 km SE), Gajah (8 kmE), Kabanjahe (13 km SE), and Naman Teran (5 km NE) (figures 37 and 38). PVMBG reported that the explosions of 2 August destroyed the lava dome at the summit, which had grown since April 2017 to about 2.3 million m³ in size before the explosion (figure 39). The volume of the lava dome was an estimated 23,700 m³ on 6 August, after the explosions.

Figure 36. Photo showing the large eruption from Sinabung on 2 August 2017, with a dark ash plume and pyroclastic flows. Image taken 5 kilometers E of the summit, looking W. Courtesy of Endro Lewa.

Figure 37. Many communities were affected by ashfall and pyroclastic flows from the large explosion at Sinabung on 2 August 2017. This village is located near the base of the E flank. Courtesy of Endro Lewa.

Figure 38. A village on the SE flank of Sinabung, was covered with ash on 3 August 2017 after a large eruption the previous day that sent a column of ash to 4.2 km altitude and a pyroclastic flow down the adjacent slope, destroying vegetation in its path. Courtesy of Xinhuanet (Xinhua/YT Haryono).

Figure 39. The dome at Sinabung on 3 August 2017 one day after its destruction in a large explosion. The volume according to PVMBG was 2.3 million cubic meters in early July and measured only 23,700 cubic meters after the explosion. Courtesy of Endro Lewa.

The explosions also produced pyroclastic flows that traveled SE and E 2.5-4.5 km and reached the Laborus river, increasing the size of a natural dam on the river that had been evolving from previous deposits. Ashfall was also reported to the E and NE at Berastagi (12 km E). Hot spots were recorded in satellite imagery on 6 and 7 August. Additional ash plumes to similar altitudes (5.5-6.4 km) were reported several other times during August (figure 40 and 41).

Figure 40. An explosion at Sinabung on 8 August 2017. The ash plume rises 2,000 m and a pyroclastic flow descends the E flank in this view from a small village about 7 km ENE of the summit. Courtesy of Endro Lewa.

Figure 41. Ash and steam plumes and block avalanches at Sinabung on 25 August 2017 in this view from a small village about 7 km ENE of the summit. Courtesy of Endro Lewa.

The impact of numerous pyroclastic flows on the SE and E flanks during 2016-2017 caused a natural dam to form on the Laborus River near Desa Sukanalu and Kutanonggal Village (figure 42). The estimate of the area covered by water behind the dam was over 100,000 m² prior to the early August explosions, about one-tenth the size of Lake Laukawar, located further upstream.

Figure 42. A natural dam on the Laborus River (right, 'Bendungan Laborus') was created by numerous pyroclastic flows; the lake area was 123,000 square meters prior to the 2-3 August explosions. Courtesy of PVMBG (Kegiatan Gunungapi Sinabung Pasca Letusan 2-3 Agustus 2017, 22 August 2017).

Activity diminished only slightly during September 2017. PVMGB reported 55 explosive events with ash plumes that rose 500-4,000 m above the summit (figure 43). Block avalanches fell 500-1,500 m down the SE flank, and five pyroclastic flows were observed in the same area which traveled 1.5 – 2.0 km. Reports of ash emissions were issued by the Washington VAAC on 17 days of the month. The highest ash plume during the month rose to 6.4 km altitude on 25 September.

Figure 43. A lava dome and ash plume at the summit of Sinabung on 17 September 2017. Courtesy of Sadrah Peranginangin.

Thermal anomalies. Thermal anomalies persisted throughout October 2016-September 2017. MODVOLC thermal alerts were reported 1-10 times every month except for June 2017. The MIROVA system recorded persistent low to moderate radiative power (figure 44) consistent with the dome growth, explosions, and block avalanches reported by PVMBG.

Figure 44. Thermal anomaly data shown on a MIROVA graph of log Radiative Power at Sinabung for the year ending 18 December 2017. Persistent intermittent pulses of thermal energy are consistent with dome growth and block avalanches reported by PVMBG. Courtesy of MIROVA.

References: Associated Press, 2017, Raw: Indonesia's Sinabung Volcano Spews Hot Ash (URL: https://www.youtube.com/watch?v=R3KhjpHVeaw), posted to YouTube 17 January 2017.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URLs: http://www.vsi.esdm.go.id/, https://magma.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral, (URL: https://magma.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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/); Xinhua News (URL: http://news.xinhuanet.com/english/2017-08/03/c_136497362.htm); Igan S. Sutawijaya (URL: https://www.facebook.com/igansutawijaya/); Endro Lewa (URL: https://www.instagram.com/endro_lewa/); Sadrah Peranginangin (URL: https://www.facebook.com/sadrah.peranginangin).

April 2018 (BGVN 43:04) Cite this Report

Large explosion with 16.8 km ash plume, 19 February 2018

Indonesia's Sinabung volcano has been highly active since its first confirmed Holocene eruption during August and September 2010; ash plumes initially rose up to 2 km above the summit, and falling ash and tephra caused fatalities and thousands of evacuations (BGVN 35:07). It remained quiet after the initial eruption until 15 September 2013, when a new eruptive phase began that has continued uninterrupted through February 2018. Ash plumes rising several kilometers, avalanche blocks falling several kilometers down the flanks, and deadly pyroclastic flows travelling more than 4 km have all been documented repeatedly during the last several years. Details of events during October 2017-March 2018, including the largest explosion to date on 19 February 2018, are covered in this report. Information is provided by, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), referred to by some agencies as CVGHM or the Indonesian Center of Volcanology and Geological Hazard Mitigation, the Darwin Volcanic Ash Advisory Centre (VAAC), and the Badan Nacional Penanggulangan Bencana (National Disaster Management Authority, BNPB). Additional information comes from satellite instruments and local observers.

When activity began in 2010, and again when eruptions resumed in 2013, many news accounts included statements that Sinabung had last been active 400 years ago, or even saying specifically that the last eruption was in 1600 CE. Those claims appear to have been caused by a misunderstanding related to the boundary time that Indonesian volcanologists use to categorize volcanoes. Those volcanoes with historical activity, defined as being about 400 years ago (corresponding to the beginning of the Dutch East India Company era), are in the "Type A" group. Those in the "Type B" group, including Sinabung prior to 2010, have not had reported activity in more than 400 years. Using charcoal associated with the most recent pyroclastic flow, Hendrasto et al. (2012) determined that the last previous eruptive activity was 1200 years before present using carbon dating techniques, or 740-880 CE (at 1 sigma).

Although activity remained high from October 2017 through March 2018, a gradual decline in the overall eruptive activity from the beginning of 2017 was apparent. The number of explosions per month generally declined, with no explosions reported during March 2018, for the first time since August 2013 (figure 45). The thermal anomaly record was similar; periods of high heat flow persisted through mid-November 2017, followed by a gradual reduction in the amount of thermal activity, although the intensity remained consistent, according to the MIROVA project (figure 46). Much of the heat flow was attributed to the dome growth at the summit; the dome was destroyed in the large explosion of 19 February 2018.

Figure 45. The number of explosions per month at Sinabung as reported by PVMBG from January 2017-March 2018. Only partial data was reported for 18-31 January 2018, and no explosions were observed during March 2018.

Figure 46. Thermal anomaly data at Sinabung from satellite-based MODIS instruments, plotted on a Log Radiative Power scale, persisted through the end of 2017 and then decreased in frequency through the end of February 2018. Much of the heat flow was attributed to a dome near the summit which was destroyed in the 19 February 2018 explosion. Graph shows thermal anomalies between 11 May 2017 and 1 April 2018. Courtesy of MIROVA.

Throughout the period from October 2017 through 19 February 2018, steam plumes were constantly rising to heights of 1,000-2,400 m above the summit. Avalanche blocks were ejected daily down the E and S flanks from 500-3,500 m, and multiple pyroclastic flows each month traveled between 1,000 and 4,600 m down the SE flank. Tens of explosions occurred monthly, generating ash plumes that rose from 500 to 5,000 m above the summit. Explosive activity was more intermittent during February than the previous months, until 19 February when the largest explosion to date occurred; it included an ash plume that rose to at least 16.8 km altitude and at least ten pyroclastic flows. In spite of the size of the explosion, no injuries or fatalities were reported as most nearby communities had been evacuated from the ongoing activity. Activity decreased substantially during March 2018; there were no explosions, block avalanches, or pyroclastic flows reported, only steam plumes rising 1,000 m above the summit.

Activity during October 2017-January 2018. During October 2017, steam plume heights reached 1,500 m above the summit. Avalanche blocks traveled down the E and S flanks 500-2,500 m, and eight pyroclastic flows traveled 1,000-4,500 m down the SE and S flanks. Ash plume heights ranged from 500 to 3,600 m above the summit. The Darwin VAAC issued 38 aviation alerts during the month. On 1 October they reported an ash plume drifting both NW at 4.6 km altitude and NE at 3.7 km. The next day, the webcam observed an ash emission that rose to 5.5 km altitude. On 4 October an ash plume was spotted in the webcam rising to 5.8 km altitude and drifting ENE. Later that day it had detached from the volcano and was seen drifting NW in satellite imagery. An ash plume on 5 October rose to 3.9 km altitude and drifted ESE. Two ash emission were reported on 7 October; the first rose to 3 km altitude, the second rose to 4.3 km, they both dissipated quickly. On 8 October, three plumes were reported. The first rose to 4.6 km and drifted WSW, the second rose to 3 km and drifted S and the third rose to 3.4 km and also drifted S. The following day, an ash plume rose to 4.6 km and drifted E. BNPB stated that on 11 October, an event at Sinabung generated an ash plume that rose 1.5 km above the crater and drifted ESE, causing ashfall in several local villages. On 12 October an event produced an ash plume that rose 2 km above the crater and was followed by pyroclastic flows traveling 1.5 and 2 km down the S and ESE flanks, respectively.

PVMBG reported ash plumes rising to 3.7 km on 11, 12, and 13 October 2017. Later on 13 October the Jakarta MWO reported an ash plume at 4.3 km. The next day PVMBG reported an ash plume at 5.5 km altitude. A plume on 15 October rose to 3 km and drifted E. A steam plume on 16 October drifted down the SE flank before drifting SE no 16 October (figure 47). On 17 October, a discrete emission rose a few hundred meters above the summit drifted NE. Later that day, an ash plume was seen in the webcam moving SE at 3.4 km. On 18 October, two ash emissions were reported. The first rose to 3.7 km and drifted E, the second rose to 3.9 km and drifted W. An ash plume rose to 4.6 km altitude on 21 October, and to 3.9 km, drifting S, on 23 October. The next day, three ash plumes were reported; the first rose to 3 km, the second to 4.6 km, and the third to 3.7, all drifting E. After five days of quiet, the webcam observed ash plumes that rose to 4.3 km on 30 October, and to 3.9 km on 31 October. Only two MODVOLC thermal alerts were issued, on 20 and 27 October.

Figure 47. A steam plume drifted down the SW flank of Sinabung before moving SE on 16 October 2017. View is from the SE. Courtesy of PVMBG.

Steam plumes were higher during November 2017, rising 2,400 m above the summit. Block avalanches traveled 500-3,000 m down the E and S flanks most days, and ten pyroclastic flows traveled between 2,000-3,500 m down the ESE and S flanks. The ash plumes rose 700-3,200 m above the summit. The Darwin VAAC issued 41 aviation alerts in November. Near-daily ash plumes were observed mostly in the webcam and occasionally in satellite imagery. They generally rose to 3.4-4.9 km altitude; the most common drift directions were S and SW. A number of times, multiple ash plumes were reported in a single day. On 14 November, four ash plumes were observed. The first rose to 3.7 km, the second and third rose to 4.6 km and drifted S and SSW, the last rose to 3.9 km and also drifted SSW. On 20 November a discrete emission produced an ash plume that rose to 5.5 km altitude and drifted SSW. Three ash plumes were recorded the next day, rising 3.9-4.6 km and drifting in multiple directions under variable winds. An ash plume on 23 November was reported by PVMBG at 6.7 km altitude drifting W, the highest noted for the month. MODVOLC thermal alerts appeared twice on 5 November, once on 14 November, and three times on 17 November.

Activity during December 2017 was similar to the previous two months; steam plumes rose 2,000 m above the summit, block avalanches traveled 500-3,500 m down the E and S flanks numerous times, and nine pyroclastic flows descended the ESE and S flanks distances ranging from 2,000 to 4,600 m. Ash plume heights were from 700-4,000 m above the summit. The Darwin VAAC issued 43 aviation alerts in December 2017. They reported ash plume heights of 3.4-4.9 km altitude on most days. Every day during 10-19 December, ash plumes were reported at altitudes of 4.6-5.5 km drifting SW, E or SE. PVMBG reported ash plumes on 26, 27 and 28 December that rose to 3.9, 5.2, and 5.5 km, respectively. BNPB reported pyroclastic flows on 27 December that traveled 3.5-4.6 km SE, and ashfall was reported in many nearby villages including Sukanalu Village (20 km SE), Tonggal Town, Central Kuta, Gamber (4 km SE), Berastepu (4 km SE), and Jeraya (6 km SE). The highest ash plume of the month rose to 6.4 km altitude on 29 December and drifted E. This was followed by another discrete ash emission the same day that rose to 5.8 km and two plumes the next day that rose to 5.2 km and drifted W. There was only one MODVOLC thermal alert issued on 7 December.

The Darwin VAAC issued 56 aviation alerts for January 2018. Multiple discrete ash emissions were reported on most days. Plume altitudes generally ranged from 3.4 to 5.5 km. A 6.1 km altitude plume was visible in satellite imagery on 18 January (figure 48). The drift directions were highly variable throughout the month. Most plumes dissipated within six hours. Incandescent blocks were reported by PVMBG falling 500-1,500 m down the ESE flank on most days when the summit was visible. They also reported a pyroclastic flow on 27 January that traveled 2,500 m ESE from the summit (figure 49). Three MODVOLC thermal alerts were issued on 6 January, and one on 12 January.

Figure 48. An ash plume rose 3,000 m from the summit of Sinabung on 18 January 2018 in this view looking at the SE flank. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 49. A pyroclastic flow descended 2,500 m down the SE flank of Sinabung on 27 January 2018 while an ash plume also drifts SE in this view of the SE flank. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Activity during February 2018. During most of February, steam plumes rose only 1,000 m above the summit, and avalanche blocks traveled 500-2,500 m down the ESE and S flanks. Far fewer ash emissions were reported than previous months, but the largest explosive event recorded to date took place on 19 February (figure 50). The Darwin VAAC issued 29 aviation alerts during February 2018. Short-lived ash emissions were reported on 1, 3, 5, 11, and 15 February. The ash plume heights ranged from 3.4-4.6 km altitude, and they drifted S or SW.

Figure 50. A very large ash plume rose to 16.8 km altitude from Sinabung on 19 February 2018. Image is from several tens of kilometers from the volcano a few hours after the eruption. No fatalities were reported. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

The large explosion was first reported by the Darwin VAAC at 0255 UTC on 19 February 2018. It produced an ash plume, which was clearly observed in satellite imagery (figure 51), that quickly rose to at least 16.8 km altitude and began drifting NW (figure 52). It also produced a large SO₂ plume that was recorded by satellite instruments (figure 53). Over the next 15 hours the plume dispersed in three different directions at different altitudes. The highest part of the plume drifted NW at 13.7 km and was visible over 300 km from the summit. The lower part of the plume drifted S initially at 6.7 km and gradually lowered to 4.3 km; it was visible 75 km from the summit before dissipating. A middle part of the plume drifted NW at 9.1 km during the middle of the day. Three subsequent minor ash emissions were observed on 20 and 25 February that rose to 3.4 km altitude. There were no VAAC reports issued during March 2018. A MODVOLC thermal alert issued on 11 February was the last for several months.

Figure 51. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite captured this natural-color image of the ash plume at Sinabung at 0410 UTC on 19 February 2018, just a few hours after it began. The ash plume rose over 16 km high and drifted in multiple directions. Courtesy of NASA Earth Observatory.

Figure 52. The large ash plume of 19 February 2018 at Sinabung, viewed here from within a few kilometers of the summit in the first hour or so after the eruption, rose quickly to over 16 km altitude. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 53. Two different Ozone Monitoring Instruments measured the SO2 plume released by Sinabung in the explosion on 19 February 2018. The upper left image was recorded about three hours after the explosions (0616-0621 UTC, 19 February 2018) by the Ozone Mapper Profiler Suite (OMPS) instrument on the Suomi NPP satellite. The upper right image was recorded about 27 hours after the explosion (0619-0802 UTC, 19 February 2018) by the Ozone Monitoring Instrument (OMI) on the Aura satellite, and shows the multi-directional dispersal of the SO2 plume during that time. The lower image uses the data captured at the same time as the upper left image and displays it using different software and detailed background information. The maximum gas concentrations reached 140 Dobson Units. Upper images courtesy of NASA Goddard Space Flight Center, and lower image courtesy of NASA Earth Observatory.

As many as 10 pyroclastic flows were observed during the 19 February explosion, traveling as far as 4.9 km SSE and 3.5 km E (figures 54 and 55). Ash and tephra as large as a few millimeters in diameter fell in areas downwind, including Simpang Empat (7 km SE), the Namanteran district, Pqyung (5 km SSW), Tiganderket (7 km W), Munthe, Kutambaru (20 km NW), Perbaji (4 km SW), and Kutarayat (figure 56 and 57).

Figure 54. A pyroclastic flow traveled several kilometers SSE from Sinabung on 19 February 2018 as tephra fell from the rising ash cloud in this view from several kilometers away to the NE. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 55. The dark gray ash plume rose skyward while the large brown pyroclastic flows traveled SE from Sinabung on 19 February 2018 as viewed from the town of Kutarakyat located 5 km NE of the volcano. Photo by Endro Rusharyanto, courtesy of the Associated Press (AP).

Figure 56. Small tephra fragments fell on the village of Gurukinayan (13 km E) and other villages SE of Sinabung during the eruption of 19 February 2018. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 57. Ash from the eruption at Sinabung on 19 February 2018 covered vegetable plants the following day in the village of Payung (5 km SSW). Photograph by Antara Foto, Ahmad Putra via Reuters.

Villagers were temporarily evacuated from nearby villages, but were able to return a few days later (figure 58). Conditions in five districts were so dark that visibility was reduced to about 5 m. In addition, ashfall was recorded as far away as the town of Lhokseumawe, 260 km N. Magma Indonesia reported that the lava dome that had been growing at the summit for some time was destroyed in the 19 February explosion (figure 59). A PVMBG volcanologist reported the volume of the destroyed lava dome was at least 1.6 million cubic meters.

Figure 58. Villagers from Gurukinayan (13 km E) were evacuated as ash spread over the town from the eruption of Sinabung on 19 February 2018, but they returned to their homes a few days later. Photographer unknown, courtesy of Sutopo Purwo Nugroho, Twitter.

Figure 59. The summit of Sinabung, before (top) and after (bottom) the large explosion of 19 February 2018. The dome size in the upper photo is similar to that shown figure 43 (BGVN 42:12) from September 2017. The lower image was taken within a week after the explosion. Courtesy of MAGMA Indonesia, via Twitter.

Reference: Hendrasto M, Surono, Budianto A, Kristianto, Triastuty H, Haerani N, Basuki A, Suparman Y, Primulyana S, Prambada O, Loeqman A, Indrastuti N, Andreas A S, Rosadi U, Adi S, Iguchi M, Ohkura T, Nakada S, Yoshimoto M, 2012. Evaluation of Volcanic Activity at Sinabung Volcano, After More Than 400 Years of Quiet. Journal of Disaster Research, vol. 7, no. 1, p. 37-44.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); Sutopo Purwo Nugroho, Head of Information Data and Public Relations Center of BNPB via Twitter (URL: https://twitter.com/Sutopo_PN); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); 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/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Associated Press (AP), Endro Rusharyanto, Photographer (URL: http://www.ap.org/); Reuters (http://www.reuters.com/).

September 2018 (BGVN 43:09) Cite this Report

No significant ash plumes seen after 22 June 2018; minor ash in early July

Sinabung volcano is located in the Karo regency of North Sumatra, Indonesia. The current eruptive episode commenced in late 2013, after phreatic activity in 2010, producing ash plumes, lava domes and flows, and pyroclastic flows that caused evacuation and relocation of nearby communities. This report covers activity from April through early July, and is based on information provided by MAGMA Indonesia, the Darwin Volcanic Ash Advisory Center (VAAC), the Center for Volcanology and Geological Hazard Mitigation (CVGHM, also known as PVMBG), satellite data, and field photographs. Sinabung has been on Alert Level IV, the highest hazard status, since 2 June 2015.

The eruption has built a pyroclastic flow and lava fan to the SE (figure 60). This activity continued into 2018, with the last significant ash plume reported on 22 June (table 8). However, minor ash emissions continued at least through 5 July 2018.

Figure 60. Satellite images showing Sinabung before and after the eruption with the newly-developed fan of pyroclastic flow, volcanic ash, and lava flow deposits. Top: Landsat-8 true color satellite image (pan-sharpened) acquired on 7 June 2013 before the eruption began. Bottom: Sentinel-2 natural color satellite image acquired on 16 July 2018, after the eruption ended. Courtesy of Sentinel Hub Playground.

Table 8. Summary of ash plumes (altitude and drift direction) and pyroclastic flows at Sinabung, April-June 2018. The summit is at 2,460 m elevation. Data courtesy of Darwin VAAC reports, MAGMA Indonesia VAAC reports, and CVGHM volcanic activity reports.

An eruption on 6 April 2018 at 1607 local time produced an ash plume that reached about 7.5 km above the summit. The eruption also produced pyroclastic flows that traveled about 3.5 km from the summit down the SE slope (figure 61). The eruption resulted in the closure of a nearby airport and ashfall affected hundreds of hectares of agricultural land. Two more notable ash plumes were reported on 12 and 19 April, to altitudes of about 2.7 and 5.5 km, respectively. A pyroclastic flow was reported during the 12 April eruption. Smaller ash and gas emissions occurred through the month.

Figure 61. Eruption of Sinabung on 6 April 2018 at 1600 local time that produced an ash plume that reached over 5 km above the summit, and pyroclastic flows that reached about 3.5 km down the SE flank. Courtesy of Agence France-Presse via Straits Times.

Two ash plumes were recorded on 19 and 20 May, rising to about 3.2 and 5 km altitude, respectively. Throughout June small diffuse gas-and-ash plumes continued (figures 62 and 63). The last activity reported by the agencies was on the 15 and 22 June, when ash plumes reached 3 and 3.5 km altitude (figure 64). Activity after 22 June was limited to seismicity and ash, gas, and steam plumes to several hundred meters above the summit (figure 65). Although an elevated thermal signature was detected in Sentinel-2 satellite data on 30 August 2018, there were no reports of renewed activity.

Figure 62. View of the Sinabung summit vent area during ash venting on 20 June 2018. This view from the SW shows the perched remains of the lava dome and collapse scar. Photo courtesy of Brett Carr, Lamont-Doherty Earth Observatory.

Figure 63. Relatively consistent ash venting at Sinabung on 20 June 2018. This view shows the pyroclastic flow fan and the 2014 lava flow in the lower center of the photo. Drone photo courtesy of Brett Carr, Lamont-Doherty Earth Observatory.

Figure 64. Small ash plume rising from Sinabung at 2106 on 22 June 2018. The ash plume reached about 1 km above the crater. Courtesy of BNPB (color adjusted).

Figure 65. Minor ash venting at Sinabung on 5 July 2018. Photo courtesy of Brett Carr, Lamont-Doherty Earth Observatory.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/, Twitter: https://twitter.com/BNPB_Indonesia ); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/, Twitter: https://twitter.com/id_magma); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Brett Carr, Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY (URL: https://www.ldeo.columbia.edu/user/bcarr); Agence France-Presse (URL: http://www.afp.com/); Straits Times (URL: https://www.straitstimes.com).

August 2019 (BGVN 44:08) Cite this Report

Large ash explosions on 25 May and 9 June 2019

Indonesia's Sinabung volcano in north Sumatra has been highly active since its first confirmed Holocene eruption during August and September 2010. It remained quiet after the initial eruption until September 2013, when a new eruptive phase began that continued uninterrupted through June 2018. Ash plumes often rose several kilometers, avalanche blocks fell kilometers down the flanks, and deadly pyroclastic flows traveled more than 4 km repeatedly during the eruption. After a pause in eruptive activity from July 2018 through April 2019, explosions took place again during May and June 2019. This report covers activity from July 2018 through July 2019 with information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), referred to by some agencies as CVGHM or the Indonesian Center of Volcanology and Geological Hazard Mitigation, the Darwin Volcanic Ash Advisory Centre (VAAC), and the Badan Nacional Penanggulangan Bencana (National Disaster Management Authority, BNPB). Additional information comes from satellite instruments and local news reports.

After the last ash emission observed on 5 July 2018, activity diminished significantly. Occasional thermal anomalies were observed in satellite images in August 2018, and February-March 2019. Seismic evidence of lahars was recorded almost every month from July 2018 through July 2019. Renewed explosions with ash plumes began in early May; two large events, on 24 May and 9 June, produced ash plumes observed in satellite data at altitudes greater than 15 km (table 9).

Table 9. Summary of activity at Sinabung during July 2018-July 2019. Steam plume heights from PVMBG daily reports. VONA reports issued by Sinabung Volcano Observatory, part of PVMBG. Satellite imagery from Sentinel-2. Lahar seismicity from PVMBG daily and weekly reports. Ash plume heights from VAAC reports. Pyroclastic flows from VONA reports.

No eruptive activity was reported after 5 July 2018 for several months, however Sentinel-2 thermal imagery on 30 August indicated a hot spot at the summit suggestive of eruptive activity. The next distinct thermal signal appeared on 6 February 2019, with a few more in late February and early March (figure 66, see table 9).

Figure 66. Sentinel-2 satellite imagery on 30 August 2018, 6 February, and 8 March 2019 showed distinct thermal anomalies suggestive of eruptive activity at Sinabung, although no activity was reported by PVMBG. Images rendered with Atmospheric Penetration, bands 12, 11, and 8A. Courtesy of Sentinel Hub Playground.

PVMBG reported the first ash emission in 11 months early on 7 May 2019. They noted that an ash plume rose 2 km above the summit and drifted ESE. The Sinabung Volcano Observatory (SVO) issued a VONA (Volcano Observatory Notice for Aviation) that described an eruptive event lasting for a little over 40 minutes. Ashfall was reported in several villages. The Jakarta Post reported that Karo Disaster Mitigation Agency (BPDB) head Martin Sitepu said four districts were affected by the eruption, namely Simpang Empat (7 km SE), Namanteran (5 km NE), Kabanjahe (14 km SE), and Berastadi (12 km E). The Darwin VAAC reported the ash plume at 4.6 km altitude and noted that it dissipated about six hours later (figure 67). The TROPOMI SO₂ instrument detected an SO₂ plume shortly after the event (figure 68).

Figure 67. Images from the explosion at Sinabung on 7 May 2019. Left and bottom right photos by Kopi Cimbang and Kalak Karo Kerina, courtesy of David de Zabedrosky. Top right photo courtesy of Sutopo Purwo Nugroho, BNPB.

Figure 68. The TROPOMI instrument on the Sentinel-5P satellite captured an SO2 emission from Sinabung shortly after the eruption on 7 May 2019. Courtesy of NASA Goddard Space Flight Center.

On 11 May 2019 SVO issued a VONA reporting a seismic eruption event with a 9 mm amplitude that lasted for about 30 minutes; clouds and fog prevented visual confirmation. Another VONA issued the following day reported an ash emission that lasted for 28 minutes but again was not observed due to fog. The Darwin VAAC did not observe the ash plumes reported on 11 or 12 May; they did report incandescent material observed in the webcam on 11 May. Sutopo Purwo Nugroho of BNPB reported that the 12 May eruption was accompanied by incandescent lava and ash, and the explosion was heard in Rendang (figure 69). The Alert Level had been at Level IV since 2 June 2015. Based on decreased seismicity, a decrease in visual activity (figure 70), stability of deformation data, and a decrease in SO₂ flux during the previous 11 months, PVMBG lowered the Alert Level from IV to III on 20 May 2019.

Figure 69. Incandescent lava and ash were captured by a webcam at Sinabung on 12 May 2019. Courtesy of Sutopo Purwo Nugroho, BNPB.

Figure 70. The summit of Sinabung emitted only steam and gas on 18 May 2019, shortly before PVMBG lowered the Alert Level from IV to III. Courtesy of PVMBG (Decreased G. Sinabung activity level from Level IV (Beware) to Level III (Standby), May 20, 2019).

A large explosion was reported by the Darwin VAAC on 24 May 2019 (UTC) that produced a high-altitude ash plume visible in satellite imagery at 15.2 km altitude moving W; the plume was not visible from the ground due to fog. The Sinabung Volcano Observatory reported that the brief explosion lasted for only 7 minutes (figure 71), but the plume detached and drifted NW for about 12 hours before dissipating. The substantial SO₂ plume associated with the event was recorded by satellite instruments a few hours later (figure 72, left). Another six-minute explosion late on 26 May (UTC) produced an ash plume that was reported by a ground observer at 4.9 km altitude drifting S (figure 72, right). About an hour after the event, the Darwin VAAC observed the plume drifting S at 6.1 km altitude; it had dissipated four hours later. Sumbul Sembiring, a resident of Kabanjahe, told news outlet Tempo.com that ash had fallen at the settlements. Two more explosions were reported on 27 May; the first lasted for a little over 12 minutes, the second (about 90 minutes later, 28 May local time) lasted for about 2.5 minutes. No ash plumes were visible from the ground or satellite imagery for either event.

Figure 71. A brief but powerful explosion at Sinabung in the early hours of 25 May 2019 (local time) produced a seven-minute-long seismic signal and a 15.2-km-altitude ash plume. Courtesy of MAGMA Indonesia and Volcano Discovery.

Figure 72. Two closely spaced eruptive events occurred at Sinabung on 24 and 26 May UTC (25 and 27 May local time). The 24 May event produced a significant SO2 plume recorded by the TROPOMI instrument a few hours afterwards (left), and a 15.2-km-altitude ash plume only recorded in satellite imagery. The event on 26 May produced a visible ash plume that was reported at 6.1 km altitude and was faintly visible from the ground (right). SO2 courtesy of NASA Goddard Space Flight Center, photograph courtesy of PVMBG and Øystein Lund Andersen.

An explosion on 9 June 2019 produced an ash plume, estimated from the ground as rising to 9.5 km altitude, that drifted S and E; pyroclastic flows traveled 3.5 km SE and 3 km S down the flanks (figure 73). The explosion was heard at the Sinabung Observatory. The Darwin VAAC reported that the eruption was visible in Himawari-8 satellite imagery, and reported by pilots, at 16.8 km altitude drifting W; about an hour later the VAAC noted that the detached plume continued drifting SW but lower plumes were still present at 9.1 km altitude drifting W and below 4.3 km drifting SE. They also noted that pyroclastic flows moving SSE were sending ash to 4.3 km altitude. Three hours later they reported that both upper level plumes had detached and were moving SW and W. After six hours, the lower altitude plumes at 4.3 and 9.1 km altitudes had dissipated; the higher plume continued moving SW at 12.2 km altitude until it dissipated within the next eight hours. Instruments on the Sentinel-5P satellite captured an SO₂ plume from the explosion drifting W across the southern Indian Ocean (figure 74).

Figure 73. A large explosion at Sinabung on 9 June 2019 produced an ash plume that rose to 16.8 km altitude and also generated pyroclastic flows (foreground) that traveled down the S and SE flanks. Left image courtesy of Sutopo Purwo Nugroho, Head of the BNPB Information and Public Relations Data Center. Right image photo source PVMBG/Mbah Rono/ Berastagi Nachelle Homestay, courtesy of Jaime Sincioco.

Figure 74. An SO2 plume from the 9 June 2019 explosion at Sinabung drifted more than a thousand kilometers W across the southern Indian Ocean. Courtesy of Sentinel Hub and Annamaria Luongo.

The SVO reported continuous ash and gas emissions at 3.0 km altitude moving ESE early on 10 June; it was obscured in satellite imagery by meteoric clouds. There were no additional VONA's or VAAC reports issued for the remainder of June or July 2019. An image on social media from 20 June 2019 shows incandescent blocks near the summit (figure 75). PVMBG reported that emissions on 25 June were white to brownish and rose 200 m above the summit and drifted E and SE.

Figure 75. Incandescent blocks at the summit of Sinabung were visible in this 20 June 2019 image taken from a rooftop terrace in Berastagi, 13 km E. Photo by Nachelle Homestay, courtesy of Jaime Sincioco.

PVMBG detected seismic signals from lahars several times during the second week of July 2019. News outlets reported lahars damaging villages in the Karo district on 11 and 13 July (figure 76). Detik.com reported that lahars cut off the main access road to Perbaji Village (4 km SW), Kutambaru Village (14 km S), and the Tiganderket connecting road to Kutabuluh (17 km WNW). In addition, Puskesmas Kutambaru was submerged in mud. Images from iNews Malam showed large boulders and rafts of trees in thick layers of mud covering homes and roads. No casualties were reported.

Figure 76. Lahars on 11 and 13 July 2019 caused damage in numerous villages around Sinabung, filling homes and roadways with mud, tree trunks, and debris. No casualties were reported. Courtesy of iNews Malam.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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/); The Jakarta Post (URL: https://www.thejakartapost.com/news/2019/05/07/mount-sinabung-erupts-again.html); Detikcom (URL: https://news.detik.com/berita/d-4619253/hujan-deras-sejumlah-desa-di-sekitar-gunung-sinabung-banjir-lahar-dingin); iNews Malam (URL: https://tv.inews.id/, https://www.youtube.com/watch?v=uAI4CpSb41k); Tempo.com (URL:https://en.tempo.co/read/1209667/mount-sinabung-erupts-on-monday-morning); David de Zabedrosky, Calera de Tango, Chile (Twitter: @deZabedrosky, URL: https://twitter.com/deZabedrosky/status/1125814504867160065/photo/1, https://twitter.com/deZabedrosky/status/1125814504867160065/photo/2); Sutopo Purwo Nugroho, BNPB (Twitter: @Sutopo_PN, URL: https://twitter.com/Sutopo_PN); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); Øystein Lund Andersen? (Twitter: @OysteinLAnderse, URL: https://twitter.com/OysteinLAnderse, URL: http://www.oysteinlundandersen.com image at https://twitter.com/OysteinLAnderse/status/1132849458142572544); Jaime Sincioco, Phillipines (Twitter: @jaimessincioca, URL: https://twitter.com/jaimessincioco); Annamaria Luongo, University of Padua, Venice, Italy (Twitter: @annamaria_84, URL:https://twitter.com/annamaria_84).

November 2020 (BGVN 45:11) Cite this Report

Explosions begin again on 8 August 2020; dome growth confirmed in late September

Indonesia’s Sinabung volcano in north Sumatra has been highly active since its first confirmed Holocene eruption during August and September 2010. It remained quiet after the initial eruption until September 2013, when a new eruptive phase began that continued through June 2018. A summit dome emerged in late 2013 and produced a large lava “tongue” during 2014. Multiple explosions produced ash plumes, block avalanches, and deadly pyroclastic flows during the eruptive period. A major explosion in February 2018 destroyed most of the summit dome. After a pause in eruptive activity from September 2018 through April 2019, explosions resumed during May and June 2019. The volcano was quiet again until an explosion on 8 August 2020 began another eruption that included a new dome. This report covers activity from July 2019 through October 2020 with information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), referred to by some agencies as CVGHM or the Indonesian Center of Volcanology and Geological Hazard Mitigation, the Darwin Volcanic Ash Advisory Centre (VAAC), and the Badan Nacional Penanggulangan Bencana (National Disaster Management Authority, BNPB). Additional information comes from satellite instruments and local news reports.

Only steam plumes and infrequent lahars were reported at Sinabung during July 2019-July 2020. A new eruption began on 8 August 2020 with a phreatic explosion and dense ash plumes. Repeated explosions were reported throughout August; ashfall was reported in many nearby communities several times. Explosions decreased significantly during September, but SO₂ emissions persisted. Block avalanches from a new growing dome were first reported in early October; pyroclastic flows accompanied repeated ash emissions during the last week of the month. Thermal data suggested that the summit dome continued growing slowly during October.

Activity during July 2019-October 2020. After a large explosion on 9 June 2019, activity declined significantly, and no further emissions or incandescence was reported after 25 June (BGVN 44:08). For the remainder of 2019 steam plumes rose 50-400 m above the summit on most days, occasionally rising to 500-700 m above the crater. Lahars were recorded by seismic instruments in July, August, September, and December. During January-July 2020 steam plumes were reported usually 50-300 m above the summit, sometimes rising to 500 m. On 21 March 2020 steam plumes rose to 700 m, and a lahar was recorded by seismic instruments. Lahars were reported on 26 and 28 April, 3 and 5 June, and 11 July.

A swarm of deep volcanic earthquakes was reported by PVMBG on 7 August 2020. This was followed by a phreatic explosion with a dense gray to black ash plume on 8 August that rose 2,000 m above the summit and drifted E; a second explosion that day produced a plume that rose 1,000 m above the summit. According to the Jakarta Post, ash reached the community of Berastagi (15 km E) along with the districts of Naman Teran (5-10 km NE), Merdeka (15 km NE), and Dolat Rayat (20 km E). Continuous tremor events were first recorded on 8 August and continued daily until 26 August. Two explosions were recorded on 10 August; the largest produced a dense gray ash plume that rose 5,000 m above the summit and drifted NE and SE (figure 77). The Darwin VAAC reported the eruption clearly visible in satellite imagery at 9.7 km altitude and drifting W. Later they reported a second plume drifting ESE at 4.3 km altitude. After this large explosion the local National Disaster Management Authority (BNPB) reported significant ashfall in three districts: Naman Teran, Berastagi and Merdeka. Emissions on 11 and 12 August were white and gray and rose 100-200 m. Multiple explosions on 13 August produced white and gray ash plumes that rose 1,000-2,000 m above the summit. Explosions on 14 August produced gray and brown ash plumes that rose 1,000-4,200 m above the summit and drifted S and SW (figure 77). The Darwin VAAC reported that the ash plume was partly visible in satellite imagery at 7.6 km altitude moving W; additional plumes were moving SE at 3.7 km altitude and NE at 5.5 km altitude.

Figure 77. Numerous explosions were recorded at Sinabung during August 2020. An ash plume rose to 5,000 m above the summit on 10 August (left) and drifted both NE and SE. On 14 August gray and brown ash plumes rose 1,000-4,200 m above the summit and drifted S, SW, SE and NE (right) while ashfall covered crops SE of the volcano. Courtesy of PVMBG (Sinabung Eruption Notices, 10 and 14 August 2020).

White, gray, and brown emissions rose 800-1,000 m above the summit on 15 and 17 August. The next day white and gray emissions rose 2,000 m above the summit. The Darwin VAAC reported an ash plume visible at 5.2 km altitude drifting SW. A large explosion on 19 August produced a dense gray ash plume that rose 4,000 above the summit and drifted S and SW. Gray and white emissions rose 500 m on 20 August. Two explosions were recorded seismically on 21 August, but rainy and cloudy weather prevented observations. White steam plumes rose 300 m on 22 August, and a lahar was recorded seismically. On 23 August, an explosion produced a gray ash plume that rose 1,500 m above the summit and pyroclastic flows that traveled 1,000 m down the E and SE flanks (figure 78). Continuous tremors were accompanied by ash emissions. White, gray, and brown emissions rose 600 m on 24 August. An explosion on 25 August produced an ash plume that rose 800 m above the peak and drifted W and NW (figure 79). During 26-30 August steam emissions rose 100-400 m above the summit and no explosions were recorded. Dense gray ash emissions rose 1,000 m and drifted E and NE after an explosion on 31 August. Significant SO₂ emissions were associated with many of the explosions during August (figure 80).

Figure 78. On 23 August 2020 an explosion at Sinabung produced a gray ash plume that rose 1,500 m above the summit and produced pyroclastic flows that traveled 1,000 m down the E and SE flanks. Courtesy of PVMBG (Sinabung Eruption Notice, 23 August 2020).

Figure 79. An explosion on 25 August 2020 at Sinabung produced an ash plume that rose 800 m above the peak and drifted W and NW. Courtesy of PVMBG (Sinabung Eruption Notice, 25 August 2020).

Figure 80. Significant sulfur dioxide emissions were measured at Sinabung during August 2020 when near-daily explosions produced abundant ash emissions. A small plume was also recorded from Kerinci on 19 August 2020. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Explosive activity decreased substantially during September 2020. A single explosion reported on 5 September produced a white and brown ash plume that rose 800 m above the summit and drifted NNE. During the rest of the month steam emissions rose 50-500 m above the summit before dissipating. Two lahars were reported on 7 September, and one each on 11 and 30 September. Although only a single explosion was reported, anomalous SO₂ emissions were present in satellite data on several days.

The character of the activity changed during October 2020. Steam plumes rising 50-300 m above the summit were reported during the first week and a lahar was recorded by seismometers on 4 October. The first block avalanches from a new dome growing at the summit were reported on 8 October with material traveling 300 m ESE from the summit (figure 81). During 11-13 October block avalanches traveled 300-700 m E and SE from the summit. They traveled 100-150 m on 14 October. Steam plumes rising 50-500 m above the summit were reported during 15-22 October with two lahars recorded on 21 October. White and gray emissions rose 50-1,000 m on 23 October. The first of a series of pyroclastic flows was reported on 25 October; they were reported daily through the end of the month when the weather permitted, traveling 1,000-2,500 m from the summit (figure 82). In addition, block avalanches from the growing dome were observed moving down the E and SE flanks 500-1,500 m on 25 October and 200-1,000 m each day during 28-31 October (figure 83). Sentinel-2 satellite data indicated a very weak thermal anomaly at the summit in late September; it was slightly larger in late October, corroborating with images of the slow-growing dome (figure 84).

Figure 81. A new lava dome appeared at the summit of Sinabung in late September 2020. Block avalanches from the dome were first reported on 8 October. Satellite imagery indicating a thermal anomaly at the summit was very faint at the end of September and slightly stronger by the end of October. The dome grew slowly between 30 September (top) and 22 October 2020 (bottom). Photos taken by Firdaus Surbakti, courtesy of Rizal.

Figure 82. Pyroclastic flows at Sinabung were accompanied ash emissions multiple times during the last week of October, including the event seen here on 27 October 2020. Courtesy of PVMBG and CultureVolcan.

Figure 83. Block avalanches from the growing summit dome at Sinabung descended the SE flank on 28 October 2020. The dome is visible at the summit. Courtesy of PVMBG and MAGMA.

Figure 84. A very faint thermal anomaly appeared at the summit of Sinabung in Sentinel 2 satellite imagery on 28 September 2020 (left). One month later on 28 October the anomaly was bigger, corroborating photographic evidence of the growing dome. Atmospheric penetration rendering (bands 12, 11, 8A) courtesy of Sentinel Hub Playground.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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/); The Jakarta Post, 3rd Floor, Gedung, Jl. Palmerah Barat 142-143 Jakarta 10270 (URL: https://www.thejakartapost.com/amp/news/2020/08/08/mount-sinabung-erupts-again-after-year-of-inactivity.html);Rizal (URL: https://twitter.com/Rizal06691023/status/1319452375887740930); CultureVolcan (URL: https://twitter.com/CultureVolcan/status/1321156861173923840).

March 2021 (BGVN 46:03) Cite this Report

Block avalanches, pyroclastic flows, and ash explosions continue through February 2021

Indonesia’s Sinabung volcano in north Sumatra had its first confirmed Holocene eruption during August and September 2010. It remained quiet until September 2013 when a new eruptive phase began that continued through mid-2018. Dome growth and destruction resulted in block avalanches, multiple explosions with ash plumes, and deadly pyroclastic flows during the period. After a pause in activity from September 2018 through April 2019, explosions resumed during May and June 2019. Dome growth began again with an explosion on 8 August 2020, and similar activity continued through October 2020. This report covers ongoing activity from November 2020 through February 2021 with information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), referred to by some agencies as CVGHM or the Indonesian Center of Volcanology and Geological Hazard Mitigation, and the Darwin Volcanic Ash Advisory Centre (VAAC). Additional information comes from satellite instruments and local news reports.

Activity at Sinabung during November 2020-February 2021 was characterized by tens of daily rock avalanches, periodic pyroclastic flows, and ash-bearing explosions. The rock avalanches traveled up to 1,000 m down the E and SE flanks. The pyroclastic flows also traveled down the E and SE flanks, and the largest reached 2.5 km from the summit. Periodic explosions produced ash plumes that rose up to 2 km above the summit and drifted in multiple directions. Although cloudy much of the time, intermittent satellite images showing two thermal anomalies at the summit suggested that the dome remained active (figure 85).

Figure 85. Two thermal anomalies were present at the summit of Sinabung several times during the report period from November 2020-February 2021, including on 2 December 2020 and 10 February 2021, suggesting ongoing dome activity. In addition, frequent pyroclastic flows produced incandescent anomalies on the E flank multiple times including on 10 February 2021. Sentinel-2 images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

White steam emissions rose 50-500 m above the summit of Sinabung during most days in November 2020. Block avalanches were frequent during the first half of the month, traveling 200-1,000 m down the S and SE flanks. The Darwin VAAC reported small ash plumes from block avalanches on 1 and 2 November that rose to 3 km altitude and quickly dissipated. Clouds prevented observations during the last week of the month, but tens of seismic events interpreted by PVMBG as block avalanches were detected. Pyroclastic flows were either observed visually or measured seismically on 2-7, 10, 12, 16, 18 and 19 November (figure 86). They most often occurred on the E or SE flanks and traveled 1,500-2,500 m. Seismic signals indicating lahars were recorded on 26, 27, and 30 November.

Figure 86. A pyroclastic flow descended the S flank of Sinabung on 7 November 2020. Courtesy of Rizal.

Nine explosions with ash plumes were reported during November 2020. On 2 November a gray ash plume rose 1,500 m above the summit, to about 3.9 km altitude, and drifted E. The next day the Darwin VAAC reported an explosion to 3.7 km altitude that drifted E. An ash explosion on 4 November was recorded seismically for 117 seconds but was not seen due to fog. An explosion on 10 November produced an ash plume that rose 2 km above the summit and drifted E, along with pyroclastic flows that traveled 1,500-2,500 m down the E and SE flanks. On 18 November an explosion created an ash plume that rose to 3.7 km altitude and drifted SW; it was measured seismically as a continuous volcanic tremor that lasted for 160 seconds. Seismic activity confirmed an explosion on 21 November, but meteoric clouds obscured observations of ash. An ash plume drifting SW at 3 km altitude, about 500 m above the summit, was reported on 25 November. On 29 November an explosion produced an ash plume to the same altitude that drifted E (figure 87). The next day seismic activity indicated another explosion, but it was not observed due to cloudy weather.

Figure 87. An ash plume at Sinabung rose to 3 km altitude and drifted E on 29 November 2020. Courtesy of PVMBG and MAGMA Indonesia.

Explosive activity decreased during December 2020. Steam plumes rose 50-500 m and tens of rock avalanches were recorded seismically every day. On 6 December block avalanches rolled 300-500 m down the E and SE flanks; they traveled 500-1,000 m down the SE flank on 8 December. During 12-14 December they traveled 1,000-1,500 m down the E and S flanks. On 30 and 31 December they were seen moving 500-1,000 m down the same flanks. Lahars were measured seismically on 4 and 5 December with no reports of damage.

An explosion on 2 December produced an ash plume that rose about 500 m above the summit and drifted ESE. Clouds and rain prevented views of the summit on 5 December, but the seismogram recorded an explosive event that lasted for 168 seconds (figure 88). The Darwin VAAC reported an ash plume moving ESE at 3 km altitude on 13 December. Sentinel-2 satellite imagery captured a thermal anomaly on the E flank on 17 December that was likely from a pyroclastic flow (figure 89). Two explosions were recorded each day on 28 and 29 December. On the first day the ash plume from the first explosion rose to 500 m and drifted S. The second explosion was not observed due to weather, but a thermal anomaly was intermittently visible. The explosions on 29 December were only recorded seismically, as was one explosion on 30 December.

Figure 88. The KESDM seismogram at Sinabung recorded an explosive event on 5 December 2020 that lasted for 168 seconds. Courtesy of PVMBG and MAGMA Indonesia.

Figure 89. A thermal anomaly on the E flank of Sinabung on 17 December 2020 was likely from a pyroclastic flow. The summit is obscured by clouds. Sentinel-2 image with Atmospheric penetration rendering (bands 12, 11, and 8a). Courtesy of Sentinel Hub Playground.

Tens of daily rock avalanches continued to be recorded during January 2021, although most were not observed. During 2-5 January they traveled 500-1,200 m down the E and SE flanks, and on 14 January they fell 700-1,000 m down the SE flank. The number of explosions with ash plumes increased significantly from December. On 3 January two explosions were recorded seismically; an ash plume from the first rose 1,000 m above the summit and drifted NW in the morning. A few hours later a second explosion was recorded but not observed due to clouds. Three explosions were recorded each day on 4 and 5 January. The first on 4 January produced a 700-m-high ash plume, the second and third sent ash 1,000 m above the summit to the W and NW (figure 90). The next day, the first explosion sent an ash plume 800 m above the summit that drifted E and SE; the other two were recorded seismically but not observed due to weather. One or two explosions were recorded daily during 6-10 January; most were obscured by clouds. One of the explosions on 8 January produced an ash plume that rose to 700 m and drifted N, and the explosion on 9 January rose to 1,000 m and drifted N and NE. Two explosions were recorded on 12 January, and two or three explosions were reported daily during 16-18 January. Explosions were also recorded on 20-21, 23, 25-27, and 29 January. The three ash plumes on 17 January all rose 500 m above the summit and drifted E, NE, or SE; the plumes on 21 and 27 January rose 500 m and drifted E and SE.

Figure 90. An explosion at Sinabung on 4 January 2021 produced an ash emission that rose 1,000 m above the summit and drifted W and NW. Courtesy of PVMBG and MAGMA Indonesia.

Steam emissions rose 50-700 m above the summit throughout February 2021. Over 100 seismic events from rock avalanches were reported daily; on 6 February a maximum of 231 events were recorded. Numerous explosions, many with pyroclastic flows, were only detected seismically on 5-12, 14, 17, 22, 25, and 28 February. On 6 February the Darwin VAAC reported a continuous ash eruption identified in satellite imagery at 3.1 km altitude drifting NW. PVMBG also reported a pyroclastic flow that traveled 2,500 m down the S flank that day. The Antara News Agency reported an ash plume rising 1,000 m above the summit from a pyroclastic flow and drifting E, SE, and S on 7 February, and another pyroclastic flow on 9 February that traveled 1,000 m down the SE flank (figure 91). Cloudy weather obscured views on most days, but during 12-14 February blocks traveled 500-1,500 m down the S, SE, and E flanks.

Figure 91. A pyroclastic flow traveled 1,000 m down the SE flank of Sinabung on 9 February 2021. Courtesy of Anadolu Agency.

The Darwin VAAC received a report on 10 February of an ash plume at 4.6 km altitude moving E; it was not identifiable in satellite imagery due to meteoric clouds. Two pyroclastic flows on 12 February moved as far as 2,000 m down the E and SE flanks. On 17 February an ash plume rose 1,000 m above the summit and drifted S and W and a pyroclastic flow was reported. A lahar was reported on 21 February. A pyroclastic flow on 22 February traveled 2,000 m down the E and SE flanks. The ash plume from the 25 February event rose to 1,500 m above the summit to about 3.9 km altitude and drifted E and SE (figure 92) and was accompanied by four pyroclastic flows that traveled 500-1,000 m down the E and SE flanks. A discrete ash plume was reported by the Darwin VAAC on 28 February that rose to 3.1 km altitude and drifted SW, dissipating withing six hours. Pyroclastic flow were observed that day moving 1,000-1,250 m down the S, SE, and E flanks.

Figure 92. The ash plume at Sinabung from a 25 February 2021 explosion rose to 1,500 m above the summit and drifted E and SE. Courtesy of PVMBG and MAGMA Indonesia.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Rizal (URL: https://twitter.com/Rizal06691023/status/1324972883634917376); Antara News Agency (URL: https://www.antaranews.com/berita/1986704/guguran-abu-gunung-sinabung-teramati-setinggi-1000-meter); Anadolu Agency (URL: https://www.aa.com.tr/ba/svijet/indonezija-u-vulkanu-sinabung-odjeknula-eksplozija/2138389).

August 2021 (BGVN 46:08) Cite this Report

Ash plumes rise to 12.2 km with pyroclastic flows on 2 March and 13-14 May 2021

Indonesia’s Sinabung volcano in north Sumatra had its first confirmed Holocene eruption during August and September 2010. It remained quiet until September 2013 when a new eruptive phase began that continued through mid-2018. Dome growth and destruction resulted in block avalanches, multiple explosions with ash plumes, and deadly pyroclastic flows during the period. After a pause in activity from September 2018 through April 2019, explosions resumed during May and June 2019. Rock avalanches, frequent, dense, ash-bearing explosions, and periodic pyroclastic flows continued through February 2021. This report covers ongoing similar activity from March through June 2021 with information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, and the Darwin Volcanic Ash Advisory Centre (VAAC). Additional information comes from satellite instruments and the Indonesian National Disaster Management Agency (BNPB).

Hundreds of block avalanches and tens of ash-bearing explosions were reported each month during March to mid-May 2021. Ash plumes rose 500-2,000 m above the summit (3,000-4,500 m altitude) on most days; occasional larger events produced much higher plumes. Two major sets of explosions, on 2 March and 13-14 May, each produced ash plumes that rose to 12.2 km altitude, more than 10 pyroclastic flows, and significant SO₂ plumes measured by satellite instruments. Reports of activity during the period came from the Sinabung Observation Post (in Surbakhti, 10 km SE of the volcano) and from geoscientists monitoring seismic instruments and webcams from remote locations; the combined information provides a more complete picture of activity at the volcano (table 10). Thermal activity was recorded by the MIROVA project and indicated a spike in radiative power that began in late February and lasted through May 2021, attributable to increased explosive activity (figure 93). Two notable sequences of explosions on 2 March and 13-14 May produced significant plumes of SO₂ that were measured by the TROPOMI instrument on the Sentinel-5P satellite (figure 94). None of the other explosions during the period produced significant SO₂ anomalies. Only two days of explosions, 3 and 6 June, occurred after 19 May through the end of June.

Table 10. A summary of information and sources reporting activity at Sinabung during March-June 2021 includes the distance block avalanches traveled, the number of eruptions, pyroclastic flows, and lahars reported by the observatory, the seismic eruptions recorded by MAGMA Indonesia, and the VONA’s issued. All heights and distances shown are in meters. Information provided by PVMBG unless otherwise noted. Courtesy of PVMBG and MAGMA Indonesia.

Figure 93. An increase in thermal activity at Sinabung during late February-May 2021 corresponded to an increase in explosive activity during the period as shown in the MIROVA graph of Log Radiative Power for 24 Aug 2020 through June 2021. Courtesy of MIROVA.

Figure 94. High level explosions at Sinabung on 2 March and 13 May 2021 produced significant plumes of SO2 that drifted NW from the volcano and were measured by the TROPOMI Instrument on the Sentinel-5P satellite. The ash plumes were reported at 12.2 km altitude. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Activity during March-June 2021. Significant explosive activity continued at Sinabung during March 2021. In a special press release on 2 March, PVMBG reported a series of pyroclastic flows that began at 0642 local time and traveled 2,000-5,000 m ESE from the summit accompanied by a column of ash that rose 4,000-5,000 m above the body of the pyroclastic flow (figure 95). MAGMA Indonesia reported three explosions that rose to about 1,000 m above the summit and drifted E and SW. The Darwin VAAC first reported that the ash emissions from the eruption rose to 7.6 km altitude (5.1 km above the summit) and drifted W; they were clearly discernable in satellite imagery. About an hour later they updated the altitude of the plume to 12.2 km based on analysis of HIMAWRI-8 imagery. In the following hours the plume was observed drifting W at 12.2 km altitude and SW at 7.6 km before dissipating. According to BNPB ashfall was noted in 17 villages in the Tiganderket District, eight villages in the Kutabuluh District, and 15 villages in the Tigabinaga District.

Figure 95. This explosion at 0836 local time was one of three at Sinabung on 2 March 2021 that produced 15 pyroclastic flows and ash plumes that rose to 12.2 km altitude according to the Darwin VAAC. The pyroclastic flows descended up to 3.7 km down the SE and E flanks. Photo by PVMBG - Sinabung PGA Post. Courtesy of PVMBG (Press Release Volcanic Activity of Mount Sinabung – North Sumatra March 2, 2021).

On most days in March steam plumes were observed rising 50-500 m above the summit; they reached 1,000 m high on 7 March. Block avalanches were reported descending the E and SE flanks 500-1,500 m on 12 days of the month. The Sinabung Observation Post reported 49 explosion earthquakes and gray ash emissions. There were 1-2 explosions on most days; six were observed on 11 March (figure 96) that all rose only 500-1,000 m above the summit and drifted W and SW with no ashfall reported. MAGMA Indonesia reported an explosion on 15 March that rose 2,000 m above the summit; the Darwin VAAC could not confirm it in satellite imagery due to meteoric clouds. For the second half of March, 1-4 explosions were reported daily; dense gray ash rose 500-1,000 m above the summit and drifted SW, W, NW, and NE.

Figure 96. Six explosions with ash emissions from Sinabung were reported on 11 March 2021. The plumes rose 500-1,000 m above the summit and drifted S and SW. Courtesy of MAGMA Indonesia.

MAGMA Indonesia reported 42 eruptions throughout March with dense gray ash emissions that rose 500-2,000 m above the summit and drifted SW, W, or NW. The Darwin VAAC issued 53 ash advisories. VONAs were issued 22 times; two on 2 and 11 March were for pyroclastic flows, the others were for ash plumes from explosions. There were 20 pyroclastic flows reported by PVMBG during the month; 15 of them occurred on 2 March when they traveled 1,000-3,700 m down the E and SE flanks and 2,300 m down the S flank (figure 97). One pyroclastic flow was reported on 1 March, and two others were reported on 3 and again on 11 March that traveled 2,000-3,000 m ESE from the summit. Three seismic signals indicative of lahars were recorded on 12, 16, and 18 March.

Figure 97. A strong thermal anomaly at Sinabung was recorded in Sentinel-2 satellite imagery on 2 March 2021. Its location near the summit on the ESE flank suggests it was related to one of the 15 pyroclastic flows observed that day. Image uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

The frequency of explosive activity increased significantly during April 2021. Block avalanches were reported on 15 days, traveling 500-1,500 m down the S and SE flanks. PVMBG reported 123 eruptions with gray ash plumes rising 500-1,000 m above the summit. VONA’s were issued for 30 events. MAGMA Indonesia reported 74 explosions with dense gray ash emissions rising 500-2,000 m above the summit. There were 1-10 explosions nearly every day; only two days had no explosions reported. Eight explosions were reported on 2 April with heights of 500-1,000 m above the summit. On 4 April PVMBG reported an ash emission to 3.7 km altitude, but the Darwin VAAC revised that estimate to 5.5 km based on satellite infrared temperature data (figure 98). During 7-8 April the VAAC reported ash emissions at 4.3 km altitude. MAGMA Indonesia reported eight explosions on 17 April with plume heights ranging from 500 to 1,500 m above the summit, drifting S and W. On 19 April emissions were reported by the Darwin VAAC drifting SE at 4.6 km altitude; they reached 4.3 km on 24 April. For the remainder of the month six or more explosions occurred most days, with altitudes of 3.0-3.9 km. Seven pyroclastic flows were reported during April. On 1 April, one traveled 1,500 m down the SE flank. One was reported on 8 April, two on 13 April, and one each on 19, 21, and 29 April. The pyroclastic flow on 21 April traveled 2,000 m down the flank. Signals indicating lahars were recorded on 12, 16, 24, 29, and 30 April.

Figure 98. PVMBG reported 123 explosions with ash at Sinabung during April 2021, including four on 4 April (top left), five on 16 April (top right), nine on 20 April (bottom left), and six on 28 April (bottom right). Courtesy of MAGMA Indonesia and PVMBG.

Substantially fewer explosions were reported during May 2021 than April, although the ash plumes were higher for several events. The Sinabung Observation Post reported 37 explosions that produced gray ash plumes rising 500-3,000 m above the summit; 1-6 explosions occurred daily through 14 May; a single explosion on 19 May was the last one recorded for the month. The ten VONA’s also recorded plume heights 700-3,000 m. MAGMA Indonesia reported 26 seismic events with dense gray emissions ranging from 500-3,500 m high. During 6-10 May ash emissions were reported 2,000 m or higher above the summit each day; six explosions were reported by PVMBG and MAGMA Indonesia on 8 May. The Darwin VAAC noted that ash plumes on 6 May rose to 4.6 km altitude. The next day the emissions rose to 5.2-5.5 km altitude and were discernable late in the day drifting NNW in RGB satellite imagery. On 8 May the ash plumes were reported at 4.3-5.2 km altitude drifting E; on 10 May two discrete events rose to 4.9 and 3.7 km and drifted S, both noted in satellite imagery (figure 99). Four explosions were reported on 11 May. Sentinel-2 satellite imagery recorded incandescent material in the large SE flank ravine that day (figure 100).

Figure 99. Three explosions at Sinabung on 10 May 2021, including this one at 0750 local time produced ash emissions that rose up to 2,500 m above the summit (4.9 km altitude) and drifted S. Courtesy of MAGMA Indonesia and PVMBG.

Figure 100. Four explosions were reported at Sinabung on 11 May 2021; a thermal anomaly extended hundreds of meters down the SE flank ravine in this Sentinel-2 satellite image. Image uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

During 13-14 May six explosions and 15 pyroclastic flows were reported by PVMBG with ash plumes 700-1,000 m above the summit, and pyroclastic flows descending the SE and E flanks 2,500-4,000 m. A larger eruption with ash to 12.2 km that drifted NW, clearly identifiable in satellite imagery, was reported by the Darwin VAAC on 13 May. A second explosion three hours later produced a plume that was identifiable in RGB satellite imagery at 9.8 km altitude moving WNW. Eruptions were ongoing on 14 May, with plumes rising to 9.1-10.7 km altitude and drifting NW (figure 101). A significant SO₂ plume was measured by satellite instruments that day. A single large explosion early on 19 May (local time) produced an ash plume to 3,500 m above the summit (5.9 km altitude). The Jakarta Meteorological Office reported the eruption to the Darwin VAAC but it was not visible in satellite imagery due to meteoric clouds. This was the last explosion reported for May. Five lahars were recorded during the month; one each day on 12, 15, and 16 May, and two on 13 May.

Figure 101. This photo was posted to Twitter on 15 May 2021 with the caption “..areas affected by the eruption of Mount Sinabung” and likely represents ashfall from the large explosions of 13-14 May 2021. Courtesy of amoy rest buying.

Very little activity was reported from Sinabung during June 2021. Steam emissions rose 50-300 m above the summit on most days, occasionally rising to 500 m. Block avalanches were reported only on 11 and 12 June. PVMBG reported two seismic eruption events, on 3 and 5 June, but they were not observed. A single pyroclastic flow occurred on 6 June, the only day a single VONA was issued. MAGMA Indonesia reported two eruption events on 4 June and one on 6 June; none were observed due to poor weather conditions. The Darwin VAAC reported a significant eruption on 6 June that sent an ash plume to 9.1 km altitude that drifted W. Initially it was not visible, but later appeared on RGB satellite imagery moving N and W. A few hours after the eruption the plume was drifting N at 4.3 km altitude, W at 7.3 km, and WSW at 9.1 km. It dissipated the following morning, and was the last explosion reported for June. Lahars were recorded on 3, 15, and 25 June.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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/); amoy rest buying (URL: https://twitter.com/jjaemshine/status/1393531437949743111).

January 2022 (BGVN 47:01) Cite this Report

Explosions, ash plumes, and block avalanches during June-September 2021

Sinabung in north Sumatra, Indonesia had its first confirmed Holocene eruption during August and September 2010. Dome growth, block avalanches, multiple explosions with ash plumes, and pyroclastic flows are common events that occur. The continuing eruption that began in August 2020 has recently consisted of ash plumes, pyroclastic flows, hundreds of block avalanches, and explosions (BGVN 46:08). This report covers intermittent explosions, ash plumes, and block avalanches from June through September 2021 with information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, and the Darwin Volcanic Ash Advisory Centre (VAAC).

White gas-and-steam emissions dominantly occurred throughout the reporting period; during June, they rose 50-500 m above the summit and drifted E, SE, SW, W, and NW (figure 102). An eruption occurred at 2004 on 3 June, though it was not visually confirmed due to cloud cover. Another event at 2335 on 6 June consisted of ash plumes and pyroclastic flows, though weather again obscured views. A Darwin VAAC notice reported an ash plume visible in satellite images, with the multi-level plume rising to 4.3 km altitude (N), 6.1 km altitude (WNW), 7.3 km altitude (W), and 9.1 km altitude (drifted W and WSW). During 11-13 June block avalanches from the summit lava dome were occasionally recorded, but not visually observed due to weather conditions. Occasional deep volcanic earthquakes occurred through September.

Figure 102. Image of a white gas-and-steam plume rising above Sinabung on 30 June 2021. Courtesy of PVMBG and MAGMA Indonesia.

During July, white gas-and-steam emissions continued to rise 100-500 m above the summit and drift in multiple directions. On 1 July at 1151 a gray plume rose 800 m above the summit and drifted SW and W. An ash plume rose 500 m above the summit and drifted ESE at 0925 on 13 July due to an eruptive or collapse event. Video taken on 13 July showed new vents on the upper W flank that generated gas-and-ash emissions. An eruptive event at 1850 on 19 July produced an ash plume that rose 1 km above the summit and extended ESE; the activity lasted about 11 minutes. A strong explosion on 28 July at 1320 produced an ash plume that rose 4.5 km above the summit and drifted E and S (figure 103) and pyroclastic flows traveled as far as 1 km down the E and SE flanks, prompting PVMBG to raise the Aviation Color Code (ACC) to Red. Ashfall was reported in areas to the E, including the subdistricts of Namanteran, Merdeka, Berastagi, and Simpang Empat; the event lasted for about 12.5 minutes. In addition, a small sulfur dioxide plume that exceeded two Dobson Units (DU) was detected above the volcano, based on data from the TROPOMI instrument on the Sentinel-5P satellite (figure 104).

Figure 103. Image of the resulting ash plume that rose 4.5 km above Sinabung from the strong explosion on 28 July 2021. Courtesy of PVMBG.

Figure 104. The explosion at Sinabung on 28 July 2021 produced a distinct sulfur dioxide plume that exceeded 2 Dobson Units (DU), based on data from the TROPOMI Instrument on the Sentinel-5P satellite. The accompanying ash plume rose 4.5 km above the summit. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Persistent white gas-and-steam emissions rose 50-500 m above the summit and drifted in different directions during August. An avalanche of incandescent material was observed descending 500-700 m to the E and SE during 4-7 August. Another block avalanche descended 700 m on 25 August. Activity decreased during September and October and mostly consisted of white gas-and-steam emissions that rose 50-800 m above the summit and drifted multiple directions. On 23 September infrared Sentinel-2 satellite imagery showed a small thermal anomaly in the summit crater (figure 105).

Figure 105. A small thermal anomaly at Sinabung was recorded in Sentinel-2 infrared satellite imagery on 23 September 2021. Image uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Firdaus Surbakti (URL: https://www.facebook.com/firdaus.surbakti).