Two major pyroclastic flows in February and August 2013; five fatalities on 10 August 2013

Mount Rokatenda, or Paluweh, on the island of Palu'e, lies north of the primary volcanic arc that cuts across Flores Island in Indonesia's Lesser Sunda Islands, and has seen infrequent activity in modern times. The previous eruption in 1985 from a summit lava dome spread 3 cm of ash over villages on the W side of the island. This report is a summary of the October 2012 to August 2013 eruption, and an update through 2016 that includes information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), the Darwin Volcanic Ash Advisory Center (VAAC), and the University of Hawai'i's MODVOLC thermal alert reporting system. Numerous news reports also covered the major explosions during 2013.

Two brief periods of increased seismicity in April 2009 and January 2012 were the only recorded activity at Paluweh since 1985, prior to an eruption that began in October 2012 and continued through August 2013. PVMBG noted the beginning of lava dome growth on 8 October. A substantial number of MODVOLC thermal alert pixels from MODIS satellite data were first recorded on 11 October 2012 and recurred regularly through 20 July 2013. The first ash plumes were reported by the Darwin VAAC on 11 November 2012 and continued several times each month through May 2013, and then again in late June and during 10-12 August. Plumes generally rose to 2-3 km and drifted between 50 and 100 km in various directions, although a large ash plume on 3 February 2013 rose to higher than 13 km and drifted over 500 km SE, S and SW, briefly impacting air travel in NW Australia. A major explosion on 10 August 2013 created a large pyroclastic flow to the NW from the summit that killed five people on the beach. No further explosions were specifically dated after 12 August 2013, and seismicity gradually decreased over the next several months.

Activity during October 2012-April 2013. PVMBG noted lava dome growth, incandescent avalanches, pyroclastic flows, and ash plumes during October 2012 through January 2013. Ejecta as large as 6 cm in diameter was deposited up to 3 km from the summit, and ashfall affected the entire island, averaging 2 cm thick in places; lahars and ash damaged homes and infrastructure on the island (BGVN 39:01). A large eruption on 2 February 2013, which produced a 13-km-high ash plume the next day, generated a substantial SO₂ signature, pyroclastic flows to the S and SW, and avalanches. Residents of eight villages were evacuated and significant ashfall was reported up to 1 mm thick in Ende (60 km S on East Nusa Tenggara Island). Thick ashfall was also reported in Ona (SE part of the island) and thin deposits were reported in other areas of the island to the W, N, and E. During a field expedition on 7 February, PVMBG staff observed that about 25% of the S portion of the dome was lost; the lava-dome volume had been an estimated 5.1 million cubic meters on 13 January, prior to the explosion.

After the large early February 2013 explosion, many intermittent low-level ash emissions continued through the last week in May, with over 175 VAAC reports issued from the Darwin VAAC during the period. NASA's Earth Observatory (EO) identified an ash plume in MODIS satellite images drifting over 440 km SW on 24 March 2013, and discoloration of the seawater from ash W of the island (figure 7).

Figure 7. NASA image acquired 24 March 2013 with the MODIS instrument shows an ash plume from Paluweh drifting over 440 km SW across Flores Island. Light-colored ash coats the southern third of Paluweh Island, and the ocean to the W of the island is colored turquoise from ash floating near the water's surface. Courtesy of NASA, GSFC.

Another NASA-EO image captured on 19 April 2013 shows the extent of ash deposits covering areas of the S and E sides of the summit where the plumes most commonly drift. A delta extending S into the Flores Sea, which was visible in imagery on 12 February and likely created by a pyroclastic flow during the large 2-3 February explosion (figure 8), was also visible.

Figure 8. NASA-EO image of Paluweh captured 19 April 2013. Note the extent of ash covering the area of the island on the S and E sides of the summit where the plumes usually drift. It also shows a delta extending S into the Flores Sea, also visible in imagery on 12 February and likely created by a pyroclastic flow during the large 2-3 February explosion. Courtesy of NASA Earth Observatory.

Activity during May-August 2013. There was a three-week break in reported ash plumes between 25 May and 19 June when a low level plume rising to 2.4 km was observed drifting 37 km SE. After this, no further activity was reported until 10 August. A large and deadly explosion took place on 10 August, producing an ash plume that rose to 4.3 km and drifted 130 km W. Details of the explosion are given in BGVN 39:01 and additional information is provided in this report. According to PVMBG, a substantial pyroclastic flow traveled NW from the summit down the Ojaubi drainage towards a village on the beach and killed five fisherman. Rescuers noted that the ground was hot and covered with 10-20 cm of ash. NASA-EO captured images before and after the 10 August 2013 eruption where the path of the pyroclastic flow to the NW is clearly visible (figure 9).

Figure 9. NASA-EO images of Paluweh (Mt. Rokatenda) on 3 August and 4 September 2013, before and after a large eruption with a deadly pyroclastic flow that traveled NW from the summit to the ocean, killing 5 people at the beach on 10 August. The delta on the S of the island was created during an earlier eruption and pyroclastic flow on 2-3 February 2013. Courtesy of NASA Earth Observatory.

Activity during 2014-2016. In April 2014, PVMBG noted that the last major explosion had been on 10 August 2013. The last 2013 ash plume recorded by the Darwin VAAC was on 12 August 2013. Visual observations of occasional eruptive activity were noted until November 2013; small explosion earthquakes were also reported as being last recorded in November. No changes were observed in the lava dome between September 2013 and March 2014. PVMBG lowered the Alert level from III to II (on a scale of 1-4) on 7 April 2014.

No additional reports of activity at Paluweh appeared until late 2015, when PVMBG noted that steam plumes rising 75-200 m above the summit were common between August and October 2015. Seismicity remained low but variable during this time as well. From November 2015 through January 2016, steam plume heights ranged from 5-150 m. Seismicity remained low; earthquakes indicating rock avalanches and fumarolic emissions were the most common type recorded (figure 10). Paluweh remained quiet throughout 2016, although in February 2017 it was still listed by PVMBG at Alert Level II, with a potential for eruptive activity.

Figure 10. Seismic activity at Paluweh between 1 January 2015 and 13 January 2016. Vertical Axis represents daily number of events for all graphs. Guguran are avalanche events, Hembusan are emission-related events, Vulkanik Dangkal (VB) are shallow volcanic events, Vulkanik Dalam (VA) are deep volcanic events, Tektonik Local are local tectonic events, and Tektonik Jauh are distant tectonic events. Courtesy of PVMBG (Paluweh report, 18 January 2016).

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/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/).

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

March 1973 (CSLP 33-73)

Eruption ejects tephra 100 m and damages local vegetation

Card 1590 (22 March 1973) Eruption ejects tephra 100 m and damages local vegetation

According to Mrs. Suryanti, a correspondent of the Vulcain Group in Indonesia, on 9 and 16 January the crater of the Paluweh Island volcano, named Rokatinda, was throwing gases, ash, and bombs to a height of about 100 m. As a consequence the greater part of the vegetation, coconut trees, and maize was burned and destroyed. Before the eruption, the volcano had displayed weak fumarolic activity. When Maurice Krafft visited this volcano in October 1971, the maximum temperature of the gases escaping from the crater was 100°C. About 2,000 people are living on the island of Paluweh.

Information Contacts: N. Suryanti, Djakarta II, Indonesia; Maurice Krafft, Equipe Vulcain, Mulhouse, France.

January 1981 (SEAN 06:01) Cite this Report

Loud explosions; intermittent tephra ejection

Activity began to increase on 5 November and continued intermittently through the end of January. On 9 November, an eruption column rose 1 km from the summit crater. Bombs fell nearby and 2 mm of ash were deposited 1 km to the W. Bombs and ash were ejected for about 15 minutes starting at 1115 on 13 November, from a summit crater vent [but see 6:2] 40 m in diameter. The tephra column reached 700 m in height. On 27 January ejecta set bushes afire near a flank village. Detonations from explosions on 31 January were heard at Kota Baru, Flores Island . . . at 0740, 0803, 0807, 0913, 1030, and 1215. No additional activity had occurred as of 5 February.

Information Contacts: A. Sudradjat and L. Pardyanto, VSI.

February 1981 (SEAN 06:02) Cite this Report

Explosions and lava dome

VSI provided further details about the intermittent explosive activity. The 40-m-diameter vent was formed during one of the early November eruptions and is situated on the upper NNE flank. Bombs from the 1-km-high eruption column on 9 November measured up to 60 cm in diameter. Beginning 18 January renewed activity was reported. A hot air wave was felt by the inhabitants of two E-flank villages. About 1,850 persons were evacuated from the danger zone. After the explosions on 31 January a new lava dome was observed in the crater. Activity declined gradually, and the volcano appeared to be normal again on 1 February at 1200. No casualties from Paluweh's November-January activity were reported.

Information Contacts: A. Sudradjat and L. Pardyanto, VSI.

August 1981 (SEAN 06:08) Cite this Report

Incandescent material; seismicity

Indonesian Meteorological Institute personnel reported that Paluweh has erupted for the second time this year. The meteorology bureau on Flores Island . . . said it recorded 809 "strong tremors" 17-22 August. "Lava and burning rocks" were repeatedly erupted on 22 August. On 24 August the bureau recorded ocean water temperatures as high as [98°C] around the island. No casualties were reported, but inhabitants evacuated the area. Crops and fishing boats were damaged.

Information Contacts: UPI.

September 1981 (SEAN 06:09) Cite this Report

Lava dome destoyed; pyroclastic flows

No pyroclastic flows were observed during the growth of the lava dome first seen 31 January (although some sliding occurred), but it generated blasts of hot air felt by residents of a flank village. They were evacuated by the end of February, after VSI had issued a volcanic hazard warning. By July, the lava dome was 200 m high, its volume exceeded 8.5 x 10⁶ m³, and its summit had become the highest point on the volcano at 875 m above sea level. Explosive activity resumed on 5 September between 2010 and 2105, producing a 1-km-high plume. This activity was followed by the destruction of the lava dome. Pyroclastic flows and nuées ardentes d'avalanche moved downslope, depositing 5-20 cm of tephra at one village, and starting fires at 36 structures, including a church and five shelters, at another. Because residents had previously been evacuated, there were no casualties. Since the destruction of the dome, the 3-component seismograph monitoring the volcano has recorded shallow earthquakes which VSI believes may be generated by sliding from remnants of the dome.

Information Contacts: A. Sudradjat and L. Pardyanto, VSI.

June 2009 (BGVN 34:06) Cite this Report

April 2009 spike in seismicity but no explosive activity or visible emissions

During 1-17 April 2009, seismicity increased at Paluweh (table 1), prompting the Center of Volcanology and Geological Hazard Mitigation (CVGHM) to raise the Alert Level from 1 to 2 (Waspada) on 18 April. CVGHM staff in the observation post did not see any gas or ash emissions. Visitors were requested to stay away from the active crater adjacent to the peak.

Table 1. Average number of daily seismic events recorded from Paluweh, April 2009. Courtesy of CVGHM.

Explosive activity had most recently been observed in May 1984 and previously during November 1980-September 1981 (SEAN 06:01, 06:02, 06:08, and 06:09), October 1973, and October 1972-January 1973. Activity in December 1963-March 1966 included lava flows, pyroclastic flows, and fatalities.

An unconfirmed news report of activity in January 2005, not reported in the Bulletin, was later found to be false. The CVGHM staff found no activity at the volcano.

As background on hazard considerations, the mouth of the principal crater opens to the S, where there is plantation agriculture almost to the volcano's peak. In the advent of a future crisis, evacuation would be complicated because a safer area is about two hours journey by motor vessel, and leaving the island might not be possible during storms or rough seas. CVGHM is in continuous contact with the provincial and regional governments, some monitor of Paluweh occurs from the hamlet of Ropa on the N-central coast of the big island of Flores, to Paluweh's S. Regional civil-defense agencies (such as SATKORLAK-PB, the Provincial Coordinating Unit for Disaster Management) and district government agencies of Sikka and Ende (such as SATLAK-PB, the Local Coordinating Body for Disaster Relief) are continually apprised of the activity level.

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

January 2014 (BGVN 39:01) Cite this Report

August 2013 pyroclastic flows took lives; dome growth stopped late 2013

This report discusses the time interval from April 2009 to early 2014, during which time Paluweh (also known as Mount Rokatenda) had vigorous explosive activity in late 2012 with dome emplacement [noted in early] October 2012. A 3 February 2013 ash plume rose to over 13 km in altitude and drifted 325-590 km SE, S, and SW. By 7 February, portions of the growing dome's S flank detached. On 10 August 2013 a pyroclastic flow killed at least 5 people on the island's N shore. The dome remained unchanged during September 2013 through at least March 2014.

Table 2 summarizes key data describing Paluweh from 17 June 2011 to 8 April 2014. In addition, Volcano Discovery showed photos attributed to local resident Ignatius Cua. They noted that Cua "reported that a small zone of dead vegetation associated with new fumarolic activity had developed in the summit region in June 2012. It appears that lava extrusion commenced at or near this zone in mid-October, marking the beginning of the 2012 eruption."

Table 2. Summary of activity recorded for Paluweh from 17 June 2011 through 8 April 2014. The information was compiled from the Indonesian Center for Volcanology and Geologic Hazard Mitigation (CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC).

A photo of the dome taken in 2012 appears in figure 1. CVGHM reported that activity at Paluweh during October 2012-January 2013 was characterized by lava-dome growth and incandescent avalanches, pyroclastic flows, and ash plumes rising as high as 4 km above the dome. Ejected material was deposited 3 km away. The whole island was affected by ashfall, which was an average of 2 cm thick on some areas. Some infrastructure and several homes were damaged by ash and lahars.

Figure 1. The unstable lava dome at Paluweh seen behind the older dome (the dark slope in the foreground in a night photo). Just prior to the photo, a large block broke off the dome's left side (upper E flank). In the aftermath, seen here, molten material gushed from the dome's interior. Photo is from December 2012. The portion of the dome seen here is on the order of 100-150 m high (from the dark basal region at right to the top. Photo courtesy of Tom Pfeiffer, Volcano Discovery.

The Darwin Volcanic Ash Advisory Centre (VAAC) reported a 3 February 2013 eruption that was outstanding in terms of altitude of the ash plume's top and the lateral distance the plume was visible in satellite imagery. The plume rose to 13.1-13.7 km and drifted 325-590 km SE, S, and SW. Eruptions around this time were also noted by news articles, some of which mentioned ashfall.

The Darwin VAAC tracked the number of volcanic ash advisories for Paluweh in comparison to 14 other volcanoes during the interval January through November 2013 (figure 2). They issued 230 VAAs for Paluweh, the second highest number for any one of the 14 volcanoes they discussed during this interval. Figure 3 shows the extent of plumes as delineated in VAAs for the same interval. As further background, figure 4 shows that during the interval 1 July 2008 through 30 June 2014 the Darwin VAAC issued approximately 800 to 1500 VAAs each year. Those advisories have bearing on delays on air travel and transport as well as on plume-derived impacts to the atmosphere.

Figure 2. A histogram showing volcanoes reported by the Darwin VAAC during an 11-month period January 2013 to November 2013. In that interval, Paluweh was the subject of 230 VAAs - the second largest number or 21% of the total 1,092 VAAs on eruptions during the same interval. The 4 cases labeled 'Test' were issued in order to check the operational functionality of the system and were excluded from the total. Courtesy of the Darwin VAAC (see ICAO, 2014).

Figure 3. A graphical summary of Darwin VAAC's reports (VAAs) issued during period January 2013 to November 2013 showing the boundaries of airspace containing ash plumes (red to red-brown polygons). Paluweh is the southernmost volcano shown and the source of the large plumes, with some restricted to the Lesser Sunda Islands and others approaching and lapping over NW Australia. Batu Tara volcano, which is adjacent and NW of Paluweh, was the source of more VAA reports than Paluweh but most of the plumes were comparatively restricted during this time interval. Courtesy of the Darwin VAAC (see ICAO, 2014).

Figure 4. Number of VAAs issued by Darwin VAAC during July 1993 to 12 since 1 July 1993 to December 2014. Note that the Australian fiscal year runs from 1 July to 30 June. Courtesy of the Darwin VAAC (see ICAO, 2014).

Figure 5 shows a Paluweh plume on 10 August 2013 courtesy of the Darwin VAAC. The VAAC reported that during 11-12 August 2013 Paluweh's ash plumes rose to an altitude of 1.8 km and drifted 110-130 km W. A news article noted that the eruptions were smaller on 12 August 2013, but pyroclastic flows continued to be observed. The Alert Level remained at 3 (on a scale of 0-4).

Figure 5. A photo taken looking N from the Maurole district of East Nusa Tenggara province with a camera phone; it shows Paluweh emitting an inclined column of hot ash on 10 August 2013. Photo courtesy of Agence France Presse/Scantix.

Dome collapse animation. A Volcano Discovery team observed Paluweh during 30 November-2 December 2012 and captured some images that can help authorities explain the processes and attendant hazards associated with unstable growing domes (figure 6). Richard Roscoe (Photovolcanica) made the source animation from a few shaky handheld photos of a dome lobe collapse during daylight on unstated date during his visit. These images were taken from a similar perspective as figure 1. He estimated the entire new dome as on the order of 200 m (at most) from base to top. He thought that the size of collapse (in the red circle on figure 6 (b)) as "maybe about 10-20 m high." Regarding the termination of the collapse event, he stated that the material travelling off-frame hit the base of the old dome and then stopped abruptly as it encountered the old dome's wall (the far side of the sloping ridge in the foreground).

Figure 6. Dome instability generating a small pyroclastic flow at Paluweh. Images b-f are screen captures from from an animation made using hand-held photos by Richard Roscoe. (a) The larger dome is seen and the yellow box shows the area of the other frames. (b) The area in red delineates the part of the dome's surface that later collapsed, an area described as a small extrusion lobe (see text). Successive photos came from later parts of the animation. Courtesy of Richard Roscoe (Photovolcanica), used with permission.

Volcano Discovery reported that Paluweh's lava dome seemed to be visibly growing on all sides, with almost constant incandescent rockfalls in multiple areas. The new dome, called Rerombola lava dome, was ~150 m high, the highest point on the island, and the basal diameter was 200-250 m. During their stay, a vent on the upper E part of the dome ejected ash for periods of several hours and produced jet-like degassing sounds. A steam-and-ash plume rose several kilometers. At the base of the dome, hot blocks had ignited local vegetation.

February 2013 has largest plumes of the reporting interval. According to CVGHM, on 1 February 2013 at 1652 an eruption generated an ash plume that rose 2 km. Pyroclastic flows and avalanches were observed. On 2 February an explosion produced an ash plume that rose 4 km and was accompanied by booms and rumbling. The ash plume drifted S and deposited ash up to 1 mm thick in East Nusa Tenggara island (Ende, 60 km S); ash was also reported in Ona (SE part of the island) and thin deposits were reported in other areas of the island to the W, N, and E. Significant portions of the S dome were lost. Prior to this, on 13 January 2013, the lava-dome volume was an estimated 5.1 million cubic meters.

Based on analyses of satellite imagery, wind data, and pilot reports, the Darwin VAAC reported that on 3 February 2013 ash plumes from Paluweh rose to altitudes of 13.1-13.7 km a.s.l. and drifted 325-590 km SE, S, and SW. The next day ash plumes at an altitude of 7.6 km a.s.l. were observed. As a result of the eruption the whole island was affected by ashfall, which was an average of 2 cm thick in some areas. Some infrastructure and several homes were damaged by ash and lahars.

Beyond Indonesia, the ash plumes from the 3 February eruption caused significant impacts. They caused a series of flight delays and related impacts on the tourist and aviation industries as they advanced towards and eventually came over the Kimberley coast in Western Australia (larger polygons on figure 3).

During 4-10 February diffuse white plumes rose 50-100 m. The Alert Level remained at 3 (on a scale of 1-4), and visitors and residents were prohibited from approaching the crater within a 3-km-radius.

Landsat visible and thermal data. A NASA Earth Observatory report posted online showed images of Paluweh from 29 April 2013. A visible wavelength image from the Landsat Data Continuity Mission's Operational Land Imager instrument shows an ash plume drifting ~50 km NE of the volcanic island. A thermal infrared image from the same satellite showed a small hot spot surrounded by cooler dark ash clouds.

Deadly 10 August 2013 pyroclastic flows. As activity persisted in the ~10 months prior to the 10 August eruption, authorities repeatedly tried to persuade residents to relocate to safer areas. Although reports regarding evacuations are variable, the Indonesian National Board for Disaster Management (BNPB) reports that about a quarter of the island's total residents had been permanently moved to nearby Flores Island since the onset of activity in October 2012. Thus, of 10,858 total island residents, about 2,700 had moved. After the 10 August eruption, the BNPB source said that at least another 1,203 had moved by 30 August.

News sources also indicated that around the time of the pyroclastic flows, a volcanologist at the monitoring post for Paluweh noted that the deadly phase of the 10 August 2013 eruption lasted 4-7 minutes. Pyroclastic flows burned trees around the beach and villages, making it difficult to reach victims. BBC News Asia report on 10 August stated six dead, four adults and two children. Regarding timing of the eruption, they quoted a CVGHM source: "Mr Surono said the latest eruption had begun at 04:27 on Saturday [10 August] (20:27 GMT Friday [9 August]) and lasted for nearly four hours." Official sources also indicated that pyroclastic flows continued hours after the initial eruption.

The Jakarta Post article gave the death toll as at least five. It stated the specific location of the deaths as "Woje Wubi to Punge beach in Rokirole village."

According to news sources, after the 10 August eruption a rescue team was sent to evacuate about 2,000 people that remained inside the 3-km exclusion zone. The news reports said that a team member described rescuing people as difficult because they were reluctant to leave their livestock and homes, but also that the ground was hot and covered in 10-20 cm of ash.

Tempo.co news issued a report in Indonesian saying that a total of 12 residents began to be evacuated from the town of Maumere, the capital of the district, as a result of the 10 August eruption. This source indicated six fatalities. It said that two motorboats had successfully evacuated hundreds of residents of four villages.

Based on analyses of satellite imagery and wind data, the VAAC reported during 10 to 13 August 2013 that an ash plume rose to an altitude of 4.3 km and drifted 130 km W.

The summit crater opens to the S and large-scale production of crops (plantation agriculture) extends almost to the volcano's peak. This southerly path is typically followed by pyroclastic flows from the dome. In contrast, the 10 August pyroclastic flow traveled down the N flank of the volcano, descending into beachside villages.

Reference: International Civil Aviation Organization (ICAO), 2014, The Twelfth Meeting Of Asia/Pacific Robex Working Group (Robex Wg/12) and Fourth Meeting Of Meteorological Hazards Task Force (MET/H TF/4), ROBEX WG/12 / MET/H TF/4 - IP/C2, 2014, Agenda Item (conjoint session; 2d; 11/03/14); ICAO Regional Sub-Office, Beijing, China 19 March 2014, ICAO, 18 pp. [URL: http://www.icao.int/APAC/Meetings/2014 METHTF4/IP-C2_ICAO_AI.C2d - Darwin VAAC Report - AUS.pdf].

Information Contacts: BNPB (the Indonesian National Board for Disaster Management) [Informasi Penanggulangan Bencana Terkini di Indonesia], Gedung Graha 55 Jl. Tanah Abang II No. 57, Jakarta, Indonesia (URL: http://www.bnpb.go.id/); Center of 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/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); Volcano Discovery (URL: http://www.volcanodiscovery.com/); and Richard Roscoe, Photovolcanica (URL: http://www.photovolcanica.com/).

April 2017 (BGVN 42:04) Cite this Report

Two major pyroclastic flows in February and August 2013; five fatalities on 10 August 2013

Mount Rokatenda, or Paluweh, on the island of Palu'e, lies north of the primary volcanic arc that cuts across Flores Island in Indonesia's Lesser Sunda Islands, and has seen infrequent activity in modern times. The previous eruption in 1985 from a summit lava dome spread 3 cm of ash over villages on the W side of the island. This report is a summary of the October 2012 to August 2013 eruption, and an update through 2016 that includes information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), the Darwin Volcanic Ash Advisory Center (VAAC), and the University of Hawai'i's MODVOLC thermal alert reporting system. Numerous news reports also covered the major explosions during 2013.

Two brief periods of increased seismicity in April 2009 and January 2012 were the only recorded activity at Paluweh since 1985, prior to an eruption that began in October 2012 and continued through August 2013. PVMBG noted the beginning of lava dome growth on 8 October. A substantial number of MODVOLC thermal alert pixels from MODIS satellite data were first recorded on 11 October 2012 and recurred regularly through 20 July 2013. The first ash plumes were reported by the Darwin VAAC on 11 November 2012 and continued several times each month through May 2013, and then again in late June and during 10-12 August. Plumes generally rose to 2-3 km and drifted between 50 and 100 km in various directions, although a large ash plume on 3 February 2013 rose to higher than 13 km and drifted over 500 km SE, S and SW, briefly impacting air travel in NW Australia. A major explosion on 10 August 2013 created a large pyroclastic flow to the NW from the summit that killed five people on the beach. No further explosions were specifically dated after 12 August 2013, and seismicity gradually decreased over the next several months.

Activity during October 2012-April 2013. PVMBG noted lava dome growth, incandescent avalanches, pyroclastic flows, and ash plumes during October 2012 through January 2013. Ejecta as large as 6 cm in diameter was deposited up to 3 km from the summit, and ashfall affected the entire island, averaging 2 cm thick in places; lahars and ash damaged homes and infrastructure on the island (BGVN 39:01). A large eruption on 2 February 2013, which produced a 13-km-high ash plume the next day, generated a substantial SO₂ signature, pyroclastic flows to the S and SW, and avalanches. Residents of eight villages were evacuated and significant ashfall was reported up to 1 mm thick in Ende (60 km S on East Nusa Tenggara Island). Thick ashfall was also reported in Ona (SE part of the island) and thin deposits were reported in other areas of the island to the W, N, and E. During a field expedition on 7 February, PVMBG staff observed that about 25% of the S portion of the dome was lost; the lava-dome volume had been an estimated 5.1 million cubic meters on 13 January, prior to the explosion.

After the large early February 2013 explosion, many intermittent low-level ash emissions continued through the last week in May, with over 175 VAAC reports issued from the Darwin VAAC during the period. NASA's Earth Observatory (EO) identified an ash plume in MODIS satellite images drifting over 440 km SW on 24 March 2013, and discoloration of the seawater from ash W of the island (figure 7).

Figure 7. NASA image acquired 24 March 2013 with the MODIS instrument shows an ash plume from Paluweh drifting over 440 km SW across Flores Island. Light-colored ash coats the southern third of Paluweh Island, and the ocean to the W of the island is colored turquoise from ash floating near the water's surface. Courtesy of NASA, GSFC.

Another NASA-EO image captured on 19 April 2013 shows the extent of ash deposits covering areas of the S and E sides of the summit where the plumes most commonly drift. A delta extending S into the Flores Sea, which was visible in imagery on 12 February and likely created by a pyroclastic flow during the large 2-3 February explosion (figure 8), was also visible.

Figure 8. NASA-EO image of Paluweh captured 19 April 2013. Note the extent of ash covering the area of the island on the S and E sides of the summit where the plumes usually drift. It also shows a delta extending S into the Flores Sea, also visible in imagery on 12 February and likely created by a pyroclastic flow during the large 2-3 February explosion. Courtesy of NASA Earth Observatory.

Activity during May-August 2013. There was a three-week break in reported ash plumes between 25 May and 19 June when a low level plume rising to 2.4 km was observed drifting 37 km SE. After this, no further activity was reported until 10 August. A large and deadly explosion took place on 10 August, producing an ash plume that rose to 4.3 km and drifted 130 km W. Details of the explosion are given in BGVN 39:01 and additional information is provided in this report. According to PVMBG, a substantial pyroclastic flow traveled NW from the summit down the Ojaubi drainage towards a village on the beach and killed five fisherman. Rescuers noted that the ground was hot and covered with 10-20 cm of ash. NASA-EO captured images before and after the 10 August 2013 eruption where the path of the pyroclastic flow to the NW is clearly visible (figure 9).

Figure 9. NASA-EO images of Paluweh (Mt. Rokatenda) on 3 August and 4 September 2013, before and after a large eruption with a deadly pyroclastic flow that traveled NW from the summit to the ocean, killing 5 people at the beach on 10 August. The delta on the S of the island was created during an earlier eruption and pyroclastic flow on 2-3 February 2013. Courtesy of NASA Earth Observatory.

Activity during 2014-2016. In April 2014, PVMBG noted that the last major explosion had been on 10 August 2013. The last 2013 ash plume recorded by the Darwin VAAC was on 12 August 2013. Visual observations of occasional eruptive activity were noted until November 2013; small explosion earthquakes were also reported as being last recorded in November. No changes were observed in the lava dome between September 2013 and March 2014. PVMBG lowered the Alert level from III to II (on a scale of 1-4) on 7 April 2014.

No additional reports of activity at Paluweh appeared until late 2015, when PVMBG noted that steam plumes rising 75-200 m above the summit were common between August and October 2015. Seismicity remained low but variable during this time as well. From November 2015 through January 2016, steam plume heights ranged from 5-150 m. Seismicity remained low; earthquakes indicating rock avalanches and fumarolic emissions were the most common type recorded (figure 10). Paluweh remained quiet throughout 2016, although in February 2017 it was still listed by PVMBG at Alert Level II, with a potential for eruptive activity.

Figure 10. Seismic activity at Paluweh between 1 January 2015 and 13 January 2016. Vertical Axis represents daily number of events for all graphs. Guguran are avalanche events, Hembusan are emission-related events, Vulkanik Dangkal (VB) are shallow volcanic events, Vulkanik Dalam (VA) are deep volcanic events, Tektonik Local are local tectonic events, and Tektonik Jauh are distant tectonic events. Courtesy of PVMBG (Paluweh report, 18 January 2016).

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/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/).