Renewed thermal and explosive activity from late January into May 2021

A massive stratovolcano in easternmost Java, Raung has over sixty recorded eruptions dating back to the late 16th Century. Explosions with ash plumes, Strombolian activity, and lava flows from a cinder cone within the 2-km-wide summit crater have been common. Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as the Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) has installed webcams to monitor activity in recent years. An eruption from late 2014 through August 2015 produced a large volume of lava within the summit crater and formed a new pyroclastic cone in the same location as the previous one. A smaller eruption during July-October 2020 was followed by explosions, ash emissions, and thermal anomalies during January-May 2021 which are covered in this report with information provided by PVMBG, the Darwin Volcanic Ash Advisory Center (VAAC), and several sources of satellite data.

The Alert Level at Raung was lowered from II to I on 27 November 2020 after the last reported activity in early October. Only occasional steam plumes were observed after that time until brown and gray emissions from the summit appeared on 21 January 2021; this led PVMBG to raise the Alert Level back to II. Daily seismicity and ash emissions increased in intensity and frequency with the strongest explosive activity reported during 7-12 February. Ash emissions continued daily throughout February and March but decreased gradually in plume height and ash content. A faint thermal anomaly appeared in satellite imagery inside the pyroclastic cone of the summit crater on 16 March, and similar anomalies were visible multiple times during April and early May. Intermittent ash emissions continued for the first half of April; only steam was observed after minor ash was detected on 14 April. The last thermal anomaly was observed on 15 May 2021. The MIROVA graph of Log Radiative Power for the year ending on 28 June 2021 clearly shows the July-October 2020 event followed by the latest activity that started in late January 2021, peaked in early February, and continued at lower thermal energy levels during March-May (figure 38).

Figure 38. The MIROVA graph of thermal energy at Raung for the year ending on 28 June 2021 clearly shows both the late July-October 2020 and the late January-May 2021 activity. The strongest explosive and thermal activity for the latest eruption occurred in early February. Courtesy of MIROVA.

After the last observations of ash in the summit emissions on 3 October 2020 and a weak thermal anomaly on the 7th (BGVN 45:12), no emissions were reported for the rest of October and November and seismicity decreased significantly. As a result, on 27 November PVMBG lowered the Alert Level from II to I (Normal). No activity was reported during December 2020, although satellite imagery on 21 December indicated substantial steam emissions from the summit crater. No further activity was reported until 21 January 2021 when harmonic tremors were detected along with gray and brown emissions seen rising 100-400 m above the crater. The Alert Level was raised back to II. Gray ash plumes 200-600 m high were reported daily through the remainder of January (figure 39), along with several hundred non-harmonic tremors each day. VONAs were issued daily from 21-24 and on 27 January, with continuous ash emissions reported rising to 3.4-3.9 km altitude and drifting E and SE. The Darwin VAAC reported that most of the emissions were not visible in satellite imagery, and their reports were based on ground observations from PVMBG, VONAs, or Pilot Reports.

Figure 39. Ash emissions at Raung began on 21 January 2021 after a three month break and were reported daily through 24 January including on 22 and 23 January 2021, shown here. Courtesy of PVMBG and MAGMA.

Activity intensified significantly at the beginning of February 2021. PVMBG reported dense gray ash emissions rising 500 m above the summit on 1 February. Ash emissions increased to 1,000 m high the next day and continued daily through 5 February. The Darwin VAAC reported continuous ash emissions rising to 3.9-4.3 km altitude (600-1,000 m above the summit) and drifting NE and E during 1-3 and 6-7 February. On 6 and 7 February loud noises and incandescence were reported and on 7 February gray and black ash emissions rose 1,200 m above the summit and drifted ESE producing ashfall at the Raung Observatory in Sragi Village (25 km SE). Multiple pilot reports to the Darwin VAAC indicated ash emissions moving E at 4.9-7 km altitude throughout the day. The next day gray and black plumes rose 2,000 m above the crater and ashfall was again reported at the Raung Observatory from the ESE drifting plume.

The plumes on 9 February were 2,500 m above the summit drifting ESE and accompanied by loud noises. Sentinel-2 satellite imagery recorded a significant thermal anomaly and a large ash plume on 9 February (figures 40 and 41); the plume drifted more than 100 km ESE and was visible beyond the E coast of Java. During 10-12 February gray and black ash plumes rose 2,000 m above the crater each day. Continuous emissions rising to 5.5 km altitude (2,200 m above the summit) were reported in multiple VONA’s first on 8 February and continuing daily through 13 February. By 14 February a ring-shaped thermal anomaly was still visible inside the summit crater (figure 42). For the remainder of the month, plume height diminished to 300-1,000 m above the summit with occasional pulses that rose to 1,200 m. The Darwin VAAC reported daily ash emissions that rose to 4.3-4.9 km altitude and drifted N and E through 20 February. From 22-27 February daily emissions were noted at 3.9-4.3 km altitude drifting NE, E, and S.

Figure 40. A major explosion at Raung on 9 February 2021 was captured in Sentinel-2 satellite imagery. It produced ash emissions that rose to 5.5 km altitude and a dense black ash plume that drifted over one hundred km ESE. A large thermal anomaly filled the summit crater. Top image uses Atmospheric penetration rendering (bands 12, 11, 8a) and bottom image uses Natural color rendering (bands 4,3,2). Courtesy of Sentinel Hub Playground.

Figure 41. Incandescence seen above the Raung summit crater and dense black and gray ash plumes occurred frequently during February 2021 including on 4, 9, 10, and 26 February. Courtesy of PVMBG and MAGMA.

Figure 42. A thermal anomaly ringed the inside of the summit crater at Raung on 14 February. Sentinel-2 image uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Continuous tremor appeared on 1 February and increased significantly in amplitude from 1 to 5 mm. They rose the next day to 14 mm amplitude and remained at 13-16 m amplitude through 6 February. They dropped to 7 mm amplitude after that until 12 February and then returned to 1 mm amplitude for the remainder of the month. A small SO2 anomaly was recorded in satellite data on 1 February and a significant plume of gas appeared on 7 February that continued daily through 12 February (figure 43).

Figure 43. A significant SO2 anomaly from Raung was captured by the TROPOMI instrument on the Sentinel 5P satellite on 7 February and continued daily through 12 February 2021. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Steam and ash emissions in March 2021 were reported daily by PVMBG. During 1-3 March the gray plumes rose 200-600 m above the crater, then from 4 to 9 March they contained moderate to heavy ash content and rose 300-1,000 m above the crater. The Darwin VAAC reported ash emissions drifting E and NE at 3.9-4.3 km altitude during 3-10 March. Plume height varied from 500-1,200 m above the crater during 10-21 March with up to moderate ash density. On 13 March the ash plume was clearly discernable in satellite imagery drifting W at 4.3 km altitude (figure 44). On 22 March the ash plume rose to 900 m and small quantities of ash were reported at the Raung Observatory in Sragi. From 23 March through the end of the month gray ash plumes were reported at 50-1,200 m high with generally low to moderate ash density. VAAC reports issued during 23-27 March reported plumes at 3.7-4.6 km altitude drifting ESE, W, and NW (figure 45). They were clearly seen in visible satellite imagery on 26 March drifting NW at 3.7 km altitude. A single faint thermal anomaly was discernable in Sentinel-2 satellite imagery from the center of the pyroclastic cone inside the summit crater on 16 March.

Figure 44. An ash plume at Raung on 13 March 2021 rose several hundred meters above the volcano and was clearly discernible in satellite images by the Darwin VAAC. Courtesy of PVMBG and MAGMA.

Figure 45. An ash plume from Raung on 23 March 2021 drifted ESE several hundred meters above the summit. Ash emissions from Raung during 23-27 March rose to 3.7-4.6 km altitude and drifted ESE, W, and NW. Courtesy of PVMBG and MAGMA.

Emissions from Raung contained ash during the first half of April 2021. The plumes were gray or white and gray and rose 50-600 m above the summit (figure 46). The Darwin VAAC reported a minor ash plume that rose to 2.4 km altitude and drifted N on 12 April. A report by PVMBG of gray plumes rising 50-400 m high on 14 April was the last indication of ash emissions for the month. For the remainder of the month only steam plumes were seen, rising 75-500 m above the summit. A webcam image taken after dark on 17 April showed incandescence at the summit crater. Two clear satellite images on 20 and 30 April revealed small thermal anomalies inside the pyroclastic cone in the summit crater (figure 47). A small SO2 plume was detected by satellite instruments on 29 April.

Figure 46. Ash emissions were weak during the first half of April 2021 at Raung as seen on 6 April 2021 (top) and only steam plumes were recorded from 15 April onward (bottom). Courtesy of PVMBG and MAGMA.

Figure 47. Small thermal anomalies were visible inside the pyroclastic cone in the summit crater of Raung on 20 and 30 April 2021. Sentinel-2 images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

For most of May 2021 cloudy skies obscured views of the volcano. Occasionally white steam plumes were observed rising up to 400 m above the summit. On 5, 10, and 15 May weak thermal anomalies located inside the pyroclastic cone in the summit crater appeared in satellite images. Distinct SO2 anomalies appeared more frequently during May than any other month of the reporting period except February (figure 48). During June 2021, no thermal anomalies were present in the five satellite images with clear views of the summit. The summit was cloudy in about half of the webcam images taken during June; when visible, white steam plumes were noted that rose generally 50-200 m except on 22 June when they rose 100-400 m high.

Figure 48. Distinct SO2 plumes drifted in multiple directions from Raung on several days during May 2021 including on 9, 10, 24, and 25 May. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

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); 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 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).

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

July 1982 (SEAN 07:07) Cite this Report

Eruption cloud on 18 July

Raung erupted 18 July, emitting dark clouds of tephra to 6,000 m. Activity apparently began with a weak earth tremor at about 0300, felt by inhabitants of the tea and coffee plantations on the slopes and in the areas around Kalibaru and Glenmore, at the S foot of the volcano. On 19 July at about 0500 an earthquake was felt, and inhabitants at the foot of Raung reported hearing two consecutive explosions. A seismograph post for Ijen Volcano (8.058°S, 114.242°W) at Pal Tuding, which also monitors Raung, registered vibrations with a maximum amplitude of 3.9 mm.

Two eruptions on 19 July were reported by a Garuda Airlines pilot flying from Jakarta (about 840 km NW of Raung) to Denpasar (on Bali, about 140 km SE) and back. One eruption occurred around 0511 and the other around 1130. The pilot estimated that columns of "smoke" reached 0.6-0.9 km height. Flights have been diverted from near the volcano.

Ash fell lightly all day, leaving a whitish coat on the leaves of tea and coffee plants. An employee of one tea plantation said part of the top leaves were damaged and withered. Light ashfall was reported until 20 July.

Information Contacts: Kompas, Jakarta; AFP.

November 1985 (SEAN 10:11) Cite this Report

Many small explosions; light ashfalls

"Raung resumed activity during November with a series of small explosions. The summit crater has not been visited since the start of the latest activity. However, observations begun 1 November from the new Raung observation post about 15 km SE of the summit at 700 m altitude (at Mangaran) indicated that the explosions have been centered along the E side of the large summit crater, near the recently active eruptive vent on the crater floor. At least 44 explosion clouds were observed during November, mostly whitish in color but dark gray ash-laden clouds were also seen. On 15 November, light ashfall was reported from SE flank villages (Bejong, Mangaran, and Seragi) and from Banjuyangi City, 35 km ESE of the volcano. The Mangaran seismometer recorded 52 explosion earthquakes during November. Activity was continuing as of 12 December."

"The last eruption of Raung that produced a lava flow was in 1973. That flow was confined to the summit crater. Explosions similar to the November activity have frequently been reported over the last decade."

Information Contacts: T. Casadevall and L. Pardyanto, VSI; Antara News Service, Jakarta.

December 1985 (SEAN 10:12) Cite this Report

Small summit explosions during November

No explosions were recorded in December.

Information Contacts: Suparto S. and T. Casadevall, VSI.

May 1989 (SEAN 14:05) Cite this Report

Strombolian activity and seismicity

Strombolian activity in the bottom of the crater was photographed by Michel Halbwach (Univ of Savoie, France) in July/August 1988, during overflights in an ultralight aircraft arranged in cooperation with the Federation Aerosport of Indonesia (FASI). Activity was continuing in March, when brownish plumes that rose 100-150 m above the summit were seen 41 times. Recorded March seismicity included: 1,771 episodes of volcanic tremor and plume emission tremor, 90 strong tectonic earthquakes, one local tectonic earthquake, and one A-type and 11 B-type volcanic earthquakes.

Additional aerial monitoring of activity at Raung and other volcanoes has been proposed by FASI and VSI.

Information Contacts: VSI.

July 1989 (SEAN 14:07) Cite this Report

Numerous small explosions

During the last week of July, 45 visible explosions ejected plumes to 75-150 m above the summit before winds carried them S. Between explosions, weak white fumes reached 50 m above the crater. Recorded earthquakes were: distant tectonic (50), local tectonic (2), volcanic A-type (1), volcanic B-type (2), explosions (1,574), and volcanic tremor (1).

Information Contacts: VSI.

July 1990 (BGVN 15:07) Cite this Report

Frequent light ash emissions

Raung continued to emit brownish-gray ash clouds to 200-300 m above the crater, with light ashfall NW of the volcano. A daily average of 104 ash pulses, one tremor event, and two tectonic earthquakes were detected during July.

Information Contacts: VSI.

August 1991 (BGVN 16:08) Cite this Report

Dense plumes

The crew of Qantas flight 41 (Sydney-Jakarta) observed a very dense black plume emerging intermittently from a flank vent on 10 September at 1508. The plume was drifting N at ~6 km altitude, well below the aircraft's altitude of nearly 12 km. A voluminous, dense, mostly white plume with small pulses of ash in its center was observed from a commercial flight two days later.

Information Contacts: ICAO; J. Post, SI.

October 1991 (BGVN 16:10) Cite this Report

Continued ash emission

Vigorous ash emissions, rising to 300-600 m, were observed from an aircraft on 3 October.

Information Contacts: N. MacLeod, Ridgefield WA, USA.

May 1992 (NASA STS 49)

Infrared Space Shuttle photograph shows devegetated summit area

An infrared Space Shuttle photograph (figure 1) taken in May 1992 showed clear views of both Raung and the Ijen volcanic complex. Neither volcano was erupting, but the caldera lake in Kawah Ijen and the devegetated caldera and summit region at Raung were obvious features. The Ijen Caldera was clearly defined, along with some post-caldera cones on its southern margin (Kawah Ijen and Gunung Merapi, Gunung Rante, and Gunung Pendil).

Figure 1. This near-vertical color infrared photograph shows both Raung volcano and the Ijen volcanic complex on the E end of Java; the summit of Baluran, at the NE tip of the island, is hidden by clouds. Raung, the tall feature near the center of this photograph with a NE-flank vent (Gunung Suket), has a very wide caldera surrounded by a grayish rim. The difference in color of the rim and the flanks is caused by the rim's lack of vegetation compared with the healthy and extensive vegetation on the flanks. The large elongate Ijen Caldera NE of Raung has numerous cones on its margin, the most obvious being Kawah Ijen with its acidic crater lake. North is to the left; the tip of the island is pointing NE. NASA Photo ID: STS049-097-050, May 1992.

Information Contacts: NASA JSC Digital Image Collection (URL: http://images.jsc.nasa.gov/).

October 1995 (BGVN 20:10) Cite this Report

Aviation report of a plume, but not seen on satellite imagery

An aviation report stated that at 1705 on 15 August "smoke" from Raung at an altitude of 6 km was drifting W. Following this report, aviation notices were posted in Indonesia, New Zealand, and Australia for the next 24 hours. No plume was observed by Australian meteorologists on satellite imagery from 1800 on 15 August through 2050 the next day.

The last reported eruption, which occurred sometime between January and June 1993, generated an ash column 600 m above the rim and caused ashfall in the surrounding area.

Information Contacts: BOM Darwin, Australia.

June 1997 (BGVN 22:06) Cite this Report

Aviators report April ash plume to 5 km and June "smoke" plume to 6 km altitude

On 10 April an ash cloud was reported drifting to the E at 5 km altitude. The Bureau of Meteorology had learned from the Volcanological Survey of Indonesia that the volcano had been erupting continuously, but ash was ejected only ~ 150 m above the crater. On 1 June a Qantas pilot described "smoke" at 6.1 km, drifting W. Similar reports were received on 18 and 22 June, but heavy clouds hampered the detection of ash in satellite imagery.

Information Contacts: Bureau of Meteorology, Northern Territory Regional Office, P.O. Box 735, Darwin NT 0801, Australia.

October 2000 (BGVN 25:10) Cite this Report

9 July ash plume ends 3-year interval without reported eruptions

At 1720 on 9 July 2000 an air report to the Darwin VAAC noted an ash cloud near Raung with a growing plume at an unknown height. The plume discharged from Raung. Visible satellite imagery taken at 1630, hours before the air report was made, disclosed Raung surrounded by scattered low clouds, with a possible low-level ash plume extending 25 km to the NW. There was no evidence of ash in subsequent satellite imagery. No signs of activity were observed at Raung by Lee Siebert when passing nearby on commercial aircraft at about noon on 10 July and mid-morning on 11 July.

Information Contacts: Darwin VAAC, Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina Northern Territory 0811 Australia (URL: http://www.bom.gov.au/info/vaac/); Lee Siebert, Global Volcanism Program, Smithsonian Institution, Washington, DC 20560-0119 USA.

July 2002 (BGVN 27:07) Cite this Report

Ash plumes to 4.6 km altitude reported in early June 2002

On 2 June 2002 at 1625, a pilot reported observing an ash plume emitted from Raung. The plume rose to a height of ~4.5 km altitude and drifted to the S. According to the Darwin VAAC, ash clouds were visible on satellite imagery a few days later. The clouds were at heights below 4.6 km altitude and were observed on 5 June at 0840 drifting S, on 7 June at 0934 drifting SW, and on 8 June at 1132 drifting NW.

According to the Volcanological Survey of Indonesia (VSI), Raung has been erupting for at least a decade, and recent eruptions are events within a single, broader eruptive period. Thus, the above-noted ash eruptions from June were noteworthy outbursts within a longer sustained eruption.

Information Contacts: Darwin Volcanic Ash Advisory Center (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Nia Haerani, Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

January 2004 (BGVN 29:01) Cite this Report

Aviation reports describe ash plumes during 1999 to 2002

Raung volcano was last discussed in BGVN 27:07, when a pilot reported ash plumes to 4.6 km altitude in early June 2002. That issue of theBulletin also noted a Volcanological Survey of Indonesia (VSI) comment that Raung had been erupting for at least a decade, with recent eruptions being events within a single, broader eruptive period.

The Darwin Volcanic Ash Advisory Center (VAAC) subsequently received reports that on 12 August 2002 ash was visible drifting NW of Raung around the summit level. The summit was partially obscured by clouds and no ash was identified on satellite imagery. On 25 August 2002, based on pilot observations and satellite imagery, the VAAC reported a visible ash plume rising to about 9.2 km, drifting to the W at high levels and to the E at lower levels.

The Darwin VAAC has an archive of their reports available on their website. Those for Raung are summarized in table 1. The last set of reports (25 August 2002) discussed a plume becoming increasingly diffuse over a 16.5-hour interval.

Table 1. Dates and principal comments in Darwin VAAC reports concerning Raung, July 1999-February 2004. Dates and times are not local but instead refer to the Prime Meridian, for example 04/2240Z means the fourth day of the stated month at 2240 UMT. Similar or duplicate message are not shown. In general, ash cloud trajectory information has been omitted. In a few cases the VAAC delineated bounding area surrounding an observed ash cloud ("OBS ASH CLOUD"), delineated with a series of latitude and longitude coordinates (eg. S00700, E11000; which translates to 7 degrees S, 110 degrees E). In the original reports, altitudes were given in shorthand (eg. FL 100, which corresponds to 10,000 feet altitude; 3,048.0 m altitude, but typically not known to better than two significant figures and thus here rounded to ~ 3.0 km altitude). Courtesy of the Darwin VAAC.

Information Contacts: Darwin Volcanic Ash Advisory Center (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Nia Haerani, Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

January 2005 (BGVN 30:01) Cite this Report

MODIS-MODVOLC infrared hot spots 3 June-8 Oct 2004; aerial photos from 2001

Though frequently active, Raung is seldom the subject of reports from either the news media or the Directorate of Volcanology and Geological Hazard Mitigation (DVGHM). The most recent Darwin VAAC report was issued late on 26 August 2002 (UTC). It noted that aviators had estimated an ash plume at ~ 10 km altitude drifting W (reported 25 August in an AIREP). Ash clouds were not visible on NOAA/GMS satellite imagery. A summary of Darwin VAAC reports of Raung for the period July 1999-August 2002 was given in BGVN 29:01.

There were nine anomalous Moderate Resolution Imaging Spectroradiometer (MODIS) observations of volcanic hot spots at Raung during 3 June-8 October 2004 (table 2). The 2004 alerts were the first detected by MODIS at Raung. Minor explosive activity documented intermittently during 1999 to 2002 (BGVN 29:01) did not have a thermal component sufficient to trigger alerts.

Table 2. Thermal anomalies at Raung observed with MODIS during 2004. Some of the UTC times were for the previous date. Spectral radiance for the hot pixels in band 21 (central wavelength of 3.959 µm) are in units of watts per square meter per steradian per micron (W-2 sr-1 µm-1). Courtesy of the Hawaiian Institute of Geophysics and Planetology.

No ground observations have been reported during 2004, but in a message from Dali Ahmad (DVGHM), he noted the absence of observed emissions during 2004. With respect to the thermal alerts, he speculated that they could conceivably have originated from brush fires. Rob Wright commented that the levels of radiance in the 2004 alerts were both "too weak and too intermittent to be lava flows" and stood near the system's lower threshold. Similar weak anomalies occur at volcanoes such as Villarrica and during intervals at Anatahan, but the source of the alerts at Raung remains uncertain.

Clear aerial photographs of Raung were taken on 26 and 30 July 2001 (figure 2) by Franz Jeker of Singapore Airlines as he flew past in descent towards, or ascent from, the Bali airport. Jeker also included a detailed map of the Raung area (figure 3).

Figure 2. A photograph taken on 26 July 2001 of a small fumarolic plume from the central crater of Raung looking SW during a fly-by of a commercial airplane across the NNE flank. Courtesy of F. Jeker.

Figure 3. Map showing relative locations of Raung volcano at the SW end of Java, and adjacent Bali. Courtesy of F. Jeker.

Information Contacts: Directorate of Volcanology and Geological Hazard Mitigation (DVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Center (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 (URL: http://modis.higp.hawaii.edu); Franz Jeker, Rigistrasse 10, 8173 Neerach, Switzerland.

September 2007 (BGVN 32:09) Cite this Report

Uncertain July 2007 ash plume; August 2007 ash plume seen for several hours

Nine anomalous Moderate Resolution Imaging Spectroradiometer (MODIS) observations of volcanic hot spots were reported during 3 June-8 October 2004 (BGVN 30:01). No other activity was reported from Raung until 26 July 2007. That day the Darwin Volcanic Ash Advisory Center (VAAC) indicated that a pilot had observed an ash plume, possibly from Raung, which their ash advisory reported as follows: "AIREP [an aircraft observation] reported ash cloud observed over volcano on eastern tip of Java. Plume up to 5000 feet [~ 1.2 km] above summit. Volcano assumed to be Raung. Ash not seen on latest satellite pass due to cloud."

Darwin VAAC produced five reports in reference to a Raung ash plume emitted on 26 August 2007. Visible wavelength imagery on MT SAT disclosed a plume at FL 150 (15,000 feet, or 4.6 km altitude) drifting E at ~ 10 km/hr (at 0430 UTC on 26 August). The last view of the cloud was reported at 0833 UTC, still at the same altitude and moving at the same velocity. That plume rose to an altitude of 1.5 km. Ash was not visible on satellite imagery. The Darwin VAAC reported that satellite imagery had detected an ash plume from Raung during 26-27 August that rose to an altitude of 4.6 km and drifted E.

Information Contacts: Darwin Volcanic Ash Advisory Center, Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, Northern Territory 0811, Australia (URL: http://www.bom.gov.au/info/vaac/).

June 2008 (BGVN 33:06) Cite this Report

New eruption during 12-17 June sends ash plumes to 4.5 km altitude

In an Antara News report, Balok Suryadi, an observer at the Center of Volcanology and Geological Hazard Mitigation (CVGHM) Raung monitoring post at Sumber Arum village, described clouds of "smoke and ash" that occurred on 12 and 13 June. He was also quoted in the 19 June article as saying that activity was "likely" continuing but that it could not be clearly monitored from the observation post.

Another ash eruption was seen rising through the clouds on 17 June 2008 around 1500. This event was photographed by Karim Kebaili while flying from Bali to Jakarta approximately 30 minutes after take-off (figure 4). The same eruption was seen at 1430 by pilot Nigel Demery, who stated that the ash cloud initially rose to about 4.5 km altitude but had dissipated on his return flight about two hours later. The Darwin VAAC was unable to identify the plume in satellite imagery due to meteorological clouds.

Figure 4. Ash plume rising from Raung at about 1500 on 17 June 2008. Courtesy of Karim Kebaili.

Thermal anomalies were detected by the MODIS instrument aboard the Terra satellite on 23 July 2005 and 15 August 2005. No additional thermal anomalies were detected through the end of June 2008. However, ash plumes were reported by pilots on 26 July 2007 and seen in satellite imagery on 26 August 2007 (BGVN 32:09).

Information Contacts: Rebecca Patrick, Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, Northern Territory 0811, Australia (URL: http://www.bom.gov.au/info/vaac); Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Nigel Demery, Indonesia; Karim Kebaili, Indonesia; Antara News (URL: http://www.antara.co.id/); 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/).

December 2016 (BGVN 41:12) Cite this Report

Strong eruptive activity and lava in the summit crater during June-August 2015

Prior to January 2014, the most recent reported activity was during 12-17 June 2008, when ash plumes were seen rising to 4.5 km altitude (BGVN 33:06). Sporadic white and brownish plume emissions were noted between 2012 and early 2015, along with periods of increased seismicity and thermal anomalies. Gray plumes, presumably due to ash, were reported beginning on 1 February 2015. Seismicity and thermal anomalies preceded stronger eruptive activity that began in mid-to-late June 2015; the last reported gray plume was on 22 August 2015. Thermal anomalies also decreased after mid-August 2015.

Activity during 2012-2013. Seismicity increased on 17 October 2012, prompting the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) to raise the Alert Level to 2 (on a scale of 1-4) on 18 October. During 18-22 October white plumes rose 50-75 m above the crater. Seismic activity increased significantly again on 22 October. That same day the Alert Level was raised to 3; visitors and residents were warned not to approach the crater within a 3-km radius. Strong thermal anomalies identified by MODVOLC, based on MODIS infrared satellite data, began on 14 October and continued through 8 November 2012. Two additional weak anomalies were detected on 29 November and 1 December 2012.

PVMBG reported that during March 2013 white plumes rose to 400 m above the summit. Seismicity decreased significantly on 25 March; tremor was absent starting in April. On 5 April the Alert level was lowered to 2. Despite decreased seismicity, four MODVOLC thermal anomalies, based on MODIS satellite data, were recorded between 29 June and 31 July 2013.

Activity during 2014. PVMBG reported that on 1 January 2014 seismicity increased. On 3 January diffuse white gas plumes rose 100 m and drifted W; on 4 January diffuse brownish plumes also rose 100 m and drifted W. On 5 January the Alert Level was raised to 2.

PVMBG reported that RSAM values showed an increase in energy during March-April 2014. Also during this timeframe, the daily number of volcanic earthquakes was dominated by tremor (with an increase in tremor amplitude). However, beginning in May, the number and the amplitude of tremor decreased.

During 1-17 June 2014, when weather permitted, a weak solfatara plume was visible rising up to 100 m above the summit. On 17 June the Alert Level was lowered to 1. Thermal anomalies, based on MODIS satellite data, were recorded beginning 28 November 2014 and continuing through 25 February 2015.

Activity during 2015. From December 2014 through January 2015, white plumes were observed rising to 500 m above the crater rim. Throughout February and during 1-14 March plumes were gray-white and rose to a maximum height of 200 m. Crater incandescence and rumbling was also reported on 14 February. During 15 March-7 April gray-brown emissions rose to 200 m; rumbling was frequently heard. During 8 April- 21 May gray and gray-brown plumes rose to 300 m. Crater incandescence was observed again on 12 April. Seismicity fluctuated and was dominated by tremor. Rumbling was frequently heard during this interval. The Alert Level remained at 2; residents and tourists were reminded not to approach the craters within a 2-km radius.

Continuous tremor was recorded during December 2014-12 January 2015; tremor was not continuous starting on 13 January, and RSAM values declined. A weak thermal anomaly was recorded on 17 April 2015.

PVMBG reported that during times of clear weather during 1-28 June, white plumes were observed rising as high as 300 m above the crater rim. Rumbling was frequently heard at the observation post. Seismic tremor sharply increased on 21 June, and crater incandescence was observed on 25 and 28 June. BNPB reported that increased activity on 28 June was characterized by Strombolian activity, roaring, ash plumes that rose 300 m, and a loud thumping sound heard 20 km away at 2000. Incandescence from the crater was clearly visible from the observation post in Banyuwangi. PVMBG raised the Alert Level to 3 on 29 June, and reminded the public not to approach the crater within a 3-km radius.

Based on notices from the Ujung Padang Meteorological Watch Office (MWO) and PVMBG, satellite images, and pilot observations, the Darwin VAAC reported that during 1 and 3-7 July ash plumes rose to altitudes of 3.7-6.1 km and drifted 25-110 km E, ESE, and SE. According to news articles, flights in and out of an airport in Bali were cancelled due to ash emissions during 3-4 July. On 5 July BNPB reported that roaring was heard from continuous explosions and Strombolian activity. Dense white-and-gray plumes rose as high as 400 m and drifted SE.

During 1-8 July PVMBG reported that gray plumes rose 100-500 m above the crater rim, crater incandescence was observed, and rumbling and thumping noises were noted. Seismicity was dominated by high-amplitude tremor, and deformation data suggested magma migrating towards the surface. BNPB reported that gray ash plumes continued to rise as high as 500 m above the crater through 11 July (figure 5). Ash plumes drifted in various directions depending on the altitude; plumes drifted SE and S at lower altitudes and SE, S, W, and N at higher altitudes.

Figure 5. Volcanic ash and clouds are illuminated by lava from the crater of Mount Raung as seen from Songgon (Banyuwangi, East Java) on 11 July 2015. Courtesy of Reuters/Zabur Karuru/Antara Foto.

Based on PVMBG notices, wind data, and satellite images, the Darwin VAAC reported that during 8-12 July ash plumes rose to an altitude of 4.3-5.2 km and drifted as far as 1,040 km E, SE, and S. According to news articles, increased activity during 9-10 July caused flight cancelations and several airports to close, including airports on Bali and Lombok, as well as Banyuwangi and Jember in East Java. One article noted that dozens of flight had been canceled during the previous week. Another article noted that the Bali airport, in addition to another airport in Java, again closed on 12 July, a day after it had reopened.

Information from PVMBG along with satellite-image and pilot observations, allowed the Darwin VAAC to report that during 15-21 July ash plumes rose to varying altitudes of 3.7-6.1 km and drifted as far as 340 km in multiple directions. On 16 July BNPB reported that a dense gray-to-black ash plume rose as high as 2 km above the crater rim and drifted WNW. Incandescent lava at the summit was visible, and tremor was continuous. Roaring and thumping sounds were reported by residents. Ashfall was reported in areas downwind, including Cumedak (19 km W) and Sumberjambe (13 km NW). According to a news article, the Juanda International Airport in Surabaya reopened on 17 July after on-and-off closures the previous week. BNPB noted that the eruption continued on 18 July with ash plumes rising as high as 1.5 km and drifting N. Tremor continued although the amplitude had declined during the previous week.

During 16-23 July PVMBG reported ash plumes rising to 2 km, and incandescence was visible at the crater. Seismicity fluctuated but remained elevated. Based on PVMBG information, and satellite-image and pilot observations, the Darwin VAAC reported that during 22-28 July ash multiple ash plumes rose to varying altitudes of 4.3-5.2 km and drifted as far as 400 km NW, W, SSW, S, and SSE. A news article from 29 July noted that 18 flights at most had been canceled during the previous few days due to the ash plumes, and that the Notohadinegoro Airport (2,100 km SW) had been temporarily closed.

On 4 August BNPB reported that during the previous three days the Strombolian eruption had increased in intensity. Ash fell in Sempu, Songgon, Glenmore, Gambiran, and Banyuwangi. On 4 August dense blackish gray ash plumes rose 800 m and drifted SE. Based on satellite-image and wind data, the Darwin VAAC reported that during 29 July-4 August multiple ash plumes rose to altitudes of 4.3-4.9 km and drifted as far as 240 km in multiple directions.

PVMBG reported that during 24 July-10 August ash plumes rose 1.5 km above the crater with visible incandescence at the crater. Seismicity fluctuated but remained elevated; RSAM values peaked on 4 August (the highest recorded since the beginning of the eruption) and then decreased significantly after mid-August (figure 6). Based on satellite observations and wind data, the Darwin VAAC reported that during 12-14, 16, and 18 August multiple ash plumes rose to altitudes of 3.7-4 km and drifted 20-110 km W and WSW (figure 7).

Figure 6. Realtime Seismic Amplitude Measurement (RSAM) measurements at Raung between 1 November and 21 September 2015. Courtesy of PVMBG.

Figure 7. On 27 July 2015 the Operational Land Imager (OLI) on Landsat 8 captured a view of ash and volcanic gases drifting NW from Raung. The lower image shows a closer view of the volcano's caldera. Courtesy of NASA Earth Observatory; image by Jesse Allen (Landsat data from the U.S. Geological Survey) and caption by Adam Voiland.

PVMBG reported that ash plumes rose as high as 1 km above the crater during 16-24 August and drifted NW. Seismicity fluctuated but continued to decrease. The Alert Level, which had remained at 3 since 29 June, was lowered to 2 on 24 August; the public was reminded not to approach the crater within a 2-km radius.

Based on weather models, webcam and satellite data, pilot observations, and information from PVMBG, the Darwin VAAC reported that on 19 August ash plumes rose to an altitude of 3.7 km and drifted 65-95 km NW, WNW, and W. On 22 August a low-level ash plume drifted 55 km NW.

PVMBG reported that, although inclement weather conditions often prevented visual observations during 25 August-21 September, white plumes were occasionally seen rising as high as 200 m above the crater. Seismicity fluctuated but continued to decrease. The Alert Level remained at 2 (on a scale of 1-4), and the public was reminded not to approach the crater within a 2-km radius.

In 2015 the MODVOLC system using infrared MODIS satellite data indicated a small anomaly on 17 April and then steady thermal anomalies beginning 20 June. The last anomaly located at the summit crater, a single weak alert pixel recorded on 29 August 2015, was a full week after the previous anomaly was identified on 22 August.

MODIS data analyzed by the Middle InfraRed Observation of Volcanic Activity (MIROVA) project from February 2015 through January 2016 (figure 8) showed a large spike in power output beginning in mid-June 2015. The slow descent after approximately the first week of August may be due to cooling of lava in the crater rather than to ongoing activity.

Figure 8. MODIS data analyzed by MIROVA shows a spike in power output coinciding with the beginning of elevated seismicity and ash plumes in June 2015. Courtesy of MIROVA.

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/); 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/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); ch-aviation GmbH, Quaderstrasse 8, 7000 Chur, Switzerland (URL: http://www.ch-aviation.com/portal/news/38959-surabaya-indonesia-reopens-despite-mt-raung-eruption); WA Today, East Perth, WA, Australia (URL: http://www.watoday.com.au/wa-news/volcano-causes-more-bali-flight-cancellations-20150704-gi56a5.html); The Weather Channel (URL: http://www.weather.com/news/news/indonesia-mount-raung-volcan); The National, Abu Dhabi Media, Abu Dhabi, United Arab Emirates (URL: http://www.thenational.ae/world/mount-raung-eruption-causes-closure-of-bali-airport-again); The Jakarta Post, PT Niskala Media Tenggara, Jl. Palmerah Barat No. 142-143, Jakarta 10270, Indonesia (URL: http://www.thejakartapost.com/news/2015/07/29/mount-raungs-eruption-cancels-18-flights-jember.html).

September 2020 (BGVN 45:09) Cite this Report

Eruptions confirmed during 2012- 2013; lava fills inner crater in November 2014-August 2015

A massive stratovolcano in easternmost Java, Raung has over sixty recorded eruptions dating back to the late 16th Century. Explosions with ash plumes, Strombolian activity, and lava flows from a cinder cone within the 2-km-wide summit crater have been the most common activity. Visual reports of activity have often come from commercial airline flights that pass near the summit; Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) has installed webcams to monitor activity in recent years. An eruption in 2015 produced a large volume of lava within the summit crater and formed a new pyroclastic cone in the same location as the previous one. Confirmation and details of eruptions in 2012, 2013, and 2014-2015 are covered in this report with information provided by PVMBG, the Darwin Volcanic Ash Advisory Center (VAAC), several sources of satellite data, and visitors to the volcano.

Newly available visual and satellite information confirm eruptions at Raung during October 2012-January 2013, June-July 2013, and extend the beginning of the 2015 eruption back to November 2014. The 2015 eruption was the largest in several decades; Strombolian activity was reported for many months and fresh lava flows covered the crater floor. Raung was quiet after the 2015 eruption ended in August of that year until July 2020.

Eruption during October 2012-January 2013. A MODVOLC thermal alert appeared inside the summit crater of Raung on 14 October 2012, followed by another four alerts on 16 October. Multiple daily alerts were reported on many days through 8 November, most within the main crater. Single alerts appeared on 29 November and 1 December 2012 (figure 9). PVMBG raised the Alert Level on 17 October from 1 to 2 due to increased seismicity and raised it further to Level 3 on 22 October. A local news report by Aris Yanto indicted that a minor Strombolian eruption occurred inside the crater on 19 October. Strombolian activity was also observed inside the inner crater on 5 November 2012 by visitors (figure 10); they reported loud rumbling sounds that could be heard up to 15 km from the crater.

Figure 9. Thermal activity at Raung during October and November 2012 included multiple days of multi-pixel anomalies, with almost all activity concentrated within the summit crater. Strombolian activity was observed on 5 November. Image shows all pixels from 23 September-1 December 2012. Courtesy of MODVOLC.

Figure 10. Strombolian activity was observed inside the inner crater of Raung on 5 November 2012 by visitors. They reported loud rumbling sounds that could be heard up to 15 km from the crater. Photo by Galih, courtesy of Volcano Discovery.

The Darwin VAAC issued an advisory of an eruption plume to 9.1 km altitude reported at 0237 UTC on 8 November 2012. In a second advisory about two hours later they noted that an ash plume was not visible in satellite imagery. A press article released by the Center for Volcanology and Geological Hazard Mitigation (PVMBG) indicated that gray ash plumes were observed on 6 January 2013 that rose 300 m above the summit crater rim. Incandescence was observed around the crater and thundering explosions were heard by nearby residents.

Eruption during June-July 2013. Two MODVOLC thermal alerts were measured inside the summit crater on 29 June 2013. A photo taken on 21 July showed minor Strombolian activity at the inner crater (figure 11). A weak SO₂ anomaly was detected in the vicinity of Raung by the OMI instrument on the Aura satellite on 27 July. Thermal alerts were recorded on 29 and 31 July. When Google Earth imageryrom 14 March 2011 created by Maxar Technologies is compared with imagery from 29 July 2013 captured by Landsat/Copernicus, dark tephra is filling the inner crater in the 2013 image; it was not present in 2011 (figure 12).

Figure 11. Strombolian activity was observed inside the inner crater at the summit of Raung on 21 July 2013. Photo by Agus Kurniawan, courtesy of Volcano Discovery.

Figure 12. Satellite imagery from Google Earth showing the eroded pyroclastic cone inside the summit crater of Raung on 14 March 2011 (left) and 29 July 2013 (right). Dark tephra deposits filling the inner crater in the 2013 image were not present in 2011. The crater of the pyroclastic cone is 200 m wide; N is to the top of the images. Courtesy of Google Earth.

Eruption during November 2014-August 2015. Information about this eruption was previously reported (BGVN 41:12), but additional details are provided here. Landsat-8 imagery from 28 October 2014 indicated clear skies and little activity within the summit crater. Local observers reported steam plumes beginning in mid-November (figure 13). MODVOLC thermal alerts within the summit crater were issued on 28 and 30 November, and then 15 alerts were issued on seven days in December. Thermal Landsat-8 imagery from cloudy days on 29 November and 15 December indicated an anomaly over the area of the pyroclastic cone inside the summit crater (figure 14).

Figure 13. Local observers reported steam plumes at Raung beginning in mid-November 2014; this one was photographed on 17 November 2014. Courtesy of Volcano Discovery.

Figure 14. Satellite evidence of new eruptive activity at Raung first appeared on 29 November 2014. The true color-pansharpened Landsat-8 image of Raung from 28 October 2014 (left) shows the summit crater and an eroded pyroclastic cone with its own crater (the inner crater) with no apparent activity. Although dense meteoric clouds on 29 November (center) and 15 December 2014 (right) blocked true color imagery, thermal imagery indicated a thermal anomaly from the center of the pyroclastic cone on both dates. Courtesy of Sentinel Hub Playground.

In January 2015 the MODVOLC system identified 25 thermal anomalies in MODIS data, with a peak of eight alerts on 8 January. Visitors to the summit crater on 6 January witnessed explosions from the inner crater approximately every 40 minutes that produced gas and small amounts of ash and tephra. They reported lava flowing continuously from the inner crater onto the larger crater floor, and incandescent activity was seen at night (figure 15). Landsat-8 images from 16 January showed a strong thermal anomaly covering an area of fresh lava (figure 16).

Figure 15. Visitors to the summit crater of Raung on 6 January 2015 witnessed explosions from the inner crater approximately every 40 minutes that produced abundant gas and small amounts of ash and tephra. Lava was flowing continuously from the inner crater onto the larger crater floor, and incandescent activity was observed at night. Photos by Sofya Klimova, courtesy of Volcano Discovery.

Figure 16. On a clear 16 January 2015, Landsat-8 satellite imagery revealed fresh lava flows NW of the pyroclastic cone within the summit crater at Raung. A strong thermal anomaly matches up with the dark material, suggesting that it flowed NW from within the pyroclastic cone. Left image is true color-pansharpened rendering, right image is thermal rendering. Courtesy of Sentinel Hub Playground.

Satellite images were obscured by meteoric clouds during February 2015, but PVMBG reported gray and brown plumes rising 300 m multiple times and incandescence and rumbling on 14 February. Visitors to the summit crater during the second half of February reported Strombolian activity with lava fountains from the inner crater, at times as frequently as every 15 minutes (figure 17). Loud explosions and rumbling were heard 10-15 km away. MODVOLC thermal alerts stopped on 25 February and did not reappear until late June.

Figure 17. A report issued on 25 February 2015 from visitors to the summit of Ruang noted large Strombolian explosions with incandescent ejecta and lava flowing across the crater floor. The fresh lava on the crater floor covered a noticeably larger area than that shown in early January (figure 15). Photo by Andi, courtesy of Volcano Discovery.

PVMBG raised the Alert Level to 2 in mid-March 2015. Weak thermal anomalies located inside and NW of the pyroclastic cone were present in satellite imagery on 21 March. PVMBG reported gray and brown emissions during March, April, and May rising as high as 300 m above the crater. Landsat imagery from 22 April showed a small emission inside the pyroclastic cone, and on 8 May showed a clearer view of the fresh black lava NW and SW of the pyroclastic cone (figure 18).

Figure 18. Fresh lava was visible in Landsat-8 satellite imagery in April and May 2015 at Raung. A small emission was present inside the pyroclastic cone at the summit of Raung on 22 April 2015 (left). Fresh dark material is also evident in the SW quadrant of the summit crater that was not visible on 16 January 2015. A clear view on 8 May 2015 also shows the extent of the fresh black material around the pyroclastic cone (right). The summit crater is 2 km wide. Courtesy of Sentinel Hub Playground.

Nine MODVOLC thermal alerts appeared inside the summit crater on 21 June 2015 after no alerts since late February, suggesting an increase in activity. The Darwin VAAC issued the first ash advisory for 2015 on 24 June noting an aviation report of recent ash. The following day the Ujung Pandang Meteorological Weather Office (MWO) reported an ash emission drifting W at 3.7 km altitude. The same day, 25 June, Landsat-8 imagery clearly showed a new lava flow on the W side of the crater and a strong thermal anomaly. The thermal data showed a point source of heat widening SW from the center of the crater and a second point source of heat that appeared to be inside the pyroclastic cone. A small ash plume was visible over the cone (figure 19). Strombolian activity and ash plumes were reported by BNPB and PVMBG in the following days. On 26 June the Darwin VAAC noted the hotspot had remained visible in infrared imagery for several days. PVMBG reported an ash emission to 3 km altitude on 29 June.

Figure 19. A new lava flow and strong thermal anomaly appeared inside the summit crater of Raung on 25 June 2015 in Landsat-8 imagery. The new flow was visible on the W side of the crater. The darker area extending SW from the rising ash plume is a shadow. The thermal data showed a point source of heat widening SW from the center of the crater and spreading out in the SW quadrant and a second point source of heat on the flank of the pyroclastic cone. Left image is True color-pansharpened rendering, and right image is thermal rendering. Courtesy of Sentinel Hub Playground.

Activity increased significantly during July 2015 (BGVN 41:12). Ash plumes rose as high as 6.7 km altitude and drifted hundreds of kilometers in multiple directions, forcing multiple shutdowns at airports on Bali and Lombok, as well as Banyuwangi and Jember in East Java. The Darwin VAAC issued 152 ash advisories during the month. Ashfall was reported up to 20 km W during July and 20-40 km SE during early August. Visitors to the summit in early July observed a new pyroclastic cone growing inside the inner crater from incandescent ejecta and dense ash emissions (figure 20). Landsat-8 imagery from 11 July showed a dense ash plume drifting SE, fresh black lava covering the 2-km-wide summit caldera floor, and a very strong thermal anomaly most intense at the center near the pyroclastic cone and cooler around the inner edges of the crater (figure 21). On 12 July, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured a view of an ash-and-gas plume drifting hundreds of kilometers SE from Raung (figure 22).

Figure 20. A new pyroclastic cone was growing inside the inner crater at the summit of Raung when photographed by Aris Yanto in early July 2015. Courtesy of Volcano Discovery.

Figure 21. Landsat-8 imagery of Raung during July 2015 indicated dense ash emissions and a large thermal anomaly caused by fresh lava. On 11 July a dense ash plume drifted SE and a strong thermal anomaly was centered inside the summit crater. The 2-km-wide crater floor was covered with fresh lava (compare with 25 June image in figure 19). Courtesy of Sentinel Hub Playground.

Figure 22. On 12 July 2015 the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured a natural-color view of a plume of ash and volcanic gases drifting hundreds of kilometers SE from Raung. Courtesy of NASA Earth Observatory.

A satellite image on 20 July showed fresh incandescent lava covering the floor of the summit crater and a dense ash plume drifting N from the summit (figure 23). Incandescent ejecta emerged from two vents on the new pyroclastic cone inside the inner crater on 26 July (figure 24). On 27 July a dense ash plume was visible again in satellite imagery drifting NW and the hottest part of the thermal anomaly was in the SE quadrant of the crater (figure 25). Substantial SO₂ plumes were recorded by the OMI instrument on the Aura satellite during July and early August 2015 (figure 26).

Figure 23. A satellite image of the summit of Raung on 20 July 2015 showed fresh, incandescent lava covering the floor of the summit crater and a dense ash plume drifting N from the summit. Thermal activity on the NE flank was likely the result of incandescent ejecta from the crater causing a fire. Image created by DigitalGlobe, captured by WorldView3, courtesy of Volcano Discovery.

Figure 24. Incandescent ejecta emerged from two vents on the new pyroclastic cone growing inside the inner crater of Raung on 26 July 2015. Photo by Vianney Tricou, used with permission, courtesy of Volcano Discovery.

Figure 25. Landsat-8 imagery of Raung during July 2015 indicated dense ash emissions and large thermal anomalies from fresh lava. The 2-km-wide crater floor was fully covered with fresh lava by 11 July. On 27 July the dense ash plume was drifting NW and the highest heat was concentrated in the SE quadrant of the crater. Courtesy of Sentinel Hub Playground.

Figure 26. Substantial plumes of sulfur dioxide from Raung were measured by the OMI instrument on the AURA satellite during July and August 2015. The first plumes were measured in mid-June; they intensified during the second half of July and the first week of August, but had decreased by mid-August. Wind directions were highly variable throughout the period. The date is recorded above each image. Courtesy of NASA Global Sulfur Dioxide Page.

Significant ash emissions continued into early August 2015 with numerous flight cancellations. The Darwin VAAC reported ash plumes rising to 5.2 km altitude and extending as far as 750 km SE during the first two weeks in August (figure 27). Satellite imagery indicated a small ash plume drifting W from the center of the crater on 12 August and weak thermal anomalies along the E and S rim of the floor of the crater (figure 28). The summit crater was covered with fresh lava on 14 August when viewed by visitors, and ash emissions rose a few hundred meters above the crater rim from a vent in the SW side of the pyroclastic cone (figure 29). The visitors observed pulsating ash emissions rising from the SW vent on the large double-crater new cinder cone. The larger vent to the NE was almost entirely inactive except for two small, weakly effusive vents on its inner walls.

Figure 27. A dense ash plume drifted many kilometers S from Raung on 2 August 2015 in this view from nearly 100 km W. Incandescence at the summit indicated ongoing activity from the major 2015 eruption. In the foreground is Lamongan volcano whose last known eruption occurred in 1898. Courtesy of Øystein Lund Andersen, used with permission.

Figure 28. Landsat-8 satellite imagery of Raung indicated a small ash plume drifting W from the center of the crater on 12 August 2015. Courtesy of Sentinel Hub Playground.

Figure 29. The summit crater of Raung on 14 August 2015 was filled with fresh lava from an eruption that began in November 2014. Ash emissions from a vent in the side of the newly grown pyroclastic cone within the crater rose a few hundred meters above the crater rim. Courtesy of Volcano Discovery.

The lengthy sequence of multiple daily VAAC reports that began in late June ended on 16 August 2015 with reports becoming more intermittent and ash plume heights rising to only 3.7-3.9 km altitude. Multiple discontinuous eruptions to 3.9 km altitude were reported on 18 August. The plumes extended about 100 km NW. The last report of an ash plume was from an airline on 22 August noting a low-level plume 50 km NW. Two MODVOLC alerts were issued that day. By 28 August only a very small steam plume was present at the center of the crater; the southern half of the edge of the crater floor still had small thermal anomalies (figure 30). The last single MODVOLC thermal alerts were on 29 August and 7 September. The Alert Level was lowered to 2 on 24 August 2015, and further lowered to 1 on 20 October 2016.

Figure 30. By 28 August 2015 only a very small steam plume was present at the center of the summit crater of Raung, and the southern half of the edge of the crater floor only had weak thermal anomalies from cooling lava. 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/); 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/); 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/);Google Earth (URL: https://www.google.com/earth/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/, https://earthobservatory.nasa.gov/images/86213/eruption-of-raung-volcano); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); Aris Yanto (URL: https://www.exploredesa.com/2012/11/mount-raung-produce-of-vulcanic-ash-plume-and-continue-eruption/); DigitalGlobe (URL: https://www.maxar.com/, https://twitter.com/Maxar/status/875449111398547457); Øystein Lund Andersen (URL: https://twitter.com/OysteinVolcano/status/1194879946042142726, http://www.oysteinlundandersen.com).

December 2020 (BGVN 45:12) Cite this Report

Explosions with ash plumes and a thermal anomaly at the summit crater, July-October 2020

A massive stratovolcano in easternmost Java, Raung has over sixty recorded eruptions dating back to the late 16th Century. Explosions with ash plumes, Strombolian activity, and lava flows from a cinder cone within the 2-km-wide summit crater have been the most common activity. Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) has installed webcams to monitor activity in recent years. An eruption from late 2014 through August 2015 produced a large volume of lava within the summit crater and formed a new pyroclastic cone in the same location as the previous one. The eruption that began in July 2020 is covered in this report with information provided by PVMBG, the Darwin Volcanic Ash Advisory Center (VAAC), and several sources of satellite data.

The 2015 eruption was the largest in several decades; Strombolian activity was reported for many months and fresh lava flows covered the crater floor (BGVN 45:09). Raung was quiet after the eruption ended in August of that year until July of 2020 when seismicity increased on 13 July and brown emissions were first reported on 16 July. Tens of explosions with ash emissions were reported daily during the remainder of July 2020. Explosive activity decreased during August, but thermal activity didn’t decrease until mid-September. The last ash emissions were reported on 3 October and the last thermal anomaly in satellite data was recorded on 7 October 2020.

Eruption during July-October 2020. No further reports of activity were issued after August 2015 until July 2020. Clear Google Earth imagery from October 2017 and April 2018 indicated the extent of the lava from the 2015 eruption, but no sign of further activity (figure 31). By August 2019, many features from the 2015 eruption were still clearly visible from the crater rim (figure 32).

Figure 31. Little change can be seen at the summit of Raung in Google Earth images dated 19 October 2017 (left) and 28 April 2018 (right). The summit crater was full of black lava flows from the 2015 eruption. Courtesy of Google Earth.

Figure 32. A Malaysian hiker celebrated his climbing to the summit of Raung on 30 August 2019. Weak fumarolic activity was visible from the base of the breached crater of the cone near the center of the summit crater, and many features of the lava flow that filled the crater in 2015 were still well preserved. Courtesy of MJ.

PVMBG reported that the number and type of seismic events around the summit of Raung increased beginning on 13 July 2020, and on 16 July the height of the emissions from the crater rose to 100 m and the emission color changed from white to brown. About three hours later the emissions changed to gray and white. The webcams captured emissions rising 50-200 m above the summit that included 60 explosions of gray and reddish ash plumes (figure 33). The Raung Volcano Observatory released a VONA reporting an explosion with an ash plume that drifted N at 1353 local time (0653 UTC). The best estimate of the ash cloud height was 3,432 m based on ground observation. They raised the Aviation Color Code from unassigned to Orange. About 90 minutes later they reported a second seismic event and ash cloud that rose to 3,532 m, again based on ground observation. The Darwin VAAC reported that neither ash plume was visible in satellite imagery. The following day, on 17 July, PVMBG reported 26 explosions between midnight and 0600 that produced brown ash plumes which rose 200 m above the crater. Based on these events, PVMBG raised the Alert Level of Raung from I (Normal) to II (Alert) on a I-II-III-IV scale. By the following day they reported 95 explosive seismic events had occurred. They continued to observe gray ash plumes rising 100-200 m above the summit on clear days and 10-30 daily explosive seismic events through the end of July; plume heights dropped to 50-100 m and the number of explosive events dropped below ten per day during the last few days of the month.

Figure 33. An ash plume rose from the summit of Raung on 16 July 2020 at the beginning of a new eruption. The last previous eruption was in 2015. Courtesy of Volcano Discovery and PVMBG.

After a long period of no activity, MIROVA data showed an abrupt return to thermal activity on 16 July 2020; a strong pulse of heat lasted into early August before diminishing (figure 34). MODVOLC thermal alert data recorded two alerts each on 18 and 20 July, and one each on 21 and 30 July. Satellite images showed no evidence of thermal activity inside the summit crater from September 2015 through early July 2020. Sentinel-2 satellite imagery first indicated a strong thermal anomaly inside the pyroclastic cone within the crater on 19 July 2020; it remained on 24 and 29 July (figure 35). A small SO₂ signature was measured by the TROPOMI instrument on the Sentinel-5P satellite on 25 July.

Figure 34. MIROVA thermal anomaly data indicated renewed activity on 16 July 2020 at Raung as seen in this graph of activity from 13 October 2019 through September 2020. Satellite images indicated that the dark lines at the beginning of the graph are from a large area of fires that burned on the flank of Raung in October 2019. Heat flow remained high through July and began to diminish in mid-August 2020. Courtesy of MIROVA.

Figure 35. Thermal anomalies were distinct inside the crater of the pyroclastic cone within the summit crater of Raung on 19, 24, and 29 July 2020. Data is from the Sentinel-2 satellite shown with Atmospheric penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

After an explosion on 1 August 2020 emissions from the crater were not observed again until steam plumes were seen rising 100 m on 7 August. They were reported rising 100-200 m above the summit intermittently until a dense gray ash plume was reported by PVMBG on 11 August rising 200 m. After that, diffuse steam plumes no more than 100 m high were reported for the rest of the month except for white to brown emissions to 100 m on 21 August. Thermal anomalies of a similar brightness to July from the same point within the summit crater were recorded in satellite imagery on 3, 8, 13, 18, and 23 August. Single MODVOLC thermal alerts were reported on 1, 8, 12, and 19 August.

In early September dense steam plumes rose 200 m above the crater a few times but were mostly 50 m high or less. White and gray emissions rose 50-300 m above the summit on 15, 20, 27, and 30 September. Thermal anomalies were still present in the same spot in Sentinel-2 satellite imagery on 2, 7, 12, 17, and 27 September, although the signal was weaker than during July and August (figure 36). PVMBG reported gray emissions rising 100-300 m above the summit on 1 October 2020 and two seismic explosion events. Gray emissions rose 50-200 m the next day and nine explosions were recorded. On 3 October, emissions were still gray but only rose 50 m above the crater and no explosions were reported. No emissions were observed from the summit crater for the remainder of the month. Sentinel-2 satellite imagery showed a hot spot within the summit crater on 2 and 7 October, but clear views of the crater on 12, 17, and 22 October showed no heat source within the crater (figure 37).

Figure 36. The thermal anomaly at Raung recorded in Sentinel-2 satellite data decreased in intensity between August and October 2020. It was relatively strong on 13 August (left) but had decreased significantly by 12 September (middle) and remained at a lower level into early October (right). Data shown with Atmospheric penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground

Figure 37. A small but distinct thermal anomaly was still present within the pyroclastic cone inside the summit crater of Raung on 7 October 2020 (left) but was gone by 12 October (middle) and did not reappear in subsequent clear views of the crater through the end of October. Satellite imagery of 7 and 12 October processed with Atmospheric penetration rendering (bands 12, 11, 8A). Natural color rendering (bands 4, 3, 2) from 17 October (right) shows no clear physical changes to the summit crater during the latest eruption. 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/); 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/); 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/); 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/); Google Earth (URL: https://www.google.com/earth/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); MJ (URL: https://twitter.com/MieJamaludin/status/1167613617191043072).

July 2021 (BGVN 46:07) Cite this Report

Renewed thermal and explosive activity from late January into May 2021

A massive stratovolcano in easternmost Java, Raung has over sixty recorded eruptions dating back to the late 16th Century. Explosions with ash plumes, Strombolian activity, and lava flows from a cinder cone within the 2-km-wide summit crater have been common. Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as the Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) has installed webcams to monitor activity in recent years. An eruption from late 2014 through August 2015 produced a large volume of lava within the summit crater and formed a new pyroclastic cone in the same location as the previous one. A smaller eruption during July-October 2020 was followed by explosions, ash emissions, and thermal anomalies during January-May 2021 which are covered in this report with information provided by PVMBG, the Darwin Volcanic Ash Advisory Center (VAAC), and several sources of satellite data.

The Alert Level at Raung was lowered from II to I on 27 November 2020 after the last reported activity in early October. Only occasional steam plumes were observed after that time until brown and gray emissions from the summit appeared on 21 January 2021; this led PVMBG to raise the Alert Level back to II. Daily seismicity and ash emissions increased in intensity and frequency with the strongest explosive activity reported during 7-12 February. Ash emissions continued daily throughout February and March but decreased gradually in plume height and ash content. A faint thermal anomaly appeared in satellite imagery inside the pyroclastic cone of the summit crater on 16 March, and similar anomalies were visible multiple times during April and early May. Intermittent ash emissions continued for the first half of April; only steam was observed after minor ash was detected on 14 April. The last thermal anomaly was observed on 15 May 2021. The MIROVA graph of Log Radiative Power for the year ending on 28 June 2021 clearly shows the July-October 2020 event followed by the latest activity that started in late January 2021, peaked in early February, and continued at lower thermal energy levels during March-May (figure 38).

Figure 38. The MIROVA graph of thermal energy at Raung for the year ending on 28 June 2021 clearly shows both the late July-October 2020 and the late January-May 2021 activity. The strongest explosive and thermal activity for the latest eruption occurred in early February. Courtesy of MIROVA.

After the last observations of ash in the summit emissions on 3 October 2020 and a weak thermal anomaly on the 7th (BGVN 45:12), no emissions were reported for the rest of October and November and seismicity decreased significantly. As a result, on 27 November PVMBG lowered the Alert Level from II to I (Normal). No activity was reported during December 2020, although satellite imagery on 21 December indicated substantial steam emissions from the summit crater. No further activity was reported until 21 January 2021 when harmonic tremors were detected along with gray and brown emissions seen rising 100-400 m above the crater. The Alert Level was raised back to II. Gray ash plumes 200-600 m high were reported daily through the remainder of January (figure 39), along with several hundred non-harmonic tremors each day. VONAs were issued daily from 21-24 and on 27 January, with continuous ash emissions reported rising to 3.4-3.9 km altitude and drifting E and SE. The Darwin VAAC reported that most of the emissions were not visible in satellite imagery, and their reports were based on ground observations from PVMBG, VONAs, or Pilot Reports.

Figure 39. Ash emissions at Raung began on 21 January 2021 after a three month break and were reported daily through 24 January including on 22 and 23 January 2021, shown here. Courtesy of PVMBG and MAGMA.

Activity intensified significantly at the beginning of February 2021. PVMBG reported dense gray ash emissions rising 500 m above the summit on 1 February. Ash emissions increased to 1,000 m high the next day and continued daily through 5 February. The Darwin VAAC reported continuous ash emissions rising to 3.9-4.3 km altitude (600-1,000 m above the summit) and drifting NE and E during 1-3 and 6-7 February. On 6 and 7 February loud noises and incandescence were reported and on 7 February gray and black ash emissions rose 1,200 m above the summit and drifted ESE producing ashfall at the Raung Observatory in Sragi Village (25 km SE). Multiple pilot reports to the Darwin VAAC indicated ash emissions moving E at 4.9-7 km altitude throughout the day. The next day gray and black plumes rose 2,000 m above the crater and ashfall was again reported at the Raung Observatory from the ESE drifting plume.

The plumes on 9 February were 2,500 m above the summit drifting ESE and accompanied by loud noises. Sentinel-2 satellite imagery recorded a significant thermal anomaly and a large ash plume on 9 February (figures 40 and 41); the plume drifted more than 100 km ESE and was visible beyond the E coast of Java. During 10-12 February gray and black ash plumes rose 2,000 m above the crater each day. Continuous emissions rising to 5.5 km altitude (2,200 m above the summit) were reported in multiple VONA’s first on 8 February and continuing daily through 13 February. By 14 February a ring-shaped thermal anomaly was still visible inside the summit crater (figure 42). For the remainder of the month, plume height diminished to 300-1,000 m above the summit with occasional pulses that rose to 1,200 m. The Darwin VAAC reported daily ash emissions that rose to 4.3-4.9 km altitude and drifted N and E through 20 February. From 22-27 February daily emissions were noted at 3.9-4.3 km altitude drifting NE, E, and S.

Figure 40. A major explosion at Raung on 9 February 2021 was captured in Sentinel-2 satellite imagery. It produced ash emissions that rose to 5.5 km altitude and a dense black ash plume that drifted over one hundred km ESE. A large thermal anomaly filled the summit crater. Top image uses Atmospheric penetration rendering (bands 12, 11, 8a) and bottom image uses Natural color rendering (bands 4,3,2). Courtesy of Sentinel Hub Playground.

Figure 41. Incandescence seen above the Raung summit crater and dense black and gray ash plumes occurred frequently during February 2021 including on 4, 9, 10, and 26 February. Courtesy of PVMBG and MAGMA.

Figure 42. A thermal anomaly ringed the inside of the summit crater at Raung on 14 February. Sentinel-2 image uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Continuous tremor appeared on 1 February and increased significantly in amplitude from 1 to 5 mm. They rose the next day to 14 mm amplitude and remained at 13-16 m amplitude through 6 February. They dropped to 7 mm amplitude after that until 12 February and then returned to 1 mm amplitude for the remainder of the month. A small SO2 anomaly was recorded in satellite data on 1 February and a significant plume of gas appeared on 7 February that continued daily through 12 February (figure 43).

Figure 43. A significant SO2 anomaly from Raung was captured by the TROPOMI instrument on the Sentinel 5P satellite on 7 February and continued daily through 12 February 2021. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Steam and ash emissions in March 2021 were reported daily by PVMBG. During 1-3 March the gray plumes rose 200-600 m above the crater, then from 4 to 9 March they contained moderate to heavy ash content and rose 300-1,000 m above the crater. The Darwin VAAC reported ash emissions drifting E and NE at 3.9-4.3 km altitude during 3-10 March. Plume height varied from 500-1,200 m above the crater during 10-21 March with up to moderate ash density. On 13 March the ash plume was clearly discernable in satellite imagery drifting W at 4.3 km altitude (figure 44). On 22 March the ash plume rose to 900 m and small quantities of ash were reported at the Raung Observatory in Sragi. From 23 March through the end of the month gray ash plumes were reported at 50-1,200 m high with generally low to moderate ash density. VAAC reports issued during 23-27 March reported plumes at 3.7-4.6 km altitude drifting ESE, W, and NW (figure 45). They were clearly seen in visible satellite imagery on 26 March drifting NW at 3.7 km altitude. A single faint thermal anomaly was discernable in Sentinel-2 satellite imagery from the center of the pyroclastic cone inside the summit crater on 16 March.

Figure 44. An ash plume at Raung on 13 March 2021 rose several hundred meters above the volcano and was clearly discernible in satellite images by the Darwin VAAC. Courtesy of PVMBG and MAGMA.

Figure 45. An ash plume from Raung on 23 March 2021 drifted ESE several hundred meters above the summit. Ash emissions from Raung during 23-27 March rose to 3.7-4.6 km altitude and drifted ESE, W, and NW. Courtesy of PVMBG and MAGMA.

Emissions from Raung contained ash during the first half of April 2021. The plumes were gray or white and gray and rose 50-600 m above the summit (figure 46). The Darwin VAAC reported a minor ash plume that rose to 2.4 km altitude and drifted N on 12 April. A report by PVMBG of gray plumes rising 50-400 m high on 14 April was the last indication of ash emissions for the month. For the remainder of the month only steam plumes were seen, rising 75-500 m above the summit. A webcam image taken after dark on 17 April showed incandescence at the summit crater. Two clear satellite images on 20 and 30 April revealed small thermal anomalies inside the pyroclastic cone in the summit crater (figure 47). A small SO2 plume was detected by satellite instruments on 29 April.

Figure 46. Ash emissions were weak during the first half of April 2021 at Raung as seen on 6 April 2021 (top) and only steam plumes were recorded from 15 April onward (bottom). Courtesy of PVMBG and MAGMA.

Figure 47. Small thermal anomalies were visible inside the pyroclastic cone in the summit crater of Raung on 20 and 30 April 2021. Sentinel-2 images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

For most of May 2021 cloudy skies obscured views of the volcano. Occasionally white steam plumes were observed rising up to 400 m above the summit. On 5, 10, and 15 May weak thermal anomalies located inside the pyroclastic cone in the summit crater appeared in satellite images. Distinct SO2 anomalies appeared more frequently during May than any other month of the reporting period except February (figure 48). During June 2021, no thermal anomalies were present in the five satellite images with clear views of the summit. The summit was cloudy in about half of the webcam images taken during June; when visible, white steam plumes were noted that rose generally 50-200 m except on 22 June when they rose 100-400 m high.

Figure 48. Distinct SO2 plumes drifted in multiple directions from Raung on several days during May 2021 including on 9, 10, 24, and 25 May. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

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); 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 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).