Frequent historical eruptions from Tanzania's Ol Doinyo Lengai have been recorded since the late 19th century. Located near the southern end of the East African Rift in the Gregory Rift Valley, the unique low-temperature carbonatitic lavas have been the focus of numerous volcanological studies; the volcano has also long been a cultural icon central to the Maasai people who live in the region. Following explosive eruptions in the mid-1960s and early 1980s the volcano entered a phase of effusive activity with the effusion of small, fluid, natrocarbonatitic lava flows within its active north summit crater. From 1983 to early 2007 the summit crater was the site of numerous often-changing hornitos (or spatter cones) and lava flows that slowly filled the crater. Lava began overflowing various flanks of the crater in 1993; by 2007 most flanks had been exposed to flows from the crater.

Seismic and effusive activity increased in mid-2007, and a new phase of explosive activity resumed in September of that year. The explosive activity formed a new pyroclastic cone inside the crater; repeated ash emissions reached altitudes greater than 10 km during March 2008, causing relocation of several thousand nearby villagers. Explosive activity diminished by mid-April 2008; by September new hornitos with small lava flows were again forming on the crater floor. Periodic eruptions of lava from fissures, spatter cones, and hornitos within the crater were witnessed throughout the next decade by scientists and others occasionally visiting the summit. Beginning in 2017, satellite imagery has become a valuable data source, providing information about both the thermal activity and the lava flows in the form of infrared imagery and the color contrast of black fresh lava and whiter cooled lava that is detectable in visible imagery (BGVN 43:10). The latest expeditions in 2018 and 2019 have added drone technology to the research tools. This report covers activity from September 2018 through August 2019 with data and images provided from satellite information and from researchers and visitors to the volcano.

Summary and data from satellite imagery. Throughout September 2018 to August 2019, evidence for repeated small lava flows was recorded in thermal data, satellite imagery, and from a few visits to or overflights of the summit crater by researchers. Intermittent low-level pulses of thermal activity appeared in MIROVA data a few times during the period (figure 187). Most months, Sentinel-2 satellite imagery generated six images with varying numbers of days that had a clear view of the summit and showed black and white color contrasts from fresh and cooled lava and/or thermal anomalies (table 27, figures 188-191). Lava flows came from multiple source vents within the crater, produced linear flows, and covered large areas of the crater floor. Thermal anomalies were located in different areas of the crater; multiple anomalies from different source vents were visible many months.

Figure 187. Intermittent low-level pulses of thermal activity were recorded in the MIROVA thermal data a few times between 21 October 2018 and the end of August 2019. Courtesy of MIROVA.

Table 27. The number of days each month with Sentinel-2 images of Ol Doinyo Lengai, days with clear views of the summit showing detectable color contrasts between black and white lava, and days with detectable thermal anomalies within the summit crater. A clear summit means more than half the summit visible or features identifiable through diffuse cloud cover. Information courtesy of Sentinel Hub Playground.

Figure 188. Sentinel-2 imagery of Ol Doinyo Lengai from September 2018 showed examples of the changing color contrasts of fresh black lava which quickly cools to whitish-brown (top row) and varying intensities and numbers of thermal anomalies on the same days (bottom row). It is clear that the color and thermal patterns change several times during the month even with only a few days of available imagery. Dates of images from left to right are 11, 16, and 21 September. The summit crater is 300 m across and 100 m deep. The top row is with Natural color rendering (bands 4, 3, 2) and the bottom row is with Atmospheric penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Figure 189. Contrasting patterns of dark and light lava flows within the summit crater of Ol Doinyo Lengai on 1 (left) and 11 (right) October 2018 show how quickly new dark flows cool to a lighter color. The flow on 1 October appears to originate in the E part of the crater; the flow in the crater on 11 October has a source in the N part of the crater. These Sentinel-2 images use Natural color rendering (bands 4,3,2). Courtesy of Sentinel Hub Playground.

Figure 190. A large flow at Ol Doinyo Lengai on 3 February 2019 filled most of the summit crater with lobes of black lava (top left) and generated one of the strongest thermal signatures of the period (top right) in these Sentinel-2 satellite images. On 20 March 2019, a small dark area of fresh material contrasted sharply with the surrounding light-colored material (bottom left); the thermal image of the same data shows a small anomaly near the dark spot (bottom right). The left column is with Natural color rendering (bands 4, 3, 2) and the right column is with Atmospheric penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Figure 191. The dark lava spots at Ol Doinyo Lengai on 18 June 2019 (top left) and 28 July 2019 (top center) produced matching thermal anomalies in the Sentinal-2 imagery (bottom left and center). On days when the summit was partly obscured by clouds such as 27 August (top right), the strong thermal signal from the summit still confirmed fresh flow activity (bottom right). The top row is with Natural color rendering (bands 4, 3, 2) and the bottom row is with Atmospheric penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Information from site visits and overflights. Minor steam and gas emissions were visible from the summit crater during an overflight on 29 September 2018. Geologist Cin-Ty Lee captured excellent images of the W flank on 20 October 2018 (figure 192). The large circular crater at the base of the flank is the 'Oldoinyo' Maar (Graettinger, 2018a and 2018b). A view into the crater from an overflight that day (figure 193) showed clear evidence of at least five areas of dark, fresh lava. An effusive eruption was visible on the crater floor on 2 March 2019 (figure 194).

Figure 192. A large maar stands out at the base of the SW flank of Ol Doinyo Lengai on 20 October 2018. Courtesy of Cin-Ty Lee (Rice University).

Figure 193. A view into the summit crater of Ol Doinyo Lengai on 20 October 2018 shows clear evidence of recent flow activity in the form of multiple dark spots of fresh lava that has recently emerged from hornitos and fissures. The lava cools to a pale color very quickly, forming the contrasting background to the fresh flows. The summit crater is 300 m across and 100 m deep. Courtesy of Cin-Ty Lee (Rice University).

Figure 194. A view into the crater floor at Ol Doinyo Lengai on 2 March 2019 showed a vent with both fresh (dark brown) and cooled (gray-white) carbonatite lavas and hornitos on the floor of the crater. The darkest material on the crater floor is from recent flows. Courtesy of Aman Laizer, Tanzania.

Research expedition in July-August 2019. In late July and early August 2019 an expedition, sponsored by the Deep Carbon Observatory (DCO) and led by researchers Kate Laxton and Emma Liu (University College London), made gas measurements, collected lava samples for the first time in 12 years, and deployed drones to gather data and images. The Ol Doinyo Lengai sampling team included Papkinye Lemolo, Boni Kicha, Ignas Mtui, Boni Mawe, Adadeus Mtui, Emma Liu, Arno Van Zyl, Kate Laxton, and their driver, Baraka. They collected samples by lowering devices via ropes and pulleys into the crater and photographed numerous active flows emerging from vents and hornitos on the crater floor (figure 195). By analyzing the composition of the first lava samples collected since the volcano's latest explosive activity in 2007, they hope to learn about recent changes to its underground plumbing system. A comparison of the satellite image taken on 28 July with a drone image of the summit crater taken by them the next day (figure 196) confirms the effectiveness of both the satellite imagery in identifying new flow features on the crater floor, and the drone imagery in providing outstanding details of activity.

Figure 195. Researchers Kate Laxton and Emma Liu collected gas and lava samples at the summit of Ol Doinyo Lengai during their 26 July-4 August 2019 expedition. They sent gas sampling devices (small white "hamster ball" in center of left image) and lava sampling devices (right) down into the crater via ropes and pulleys. The crater is 300 m across and 100 m deep. Courtesy of Kate Laxton (University College London).

Figure 196. A clear view by drone straight down into the crater at Ol Doinyo Lengai on 29 July 2019 provides valuable information about ongoing activity at the remote volcano. N is to the top. The summit crater is 300 m across and 100 m deep. The same configuration of fresh and cooled lava can be seen in Sentinel-2 imagery taken on 28 July 2019 (inset, N to the top). Courtesy of Emma Liu (University College London) and Sentinel Hub Playground.

With the drone technology, they were able to make close-up observations of features on the north crater floor such as the large hornito on the inner W wall of the crater (figure 197), an active lava pond near the center of the crater (figure 198), and several flows resurfacing the floor of the crater while they were there (figure 199). A large crack that rings the base of the N cone had enlarged significantly since last measured in 2014 (figure 200).

Figure 197. A closeup view of the large hornito in the W wall of the Ol Doinyo Lengai summit crater on 26 July 2019 shows recent activity from the vent (dark material). See figure 197 for location of hornito against W wall. View is to the NW. Courtesy of Emma Liu (University College London).

Figure 198. Incandescence from the lava pond in the center of the crater was still visible at 0627 on 29 July 2019 at Ol Doinyo Lengai; incandescence from the large hornito in the NW quadrant (behind the lava pond) had been visible when the researchers arrived at the summit at about 0500 that morning. The crater floor is continually resurfaced by ultra-low viscosity natrocarbonatite lava flows. The lava hydrates on contact with air within hours, changing color from black to grey/white in a very short time. View towards the N. Courtesy of Kate Laxton (University College London).

Figure 199. On 30 July 2019 a lava flow from a hornito cluster resurfaced the NE quadrant of the crater floor at Ol Doinyo Lengai. The initial outbreak occurred at 0819, was vigorous, and ended by 0823. Lava continued to flow out of the hornito cluster at intervals throughout the day. Image facing NE, courtesy of Kate Laxton (University College London).

Figure 200. The circumferential crack near the base of the N cone of Ol Doinyo Lengai is seen here being inspected by Emma Liu on 30 July 2019 where it intersects the Western Summit Trail. View is to the S. Significant widening of the crack is seen when compared with a similar image of the same crack from March 2014 (figure 172, BGVN 39:07). Local observers reported that the crack continued to widen after July 2019. Courtesy of Kate Laxton (University College London).

The color of the flows on the crater floor changed from grays and browns to blues and greens after a night of rainfall on 31 July 2019 (figure 201). Much of the lava pond surface was crusted over that day, but the large hornito in the NW quadrant was still active (figure 202), and both the pond and another hornito produced flows that merged onto the crater floor (figure 203).

Figure 201. The active crater at Ol Doinyo Lengai is on the north side of and slightly below the topographic summit of the mountain (in the background). After overnight rain, lava flows on the crater floor turned various shades of greys, whites, blues, and greens on 31 July 2019. View to the SW, drone image. Courtesy of Emma Liu (University College London).

Figure 202. A closeup view to the NW of the Ol Doinyo Lengai north crater on 31 July 2019 shows the blue and green tones of the hydrated lavas after the previous night's rains. The lava pond is at high-stand with much of the surface crusted over. The adjacent hornito is still active and breached to the NE. Courtesy of Emma Liu (University College London).

Figure 203. Two fresh lava flows merge over the hydrated crater floor of the north crater at Ol Doinyo Lengai on 31 July 2019. One comes from a small hornito just out of view to the SW (lower right) and the other from the overflowing lava pond (left), merging in the SE quadrant. The colors of the two flows differ; the pond lava appears jet black, and the hornito lava is a lighter shade of brown. View to the SE, courtesy of Emma Liu (University College London).

On 1 August 2019 much of the crater floor was resurfaced by a brown lava that flowed from a hornito E of the lava pond (figure 204). Images of unusual, ephemeral features such as "spatter pots," "frozen jets," and "frothy flows" (figure 205) help to characterize the unusual magmatic activity at this unique volcano (figure 206).

Figure 204. On 1 August 2019 at Ol Doinyo Lengai brown lava flowed from a hornito directly E of the lava pond (above the pond in figure 203) and resurfaced much of the S portion of the crater floor. At the far left of the image, the white (hydrated) lava jet aimed away from the hornito was solidified in mid-flow. View to the SE, courtesy of Emma Liu (University College London).

Figure 205. Frothy pale-brown lava flowed across the SE quadrant of the crater floor (right) at Ol Doinyo Lengai on 4 August 2019 from an uncertain source between the adjacent hornito and lava pond which appears nearly crusted over. Spattering from a "spatter pot" (inset) and a small flow also headed NE from the hornito cluster E of the pond (behind pond). Courtesy of Kate Laxton (University College London).

Figure 206. A view from the summit peak of Ol Doinyo Lengai on 4 August 2019 looking at the entire N cone and the swale between it and the peak. The crack shown in figure 201 rings the base of cone; the main summit trail intersects the crack near the bottom center of the cone. The researcher's campsite on the W flank (left) shows the scale of the cone. The East African Rift wall and Lake Natron are visible in the background on the left and right, respectively. Courtesy of Kate Laxton (University College London).

References: Graettinger, A. H., 2018a, MaarVLS database version 1, (URL: https://vhub.org/resources/4365).

Graettinger, A. H., 2018b, Trends in maar crater size and shape using the global Maar Volcano Location and Shape (MaarVLS) database. Journal of Volcanology and Geothermal Research, v. 357, p. 1-13. https://doi.org/10.1016/j.jvolgeores.2018.04.002.

Geologic Background. The symmetrical Ol Doinyo Lengai is the only volcano known to have erupted carbonatite tephras and lavas in historical time. The prominent stratovolcano, known to the Maasai as "The Mountain of God," rises abruptly above the broad plain south of Lake Natron in the Gregory Rift Valley. The cone-building stage ended about 15,000 years ago and was followed by periodic ejection of natrocarbonatitic and nephelinite tephra during the Holocene. Historical eruptions have consisted of smaller tephra ejections and emission of numerous natrocarbonatitic lava flows on the floor of the summit crater and occasionally down the upper flanks. The depth and morphology of the northern crater have changed dramatically during the course of historical eruptions, ranging from steep crater walls about 200 m deep in the mid-20th century to shallow platforms mostly filling the crater. Long-term lava effusion in the summit crater beginning in 1983 had by the turn of the century mostly filled the northern crater; by late 1998 lava had begun overflowing the crater rim.

Information Contacts: Cin-Ty Lee, Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main St., Houston, TX 77005-1827, USA (URL: https://twitter.com/CinTyLee1, images at https://twitter.com/CinTyLee1/status/1054337204577812480, https://earthscience.rice.edu/directory/user/106/); Emma Liu, University College London, UCL Hazards Centre (Volcanology), Gower Street, London, WC1E 6BT, United Kingdom (URL: https://twitter.com/EmmaLiu31, https://www.ucl.ac.uk/earth-sciences/people/academic/dr-emma-liu); Kate Laxton, University College London, UCL Earth Sciences, Gower Street, London, WC1E 6BT, United Kingdom (URL: https://twitter.com/KateLaxton, https://www.ucl.ac.uk/earth-sciences/people/research-students/kate-laxton); Deep Carbon Observatory, Carnegie Institution for Science, 5251 Broad Branch Road NW, Washington, DC 20015-1305, USA (URL: https://deepcarbon.net/field-report-ol-doinyo-lengai-volcano-tanzania); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Aman Laizer, Volcanologist, Arusha, Tanzania (URL: https://twitter.com/amanlaizerr, image at https://twitter.com/amanlaizerr/status/1102483717384216576).

Typical activity at Ulawun consists of occasional weak explosions with ash plumes. During 2018 explosions occurred on 8 June, 21 September, and 5 October (BGVN 43:11). The volcano is monitored primarily by the Rabaul Volcano Observatory (RVO) and Darwin Volcanic Ash Advisory Centre (VAAC). This report describes activity from November 2018 through August 2019; no volcanism was noted during this period until late June 2019.

Activity during June-July 2019. RVO reported that Real-time Seismic-Amplitude Measurement (RSAM) values steadily increased during 24-25 June, and then sharply increased at around 0330 on 26 June. The RSAM values reflect an increase in seismicity dominated by volcanic tremor. An eruption began in the morning hours of 26 June with emissions of gray ash (figure 17) that over time became darker and more energetic. The plumes rose 1 km and caused minor ashfall to the NW and SW. Local residents heard roaring and rumbling during 0600-0800.

Figure 17. Photograph of a small ash plume rising from the summit crater of Ulawun taken by a helicopter pilot at 1030 local time on 26 June 2019. According to the pilot, the amount of ash observed was not unusual. Image has been color adjusted from original. Courtesy of Craig Powell.

The Darwin VAAC issued several notices about ash plumes visible in satellite data. These stated that during 1130-1155 ash plumes rose to altitudes of 6.7-8.5 km and drifted W, while ash plumes that rose to 12.8-13.4 km drifted S and SW. A new pulse of activity (figures 17 and 18) generated ash plumes that by 1512 rose to an altitude of 16.8 km and drifted S and SE. By 1730 the ash plume had risen to 19.2 km and spread over 90 km in all directions. Ash from earlier ejections continued to drift S at an altitude of 13.4 km and W at an altitude of 8.5 km. RVO stated that RSAM values peaked at about 2,500 units during 1330-1600, and then dropped to 1,600 units as the eruption subsided.

Figure 18. Photograph of Ulawun taken by a helicopter pilot at 1310 local time on 26 June 2019 showing a tall ash plume rising from the summit crater. Image has been color adjusted from original. Courtesy of Craig Powell.

Figure 19. Photograph of Ulawun taken by a helicopter pilot at 1350 local time on 26 June 2019 showing a close-up view of the ash plume rising from the summit crater along with an area of incandescent ejecta. According to the pilot, this was the most active phase. Image has been color adjusted from original. Courtesy of Craig Powell.

According to RVO, parts of the ash plume at lower altitudes drifted W, causing variable amounts of ashfall in areas to the NW and SW. A pyroclastic flow descended the N flank. Residents evacuated to areas to the NE and W; a news article (Radio New Zealand) noted that around 3,000 people had gathered at a local church. According to another news source (phys.org), an observer in a helicopter reported a column of incandescent material rising from the crater, residents noted that the sky had turned black, and a main road in the N part of the island was blocked by volcanic material. Residents also reported a lava flow near Noau village and Eana Valley. RVO reported that the eruption ceased between 1800 and 1900. Incandescence visible on the N flank was from either a lava flow or pyroclastic flow deposits.

On 27 June diffuse white plumes were reported by RVO as rising from the summit crater and incandescence was visible from pyroclastic or lava flow deposits on the N flank from the activity the day before. The seismic station 11 km NW of the volcano recorded low RSAM values of between 2 and 50. According to the Darwin VAAC a strong thermal anomaly was visible in satellite images, though not after 1200. Ash from 26 June explosions continued to disperse and became difficult to discern in satellite images by 1300, though a sulfur dioxide signal persisted. Ash at an altitude of 13.7 km drifted SW to SE and dissipated by 1620, and ash at 16.8 km drifted NW to NE and dissipated by 1857. RVO noted that at 1300 on 27 June satellite images captured an ash explosion not reported by ground-based observers, likely due to cloudy weather conditions. The Alert Level was lowered to Stage 1 (the lowest level on a four-stage scale).

RSAM values slightly increased at 0600 on 28 June and fluctuated between 80 to 150 units afterwards. During 28-29 June diffuse white plumes continued to rise from the crater (figure 20) and from the North Valley vent. On 29 June a ReliefWeb update stated that around 11,000 evacuated people remained in shelters.

Figure 20. Photograph of the steaming summit crater at Ulawun taken by a helicopter pilot at 0730 local time on 29 June 2019. Image has been color adjusted from original. Courtesy of Craig Powell.

According to RVO, diffuse white plumes rose from Ulawun's summit crater and the North Valley vent during 1-4 July and from the summit only during 5-9 July. The seismic station located 11 km NW of the volcano recorded three volcanic earthquakes and some sporadic, short-duration, volcanic tremors during 1-3 July. The seismic station 2.9 km W of the volcano was restored on 4 July and recorded small sub-continuous tremors. Some discrete high-frequency volcanic earthquakes were also recorded on most days. Sulfur dioxide emissions were 100 tonnes per day on 4 July. According to the United Nations in Papua New Guinea, 7,318 people remained displaced within seven sites because of the 26 June eruption.

Activity during August 2019. During 1-2 August RVO reported that white-to-gray vapor plumes rose from the summit crater and drifted NW. Incandescence from the summit crater was visible at night and jetting noises were audible for a short interval. RSAM values fluctuated but peaked at high levels. During the night of 2-3 August crater incandescence strengthened and roaring noises became louder around 0400. An explosion began between 0430 and 0500 on 3 August; booming noises commenced around 0445. By 0600 dense light-gray ash emissions were drifting NW, causing ashfall in areas downwind, including Ulamona Mission (10 km NW). Ash emissions continued through the day and changed from light to dark gray with time.

The eruption intensified at 1900 and a lava fountain rose more than 100 m above the crater rim. A Plinian ash plume rose 19 km and drifted W and SW, causing ashfall in areas downwind such as Navo and Kabaya, and as far as Kimbe Town (142 km SW). The Darwin VAAC reported that the ash plume expanded radially and reached the stratosphere, rising to an altitude of 19.2 km. The plume then detached and drifted S and then SE.

The Alert Level was raised to Stage 3. The areas most affected by ash and scoria fall were between Navo (W) and Saltamana Estate (NW). Two classrooms at the Navo Primary School and a church in Navo collapsed from the weight of the ash and scoria; one of the classroom roofs had already partially collapsed during the 26 June eruption. Evacuees in tents because of the 26 June explosion reported damage. Rabaul town (132 km NE) also reported ashfall. Seismicity declined rapidly within two hours of the event, though continued to fluctuate at moderate levels. According to a news source (Radio New Zealand, flights in and out of Hoskins airport in Port Moresby were cancelled on 4 August due to tephra fall. The Alert Level was lowered to Stage 1. Small amounts of white and gray vapor were emitted from the summit crater during 4-6 August. RVO reported that during 7-8 August minor emissions of white vapor rose from the summit crater.

Additional observations. Seismicity was dominated by low-level volcanic tremor and remained at low-to-moderate levels. RSAM values fluctuated between 400 and 550 units; peaks did not go above 700. Instruments aboard NASA satellites detected high levels of sulfur dioxide near or directly above the volcano on 26-29 June and 4-6 August 2019.

Thermal anomalies, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, were observed at Ulawun only on 26 June 2019 (8 pixels by the Terra satellite, 4 pixels by the Aqua satellite). The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected three anomalies during the reporting period, one during the last week of June 2019 and two during the first week of August, all three within 3 km of the volcano and of low to moderate energy.

Geologic Background. The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it); ReliefWeb (URL: https://reliefweb.int/); Radio New Zealand (URL: https://www.rnz.co.nz); phys.org (URL: https://phys.org); United Nations in Papua New Guinea (URL: http://pg.one.un.org/content/unct/papua_new_guinea/en/home.html).

Sarychev Peak, located on Matua Island in the central Kurile Islands of Russia, has had eruptions reported since 1765. Renewed activity began in October 2017, followed by a major eruption in June 2009 that included pyroclastic flows and ash plumes (BGVN 43:11 and 34:06). Thermal anomalies, explosions, and ash plumes took place between September and October 2018. A single ash explosion occurred in May 2019. Another ash plume was seen on 11 August, and small thermal anomalies were present in infrared imagery during June-October 2019. Information is provided by the Sakhalin Volcanic Eruption Response Team (SVERT) and the Tokyo Volcanic Ash Advisory Center (VAAC), with satellite imagery from Sentinel-2.

Satellite images from Sentinel-2 showed small white plumes from Sarychev Peak during clear weather on 4 and 14 August 2019 (figure 27); similar plumes were observed on a total of nine clear weather days between late June and October 2019. According to SVERT and the Tokyo VAAC, satellite data from HIMAWARI-8 showed an ash plume rising to an altitude of 2.7 km and drifting 50 km SE on 11 August. It was visible for a few days before dissipating. No further volcanism was detected by SVERT, and no activity was evident in a 17 August Sentinel-2 image (figure 27).

Figure 27. Small white plumes were visible at Sarychev Peak in Sentinel-2 satellite images on 4 and 14 August 2019 (left and center). No activity was seen on 17 August (right). All three Sentinel-2 images use the "Natural Color" (bands 4, 3, 2) rendering; courtesy of Sentinel Hub Playground.

Intermittent weak thermal anomalies were detected by the MIROVA system using MODIS data from late May through 7 October 2019 (figure 28). Sentinel-2 satellite imagery from 28 June, 13 and 23 July, 9 August, and 21 October showed a very small thermal anomaly, but on 28 September a pronounced thermal anomaly was visible (figure 29). No additional thermal anomalies were identified from any source after 7 October through the end of the month.

Figure 28. Thermal anomalies detected at Sarychev Peak by the MIROVA system (Log Radiative Power) using MODIS data for the year ending on 9 October 2019. Courtesy of MIROVA.

Figure 29. Sentinel-2 satellite images of Sarychev Peak on 23 June and 28 September 2019. A small thermal anomaly is visible on the eastern side of the crater on 23 June (left, indicated by arrow), while the thermal anomaly is more pronounced and visible in the middle of the crater on 28 September (right). Both Sentinel-2 satellite images use the "False Color (Urban)" (bands 12, 11, 4) rendering; courtesy of Sentinel Hub Playground.

Geologic Background. Sarychev Peak, one of the most active volcanoes of the Kuril Islands, occupies the NW end of Matua Island in the central Kuriles. The andesitic central cone was constructed within a 3-3.5-km-wide caldera, whose rim is exposed only on the SW side. A dramatic 250-m-wide, very steep-walled crater with a jagged rim caps the volcano. The substantially higher SE rim forms the 1496 m high point of the island. Fresh-looking lava flows, prior to activity in 2009, had descended in all directions, often forming capes along the coast. Much of the lower-angle outer flanks of the volcano are overlain by pyroclastic-flow deposits. Eruptions have been recorded since the 1760s and include both quiet lava effusion and violent explosions. Large eruptions in 1946 and 2009 produced pyroclastic flows that reached the sea.

Information Contacts: Sakhalin Volcanic Eruption Response Team (SVERT), Institute of Marine Geology and Geophysics, Far Eastern Branch, Russian Academy of Science, Nauki st., 1B, Yuzhno-Sakhalinsk, Russia, 693022 (URL: http://www.imgg.ru/en/, http://www.imgg.ru/ru/svert/reports); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Asamayama (also known as Asama), located in the Kanto-Chubu Region of Japan, previously erupted in June 2015. Activity included increased volcanic seismicity, small eruptions which occasionally resulted in ashfall, and SO₂ gas emissions (BGVN 41:10). This report covers activity through August 2019, which describes small phreatic eruptions, volcanic seismicity, faint incandescence and commonly white gas plumes, and fluctuating SO₂ emissions. The primary source of information for this report is provided by the Japan Meteorological Agency (JMA).

Activity during October 2016-May 2019. From October 2016 through December 2017, a high-sensitivity camera captured faint incandescence at night accompanied by white gas plumes rising above the crater to an altitude ranging 100-800 m (figure 44). A thermal anomaly and faint incandescence accompanied by a white plume near the summit was observed at night on 6-7 and 21 January 2017. These thermal anomalies were recorded near the central part of the crater bottom in January, February, and November 2017, and in May 2019. After December 2017 the faint incandescence was not observed, with an exception on 18 July 2018.

Figure 44. A surveillance camera observed faint incandescence at Asamayama in February 2017. Left: Onimushi surveillance camera taken at 0145 on 5 February 2017. Right: Kurokayama surveillance camera taken at 0510 on 1 February 2017. Courtesy of JMA (Monthly Report for February 2017).

Field surveys on 6, 16, and 28 December 2016 reported an increased amount of SO₂ gas emissions from November 2016 (100-600 tons/day) to March 2017 (1,300-3,200 tons/day). In April 2017 the SO₂ emissions decreased (600-1,500 tons/day). Low-frequency shallow volcanic tremors decreased in December 2016; none were observed in January 2017. From February 2017 through June 2018 volcanic tremors occurred more intermittently. According to the monthly JMA Reports on February 2017 and December 2018 and data from the Geographical Survey Institute's Global Navigation Satellite Systems (GNSS), a slight inflation between the north and south baseline was recorded starting in fall 2016 through December 2018. This growth become stagnant at some of the baselines in October 2017.

Activity during August 2019. On 7 August 2019 a small phreatic eruption occurred at the summit crater and continued for about 20 minutes, resulting in an ash plume that rose to a maximum altitude of 1.8 km, drifting N and an associated earthquake and volcanic tremor (figure 45). According to the Tokyo Volcanic Ash Advisory (VAAC), this plume rose 4.6 km, based on satellite data from HIMAWARI-8. A surveillance camera observed a large volcanic block was ejected roughly 200 m from the crater. According to an ashfall survey conducted by the Mobile Observation Team on 8 August, slight ashfall occurred in the Tsumagoi Village (12 km N) and Naganohara Town (19 km NE), Gunma Prefecture (figure 46 and 47). About 2 g/m2 of ash deposit was measured by the Tokyo Institute of Technology. Immediately after the eruption on 7 August, seismicity, volcanism, and SO₂ emissions temporarily increased and then decreased that same day.

Figure 45. Surveillance camera images of Asamayama showing the small eruption at the summit crater on 7 August 2019, resulting in incandescence and a plume rising 1.8 km altitude. Both photos were taken on 7 August 2019.Courtesy of JMA (Monthly Report for August 2019).

Figure 46. A photomicrograph of fragmented ejecta (250-500 µm) from Asamayama deposited roughly 5 km from the crater as a result of the eruption on 7 August 2019. Courtesy of JMA (Monthly Report for August 2019).

Figure 47. Photos of ashfall in a nearby town NNE of Asamayama due to the 7 August 2019 eruption. Courtesy of JMA (Daily Report for 8 August 2019).

Another eruption at the summit crater on 25 August 2019 was smaller than the one on 7 August. JMA reported the resulting ash plume rose to an altitude of 600 m and drifted E. However, the Tokyo VAAC reported that the altitude of the plume up to 3.4 km, according to satellite data from HIMAWARI-8. A small amount of ashfall occurred in Karuizawa-machi, Nagano (4 km E), according to interview surveys and the Tokyo Institute of Technology.

Geologic Background. Asamayama, Honshu's most active volcano, overlooks the resort town of Karuizawa, 140 km NW of Tokyo. The volcano is located at the junction of the Izu-Marianas and NE Japan volcanic arcs. The modern Maekake cone forms the summit and is situated east of the horseshoe-shaped remnant of an older andesitic volcano, Kurofuyama, which was destroyed by a late-Pleistocene landslide about 20,000 years before present (BP). Growth of a dacitic shield volcano was accompanied by pumiceous pyroclastic flows, the largest of which occurred about 14,000-11,000 BP, and by growth of the Ko-Asama-yama lava dome on the east flank. Maekake, capped by the Kamayama pyroclastic cone that forms the present summit, is probably only a few thousand years old and has an historical record dating back at least to the 11th century CE. Maekake has had several major plinian eruptions, the last two of which occurred in 1108 (Asamayama's largest Holocene eruption) and 1783 CE.

Information Contacts: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/).

Villarrica is a frequently active volcano in Chile with an active lava lake in the deep summit crater. It has been producing intermittent Strombolian activity since February 2015, soon after the latest reactivation of the lava lake; similar activity continued into 2019. This report summarizes activity during March-August 2019 and is based on reports from the Southern Andes Volcano Observatory (Observatorio Volcanológico de Los Andes del Sur, OVDAS), part of Chile's National Service of Geology and Mining (Servicio Nacional de Geología y Minería, SERNAGEOMIN), Projecto Observación Villarrica Internet (POVI), part of the Fundacion Volcanes de Chile research group, and satellite data.

OVDAS-SERNAGEOMIN reported that degassing continued through March with a plume reaching 150 m above the crater with visible incandescence through the nights. The lava lake activity continued to fluctuate and deformation was also recorded. POVI reported sporadic Strombolian activity throughout the month with incandescent ejecta reaching around 25 m above the crater on 17 and 24 March, and nearly 50 m above the crater on the 20th (figure 76).

Figure 76. A webcam image of Villarrica at 0441 on 20 March 2019 shows Strombolian activity and incandescent ejecta reaching nearly 50 m above the crater. People are shown for scale in the white box to the left in the blue background image that was taken on 27 March. Photos taken about 6 km away from the volcano, courtesy of POVI.

There was a slight increase in Strombolian activity reported on 7-8 April, with incandescent ballistic ejecta reaching around 50 m above the crater (figure 77). Although seismicity was low during 14-15 April, Strombolian activity produced lava fountains up to 70 m above the crater over those two days (figure 78). Activity continued into May with approximately 12 Strombolian explosions recorded on the night of 5-6 May erupting incandescent ejecta up to 50 m above the crater rim. Another lava fountaining episode was observed reaching around 70 m above the crater on 14 May (figure 79). POVI also noted that while this was one of the largest events since 2015, no significant changes in activity had been observed over the last five months. Throughout May, OVDAS-SERNAGEOMIN reported that the gas plume height did not exceed 170 m above the crater and incandescence was sporadically observed when weather allowed. SWIR (short-wave infrared) thermal data showed an increase in energy towards the end of May (figure 80).

Figure 77. Strombolian activity at Villarrica on 7-8 April 2019 producing incandescent ballistic ejecta reaching around 50 m above the crater. Courtesy of POVI.

Figure 78. Images of Villarrica on 15 April show a lava fountain that reached about 70 m above the crater. Courtesy of POVI.

Figure 79. These images of Villarrica taken at 0311 and 2220 on 14 May 2019 show lava fountaining reaching 70-73 m above the crater. Courtesy of POVI.

Figure 80. This graph shows the variation in short-wave infrared (SWIR) energy with the vertical scale indicating the number of pixels displaying high temperatures between 23 June 2018 and 29 May 2019. Courtesy of POVI.

Ballistic ejecta were observed above the crater rim on 17 and 20 June 2019 (figure 81), and activity was heard on 20 and 21 June. Activity throughout the month remained similar to previous months, with a fluctuating lava lake and minor explosions. On 15 July a thermal camera imaged a ballistic bomb landing over 300 m from the crater and disintegrating upon impact. Incandescent material was sporadically observed on 16 July. Strombolian activity increased on 22 July with the highest intensity activity in four years continuing through the 25th (figure 82).

Figure 81. Ballistic ejecta is visible above the Villarrica crater in this infrared camera (IR940 nm) image taken on 17 June 2019. Courtesy of POVI.

Figure 82. Strombolian activity at Villarrica on 22, 23, and 24 July with incandescent ballistic ejecta seen here above the summit crater. Courtesy of POVI.

On 6 August the Alert Level was raised by SERNAGEOMIN from Green to Yellow (on a scale of Green, Yellow, Orange, and Red indicating the greatest level of activity) due to activity being above the usual background level, including ejecta confirmed out to 200 m from the crater with velocities on the order of 100 km/hour (figure 83). The temperature of the lava lake was measured at a maximum of 1,000°C on 25 July. POVI reported the collapse of a segment of the eastern crater rim, possibly due to snow weight, between 9 and 12 August. The MIROVA system showed an increase in thermal energy in August (figure 84) and there was one MODVOLC thermal alert on 24 July.

Figure 83. Observations during an overflight of Villarrica on 25 July 2019 showed that ballistic ejecta up to 50 cm in diameter had impacted out to 200 m from the crater. The velocities of these ejecta were likely on the order of 100 km/hour. The maximum temperature of the lava lake measured was 1,000°C, and 500°C was measured around the crater. Courtesy of SERNAGEOMIN.

Figure 84. Thermal activity at Villarrica detected by the MIROVA system shows an increase in detected energy in August 2019. Courtesy of MIROVA.

Geologic Background. Glacier-clad Villarrica, one of Chile's most active volcanoes, rises above the lake and town of the same name. It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. A 6-km-wide caldera formed during the late Pleistocene. A 2-km-wide caldera that formed about 3500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesitic cone at the NW margin of the Pleistocene caldera. More than 30 scoria cones and fissure vents dot the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Historical eruptions, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

Information Contacts: Proyecto Observación Villarrica Internet (POVI) (URL: http://www.povi.cl/); Servicio Nacional de Geología y Minería (SERNAGEOMIN), Observatorio Volcanológico de Los Andes del Sur (OVDAS), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

The andesitic Volcán El Reventador lies east of the main volcanic axis of the Cordillera Real in Ecuador and has historical eruptions with numerous lava flows and explosive events going back to the 16th century. An eruption in November 2002 generated a 17-km-high eruption cloud, pyroclastic flows that traveled 8 km, and several lava flows. Eruptive activity has been continuous since 2008. Daily explosions with ash emissions and ejecta of incandescent blocks rolling hundreds of meters down the flanks have been typical for many years. Alameida et al. (2019) provide an excellent summary of recent activity (2016-2018) and monitoring. Activity continued during February-July 2019, the period covered in this report, with information provided by Ecuador's Instituto Geofisico (IG-EPN), the Washington Volcano Ash Advisory Center (VAAC), and infrared satellite data.

Persistent thermal activity accompanied daily ash emissions and incandescent block avalanches during February-July 2019 (figure 111). Ash plumes generally rose 600-1,200 m above the summit crater and drifted W or NW; incandescent blocks descended up to 800 m down all the flanks. On 25 February an ash plume reached 9.1 km altitude and drifted SE, causing ashfall in nearby communities. Pyroclastic flows were reported on 18 April and 19 May traveling 500 m down the flanks. Small but distinct SO₂ emissions were detectible by satellite instruments a few times during the period (figure 112).

Figure 111. The thermal energy at Reventador persisted throughout 4 November 2018 through July 2019, but was highest in April and May. Courtesy of MIROVA.

Figure 112. Small SO2 plumes were released from Reventador and detected by satellite instruments only a few times during February-July 2019. Columbia's Nevada del Ruiz produced a much larger SO2 signal during each of the days shown here as well. Top left: 26 February; top right: 27 February; bottom left: 3 April; bottom right: 4 April. Courtesy of NASA Goddard Space Flight Center.

The Washington VAAC issued multiple daily ash advisories on all but two days during February 2019. IGEPN reported daily ash emissions rising from 400 to over 1,000 m above the summit crater. Incandescent block avalanches rolled 400-800 m down the flanks on most nights (figure 113). Late on 8 February the Washington VAAC reported an ash plume moving W at 5.8 km altitude extending 10 km from the summit. Plumes rising more than 1,000 m above the summit were reported on 9, 13, 16, 18, 19, and 25 February. On 25 February the Washington VAAC reported an ash plume visible in satellite imagery drifting SE from the summit at 9.1 km altitude that dissipated quickly, and drifted SSE. It was followed by new ash clouds at 7.6 km altitude that drifted S. Ashfall was reported in San Luis in the Parish of Gonzalo Díaz de Pineda by UMEVA Orellana and the Chaco Fire Department.

Figure 113. Emission of ash from Reventador and incandescent blocks rolling down the cone occurred daily during February 2019, and were captured by the COPETE webcam located on the S rim of the caldera. On 1 February (top left) incandescent blocks rolled 600 m down the flanks. On 13 February (top right) ash plumes rose 800 m and drifted W. On 16 February (bottom left) ash rose to 1,000 m and drifted W. On 18 February (bottom right) the highest emission exceeded 1,000 m above the crater and was clearly visible in spite of meteoric clouds obscuring the volcano. Courtesy of IGEPN (Daily reports 2019-32, 44, 47, and 49).

Ash plumes exceeded 1,000 m in height above the summit almost every day during March 2019 and generally drifted W or NW. The Washington VAAC reported an ash plume visible above the cloud deck at 6.7 km altitude extending 25 km NW early on 3 March; there were no reports of ashfall nearby. Incandescent block avalanches rolled 800 m down all the flanks the previous night; they were visible moving 300-800 m down the flanks most nights throughout the month (figure 114).

Figure 114. Ash plumes and incandescent block avalanches occurred daily at Reventador during March 2019 and were captured by the COPETE webcam on the S rim of the caldera. On 3 March (top left) a possible pyroclastic flow traveled down the E flank in the early morning. Ash plumes on 17 and 18 March (top right, bottom left) rose 900-1,000 m above the summit and drifted W. On 23 March (bottom right) ash plumes rose to 1,000 m and drifted N while incandescent blocks rolled 600 m down the flanks. Courtesy of IGEPN (Daily reports 2019 62, 76, 77, and 82).

During April 2019 ash plume heights ranged from 600 to over 1,000 m above the summit each day, drifting either W or NW. Incandescent avalanche blocks rolled down all the flanks for hundreds of meters daily; the largest explosions sent blocks 800 m from the summit (figure 115). On 18 April IGEPN reported that a pyroclastic flow the previous afternoon had traveled 500 m down the NE flank.

Figure 115. Ash plumes and incandescent block avalanches occurred daily at Reventador during April 2019. On 3 April, ash emissions were reported drifting W and NW at 1,000 m above the summit (top left). On 14 April ash plumes rose over 600 m above the summit crater (top right). The 3 and 14 April images were taken from the LAVCAM webcam on the SE flank. Incandescent block avalanches descended 800 m down all the flanks on 15 April along with ash plumes rising over 1,000 m above the summit (bottom left), both visible in this image from the COPETE webcam on the S rim of the caldera. A pyroclastic flow descended 500 m down the NE flank on 17 April and was captured in the thermal REBECA webcam (bottom right) located on the N rim of the caldera. Courtesy of IGEPN (Daily reports 2019-93, 104, 105, and 108).

On most days during May 2019, incandescent block avalanches were observed traveling 700-800 m down all the flanks. Ash plume heights ranged from 600 to 1,200 m above the crater each day of the month (figure 116) they were visible. A pyroclastic flow was reported during the afternoon of 19 May that moved 500 m down the N flank.

Figure 116. Even on days with thick meteoric clouds, ash plumes can be observed at Reventador. The ash plumes reached 1,000 m above the crater on 8 May 2019 (top left). The infrared webcam REBECA on the N rim of the caldera captured a pyroclastic flow on the N flank on the afternoon of 19 May (top right). Strong explosions on 23 May sent incandescent blocks and possible pyroclastic flows at least 800 m down all the flanks (bottom left). Ash plumes reached 1,000 m above the summit on 27 May and drifted W (bottom right). Images on 8, 23, and 27 May taken from the COPETE webcam on the S rim of the caldera. Courtesy of IGEPN (Daily Reports 2019-128, 140, 143, and 147).

Activity diminished somewhat during June 2019. Ash plumes reached 1,200 m above the summit early in June but decreased to 600 m or less for the second half of the month. Meteoric clouds prevented observation for most of the third week of June; VAAC reports indicated ash emissions rose to 5.2 km altitude on 19 June and again on 26 June (about 2 km above the crater). Incandescent blocks were reported traveling down all of the flanks, generally 500-800 m, during about half of the days the mountain was visible (figure 117). Multiple VAAC reports were also issued daily during July 2019. Ash plumes were reported by IGEPN rising over 600 m above the crater every day it was visible and incandescent blocks traveled 400-800 m down the flanks (figure 118). The Darwin VAAC reported an ash emission on 9 July that rose to 4.9 km altitude as multiple puffs that drifted W, extending about 35 km from the summit.

Figure 117. Activity diminished slightly at Reventador during June 2019. Incandescent material was visible on the N flank from infrared webcam REBECA on the N rim of the caldera on 6 June (top left). On 7 June ash rose over 1,000 m above the summit and drifted N and W (top right) as seen from the COPETE webcam on the S rim of the caldera. Incandescent block avalanches rolled 600 m down all the flanks on 8 June (bottom left) and were photographed by the LAVCAM webcam located on the SE flank. An ash plume rose to 1,000 m on 25 June and was photographed from the San Rafael waterfall (bottom right). Courtesy of IGEPN (Daily Reports 2019-157, 158, 159, and 176).

Figure 118. Daily explosive activity was reported at Reventador during July 2019. On 9 and 10 July ash plumes rose over 600 m and drifted W and incandescent blocks descended 800 m down all the flanks (top row), as seen from the LAVCAM webcam on the SE flank. On 27 July many of the large incandescent blocks appeared to be several m in diameter as they descended the flanks (bottom left, LAVCAM). On 1 August, a small steam plume was visible on a clear morning from the CORTESIA webcam located N of the volcano. Courtesy of IGEPN Daily reports (2019-190, 191, 208, and 213).

References: Almeida M, Gaunt H E, and Ramón P, 2019, Ecuador's El Reventador volcano continually remakes itself, Eos, 100, https://doi.org/10.1029/2019EO117105. Published on 18 March 2019.

Geologic Background. Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well east of the principal volcanic axis. The forested, dominantly andesitic Volcán El Reventador stratovolcano rises to 3562 m above the jungles of the western Amazon basin. A 4-km-wide caldera widely breached to the east was formed by edifice collapse and is partially filled by a young, unvegetated stratovolcano that rises about 1300 m above the caldera floor to a height comparable to the caldera rim. It has been the source of numerous lava flows as well as explosive eruptions that were visible from Quito in historical time. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the caldera. The largest historical eruption took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.

Information Contacts: Instituto Geofísico (IG-EPN), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec ); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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/).

Raikoke in the central Kuril Islands lies 400 km SW of the southern tip of Russia's Kamchatcka Peninsula. Two significant eruptive events in historical times, including fatalities, have been recorded. In 1778 an eruption killed 15 people "under the hail of bombs" who were under the command of Captain Chernyi, returning from Matua to Kamchatka. This prompted the Russian military to order the first investigation of the volcanic character of the island two years later (Gorshkov, 1970). Tanakadate (1925) reported that travelers on a steamer witnessed an ash plume rising from the island on 15 February 1924, observed that the island was already covered in ash from recent activity, and noted that a dense steam plume was visible for a week rising from the summit crater. The latest eruptive event in June 2019 produced a very large ash plume that covered the island with ash and dispersed ash and gases more than 10 km high into the atmosphere. The volcano is monitored by the Sakhalin Volcanic Eruption Response Team, (SVERT) part of the Institute of Marine Geology and Geophysics, Far Eastern Branch of the Russian Academy of Sciences (IMGG FEB RAS) and the Kamchatka Volcanic Eruption Response Team (KVERT) which is part of the Institute of Volcanology and Seismology, Far Eastern Branch of the Russian Academy of Sciences (IVS FEB RAS).

A brief but intense eruption beginning on 21 June 2019 sent major ash and sulfur dioxide plumes into the stratosphere (figures 1 and 2); the plumes rapidly drifted over 1,000 km from the volcano. Strong explosions with dense ash plumes lasted for less than 48 hours, minor emissions continued for a few more days; the SO₂, however, continued to circulate over far eastern Russia and the Bering Sea for more than three weeks after the initial explosion. The eruption covered the island with centimeters to meters of ash and enlarged the summit crater. By the end of July 2019 only minor intermittent steam emissions were observed in satellite imagery.

Figure 1. On the morning of 22 June 2019, astronauts on the International Space Station captured this image of a large ash plume rising from Raikoke in the Kuril Islands. The plume reached altitudes of 10-13 km and drifted E during the volcano's first known explosion in 95 years. Courtesy of NASA Earth Observatory.

Figure 2. A large and very dense SO2 plume (measuring over 900 Dobson Units (DU)) drifted E from Raikoke in the Kuril Islands on 22 June 2019, about 8 hours after the first known explosion in 95 years. Courtesy of NASA Goddard Space Flight Center.

Summary of 2019 activity. A powerful eruption at Raikoke began at 1805 on 21 June 2019 (UTC). Volcano Observatory Notices for Aviation (VONA's) issued by KVERT described the large ash plume that rapidly rose to 10-13 km altitude and extended for 370 km NE within the first two hours (figure 3). After eight hours, the plume extended 605 km ENE; it had reached 1,160 km E by 13 hours after the first explosion (figure 4). The last strong explosive event, according to KVERT, producing an ash column as high as 10-11 km, occurred at 0540 UTC on 22 June. SVERT reported a series of nine explosions during the eruption. Over 440 lightning events within the ash plume were detected in the first 24 hours by weather-monitoring equipment. The Japanese Ministry of Transportation reported that almost 40 planes were diverted because of the ash plume (figure 5).

Figure 3. A dense ash plume drifted E from Raikoke on 22 June 2019 from a series of large explosions that lasted for less than 24 hours, as seen in this Terra satellite image. The plume was detected in the atmosphere for several days after the end of the eruptive activity. Courtesy of NASA Earth Observatory.

Figure 4. The ash plume from Raikoke volcano that erupted on 21 June 2019 drifted over 1,000 km E by late in the day on 22 June, as seen in this oblique, composite view based on data from the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite. Courtesy of NASA Earth Observatory.

Figure 5. Numerous airplanes were traveling on flight paths near the Raikoke ash plume (black streak at center) early on 22 June 2019. The Japanese Ministry of Transportation reported that almost 40 planes were diverted because of the plume. Courtesy of Flightradar24 and Volcano Discovery.

On 23 June (local time) the cruise ship Athena approached the island; expedition member Nikolai Pavlov provided an eyewitness account and took remarkable drone photographs of the end of the eruption. The ship approached the W flank of the island in the late afternoon and they were able to launch a drone and photograph the shore and the summit. They noted that the entire surface of the island was covered with a thick layer of light-colored ash up to several tens of centimeters thick (figure 6). Fresh debris up to several meters thick fanned out from the base of the slopes (figure 7). The water had a yellowish-greenish tint and was darker brown closer to the shore. Dark-brown steam explosions occurred when waves flowed over hot areas along the shoreline, now blanketed in pale ash with bands of steam and gas rising from it (figure 8). A dense brown ash plume drifted W from the crater, rising about 1.5 km above the summit (figure 9).

Figure 6. The entire surface of the island of Raikoke was covered with a thick layer of light-colored ash up to several tens of centimeters thick on 23 June 2019 when photographed by drone from the cruise ship Athena about 36 hours after the explosions began. View is of the W flank. Photo by Nik Pavlov; courtesy of IVS FEB RAS.

Figure 7. Fresh ash and volcanic debris up to several meters thick coated the flanks of Raikoke on 23 June 2019 after the large explosive eruption two days earlier. View is by drone of the W flank. Photo by Nik Pavlov; courtesy of IVS FEB RAS.

Figure 8. The 21 June 2019 eruption of Raikoke covered the island in volcanic debris. The formerly vegetated areas (left, before eruption) were blanketed in pale ash with bands of steam and gas rising all along the shoreline (right, on 23 June 2019) less than two days after the explosions began. The open water area between the sea stack and the island was filled with tephra. Photos by Nik Pavlov; courtesy of IVS FEB RAS.

Figure 9. At the summit of Raikoke on 23 June 2019, a dense brown ash plume drifted W from the crater, rising about 1.5 km, two days after a large explosive eruption. Drone photo by Nik Pavlov; courtesy of IVS FEB RAS.

Early on 23 June, the large ash cloud continued to drift E and then NE at an altitude of 10-13 km. At that altitude, the leading edge of the ash cloud became entrained in a large low pressure system and began rotating from SE to NW, centered in the area of the Komandorskiye Islands, 1,200 km NE of Raikoke. By then the farthest edge of ash plume was located about 2,000 km ENE of the volcano. Meanwhile, at the summit and immediately above, the ash plume was drifting NW on 23 June (figures 9 and 10). Ashfall was reported (via Twitter) from a ship in the Pacific Ocean 40 km from Raikoke on 23 June. Weak ashfall was also reported in Paramushir, over 300 km NE the same day. KVERT reported that satellite data from 25 June indicated that a steam and gas plume, possibly with some ash, extended for 60 km NW. They also noted that the high-altitude "aerosol cloud" continued to drift to the N and W, reaching a distance of 1,700 km NW (see SO₂ discussion below). By 27 June KVERT reported that the eruption had ended, but the aerosols continued to drift to the NW and E. They lowered the Aviation Alert Level to Green the following day.

Figure 10. The brown ash plume from Raikoke was drifting NW on 23 June 2019 (left), while the remnants of the ash from the earlier explosions continued to be observed over a large area to the NE on 25 June (right). The plume in the 23 June image extends about 30 km NW; the plume in the 25 June image extends a similar distance NE. Natural color rendering (bands 4, 3, 2) of Sentinel-2 imagery, courtesy of Sentinel Hub Playground.

Tokyo and Anchorage VAAC Reports. The Tokyo VAAC first observed the ash plume in satellite imagery at 10.4 km altitude at 1850 on 21 June 209, just under an hour after the explosion was first reported by KVERT. About four hours later they updated the altitude to 13.1 km based on satellite data and a pilot report. By the evening of 22 June the high-level ash plume was still drifting ESE at about 13 km altitude while a secondary plume at 4.6 km altitude drifted SE for a few more hours before dissipating. The direction of the high-altitude plume began to shift to the NNW by 0300 on 23 June. By 0900 it had dropped slightly to 12.2 km and was drifting NE. The Anchorage VAAC reported at 2030 that the ash plume was becoming obscured by meteorological clouds around a large and deep low-pressure system in the western Bering Sea. Ash and SO₂ signals in satellite imagery remained strong over the region S and W of the Pribilof Islands as well as over the far western Bering Sea adjacent to Russia. By early on 24 June the plume drifted NNW for a few hours before rotating back again to a NE drift direction. By the afternoon of 24 June, the altitude had dropped slightly to 11.6 km as it continued to drift NNE.

The ash plume was still clearly visible in satellite imagery late on 24 June. An aircraft reported SO₂ at 14.3 km altitude above the area of the ash plume. The plume then began to move in multiple directions; the northern part moved E, while the southern part moved N. The remainder was essentially stationary, circulating around a closed low-pressure zone in the western Bering Sea. The ash plume remained stationary and slowly dissipated as it circulated around the low through 25 June before beginning to push S (figure 11). By early on 26 June the main area of the ash plume was between 325 km WSW of St. Matthew Island and 500 km NNW of St. Lawrence Island, and moving slowly NW. The Anchorage VAAC could no longer detect the plume in satellite imagery shortly after midnight (UTC) on 27 June, although they noted that areas of aerosol haze and SO₂ likely persisted over the western Bering Sea and far eastern Russia.

Figure 11. This RGB image created from a variety of spectral channels from the GOES-17 (GOES-West) satellite shows the ash and gas plume from Raikoke on 25 June 2019. The brighter yellows highlight features that are high in SO2 concentration. Highlighted along the bottom of the image is the pilot report over the far southern Bering Sea; the aircraft was flying at an altitude of 11 km (36,000 feet), and the pilot remarked that there were multiple layers seen below that altitude which had a greyish appearance (likely volcanic ash). Courtesy of NOAA and Scott Bachmeier.

Sulfur dioxide emissions. A very large SO₂ plume was released during the eruption. Preliminary total SO₂ mass estimates by Simon Carn taken from both UV and IR sensors suggested around 1.4-1.5 Tg (1 Teragram = 10⁹ Kg) that included SO₂ columns within the ash plume with values as high as 1,000 Dobson Units (DU) (figure 12). As the plume drifted on 23 and 24 June, similar to the ash plume as described by the Tokyo VAAC, it moved in a circular flow pattern as a result of being entrained in a low-pressure system in the western Bering Sea (figure 13). By 25 June the NW edge of the SO₂ had reached far eastern Russia, 1,700 km from the volcano (as described by KVERT), while the eastern edges reached across Alaska and the Gulf of Alaska to the S. Two days later streams of SO₂ from Raikoke were present over far northern Siberia and northern Canada (figure 14). For the following three weeks high levels of SO₂ persisted over far eastern Russia and the Bering Sea, demonstrating the close relationship between the prevailing weather patterns and the aerosol concentrations from the volcano (figure 15).

Figure 12. A contour map showing the mass and density of SO2 released into the atmosphere from Raikoke on 22 June 2019. Courtesy of Simon Carn.

Figure 13. Streams of SO2 from Raikoke drifted around a complex flow pattern in the Bering Sea on 23 and 24 June 2019. Data from TROPOMI instrument on the Sentinel-5P satellite, courtesy of NASA Goddard Space Flight Center and Simon Carn.

Figure 14. SO2 plumes from Raikoke dispersed over a large area of the northern hemisphere in late June 2019. By 25 June (top) the SO2 plumes had dispersed to far eastern Russia, 1,700 km from the volcano, while the eastern edges reached across Alaska and the Gulf of Alaska to the S. By 27 June (bottom) streams of SO2 were present over far northern Siberia and northern Canada, and also continued to circulate in a denser mass over far eastern Russia. Data from TROPOMI instrument on the Sentinel-5P satellite, courtesy of NASA Goddard Space Flight Center and Simon Carn.

Figure 15. For the first two weeks of July 2019, high levels of SO2 from the 21 June 2019 eruption of Raikoke persisted over far eastern Russia and the Bering Sea entrained in a slow moving low-pressure system, demonstrating the close relationship between the prevailing weather patterns and the aerosol concentrations from the volcano. Data from TROPOMI instrument on the Sentinel-5P satellite, courtesy of NASA Goddard Space Flight Center.

Changes to the island. Since no known activity had occurred at Raikoke for 95 years, the island was well vegetated on most of its slopes and the inner walls of the summit crater before the explosion (figure 16). The first clear satellite image after the explosion, on 30 June 2019, revealed a modest steam plume rising from the summit crater, pale-colored ash surrounding the entire island, and new deposits of debris fans extending out from the NE, SW, and S flanks. Part of a newly enlarged crater was visible at the N edge of the old crater. Two weeks later only a small steam plume was present at the summit, making the outline of the enlarged crater more visible; the extensive shoreline deposits of fresh volcanic material remained. A clear view into the summit crater on 23 July revealed the size and shape of the newly enlarged summit crater (figure 17).

Figure 16. Changes at Raikoke before and after the 21 June 2019 eruption were clear in Sentinel-2 satellite imagery. The island was heavily vegetated on most of its slopes and the inner walls of the summit crater before the explosion (top left, 3 June 2019). The first clear satellite image after the explosion, on 30 June 2019 revealed a steam plume rising from the summit crater, pale-colored ash surrounding the entire island, and new deposits of debris fans extending out from the NE, SW, and S flanks (top right). Part of a newly enlarged crater was visible at the N edge of the old crater. Two weeks later only a small steam plume was present at the summit, making the outline of the enlarged crater more visible; the extensive shoreline deposits of fresh volcanic material remained (bottom right, 13 July 2019). A clear view into the summit crater on 23 July revealed the new size and shape of the summit crater (bottom left). Natural Color rendering (bands 4, 3, 2), courtesy of Sentinel Hub Playground.

Figure 17. Sentinel-2 satellite imagery of the summit crater of Raikoke before (left) and after (right) the explosions that began on 21 June 2019. The old crater rim is outlined in red in both images. The new crater rim is outlined in yellow in the 23 July image. Natural Color rendering (bands 4, 3, 2), courtesy of Sentinel Hub Playground.

References: Gorshkov G S, 1970, Volcanism and the Upper Mantle; Investigations in the Kurile Island Arc, New York: Plenum Publishing Corp, 385 p.

Tanakadate H, 1925, The volcanic activity in Japan during 1914-1924, Bull Volc. v. 1, no. 3.

Geologic Background. A low truncated volcano forms the small barren Raikoke Island, which lies 16 km across the Golovnin Strait from Matua Island in the central Kuriles. The oval-shaped basaltic island is only 2 x 2.5 km wide and rises above a submarine terrace. An eruption in 1778, during which the upper third of the island was said to have been destroyed, prompted the first volcanological investigation in the Kuril Islands two years later. Incorrect reports of eruptions in 1777 and 1780 were due to misprints and errors in descriptions of the 1778 event (Gorshkov, 1970). Another powerful eruption in 1924 greatly deepened the crater and changed the outline of the island. Prior to a 2019 eruption, the steep-walled crater, highest on the SE side, was 700 m wide and 200 m deep. Lava flows mantle the eastern side of the island.

Information Contacts: Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Sakhalin Volcanic Eruption Response Team (SVERT), Institute of Marine Geology and Geophysics, Far Eastern Branch, Russian Academy of Science, Nauki st., 1B, Yuzhno-Sakhalinsk, Russia, 693022 (URL: http://www.imgg.ru/en/, http://www.imgg.ru/ru/svert/reports); Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); 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); NOAA, Cooperative Institute for Meteorological Satellite Studies (CIMSS), Space Science and Engineering Center (SSEC), University of Wisconsin-Madison, 1225 W. Dayton St. Madison, WI 53706, (URL: http://cimss.ssec.wisc.edu/); Simon Carn, Geological and Mining Engineering and Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA (URL: http://www.volcarno.com/, Twitter: @simoncarn); Scott Bachmeier, Cooperative Institute for Meteorological Satellite Studies (CIMSS), Space Science and Engineering Center (SSEC), University of Wisconsin-Madison, 1225 W. Dayton St. Madison, WI 53706; Flightradar24 (URL: https://www.flightradar24.com/51,-2/6); Volcano Discovery (URL: http://www.volcanodiscovery.com/).

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Geologic Background. Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical andesitic-to-dacitic edifice is at the southern end of the four overlapping summit craters. The youngest deposit is a SE-flank pyroclastic flow 14C dated by Hendrasto et al. (2012) at 740-880 CE. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); The Jakarta Post (URL: https://www.thejakartapost.com/news/2019/05/07/mount-sinabung-erupts-again.html); Detikcom (URL: https://news.detik.com/berita/d-4619253/hujan-deras-sejumlah-desa-di-sekitar-gunung-sinabung-banjir-lahar-dingin); iNews Malam (URL: https://tv.inews.id/, https://www.youtube.com/watch?v=uAI4CpSb41k); Tempo.com (URL:https://en.tempo.co/read/1209667/mount-sinabung-erupts-on-monday-morning); David de Zabedrosky, Calera de Tango, Chile (Twitter: @deZabedrosky, URL: https://twitter.com/deZabedrosky/status/1125814504867160065/photo/1, https://twitter.com/deZabedrosky/status/1125814504867160065/photo/2); Sutopo Purwo Nugroho, BNPB (Twitter: @Sutopo_PN, URL: https://twitter.com/Sutopo_PN); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); Øystein Lund Andersen? (Twitter: @OysteinLAnderse, URL: https://twitter.com/OysteinLAnderse, URL: http://www.oysteinlundandersen.com image at https://twitter.com/OysteinLAnderse/status/1132849458142572544); Jaime Sincioco, Phillipines (Twitter: @jaimessincioca, URL: https://twitter.com/jaimessincioco); Annamaria Luongo, University of Padua, Venice, Italy (Twitter: @annamaria_84, URL:https://twitter.com/annamaria_84).

The remote island of Semisopochnoi in the western Aleutians is dominated by a caldera measuring 8 km in diameter that contains a small lake (Fenner Lake) and a number of post-caldera cones and craters. A small (100 m diameter) crater lake in the N cone of Semisopochnoi's Cerberus three-cone cluster has persisted since January 2019. An eruption at Sugarloaf Peak in 1987 included an ash plume (SEAN 12:04). Activity during September-October 2018 included increased seismicity and small explosions (BGVN 44:02). The primary source of information for this reporting period of July-August 2019 comes from the Alaska Volcano Observatory (AVO), when there were two low-level eruptions.

Seismicity rose above background levels on 5 July 2019. AVO reported that data from local seismic and infrasound sensors likely detected a small explosion on 16 July. A strong tremor on 17 July generated airwaves that were detected on an infrasound array 260 km E on Adak Island. In addition to this, a small plume extended 18 km WSW from the Cerberus vent, but no ash signals were detected in satellite data. Seismicity decreased abruptly on 18 July after a short-lived eruption. Seismicity increased slightly on 23 July and remained elevated through August.

On 24 July 2019 AVO reported that satellite data showed that the crater lake was gone and a new, shallow inner crater measuring 80 m in diameter had formed on the crater floor, though no lava was identified. Satellite imagery indicated that the crater of the Cerberus N cone had been replaced by a smooth, featureless area of either tephra or water at a level several meters below the previous floor. Satellite imagery detected faint steam plumes rising to 5-10 km altitude and minor SO₂ emissions on 27 July. Satellite data showed a steam plume rising from Semisopochnoi on 18 August and SO2 emissions on 21-22 August. Ground-coupled airwaves identified in seismic data on 23-24 August was indicative of additional explosive activity.

Geologic Background. Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. It formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice. The high point of the island is 1221-m-high Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island's northern part. The three-peaked 774-m-high Mount Cerberus volcano was constructed during the Holocene within the caldera. Each of the peaks contains a summit crater; lava flows on the northern flank of Cerberus appear younger than those on the southern side. Other post-caldera volcanoes include the symmetrical 855-m-high Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera. Most documented historical eruptions have originated from Cerberus, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone within the caldera could have been active during historical time.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.gov/).

Krakatau volcano in the Sunda Strait between Java and Sumatra, Indonesia experienced a major caldera collapse around 535 CE; it formed a 7-km-wide caldera ringed by three islands. Remnants of this volcano joined to create the pre-1883 Krakatau Island which collapsed during the major 1883 eruption. Anak Krakatau (Child of Krakatau), constructed beginning in late 1927 within the 1883 caldera (BGVN 44:03, figure 56), was the site of over 40 smaller episodes until 22 December 2018 when a large explosion and tsunami destroyed most of the 338-m-high edifice (BGVN 44:03). Subsequent activity from February-July 2019 is covered in this report with information provided by the Indonesian Center for Volcanology and Geological Hazard Mitigation, referred to as Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG). Aviation reports are provided by the Darwin Volcanic Ash Advisory Center (VAAC), and photographs from several social media sources.

The cyclical nature of the growth and destruction of Krakatau was made apparent again in the explosive events of 22 December 2018-6 January 2019, when much of the island of Anak Krakatau was destroyed in a series of events that included a deadly tsunami from a flank collapse, a Vulcanian explosion, and several days of Surtseyan phreatomagmatic activity (figure 83) (Gouhier and Paris, 2019). Due to the location of the volcano in the middle of Sunda Strait, surrounded by coastal communities, damage from the tsunami was once again significant; over 400 fatalities and 30,000 injuries were reported along with damage to thousands of homes, businesses, and boats (figure 84) (BGVN 44:03). After a small explosion on 8 January 2019, the volcano remained quiet until 14 February when a new seismic event was recorded. Intermittent explosions increased in frequency and continued through July 2019; images of Surtseyan explosions with ejecta and steam rising a few hundred meters were occasionally captured by authorities patrolling the Krakatau Islands Nature Preserve and Marine Nature Reserve (KPHK), and by a newly installed webcam.

Figure 83. The dramatic morphologic changes of Anak Krakatau before and after the explosive events of 22 December 2019-6 January 2019 were apparent in these Planet Labs, Inc. images published by the BBC. Left: Planet Lab's Dove satellite captured this clear image of the 338-m-high cone with a summit crater on 17 December 2018. Center: The skies cleared enough on 30 December to reveal the new crater in place of the former cone after the explosions and tsunami of 22-23 December, and multiple subsequent explosions. Right: Surtseyan explosions continued daily through 6 January; Planet Labs captured this event on 2 January 2019. Courtesy of BBC and Planet Labs, Inc.

Figure 84. The location of Anak Krakatau in the middle of Sunda Strait surrounded by populated coastal communities (left) places great risk on those communities from explosive events and tsunamis at the volcano, such as what occurred during the 22 December 2018-6 January 2019 destruction of Anak Krakatau. The village of Tanjung in South Lampung (right) was especially hard hit. Map courtesy of BBC News, and photo courtesy of Daily Mail.

Three explosions were reported on 14, 18, and 23 February. No ash plume was observed on 14 February. The event on 18 February produced a dense gray ash plume that rose 720 m and drifted SSW. On 23 February the plume was white and rose 500 m, drifting ENE. During most days, no emissions were observed; occasional plumes of steam rose 50-100 m above the crater. Authorities visited the island on 15 February and observed the new crater lake and ash-covered flank of the remnant cone (figure 85 and 86).

Figure 85. The denuded slope and new crater at Anak Krakatau on 15 February 2019. Bright orange discoloration of the water on the W side of the volcano is from recent iron-rich discharge. The new summit was measured at 155 m high. Verlaten Island is in the background. Courtesy of Sutopo Purwo Nugroho, BNPB.

Figure 86. The new crater at Anak Krakatau on 15 February 2019. Fumarolic activity is visible in the narrow strip between the crater and the bay; bright orange discoloration of the water on the W side of the volcano is from recent iron-rich discharge. Courtesy of Sutopo Purwo Nugroho, BNPB.

Activity increased during March 2019 with 14 seismic events recorded. Four events on 14 March were reported, with durations ranging from 30 seconds to 4 minutes; neither ash nor steam plumes were reported from these events. Events on 16, 17, and 18 March produced N-drifting white steam plumes that were reported at altitudes of 1.2 km, 650 m, and 350 m, respectively (figure 87). Multiple additional explosions were reported on 24, 30, and 31 March; dense white plumes drifted NE on 30 and 31 March. Nearby rangers for the KPHK who witnessed the explosions on 30 March reported material rising 500-1,000 m above the crater (figure 88). The duration of the seismic events associated with the explosions ranged from 40 seconds to 5 minutes during the second half of March. PVMBG lowered the Alert Level from III to II on 25 March, noting that while explosions continued, the intensity and frequency had decreased; none of the explosions were heard at the Pasauran-Banten (SE) or Kalianda-Lampung (NE) stations that were each about 50 km away.

Figure 87. An eruption at Krakatau on 18 March 2019 produced a steam plume that rose several hundred meters, barely visible from a community across the strait. Courtesy of Oystein Anderson and PVMBG.

Figure 88. White steam and dark ejecta were observed at Anak Krakatau during an explosion on 30 March 2019 by the local patrol team from BKSDA Bengkulu-Ministry of LHK, which manages the Krakatau Islands Nature Preserve and Marine Nature Reserve. Courtesy of Krakatau Islands KPHK.

Although the number of reported seismic events increased significantly during April and May 2019, with 22 VONA's issued during April and 41 during May, only a single event had witnessed evidence of ejecta on 3 April (figure 89). The KPHK patrol that monitors conditions on the islands observed the first plant life returning on Sertung Island (5 km W of Anak Krakatau) on 5 April 2019, emerging through the several centimeters of fresh ash from the explosions and tsunami in late December and early January (figure 90). A 200-m-high steam plume was observed on 14 April, and plumes drifted NE and E on 27 and 29 April.

Figure 89. Rangers for KPHK photographed a Surtseyan explosion with tephra and steam at Anak Krakatau on 3 April 2019. Courtesy of Krakatau Islands KPHK.

Figure 90. A new plant on nearby Sertung Island emerges on 5 April 2019 through several centimeters of fresh ash from the Anak Krakatau explosions of December 2018 and January 2019. Courtesy of Krakatau Islands KPHK.

Members of an expedition to the island on 4 May 2019 photographed the still-steaming lake inside the new crater and the eroding ash-covered slopes (figure 91). Only the explosions on 10 and 17 May produced visible steam plumes that month, to 300-350 m high. By 15 May 2019 a new station had been installed at Anak Krakatau by PVMBG (figure 92). Four separate seismic events were recorded that day. Fog covered the island on a daily basis, and very few visible steam plumes were reported throughout April and May. The durations of the explosion events ranged from 30 seconds to 13 minutes (on 10 May); most of the events lasted for 1-2 minutes.

Figure 91. Members of an expedition photographed the water-filled crater and ash-laden slopes of Anak Krakatau on 4 May 2019. Top image is looking S with Rakata island in the background, bottom image is looking W from the flank of the cone remnant. Photo by Galih Jati, courtesy of Volcano Discovery.

Figure 92. By 15 May 2019 a new seismic station had been installed at Anak Krakatau by PVMBG. Four separate seismic events were recorded on 15 May 2019. Courtesy of Krakatau Islands KPHK.

Nine explosive events were reported during June 2019, but none produced visible steam or ash plumes until 25 June when a PVMBG webcam placed on Anak Krakatau captured a video of a Surtseyan event that lasted for about one minute. Dark gray ejecta shot tens of meters into the air over the lake, accompanied by billowing steam plumes which soon engulfed the webcam (figure 93). The other explosive events during March-July were likely similar, but frequent fog and the short-lived nature of the events made visual evidence scarce from webcams located 50 km away. During July there were 21 VONAs issued reporting similar seismic events that lasted from 30 seconds to 5 minutes; no plumes or sounds were seen or heard.

Figure 93. Dark gray ejecta and billowing steam plumes were captured by a newly installed PVMBG webcam during an explosion at Anak Krakatau on 25 June 2019. The water-laden ash rose tens of meters and scattered ejecta around the island. See Information Contacts for a link to the video. Courtesy of Devy Kamil Syahbana and PVMBG.

Satellite imagery provided solid evidence that activity at Anak Krakatau during February-July 2019 included underwater venting. Dark orange submarine plumes were visible drifting away from the SW flank of the volcano near the new crater multiple times each month (figure 94). The patterns of the plumes varied in size and intensity, suggesting repeated injections of material into the water. The thermal activity showed a marked decline from the period prior to the large explosions and tsunami on 22-23 December 2018. Very little thermal activity was reported during January-March 2019, it increased moderately during April-July 2019 (figure 95).

Figure 94. Dark orange plumes were visible in the seawater around Anak Krakatau during February-July 2019, strongly suggesting submarine discharges from the volcano. Top left: On 2 February 2019 the plume was discharging to the SW and visible in the water for nearly 10 km. Top center and right: on 29 March and 3 April the brightest areas of discharge were off the immediate SW flank; the plumes were drifting both NW and SE around the island. By 28 May (bottom left) the discharge was concentrated close to the SW flank with multiple underwater plumes suggesting several emission points. The only satellite image evidence suggesting a subaerial eruption appeared on 9 June (bottom center) when a dense steam plume rising and possible ejecta in the crater were visible. By 27 July (bottom right), discharge was still visible from the underwater vents on the SW flank, and the gradual filling in of the embayment on the W flank, when compared with the 2 February image, was clear. The island is about 2 km in diameter. Sentinel-2 satellite images with natural color rendering (bands 4,3,2) courtesy of Sentinel Hub Playground.

Figure 95. Thermal activity dropped abruptly at Anak Krakatau after the major flank collapse, explosions, and tsunami on 22-23 December 2018; it remained quiet through March and increased modestly during April-July 2019. Courtesy of MIROVA.

References: Gouhier, M, and Paris, R, 2019, SO₂ and tephra emissions during the December 22, 2018 Anak Krakatau flank-collapse eruption, Volcanica 2(2): 91-103. doi: 10.30909/vol.02.02.91103.

Geologic Background. The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

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/); Krakatau Islands KPHK, Conservation Area Region III Lampung, BKSDA Bengkulu-Ministry of LHK, (URL: https://www.instagram.com/krakatau_ca_cal); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); BBC News, (URL: https://www.bbc.com, article at https://www.bbc.com/news/science-environment-46743362); Planet Labs Inc. (URL: http://www.planet.com/); Sutopo Purwo Nugroho, BNPB (Twitter: @Sutopo_PN, URL: https://twitter.com/Sutopo_PN, image at https://twitter.com/Sutopo_PN/status/1101007655290589185/photo/1); Øystein Lund Andersen? (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: http://www.oysteinlundandersen.com, image at https://twitter.com/OysteinLAnderse/status/1107479025126039552/photo/1); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/), images at https://www.volcanodiscovery.com/krakatau/news/80657/Krakatau-volcano-Indonesia-activity-update-and-field-report-increasing-unrest.html; Devy Kamil Syahbana, Volcanologist, Bandung, Indonesia, (URL: https://twitter.com/_elangtimur, video at https://twitter.com/_elangtimur/status/1143372011177033728); The Daily Mail (URL: https://www.dailymail.co.uk, article at https://www.dailymail.co.uk/sciencetech/article-6910895/FORTY-volcanoes-world-potential-Anak-Krakatoa-eruptions.html) published 11 April 2019.

The Mount Bromo pyroclastic cone within the Tengger Caldera erupts frequently, typically producing gas-and-steam plumes, ash plumes, and explosions (BGVN 44:05). Information compiled for the reporting period of May-July 2019 is from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC).

The eruptive activity at Tengger Caldera that began in mid-February continued through late July 2019, including white-and-brown ash plumes, ash emissions, and tremors. During the months of May through June 2019, white plumes rose between 50 to 600 m above the summit. Satellite imagery captured a small gas-and-steam plume from Bromo on 5 June (figure 18). Low-frequency tremors were recorded by a seismograph from May through July 2019.

Figure 18. Sentinel-2 satellite image showing a small gas-and-steam plume rising from the Bromo cone (center) in the Tengger Caldera on 5 June 2019. Thermal (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

According to PVMBG and a Volcano Observatory Notice for Aviation (VONA), an ash eruption occurred on 19 July 2019; however, no ash column was observed due to weather conditions. A seismograph recorded five earthquakes and three shallow volcanic tremors the same day. In addition, rainfall triggered a lahar on the SW flank of Bromo.

On 28 July the Darwin VAAC reported that ash plumes originating from Bromo rose to a maximum altitude of about 3.9 km and drifted NW from the summit, based on webcam images and pilot reports. PVMBG reported that lower altitude ash plumes (2.4 km) on the same day were also recorded by webcam images, satellite imagery (Himawari-8), and weather models.

Geologic Background. The 16-km-wide Tengger caldera is located at the northern end of a volcanic massif extending from Semeru volcano. The massive volcanic complex dates back to about 820,000 years ago and consists of five overlapping stratovolcanoes, each truncated by a caldera. Lava domes, pyroclastic cones, and a maar occupy the flanks of the massif. The Ngadisari caldera at the NE end of the complex formed about 150,000 years ago and is now drained through the Sapikerep valley. The most recent of the calderas is the 9 x 10 km wide Sandsea caldera at the SW end of the complex, which formed incrementally during the late Pleistocene and early Holocene. An overlapping cluster of post-caldera cones was constructed on the floor of the Sandsea caldera within the past several thousand years. The youngest of these is Bromo, one of Java's most active and most frequently visited volcanoes.

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/).

Large areas of floating pumice, termed rafts, were encountered by sailors in the northern Tonga region approximately 80 km NW of Vava'u starting around 9 August 2019; the pumice reached the western islands of Fiji by 9 October (figure 7). Pumice rafts are floating masses of individual clasts ranging from millimeters to meters in diameter. The pumice clasts form when silicic magma is degassing, forming bubbles as it rises to the surface, which then rapidly cools to form solid rock. The isolated vesicles formed by the bubbles provide buoyancy to the rock and in turn, the entire pumice raft. These rafts are spread and carried by currents across the ocean; rafts originating in the Tonga area can eventually reach Australia. This report summarizes the pumice raft eruption from early August 2019 using witness accounts and satellite images (acquisition dates are given in UTC). Pending further research, the presumed source is the unnamed Tongan seamount (volcano number 243091) about 45 km NW of Vava'u, the origin of an earlier pumice raft produced during an eruption in 2001.

Figure 7. The path of the pumice from the unnamed Tongan seamount from 9 August to 9 October 2019 based on eye-witness accounts and satellite data discussed below, as well as additional Aqua/MODIS satellite images from NASA Worldview. Blue Marble MODIS/NASA Earth Observatory base map courtesy of NASA Worldview.

The first sighting of pumice was around 1430 on 9 August NW of Vava'u in Tonga (18° 22.068' S, 174° 50.800' W), when Shannon Lenz and Tom Whitehead on board SV Finely Finished initially encountered isolated rocks and smaller streaks of pumice clasts. The area covered by rock increasing to a raft with an estimated thickness of at least 15 cm that extended to the horizon in different directions, and which took 6-8 hours to cross (figure 8). There was no sulfur smell and the sound was described as a "cement mixer, especially below deck." There was also no plume or incandescence observed. Their video, posted to YouTube on 17 August, showed a thin surface layer of cohesive interconnected irregular streaks of pumice with the ocean surface still visible between them. Later footage showed a continuous, undulating mass of pumice entirely covering the ocean surface. Larger clasts are visible scattered throughout the raft. The pumice raft was visible in satellite imagery on this day NW of Late Island (figure 9). By 11 August the raft had evolved into a largely linear feature with smaller rafts to the SW (figure 10). Approximately four hours later, about 15 km to the WSW, Rachel Mackie encountered the pumice. Initially the pumice was "ribbons several hundred meters long and up to 20m wide. It was quite fine and like a slick across the surface of the water." By 2130 they were surrounded by the pumice, and around 25 km away the smell of sulfur was noted.

Figure 8. The pumice raft from the unnamed Tongan seamount on 9 August 2019 taken by Shannon Lenz and Tom Whitehead on board SV Finely Finished. The photos show the pumice raft extending to the horizon in different directions. Scattered larger clasts protrude from the relatively smooth surface that entirely obscures the ocean surface. Courtesy of Shannon Lenz and Tom Whitehead via noonsite.

Figure 9. The pumice raft from the unnamed Tongan seamount on 9 August 2019 (UTC) can be seen NW of Late Island of Tonga in this Aqua/MODIS satellite image. The dashed white line encompasses the visible pumice. The location of the pumice in this image is shown in figure 7. Courtesy of NASA WorldView.

Figure 10. The Sentinel-2 satellite first imaged the pumice from the unnamed Tongan seamount on 11 August 2019 (UTC). This image indicates the pumice distribution with the main raft towards the W and the easternmost area of pumice approximately 45 km away. The eastern tip of the pumice area is located approximately 30 km WNW of Lake islands in Tonga. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

Michael and Larissa Hoult aboard the catamaran ROAM encountered the raft on 15 August (figure 11). They initially saw isolated clasts ranging from marble to tennis ball size (15-70 mm) at 18° 46′S, 174° 55'W. At around 0700 UTC (1900 local time) they noted the smell of sulfur at 18° 55′S, 175° 21′W, and by 0800 UTC they were immersed in the raft with visible clasts ranging from marble to basketball (25 cm) sizes. At this point the raft was entirely obscuring the ocean surface. On 16 and 21 August the pumice continued to disperse and drift NW (figures 12 and 13). On 20 August Scott Bryan calculated an average drift rate of around 13 km/day, with the pumice on this date about 164 km W of the unnamed seamount.

Figure 11. Images of pumice from the unnamed Tongan seamount encountered by Michael and Larissa Hoult aboard the catamaran Roam on 15 August. Left: Larissa takes photographs with scale of pumice clasts; top right: a closeup of a pumice clast showing the vesicle network preserving the degassing structures of the magma; bottom left: Michael holding several larger pumice clasts. The location of their encounter with the pumice is shown in figure 7. Courtesy of SailSurfROAM.

Figure 12. The pumice from the unnamed Tongan seamount (volcano number 243091) on 16 August 2019 UTC. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

Figure 13. On 21 August 2019 (UTC) the pumice from the unnamed Tongan seamount (volcano number 243091) had drifted at least 120 km WNW of Late Island in Tonga. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

An online article published by Brad Scott at GeoNet on 9 September reported the preliminary size of the raft to be 60 km2, significantly smaller than the 2012 Havre seamount pumice raft that was 400 km2. Satellite identification of pumice-covered areas by GNS scientists showed the material moving SSW through 14 August (figure 14).

Figure 14. A compilation of mapped pumice raft extents from 9 August (red line) through to 14 August (dark blue) from Suomi NPP, Terra, Aqua, and Sentinel-2 satellite images. The progression of the pumice raft is towards the SW. Courtesy of Salman Ashraf, GNS Science.

On 5 September the Maritime Safety Authority of Fiji (MSAF) issued a notice to mariners stating that the pumice was sighted in the vicinity of Lakeba, Oneata, and Aiwa Islands and was moving to the W. On 6 September a Planet Labs satellite image shows pumice encompassing the Fijian island of Lakeba over 450 km W of the Tongan islands (figure 15). The pumice entered the lagoon within the barrier reef and drifted around the island to continue towards the W. The pumice was imaged by the Landsat 8 satellite on 26 September as it moved through the Fijian islands, approximately 760 km away from its source (figure 16). The pumice is segmented into numerous smaller rafts of varying sizes that stretch over at least 140 km. On 12 September the Fiji Sun reported that the pumice had reached some of the Lau islands and was thick enough near the shore for people to stand on it.

Figure 15. Planet Labs satellite images show Lakeba Island to the E of the larger Viti Levu Island in the Fiji archipelago. The top image shows the island on 7 July 2019 prior to the pumice raft from the unnamed Tongan seamount. The bottom image shows pumice on the sea surface almost entirely encompassing the island on 6 September. The location of the pumice in this image is shown in figure 7. Courtesy of Planet Labs.

Figure 16. Landsat 8 satellite images show the visible extent of the unnamed seamount pumice on 26 September 2019 (UTC), up to approximately 760 km from the Tongan islands. The pumice seen here extends over a distance of 140 km. The top image shows the locations of the other three images in the white boxes, with a, b, and c indicating the locations. White arrows point to examples of the light brown pumice rafts in these images, seen through light cloud cover. The island in the lower right is Koro Island, the island to the lower left is Viti Levu, and the island to the top right is Vanua Levu. The location of the pumice in this image is shown in figure 7. Landsat 8 true color-pansharpened satellite images courtesy of Sentinel Hub.

Pumice had reached the Yasawa islands in western Fiji by 29 September and was beginning to fill the eastern bays (figure 17). By 9 October bays had been filled out to 500-600 m from the shore, and pumice had also passed through the islands to continue towards the W (figure 18). At this point the pumice beyond the islands had broken up into linear segments that continued towards the NW.

Figure 17. These Sentinel-2 satellite images show the pumice from the unnamed Tongan seamount drifting towards the Yasawa islands of Fiji. The 24 September 2019 (UTC) image shows the beaches without the pumice, the 29 September image shows pumice drifting westward towards the islands, and the 9 October image shows the bays partly filled with pumice out to a maximum of 500-600 m from the shore. These islands are approximately 850 km from the Tongan islands. The Yasawa islands coastline impacted by the pumice shown in these images stretches approximately 48 km. The location of the pumice in this image is shown in figure 7. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub.

Figure 18. This Sentinel-2 satellite image acquired on 9 October 2019 (UTC) shows expanses of pumice from the unnamed Tongan seamount that passed through the Yasawa islands of Fiji and was continuing NWW, seen in the center of the image. The location of the pumice in this image is shown in figure 7. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub.

Geologic Background. A submarine volcano along the Tofua volcanic arc was first observed in September 2001. The newly discovered volcano lies NW of the island of Vava'u about 35 km S of Fonualei and 60 km NE of Late volcano. The site of the eruption is along a NNE-SSW-trending submarine plateau with an approximate bathymetric depth of 300 m. T-phase waves were recorded on 27-28 September 2001, and on the 27th local fishermen observed an ash-rich eruption column that rose above the sea surface. No eruptive activity was reported after the 28th, but water discoloration was documented during the following month. In early November rafts and strandings of dacitic pumice were reported along the coast of Kadavu and Viti Levu in the Fiji Islands. The depth of the summit of the submarine cone following the eruption determined to be 40 m during a 2007 survey; the crater of the 2001 eruption was breached to the E.

Information Contacts: GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Salman Ashraf, GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/, https://www.geonet.org.nz/news/8RnSKdhaWOEABBIh0bHDj); Brad Scott, New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/, https://www.geonet.org.nz/news/8RnSKdhaWOEABBIh0bHDj); Scott Bryan, School of Earth, Environmental & Biological Sciences, Science and Engineering Faculty, Queensland University of Technology, R Block Level 2, 204, Gardens Point (URL: https://staff.qut.edu.au/staff/scott.bryan); Shannon Lenz and Tom Whitehead, SV Finely Finished (URL: https://www.noonsite.com/news/south-pacific-tonga-to-fiji-navigation-alert-dangerous-slick-of-volcanic-rubble/, YouTube: https://www.youtube.com/watch?v=PEsHLSFFQhQ); Michael and Larissa Hoult, Sail Surf ROAM (URL: https://www.facebook.com/sailsurfroam/); Rachel Mackie, OLIVE (URL: http://www.oliveocean.com/, https://www.facebook.com/rachel.mackie.718); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); Fiji Sun (URL: https://fijisun.com.fj/2019/09/12/pumice-menace-hits-parts-of-lau-group/).

The submarine Axial Seamount volcano is located about 470 km offshore of the Oregon coast. An eruption inferred to have started at 2230 on 23 April 2015 with an earthquake swarm (BGVN 40:03) was confirmed during a 14-29 August 2015 research cruise by the R/V Thompson. According to a personal communication on 23 June 2015 from Bill Chadwick (Oregon State University and NOAA), the length of the eruption is unknown, but it was "very likely days to weeks since the deflation lasted for about 10 days and the temperature signals lasted about a month."

The research cruise revealed new lava flows observed from bathymetric data and observations made during a remotely operated underwater vehicle ROV Jason dive. This eruption "produced the largest volume of erupted lava since monitoring and mapping began in the mid-1980's" (Chadwick and others, 2016). Two large lava flows from the N rift zone (8-16 km N of the summit caldera) were at most 127 m thick; some of the thicker areas had drained collapse features indicating molten interiors when emplaced. The ROV traversed the flows for about 2 km. New, thinner lava flows (figure 13) were also identified in the NE summit caldera and on the NE rim.

Figure 13. Collecting a fragment of lava from the 2015 eruption of Axial Seamount with an arm of the AUV. Credit: Monterey Bay Aquarium Research Institute (MBARI); from Phys.org (2016).

Three recently published papers, Chadwick and others (2016), Nooner and Chadwick (2016), and Wilcock and others (2016), detail the results of eruptive activity in 1998, 2011, and 2015, based on new data from a research cruise conducted after the 2015 eruption (figures 14 and 15). Scientists from the Monterey Bay Aquarium Research Institute (MBARI) issued a new seafloor map (figure 16) of the area of Axial north of the one shown in figure 14, based on underwater surveys conducted in August 2016, uncovering a number of previously undocumented flows from the 2015 eruption (Phys.org, 2016). MBARI ran identical sets of autonomous underwater vehicles (AUV) survey lines across the entire Axial caldera in 2011, 2014, 2015, and 2016, and during the 2016 survey the AUV collected seafloor samples (figure 13).

Figure 14. Map of the summit caldera of Axial Seamount. Locations of mobile pressure recorders (MPR) benchmarks (white circles) and bottom pressure recorders (BPR) instruments (red and blue circles) are indicated. Numbers show vertical displacements in centimeters at each of the MPR benchmarks between 14 September 2013 and 25 August 2015, a period that included pre-eruption inflation, co-eruption deflation, and post-eruption inflation. Numbers in parentheses show subsidence in centimeters during deflation only, as measured by the BPRs. BPRs on the Ocean Observatories Initiative (OOI) Cabled Array (red dots) include tiltmeters. The map also shows locations of 2015 lava flows and eruptive fissures (white outlines and red lines, respectively) and 2011 lava flows and eruptive fissures (gray outlines and yellow lines, respectively). From Nooner and Chadwick (2016).

Figure 15. Map of 2015 lava flows (black outlines) and new fissures (red lines) in the summit caldera of Axila Seamount and on the north rift zone. Also shown are 2011 lava flows (gray outlines) and eruptive fissures (yellow lines) on the south rift zone. Lava samples collected by ROV are shown by dots, colored according to their MgO content. Dashed white outline indicates a magma reservoir from multichannel seismic results, with a dotted white line separating zones of high melt (south) from crystal mush (north). Canadian American Seamount (CASM) vent field and implanted benchmark AX-101 are labeled. From Chadwick and others (2016).

Figure 16. Part of the new map of Axial Seamount produced by MBARI researchers. Black outlines show lava flows from 2015 eruption. From Phys.org (2016).

According to Wilcock and others (2016), the earthquake rates increases from less than 500 per day to as many as about 2000 per day prior to the eruption on 24 April 2015, then decreased rapidly over the next month following the seismic crisis to a background level of 20 per day. During the eruption there were 600 earthquakes measured every hour, and the seafloor at Axial dropped suddenly by about 2.4 m.

Precise pressure sensors measure vertical movements of the seafloor that take place as the volcano gradually inflates (see figure 14). Deformation of the Axial volcano seafloor as measured by pressure sensors (figure 17) indicated gradual inflation followed by rapid deflation during the three most recent eruptions in 1998, 2011, and 2015.

Figure 17. Deformation time series at the Axial Seamount caldera center, showing change in seafloor elevation as a function of time from 1998 to about May 2016. Long-term time series of inflation and deflation at the center of the caldera to 19 May 2016. Purple open dots represent mobile pressure recorder measurements (error bars indicate 1 SD); blue curves show bottom pressure recorder data (drift-corrected after 2000). The relative depth of data before and after the 1998–2000 gap in measurements is unknown. From Nooner and Chadwick (2016).

References: Chadwick, W.W., Jr., Paduan, J.B., Clague, D.A., Dreyer, B.M., Merle, S.G., Bobbitt, A.M., Caress, D.W., Philip, B.T., Kelley, D.S., and Nooner, S.L., 2016 (15 December), Voluminous eruption from a zoned magma body after an increase in supply rate at Axial Seamount, Geophysical Research Letters, v. 43, issue 23, pp. 12,063-12,070; DOI: 10.1002/2016GL071327.

Nooner, S.L., and Chadwick, W.W., Jr., 2016 (16 December), Inflation-predictable behavior and co-eruption deformation at Axial Seamount, Science, v. 354, issue 6318, pp. 1399-1403; DOI: 10.1126/science.aah4666.

Phys.org, 2016 (15 Dec), MBARI's seafloor maps provide new information about 2015 eruption at Axial Seamount (URL: https://phys.org/news/2016-12-mbari-seafloor-eruption-axial-seamount.html).

Wilcock, W.S.D., Tolstoy, M., Waldhauser, F., Garcia, C., Tan, Y.J., Bohnenstiehl, D.R., Caplan-Auerbach, J., Dziak, R.P., Arnulf, A.F., and Mann, M.E., 2016 (16 Dec), Seismic constraints on caldera dynamics from the 2015 Axial Seamount eruption, Science, v. 354, issue 6318, pp. 1395-1399; DOI: 10.1126/science.aah5563.

Geologic Background. Axial Seamount rises 700 m above the mean level of the central Juan de Fuca Ridge crest about 480 km W of Cannon Beach, Oregon, to within about 1400 m of the sea surface. It is the most magmatically robust and seismically active site on the Juan de Fuca Ridge between the Blanco Fracture Zone and the Cobb offset. The summit is marked by an unusual rectangular-shaped caldera (3 x 8 km) that lies between two rift zones and is estimated to have formed about 31,000 years ago. The caldera is breached to the SE and is defined on three sides by boundary faults of up to 150 m relief. Hydrothermal vents with biological communities are located near the caldera fault and along the rift zones. Hydrothermal venting was discovered north of the caldera in 1983. Detailed mapping and sampling efforts have identified more than 50 lava flows emplaced since about 410 CE (Clague et al., 2013). Eruptions producing fissure-fed lava flows that buried previously installed seafloor instrumentation were detected seismically and geodetically in 1998 and 2011, and confirmed shortly after each eruption during submersible dives.

Information Contacts: William Chadwick, Cooperative Institute for Marine Resources Studies (CIMRS), Oregon State University, and NOAA/PMEL Earth-Ocean Interactions Program, Hatfield Marine Science Center, 2115 S.E. OSU Dr., Newport, OR 97365, USA (URL: http://www.pmel.noaa.gov/eoi/).

The eruptive activity at Barren Island that began in October 2013 continued through at least mid-June 2014 (BGVN 39:07). Another eruptive cycle began in March 2015 and continued through 28 February 2016, based on MODIS/MODVOLC thermal anomalies. However, MIROVA hotspots were regular through mid-May 2016, and then sporadic throughout the rest of 2016. The next clear episode began on 15 January 2017 and continued through at least February 2017. Scientists aboard a research ship observed explosions, fire fountains, and lava flows in January 2017.

Activity during October 2013-June 2014. Evidence of renewed activity in the form of lava flows was seen in MODVOLC thermal anomaly data beginning on 12 October 2013. Thermal alert pixels were frequent through 12 February 2014, followed by single anomalies on 12 March and 20 April 2014. Ash plumes were also observed during January-April 2014. Thermal infrared MODIS data processed by the MIROVA system revealed frequent anomalies in April through early May 2014, and in late May to early June; another anomaly was seen in mid-June 2014.

Activity during July 2014-June 2015. No thermal anomalies were seen in MIROVA data for at least five weeks (figure 24), between early June and late July 2014, and then continuing intermittently through the first half of March 2015. The only reported plumes during this time were in the week of 3-9 September 2014 and 22-28 April 2015, but in each case as could not be identified in satellite imagery.

Figure 24. Thermal anomaly MIROVA radiative power data from Barren Island during 7 June 2014-6 June 2015. A weak mid-June 2014 anomaly is followed by intermittent weak activity during late July 2014 through mid-March 2015. A strong period of thermal anomalies in March and April 2015 decreased in intensity but continued into early June 2015. Courtesy of MIROVA.

A strong thermal signature resumed on 17 March 2015 (figure 24) and continued for about three weeks before decreasing in intensity. Lower-level thermal activity continued through the first half of June. Thermal anomalies seen in MODVOLC data also resumed on 17 March, and were frequent through 12 June. Eruptions of ash were observed during 5-7 and 12-13 June 2015, with plumes rising to an altitude of 2-3 km and drifting up to 55 km downwind (table 5).

Table 5. Ash plumes at Barren Island, June 2015-February 2016. Legend: Satellite=analysis of satellite images, wind=wind data. Data provided by the Darwin Volcanic Ash Advisory Centre.

Activity during July 2015-May 2016. Thermal activity paused again for approximately a month in the second half of June and first half of July 2015. Regular thermal anomalies in MODVOLC data stopped after 12 June and resumed on 16 July. Episodic clusters of anomalies with gaps of 1-3 weeks continued until 28 February 2016. Although MODVOLC data did not show thermal anomalies after February 2016, MIROVA data showed ongoing activity until approximately 17 May (figure 25).

A few ash plumes were seen during this period, on 19 August, 22 September, and 8-9 October 2015 (table 5). There were no reported plumes in November or December 2015, but were seen once again in January and February 2016. Plumes typically rose to an altitude of 1.5-2 km and drifted 45-100 km downwind; the longest plume extended 1665 km SW.

Figure 25. Thermal anomaly MIROVA log radiative power data from Barren Island during 21 February 2016-20 February 2017. Regular activity is evident from late February through mid-May 2016. After a gap of about two months, there are only infrequent anomalies through mid-January 2017, after which another episode of frequent anomalies began. Courtesy of MIROVA.

Activity during June 2016-February 2017. Eruptive activity apparently stopped around 16-17 May 2016 for at least seven weeks. MODIS thermal data captured by MIROVA showed a few anomalies (less than 20) from the second half of July through the first half of December 2016 (figure 25). Considering the remote location and rare direct observations at this island volcano, it is possible that the anomalies represent intermittent lava emissions. Regular thermal anomalies were recorded by both MIROVA and MODVOLC beginning on 15 January that were continuing at the end of February 2017.

The National Institute of Oceanography (NIO), part of the Indian Council of Scientific and Industrial Research (CSIR), reported activity on 23 January 2017. Scientists aboard a research vessel were collecting sea floor samples when they observed a sudden ash emission. The team moved closer, about 1.6 km from the volcano, and noted small eruptive episodes lasting 5-10 minutes. Ash emissions were visible in the daytime, and lava fountains feeding lava flows on the flanks were visible at night. The team revisited the volcano on 26 January and observed similar activity over four hours. They sampled sediments and water in the vicinity of the eruption and recovered volcanic ejecta.

Geologic Background. Barren Island, a possession of India in the Andaman Sea about 135 km NE of Port Blair in the Andaman Islands, is the only historically active volcano along the N-S volcanic arc extending between Sumatra and Burma (Myanmar). It is the emergent summit of a volcano that rises from a depth of about 2250 m. The small, uninhabited 3-km-wide island contains a roughly 2-km-wide caldera with walls 250-350 m high. The caldera, which is open to the sea on the west, was created during a major explosive eruption in the late Pleistocene that produced pyroclastic-flow and -surge deposits. Historical eruptions have changed the morphology of the pyroclastic cone in the center of the caldera, and lava flows that fill much of the caldera floor have reached the sea along the western coast.

Information Contacts: 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/); The National Institute of Oceanography (NIO), Council of Scientific and Industrial Research (CSIR), New Delhi, India (URL: http://www.nio.org/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

Intermittent weak explosions at Gamalama resulting in ash plumes have occurred for many decades, most recently in September 2012, December 2014, and July-September 2015 (BGVN 40:12). This report covers activity between 1 December 2015 and February 2017. Data were primarily drawn from reports issued by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Center for Volcanology and Geological Hazard Mitigation) and the Darwin Volcanic Ash Advisory Centre (VAAC).

During 1 January-6 March 2016, PVMBG noted that seismicity fluctuated but decreased overall; shallow volcanic earthquakes and signals indicating emissions appeared on 3 March and a series of deep volcanic earthquakes were detected on 6 March. The Alert Level remained at 2 (on a scale of 1-4), and visitors and residents were warned not to approach the crater within a 1.5-km radius.

PVMBG reported that, at 0628 on 3 August 2016, a weak explosion generated an ash plume that rose 500-600 m above the crater and drifted SE and S. Ash emissions decreased at 0655. Consistent with this, the Darwin VAAC, based on analyses of satellite imagery and wind model data, and information from PVMBG, reported that ash plumes reached a maximum altitude of 2.7 km (summit elevation is 1.7 km) and drifted S, SE, E, and NE. Ashfall was reported in areas on the SSE flank, including the Ake Huda area.

A news account (Jakarta Globe) stated that the Babullah Airport in Ternate, North Maluku, was closed for a day while volcanic ash was cleared from the runway (about 6 km ENE of the volcano). On 5 August PVMBG noted that seismicity continued to be elevated, although inclement weather prevented visual observations.

Geologic Background. Gamalama is a near-conical stratovolcano that comprises the entire island of Ternate off the western coast of Halmahera, and is one of Indonesia's most active volcanoes. The island was a major regional center in the Portuguese and Dutch spice trade for several centuries, which contributed to the thorough documentation of Gamalama's historical activity. Three cones, progressively younger to the north, form the summit. Several maars and vents define a rift zone, parallel to the Halmahera island arc, that cuts the volcano. Eruptions, recorded frequently since the 16th century, typically originated from the summit craters, although flank eruptions have occurred in 1763, 1770, 1775, and 1962-63.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as 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/); Jakarta Globe (URL: http://jakartaglobe.id/).

The submarine Kavachi volcano in the Solomon Islands south of Gatokae and Vangunu islands is frequently active but rarely observed. Consistent activity was reported for more than 4 years between November 1999 and August 2003. An 8-month period of quiet was broken with another explosive eruption above the ocean surface on 15 March 2004 (BGVN 30:03). No observations of ongoing activity are known over the next two years, though eruptions may have continued. Satellite imagery using the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) during 2006-2016 frequently revealed evidence of activity, on at least 35 days, using the Visible Near Infrared (VNIR) bands. Very little ASTER imagery is available for Kavachi during 2001-2005.

ASTER images on 27 February and 24 March 2006 (figure 13) show renewed activity. Vigorous upwelling along with turbulent ash-laden water and a sulfur odor was witnessed on 6 April 2007 (BGVN 32:07). An ASTER image on 15 June 2007 (figure 14) showed pulses of discolored water originating from the vent, confirming ongoing activity. A small area of discolored water was next seen in satellite imagery on 12 December 2007. A small plume of discolored water appeared in ASTER imagery again on 26 February 2008. On 20 March 2008 the Landsat 7 Enhanced Thematic Mapper captured an image of an ash-and-steam eruption plume extending about 25 km NNE towards Gatokae (figure 15). The next satellite evidence of discolored water plumes were on 7 October 2008.

Figure 13. ASTER VNIR satellite image showing a submarine plume of discolored water originating above the summit of Kavachi, 24 March 2006. There appears to be turbulence at the ocean surface and a possible line of pumice along the lower left edge of the discolored area. Courtesy NASA/METI/AIST/Japan Spacesystems, and U.S./Japan ASTER Science Team, ASTER via the Image Database for Volcanoes.

Figure 14. ASTER VNIR satellite image showing a submarine plume of discolored water originating above the summit of Kavachi, 15 June 2007. Distinct pulses of activity, possibly individual explosions at the bright surface origin spot, can be identified based on the increasing diffusion of suspended particulates with distance from the source. Courtesy NASA/METI/AIST/Japan Spacesystems, and U.S./Japan ASTER Science Team, ASTER via the Image Database for Volcanoes.

Figure 15. Satellite image showing an eruption plume from Kavachi on 20 March 2008 taken using the Enhanced Thematic Mapper on Landsat 7. Image modified using the "Percent Clip" option. Courtesy of USGS LandsatLook Viewer.

An image on 11 November 2009 showed a larger very bright spot above the summit, possibly indicating turbulent activity at the ocean surface. Evidence of activity became more frequent in 2010, with imagery showing plumes on 15 February, 19 March, 23 June, 11 September, and 30 November. Submarine plumes continued to be visible often in ASTER images the following year, on 1 January, 13 March, 9 May, and 16 October 2011. The next available satellite image with a discolored submarine plume from Kavachi was on 9 April 2012. Additional plumes were seen on 16 April, 3 June (figure 16), 31 August, and 26 November 2012.

Figure 16. ASTER VNIR satellite image showing a submarine plume of discolored water originating above the summit of Kavachi, 3 June 2012. There appears to be a small island or area of persistent ash-laden surface turbulence at the source of the plume. Courtesy NASA/METI/AIST/Japan Spacesystems, and U.S./Japan ASTER Science Team, ASTER via the Image Database for Volcanoes.

Intermittent satellite evidence of ongoing activity continued in 2013 with a discolored water plumes on 28 April, 15 June, 8 July, 25 August, 10 September, and 8 December. On 24 September 2013, Brennan Phillips of the University of Rhode Island passed within 2 km of the main peak onboard the M/Y Alucia but "did not see any visual eruptive activity on the surface."

Although the imagery is not conclusive, many of the ASTER images after 3 June 2012 appeared to show a small island. On 9 January 2014 the ASTER imagery was much clearer, providing greater visual evidence that eruptive activity had built a small island from which discolored water plumes were emanating (figure 17). A few weeks later, on 29 January, the Earth Observing 1 (EO1) Advanced Land Imager (ALI) obtained an image of a submarine plume (BGVN 39:07) and turbulent source area similar to those seen in ASTER imagery. Additional activity was in evidence on 21 March and 8 May.

Figure 17. ASTER VNIR satellite image showing a submarine plume of discolored water originating above the summit of Kavachi, 9 January 2014. A distinct small island or area of persistent ash-laden surface turbulence can be readily identified at the source of the plume. Courtesy NASA/METI/AIST/Japan Spacesystems, and U.S./Japan ASTER Science Team, ASTER via the Image Database for Volcanoes.

A cruise ship operated by EYOS Expeditions reported an eruption "at least four times" on 10 June 2014 (figure 18). The Expeditions' website noted that a staff member "spotted on the horizon discolored water and disturbances on the surface. As the vessel approached closer a few large plumes of water broke the surface about once every 10 minutes. Just before the ship left, however, [the] sea seemed to erupt and a massive plume of water and ash shot high into the air…." The island, or possibly an eruption exhibiting turbulence with abundant ash at the surface, appeared again on a 9 November 2014 image, and submarine plumes were evident in an 11 December 2014 image.

Figure 18. Photo of an eruption sequence from Kavachi on 10 June 2014 taken from a cruise ship. Courtesy of EYOS Expeditions.

An expedition for National Geographic in January 2015 took place during a rare lull in volcanic activity that enabled access to the volcano for mapping and sampling. B. Phillips reported that no eruptive activity was seen while at the summit location on 12-14 and 18 January 2015, but there was a large surface plume and lots of off-gassing from the crater rim; ASTER imagery confirmed a plume of discolored water on 12 January. Autonomous cameras deployed directly into the crater observed sharks, reef fish, and what appear to larvaceans (National Geographic, 2015).

Satellite imagery showed discolored submarine plumes on 18 October 2015, but then not again until 26 August 2016. Eruptions were witnessed on a second visit by B. Phillips for National Geographic during 31 October-1 November 2016 (see National Geographic, 2017). Activity consisted of phreato-magmatic explosions approximately every 7 minutes that sent steam, ash, and incandescent tephra up to 50 m above the ocean surface. There was an occasional larger eruption roughly every hour. A remotely operated surface "drone" with a GoPro camera was right at the edge of the explosion but remained functional. Small lava particles stuck to the PVC hull of the vehicle itself were recovered and given to the Marine Geological Samples Laboratory (MGSL) of the Graduate School of Oceanography (GSO), University of Rhode Island."

Bathymetric survey. A paper by Phillips and others (2016) following the January 2015 visit included medium-resolution bathymetry of the main peak (figure 19), along with benthic imagery, biological observations, petrological and geochemical analysis of samples from the crater rim, measurement of water temperature and gas flux over the summit, and descriptions of the hydrothermal plume structure. Based on the bathymetry, the summit was described by Phillips and others (2016) as being oblong with a pockmarked crater measuring approximately 75 x 120 m, and a rim rising to an average of 24 m depth. The deepest soundings on the peak were about 70 m and indicated asymmetrical terrain surrounded by almost uniform flanks with 18° slopes that descend to depths greater than 1,000 m. They confirmed the existence of a "southwest extension," or secondary summit rising to 260 m depth 1.3 km SW of the main summit.

Figure 19. Bathymetry of Kavachi submarine volcano and the summit crater (inset, lower right). Red circles indicate locations of water column profiles and benthic imagery. White diamonds locate baited drop cameras deployments. The blue line delineates the path of a surface drifter that measured temperature and atmospheric CO2, The contour map and the inset at lower right were created from approximately 85,000 depth soundings visualized and edited as a three-dimensional point-cloud using IVS Fledermaus. The location map (upper right) was created with Generic Mapping Tools (v 4.5) using data available from Marine Geoscience Data System's Global Multi-Resolution Topography Data Synthesis (v 3.1). From Philips and others (2016).

References: National Geographic, 2015, Sharks discovered inside underwater volcano (exclusive video) (URL: http://video.nationalgeographic.com/video/expedition-raw/150708-sciex-exraw-sharks-underwater-volcano; https://www.youtube.com/watch?v=0e3t18rrjOA).

National Geographic, 2017, Robot vs. Volcano: "Sometimes It's Just Fun to Blow Stuff Up" (exclusive) (URL: http://video.nationalgeographic.com/video/expedition-raw/170419-sciex-exraw-robot-vs-volcano-sometimes-just-fun-to-blow-stuff-up; https://www.youtube.com/watch?v=Ca0zAAIVK3E).

Phillips, B.T., Dunbabin, M., Henning, B., Howell, C., DeCiccio, A., Flinders, A., Kelley, K.A., Scott, J.J., Albert, S., Carey, S., Tsadok, R., and Grinham, A., 2016. Exploring the "Sharkcano": Biogeochemical observations of the Kavachi submarine volcano (Solomon Islands), Oceanography v. 29(4), p. 160-169 (https://doi.org/10.5670/oceanog.2016.85).

Geologic Background. Named for a sea-god of the Gatokae and Vangunu peoples, Kavachi is one of the most active submarine volcanoes in the SW Pacific, located in the Solomon Islands south of Vangunu Island about 30 km N of the site of subduction of the Indo-Australian plate beneath the Pacific plate. Sometimes referred to as Rejo te Kvachi ("Kavachi's Oven"), this shallow submarine basaltic-to-andesitic volcano has produced ephemeral islands up to 1 km long many times since its first recorded eruption during 1939. Residents of the nearby islands of Vanguna and Nggatokae (Gatokae) reported "fire on the water" prior to 1939, a possible reference to earlier eruptions. The roughly conical edifice rises from water depths of 1.1-1.2 km on the north and greater depths to the SE. Frequent shallow submarine and occasional subaerial eruptions produce phreatomagmatic explosions that eject steam, ash, and incandescent bombs. On a number of occasions lava flows were observed on the ephemeral islands.

Information Contacts: EYOS Expeditions, Knox House, 16-18 Finch Rd, Douglas, Isle of Man, IM1 2PT (URL: http://www.eyos-expeditions.com/2014/07/kavachi-volcano/, https://my.yb.tl/eyosexpeditions/1604/); Brennan Phillips, Harvard University, Wyss Institute for Biologically Inspired Engineering, Wood Lab, 60 Oxford St., Cambridge, MA 02138 USA; Image Database for Volcanoes, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST) (URL: https://gbank.gsj.jp/vsidb/image/index-E.html, https://gbank.gsj.jp/vsidb/image/Kavachi/aster_p1.html); USGS LandsatLook Viewer (URL: https://landsatlook.usgs.gov/).

Intermittent ash explosions during the last century have characterized activity at Japan's Kuchinoerabujima volcano, located at the northern end of the Ryukyu Islands approximately 260 km S of Nagasaki, Japan. Brief periods of higher seismicity had been detected in the last approximately 30 years, although no explosions had been recorded since 1980 (BGVN 35:11 and 38:01). A new explosion occurred on 3 August 2014, and activity remained elevated through June 2015. Information on the latest activity is provided by the Japan Meteorological Agency (JMA) monthly reports and aviation alerts are from the Tokyo Volcanic Ash Advisory Center (VAAC).

A modest explosion from Shindake crater on 3 August 2014 caused JMA to increase the Alert Level at the volcano. Activity decreased shortly after the explosion, and only steam plumes, fumarolic activity, and occasional incandescence were observed for the next nine months. A large explosion on 29 May 2015 generated a gray-black ash plume that rose to over 9 km altitude and sent pyroclastic flows down the flanks; JMA increased the Alert Level and ordered evacuation of local residents. Activity declined after a few days, and Shindake remained quiet until a smaller explosion on 18 June 2015. The ash plume did not exceed 1 km, but ashfall was reported in towns on neighboring islands and in areas up to 80 km E. Two additional smaller explosions were reported on 18 and 19 June. Seismicity decreased significantly after the 19 June explosion, but SO₂ emissions remained elevated until October 2015. The JMA did not lower the Alert Level until June 2016.

Activity during August 2014-February 2015. JMA reported an eruption from the vicinity of Shindake crater around noon local time on 3 August 2014, with a gray plume rising more than 800 m above the crater rim. This led to an increase in the Alert Level from 1 (Normal) to 3 (Do not approach the volcano) on a 5-level scale. An overflight confirmed traces of ash on the W flank. The Tokyo VAAC reported that the plume rose to an altitude greater than 1.5 km and drifted N. On 5 August, seismicity decreased, and views from a remote web camera showed a white plume rising 50 m above the crater rim. For the rest of August, seismicity remained low and steam plumes rose 50 to 800 m above the crater.

During September 2014, white plumes were generally observed 200-800 m above the crater when visibility was not obscured by weather; seismicity remained low. Scientists conducting a field survey on 12 September found SO₂ emissions at 300 metric tons per day (t/d), higher than the background value of 60 t/d measured on 21 May 2014. Occasional earthquakes were recorded in October 2014, and the volume of gas emissions remained relatively high compared with before the August eruption; steam-and-gas plumes rose to 600 m above the crater rim. During field surveys on 7 and 8 October scientists measured SO₂ emissions of 500 t/d. Gas emissions rose from within the Shindake crater, around a thermally anomalous fissure at the W edge of the crater, as well as from a new fumarole on the SW flank of the crater. In November, plumes continued to rise as high as 1,000 m above the crater. In another survey on 9 December 2014, scientists found that SO₂ levels had increased to 1,700 t/d.

Emissions of SO₂ remained high during the second half of January 2015, ranging from 1,100 to 3,100 t/d. A M 2.2 seismic event located 5 km beneath the island was recorded on 24 January. Observations made during field surveys in February confirmed continued steam emissions, and thermal anomalies from the W crater rim fissure and the new fissure on the SW flank. SO₂ emissions decreased slightly from January levels to a range of 400 to 2,700 t/d in February, and steam plumes continued to rise 400-700 m above the crater.

Activity during March-June 2015. Incandescence at night was first recorded at the Shindake Crater from 24 to 31 March 2015 with a high-sensitivity camera. Aerial observation on 25 March by JMA and JCG (Japan Coast Guard) indicated a temperature rise and continued fumarolic activity around the thermal anomaly W of the crater rim. SO₂ emissions remained high in March (1,000 to 3,700 t/d) and April (900 to 2,600 t/d), and steam plumes rose to 1 km above the crater. Incandescence was occasionally observed at night during April and again during 18-22 May; fumarolic activity continued along with a rise in temperature at the W and SW fissures. Steam plumes were observed rising to 600 m above the crater in May.

According to JMA, at 0959 local time on 29 May 2015, a large explosive phreatomagmatic eruption generated a gray-black ash plume that rose to over 9 km altitude and drifted ESE (figure 5). The plume was reported by the Tokyo VAAC to be at 10.9 km altitude about an hour after the eruption. The largest of several pyroclastic flows descended NW from the SW side of the crater in the Mukaehama district and reached the coast. Based on these events, JMA raised the Volcanic Alert Level to 5 (Evacuate). Aerial observation conducted on the same day (in collaboration with the Kyushu Regional Bureau of the Ministry of Land, Infrastructure, Transport and Tourism) revealed additional pyroclastic flows moving in nearly all directions from the Shindake crater (figure 6) including flows reaching halfway down the mountain to the SW and SE of the crater. Seismicity increased immediately after the eruption, but had decreased by midday.

Figure 5. Ash plume from Kuchinoerabujima's Shindake Crater during an explosion on 29 May 2015. The plume height was reported by the Tokyo VAAC as 10.9 km altitude. Photo taken from the neighboring island of Yakushima by Itaru Takaku. Courtesy of Kyodo News and The Japan Times.

Figure 6. Google Earth imagery dated 5 June 2015, one week after a large explosion which generated several pyroclastic flows around the summit crater at Kuchinoerabujima. Note the brown areas extending in most directions away from the summit crater (beneath the white clouds), all the way to the coast on the NW and W flanks that are the result of the pyroclastic flows that occurred on 29 May 2015. Courtesy of Google Earth.

According to a news article (The Japan Times), all residents and visitors (141 people) were safely evacuated by a ferry, coast guard ship, and helicopter to neighboring Yakushima Island (25 km SE). A resident of Yakushima reported that ash reached the island. Later that day, ash plumes rose 200 m and drifted SW.

Ash plumes continued the next day, 30 May, rising only 1.2 km. A field team observed discolored trees on the SE and SW flanks, and fallen trees near the coast on the NW flank. Cloud cover prevented views of the eruption area, but the team was able to confirm continued fumarolic activity and incandescence in the W part of the crater. Seismicity continued at low levels, and during the first week of June white plumes rose 100-400 m above the crater rim.

Another smaller eruption on 18 June 2015 caused lapilli and ash to fall on the E side of the island. Ash was reported in Yakushima Town (44 km ESE on Yakushima Island), Nishinoomote City (80 km NE on Tanegashima Island), and Nakatane Town (72 km E on Tanegashima). Small eruptions also occurred at 1631 on 18 June and at 0943 on 19 June. Tokyo VAAC reported the larger 18 June eruption, but plume heights were below 1 km, and not observed on satellite. Aerial observations on 20 June by JMA revealed no traces of new pyroclastic-flow deposits around the crater or on the flanks.

Post-eruption observations through June 2016. Emissions of SO₂ remained elevated during June 2015 (800-1,700 t/d), and decreased somewhat in July to 500-700 t/d. They decreased further to 200-300 t/d in August. Increased seismicity was recorded briefly from 1-3 and 6-11 August. SO₂ emissions continued to decline in September, except for a spike of 700 t/d on 10 September. Thermal infrared observations taken during a field survey in October 2015 indicated a decrease in temperature around the fissure W of the crater rim since the 29 May eruption. Emissions of SO₂ remained below 300 t/d for the remainder of 2015 and no further activity was reported, although the Alert Level remained at 5. On 14 June 2016, JMA lowered the Alert Level to 3; seismic activity and SO₂ flux values were below levels detected prior to the May-June 2015 eruption.

Geologic Background. A group of young stratovolcanoes forms the eastern end of the irregularly shaped island of Kuchinoerabujima in the northern Ryukyu Islands, 15 km W of Yakushima. The Furudake, Shindake, and Noikeyama cones were erupted from south to north, respectively, forming a composite cone with multiple craters. The youngest cone, centrally-located Shindake, formed after the NW side of Furudake was breached by an explosion. All historical eruptions have occurred from Shindake, although a lava flow from the S flank of Furudake that reached the coast has a very fresh morphology. Frequent explosive eruptions have taken place from Shindake since 1840; the largest of these was in December 1933. Several villages on the 4 x 12 km island are located within a few kilometers of the active crater and have suffered damage from eruptions.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Google Earth (URL: https://www.google.com/earth/); The Japan Times (URL: http://www.japantimes.co.jp/news/2015/05/29/national/volcano-erupts-isle-kagoshima-prompting-evacuation-order/).

The remote island of Manam, 13 km off the northern coast of mainland Papua New Guinea is a basaltic-andesitic stratovolcano that has a 400-year history of recorded evidence for recurring low-level ash plumes and occasional Strombolian emissions, lava flows, pyroclastic avalanches, and large ash plumes. Pyroclastic flows and Strombolian activity during much of 2012 and 2013 were accompanied by numerous ash plumes rising a few kilometers above the summit (BGVN 38:06, 39:08). Activity between January 2014 and January 2017, described below, includes persistent thermal anomalies during most of this time, and a major ash plume rising to nearly 20 km altitude on 31 July 2015.

Monitoring is done by Papua New Guinea's Rabaul Volcano Observatory (RVO), part of the Department of Mineral Policy and Geohazards Management (DMPGM). This information is supplemented with aviation alerts from the Darwin Volcanic Ash Advisory Center (VAAC). MODIS thermal anomaly satellite data is recorded by the University of Hawai'i's MODVOLC thermal alert recording system, and the Italian MIROVA system.

MIROVA thermal anomaly data suggests Manam was intermittently active from at least late June 2014 through the end of the year. A single ash plume was reported on 6 September and two more were observed on 21 and 22 December. The appearance of MODVOLC thermal anomalies in late January 2015 that grew more frequent through April indicated increasing activity along with sporadic low-level ash plumes in late February and late April. Persistent levels of thermal anomalies and ash plume reports continued in May through early July.

On 31 July 2015 at about 1130 local time a large explosion sent an ash plume to nearly 20 km altitude, spreading volcanic blocks and ash over a wide area, and injuring two people. A second substantial ash plume rose to 6.4 km on 8 August. This was followed by three more small plumes in August, one in September, and two in October 2015 (on 8 and 29) before the volcano quieted down for a few months.

Thermal anomalies were present at the end of January 2016, and an ash plume was observed on 4 March 2016. New thermal anomalies intensified until June and then tapered off in early July. Persistent but more intermittent thermal anomalies continued throughout the year and were ongoing as of early January 2017.

Activity during 2014. Numerous explosions during 2013 tapered off at the end of the year, with the last ash emissions reported on 15 December 2013. In January 2014, RSAM values were lower but still fluctuating above background levels. A report from RVO in early April noted that both summit craters remained quiet through March 2014, with no audible noises or incandescence visible at night. The seismicity remained within background levels of 160-180 RSAM and daily volcanic event counts ranged from 830 to 920. Tiltmeter data showed no significant short-term changes, but over the previous three months there was a gradual inflationary trend towards the summit area. The Alert Level was lowered to Stage 1.

A thermal anomaly appears at the very end of June 2014 in the first available MIROVA LRP data (figure 30). This is followed by additional thermal anomalies in August, October, and November. The Darwin VAAC reported a small ash plume on 6 September 2014 that rose to 2.1 km altitude (300 m above the summit) and drifted 37 km NW. It was visible on infrared satellite imagery for a few hours before dissipating. In their report for October 2014, RVO noted that Manam remained quiet for the month with no audible noises or incandescence; seismicity remained at low to moderate levels, and daily volcanic-event counts ranged between 860 and 920. They also observed that the long-term inflationary trend at the summit observed since the beginning of 2014 continued. Small amounts of white-gray ash drifting SE were reported by RVO on 21 and 22 December from the Southern Crater, with a plume height of only 200 m. They also noted continued E-W inflation.

Figure 30. MIROVA Log VRP data for Manam from 22 June 2014 through 22 June 2015. Intermittent thermal anomalies are recorded at the end of June, early and late August, early October, and mid-November 2014. Thermal activity increased in frequency and intensity starting in the second half of January 2015. Courtesy of MIROVA.

Activity during 2015. RVO noted incandescence from the Main Crater beginning on 19 January 2015, growing stronger during the last week of the month, matching observations in the MIROVA data (figure 30). A MODVOLC thermal alert pixel appeared on 23 January. Seismicity also changed after the middle of the month when RSAM values rose above 200 on 16 January and went as high as 500 on 31 January, after which they declined rapidly and remained low during February.

In February 2015, seismicity was characterized by small to moderate sub-continuous and continuous volcanic tremors. Increased incandescence was also evident from the Main Crater during February. RVO reported weak-to-bright steady incandescence during 7-10, 21, and 26 February. MODVOLC captured two thermal alert pixels on 8 February, and MIROVA reported an anomaly at the end of the first week and during the last week of the month. An ash plume was observed in satellite data by the Darwin VAAC on 24 February; the plume rose to 3 km altitude (1.2 km above the summit) and drifted 37 km W. RSAM values rising to 500 by 18 March led RVO to raise the Alert Level that day to Stage 2. Visual observations were difficult due to weather during much of the month, but MODVOLC reported thermal alert pixels on 19 and 26 March, and MIROVA captured several anomalies at the beginning of a period of increased frequency and intensity of thermal anomalies that lasted through mid-June (figure 30).

RVO reported that during April 2015 both craters released variable amounts of white vapor. Clearer skies revealed incandescence from the Southern Crater during nine nights of the month and seven times from the Main Crater. This is consistent with satellite thermal anomaly observations by MODVOLC on six different days, with four of them being multiple pixel alerts, and numerous anomalies captured by MIROVA. Two ash eruptions were reported by the Darwin VAAC on 27 and 30 April. The first low-level plume rose to 2.4 km and was observed in satellite imagery extending over 100 km to the W before dissipating on 28 April. The second plume was observed at the same altitude drifting 150 km NW. Seismicity remained high during April, still characterized by discreet small to moderate low-frequency earthquakes, and RSAM values ranged between 300 and 650, increasing during the month. Ground deformation GPS measurements at the end of April confirmed the continuing inflationary trend recorded by the electronic tiltmeters since the last measurements taken in May 2013 (figure 31).

Figure 31. Electronic tilt measurements at Manam between 26 February 2011 and 1 May 2015 show a continuing inflationary trend. Eruptions in August 2012 and January 2013 are shown by red arrows. Courtesy of RVO (Volcano Information Bulletin 01-042015, 4 May 2015).

Multiple sources of satellite data confirmed that Manam was active during May 2015. MODVOLC thermal alert pixels were reported from MODIS data captured on 6 and 22 May; MIROVA thermal anomalies were frequent. Ash plumes were reported from visible satellite imagery by the Darwin VAAC on 13 May at 3 km altitude drifting 37 km NE; SO₂ plumes were captured by NASA's OMI instrument on the Aura satellite on 2, 12, 13, and 20 May (figure 32).

Figure 32. SO2 plumes captured by NASA's OMI instrument on the Aura satellite for Manam during May 2015. Clockwise from top left: 2 May, 12 May, 13 May, and 20 May. Missing data (gray stripes) are due to OMI row anomaly. Courtesy of NASA/GSFC.

During June and early July 2015 there were four series of Volcanic Ash advisory reports from the Darwin VAAC. The first, on 21 and 22 June, reported a 3-km-altitude ash plume that extended over 35 km N and NW. The second, from 28 to 30 June, had altitudes that started at 2.4 and rose to 3 km, and drifted 75 km NE. A third plume emerged late on 30 June and lasted through 1 July, drifting 130 km E at 2.4 km altitude. A fourth plume reported on 2 July was confirmed by RVO as only a steam plume with no ash, and was seen in satellite imagery drifting 45 km E at 2.4 km altitude. A single MODVOLC thermal alert pixel was recorded on 7 July.

RVO reported a significant eruption on 31 July 2015 from the Southern Crater beginning about 1130 local time. They observed that low roaring noises marked the onset of the explosion followed by continuous ejection of scoria until about 1330. Fist-sized volcanic debris was reported at Warisi village on the E side of the island. At Baliau on the N side, clasts were about 10-20 cm in diameter. Two people were reportedly knocked unconscious from the falling scoria. Strong emissions of dark gray ash clouds followed the ejection of scoria and continued into the early afternoon. By 1740 emissions consisted of light gray ash clouds. The news source One Papua New Guinea reported that fine ash began to fall over Bogia (25 km SW on the mainland) around 1245 local time.

The ash plume was initially observed in satellite imagery by the Darwin VAAC at 19.8 km altitude spreading out in all direction for 100 km. It was captured by the Japanese Himawari-8 satellite (figure 33); an animation of the imagery showing the eruption was provided by Miller et al. (2016). Four hours later, the plume was visible 370 km to the SW. A lower-altitude ash plume at 6.7 km was observed the next day extending over 100 km SW. A significant SO₂ plume was partially captured by the Aura instrument on the OMI satellite the next day, and measured an SO₂ mass of 3.206 kilotons.

Figure 33. Ash cloud from Manam captured with True Color imagery by the Himawari-8 satellite on 31 July 2015 at 1150 local time, showing ash dispersing in all directions shortly after the explosion. Data courtesy of JMA (Japan Meteorological Agency), annotated image courtesy of RAMMB/CIRA (in Q4 report for 2015). An animation of the imagery showing the eruption is provided by Miller et al. (2016).

The Darwin VAAC reported a new small ash plume on 6 August 2015 rising to 2.7 km drifting around 40 km to the NW, and another large ash plume on 8 August that initially rose to 6.4 km and drifted SSW. Pilots reported the ash at 5.8 km altitude about 90 km W of Kiunga Airport which is located 475 km SW of Manam. About 24 hours later, pilots reported another ash plume at 6 km altitude 150 km SE of the volcano. A hot spot was observed at the summit on 9 August; two MODVOLC thermal alert pixels appeared that day, and another one appeared on 15 August. A small plume was reported on 21 August, only rising to 2.1 km and drifting about 8 km ESE. This was followed two hours later by an ash plume observed 16 km NW at the same altitude, which continued to drift NW to 75 km before dissipating. Additional ash plumes were reported from 26-28 August rising to 2.4 km and drifting from 35 to 75 km, first NE, then N and NW; a small plume was reported on 31 August at 2.1 km drifting 75 km N before dissipating that day.

A single MODVOLC thermal alert pixel on 4 September was the last recorded in 2015. The next plume on 7 September was small, rising only to 2.1 km and drifting 75 km NW, briefly observed in one satellite before dissipating. It was a month until the next ash plume on 8 October 2015, when Darwin VAAC made a satellite observation of a plume at 1.8 km drifting 45 km NW. The last ash plume of 2015 was captured in satellite images on 29 October between 2.1 and 2.4 km altitude around 35 km NW.

Activity during 2016. The MIROVA data recorded thermal activity on about 29 January 2016 that increased in intensity and frequency in early March (figure 34). A small ash plume on 4 March rose to 3 km altitude and drifted about 90 km SE according to the Darwin VAAC. Increased thermal activity was recorded in MODVOLC thermal alert pixels and MIROVA data from early March through mid-July. There were no reports from the RVO during this time. The first MODVOLC alert was recorded on 7 March and they were persistent, almost every week, through the second week of July. On 13 July, an ash plume was observed by the Darwin VAAC in satellite imagery at 3 km altitude drifting 55 km W for a few hours before dissipating. After that, single-pixel MODVOLC thermal alerts were recorded on 20 September and 6 October. The MIROVA analysis of the MODIS data records a similar picture with a clear increase in the frequency and intensity of anomalies between early March and mid-July (figure 34); continuing pulses of thermal anomalies are present every month into January 2017.

Figure 34. Log Radiative Power from MODIS thermal anomaly data recorded by MIROVA for Manam between 19 January 2016 and 18 January 2017. The increased frequency and intensity of thermal anomalies between early March and mid-July agrees well with other indicators of volcanic activity. Additionally, the MIROVA data suggests continued intermittent activity through 18 January 2017. Courtesy of MIROVA.

Reference: Miller S D, Schmit T L, Seaman C J, Lindsey D T, Gunshor M M, Kohrs R A, Sumida Y, Hillger D, 2016, A Sight for Sore Eyes: The Return of True Color to Geostationary Satellites, Bulletin of the American Meteorological Society, vol. 97, no. 10. DOI: http://dx.doi.org/10.1175/BAMS-D-15-00154.1. Animated imagery of the 31 July 2015 eruption can be viewed at http://journals.ametsoc.org/doi/suppl/10.1175/BAMS-D-15-00154.1/suppl_file/10.1175_BAMS-D-15-00154.2.html .

Geologic Background. The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical 1807-m-high basaltic-andesitic stratovolcano to its lower flanks. These "avalanche valleys" channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island's shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most historical eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent historical eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; 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 Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Regional and Mesoscale Meteorology Branch (RAMMB) / Cooperative Institute for Research in the Atmosphere (CIRA), NOAA/NESDIS, Colorado State University, Fort Collins, CO 80523-1375, USA (URL: http://rammb.cira.colostate.edu/); One Papua New Guinea (URL: http://www.onepng.com/2015/07/manam-volcano-erupts.html).

Pavlof volcano, near the end of the Alaska Peninsula 970 km SW of Anchorage, frequently produces explosive eruptions from the summit vents and occasional lava flows. The largest confirmed historical eruption took place in 1911 when a fissure opened on the N flank; it has erupted more than 25 times since then. The last reported eruption in mid-November 2014 included lava fountaining from a vent just N of the summit, and flows of rock debris and ash descending the N flank, along with an ash plume that rose to around 9 km altitude and drifted 300 km NW. Pavlof was quiet in 2015, but then abruptly renewed activity in late March 2016. It is monitored primarily by the Alaska Volcano Observatory (AVO) and the Anchorage Volcanic Ash Advisory Center (VAAC).

A sudden vigorous eruption that began on 27 March 2016 lasted for about 20 hours, sending ash to 11 km altitude, producing a plume dispersed NE for 1,200 km, and a similarly large SO₂ plume. The volcano was then quiet until a short-lived, smaller ash emission occurred in mid-May for eight days. Intermittent low-level ctivity picked up again from late June through late July 2016, characterized by minor emissions of dark-colored ash and steam rising to 4.5 km altitude. Fallout of ash was limited to the flanks of the volcano and the immediate area around Pavlof. The last report of ash emissions was on 30 July, although low-amplitude tremors and steam plumes persisted through August, and intermittent thermal anomalies from the summit continued through the end of 2016.

After a short and intense eruption between 12 and 15 November 2014 (BGVN 40:04), activity decreased quickly to background levels. The AVO had reduced the Aviation Color Code (ACC) from Red (highest) to Orange on 16 November, and from Orange to Yellow on 25 November. Seismicity remained slightly above background levels until early January. On 15 January 2015 the AVO reduced the ACC to the lowest level of Green where it remained for over a year until it was changed abruptly to Red on 28 March 2016 at the start of a new eruption.

AVO reported that seismicity began to increase at 1553 on 27 March 2016, characterized by a quick onset of continuous tremor. An ash plume rose to an altitude of 6.1 km, and by 1618 was drifting N (figure 13). During the night, lava fountaining from the summit crater was observed by mariners, pilots, and residents of nearby Cold Bay (60 km SW).

Figure 13. Pavlof erupts, sending a plume of volcanic ash into the air on the evening of 27 March 2016 (AKDT) as photographed by a passenger on a plane travelling to Anchorage from Dutch Harbor. Courtesy of Colt Snapp.

On 28 March, tremor levels remained high; lightning in the ash plume was detected in the morning, and infrasound data from a sensor network in Dillingham (470 km NE) indicated sustained ash emissions. At 0700 a continuous ash plume was evident in satellite images drifting more than 650 km NE, and a MODIS image captured at midday revealed the extent and substantial thickness of the cloud (figure 14). A SIGMET (significant meteorological information notice) issued by the National Weather Service (NWS) Alaska Aviation Weather Unit indicated that the maximum ash-cloud altitude was approaching 11 km. Strongly elevated surface temperatures also suggested the presence of lava flows.

Figure 14. The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on a NASA satellite acquired this image of the ash plume from Pavlof at 1145 Alaska time (2145 UTC) on 28 March 2016 extending several hundred km to the NE. Courtesy of NASA Earth Observatory.

The energetic ash-producing phase of the eruption lasted from 1600 AKDT (00:00 UTC) on 27 March until about 1230 AKDT (20:30 UTC) on 28 March, and produced an ash cloud that stretched NE over Bristol Bay and interior Alaska for over 1,200 km. As a result, over 40 Alaska Airlines flights to and from Fairbanks, Alaska, were cancelled according to NBC News. Minor ashfall (0.8 to 6.3 mm or 1/32 to 1/4 in) was reported in the nearby community of Nelson Lagoon (80 km NW) and trace ashfall (less than 0.8 mm) was confirmed near Dillingham (470 km NE). A large SO₂ plume also drifted NE from the volcano extending all the way across Alaska to Yukon Territory and British Columbia in Canada (figure 15).

Figure 15. A large SO2 plume trails NE from Pavlof on 28 March 2016 after a substantial explosion sent an ash plume to nearly 12 km altitude. The ash cloud and the SO2 plume both extended for 1,200 km NE across interior Alaska. Courtesy of NASA/GSFC.

Seismicity and infrasound signals had decreased to low enough levels by 1230 on 28 March that the AVO lowered the Aviation Color Code to Orange and the Volcano Alert Level to Watch. However, seismic tremor remained above background levels. Ash emissions decreased through the night and were barely visible in a satellite image acquired at 0625 AKDT on 29 March. Remnant ash continued to drift over Bristol Bay and areas of interior Alaska. The webcam at Cold Bay recorded intermittent, low-level ash plumes rising as high as 4.6 km.

Thermal anomalies, measured by MODIS satellite sensors and analyzed by MODVOLC, appeared from 28 March (0025 UTC) through 29 March 2016 (1360 UTC), with 20 pixels recorded on 28 March. The MIROVA system also recorded an abrupt spike to 'Very High' thermal anomaly levels on 28 March, dropping slightly in the next two days (figure 16) and then disappearing a few days later. Low-power anomalies were detected on 2 and 6 April, and then ceased for several months.

Figure 16. MIROVA Log Radiative Power data for Pavlof between 28 December 2015 and 28 December 2016. Note the 'Very High' level spike in Log Radiative Power during 28-30 March 2016. Values dropped significantly in early April and then disappeared for several months. Low VRP values reappeared in late August and were intermittent for the remainder of 2016. AVO determined that the summit crater was enlarged as a result of the March 2016 explosion; the new crater geometry possibly allowed satellite sensors to more easily detect emissions of hot gases from the vent. Ongoing observations of moderately elevated surface temperatures between August and December 2016 likely reflect this change in the crater, and do not indicate new eruptive activity or rising magma, according to AVO scientists. Courtesy of MIROVA.

The AVO reported that the intensity of the eruption greatly decreased during 29-30 March, although The Canadian Press reported that ash from the eruption had caused flights in and out of Yellowknife and Regina, Canada, to be cancelled on those dates. Elevated surface temperatures identified in satellite data and visual observations of low-level, intermittent ash plumes were noted during brief breaks in poor weather conditions during these days. Airwave signals, indicative of small explosions at the summit, were recorded on 3 April, but tremors had ceased by the next day. On 6 April AVO noted no signs of ash emissions or lava effusion during the previous week, and seismicity was at low levels. Thermal anomalies at the summit were occasionally visible, though likely indicating cooling processes of previously erupted lava. AVO lowered the Aviation Color Code to Yellow and Volcano Alert Level to Advisory on 6 April. After two more weeks of no activity, the ACC was lowered to Green/Normal on 22 April 2016.

On 13 May 2016 the AVO raised the Aviation Color Code back to Orange as a result of increased seismicity typically associated with minor eruptive activity. Four minor ash eruptive episodes were inferred from seismic data between 13 and 16 May. On 14 May, local observers in Cold Bay reported ash emissions below 5 km in the vicinity of the volcano. According to the Anchorage VAAC, on 15 May a minor eruption was noted on the Cold Bay web camera, but volcanic ash was not visible in satellite data. Elevated surface temperatures were detected in satellite data on 15 May. Periods of elevated volcanic tremor and a small explosion associated with minor ash emissions was noted on 17 May; observers in Cold Bay and Sand Point (90 km E) reported ash emissions interspersed with steam emissions. The Anchorage VAAC noted that strong winds caused resuspension of volcanic ash on the lee side of Pavlof on 17 and 18 May. The AVO lowered the ACC to Yellow on 20 May and noted that all volcanic ash clouds produced during the 13-17 May event were below 4.5 km altitude, and that no lava effusion or fountaining was detected. Weak seismic tremor and small explosions were observed on 21 May, after which activity ceased. The AVO lowered the ACC to Green on 17 June.

Seismic activity increased again on 30 June for about a week, prompting the AVO to raise the ACC to Yellow on 1 July 2016; minor steam emissions were also observed in the web camera. AVO technicians installed a new web camera in the Black Hills area north of the volcano near the Bering Sea coast in early July. On 11 July, weakly elevated surface temperatures were observed at the summit in satellite imagery and a steam and gas cloud extended SW for about 80 km. Minor ash emissions reaching a few tens of meters above the summit were observed that afternoon extending a few kilometers to the SW. Small ash emissions were again observed on 18 July along with an increase in seismic tremor for about 48 hours.

On 28 July a low-intensity eruption with vigorous degassing produced a steam-rich plume and minor ash emissions. As a result, the AVO raised the ACC to Orange. The drifting steam and ash cloud was below 4.6 km above sea level and dissipated rapidly. The Anchorage VAAC reported steam and minor ash emissions continuing through 30 July.

A decline in activity led AVO to lower the ACC to Yellow on 4 August. Periods of low-amplitude tremor continued, but no plumes or thermal signals at the summit were detected. Elevated surface temperatures at the summit were observed in satellite data on 8 August, and a low-level but persistent steam plume was visible in web camera images on 11 August. A large steam plume was noted by observers in Sand Point on 15 August. Elevated surface temperatures were detected through cloud cover in satellite data on 20 and 25 August. Low-level unrest continued through the fall with persistent degassing from the summit and elevated surface temperatures detected in satellite data. A robust steam plume on 31 August reached 4.6 km, but there was no evidence of ash and it dissipated rapidly.

Several times during late September during clear views, webcam images showed a persistent steam plume from the summit crater. Elevated surface temperatures in the summit crater were observed in satellite images on 25, 28, and 29 September, and again during 4-6, 13-14, and 16 October. In early November, the AVO determined that the summit crater was larger and more centrally located than before, as a result of the March 2016 explosion. The new crater geometry possibly allowed satellite sensors to more easily detect emissions of hot gases from the vent. Ongoing observations of moderately elevated surface temperatures (figure 16) likely reflect this change in the crater, and do not indicate new eruptive activity or rising magma. Seismicity remained slightly above background levels through the end of 2016, and the ACC remained at Yellow.

Geologic Background. The most active volcano of the Aleutian arc, Pavlof is a 2519-m-high Holocene stratovolcano that was constructed along a line of vents extending NE from the Emmons Lake caldera. Pavlof and its twin volcano to the NE, 2142-m-high Pavlof Sister, form a dramatic pair of symmetrical, glacier-covered stratovolcanoes that tower above Pavlof and Volcano bays. A third cone, Little Pavlof, is a smaller volcano on the SW flank of Pavlof volcano, near the rim of Emmons Lake caldera. Unlike Pavlof Sister, Pavlof has been frequently active in historical time, typically producing Strombolian to Vulcanian explosive eruptions from the summit vents and occasional lava flows. The active vents lie near the summit on the north and east sides. The largest historical eruption took place in 1911, at the end of a 5-year-long eruptive episode, when a fissure opened on the N flank, ejecting large blocks and issuing lava flows.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://www.dggs.alaska.gov/); Anchorage Volcanic Ash Advisory Center (VAAC), Alaska Aviation Weather Unit, NWS NOAA US Dept of Commerce, 6930 Sand Lake Road, Anchorage, AK 99502-1845(URL: http://www.ssd.noaa.gov/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); Colt Snapp (URL: https://twitter.com/colt_snapp/status/714345047173369856); The Canadian Press, via Vancouver Observer (URL: http://www.vancouverobserver.com/news/environment/flights-cancelled-and-out-regina-yellowknife-after-volcano-alaska); NBC News (URL: http://www.nbcnews.com/news/weather/pavlof-volcano-erupts-covering-400-miles-alaska-ash-n546956).

Poás is characterized by intermittent explosions from its hot crater lake. Several occurred in 2014 (BGVN 40:11). This report covers activity from 1 January 2015 through February 2017. There were no reports of activity during 2015 through May 2016. Phreatic eruptions were recorded between 5 June and 16 August 2016.

According to news articles (La Prensa Libre, Prensa Latina), phreatic explosions from the hot crater lake occurred multiple times in June 2016. Explosions at 0900 on 5 June, at 1854 on 13 June, and at 1952 on 14 June ejected water and steam many meters above the lake's surface. Three small explosions, lasting about five seconds each based on the seismic signals, occurred during 0600-0603 on 18 June and ejected water, steam, and debris no more than 50 m above the lake's surface. Phreatic explosions were also registered on 19 June.

According to the Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA), a small phreatic explosion from the lake was recorded at 0819 on 25 July 2016. The explosion ejected material 50 m above the lake surface.

News accounts (Q Costa Rica, La Prensa Libre) reported that at 1409 local time on 16 August 2016 an explosion sent a column of gas to a height of 100 m above the crater; the activity lasted 2 minutes. An OVSICORI-UNA video of this explosion was posted in the news articles.

Geologic Background. The broad, well-vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since the first historical eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/); La Prensa Libre (URL: https://www.laprensalibre.cr/); Prensa Latina (URL: http://www.plenglish.com/); Q Costa Rica News (URL: http://qcostarica.com/).

An eruption at Sheveluch has been ongoing since 1999, and recent activity there was previously described through August 2015 (BGVN 42:02). During September 2015-February 2016, the same type of activity prevailed, with lava dome extrusion, incandescence, hot block avalanches, fumarolic activity, and occasional strong explosions that generated ash plumes. The following data comes from Kamchatka Volcanic Eruption Response Team (KVERT) reports. During this period the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

KVERT reported that during 1 September 2015-28 February 2016, lava-dome extrusion onto the N flank was accompanied by fumarolic activity, dome incandescence, hot avalanches, and ash explosions. Satellite images detected an almost daily, and sometimes intense, thermal anomaly over the dome. Ash plumes generated by occasional explosions, hot avalanches, and sometimes strong winds rose to altitudes of 2.5-7 km and drifted primarily SE during September-December 2015 (up to 185 km) and in more variable directions (up to 200 km) during January-March 2016. A series of photos taken in late 2015 shows characteristic types of activity, including small explosions and hot avalanches on 28 October (figure 39), an explosion and pyroclastic flow on 22 November (figure 40), and incandescence on 25 November (figure 41).

Figure 39. Photo of Sheveluch during a sequence of small explosions and hot avalanches from the lava dome's E flank that sent ash up to 4 km altitude on 28 October 2015. Ash can be seen falling out of the plume on the lower flank. Courtesy of Y. Demyanchuk, Institute Volcanology and Seismology FEB RAS, KVERT.

Figure 40. Photo of Sheveluch with an ash plume rising during a larger explosion and a pyroclastic flow moving down the SW flank of the lava dome on 22 November 2015. Courtesy of Y. Demyanchuk, Institute Volcanology and Seismology FEB RAS, KVERT.

Figure 41. Photo showing a strong fumarolic plume from Sheveluch and incandescence caused by hot avalanches from the lava dome on 25 November 2015. Courtesy of Y. Demyanchuk, Institute Volcanology and Seismology FEB RAS, KVERT.

Thermal anomalies based on MODIS satellite instruments analyzed using the MODVOLC algorithm were frequent during the current reporting period, in contrast to March-August 2015 (BGVN 42:02). From September 2015-February 2016, thermal anomalies were detected 10-15 days each month. On 22 November, seven pixels were recorded.

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 km3 volcano is one of Kamchatka's largest and most active volcanic structures. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far East Division, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); 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/).

Soputan stratovolcano on the northern tip of Indonesia's island of Sulawesi has had historically observed eruptions since the 18th century, possibly earlier. The locus of eruptions has included both the summit crater and a NE-flank vent that was active during 1906-1924. Since the 1980's, continuing lava-dome growth has been punctuated by ash explosions, lava flows, and Strombolian eruptions every few years. When these events last occurred between January and March 2015, they were accompanied by strong thermal anomalies and elevated seismicity which continued into early July 2015 (BGVN 41:05). This report covers the period from July 2015 through September 2016.

Increased seismicity in November 2015 signaled the beginning of a new eruptive episode, with explosions in January and February 2016. Soputan is monitored by PVMBG (Pusat Vulkanologi dan Mitigasi Bencana Geologi), Badan Nasional Penanggulangan Bencana (BNPB) which is the Indonesian National Disaster Management Agency, and aviation alerts are managed by the Darwin VAAC (Volcanic Ash Advisory Center). Information is also provided by the University of Hawaii's MODVOLC Thermal Alert System and the MIROVA project, an Italian collaboration; both groups analyze the MODIS satellite data for thermal anomalies related to volcanoes.

Soputan erupted a significant ash plume to over 12 km altitude on 4 January 2016 after a few months of increasing seismicity. Lava flows, Strombolian eruptions, and a pyroclastic flow were observed the next day. Another large ash plume to 13 km altitude occurred on 14 January. A series of explosions beginning on 6 February resulted in more ash plumes, lava flows, and Strombolian eruptions for about 24 hours, after which activity decreased significantly. Several villages within 20 km reported ashfall from these events. The last reported activity was on 7 February 2016, although thermal anomaly data extended well into April. Seismicity had declined significantly by mid-April when the Alert Level was lowered.

Activity during July-November 2015. PVMBG lowered the Alert Level to II (second lowest on a four-level scale) on 3 July 2015, citing reduced harmonic tremor and stable RSAM (Real-time Seismic amplitude measurements) at background levels compared with the eruptive activity between January and March 2015. They did not issue another update until 3 November 2015.

MODVOLC thermal alert information from MODIS (Moderate Resolution Imaging Spectroradiometer) satellite data indicated anomalies in the vicinity of Soputan twice in September and four times in October 2015, but the locations were far enough from the volcano to suggest that they were not related to volcanic activity. This is corroborated with the MIROVA (Middle InfraRed Observation of Volcanic Activity) data from this same period which also recorded increases in Volcanic Radiative Power (VRP) in September and October. The locations indicated by MIROVA are mostly greater than 5 km from the summit, also suggesting a non-volcanic source (figure 12).

Figure 12. MIROVA analysis of MODIS data for 6 September 2015 through 6 September 2016 for Soputan. Moderate to High values in September and October 2015 are noted in black, indicating sources more than 5 km from the volcano and likely not related to eruptive activity. Low values in blue between 6 September and mid-December are from an unknown source within 5 km of the summit. The spikes on 4-6 January 2016 and 6-8 February correspond to observed ash plumes, lava flows, pyroclastic flows, and Strombolian eruptions reported by PVMBG. Courtesy of MIROVA.

Additional thermal anomaly signals in the MIROVA data from mid-September through early December 2015 appear to be sourced within 5 km of the summit (figure 12), but their origin is unknown. PVMBG makes no mention of active eruptions or ash plumes during this time. PVMBG maintained the Level II alert status and documented clear skies with diffuse white steam plumes rising between 20 and 200 m from the summit crater during the last half of October and November, unchanged since July. They noted, however, that the frequency of several types of earthquakes began a gradual increase in the middle of October.

Activity during January-September 2016. Elevated seismicity continued until 4 January 2016. Photos taken on 3 and 4 January showed an increase in the density of the white-to-light-gray emissions rising to 300 m above the summit (figure 13).

Figure 13. Emissions (white to light-gray) rise from Soputan on 3 January 2016, about 24 hours prior to a significant ash eruption (colors adjusted from original image). Courtesy of PVMBG (Soputan activity report through 4 January 2016).

Dense reddish-white emissions rose 300 m above the summit early in the day on 4 January. A thermal image taken that day indicated that lava was present at the summit; PVMBG raised the Alert Level to III. Seismic amplitude (RSAM) values had also increased sharply in the preceding 12 hours, and tilt measurement data indicated significant inflation of the volcano. BNPB reported an ash eruption at 2053 local time, with a plume rising 2 km from the summit and drifting SE, and incandescent lava flowing down the E flank. Minor ashfall was reported in Langowan (12 km NE) in the Minahasa District. The Darwin VAAC raised the Aviation Color Code (ACC) to Red at 2230 local time and reported an ash plume at 12.8 km altitude drifting west 30 minutes later. This was followed in the next 24 hours by two more plumes that rose to 10.6 km and drifted NW to NE (figure 14). Continuous emissions rising to about 3.7 km were observed until early 7 January.

Figure 14. Soputan eruption during the morning hours of 5 January 2016 (local time). Photograph location uncertain but likely taken in the vicinity of Ronoketang, about 12 km S. Courtesy of PVMBG.

A Strombolian phase early on 5 January lasted about 40 minutes and sent incandescent material 250 m high, according to BNPB. Sounds resembling thunder followed, and then a pyroclastic flow traveled 2.5 km down the ENE flank. An ash cloud rose 6.5 km above the summit crater rim (8.3 km altitude) and drifted W. Several villages in the districts of West Langowan (8 km E), Tompaso (11 km NE), and East Ratahan (14 km SE) reported ashfall.

MODVOLC thermal alert pixels likely associated with the eruption were reported during 6-8 January. A small cluster on 10 January located on the NE flank possibly indicated flowing or cooling lava. The Darwin VAAC reported another large ash plume on 14 January that rose to 13.7 km and drifted 45 km NE before dissipating.

A new series of explosions began on 6 February 2016. Ash plumes rose to 7 km altitude, later dropping to the range of 4.3-6 km, with continuous emissions drifting up to 75 km WSW through the next day. PVMBG reported lava flows on the N and E flanks; Strombolian explosions witnessed from the observation post in the village of Silian (about 10 km from the volcano) ejected material 300 m high. BNPB reported Strombolian activity on 7 February with ejected material as high as 1,000 m above the summit crater. Pyroclastic flows were also observed moving up to 2 km down the E flank. Seismic amplitudes remained high, indicating the active movement of magma within the volcano. Ashfall was reported in multiple districts including Pasan (5 km SSE), Tombatu (16 km SSW), Belang (17 km SSE), and Ratatotok (20 km S). The MODIS thermal anomaly data resulted in a very strong (32 pixel) MODVOLC thermal alert on 6 February. This corresponded with the Volcanic Radiative Power (VRP) spike presented in the MIROVA information for the same period (figure 12).

For the rest of February, only diffuse white steam plumes rose 75 m, except for a 700-m-high plume reported on 12 February by PVMBG; three MODVOLC thermal alert pixels were recorded on 11 and one on 13 February. Minor steam emissions rose to 100 m at the end of March, but the frequency of earthquakes associated with avalanches and low-frequency earthquakes were still elevated above background levels. The intensity of the avalanche-related earthquakes began to decline in the second week in April according to PVMBG. No incandescence was observed at the summit by the third week of April, and the decreasing frequency and amplitude of the earthquakes led PVMBG to lower the Alert Level to II on 21 April 2016. Between May and mid-September 2016, emissions from the volcano were characterized by white plumes of variable density ranging from 20 to 300 m above the crater and seismicity remained low (figure 15). The Alert Level remained at II.

Figure 15. Seismicity at Soputan from 1 January 2015 through 14 September 2016. Dates of eruptive events are shown with red bars. Vertical axis on all graphs is daily frequency. LETUSAN is eruption, vertical axis on the right is height in meters above summit of ash plume observed by PVMBG; HEMBUSAN is emission related seismicity; GUGURAN is seismicity associated with rock avalanches; VULKANIK DANGKAL are shallow volcanic earthquakes; VULKANIK DALAM are deep volcanic earthquakes; TECTONIK JAUH are remote tectonic earthquakes. Courtesy of PVMBG (Soputan Report of activity through 14 September 2016).

Geologic Background. The Soputan stratovolcano on the southern rim of the Quaternary Tondano caldera on the northern arm of Sulawesi Island is one of Sulawesi's most active volcanoes. The youthful, largely unvegetated volcano is located SW of Riendengan-Sempu, which some workers have included with Soputan and Manimporok (3.5 km ESE) as a volcanic complex. It was constructed at the southern end of a SSW-NNE trending line of vents. During historical time the locus of eruptions has included both the summit crater and Aeseput, a prominent NE-flank vent that formed in 1906 and was the source of intermittent major lava flows until 1924.

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 (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/); 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/).

In discussing the week ending on 12 September, "Earthweek" (Newman, 1997) incorrectly claimed that a volcano named "Mount Pinukis" had erupted. Widely read in the US, the dramatic Earthweek report described terrified farmers and a black mushroom cloud that resembled a nuclear explosion. The mountain's location was given as "200 km E of Zamboanga City," a spot well into the sea. The purported eruption had received mention in a Manila Bulletin newspaper report nine days earlier, on 4 September. Their comparatively understated report said that a local police director had disclosed that residents had seen a dormant volcano showing signs of activity.

In response to these news reports Emmanuel Ramos of the Philippine Institute of Volcanology and Seismology (PHIVOLCS) sent a reply on 17 September. PHIVOLCS staff had initially heard that there were some 12 alleged families who fled the mountain and sought shelter in the lowlands. A PHIVOLCS investigation team later found that the reported "families" were actually individuals seeking respite from some politically motivated harassment. The story seems to have stemmed from a local gold rush and an influential politician who wanted to use volcanism as a ploy to exclude residents. PHIVOLCS concluded that no volcanic activity had occurred. They also added that this finding disappointed local politicians but was much welcomed by the residents.

PHIVOLCS spelled the mountain's name as "Pinokis" and from their report it seems that it might be an inactive volcano. There is no known Holocene volcano with a similar name (Simkin and Siebert, 1994). No similar names (Pinokis, Pinukis, Pinakis, etc.) were found listed in the National Imagery and Mapping Agency GEOnet Names Server (http://geonames.nga.mil/gns/html/index.html), a searchable database of 3.3 million non-US geographic-feature names.

The Manila Bulletin report suggested that Pinokis resides on the Zamboanga Peninsula. The Peninsula lies on Mindanao Island's extreme W side where it bounds the Moro Gulf, an arm of the Celebes Sea. The mountainous Peninsula trends NNE-SSW and contains peaks with summit elevations near 1,300 m. Zamboanga City sits at the extreme end of the Peninsula and operates both a major seaport and an international airport.

[Later investigation found that Mt. Pinokis is located in the Lison Valley on the Zamboanga Peninsula, about 170 km NE of Zamboanga City and 30 km NW of Pagadian City. It is adjacent to the two peaks of the Susong Dalaga (Maiden's Breast) and near Mt. Sugarloaf.]

References. Newman, S., 1997, Earthweek, a diary of the planet (week ending 12 September): syndicated newspaper column (URL: http://www.earthweek.com/).

Manila Bulletin, 4 Sept. 1997, Dante's Peak (URL: http://www.mb.com.ph/).

Simkin, T., and Siebert, L., 1994, Volcanoes of the world, 2nd edition: Geoscience Press in association with the Smithsonian Institution Global Volcanism Program, Tucson AZ, 368 p.

Information Contacts: Emmanuel G. Ramos, Deputy Director, Philippine Institute of Volcanology and Seismology, Department of Science and Technology, PHIVOLCS Building, C. P. Garcia Ave., University of the Philippines, Diliman campus, Quezon City, Philippines.

Xinhua News Agency filed a news report on 27 February under the headline "Volcano erupts in Somalia" but the veracity of the story now appears doubtful. The report disclosed the volcano's location as on the W side of the Gedo region, an area along the Ethiopian border just NE of Kenya. The report had relied on the commissioner of the town of Bohol Garas (a settlement described as 40 km NE of the main Al-Itihad headquarters of Luq town) and some or all of the information was relayed by journalists through VHF radio. The report claimed the disaster "wounded six herdsmen" and "claimed the lives of 290 goats grazing near the mountain when the incident took place." Further descriptions included such statements as "the volcano which erupted two days ago [25 February] has melted down the rocks and sand and spread . . . ."

Giday WoldeGabriel returned from three weeks of geological fieldwork in SW Ethiopia, near the Kenyan border, on 25 August. During his time there he inquired of many people, including geologists, if they had heard of a Somalian eruption in the Gedo area; no one had heard of the event. WoldeGabriel stated that he felt the news report could have described an old mine or bomb exploding. Heavy fighting took place in the Gedo region during the Ethio-Somalian war of 1977. Somalia lacks an embassy in Washington DC; when asked during late August, Ayalaw Yiman, an Ethiopian embassy staff member in Washington DC also lacked any knowledge of a Somalian eruption.

A Somalian eruption would be significant since the closest known Holocene volcanoes occur in the central Ethiopian segment of the East African rift system S of Addis Ababa, ~500 km NW of the Gedo area. These Ethiopian rift volcanoes include volcanic fields, shield volcanoes, cinder cones, and stratovolcanoes.

Information Contacts: Xinhua News Agency, 5 Sharp Street West, Wanchai, Hong Kong; Giday WoldeGabriel, EES-1/MS D462, Geology-Geochemistry Group, Los Alamos National Laboratory, Los Alamos, NM 87545; Ayalaw Yiman, Ethiopian Embassy, 2134 Kalorama Rd. NW, Washington DC 20008.

Following the Ms 7.8 earthquake in Turkey on 17 August (BGVN 24:08) an Email message originating in Turkey was circulated, claiming that volcanic activity was observed coincident with the earthquake and suggesting a new (magmatic) volcano in the Sea of Marmara. For reasons outlined below, and in the absence of further evidence, editors of the Bulletin consider this a false report.

The report stated that fishermen near the village of Cinarcik, at the E end of the Sea of Marmara "saw the sea turned red with fireballs" shortly after the onset of the earthquake. They later found dead fish that appeared "fried." Their nets were "burned" while under water and contained samples of rocks alleged to look "magmatic."

No samples of the fish were preserved. A tectonic scientist in Istanbul speculated that hot water released by the earthquake from the many hot springs along the coast in that area may have killed some fish (although they would be boiled rather than fried).

The phenomenon called earthquake lights could explain the "fireballs" reportedly seen by the fishermen. Such effects have been reasonably established associated with large earthquakes, although their origin remains poorly understood. In addition to deformation-triggered piezoelectric effects, earthquake lights have sometimes been explained as due to the release of methane gas in areas of mass wasting (even under water). Omlin and others (1999), for example, found gas hydrate and methane releases associated with mud volcanoes in coastal submarine environments.

The astronomer and author Thomas Gold (Gold, 1998) has a website (Gold, 2000) where he presents a series of alleged quotes from witnesses of earthquakes. We include three such quotes here (along with Gold's dates, attributions, and other comments):

(A) Lima, 30 March 1828. "Water in the bay 'hissed as if hot iron was immersed in it,' bubbles and dead fish rose to the surface, and the anchor chain of HMS Volage was partially fused while lying in the mud on the bottom." (Attributed to Bagnold, 1829; the anchor chain is reported to be on display in the London Navy Museum.)

(B) Romania, 10 November 1940. ". . . a thick layer like a translucid gas above the surface of the soil . . . irregular gas fires . . . flames in rhythm with the movements of the soil . . . flashes like lightning from the floor to the summit of Mt Tampa . . . flames issuing from rocks, which crumbled, with flashes also issuing from non-wooded mountainsides." (Phrases used in eyewitness accounts collected by Demetrescu and Petrescu, 1941).

(C) Sungpan-Pingwu (China), 16, 22, and 23 August 1976. "From March of 1976, various large anomalies were observed over a broad region. . . . At the Wanchia commune of Chungching County, outbursts of natural gas from rock fissures ignited and were difficult to extinguish even by dumping dirt over the fissures. . . . Chu Chieh Cho, of the Provincial Seismological Bureau, related personally seeing a fireball 75 km from the epicenter on the night of 21 July while in the company of three professional seismologists."

Yalciner and others (1999) made a study of coastal areas along the Sea of Marmara after the Izmet earthquake. They found evidence for one or more tsunamis with maximum runups of 2.0-2.5 m. Preliminary modeling of the earthquake's response failed to reproduce the observed runups; the areas of maximum runup instead appeared to correspond most closely with several local mass-failure events. This observation together with the magnitude of the earthquake, and bottom soundings from marine geophysical teams, suggested mass wasting may have been fairly common on the floor of the Sea of Marmara.

Despite a wide range of poorly understood, dramatic processes associated with earthquakes (Izmet 1999 apparently included), there remains little evidence for volcanism around the time of the earthquake. The nearest Holocene volcano lies ~200 km SW of the report location. Neither Turkish geologists nor scientists from other countries in Turkey to study the 17 August earthquake reported any volcanism. The report said the fisherman found "magmatic" rocks; it is unlikely they would be familiar with this term.

The motivation and credibility of the report's originator, Erol Erkmen, are unknown. Certainly, the difficulty in translating from Turkish to English may have caused some problems in understanding. Erkmen is associated with a website devoted to reporting UFO activity in Turkey. Photographs of a "magmatic rock" sample were sent to the Bulletin, but they only showed dark rocks photographed devoid of a scale on a featureless background. The rocks shown did not appear to be vesicular or glassy. What was most significant to Bulletin editors was the report author's progressive reluctance to provide samples or encourage follow-up investigation with local scientists. Without the collaboration of trained scientists on the scene this report cannot be validated.

References. Omlin, A, Damm, E., Mienert, J., and Lukas, D., 1999, In-situ detection of methane releases adjacent to gas hydrate fields on the Norwegian margin: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Yalciner, A.C., Borrero, J., Kukano, U., Watts, P., Synolakis, C. E., and Imamura, F., 1999, Field survey of 1999 Izmit tsunami and modeling effort of new tsunami generation mechanism: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Gold, T., 1998, The deep hot biosphere: Springer Verlag, 256 p., ISBN: 0387985468.

Gold, T., 2000, Eye-witness accounts of several major earthquakes (URL: http://www.people.cornell.edu/ pages/tg21/eyewit.html).

Information Contacts: Erol Erkmen, Tuvpo Project Alp.

In December 2002 information appeared in Mongolian and Russian newspapers and on national TV that a volcano in Central Mongolia, the Har-Togoo volcano, was producing white vapors and constant acoustic noise. Because of the potential hazard posed to two nearby settlements, mainly with regard to potential blocking of rivers, the Director of the Research Center of Astronomy and Geophysics of the Mongolian Academy of Sciences, Dr. Bekhtur, organized a scientific expedition to the volcano on 19-20 March 2003. The scientific team also included M. Ulziibat, seismologist from the same Research Center, M. Ganzorig, the Director of the Institute of Informatics, and A. Ivanov from the Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences.

Geological setting. The Miocene Har-Togoo shield volcano is situated on top of a vast volcanic plateau (figure 1). The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Pliocene and Quaternary volcanic rocks are also abundant in the vicinity of the Holocene volcanoes (Devyatkin and Smelov, 1979; Logatchev and others, 1982). Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Figure 1. Photograph of the Har-Togoo volcano viewed from west, March 2003. Courtesy of Alexei Ivanov.

Observations during March 2003. The name of the volcano in the Mongolian language means "black-pot" and through questioning of the local inhabitants, it was learned that there is a local myth that a dragon lived in the volcano. The local inhabitants also mentioned that marmots, previously abundant in the area, began to migrate westwards five years ago; they are now practically absent from the area.

Acoustic noise and venting of colorless warm gas from a small hole near the summit were noticed in October 2002 by local residents. In December 2002, while snow lay on the ground, the hole was clearly visible to local visitors, and a second hole could be seen a few meters away; it is unclear whether or not white vapors were noticed on this occasion. During the inspection in March 2003 a third hole was seen. The second hole is located within a 3 x 3 m outcrop of cinder and pumice (figure 2) whereas the first and the third holes are located within massive basalts. When close to the holes, constant noise resembled a rapid river heard from afar. The second hole was covered with plastic sheeting fixed at the margins, but the plastic was blown off within 2-3 seconds. Gas from the second hole was sampled in a mechanically pumped glass sampler. Analysis by gas chromatography, performed a week later at the Institute of the Earth's Crust, showed that nitrogen and atmospheric air were the major constituents.

Figure 2. Photograph of the second hole sampled at Har-Togoo, with hammer for scale, March 2003. Courtesy of Alexei Ivanov.

The temperature of the gas at the first, second, and third holes was +1.1, +1.4, and +2.7°C, respectively, while air temperature was -4.6 to -4.7°C (measured on 19 March 2003). Repeated measurements of the temperatures on the next day gave values of +1.1, +0.8, and -6.0°C at the first, second, and third holes, respectively. Air temperature was -9.4°C. To avoid bias due to direct heating from sunlight the measurements were performed under shadow. All measurements were done with Chechtemp2 digital thermometer with precision of ± 0.1°C and accuracy ± 0.3°C.

Inside the mouth of the first hole was 4-10-cm-thick ice with suspended gas bubbles (figure 5). The ice and snow were sampled in plastic bottles, melted, and tested for pH and Eh with digital meters. The pH-meter was calibrated by Horiba Ltd (Kyoto, Japan) standard solutions 4 and 7. Water from melted ice appeared to be slightly acidic (pH 6.52) in comparison to water of melted snow (pH 7.04). Both pH values were within neutral solution values. No prominent difference in Eh (108 and 117 for ice and snow, respectively) was revealed.

Two digital short-period three-component stations were installed on top of Har-Togoo, one 50 m from the degassing holes and one in a remote area on basement rocks, for monitoring during 19-20 March 2003. Every hour 1-3 microseismic events with magnitude <2 were recorded. All seismic events were virtually identical and resembled A-type volcano-tectonic earthquakes (figure 6). Arrival difference between S and P waves were around 0.06-0.3 seconds for the Har-Togoo station and 0.1-1.5 seconds for the remote station. Assuming that the Har-Togoo station was located in the epicentral zone, the events were located at ~1-3 km depth. Seismic episodes similar to volcanic tremors were also recorded (figure 3).

Figure 3. Examples of an A-type volcano-tectonic earthquake and volcanic tremor episodes recorded at the Har-Togoo station on 19 March 2003. Courtesy of Alexei Ivanov.

Conclusions. The abnormal thermal and seismic activities could be the result of either hydrothermal or volcanic processes. This activity could have started in the fall of 2002 when they were directly observed for the first time, or possibly up to five years earlier when marmots started migrating from the area. Further studies are planned to investigate the cause of the fumarolic and seismic activities.

At the end of a second visit in early July, gas venting had stopped, but seismicity was continuing. In August there will be a workshop on Russian-Mongolian cooperation between Institutions of the Russian and Mongolian Academies of Sciences (held in Ulan-Bator, Mongolia), where the work being done on this volcano will be presented.

References. Devyatkin, E.V. and Smelov, S.B., 1979, Position of basalts in sequence of Cenozoic sediments of Mongolia: Izvestiya USSR Academy of Sciences, geological series, no. 1, p. 16-29. (In Russian).

Logatchev, N.A., Devyatkin, E.V., Malaeva, E.M., and others, 1982, Cenozoic deposits of Taryat basin and Chulutu river valley (Central Hangai): Izvestiya USSR Academy of Sciences, geological series, no. 8, p. 76-86. (In Russian).

Geologic Background. The Miocene Har-Togoo shield volcano, also known as Togoo Tologoy, is situated on top of a vast volcanic plateau. The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Information Contacts: Alexei V. Ivanov, Institute of the Earth Crust SB, Russian Academy of Sciences, Irkutsk, Russia; Bekhtur andM. Ulziibat, Research Center of Astronomy and Geophysics, Mongolian Academy of Sciences, Ulan-Bator, Mongolia; M. Ganzorig, Institute of Informatics MAS, Ulan-Bator, Mongolia.

An eruption at Mount Elgon was mistakenly inferred when fumes escaped from this otherwise quiet volcano. The fumes were eventually traced to dung burning in a lava-tube cave. The cave is home to, or visited by, wildlife ranging from bats to elephants. Mt. Elgon (Ol Doinyo Ilgoon) is a stratovolcano on the SW margin of a 13 x 16 km caldera that straddles the Uganda-Kenya border 140 km NE of the N shore of Lake Victoria. No eruptions are known in the historical record or in the Holocene.

On 7 September 2004 the web site of the Kenyan newspaper The Daily Nation reported that villagers sighted and smelled noxious fumes from a cave on the flank of Mt. Elgon during August 2005. The villagers' concerns were taken quite seriously by both nations, to the extent that evacuation of nearby villages was considered.

The Daily Nation article added that shortly after the villagers' reports, Moses Masibo, Kenya's Western Province geology officer visited the cave, confirmed the villagers observations, and added that the temperature in the cave was 170°C. He recommended that nearby villagers move to safer locations. Masibo and Silas Simiyu of KenGens geothermal department collected ashes from the cave for testing.

Gerald Ernst reported on 19 September 2004 that he spoke with two local geologists involved with the Elgon crisis from the Geology Department of the University of Nairobi (Jiromo campus): Professor Nyambok and Zacharia Kuria (the former is a senior scientist who was unable to go in the field; the latter is a junior scientist who visited the site). According to Ernst their interpretation is that somebody set fire to bat guano in one of the caves. The fire was intense and probably explains the vigorous fuming, high temperatures, and suffocated animals. The event was also accompanied by emissions of gases with an ammonia odor. Ernst noted that this was not surprising considering the high nitrogen content of guano—ammonia is highly toxic and can also explain the animal deaths. The intense fumes initially caused substantial panic in the area.

It was Ernst's understanding that the authorities ordered evacuations while awaiting a report from local scientists, but that people returned before the report reached the authorities. The fire presumably prompted the response of local authorities who then urged the University geologists to analyze the situation. By the time geologists arrived, the fuming had ceased, or nearly so. The residue left by the fire and other observations led them to conclude that nothing remotely related to a volcanic eruption had occurred.

However, the incident emphasized the problem due to lack of a seismic station to monitor tectonic activity related to a local triple junction associated with the rift valley or volcanic seismicity. In response, one seismic station was moved from S Kenya to the area of Mt. Elgon so that local seismicity can be monitored in the future.

Information Contacts: Gerald Ernst, Univ. of Ghent, Krijgslaan 281/S8, B-9000, Belgium; Chris Newhall, USGS, Univ. of Washington, Dept. of Earth & Space Sciences, Box 351310, Seattle, WA 98195-1310, USA; The Daily Nation (URL: http://www.nationmedia.com/dailynation/); Uganda Tourist Board (URL: http://www.visituganda.com/).