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, Amedeus 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 explosive eruption that began on 10 May is the first documented eruption from Anatahan in historical time. There were no residents on the island due to their evacuation following a shallow earthquake swarm in 1990 (Moore and others, 1994), and another in 1993 (Sako and others, 1995). Anatahan is a composite volcano that erupts lavas that are primarily dacitic in composition. It has the largest caldera of the volcanoes in the Commonwealth of the Northern Mariana Islands (CNMI). The presence of this caldera indicates that large explosive eruptions are possible.

Strong activity continued over the next few days (BGVN 28:04), with high ash plumes seen in satellite imagery. The area within ~55 km of the island was also placed off-limits to all boats and aircraft not approved by the CNMI Emergency Management Office (EMO). A smaller but nearly continuous eruption column rose from the E crater of Anatahan for the next several weeks. Activity was continuing in early July, but at low levels.

The EMO invited USGS scientists to provide assistance in tracking the volcano's activity and assessing potential hazards shortly after the eruption began. USGS scientists first arrived in Saipan on 30 May to work directly with EMO officials to install and maintain monitoring equipment and interpret data from overflights and a single seismometer operating on Anatahan. This station became operational on 5 June.

Beginning of the eruption, 10-12 May 2003. On 6 May researchers from Washington University, Scripps Institution of Oceanography, and the EMO aboard the MV Super Emerald deployed a seismograph on Anatahan as part of a joint US-Japan Mariana Subduction Imaging Experiment, which is funded by the National Science Foundation. There were no indications of an impending eruption. During the night of 10-11 May the ship was again approaching Anatahan when scientists observed a tremendous lightning display ahead. As morning broke, they saw a pillar of steam and ash billowing to an altitude of 9 km. The ship had to detour around the island to avoid the ashfall.

Initial reports indicated that the eruption began around 2100 on 10 May. Satellite data interpreted by the Washington Volcanic Ash Advisory Center (VAAC) showed that the eruption appeared to have started by 1730. An ash plume was clearly visible in imagery at 2232, resulting in an advisory being issued to the aviation community at 2300 (1300 UTC). Plume heights were reported to be 10-12 km in the early stages of the eruption, with one ash advisory indicating ash to 13.4 km altitude on the 11th. At times multiple clouds were moving in different directions at different altitudes.

On 13 May Joe Kaipat from the CNMI Emergency Management Office (EMO) and seismologist Doug Weins (Washington University) flew to Sarigan (6.5 km W of Anatahan) to retrieve seismic data from a broadband instrument installed on 6 May. Records from the Sarigan station showed increased seismicity commencing at about 1300 on 10 May. The activity remained very strong for about 36 hours before decreasing.

Activity during 13-30 May 2003. A helicopter overflight on 13 May showed that the island was still erupting, but with less intensity than on 11 May. Large volcanic bombs were observed flying high in the air over the crater region, and the whole W side of the island was covered with ash, including the seismograph site. The village appeared to have 15-30 cm of ash (figure 5). Ash advisories for 13-14 May reported that a dense ash cloud was drifting W away from the island, but that it was not continuous and varied in size. Ash plumes through 17 May generally drifted NW or WNW. The eruption clouds through May after the initial activity were generally below ~6 km.

Figure 5. The village on Anatahan covered with ash, 13 May 2003. The recently deployed seismograph is barely visible in the clearing to the left. Note the ash on the roofs. Courtesy of Doug Weins.

On 18 May the EMO group took an overflight accompanied by David Hilton (Scripps Institution of Oceanography) and Tobias Fischer (University of New Mexico). They reported a rising plume comprised of steam and ash. The cloud was much lighter in color, with a reduced ash component compared to the initial phases of the eruption. Bombs, possibly up to several meters in size, were being tossed into the air; most fell back into the E crater. The ash was being blown W, but most of the ashfall was still on the E side of the island. The team landed on the E side of the island and deployed a PS- 2 seismometer that appears to have recorded earthquakes and some tremor. At that site they found ejecta thought to be from the initial stage of the eruption. The ground/vegetation near and under the ejecta was not scorched. Most of the material appeared to be non- juvenile. The largest fragments were up to 50 cm across. The team heard "booms" coming from the crater.

The ongoing explosive activity excavated a deep crater within Anatahan's E crater. Scientists estimated the inner crater was nearly at sea level by about 20 May; before the eruption, the floor of the E crater was 68 m above sea level. On 20 May the EMO group took an overflight and installed a telemetered seismic station. Pressure waves from detonations in the E crater were felt on the E flank. From a helicopter the team also observed rocks several meters across being thrown up above the E crater rim and falling back into the crater. Ash continued to fall on the western two-thirds of the island and out to sea. The ash cloud size and length was variable during 17-23 May; it continued in general to drift WNW from the island, at times spreading over a wide area.

On 23-24 May, typhoon Chan-hom shifted the prevailing east winds to the S, blowing the eruption column toward Saipan and Guam. Light ashfall resulted in flight cancellations and the closure of the Saipan and Guam international airports. Residents of Saipan reported a rotten egg smell associated with the ashfall. The report from Saipan was that 1-2 mm of ash had fallen on the island.

EMO personnel took an overflight on 27 May and reported that ash cloud heights reached 3 km, significantly lower than during the first few days of the eruption. The ash cloud was more opaque and laden with ash; the color was closer to that of 10-11 May than more recent plumes. The streaming ash cloud, still exhibiting variable size and length, drifted NW and NNW through 29 May.

Fieldwork on 21 May 2003. Hilton and Fischer arrived by ship at Anatahan at approximately 0630 on 21 May. The activity level was similar to that on their visit 2 days earlier. The ship sailed through the ashfall out to the SW side of the island, and continued along the W coast. The W coast was draped in ash; vegetation was completely covered giving the island a gray pallor. They landed at 0815 and spent ~4 hours ashore. A trench through the recent deposits on the beach area exposed a 25-cm section from the present eruptive phase with three main layers. The lowermost layer consisted of ~5 cm of fine-grained ash. Next was a layer ~15 cm thick comprised of accretionary lapilli with some fine ash. At the top was a 5-cm-thick layer that was a mixture of coarser grained ash and angular clasts of scoriaceous material. The abandoned village, where a team led by Patrick Shore (Washington University) was working on the seismic station installed on 6 May, was similarly covered in ash with many buildings having collapsed roofs. Two sections also revealed initial ash, covered by accretionary lapilli, then a mixture of ash and scoriaceous material. Pumice was floating in water-collection vessels by the buildings.

From the ship the scientists set up the COSPEC instrument and started a traverse through the plume around 1330. The telescope was oriented vertically and the ship made a N-to-S transect through the volcanic plume at a distance of ~1.5 km from shore. Sulfur dioxide (SO₂) in the plume was recorded immediately. The transect took 50 minutes until no SO₂ was being detected. In addition, they sailed through the ash fallout. During the traverse, the volcano erupted every 5 minutes with a deep resonating boom. The width of the volcanic plume was ~6 km and its direction was to the SW. From the COSPEC measurements and wind speed data provided by NOAA, the SO₂ flux was estimated to be 3,000-4,500 metric tons/day. As the group sailed away from the island around 1430 there was a very large eruption with a significantly louder "boom" than had been heard previously, followed by a dark billowing ash-laden plume.

MODVOLC Thermal Alerts. Thermal satellite observations of the current eruption of Anatahan provided by the HIGP MODIS Thermal Alert Team (http://modis.higp.hawaii.edu) confirmed that activity was heavily concentrated in the E crater (figure 6). The most recent hot-spot (as of 1700 UTC on 28 May) was observed on 24 May. The large amounts of ash produced during the eruption will have obscured some thermal anomalies from the MODIS sensor. Plumes were clearly visible on MODIS imagery on 14, 21, 22, 25, 26, 28, and 30 May (figure 7). The persistent, long plume from this island volcano was frequently detected in imagery from a wide variety of satellite platforms.

Figure 6. Summary of MODIS thermal alerts detected at Anatahan, 11-28 May 2003. Each dot defines the geodetic location of the pixels flagged by the MODVOLC algorithm (Wright and others, 2002) as containing volcanic hot-spots. However, although the coordinate describes the center point of each pixel, the hot-spots could have been located anywhere in the square boxes (which portray the nominal 1-km pixel size of the MODIS instrument.) The shaded circles denote the absolute limits within which the volcanic hot-spots responsible for the anomalies must have been sited (based on a statistical analysis of long-term hot-spot location stability at other volcanoes). The hot-spot locations are referenced to WGS-84 ellipsoid. Map coordinates are in UTM zone 55 (north). Courtesy of the HIGP MODIS Thermal Alert Team (http://modis.higp.hawaii.edu).

Figure 7. Ash plume from Anatahan (indicated by arrows) visible in MODIS imagery from the Aqua satellite, 0320 UTC on 30 May. Image processed by NOAA with data from NASA. Courtesy of NOAA/NASA.

SO₂ data from TOMS. Simon Carn reported that the Earth Probe Total Ozone Mapping Spectrometer (EP TOMS) has observed SO₂ and ash emissions from the ongoing eruption. No emissions were detected in the EP TOMS overpass at 0116 UTC on 10 May, several hours before the reported eruption onset. On May 11 a data gap over the Marianas prevented detection of proximal emissions, though a small ash cloud (no larger than ~120 km across) was detected ~500 km ESE of Anatahan at 0027 UTC. Washington VAAC estimates suggested a height of 14-15 km for this cloud. A weak SO₂ cloud was also observed, displaced from the ash cloud and centered ~560 km SE of Anatahan. This cloud contained an estimated SO₂ mass of ~10 kilotons (kt), but it is suspected to be only the distal end of a larger SO₂ plume obscured by the data gap. Diffuse ash was also apparent at least 500 km W of the volcano at 0205 UTC, but no measurable SO₂.

The EP TOMS orbit was better placed on 12 May at 0115 UTC. At this time an ash cloud extending ~560 km on its long axis was centered ~570 km W of Anatahan. An SO₂ cloud, again displaced from the ash, extended ~1,100 km from a point ~510 km W of the volcano to a point ~700 km SE of it. This cloud contained ~110 kt of SO₂. On 13 May a data gap covered the Marianas though ash was detected farther W, with no significant new SO₂ evident. On 14 May a low-level SO₂ plume appeared to be drifting W from Anatahan.

As of May 30 the Earth Probe TOMS instrument continued to detect significant SO₂ emissions from Anatahan. No TOMS data were collected during 15-23 May due to a technical fault on the spacecraft. Thereafter, TOMS detected SO₂ clouds in the region of Anatahan on 24 May (~19 kt SO₂), 25 May (~23 kt minimum), 26 May (~35 kt), 28 May (~70 kt), and 30 May (~50-100 kt). Data gaps covered the Marianas on other days. Given the persistent ash plume from the volcano reported by the Washington VAAC, these SO₂ clouds are presumed to be the product of continuous emissions and not discrete explosive events.

Observations from 20 May-8 June 2001. Anatahan was visited during 20 May-8 June 2001 as part of fieldwork in the Northern Marianas (Trusdell and others, 2001), including helicopter observations on 4 June. At that time line lengths on the Anatahan EDM network were measured and showed no significant changes. Most line lengths exhibited small contractions when compared to the data from the 1994 survey. Deformation appeared to be slowing down with no significant changes. Temperatures were measured for several boiling pots and springs on the floor of the E crater. The temperature of the ponds as well as fumaroles ranged from a minimum of 96.7°C to a maximum of 100.3°C.

References. Moore, R.B., Koyanagi, R.Y., Sako, M.K., Trusdell, F.A., Kojima, G., Ellorda, R.L., and Zane, S., 1994, Volcanologic investigations in the Commonwealth of the Northern Mariana Islands, September-October 1990: U.S. Geological Survey Open-File Report 91-320, 31 p.

Sako, M.K., Trusdell, F.A., Koyanagi, R.Y., Kojima, G., and Moore, R.B., 1995, Volcanic investigations in the Commonwealth of the Northern Mariana Islands, April to May 1994: U.S. Geological Survey Open-File Report 94-705, 57 p.

Trusdell, F.A., Sako, M.K., Moore, R.B., Koyanagi, R.Y., and Schilling, S., 2001, Preliminary studies of seismicity, ground deformation, and geology, Commonwealth of the Northern Mariana Islands, May 20 to June 8, 2001: U.S. Geological Survey, prepared for the Office of the Governor, the Emergency Management Office, and the Office of the Mayor of the Northern Islands, Commonwealth of the Northern Mariana Islands.

Wright, R., Flynn, L.P., Garbeil, H., Harris, A.J.L., and Pilger, E., 2002, Automated volcanic eruption detection using MODIS: Remote Sensing of Environment, v. 82, p. 135-155.

Geologic Background. The elongate, 9-km-long island of Anatahan in the central Mariana Islands consists of a large stratovolcano with a 2.3 x 5 km compound summit caldera. The larger western portion of the caldera is 2.3 x 3 km wide, and its western rim forms the island's high point. Ponded lava flows overlain by pyroclastic deposits fill the floor of the western caldera, whose SW side is cut by a fresh-looking smaller crater. The 2-km-wide eastern portion of the caldera contained a steep-walled inner crater whose floor prior to the 2003 eruption was only 68 m above sea level. A submarine cone, named NE Anatahan, rises to within 460 m of the sea surface on the NE flank, and numerous other submarine vents are found on the NE-to-SE flanks. Sparseness of vegetation on the most recent lava flows had indicated that they were of Holocene age, but the first historical eruption did not occur until May 2003, when a large explosive eruption took place forming a new crater inside the eastern caldera.

Information Contacts: Juan Takai Camacho and Ramon Chong, Commonwealth of the Northern Mariana Islands Emergency Management Office, P.O. Box 10007, Saipan, MP 96950 (URL: http://www.cnmihsem.gov.mp/); Frank Trusdell, Hawaiian Volcano Observatory, PO Box 51, Hawaii National Park, HI, 96718-0051 (URL: https://volcanoes.usgs.gov/nmi/activity/); Doug Wiens and Patrick Shore, Washington University, St. Louis, McDonnell Hall 403 Box 1169, St. Louis, MO 63130; Allan Sauter and David Hilton, Scripps Institution of Oceanography, UCSD, 9500 Gilman Drive, La Jolla CA, 92093-0225; Washington VAAC, Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ssd.noaa.gov/); Simon A. Carn, TOMS Volcanic Emissions Group, Joint Center for Earth Systems Technology (NASA/UMBC), University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA (URL: https://so2.gsfc.nasa.gov/); Rob Wright, Luke Flynn, Harold Garbeil, Andy Harris, Matt Patrick, Eric Pilger, and Scott Rowland, Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); George Stephens, Operational Significant Event Imagery (OSEI) team, World Weather Bldg., 5200 Auth Rd Rm 510 (E/SP 22), NOAA/NESDIS, Camp Springs, MD 20748USA.

A satellite-based interferometric synthetic aperture radar (InSAR) survey of the remote central Andes volcanic arc (Pritchard and Simons, 2002) revealed deformation in the Robledo caldera between May 1992 and October 2000 (figure 1). Subsidence was detected, with a maximum deformation rate in the radar line-of-sight of 2-2.5 cm/year. The subsidence rate seemed to be decreasing with time. The inferred source depth was 4.5-6 km below sea level. Additional details about the study and analysis are available in Pritchard and Simons (2002).

Figure 1. Shaded relief topographic map of the central Andes with insets showing areas of deformation detected by Pritchard and Simons (2002). Interferograms (draped over shaded relief) indicate active deformation; each color cycle corresponds to 5 cm of deformation in the radar line-of-sight (LOS). The LOS direction from ground to spacecraft (black arrow) is inclined 23° from the vertical. Black squares indicate radar frames, and black triangles show potential volcanic edifices. Courtesy of Matthew Pritchard.

Reference. Pritchard, M., and Simons, M., 2002, A satellite geodetic survey of large-scale deformation of volcanic centres in the Central Andes: Nature, v. 418, p. 167-170.

Geologic Background. The Cerro Blanco volcanic complex contains the 6-km-wide Cerro Blanco caldera (also known as the Robledo caldera) in NW Argentina and is located 80 km SW of the much larger and better known Cerro Galán caldera. Cerro Blanco was the site of the largest known Holocene eruption in the Central Andes about 4200 years BP (Fernandez-Turiel et al., 2013). The rhyolitic eruption produced plinian ashfall deposits of about 110 km3 and widespread ignimbrite deposits. The Holocene Cerro Blanco del Robledo lava dome is located on the southern rim of the caldera and is surrounded by extensive rhyolitic pumice-fall deposits. Satellite geodetic surveys in the central Andes (Pritchard and Simons, 2002) showed subsidence of the caldera in the 1990s.

Information Contacts: Matthew Pritchard and Mark Simons, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA (URL: http://www.gps.caltech.edu/).

The eruption that began on 18 April 2003 (BGVN 28:04) continued throughout May and into early June. According to observers, ash fell on the town of Severo-Kurilsk (~60 km from the volcano) on 1 May. Observers from Vasiliev Cape noted weak fumarolic activity on 3 May and satellite data from the USA and Russia that day revealed a gas-and-steam plume more than 150 km long and moving towards the ESE and S. Satellite data continued to show gas-and-steam plumes, possibly containing ash, throughout the remainder of May (table 1). Satellite imaging was obscured by clouds on other days. On 13 May, ash deposits were reported on the ENE and SSE flanks of the volcano and near the summit. At 1800 on 15 May, observers on Paramushir Island reported a strong ashfall at Podgorny settlement.

Table 1. Satellite data reports of gas-and-steam and ash plumes emanating from Chikurachki, May 2003. Courtesy of KVERT.

During the period 1930 to 2310 on 27 May, Leonid Kotenko on Paramushir Island reported that ash explosions attaining heights of 500 m above the crater were observed from Shelekhov Bay. The ash plume at 0900 on 28 May (2200 UTC, 27 May), rose 4,000 m above the crater. On 29 May an ash plume rose ~1,200 m above the crater and ash fell on the town of Severo-Kurilsk.

Additional information about the 2002 eruption. Previous KVERT reports indicated that the eruption that began on 25 January 2002 had continued through 16 March (BGVN 27:04), but no further reports were made about that activity. However, later information was received that showed the eruption continuing through at least 22 April. According to satellite data from AVO for 18 March, two consecutive GMS infrared images (1732 and 1832 UTC) showed a narrow, ~150-km-long cloud, which extended SE from Paramushir Island. There was no indication of ash based on the split-window technique. On the afternoon of 20 March, a gas-and-steam plume with some ash extended 200 km SE. Paramushir Island was obscured by clouds during the next 2 weeks. On 6 May L. Kotenko (A KVERT contact on the island) reported that hunters had observed fresh ash deposits on the SW flank on 22 April and that ashfall was also noted in Severo-Kurilsk.

Geologic Background. Chikurachki, the highest volcano on Paramushir Island in the northern Kuriles, is actually a relatively small cone constructed on a high Pleistocene volcanic edifice. Oxidized basaltic-to-andesitic scoria deposits covering the upper part of the young cone give it a distinctive red color. Frequent basaltic plinian eruptions have occurred during the Holocene. Lava flows from 1781-m-high Chikurachki reached the sea and form capes on the NW coast; several young lava flows also emerge from beneath the scoria blanket on the eastern flank. The Tatarinov group of six volcanic centers is located immediately to the south of Chikurachki, and the Lomonosov cinder cone group, the source of an early Holocene lava flow that reached the saddle between it and Fuss Peak to the west, lies at the southern end of the N-S-trending Chikurachki-Tatarinov complex. In contrast to the frequently active Chikurachki, the Tatarinov volcanoes are extensively modified by erosion and have a more complex structure. Tephrochronology gives evidence of only one eruption in historical time from Tatarinov, although its southern cone contains a sulfur-encrusted crater with fumaroles that were active along the margin of a crater lake until 1959.

Information Contacts: Olga Girina, Kamchatka Volcanic Eruptions Response Team (KVERT), a cooperative program of the Institute of Volcanic Geology and Geochemistry, Far East Division, Russian Academy of Sciences, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia, the Kamchatka Experimental and Methodical Seismological Department (KEMSD), GS RAS (Russia), and the Alaska Volcano Observatory (USA); 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 and Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.

Eruptions are common at Piton de la Fournaise, with the most recent activity occurring in January 2002 (BGVN 26:12) and November-December 2002 (BGVN 27:11). At the end of the November 2002 eruption, seimicity beneath Dolomieu crater increased from 28 November to 23 December. On 22 December there were 5,700 seismic events recorded. At 1002 on 23 December a magnitude 3 event occurred and seismicity stopped. The next day a new crater was observed in the SW part of the larger Dolomieu crater.

Since March 2003, the extensometer network and GPS measurements had indicated inflation of Piton de la Fournaise. A new eruption began on 30 May within Dolomieu crater. The eruption proceeded in multiple phases through at least 24 June; activity through 6 June is reported below.

Seismicity increased slightly on 28 May. At 1137 on the morning of 30 May a seismic crisis began that lasted 17 minutes with a total of 34 events. Tremor appeared at 1155 beneath Dolomieu crater, and an eruption started within the pit crater formed on 23 December 2002. Lava fountaining was observed until 1400, after which most surface activity stopped. A lava flow ~400 m long and 250 m wide extended into the W part of Dolomieu. The total volume of lava emitted during the 30 May activity was estimated to be 0.2-0.3 x 10⁶ m³. Seismicity beneath the crater continued, with intermittent weak tremor being registered through 3 June. No deflation was detected, and there was strong degassing in the collapse area.

On 4 June at 1155 the eruption started again from the same site, enlarging the lava flow in the W part of Dolomieu crater. Lava fountains reached 15 m in height. Steady lava emission continued into 6 June (figures 69 and 70). Volcanic tremor remained stable until the morning of 6 June, when a decreasing tendency was noted. After a short phreatic eruption, the second phase of this eruption stopped on the evening of 6 June. The lava-flow field had grown to ~600 x 400 m in size by that time (figure 71).

Figure 69. Photograph of the SW part of Dolomieu crater at Piton de la Fournaise at 0812 on 6 June 2003 showing the active vent and part of the recent lava-flow field. View is towards the W. Courtesy of OVPF.

Figure 70. Photograph of the W part of Dolomieu crater at Piton de la Fournaise at 0850 on 6 June 2003 showing the active vent and most of the recent lava-flow field. View is towards the SW. Courtesy of OVPF.

Figure 71. Topographic map of Dolomieu crater at Piton de la Fournaise showing the extent of the lava-flow field on 30 May and 6 June 2003. Elevations are in meters, and the Gauss-Laborde Piton des Neiges system is used for the map coordinates. Courtesy of OVPF.

Geologic Background. The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.

Information Contacts: Observatoire volcanologique du Piton de la Fournaise (OVPF), Institut de Physique du Globe de Paris, 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France.

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.

During 6 January-4 May 2003 explosions produced ash that fell on various parts of the crater. The S (main) crater emitted "white-gray ash" that reached 150-400 m high. On some nights, a red glow was visible reaching 25-50 m over the crater. The N crater emitted a "white-thin ash" plume that reached 50-300 m high. Fluctuating seismicity was dominated by multiphase earthquakes and emissions (table 7). The Alert Level remained at level 3 (on a scale of 1 to 4) through at least 4 May.

Table 7. Seismicity at Karangetang during 6 January-4 May 2003. Courtesy VSI.

On 11 and 12 January, ash explosions at the S crater were accompanied by glowing material that reached 200 m high and scattered 500 m toward the E and W parts of the crater. An ash column rose up to 500 m above the crater. Two explosions at the S crater on 14 January produced an ash column up to 300 m high; glowing material rose up to 50 m and fell around the crater. Some of the material entered the Beha River, and ash fell into the sea E of the island. Explosions on 29 January and 6 February caused ashfall SW (Beong village) and SSW (Akesembeka village, Tarurane, Tatahadeng, Bebali, and Salili), respectively. A booming noise was heard frequently throughout the report period, and during early February was sometimes accompanied by thick gray emissions up to 350 m above the crater.

Beginning in early March, the booming noise was accompanied by glowing lava avalanches that traveled from the summit towards the Kahetang (1,250 m), Batuawang (750 m), Batang (1,000 m), and Beha (750 m) rivers. On 6 March an explosion from the S crater ejected ash 750 m high that fell in the E part of the crater. The noises and avalanches decreased during mid-to-late March.

An explosion on 15 April was followed by lava avalanches toward the W and S parts of the crater. A loud blasting sound was heard, and a dark-gray ash column reached 1,500 m. Ash fell to the E around Dame and Karalung villages, and over the sea. Lava avalanches from the S crater traveled 1,000 m toward the Batang and Batu rivers. On 20 April another explosion produced a 1,500-m-high ash column, and ash fell E over the sea. This explosion was followed by lava avalanches and a pyroclastic flow toward the Batang river that reached as far as 2,500 m. Lava avalanches extended 1,500 m down the S and W slopes. Blasting noises occurred for about 3 minutes.

On 22 April an explosion ejected ash and glowing material. The ash column reached 1,750 m and ash fell on the W slope, including Lehi, Mini, Kinali, and Hiung villages, while glowing material rose up to 750 m. This explosion was followed by lava avalanches towards the W and S that were accompanied by a pyroclastic flow toward the Batang river that extended 2,250 m. On 24 April, an explosion ejected ash to 750 m and ash fell eastward into the sea. Glowing material from the explosion traveled toward the W slope. During late April, the booming noises were once again accompanied by continuous glowing avalanches. These decreased during the first days of May.

Geologic Background. Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi island. The stratovolcano contains five summit craters along a N-S line. It is one of Indonesia's most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented in the historical record (Catalog of Active Volcanoes of the World: Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts have produced pyroclastic flows.

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

According to the Kamchatka Volcanic Eruptions Response Team (KVERT), the alert level Color Code remained at Yellow (volcano is restless; eruption may occur) from October 2002 to 27 February 2003, when it was dropped to Green (volcano is dormant; normal seismicity and fumarolic activity). The level was raised again to Yellow in March, lowered to Green on 29 March, and raised to Yellow on 18 April, where it remained through May. Seismicity was above background levels until 20 February, after which it fluctuated between at and above background levels until 16 May, when seismicity remained above background levels. All times are local (= UTC + 11 hours, + 12 hours after 26 October).

Activity during October 2002. From 4 to 31 October, ~200-250 local shallow seismic events occurred per day. The character of the seismicity indicated ash-and-gas explosions to heights of 1,000 m above the volcano (~2,500 m altitude) and gas blow-outs. A faint 10-km-long plume extending SSE was visible in an AVHRR satellite image; no ash was detected. Seismicity on 25-26 October indicated possible vigorous gas emissions lasting 5-10 minutes, with the probability of a lava flow. At 1350 on 31 October, pilots reported that an ash plume rose 4 km and extended SE. According to seismic data from the Kamchatka Experimental and Methodical Seismological Department (KEMSD), the character of seismicity after 1400 on 31 October indicated a moving lava flow. At 1314 on 31 October, the MODIS satellite image showed a large bright thermal anomaly at the volcano and a plume ~60 km long that extended WSW. At 1100 on 1 November, pilots reported that an ash plume rose 4 km and extended SE.

Activity during November 2002. Local shallow seismic events totaled ~200-250 each day. The character of the seismicity indicated ash-and-gas explosions to heights of 1,000-2,000 m above the volcano and vigorous gas emissions lasting 5-10 minutes. At 1605 on 1 November, a 50-km-long plume was observed extending E in satellite imagery; no ash was detected. According to data from KEMSD, at 2357 on 20 November, a seismic event lasting 20 minutes indicated that ash explosions to heights of 1,000 m above the crater and hot avalanches possibly occurred. On 27 November, a >100-km gas-and-steam plume extending ESE from the crater of the volcano was observed in MODIS satellite imagery. Helicopter observations by KVERT scientists at 1151 on 1 December identified an ash plume to ~500 m above the crater extending SE.

Activity during December 2002. Local shallow seismic events totaled ~190-230 each day. The character of seismicity indicated that ash-gas explosions to heights of 1,000 m above the volcano (~2,500 m altitude) and vigorous gas emissions lasting 5-10 minutes were possibly occurring. The top of the volcano and its SE flank were covered with recent ashfall and debris from continuing Vulcanian / Strombolian eruptions. The old crater was covered by the new cinder-ash cone. On 12 December, two sectors of ash falls extending S and SE from the volcano were noted in a MODIS satellite image.

Activity during January 2003. Local shallow seismic events totaled ~110-200 each day. The character of seismicity indicated that ash-gas explosions to heights of 1,000 m above the volcano (~2,500 m or 8,200 ft. ASL) and vigorous gas emissions lasting 5-10 minutes were possibly occurring. From 1559 until 1609 on 8 January, a series of shallow events that possibly indicated hot avalanches were registered. On 9 January, a ~50-km plume extending ESE from the volcano was noted.

Activity during February 2003. The alert level Color Code remained at Yellow until 27 February, when it was lowered to Green (volcano is dormant; normal seismicity and fumarolic activity). According to satellite data from Russia, a weak thermal anomaly was noted on 3 February. Seismic activity was at background levels on 20-23 February.

Activity during March 2003. The alert level Color Code was raised to Yellow as the activity of the volcano slightly increased. Seismic activity was at background levels on 13-18 March and slightly above background levels on 19 March when seismic data indicated possible hot avalanches. Weak volcanic earthquakes were also registered on this day. According to MODIS-satellite data from Russia and the USA, ash deposits extending more than 30 km SW from the volcano on 17-20 March and gas-steam plumes drifting more than 15 km NW and SW on 18 March and on 20 March, respectively, were noted. Seismic activity dropped to background levels for the week of 20 March. According to satellite data from Russia, a weak thermal anomaly was observed on 25 March, and a gas-and-steam plume extending 10 km ESE was noted on 28 March. According to helicopter observations on 31 March by the Institute of Volcanology (IV), Far East Division, Russian Academy of Sciences, the large old active crater of the volcano and its black ESE flank were noted, but the new cinder-ash cone was not seen. This cone was probably destroyed and its products formed ash-deposits extending >35 km ESE, which were noted on the 17-18 March MODIS-satellite images.

Activity during April 2003. The alert level Color Code was dropped to Green during the week of 29 March-4 April, when seismic activity was at background levels. Seismicity rose above background levels during the week of 18-24 April, when ~40-100 volcanic earthquakes per day were recorded, and the hazard status was raised to Yellow. The character of the seismicity indicated ash-and-gas explosions up to 1,000 m above the crater. According to satellite data from Russia, ash deposits up to 35 km or longer extended in different directions on 19-22 April. According to observers from IV, on 18-24 April occasional ash-gas explosions up to 2,500 m above the crater occurred each day, and on 21 April, an ash-gas plume rose 1,500 m. Seismic activity was above background levels on 24-27 April and at background levels on 27-30 April. During 24-26 April 50-100 volcanic earthquakes per day were registered. The character of the seismicity indicated that three eruption events (possibly ash-and-gas explosions and rock avalanches) occurred on 24 April. According to satellite data from Russia, wide ash deposits longer than 35 km and three narrow ash deposits less than 5 km long extending SE and W and SW from the volcano, respectively, were noted on 25 April and 28-29 April. According to observers from IV FED RAS, on 24 April, an ash-gas plume rose 2,500 m above the crater.

Activity during May 2003. The alert level Color Code remained at Yellow for the month, with intermittent explosive eruptions continuing. Occasional explosions up to 1,500 m above the volcano, producing ash, were considered to be possible, as well as ashfall within a few tens of kilometers. Seismic activity was at background levels during 3-16 May. According to satellite data from Russia, the summit of the volcano was black on 4 May. For the week of 10-16 May, seismic data indicated that 10 ash-and-gas explosions reached heights up to 1,000 m above the crater, and hot avalanches possibly occurred. According to satellite data from the USA and Russia, a weak 1-pixel thermal anomaly on 14 May, and strips of ash deposits extending >10 km to the S, SSE and SE on 14-15 May were noted. Seismicity was above background levels on 16-30 May.

During 18-21 May, 150-320 local shallow events occurred per day. The character of the seismicity indicated ash-and-gas explosions to heights of 1,000 m above the volcano, gas blow-outs and hot avalanches. According to satellite data from the USA and Russia, a 2-4-pixel thermal anomaly was observed during 18-22 May. Ash deposits on snow E and SE of the volcano were noted on 18 May. Gas-steam plumes extending up to 45 km NE and N of the volcano on 19 and 21 May were noted. For the week of 24-30 May, 280-330 local shallow seismic events occurred per day. The character of the seismicity indicated ash-and-gas explosions to heights of 1,000 m and gas blow-outs. A thermal anomaly continued to be observed. On 25-26 May, gas-and-steam plumes extending 15-115 km SSE from the volcano were noted. Ash deposits on the snow in a different direction from the volcano were noted on 26-27 May.

Geologic Background. Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

Information Contacts: Olga Girina, Kamchatka Volcanic Eruptions Response Team (KVERT), a cooperative program of the Institute of Volcanic Geology and Geochemistry, Far East Division, Russian Academy of Sciences, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia, the Kamchatka Experimental and Methodical Seismological Department (KEMSD), GS RAS (Russia), and the Alaska Volcano Observatory (USA); 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 and Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.

From December 2002 through June 2003, lava from Kilauea continued to flow down the S flanks and into the ocean at several points. Seismicity generally continued at normal (background) levels. The Mother's Day flow, which began erupting 12 May 2002, continued through June 2003 (figure 158).

Figure 158. Map of lava flows erupted during 1983 through 16 May 2003 from Pu`u `O`o and Kupaianaha. The most recently active flows are on the SW side of the flow-field. Courtesy of HVO.

Lava flows. During December 2002, lava continued to flow into the sea at entry points from two lava deltas. Moderate-to-large littoral explosions tossed spatter onto the front of the West Highcastle delta. Surface lava flows were visible on the coastal flat. On 15 December, shortly after 0700, the Wilipe'a lava delta partially collapsed, losing about 1/3 of its area. The tip of the delta retreated shoreward about 260 m and most of the collapse was in the central part of the delta. Around 15 and 16 December a substantial collapse occurred at the West Highcastle delta. On 28 December moderate collapses occurred at the Wilipe'a lava delta, apparently in the area of the 15 December collapse. Surface lava flows were visible on the coastal flat and upslope on Pulama pali.

During January and February 2003, lava continued to flow into the sea at the West Highcastle entry. Surface lava flows were visible on the coastal flat and upslope of it on Paliuli. Most of the surface lava flows on the coastal flat crusted over, so that less incandescence was visible than previously. Relatively large surface lava flows were visible starting on 21 January around 2035. Around 28 January a large lava breakout occurred from the West Highcastle lava tube about 170 m inland from the old sea cliff. As of 2 February the area of the new breakout was about 6.15 hectares (6.15 x 10⁴ m²), and surface flows and lava in lava tubes traveled down the Pulama pali fault scarp. The Chain of Craters road was closed due to a wildfire that was started by lava flows. Surface lava flows continued to travel through vegetation, igniting fires and causing methane explosions. Rangers' office huts, restrooms, and signs were moved out of the path of the lava flow, which reached the Chain of Craters Road on 19 February at 1005. Beginning 15 February and going into March, lava flowed into the sea at the Kohala entry. Fresh lava oozed out of the cooling Kohala lava flow, both within the body of the flow and along its E margin.

During 26 February to 3 March lava continued to enter the sea at the West Highcastle entry, but the lava-flow rate was reduced to a small trickle at the Kohala entry. Small surface flows occurred along the W edge of the Kohala lava flow and surface lava flows were visible above the Pulama pali fault scarp. Tongues of lava were visible traveling down Pulama pali, part of the activity that began on 12 May 2002 (named the Mother's Day flow).

Through April 2003, Kilauea continued to erupt, sending lava down its SE flank either traveling over the land surface or through tubes. Lava entered the sea at the West Highcastle entry; activity there was sometimes weak, though one or more glowing areas were typically seen. On 16 April a large tract of land not over-run by surrounding lava (a kipuka or ahu in the local parlance) remained within the Kohola lava flow, still ~30 cm above the top of inflated lavas that surround it. On the eastern margin of the swath of lava flows going down the steep slopes of Pulama pali, one partly crusted-over lava stream was highly visible. The crater of Pu`u `O`o was dark and obscured by fumes, but eruptive activity at Pu`u `O`o continued unabated. The flows on Pulama pali were frequently visible at night as streams of incandescence from the top of the pali down to the coastal flats. Late in April, the E arm of the Mother's Day flow split in two with the W segment being more active. A new ocean entry near Lae'apuki only lasted a day before the flow stagnated. Scattered surface breakouts were seen throughout the inflating Kohola flow, especially on its W side. As of 24 April, lava entered the ocean at two points along the West Highcastle delta.

In early May, lava flows continued to descend the S flanks and pour into the sea. On 12 May lava began to enter the sea again at the West Highcastle lava delta. Surface lava flows were visible on the coastal flat and the Pulama Pali fault scarp. During June, lava continued to flow down Kilauea's SE flank, with surface lava flows occasionally visible on the coastal flat and upslope at Pulama pali, and Paliuli. Small amounts of lava continued to flow into the sea at Highcastle beach.

Geophysical activity. During December 2002 and January 2003, seismicity was generally at normal levels. The swarm of long-period earthquakes and tremor beneath Kilauea's caldera, occasionally seismically active since June 2002, continued to show some short bursts of tremor interspersed with small earthquakes. Small inflation and deflation events occurred at Pu`u `O`o and Uwekahuna tilt meters. The Pu`u `O`o tiltmeter showed deflation for about one week from 10 to 17 December. During 27-28 December, slight deflation occurred at the Uwekahuna and Pu`u `O`o tiltmeters.

Kilauea's summit began to deflate on 20 January 2003 at 1710, and Pu`u `O`o began to deflate a few tens of minutes later. Both areas deflated well into the next day. On the 21st at 1610 rapid, brief inflation began at the summit. The inflation and preceding deflation were centered near the NE corner of Halemaumau Crater, the normal center of small deformation events. Seismicity increased with the deformation events, returning to normal levels afterwards. By 22 January seismicity had returned to its normal level, with the long-lasting swarm of long-period earthquakes and tremor at Kilauea's summit continuing at weak-to-moderate levels.

During February and March, seismicity was at background levels. The long-lasting swarm of long-period earthquakes and tremor at Kilauea's summit continued at low-to-moderate levels. On 9 and 10 February, short periods of deflation and inflation occurred at the Uwekahuna and Pu`u `O`o tiltmeters. Moderate tremor was recorded by the nearest seismometer to Pu`u `O`o until the seismometer broke on 5 March. Moderate deflation occurred on 8 March, first at the Uwekahuna tiltmeter and then at the Pu`u `O`o tiltmeter. According to a news report, a member of a tour group suffered burns on 10 March when he fell on hot lava while hiking near Chain of Craters road.

For about a week in early April, volcanic tremor at Pu`u `O`o was relatively high and small deformation changes occurred, mostly at Pu`u `O`o. During 16-17 April, the Uwekahuna tiltmeter at Kilauea's summit recorded three small inflations, the last apparently right at its crest. Pu`u `O`o has generally followed suit, though in this case showing only two of the inflations very well. These tilts are not major but continue to illustrate the clear connection between Kilauea's summit, where most tilt events start, and Pu`u `O`o, 20 km away, where the tilt events follow a few minutes later. Seismicity during the week was at low to normal levels. Instruments continued to register the summit swarm of long-period earthquakes and tremor, which began last June. Volcanic tremor at Pu`u `O`o remained elevated, as has been the norm for more than a week.

During 30 April to 6 May, distances measured across Kilauea caldera between two points ~10 km apart, remained stable as they have since early 2003. There had been consistent progressive lengthening of this distance during late 2001 through mid-2002, and some minor fluctuations after that. In general, tilt during late April through 2 May changed little at Uwekahuna station (W side of the caldera), and showed a progressive decline at Pu`u `O`o station (E of the caldera). In the first few days of May slight inflationary tilt appeared at both stations.

Seismicity at Kilauea's summit was at moderate-to-high levels from about 1 June through 14 June, with many small, low-frequency earthquakes occurring at shallow depths beneath the summit caldera. The tiny earthquakes occurred at the notably high rate of 2-4 per minute. Little or no volcanic tremor accompanied the swarm, however. Volcanic tremor at Pu`u `O`o remained moderate to high, as is the norm. A quasi-cyclic inflation and deflation occurred at Kilauea's summit and at Pu`u `O`o during the week of 6-13 June, but did not culminate in significant overall tilt.

Geologic Background. Kilauea, which overlaps the E flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 km2, destroying nearly 200 houses and adding new coastline to the island.

Information Contacts: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawaii National Park, HI 96718, USA (URL: https://volcanoes.usgs.gov/observatories/hvo/).

During 6 January-4 May 2003, higher-than-normal activity was dominated by deep and shallow volcanic earthquakes (table 5), along with gas-and-ash emissions. Several explosions occurred during a period of increased activity in late January-early April. Throughout the report period, a "white-thick ash" emission rose 25-500 m above Tompaluan crater. The Volcanological Survey of Indonesia (VSI) issued a special report during 1-13 February 2003 that described activity in 2002 and early 2003 leading up to the recent increase in activity (table 6).

Table 5. Seismicity at Lokon during 6 January-4 May 2003. Courtesy VSI.

Table 6. Summary of a special report of activity at Lokon during 2002-2003. Courtesy VSI.

On 25 January, there was a felt shock (I on the MMI scale). During late January, ash emissions from the crater thickened and emission earthquakes increased. On 3 February the number of deep volcanic earthquakes began to increase at 0600; by 1000, 35 had occurred.

Ash emissions continued to thicken and deep and shallow volcanic earthquakes increased during early February. Emission earthquakes also increased, indicating some low ash explosions. On 8 February at 0443 an explosion ejected ash and glowing material. A booming sound was heard for 30 seconds. A dense ash cloud reached 1,400 m above the crater. Ash fell over the S part of the crater and around Kayau, Tara-tara I and II, and Woloan II and III villages. Ashfall reached thicknesses of 0.5-1 mm. The Alert Level was increased from 2 to 3 (on a scale of 1-4).

Explosions occurred on 10 February at 1405 and 2219. The maximum amplitude of the explosion earthquakes was 50 mm. The height of the ash column could not be observed due to heavy rain. Explosion activity continued on 12 and 16 February. VSI reported that the Alert Level was increased to 4 on 12 February at 0800. From that time through 1100 on 12 February, shallow volcanic earthquakes increased to a total of 164. An explosion followed at 1102, but the ash column could not be observed due to heavy rain. Tremor was recorded beginning on 13 February with amplitudes of 0.5-38 mm.

VSI reported that during 18-20 February, there were 16 explosions and a "white-gray ash" column rose 500 m. An explosion on 22 February was preceded by a swarm of 224 shallow volcanic earthquakes. On 21 February, 29 deep volcanic earthquakes occurred. Within two days, the number of volcanic earthquakes decreased gradually and ended with a large explosion on 23 February at 1034. The explosion was accompanied by thundering and a booming sound, and a "thick-gray ash" column reached 2,500 m above the crater. Ash drifted toward the SE. Tremor (with an amplitude of 1-20 mm) began soon after the explosion. Lokon was at Alert Level 3 during 17-23 February.

During 24 February-2 March, 12 explosions occurred and a "white-gray ash" column rose 300 m. An explosion on 2 March at 2129 was accompanied by glowing material that fell within the crater. A dark gray ash column rose 1,500 m above the crater and ash fell toward the Tondano area (~14.5 km from the crater) with a thickness of ~1 mm. Tremor (with amplitudes of 0.5-25 mm) began soon after the explosion. The explosion had been preceded by a swarm of 204 shallow volcanic earthquakes. A total of 77 deep volcanic earthquakes occurred during 26 February-1 March 2003. Following the 2 March explosion, there were 2 medium-intensity explosions that produced a ~600-m-high "white-gray ash" column.

Ash explosions and emission earthquakes ended on 14 March. On 24 March, the Alert Level was lowered to 2. Normal activity continued, comprised mainly of "white-thick ash" emissions from Tompaluan crater that reached up to 300 m. Tremor continued with amplitudes of 0.5-12 mm.

On 27 March at 0156, an explosion produced a 1,500-m-high ash column that was accompanied by glowing material. Booming and blasting sounds were heard. Ash drifted S and some fell around the edifice, while glowing material reached 400 m high before falling around the crater. Activity was low after the explosion. Tremor continued with amplitudes of 0.5-24 mm.

Following another explosion on 1 April, activity at Lokon decreased. A "white-thick ash" plume continued to rise 100-450 m above the crater. Seismicity was dominated by tremor with amplitudes of 0.5-25 mm. Shallow volcanic earthquakes increased on 15 April to 106 events. Through 20 April, the daily number of shallow volcanic earthquakes fluctuated between 23 and 56 events, but there were no explosions. Activity remained low, but above normal, through at least 4 May.

Geologic Background. The twin volcanoes Lokon and Empung, rising about 800 m above the plain of Tondano, are among the most active volcanoes of Sulawesi. Lokon, the higher of the two peaks (whose summits are only 2 km apart), has a flat, craterless top. The morphologically younger Empung volcano to the NE has a 400-m-wide, 150-m-deep crater that erupted last in the 18th century, but all subsequent eruptions have originated from Tompaluan, a 150 x 250 m wide double crater situated in the saddle between the two peaks. Historical eruptions have primarily produced small-to-moderate ash plumes that have occasionally damaged croplands and houses, but lava-dome growth and pyroclastic flows have also occurred. A ridge extending WNW from Lokon includes Tatawiran and Tetempangan peak, 3 km away.

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported small ash and steam explosions from the Mayon volcano on 5 April, 6 May, and 14 May 2003. The alert status for the area around the volcano remained at Alert Level 1 on a scale of 0-5 (indicating an increased likelihood for steam-driven or ash explosions to occur with little or no warning). PHIVOLCS reminded the public to continue avoiding entry into the 6-km-radius Permanent Danger Zone (PDZ), especially in the sectors where life-threatening volcanic flows might be channeled by gullies.

Activity during April 2003. Following a small ash explosion on 17 March 2003 (BGVN 28:03), a brief burst of ash and steam occurred at about 0600 on 5 April. The ash column rose to ~1.5 km above the summit crater before being blown SW. The explosion was recorded as a low-frequency volcanic earthquake, signifying a shallow source. Prior to the explosion, the volcano's seismic network had detected three small low-frequency volcanic earthquakes and three low-frequency short-duration harmonic tremors in the past 24 hours. Electronic tiltmeters indicated continuing slight inflation of the edifice. The increases in activity strongly indicated the likelihood of sudden ash explosions. Although no major eruption was expected immediately after the explosion of 5 April, there was growing evidence that magma was ascending the volcano's conduit.

Activity during May 2003. A small explosion from the crater at 0721 on 6 May produced a brownish ash-and-steam column that rose to ~450 m above the summit crater and was blown SW. The ash-and-steam column rose slowly with minimal noticeable force and was not detected by the volcano's seismic network, indicating a very shallow source. No significant seismicity occurred prior to the explosion. However, electronic tiltmeters on the N and S flanks continued to show inflation. Likewise, a precise leveling survey on 24 April 2003 showed a general inflation of the N flank. Alert Level 1 remained in effect.

At 1813 on 14 May, a small ash puff was emitted from the summit crater. This very brief explosion caused a small volume of ash and steam to rise less than 100 m above the crater and to later be blown NW. The Mayon Resthouse and Sta Misericordia seismic stations recorded the ash puff as a small-amplitude event. Prior to the ash explosion, one short-duration tremor was recorded. Volcanic gas outputs were notably moderate in volume, and the sulfur dioxide emission rates increased from the previous 1,824 metric tons per day (t/d) to ~3,088 t/d. The seismic characteristics associated with the ash and steam emission appeared similar to, though smaller than, previous explosions since 22 October 2002, indicating that this ash puff was very minor. This assessment was also consistent with the smaller volume of ash produced.

Geologic Background. Beautifully symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the Philippines' most active volcano. The structurally simple edifice has steep upper slopes averaging 35-40 degrees that are capped by a small summit crater. Historical eruptions date back to 1616 and range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, PHIVOLCS Building, C.P. Garcia Avenue, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost. gov.ph/).

Monowai is a frequently active submarine volcano, with a volcanic swarm recorded in November 2002 (BGVN 28:02) and another during April-May 2003. A major part of its volcanic activity is detected by hydro-acoustic waves (also called T-waves) generated during the eruptions, through the Réseau Sismique Polynésien (RSP), the French Polynesian seismic network (table 1).

Table 1. Seismic station codes and coordinates of instruments in the French Polynesian seismic network. Courtesy of RSP.

A strong volcanic swarm located on the Monowai seamount was recorded during April-May 2003 (figure 13). This volcanic swarm was very well located around Monowai, using the inversion of the arrival times of T-waves recorded by the network. As an example of the precision of location, with the contribution of some IRIS stations like RAR (Cook Island) to enlarge the array dimension, the ellipse of error can typically be 13 km on the major axis and 2 km on the minor axis, with a Root Mean Squared (RMS) of 0.25 s.

Figure 13. T-wave amplitude versus time for the TVO seismic station, showing the three distinct and well separated episodes of the Monowai Seamount swarm. Courtesy of RSP.

This volcanic swarm was composed of three episodes lasting 4-5 days each. It started suddenly on 10 April 2003 with a rate of 100 events per day (about one signal every 10 minutes) and reached a maximum intensity later that day. The average rate over the first four days was 75 events per day (300 signals between 10 and 14 April), but the number of events detected is thought to be underestimated by a factor of at least 3 to 5 because only the main packets of recorded T-waves were picked. Volcanic activity started again during 19 April, with 120 events recorded in the next five days. The last episode occurred between 3 and 6 May, with ~100 volcanic signals recorded. The swarm ended as suddenly as it started.

Geologic Background. Monowai, also known as Orion seamount, rises to within 100 m of the sea surface about halfway between the Kermadec and Tonga island groups. The volcano lies at the southern end of the Tonga Ridge and is slightly offset from the Kermadec volcanoes. Small parasitic cones occur on the N and W flanks of the basaltic submarine volcano, which rises from a depth of about 1500 m and was named for one of the New Zealand Navy bathymetric survey ships that documented its morphology. A large 8.5 x 11 km wide submarine caldera with a depth of more than 1500 m lies to the NNE. Numerous eruptions from Monowai have been detected from submarine acoustic signals since it was first recognized as a volcano in 1977. A shoal that had been reported in 1944 may have been a pumice raft or water disturbance due to degassing. Surface observations have included water discoloration, vigorous gas bubbling, and areas of upwelling water, sometimes accompanied by rumbling noises.

Information Contacts: Dominique Reymond and Olivier Hyvernaud, Laboratoire de Geophysique, CEA/DASE/LDG Tahiti, PO Box 640, Papeete, French Polynesia.

Nyiragongo, located along the East African Rift (figure 27), ceased generating flank lava flows following its January 2002 eruption, but remained active inside its summit crater where it hosts a restless lava lake. Observations made by staff from the Goma Volcano Observatory (GVO) in August 2002 included the opening of a new sinkhole, and measurements of CO₂ and O₂ gas concentrations at three fumarolic areas (locally termed mazukus). For context, handbook values for CO₂ concentrations and their resulting symptoms in humans are discussed. The GVO has also brought to light reports from local residents of abnormally rapid ripening of picked bananas (and in some cases yams) prior to the January 2002 eruption.

Figure 27. Schematic map illustrating the trend of the East African rift. The rift's overall shape is curved, concave towards the E, and it contains a central segment composed of two branches passing on the E and W sides of Lake Victoria (V). The overlapping triangles labeled N at the N end of the rift's Western segment identify the approximate location of Nyamuragira and Nyiragongo volcanoes N of Lake Kivu. The latter volcano sits to the E and closer Lake Kivu. This figure is based on one in an online book by W.J. Klius and R.I. Tilling of the US Geological Survey. A smaller scale map showing some often mentioned local features appeared in BGVN 26:03 (Nyamuragira report).

This report also discusses GVO and resident volcanologist summit crater visits during late November 2002-early May 2003. In all cases the lava lake within the summit crater remained dynamic, with one or more windows on the crater floor exposing agitated molten lava. During this interval, degassing continued and tephra fell on the upper flanks. A summary of some ancillary observations such as seismicity measured on the GVO network is also provided.

A later section discusses ash plumes as described in aviation reports. Ash clouds extended as visible swaths on satellite imagery for up to ~100 km from the volcano. These reports include some as recent as 15 May 2003. The final section discusses MODIS thermal imagery during late 2002 through early 2003. The 2003 MODIS data reflect the lava lake seen deep within the summit crater. Finally, satellite data show atmospheric SO₂ burdens for the Nyiragongo-Nyamuragira region during 13 December 2002 to 15 June 2003.

GVO's August 2002 field observations. On 12 August 2002 GVO was called to Bugarura village upslope from Munigi on the S flank. A new sinkhole had developed that morning, leaving a steaming opening ~3-4 m in diameter. Scientists could not see the opening's bottom through the steam, but they timed falling stones and estimated the sinkhole's depth at ~15 m. The odorless gas being emitted led them to believe that the steam chiefly represented vaporized groundwater.

GVO staff and collaborators hoped to advance gas monitoring efforts by measuring CO₂ and other escaping gases at multiple sites in the region. They continued to make spot-checks with hand-held devices, but also sought a more-nearly continuous record from dedicated monitoring instruments. Although noxious gases are a familiar problem in volcanic areas, some of the gas concentrations in the rift are surprisingly high for areas adjacent human habitation. The Swahili word mazuku allegedly connotes places associated with "evil winds," and the term is currently used to describe fumarolic areas, which have also been described as dry gas vents.

Possible precursors to January 2002 eruption. In the weeks before the 17 January 2002 eruption, there were widespread reports of picked crops ripening at unusually rapid rates. From the settlements of Rusayo (8 km SW of the summit) and Katale (~18 km NNE of the summit and ~10 km NE of Nyamuragira's summit) people reported in early January that the normal 5-day ripening processes of bananas placed in the ground decreased to only 2 days. From Rusayo, people also reported that sweet potatoes, which are normally sun-dried on the ground surface, dried even without sun. GVO observers saw this first-hand and, as a result sought funds to hire porters and observe Nyiragongo directly, but the eruption began before the expedition started.

Although radiant or conductive heat may have been a factor (since heat speeds up the ripening process), heat's transport to broad areas on the surface by conduction through rocks would be comparatively slow. Heat at depth may have more rapidly reached the surface in the form of heated, liberated gases (such as steam). Discussions with gas chemist Vern Brown and a scan of the literature also revealed that the release of certain gases could conceivably have played another role as well. Both acetylene (C₂H₂, a colorless, flammable gas with an odor similar to garlic and slightly less dense than air) and C₂H₄ (ethylene, a colorless, faintly odorous gas less dense than air) speed up the ripening process in many agricultural products (including bananas and yams). Ethylene can cause banana peels to shift from green to yellow at low (ppm) concentrations. These gases occur naturally and may form or escape in association with heating organic material. In contrast, CO₂ generally slows the ripening process. For the interval prior to the January 2002 eruption, observers lack documentation of increases in degassing or heating.

Seismicity and crater visits, November 2002-May 2003. Multiple GVO crater visits were documented: 23-25 November 2002; 9-10 and 21-22 January 2003; 4-5 and 25-26 February 2003; 18-19 March 2003; 22-24 April 2003; 6 May 2003. GVO also sent out occasional updates discussing seismicity and other observations.

During 23-25 November 2002, GVO team members Kasereka Mahinda, Ciraba Mateso, Arnaud Lemarchand, and Jacques Durieux watched the active lava lake on the crater floor. The lake was then located within the southern crater in the 16 November collapsed area. Two broad openings lay at the bottom of this new depression; both permitted viewers to see the lava lake's surface. A third, smaller opening ejected only high-temperature gases. The great quantity of gas occupying the bottom of the crater thwarted efforts to carry out a precise laser-based measurement of the depth to the lava-lake surface. The visual estimate for this depth from the summit was ~700 m.

The lava lake was very active, as it was before 1977. The lava surface was disturbed by the rise of abundant large gas bubbles. Breaking bubbles threw molten fragments onto the margins of the two openings. Consistent with the bubbles and constant degassing, a gas plume was visible at night from Goma. Occasionally, light dustings of tephra and Pele's hair came from the crater and fell on the surrounding areas. Although the current lake was impressive, the observers pointed out that the crater has contained a dynamic lava lake for nearly 50 years. The earlier lake's surface was much larger and stood nearly 500 m higher.

Jean-Christophe Komorowski accompanied GVO staff on a climb up Nyiragongo on 9-10 January 2003. While on the upper slopes, the climbers heard a few detonations associated with more energetic gas plumes. From the rim they saw a deep pit in the SW part of the inner crater. There were two vents on the crater floor separated by a thin rocky ridge. The SW vent (vent A) was characterized by a high-pressure fluctuating gas jet that gave off very loud roaring noises, along with flames of incandescent and combusting gases. Condensing steam clouds here were dense, rendering visual observations difficult. The other active vent (vent B) was just to the NE and consisted of an area of stable incandescence at least 100 m in diameter with an active lava fountain. Projections of lava spatter there took place every 30-60 seconds and typically reached 40-60 m in height.

The large area of incandescence indicated that a small lava lake must have been present deep in the pit, although the observers never saw the moving lava surface. Peak high-pressure degassing in vent A did not necessarily correlate with peak lava fountaining activity at vent B. Observations were conducted for several hours at night and during the day. Laser binocular measurements established the crater floor's depth at ~800 m. Very light ash consisting of Pele's hair and tears, and millimeter-sized vitric scoria fragments fell continuously on the rim. Conditions were made difficult at times when the SO₂-rich gas plume blew towards the W.

Acid rain that flushed the volcano's SO₂ gas plume, sampled at elevation 2,600 m, had a pH of 2.26. In contrast, rain collected in Kibati (below 2,000 m on the SSE flank) on 6 January had a pH of 6.15. Damage to about two-thirds of the vegetation by acid plume condensates was evident above 2,900 m on the SW and S flanks.

Compared to the last visit by GVO staff, 30-31 December 2002, degassing had increased significantly. However the level of the lava in the crater and/or lake had not risen and might have dropped lower in the conduit. The gas-plume height, measured regularly by the GVO, reached 4,500-5,000 m altitude. At times, although the very loud roaring sound remained unchanged, the entire crater became gas-filled to an extent that incandescence was entirely blocked, even from the vantage of surrounding villages. Information brought regularly to the attention of the GVO by the populations of Kibati, Mudja, Mutaho, and Rusayo villages attested to their exposure to the gas and ash plumes from Nyiragongo. Through at least early May 2003 the volcano's hazard status remained at yellow ("vigilance," the second lowest level on a 4-step scale).

Another climb enabled observers to peer into the crater during 21-22 January 2003 (figure 28). Compared to the 9-10 January observations, only one opening remained active inside the crater. The former vent A probably disappeared following a collapse. The active opening had about the same diameter and its lava fountain attained similar heights compared to earlier vent B observations. The level of the lava had not changed in the crater, remaining deep in the volcanic conduit. Degassing had increased significantly. Periodically more vigorous lava fountains sent smaller fragments to higher elevation that cooled to black scoria fragments. A small scoria cone had started to build around the active vent. Recent small lake overflows formed thin lobate lava sheets around the vent. The ascent velocity of individual gas plumes within the crater varied between 7 and 12 m/s.

Figure 28. A photo of Nyiragongo's crater and the one opening in the lava lake visible on 22 January 2003. Copyrighted photo used with permission of GVO.

A series of incandescent pits extended to the SE of the active pit along a line that corresponds to a major pre-existing fault-fracture system trending N25°W. This system transected the crater from NW to SE and linked with the upper Shaheru fracture and 1977 vent network that reactivated in 2002. A hot fracture zone trended N10°E-N20°E in the NE part of the crater wall. This zone had extended into the active deep crater forming a conspicuous, elongate, vertical-walled canyon. Observers frequently heard and saw rockfalls, and noted that those events often generated plumes that spread and deposited ash over local vegetation. Intra-crater ash reached 5 mm in thickness. The gas plume remained rich in SO₂. Rain water collected at the top of Nyiragongo had a pH of 2.84.

The late-January plume height estimated during favorable atmospheric conditions by GVO members varied from 4,500 to 5,500 m altitude. Often, the prevailing wind carried ash, cinder, and Pele's hair S towards Kibati, Rusayo, Mudja, and Mutaho villages.

A 13 February GVO report said that for four consecutive days, Pele's hair fell in Goma, 17 km SSW. Although cloudy and foggy due to the start of the rainy season, Nyiragongo's plume reached at least 5 km above the crater. Between Goma and the Nyiragongo stood heavy gray-to-black ash-rich clouds. The fall of Pele's hair was due to lava fountains inside the crater.

The same report noted that seismicity was probably lower than the previous week and consisted of low tremor, few long-period earthquakes, and almost no tectonic earthquakes. Very small-amplitude seismic noise (small earthquakes) occurred, presumably due to collapses and perhaps intra-crater explosions.

GVO went on to say that one side effect of the ash falls was that villages around Goma had serious water shortages, since they rely on collecting rainfall. All UN agencies and NGOs were informed and asked to start potable water distribution around Goma. A few more physical problems might arise because of the Pele's hair, including stress on people's eyes and breathing. Crops around the volcano in some cases have been burned by acid rains and ash, while cattle might also suffer from ingestion of ash-polluted grass.

The 25-26 February ascent revealed more robust activity than observers had seen on their 4-5 February visit. By the latter date, all vegetation had died near the main crater. Approaching the rim in the upper 220 m of the ascent, tephra falls had accumulated to form deposits several centimeters thick; those, along with acidic plumes, had killed plants. The flora and fauna at lower elevations were still surviving, although they showed signs of serious stress. Loud sounds were audible several kilometers from the central crater. Intra-crater activity seemed intense, but thick fumes in the crater area thwarted day-time visibility. On 25 February views from the W rim revealed that a spatter cone had begun to grow on the crater floor. Lava fountaining occurred all night; discharging lava probably rose more than 100 m high, but it was difficult to assess the maximum rise height. Lava fountains chiefly came out at one spot, although a second, much smaller point of emission gave off mainly flames and sometimes scoria. Pele's hair fell all night long.

An update disseminated on 27 February 2003 noted that compared to previous weeks, during 21-27 February Nyiragongo's activity had decreased, although seismicity measured on the S flanks continued to contain low-amplitude tremor. S-flank seismicity also contained comparatively few long-period (LP) earthquakes. The update also said that local winds had begun to blow predominantly from the ENE, thus sweeping plumes and associated tephra falls clear of Goma. A 22 February visit to the SW-flank settlement of Rusayo revealed conspicuous tephra deposits on roofs and trapped in the crevices of banana trees.

During a visit to Nyiragongo on 18-19 March, GVO scientists observed a thick plume engulfing the crater. Two possible emission points were noted; one was related to powerful lava and ash emissions, and the other was related to a much weaker white-pink plume. An inner active cone was visible in the crater and was at least 200 m in diameter. Lava fountains rose to maximum heights of 150-200 m and as low as 50 m. Scoria ejection made observations difficult at times. Several permanent fumaroles, also observed during the previous visit, were seen in the crater.

Dario Tedesco noted that the cone morphology seemed slightly different from the trip 3 weeks earlier. He observed that on the N side of the crater a new platform had been formed, probably due to the continuous accumulation of ejecta, scoria, and ash. The team saw a huge lava fountain of at least 150-200 m in height. In contrast, when viewed in late February, fountains seemed to remain below ~100 m in height. The lava fountains generated abundant falling ash of millimeter size at the observation point, a process that lasted all night long.

Stronger and higher lava fountains, reaching almost 300 m high, were witnessed at 0230 on 19 March. The eruptive vigor as well as the intensity of the falling tephra declined at 0530. The last witnessed activity was of 50-m-high fountains. A second pit was noted on the E side of the crater that had been hidden during the night by the very thick plume.

For many days prior to visits on 22-24 April the seismic stations considered most representative of the Nyiragongo activity only registered very weak and steady continuous tremor. Although other types of seismicity were absent in the, A-type and C-type earthquakes occurred near the volcano. Despite the comparative seismic quiet, a prominent gas plume rose from the volcano. When weather conditions permitted, the plume top was measured at 5-6 km altitude.

The 22-24 April field excursion noted five distinct vents on the crater floor, almost continuous emissions of tephra, an agitated molten-lake surface that included emerging gas, and lava splashing 50-60 m high. Occasional waves of lava rolled across portions of the crater floor and walls. Excursion members also witnessed crater-wall collapses taking place along the NW and S fracture zones.

Widely felt earthquakes also continued in the region, presumably related to extension along the massive East African rift system. For example, three C-type events occurred on 23 April below Nyiragongo at a depth of ~15 km. During the whole day of 24 April, sustained tremor plus C-type events registered. On 25 April a few seismic events occurred amid sustained tremor. A main volcano-tectonic shock had been recorded and later a series of A-type events in the Nyiragongo field, between the S flank and Lake Kivu. Increasing tremor followed. For the rest of the week, the seismic network recorded a concentration of volcanic events to the NW and the S of the volcano, along the preferential fracture axis.

On 2-3 May unusually dense ash plumes were visible from Goma. Continuous ashfall occurred in many villages close to the volcano, and permanent tremor and long-period earthquakes were recorded. SO₂ emission rates were relatively high during 1-6 May, with the largest emission on 3 May (~50,000 tons, see TOMS data below). UN peace keepers provided a 3 May helicopter flight that gave volcanologists clear views of the crater. The lava lake's molten surface appeared slightly larger than during a visit to the crater rim on 22-24 April. At that time a significant plume containing gas and ash rose high above the volcano.

On 6 May GVO climbers entered the village of Kibati, the usual departure point for the ascent, ~8 km from the crater rim. Kibati residents told how ash falls and acid rains had negatively affected local crops. For example, bean leaves had been burnt in many places. Along the ascent, at 2,260 m elevation, Pele's hair was found, including some intact individual strands 30 cm long. At 2,700 m elevation, thin ash grains completely covered the vegetation. At 3,200 m elevation on the S flank (~270 m below the summit), all vegetation had died.

Atmospheric conditions initially allowed quite clear views from the crater rim. The lava lake underwent violent outbursts from bursting of gas bubbles estimated at up to 40 m wide. The resulting projections of spatters and surges splashed on the walls of the pit. The lake had regained its former dimensions (~60 m across). The wider lake, recently seen from helicopter, had shrunken, leaving a solid platform on its side. Pressure of the escaping gases seemed very high and yielded a continuous roaring. GVO climbers again witnessed intermittent pale yellow-green flames hurling from the vents up to 50 m high.

At 0644 on 6 May a seismic shock was felt by the team on top of the volcano. It was recorded by the whole network as a low-amplitude long-period earthquake. Then, fog and gases halted further sightings into the crater. The fog lifted around 0100 on 7 May; at this time viewers saw a small narrow lava flow in the southern inner wall adjacent the active pit's margin ~200 m above the crater floor. The lava escaped out of what looked like a tunnel or tube. Although the lava descended at a steep angle and appeared to escape from the tube at a constant rate, its rate of advance remained slow. The lava front had not made it to the crater center. Below the tube, however, intricate individual lava flows had formed a long delta.

Aviation reports. A Volcanic Ash Advisory (VAA) for Nyiragongo was issued by the Toulouse Volcanic Ash Advisory Center (VAAC) on 6 March 2003. That advisory stated, "A cloud probably containing ash can be seen on [visible wavelength] METEOSAT imagery extending 100 NM [(nautical miles, 185 km)] westward from the volcano. "Several hours later the ash cloud was no longer visible. Advisories were also issue on 9, 12, 14, and 15 May 2003. The one for 9 May noted "Renewed activity since early May. Ash plume witnessed during a helicopter flight around early May up to 5-6 km above sea level. Many ash falls and acid rains all around the volcano." No cloud was observable due to convective weather clouds. The reports on 14 and 15 May stated, "According to Goma observatory [GVO], a plume of steam and ash is often emitted since early May. It may rise 1,500-2,500 m above the volcano's summit. No new message from Goma observatory since early May." Meteorological satellite (METEOSAT) imagery was unable to detect an ash cloud on 14 May due to weather clouds around the volcano.

MODVOLC Thermal Alerts. During early 2002 to early 2003 Nyiragongo was monitored on a daily basis with thermal satellite imagery (1-km pixel size). Investigators Matt Patrick, Luke Flynn, Harold Garbeil, Andy Harris, Eric Pilger, Glyn Williams-Jones, and Rob Wright used NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instrument and processed these data using the automated MODIS thermal alert system at the University of Hawaii, Manoa.

Prior to the January 2002 eruption, Nyiragongo activity appeared insignificant; anomalies were absent from the start of the MODIS-based alert system in April 2000, and through all of 2001. Anomalous pixels remained absent during 24 February-12 June 2002. The absence of anomalies could be explained either by a lack of exposure of the lava lake or by cloud cover obscuring the heat source from the satellite's view.

Nyiragongo's major effusive eruption in mid-January 2002 caused strong initial thermal anomalies (figure 29). Lava flows extending down the S flank to Lake Kivu resulted in anomalies as large as 45 pixels. Afterwards, the anomalies diminished quickly. Small intermittent anomalies (1-3 pixels) occurred near the summit for the remainder of 2002 and into early 2003, consistent with the kind of lava-lake activity described above.

Figure 29. A plot illustrating MODIS data for Nyiragongo with the sum for short-wave (4 micron, band 21) radiance as well as the sum for long-wave (12 micron, band 32) radiance for all anomalous pixels in each image. The x-axis (time axis) starts before the eruption in December 2001 and ends in early 2003. Courtesy of Hawaii Institute of Geophysics and Planetology, University of Hawaii, Manoa.

Atmospheric SO₂. The Earth Probe Total Ozone Mapping Spectrometer (EP TOMS) SO₂ data presented in figure 30 are preliminary. The bars indicated as "TOMS SO₂" plotted on the lower axis of the chart represent EP TOMS measurements on days when the signal was large enough to allow retrieval of the SO₂ mass. The height of these bars corresponds with the y-axis scale. Note that these values represent the SO₂ mass in a satellite 'snapshot' of the volcanic cloud taken around local noon, and not an SO₂ flux. The bars indicated as "Inferred SO₂" on the lower axis denote days on which the presence of SO₂ could be inferred from EP TOMS data, but the signal was too weak to allow retrieval of an atmospheric SO₂ mass. Hence these bars are non-quantitative, but they indicate that non-trivial SO₂ emissions probably occurred.

Figure 30. Preliminary atmospheric SO2 data taken from satellite measurements of the Nyiragongo-Nyamuragira region during 13 December 2002 to 15 June 2003. The data along the lower axis are from the EP TOMS instrument; the data on the upper axis are from the GOME instrument on the European satellite ERS-2. Only the data described as "TOMS SO2" are quantitative (see text). Blank spaces for certain days and time intervals on the chart imply that either a data gap occurred over the region, or that no SO2 was detected. One of these blank intervals in the EP TOMS data took place during 15-23 May 2003, in this case due to the one instrument shutdown during the data-collection period. Courtesy of Simon Carn.

More, non-quantitative data appear as bars indicated as "GOME detection" along the upper axis of figure 30; in this case, showing dates when another instrument detected SO₂ emissions in the region. These emission dates denote SO₂ detection over central Africa by the European GOME (Global Ozone Monitoring Experiment) instrument aboard the ERS-2 satellite. GOME measurements are based on scans by a visible- and ultraviolet-wavelength spectrometer. GOME has inferior spatial and temporal resolution to EP TOMS, but is more sensitive to atmospheric SO₂.

TOMS SO₂ mass retrievals are dependent on the altitude of the volcanic plume and are also affected by meteorological cloud cover, and therefore may be adjusted as more information becomes available. The largest of these preliminary estimates during this interval was in excess of 50 kilotons (kt) SO₂. These peaks in the first half of May 2003 were truncated by an instrument shutdown during 15-23 May. Given the crater and plume observations by GVO, and other data discussed above, the vast majority of the SO₂ shown on figure 30 was probably emitted by Nyiragongo.

CO₂ gas concentrations at three mazukus on the flanks of Nyiragongo in vicinity of Lac Vert at the ground surface measured up to ~40% by volume, but concentrations of the heavier-than-air gas dropped quickly with height above the ground surface. Spot measurements were made with a Geotechnical Instruments multi-gas landfill analyzer. Field notes reported CH4 concentrations consistently at zero and O₂ concentrations at only one site where it was 22 vol. % at the ground surface and 16-17 vol. % nearby. The 15 August 2002 field excursion was led by GVO scientists Mathieu Yalire, Ciraba Mateso, and Kasereka Mahinda, with Chris Newhall present.

Effects of carbon dioxide. People in the region apparently understand the hazard of escaping CO₂ gas, and in the past several years CO₂ gas exposure has not led to reported human fatalities. CO₂ gas, which is more dense than air at equivalent temperature and pressure, can be lethal to humans at 9-12 vol. % concentrations in as little as 5 minutes. The US standards for indoor air quality suggest that long-term human exposures remain below 0.1-0.2 vol. %, and that short-term (10- to 15-minute) exposures remain below 3 vol. %. The odor of CO₂ is too weak to warn of dangerous concentrations. Table 9 lists some symptoms associated with the inhalation of air containing progressively higher levels of CO₂.

Table 9. The AGA Gas Handbook included these CO₂ gas concentrations (in volume percent) and accompanying symptoms for adults in good health (after Ahlberg, 1985).

Reference. Ahlberg, K., 1985, AGA Gas Handbook: Properties & Uses of Industrial Gases, AB, Lidingo/Sweden, ISBN 91-970061-1-4 (out of print).

Geologic Background. One of Africa's most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. The steep slopes of a stratovolcano contrast to the low profile of its neighboring shield volcano, Nyamuragira. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

Information Contacts: Celestin Kasereka Mahinda, Kavotha Kalendi Sadaka, Jean-Pierre Bajope, Ciraba Mateso, and Mathieu Yalire, Goma Volcano Observatory (GVO), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, D.R. Congo; Dario Tedesco, Jacques Durieux, Jean-Christophe Komorowski, Jack Lockwood, Chris Newhall, Paolo Papale, Arnaud LeMarchand, and Orlando Vaselli, UN-OCHA resident volcanologists, c/o UN Office for the Coordination of Humanitarian Affairs, United Nations Geneva , Palais des Nations,1211 Geneva 10, Switzerland (URL: http://www.unog.ch); Tolouse Volcanic Ash Advisory Center (VAAC), Toulouse, Météo-France, 42 Avenue G. Coriolis, 31057 Toulouse Cedex, France (URL: http://www.meteo.fr/vaac/); Matt Patrick, Luke Flynn, Harold Garbeil, Andy Harris, Eric Pilger, Glyn Williams-Jones, and Rob Wright, Hawaii Institute of Geophysics and Planetology, University of Hawaii, Manoa (URL: http://modis.higp.hawaii.edu/); Vern Brown, President, ENMET Corporation, P.O. Box 979, Ann Arbor, Michigan 48106-0979 (URL: http://www.enmet.com/); Simon A. Carn, TOMS Volcanic Emissions Group, Joint Center for Earth Systems Technology (NASA/UMBC), University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250 USA (URL: https://so2.gsfc.nasa.gov/).

Since the middle of March 2003 the temperature of Ruapehu's summit Crater Lake had been slowly rising. The lake temperature rose from 30°C on 5 March (BGVN 28:02) to a high of 41.6°C on 15 May (table 11). Similar values were recorded in January 2003 when the lake temperature reached 42°C. This is the fourth time that the temperature of the Crater Lake has risen above 35°C since the start of 2001, and the temperature has been above 30°C since December 2002. It is not unusual for the temperature to cycle over periods of 6-9 months; minor hydrothermal activity can occur in the lake during temperature peaks. Lake temperatures dropped steadily from 41°C after mid-May. However, during the late morning of 26 May a steam plume was observed rising 200-300 m above Crater Lake. No seismicity accompanied this plume, suggesting that it was generated by atmospheric conditions alone (a warm lake and a cold, windless, morning). Steam plumes were also observed on 28 March and 21 April.

Table 11. Lake water temperatures measured at Ruapehu's Crater Lake, 5 March-1 June 2003. Courtesy of IGNS.

Weak intermittent seismic tremor was recorded through early April, then remained at a constant moderate level during 12-17 April. The following week, 18-24 April, there was an increase in tremor accompanied by discrete volcanic earthquakes. By 2 May volcanic tremor levels had declined, but volcanic earthquakes continued to occur. Levels of volcanic tremor fluctuated during the week of 3-9 May, with several periods of enhanced tremor and small volcanic earthquakes. Tremor had declined by 16 May, and seismicity remained very low through the 30th. The level of volcanic tremor began to increase slightly in early June, but the lake temperature was still declining during the week of 7-13 June. Very low levels of activity continued through the 20th. There were no significant changes observed in the lake water chemistry. The hazard status remained unchanged at Alert Level 1.

Geologic Background. Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The 110 km3 dominantly andesitic volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 ring plain of volcaniclastic debris, including the Murimoto debris-avalanche deposit on the NW flank. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. A single historically active vent, Crater Lake, is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene. Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent, and tephra characteristics suggest that the crater lake may have formed as early as 3000 years ago. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys.

Information Contacts: Institute of Geological & Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

A satellite-based interferometric synthetic aperture radar (InSAR) survey of the remote central Andes volcanic arc (Pritchard and Simons, 2002) revealed deformation in the Sabancaya area during June 1992-mid 1997. Inflation was detected ~2.5 km E of the Hualca Hualca cone and 7 km N of Sabancaya (figure 16), with the maximum deformation rate in the radar line-of-sight being ~2 cm/year. While not temporally well-constrained, this inflation seems to have stopped in 1997, perhaps related to the large eruption of Sabancaya in May 1997 (BGVN 22:07). No deformation was observed between mid 1997-December 2001. The inferred source depth was 11-13 km below sea level. Additional details about the study and analysis are available in Pritchard and Simons (2002).

Reference. Pritchard, M., and Simons, M., 2002, A satellite geodetic survey of large-scale deformation of volcanic centres in the Central Andes: Nature, v. 418, p. 167-170.

Geologic Background. Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning "tongue of fire" in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of historical eruptions date back to 1750.

Information Contacts: Matthew Pritchard and Mark Simons, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA (URL: http://www.gps.caltech.edu/).

At Santiaguito, the active lava-flow front continued to generate ash plumes through early 2002 (BGVN 27:05). INSIVUMEH reported that during January-October 2002, activity at Santiaguito included lahars, explosions, growth of the lava dome, and collapses from the Caliente dome. The main lahar during that period occurred on 8 January 2002. Farmers in the Monte Claro area heard rockfalls on the W flank. Field inspections near the San Isidro ravine showed an abundance of material deposited by mudflows and other volcanic debris, mainly fine ash. These deposits formed ash knolls called "hummocks." The San Isidro ravine begins at the Nimá II river, now covered by the SW lava flow, which created a dam ~200-300 m high. A rupture of the dam in the high part of the Brujo dome contributed fine material and blocks to the high-velocity lahar, which traveled ~4 km until it was stopped by old landslide deposits.

At the height of the Property Florida, there are old lahar deposits, possibly from the eruptions of Santa Maria in 1902 and/or Santiaguito in 1929, with blocks of 1, 2, 3, and 5 m in diameter. With the arrival of the rainy season, San Isidro, which became a new channel for lahars from May to October, had at least six "strong" lahars. The active lava flow from July 1999 had stopped its advance in the channel of the Nimá II river as of April 2002.

Since renewal of activity in April and May 2002, a new lava flow had been advancing on top of the high part of the existing lava flow, in front of the Santiaguito viewpoint. This constant movement was filling up the ravine that divided the lava flow from the El Faro farm. The new lava flow quickly built a small lobe reaching ~300 m high. It advanced in a fan shape toward the S and W flanks, with continuous collapses from the front.

A volcanic ash advisory issued on 16 August was based on a report from INSIVUMEH about a dome collapse with some near-summit ash. However, no ash was evident in GOES-8 satellite imagery. After 29 August there were frequent collapses from the crater rim of the Caliente cone, generating pyroclastic flows that extended to the base of the domes. The greatest collapse occurred on 3 October, accompanied by a strong explosion and several pyroclastic flows that descended all flanks of the volcano at high speeds, covering the volcano completely in a few minutes and producing abundant ashfall on the SW flank. During October there were continued collapses of the crater rim.

In the early hours of 17 October the inhabitants of the El Faro and La Florida farms, and areas such as Palmar Nuevo and part of San Felipe Retalhuleu, heard a strong explosion. At OVSAN (Vulcanológico Observatory of Santiaguito Volcano), this activity was felt, and a collapse of the dome from the edge of the crater was seen. After 19 October moderate and strong explosions occurred at a rate of 3-5 per hour, some accompanied by rumblings. There was also an increase in the number of phreatomagmatic ash explosions that sent abundant gray ash 800-1,200 m high, dispersed mainly on the SW flank. In November observers reported constant collapses of the SE and E lava flows. On the morning of 11 November there was a series of collapses from the S lava flow, and heavy ashfall on the seismic station housing.

Geologic Background. Symmetrical, forest-covered Santa María volcano is part of a chain of large stratovolcanoes that rise above the Pacific coastal plain of Guatemala. The sharp-topped, conical profile is cut on the SW flank by a 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank, and was formed during a catastrophic eruption in 1902. The renowned Plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic-andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four vents, with activity progressing W towards the most recent, Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

Information Contacts: Otoniel Matías and Gustavo Chigna, Unit of Volcanology, Geologic Department of Investigation and Services, Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hidrologia (INSIVUMEH), 7a Av. 14-57, Zona 13, Guatemala City, Guatemala; Washington VAAC, Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ssd.noaa.gov/).

The latest eruptive episode from Stromboli began on 28 December 2002 (BGVN 28:01) and included a significant explosion on 5 April (BGVN 28:04). This report includes field observations provided by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) through mid-June 2003. Thermal alerts based on infrared satellite imagery over the course of this eruption have been compiled and summarized by scientists at The Open University.

Activity during 17 April-16 June 2003. Effusion of lava from vents located at ~600 m elevation, on the upper eastern corner of the Sciara del Fuoco, continued until 16 June with a generally decreasing effusion rate. This caused a significant increase in the thickness of the lava field formed since 15 February to over 50 m. Since the 5 April eruption, the summit craters of the volcano have been blocked by fallout material obstructing the conduit. Small, occasional, short-lived explosions of hot juvenile material were observed on 17 April during a helicopter survey with a hand-held thermal camera, and on 3 May from the SAR fixed camera located at 400 m elevation on the E rim of the Sciara del Fuoco.

The effusion rate from the 600-m-elevation vents on the Sciara del Fuoco showed a significant decline between 1 and 4 May, when inflation of the upper lava flow field was detected through daily helicopter-borne thermal surveys. Inflation stopped on 6 May, when two new vents opened on the inflated crust of the flow field, causing drainage and spreading new lava flows along the Sciara del Fuoco. Between the end of May and early June, gas-rich magma was extruded from the 600 m vents on the upper Sciara del Fuoco. Spattering built up two hornitos, which in a few days reached an estimated height of over 6 m. This activity was accompanied by lava flow effusion along the upper Sciara del Fuoco, with lava descending to 150 m elevation.

On 1 June, Strombolian activity resumed at Crater 1 (NE crater). It was revealed first through helicopter-borne thermal surveys, and then by direct observations from the eastern Sciara del Fuoco rim. Most of the ejecta fell within the crater, and from the lower slopes of the volcano only pulsating dark ash emissions were observed. Strombolian activity stopped around 6 June, and occasional lava flows occurred at the hornitos at 600 m elevation on 11 June. The summit craters showed discontinuous ash emission until mid-June, and the SAR fixed camera at 400 m elevation showed a Strombolian explosion with abundant ash emission on the night of 15 June.

MODVOLC Thermal Alerts. MODIS thermal anomalies for Stromboli covering the period from the start of MODIS data acquisition over Europe in May 2000 until the present were compiled using data available at http://modis.higp.hawaii.edu/.

With the exception of single-pixel alerts on 8 July and 19 September 2000 (with alert ratios of -0.798 and -0.794, both barely above the -0.800 automatic detection threshold of the thermal alerts algorithm), activity at Stromboli remained below the automatic detection threshold until November 2002 (figure 74). In that month there were two single-pixel alerts, barely above detection threshold (-0.790 on 12 November and -0.792 on 28 November). Thermal infrared radiance was higher than ever before at the time of the MODIS overpass on 20 December 2002, when there was a two-pixel alert, with alert ratios of -0.667 and -0.749.

Figure 74. Alert-ratio, number of alert pixels, and summed 4 µm (MODIS band 21) spectral radiance for MODIS thermal alerts on Stromboli between 1 November 2002 and 13 May 2003. MODIS data courtesy of the HIGP MODIS Thermal Alert Team.

These five dates were the only MODIS thermal alerts prior to the start of effusive activity on 28 December 2002 (BGVN 27:12 and 28:01). The source of the radiance to trigger these alerts was evidently incandescence at one or more of the active vents. In the case of a volcano such as Stromboli, prior to December 2002, isolated thermal alerts are more likely to represent the chance coincidence of a short-lived peak of incandescence with the time of MODIS overpass, rather than a sustained emission of infrared radiation. However the November-December 2002 thermal alerts can with hindsight be seen to have been indicators of enhanced activity in the lead-up to the 28 December effusive eruption.

On 28 December 2002 MODIS recorded its highest ever alert ratio at Stromboli (+0.419) and highest summed radiance at 4.0 µm (MODIS band 21) in a seven-pixel alert, corresponding to the daily MODIS overpass at 2115 UTC. This is a record of radiance from 300-m-wide lava flows from the NE crater (BGVN 27:12). Subsequent to that date, thermal alerts have occurred persistently at Stromboli, and evidently reflect ongoing lava effusion. The general trend of the highest alert ratio on each date, the number of alert pixels, and the summed 4.0 µm radiance for all alert pixels on each date shows an exponential decline.

There are no thermal alerts for 3-7 April 2003 inclusive, which could be because of cloud cover. There is thus no direct record of the explosion on the morning of 5 April that completely covered the upper 200 m of the volcano with bombs. However, the mild intensification of subsequent thermal-alerts indicates slight re-invigoration of the on-going lava effusion.

Geologic Background. Spectacular incandescent nighttime explosions at this volcano have long attracted visitors to the "Lighthouse of the Mediterranean." Stromboli, the NE-most of the Aeolian Islands, has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent horseshoe-shaped scarp formed about 5,000 years ago due to a series of slope failures that extend to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Information Contacts: Sonia Calvari, Istituto Nazionale di Geofisica e Vulcanologia, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/); David A Rothery and Diego Coppola, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom. MODIS data courtesy of the HIGP MODIS Thermal Alert Team.

A large-scale concentric pattern of deformation was detected between May 1996 and December 2000 centered on Uturuncu volcano, Bolivia (figure 1), based on satellite geodetic surveys (Pritchard and Simons, 2002). The observed deformation is primarily surface uplift with a maximum rate at the uplift center of 1-2 cm/year in the radar line-of-sight direction (figure 2). A reconnaissance investigation by a team composed of scientists from Bolivia, Chile, the USA, and the UK, took place during 1-6 April 2003 to identify any other signs of volcanic unrest and assess past volcanic behavior.

Figure 1. Photograph of Uturuncu viewed from the south, April 2003. Courtesy of Steve Sparks.

Figure 2. Shaded relief topographic map of the central Andes with insets showing areas of deformation detected by Pritchard and Simons (2002). Interferograms (draped over shaded relief) indicate active deformation; each color cycle corresponds to 5 cm of deformation in the radar line-of-sight (LOS). The LOS direction from ground to spacecraft (black arrow) is inclined 23° from the vertical. Black squares indicate radar frames, and black triangles show potential volcanic edifices. Courtesy of Matthew Pritchard.

A single-component vertical one-second seismometer was placed at five locations for periods of up to 14 hours. Data were recorded at a rate of 100 samples per second on a laptop computer. Persistent low-level seismicity was observed mainly from one source location on the NW flank, close to the center of deformation observed by satellite surveys. Two other sources within the volcanic edifice could not be located with the available data. The rate of volcanic earthquakes was up to 15 per hour, and the magnitudes were in the 0.5-1.5 range based on coda length. The sources were considered to be within 3-4 km of the surface (much shallower than the deformation source); more accurate information will be available when the data are analyzed further.

The summit region of Uturuncu has two active fumarole fields with substantial sulfur production and areas of clay-silica hydrothermal alteration. Maximum temperatures in four fumaroles were measured at 79-80°C. A hot spring on the NW flanks had a temperature of 20°C.

Uturuncu is a stratovolcano composed of hypersthene andesites, hypersthene-biotite dacites, and biotite-hornblende dacites. Almost all the exposed products are extensive coulée-type lavas and domes; no pyroclastic deposits were observed. Flow features are well-preserved on the youngest lavas. A wide variety of xenoliths were found in most lavas, including mafic magmatic inclusions, cumulates, microcrystalline igneous inclusions, and hornfels of possible basement rocks including sandstones and calcareous rock types.

Lavas around the summit area appear to be the most recent products, but have been affected by glaciation; there is however no present-day ice. There is thus no evidence yet for Holocene activity. The recent unrest manifested by substantial ground deformation and reconnaissance seismicity indicate, however, that a magmatic system is still present and therefore further monitoring is warranted.

Reference. Pritchard, M., and Simons, M., 2002, A satellite geodetic survey of large-scale deformation of volcanic centres in the Central Andes: Nature, v. 418, p. 167-170.

Geologic Background. Uturuncu, the highest peak of SW Bolivia, displays fumarolic activity, and postglacial lava flows were noted by Kussmaul et al. (1977). Inspection of satellite images of the 6008-m-high peak, located SE of Quetana, did not show evidence for postglacial activity (de Silva and Francis, 1991). Andesitic and dacitic lava flows dominate on Uturuncu, and no pyroclastic deposits were observed during recent field work. Although young lava flows display well-preserved flow features, youthful-looking summit lava flows showed evidence of glaciation. Two active sulfur-producing fumarole fields are located near the summit, and large-scale ground deformation was observed beginning in May 1992 (Pritchard and Simons, 2002), indicating, along with seismicity detected in 2009-10 (Jay et al., 2012), that a magmatic system is still present.

Information Contacts: Mayel Sunagua and Ruben Muranca, Geological Survey of Bolivia, SERGEOMIN, Casilla 2729, La Paz, Bolivia; Jorge Clavero, Geological Survey of Chile, Servicio Nacional de Geología y Minería (SERGEOMIN), Avenida Santa María 0104, Casilla 10465, Santiago, Chile; Steve McNutt, Alaska Volcano Observatory and Geophysical Institute, University of Alaska Fairbanks, 903 Koyukuk Drive, PO Box 757320, Fairbanks, AK 99775-7320, USA (URL: http://www.avo.alaska.edu/); Matthew Pritchard, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA (URL: http://www.gps.caltech.edu/); C. Annen, M. Humphreys, A. le Friant, and R.S.J. Sparks, Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK.

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/).