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Bulletin of the Global Volcanism Network

All reports of volcanic activity published by the Smithsonian since 1968 are available through a monthly table of contents or by searching for a specific volcano. Until 1975, reports were issued for individual volcanoes as information became available; these have been organized by month for convenience. Later publications were done in a monthly newsletter format. Links go to the profile page for each volcano with the Bulletin tab open.

Information is preliminary at time of publication and subject to change.


Recently Published Bulletin Reports

Ol Doinyo Lengai (Tanzania) Multiple lava flows within the summit crater, September 2018-August 2019

Ulawun (Papua New Guinea) Explosions on 26 June and 3 August 2019 send plumes above 19 km altitude

Sarychev Peak (Russia) Ash plume on 11 August; thermal anomalies from late May to early October 2019

Asamayama (Japan) Ashfall from phreatic eruptions on 7 and 25 August 2019

Villarrica (Chile) Strombolian activity continued during March-August 2019 with an increase in July

Reventador (Ecuador) Daily ash emissions and incandescent block avalanches continue, February-July 2019

Raikoke (Russia) Short-lived series of large explosions 21-23 June 2019; first recorded activity in 95 years

Sinabung (Indonesia) Large ash explosions on 25 May and 9 June 2019

Semisopochnoi (United States) Small explosions detected between 16 July and 24 August 2019

Krakatau (Indonesia) Repeated Surtseyan explosions with ash and steam during February-July 2019

Tengger Caldera (Indonesia) Ash emissions on 19 and 28 July 2019; lahar on the SW flank of Bromo

Unnamed (Tonga) Submarine eruption in early August creates pumice rafts that drifted west to Fiji



Ol Doinyo Lengai (Tanzania) — September 2019 Citation iconCite this Report

Ol Doinyo Lengai

Tanzania

2.764°S, 35.914°E; summit elev. 2962 m

All times are local (unless otherwise noted)


Multiple lava flows within the summit crater, September 2018-August 2019

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 (see Caption) 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.

Month Sentinel-2 Images Clear Summit with Lava Color Contrasts Thermal anomalies
Sep 2018 6 5 5
Oct 2018 7 4 3
Nov 2018 6 2 0
Dec 2018 5 1 1
Jan 2019 6 5 3
Feb 2019 6 5 6
Mar 2019 6 5 5
Apr 2019 6 1 0
May 2019 6 3 2
Jun 2019 6 3 3
Jul 2019 6 5 5
Aug 2019 6 5 3
Figure (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) Figure 194. A view into the crater floor at Ol Doinyo Lengai on 2 March 2019 showed a vent with both fresh (dark brown) and cooled (gray-white) carbonatite lavas and hornitos on the floor of the crater. The darkest material on the crater floor is from recent flows. Courtesy of Aman Laizer, Tanzania.

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

Figure (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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).


Ulawun (Papua New Guinea) — September 2019 Citation iconCite this Report

Ulawun

Papua New Guinea

5.05°S, 151.33°E; summit elev. 2334 m

All times are local (unless otherwise noted)


Explosions on 26 June and 3 August 2019 send plumes above 19 km altitude

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Russia) — November 2019 Citation iconCite this Report

Sarychev Peak

Russia

48.092°N, 153.2°E; summit elev. 1496 m

All times are local (unless otherwise noted)


Ash plume on 11 August; thermal anomalies from late May to early October 2019

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Japan) — September 2019 Citation iconCite this Report

Asamayama

Japan

36.406°N, 138.523°E; summit elev. 2568 m

All times are local (unless otherwise noted)


Ashfall from phreatic eruptions on 7 and 25 August 2019

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Chile) — September 2019 Citation iconCite this Report

Villarrica

Chile

39.42°S, 71.93°W; summit elev. 2847 m

All times are local (unless otherwise noted)


Strombolian activity continued during March-August 2019 with an increase in July

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


Reventador (Ecuador) — August 2019 Citation iconCite this Report

Reventador

Ecuador

0.077°S, 77.656°W; summit elev. 3562 m

All times are local (unless otherwise noted)


Daily ash emissions and incandescent block avalanches continue, February-July 2019

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (Russia) — August 2019 Citation iconCite this Report

Raikoke

Russia

48.292°N, 153.25°E; summit elev. 551 m

All times are local (unless otherwise noted)


Short-lived series of large explosions 21-23 June 2019; first recorded activity in 95 years

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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/).


Sinabung (Indonesia) — August 2019 Citation iconCite this Report

Sinabung

Indonesia

3.17°N, 98.392°E; summit elev. 2460 m

All times are local (unless otherwise noted)


Large ash explosions on 25 May and 9 June 2019

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

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

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

Month Steam Plume Heights (m) Dates of VONA reports Satellite Thermal Anomalies (date) Seismicity indicating Lahars (date) Ash Plume Altitude (date and distance) Pyroclastic flows
Jul 2018 100-700 -- -- -- -- --
Aug 2018 50-700 -- 30 1, 20 -- --
Sep 2018 100-500 -- -- 1st week, 12, 29 -- --
Oct 2018 50-1,000 -- -- 1 -- --
Nov 2018 50-350 -- -- 14 -- --
Dec 2018 50-500 -- -- 30 -- --
Jan 2019 50-350 -- -- -- -- --
Feb 2019 100-400 -- 6, 21 -- -- --
Mar 2019 50-300 -- 3, 8 27 -- --
Apr 2019 50-400 -- -- 2, 4, 11 -- --
May 2019 200-700 7, 11, 12, 24, 26, 27 (2) -- 4, 14 7 (4.6 km), 24 (15.2 km), 25 (6.1 km) --
June 2019 50-600 9, 10 -- -- 9 (16.8 km), 10 (3.0 km) 9-3.5 km SE, 3.0 km S
July 2019 100-700 -- -- 10, 12, 14, 16, 4th week -- --

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


Semisopochnoi (United States) — September 2019 Citation iconCite this Report

Semisopochnoi

United States

51.93°N, 179.58°E; summit elev. 1221 m

All times are local (unless otherwise noted)


Small explosions detected between 16 July and 24 August 2019

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 (Indonesia) — August 2019 Citation iconCite this Report

Krakatau

Indonesia

6.102°S, 105.423°E; summit elev. 813 m

All times are local (unless otherwise noted)


Repeated Surtseyan explosions with ash and steam during February-July 2019

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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.


Tengger Caldera (Indonesia) — August 2019 Citation iconCite this Report

Tengger Caldera

Indonesia

7.942°S, 112.95°E; summit elev. 2329 m

All times are local (unless otherwise noted)


Ash emissions on 19 and 28 July 2019; lahar on the SW flank of Bromo

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 (see Caption) 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/).


Unnamed (Tonga) — November 2019 Citation iconCite this Report

Unnamed

Tonga

18.325°S, 174.365°W; summit elev. -40 m

All times are local (unless otherwise noted)


Submarine eruption in early August creates pumice rafts that drifted west to Fiji

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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/).

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Bulletin of the Global Volcanism Network - Volume 23, Number 09 (September 1998)

Managing Editor: Richard Wunderman

Ambrym (Vanuatu)

Long-active lava lake continues to hold bubbling lava

Azul, Cerro (Ecuador)

Flank and caldera eruptions continue

Colima (Mexico)

Explosion on 6 July follows seven months of seismic unrest

Etna (Italy)

Summary of summit eruptive activity during August 1997-January 1998

Fournaise, Piton de la (France)

Activity ends with fissure eruptions outside the caldera

Guagua Pichincha (Ecuador)

Phreatic discharges and shallow, near-vent seismicity continue

Hokkaido-Komagatake (Japan)

Phreatic eruption spreads ash 25 October

Iwatesan (Japan)

Nearby M 6.2 earthquake on 3 September, but volcano still slumbering

Klyuchevskoy (Russia)

Explosions, ash 2-3 September raise concern to yellow alert

Lengai, Ol Doinyo (Tanzania)

New cones, vigorous activity since February

Masaya (Nicaragua)

Integrated scientific studies of the caldera area

Popocatepetl (Mexico)

Several episodes of ash emission during September

Sete Cidades (Portugal)

Seismic swarm on submarine flank

Sheveluch (Russia)

Ash explosions and pyroclastic flow during 3 September

Soufriere Hills (United Kingdom)

Continuing decrease in activity; hazards reassessed

Yasur (Vanuatu)

Ongoing eruption, felt earthquake, and fresh glass chemical analysis



Ambrym (Vanuatu) — September 1998 Citation iconCite this Report

Ambrym

Vanuatu

16.25°S, 168.12°E; summit elev. 1334 m

All times are local (unless otherwise noted)


Long-active lava lake continues to hold bubbling lava

This long-active caldera was visited by John Seach during 4-7 September 1998. At Niri Mbwelesu Taten, a small collapse pit, strong degassing was observed as well as yellow sulfurous deposits on the NW wall. During the night, degassing was heard from a distance of 4 km and white vapor tinged with blue was constantly emitted from the pit.

Niri Mbelesu crater was constantly full of vapor resulting in poor visibility. But bubbling lava was heard and at night the clouds reflected a red glow from the crater.

At Mbwelesu crater, an active elongated lava lake (~100 x 30 m) was observed. The larger explosions threw lava high into the air and onto the crater wall. To the east of the lava lake a smaller elongated vent contained lava. On the NW wall of the crater was a circular vent 20 m in diameter from which no lava was extruded.

Benbow crater was climbed from the S. The sound of bubbling lava was heard but not observed, and there was a very intense night glow.

Geologic Background. Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides arc. A thick, almost exclusively pyroclastic sequence, initially dacitic, then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major plinian eruption with dacitic pyroclastic flows about 1900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the caldera floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.

Information Contacts: John Seach, P.O. Box 16, Chatsworth Island, N.S.W. 2469, Australia.


Cerro Azul (Ecuador) — September 1998 Citation iconCite this Report

Cerro Azul

Ecuador

0.92°S, 91.408°W; summit elev. 1640 m

All times are local (unless otherwise noted)


Flank and caldera eruptions continue

This eruption began between 1229 and 1304 on 15 September (BGVN 23:08). The event was first recognized by University of Hawaii scientists monitoring thermal images from the GOES-8 geostationary satellite. A dominant plume reaching over 150 km SW developed between 1345 and 1545 on 15 September, and a minor plume trended NW carried by the prevailing surface winds. Overflights revealed two new vents in the summit caldera, and a flank fissure eruption 8 km SE of the caldera (figure 1).

Figure (see Caption) Figure 1. Photograph of the S part of Isabela Island, taken from the Space Shuttle in 1983, showing the site of the September 1998 flank eruption. Puerto Villamil and the scientific station at Tomas de Berlanga (or Santo Tomas) are the only inhabited locations on the island. White zones over the island are clouds. Courtesy of the GOES Hotspot Monitoring System.

The first scientists reaching the volcano were from Ecuador's Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN) and ORSTOM. They described the flank eruption site as a SE-directed radial fissure, 400-500 m long, and between 680 and 630 m elevation. Lava fountaining (to ~200 m) built an elongate cinder cone 50 m high during the team's 19-25 September observations. The main cone was breeched on the E, issuing flows that traveled over 8 km E before turning S toward the sea. During the night of 24-25 September a break in the main cone fed a new flow to the SE. All were 3-5-m-thick aa flows, and the longest ended 2 km from the coast.

University of Idaho graduate student Rachel Ellisor arrived on the night of 22 September, and described additional details of the flank eruption, including a smaller cone (NW of the main cone) with low fountains feeding a flow moving more directly S toward the sea. This flow was sampled daily; its velocity ranged from 0.001 to 10-20 km/hour and its thickness was described as 2-3 m at the front but 10-12 m in the interior. Gas clouds billowed from the fissure's SE end, and fountains issued from the main vent.

Ellisor took a 1 October overflight and described the intracaldera flows. One issued from a small vent (20-30 m high) on the S bench and flowed NW onto the caldera floor, while a larger cone (~60 m high) on the W caldera floor fed flows eastward into the shallow lake. Intracaldera activity had ended by 1 October.

Returning to the flank eruption, Ellisor reported that three large cones (60-80 m high) had been built in a N-S orientation. The mid-September flows (to the E, then S) had stagnated on the coastal flats, and their thickness was estimated at 5-15 m (interior) to 1-3 m (fronts). Increased activity on 6 October fed new flows building a channel system directly S of the main fissure. Ellisor's most recent report was dated 13 October, but GOES-8 images showed a thermal anomaly continuing through 4 November, the eruption's 51st day.

During 19-25 September, scientists from IG-EPN and ORSTOM installed three digital and one analog seismic station between the coast and the active vent. The distance between end stations was 8.5 km. Seismic signals registered during the study were composed of permanent tremor with an amplitude of 20 µm/s (2.4 km from the vent) and with a dominant frequency of 1.6 Hz. No rock-fall or long-period events were registered. One station 4 km from the vent continued working after the group returned to Quito.

Geologic Background. Located at the SW tip of the J-shaped Isabela Island, Cerro Azul contains a steep-walled 4 x 5 km nested summit caldera complex that is one of the smallest diameter, but at 650 m one of the deepest in the Galápagos Islands. The shield volcano is the second highest of the archipelago. A conspicuous bench occupies the SW and west sides of the caldera, which formed during several episodes of collapse. Youthful lava flows cover much of the caldera floor, which has also contained ephemeral lakes. A prominent tuff cone located at the ENE side of the caldera is evidence of episodic hydrovolcanism. Numerous spatter cones dot the western flanks. Fresh-looking lava flows, many erupted from circumferential fissures, descend the NE and NW flanks. Historical eruptions date back only to 1932, but Cerro Azul has been one of the most active Galápagos volcanoes since that time. Solfataric activity continues within the caldera.

Information Contacts: P. Samaniego, F. Desmulier, J.P. Metaxian, M. Ruiz, and M. Vaca, Instituto Geofísico, Escuela Politécnica Nacional, AP 17-01-2759, Quito, Ecuador; ORSTOM (L'Institut Français de Recherche Scientifique pour le Développement en Coopération), AP 17-11-6596, Quito, Ecuador (URL: http://www.ird.fr/); Rachel Ellisor and Dennis Geist, Dept. of Geology and Geological Engineering, University of Idaho, Moscow, ID 83843 USA (URL: https://www.uidaho.edu/sci/geology/); Peter Mouginis-Mark and Luke Flynn, GOES Hotspot Monitoring System, Hawaii Institute of Geophysics and Planetology, University of Hawaii, 2525 Correa Road, Honolulu, Hawaii 96822 USA (URL: http://modis.higp.hawaii.edu/).


Colima (Mexico) — September 1998 Citation iconCite this Report

Colima

Mexico

19.514°N, 103.62°W; summit elev. 3850 m

All times are local (unless otherwise noted)


Explosion on 6 July follows seven months of seismic unrest

After seven months of seismic unrest (small swarms, with durations lasting some few hours to as much as 90 hours), at 1858 on 6 July an explosion at the summit dome was similar in behavior and about half of the magnitude of an explosion in 1994.

A microbarograph 8 km SW of the summit at La Yerbabuena failed to register the explosion's shock wave, and the events were not noticed by residents of that settlement or La Becerrera (12 km SW of the summit), nor were these effects noticed by rangers at Rancho El Jabali (12 km SSW of the summit). Residents did report light rain and a bit of thunder and lightning at 1900, which may have helped conceal, or have been confused with, the sound of the explosion.

Seen through a microscope, plant leaves contained ash residue left after rainfall: mineral particles and hydrothermally altered rock fragments under 0.5 mm in diameter, often of light cream color, and similar to those collected at Yerbabuena after the 1994 explosion.

Melchor Ursua of the Civil Defense reported that at 1900 residents of Tonila (13.5 km SE of the summit) observed a small black mushroom cloud rise above the summit accompanied by the sound of thunder or explosion. At 2300 that day from La Yerbabuena, observers Navarro, Breton, and Santaana saw fumarolic gases blown around the W face of the volcano, but in the faint moonlight he failed to discern any glow or ash from the crater.

The last seismic crisis started around 2200 on 2 July 1998 and ended at 1858 on 6 July: a vigorous swarm of earthquakes, which according to Gabriel Reyes comprised ~1,000 events a day for the last 3 days. One event with coda magnitude (Mc) 3.5-4.0 gained registry at all network stations including those near the coast at Tecoman and Armeria; it was interpreted as related to the above-discussed explosion. The seismic quiet afterwards consisted of zero events in a pattern reminiscent of 1994 when quiet prevailed for about 12 hours.

Noteworthy swarms during 1997 occurred on 20 March, 16, 21, and 30 June, 28 November, and 5 December. Compared to the 1997 swarms, this one (2-6 July 1998) was the largest and most energetic.

During the latest swarm the volcano was only visible from 0800 to 1000. After 160 mm of rain had fallen at La Yerbabuena, a lahar swept downslope between 1400 and 1800 on 2 July, blocking passage across the Becerrera River valley 12.5 km SW of the summit.

During 1900-2000 on 7 July, the seismic station closest to the W flank (SOMA, 1.7 km NW from the summit) registered strong, continuous mass wasting and later, during 2200-2300, a relatively strong volcanic event. Seismic quiet returned later, but vigorous fumarolic emissions were blown W. An update on 28 October noted that for a few weeks after the explosion the volcano displayed unrest, including about 23 seismic swarms, each enduring for 2 to 6-8 hours. All the seismic information was provided by the Colima seismic network (RESCO). The last swarm occurred on 25 October and prevailed for 13 hours.

Geologic Background. The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the 4320 m high point of the complex) on the north and the 3850-m-high historically active Volcán de Colima at the south. A group of cinder cones of late-Pleistocene age is located on the floor of the Colima graben west and east of the Colima complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, and have produced a thick apron of debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions (most recently in 1913) have destroyed the summit and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.

Information Contacts: Carlos Navarro Ochoa, Colima Volcano Observatory, Universidad de Colima, Ave. 25 de Julio 965, Colima 28045, Colima, México.


Etna (Italy) — September 1998 Citation iconCite this Report

Etna

Italy

37.748°N, 14.999°E; summit elev. 3295 m

All times are local (unless otherwise noted)


Summary of summit eruptive activity during August 1997-January 1998

The following report summarizes activity observed at each of the four summit craters of Etna from August 1997 through 15 January 1998. Events through 8 January 1998 at Bocca Nuova, Southeast Crater, Northeast Crater, and Voragine are described below separately. A seismic crisis during 9-12 January was followed by a brief decrease in activity at all of the craters. Significant eruptive episodes after mid-January 1998 will be described in future issues.

Information for this report was compiled by Boris Behncke at the University of Catania and published on his internet web site. The compilation was based on personal visits to the summit, telescopic observations from Catania, monitoring of images posted on the internet from the camera maintained by the Istituto Internazionale di Vulcanologia (IIV), and other sources.

Visits to the summit craters in late September and early October 1997 revealed continuing vigorous activity from Bocca Nuova and Southeast Crater while more sporadic activity was occurring at the Voragine and Northeast Crater. This pattern continued through November and December. The overall activity on 8 January 1998 at Bocca Nuova, Northeast Crater, and Voragine was notably diminished; it was the lowest observed in six months.

Activity at Bocca Nuova. During late August, lava ejections from Bocca Nuova (BN) became significantly more vigorous. Both eruptive centers in this crater often ejected lava bombs outside the crater, with many falling on its S rim. Occasional explosions ejected bombs on the lower S flank of the central cone. The number of active vents in Bocca Nuova increased to seven on 28 August, but was down to five just two days later. The bombardment and explosions led to collapse on the E side of Bocca Nuova, lowering the septum between BN and Voragine (informally named "diaframma" among local volcanologists), and eroding the remains of a 1964 cone.

Visits to the summit in late September and early October revealed continuing activity. As of 14 October, Bocca Nuova's activity was gradually increasing, and the crater was being filled in. The northern of its two eruptive centers had a broad cone with a crater 50-100 m wide, which at times was completely filled with fountaining lava. Fountains often sent spatter and bombs high above the rim, and large ejecta fell outside the crater up to 100 m away. Bombs as large as 40 cm in diameter fell onto the area where the best views of the erupting cone in BN are obtained. Explosions in the SE eruptive center at times sent pyroclastic material all over the S flank of Etna's summit cone.

On 6 November the northern eruptive center was vigorously active. The cone at that site had grown to ~50 m below the NW crater rim. The SE eruptive center was much less violent than in previous months; on the crater wall above it a large overhanging hollow had been carved out by explosions. On the evening of 6 November, Strombolian explosions occurred at intervals of 1-5 seconds, with some jets rising up to 200 m above the cone's summit. An episode of spectacular lava fountaining from BN occurred on 25 November when huge bursts of incandescent bombs developed into a continuous fountain from the SE eruptive center. On 28 November the clouds over the mountain cleared, permitting the view of a huge vapor column rising almost vertically to about 1,500 m above the summit. This unusually large plume was due to an approaching cold front that led to increased condensation.

Explosive activity and gas emissions within BN accompanied a lava flow from Southeast Crater during 9-11 December. Intermittent activity on 12 December, stronger than during the previous 17 days, ejected high bursts of incandescent bombs from BN's southeastern vents. Activity through 15 December was very vigorous, and eruptions continued through 21 December. Glow was visible above BN's two eruptive centers on 26 December and over the E part of the crater on 31 December.

On the evening of 7 January, several jets of incandescent bombs rose over the SE crater lip, and a few bombs fell onto the remains of the 1964 cone. As of 8 January the large cone in the N part of the crater floor had partially collapsed, creating a crater ~150 m in diameter. Frequent rockfalls occurred within this crater. Subsidence of the cone and the adjacent crater floor had created a set of circumferential fractures several meters wide. The most recent activity at this eruptive center appears to have been the extrusion of a lava flow that covered the E and SE sides of the BN floor. The vents at the SE eruptive center were the site of weak Strombolian explosions every 10-15 minutes. Most, if not all, activity occurred from the lowermost vent in the SW part of the eruptive center. A complex cone around these vents had grown notably since the visit on 6 November 1997, with the rim of the highest vent being at about the same elevation as the N rim of Bocca Nuova. Large parts of the crater wall above the SE eruptive center had collapsed, probably before the most recent cone growth (all collapse debris was buried).

Activity at Southeast Crater. Strombolian and effusive activity continued from Southeast Crater (SEC), whose intracrater cone could be seen on 1 September through a gap in the NE crater rim from coastal areas to the E. During a visit on 30 August, lava fountains rose up to 150 m above the cone, and three vents were active. There had been significant infilling of the deep southern part of SEC since effusive activity shifted to the cone's NW flank sometime before 11 August. Before then, lava had repeatedly spilled onto the SE flank of the cone.

Visits to the summit craters in late September and early October revealed continuing vigorous activity. While effusive vents were active on the W base of the cone from 10 August to mid-September, lava again issued from E-flank vents in late September, causing renewed overflows onto the outer SW flank of the cone. By mid-October the cone within SEC had grown to about the height of the highest point on the crater rim. Explosive activity was the same as during previous months, and lava effusion continued from the flanks of the cone.

At dusk on 2 November there were continuous Strombolian bursts from SEC. A visit on 6 November revealed very weak and erratic Strombolian activity. For the first time in many months there was no lava effusion at SEC, although guides at Torre del Filosofo reported that a small lava flow had spilled over the low SE rim of the crater three days earlier. After sunset on 6 November, Strombolian bursts from SEC could be seen from Catania (Palazzo delle Scienze).

Telescope observations from the roof of the Palazzo delle Scienze in Catania on 3-4 December revealed vigorous Strombolian activity at SEC and significant growth of its central conelet, which stood much higher than the surrounding crater rims. Activity on the evening of 5 December was documented with the IIV camera until bad weather hid the summit. At dusk, activity at SEC increased, and strong explosions heralded lava emission to the NE side of the intracrater cone. A more significant lava flow was erupted from SEC on the late afternoon of 9 December, accompanied by vigorous explosive activity at the intracrater cone and within Bocca Nuova. The SEC lava flow overrode previous flows on the SE flank of the cone.

The 9 December lava flow was visible on 11 December, contrasting against freshly fallen snow. Seen from Palazzo delle Scienze, this flow extended much farther downslope than previous flows on the SE flank of the cone, but its front was still several hundred meters from the steep W flank of Valle del Bove. The flow had apparently stopped (no steam was visible at the contact of the lava with the snow). Two smaller lava lobes were erupted onto the SE flank of SEC's cone, about two-thirds of the way down the cone's flank. The active central cone appeared to have lost some height during the strong explosions; Strombolian activity was still vigorous and at times accompanied by weak ash emissions. Vigorous activity at SEC, with some large explosions, continued during 12-15 December, with lava flows spilling over the SE rim and some SE-flank lava extending far beyond the base of the cone. The new flow passed only about 600 meters NE from the Torre del Filosofo mountain hut, ~1 km from SEC. As of 17 December the lava flows erupted from SEC during the previous few days were still confined to the SE flank of the cone. None of the new flows had extended as far as those on 9 and 12-13 December. Over 20-21 December, nearly continuous explosive activity at the SEC intracrater cone sent lava onto its SE and SSE flanks. The cone regained the height lost after 5 December. A 22 December afternoon episode of vigorous lava fountaining as high as 200 m from SEC lasted about 1 hour. A lava flow erupted onto the SE flank of SEC appeared to be no longer than ~200 m.

Activity at SEC in late December and early January was spectacular. On 25 December, continuous Strombolian activity occurred from the central conelet and lava flowed down the SE flank to its base, covering previous flows. Three active lava flows were visible on the SE flank on the 26th. Sometime between early 29 and early 30 December, more lava flows spilled down the S flank of SEC, and a peculiar flow moved down on the SW flank, bifurcating on the lower slope. On the evening of the 30th, active flows were visible on the S flank while the SW flow only showed incandescence in its upper part. On the evening of 31 December, incandescent lava was visible on the lip of SEC in many places while active flows were descending on the S flank. On 7 January the SW flow was incandescent along its full length, with the W lobe extending to the base of the SEC cone.

On 8 January Southeast Crater gave off continuous Strombolian explosions from two vents at the summit of the intracrater cone and lava emission from its SE base. The summit of the cone was distinctly (~5-7 m) higher than the highest point ("Fortino") on the NE rim of SEC. Lateral growth of the cone was most significant in the N and NE parts of SEC where all lava flows and effusive vents active between July and September 1997 had been buried. The lava field surrounding the central cone had risen significantly, causing overflows on the E, SE, S, and SW sides. Only a segment of the NE crater rim stood a few meters above the lava fill; the W and NW part of the rim stood 20 m above the lava field and the cone's base. Three craters were present on the central cone, two of which were erupting. Activity would occur from one vent at any given time while the other was silent. The N vent ejected bombs and scoriae onto the N and NW crater rim and beyond. The S vent produced loud bangs and showered the E and SE flanks of the cone with pyroclastics. The effusive vent on the SE side of the cone had crusted over, and lava issued only on the SW rim of SEC where it overflowed, forming a narrow (1.5 m) flow with distinct lateral levees extending to the base of the SEC cone. The flow bypassed a cone formed in 1971 on its E side; when reaching the almost horizontal plain below the steep SW flank of SEC, it broadened and thickened notably and advanced slowly in the direction of the 1971 "Observatory cone." Within 3.5 hours on 8 January, the flow front advanced ~15 m through thick snow, forming an offshoot on the W side of the ~20-m-wide lava front. None of the other flows on the S flank of SEC showed any signs of movement or incandescence. The distance from the Torre del Filosofo mountain hut to the nearest flow front was ~1 km; the active flow did not threaten this structure.

Activity at Northeast Crater. During the second half of July Northeast Crater (NEC) occasionally ejected incandescent bombs from a deep pit in the central part of the crater; fine ash fell outside the pit. Visits to the summit craters in late September and early October revealed sporadic activity. NEC frequently emitted ash plumes during the first week of October, and on the evening of 10 October, incandescent ejections rose as high as 50 m above the crater rim. Strong gas emission was occurring from NEC on 11 December. NEC was essentially quiet on 8 January, with only light steam emissions from its central pit and some of the June-August 1996 vents in the SW part of the crater. Steam emission was more abundant, and at times pulsating, from a collapse pit in the S part of the crater. This pit was also the site of frequent avalanching and rockfalls that generated plumes of brown ash. No fresh magmatic products were found in the vicinity of the central and southern pits.

Activity at Voragine. A small cone began to form on the floor of Voragine in late July, and Strombolian activity was observed on 5 August. On 30 August, the cone was mildly steaming, and the surrounding deposit of black scoriae was partly covered by blocks that had collapsed from the septum between Voragine and Bocca Nuova. The first effusive activity from the Voragine in many years occurred in late September, forming a small lava field on the crater floor. Strombolian activity was weak on 28 September but very vigorous on 9 October; one day later it was again weak. The Voragine was explosively active from the central conelet on 6 November, and another weakly explosive vent had formed at the SW base of the diaframma between the Voragine from Bocca Nuova.

The cone in the central part of the Voragine was quiet on 8 January, with only slight emission of bluish gas. Its horseshoe-shaped crater was open to the SE; a small lava flow had issued from the open side of the cone. The vent on the SW side of the crater floor, which was first observed on 6 November 1997, had enlarged and was surrounded by a low half-cone leaning against the base of the diaframma. This vent produced weak explosions that mainly expulsed hot gas and a few pyroclasts. When viewed from the E rim of the Voragine, the conduit of this vent was seen to be inclined SW, diving below the diaframma.

Seismic crisis of 9-12 January 1998. The most intense seismic crisis during the current eruptive cycle occurred during 9-12 January and caused widespread media attention. From the afternoon of 9 January through 11 January about 200 earthquakes occurred in an area on the W and SW flanks of the volcano. The strongest shock (M 3.7) damaged a church in Biancavilla. No other damage or injuries were reported. Most epicenters were between Monte Nunziata and Monte Palestra, two ancient cones on the W flank. Seismicity diminished late on 10 January.

Strong ash emissions from BN on the morning of 11 January indicated further collapse in that crater, caused by earlier subsidence of the magmatic column. It is assumed that the magma intruded into a new fracture within the W side of the volcanic edifice. On 12 January ash emission from BN was almost continuous, but strong ash emissions also occurred from NEC. Activity at SEC continued with Strombolian bursts and emission of lava flows onto the SW, S, and SE flanks of the cone. The peculiar SW flow seemed to be waning; during the previous few days it had formed several minor lobes adjacent to the main one; the flow front seemed to have reached the base of the 1971 "Observatory cone."

Another seismic swarm occurred below the W flank on the afternoon of 12 January, with twelve earthquakes in 20 minutes, the strongest being M 3.1. Epicenters were closer to the summit craters than those of the preceding swarm, clustering 2-3 km E of Monte Palestra. Focal depths were ~4 km below sea level; no damage was reported. No significant change was noted in the eruptive activity at Southeast Crater, which had three active flows moving down its SW, S, and SE flanks.

Summit activity during 13-15 January 1998. Strombolian activity on the evening of 13 January at the intracrater cone in SEC was vigorous, while active lava was only visible near the crater rim in three places. A very faint glow reappeared at the SE eruptive center in BN. Strong ash emissions occurred from BN throughout the day. Seismic and eruptive activity were low on 14 January. The only visibly active crater was SEC, which was vigorous on the 13th but showed a marked diminution of activity towards midnight. At nightfall on 14 January SEC had very few and weak explosions, and there was no active lava flow on its outer flanks. No glow was visible above BN. This was the lowest level of activity observed in about a year. Seismic activity resumed late on 14 January with a series of about ten weak earthquakes below the W flank (Monte Palestra area) and several shocks beneath the SW slope, some 5 km above Biancavilla. Hypocenters were ~6 km below the surface on the W flank but much shallower on the SW flank. Activity at SEC dropped to very low levels: very few and weak explosions from the intracrater cone were observed on 14 January and no active lava was visible on the outer flanks of the crater.

Geologic Background. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km horseshoe-shaped caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Information Contacts: Boris Behncke, Istituto di Geologia e Geofisico, Palazzo delle Scienze, Università di Catania, Corso Italia 55, 95129 Catania, Italy.


Piton de la Fournaise (France) — September 1998 Citation iconCite this Report

Piton de la Fournaise

France

21.244°S, 55.708°E; summit elev. 2632 m

All times are local (unless otherwise noted)


Activity ends with fissure eruptions outside the caldera

The eruption that began in March (BGVN 23:03) diminished during August and September. Observatoire Volcanologique du Piton de la Fournaise (OVPF) considers the eruption ended. The most significant activity during the last two months took place outside the caldera.

A small fissure eruption began on 9 August north of the caldera. Lava issued from this fissure, which was located ~500 m from the caldera wall near Nez Coupé Sainte Rose (figure 49). The initial eruption lasted only 24 hours, but a second fissure eruption began 14 August in the same area closer to the caldera wall. No fountains were observed with the second fissure, although the lava was very fluid. Flows eventually measured 200-300 m wide and ~2 km long. They moved parallel to the caldera wall until 14 September when they stopped ~500 m above Trou Caron. Some of the lava reached the edge of the caldera and spilled over onto the Plaine des Osmondes through three separate rivulets. A flow that was moving towards the upper part of Bois Blanc (a village located on the east coast) stopped by 25 August.

Figure (see Caption) Figure 49. Map of the NE quadrant of Piton de la Fournaise showing important craters and other features. The dark tone represents the caldera wall, the light-gray areas indicate the extent of lava flows dating from 1972. The medium-gray shows flows since March 1998. Courtesy of OVPF.

During September, some night incandescence due to the lava lake at Piton Kapor was seen. Only weak tremor was observed. Beginning 5 September some gas-piston events were recorded; these had likely taken place before, but had remained undetected during stronger episodes of tremor.

This eruption, including all tremor and degassing at Piton Kapor, ended 21 September, after 196 days of activity. It thus comprised the volcano's longest and one of it's most voluminous eruptions of this century.

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: Thomas Staudacher, Observatoire Volcanologique du Piton de la Fournaise (OVPF), 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France.


Guagua Pichincha (Ecuador) — September 1998 Citation iconCite this Report

Guagua Pichincha

Ecuador

0.171°S, 78.598°W; summit elev. 4784 m

All times are local (unless otherwise noted)


Phreatic discharges and shallow, near-vent seismicity continue

The volcanic crisis near Quito (figure 10) continued with a series of phreatic discharges and an E-dipping zone of earthquakes that rose to within a few kilometers of the surface (figure 2). With potentially dramatic significance to Ecuador's Capital (1995 urban population, 1,270,000 residents; suburban, 258,000 residents), the eruption has spurred a strong educational response in both the regional press and on an official web site. These discourses have repeated noteworthy points: the volcano's last vigorous eruption was in 1660; its recurrence intervals have oscillated between about 400 and 600 years; its last major eruption took place 338 years ago; and its phreatic eruptions have repeated during the past 15 years. Phreatic eruptions began on on 7 August (BGVN 23:08); since then the Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN) has made available daily reports on activity during 30 September to 27 October, which we summarize here.

Figure (see Caption) Figure 10. Simplified schematic showing Guagua Pichincha, Quito's urban areas (elongate zone with selected roads), and hazard designations associated with the volcano. Revised from a color hazard map on the IG-EPN website and keyed as follows: 1) Maximum danger (including major risks of hot volcanic flows, lahars, and ashfall - requiring total evacuation); 2) Minor danger (minor risk of ash clouds, hot volcanic flows, and lahars - areas immediately abandoned should an eruption be either imminent or large); 3) Lahar risk along drainage areas; and 4-6) graded risk of ashfalls. The bold arrows help identify the location of source vents and portray ejecta trajectories representative of those that might occur during an eruption. For more detail, see Hall and von Hillebrandt (1988). Courtesy of the Instituto Geofisico, Escuela Politécnica Nacional.

Activity and observations. The epicenters of located earthquakes during April-October 1988 generally clustered around the caldera (figure 11). This was particularly the case for volcano-tectonic (VT) earthquakes, which in cross-section view tended to lie underneath the caldera. The located long-period (LP) events generally propagated from greater depths and in cross-section view defined a broad E-dipping zone. Thus far in the crisis there has been an alternating pattern of seismicity and seismically detected explosions (figure 12). During late September through late October there were often 1-2 daily explosions.

Figure (see Caption) Figure 11. (top) Located seismic events at Guagua Pichincha during April-October 1998 were mainly centered around the caldera. The abbreviations VT and LP refer to volcano-tectonic and long-period events. The LP events showed a tendency to lie farther outboard, on the volcano's E slopes. (bottom) A cross section showing hypocenters for the same seismic events, which reveals the E-dipping attitude of located events. Courtesy of the Instituto Geofisico, Escuela Politécnica Nacional.
Figure (see Caption) Figure 12. Histograms for Guagua Pichincha showing both the daily number of earthquakes, including (a) volcano tectonic (VT), (b) long-period (LP), (c) multiphase (MP), and (d) the daily number of seismically detected explosions. Courtesy of the Instituto Geofisico, Escuela Politécnica Nacional.

On 3 October observers confirmed the presence of new fumaroles on the dome's W edge; nearby, in the headwaters of the Rio Cristal, they noted a new fumarole field. A phreatic explosion was heard at 0400 on 5 October by residents of Lloa. The explosion was the thirty-first such event in the sequence initiated on 7 August. It ranked among the most energetic seen to this point of the crisis, comparable to those on 8 and 24 August, and 29 September. The 5 October explosion followed 50 minutes of tremor registered at station YANA (7 km NE of the crater; "C" on figure 13). Small seismic events continued until 0800 that day. This explosion left a fresh ash layer in the caldera that revealed a new vent near the older one but above it to the S.

Figure (see Caption) Figure 13. Contour map (200-m interval) indicating noteworthy sites surrounding Guagua Pichincha, including the valley embracing Quito and some of the key W-slope rivers that drain the breached caldera and environs. The map indicates settlements of Nono and Lloa (darkened rectangles) and seismic stations installed and maintained by various groups (open rectangles). These stations are designated by the following call letters: A, FARH; B, NONO; C, YANA; D, PINO; E, QWR; F, TERV; G, GGP; H, (uncertain); J, TOAZ; K, PIEZ; L, JORG; and M, MGUL. Courtesy of the Instituto Geofisico, Escuela Politécnica Nacional.

The seismic swarm NE of the caldera (BGVN 23:08) continued; between June and early October there were 3,200 events; ~10 had a magnitude (MR) over 3.9. On 4 October instruments detected ~30 earthquakes, the strongest MR 3.5. A MR 3.6 earthquake struck this zone on 10 October and was felt locally in the settlements of Pomasqui and San Antonio.

Measured deformation was not detected for the interval 15 September-7 October. Although not plotted, tremor has occurred. For example, at 2214 on 7 October station PINO detected tremor for 19 minutes while station YANA registered it for 7 minutes. On 11 and 12 October tremor followed phreatic explosions and in the former case, prevailed for 20 minutes at stations near the crater.

Mass wasting on the SE flank ~11 km from the caldera (in Quito's San Roque sector) on 9 October covered an old school, part of a church, threatened several smaller structures, and blocked vehicular traffic. Roughly 20 people were evacuated.

On 12 October condensing gases escaping the dome at a fumarole called "La Locomotora" rose 200 m. Around this time the 1981 explosion crater also emitted a moderate flow of gray gases but new fractures or fumaroles were absent.

At 1621 on 14 October a phreatic explosion at the 1981 vent sent fine material over the NE part of the caldera and left a visible coating ~300 m up the caldera walls. The associated grayish-white plume formed a ~3-km-tall column. Clear weather enabled residents of Quito to see the plume. Geophysical instruments detected the event at widely scattered locations. COSPEC registered the first clear SO2 signal, a 300 ppm concentration in the plume. Guards at a local observation post smelled strong sulfur, particularly when gases from La Locomotra fumarole blew past.

An explosion at 0947 on 16 October sent a plume to ~2 km. Again, Quito residents saw the plume, but an explosion the next morning was shrouded from view by weather clouds. The latter explosion was considered moderate; it was associated with ~5 minutes of tremor centered around 1.2-Hz frequency and scientists working nearby (at station PINO) saw a gray-white cloud develop. A 17 October explosion was shrouded in clouds. The phreatic explosions on 14, 15, 16, and 17 October yielded respective reduced seismic displacements of 11, 4.2, 9.8, and 3.2 cm2.

A view into the caldera on the morning of 18 October disclosed relatively passive outgassing from the 1981 and 1988 explosion craters. La Locomotra and other fumaroles on the central dome had clearly increased their output, feeding a plume ~700 m high. Another moderate explosion on 25 October was followed by 3 hours of tremor.

A flight on the morning of 27 October revealed only modest degassing, a 300-m-high plume, and an SO2 concentration below the COSPEC's detection limit. Minard Hall also recognized that the 1981 crater and one formed in September 1998 had coalesced. The wall isolating them had apparently been weakened by repeated phreatic eruptions.

Risk mapping. The highest risk settlements include Lloa (figures 1 and 4) and Mindo. The latter lies on the river of the same name about 22 km NW of the caldera; it lies off of maps in this report but is depicted on the larger hazard map of Hall and von Hillebrandt (1988). One branch of the Mindo river's headwaters begin just N of the breach in the caldera (figure 4). Rivers draining the breached W-flank and nearby NW-flank (e.g. Rio Cristal and Rio Mindo) were assigned a higher category of risk for lahars than any lahar-risk zones on the E flanks (figure 1).

New fieldwork has been aimed at inspecting older lahar deposits in vicinity of the settlements of Mindo and Nono. Nono, on the NNE flank (figures 2 and 4), lies at mouth of a narrow N-S valley that cuts across much of the volcano's E to NNE flanks.

Partnerships. The following describes some of the civic and media efforts to communicate volcanic hazards. On 30 September Ecuador's president requested that a safety committee be formed (Comité Especial de Seguimento, CES). The committee was charged with integrating Civil Defense, the IG-EPN, and the City of Quito. In overcast conditions on 24 August a film crew from TeleAmazonas shot footage of an explosion plume not otherwise visible in Quito. These glimpses, and later examples of widely visible plumes, surely helped residents grasp the immediacy and some of the power of the eruption.

Authorities raised the hazard status to Yellow on 1 October. On 3 October a new video system started to monitor the inner crater. This advance was supported by "Ecuavista" in coordination with "911 of the City of Quito," the phone number for the City's communications base.

A 2 October announcement told of a downtown Quito information center implemented to release daily circulars at bearing official volcanological information. Thanks to a partnership between the information center and IBM of Ecuador, the former gained access to the internet, email, and a modern computing environment The radio station "Zaracay," which can be received widely, including the urban and Mindo areas, was also designated as a conduit for public announcements.

By 7 October the seismic network consisted of 12 stations with real-time data transmission. Collaborating scientific teams and monitoring equipment have come from both the U.S. Geological Survey as well as ORSTOM (the French Scientific Research Institute for Development through cooperation). Contingency plans have surfaced, dealing with the issue of transportation during the higher stages of alert (Orange and Red). Public announcements have broached the need to maintain the integrity of the municipal infrastrucure in the event of an eruption, including crews to clean ash (from roads, power lines, etc.).

Reference. Hall, Minard, and von Hillebrandt M., Christa G., 1988, Mapa de los peligros volcanicos poteciales asociados con el volcan Guagua Pichincha; Republica del Ecuador (1:50,000).

Geologic Background. Guagua Pichincha and the older Pleistocene Rucu Pichincha stratovolcanoes form a broad volcanic massif that rises immediately to the W of Ecuador's capital city, Quito. A lava dome is located at the head of a 6-km-wide breached caldera that formed during a late-Pleistocene slope failure ~50,000 years ago. Subsequent late-Pleistocene and Holocene eruptions from the central vent in the breached caldera consisted of explosive activity with pyroclastic flows accompanied by periodic growth and destruction of the central lava dome. One of Ecuador's most active volcanoes, it is the site of many minor eruptions since the beginning of the Spanish era. The largest historical eruption took place in 1660, when ash fell over a 1000 km radius, accumulating to 30 cm depth in Quito. Pyroclastic flows and surges also occurred, primarily to then W, and affected agricultural activity, causing great economic losses.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador; El Comercio newspaper, Quito, Ecuador (URL: http://www.elcomercio.com); El Universo newspaper, Quito, Ecuador (URL: http://www.eluniverso.com); La Hora newspaper, Quito, Ecuador (URL: http://www.lahora.com); Volcanic Disaster Assistance Program, U.S. Geological Survey, 5400 MacArthur Blvd., Vancouver, Washington 98661 USA (URL: https://volcanoes.usgs.gov/observatories/cvo/); ORSTOM, A.P. 17-11-6596, Quito, Ecuador (URL: http://www.ird.fr/).


Hokkaido-Komagatake (Japan) — September 1998 Citation iconCite this Report

Hokkaido-Komagatake

Japan

42.063°N, 140.677°E; summit elev. 1131 m

All times are local (unless otherwise noted)


Phreatic eruption spreads ash 25 October

The Japan Meteorological Agency (JMA) issued an advisory and three observation reports concerning Hokkaido-Komaga-take volcano on 25 October following a small-scale phreatic eruption that began at 0912 the same day. Ash rose in a column to a height of ~1,200 m above the crater. The eruptive activity soon declined. There were no report of injuries or damage caused by the eruption, and no evacuation order was issued.

Volcanologists surveyed the activity from a helicopter the afternoon of 25 October (figure 2). They reported that the eruption originated from the same crater that opened during the 1929 eruption, which was also the site of the March 1996 eruption. Ash covered a significant area around and to the E of the crater. The scale of this eruption apparently was smaller than that of the March 1996 eruption.

Figure (see Caption) Figure 2. An aerial view of Komaga-take showing fuming activity from the 1929 Crater about 6 hours after the 25 October 1998 eruption. View is from the SE looking towards the Komanose Rim (back) and the Sawaradake Rim (back right). The 1942 Large Fissure (middle, diagonal) and the 1996 Southern Fissure Crater (middle center) can also be seen. Hyoutan Crater (front center) is adjacent to the 1929 Crater. Photograph by Bousai Heli; courtesy of Hiromu Okada, Usu Volcano Observatory.

Volcanic tremor lasting six minutes was associated with this eruption. In addition, five volcanic earthquakes were recorded in the 12 hours following the first eruption signs.

Komaga-take is located 30 km N of Hakodate City (population 320,000). The andesitic stratovolcano has a 2-km-wide horseshoe-shaped caldera open to the E. The volcano has generated large pyroclastic eruptions, including major historical eruptions in 1640, 1856, and 1929. In the 1640 eruption, debris from a partial summit collapse entered the sea resulting in a tsunami that killed 700 people. Although the 1929 eruption was one of the largest 20th-century eruptions in Japan, it may not have had clear geophysical precursors.

Geologic Background. Much of the truncated Hokkaido-Komagatake andesitic volcano on the Oshima Peninsula of southern Hokkaido is Pleistocene in age. The sharp-topped summit lies at the western side of a large breached crater that formed as a result of edifice collapse in 1640 CE. Hummocky debris avalanche material occurs at the base of the volcano on three sides. Two late-Pleistocene and two Holocene Plinian eruptions occurred prior to the first historical eruption in 1640, which began a period of more frequent explosive activity. The 1640 eruption, one of the largest in Japan during historical time, deposited ash as far away as central Honshu and produced a debris avalanche that reached the sea. The resulting tsunami caused 700 fatalities. Three Plinian eruptions have occurred since 1640; in 1694, 1856, and 1929.

Information Contacts: J. Miyamura, Sapporo District, Japan Meteorological Agency, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan; Hiromu Okada, Usu Volcano Observatory, Institute of Seismology and Volcanology, Hokkaido University, Sohbetsu-cho, Hokkaido 052-0103, Japan.


Iwatesan (Japan) — September 1998 Citation iconCite this Report

Iwatesan

Japan

39.853°N, 141.001°E; summit elev. 2038 m

All times are local (unless otherwise noted)


Nearby M 6.2 earthquake on 3 September, but volcano still slumbering

A strong earthquake occurred 10 km SW of the summit of Iwate volcano at 1658 on 3 September. The Richter magnitude was 6.1 and the depth ~7 km. The mechanism was E-W compression on a reverse fault. A N-S-trending surface rupture appeared, despite the event's non-extreme magnitude. The aftershock area resulting from the earthquake differed from typical earthquakes on Iwate and the relationship between the earthquake and the volcano, if any, is not understood. This was the largest earthquake since August 1996 when a M 5.9 tremor struck.

A 3 September Reuters news article mentioned that a powerful earthquake took place, centered in the ski resort area of Shizukuishi, a mountainous region near Iwate volcano. The report claimed the epicenter was 5 km underground and police said that the event slightly injured at least nine people.

Geologic Background. Viewed from the east, Iwatesan volcano has a symmetrical profile that invites comparison with Fuji, but on the west an older cone is visible containing an oval-shaped, 1.8 x 3 km caldera. After the growth of Nishi-Iwate volcano beginning about 700,000 years ago, activity migrated eastward to form Higashi-Iwate volcano. Iwate has collapsed seven times during the past 230,000 years, most recently between 739 and 1615 CE. The dominantly basaltic summit cone of Higashi-Iwate volcano, Yakushidake, is truncated by a 500-m-wide crater. It rises well above and buries the eastern rim of the caldera, which is breached by a narrow gorge on the NW. A central cone containing a 500-m-wide crater partially filled by a lake is located in the center of the oval-shaped caldera. A young lava flow from Yakushidake descended into the caldera, and a fresh-looking lava flow from the 1732 eruption traveled down the NE flank.

Information Contacts: Yukio Hayakawa, Faculty of Education, Gunma University, Aramaki, Maebashi 371, Japan; Reuters Limited, 1700 Broadway, New York, NY 10019 USA (URL: http://www.reuters.com/).


Klyuchevskoy (Russia) — September 1998 Citation iconCite this Report

Klyuchevskoy

Russia

56.056°N, 160.642°E; summit elev. 4754 m

All times are local (unless otherwise noted)


Explosions, ash 2-3 September raise concern to yellow alert

During 2-28 September, seismicity under the volcano was generally above background levels. Hypocenters were concentrated at two levels: near the summit crater and at depths of 25-30 km. Clouds often prevented observations.

On 2 September a fumarolic plume was observed during the daylight hours rising 50 m above the summit. Beginning at 2218 that day, a 33-minute series of explosive earthquakes was recorded, and at 2245 an ash explosion produced a plume that rose 4-5 km above the crater. On 3 September, scientists noticed that ash had been deposited in a 2-km-long zone on the NE slope. A plume of gas, with no ash content, rose 500 m above the volcano during 3-4 September, but had stopped by 5 September. Because of the increase in activity, the alert status was changed to Yellow, meaning more significant eruptions may occur.

No fumarolic plumes were seen during 8, 18, and 27 September, but plumes rising up to 100 m above the summit were seen during 13, 16, 17, 21, and 24 September. The alert color code returned to Green on 21 September, indicating normal activity.

Geologic Background. Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Information Contacts: Olga Chubarova, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Tom Miller, Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.


Ol Doinyo Lengai (Tanzania) — September 1998 Citation iconCite this Report

Ol Doinyo Lengai

Tanzania

2.764°S, 35.914°E; summit elev. 2962 m

All times are local (unless otherwise noted)


New cones, vigorous activity since February

From February through August 1998, several visitors to the crater of Ol Doinyo Lengai produced photographs and descriptions of eruptive activity. The following are taken from a summary of those visits provided by Celia Nyamweru, including detailed observations of certain hornitos made by Fred Belton and Chris Weber during their visits in June and August.

Orientation. Figure 51 locates the prominent features in the crater based on a photograph taken on 23 February 1998. A similar sketch map based on a photograph taken in February 1997 from nearly the same perspective appeared in a previous report (BGVN 23:06). Among the conspicuous new features appearing in 1998 are three large hornitos labeled T45, T46, and T47. T45 was described in February 1998 as being "possibly a new cone," but it may have been active as early as December 1997; by August it had grown to a height of ~7 m and was the dominant landmark in the E of the crater. T46 is a broad, darkly colored feature near the T20/T44 cluster. T46 was erroneously identified as T47 in the last Bulletin report. T47 is a tall, very narrow cone with a pointed top. It is located in the south-central area of the crater near the site of T23, which has nearly vanished. The cone cluster known as "A" has completely disappeared beneath recent lava.

Figure (see Caption) Figure 51. View of the crater of Ol Doinyo Lengai looking N from the S crater wall as it appeared 23 February 1998. The oblique view has a variable scale: it is ~ 300 m from T47 to C, and ~ 100 m from T47 to both T37S and T26/T27. Courtesy of C. Nyamweru from a photo by J.S. Antonio.

General appearance. During a visit to the summit on 12 March, observers noted no major changes to the crater since 23 February. Pale-brown, brown, and gray lava of differing ages covered the floor (figure 52). Pahoehoe flow patterns were clear in some areas, particularly N and NE of T45. An open vent in the T23 area contained a bubbling lava pool and steam issued from various vents. T47 was described as a very tall cone with a vertical crack and sharp peak, making it easily distinguishable from other nearby cones.

Figure (see Caption) Figure 52. Composite panoramic view to the SW from the E crater rim taken on 12 March. T45 is prominent in the foreground. The scale is oblique: it is ~ 150 m from T45 to T47 and ~ 100 m from T45 to T40. Courtesy of C. Nyamweru; photos by B.A. Gadiye.

An aerial photograph taken during May showed no important changes (figure 53). No steam or fresh lava was seen. The crater floor was covered with white or pale gray lava. A summit visit on 12 June revealed few changes (figure 54). No fresh lavas were seen, but recent flows of gray and brown lava were noticed, particularly in the area of T45 and from T37S in the direction of T24.

Figure (see Caption) Figure 53. Aerial view of the Ol Doinyo Lengai crater looking to the SE in May 1998. Courtesy of C. Nyamweru; photo by B. Wangermez.
Figure (see Caption) Figure 54. Composite panoramic view of Ol Doinyo Lengai looking SW from the E crater rim (compare with figure 52) taken on 12 June. Courtesy of C. Nyamweru; photos by B.A. Gadiye.

There were no signs of fresh surface activity when observers arrived on 17 June. The entire crater floor was grayish white and mostly soft, and no new spatter was visible on any hornito. The lowest point on the crater rim, to the NW, was 30 cm above the crater floor. T47 was the tallest cone in the crater (~11 m) and was lightly steaming. A 150-m-long steaming fracture, rich in sulfur deposits, was oriented SW-NE; the fracture passed over the site of T41 and T42, both of which had disappeared.

During visits through the first week of August, the steaming fissure was no longer visible, but a new fissure of the same type had developed. This was oriented NW-SE with its SE end located near the base of T20. T37S had two small cones recently added to the S part of its summit and a small lava flow down its W flank. A few clots of lava were ejected from T44C around 1300 on 2 August; although no taller, it showed recently added lava cascades on its N flank. At 0615 on 7 August T44 splashed black liquid lava out of its 6-m-high peak.

T37N1. On 17 June, T37N1 was open to the SE and contained a lava platform consisting of a 2-m-diameter circular pit beneath a 5-m overhanging wall. The pit opened into a cave that was ~4 m deep. A small spatter cone, 4 m W and 2.5 m above the pit, was located on the shoulder of the overhanging wall. At 0630 on 18 June a vigorously sloshing pond of very gas-rich lava rose slowly inside the circular pit. Lava was also visible through the vent of the spatter cone. Within an hour the pond overflowed and the spatter cone began ejecting lava clots up to 2 m above the cone, eventually producing pahoehoe and aa flows that traveled ~100 m ESE. This activity continued until 1200. At 1815 on 19 June a 20-minute eruption resulted in an overflow of the pond. Continuous lava fountains rose up to 1 m above the spatter cone, covering the flows from the previous day. At 1600 on 20 June an eruption lasting more than 15 hours began with a high-volume pond overflow and explosions every 2 seconds from the spatter cone. By 2245 the explosions had stopped and an orange flame was seen at the cone's vent. Lava continued to pour from the pond all night. A tube-fed flow first traveled N, then curved E as a narrow strip ~80 m long containing a single tube, and finally spread out into a wide stacked flow-field that piled up against the E rim.

At 1800 on 5 August a lava lake was seen in the cave under the spatter cone, ~5 m below the rim. At 1930 the lake began to glow dull red in the darkness, revealing that the cave was much larger than it had first appeared. The entire T37N1 hornito was hollow with a lake slowly rising inside that flowed toward the SW and entered a westward-directed tube or cave. As the lake rose higher lava appeared on the crater floor at the W base of T37N1, flowing slowly along the bottom of an old tube. Within 10 minutes the lake rose up to vent level and began to slosh over the rim, but lava could no longer be seen on the crater floor. From 2000 to 2330 the lake overflowed numerous times and lava advanced to a point near the base of T5T9. Due to frequent fluctuations in lake level, no long tubes developed; instead the flows were short and thickly stacked.

Similar activity occurred in the early morning hours of 6 August; just before 0715 the lake was ~3 m below the rim of the spatter cone, which had been increased in height and reduced in diameter during the eruption. The open interior of T37N1 filled with lava to a depth of 2 m, completely burying the pit that had contained the overflowing lava pond in June. The T37N1 spatter cone, positioned on the W side of the new, higher lava platform, was taller and had a larger vent than in June. Foaming white to pale gray carbonatite lava splashed out and fed short lava flows a few meters long down the W slope. Its vent opened into a large cave, ~8 m deep. A recent tube-fed flow from the vent extended to the W crater wall. The vesiculation of the gas-rich lava was high. Activity stopped around 1100 causing a 4-m drop of the lava level.

T48. At 0800 on 18 June (while T37N1 was erupting) T48 produced lava fountains up to 3 m high for 10 minutes, forming short aa flows on its N side. Throughout the morning of 19 June it occasionally ejected solid lapilli along with loud puffs of steam. At 2335 that night it began exploding loudly every 2 seconds and produced lava fountains up to 7 m high. After less than 2 minutes of these explosions the fountains decreased in height to 3 m but increased in volume. Each explosion covered the NW half of T48 with a thick layer of spatter that glowed dull red.

By August T48 had increased in height by at least 2 m and had produced many fresh flows extending in all directions. Aerial photographs taken by Benoit Wangermez on 1 August showed several fresh lava flows originating from vents in the approximate location of T48 and T49 extending to the NE and W crater rims. At 1300 on 2 August, low lava fountaining began from the summit vent and within an hour a lava stream was cascading down the nearly vertical SW flank of T48. Over the next 7 hours a large tube formed from the summit down the SW flank. Lava from this tube advanced past the N slope of T20 more than halfway to the WNW crater wall. Near the base of T48 the tube was ~60 cm in diameter and had several skylights from which lava often overflowed. The lava was gas-rich with a surface that appeared to be covered with gray foam.

The eruption continued all night but lava never reached the crater wall. At 0800 on 3 August a close inspection of the vertical lava tube revealed a small crack expelling hot air. Near 1000 the tube ruptured at that point, creating a powerful horizontal lava fountain that played on the N flank and base of nearby T44C. As the rupture progressed, other fountains directed at various angles of inclination developed, and eventually a flow began to form a second tube. The original tube was still full of flowing lava. By 1800 no lava was visible in the skylights. At 1930 a thin lava stream was spraying horizontally from the E side of T48's summit. At 0600 on 4 August T48 was inactive but at 0800 fountains developed on its upper east flank, creating pahoehoe and aa flows that reached the base of T40B. Similar activity continued until 2000. There was no further activity until 2330 on 5 August when a wide lava fountain sprayed horizontally for 20 minutes from just above a small ledge on the E flank, 2 m below the summit.

On 6 August at 1400 lava splashed out of two openings close to the peak of T48. Black, degassed, very liquid lava fed little lava flows reaching 8 m down the E slope. The activity stopped shortly after 1600.

T40. Sloshing lava was heard inside T40 during the entire June visit. During the night of June 19 a pahoehoe flow traveled ~10 m from a small vent in its base. Lava flowed into a cave under a low, broad hornito just NE of T40. This new lava flow was ~1 m thick. The cave had contained an impressive group of white lava stalactites. On 20 June a 3-m2 section of the SW flank collapsed into its interior.

On 2 August at 1000 occasional lava clots were being ejected from T40's summit, but this continued for only ~30 minutes. During the August visit T40 was noisily degassing. The collapse pit that formed on 20 June in the SW flank of T40 was no longer visible, having been filled in by lava. Recent flows extended a short distance SW and SE of T40, partially covering a low mound to the SE. A tall, narrow cone had very recently been formed on the summit of T40 and was the source of several very fresh aa flows extending to the base of T40.

T49. A small cone just NE of T49 extended toward the NW and grew in height between visits. Sloshing lava was frequently heard there. After several earthquakes during the night of 6 August, at 0408 on 7 August a loud explosion blew off the top and N side of T49. Rocks up to 1 m3 were thrown or rolled a few meters. A dark-red lava fountain ~15 m high continued until 0413 with a loud, jet-like noise. Pahoehoe lava with little viscosity (1-5 Pa s) splashed N of T49 and traveled NW. The flow was thin (10-20 cm) and stopped shortly after the end of the eruption. The amount of erupted lava was ~70-100 m3. Lava pearls up to 4 mm diameter and fine ash were blown over 200 m NW.

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: Celia Nyamweru, Department of Anthropology, St. Lawrence University, Canton, NY 13617 USA (URL: http://blogs.stlawu.edu/lengai/); Fredrick A. Belton, 3555 Philsdale Ave., Memphis, TN 38111; Christoph Weber, Kruppstr 171, 42113 Wuppertal, Germany.


Masaya (Nicaragua) — September 1998 Citation iconCite this Report

Masaya

Nicaragua

11.984°N, 86.161°W; summit elev. 635 m

All times are local (unless otherwise noted)


Integrated scientific studies of the caldera area

Four teams of Canadian, British, and Nicaraguan volcanologists carried out studies of Masaya caldera during January-April and September 1998. The volcano was examined using correlation spectroscopy (COSPEC), microgravity, Open Path Fourier Transform Infrared spectroscopy (OP-FTIR), and soil-gas studies.

Vent degassing appeared to have increased significantly. COSPEC measurements during February-April 1998 showed SO2 flux varying from 680 t/d to a maximum of 5,580 t/d. Measurements made during the previous year (January-March 1997) showed more stable fluxes of approximately 380 t/d. Measurements in September 1998 showed flux levels varying from 320 to 1,420 t/d.

OP-FTIR measured from the Plaza Oviedo overlooking the "Santiago" pit crater showed consistent SO2/HCl and HCl/HF volume ratios of 2 and 7, respectively. Using the COSPEC-derived SO2 flux, scientists inferred HCl fluxes of 340 to 2,790 t/d and HF fluxes of 97 to 797 t/d.

CO2 soil-gas measurements at the foot of the Comalito cinder cone increased from 23 to 31.3% between March 1997 and February 1998. Fumarole temperatures also increased from 70 to 84°C during February 1998.

Microgravity surveys during March 1997-February 1998 showed a slight increase in gravity immediately beneath the Santiago pit crater. They also showed evidence (increased noise recorded on the meter) of significant seismic activity around the Santiago crater. Similar measurements acquired in September 1998 indicated increased seismic activity throughout the caldera.

Temperatures at the active vent, measured using a Cyclops infrared camera, ranged between 170 and 400°C. The higher measurements occurred when incandescence of the vent walls was visible. In March, a small fumarole emitting low levels of gas appeared, ~15 m from the active vent.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras pyroclastic shield volcano and is a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The twin volcanoes of Nindirí and Masaya, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6500 years ago. Historical lava flows cover much of the caldera floor and have confined a lake to the far eastern end of the caldera. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals cause health hazards and crop damage.

Information Contacts: Glyn Williams-Jones, Dave Rothery, Hazel Rymer, Peter Francis, and Lisa Boardman, Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, United Kingdom; Alexandre Beaulieu, Dany Harvey, Pierre Delmelle, Katie St-Amand, and John Stix, Département de Géologie, Université de Montréal, Montréal, Québec H3C 3J7, Canada; Mike Burton, Clive Oppenheimer, and Matthew Watson, Department of Geography, University of Cambridge, Downing Place, Cambridge, CB2 3EN, United Kingdom (URL: http://www.geog.cam.ac.uk/); Hélène Gaonac'h, Département des sciences de la Terre, Université du Québec - Montréal, Montréal, Québec H3C 3P8, Canada; Martha Navarro and Wilfried Strauch, INETER, Apartado Postal 2110, Managua, Nicaragua; Benjamin van Wyk de Vries, Departement des Sciences de la Terre, Universite Blaise Pascal, 63038 Clermont-Ferrand, France.


Popocatepetl (Mexico) — September 1998 Citation iconCite this Report

Popocatepetl

Mexico

19.023°N, 98.622°W; summit elev. 5393 m

All times are local (unless otherwise noted)


Several episodes of ash emission during September

Following a large ash exhalation on 8 September (BGVN 23:08), eruptive activity at Popocatépetl decreased in intensity and duration. CENEPRED reported a few moderate emissions during September that caused local ashfall.

Small-volume, discrete, short-duration emissions containing ash, sometimes accompanied by steam and gas, were recorded occasionally during the period 9-15 September. Brief episodes of harmonic tremor were also recorded. During the night of 14 September glow reflected from clouds over the crater was seen.

Moderate exhalations of steam, gas, and light ash took place during 16 September. Several brief episodes of high-frequency tremor were recorded that afternoon; the largest emissions occurred at 1546-1552, 1604, and 1611. Ashfall was reported at Amecameca, 20 km NW of the volcano. Despite bad weather that reduced visibility most of the day, a dense column of steam and gas was seen rising 700 m above the summit before being blown to the NW. Activity decreased to stable background levels on 17 September. A dense steam and gas cloud seen on the morning of 18 September dispersed to the NE; as the cloud gained altitude, its direction changed to the south. SO2 measurements showed significant increases following the 16 September explosion over levels earlier in the month.

Another moderate increase in eruptive activity began a few days later. A steam and gas column rising 1 km above the summit was observed during 20 September. Brief, moderately intense emissions of steam and gas, sometimes with light ash puffs, took place throughout the morning of 21 September. An explosion at 1148 that morning produced light ashfall in towns up to 20 km NW of Popocatépetl. A similar but less intense event occurred at 1543. Emissions decreased to relatively low levels until 1225 on 22 September when a moderate explosion lasting 7 minutes produced a steam, gas, and ash plume that rose 4 km above the summit. Visibility during 22 August was poor due to bad weather, but a large ash cloud near the crater was detected by Doppler radar. Ash was dispersed during the afternoon NW of the volcano, producing light ash falls in the suburban SE of metropolitan México City.

Following the explosion on 22 September, eruptive activity paused until a similar explosion occurred at 1829 on 23 September. This explosion lasted 6 minutes and produced a 3-km high column of steam, gas, and ash. Ash fall was reported in towns SW of the volcano. Eruptive activity soon decreased again, stabilizing at low levels of small, isolated emissions of steam and gas, typical of earlier in September. An exhalation at 1025 on 24 September was followed by 30 minutes of low-frequency harmonic tremor. An A-type earthquake of M 2.1 located 1.8 km E of the crater at a depth of 3.9 km was recorded at 2224 on 24 September, and another moderate exhalation lasting 7 minutes began at 2332.

Geologic Background. Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Information Contacts: Servando De la Cruz-Reyna1,2 Roberto Quaas1,2 Carlos Valdés G.2 and Alicia Martinez Bringas1; 1 Centro Nacional de Prevencion de Desastres (CENAPRED) Delfin Madrigal 665, Col. Pedregal de Santo Domingo, Coyoacan, 04360, México D.F. (URL: https://www.gob.mx/cenapred/); and 2 Instituto de Geofisico, UNAM, Coyoacán 04510, México D.F., México.


Sete Cidades (Portugal) — September 1998 Citation iconCite this Report

Sete Cidades

Portugal

37.87°N, 25.78°W; summit elev. 856 m

All times are local (unless otherwise noted)


Seismic swarm on submarine flank

Since June 1998, increasing seismic activity in the vicinity of Sete Cidades volcano has resulted in occasional seismic swarms. On the night of 2-3 August about 120 events were registered in 3 hours. During that period, five earthquakes were felt along the W coast, the strongest with a magnitude of 3.1 reached a maximum intensity of V (MM) at Ginetes e Varzea. Similarly, on 2 September in Sao Miguel more than 120 events occurred beneath the sea floor over a period of about 4 hours near shore between Ponta da Ferraria and Mosteiros. One of the five felt earthquakes during this period also reached an intensity of V (MM). There were no reports of injury or damage from any of these events.

Geologic Background. Sete Cidades volcano at the western end of Sao Miguel Island contains a 5-km-wide summit caldera, occupied by two caldera lakes, that is one of the scenic highlights of the Azores. The steep-walled, 500-m-deep caldera was formed about 22,000 years ago, and at least 22 post-caldera eruptions have occurred. A large group of Pleistocene post-caldera trachytic lava domes, lava flows, and pyroclastic-flow deposits is found on the western-to-northern flanks. A nearly circular ring of six Holocene pyroclastic cones occupies the caldera floor. These have been the source of a dozen trachytic pumice-fall deposits erupted during the past 5000 years. Sete Cidades is one of the most active Azorean volcanoes. Historical eruptions date back to the 15th century and have occurred from within the caldera and from submarine vents off the west coast.

Information Contacts: João Luis Gaspar and Nicolau Wallenstein, Departamento de Geociencias, Centro de Vulcanologia, Universidade dos Açores, Rua Mae de Deus, 9500 - Ponta Delgada, Sao Miguel, Açores, Portugal.


Sheveluch (Russia) — September 1998 Citation iconCite this Report

Sheveluch

Russia

56.653°N, 161.36°E; summit elev. 3283 m

All times are local (unless otherwise noted)


Ash explosions and pyroclastic flow during 3 September

Seismicity remained generally at background levels during 2-28 September. A plume on 2-3 September was seen rising 200 m above the volcano. At 1622 on 3 September, ash explosions produced a cloud that rose 5 km above the summit, and extended 100 km NNE. Pyroclastic flows moving SW were observed at this time. The explosion was also accompanied by a 9-minute series of shallow earthquakes and tremor. The level-of-concern color code remained Green. Observation was restricted by cloud during much of the month.

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

Information Contacts: Olga Chubarova, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Tom Miller, Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.


Soufriere Hills (United Kingdom) — September 1998 Citation iconCite this Report

Soufriere Hills

United Kingdom

16.72°N, 62.18°W; summit elev. 915 m

All times are local (unless otherwise noted)


Continuing decrease in activity; hazards reassessed

The following summarizes the Montserrat Volcano Observatory's (MVO) scientific reports for July and August, except information concerning the 3 July pyroclastic flows, which was reported in BGVN 23:07.

Summary. In the weeks following the 3 July pyroclastic flows, no fresh magma reached the surface; however, vesicular ballistic blocks were recovered from craters on Perches Mountain suggesting that there may have been a small Vulcanian explosion. SO2-flux levels declined steadily throughout July to an average of 1,000 metric tons/day (t/d). Vigorous steam-and-ash venting continued from the dome-collapse scar until the end of July. Activity in August was dominated by several small dome-collapse events and a period of enhanced steam-and-ash venting in the middle of the month. The dome-collapse events were caused by the gravitational collapse of weakened dome rock. The ash venting was intense one day but waned over following days to normal levels. MiniCOSPEC results showed a peak that coincided with the enhanced venting, but there was an overall decline from ~1,000 t/d at the beginning of the month to ~500 t/d at the end of the month.

Visual observations. Ash-and-steam venting immediately after the 3 July event was vigorous. Significant pulses of steam-and-ash continued for 2-3 weeks and fumarolic activity was evident on the S and N flanks of the dome.

A steep buttress overhanging the 3 July scar collapsed on 16 August generating pyroclastic flows that reached the Tar River delta. Large fragments of the buttress were left in the area of the scar's mouth. On 19 August fumarolic activity in the scar increased in intensity: fumaroles on the back wall and at the base of the scar discharged copious quantities of steam and ash in jets. The next day activity decreased in intensity and the fumaroles were generally issuing steam only. Some of the fumaroles were temporarily buried following a rockfall within the scar on 20 August. The fumarolic activity declined steadily, and by 22 August activity had declined to levels observed in the first week of August.

Mudflows continued to be a problem in July. Mudflow deposits built up beneath the Belham Bridge until there was a clearance of only about 30 cm.

Seismicity. After 5 July, seismicity returned to levels similar to the previous month, with the exception of a swarm of volcano-tectonic earthquakes on 25 July (figure 43). This swarm had no outward manifestation at the volcano and activity returned to low levels by the next day.

Figure (see Caption) Figure 43. Seismicity recorded at Soufriere Hills by type during July and August 1998. Data courtesy of MVO.

Seismicity during August was generally low. Activity was dominated by small volcano-tectonic earthquakes located ~3 km below the dome, with occasional rockfalls and pyroclastic-flow signals. On 13 August there were two episodes (at 0519 and 1455) of pyroclastic flow in the White River valley. These flows traveled 1.8 km from the dome and were caused by the collapse of weakened dome rock. Active fumaroles on the Galways side of the dome near Chances Peak undermined part of the dome. A scar immediately above the fumarolic area is believed to be the source of the pyroclastic flows. Each episode was followed by about an hour of continuous rockfall activity. On 19 August a rockfall signal was followed by tremor, which corresponded to vigorous ash venting. The signal lasted two days and varied in amplitude. At times of highest amplitude the tremor was nearly monochromatic at 4 Hz.

Ground deformation. Measurements from GPS survey sites on the flanks of the volcano and in the N of the island indicated widespread major reductions in movement during July. The Hermitage site indicated continued slow movement NE at rate of ~0.5 cm/month. The GPS site at Perches was destroyed in the 3 July event; ballistics were scattered over Perches Mountain and the GPS site was later found at the edge of a 3.4 m diameter impact crater. The rates of movement of sites in August were within the instrumental error. The GPS kit was used for one week by volcanologists from the University of Rhode Island who were conducting a bathymetric survey of the fans at the mouths of the Tar River and White Rivers valleys.

The EDM reflector on Peak B was measured from Windy Hill. The increase in distance of 5 cm during the period May-July may have been caused partially by release associated with the 3 July collapse. The line had shortened by 9 cm between 25 January and 13 May, but between May and August the distance lengthened by a total 8 cm (within 1 cm of its original length) possibly indicating a relaxation in the confining pressure.

Volume measurements. A kinematic GPS survey of the Tar River fan was completed in July. The total volume of the fan was estimated to be 22.1 x 106 m3. A previous survey in August 1997 gave a volume of 15.7 x 106 m3. Much of the increase resulted from the 3 July collapse, which extended the fan 350 m N, although a small part of the increase was due to the accumulation of pyroclastic-flow deposits during the September-October 1997 explosion sequence (BGVN 22:10 and 22:11). The E limit of the fan, defined by a steep shelf extending into the sea, was unchanged. A small deposit was left on the S side of the fan, although above the established shoreline there was only a thin layer of pyroclastic-flow deposits.

No volume measurements were made in August. Attempts to survey the 3 July collapse scar were foiled by deteriorating weather conditions and a lack of helicopter fuel.

Environmental monitoring. MiniCOSPEC observations recommenced on 5 July. In early July SO2 flux was generally between 1,000 and 2,500 metric tons/day (t/d). On 13 July SO2 flux measured 4,150 t/d, the highest ever recorded at Montserrat. Throughout the remainder of July there was a gradual decline in SO2 flux to an average of 1,000 t/d at the end of the month. The cause of the relatively high gas flux in the apparent absence of magmatic activity was being investigated, but may relate to perturbations in the hydrothermal system caused by the dome collapse on 3 July 1998.

MiniCOSPEC measurements in early August showed a consistent SO2 flux of ~500-1000 t/d. On 19 August levels rose to 1,400 t/d as a result of enhanced venting. Towards the end of the month poor weather limited the number of COSPEC measurements, but there appeared to be a slight decrease to an average of ~500 t/d. Throughout late August the wind direction was variable due to tropical storms in the area. On occasions when the wind blew to the N or NW a strong smell of sulfurous gases was detected in the inhabited area of Montserrat.

Sulfur dioxide diffusion tubes exposed between 29 June and 13 July clearly reflect the high emissions in early July (table 31). The Plymouth area in particular was subjected to very high concentrations of gas. In the second half of July SO2 concentrations in Plymouth were reduced by half. Populated areas N of the Belham River valley were, as usual, only subjected to very low SO2 levels in July. In August there was a general decline of SO2 in the atmosphere. An additional monitoring site in the N of the island was installed to assess SO2 during shifts in wind direction.

Table 31. Sulfur dioxide diffusion-tube results, 29 June-11 August 1998. Levels are in parts per billion (ppb). Courtesy of MVO.

Station 29 Jun-13 Jul 1998 13 Jul-27 Jul 1998 27 Jul-11 Aug 1998
Police HQ, Plymouth 207.9 116.5 131.5
St. George's Hill 22.05 8.55 9.55
Weekes 5.75 4.1 2.85
MVO south 4.3 3.85 --
Lawyers 2.2 0 3.8
Vue Pointe Hotel -- -- 3.25

Hazard assessment. A meeting was held 14-16 July at McChesney's Estate to assess the current hazards and risks associated with Soufriere Hills Volcano. The meeting brought together many of the senior scientists who have worked at MVO during the three-year volcanic crisis. Those who took part were Richie Robertson, Lloyd Lynch and John Shepherd from the Seismic Research Unit in Trinidad; Simon Young, Sue Loughlin, Tony Reedman, and Gill Norton from the British Geological Survey; and many other senior scientists from around the world including Steve Sparks from Bristol University, Peter Baxter from Cambridge University, Barry Voight from Penn State University, Joe Devine from Brown University, Peter Francis from the Open University, Keith Rowley, and Willy Aspinall. Richard Luckett and Richard Herd from MVO provided up-to-date information about the current status of Soufriere Hills volcano.

Discussion was held on various aspects of the activity over the previous six months, including the event on 3 July. Related issues, including the safety of Bramble airport, were also addressed. An assessment of the level of risk associated with the volcano was undertaken. A report was presented to the government of Montserrat and the U.K. on 29 July after which the findings were made public.

According to the report, MVO judged it likely that the volcano has entered a period of repose, with the probability of no further magmatic eruptions in the next 6 months set at about 95%. MVO was confident that renewed magma ascent and escalation to dangerous levels of activity could be identified, although they cautioned that escalation might take place in a very short period of time (e.g. a matter of hours). Most of the island was perceived to be under reduced risk, but areas S of the Belham River Valley remain vulnerable to serious volcanic hazards including pyroclastic flows related to the collapse of the dome, mud flows, and exposure to fine ash. Further dome collapses were deemed likely and could affect all flanks of the volcano, especially the Tar River, Gages Valley, Plymouth area, Galways, and the NE slopes. There is potential for a variety of events to take place, including steam explosions, mud flows, and ash falls, for many years to come but the risks will decline with time. Health risk analysis showed that if magmatic activity does not resume, the potential for harmful exposure to ash will be limited and the risk of developing silicosis will be low in Zones 1 to 3. The same would apply to Population Zone 4 north of the Belham Valley after a clean-up operation has been safely completed. A public education program on the health risks of ash was recommended, including guidance on protection measures during the clean up. Certain groups could be at risk from much higher exposure (e.g. outdoor workers and asthma sufferers) and there may be unknown long-term health risks to young children.

The Volcanic Executive Group (VEG), chaired by Governor Tony Abbott, met to consider the Scientific Review. A statement from the Governor's Office following the meeting rescinded the recommendation that residents leave the Central Zone. Also, there was no longer any objection to commercial organizations operating within the Central Zone. The clean up of Friths, Salem, and Old Towne, which commenced some weeks ago, was intensified. The VEG sought advice on how to ensure that the Zone will be cleaned so that children and those with respiratory problems will not be affected on reoccupation.

Geologic Background. The complex, dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. The volcano is flanked by Pleistocene complexes to the north and south. English's Crater, a 1-km-wide crater breached widely to the east by edifice collapse, was formed about 2000 years ago as a result of the youngest of several collapse events producing submarine debris-avalanche deposits. Block-and-ash flow and surge deposits associated with dome growth predominate in flank deposits, including those from an eruption that likely preceded the 1632 CE settlement of the island, allowing cultivation on recently devegetated land to near the summit. Non-eruptive seismic swarms occurred at 30-year intervals in the 20th century, but no historical eruptions were recorded until 1995. Long-term small-to-moderate ash eruptions beginning in that year were later accompanied by lava-dome growth and pyroclastic flows that forced evacuation of the southern half of the island and ultimately destroyed the capital city of Plymouth, causing major social and economic disruption.

Information Contacts: Montserrat Volcano Observatory (MVO), c/o Chief Minister's Office, PO Box 292, Plymouth, Montserrat, West Indies (URL: http://www.mvo.ms/); Richard Aspin, Information & Education Unit, Emergency Dept., St Johns Village, Montserrat, Leeward Islands, West Indies.


Yasur (Vanuatu) — September 1998 Citation iconCite this Report

Yasur

Vanuatu

19.532°S, 169.447°E; summit elev. 361 m

All times are local (unless otherwise noted)


Ongoing eruption, felt earthquake, and fresh glass chemical analysis

On 9 September 1998, an earthquake was felt in a village 3 km from Yasur; simultaneously, loud explosions were heard from the volcano. When the summit was visited by John Seach during 10-11 September, five craters inside the main summit crater in the pyroclastic cone were found to be active. Crater A, large and on the S, displayed quiet explosions followed by brown ash emission. Other craters were quiet with only gas emissions. These included the smaller Crater B, in the center of the main crater; the larger Crater C, on the N; the small Crater D located W of Crater B; and Crater E, on the SW wall of the main crater.

During 4 hours of observation on 10 September, 51 explosions were observed from four craters: Crater A, 25 explosions; Crater B, 9; Crater C, 13; and Crater D, 4. Bombs thrown from Craters B, C, and D fell back into the vent or onto the crater wall. Some larger explosions, every 20-30 minutes, threw bombs 350 m high. During the night, bombs thrown onto the crater wall glowed for up to 6 minutes. The explosions and shaking were felt up to 3 km away.

A fresh bomb collected in August 1997 (BGVN 22:08) was recently analyzed by microprobe (table 1).

Table 1. Major element analysis of Yasur glass taken from an average of five analyses on fresh glass bomb collected in August 1997. All iron is shown as FeO. Microprobe analysis courtesy of Timothy O'Hearn; sample courtesy of Steve and Donna O'Meara, and Robert Benward.

Component Weight %
SiO2 58.61
TiO2 0.95
Al203 15.07
FeOt 8.68
MnO 0.25
MgO 2.49
CaO 5.44
Na2O 3.52
K2O 3.78
P2O5 0.66
Total 99.46

Geologic Background. Yasur, the best-known and most frequently visited of the Vanuatu volcanoes, has been in more-or-less continuous Strombolian and Vulcanian activity since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island, this mostly unvegetated pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide, horseshoe-shaped caldera associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

Information Contacts: John Seach, P.O. Box 16, Chatsworth Island, N.S.W. 2469, Australia; Tim O'Hearn, Department of Mineral Sciences, Smithsonian Institution, Washington, DC 20560-0119 USA.

Atmospheric Effects

The enormous aerosol cloud from the March-April 1982 eruption of Mexico's El Chichón persisted for years in the stratosphere, and led to the Atmospheric Effects section becoming a regular feature of the Bulletin. Descriptions of the initial dispersal of major eruption clouds remain with the individual eruption reports, but observations of long-term stratospheric aerosol loading will be found in this section.

Atmospheric Effects (1980-1989)  Atmospheric Effects (1995-2001)

Special Announcements

Special announcements of various kinds and obituaries.

Special Announcements

Additional Reports

Reports are sometimes published that are not related to a Holocene volcano. These might include observations of a Pleistocene volcano, earthquake swarms, or floating pumice. Reports are also sometimes published in which the source of the activity is unknown or the report is determined to be false. All of these types of additional reports are listed below by subregion and subject.

Kermadec Islands


Floating Pumice (Kermadec Islands)

1986 Submarine Explosion


Tonga Islands


Floating Pumice (Tonga)


Fiji Islands


Floating Pumice (Fiji)


Andaman Islands


False Report of Andaman Islands Eruptions


Sangihe Islands


1968 Northern Celebes Earthquake


Southeast Asia


Pumice Raft (South China Sea)

Land Subsidence near Ham Rong


Ryukyu Islands and Kyushu


Pumice Rafts (Ryukyu Islands)


Izu, Volcano, and Mariana Islands


Acoustic Signals in 1996 from Unknown Source

Acoustic Signals in 1999-2000 from Unknown Source


Kuril Islands


Possible 1988 Eruption Plume


Aleutian Islands


Possible 1986 Eruption Plume


Mexico


False Report of New Volcano


Nicaragua


Apoyo


Colombia


La Lorenza Mud Volcano


Pacific Ocean (Chilean Islands)


False Report of Submarine Volcanism


Central Chile and Argentina


Estero de Parraguirre


West Indies


Mid-Cayman Spreading Center


Atlantic Ocean (northern)


Northern Reykjanes Ridge


Azores


Azores-Gibraltar Fracture Zone


Antarctica and South Sandwich Islands


Jun Jaegyu

East Scotia Ridge


Additional Reports (database)

08/1997 (BGVN 22:08) False Report of Mount Pinokis Eruption

False report of volcanism intended to exclude would-be gold miners

12/1997 (BGVN 22:12) False Report of Somalia Eruption

Press reports of Somalia's first historical eruption were likely in error

11/1999 (BGVN 24:11) False Report of Sea of Marmara Eruption

UFO adherent claims new volcano in Sea of Marmara

05/2003 (BGVN 28:05) Har-Togoo

Fumaroles and minor seismicity since October 2002

12/2005 (BGVN 30:12) Elgon

False report of activity; confusion caused by burning dung in a lava tube



False Report of Mount Pinokis Eruption (Philippines) — August 1997

False Report of Mount Pinokis Eruption

Philippines

7.975°N, 123.23°E; summit elev. 1510 m

All times are local (unless otherwise noted)


False report of volcanism intended to exclude would-be gold miners

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.


False Report of Somalia Eruption (Somalia) — December 1997

False Report of Somalia Eruption

Somalia

3.25°N, 41.667°E; summit elev. 500 m

All times are local (unless otherwise noted)


Press reports of Somalia's first historical eruption were likely in error

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.


False Report of Sea of Marmara Eruption (Turkey) — November 1999

False Report of Sea of Marmara Eruption

Turkey

40.683°N, 29.1°E; summit elev. 0 m

All times are local (unless otherwise noted)


UFO adherent claims new volcano in Sea of Marmara

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.


Har-Togoo (Mongolia) — May 2003

Har-Togoo

Mongolia

48.831°N, 101.626°E; summit elev. 1675 m

All times are local (unless otherwise noted)


Fumaroles and minor seismicity since October 2002

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 (see Caption) 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 (see Caption) 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 (see Caption) 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.


Elgon (Uganda) — December 2005

Elgon

Uganda

1.136°N, 34.559°E; summit elev. 3885 m

All times are local (unless otherwise noted)


False report of activity; confusion caused by burning dung in a lava tube

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/).