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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

Stromboli (Italy) Constant explosions from both crater areas during November 2018-February 2019

Krakatau (Indonesia) Ash plumes, ballistic ejecta, and lava extrusion during October-December; partial collapse and tsunami in late December; Surtseyan activity in December-January 2019

Masaya (Nicaragua) Lava lake persists with decreased thermal output, November 2018-February 2019

Santa Maria (Guatemala) Daily explosions cause steam-and-ash plumes and block avalanches, November 2018-February 2019

Reventador (Ecuador) Multiple daily explosions with ash plumes and incandescent blocks rolling down the flanks, October 2018-January 2019

Kuchinoerabujima (Japan) Weak explosions and ash plumes beginning 21 October 2018

Kerinci (Indonesia) A persistent gas-and-steam plume and intermittent ash plumes occurred from July 2018 through January 2019

Yasur (Vanuatu) Eruption continues with ongoing explosions and multiple active crater vents, August 2018-January 2019

Ambae (Vanuatu) Ash plumes and lahars in July 2018 cause evacuation of the island; intermittent gas-and-steam and ash plumes through January 2019

Agung (Indonesia) Ongoing intermittent ash plumes and frequent gas-and-steam plumes during August 2018-January 2019

Erebus (Antarctica) Lava lakes persist through 2017 and 2018

Villarrica (Chile) Intermittent Strombolian activity ejects incandescent bombs around crater rim, September 2018-February 2019



Stromboli (Italy) — March 2019 Citation iconCite this Report

Stromboli

Italy

38.789°N, 15.213°E; summit elev. 924 m

All times are local (unless otherwise noted)


Constant explosions from both crater areas during November 2018-February 2019

Nearly constant fountains of lava at Stromboli have served as a natural beacon in the Tyrrhenian Sea for at least 2,000 years. Eruptive activity at the summit consistently occurs from multiple vents at both a north crater area (N Area) and a southern crater group (CS Area) on the Terrazza Craterica at the head of the Sciara del Fuoco, a large scarp that runs from the summit down the NW side of the island. Thermal and visual cameras that monitor activity at the vents are located on the nearby Pizzo Sopra La Fossa, above the Terrazza Craterica, and at a location closer to the summit craters.

Eruptive activity from November 2018 to February 2019 was consistent in terms of explosion intensities and rates from both crater areas at the summit, and similar to activity of the past few years (table 5). In the North Crater area, both vents N1 and N2 emitted a mixture of coarse (lapilli and bombs) and fine (ash) ejecta; most explosions rose less than 80 m above the vents, some reached 150 m. Average explosion rates ranged from 4 to 21 per hour. In the CS crater area continuous degassing and occasional intense spattering were typical at vent C, vent S1 was a low-intensity incandescent jet throughout the period. Explosions from vent S2 produced 80-150 m high ejecta of ash, lapilli and bombs at average rates of 3-16 per hour. Thermal activity at Stromboli was actually higher during November 2018-February 2019 than it had been in previous months as recorded in the MIROVA Log Radiative Power data from MODIS infrared satellite information (figure 139).

Table 5. Summary of activity levels at Stromboli, November 2018-February 2019. Low intensity activity indicates ejecta rising less than 80 m and medium intensity is ejecta rising less than 150 m. Data courtesy of INGV.

Month N Area Activity CS Area Activity
Nov 2018 Low- to medium-intensity explosions at both N1 and N2, lapilli and bombs mixed with ash, explosion rates of 6-16 per hour. Continuous degassing at C; intense spattering on 26 Nov. Low- to medium-intensity incandescent jetting at S1. Low- to medium-intensity explosions at S2 with a mix of coarse and fine ejecta and explosion rates of 3-18 per hour.
Dec 2018 Low- to medium-intensity explosions at both N1 and N2, coarse and fine ejecta, explosion rates of 4-21 per hour. Three days of intense spattering at N2. Continuous degassing at C; intense spattering 1-2 Dec. Low- to medium-intensity incandescent jets at S1, low and medium-intensity explosions of coarse and fine material at S2. Average explosion raters were 10-18 per hour at the beginning of the month, 3-4 per hour during last week.
Jan 2019 Low- to medium-intensity explosions at N1, coarse ejecta. Low- to medium-intensity and spattering at N2, coarse and fine ejecta. Explosion rates of 9-16 per hour. Continuous degassing and low-intensity explosions of coarse ejecta at C. Low-intensity incandescent jets at S1. Low- and medium-intensity explosions of coarse and fine ejecta at S2.
Feb 2019 Medium-intensity explosions with coarse ejecta at N1. Low-intensity explosions with fine ash at N2. Explosion rates of 4-11 per hour. Continuous degassing and low-intensity explosions with coarse and fine ejecta at C and S2. Low intensity incandescent jets at S1. Explosion rates of 2-13 per hour.
Figure (see Caption) Figure 139.Thermal activity at Stromboli increased during November 2018-February 2019 compared with the preceding several months as recorded in the MIROVA project log radiative power data taken from MODIS thermal satellite information. Courtesy of MIROVA.

Activity at the N area was very consistent during November 2018 (figure 140). Explosions of low-intensity (less than 80 m high) to medium-intensity (less than 150 m high) occurred at both the N1 and N2 vents and produced coarse material (lapilli and bombs) mixed with ash, at rates averaging 6-16 explosions per hour. In the SC area continuous degassing was reported from vent C with a brief period of intense spattering on 26 November. At vent S1 low- to medium-intensity incandescent jetting was reported. At vent S2, low- and medium-intensity explosive activity produced a mixture of coarse and fine (ash) material at a frequency of 3-18 events per hour.

Figure (see Caption) Figure 140. The Terrazza Craterica at Stromboli on 12 November 2018 as viewed by the thermal camera placed on the Pizzo sopra la Fossa, showing the two main crater areas and the active vents within each area that are discussed in the text. Heights above the crater terrace, as indicators of intensity of the explosions, are shown divided into three intervals of low (basso), medium (media), and high (alta). Courtesy of INGV (Report 46/2018, Stromboli, Bollettino Settimanale 05/11/2018 - 11/11/2018, data emissione 13/11/2018).

Similar activity continued during December at both crater areas, although there were brief periods of more intense activity. Low- to medium-intensity explosions at both N area vents produced a mixture of coarse and fine-grained material at rates averaging 4-21 per hour. During 6-7 December ejecta from the N vents fell onto the upper part of the Sciara del Fuoco and rolled down the gullies to the coast, producing tongues of debris (figure 141). An explosion at N1 on 12 December produced a change in the structure of the crater area. During 10-16 December the ejecta from the N area landed outside the crater on the Sciara del Fuoco. Intense spattering was observed from N2 on 18, 22, and 31 December. In the CS area, continuous degassing took place at vent C, along with a brief period of intense spattering on 1-2 December. Low to medium intensity incandescent jets persisted at S1 along with low-and medium-intensity explosions of coarse and fine-grained material at vent S2. Rates of explosion at the CS area were higher at the beginning of December (10-18 per hour) and lower during the last week of the month (3-4 per hour).

Figure (see Caption) Figure 141. Images from the Q 400 thermal camera at Stromboli taken on 6 December 2018 showed the accumulation of pyroclastic material in several gullies on the upper part of the Sciara del Fuoco following an explosion at vent N2 at 1520 UTC. The images illustrate the rapid cooling of the pyroclastic material in the subsequent two hours. Courtesy of INGV (Report 50/2018, Stromboli, Bollettino Settimanale, 03/12/2018 - 09/12/2018, data emissione 11/12/2018).

Explosive intensity was low (ejecta less than 80 m high) at vent N1 at the beginning of January 2019 and increased to medium (ejecta less than 150 m high) during the second half of the month, producing coarse ejecta of lapilli and bombs. Intensity at vent N2 was low to medium throughout the month with both coarse- and fine-grained material ejected. Explosions from N2 sent large blocks onto the Sciara del Fuoco several times throughout the month and usually was accompanied by intense spattering. Explosion rates varied, with averages of 9 to 16 per hour, throughout the month in the N area. In the CS area continuous degassing occurred at vent C, and low-intensity explosions of coarse-grained material were reported during the second half of the month. Low-intensity incandescent jets at S1 along with low- and medium-intensity explosions of coarse and fine-grained material at S2 persisted throughout the month.

A helicopter overflight of Stromboli on 8 January 2019 allowed for detailed visual and thermal observations of activity and of the morphology of the vents at the summit (figure 142). Vent C had two small hornitos, and a small scoria cone was present in vent S1, while a larger crater was apparent at S2. In the N crater area vent N2 had a large scoria cone that faced the Sciara del Fuoco to the north; three narrow gullies were visible at the base of the cone (figure 143). Vent S1 was a large crater containing three small vents aligned in a NW-SE trend; INGV scientists concluded the vents formed as a result of the 12 December 2018 explosion. Thermal images showed relatively low temperatures at all fumaroles compared with earlier visits.

Figure (see Caption) Figure 142. Thermal images from Stromboli taken during the overflight of 8 January 2019 showed the morphological structure of the individual vents of the N and CS crater areas. Courtesy of INGV (Report 03/2019, Stromboli, Bollettino Settimanale, 07/01/2019 - 13/01/2019, (data emissione 15/01/2019).
Figure (see Caption) Figure 143. An image taken at Stromboli during the overflight of 8 January 2019 shows the morphological structure of the summit Terrazza Craterica with three gullies at the base of the scoria cone of vent N2. The top thermal image (inset a) shows that the fumaroles in the upper part of the Sciara del Fuoco have low temperatures. Courtesy of INGV (Report 03/2019, Stromboli, Bollettino Settimanale, 07/01/2019 - 13/01/2019, data emissione 15/01/2019).

Activity during February 2019 declined slightly from the previous few months. Explosions at vent N1 were of medium-intensity and produced coarse material (lapilli and bombs). At N2, low-intensity explosions produced fine ash. Average explosion rates in the N area ranged from 4-11 per hour. At the CS area, continuous degassing and low-intensity explosions produced coarse and fine-grained material from vents C and S2 while low-intensity incandescent jets were active at S1. The explosion rates at the CS area averaged 2-13 per hour.

Geologic Background. Spectacular incandescent nighttime explosions at this volcano have long attracted visitors to the "Lighthouse of the Mediterranean." Stromboli, the NE-most of the Aeolian Islands, has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period from about 13,000 to 5000 years ago was followed by formation of the modern edifice. The active summit vents are located at the head of the Sciara del Fuoco, a prominent horseshoe-shaped scarp formed about 5000 years ago as a result of the most recent of a series of slope failures that extend to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy, (URL: http://www.ct.ingv.it/en/); 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/).


Krakatau (Indonesia) — March 2019 Citation iconCite this Report

Krakatau

Indonesia

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

All times are local (unless otherwise noted)


Ash plumes, ballistic ejecta, and lava extrusion during October-December; partial collapse and tsunami in late December; Surtseyan activity in December-January 2019

Krakatau volcano, between Java in Sumatra in the Sunda Straight of Indonesia, is known for its catastrophic collapse in 1883 that produce far-reaching pyroclastic flows, ashfall, and tsunami. The pre-1883 edifice had grown within an even older collapse caldera that formed around 535 CE, resulting in a 7-km-wide caldera and the three surrounding islands of Verlaten, Lang, and Rakata (figure 55). Eruptions that began in late December 1927 (figures 56 and 57) built the Anak Krakatau cone above sea level (Sudradjat, 1982; Simkin and Fiske, 1983). Frequent smaller eruptions since that time, over 40 short episodes consisting of ash plumes, incandescent blocks and bombs, and lava flows, constructed an island reaching 338 m elevation.

Figure (see Caption) Figure 55. The three islands of Verlaten, Lang, and Rakata formed during a collapse event around 535 CE. Another collapse event occurred in 1883, producing widespread ashfall, pyroclastic flows, and triggering a tsunami. Through many smaller eruptions since then, Anak Krakatau has since grown in the center of the caldera. Sentinel-2 natural color (bands 4, 3, 2) satellite image acquired on 16 November 2018, courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 56. Photo sequence (made from a film) at 6-second intervals from the early phase of activity on 24 January 1928 that built the active Anak Krakatau cone above the ocean surface. Plume height reached about 1 km. View is from about 4.5 km away at a beach on Verlaten Island looking SE towards Rakata Island in the right background. Photos by Charles E. Stehn (Netherlands Indies Volcanological Survey) from the E.G. Zies Collection, Smithsonian Institution.
Figure (see Caption) Figure 57. Submarine explosions in January 1928 built the active Anak Krakatau cone above the ocean surface. View is from about 600 m away looking E towards Lang Island in the background. Photos by Charles E. Stehn (Netherlands Indies Volcanological Survey) from the E.G. Zies Collection, Smithsonian Institution.

Historically there has been a lot of confusion about the name and preferred spelling of this volcano. Some have incorrectly made a distinction between the pre-1883 edifice being called "Krakatoa" and then using "Krakatau" for the current volcano. Anak Krakatau is the name of the active cone, but the overall volcano name is simply Krakatau. Simkin and Fiske (1983) explained as follows: "Krakatau was the accepted spelling for the volcano in 1883 and remains the accepted spelling in modern Indonesia. In the original manuscript copy submitted to the printers of the 1888 Royal Society Report, now in the archives of the Royal Society, this spelling has been systematically changed by a neat red line through the final 'au' and the replacement 'oa' entered above; a late policy change that, from some of the archived correspondence, saddened several contributors to the volume."

After 15 months of quiescence Krakatau began a new eruption phase on 21 June 2018, characterized by ash plumes, ballistic ejecta, Strombolian activity, and lava flows. Ash plumes reached 4.9 km and a lava flow traveled down the SE flank and entered the ocean. This report summarizes the activity from October 2018 to January 2019 based on reports by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Indonesian Center for Volcanology and Geological Hazard Mitigation (CVGHM), MAGMA Indonesia, the National Board for Disaster Management - Badan Nasional Penanggulangan Bencana (BNPB), the Darwin Volcanic Ash Advisory Center (VAAC), satellite data, and eye witness accounts.

Activity during October-21 December 2018. The eruption continued to eject incandescent ballistic ejecta, ash plumes, and lava flows in October through December 2018. On 22 December a partial collapse of Anak Krakatau began, dramatically changing the morphology of the island and triggering a deadly tsunami that impacted coastlines around the Sunda Straight. Following the collapse the vent was located below sea level and Surtseyan activity produced steam plumes, ash plumes, and volcanic lightning.

Sentinel-2 satellite images acquired through October show incandescence in the crater, lava flows on the SW flank, and incandescent material to the S to SE of the crater (figure 58). This correlates with eyewitness accounts of explosions ejecting incandescent ballistic ejecta, and Volcano Observatory Notice for Aviation (VONA) ash plume reports. The Darwin VAAC reported ash plumes to 1.5-2.4 km altitude that drifted in multiple directions during 17-19 October, but throughout most of October visual observations were limited due to fog. A video shared by Sutopo on 24 October shows ash emission and lava fountaining producing a lava flow that entered the ocean, resulting in a white plume. Video by Richard Roscoe of Photovolcanica shows explosions ejecting incandescent blocks onto the flanks and ash plumes accompanied by volcanic lightning on 25 October.

Figure (see Caption) Figure 58. Sentinel-2 thermal satellite images showing lava flows, incandescent avalanche deposits, and incandescence in the crater of Anak Krakatau during October 2018. Courtesy of Sentinel-2 hub playground.

Throughout November frequent ash plumes rose to 0.3-1.3 km altitude, with explosion durations spanning 29-212 seconds (figure 59). Observations by Øystein Lund Andersen describe explosions ejecting incandescent material with ash plumes and some associated lightning on 17 November (figure 60).

Figure (see Caption) Figure 59. Sentinel-2 satellite images showing ash plumes at Krakatau during 6-16 November 2018. Natural color (Bands 4, 3, 2) Sentinel-2 images courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 60. Krakatau erupting an ash plume and incandescent material on 17 November 2018. Courtesy of Øystein Lund Andersen.

During 1-21 December intermittent explosions lasting 46-776 seconds produced ash plumes that rose up to 1 km altitude. Thermal signatures were sporadically detected by various satellite thermal infrared sensors during this time. On 22 December ash plumes reached 0.3-1.5 km through the day and continuous tremor was recorded.

Activity and events during 22-28 December 2018. The following events during the evening of the 22nd were recorded by Øystein Lund Andersen, who was photographing the eruption from the Anyer-Carita area in Java, approximately 47 km from Anak Krakatau. Starting at 1429 local time, incandescence and ash plumes were observed and the eruption could be heard as intermittent 'cannon-fire' sounds, sometimes shaking walls and windows. An increase in intensity was noted at around 1700, when the ash column increased in height and was accompanied by volcanic lightning, and eruption sounds became more frequent (figure 61). A white steam plume began to rise from the shore of the southern flank. After sunset incandescent ballistic blocks were observed impacting the flanks, with activity intensity peaking around 1830 with louder eruption sounds and a higher steam plume from the ocean (figure 62).

Figure (see Caption) Figure 61. Ash plumes at Krakatau from 1429 to 1739 on 22 December 2018. Courtesy of Øystein Lund Andersen.
Figure (see Caption) Figure 62. Krakatau ejecting incandescent blocks and ash during 1823-1859 on 22 December 2018. The top and middle images show the steam plume at the shore of the southern flank. Courtesy of Øystein Lund Andersen.

PVMBG recorded an eruption at 2103. When viewed at 2105 by Øystein Lund Andersen, a dark plume across the area blocked observations of Anak Krakatau and any incandescence (figure 63). At 2127-2128 the first tsunami wave hit the shore and traveled approximately 15 m inland (matching the BNPB determined time of 2127). At approximately 2131 the sound of the ocean ceased and was soon replaced by a rumbling sound and the second, larger tsunami wave impacted the area and traveled further inland, where it reached significant depths and caused extensive damage (figures 64 and 65). After the tsunami, eruption activity remained high and the eruption was heard again during intervals from 0300 through to early afternoon.

Figure (see Caption) Figure 63. Krakatau is no longer visible at 2116 on 22 December 2018, minutes before the first tsunami wave arrived at west Java. A dark ash plume takes up much of the view. Courtesy of Øystein Lund Andersen.
Figure (see Caption) Figure 64. The second tsunami wave arriving at Anyer-Carita area of Java after the Krakatau collapse. This photo was taken at 2133 on 22 December 2018, courtesy of Øystein Lund Andersen.
Figure (see Caption) Figure 65. Photographs showing damage caused in the Anyer-Carita area of Java by the tsunami that was triggered by the partial collapse of Krakatau. From top to bottom, these images were taken approximately 40 m, 20 m, and 20 m from the shore on 23 December 2018. Courtesy of Øystein Lund Andersen.

Observations on 23 December reveal steam-rich ash plumes and base surge traveling along the water, indicative of the shallow-water Surtseyan eruption (figure 66). Ashfall was reported on the 26th in several regions including Cilegon, Anyer, and Serang. The first radar observations of Krakatau were on 24 December and showed a significant removal of material from the island (figure 67). At 0600 on the 27th the volcanic alert level was increased from II to III (on a scale of I-IV) and a VONA with Aviation Color Code Red reported an ash plume to approximately 7 km altitude that dispersed to the NE. When Anak Krakatau was visible, Surtseyan activity and plumes were observed through the end of December. On 28 December, plumes reached 200-3000 m. At 0418 the eruption paused and the first observation of the post-collapse edifice was made. The estimated removed volume (above sea level) was 150-180 million m3, leaving a remaining volume of 40-70 million m3. The summit of the pre-collapse cone was 338 m, while the highest point post-collapse was reduced to 110 m. Hundreds of thousands of lightning strokes were detected during 22-28 December with varying intensity (figure 68).

Figure (see Caption) Figure 66. Steam-rich plumes and underlying dark ash plumes from Surtseyan activity at Krakatau on 23 December 2018. Photos by Instagram user @didikh017 at Grand Cava Susi Air, via Sutopo.
Figure (see Caption) Figure 67. ALOS-2 satellite radar images showing Krakatau on 20 August 2018 and 24 December 2018. The later image shows that a large part of the cone of Anak Krakatau had collapsed. Courtesy of Geospatial Information Authority of Japan (GSI) via Sutopo.
Figure (see Caption) Figure 68. Lightning strokes during the eruption of Krakatau within a 20 km radius of the volcano for 30 minute intervals on 23, 25, 26, and 28 December 2018. Courtesy of Chris Vagasky.

Damage resulting from the 22 December tsunami. On the 29 December the damage reported by BNPB was 1,527 heavily damaged housing units, 70 with moderate damage, 181 with light damage, 78 damaged lodging and warung units, 434 damaged boats and ships and some damage to public facilities. Damage was recorded in the five regencies of Pandenglang, Serang, South Lampung, Pesawaran and Tanggamus. A BNPB report on 14 January gave the following figures: 437 fatalities, 10 people missing, 31,943 people injured, and 16,198 people evacuated (figure 69). The eruption and tsunami resulted in damage to the surrounding islands, with scouring on the Anak-Krakatau-facing slope of Rakata and damage to vegetation on Kecil island (figure 70 and 71).

Figure (see Caption) Figure 69. The impacts of the tsunami that was triggered by a partial collapse of Anak Krakatau from an update given on 14 January 2019. Translations are as follows. Korban Meninggal: victims; Korban hilang: missing; Korban luka-luka: injured; Mengungsi: evacuated. The color scale from green to red along the coastline indicates the breakdown of the human impacts by area. Courtesy of BNPB.
Figure (see Caption) Figure 70. Damage on Rakata Island from the Krakatau tsunami. This part of the island is facing Anak Krakatau and the scoured area was estimated to be 25 m high. Photographs taken on 10 January 2019 by James Reynolds.
Figure (see Caption) Figure 71. Damage to vegetation on Kecil island to the East of Krakatau, from the Krakatau December 2018 eruption. Photographs taken on 10 January 2019 by James Reynolds.

Activity during January 2019. Surtseyan activity continued into January 2019. Øystein Lund Andersen observed the eruption on 4-5 January. Activity on 4 January was near-continuous. The photographs show black cock's-tail jets that rose a few hundred meters before collapsing (figure 72), accompanied by white lateral base surge that spread from the vent across the ocean (figure 73), and white steam plumes that were visible from Anyer-Carita, West Java. In the evening the ash-and-steam plume was much higher (figure 74). It was also noted that older pumice had washed ashore at this location and a coating of sulfur was present along the beach and some of the water surface. Activity decreased again on the 5th (figure 75) with a VONA reporting an ash plume to 1.5 km towards the WSW. SO2 plumes were dispersed to the NE, E, and S during this time (figure 76).

Figure (see Caption) Figure 72. Black ash plumes and white steam plumes from the Surtseyan eruption at Krakatau on 4 January 2019. Courtesy of Øystein Lund Andersen.
Figure (see Caption) Figure 73. An expanding base surge at Krakatau on 4 January 2019 at 0911. Courtesy of Øystein Lund Andersen.
Figure (see Caption) Figure 74. Ash-and-steam plumes at Krakatau at 1702-2250 on 4 January 2018. Lightning is illuminating the plume in the bottom image. Courtesy of Øystein Lund Andersen.
Figure (see Caption) Figure 75. Ash plumes at Krakatau on 5 January 2019 at 0935. Courtesy of Øystein Lund Andersen.
Figure (see Caption) Figure 76. Sulfur dioxide (SO2) emissions produced by Krakatau and drifting to the NE, E, and SE on 3-6 January 2018. Dates and times of the periods represented are listed at the top of each image. Courtesy of the NASA Space Goddard Flight Center.

During 5-9 January intermittent explosions lasting 20 seconds to 13 minutes produced ash plumes rising up to 1.2 km and dispersing E. From 11 to 19 January white plumes were observed up to 500 m. Observations were prevented due to fog during 20-31 January. MIROVA thermal data show elevated thermal anomalies from July through January, with a decrease in energy in November through January (figure 77). The radiative power detected in December-January was the lowest since June 2018.

Figure (see Caption) Figure 77. Log radiative power MIROVA plot of MODIS thermal infrared data for June 2018-January 2019. The peaks in energy correlate with observed lava flows. Courtesy of MIROVA.

Morphological changes to Anak Krakatau. Images taken before and after the collapse event show changes in the shoreline, destruction of vegetation, and removal of the cone (figure 78). A TerraSAR-X image acquired on 29 January shows that in the location where the cone and active vent was, a bay had formed, opening to the W (figure 79). These changes are also visible in Sentinel-2 satellite images, with the open bay visible through light cloud cover on 29 December (figure 80).

By 9 January a rim had formed, closing off the bay to the ocean and forming a circular crater lake. Photos by James Reynolds on 11 January show a new crater rim to the W of the vent, which was filled with water (figure 81). Steam and/or gas emissions were emanating from the surface in that area. The southern lava delta surface was covered with tephra, and part of the lava delta had been removed, leaving a smooth coastline. By the time these images were taken there was already extensive erosion of the fresh deposits around the island. Fresh material extended the coast in places and filled in bays to produce a more even shoreline.

Figure (see Caption) Figure 78. Krakatau on 5 August 2018 (top) and on 11 January 2019 showing the edifice after the collapse event. The two drone photographs show approximately the same area. Courtesy of Øystein Lund Andersen (top) and James Reynolds (bottom).
Figure (see Caption) Figure 79. TerraSAR-X radar images showing the morphological changes to Krakatau with the changes outlined in the bottom right image as follows. Red: 30 August 2018 (upper left image); blue: 29 December 2018 (upper right image); yellow: 9 January 2019 (lower left image). Part of the southern lava delta was removed and material was added to the SE and NE to N shoreline. In the 29 December image the cone has collapsed and in its place is an open bay, which had been closed by a new rim by the 9 January. Courtesy of BNPB, JAXA Japan Aerospace Exploration Agency, and Badan Informasi Geospasial (BIG).
Figure (see Caption) Figure 80. Sentinel-2 satellite images showing the changing morphology of Krakatau. The SW section is where the cone previously sat and collapsed in December 2018. In the upper right image the cone and southern lava delta are gone and there are changes to the coastline of the entire island. Natural color (bands 4, 3, 2) Sentinel-2 satellite images courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 81. Drone footage of the Krakatau crater and new crater rim taken on 11 January 2019. The island is coated in fresh tephra from the eruption and the orange is discolored water due to the eruption. The land between the crater lake and the ocean built up since the collapse and the hot deposits are still producing steam/gas. Courtesy of James Reynolds.
Figure (see Caption) Figure 82. An aerial view of Krakatau with the new crater on 13 January 2019. Courtesy of BNPB.

References. Simkin, T., and Fiske, R.S., 1983, Krakatau 1883: the volcanic eruption and its effects: Smithsonian Institution Press, Washington DC, 464 p. ISBN 0-87474-841-0.

Sudradjat (Sumartadipura), A., 1982. The morphological development of Anak Krakatau Volcano, Sunda Straight. Geologi Indonesia, 9(1):1-11.

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: Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); Sutopo Purwo Nugroho, BNPB (Twitter: @Sutopo_PN, URL: https://twitter.com/Sutopo_PN ); Geospatial Information Authority of Japan (GSI), 1 Kitasato, Tsukuba, Ibaraki 305-0811, Japan. (URL: http://www.gsi.go.jp/ENGLISH/index.html); Badan Informasi Geospasial (BIG), Jl. Raya Jakarta - Bogor KM. 46 Cibinong 16911, Indonesia. (URL: http://www.big.go.id/atlas-administrasi/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); JAXA | Japan Aerospace Exploration Agency, 7-44-1 Jindaiji Higashi-machi, Chofu-shi, Tokyo 182-8522 (URL: https://global.jaxa.jp/); 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); Øystein Lund Andersen? (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: https://www.oysteinlundandersen.com/krakatau-volcano-witnessing-the-eruption-tsunami-22december2018/); James Reynolds, Earth Uncut TV (Twitter: @EarthUncutTV, URL: https://www.earthuncut.tv/, YouTube: https://www.youtube.com/channel/UCLKYsEXfI0PGXeKYL1KV7qA); Chris Vagasky, Vaisala Inc., Louisville, Colorado (URL: https://www.vaisala.com/en?type=1, Twitter: @COweatherman, URL: https://twitter.com/COweatherman).


Masaya (Nicaragua) — March 2019 Citation iconCite this Report

Masaya

Nicaragua

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

All times are local (unless otherwise noted)


Lava lake persists with decreased thermal output, November 2018-February 2019

Nicaragua's Volcan Masaya has an intermittent lava lake that has attracted visitors since the time of the Spanish Conquistadores; tephrochronology has dated eruptions back several thousand years. The unusual basaltic caldera has had historical explosive eruptions in addition to lava flows and an actively circulating lava lake. An explosion in 2012 ejected ash to several hundred meters above the volcano, bombs as large as 60 cm fell around the crater, and ash fell to a thickness of 2 mm in some areas of the park. The reemergence of the lava lake inside Santiago crater was reported in December 2015. By late March 2016 the lava lake had grown and intensified enough to generate a significant thermal anomaly signature which has varied in strength but continued at a moderate level into early 2019. Information for this report, which covers the period from November 2018 through February 2019, is provided by the Instituto Nicareguense de Estudios Territoriales (INETER) and satellite -based imagery and thermal data.

The lava lake in Santiago Crater remained visible and active throughout November 2018 to February 2019 with little change from the previous few months (figure 70). Seismic amplitude RSAM values remained steady, oscillating between 10 and 40 RSAM units during the period.

Figure (see Caption) Figure 70. A small area of the lava lake inside Santiago Crater at Masaya was visible from the rim on 25 November 2018 (left) and 17 January 2019 (right). Left image courtesy of INETER webcam; right image courtesy of Alun Ebenezer.

Every few months INETER carries out SO2 measurements by making a transect using a mobile DOAS spectrometer that samples for gases downwind of the volcano. Transects were done on 9-10 October 2018, 21-24 January 2019, and 18-21 February 2019 (figure 71). Average values during the October transect were 1,454 tons per day, in January they were 1,007 tons per day, and in February they averaged 1,318 tons per day, all within a typical range of values for the last several months.

Figure (see Caption) Figure 71. INETER carries out periodic transects to measure SO2 from Masaya with a mobile DOAS spectrometer. Transects taken along the Ticuantepe-La Concepcion highway on 9-10 October 2018 (left) and 21-24 January 2019 (right) showed modest levels of SO2 emissions downwind of the summit. Courtesy of INETER (Boletín Sismos y Volcanes de Nicaragua. Octubre 2018 and Enero 2019).

During a visit by INETER technicians in early November 2018, the lens of the Mirador 1 webcam, that had water inside it and had been damaged by gases, was cleaned and repaired. During 21-24 January 2019 INETER made a site visit with scientists from the University of Johannes Gutenberg in Mainz, Germany, to measure halogen species in gas plumes, and to test different sampling techniques for volcanic gases, including through spectroscopic observations with DOAS equipment, in-situ gas sampling (MultiGAS, denuders, alkaline traps), and using a Quadcopter UAV (drone) sampling system.

Periodic measurements of CO2 from the El Comalito crater have been taken by INETER for many years. The most recent observations on 19 February 2019 indicated an emission rate of 46 +/- 3 tons per day of CO2, only slightly higher than the average value over 16 measurements between 2008 and 2019 (figure 72).

Figure (see Caption) Figure 72. CO2 measurements taken at Masaya on 19 February 2019 were very close to the average value measured during 2008-2019. Courtesy of INETER (Boletín Sismos y Volcanes de Nicaragua, Febrero 2019).

Satellite imagery (figure 73) and in-situ thermal measurements during November 2018-February 2019 indicated constant activity at the lava lake and no significant changes during the period. On 14 January 2019 temperatures were measured with the FLIR SC620 thermal camera, along with visual observations of the crater; abundant gas was noted, and no explosions from the lake were heard. The temperature at the lava lake was measured at 107°C, much cooler than the 340°C measured in September 2018 (figure 74).

Figure (see Caption) Figure 73. Sentinel-2 satellite imagery (geology, bands 12, 4, and 2) clearly indicated the presence of the active lava lake inside Santiago crater at Masaya during November 2018-February 2019. North is to the top, and the Santigo crater is just under 1 km in diameter for scale. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 74. Thermal measurements were made at Masaya on 14 January 2019 with a FLIR SC620 thermal camera that indicated temperatures over 200°C cooler than similar measurements made in September 2018.

Thermal anomaly data from satellite instruments also confirmed moderate levels of ongoing thermal activity. The MIROVA project plot indicated activity throughout the period (figure 75), and a plot of the number of MODVOLC thermal alerts by month since the lava lake first appeared in December 2015 suggests constant activity at a reduced thermal output level from the higher values in early 2017 (figure 76).

Figure (see Caption) Figure 75. Thermal anomalies remained constant at Masaya during November 2018-February 2019 as recorded by the MIROVA project. Courtesy of MIROVA.
Figure (see Caption) Figure 76. The number of MODVOLC thermal alerts each month at Masaya since the lava lake first reappeared in late 2015 reached its peak in early 2017 and declined to low but persistent levels by early 2018 where they have remained for a year. Data courtesy of MODVOLC.

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: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Alun Ebenezer (Twitter: @AlunEbenezer, URL: https://twitter.com/AlunEbenezer).


Santa Maria (Guatemala) — March 2019 Citation iconCite this Report

Santa Maria

Guatemala

14.757°N, 91.552°W; summit elev. 3745 m

All times are local (unless otherwise noted)


Daily explosions cause steam-and-ash plumes and block avalanches, November 2018-February 2019

The dacitic Santiaguito lava-dome complex on the W flank of Guatemala's Santa María volcano has been growing and actively erupting since 1922. The youngest of the four vents in the complex, Caliente, has been erupting with ash explosions, pyroclastic, and lava flows for more than 40 years. A lava dome that appeared within the summit crater of Caliente in October 2016 has continued to grow, producing frequent block avalanches down the flanks. Daily explosions of steam and ash also continued during November 2018-February 2019, the period covered in this report, with information primarily from Guatemala's INSIVUMEH (Instituto Nacional de Sismologia, Vulcanologia, Meterologia e Hidrologia) and the Washington VAAC (Volcanic Ash Advisory Center).

Activity at Santa Maria continued with little variation from previous months during November 2018-February 2019. Plumes of steam with minor magmatic gases rose continuously from the Caliente crater 100-500 m above the summit, generally drifting SW or SE before dissipating. In addition, daily explosions with varying amounts of ash rose to altitudes of around 2.8-3.5 km and usually extended 20-30 km before dissipating. Most of the plumes drifted SW or SE; minor ashfall occurred in the adjacent hills almost daily and was reported at the fincas located within 15 km in those directions several times each month. Continued growth of the Caliente lava dome resulted in daily block avalanches descending its flanks. The MIROVA plot of thermal energy during this time shows a consistent level of heat flow with minor variations throughout the period (figure 89).

Figure (see Caption) Figure 89. Persistent thermal activity was recorded at Santa Maria from 6 June 2018 through February 2019 as seen in the MIROVA plot of thermal energy derived from satellite thermal data. Daily explosions produced ash plumes and block avalanches that were responsible for the continued heat flow at the volcano. Courtesy of MIROVA.

During November 2018 steam plumes rose to altitudes of 2.8-3.2 km from Caliente summit, usually drifting SW, sometimes SE. Several ash-bearing explosions were reported daily, rising to 3-3.2 km altitude and also drifting SW or SE. The highest plume reported by INSIVUMEH rose to 3.4 km on 25 November and drifted SW. The Washington VAAC reported an ash emission on 9 November that rose to 4.3 km altitude and drifted W; it dissipated within a few hours about 35 km from the summit. On 11 November another plume rose to 4.9 km altitude and drifted NW. INSIVUMEH issued a special report on 2 November noting an increase in block avalanches on the S and SE flanks, many of which traveled from the crater dome to the base of the volcano. Nearly constant avalanche blocks descended the SE flank of the dome and occasionally traveled down the other flanks as well throughout the month. They reached the bottom of the cone again on 29 November. Ashfall was reported around the flanks more than once every week and at Finca Florida on 12 November. Finca San Jose reported ashfall on 11, 13, and 23 November, and Parcelamiento Monte Claro reported ashfall on 15, 24, 25, and 27 November.

Constant degassing from the Caliente dome during December 2018 formed white plumes of mostly steam that rose to 2.6-3.0 km altitude during the month. Weak explosions averaging 9-13 per day produced gray ash plumes that rose to 2.8-3.4 km altitude. The Washington VAAC reported an ash emission on 4 December that extended 25 km SW of the summit at 3.0 km altitude and dissipated quickly. Small ash plumes were visible in satellite imagery a few kilometers WNW on 8, 12, 30, and 31 December at 4.3 km altitude; they each dissipated within a few hours. Ashfall was reported in Finca Monte Claro on 1 and 4 December, and in San Marcos Palajunoj on 26 and 30 December along with Loma Linda. On 28 December ashfall on the E flank affected the communities of Las Marías, Calahuache, and El Nuevo Palmar. Block avalanches occurred daily, sending large blocks to the base of the volcano that often stirred up small plumes of ash in the vicinity (figure 90).

Figure (see Caption) Figure 90. Activity during December 2018 at Santa Maria included constant degassing of steam plumes, weak explosions with ash plumes, and block avalanches rolling down the flanks to the base of the cone. Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo: Volcán Santiaguito (1402-03), Diciembre 2018).

Multiple explosions daily during January 2019 produced steam-and-ash plumes (figure 91). Constant degassing rising 10-500 m emerged from the SSE part of the Caliente dome, and ashfall, mainly on the W and SW rim of the cone, was a daily feature. Seismic station STG-3 detected 10-18 explosions per day that produced ash plumes, which rose to between 2.7 and 3.5 km altitude. The Washington VAAC noted a faint ash emission in satellite imagery on 1 January that was about 25 km W of the summit at 4.3 km altitude. A new emission appeared at the same altitude on 4 January about 15 km NW of the summit. A low-density emission around midday on 5 January produced an ash plume that drifted NNE at 4.6 km altitude. Ash plumes drifted W at 4.3 km altitude on 11 and 14 January for short periods of time before dissipating.

Figure (see Caption) Figure 91. Explosions during January produced numerous steam-and-ash plumes at the Santiaguito complex of Santa Maria. A moderate explosion on 31 January 2019 produced an ash plume that rose to about 3.1 km altitude (top). A thermal image and seismograph show another moderate explosion on 18 January 2019 that also rose nearly vertically from the summit of Caliente. Courtesy of INSIVUMEH (Informe mensual de actividad Volcanica enero 2019, Volcan Santiaguito).

Ash drifted mainly towards the W, SW, and S, causing ashfall in the villages of San Marcos Palajunoj, Loma Linda, Monte Bello, El Patrocinio, La Florida, El Faro, Patzulín and a few others several times during the month. The main places where daily ashfall was reported were near the complex, in the hilly crop areas of the El Faro and San José Patzulín farms (figure 92). Blocks up to 3 m in diameter reached the base of the complex, stirring up ash plumes that settled on the immediate flanks. Juvenile material continued to appear at the summit of the dome during January; the dome had risen above the edge of the crater created by the explosions of 2016. Changes in the size and shape of the dome between 23 November 2018 and 13 January 2019 showed the addition of material on the E and SE side of the dome, as well as a new effusive flow that travelled 200-300 m down the E flank (figure 93).

Figure (see Caption) Figure 92. Near-daily ashfall affected the coffee plants at the El Faro and San José Patzulín farms (left) at Santiaguito during January 2019. Large avalanche blocks descending the flanks, seen here on 23 January 2018, often stirred up smaller ash plumes that settled out next to the cone. Courtesy of INSIVUMEH (Informe mensual de actividad Volcanica enero 2019, Volcan Santiaguito).
Figure (see Caption) Figure 93. A comparison of the growth at the Caliente dome of the Santiaguito complex at Santa Maria between 23 November 2018 (top) and 13 January 2019 (bottom) shows the emergence of juvenile material and a 200-300 m long effusive flow that has moved slowly down the E flank. Courtesy of INSIVUMEH (Informe mensual de actividad Volcanica enero 2019, Volcan Santiaguito).

Persistent steam rising 50-150 m above the crater was typical during February 2019 and accompanied weak and moderate explosions that averaged 12 per day throughout the month. White and gray ash plumes from the explosions rose to 2.8-3.3 km altitude; daily block avalanches usually reached the base of the dome (figure 94). Ashfall occurred around the complex, mainly on the W, SW, and NE flanks on a daily basis, but communities farther away were affected as well. The Washington VAAC reported an ash plume on 7 February in visible satellite imagery moving SW from the summit at 4.9 km altitude. The next day a new ash plume was located about 20 km W of the summit, dissipating rapidly, at 4.3 km altitude. Ashfall drifting SW affected Palajuno Monte Claro on 5, 9, 15, and 16 February. Ash drifting E and SE affected Calaguache, Las Marías and surrounding farms on 14 and 17 February, and fine-grained ash drifting SE was reported at finca San José on 21 February.

Figure (see Caption) Figure 94. Activity at the Caliente dome of the Santiaguito complex at Santa Maria included daily ash-and-steam explosions and block avalanches descending the sides of the dome in February 2019. A typical explosion on 2 February 2019 produced an ash plume that rose to about 3 km altitude and drifted SW (left). A block avalanche on 14 February descended the SE flank and stirred up small plumes of ash in the vicinity (right, top); the avalanche lasted for 88 seconds and registered with seismic frequencies between 3.46 and 7.64 Hz (right bottom). Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo: Volcán Santiaguito (1402-03), Semana del 01 al 08 de febrero de 2019).

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

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); 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/).


Reventador (Ecuador) — March 2019 Citation iconCite this Report

Reventador

Ecuador

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

All times are local (unless otherwise noted)


Multiple daily explosions with ash plumes and incandescent blocks rolling down the flanks, October 2018-January 2019

The andesitic Volcán El Reventador lies well 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. The 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. Activity continued during October 2018-January 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.

Multiple daily reports were issued from the Washington VAAC throughout the entire October 2018-January 2019 period. Plumes of ash and gas usually rose to altitudes of 4.3-6.1 km and drifted about 20 km in prevailing wind directions before either dissipating or being obscured by meteoric clouds. The average number of daily explosions reported by IG-EPN for the second half of 2018 was more than 20 per day (figure 104). The many explosions during the period originated from multiple vents within a large scarp that formed on the W flank in mid-April (BGVN 43:11, figure 95) (figure 105). Incandescent blocks were observed often in the IG webcams; they traveled 400-1,000 m down the flanks.

Figure (see Caption) Figure 104. The number of daily seismic events at El Reventador for 2018 indicated high activity during the first and last thirds of the year; more than 20 explosions per day were recorded many times during October-December 2018, the period covered in this report. LP seismic events are shown in orange, seismic tremor in pink, and seismic explosions with ash are shown in green. Courtesy of IG-EPN (Informe Anual del Volcán El Reventador – 2018, Quito, 29 de marzo del 2019).
Figure (see Caption) Figure 105. Images from IG's REBECA thermal camera showed the thermal activity from multiple different vents at different times during the year (see BGVN 43:11, figure 95 for vent locations). Courtesy if IG (Informe Anual del Volcán El Reventador – 2018, Quito, 29 de marzo del 2019).

Activity during October 2018-January 2019. During most days of October 2018 plumes of gas, steam, and ash rose over 1,000 m above the summit of Reventador, and most commonly drifted W or NW. Incandescence was observed on all nights that were not cloudy; incandescent blocks rolled 400-800 m down the flanks during half of the nights. During episodes of increased activity, ash plumes rose over 1,200 m (8, 10-11, 18-19 October) and incandescent blocks rolled down multiple flanks (figure 106).

Figure (see Caption) Figure 106. Ash emissions rose over 1,000 m above the summit of Reventador numerous times during October 2018, and large incandescent blocks traveled hundreds of meters down multiple flanks. The IG-EPN COPETE webcam that captured these images is located on the S caldera rim. Courtesy of IG Daily Reports (Informe diario del estado del Volcan Reventador, numbers 2018-282, 292, 295, 297).

Similar activity continued during November. IG reported 17 days of the month with steam, gas, and ash emissions rising more than 1,000 m above the summit. The other days were either cloudy or had emissions rising between 500 and 1,000 m. Incandescent blocks were usually observed on the S or SE flanks, generally travelling 400-600 m down the flanks. The Washington VAAC reported a discrete ash plume at 6.1 km altitude drifting WNW about 35 km from the summit on 15 November. The next day, intermittent puffs were noted moving W, and a bright hotspot at the summit was visible in satellite imagery. During the most intense activity of the month, incandescent blocks traveled 800 m down all the flanks (17-19 November) and ash plumes rose over 1,200 m (23 November) (figure 107).

Figure (see Caption) Figure 107. Ash plumes rose over 1,000 m above the summit on 17 days during November 2018 at Reventador, and incandescent blocks traveled 400-800 m down the flanks on many nights. Courtesy of IG Daily Reports (Informe diario del estado del Volcan Reventador, numbers 2018-306, 314, 318, 324).

Steam, gas, and ash plumes rose over 1,200 m above the summit on 1 December. The next day, there were reports of ashfall in San Rafael and Hosteria El Hotelito, where they reported an ash layer about 1 mm thick was deposited on vehicles during the night. Ash emissions exceeded 1,200 m above the summit on 5 and 6 December as well. Incandescent blocks traveled 800 m down all the flanks on 11, 22, 24, and 26 December, and reached 900 m on 21 December. Ash emissions rising 500 to over 1,000 m above the summit were a daily occurrence, and incandescent blocks descended 500 m or more down the flanks most days during the second half of the month (figure 108).

Figure (see Caption) Figure 108. Ash plumes that rose 500 to over 1,000 m were a daily occurrence at Reventador during December 2018. Incandescent blocks traveled as far as 900 m down the flanks as well. Courtesy of IG Daily Reports (Informe diario del estado del Volcan Reventador, numbers 2018-340, 351, 353, 354, 358, 359).

During the first few days of January 2019 the ash and steam plumes did not rise over 800 m, and incandescent blocks were noted 300-500 m down the S flank. An increase in activity on 6 January sent ash-and-gas plumes over 1,000 m, drifting W, and incandescent blocks 1,000 m down many flanks. For multiple days in the middle of the month the volcano was completely obscured by clouds; only occasional observations of plumes of ash and steam were made, incandescence seen at night through the clouds confirmed ongoing activity. The Washington VAAC reported continuous ash emissions moving SE extending more than 100 km on 12 January. A significant explosion late on 20 January sent incandescent blocks 800 m down the S flank; although it was mostly cloudy for much of the second half of January, brief glimpses of ash plumes rising over 1,000 m and incandescent blocks traveling up to 800 m down numerous flanks were made almost daily (figure 109).

Figure (see Caption) Figure 109. Even during the numerous cloudy days of January 2019, evidence of ash emissions and significant explosions at Reventador was captured in the Copete webcam located on the S rim of the caldera. Courtesy of IG Daily Reports (Informe diario del estado del Volcan Reventador, number 2019-6, 21, 26, 27).

Visual evidence from the webcams supports significant thermal activity at Reventador. Atmospheric conditions are often cloudy and thus the thermal signature recorded by satellite instruments is frequently diminished. In spite of this, the MODVOLC thermal alert system recorded seven thermal alerts on three days in October, four alerts on two days in November, six alerts on two days in December and three alerts on three days in January 2019. In addition, the MIROVA system measured moderate levels of radiative power intermittently throughout the period; the most intense anomalies of 2018 were recorded on 15 October and 6 December (figure 110).

Figure (see Caption) Figure 110. Persistent thermal activity at Reventador was recorded by satellite instruments for the MIROVA system from 5 April 2018 through January 2019 in spite of frequent cloud cover over the volcano. The most intense anomalies of 2018 were recorded on 15 October and 6 December. Courtesy of MIROVA.

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); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); 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/).


Kuchinoerabujima (Japan) — March 2019 Citation iconCite this Report

Kuchinoerabujima

Japan

30.443°N, 130.217°E; summit elev. 657 m

All times are local (unless otherwise noted)


Weak explosions and ash plumes beginning 21 October 2018

Activity at Kuchinoerabujima is exemplified by interim explosions and periods of high seismicity. A weak explosion occurred on 3 August 2014, the first since 1980, and was followed by several others during 29 May-19 June 2015 (BGVN 42:03). This report describes events through February 2019. Information is based on monthly and annual reports from the Japan Meteorological Agency (JMA) and advisories from the Tokyo Volcanic Ash Advisory Center (VAAC). Activity has been limited to Kuchinoerabujima's Shindake Crater.

Activity during 2016-2018. According to JMA, between July 2016 and August 2018, the volcano was relatively quiet. Deflation had occurred since January 2016. On 18 April 2018 the Alert Level was lowered from 3 to 2 (on a scale of 1-5). A low-temperature thermal anomaly persisted near the W fracture in Shindake crater. During January-March 2018, both the number of volcanic earthquakes (generally numerous and typically shallow) and sulfur dioxide flux remained slightly above baselines levels in August 2014 (60-500 tons/day compared tp generally less than 100 tons/day in August 2014).

JMA reported that on 15 August 2018 a swarm of deep volcanic earthquakes was recorded, prompting an increase in the Alert Level to 4. The earthquake hypocenters were about 5 km deep, below the SW flanks of Shindake, and the maximum magnitude was 1.9. They occurred at about the same place as the swarm that occurred just before the May 2015 eruption. Sulfur dioxide emissions had increased since the beginning of August; they were 1,600, 1,000, and 1,200 tons/day on 11, 13, and 17 August, respectively. No surficial changes in gas emissions or thermal areas were observed during 16-20 August. On 29 August, JMA downgraded the Alert Level to 3, after no further SO2 flux increase had occurred in recent days and GNSS measurements had not changed.

A very weak explosion was recorded at 1831 on 21 October, with additional activity between 2110 on 21 October and 1350 on 22 October; plumes rose 200 m above the crater rim. During an overflight on 22 October, observers noted ash in the emissions, though no morphological changes to the crater nor ash deposits were seen. Based on satellite images and information from JMA, the Tokyo VAAC reported that during 24-28 October ash plumes rose to altitudes of 0.9-1.5 km and drifted in multiple directions. During a field observation on 28 October, JMA scientists did not observe any changes in the thermal anomalies at the crater.

JMA reported that during 31 October-5 November 2018, very small events released plumes that rose 500-1,200 m above the crater rim. On 6 November, crater incandescence began to be periodically visible. During 12-19 November, ash plumes rose as high as 1.2 km above the crater rim and, according to the Tokyo VAAC, drifted in multiple directions. Observers doing fieldwork on 14 and 15 November noted that thermal measurements in the crater had not changed. Intermittent explosions during 22-26 November generated plumes that rose as high as 2.1 km above the crater rim. During 28 November-3 December the plumes rose as high as 1.5 km above the rim.

JMA reported that at 1637 on 18 December an explosion produced an ash plume that rose 2 km and then disappeared into a weather cloud. The event ejected material that fell in the crater area, and generated a pyroclastic flow that traveled 1 km W and 500 m E of the crater. Another weak explosion occurred on 28 December, scattering large cinders up to 500 m from the crater.

The Tokyo VAAC did not issue any ash advisories for aviation until 21 October 2018, when it issued at least one report every day through 13 December. It also issued advisories on 18-20 and 28 December.

Activity during January-early February 2019. JMA reported that at 0919 local time on 17 January 2019 an explosion generated a pyroclastic flow that reached about 1.9 km NW and 1 km E of the crater. It was the strongest explosion since October 2018. In addition, "large cinders" fell about 1-1.8 km from the crater.

Tokyo VAAC ash advisories were issued on 1, 17, 20, and 29 January 2018. An explosion at 1713-1915 on 29 January produced an ash plume that rose 4 km above the crater rim and drifted E, along with a pyroclastic flow. Ash fell in parts of Yakushima. During 30 January-1 February and 3-5 February, white plumes rose as high as 600 m. On 2 February, an explosion at 1141-1300 generated a plume that rose 600 m. No additional activity during February was reported by JMA. The Alert Level remained at 3.

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

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


Kerinci (Indonesia) — February 2019 Citation iconCite this Report

Kerinci

Indonesia

1.697°S, 101.264°E; summit elev. 3800 m

All times are local (unless otherwise noted)


A persistent gas-and-steam plume and intermittent ash plumes occurred from July 2018 through January 2019

Kerinci is a frequently active volcano in Sumatra, Indonesia. Recent activity has consisted of intermittent explosions, ash, and gas-and-steam plumes. The volcano alert has been at Level II since 9 September 2007. This report summarizes activity during July 2018-January 2019 based on reports by The Indonesia volcano monitoring agency, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), MAGMA Indonesia, notices from the Darwin Volcano Ash Advisory Center (Darwin VAAC), and satellite data.

Throughout this period dilute gas-and-steam plumes rising about 300 m above the summit were frequently observed and seismicity continued (figure 6). During July through January ash plumes were observed by the Darwin VAAC up to 4.3 km altitude and dispersed in multiple directions (table 7 and figure 7).

Figure (see Caption) Figure 6. Graph showing seismic activity at Kerinci from November 2018 through February 2019. Courtesy of MAGMA Indonesia.

Table 7. Summary of ash plumes (altitude and drift direction) for Kerinci during July 2018 through January 2019. The summit is at 3.5 km altitude. Data courtesy of the Darwin Volcanic Ash Advisory Center (VAAC) and MAGMA Indonesia.

Date Ash plume altitude (km) Ash plume drift direction
22 Jul 2018 4.3 SW
28-30 Sep 2018 4.3 SW, W
02 Oct 2018 4.3 SW, W
18-22 Oct 2018 4.3 N, W, WSW, SW
19 Jan 2019 4 E to SE
Figure (see Caption) Figure 7. Dilute ash plumes at Kerinci during July 2018-January 2019. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub Playground.

Based on satellite data, a Darwin VAAC advisory reported an ash plume to 4.3 km altitude on 22 July that drifted to the SW and S. Only one day with elevated thermal emission was noted in Sentinel-2 satellite data for the entire reporting period, on 13 September 2018 (figure 8). No thermal signatures were detected by MODVOLC. On 28-29 September there was an ash plume observed to 500-600 m above the peak that dispersed to the W. Several VAAC reports on 2 and 18-22 October detected ash plumes that rose to 4.3 km altitude and drifted in different directions. On 19 January from 0734 to 1000 an ash plume rose to 200 m above the crater and dispersed to the E and SE (figure 9).

Figure (see Caption) Figure 8. Small thermal anomaly at Kerinci volcano on 13 September 2018. False color (urban) image (band 12, 11, 4) courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 9. Small ash plume at Kerinci on 19 January 2018 that reached 200 m above the crater and traveled west. Courtesy of MAGMA Indonesia.

Geologic Background. Gunung Kerinci in central Sumatra forms Indonesia's highest volcano and is one of the most active in Sumatra. It is capped by an unvegetated young summit cone that was constructed NE of an older crater remnant. There is a deep 600-m-wide summit crater often partially filled by a small crater lake that lies on the NE crater floor, opposite the SW-rim summit. The massive 13 x 25 km wide volcano towers 2400-3300 m above surrounding plains and is elongated in a N-S direction. Frequently active, Kerinci has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838.

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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Yasur (Vanuatu) — February 2019 Citation iconCite this Report

Yasur

Vanuatu

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

All times are local (unless otherwise noted)


Eruption continues with ongoing explosions and multiple active crater vents, August 2018-January 2019

According to the Vanuatu Meteorology and Geo-Hazards Department (VMGD), which monitors Yasur, the volcano has been in essentially continuous Strombolian activity since Captain Cook observed ash eruptions in 1774, and undoubtedly before that time. VMGD reported that, based on visual observations and seismic data, activity continued through January 2019, with ongoing, sometimes strong, explosions. The Alert Level remained at 2 (on a scale of 0-4). VMGD reminded residents and tourists to remain outside the 395-m-radius permanent exclusion zone and warned that volcanic ash and gas could reach areas influenced by trade winds.

Thermal anomalies, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, were recorded 6-15 days per month during the reporting period, sometimes with multiple pixels. The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, also based on analysis of MODIS data, detected numerous hotspots every month. Active crater vents were also frequently visible in Sentinel-2 satellite imagery (figure 50).

Figure (see Caption) Figure 50. Sentinel-2 satellite color infrared image (bands 8, 4, 3) of Yasur on 17 November 2018 showing at least three distinct heat sources in the crater. Courtesy of Sentinel Hub Playground.

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: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department, Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Ambae (Vanuatu) — February 2019 Citation iconCite this Report

Ambae

Vanuatu

15.389°S, 167.835°E; summit elev. 1496 m

All times are local (unless otherwise noted)


Ash plumes and lahars in July 2018 cause evacuation of the island; intermittent gas-and-steam and ash plumes through January 2019

Ambae is one of the active volcanoes of Vanuatu in the New Hebrides archipelago. Recent eruptions have resulted in multiple evacuations of the local population due to ashfall. The current eruption began in September 2017, with the initial episode ending in November that year. The second episode was from late December 2017 to early February 2018, and the third was during February-April 2018. The Alert Level was raised to 3 in March, then lowered to Level 2 again on 2 June 2018. Eruptive activity began again on 1 July and produced thick ash deposits that significantly impacted the population, resulting in the full evacuation of the Island of Ambae. This report summarizes activity from July 2018 through January 2019 and is based on reports by the Vanuatu Meteorology and Geo-hazards Department (VMGD), The Vanuatu Red Cross, posts on social media, and various satellite data.

On 1 July Ambae entered a new eruption phase, marked by an ash plume that resulted in ashfall on communities in the W to NW parts of Ambae Island and the NE part of Santo Island (figure 78). On 9-10 July VMGD reported that a small eruption continued with activity consisting of ongoing gas-and-steam emissions. An observation flight on 13 July confirmed that the eruption was centered at Lake Voui and consisted of explosions that ejected hot blocks with ongoing gas-and-steam and ash emissions. Populations on Ambae and a neighboring island could hear the eruption, smell the volcanic gases, and see incandescence at night.

Figure (see Caption) Figure 78. Ash plume at Ambae on 1 July 2018 that resulted in ashfall on the W to NW parts of the island, and on the NE part of Santo Island. Courtesy of VMGD.

On 16 July the Darwin VAAC reported an ash plume to 9.1 km that drifted to the NE. During 16-24 July daily ash plumes from the Lake Voui vent rose to altitudes of 2.3-9.1 km and drifted N, NE, E, and SE (figure 79 and 80). Radio New Zealand reported that on the 16th significant ash emission blocked out sunlight, making the underlying area dark at around 1600 local time. Much of E and N Ambae Island experienced heavy ashfall and the eruption could be heard over 30 km away. The Vanuatu Red Cross Society reported worsening conditions in the south on 24 July with ashfall resulting in trees falling and very poor visibility of less than 2 m (figures 81, 82, and 83). The Daily Post reported that by 19 July lahars had washed away two roads and other roads were blocked to western Ambae. Volcanologists who made their way to the area reported widespread damage (figure 84). The Alert Level was raised from level 2 to 3 (on a scale of 0-5) on 21 July due to an increase in ash emission and more sustained plumes, similar to March 2018 activity.

Figure (see Caption) Figure 79. Ash plumes produced by the Ambae eruption in July 2018 as seen in Terra/MODIS visible satellite images. Images courtesy of NASA Worldview.
Figure (see Caption) Figure 80. Sentinel-2 satellite image of an ash plume from Ambae in Vanuatu on 23 July 2018 with the inset showing the ash plume at the vent. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 81. Ashfall at Ambae, posted on 25 July 2018. Courtesy of the Vanuatu Red Cross Society.
Figure (see Caption) Figure 82. An ash plume at Ambae in July during a day and a half of constant ashfall, looking towards the volcano. Courtesy of Michael Rowe.
Figure (see Caption) Figure 83. Ashfall from the eruption at Ambae blocked out the sun near the volcano on 24 July 2018. Courtesy of the Vanuatu Red Cross Society.
Figure (see Caption) Figure 84. Impacts of ashfall near Ambae in July 2018. Photos by Nicholson Naki, courtesy of the Vanuatu Red Cross (posted on 22 July 2018).

At 2100 on 26 July the ongoing explosions produced an ash plume that rose to 12 km and spread NE, E, SE. A state of emergency was announced by the Government of Vanuatu with a call for mandatory evacuations of the island. Ash emissions continued through the next day (figure 85 and 86) with two episodes producing volcanic lightning at 1100-1237 and 1522-2029 on 27 July (figure 87). The Darwin VAAC reported ash plumes up to 2.4-6.4 km, drifting SE and NW, and pilots reported heavy ashfall in Fiji. Large SO2 plumes were detected accompanying the eruptions and moving towards the E (figure 88).

Figure (see Caption) Figure 85. Ash plumes at Ambae at 0830 and 1129 local time on 27 July 2018. The ash plume is significantly larger in the later image. Webcam images from Saratamata courtesy of VMGD.
Figure (see Caption) Figure 86. Two ash plumes from Ambae at 1200 on 27 July 2018 as seen in a Himawari-8 satellite image. Courtesy of Himawari-8 Real-time Web.
Figure (see Caption) Figure 87. Lightning strokes detected at Ambae on 27 July 2018. There were two eruption pulses, 1100-1237 (blue) and 1522-2029 local time (red) that produced 185 and 87 lightning strokes, respectively. Courtesy of William A. Brook, Ronald L. Holle, and Chris Vagasky, Vaisala Inc.
Figure (see Caption) Figure 88. Aura/OMI data showing the large SO2 plumes produced by Ambae in Vanuatu during 22-31 July 2018. Courtesy of NASA Goddard Space Flight Center.

Video footage showed a lahar blocking a road around 2 August. The government of Vanuatu told reporters that the island had been completely evacuated by 14 August. A VMGD bulletin on 22 August reported that activity continued with ongoing gas-and-steam and sometimes ash emissions; residents on neighboring islands could hear the eruption, smell volcanic gases, and see the plumes.

On 1 September at 2015 an explosion sent an ash plume to 4-11 km altitude, drifting E. Later observations in September showed a decrease in activity with no further explosions and plumes limited to white gas-and-steam plumes. On 21 September VMGD reported that the Lake Voui eruption had ceased and the Alert Level was lowered to 2.

Observed activity through October and November dominantly consisted of white gas-and-steam plumes. An explosion on 30 October at 1832 produced an ash plume that rose to 4-5 km and drifted E and SE. Satellite images acquired during July-November show the changing crater area and crater lake water color (figure 89). VMGD volcano alert bulletins on 6, 7, and 21 January 2019 reported that activity continued with gas-and-steam emissions (figure 90). Thermal energy continued to be detected by the MIROVA system through January (figure 91).

Figure (see Caption) Figure 89. The changing lakes of Ambae during volcanic activity in 2018. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 90. A steam plume at Ambae on 21 January 2019. Courtesy of VMGD.
Figure (see Caption) Figure 91. Log radiative power MIROVA plot of MODIS infrared data at Ambae for April 2018 through January 2019 showing the increased thermal energy during the July 2018 eruption and continued activity. Courtesy of MIROVA.

Geologic Background. The island of Ambae, also known as Aoba, is a massive 2500 km3 basaltic shield that is the most voluminous volcano of the New Hebrides archipelago. A pronounced NE-SW-trending rift zone dotted with scoria cones gives the 16 x 38 km island an elongated form. A broad pyroclastic cone containing three crater lakes (Manaro Ngoru, Voui, and Manaro Lakua) is located at the summit within the youngest of at least two nested calderas, the largest of which is 6 km in diameter. That large central edifice is also called Manaro Voui or Lombenben volcano. Post-caldera explosive eruptions formed the summit craters about 360 years ago. A tuff cone was constructed within Lake Voui (or Vui) about 60 years later. The latest known flank eruption, about 300 years ago, destroyed the population of the Nduindui area near the western coast.

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD), Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); Wellington Volcanic Ash Advisory Centre (VAAC), Meteorological Service of New Zealand Ltd (MetService), PO Box 722, Wellington, New Zealand (URL: http://www.metservice.com/vaac/, http://www.ssd.noaa.gov/VAAC/OTH/NZ/messages.html); 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/); NASA Worldview (URL: https://worldview.earthdata.nasa.gov/); 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/); Himawari-8 Real-time Web, developed by the NICT Science Cloud project in NICT (National Institute of Information and Communications Technology), Japan, in collaboration with JMA (Japan Meteorological Agency) and CEReS (Center of Environmental Remote Sensing, Chiba University) (URL: https://himawari8.nict.go.jp/); Vanuatu Red Cross Society (URL: https://www.facebook.com/VanuatuRedCross); William A. Brooks and Ronald L. Holle, Vaisala Inc., Tucson, Arizona, and Chris Vagasky, Vaisala Inc., Louisville, Colorado (URL: https://www.vaisala.com/); Michael Rowe, The University of Auckland, 23 Symonds Street, Auckland, 1010, New Zealand (URL: https://unidirectory.auckland.ac.nz/profile/michael-rowe); Radio New Zealand, 155 The Terrace, Wellington 6011, New Zealand (URL: https://www.radionz.co.nz/international/pacific-news/359231/vanuatu-provincial-capital-moves-due-to-volcano); Vanuatu Daily Post (URL: http://dailypost.vu/).


Agung (Indonesia) — February 2019 Citation iconCite this Report

Agung

Indonesia

8.343°S, 115.508°E; summit elev. 2997 m

All times are local (unless otherwise noted)


Ongoing intermittent ash plumes and frequent gas-and-steam plumes during August 2018-January 2019

Agung is an active volcano in Bali, Indonesia, that began its current eruptive episode in September 2017. During this time activity has included ash plumes, gas-and-steam plumes, explosions ejecting ballistic blocks onto the flanks, and lava extrusion within the crater.

This report summarizes activity from August 2018 through January 2019 based on information from Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Indonesian Center for Volcanology and Geological Hazard Mitigation (CVGHM), MAGMA Indonesia, the National Board for Disaster Management - Badan Nasional Penanggulangan Bencana (BNPB), the Darwin Volcanic Ash Advisory Center (VAAC), and satellite data.

During August 2018 through January 2019 observed activity was largely gas-and steam plumes up to 700 m above the crater (figures 39 and 40). In late December and January there were several explosions that produced ash plumes up to 5.5 km altitude, and ejected ballistic blocks.

Figure (see Caption) Figure 39. Graph showing the observed white gas-and-steam plumes and gray ash plumes at Agung during August 2018 through January 2019. The dates showing no data points coincided with cloudy days where the summit was not visible. Data courtesy of PVMBG.
Figure (see Caption) Figure 40. A white gas-and-steam plume at Agung on 21 December 2018. Courtesy of MAGMA Indonesia.

The Darwin VAAC reported an ash plume on 8-9 August based on satellite data, webcam footage, and ground report information. The ash plume rose to 4.3 km and drifted to the W. They also reported a diffuse ash plume to 3.3 km altitude on 16-17 August based on satellite and webcam data. During September through November there were no ash plumes observed at Agung; activity consisted of white gas-and-steam plumes ranging from 10-500 m above the crater.

Throughout December, when observations could be made, activity mostly consisted of white gas-and-steam plumes up to 400 m above the crater. An explosion occurred at 0409 on 30 December that lasted 3 minutes 8 seconds produced an ash plume rose to an altitude of 5.5 km and moved to the SE and associated incandescence was observed at the crater. Light Ashfall was reported in the Karangasem regency to the NE, including Amlapura City and several villages such as in Seraya Barat Village, Seraya Tengah Village, and Tenggalinggah Village (figure 41).

Figure (see Caption) Figure 41. A webcam image of an explosion at Agung that began at 0409 on 30 December 2018. Light Ashfall was reported in the Karangasem regency. Courtesy of PVMBG.

White gas-and-steam plumes continued through January 2019 rising as much as 600 m above the crater. Several Volcano Observatory Notices for Aviation (VONAs) were issued during 18-22 January. An explosion was recorded at 0245 on 19 January that produced an ash plume to 700 m above the crater and ejected incandescent blocks out to 1 km from the crater. On 21 January another ash plume rose to an estimated plume altitude of 5.1 km. The next morning, at 0342 on the 22nd, an ash plume to an altitude of 2 km that dispersed to the E and SE.

Satellite data shows continued low-level thermal activity in the crater throughout this period. MIROVA thermal data showed activity declining after a peak in July, and a further decline in energy in September (figure 42). Low-level thermal activity continued through December. Sentinel-2 thermal data showed elevated temperatures within the ponded lava in the crater (figure 43).

Figure (see Caption) Figure 42. Log radiative power MIROVA plot of MODIS infrared data for May 2018 through January 2019 showing thermal anomalies at Agung. The black data lines indicate anomalies more than 10 km from the crater, which are likely due to fires. Courtesy of MIROVA.
Figure (see Caption) Figure 43. Sentinel-2 thermal satellite images showing areas of elevated temperatures within the lava ponded in the Agung crater during August 2018 through January 2019. Courtesy of Sentinel Hub Playground.

Geologic Background. Symmetrical Agung stratovolcano, Bali's highest and most sacred mountain, towers over the eastern end of the island. The volcano, whose name means "Paramount," rises above the SE caldera rim of neighboring Batur volcano, and the northern and southern flanks extend to the coast. The summit area extends 1.5 km E-W, with the high point on the W and a steep-walled 800-m-wide crater on the E. The Pawon cone is located low on the SE flank. Only a few eruptions dating back to the early 19th century have been recorded in historical time. The 1963-64 eruption, one of the largest in the 20th century, produced voluminous ashfall along with devastating pyroclastic flows and lahars that caused extensive damage and many fatalities.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); 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/); 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).


Erebus (Antarctica) — January 2019 Citation iconCite this Report

Erebus

Antarctica

77.53°S, 167.17°E; summit elev. 3794 m

All times are local (unless otherwise noted)


Lava lakes persist through 2017 and 2018

Between the early 1980's through 2016, activity at Erebus was monitored by the Mount Erebus Volcano Observatory (MEVO), using seismometers, infrasonic recordings to measure eruption frequency, and annual scientific site visits. MEVO recorded occasional explosions propelling ash up to 2 km above the summit of this Antarctic volcano and the presence of two, sometimes three, lava lakes (figure 26). However, MEVO closed in 2016 (BGVN 42:06).

Activity at the lava lakes in the summit crater can be detected using MODIS infrared detectors aboard the Aqua and Terra satellites and analyzed using the MODVOLC algorithm. A compilation of thermal alert pixels during 2017-2018 (table 4, a continuation of data in the previous report) shows a wide range of detected activity, with a high of 182 alert pixels in April 2018. Although no MODVOLC anomalies were recorded in January 2017, detectors on the Sentinel-2 satellite imaged two active lava lakes on 25 January.

Table 4. Number of MODVOLC thermal alert pixels recorded per month from 1 January 2017 to 31 December 2018 for Erebus by the University of Hawaii's thermal alert system. Table compiled by GVP from data provided by MODVOLC.

Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec SUM
2017 0 21 9 0 0 1 11 61 76 52 0 3 234
2018 0 21 58 182 55 17 137 172 103 29 0 0 774
SUM 0 42 67 182 55 18 148 233 179 81 0 3 1008
Figure (see Caption) Figure 26. Sentinel-2 images of the summit crater area of Erebus on 25 January 2017. Top: Natural color filter (bands 4, 3, 2). Bottom: Atmospheric penetration filter (bands 12, 11, 8A) in which two distinct lava lakes can be observed. The main crater is 500 x 600 m wide. Courtesy of Sentinel Hub Playground.

Geologic Background. Mount Erebus, the world's southernmost historically active volcano, overlooks the McMurdo research station on Ross Island. The 3794-m-high Erebus is the largest of three major volcanoes forming the crudely triangular Ross Island. The summit of the dominantly phonolitic volcano has been modified by one or two generations of caldera formation. A summit plateau at about 3200 m elevation marks the rim of the youngest caldera, which formed during the late-Pleistocene and within which the modern cone was constructed. An elliptical 500 x 600 m wide, 110-m-deep crater truncates the summit and contains an active lava lake within a 250-m-wide, 100-m-deep inner crater. The glacier-covered volcano was erupting when first sighted by Captain James Ross in 1841. Continuous lava-lake activity with minor explosions, punctuated by occasional larger strombolian explosions that eject bombs onto the crater rim, has been documented since 1972, but has probably been occurring for much of the volcano's recent history.

Information Contacts: 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Villarrica (Chile) — March 2019 Citation iconCite this Report

Villarrica

Chile

39.42°S, 71.93°W; summit elev. 2847 m

All times are local (unless otherwise noted)


Intermittent Strombolian activity ejects incandescent bombs around crater rim, September 2018-February 2019

Historical eruptions at Chile's Villarrica, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. An intermittently active lava lake at the summit has been the source of explosive activity, incandescence, and thermal anomalies for several decades. Sporadic Strombolian activity at the lava lake and small ash emissions have continued since the last large explosion on 3 March 2015. Similar continuing activity during September 2018-February 2019 is covered in this report, with information provided primarily by 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), and Projecto Observación Villarrica Internet (POVI), part of the Fundacion Volcanes de Chile, a research group that studies volcanoes across Chile.

After ash emissions during July 2018 and an increase in of thermal activity from late July through early September 2018 (BGVN 43:10), Villarrica was much quieter through February 2019. Steam plumes rose no more than a few hundred meters above the summit and the number of thermal alerts decreased steadily. Intermittent Strombolian activity sent ejecta a few tens of meters above the summit crater, with larger bombs landing outside the crater rim. A small pyroclastic cone appeared at the surface of the lava lake, about 70 m below the rim, in November. The largest lava fountain rose 35 m above the crater rim in late January 2019.

Steam plumes rose no more than 300 m above the crater during September 2018 and were less than 150 m high in October; incandescence at the summit was visible during clear nights, although a gradual decrease in activity suggested a lowering of the lake level to SERNAGEOMIN. SERNAGEOMIN attributed an increase in LP seismic events from 1,503 in September to 5,279 in October to dynamics of the lava lake inside the summit crater; counts decreased gradually in the following months.

POVI reported webcam evidence of Strombolian activity with ejecta around the crater several times during November 2018. On 5 November the webcam captured an image of an incandescent bomb, more than a meter in diameter, that landed on the NW flank. The next day, explosions sent ejecta 50 m above the edge of the crater, and pyroclastic debris landed around the perimeter. Significant Strombolian explosions on 16 November sent incandescent bombs toward the W rim of the crater (figure 71). The POVI webcam in Pucón captured incandescent ejecta landing on the crater rim on 23 November. POVI scientists observed a small pyroclastic cone, about 10-12 m in diameter, at the bottom of the summit crater on 19 November (figure 72); it was still visible on 25 November.

Figure (see Caption) Figure 71. Strombolian activity at the summit of Villarrica was captured several times in the POVI webcam located in Pucón. An explosion on 5 November 2018 ejected a meter-sized bomb onto the NW flank (left). On 16 November, incandescent bombs were thrown outside the W rim of the crater (right). Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).
Figure (see Caption) Figure 72. A small pyroclastic cone was visible at the bottom of the summit crater at Villarrica (about 70 m deep) on 19 November 2018 (left); it was still visible on 25 November (right). Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

During December 2018 webcam images showed steam plumes rising less than 350 m above the crater. Infrasound instruments identified two small explosions related to lava lake surface activity. SERNAGEOMIN noted a minor variation in the baseline of the inclinometers; continued monitoring indicated the variation was seasonal. A compilation by POVI of images of the summit crater during 2018 showed the evolution of the lava lake level during the year. It had dropped out of sight early in the year, rose to its highest level in July, and then lowered slightly, remaining stable for the last several months of the year (figure 73).

Figure (see Caption) Figure 73. Evolution of the lava pit at Villarrica during 2018. During July the lava lake level increased and for November and December no significant changes were observed. Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

Between 25 December 2018 and 15 January 2019, financed with funds contributed by the Fundación Volcanes de Chile, POVI was able to install new HD webcams with continuous daily image recording, greatly improving the level of detail data available of the activity at the summit. POVI reported that after a five-week break, Strombolian explosions resumed on 3 January 2019; the lava fountains rose 20 m above the crater rim, and pyroclastic ejecta fell to the E. On 24 January the Strombolian explosions ejected ash, lapilli, and bombs up to 15 cm in diameter; the lava fountain was about 35 m high.

An explosion on 7 February reached about 29 m above the crater's edge; on 9 February a lava fountain three meters in diameter rose 17 m above the crater rim. Sporadic explosions were imaged on 12 February as well (figure 74). During a reconnaissance overflight on 24 February 2019, POVI scientists observed part of the lava pit at the bottom of the crater (figure 75). As of 28 February they noted a slight but sustained increase in the energy of the explosions. SERNAGEOMIN noted that steam plumes rose 400 m in January and 150 m during February, and incandescence was visible on clear nights during both months.

Figure (see Caption) Figure 74. Strombolian activity at Villarrica in January and February 2019 was imaged with a new HD webcam on several occasions. On 24 January 2019 explosions ejected ash, lapilli, and bombs up to 15 cm in diameter; the lava fountain was about 35 m high (left); on 12 February 2019 explosions rose about 19 m above the crater rim (right). Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).
Figure (see Caption) Figure 75. During a reconnaissance overflight on 24 February 2019, POVI scientists observed part of the lava pit at the bottom of the crater at Villarrica; gas and steam emissions and incandescence from small explosions were noted. Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

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: 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/); Proyecto Observación Villarrica Internet (POVI) (URL: http://www.povi.cl/).

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Bulletin of the Global Volcanism Network - Volume 42, Number 09 (September 2017)

Managing Editor: Edward Venzke

Barren Island (India)

Decreased and intermittent thermal anomalies after mid-March 2017

Bogoslof (United States)

Ash-bearing explosions begin in December 2016; lava dome emerges in June 2017

Bristol Island (United Kingdom)

First eruption since 1956; lava flows and ash plumes, April-July 2016

Etna (Italy)

Lava flows during May 2016 followed by new fracture zones and major subsidence at the summit craters

Fogo (Cape Verde)

November 2014-February 2015 eruption destroys two villages, lava displaces over 1000 people

Krakatau (Indonesia)

Eruption during 17-19 February 2017 sends large lava flow down the SE flank

Langila (Papua New Guinea)

Eruption continues, intensifying from mid-December 2016 through July 2017

Masaya (Nicaragua)

Persistent lava lake and gas plume activity, with intermittent ash emission, through mid-July 2017

Popocatepetl (Mexico)

Ongoing steam, gas, ash emissions, and lava dome growth and destruction, July 2016-July 2017

Sangeang Api (Indonesia)

Weak Strombolian activity and occasional weak ash plumes, 15 July-12 August 2017



Barren Island (India) — September 2017 Citation iconCite this Report

Barren Island

India

12.278°N, 93.858°E; summit elev. 354 m

All times are local (unless otherwise noted)


Decreased and intermittent thermal anomalies after mid-March 2017

Following sporadic activity during the second half of 2016, a new period of strong thermal anomalies suggestive of lava flows began in mid-January 2017 (BVGN: 42:03). Scientists on a nearby research vessel observed ash emissions and lava fountains that fed lava flows during 23-26 January. Subsequent possible activity, as shown by MODIS thermal anomalies detected by MIROVA (figure 26), continued at similar levels until mid-March, after the anomalies became more intermittent and decreased in power through at least 2 September. Thermal alerts in MODVOLC were recorded during 15 January-8 March 2017.

Figure (see Caption) Figure 26. Thermal anomaly MIROVA log radiative power data from Barren Island during early September 2016-1 September 2017. Regular, low-moderate activity is evident beginning in late January through April 2017, but it thereafter wanes. Courtesy of MIROVA.

Geological Survey of India cruise in May 2015. Some observations and photos of activity on 14 and 31 May 2015 have been provided by Sachin Tripathi, a geologist at the Geological Survey of India, who was close to the volcano during the SR-013 cruise of the RV Samudra Ratnakar. On 14 May the plumes were described as light gray "mushroom shaped" clouds. Tripathi further noted that the activity occurred in discrete pulses; he observed two such events during an 8-minute period that sent ash plumes 300-400 m high (figure 27). Eruptive pulses on 31 May lasted about 20-25 seconds, with an interval of 4-5 minutes. The plumes on that day were light gray to gray, and rose to around 50-100 m. The NE portion of the island was covered with ash (figure 28).

Figure (see Caption) Figure 27. Two images from a video that illustrate the pulsating eruption at Barren Island on 14 May 2015. The top image shows the remains of an older plume above the island and a new plume just rising from the summit. The bottom image shows the ash plume rising to about 300-400 m above the island. Courtesy of Sachin Tripathi, Geological Survey of India.
Figure (see Caption) Figure 28. Photograph of an ash plume rising from the active vent at Barren Island on 31 May 2015. Ashfall can be seen covering the NE portion of the island. Courtesy of Sachin Tripathi, Geological Survey of India.

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

Information Contacts: Sachin Tripathi, Geological Survey of India; 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/).


Bogoslof (United States) — September 2017 Citation iconCite this Report

Bogoslof

United States

53.93°N, 168.03°W; summit elev. 150 m

All times are local (unless otherwise noted)


Ash-bearing explosions begin in December 2016; lava dome emerges in June 2017

Bogoslof lies 40 km N of the main Aleutian arc, over 1,350 km SW of Anchorage, Alaska (figure 2). Its intermittent eruptive history, first recorded in the late 18th century, has created and destroyed several distinct islands that are responsible for a unique and changing landscape at the summit of this submarine volcano, and produced multiple explosive ash-bearing plumes. The last subaerial eruption, in July 1992, created a lava dome on the N side of the island, adjacent to an eroded dome created in 1927 (BGVN 17:07, figure 1). A new eruption began on 20 December 2016, and was ongoing through July 2017. Information comes from the Alaska Volcano Observatory (AVO) and the Anchorage Volcanic Ash Advisory Center (VAAC).

Figure (see Caption) Figure 2. Index map showing the location of Bogoslof. Adapted from Beget et al. (2005). Courtesy of AVO.

AVO notes that there is no ground-based monitoring equipment on Bogoslof, so monitoring is accomplished using satellite images, information from the Worldwide Lightning Location Network pertaining to volcanic-cloud lightning, and data from seismic and infrasound (airwave sensor) instruments. The infrasound instruments are located on neighboring Umnak (100 km SW) and Unalaska Islands (85 km SE) and further away at Sand Point (500 km E) on Popof Island, and on the Alaska mainland in Dillingham (825 km NE). AVO also receives reports from observers on ships and airplanes.

The first eruption at Bogoslof since 1992 began during mid-December 2016, when an ash plume was seen on 20 December. Numerous explosions were recorded via seismic, infrasound, lightning, satellite, and visual observations until 19 February 2017, and the morphology of the island changed significantly during that time. Ashfall was reported in Unalaska on 31 January. A large explosion on 7 March produced a substantial ash plume, and was followed by four days with earthquake swarms that lasted for hours. An explosion on 16 May produced an ash plume that rose to over 10 km altitude. A larger explosion on 28 May created tephra jets, pyroclastic fall and flow material around the island, and a possible 13.7-km-high ash plume. A substantial submarine sediment plume was observed in early June, followed by confirmation of a lava dome above the ocean surface during 5-6 June. A series of explosions during 10 June destroyed the lava dome. Explosions producing ash plumes that rose to altitudes above 10 km occurred on 23 June and 2 July; several additional smaller explosions were recorded through mid-July.

Activity during December 2016-February 2017. According to AVO, Bogoslof showed signs of unrest beginning on 12 December 2016 in seismic, infrasound (air-wave), and satellite data. Ash emissions may have occurred on 16 and 19 December on the basis of recorded lightning strikes, seismic data, and sulfur dioxide clouds detected by satellite instruments, though there were no direct visual observations from satellite or ground observers. On 20 December, a powerful, short-lived explosion at about 1535 AKST (0035 UTC 21 December) sent ash to over 10.3 km altitude which then drifted S (figure 3).

Figure (see Caption) Figure 3. Bogoslof's eruption plume was captured on 20 December shortly after 1530 AKST from an aircraft at 36,000 feet (10.9 km). The aircraft was about 20 miles N of Bogoslof Island flying W. Photo by Paul Tuvman, courtesy of AVO.

An explosion on 21 December at 1610 AKST was detected in satellite images and seismic data from neighboring islands. This eruption lasted about 30 minutes and sent ash as high as 10.7 km which then drifted N. Satellite images from the next day showed that a small new island had formed just offshore of the NE end of the main island. The previous shore and much of the NE side of Bogoslof Island adjacent to the new island was mostly removed and, according to AVO, was likely the site of the new, underwater vent; deposition of material was visible on the W side of the island (figure 4).

Figure (see Caption) Figure 4. Analysis of shoreline change and vent location from the 20-21 December 2016 eruption of Bogoslof. The base image is from 19 March 2015 and the analysis was conducted using data from 22 December 2016, a day after the large explosive eruption on 21 December. Note that the location of the vent for the eruption was underwater or near the shoreline on the NE part of Bogoslof Island. Deposits have enlarged portions of the island and were interpreted by AVO to be comprised of coarse-grained volcanic ash and blocks of lava. The areas marked with "+" are material that was added during the eruption. The area marked with "-" represents material removed during the eruption. Courtesy of AVO.

During the morning of 23 December 2016, observers aboard a Coast Guard vessel reported ash emission, lightning, and the ejection of incandescent lava and fragmental material. Ash emission and lava ejection subsided after about an hour. The ash cloud was carried N over the Bering Sea and did not penetrate above the regional cloud tops at 9.1 km altitude. Similar, repeated, short-duration explosions continued every few days through 19 February 2017 before the first break in activity (table 1).

Table 1. Observations of activity at Bogoslof, December 2016-July 2017, as reported by AVO and the Anchorage VAAC. Date is local AKST or AKDT (starting 10 June). Plume altitude in kilometers. Drift is direction and distance in kilometers.

Date Time (local) Observation and notes Plume Altitude (km) Drift Detection Method
12 Dec 2016 -- "Unrest" -- -- Seismic, infrasound, satellite
16 Dec 2016 -- Possible ash emissions -- -- Lightning, seismic, SO2
19 Dec 2016 -- Possible ash emissions -- -- Lightning, seismic, SO2
20 Dec 2016 1530 Explosive eruption with ash plume 10.3 S Pilot, satellite
21 Dec 2016 1610 30-minute-long explosion with ash plume 10.7 N Satellite, seismic
23 Dec 2016 0930 Explosion with ash, lightning, incandescent lava, and debris, 60 minute duration Below 9.1 N Coast Guard observers from nearby vessel
25 Dec 2016 evening Tremor, possible minor, low-level ash emission, lightning -- -- Seismic, lightning
26 Dec 2016 1405 Ash Plume 9.1 WSW Lightning, seismic, satellite
28 Dec 2016 1755 Tremor, 50 minutes, Cloud cover obscured -- -- Seismic
29 Dec 2016 1900, 2345 Continuous tremor at 1900, 30-minute-long ash producing event at 2345 6.1 NE Seismic station on Umnak, infrasound, satellite
30 Dec 2016 2230 Explosive event, 45 minutes, Cloud cover obscured -- -- Seismic, infrasound, lightning
31 Dec 2016 0500 Low-level eruptive activity, continuous; cloud cover obscured; windy conditions affect local seismic stations -- -- Dillingham infrasound
02 Jan 2017 1353 Minor explosions, 10 minutes of increased seismicity, cloud cover obscured -- -- Seismic, infrasound
03 Jan 2017 2118 Seismic activity, 5 minutes, ash plume 10.0 N Seismic, infrasound, lightning, satellite
05 Jan 2017 1324 Increased seismicity, ash plume, detached 10.7 NNW Seismic, lightning, satellite, pilot
08 Jan 2017 2233, 2256 Two strong seismic pulses, two volcanic clouds 10.7 NW Seismic, infrasound, satellite
12 Jan 2017 1123, 1230 Two short-lived explosions, plumes 5.5, 4.4 -- Seismic, pilot
14 Jan 2017 2126, 2216 Six explosions, beginning 2216, no ash plumes observed -- -- Seismic, lightning
17 Jan 2017 0400, 0740 Increasing tremor signal, Steam with minor ash 4.6 -- Seismic, satellite
18 Jan 2017 1320 Explosion, dark ash cloud, strong thermal anomaly around vent 9.4 NE Seismic, pilot, lightning, infrasound, satellite, SO2, MODVOLC
20 Jan 2017 1317 Explosion, ice-rich ash plume, lava at vent 11.0 SE Seismic, lightning, pilot, satellite imagery of lava, infrasound
22 Jan 2017 1409 Explosion, ash plume 9.1 -- Lightning, satellite
24 Jan 2017 0453 Explosion, ice-rich cloud with likely ash 7.6-10.7 E Seismic, lightning
26 Jan 2017 0650, 0706 Exposion, ice-rich cloud with likely ash; ash drifted in multiple directions 9.8, 6.1 SE, NE Seismic, lightning
27 Jan 2017 0824 Explosion, ice-rich cloud with likely ash 7.6 -- Seismic, lightning
30 Jan 2017 2020 Eruption cloud, more than 10 short explosions, Trace ashfall in Dutch Harbor (98 km E) and strong SO2 odor 7.6 125 km SE Seismic, infrasound, lightning, satellite
03 Feb 2017 0457, 0533 Increased seismicity, small explosions, no ash detected -- -- Seismic, infrasound
03 Feb 2017 1641 Seismic event, small plume 7.6 40 km N Infrasound, satellite, pilot
5, 7, 8 Feb 2017 -- Weakly elevated surface temp -- -- Satellite
13 Feb 2017 0724 Increased seismicity, no ash emissions above 3 km -- -- Seismic, satellite
17 Feb 2017 0955, 1546 Explosive event, ash plume 11.6, 7.6 N Seismic, satellite, pilot, infrasound, lightning
18 Feb 2017 0450 Explosion, ash emissions 7.6 SW Seismic, infrasound, lightning, satellite
19 Feb 2017 1708-1745 Series of short explosive pulses, plume 7.6 160 km SE Seismic, infrasound, satellite
07-08 Mar 2017 2236 3 hour explosive event, large ash plume, over 1,000 lightning strokes 10.7 E Seismic, lightning, infrasound
09-10 Mar 2017 1750 Earthquake swarm, 20 hours -- -- Seismic
10-11 Mar 2017 1900 Earthquake swarm, 10 hours -- -- Seismic
12 Mar 2017 0500 Earthquake swarm -- -- Seismic
13 Mar 2017 1131 Seismic event, small ash cloud, weakly elevated surface temps 5.5 90 km SSW Seismic, satellite
16 May 2017 2232 Increased seismicity, ash plume, 73 minutes 10.4 SW Seismic, infrasound, lightning, satellite, pilot
28 May 2017 1416 Explosion, ash plume, 50 minutes, plume visible for 4 days 10.7-13.7 W, NE Seismic, satellite, pilot
31 May 2017 1842 Several hour-long seismic swarm followed by short duration explosion, volcanic cloud 7.3 WNW Seismic, infrasound, satellite
05 Jun 2017 0750 Explosion, small volcanic cloud -- -- Seismic, pilot
06 Jun 2017 0600 Brief explosive event, possible plume, lava dome emerges 1.8 -- Seismic, infrasound, satellite
10 Jun 2017 0318 Explosive eruption, ash-rich cloud 10.4 NW Seismic, infrasound, lightning, satellite
12 Jun 2017 1747 Series of explosive events, ash plumes 7.6 SE Seismic, infrasound
13 Jun 2017 0817 Six-minute long explosion, no plume observed -- -- Seismic, infrasound
23 Jun 2017 1649 Five explosions, ash plume 11.0 400-490 km E Seismic, infrasound
26 Jun 2017 1645 14-minute explosion, ash plume 7.6 -- Seismic
27 Jun 2017 0317 14-minute explosion, ash plume 9.1 NW Seismic, lightning
30 Jun 2017 0124 Explosion, 20 minutes, small cloud -- 16 km N Seismic
02 Jul 2017 1248 16-minute explosion, ash plume 11 E Seismic, infrasound
04 Jul 2017 1651 13-minute explosive event, eruption cloud 8.5 SE Seismic
04 Jul 2017 1907 11-minute-long explosion, small cloud 9.8 SE Seismic
08 Jul 2017 1015 Two eruption pulses, ash plume 9.1 N Seismic, satellite
09 Jul 2017 2347 Two eruptions, 5-minutes and 7-minutes long, small ash cloud 6.1 SE Seismic, satellite
10 Jul 2017 1000, 1706 Two explosions, no confirmed ash -- -- Seismic, infrasound

AVO reported that photos taken by a pilot on 10 January showed Bogoslof covered with dark gray ash, and a roughly 300-m-diameter submarine explosion crater on the E side of the island. The dark (ash-rich) plume from an explosion on 18 January (figure 5) was identified in satellite images and observed by a pilot; the event produced lightning strikes and infrasound signals detected by sensors in Sand Point and Dillingham. Analysis of a satellite image suggested the presence of very hot material (possibly lava) at the surface immediately surrounding the vent, which was the first such observation since the beginning of the eruption. The first MODVOLC thermal alerts were issued on 18 January.

Figure (see Caption) Figure 5. A large explosion at Bogoslof on 18 January 2017 produced a dark ash cloud that rose to 9.4 km and drifted NE. Captured by MODIS on NASA's Terra satellite. Courtesy of NASA Earth Observatory.

AVO analysis of satellite images from 16 and 18 January 2017 (before the eruption that day) showed that the vent area, which formed on the NE end of the island in shallow water, had been filling in with eruptive material and building out of the water. On 20 January, satellite images showed an ice-rich plume and lava present at the vent. Prevailing winds carried the plume to the SE over the SW end of Unalaska Island, but no ash fall was reported. A high spatial resolution satellite image collected on 24 January showed AVO that the explosive eruptions continued to change the morphology of the island and the coastline (see figure 7). The eruptive vent, however, remained below sea level in the N portion of a figure-eight-shaped bay, as indicated by the presence of upwelling volcanic gases. There was no sign of lava at the surface.

A series of more than 10 short-duration explosions beginning on 30 January (AKST) and detected in seismic, infrasound, and lightning data, resulted in an ash plume that rose to 7.6 km altitude and drifted 125 km SE. Trace amounts of ashfall and a strong SO2 odor were reported in Dutch Harbor on Unalaska Island (98 km E) (figure 6). Satellite images acquired on 31 January showed additional significant changes to the morphology of the island (figure 7). AVO stated that freshly erupted volcanic rock and ash had formed a barrier that separated the vent from the sea.

Figure (see Caption) Figure 6. Trace ashfall in Unalaska, Alaska, on 31 January 2017 from Bogoslof. Courtesy of AVO.
Figure (see Caption) Figure 7. Changes in the morphology of Bogoslof Island resulting from the ongoing 2016-17 eruption. The 30-31 January 2017 eruptive activity generated roughly 0.4 square kilometers of new land. As of 31 January 2017 the island area was 1.02 square kilometers, roughly three times the size of the pre-eruption island. Nearly all of this new material consisted of unconsolidated pyroclastic fall and flow (surge) deposits that are highly susceptible to wave erosion. Courtesy of AVO.

On 19 February 2017, a series of short-lived explosive pulses resulted in a plume that drifted 160 km SE over Unalaska Island. AVO geologists on the island described the cloud has having a white upper portion and a slightly darker lower portion. A satellite image from 23 February showed that the vent location at Bogoslof remained underwater. After the 19 February events, the volcano was quiet for two weeks.

Activity during March 2017. A 3-hour-long explosive event occurred overnight during 7-8 March 2017 and produced numerous strokes of volcanic lightning, high levels of seismicity and infrasound, and an ash cloud up to 10.7 km altitude that moved E over Unalaska Island. The seismicity was among the highest levels observed for the eruption sequence that began in mid-December 2016, and the more than 1,000 detected lightning strokes were by far the highest number observed to date. The eruptive activity again changed the shape of the island and temporarily dried out the vent area. Satellite images from 8 March showed that the W coast of the island appeared to have grown significantly due to the eruption of new volcanic ash and blocks. A new vent was also identified on the NW side of the island, and the lava dome emplaced during the 1992 eruption was partially destroyed (figure 8).

Figure (see Caption) Figure 8. A Worldview-2 satellite image of Bogoslof Island on 11 March 2017 showing features and changes resulting from the 7-8 March 2017 activity. A new vent developed on the NW shore of the island adjacent to the lava dome that formed during the 1992 eruption. Most of the deposits on the surface appear fine-grained and were likely emplaced by pyroclastic base surges. The surface of these deposits exhibit ripples, dunes, and ballistic impact craters. The scalloped appearing shoreline of the intra-island lake is probably the result of groundwater related erosion (sapping) of the pyroclastic deposits as water refills the lake. Most or all of the water in the lake was likely expelled by the eruption column exiting the primary or other vents. The area of Bogoslof Island in this image is about 0.98 square kilometers. Image data provided under Digital Globe NextView License. Courtesy of AVO.

Two earthquake swarms were detected during 9-11 March; the first began at 1750 on 9 March and ended at 1400 on 10 March, and the second was detected from 1900 on 10 March to 0500 on 11 March. Mildly elevated surface temperatures were identified in satellite data during 10-11 March. A third swarm began at 0500 on 12 March. A 12-minute-long explosive event, beginning at 1131 on 13 March, produced a small ash cloud that rose to an altitude of 5.5 km and drifted SSW. AVO noted that after the event, the level of seismic activity declined and the repeating earthquakes of the previous several days had stopped. Weakly elevated surface temperatures were observed in two satellite images from 13 March. A photograph taken by a pilot showed a low-level, billowy steam plume rising from the general area of the intra-island lake. Except for weakly elevated surface temperatures in satellite data, no significant activity was reported during the rest of March. The only activity detected during April 2017 was a brief increase in seismicity on 15 April. Aerial reconnaissance by the US Coast Guard on 8 May showed the dramatic changes of the island's shape (figure 9).

Figure (see Caption) Figure 9. Bogoslof Island viewed from the NW on 8 May 2017. Fire Island (a remnant of lava from an 1883 eruption) is in the right foreground, and the new steaming lake that includes the submarine vent is behind the two dome remnants in the mid-ground. The 1992 lava is the remnant on the left and the 1926-28 lava is on the right. Bogoslof Island aerial reconnaissance courtesy of U.S. Coast Guard Air Station Kodiak and U.S.C.G. Cutter Mellon. Photo by Max Kaufman, courtesy of AVO.

Activity during May-July 2017. Following a pause in explosive activity that lasted a little over two months, Bogoslof erupted explosively at 2232 (AKDT) on 16 May. The eruption, which lasted about 70 minutes, was detected by seismic and infrasound sensors on neighboring islands and the resulting ash-cloud-generated volcanic lightning that was detected by the Worldwide Lightning Location Network. A pilot report and satellite images showed that the plume rose as high as 10.4 km, and then drifted SW. Trace ashfall was reported in the community of Nikolski on Umnak Island (125 km SW). A drifting sulfur dioxide cloud from the eruption was detected for several days using satellite-based sensors. The eruption altered the northern coastline of the island, with the crater lake breached by a 550-m-wide gap along the N shore. Part of the NE shore had been extended 300 m due to new tephra deposits.

Another large explosion began at 1416 on 28 May 2017. Pilot and satellite observations indicated that ash plumes rose at least 10.7 km and possibly as high as 13.7 km altitude (figure 10). An observer on Unalaska Island reported seeing a large white-gray mushroom cloud form over Bogoslof, with ashfall to the W. The event lasted 50 minutes. On 29 May the ash cloud continued to drift NE, and on 2 June, an SO2 plume from the event was still visible in satellite data drifting over the Hudson Bay region.

Figure (see Caption) Figure 10. Enlarged portions of 28 May 2017 satellite image of Bogoslof Island. Inset image on lower left shows pyroclastic fall and flow material emplaced over water. Some of the material appears to have been disturbed, possibly by the force of the eruption column. It is unclear if this material represents new land or material floating on the water. Tephra jets are common features of many shallow submarine eruptions. The inset image in the upper right shows a weak base surge propagating from the base of the eruption column across the tuff ring. Image data provided under the Digital Globe NextView License. Courtesy of AVO.

On 5 June, a vessel in the area reported vigorous steaming and a white plume rising at least a kilometer above sea level. Also, a substantial submarine sediment plume was seen in satellite imagery drifting N from the lagoon area (figure 11). A brief explosive event at 0600 on 6 June likely produced a low-level (less than 3 km) emission. A possible plume at 1.8 km that quickly dissipated was identified in a satellite image following the detection of the activity in seismic and infrasound data.

Figure (see Caption) Figure 11. Landsat-8 image of Bogoslof from 5 June 2017 at 2200 UTC (1400 AKDT). This composite image of visible and thermal infrared data shows a sediment plume in the ocean that extends from the vent region in the horseshoe-shaped lagoon. Warm water outflow is highlighted in color extending northward from the lagoon where it mixes with colder ocean water. A hot vent just S of the lagoon can be seen in orange, and several small puffs of white steam are visible coming from this region. Courtesy of NASA Earth Observatory.

AVO reported that a new lava dome breached the surface of the ocean on or around 6 June 2017; it was the first observation of lava at the surface since the start of the eruption in mid-December 2016 (figure 12). The dome was an estimated 110 m in diameter on 7 June, and then grew to 160 m in diameter by 9 June. Four short-duration explosions were detected in seismic and/or infrasound data between 5 and 7 June, and generated volcanic clouds that in many cases were too small to be observed in satellite data. AVO reported that robust steaming was identified in satellite data and by observers aboard a U.S. Fish and Wildlife Service ship in the region following the emergence of the lava dome likely due to, or enhanced by, the effusion of lava into the ocean.

Figure (see Caption) Figure 12. Comparison of satellite radar images from 31 May and 8 June 2017 of Bogoslof showing the newly emplaced lava dome. The diameter of the short-lived dome was about 110 m. N is to the top. Courtesy of AVO.

A series of six explosions was detected on 10 June, starting with a 2-hour explosive event that emitted an ash-rich cloud to 10.4 km altitude that was detected in seismic, infrasound, lightning, and satellite data. This event destroyed the 160-m-diameter lava dome that was first observed on 5 June (figure 13). On 12 June, a series of four small explosions lasting 10-30 minutes each emitted volcanic clouds that rose to a maximum height of 7.6 km, and dissipated within about 30 minutes. On 13 June, a six-minute-long explosion occurred, although no ash cloud was observed in satellite imagery likely because it's altitude was below detection limits.

Figure (see Caption) Figure 13. Worldview satellite image of Bogoslof taken at 2313 UTC on 12 June 2017. Note that N is to the lower left of the image. The circular embayments were formed by a series of more than 40 explosions that began in mid-December 2016. These explosions have greatly reshaped the island as material was removed and redeposited as air fall. Vigorous steaming was observed S of the most active vent areas in the lagoon. Lava extrusion produced a circular dome that first rose above the water on 5 June and grew to a diameter of ~160 m before being destroyed by an explosion early in the day on 10 June. Large blocks of the destroyed dome can be seen littering the surface of the island near the lagoon. Courtesy of AVO.

Weakly elevated surface temperatures detected in satellite imagery on 10 and 11 June suggested to AVO that a new lava dome was extruding beneath the ocean surface. Satellite imagery showed persistent degassing from the island in between explosions. In addition, residents of Unalaska/Dutch Harbor reported smelling sulfur on 12 June, and winds were consistent with a source at Bogoslof. AVO reported that elevated surface temperatures and a small steam emission were identified in satellite images during 13-14 and 16 June. A 13-km-long steam plume was visible on 18 June.

A series of nine explosions were detected in seismic and/or infrasound data during the night of 23 June, the largest of which produced a volcanic cloud reaching an altitude of 11 km that drifted well over 400 km E (figure 14). Additional explosions on 26 and 27 June sent volcanic clouds to 7.6 and 9.1 km altitude, respectively. Winds carried most of these plumes N and NE; AVO received no reports of ashfall from local communities. Bogoslof erupted again on 29 June and produced a small plume, and several times during the first two weeks of July explosions produced larger plumes that rose to 8.5-11 km altitude. Two explosions that occurred on 10 July without producing observed ash were the last for the rest of the month. Weakly elevated surface temperatures were observed in clear satellite images on 12 and 16 July. No further activity was reported for the rest of July 2017.

Figure (see Caption) Figure 14. Ash plume rising above Bogoslof, 1814 AKDT, 23 June 2017. The view is from Mutton Cove on SW Unalaska Island about 67 km SE of the volcano. AVO estimated the volcanic cloud reached about 11 km above sea level. Photo by Masami Sugiyama courtesy of Allison Everett and AVO.

A modest thermal signal was detected by the MIROVA system between February and July 2017 consistent with the activity that suggested lava dome growth during that time (figure 15).

Figure (see Caption) Figure 15. MIROVA Log Radiative Power graph of thermal energy at Bogoslof for the year ending on 17 August 2017. A low-level thermal anomaly was first detected in early March, and was intermittent through early July. Courtesy of MIROVA.

References: Beget, J.E., Larsen, J.F., Neal, C.A., Nye, C.J., and Schaefer, J.R., 2005, Preliminary volcano-hazard assessment for Okmok Volcano, Umnak Island, Alaska: Alaska Division of Geological & Geophysical Surveys Report of Investigation 2004-3, 32 p., 1 sheet, scale 1:150,000.

Geologic Background. Bogoslof is the emergent summit of a submarine volcano that lies 40 km north of the main Aleutian arc. It rises 1500 m above the Bering Sea floor. Repeated construction and destruction of lava domes at different locations during historical time has greatly modified the appearance of this "Jack-in-the-Box" volcano and has introduced a confusing nomenclature applied during frequent visits of exploring expeditions. The present triangular-shaped, 0.75 x 2 km island consists of remnants of lava domes emplaced from 1796 to 1992. Castle Rock (Old Bogoslof) is a steep-sided pinnacle that is a remnant of a spine from the 1796 eruption. Fire Island (New Bogoslof), a small island located about 600 m NW of Bogoslof Island, is a remnant of a lava dome that was formed in 1883.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://www.dggs.alaska.gov/); Anchorage Volcanic Ash Advisory Center (VAAC), Alaska Aviation Weather Unit, NWS NOAA US Dept of Commerce, 6930 Sand Lake Road, Anchorage, AK 99502-1845(URL: http://vaac.arh.noaa.gov/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/).


Bristol Island (United Kingdom) — September 2017 Citation iconCite this Report

Bristol Island

United Kingdom

59.017°S, 26.533°W; summit elev. 1100 m

All times are local (unless otherwise noted)


First eruption since 1956; lava flows and ash plumes, April-July 2016

Bristol Island, near the southern end of the seven South Sandwich Islands in the isolated Southern Atlantic Ocean, lies 800 km SE of South Georgia Island at latitude 59° S. Historic eruptions occurred on Bristol Island in 1823, the 1930s, and the 1950s. A new eruption was reported from Mount Sourabaya, a cone near the center of the island, beginning at the end of April 2016. It produced ash plumes and strong thermal anomalies most likely generated by lava flows until the end of July 2016. Information about Bristol Island comes from NASA Earth Observatory and other satellite imagery data, and the Buenos Aires Volcanic Ash Advisory Center (VAAC).

Evidence for a new eruption at Bristol Island first appeared in Landsat 8 imagery on 24 April 2016 as a large steam plume and a thermal anomaly at the summit (figure 1). Another image on 1 May showed the still-active plume and an elongation of the thermal anomaly to the W, suggesting that lava may have breached the crater rim. Two MODVOLC thermal alerts also appeared on 24 April; their frequency and intensity increased significantly in subsequent days.

Figure (see Caption) Figure 1. The Operational Land Imager (OLI) on the Landsat 8 satellite acquired these two false-color images on 24 April (upper) and 1 May (lower) 2016 of an eruption at Mount Sourabaya, a stratovolcano on Bristol Island. The images were built from a combination of shortwave-infrared, near-infrared, and red light (Landsat bands 6-5-4) that helps detect the heat signature of an eruption. Both images show what could be lava (red-orange), while white plumes of steam trail away from the crater. In the lower (1 May) image, the thermal anomaly extends farther to the W, suggesting a lava flow. The band combination makes the ice cover of the island appear bright blue-green. Courtesy of NASA Earth Observatory.

The number of daily MODVOLC thermal alerts increased during May 2016 to as many as 35 on 26 May. On many days, more than 10 thermal alerts were issued. The distribution of the alert pixels suggested that an E-W linear feature such as one or more lava flows was responsible for many of the thermal anomalies (figure 2).

Figure (see Caption) Figure 2. MODVOLC thermal alerts for Bristol Island during selected dates in late April and May 2016. Top left: Nine thermal alerts issued during 25-30 April form two linear features trending WNW and WSW. Top right: 59 alerts issued during 11-15 May suggest intensification of heat flow. Lower left: 35 alerts on 26 May are scattered over a wide area. Lower right: 20 alerts issued on 29 May are concentrated in an E-W trending distribution, suggesting one or more flows of some kind as the heat source. Courtesy of HIGP MODVOLC Thermal Alerts System.

A Moderate Resolution Imaging Spectroradiometer (MODIS) satellite image of Bristol Island acquired on 28 May 2016 showed an ash plume from Mt. Sourabaya drifting NE (figure 3). The Buenos Aires VAAC issued the first reports of gas and possible ash plumes on 29 May 2016, noting that they drifted as far as 185 km N, NNE, and SE at an altitude of approximately 1.5 km.

Figure (see Caption) Figure 3. On 28 May 2016, the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA's Terra satellite acquired this natural-color image of an ash plume streaming NE from Bristol Island. The plume casts a shadow on the sea ice below. Most of the white in the image is likely ice, rather than clouds. Courtesy of NASA Earth Observatory.

The Buenos Aires VAAC issued multiple daily ash advisories during 29 May-7 June 2016. They noted that weather clouds mostly prevented satellite observations of Mount Sourabaya during 1-6 June, though a thermal anomaly was detected during 1-2 and 5-7 June. Satellite images from Suomi NPP/VIIRS often showed possible ash plumes mixed with clouds, but revealed distinct plumes on 2 and 4 June (figure 4) drifting E, and on 7 June towards the NE. On 16 June, a diffuse plume of volcanic ash was reported by the Buenos Aires VAAC moving SE at about 1.5 km altitude. MODVOLC thermal alerts continued even more strongly in June than during May. On almost every day, more than ten alerts were recorded, and they continued with a broad E-W distribution similar to that seen during May.

Figure (see Caption) Figure 4. An ash plume can be seen drifting E on 4 June 2016 from Bristol Island in this Suomi NPP/VIIRS image (Corrected Reflectance – True Color). Courtesy of NASA Worldview.

On 16 and 18 July, ash seen in Suomi NPP/VIIRS imagers appeared to be drifting NE, and on 19 July a faint thin ash plume was identified drifting 100 km NE; the persistent thermal anomaly continued to be visible. No further VAAC reports were issued after 21 July. Numerous MODVOLC thermal alerts continued during most days of July, until they stopped abruptly after the 17 alerts issued on 26 July (figure 5). The MIROVA thermal anomaly system captured a strong signal from Bristol Island between late April and late July 2016 (figure 6).

Figure (see Caption) Figure 5. MODVOLC thermal alerts during July 2016 suggest multiple origin points for the substantial thermal anomalies. Top left: the distribution of the 23 alerts issued on 3 July suggests multiple origin points. Top right: two distinct sources are apparent from the 15 alerts issued on 7 July. Lower left: the 30 alerts issued on 13 July are spread over a large E-W area and reflect multiple source points. Lower right: the 17 Alerts on 26 July show NE-SW trending elongate zones of thermal anomalies. Courtesy of HIGP MODVOLC Thermal Alerts System.
Figure (see Caption) Figure 6. A strong thermal anomaly signal is apparent at Bristol Island during April-July 2016 in the MIROVA thermal anomaly data. Both blue and black lines signify eruptive activity. Courtesy of MIROVA.

Two satellite images, from 21 August and 22 September 2016, confirm the presence of new lava fields around the summit of Mount Sourabaya that were created during the April-July 2016 eruption (figure 7).

Figure (see Caption) Figure 7. Satellite imagery of Mount Sourabaya on Bristol Island on 21 August and 22 September 2016 after the eruptive episode of April-July shows evidence of lava flows onto ice and snow surrounding the summit. The upper image is from the Landsat Viewer/EOS Data Analytics annotated by the South Sandwich Islands blog; the lower image is a Landsat 8 image annotated by Cultur Volcan.

Geologic Background. The 9 x 10 km Bristol Island near the southern end of the South Sandwich arc lies across Fortser's Passage from the Southern Thule Islands and forms one of the largest islands of the chain. Largely glacier-covered, it contains a horseshoe-shaped ridge at the interior extending northward from the highest peak, 1100-m-high Mount Darnley. A steep-sided flank cone or lava dome, Havfruen Peak, is located on the east side, and a young crater and fissure are on the west flank. Three large sea stacks lying off Turmoil Point at the western tip of the island may be remnants of an older now-eroded volcanic center. Both summit and flank vents have been active during historical time. The latest eruption, during 1956, originated from the west-flank crater, and deposited cinder over the icecap. The extensive icecap and the difficulty of landing make it the least explored of the South Sandwich Islands.

Information Contacts: NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Worldview (URL: https://worldview.earthdata.nasa.gov/); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php?lang=es); 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/); South Sandwich Islands Volcano Monitoring Blog (URL: http://southsandwichmonitoring.blogspot.com/); Cultur Volcan, Journal d'un volcanophile (URL: https://laculturevolcan.blogspot.com/).


Etna (Italy) — September 2017 Citation iconCite this Report

Etna

Italy

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

All times are local (unless otherwise noted)


Lava flows during May 2016 followed by new fracture zones and major subsidence at the summit craters

Italy's Mount Etna on the island of Sicily has had historically recorded eruptions for the past 3,500 years. Lava flows, explosive eruptions with ash plumes, and lava fountains commonly occur from its major summit crater areas, the North East Crater (NEC), the Voragine-Bocca Nuova complex (VOR-BN), the South East Crater (SEC) (formed in 1978), and the New South East Crater (NSEC) (formed in 2011). The Etna Observatory, which provides weekly reports and special updates on activity, is run by the Catania Branch of Italy's Istituo Nazionale di Geofisica e Vulcanologica (INGV). This report uses information from INGV to provide a detailed summary of events between April 2016 and January 2017.

Summary of April 2016-January 2017 activity. A new eruptive episode at Etna began on 15 May 2016 and included activity around all four major summit cones; Strombolian activity began at NSEC on 15-16 May, from a pit on the E flank of the cone. The following night, thermal webcams suggested Strombolian activity at NEC. This ceased on 18 May when Strombolian activity started at VOR that also produced a large ash plume. Lava then overflowed the W rim of BN and headed W multiple times during the next few days. A different flow emerged from a fracture on the SE side of VOR near SEC on 21 May. Activity from all of the active vents had ended by 26 May. New fracture zones trending N-S and NE-SW, and extensive subsidence within VOR were observed at the summit craters at the end of May after the episode ceased.

Intermittent weak ash emissions during late May and July and intense degassing from several craters were the primary activity until explosive activity at VOR began on 7 August and opened a new vent along the inner wall of the NE rim. Strong subsidence followed at VOR and BN during August and September, creating a single large crater that included both areas. Dense ash emissions from the vent on the upper E flank of NSEC in mid-October and a few modest ash emissions from VOR and NSEC were observed. There was also persistent incandescence from the new vent at VOR and its continued subsidence through early January 2017. After the spike in activity during May 2016, heat flow diminished, but was persistent throughout the period (figure 174).

Figure (see Caption) Figure 174. MIROVA log radiative power thermal anomaly graph of activity at Etna from late May 2016 through early January 2017. A major effusive eruptive event with lava flows and Strombolian activity caused a spike in heat flow during late May 2016, but heat flow was persistent throughout the period. Courtesy of MIROVA.

Activity during March-April 2016. After the major lava fountains and ash plumes of the first week of December 2015 (BGVN 42:05), eruptive activity was lower through March 2016. Sporadic ash emissions and minor incandescence were reported a few times each month. The largest event was an explosion on 23 February 2016; it produced an ash plume that drifted NE and caused ashfall in communities as far as 40 km away.

Continuous degassing accompanied dense ash emissions from the North East Crater (NEC) and the New South East Crater (NSEC) during 31 March-1 April 2016. Winds sent material to the SW, and then changed direction to the N the following day, dispersing pyroclastic material around the crater area. Ash emissions continued to be weak but persistent for the rest of April from NEC and NSEC, while only minor degassing was observed from the Voragine-Bocca Nuova complex (VOR-BN). A new pit crater was observed near the center of BN from the gradual collapse of the crater between 19 February and 15 April 2016.

Activity during May 2016. Although visibility was limited due to weather in early May 2016, discontinuous explosive activity with minor ash emissions was observed over several days from NEC and NSEC near the top of Valle del Bove (a large valley SE of the summit crater area). Weak incandescence from NSEC was detected by the high-resolution webcam at Monte Cagliato for the first time in several months during the night of 16 May, and marked the beginning of a new eruptive episode that lasted until 25 May 2016, involving activity at all four summit crater areas (figure 175).

Figure (see Caption) Figure 175. The four summit craters at Etna shown in a DEM from 2014 created and modified by INGV's Aerogeophysical Laboratory. The black hatched lines outline the rims of the craters. BN = Bocca Nuova, VOR = Voragine; they are delimited by a single crater rim after the explosive activity of December 2015; NEC = North East Crater; SEC = South East Crater with cone of the New South East Crater (NSEC) on its SE flank. Activity from the 17-25 May 2016 episode is shown in red and yellow and discussed in the text. Courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 16/05/2016-22/05/2016, Reporte No. 21/2016).

Explosive activity first observed during the night of 15-16 May 2016 at NSEC came from a pit on the E flank of the cone. The following night, webcams also showed a thermal anomaly at NEC, interpreted by INGV as probable Strombolian activity. At first light on 17 May, intense degassing was observed from NEC which lasted throughout the day and included minor ash emissions. Strong explosions from NEC were heard about 10 km from the crater. Strombolian activity rising tens of meters above the rim was first observed around 2000 UTC. During the night of 17-18 May, intermittent flashes, likely from explosive activity, originated from the pit on the E flank of NSEC.

Continued explosions at NEC during the morning of 18 May produced an ash cloud that drifted ESE. This activity ceased around 1050 UTC, when Strombolian activity began at VOR that rapidly evolved into a lava fountain. The activity also created an ash plume that rose to an altitude of 7 km and drifted due E. The lava fountain continued until about 1430 UTC. Shortly after the Strombolian activity began at VOR (around 1100 UTC), lava overflowed the W rim of BN and headed W towards Monte Nunziata. It traveled for about 2 km and stopped at an elevation of around 2,100 m based on observations from the Bronte thermal webcam. Also at 1100 UTC, a small explosive vent opened at the base of the N side of NEC (Bocca 1 in red, figure 175) that spattered for a few minutes. Around 1530 UTC, an improvement in weather conditions permitted observation of a new lava flow in the Valle del Bove. The flow, fed by a vent at the base of the E side of NEC (Bocca 2 in red, figure 175), headed E towards Monte Simone, and stopped at an elevation of approximately 2,400 m.

By the morning of 19 May, although adverse weather conditions prevented observations, a sudden increase in the amplitude of tremor and loud explosions heard in communities E and S of the volcano suggested another explosive episode at VOR. A dense eruptive cloud drifted E. A new lava flow emerged from the W rim of BN, and headed W on top of the flow from the previous day. It divided into several arms, the longest of which flowed about 1,800 m, near Monte Nunziata, without reaching the nearby highway. Strombolian activity was again observed at VOR beginning around 1900 UTC on 20 May when weather conditions improved.

Beginning around 0140 UTC on 21 May 2016, a rapid escalation of the amplitude of volcanic tremor occurred together with increased explosions from VOR. Around 0200 a small lava flow was observed from a fracture at the base of the SE side of the cone of VOR near the base of SEC (the yellow flow marked on figure 175). The intense explosive activity at VOR generated a plume that drifted S. Tremor amplitude decreased suddenly around 0600. Lava was observed overflowing the W rim of BN around 0700, covering the flows of the previous days. Strombolian activity was again observed from VOR during the night of 21-22 May. Sporadic ash emissions from the pit on the E flank of NSEC during the early morning of 22 May quickly dissipated. That afternoon, renewed Strombolian activity began at NEC which intensified and then ended during the following night (figure 176).

Figure (see Caption) Figure 176. Volcanic activity at Etna during 20-22 May 2016. a) intense explosive activity of 21 May at VOR, taken from the thermal webcam at Monte Cagliato; b) the lava flow from the fracture on the SE side of VOR during the explosive activity of 21 May, photo by Alessandro Lo Piccolo; c) intense degassing on 20 May from the fracture that fed the lava flow shown in (b) the following day, taken from the Piano delle Concazze; d) the overflow from the western edge of BN during 21 May, taken from Bronte's thermal webcam; e) Strombolian activity at VOR taken by the high definition camera of Monte Cagliato at 1845 UTC on 22 May; f) ash emission from the pit on the E flank of the NSEC, taken with the camera at Monte Cagliato on 22 May at 0630 UTC. Courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 16/05/2016-22/05/2016, Reporte No. 21/2016).

A new round of weak Strombolian activity began at VOR around 1900 on 23 May 2016. Activity continued until 1750 on 24 May when explosive activity increased sharply. Vigorous Strombolian activity peaked during the night of 24-25 May. Incandescent material rose a few hundred meters into the air, and mostly fell back into the crater. It was not accompanied by a lava flow or ash plume. Activity began decreasing during the afternoon of 25 May, and ceased sometime during the following night. Both ground-based and aerial observations by INGV personnel on 26 and 27 May confirmed the end of the eruptive episode and documented its effects (figure 177).

Figure (see Caption) Figure 177. The summit area of Etna seen from the north on 27 May 2016 after the eruptive episode of 15-25 May. At the North East Crater (NEC), the black dashed line shows the position of its rim prior to the eruptive phase that started on 15 May. Large areas of the crater rim collapsed on both the N and S sides. The S side of the collapsed NEC rim intersects a fracture zone that forms a graben (yellow arrows) that trends N-S and cuts across the E rim of the VOR. A second graben trends SE from the VOR. Fumarolic activity is visible in both structures. Degassing is also visible from a vent at the bottom of VOR (red arrow within VOR). The NW-SE trending graben that extends between VOR and SEC appears to terminate at the eruptive vent created on 21 May (red arrow between NSEC and SEC). However, slope failure on the N flank of the SEC cone (white arrows) suggests to INGV geologists that the structural zone continues SE towards NSEC. Inset photo is an image of NEC captured with the thermal camera by Sonia Calvari, showing the NEC crater bottom filled with the detritus from the collapse of the southern crater wall. Courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 23/05/2016-29/05/2016, No. 22/2016).

A N-S trending fracture zone about 400 m wide and 1,300 m long was observed extending S beginning at the northern side of NEC, crossing the E rim of the Central Crater (the combined VOR-BN complex), where it changes direction and extends SE toward the SEC (figure 178). A vent at the base of the saddle between SEC and VOR fed weak effusive activity on 21 May. Tens of meters of collapse within the graben contributed to the destruction of the S rim of NEC, significantly changing its shape and filling it with debris.

Figure (see Caption) Figure 178. The summit area of Etna seen from the SE on 27 May 2016. The yellow arrows highlight a new NW-SE trending fracture system that produced a near-symmetrical graben on the E side of the Central Crater (the combined VOR-BN complex). It then veers to the N and joins with another graben (the black arrow) that breaches the rim of the NEC. The dotted black line highlights the portion of collapsed NEC rim during the recent eruptive period. Courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 23/05/2016-29/05/2016, No. 22/2016).

Major subsidence at VOR after the end of the Strombolian activity of 23-26 May 2016 created numerous sub-circular concentric fractures within the crater with a vent degassing at the base (figure 179). The BN area was filled with the eruptive material that had overflowed the W rim (figure 180).

Figure (see Caption) Figure 179. Detail of the Central Crater (CC), comprising the VOR and BN craters at Etna. View is from the NW on 27 May 2016. The concentric subcircular fractures with a degassing vent located at the bottom of the crater (red arrow) formed during collapse immediately after the end of the Strombolian activity at VOR from 23 to 26 May 2016. The yellow arrows (above) show the position of the graben responsible for the collapse of part of the NEC. The white arrows (bottom) highlight the western portion of the N-S oriented fracture zone, which affects NEC, VOR, and BN. Courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 23/05/2016-29/05/2016, No. 22/2016).
Figure (see Caption) Figure 180. View of the summit of Etna from the WSW on 27 May 2016. In the foreground is the Central Crater, consisting of VOR and BN. The two white arrows point to the overflow area of the lava flows from the W edge of BN during 18-21 May. The yellow arrows highlight the main fractures bordering the E side of the crater area, extending from NEC to SEC. The dotted black line highlights the portion of collapsed NEC during the recent eruptive period. The three red arrows highlight the locations of the recent eruptive vents: north of NEC (far left), within the VOR, and at the base of the saddle between the Central Crater and the SEC. Courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 23/05/2016-29/05/2016, No. 22/2016).

Activity during June 2016-January 2017.A weak ash emission from VOR on the morning of 31 May 2016 was the only additional eruptive activity during May. INGV volcanologists making ground observations on 3 June noted about 10 m of subsidence of the lava surface filling BN and continued collapse at the center of VOR. Intense degassing of mostly water vapor occurred from the fracture on the SE side of VOR. Strong degassing continued from all the new fracture zones at the summit during June and July. Ground-based thermal imagery recorded on 16 June indicated temperatures as high as 300°C around the fractures within the Central Crater. A helicopter overflight on 14 July showed few changes in the graben system first documented at the end of May, except for continued collapse near the S rim of NEC. Minor ash emissions resumed at NSEC; they were observed during 10-14, 19-21, and 26-28 July. Explosions were heard from the W side of BN during a visit by INGV scientists on 28 July.

Intense and persistent degassing continued during August 2016 from NEC and from the fractures between NEC and VOR (figure 181). Incandescence was observed within the fractures on 4 August. NSEC produced minor ash emissions again during 4-5 August. Low intensity explosive activity began at VOR on 7 August, but no material was ejected beyond the crater rim. An incandescent vent was observed within the collapsed inner wall of VOR on 10 August (figure 182). Explosive activity and incandescence was intermittent from this vent during 7-22 August. The apparent temperature at the vent as measured by thermal camera was greater than 580°C on 22 August. Weak and episodic ash emissions also occurred from a vent on the upper E side of NSEC on 27 and 29 August. Incandescent degassing continued at the 7 August VOR vent throughout September, along with persistent fumarolic emissions from the fracture zones.

Figure (see Caption) Figure 181. Intense degassing within NEC and along the fractures between NEC and VOR at Etna on 3 August 2016. This view to the N shows the rim of NEC at the top and the new graben that breaches the rim. Photo by B. Behncke, courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 01/08/2016 - 07/08/2016, No. 32/2016).
Figure (see Caption) Figure 182. A new vent opened on 7 August 2016 from the collapse of the inner wall of VOR near its NE rim at Etna. Photo by B. Behncke on 10 August 2016, courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 08/08/2016-14/08/2016, No. 33/2016).

A series of low-frequency seismic events were recorded at the summit on 10 October, some accompanied by explosive sounds. The strongest seismic event produced ash and hot gas that was recorded by two thermal cameras during the early afternoon. The ash rose from the W part of BN about 100 m above the rim and drifted rapidly E. During an inspection on 12 October, INGV scientists noted that subsidence of about 50 m had occurred within the BN, centered near the W crater wall, and was ongoing. They observed the sudden dropping of material along concentric fractures accompanied by reddish ash and modest steam emissions. One of these events exposed an incandescent area within the fresh lava (figure 183).

Figure (see Caption) Figure 183. The bottom of the BN crater at Etna on 12 October 2016 during a collapse within the peak subsidence zone, showing incandescent material under the fresh lava. Photo by B. Behncke, courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 10/10/2016-16/10/2016, No. 42/2016).

Dense ash emissions were produced on 17 October from the 25 November 2015 vent on the upper E flank of the NSEC (figure 184). A diffuse brown ash plume was observed the next day during a field inspection of the area. Intermittent diffuse brown ash emissions were again observed on 6 November. Persistent fumaroles from the vent at VOR and bottom subsidence at BN continued during November where two distinct areas of subsidence (BN-1 and BN-2) were visible (figure 185).

Figure (see Caption) Figure 184. A Digital Elevation Map of the summit crater area at Etna (DEM 2014, Aerogeophysics Laboratory - Section 2 modified) showing the active degassing areas during August-December 2016. The yellow dot shows the position of the vent opened on 7 August 2016 in the upper part of the E wall of the VOR; the red dot indicates the location of the vent opened in November 2015 on the upper E flank of the NSEC, from which minor ash emitted during October and November 2016. Courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 31/10/2016-06/11/2016, No. 45/2016).
Figure (see Caption) Figure 185. An aerial view from the W of the summit crater area of Etna on 13 November 2016 annotated with areas of activity. The Central Crater (CC), highlighted by the dashed yellow line. Inside, the VOR and BN have coalesced; two depressions (BN-1 and BN-2) were undergoing constant, slow subsidence (especially BN-1) with enough heat released to prevent snow buildup. The subsidence of BN-1 and BN-2 began on 10 October 2016. Near the E edge of the VOR, gas emissions continued from the 7 August 2016 vent 'Bocca attiva dal 7 Agosto 2016'. Photo by Piero Berti, courtesy of INGV (Bollettino settimanale sul monitoraggio vulcanico, geochimico e sismico del vulcano Etna, 07/11/2016-13/11/2016, No. 46/2016).

Intermittent, low-intensity incandescence at the VOR vent appeared during the night of 28-29 November 2016. Sporadic, minor ash emissions occurred from the saddle area between SEC and NSEC during 15 December. Incandescence that evening from the VOR vent was also recorded on the webcams. A light coating of ash and a few lithic blocks appeared the next morning in the fresh snow on the flank of the SEC. Modest ash emissions from the same area continued intermittently through the end of December. On 31 December, a diffuse ash plume was also noted from the vent on the upper E flank of NSEC. Sporadic incandescence continued from the VOR vent during early January 2017.

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: Sezione di Catania - Osservatorio Etneo, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/it/); 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/).


Fogo (Cape Verde) — September 2017 Citation iconCite this Report

Fogo

Cape Verde

14.95°N, 24.35°W; summit elev. 2829 m

All times are local (unless otherwise noted)


November 2014-February 2015 eruption destroys two villages, lava displaces over 1000 people

The 25-km-wide island of Fogo in the Cape Verde Islands, 750 km W of Dakar, Senegal, is a single massive stratovolcano with a 9-km-wide summit caldera (Cha Caldera) that is breached to the east. A steep-sided central cone, Pico, rises more than a kilometer above the caldera floor, and is capped by a 500-m-wide, 150-m-deep summit crater; it was apparently almost continuously active from the time of Portuguese settlement in 1500 CE until around 1760. Several lava flows that erupted during the eighteenth and nineteenth centuries reached the eastern coast below the breached caldera rim (BGVN 20:03, figure 1). Lava flows in 1951 and 1995 were contained within the W half of the Cha Caldera, as were the flows from the November 2014-February 2015 eruption (figure 16) described below. Information for this report comes from the Toulouse Volcanic Ash Advisory Center (VAAC), the Observatório Vulcanológico de Cabo Verde (OVCV), and satellite and news data from several sources.

Figure (see Caption) Figure 16. The Advanced Land Imager (ALI) on the Earth-Observing 1 (EO-1) satellite captured this image on 24 December 2014 of the eruption at Fogo that began on 23 November 2014. The top image offers a broad view of the island's most distinctive feature: Cha Caldera. The nine-kilometer wide caldera has a western wall that towers a kilometer above the crater floor. The eastern half of the crater wall is gone, erased by an ancient collapse. The lower image shows a more detailed view of the caldera. The volcanic plume streams from a fissure at the SW base of Pico de Fogo, the island's highest point. Both of the villages destroyed by the eruption, Portela and Bangaeira, were located within the caldera. In late November, lava poured into Portela; by 8 December it had entered Bangaeira. The volcanic plume obscures the remains of the two villages, but the white roofs of a few structures are visible on the upper left side of the image. In addition to the north flow that affected the villages, the 2014 eruption also produced flows that moved S and W. Courtesy of NASA Earth Observatory.

The April-May 1995 eruption produced lava flows from a vent at the SW base of the Pico cone (BGVN 20:05, figure 3) that flowed SW and NW from the vent. They cut off the main access road to the larger villages of Portela and Bangaeira along the NW side of the caldera, but the approximately 1,300 residents from the various communities within the caldera were all safely evacuated, and the villages were spared. Effusive activity produced Strombolian fountains, pyroclastic material, ash plumes, and both pahoehoe and aa lava flows. The lava flows destroyed the small settlement of Boca de Fonte (population 56) near the caldera wall about 2 km W of the eruption center, and reached to within 300 m of Portela village. By the time it was over at the end of May 1995, new lava flows covered about 6.3 km2 of land, and ranged from one to over twenty meters thick.

The most recent eruption at Fogo began with lava flows emerging from a similar fissure vent at the base of Pico on 23 November 2014 (figure 17), and continued through 8 February 2015 according to OVCV; the flows covered about 4 km2 of land. The villages of Portela and Bangaeira, located 4-5 km NW of Pico with a combined population of about 1,000 residents, were not spared during the 2014-15 eruption as they had been in 1995; both villages were largely destroyed (figure 18), although their inhabitants were safely rescued. The eruption began from a fissure near the 1995 vent, but it soon emerged from multiple vents along the fissure with Strombolian activity (figure 19), explosions, lava fountains, and ash emissions.

Figure (see Caption) Figure 17. Lava and gas emerge from a fissure at Fogo on 24 November 2014, one day after the eruption began in this satellite image used by Google Earth. The fissure is located at the SW base of Pico, the cone within the Cha Caldera. Image copyright by DigitalGlobe, courtesy of Google Earth.
Figure (see Caption) Figure 18. The villages of Portela and Bangaeira were destroyed by the lava flows at Fogo during late November 2014-February 2015. This image of a home in Portela trapped in a lava flow was taken between 30 November and 3 December 2014. Photo copyright by Martin Rietze, used with permission.
Figure (see Caption) Figure 19. Strombolian activity at dawn on 30 November 2014 from multiple fissure vents at Fogo. Copyright by Martin Rietze, used with permission.

The lava flows consisted of three primary lobes that traveled NNW, S, and W (BGVN 39:11, figure 8). During the earliest days of the eruption in late November, lava flowed to the NNW destroying much of Portela (figure 20 and 21) and to the S from the main fissure. The flow to the S ceased after 30 November.

Figure (see Caption) Figure 20. Lava advances NNW on the community of Portela at Fogo sometime during 30 November-3 December 2014. Photo copyright by Martin Rietze, used with permission.
Figure (see Caption) Figure 21. A lava flow consumes a house in the village of Portela at Fogo on 30 November 2014. Copyright by Martin Rietze, used with permission.

The main flows continued NNW into the first week of December; they destroyed the remaining structures in Portela and caused extensive damage in Bangaeira and at the Parque Natural de Fogo headquarters (figures 22 and 23). A third lobe flowed to the W of the fissure during the second half of December, reaching the base of the 1-km-high caldera rim where it damaged farms and infrastructure in the small village of Ilhéu de Losna (see figure 16). The lava had ceased advancing by early January.

Figure (see Caption) Figure 22. Lava flow on 1 December 2014 at Fogo emerges from a fissure vent. Photo copyright by Martin Rietze, used with permission.
Figure (see Caption) Figure 23. Advancing lava flow with blocky (aa) texture at Fogo during 30 November-3 December 2014. Photo copyright by Martin Rietze, used with permission.

The MODVOLC thermal alert system issued eight thermal alerts from the lava flows (figure 24) on 23 November 2014. Tens of alerts were reported almost daily through 19 December, with a peak of 46 alerts on 30 November. For the rest of December, as many as 10 alerts a day were recorded. By January 2015, they became more intermittent, with no more than three alerts issued in any day, and they occurred on only 11 days of the month. The final two thermal alerts were recorded on 7 February 2015.

Figure (see Caption) Figure 24. A cascade of lava flows from a fissure vent at Fogo during 30 November-3 December 2014. Photo copyright by Martin Rietze, used with permission.

Ash emissions from the fissure vents were intermittent throughout the eruption (figures 25). The first major plume on 24 November 2014 was reported by the Toulouse VAAC as consisting largely of SO2, with very little ash. It rose to 9.1 km altitude, drifted 220 km NW, and caused minor ashfall on the flanks of the volcano. After the initial plume of mostly SO2, ash emissions from the vent were generally below 3.9 km altitude and limited to the immediate area of the island (figure 26).

Figure (see Caption) Figure 25. Residents flee with their belongings as ash emissions and lava flows emerge from multiple vents on the SW flank of Pico cone at Fogo during the last week of November 2014. Photo by Joao Relvas/Lusa, courtesy of The Observador, published on 30 November 2014.
Figure (see Caption) Figure 26. Ash explosion and incandescent material erupted from a fissure vent during 30 November-3 December 2014. Photo copyright by Martin Rietze, used with permission.

Ash was reported rising to 2 km above the summit (4.8 km altitude) on 2 December (figure 27), and ashfall was reported near San Felipe (17 km SW). Ash and SO2 emissions decreased in mid-December; the next plume was reported on 21 December rising 800 m above the summit. Additional plumes during 30 December-2 January rose 400-900 m above the cone and occasionally sent tephra up to 40 m away. Several explosions of gas-and-ash plumes during 8-12 January produced plumes that rose up to 2 km above the summit and drifted E or SE. The largest plume, on 12 January, was very dense and dark-gray, it rose 2 km and drifted E; tephra was also ejected 50 m above the crater and was observed by people in San Felipe and other parts of the island.

Figure (see Caption) Figure 27. Ash emission on 2 December 2014 from the fissure vent at Fogo. The plume was reported at 2 km above the summit of Pico. Photograph copyright by Martin Rietze, used with permission.

Satellite data on SO2 flux from Fogo corroborated the VAAC reports of the high SO2 content in the emissions, especially during the first two weeks of the eruption when Dobson Unit (DU) values greater than 2 were recorded several times, and the plume areas covered several hundred thousand square kilometers (figure 28).

Figure (see Caption) Figure 28. Sulfur dioxide plumes measured with the Aura Instrument on the OMI satellite show substantial amounts of SO2 released from Fogo during the eruption of November 2014-February 2015. Top Left: The SO2 plume captured on 24 November covered over 325,000 km2 and registered over 40 Dobson Units (DU), a measure of the molecular density of SO2 in the atmosphere; Top Right: the plume on 26 November covered almost 700,000 km2 and drifted N and E; Lower Left: on 1 December the 590,000 km2 plume drifted in multiple directions from the vent; Lower Right: on 3 December the large plume drifted NE and registered at almost 20 DU. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. The island of Fogo consists of a single massive stratovolcano that is the most prominent of the Cape Verde Islands. The roughly circular 25-km-wide island is truncated by a large 9-km-wide caldera that is breached to the east and has a headwall 1 km high. The caldera is located asymmetrically NE of the center of the island and was formed as a result of massive lateral collapse of the ancestral Monte Armarelo edifice. A very youthful steep-sided central cone, Pico, rises more than 1 km above the caldera floor to about 100 m above the caldera rim, forming the 2829 m high point of the island. Pico, which is capped by a 500-m-wide, 150-m-deep summit crater, was apparently in almost continuous activity from the time of Portuguese settlement in 1500 CE until around 1760. Later historical lava flows, some from vents on the caldera floor, reached the eastern coast below the breached caldera.

Information Contacts: Toulouse Volcanic Ash Advisory Center (VAAC), Météo-France, 42 Avenue Gaspard Coriolis, F-31057 Toulouse cedex, France (URL: http://www.meteo.fr/vaac/); Observatório Vulcanológico de Cabo Verde (OVCV), Departamento de Ciência e Tecnologia, Universidade de Cabo Verde (Uni-CV), Campus de Palmarejo, Praia, Cape Verde (URL: https://www.facebook.com/pages/Observatorio-Vulcanologico-de-Cabo-Verde-OVCV/175875102444250); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Google Earth (URL: https://www.google.com/earth/); The Observador (URL: http://observador.pt/2014/11/30/erupcoes-vulcanicas-da-ilha-fogo-evoluem-para-estado-critico/); Martin Rietze, Photographer (URL: http://www.mrietze.com/web13/Fogo_f14.htm).


Krakatau (Indonesia) — September 2017 Citation iconCite this Report

Krakatau

Indonesia

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

All times are local (unless otherwise noted)


Eruption during 17-19 February 2017 sends large lava flow down the SE flank

The most recent reported eruptive activity from the Anak Krakatau cone was a pilot report of an ash plume on 31 March 2014 (BGVN 40:08). Monitoring reports by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) from January 2014 through July 2015 only noted seismicity and fumarolic emissions.

The only indication of possible eruptive activity in the second half of 2015 through 2016 reported by PVMBG was a Volcano Observatory Notice for Aviation (VONA) on 20 June. The seismograph at the Anak Krakatau Volcano Observatory detected an eruption at 0551 local time (2251 UTC), but the eruption was not observed visually because of cloudy weather. There had been a swarm of volcanic earthquakes about one day earlier, and seismicity had significantly increased 3 hours before the eruption. After the eruption, seismicity gradually decreased. Although thermal anomalies were frequently recorded in 2016 (figure 36, bottom), they may have been a result of strong hot fumaroles at the summit dome; no PVMBG or tourist reports indicated active lava flows or ash plumes.

Figure (see Caption) Figure 36. Thermal anomalies at Krakatau identified by the MIROVA system using MODIS data for the year ending 19 February 2017. The record indicates regular thermal signatures, which may be a result of strong fumarolic activity in the summit crater. Courtesy of MIROVA.

The PVMBG reported that seismicity was dominated by shallow volcanic earthquakes in February 2017. In a Volcano Observatory Notice for Aviation (VONA), the aviation color code was reported to be raised to Orange. Emission earthquakes increased beginning on 17 February and gradually formed continuous tremor. At 1535 on 17 February 2017 at 1535 infrared MODIS data recorded by MODVOLC measured a 2-pixel thermal alert from the Aqua satellite, and on 18 February 2017 at 0650 a 2-pixel thermal alert was measured from the Terra satellite. Satellite thermal anomalies identified by the MIROVA system showed a strong sequence of anomalies around this same time (figure 36, top). Harmonic tremor began to be recorded at 1810 on 19 February. Almost an hour later, at 1904, Strombolian explosions ejected incandescent material 200 m high.

O.L. Andersen, a professional photographer, visited Anak Krakatau 25-26 February 2017. The eruption earlier in the month had resulted in a new lava flow on the SE flank (figure 37) where the September 2012 lava flow was located. He observed that "The new layer of lava-flow is black, compared to the red color of the 2012 lava flow. The lava flow has cooled down since the material was deposited. Fresh volcanic blocks were also seen distributed on the SE, S, E flank of Krakatau." No eruptions of ash were observed by Andersen, but gas emissions were present. Further, Andersen noted "After having studied aerial views of the crater area (figure 38), it seems that the source vent of the new lava-flow, is the same vent (main, central vent) that was involved in the 2012 eruption. On the top of the vent, it now seems to be a lava-dome...."

Figure (see Caption) Figure 37. The new lava flow on Anak Krakatau of February 2017 shows up as black material on top of the more reddish colored lava from the September 2012 event. The flow came from the new vent at the summit. Copyrighted image courtesy of O.L. Andersen (used with permission).
Figure (see Caption) Figure 38. Aerial view of the summit of Anak Krakatau taken looking E on 25 February 2017. The new lava shows as a black flow from the summit toward the upper right into the ocean. The northern vent is on the crater rim left of the center of the photograph. Copyrighted image courtesy of O.L. Andersen (used with permission).

A comparison of photos from October 2015 and February 2017 composed by Andersen showed the morphological changes during that time, including the new dome and lava flows (figure 39). Incandescence was obvious at night (figure 40) and from aerial observations of the lava dome Andersen noted that the area with incandescence was small, and that "the lava dome did not appear to be overly active." Andersen observed further that the "main crater and summit area today seem to be of a more complex and dynamic character than it was before the eruption of September 2012. From footage of 2010/2011 the main crater was seen to be broad and fairly deep. Now the main crater is filled with material, with two lava flows originating from this vent running down on the SW and E flanks. On the northern side of the summit an eruption vent is also clearly observed...."

Figure (see Caption) Figure 39. A comparison of the Anak Krakatau summit area of 26 February 2017 and 11 October 2015 taken looking west. Note the new dome in the center of the 2017 photo and the new lava that came from the vent and flowed down the SE slope of the volcano. Copyrighted image courtesy of O.L. Andersen (used with permission).
Figure (see Caption) Figure 40. Incandescence from Anak Krakatau on the evening of 25 February 2017. Copyrighted image courtesy of O.L. Andersen (used with permission).

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: Øystein Lund Andersen (URL: http://www.oysteinlundandersen.com/krakatau-volcano/visit-to-anak-krakatau-volcano-february-2017/); Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); 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/).


Langila (Papua New Guinea) — September 2017 Citation iconCite this Report

Langila

Papua New Guinea

5.525°S, 148.42°E; summit elev. 1330 m

All times are local (unless otherwise noted)


Eruption continues, intensifying from mid-December 2016 through July 2017

Eruptive activity at Langila was intermittent during 2016, with ash plumes seen during April-May and November-December (BGVN 42:01); thermal anomalies were somewhat more commonly detected, but were also intermittent. No reports were available from the Rabaul Volcano Observatory during January-July 2017, but volcanic ash warnings were issued by the Darwin Volcanic Ash Advisory Centre (VAAC). Thermal anomaly data acquired by satellite-based MODIS instruments showed a strong increase in activity beginning in mid-December 2016 that was ongoing as of early August 2017.

Ash plumes were reported frequently during the first half of 2017 except during March and early April. The plumes rose to altitudes between 1.8 and 3 km (table 4). The aviation color code has remained at Orange (third highest of a four-step universal volcanic ash alert level system for aviation) throughout 2016 and through July 2017.

Table 4. Ash plumes from Langila reported during January-June 2017. Observations are based on analyses of satellite imagery and wind data; dates are based on local time. Courtesy of the Darwin VAAC.

Date Max. Plume Altitude (km) Drift
02 Jan 2017 2.1 NE
05 Jan 2017 2.4 45 km W
12-13, 15 Jan 2017 2.1 ESE and SE
25-27 Jan 2017 1.8-3 NW and N
17-18 Feb 2017 1.8 SE
24 Feb 2017 2.4 N
23-25 Apr 2017 2.1 55 km S and SE
26 Apr 2017 2.1 E and NE
02 May 2017 2.1 E and NE
10-14 May 2017 1.8-2.4 N, NW, and S
19 May 2017 4.6 ~170 km WSW
19-20 May 2017 1.8 N and NNW
23 May 2017 2.1, 3 NW, SW
24-27 May 2017 2.1-3 75-85 km W and NW
01 Jun 2017 1.8 N and NW
07 Jun 2017 2.1 45 km NW
12 Jun 2017 1.8 WNW
20 Jun 2017 2.1 NW
21 Jun 2017 2.1 95 km NW

Thermal alerts, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, were identified often during December 2016 through June 2017. The MIROVA volcano hotspot detection system, also based on analysis of MODIS data, detected occasional anomalies from August 2016 through late December 2016 (BGVN 42:01), followed by more continuous anomalies through late July 2017 (figure 6). The most intense anomalies over this time period occurred from mid-April to early May 2017.

Figure (see Caption) Figure 6. Plot of MIROVA thermal anomaly MODIS data for the year ending on 8 August 2017. Courtesy of MIROVA.

Geologic Background. Langila, one of the most active volcanoes of New Britain, consists of a group of four small overlapping composite basaltic-andesitic cones on the lower eastern flank of the extinct Talawe volcano. Talawe is the highest volcano in the Cape Gloucester area of NW New Britain. A rectangular, 2.5-km-long crater is breached widely to the SE; Langila volcano was constructed NE of the breached crater of Talawe. An extensive lava field reaches the coast on the north and NE sides of Langila. Frequent mild-to-moderate explosive eruptions, sometimes accompanied by lava flows, have been recorded since the 19th century from three active craters at the summit of Langila. The youngest and smallest crater (no. 3 crater) was formed in 1960 and has a diameter of 150 m.

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


Masaya (Nicaragua) — September 2017 Citation iconCite this Report

Masaya

Nicaragua

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

All times are local (unless otherwise noted)


Persistent lava lake and gas plume activity, with intermittent ash emission, through mid-July 2017

Masaya volcano near the Pacific Ocean in Nicaragua (figure 52) is one of the most active volcanos in that country. The period from October 2015 through August 2016 saw the re-emergence of the lava lake, increased seismic frequency and amplitude, intermittent explosive activity, and continued strong thermal anomalies from satellite and ground based sources as a result of the newly active lava lake. (BGVN 41:08). Thermal satellite data analyzed by MIROVA measured moderate volcanic radiative power beginning January 2016 and continuing regularly through August 2016. The Instituto Nicareguense de Estudios Territoriales (INETER), Sistema Nacional para la Prevencion, Mitigacion y Atencion de Desastres (SINAPRED), and the Washington Volcanic Ash Advisory Center (VAAC) monitor the volcano's activity and provide regular reports.

Figure (see Caption) Figure 52. Maps and aerial photo of the Masaya complex. (a) Regional location map showing of Masaya. (b) Map showing the Las Sierras Caldera enclosing the Masaya caldera, which in turn encloses the recent vents (black dots); distances to major towns (circles) and cities are given. (c) Map of active crater area showing structural features, such as eruptive fissures (dashed lines), pit crater edges (filled triangles),and explosion crater edges (open triangles); lava flows and lakes (shaded) and tephra cover (blank) are also shown including dates of eruption (e.g. L1772 is the 1772 flow and F1906 is the fissure that erupted gas in 1906). (d) Aerial photo of the same area as the map in (c). From Rymer and others (1998).

Ash and steam emissions have been reported by the Washington VAAC from satellite data from August 2016 through mid-July 2017, the latest on 13 May 2017 when both satellite images showed and a pilot observed a W-drifting ash emission from Masaya. Plumes with possible ash content were noted on 15 August, 28 August, and 3 November 2016. Plumes identified on 5 and 21 January 2017 were stated to have minor ash content. Monthly reports from INETER consistently noted ongoing gas emissions, lava lake activity, and variable seismicity.

Since August 2016, thermal anomalies recorded by MIROVA seemed nearly constant in power level and regularity until about May 2017, at which time both seemed to decrease slightly (figure 53). Since mid-May 2017, MODIS thermal satellite data processed by MODVOLC measured thermal alerts have decreased from nearly daily in July 2016 to 4-6/month through July 2017.

Figure (see Caption) Figure 53. Thermal anomaly data identified by the MIROVA system at Masaya for the year ending 11 July 2017. Courtesy of MIROVA.

INETER reported that from 1 to 5 May 2017 fieldwork was conducted with scientists from the University of McGill (Canada) and the Volcanological and Seismological Observatory of Costa Rica (OVSICORI). Measurements of sulfur dioxide (SO2) in the plume emitted by the Santiago crater were carried out using the DOAS Mobile technique, and samples of hydrogen sulfide (H2S), hydrogen bromide (HBr) and bromine chloride (BrCl) were collected to be analyzed by ion chromatography at McGill (figures 54 and 55).

Figure (see Caption) Figure 54. Scientists from the University of McGill and OVSICORI installed different equipment for gas measurements near the Santiago crater at Masaya during 1-5 May 2017. Courtesy of INETER (Boletín mensual Sismos y Volcanes de Nicaragua. Mayo, 2017).
Figure (see Caption) Figure 55. Drones were used by University of McGill and OVSICORI scientists to measure sulfur dioxide (SO2) gases at the altitude of the gas plume at Masaya during 1-5 May 2017. Courtesy of INETER (Boletín mensual Sismos y Volcanes de Nicaragua. Mayo, 2017).

During the INETER field monitoring that took place on 22 May 2017, strong convection of the lake was observed, as were landslides on almost all of the walls. Fumaroles were seen that are possibly not new, but were active due to recent rainfall. The landslides on the W wall of the crater have been occurring since the end of February (figure 56). They are believed by INETER to be caused by undercutting of the walls by lava lake convection (figure 57).

Figure (see Caption) Figure 56. Collapse on the W wall of Santiago crater at Masaya reported by Park rangers on 15 May 2017. Courtesy of INETER (Boletín mensual Sismos y Volcanes de Nicaragua. Mayo, 2017).
Figure (see Caption) Figure 57. Lava lake in Santiago crater of Masaya in May 2017. Courtesy of INETER (Boletín mensual Sismos y Volcanes de Nicaragua. Mayo, 2017).

References. Rymer, H., van Wyk de Vries, B., Stix, J., and Williams-Jones, G., 1998, Pit crater structure and processes governing persistent activity at Masaya Volcano, Nicaragua. Bull. Volcanol., v. 59, pp. 345-355.

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: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://webserver2.ineter.gob.ni/vol/dep-vol.html); 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/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Sistema Nacional para la Prevencion, Mitigacion y Atencion de Desastres, (SINAPRED), Edificio SINAPRED, Rotonda Comandante Hugo Chávez 50 metros al Norte, frente a la Avenida Bolívar, Managua, Nicaragua (URL: http://www.sinapred.gob.ni/).


Popocatepetl (Mexico) — September 2017 Citation iconCite this Report

Popocatepetl

Mexico

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

All times are local (unless otherwise noted)


Ongoing steam, gas, ash emissions, and lava dome growth and destruction, July 2016-July 2017

Frequent historical eruptions have occurred since pre-Columbian time at México's Popocatépetl. More recently, activity picked up in the mid-1990s after about 50 years of quiescence. The current eruption, which has been ongoing since January 2005, has included frequent ash plumes rising generally 1-4 km above the 5.4-km-elevation summit, and numerous episodes of lava-dome growth and destruction within the 500-m-wide summit caldera. Multiple emissions of steam and gas occur daily, many contain small amounts of ash. Larger, more explosive events that generate ashfall in neighboring communities usually occur every month or two. Information about Popocatépetl comes from daily reports provided by México's Centro Nacional de Prevención de Desastres (CENAPRED). Many ash emissions are also reported by the Washington Volcanic Ash Advisory Center (VAAC). Satellite visible and thermal imagery and SO2 data also provide important observations. Activity through June 2016 was typical of the ongoing eruption with near-constant emissions of water vapor, gas, and ash, and at least two episodes of dome growth and destruction (BGVN 42:07). This report covers similar activity through July 2017.

Activity at Popocatépetl during July 2016-July 2017 was typical of the ongoing eruption since 2005. Near constant steam-and-gas emissions often contained minor amounts of ash. Explosions with ash plumes occurred several times a week during most months. Incandescence at the summit was usually visible on clear nights; nighttime explosions revealed incandescent blocks travelling 100 m or more down the flanks. Large ash explosions on 25 and 26 November 2016 sent ash plumes to 11.5 and 10.9 km altitude, respectively. Ashfall was reported from communities within about 35 km on five different occasions. Thermal activity slowly increased during 2016 to high levels indicative of dome growth during December 2016 and January 2017; they diminished early in 2017 and then fluctuated through July 2017. Sulfur dioxide plumes were persistent in satellite data with plume densities generally exceeding two Dobson Units (DU) several times each month.

Activity during July-September 2016. Intermittent activity continued during July 2016. Tens of daily emissions of gas and steam were reported during the first and last weeks of the month; explosions with ash plumes also generally occurred daily during those weeks, and incandescence was visible on clear nights. The Washington VAAC reported ash emissions observed on 3 July at 7.9 km altitude drifting W, 2.5 km above the summit. Explosions on 4 July produced ash plumes that rose to 8.5 km altitude, just over 3 km above the crater and drifted WSW. Ashfall was reported in Atlatlahucan (30 km WSW) and Tepetlixpa (20 km W). Continuous ash emissions rising to just under 6 km altitude were seen in satellite imagery on 10 July extending almost 40 km W from the summit. Multiple daily explosions occurred during 24-26 July (figure 84). A small cloud of volcanic ash was centered about 35 km W of the summit early on 25 July at 5.8 km altitude. Later in the day, another plume was observed at 7 km altitude drifting WNW and then WSW before dissipating. Satellite imagery confirmed an ash emission on 30 July that rose to 6.7 km altitude and drifted W-WSW. MODVOLC thermal alerts were issued on 3, 10 (2) and 27 July. Small SO2 plumes were recorded daily by the Aura instrument on the OMI satellite. Most measured around two Dobson Units (DU) with an area of about 100,000 km2.

Figure (see Caption) Figure 84. An ash plume at Popocatépetl drifts W from the summit on 25 July 2016 as captured by the ALTZOMONI CENAPRED webcam located about 10 km N of the volcano. Courtesy of CENAPRED.

Tens of daily emissions were common during August 2016, some of which contained minor amounts of ash. Six landslides were detected by the seismic network on 11 August (figure 85). The two largest had volumes of 440 and 220 m3. The Washington VAAC reported an ash plume moving NW at 7.3 km altitude just after midnight on 1 August, extending about 35 km from the summit. A short while later, continuous emissions were reported extending up to 75 km W at 6.1 km altitude. By 0910 UTC, they extended 220 km WNW at 7.3 km altitude. The edge of the plume farthest from the summit had reached close to 500 km W by 1945 UTC when it was last observed. The webcam captured an emission on 11 August but it was not visible in satellite imagery due to weather clouds. An explosion on 12 August generated an ash plume that rose 2.5 km above the 5.4-km-high summit crater and drifted WNW, causing ashfall in Ozumba (18 km W) and Atlautla (16 km W). An explosion at 0034 on 13 August ejected incandescent material onto the flanks. An ash emission was seen in satellite imagery at 8.2 km altitude about 35 km W of the summit later in the morning. Another ash emission was observed with the webcam midday on 15 August that produced an ash plume that rose to 8.5 km altitude and drifted WSW. An ash plume on 21 August drifted W at 6.1 km altitude, and one on 28 August was observed in satellite imagery moving NNW below 7.3 km altitude. Two explosions on 27 August at 1505 and 1537, and one at 0559 on 28 August sent incandescent fragments down the flanks.

Figure (see Caption) Figure 85. A landslide on 11 August 2016 at Popocatépetl was captured by the Tlamacas CENAPRED Webcam located about 5 km N of the summit. Courtesy of CENAPRED.

MODVOLC thermal alerts were issued on 1 (4), 3, 4, 11 (2), 13, and 29 August 2016. SO2 plumes were also captured daily by the Aura Instrument on the OMI satellite, with similar values to those recorded during July. During an overflight of Popocatépetl on 30 August 2016 CENAPRED scientists confirmed that explosions during 27-28 August had destroyed lava dome 69 (first identified on 1 August). The crater which had hosted the dome was 300 m in diameter and 30 m deep (figure 86).

Figure (see Caption) Figure 86. An overflight of Popocatépetl on 30 August 2016 confirmed that explosions during 27-28 August had destroyed lava dome 69 (first identified on 1 August). The crater which had hosted the dome was 300 m in diameter and 30 m deep. Courtesy of CENAPRED.

Only one MODVOLC thermal alert was reported on 14 September 2016. SO2 emissions continued at similar levels to the previous months. Tens of daily steam-and-gas emissions were recorded and crater incandescence was visible on clear nights. An explosion on 8 September produced an ash plume that rose 1.5 km above the crater. On 11 September, an explosion generated a plume that rose 1 km, and an explosion that night ejected incandescent material onto the flanks. CENAPRED reported two volcanic ash emissions on 14 September that rose to 7.3 km. Weather clouds prevented satellite observations of the first, but the second one was observed extending 10 km W of the summit, and reached about 50 km before dissipating. Minor amounts of volcanic ash and steam on 23 September extended NW about 30 km from the summit at 5.5 km altitude. The Mexico City Meteorological Weather Office (MWO) reported volcanic ash at 7.3 km altitude on 29 September, but it was not observed in satellite imagery due to weather clouds.

Activity during October-December 2016. An increase in thermal activity was responsible for ten MODVOLC thermal alerts on 4, 7, 14, 16 (2), 20, 23, 27, 28, and 30 October 2016. Although near-constant steam-and-gas emissions continued, some with minor amounts of ash, there was only one observation of an ash plume from the Washington VAAC, on 28 October at 6.4 km altitude drifting SW. Sulfur dioxide emissions appeared to decrease in the Aura satellite data, although there were values measured over two DU at least four days of the month. Fewer ash emissions were reported during November 2016 as well, but ten MODVOLC thermal alerts were reported on 5, 14, 24, 25, 26 (2), 28, and 30 (3) November.

Ash emissions increased significantly during the last week of November. An ash plume at 5.5 km altitude was visible 55 km E of the summit on 24 November. A larger emission on 25 November was observed at 9.1 km altitude towering above the summit and drifting N (figure 87) with additional ash emissions at 7.3 km altitude drifting SE. Ashfall was reported from this event in areas downwind, including in the municipalities of Atlixco (25 km SE), Tochimilco (15 km SSE), and San Pedro Benito Juárez (12 km SE). Emissions were observed as high as 11.5 km altitude drifting NE later in the day; they continued drifting ENE at 7.9 km into the next day before dissipating 250 km from the summit. A new ash emission on 26 November rose to 10.9 km altitude. It was visible 300 km S of the summit while a second ash cloud was centered 150 km S at 5.2 km altitude. Later in the day, an ash emission was observed at 6.7 km drifting SW.

Figure (see Caption) Figure 87. An ash plume at Popocatépetl rises toward 9.1 km altitude on 25 November 2016 as viewed from CENAPRED'S Altzomoni WEBCAM, located about 10 km N of the summit. Courtesy of CENAPRED.

During 28-29 November 2016 there was another pulse of activity with 48 detected emissions. Beginning at 0559 on 28 November, water vapor, gas, and ash emissions became constant, rising as high as 1.5 km above the crater rim and drifting NE. Incandescent fragments were ejected 300-800 m from the crater, mainly onto the NE flank during the next night (figure 88). Ash fell in Atlixco, Chiautzingo (25 km NE), Domingo Arenas (22 km NE), Huejotzingo (27 km NE), Juan C. Bonilla (33 km NE), San Andrés Calpan (18 km NE), and San Martín Texmelucan (Puebla state, 35 km NNE), and in San Miguel (Tlaxcala state). Plumes from these emissions were reported on 29 November at 7.3 km altitude, and they drifted as far as 170 km NE; remnant ash was observed over the Gulf of Mexico on 30 November. Emission intensity increased again on 30 November and a new continuous plume at 6.4 km altitude extended 370 km NE before dissipating. At 1500 UTC on 30 November, a second higher plume was reported by the Washington VAAC at 9.3 km altitude centered 400 km NE of the summit. The continuous emissions became intermittent on 1 December; the last of the emissions dissipated about 200 km NE of the summit. A short puff noted on the webcam late on 1 December was the last VAAC report for 2016.

Figure (see Caption) Figure 88. Incandescent fragments were ejected 300-800 m onto the NE flank of Popocatépetl on 29 November 2016, as seen from the Tlamacas webcam located about 5 km N of the volcano. Courtesy of CENAPRED.

While ash emissions decreased during December 2016, steam-and-gas emissions continued, and thermal activity increased. MODVOLC alerts were reported 24 times on 17 different days. More substantial SO2 plumes than seen in previous months were also captured by the Aura satellite instrument on 8 and 31 December (figure 89). A new lava dome (71) first detected by CENAPRED on 29 and 30 November had almost completely filled the internal crater by 12 December (figure 90), reaching 280 m in diameter and 50 m thick. The volume of the dome was estimated to be about 3 million m3.

Figure (see Caption) Figure 89. The Aura Instrument on the OMI satellite captured substantial SO2 plumes from Popocatépetl on 8 (top) and 31 (bottom) December 2016. The plume on 8 December drifted NE for several hundred kilometers, and had a maximum DU (Dobson Unit) value of 6.02. The plume on 31 December drifted N and then NE a similar distance and recorded a DU value of 4.91. Courtesy of NASA Goddard Space Flight Center.
Figure (see Caption) Figure 90. A new lava dome was photographed at the summit of Popocatépetl during an overflight on 12 December 2016. Courtesy of CENAPRED.

Activity during January-April 2017. Low-intensity steam-and-gas emissions continued during January 2017; incandescence was regularly observed at the summit. During January, only one emission was reported by the Washington VAAC, on 23 January at 7.6 km altitude drifting NW. They noted that the satellite imagery indicated the emission was mostly gas and water vapor with minor amounts of ash. Thermal activity continued to increase in January 2017 with 35 alerts reported on 26 days of the month. The increase in thermal activity was also visible in the MIROVA log radiative power information plotted from the MODIS thermal anomaly data (figure 91). SO2 plumes were also notable through 18 January, after which they decreased in both size and density in satellite data.

Figure (see Caption) Figure 91. MIROVA log radiative power data for Popocatépetl for the 12 months leading up to 4 August 2017. The increase in thermal activity beginning in late November 2016 corresponds to observations by CENAPRED of the growth of a new lava dome at the summit. Courtesy of MIROVA.

Ash emissions were reported on three days during February 2017. A plume on 7 February rose to 5.8 km altitude and drifted W, dissipating quickly. A plume on 12 February was reported at 6.1 km altitude drifting 10 km N of the summit. An ash emission was recorded on the CENAPRED webcam on 15 February (figure 92); it was seen in satellite imagery at 6.7 km altitude drifting NE, and dissipated after about six hours. Thermal activity decreased during February relative to January. MODVOLC only reported 16 thermal alerts on 11 days of the month.

Figure (see Caption) Figure 92. An ash emission from Popocatépetl on 15 February 2017 was later observed in satellite imagery at 6.7 km altitude drifting NE. Image taken by the Altzomoni webcam, located about 10 km N of the volcano. Courtesy of CENAPRED.

Continued steam-and-gas emissions during March 2017 were accompanied by a few ash-bearing explosions. The webcam captured an ash emission on 8 March that the Washington VAAC observed in satellite imagery drifting N at 5.8 km altitude. Another emission late on 11 March rose to 6.1 km and drifted E; it contained mostly gas with only small amounts of ash. Late on 28 March, an ash cloud was observed in satellite imagery centered about 50 km ENE of the summit at 5.8 km altitude. Thermal activity continued to decrease with only ten MODVOLC thermal alerts issued on six different days during March.

Thermal alerts were fewer still during April 2017; one appeared on 6 April, and then a cluster of six were reported during 24-30 April. Ash emissions were reported by the Washington VAAC on 16, 20, 24, and 25 April. Constant emissions were seen by the webcam on 16 April; they likely contained ash, and were estimated to be at 6.1 km altitude. A small puff of ash was seen in satellite imagery on 20 April drifting S to about 35 km at the same altitude. Multiple emissions of ash mixed with steam and gas were observed in satellite imagery on 24 April moving SE at 5.6 km altitude. Constant steam-and-gas emissions continued throughout the month, with incandescence visible on clear nights. Tephra from explosions on 26 and 27 April was ejected 100 m NE of the crater.

Activity during May-July 2017. Thermal activity increased somewhat during May 2017. Seventeen MODVOLC alerts were reported on 13 different days. SO2 emissions with DU values greater than two occurred eight times during the month. Low intensity explosions with water vapor, gas, and ash emissions occurred daily throughout the month. On 18 May, the Washington VAAC reported an ash plume at 7.3 km altitude drifting N, and they observed a bright hotspot in shortwave imagery. Multiple emissions were later observed, with plumes rising to 7.6 km, moving NNE 70 km from the summit. A small puff of ash was seen in satellite imagery on 21 May at 7 km altitude approximately 25 km from the summit moving N. The leading edge of a new emission was observed the next day about 45 km SSW of the summit at 6.1 km altitude. An ash emission was observed on the CENAPRED webcam on 30 May, but weather clouds obscured any satellite observations.

MODVOLC thermal alerts were reported on 6, 16, 17, 18(3) and 21 June 2017. Observers noted material being ejected 200 m from the crater on 3 June. Cloud cover obscured satellite and webcam views of a reported ash plume on 12 June. A small ash emission was reported on 13 June 16 km W of the summit at 7.0 km altitude.

A series of ash emissions were reported by the Washington VAAC almost daily during 2-11 July 2017. A social media post by CENAPRED and a webcam image showed an ash emission (figure 93) on 2 July. It was observed by the Washington VAAC in satellite imagery moving SW at 6.7 km altitude. Minor ashfall on 2 July was also noted in Ozumba (18 km W), Amecameca (19 km NW), Tlalmanalco (26 km NW), Chalco (38 km NW), Ayapango (22 km NW), Tenango del Aire (28 km NW), and San Pedro Nexapa (14 km NW). An emission on 3 July was confirmed in visible satellite imagery drifting WNW at 6.7 km altitude. On 4 July, a plume was observed in satellite imagery 25 km NE of the summit at 7.6 km altitude. An ash emission observed in the webcam early on 6 July was not visible in satellite imagery due to weather clouds, but a larger emission that evening was spotted with difficulty at 7.6 km altitude, in spite of the weather clouds. CENAPRED reported that the plume was clearly visible nearly 2 km above the summit. The next day, clouds obscured the summit from the webcam, but an ash emission was clearly visible in satellite imagery at 7.6 km altitude moving NW. The webcam recorded additional emissions on 9 and 11 July; they were obscured from satellite images by weather clouds. A plume of mostly gas and steam with a small amount of ash near the summit extended 55 km W of the summit on 31 July at 6.4 km altitude.

Figure (see Caption) Figure 93. An ash emission at Popocatépetl on 2 July 2017 as seen from the Altzomoni webcam, 10 km N of the volcano. Courtesy of CENAPRED.

MODVOLC thermal alerts were reported on 13-15, 21, 23 (2) and 28 July. Sulfur dioxide plumes with densities between one and two Dobson Units were captured by the Aura Instrument on the OMI satellite almost every day of the month.

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: Centro Nacional de Prevención de Desastres (CENAPRED), Av. Delfín Madrigal No.665. Coyoacan, México D.F. 04360, México (URL: http://www.cenapred.gob.mx/), Daily Report Archive (URL: https://www.gob.mx/cenapred/archivo/articulos?order=DESC&page=1); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).


Sangeang Api (Indonesia) — September 2017 Citation iconCite this Report

Sangeang Api

Indonesia

8.2°S, 119.07°E; summit elev. 1949 m

All times are local (unless otherwise noted)


Weak Strombolian activity and occasional weak ash plumes, 15 July-12 August 2017

Strong explosions at Sangeang Api on 30-31 May 2014 generated ash plumes that rose as high as 15 km altitude, followed by less intense activity that produced ash plumes during the first half of June 2014 and 1 July-1 November 2015 (BGVN 41:10). No further activity was reported by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) and Darwin Volcanic Ash Advisory Centre (VAAC) until June 2017.

The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected thermal anomalies in MODIS satellite data near the summit during the second week of January 2017, when four were recorded (figure 16). The number increased significantly beginning with the latter half of February. Another increase in the number and power of the anomalies took place at the beginning of June 2017 and continued into mid-August.

Figure (see Caption) Figure 16. Thermal anomalies identified by the MIROVA system (radiative power) at Sangeang Api for the year ending 11 August 2017. Note that the anomaly lines in late 2016 are not on the island. Courtesy of MIROVA.

Thermal anomalies identified using the MODVOLC algorithm were first recorded on 25 February 2017. Over the same time period as the MIROVA data, through 11 August, there were 105 thermal alerts. Cumulatively, the locations of the alert pixels define an area extending from the summit crater to about 2.5 km down the E flank (figure 17).

Figure (see Caption) Figure 17. Thermal anomalies (alert pixels) identified by the MODVOLC system at Sangeang Api for 25 February-11 August 2017. The eastern-most pixels are at the summit area. Courtesy of HIGP - MODVOLC Thermal Alerts System.

According to PVMBG, a small Strombolian eruption at 1154 on 15 July 2017 generated an ash plume that rose 100-200 m above the crater rim and drifted SW. Seismicity had increased starting in April. Based on analyses of satellite imagery, PVMBG observations, and wind data, the Darwin VAAC reported that on 16 July an ash plume rose to an altitude of 2.1 km, or 200 m above the crater rim, and drifted NW. The Darwin VAAC also reported ash plumes to altitudes of 2.4-4.3 km on 19-20 July, 29-30 July, 7-8 August, and 12 August 2017; in most cases they drifted NW.

Geologic Background. Sangeang Api volcano, one of the most active in the Lesser Sunda Islands, forms a small 13-km-wide island off the NE coast of Sumbawa Island. Two large trachybasaltic-to-tranchyandesitic volcanic cones, 1949-m-high Doro Api and 1795-m-high Doro Mantoi, were constructed in the center and on the eastern rim, respectively, of an older, largely obscured caldera. Flank vents occur on the south side of Doro Mantoi and near the northern coast. Intermittent historical eruptions have been recorded since 1512, most of them during in the 20th century.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); 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/).

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.

View Atmospheric Effects Reports

Special Announcements

Special announcements of various kinds and obituaries.

View Special Announcements Reports

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/).