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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 17, Number 05 (May 1992)

Managing Editor: Lindsay McClelland

Aira (Japan)

Explosions and seismic swarms continue

Antuco (Chile)

Fumarolic activity in summit crater's small scoria cone

Arenal (Costa Rica)

Lava flows continue to advance; stronger and more frequent explosions

Asosan (Japan)

Mud/water ejections from heating crater lake; tremor episodes

Avachinsky (Russia)

Fumarolic activity around 1991 dome

Barren Island (India)

Continued gas emission from central crater and lava flow; animal and plant life recovering

Bezymianny (Russia)

Gas emission from center of dome

Etna (Italy)

Fissure eruption continues; lava diverted; lava field described

Fuego (Guatemala)

Seismicity and continued fumarolic activity

Galeras (Colombia)

Occasional explosions eject ash; strong fumarolic activity on 1991 dome; earthquakes and tremor decline

Heard (Australia)

Plumes and glow; volcano morphology and 1986-87 activity described; 1992 summit eruption

Ijen (Indonesia)

Infrared Space Shuttle photograph shows caldera and crater lake

Irazu (Costa Rica)

Fumarolic activity in and around crater lake; low-frequency seismicity

Kanlaon (Philippines)

Small ash emission

Kilauea (United States)

Lava production from episode-51 vent interrupted by brief pauses; lava lake in nearby crater

Klyuchevskoy (Russia)

Small explosions eject ash

Kozushima (Japan)

Continued seismic swarms

Langila (Papua New Guinea)

Moderate explosive activity from 2 craters

Lascar (Chile)

New dome fills base of crater; occasional explosions

Manam (Papua New Guinea)

Strong explosions from summit craters; lava flows; avalanches

Pacaya (Guatemala)

Numerous explosions; lava flows; temporary evacuations

Pinatubo (Philippines)

Rains on 1991 deposits produce destructive mudflows

Poas (Costa Rica)

Thermal activity in crater lake feeds 1-km plume; frequent earthquakes and occasional tremor

Rabaul (Papua New Guinea)

Seismic swarm; uplift over broad area

Raung (Indonesia)

Infrared Space Shuttle photograph shows devegetated summit area

Rincon de la Vieja (Costa Rica)

Thermal activity from crater lake; occasional seismicity

Rinjani (Indonesia)

Infrared Space Shuttle photo of Lombok Island during May 1992

Ruapehu (New Zealand)

Thermal activity but no phreatic eruptions from Crater Lake

Saba (Netherlands)

Seismic swarm

Santa Maria (Guatemala)

Frequent explosions feed small ash columns; continued erosion threatens vent area

Spurr (United States)

Ash eruption follows increased seismicity and thermal activity

Stromboli (Italy)

Frequent explosions; increased seismicity

Suwanosejima (Japan)

Tephra clouds from frequent explosions

Tongariro (New Zealand)

Fumarole temperatures and gas chemistry unchanged from 1989; no significant deformation or seismicity

Unzendake (Japan)

Lava-dome growth and pyroclastic flows

Villarrica (Chile)

Volcanic earthquakes and tremor

White Island (New Zealand)

Continued tephra ejection from three vents



Aira (Japan) — May 1992 Citation iconCite this Report

Aira

Japan

31.593°N, 130.657°E; summit elev. 1117 m

All times are local (unless otherwise noted)


Explosions and seismic swarms continue

Eight explosions occurred . . . in May . . . . The month's highest ash plume rose 2,500 m on 22 May. Seismic swarms were recorded seven times in May, each lasting for ~5 hours, normal for the volcano.

Geologic Background. The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan's most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the Aira caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim of Aira caldera and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4850 years ago, after which eruptions took place at Minamidake. Frequent historical eruptions, recorded since the 8th century, have deposited ash on Kagoshima, one of Kyushu's largest cities, located across Kagoshima Bay only 8 km from the summit. The largest historical eruption took place during 1471-76.

Information Contacts: JMA.


Antuco (Chile) — May 1992 Citation iconCite this Report

Antuco

Chile

37.406°S, 71.349°W; summit elev. 2979 m

All times are local (unless otherwise noted)


Fumarolic activity in summit crater's small scoria cone

During a February overflight, fumarolic activity was visible in the small scoria cone nested within the main crater. Weak summit fumaroles had previously been observed during visits in 1969, 1982, and March 1984. Fumarolic activity has apparently been continuous, but of variable intensity, from the cone since the volcano's last eruption in 1869. Lava flows from Antuco dammed Laja Lake's outlet in 1853, causing the water level to rise around 20 m.

Geologic Background. Antuco volcano, constructed to the NE of the Pleistocene Sierra Velluda stratovolcano, rises dramatically above the SW shore of Laguna de la Laja. Antuco has a complicated history beginning with construction of the basaltic-to-andesitic Sierra Velluda and Cerro Condor stratovolcanoes of Pliocene-Pleistocene age. Construction of the Antuco I volcano was followed by edifice failure at the beginning of the Holocene that produced a large debris avalanche which traveled down the Río Laja to the west and left a large 5-km-wide horseshoe-shaped caldera breached to the west. The steep-sided modern basaltic-to-andesitic cone of has grown 1000 m since then; flank fissures and cones have also been active. Moderate explosive eruptions were recorded in the 18th and 19th centuries from both summit and flank vents, and historical lava flows have traveled into the Río Laja drainage.

Information Contacts: H. Moreno, SAVO, Temuco.


Arenal (Costa Rica) — May 1992 Citation iconCite this Report

Arenal

Costa Rica

10.463°N, 84.703°W; summit elev. 1670 m

All times are local (unless otherwise noted)


Lava flows continue to advance; stronger and more frequent explosions

Two lobes of the lava flow active since November continued to extend down the W flank in May, with an estimated total volume of 3 x 106 m3 of lava. The northernmost lobe divided into several fronts; the longest reached to ~800 m elevation, while the most active front became channeled in a valley at ~855 m elevation on 14 May. A lava temperature of 820°C was measured at the front using an infrared thermometer. The southern lobe continued to travel along a more gentle slope to ~700 m elevation, covering and burning roughly 100 m2 of forest and grasslands. Summit incandescence, visible at night, suggested to scientists that a lava lake was feeding the active lava flow. Small pyroclastic flows occurred sporadically. One observed at 0723 on 13 May flowed down the W flank to 1,200 m elevation.

Explosive activity increased in number and magnitude from preceding months, especially since 26 May, when new explosions produced ash columns >1 km high and bombs fell to 1,000 m elevation. Between 23 April and 12 May, 80 g/m2 ash had accumulated 1.8 km W of the crater (at 740 m elevation). Samples were composed of very fine ash (40%), and fine and medium-sized scoria fragments and plagioclase crystals (60%). Volcanic earthquakes averaged 10/day in May (compared to 6 and 15 daily in April and March, respectively), with maxima of 20-24 on 15, 23, and 28 May. The month's highest levels of tremor were recorded on 7, 12, 14, 17, and 22 May.

Geologic Background. Conical Volcán Arenal is the youngest stratovolcano in Costa Rica and one of its most active. The 1670-m-high andesitic volcano towers above the eastern shores of Lake Arenal, which has been enlarged by a hydroelectric project. Arenal lies along a volcanic chain that has migrated to the NW from the late-Pleistocene Los Perdidos lava domes through the Pleistocene-to-Holocene Chato volcano, which contains a 500-m-wide, lake-filled summit crater. The earliest known eruptions of Arenal took place about 7000 years ago, and it was active concurrently with Cerro Chato until the activity of Chato ended about 3500 years ago. Growth of Arenal has been characterized by periodic major explosive eruptions at several-hundred-year intervals and periods of lava effusion that armor the cone. An eruptive period that began with a major explosive eruption in 1968 ended in December 2010; continuous explosive activity accompanied by slow lava effusion and the occasional emission of pyroclastic flows characterized the eruption from vents at the summit and on the upper western flank.

Information Contacts: G. Soto, R. Barquero, and G. Alvarado, ICE; M. Fernández, Univ de Costa Rica; E. Fernández, J. Barquero, and V. Barboza, OVSICORI.


Asosan (Japan) — May 1992 Citation iconCite this Report

Asosan

Japan

32.884°N, 131.104°E; summit elev. 1592 m

All times are local (unless otherwise noted)


Mud/water ejections from heating crater lake; tremor episodes

Isolated volcanic tremor episodes began to increase in October 1991, reaching about 100 events/day by the end of May. The increase in seismic activity followed a period of quiet after the July 1989-December 1990 eruptive phase. Ejections of mud and water, the first since June 1991, were observed within the active crater lake . . . on 23 April. Similar ejections, to 5 m height, were observed on 27 April, 1 and 27 May, and 2 June. The lake's surface temperature has been increasing since March-May 1991 when it was 20-30°C, reaching ~70°C (measured by infrared thermometer) in May. Weak mud ejections have been common in the past, during the period between eruptive phases when the crater is normally occupied by a lake, but have not been observed during the lowest levels of activity.

Geologic Background. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Information Contacts: JMA.


Avachinsky (Russia) — May 1992 Citation iconCite this Report

Avachinsky

Russia

53.256°N, 158.836°E; summit elev. 2717 m

All times are local (unless otherwise noted)


Fumarolic activity around 1991 dome

Fumarolic activity was occurring from numerous points around the margins of the January 1991 lava dome during a 13 May overflight. Numerous circumferential and radial fissures, previously observed in October 1991, covered the dome's surface, but the small lava flows that extended down the SSE and SW flanks were no longer visible.

Geologic Background. Avachinsky, one of Kamchatka's most active volcanoes, rises above Petropavlovsk, Kamchatka's largest city. It began to form during the middle or late Pleistocene, and is flanked to the SE by the parasitic volcano Kozelsky, which has a large crater breached to the NE. A large horseshoe-shaped caldera, breached to the SW, was created when a major debris avalanche about 30,000-40,000 years ago buried an area of about 500 km2 to the south underlying the city of Petropavlovsk. Reconstruction of the volcano took place in two stages, the first of which began about 18,000 years before present (BP), and the second 7000 years BP. Most eruptive products have been explosive, with pyroclastic flows and hot lahars being directed primarily to the SW by the breached caldera, although relatively short lava flows have been emitted. The frequent historical eruptions have been similar in style and magnitude to previous Holocene eruptions.

Information Contacts: H. Gaudru, SVE, Switzerland; G. de St. Cyr, T. de St. Cyr, and I. de St. Cyr, Lyon, France; T. Vaudelin, Genève, Switzerland.


Barren Island (India) — May 1992 Citation iconCite this Report

Barren Island

India

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

All times are local (unless otherwise noted)


Continued gas emission from central crater and lava flow; animal and plant life recovering

A multidisciplinary team from the GSI, IMD, CARI, and the Wildlife Dept visited Barren Island on 21-22 May. Hot gas was emerging from the funnel-shaped [300-m-deep] crater, which had an estimated diameter of [400 m] at the rim. The 1991 lava flow that extended to the coast was covered with rain-compacted scoriae and ash, and had a smooth, flat surface like a paved road. The flow's surface temperature was 40°C, but at 1/3 m depth it exceeded the thermometer's 360°C limit. Gases were emitted from small holes in the flow. A portable seismograph recorded several mild seismic events.

Some burnt ficus trees on the NW coast were sprouting new shoots, but badly charred ones appeared dead. Crabs were plentiful, even on the lava flow, and 25 feral goats were counted in one hour in the surrounding hills. Many birds were visible, but rats were completely absent. The water around the island was clear and of normal temperature, and fish were observed.

Further References. Haldar, D., Laskar, T., Bandyapadhyay, P.C., Sarkar, N.K., and Biswas, J.K., 1992, Volcanic eruption of the Barren Island volcano, Andaman Sea: J. of the Geological Society of India, v. 39, no. 5, p. 411-419.

Haldar, D., Laskar, T., Bandyapadhyay, P.C., Sarkar, N.K., and Biswas, J.K., 1992, A note on the recent eruption of the Barren Island volcano: Indian Minerals, v. 46, no. 1, p. 77-88.

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: S. Acharya, SANE.


Bezymianny (Russia) — May 1992 Citation iconCite this Report

Bezymianny

Russia

55.972°N, 160.595°E; summit elev. 2882 m

All times are local (unless otherwise noted)


Gas emission from center of dome

Gas emission from the center of Novy Dome produced a white-and-brown plume that covered the dome complex, especially its NE side, during an 18 May visit. No evidence of recent collapse was visible.

Geologic Background. Prior to its noted 1955-56 eruption, Bezymianny had been considered extinct. The modern volcano, much smaller in size than its massive neighbors Kamen and Kliuchevskoi, was formed about 4700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7000 years ago. Three periods of intensified activity have occurred during the past 3000 years. The latest period, which was preceded by a 1000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large horseshoe-shaped crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

Information Contacts: H. Gaudru, SVE, Switzerland; G. de St. Cyr, T. de St. Cyr, and I. de St. Cyr, A.V. Lyon, France; T. Vaudelin, Genève, Switzerland.


Etna (Italy) — May 1992 Citation iconCite this Report

Etna

Italy

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

All times are local (unless otherwise noted)


Fissure eruption continues; lava diverted; lava field described

The following is from R. Romano. Lava production from the fissure ... was continuing without noticeable variation in mid-June. Gas emission, from four explosion vents between 2,335 and 2,215 m elevation, has diminished along the upper part of the fissure. The main lava channel has roofed over, but lava was visible through a skylight beginning at 2,205 m elevation, where the effusion rate was estimated at 6-8 m3/s and the flow velocity at ~ 1 m/s on 7 and 13 June. Three more skylights were open along the main channel to 2,020 m asl. An overflow occurred on 12 June from one of the skylights, at 2,075 m altitude, but lava advanced only a few meters before returning to the main channel. This overflow was still active the next day. Ephemeral vents from the main tube remained active through the end of May: in the Valle del Bove; below the Valle del Bove in Val Calanna; and near the distal end of the flow field, along a deep gully under Portella Calanna (figure 48). Lava flows emerged more or less continuously from the latter vents, but did not descend below 800 m altitude. The total volume of lava produced by the eruption is estimated at 150 x 106 m3.

Figure (see Caption) Figure 48. Status of activity within Etna's flow field on 18 May 1992, after 153 days of activity. Modified by Hughes and Bulmer from map by Romano in 17:4. Contour interval, 100 m.

Lava diversion. An earthen barrier built in a valley above the town of Zafferana Etnea in early January was breached by lava on 7 April. Lava overran a series of additional barriers the following week but stopped before reaching the town. Subsequent hazards efforts focused on reducing the lava supply to the end of the flow, by obstructing the main lava tube near the vent and disrupting lava production at ephemeral vents (17:3-4).

F. Barberi and L. Villari report successful lava diversion from the main tube, at a site 500 m downslope from the primary eruptive vent. In this area, at ~ 2,000 m elevation on the W wall of the Valle del Bove, lava was carried through a single tube locally broken by skylights. On 27 May, about 2/3 of the tube's lava was diverted into an artificially excavated channel by blasting through the 2-3-m-thick wall of the right levee. Two days later, bulldozers obstructed the natural channel by pushing large blocks of lava into it. By 1815 that day, all of the lava output (~30 m3/s) was flowing into the artificial channel. In effect, the diversion returned the active flow front to its position a few days after the onset of the eruption. Lava was moving downslope along the same path as the earlier main flow, but was > 6 km upslope from its previously most advanced front.

Flows generated by lava diversion efforts. R. Romano reports that as of 13 June, a vent remained active at the site of the first lava diversion. Although the vent has been shrinking, it continued to feed a flow that has advanced over lava from previous months, forming tubes and various ephemeral vents, many of which were near the S wall of the Valle del Bove. The ephemeral vents produced two lava flows, one near the S wall of the Valle del Bove at around 1,700 m elevation, the other in a more central position, at ~ 1,800 m asl on the main lava field. The lava flows that formed after the first diversion advanced more than a kilometer over the center of the lava field. Flows that followed the second diversion remained predominantly near the S wall of the Valle del Bove, passing and encircling a site at 1,575 m asl (Poggio Canfareddi), 2 km from their point of origin, on 3 June. This lava front stopped advancing on 5 June and several superposing lobes began to develop.

Seismicity and summit activity. Weak seismic activity began on 29 May, followed by an increase in volcanic tremor on 31 May that continued until the next day. Ash emissions, sometimes voluminous, occurred from the central craters at irregular intervals on 31 May and 1 June, first from the W vent (Bocca Nuova) then from the E vent (La Voragine). Only weak degassing preceded the ash ejection, but gas emission became more consistent beginning 2 June. COSPEC measurements yielded SO2 flux values of ~ 10,000 t/d. Flashes from the summit craters were observed during the evening of 7 June from the W flank. Fieldwork on 12 June revealed that Northeast Crater was obstructed, with only fumarolic activity along the walls.

EDM data. S. Saunders reports that four lines of an EDM network on the upper S flank were remeasured on 7 May, showing a 138-ppm contraction that was interpreted as deflation during the eruption. Between July and October 1991, total extensional strain along these lines was 88 ppm, indicating pre-eruption inflation. Strain along these lines has returned to near pre-eruption levels.

Landsat Thematic Mapper data. The following is from D. Rothery. "The 1991-92 sustained lava eruption of Etna provides an opportunity to study lava flow development by remote sensing. The first cloud-free Landsat Thematic Mapper (TM) image of the eruption was recorded on 2 January at approximately 1000 (figure 49). Landsat repeats its coverage on a 16-day cycle; the next cloud-free acquisition was on 22 March and we are still awaiting receipt of those data. By manipulating radiance measurements in two wavebands, we hope to be able to constrain the surface temperature distribution of this flow along its length. The most noteworthy aspects of the 2 January data are: 1) There is a narrow 700-m length near the source that is radiant in TM band 4 (0.76-0.90 mm wavelength). As far as we know, this is the first time that thermal radiance in TM band 4 has been reported over a volcano. Field observations (A. Borgia) on 2 and 3 January show that this feature corresponds to a 10-15-m-wide open channel at the source of the flow. 2) The entire 6.5-km-long active flow is radiant in TM band 7 (2.08-2.35 mm wavelength). At least some of the areas that are also radiant in band 5 (1.55-1.75 mm) occur when the flow spills down a steep slope, breaking apart the raft of blocks and crust that otherwise blanket the underlying lava at near-magmatic temperatures."

Figure (see Caption) Figure 49. Extracts of Landsat TMr images of Etna, 2 January 1992, in band 4 (0.76-0.90 mm wavelength, left) and band 7 (2.08-2.35 mm wavelength, right) at pixel sizes of 30 x 30 m. In band 4, much of Etna is snow-covered (white), while the active lava flow is the darkest land feature because of its very low reflectance in this part of the spectrum (very-near infrared). Thermal radiance is confined to a narrow channel near the source and is not evident at this scale. In band 7, the active flow is radiant through most of its length. Bright lines are caused by sensor overload. Courtesy of D. Rothery.

Lava field characteristics. The following is an excerpt from a preliminary report by Wyn Hughes and Mark Bulmer, describing the eruption as of 18 May.

Lava leaving the eruptive vent advanced through a tube system that extended downslope to the foot of the western backwall of the Valle del Bove at 1,850 m asl. Several skylights were spaced at intervals along it. At the break in slope, numerous active ephemeral vents issued new lava-flow units onto the surface of the flow field (figure 48). These did not travel far from their source. Surface activity was otherwise absent within the Valle del Bove; lava was being efficiently transported through tubes toward the flow front. One tube system (with skylights and fume) could be traced through the center of the flow field in the Valle del Bove, toward Val Calanna. At the distal end of the Valle del Bove, several pressure ridges were visible, oriented perpendicular to the underlying ground slope.

Most of the surface activity was occurring in Val Calanna, where intense ephemeral vent activity was issuing new lava-flow units onto the flow-field surface. Lava was being supplied to this area through a series of tubes that descended from the Valle del Bove. Most of the activity in Val Calanna appeared to be supplied by a major tube system that could be traced (by skylights and fume) descending the backwall along its S margin (Salto della Giumenta). A smaller tube system probably supplied some ephemeral vents on the N margin of Val Calanna (S foot of Mte. Calanna).

In Val Calanna, effusive activity was mainly concentrated along the S margin of the flow field, where lava had ponded along the S wall of Val Calanna, and behind the man-made earthen barrier. From there, ephemeral vents in the crust fed numerous new lava-flow units, supplying three regions. Where lava moved directly NE, these were progressively widening the flow field at 1,050 m altitude. Flows that initially moved NE, but then changed to a more easterly direction, were supplying units that flowed around the N margin of the buried man-made barrier. Near the barrier, although active aa-textured flow fronts and channel-fed flow units could be traced on the surface of the flow field, most of the activity that contributed to its widening was supplied from tubes in the previous days' flow units. Ephemeral vents at 1,000 m elevation on the N margin of the buried man-made barrier supplied new flow units that were widening the field to the NE. However, these flow units were abutting the distal levee of the 1852-53 flow field, which was largely hindering the widening. On 18 May, some of these slow-moving tube-fed lavas managed to flow out of Val Calanna, and began the steep descent towards Zafferana. This activity was occurring on the NE side of the flow field. Three ephemeral vents had opened just below the S margin of the man-made barrier. A short distance downslope, flows from these vents combined to feed a front that advanced quite rapidly down the SW side of the flow field on the night of 17 May. By the next morning, and after destroying an abandoned dwelling during the night, the rate of advance had decreased, with the front at ~ 870 m asl. All of these active regions were being channel/tube-fed by lava from along the S wall of Val Calanna, which in turn was being supplied by tubes that descended from the Valle del Bove.

Flow-field morphology. Although the flow field was widening somewhat towards the NE end of Val Calanna, the activity was dominated by ephemeral vents extruding new flow units onto the surface of the original field. This was mainly occurring at ~ 1,800 and 1,050 m altitude, where the backwalls of the Valle del Bove and Val Calanna give way to their respective floors (figures 48 and 50). The surface activity was rapidly burying aa channel-fed flow units from early in the eruption. They could only be seen among the flows that had gone around the N margin of Mte. Calanna, and as isolated inliers on the floor of Val Calanna.

Figure (see Caption) Figure 50. Profile of the pre-eruption terrain in the 1991-92 lava field at Etna. Sites of ephemeral vent activity and zones of lava tubes and channel-fed units are shown diagrammatically. Courtesy of J.W. Hughes and M. Bulmer.

New flow units from ephemeral vents generally emerged with pahoehoe surface textures, in contrast to the early activity whose products had entirely aa textures. The flow-field surface on the floor of Val Calanna, as already occurred in the Valle del Bove, was slowly becoming dominated by pahoehoe textures. Small-scale pahoehoe textures, similar to those described by Pinkerton and Sparks (1978) for the sub-terminal 1975 flow field, prevailed around the ephemeral vents in Val Calanna. However, among the more active vents, pahoehoe slab textures that characterized the near-vent surfaces of new channel-fed flow units progressively changed to aa with increasing distance from the vent area.

Comparison with historical flow fields on Etna. The current ephemeral vent activity within the 1991-92 flow field is consistent with the pattern of historical eruptions that lasted > 100 days (Hughes, 1992). By then, the early channel-fed aa activity that characterized the lengthening and widening phases in the flow field's growth had given way to a tumulus-building phase at the vent area — for example, 1865 (Fouque, 1865); or at a break in slope below the vent area — for example, 1950-51 (Cumin 1954) and 1983 (Frazzetta and Romano, 1984). Important in the emplacement of the 1983 flow field was the evolution of the main supply channel near the vent into a lava tube. By the eruption's 60th day, the tube formed a continuous link between the vent and the lava mound that had accumulated around the break in slope at 2,000 m altitude. The hydrostatic pressures generated within the lava tube were then sufficient to lift and fracture the roof of the lava mound, allowing the escape of lava through ephemeral vent activity. This sequence of events signified the early stages of tumulus development. The present activity occurring at 1,800 m altitude within the Valle del Bove is similar.

The second area of ephemeral vent activity away from the vent area and initial break in slope appears, however, to be unique to the 1991-92 flow field; a similar phenomenon has not been documented for Etna flow fields of the last 250 years. For most, the concave profile of the volcano's flanks (figure 51) meant that once the lava had descended from the steep upper slopes it only encountered progressively gentler gradients. However, the terrain over which the 1991-92 lavas have flowed is much more irregular, with a terraced appearance. The steep terrain around the vent in the upper Valle del Bove is duplicated downslope in the upper reaches of Val Calanna. The morphologic positions of the ephemeral vent activity within the Valle del Bove and Val Calanna are similar (figure 50); both occur at the foot of a steep slope down which lava is transported through tubes. It must be concluded that conditions favoring tumulus construction have also been duplicated within Val Calanna.

Figure (see Caption) Figure 51. Profiles of the N, S, E, and W flanks of Etna. Courtesy of J. W. Hughes and M. Bulmer.

References. Cumin, G., 1954, L'eruzione laterale del Novembre 1950-Dicembre 1951: BV, v. 15, p. 3-70.

Fouque, F., 1865, Sur l'eruption de l'Etna du 1st Fevrier 1865: C. Rend. Acad. Sci. Paris; v. 60, p. 1331-1334; and v. 61, p. 210-212.

Frazzetta, G., and Romano, R., 1984, The 1983 Etna eruption: event chronology and morphological evolution of the flows: BV, v. 47, p. 1079-1096.

Hughes, J.W., 1992, The Influence of volcanic systems on the morphological evolution of lava flow fields: Ph.D. dissertation, University of London, 255 p.

Pinkerton, H., and Sparks, R.S.J., 1976, The subterminal lavas, Mount Etna: a case history of the formation of a compound lava flow field: JVGR, v. 1, p. 167-182.

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: F. Barberi, Univ di Pisa; L. Villari, IIV; R. Romano and T. Caltabiano, IIV; P. Carveni, M. Grasso, and C. Monaco, Univ di Catania; W. McGuire and A. Morrell, Cheltenham and Gloucester College of Higher Education; S. Saunders, West London Institute; D. Rothery, A. Borgia, R. Carlton, and C. Oppenheimer, Open Univ; J. Wyn Hughes and M. Bulmer, Univ College London.


Fuego (Guatemala) — May 1992 Citation iconCite this Report

Fuego

Guatemala

14.473°N, 90.88°W; summit elev. 3763 m

All times are local (unless otherwise noted)


Seismicity and continued fumarolic activity

An apparent harmonic tremor episode was recorded in mid-April, prompting the placement of several additional portable seismometers on the volcano in early May. Since then, several tectonic earthquakes have been recorded, but no harmonic tremor. Fumarolic activity continued in the summit crater.

Geologic Background. Volcán Fuego, one of Central America's most active volcanoes, is one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between 3763-m-high Fuego and its twin volcano to the north, Acatenango. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at Acatenango. In contrast to the mostly andesitic Acatenango, eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

Information Contacts: E. Sánchez, and Otoniel Matías, INSIVUMEH, Guatemala; Michael Conway, Michigan Technological Univ.


Galeras (Colombia) — May 1992 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


Occasional explosions eject ash; strong fumarolic activity on 1991 dome; earthquakes and tremor decline

Gas emission continued in May, occasionally accompanied by explosions that produced very fine ash, and noise from various points in the active crater. The observed explosions were associated with long-period earthquakes or variations in background tremor. SO2 flux was at low to moderate levels, ranging from ~250 to 650 t/d. Increased fumarole temperatures were measured on the SW (at Deformes fumarole) and W (at Besolima fissure) flanks of the cone, while strong fumarolic activity continued on the NW side of the 1991 dome.

Long-period seismicity and spasmodic tremor declined noticeably in May (figure 54). The few recorded high-frequency events were centered towards the W side of the crater, near the active cone, at <4.5 km depth, and M <2.0. A tremor episode that began on 31 May at 0451 was composed of two bands with durations of 33 and 18 minutes, separated by six tremor-free minutes. The tremor's dominant period was 0.5-1.0 seconds, and the released energy roughly 2.0 x 1011 ergs (reduced displacement of Rayleigh waves of 56 cm2 at the station 1.5 km from the crater). Another tremor episode, lasting 27 minutes with dominant periods of 0.2-0.4 seconds, was recorded in April. These tremor events were similar to those recorded in July-December 1991, associated with the formation and growth of the lava dome. A large long-period event recorded at 1920 on 6 June had a period of 1.5 seconds, and reduced displacements of 59 cm2 for Rayleigh waves, and 42 cm2 for body waves.

Figure (see Caption) Figure 54. Daily reduced displacement of long-period seismicity (top) and spasmodic tremor episodes (bottom) at Galeras, May 1992. Courtesy of INGEOMINAS.

Electronic tiltmeter measurements in May indicated deformation trends similar to April. The tiltmeter [at Crater Station] indicated continued deflation, while the tiltmeter [at Peladitos Station] suggested minor inflation (see figure 58).

Geologic Background. Galeras, a stratovolcano with a large breached caldera located immediately west of the city of Pasto, is one of Colombia's most frequently active volcanoes. The dominantly andesitic complex has been active for more than 1 million years, and two major caldera collapse eruptions took place during the late Pleistocene. Long-term extensive hydrothermal alteration has contributed to large-scale edifice collapse on at least three occasions, producing debris avalanches that swept to the west and left a large horseshoe-shaped caldera inside which the modern cone has been constructed. Major explosive eruptions since the mid-Holocene have produced widespread tephra deposits and pyroclastic flows that swept all but the southern flanks. A central cone slightly lower than the caldera rim has been the site of numerous small-to-moderate historical eruptions since the time of the Spanish conquistadors.

Information Contacts: J. Romero, INGEOMINAS-Observatorio Vulcanológico del Sur.


Heard (Australia) — May 1992 Citation iconCite this Report

Heard

Australia

53.106°S, 73.513°E; summit elev. 2745 m

All times are local (unless otherwise noted)


Plumes and glow; volcano morphology and 1986-87 activity described; 1992 summit eruption

[The following from Graeme Wheller] includes observations of continued activity in late 1986 and early 1987, and a renewed eruption in 1992.

Volcano morphology. Heard Island consists of two volcanic cones, Big Ben and Mt. Dixon, joined by a narrow isthmus (figure 2). Both cones are young, but only Big Ben has been observed to erupt. Many young lavas, including two that are unvegetated, lie on the flanks of Mt. Dixon. The separation of the two volcanoes is evident from the contrasting petrographic, geochemical, and isotopic characteristics of their respective eruptives [(Barling and others, 1994)].

Figure (see Caption) Figure 2.Geologic sketch map of Heard Island (after Barling, 1990) showing the location of the lava flow observed by Rod Ledingham in mid-January 1993.

Big Ben is a large, glacier-covered, composite cone 20-25 km in diameter at sea-level, consisting mainly of basaltic lavas and lesser ash and scoria. Its summit region consists of a SW-facing semi-circular ridge 5-6 km in diameter, 2,200-2,400 m asl. The ridge appears to have formed from breaching of the SW flank of Big Ben, possibly by landsliding caused by seismicity or a laterally directed blast. The E, N, and W flanks of Big Ben have been deeply scoured by glacial erosion, forming high-standing radial ribs to 7-8 km long.

Eruptions have built a new regularly shaped cone, Mawson Peak, within the breached region of the summit. Mawson Peak is snow-and ice-covered on all sides, . . . and its SW flank slopes smoothly to the coast. All . . . historical volcanism has apparently originated at the summit of Mawson Peak.

Young volcanic deposits. Mt. Dixon, much smaller than Big Ben, appears to be the latest manifestation of volcanic activity that has created a peninsula 9 km long and up to 5 km wide extending from the NW side of Big Ben. Mt. Dixon, at the end of the peninsula, is a glacier-covered rounded cone 706 m tall. More than 20 separate relatively young basaltic lava flows have been identified on its flanks, including two that are largely vegetation-free and may have been erupted within the last few hundred years. These lavas have flowed from vents on the upper flanks of Mt. Dixon, except for one from a fissure marked by an elongate scoria ridge ~1 km long near the base of the S flank. A crater ~50 m in diameter occurs at the head of one W-flank flow ~1 km inland. Several small hornitos occur on the lava flow near this crater. One is still well-formed, ~2.5 m high and 3-4 m in diameter, but the others have largely collapsed. On the W and N flanks of Mt. Dixon, particularly near Red Island, trachytic lavas lie beneath the basalt lavas.

Eleven parasitic scoria cones and associated small basaltic lava flows occur around the coastline . . . . Some are at or near the edges of vertical sea cliffs, indicating that erosion by the sea may have obliterated other cones. The parasitic cones are typically ~100 m high and well-formed with deep central craters. Lava spatter usually occurs abundantly around the upper parts of the cones. Lavas produced from these vents are typically small-volume pahoehoe flows. From their morphology and relative lack of vegetation, the cones and their lavas may be only a few thousand years old. On Azorella Peninsula, the parasitic cone forms the W side of Corinth Head which, together with Rogers Head, appears to be a remnant of an older and much larger cone formed of thinly stratified leucocratic tuff. The basaltic flow erupted from the Corinth Head crater contains partly collapsed tumuli and lava tunnels.

A similarly youthful, trachytic, airfall (Plinian?) pumice deposit 1-1.5 m thick occurs at the E end of the island. The lower 0.5 m of the deposit is distinctly darker than the upper part, showing a sharp horizontal transition. The deposit is overlain by moraine but underlying material is not visible. Similar deposits are not known from any other parts of the island. Although it is primary deposit and must therefore have been produced by an eruption on Heard Island, the location of its originating vent is not known.

December 1986-January 1987 activity. A deep, well-formed crater at the top of Mawson Peak was discovered on helicopter overflights in December 1986 and January 1987, during the 1986/87 Heard Island ANARE. On 21 December, a brief landing was made on the summit beside the crater. The crater was cylindrical and, from visual estimates, ~40-50 m in diameter and 50-70 m deep, with vertical walls exposing dark horizontal ash layers thinly coated in yellow sulfur. The crater was floored by a black ropy lava surface in which small patches of red lava periodically appeared, indicating an active lava lake within the crater. Larger red patches, ~ 5-10 m across, appeared less frequently, accompanied by gentle emissions of a little blue smoke. Minor steam emission also occurred from around the crater rim and from a rocky area on the crater's E side. The crater appears to have been formed by the 1985/87 eruption because it was not seen by climbing parties that reached the summit of Mawson Peak in 1965 and 1983.

A new pahoehoe lava flow in a glacial valley on Mawson Peak's SW flank was also discovered during the 1986/87 ANARE. The flow extended ~8-9 km from the summit crater rim, where it exited through a deep V-shaped notch, to within 2-3 km of the coast (near Cape Arkona). Small amounts of steam emanated from parts of the flow, which probably formed in January 1985, as observed from the Marion Dufresne.

1992 summit activity. Satellite images and observations from the ANARE base revealed eruptive activity in 1992. Data from the NOAA 11 polar orbiter showed plumes extending 300 km NNE then E from the island on 17 January at about 1720, and 200 km NE the next day at 0300. Weather in the region is usually cloudy, and no other activity was evident . . . until a short-lived thermal anomaly was detected on 18 May at 2146. The ANARE team had not yet reached Heard Island on 17 January, but the summit area was visible for 20 days in March, 18 days in April, and 7 days in May (as of the 29th). Gas had been emerging from the summit during fieldwork in mid-1990, but no activity was evident in 1992 until 29 May, when an orange glow was first noticed above the mountain at 2130. The glow rapidly intensified and appeared to be pulsating, faded after about a minute, then reappeared a few minutes later. Three or four such cycles were observed, with glow intensity changing randomly. Glow faded for the last time at about 2200. Although some auroral activity occurred that night, none of the observers believed that it was the source of the glow. Activity was next reported on 8 June, when vapor began to emerge from the summit at about 1430, soon forming a plume to the SE. Mist soon obscured the activity. Traces of steam were also visible on 10 June.

Reference. Barling, J., 1990, Heard and McDonald Islands, in Le Masurier, W., and Thomson, J., eds., Volcanoes of the Antarctic Plate and southern Oceans: American Geophysical Union, Washington DC, p. 435-441.

Further References. Barling, J., Goldstein, S.L., and Nicholls, I.A., 1994, Geochemistry of Heard Island (southern Indian Ocean): characterisation of an enriched mantle component and implications for enrichment of sub-Indian Ocean mantle: Journal of Petrology, v. 35, p. 1017-1053.

Hilton, D.R., Barling, J., and Wheller, G.E., 1995, Effect of shallow-level contamination on the helium isotope systematics of ocean-island lavas: Nature, v. 373, p. 330-333.

Geologic Background. Heard Island on the Kerguelen Plateau in the southern Indian Ocean consists primarily of the emergent portion of two volcanic structures. The large glacier-covered composite basaltic-to-trachytic cone of Big Ben comprises most of the island, and the smaller Mt. Dixon volcano lies at the NW tip of the island across a narrow isthmus. Little is known about the structure of Big Ben volcano because of its extensive ice cover. The historically active Mawson Peak forms the island's 2745-m high point and lies within a 5-6 km wide caldera breached to the SW side of Big Ben. Small satellitic scoria cones are mostly located on the northern coast. Several subglacial eruptions have been reported in historical time at this isolated volcano, but observations are infrequent and additional activity may have occurred.

Information Contacts: G. Wheller, CSIRO Division of Exploration Geoscience, Australia; R. Varne, Univ of Tasmania; A. Vrana, K. Green, and T. Jacka, Australian Antarctic Division, Tasmania; W. Gould, NOAA/NESDIS.


Ijen (Indonesia) — May 1992

Ijen

Indonesia

8.058°S, 114.242°E; summit elev. 2769 m

All times are local (unless otherwise noted)


Infrared Space Shuttle photograph shows caldera and crater lake

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

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

Geologic Background. The Ijen volcano complex at the eastern end of Java consists of a group of small stratovolcanoes constructed within the large 20-km-wide Ijen (Kendeng) caldera. The north caldera wall forms a prominent arcuate ridge, but elsewhere the caldera rim is buried by post-caldera volcanoes, including Gunung Merapi, which forms the high point of the complex. Immediately west of the Gunung Merapi stratovolcano is the historically active Kawah Ijen crater, which contains a nearly 1-km-wide, turquoise-colored, acid lake. Picturesque Kawah Ijen is the world's largest highly acidic lake and is the site of a labor-intensive sulfur mining operation in which sulfur-laden baskets are hand-carried from the crater floor. Many other post-caldera cones and craters are located within the caldera or along its rim. The largest concentration of cones forms an E-W zone across the southern side of the caldera. Coffee plantations cover much of the caldera floor, and tourists are drawn to its waterfalls, hot springs, and volcanic scenery.

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


Irazu (Costa Rica) — May 1992 Citation iconCite this Report

Irazu

Costa Rica

9.979°N, 83.852°W; summit elev. 3432 m

All times are local (unless otherwise noted)


Fumarolic activity in and around crater lake; low-frequency seismicity

During May, water in the crater lake returned to the level of the previous summer. Fumarolic emissions N of the lake decreased, while subaqueous fumaroles in the SE, E, and N parts of the lakes remained active. Small landslides occurred along the crater's E, N, and SW walls. A monthly total of 126 earthquakes was recorded (at station IRZ2, 5 km W of the crater), with a M 1.8 event centered 3.6 km SW of the crater, at 1 km depth, on 5 May. Low-frequency seismicity continued through May.

Geologic Background. Irazú, one of Costa Rica's most active volcanoes, rises immediately E of the capital city of San José. The massive volcano covers an area of 500 km2 and is vegetated to within a few hundred meters of its broad flat-topped summit crater complex. At least 10 satellitic cones are located on its S flank. No lava flows have been identified since the eruption of the massive Cervantes lava flows from S-flank vents about 14,000 years ago, and all known Holocene eruptions have been explosive. The focus of eruptions at the summit crater complex has migrated to the W towards the historically active crater, which contains a small lake of variable size and color. Although eruptions may have occurred around the time of the Spanish conquest, the first well-documented historical eruption occurred in 1723, and frequent explosive eruptions have occurred since. Ashfall from the last major eruption during 1963-65 caused significant disruption to San José and surrounding areas.

Information Contacts: E. Fernández, J. Barquero, and V. Barboza, OVSICORI.


Kanlaon (Philippines) — May 1992 Citation iconCite this Report

Kanlaon

Philippines

10.412°N, 123.132°E; summit elev. 2435 m

All times are local (unless otherwise noted)


Small ash emission

Newspapers reported a 1-km-high ash emission and ashfall at flank towns on 10 June, coinciding with a minor earthquake. There were no reports of injuries.

Geologic Background. Kanlaon volcano (also spelled Canlaon), the most active of the central Philippines, forms the highest point on the island of Negros. The massive andesitic stratovolcano is dotted with fissure-controlled pyroclastic cones and craters, many of which are filled by lakes. The largest debris avalanche known in the Philippines traveled 33 km SW from Kanlaon. The summit contains a 2-km-wide, elongated northern caldera with a crater lake and a smaller, but higher, historically active vent, Lugud crater, to the south. Historical eruptions, recorded since 1866, have typically consisted of phreatic explosions of small-to-moderate size that produce minor ashfalls near the volcano.

Information Contacts: Reuters.


Kilauea (United States) — May 1992 Citation iconCite this Report

Kilauea

United States

19.421°N, 155.287°W; summit elev. 1222 m

All times are local (unless otherwise noted)


Lava production from episode-51 vent interrupted by brief pauses; lava lake in nearby crater

Lava production at the E-51 vent halted on 28 April. Shallow long-period (LPC-A type, 3-5 Hz) microearthquake counts declined for a few days, then increased to > 200 events daily between the mornings of 1-3 May. During the interval of eruptive quiet, the small lava lake in Pu`u `O`o crater rose until it spilled onto the crater floor on 3 May.

The lava lake was still overflowing when activity resumed at the E-51 vent the next day. Channelized lava flows covered much of the S flank of the E-51 shield between 4 and 22 May, many forming tubes that extended to the shield's base. Flows emerged from the tubes under enough pressure to create dome fountains at their heads. Some ponding occurred at the base of the shield before flows advanced S and E. The perched lava pond on the E-51 shield fed large overflows as well as small aa flows on the shield's NW flank. The pond level fluctuated, dropping as much as 15 m below the rim when the eruption paused again on 22 May.

Shallow long-period (LPC-B type, 1-3 Hz) microearthquake rates were nearly 100/day 8-11 May, declined for a few days, then increased again 15-21 May, peaking on the 17th when 442 were detected. As these events declined, an increase in LPC-A types was noted. The amplitude of eruption tremor remained low, then abruptly dropped to near background on 22 May at about 1300.

The eruption resumed on 27 May, for the first time re-occupying tubes formed during the previous active period. Activity paused again on 29 May, resuming on 2 June, again using the same tubes on the S flank of the shield.

The lava lake in Pu`u `O`o remained active throughout May. Its level fluctuated between 35 and 70 m below the crater rim, periodically overflowing onto the crater floor. Collapses of the crater walls and floor left the lake with a smaller diameter, against the E crater wall.

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

Information Contacts: T. Mattox and P. Okubo, HVO.


Klyuchevskoy (Russia) — May 1992 Citation iconCite this Report

Klyuchevskoy

Russia

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

All times are local (unless otherwise noted)


Small explosions eject ash

During a 13 May visit, two explosions (at 1130 and 1428) ejected ash clouds to 1,000 m above the summit. A third explosion was noted at 0140 the next day, but no additional activity was observed during the 14-15 May journey from the volcano.

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

Information Contacts: H. Gaudru, SVE, Switzerland; G. de St. Cyr, T. de St. Cyr, and I. de St. Cyr, A.V. Lyon, France; T. Vaudelin, Genève, Switzerland.


Kozushima (Japan) — May 1992 Citation iconCite this Report

Kozushima

Japan

34.219°N, 139.153°E; summit elev. 572 m

All times are local (unless otherwise noted)


Continued seismic swarms

Abnormal seismicity continued around the volcano in May, when 2 earthquake swarms were recorded. On 8 May a swarm occurred 2-3 km E of the island, with M <3.9. The second, on 14-16 May, occurred 3-4 km NW, with the largest event (M 4.9) recorded at 0731 on 15 May. No surface anomalies were observed.

Geologic Background. A cluster of rhyolitic lava domes and associated pyroclastic deposits form the small 4 x 6 km island of Kozushima in the northern Izu Islands. Kozushima lies along the Zenisu Ridge, one of several en-echelon ridges oriented NE-SW, transverse to the trend of the northern Izu arc. The youngest and largest of the 18 lava domes, 574-m-high Tenjoyama, occupies the central portion of the island. Most of the older domes, some of which are Holocene in age, flank Tenjoyama to the north, although late-Pleistocene domes are also found at the southern end of the island. Only two possible historical eruptions, from the 9th century, are known. A lava flow may have reached the sea during an eruption in 832 CE. Tenjosan lava dome was formed during a major eruption in 838 CE that also produced pyroclastic flows and surges. Earthquake swarms took place during the 20th century.

Information Contacts: JMA.


Langila (Papua New Guinea) — May 1992 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)


Moderate explosive activity from 2 craters

"Moderate eruptive activity continued during May. Crater 3 was the most steadily active. Throughout the month it produced intermittent weak and loud explosions with forceful emission of grey ash columns rising to several hundred meters above the crater. No night glow was seen until 29 May. Activity at Crater 2 was moderately strong on 1 May, with forceful dark ash clouds rising several km above the crater. After the 1 May episode, activity was relatively mild. Other than moderate volumes of white and occasionally blue vapour emission, it only produced Vulcanian explosions on 11 and 18 May.

"Both craters were reactivated on the last few days of the month. Weak incandescent projections started at Crater 3 on the night of 29-30 May. On 30 May, low to loud explosions and whooshing noises accompanied bright Strombolian ejections to 700 m above the crater. Also on 30 May, a thick, dark ash column a few km high was emitted by Crater 2, with nighttime incandescent fragments rising 125 m above the crater. On 31 May, the activity was mainly from Crater 3, with ongoing high Strombolian projections, emission of a thick grey ash column several km high, and the production of a new, short lava flow down the NW flank of the cone. Unfortunately, failure of both seismic stations prevented recording of any related seismicity. The recurring activity from both craters continued into early June, producing much ashfall on the downwind coastal areas."

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: P. de Saint-Ours and C. McKee, RVO.


Lascar (Chile) — May 1992 Citation iconCite this Report

Lascar

Chile

23.37°S, 67.73°W; summit elev. 5592 m

All times are local (unless otherwise noted)


New dome fills base of crater; occasional explosions

On 4 March, a new lava dome was observed in the active crater . . . at the base of the S wall (17:3).

Following a request by local authorities (Intendencia and Oficina Regional de Emergencia, II Región), the Chilean Air Force overflew the volcano at 1245 on 20 March. The high-quality vertical photographs obtained of the summit area enabled an accurate estimation of the dome's size and volume. The dome appeared to fill the entire, nearly circular, base of the crater (180-190 m in diameter; figure 10), with a thickness of ~40 m, and an estimated volume of 1.1 x 106 m3. It had steep walls and was devoid of a talus apron. The blocky, rugged surface of the dome appeared to have formed as a smaller, black central elongated plug (85 x 115 m) intruded a dark-brownish older external rim. Strong fumarolic activity occurred along the NE edge of the dome, which strongly resembled the one observed in March and April 1989.

Figure (see Caption) Figure 10. Sketch map of the summit area of Lascar, prepared from vertical airphotos taken during an overflight by the Chilean Air Force on 20 March, showing the new lava dome. Courtesy of M. Gardeweg.

Observations from Talabre indicated that fumarolic activity had remained vigorous since late March, with eruption columns often 2-3 times larger than normal. The plume was usually yellowish to gray instead of its typical white until May, when a continuous dense gray plume was observed. Ashfall was reported on 15 May at 1050, accompanied by a gray eruption column estimated to be 1,500-2,000 m high (about 6x normal). On 21 May at 1130, an abrupt increase in the plume to a few kilometers height was observed by residents of nearby villages, and by people to 145 km W. The volcano "roared" for 10 minutes according to a witness (Luciano Sozo of Talabre) near the volcano. A second large explosion was reported that day at 1322 by Talabre residents. Following reports of night glow on 21-23 May, activity apparently returned to normal, with small pale-gray to white plumes and an absence of night glow. Although the May explosions were not as large as those in September 1986 and February 1990, scientists suggested that they might correspond to explosive destruction of part of the summit dome. Onset of winter and the partial covering of the cone by snow prevented visits to the summit, prompting a recommendation to the local authorities for new overflights and airphotos to monitor the development of the dome.

Several earthquakes recorded by the regional seismic network corresponded to large earthquakes centered away from the volcano, and were recorded by seismometers to the W. However, at least 4 small earthquakes were recorded between 24 April and late May only in villages closer to Lascar. The absence of seismometers near the volcano has prevented detailed monitoring of its seismicity.

Geologic Background. Láscar is the most active volcano of the northern Chilean Andes. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters. Prominent lava flows descend its NW flanks. An older, higher stratovolcano 5 km E, Volcán Aguas Calientes, displays a well-developed summit crater and a probable Holocene lava flow near its summit (de Silva and Francis, 1991). Láscar consists of two major edifices; activity began at the eastern volcano and then shifted to the western cone. The largest eruption took place about 26,500 years ago, and following the eruption of the Tumbres scoria flow about 9000 years ago, activity shifted back to the eastern edifice, where three overlapping craters were formed. Frequent small-to-moderate explosive eruptions have been recorded since the mid-19th century, along with periodic larger eruptions that produced ashfall hundreds of kilometers away. The largest historical eruption took place in 1993, producing pyroclastic flows to 8.5 km NW of the summit and ashfall in Buenos Aires.

Information Contacts: M. Gardeweg, SERNAGEOMIN, Santiago.


Manam (Papua New Guinea) — May 1992 Citation iconCite this Report

Manam

Papua New Guinea

4.08°S, 145.037°E; summit elev. 1807 m

All times are local (unless otherwise noted)


Strong explosions from summit craters; lava flows; avalanches

"The eruption continued strongly in May with new paroxysmal phases of activity at Southern Crater on 10, 14, 16, 23, and 31 May. Main Crater was active 2-7 May, 14-16 May, and 26 May through the end of the month. New lava flows were emitted into the NE valley during these periods. Unlike former episodes of strong eruptive activity (i.e. 1974, 1984), the current episode involves both summit craters, in an intermittent pattern. Following a period of strong, lava-producing activity from Main Crater in April, Southern Crater was reactivated on 2 May. This crater had been blocked by sluggish lava and/or rubble from its last paroxysmal phase (11 April), and was re-opened after several loud explosions and ejection of dark, ash-laden columns with incandescent blocks up to 980 m high. On 3 May, and for a few days after, activity at Southern Crater consisted of intermittent explosions producing debris avalanches that were channelled into the upper SW valley. Main Crater became the center of activity again on 4 May. At approximately 1100, it started to produce a strong, sustained ash column that rose 1,000-3,000 m above the summit, deep roaring sounds, and an increase in the level of seismicity. At night, a bright glow and incandescent projections (to 125 m) were visible from Tabele Observatory . . . , but an aerial inspection on 5 May revealed that a new lava flow was being emitted from a fissure on the flank of the dark scoria cone now occupying Main Crater, at ~1,600 m elev. The lava flow overrode earlier flows emitted in April down to ~500 m elev, then followed a stream channel on the S side of the valley. Summit activity waned on 6 May and the flow stopped on 7 May, at ~60 m elevation, after advancing 4.5 km.

"On the following day (8 May), the level of activity increased in Southern Crater with Strombolian projections up to 300 m above the crater rim. At 1415 on 9 May, a second vent became active. Both vents then displayed sub-continuous Strombolian projections up to 100 m (N vent) and 500 m (Iabu vent), while the level of seismicity, which consisted of a succession of low-frequency events and microtremor, increased. This activity culminated in a paroxysmal phase on the night of 9-10 May. At 0040, a deep roaring sound was heard. This became louder and was followed by the outrush of incandescent lava fragments up to 1,000 m above the crater. During the following hours, the high output rate of lava spatter was maintained, accompanied by very loud explosion sounds that shook walls and windows at the Observatory . . . . Concurrently, lightning-and-thunder effects were occurring in the 3,000-m-high vapor-and-tephra cloud generated by the eruption and by the pyroclastic avalanches into both the SE and SW valleys. A lava flow poured out of Iabu vent, tumbled into the SW valley, and progressed down to 600 m elev during the following day.

"Seismicity and eruptive activity were low for the three following days but another paroxysmal phase of activity occurred in the early morning of 14 May. From 0200, weak roaring and explosion sounds were heard and Strombolian projections (50-125 m above the crater rim) resumed from the N vent of Southern Crater, while seismicity steadily built. Between 0430 and 0700, continuous incandescent projections were reaching heights of 500 m (Iabu vent) to 1,100 m (N vent), with spatter falling back as far as the foot of the terminal cone. A lava flow from Iabu vent tumbled into the SW valley. Even after the Strombolian activity stopped at the summit, the lava flow continued throughout the day and the following night, progressing down the valley to 200 m elev, a total length of 3.8 km. After 0700 on 14 May, emissions from Southern Crater had changed to produce a silent ash column that died out at about 0900. In the afternoon, explosions related to deep Strombolian activity in Main Crater were observed at ~10/minute, and at night the incandescent projections were seen rising to 400 m above the crater rim. By the morning of 15 May, Main Crater was emitting a silent, thick, billowy column of grey ash that lasted until 16 May. In the afternoon of 16 May, Southern Crater entered yet another paroxysmal phase, similar to the one on 14 May. This time only Iabu vent was active, displaying a glowing ribbon of new lava flowing into the SW valley, to an estimated 400 m elev. Strombolian activity died out around 2030 on 16 May, as did the lava flow the next afternoon.

"After a few uneventful days with only white and blue vapours released from multiple cracks around the craters, the eruption resumed from Southern Crater on 20 May. This time a new vent on the W side of the crater was active. Until 23 May, it produced weak, intermittent, ash-laden explosions, with nighttime incandescent projections up to 180-250 m above the crater. The seismicity built up from 0300 on 23 May. By 1130, after a marked increase in activity over 30 minutes, Southern Crater entered yet another phase of intense Strombolian eruption that lasted until 1430. This was followed by discontinuous Strombolian eruptions until late afternoon. A new lava flow from Iabu vent progressed into the SW valley to an estimated 600 m elevation. There was weak fluctuating activity in Southern Crater for another week, during which Main Crater was reactivated, producing weak to strong Strombolian eruptions with variable amounts of ash. Another paroxysmal phase of activity occurred at Southern Crater on 31 May, between 1330 and 1700. It produced a thick, dark-grey cloud and was accompanied by continuous roaring sounds and another lava flow into the SW valley.

"Water-tube tilt measurements at Tabele Observatory first showed a 2 µrad radial deflation, then a steady recovery throughout the month. Other dry tilt and levelling lines around the island were checked repeatedly but showed no significant change.

"The intermittent, recurring activity in the two craters has the effect of markedly modifying their configuration between each aerial reconnaissance. Following the ash eruption in mid-May, the scoria and spatter cone that initially occupied Main Crater was changed into a somma-type feature, with a 50-m-wide vertical crater in the center. Likewise, repeated emissions of lava flows into the SW and NE valleys are significantly modifying their topography; the volumes of erupted material are being calculated. Each eruptive phase also produced a few mm to cm of ash and lapilli falls onto coastal areas on the NW and SE sides of the island. These deposits are not yet significant enough to dangerously affect villages and subsistence gardens."

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

Information Contacts: P. de Saint-Ours and C. McKee, RVO.


Pacaya (Guatemala) — May 1992 Citation iconCite this Report

Pacaya

Guatemala

14.382°N, 90.601°W; summit elev. 2569 m

All times are local (unless otherwise noted)


Numerous explosions; lava flows; temporary evacuations

Activity was unusually high through May, with several thousand explosions recorded seismically every day (figure 10). Powerful pyroclastic episodes in early May temporarily forced the evacuations of villages near the W base of the volcano. During the first week of May, two lava flows were extruded from vents near the NW and S summit of MacKenney cone.

Figure (see Caption) Figure 10. Daily number of explosions recorded seismically at Pacaya, January-March 1992. Stars mark the strongest eruptive episodes. Prepared by INSIVUMEH.

Pacaya has erupted almost continuously since January-February 1990, when Strombolian activity was observed producing a new cone. Strong Strombolian activity destroyed the new cone and lava emission began in July 1990. Since then, lava emission has continued, and periodic increases in explosive activity have resulted in crop damage and the evacuation of up to 1,500 people.

Geologic Background. Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and was last active in the 19th century. During the past several decades, activity has consisted of frequent strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.

Information Contacts: E. Sanchez and Otoniel Matías, INSIVUMEH, Guatemala City; Michael Conway, Michigan Technological Univ, USA; Rodolfo Morales, INSIVUMEH, Guatemala City.


Pinatubo (Philippines) — May 1992 Citation iconCite this Report

Pinatubo

Philippines

15.13°N, 120.35°E; summit elev. 1486 m

All times are local (unless otherwise noted)


Rains on 1991 deposits produce destructive mudflows

Increased steam emission from Pinatubo's summit caldera was periodically observed in 1992, often accompanied by low-frequency harmonic tremors believed to be associated with sudden release of pressurized gas and steam from shallow depth. However, seismicity at the volcano continued to decline. Felt shocks with intensities of I-V (Rossi-Forel scale) were reported until mid-May.

Numerous mudflows descended the volcano's flanks, as heavy local rainfall mobilized large quantities of unconsolidated material deposited during the June 1991 eruption (16:5-6). The more significant events occurred on 18-19 February, 5 April, 10 and 31 May, and 1 and 4 June, affecting low-lying areas NE, SE, and SW of the volcano. Dams along the Pasig-Potrero and Sacobia rivers (SE and E flank, respectively) were destroyed during these relatively minor mudflow events and residents of Angeles (25 km E) reported slight to moderate ashfall from secondary explosions in pyroclastic-flow deposits within the Sacobia Pyroclastic Fan (SPF). Civil authorities have attempted to limit damage from the mudflows in the three provinces surrounding the volcano (Tarlac, Pampanga, and Zambales) by constructing Sabo dams and catchment basins, and by dredging channels, at a cost of more than $300,000,000. More than 250 school buildings were prepared as evacuation centers and the government advised people living near river banks to move to safer ground.

On 4 April, a major secondary explosion occurred at the toe of the SPF (drained by the Sacobia-Bamban and Abacan rivers), producing a 1.2-km-high ash plume. The explosion triggered a landslide that developed into a secondary pyroclastic flow, travelling 3 km down the Sacobia River and 2 km down the Abacan River. Numerous explosions followed, minutes apart. The secondary flow deposit, 14 m thick 3 km from the explosion site, buried three Sabo dams along the Abacan and two along the Sacobia River. A moderate amount of ashfall (~4 mm) was reported by residents at Clark Air Base/Pinatubo Volcano Observatory and Angeles. The flow left a deep escarpment, cutting the Abacan River off from the SPF, its source of mudflow material. The upper reaches of the river have been captured, and now flow down to the Sacobia-Bamban River, with only a muddy trickle expected to reach the Abacan.

With the advent of the rainy season (June-November), larger mudflows, with accompanying flooding and siltation, were expected in low-lying areas along the major river channels draining the volcano. As of early June, about 70,000 of the roughly 250,000 people displaced during the 1991 eruption and subsequent mudflows remained in evacuation centers and resettlement areas.

Geologic Background. Prior to 1991 Pinatubo volcano was a relatively unknown, heavily forested lava dome complex located 100 km NW of Manila with no records of historical eruptions. The 1991 eruption, one of the world's largest of the 20th century, ejected massive amounts of tephra and produced voluminous pyroclastic flows, forming a small, 2.5-km-wide summit caldera whose floor is now covered by a lake. Caldera formation lowered the height of the summit by more than 300 m. Although the eruption caused hundreds of fatalities and major damage with severe social and economic impact, successful monitoring efforts greatly reduced the number of fatalities. Widespread lahars that redistributed products of the 1991 eruption have continued to cause severe disruption. Previous major eruptive periods, interrupted by lengthy quiescent periods, have produced pyroclastic flows and lahars that were even more extensive than in 1991.

Information Contacts: R. Punongbayan, Perla J. Delos Reyes, Renatu U. Solidum, and Ronnie C. Torres, PHIVOLCS; Reuters; UPI.


Poas (Costa Rica) — May 1992 Citation iconCite this Report

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Thermal activity in crater lake feeds 1-km plume; frequent earthquakes and occasional tremor

Fumarolic activity continued in the crater lake in May, producing a continuous 1-km-high plume. Residents of the S and SW flanks reported sulfur odors. A total of 7,085 low-frequency earthquakes was recorded in May (at station POA2, 2.7 km SW), with a daily average of 229, compared to 250/day in April. Medium-frequency tremor was recorded sporadically. Twelve volcano-tectonic earthquakes were recorded in May, with a M 2.5 event centered 7 km ESE of the crater, at 7.5 km depth, on 18 May.

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

Information Contacts: E. Fernández, J. Barquero, and V. Barboza, OVSICORI.


Rabaul (Papua New Guinea) — May 1992 Citation iconCite this Report

Rabaul

Papua New Guinea

4.271°S, 152.203°E; summit elev. 688 m

All times are local (unless otherwise noted)


Seismic swarm; uplift over broad area

"Slow magmatic inflation continued in May, although an unusual swarm of seismic activity took place at the beginning of the month. Seismic activity in the usual annular seismic zone remained at a low level throughout May, with a total of 125 events. Starting on 2 May, however, an unusual swarm of earthquakes occurred 4.5-5 km under the N (older and inactive) rim of the caldera, slightly E of Rabaul township. Approximately 300 such events were recorded 2-19 May, with ~140 occurring on 3 May. A dozen were felt by residents. Five events were of ML >=3.0, the largest ML 4.2. Levelling measurements on 4 June indicated that uplift had occurred over a broad area of the caldera since the previous measurements on 11 May. This suggests a deeper source than usual. The biggest changes (20 mm) were recorded at the S end of Matupit Island."

Geologic Background. The low-lying Rabaul caldera on the tip of the Gazelle Peninsula at the NE end of New Britain forms a broad sheltered harbor utilized by what was the island's largest city prior to a major eruption in 1994. The outer flanks of the 688-m-high asymmetrical pyroclastic shield volcano are formed by thick pyroclastic-flow deposits. The 8 x 14 km caldera is widely breached on the east, where its floor is flooded by Blanche Bay and was formed about 1400 years ago. An earlier caldera-forming eruption about 7100 years ago is now considered to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the northern and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and western caldera walls. Several of these, including Vulcan cone, which was formed during a large eruption in 1878, have produced major explosive activity during historical time. A powerful explosive eruption in 1994 occurred simultaneously from Vulcan and Tavurvur volcanoes and forced the temporary abandonment of Rabaul city.

Information Contacts: P. de Saint-Ours and C. McKee, RVO.


Raung (Indonesia) — May 1992

Raung

Indonesia

8.119°S, 114.056°E; summit elev. 3260 m

All times are local (unless otherwise noted)


Infrared Space Shuttle photograph shows devegetated summit area

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

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

Geologic Background. Raung, one of Java's most active volcanoes, is a massive stratovolcano in easternmost Java that was constructed SW of the rim of Ijen caldera. The unvegetated summit is truncated by a dramatic steep-walled, 2-km-wide caldera that has been the site of frequent historical eruptions. A prehistoric collapse of Gunung Gadung on the W flank produced a large debris avalanche that traveled 79 km, reaching nearly to the Indian Ocean. Raung contains several centers constructed along a NE-SW line, with Gunung Suket and Gunung Gadung stratovolcanoes being located to the NE and W, respectively.

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


Rincon de la Vieja (Costa Rica) — May 1992 Citation iconCite this Report

Rincon de la Vieja

Costa Rica

10.83°N, 85.324°W; summit elev. 1916 m

All times are local (unless otherwise noted)


Thermal activity from crater lake; occasional seismicity

The active crater lake (150-200 m diameter) was gray to dirty white during May fieldwork, with weak, intermittent bubbling. Fumarolic activity in the E part of the crater, where water was slightly greenish, was stronger than during February fieldwork. The activity, audible at the crater rim, produced a plume that rose more than 100 m (the height of the crater wall), and was visible several kilometers N. Crater-lake level had dropped about 30 cm since February, while the temperature remained at 37°C and the pH at 1.6. Small mats of sulfur were visible on the lake surface. Weak vapor emission began at several points along a fissure (first observed in February) near the SE and SW rim, with temperatures of 55°C and 60°C, respectively.

Six microearthquakes were recorded in May (at OVSICORI station RIN3, 5 km S). A 16-minute tremor episode (1-2.5 Hz) was recorded on 22 May.

Geologic Background. Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge that was constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of 1916-m-high Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A plinian eruption producing the 0.25 km3 Río Blanca tephra about 3500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Information Contacts: G. Soto, R. Barquero, and Guillermo E. Alvardo, ICE; Mario Fernández, Univ. de Costa Rica; E. Fernández, J. Barquero, and V. Barboza, OVSICORI.


Rinjani (Indonesia) — May 1992

Rinjani

Indonesia

8.42°S, 116.47°E; summit elev. 3726 m

All times are local (unless otherwise noted)


Infrared Space Shuttle photo of Lombok Island during May 1992

Rinjani volcano on the island of Lombok (figure 1) is second in height among Indonesian volcanoes only to Sumatra's Kerinci volcano.

Figure (see Caption) Figure 1. Black-and-white reproduction of a Space Shuttle infrared photograph of Lombok Island and Rinjani sometime during 7-16 May 1992. The elevation-controlled shading is thought to reflect vegetation zones. NASA photograph number STS-49-97-051.

Geologic Background. Rinjani volcano on the island of Lombok rises to 3726 m, second in height among Indonesian volcanoes only to Sumatra's Kerinci volcano. Rinjani has a steep-sided conical profile when viewed from the east, but the west side of the compound volcano is truncated by the 6 x 8.5 km, oval-shaped Segara Anak (Samalas) caldera. The caldera formed during one of the largest Holocene eruptions globally in 1257 CE, which truncated Samalas stratovolcano. The western half of the caldera contains a 230-m-deep lake whose crescentic form results from growth of the post-caldera cone Barujari at the east end of the caldera. Historical eruptions dating back to 1847 have been restricted to Barujari cone and consist of moderate explosive activity and occasional lava flows that have entered Segara Anak lake.

Information Contacts:


Ruapehu (New Zealand) — May 1992 Citation iconCite this Report

Ruapehu

New Zealand

39.28°S, 175.57°E; summit elev. 2797 m

All times are local (unless otherwise noted)


Thermal activity but no phreatic eruptions from Crater Lake

The lake's temperature, measured during fieldwork on 6 May, had risen slightly to 34.5°C, but there was no evidence of further phreatic activity. Moderate upwelling over the N vents produced yellow slicks in the moderately steaming, battleship-gray lake. No upwelling from the central vent was visible. EDM data showed continued minor inflation across the lake.

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

Information Contacts: P. Otway, DSIR Wairakei.


Saba (Netherlands) — May 1992 Citation iconCite this Report

Saba

Netherlands

17.63°N, 63.23°W; summit elev. 887 m

All times are local (unless otherwise noted)


Seismic swarm

A high-frequency seismic swarm began at the volcano on 4 June, peaking on 10-11 June, and centered along a roughly NE-SW zone 20 km long (figure 1). Of the numerous earthquakes recorded by the regional seismic network (most stations are E or S of the island), 12 were locatable. These events were concentrated at ~8 km depth (1-65 km depth range) and had magnitudes between 2.9 and 4.4 (the largest, at 27 km depth, was recorded at 0148 on 11 June). Several earthquakes were felt by island residents, but there were no reports of damage or injuries. On 13 June, a portable 3-component seismograph was installed on the island, previously uninstrumented, to supplement the regional seismic network, but activity declined, and only two additional events had been located as of 16 June.

Figure (see Caption) Figure 1. Epicenter map of 12 earthquakes near Saba, 4-16 June 1992. Courtesy of the Seismic Research Unit, UWI.

Geologic Background. Saba, the northernmost active volcano of the West Indies, is a small 5-km-diameter island forming the upper half of a large stratovolcano that rises 1500 m above the sea floor. Its eruptive history is characterized by the emplacement of lava domes and associated pyroclastic flows. The summit of the volcano, known as Mount Scenery (or The Mountain), is a Holocene lava dome that overtops a major collapse scarp that formed about 100,000 years ago. Flank domes were constructed on the SW, SE, east, and NE sides of the island near the coast. A large andesitic lava flow entered the sea on the NE flank, forming the Flat Point Peninsula, the only site level enough on which to locate the island's airport. The village of The Bottom overlies pyroclastic-surge deposits that contain European pottery fragments and were radiocarbon dated at 280 +/- 80 years before present. The village was settled in 1640 on grassy meadows on the volcano's flanks reflecting initial vegetation recovery following destruction of tropical rainforests by pyroclastic flows and surges. Lava dome growth may also have occurred during this SW-flank eruption.

Information Contacts: L. Lynch, UWI; A. Smith, Univ of Puerto Rico.


Santa Maria (Guatemala) — May 1992 Citation iconCite this Report

Santa Maria

Guatemala

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

All times are local (unless otherwise noted)


Frequent explosions feed small ash columns; continued erosion threatens vent area

The dome was observed from the old "Hotel Magermann" site and the Santiaguito Volcano Observatory (NW of and 7 km S of the dome, respectively) during 21-24 May fieldwork by Michigan Technological Univ and INSIVUMEH scientists. Between 50 and 100 explosions occurred daily at Caliente vent (figure 24), typically producing relatively weak vertical columns to 500-2,000 m height. The plume was white to light gray, with a small convecting section (100-300 m high) at the base. Fine ash observed several kilometers from the vent consisted of dense, pulverized dacite and fragments of plagioclase; the eruptions were probably phreatic. Between explosions, passive gas emissions rose several hundred meters.

Figure (see Caption) Figure 24. Daily number of explosions recorded seismically at Santiaguito, March-April 1992. The arrow marks an unusually strong eruptive event and pyroclastic flow. Prepared by INSIVUMEH.

Several small, gray, vertical plumes were observed rising from near the SE base of Caliente, probably resulting from collapse at the front of a block lava flow. Although inclement weather prevented closer observation, plume locations suggested that the block lava flow had not progressed far since observations in late November 1991.

An extensive network of gullies, first observed on the N slope of Santiaguito in January 1990, has extended E to include Caliente vent. Rapid mass wasting, which began on the central dome (El Monje), resulted in numerous gullies that coalesced, greatly changing the appearance of the N flank. Scientists noted that continued erosion could severely undercut the large spines on Caliente's upper N flank, possibly causing their collapse and a subsequent rapid depressurization of the shallow magma system beneath Caliente. They warned that sudden depressurization could produce an extremely powerful pyroclastic eruption at the dome. One of INSIVUMEH's goals during its "Decade Volcano" program at Santiaguito is to monitor erosion processes and quantify mass-wasting rates at the dome.

The onset of the rainy season has annually caused an increased number of lahars in drainages S of the volcano. On 20 May, a lahar swept 12 km down the Río Nimá II. Fresh lahar deposits (about 1 m thick) found on terraces above the river's central channel indicated that the lahar was at least 2-3 m thick and 15-30 m wide.

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: Michael Conway, Michigan Technological Univ; Otoniel Matías, INSIVUMEH.


Spurr (United States) — May 1992 Citation iconCite this Report

Spurr

United States

61.299°N, 152.251°W; summit elev. 3374 m

All times are local (unless otherwise noted)


Ash eruption follows increased seismicity and thermal activity

Seismicity continued at abnormally high levels through early June. Much of the elevated seismicity since August 1991 has been concentrated beneath the main summit, and more recently beneath Crater Peak, 3 km S. The events occurred at 0-5 km depth. Most had magnitudes <1.0; maximum magnitude was 1.7. No long-period events have been recorded.

A localized increase in seismicity was recorded at about 0700 on 6 June, centered immediately beneath Crater Peak. The seismicity, different from previously recorded events, was characterized by bursts of 1-5-minute duration. These bursts of tremor-like activity were small, comparable to events that are often associated with hydrothermal activity at other volcanoes. Similar seismicity continued beneath Crater Peak in the succeeding weeks.

Geologists overflew Crater Peak on 8 June. Its small turquoise-colored crater lake (previously measured at 55°C), appeared darker than before and thermal upwelling was visible at the E end of the lake. Only a trace of SO2 was measured in the plume, similar to October 1991. During a visit on 11 June, the crater lake was dark gray, with a temperature of 50°C and a pH of 2.5. The large upwelling was still visible, as were a dozen smaller features, mostly near the E side of the lake. An increase in fumarolic activity was noted in the crater. One prominent fumarole in the talus cone N of the lake was gushing water, and periodically produced several 1-m-high geysers.

On 27 June, a series of explosive pulses produced a substantial ash plume. The eruption was preceded by increased seismicity, including a pair of tremor bursts lasting 2 1/2 hours each on 24 and 25 June, twice as long as any other episodes since they were first recorded on 6 June. An overflight on 26 June at about 1100 showed that the level of Crater Peak's lake had dropped, perhaps indicating increased heating. Continuous tremor began at 1204, and a swarm of volcano-tectonic earthquakes started at 0300 the next morning.

A moderate explosive eruption that began at 0704 on 27 June sent ash to about 8 km altitude. Additional seismic signals that may have indicated eruptive pulses were received at 0814 and 0904. Weather clouds obscured the volcano, limiting direct ground-based or satellite observations of the eruption, but the plume could be tracked as it spread N, away from populated areas. About 0.3 cm of sand-sized ash fell at Finger Lake, roughly 100 km N of the volcano. By late morning, satellite images showed that the plume extended 335 km at an azimuth of 005°, and had a maximum width of 75 km, about 200 km from the volcano. Pilot reports indicated that the top of the cloud was at about 9 km altitude. By midafternoon, the plume, heading 010°, was 670 km long and reached 200 km width 450 km from Spurr. Its base was reported at about 1500 m altitude from an aircraft roughly 400 km NNE of Spurr. After initially moving N, the plume turned toward the S and E, and had spread over western and central Canada by 29 June, when its narrow leading edge was over southern Lake Winnipeg, roughly 3500 km SE of the volcano. No new eruptions had been reported at press time, but a pilot saw a white cloud rising vertically from the volcano to 6-7.5 km altitude on 28 June at 0340. During an overflight early 29 June, the volcano was steaming, and debris and some incandescent material were present in and around the crater, but no major morphologic changes were evident. Mudflows and flooding associated with the eruption were apparently relatively minor.

Geologic Background. The summit of Mount Spurr, the highest volcano of the Aleutain arc, is a large lava dome constructed at the center of a roughly 5-km-wide horseshoe-shaped caldera open to the south. The volcano lies 130 km W of Anchorage and NE of Chakachamna Lake. The caldera was formed by a late-Pleistocene or early Holocene debris avalanche and associated pyroclastic flows that destroyed an ancestral edifice. The debris avalanche traveled more than 25 km SE, and the resulting deposit contains blocks as large as 100 m in diameter. Several ice-carved post-caldera cones or lava domes lie in the center of the caldera. The youngest vent, Crater Peak, formed at the breached southern end of the caldera and has been the source of about 40 identified Holocene tephra layers. Spurr's two historical eruptions, from Crater Peak in 1953 and 1992, deposited ash on the city of Anchorage.

Information Contacts: AVO; SAB, NOAA/NESDIS; AP.


Stromboli (Italy) — May 1992 Citation iconCite this Report

Stromboli

Italy

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

All times are local (unless otherwise noted)


Frequent explosions; increased seismicity

Seismic activity remained at a low level (around 100 explosions/day) from the beginning of 1992 through 8 April, when the seismic station was shut down for maintenance and conversion to a 3-component system. When operations resumed on 17 May, seismicity was unusually high, and the number of recorded events on 19 May was the largest since the station was installed in October 1989 (figure 25). Tremor amplitude briefly remained at November 1991 levels, but decreased rapidly beginning 20 May.

Figure (see Caption) Figure 25. Seismicity recorded at Stromboli, January-May 1992. Open bars show the total number of seismic events/day, while solid bars tally those with ground velocities exceeding 100 mm/s. The line represents tremor energy computed using 60-second samples taken every hour, then averaged daily. Courtesy of M. Riuscetti.

Daily summit observations 10-19 May revealed that activity was concentrated in craters C1 (vent 1) and C3 (vent 4) with glowing tephra ejected to 100-150 m height. Noisy vapor emissions lasting 15-20 seconds, accompanied by modest spatter ejection, occurred from a fissure in C2, on the W rim. Very modest activity continued from the small spatter cone in C3.

During the night of 16-17 May, Beat Gasser saw activity from several vents. Loud explosions occurred ~4 times an hour from C1, ejecting lava to as much as 300 m height for 5-10 seconds. Several explosions typically occurred at intervals of 5-10 minutes, followed by ~30 minutes of repose. Between explosions, a steady red glow and lava spattering were visible inside the crater, with spatter seldom reaching the crater's outer walls. Spattering declined before explosions. Crater C2 produced noisy 10-15-second gas emissions about once an hour. Ejections of a few red tephra fragments from C2 were seen during the night. East of C2, a steady red glow was visible at night within a small vent that was the source of pulsing gas emissions at 3-second intervals. Eruptions occurred about twice an hour from C3, but like those from C1 were not evenly spaced. Two eruptions typically occurred roughly 10 minutes apart, followed by nearly an hour of quiet. The three active craters never erupted simultaneously, and their eruptions were separated by intervals of at least 5 minutes.

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: M. Riuscetti, Univ di Udine; B. Gasser, Kloten, Switzerland.


Suwanosejima (Japan) — May 1992 Citation iconCite this Report

Suwanosejima

Japan

29.638°N, 129.714°E; summit elev. 796 m

All times are local (unless otherwise noted)


Tephra clouds from frequent explosions

Island residents reported frequent explosions, ashfalls, and rumbling in early and mid-May. Ash plumes were observed rising to 1.5-2.0 km elevation by Japanese airline pilots on 1-3 May, and a plume was visible on a NOAA weather satellite image at 1538 on 1 May.

Recently, the volcano had been active several times a year, with frequent explosions producing ash clouds and detectable ashfall. During peaks in activity, ash clouds rose to 2-3 km height and tens of small explosions occurred per minute. Eruptive episodes typically lasted for a few days to a month. Explosions had been reported earlier in 1992 on 1-4, 10, and 25-31 January, 4-14 and 21-28 February, 2-4 and 11-12 March, and 15-16 April.

Geologic Background. The 8-km-long, spindle-shaped island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. The summit of the volcano is truncated by a large breached crater extending to the sea on the east flank that was formed by edifice collapse. Suwanosejima, one of Japan's most frequently active volcanoes, was in a state of intermittent strombolian activity from Otake, the NE summit crater, that began in 1949 and lasted until 1996, after which periods of inactivity lengthened. The largest historical eruption took place in 1813-14, when thick scoria deposits blanketed residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed forming a large debris avalanche and creating the horseshoe-shaped Sakuchi caldera, which extends to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

Information Contacts: JMA; W. Gould, NOAA.


Tongariro (New Zealand) — May 1992 Citation iconCite this Report

Tongariro

New Zealand

39.157°S, 175.632°E; summit elev. 1978 m

All times are local (unless otherwise noted)


Fumarole temperatures and gas chemistry unchanged from 1989; no significant deformation or seismicity

Fumarole temperatures (93.9 & 94.3°C) and preliminary gas chromatograph data collected on 7 April were unchanged since the previous fieldwork in March 1989. No significant deformation was evident. Seismicity has remained relatively low.

Geologic Background. Tongariro is a large andesitic volcanic massif, located immediately NE of Ruapehu volcano, that is composed of more than a dozen composite cones constructed over a period of 275,000 years. Vents along a NE-trending zone extending from Saddle Cone (below Ruapehu volcano) to Te Mari crater (including vents at the present-day location of Ngauruhoe) were active during several hundred years around 10,000 years ago, producing the largest known eruptions at the Tongariro complex during the Holocene. North Crater stratovolcano, one of the largest features of the massif, is truncated by a broad, shallow crater filled by a solidified lava lake that is cut on the NW side by a small explosion crater. The youngest cone of the complex, Ngauruhoe, has grown to become the highest peak of the massif since its birth about 2500 years ago. The symmetrical, steep-sided Ngauruhoe, along with its neighbor Ruapehu to the south, have been New Zealand's most active volcanoes during historical time.

Information Contacts: P. Otway, DSIR Geology & Geophysics, Wairakei.


Unzendake (Japan) — May 1992 Citation iconCite this Report

Unzendake

Japan

32.761°N, 130.299°E; summit elev. 1483 m

All times are local (unless otherwise noted)


Lava-dome growth and pyroclastic flows

Lava-dome growth continued through mid-June, and pyroclastic flows were frequently generated by partial collapse of the dome complex. The new dome (7) which first appeared on 24 March (correction to 17:3-4), continued to grow, reaching 150 m length by the end of May. Lava extrusion formed "banana peel" and sometimes "petal" structures (petal with two lobes). Swelling of the cryptodome raised its summit to 1,390 m elevation, 30 m higher than the pre-eruption summit. Lava blocks on the surface of the cryptodome were reddish in color and small (< 10 m across, commonly a few m across), suggesting to geologists that they had broken into pieces during intrusion. Earthquakes, probably occurring within the dome complex, frequently triggered collapse of the cryptodome, causing it to develop a conical shape with a relatively smooth surface.

Collapses occurred at both sides of the growing lobes on dome 7, as well as at the dome front. One rockfall, measured by the GSJ with a theodolite, was estimated to have a volume of 1.2 x 105 m3. Pyroclastic flows generated from rockfalls traveled primarily down the dome complex's SE flank towards Mt. Iwatoko and into the Akamatsu valley, extensively burying its gentle slope (figure 42). Ash clouds accompanying the flows rose to about 1,000 m, with a maximum height of 1,400 m on 19 May. The pyroclastic-flow-deposit distribution was little changed from previous months. During mid-May to mid-June, 2-3 flows extended > 2 km/day, a flow 2.5 km long occurred every two days, and no flows reached > 3 km from the dome complex. Longer flows had a tendency to erode the steeper, upstream area, then deposit in the middle and downstream areas. The eroded upstream channels were subsequently filled by less-energetic flows. The longer flows tended to follow topographic lows quite closely, and as the saddle in the Akamatsu Valley was filled (~ 2.2 km SE from the front of dome 7), the height of the S cliff decreased from 30 to 10 m by early June. A deposition rate of ~ 35 cm/day was calculated for the mid-May to mid-June period.

Figure (see Caption) Figure 42. Map showing distribution of 1991-92 pyroclastic flow deposits at Unzen, mid-June 1992. 1991 pyroclastic surge deposits are not shown. Courtesy of Setsuya Nakada.

The magma-supply rate, based on mapping by the Geographical Survey Institute, was estimated to be roughly 2 x 105 m3/day for late February-late April, the lowest value since June 1991 (prior reported rates ranged from 2.5 to 3.5 x 105 m3/day). The low magma-supply rate reflects the low level of activity in April, when the lava domes grew very little, large pyroclastic flows were rare, and seismicity was at low levels. Estimates of magma supply in May-early June suggest that the rate had returned to ~ 3 x 105 m3/day. Geologists believe that the supply rate has probably fluctuated considerably since February. The volume of the dome complex was estimated to be 44 x 106 m3 on 25 April (similar to that of late February); combined pyroclastic flow and avalanche deposits, 50 x 106 m3 (dense rock equivalent); indicating a total erupted volume of ~ 94 x 106 m3.

Continued geomagnetic measurements by Kyoto Univ scientists show that the degree of demagnetization around the dome complex had decreased from mid-March. Demagnetization was strongest when lava first appeared in May 1991, and continued steadily until February 1992. Electronic distance measurements collected by the GSJ also showed the strongest shortening (between the summit and a point ~ 1.5 km away) in May 1991, and steady shortening through recent months, implying continuous swelling of the summit region.

Small earthquakes continued to occur beneath and within the dome complex, with 50-150/day in May-early June. A total of 3,235 earthquakes was recorded in May, similar to April. The daily number of seismically detected pyroclastic flows ranged from 5 to 17, with a total of 337 events, similar to previous months.

The evacuated area E of the volcano, in Shimabara and Fukae town, was reduced somewhat in June, decreasing the number of evacuees from 7,600 in May [to] about 6,750 by 11 June.

Geologic Background. The massive Unzendake volcanic complex comprises much of the Shimabara Peninsula east of the city of Nagasaki. An E-W graben, 30-40 km long, extends across the peninsula. Three large stratovolcanoes with complex structures, Kinugasa on the north, Fugen-dake at the east-center, and Kusenbu on the south, form topographic highs on the broad peninsula. Fugendake and Mayuyama volcanoes in the east-central portion of the andesitic-to-dacitic volcanic complex have been active during the Holocene. The Mayuyama lava dome complex, located along the eastern coast west of Shimabara City, formed about 4000 years ago and was the source of a devastating 1792 CE debris avalanche and tsunami. Historical eruptive activity has been restricted to the summit and flanks of Fugendake. The latest activity during 1990-95 formed a lava dome at the summit, accompanied by pyroclastic flows that caused fatalities and damaged populated areas near Shimabara City.

Information Contacts: S. Nakada, Kyushu Univ; JMA.


Villarrica (Chile) — May 1992 Citation iconCite this Report

Villarrica

Chile

39.42°S, 71.93°W; summit elev. 2847 m

All times are local (unless otherwise noted)


Volcanic earthquakes and tremor

Seismicity was recorded at the volcano during March-May by a telemetered seismic station (VNV) 4.5 km from the summit, at 1,400 m elev. The average tremor frequency decreased slightly from 1.9 Hz (in March-April) to 1.8 Hz (in May). Tremor frequency also decreased with distance from the summit. Average frequencies of 1.9, 0.8, and 0.6 Hz were recorded 4.5 km (station VNV), 18.7 km (station PP) and 21 km (station PL) from the volcano, respectively, in April. Since 28 May, activity has increased, and both tremor and volcanic earthquakes have been recorded.

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: G. Fuentealba and P. Peña, Univ de La Frontera; M. Petit-Breuilh, Fundación Andes, Temuco.


White Island (New Zealand) — May 1992 Citation iconCite this Report

White Island

New Zealand

37.52°S, 177.18°E; summit elev. 321 m

All times are local (unless otherwise noted)


Continued tephra ejection from three vents

Voluminous emission of lithic-dominated fine ash continued into May from three vents in the 1978/92 Crater complex. No obvious changes have occurred to crater morphology since the formation of a new collapse crater (Princess) in mid-April.

No ash was being emitted during 5 May fieldwork. Most of the gas emission occurred from a crater (Wade) that had ... enlarged considerably since February 1992. It occupied much of the floor of the 1978/92 Crater complex, with only narrow divides separating it from neighboring craters TV1... and May 91. A few ash-free ballistic blocks, apparently erupted from Princess Crater since heavy rain two days earlier, had fallen within ~50 m of the 1978/92 crater rim.

When geologists returned on 12 May, voluminous clouds of steam and light-gray ash were emerging from Princess, Wade, and TV1 Craters. The Wade/Princess and TV1/Princess pairs were sometimes simultaneously active. Ash from Princess Crater collected at 1125 was in accretionary flakes 1-3 mm across, composed of silt- to sand-sized pulverized andesite, along with much hydrothermal opal-C, anhydrite, natroalunite, and pyrite. Additional blocks, probably from TV1 Crater, had been deposited in an arc extending 50-100 m E of the 1978/92 complex rim. Fine gray ash coated the blocks, about half of which were weakly vesicular to scoriaceous andesite with xenoliths of thermally altered lithic material. Fractures on the N side of the subsided area, which developed next to Princess Crater in mid-April, suddenly began emitting steam along a zone 20-30 m long at about 1100; Princess Crater was active at the time, but neighboring TV1 was not. Fresh-looking, tephra-free surfaces suggested that movement was continuing along new fractures at the S wall of Main Crater. A trench dug at the rim of the 1978/92 Crater complex revealed 1.5 m of tephra accumulation since April 1991.

Seismicity showed little change since late April. A-type events were recorded 1-11 times a day, while B-types were less than 6/day. Variable-frequency volcanic tremor continued until about 27 April in 2-18-hour episodes. No additional tremor was evident until 13 May, when medium-frequency, low-amplitude signals followed an E-type eruption signature at 0843 (see below). The occurrence of tremor continued to correlate well with observed ash emission. E-type eruption signatures were detected 21 April at 1758; 26 April at 0804, 1425, and 2008; 27 April at 0116; 2 May at 2157 and 2208; 8 May at 0816; 9 May at 0724; 10 May at 0905; 11 May at 0040; 13 May at 0843 and 0855; 14 May at 0452 and 0629; and 17 May at 0119 and 1135. The last event was associated with an ash eruption seen during a COSPEC survey, which yielded an average SO2 emission rate of 350 t/d; see table 9 for a comparison with previous COSPEC data. The eruption, observed at 1139, fed a billowing cloud that rose 2,000 m. SO2 in the leading edge of the cloud corresponded to an emission rate of 950 t/d.

Table 9. SO2 emission measured by COSPEC at White Island, December 1983-May 1992. Courtesy of P. Kyle and W. Giggenbach.

Date SO2 Emissions (t/d)
23 Dec 1983 1200 ± 300
21 Nov 1984 320 ± 120
07 Jan 1985 350 ± 150
07 Feb 1986 570 ± 100
12 Jan 1987 830 ± 200
04 Nov 1987 900 ± 100
14 Dec 1990 362 ± 80
17 May 1992 350 ± 50

Deformation data showed continued subsidence E of the 1978/92 Crater rim (in the Donald Mound area) at rates that were apparently only slightly lower than in 1991. No acceleration in deformation had been detected over the April 1992 subsidence area in the 16 months preceding December 1991. Magnetic and gravity changes were small. Fumarole temperatures measured by an IR pyrometer have declined since March. The maximum value in mid-May was 211°C, probably depressed by heavy rains the preceding week.

Geologic Background. Uninhabited 2 x 2.4 km White Island, one of New Zealand's most active volcanoes, is the emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes; the summit crater appears to be breached to the SE, because the shoreline corresponds to the level of several notches in the SE crater wall. Volckner Rocks, four sea stacks that are remnants of a lava dome, lie 5 km NNE. Intermittent moderate phreatomagmatic and strombolian eruptions have occurred throughout the short historical period beginning in 1826, but its activity also forms a prominent part of Maori legends. Formation of many new vents during the 19th and 20th centuries has produced rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project.

Information Contacts: I. Nairn, DSIR Geology & Geophysics, Rotorua.

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/).