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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

Sabancaya (Peru) Explosions, gas-and-ash plumes, and thermal activity persist during November 2022-April 2023

Sheveluch (Russia) Significant explosions destroyed part of the lava-dome complex during April 2023

Bezymianny (Russia) Explosions, ash plumes, lava flows, and avalanches during November 2022-April 2023

Chikurachki (Russia) New explosive eruption during late January-early February 2023

Marapi (Indonesia) New explosive eruption with ash emissions during January-March 2023

Kikai (Japan) Intermittent white gas-and-steam plumes, discolored water, and seismicity during May 2021-April 2023

Lewotolok (Indonesia) Strombolian eruption continues through April 2023 with intermittent ash plumes

Barren Island (India) Thermal activity during December 2022-March 2023

Villarrica (Chile) Nighttime crater incandescence, ash emissions, and seismicity during October 2022-March 2023

Fuego (Guatemala) Daily explosions, gas-and-ash plumes, avalanches, and ashfall during December 2022-March 2023

Santa Maria (Guatemala) Active lava flows, explosions, ash plumes, and ashfall during December 2022-March 2023

Reventador (Ecuador) Daily explosions, gas-and-ash emissions, crater incandescence, and block avalanches during December 2022-March 2023



Sabancaya (Peru) — May 2023 Citation iconCite this Report

Sabancaya

Peru

15.787°S, 71.857°W; summit elev. 5960 m

All times are local (unless otherwise noted)


Explosions, gas-and-ash plumes, and thermal activity persist during November 2022-April 2023

Sabancaya is located in Peru, NE of Ampato and SE of Hualca Hualca. Eruptions date back to 1750 and have been characterized by explosions, phreatic activity, ash plumes, and ashfall. The current eruption period began in November 2016 and has more recently consisted of daily explosions, gas-and-ash plumes, and thermal activity (BGVN 47:11). This report updates activity during November 2022 through April 2023 using information from Instituto Geophysico del Peru (IGP) that use weekly activity reports and various satellite data.

Intermittent low-to-moderate power thermal anomalies were reported by the MIROVA project during November 2022 through April 2023 (figure 119). There were few short gaps in thermal activity during mid-December 2022, late December-to-early January 2023, late January to mid-February, and late February. According to data recorded by the MODVOLC thermal algorithm, there were a total of eight thermal hotspots: three in November 2022, three in February 2023, one in March, and one in April. On clear weather days, some of this thermal anomaly was visible in infrared satellite imagery showing the active lava dome in the summit crater (figure 120). Almost daily moderate-to-strong sulfur dioxide plumes were recorded during the reporting period by the TROPOMI instrument on the Sentinel-5P satellite (figure 121). Many of these plumes exceeded 2 Dobson Units (DU) and drifted in multiple directions.

Figure (see Caption) Figure 119. Intermittent low-to-moderate thermal anomalies were detected during November 2022 through April 2023 at Sabancaya, as shown in this MIROVA graph (Log Radiative Power). There were brief gaps in thermal activity during mid-December 2022, late December-to-early January 2023, late January to mid-February, and late February. Courtesy of MIROVA.
Figure (see Caption) Figure 120. Infrared (bands 12, 11, 8A) satellite images showed a constant thermal anomaly in the summit crater of Sabancaya on 14 January 2023 (top left), 28 February 2023 (top right), 5 March 2023 (bottom left), and 19 April 2023 (bottom right), represented by the active lava dome. Sometimes gas-and-steam and ash emissions also accompanied this activity. Courtesy of Copernicus Browser.
Figure (see Caption) Figure 121. Moderate-to-strong sulfur dioxide plumes were detected almost every day, rising from Sabancaya by the TROPOMI instrument on the Sentinel-5P satellite throughout the reporting period; the DU (Dobson Unit) density values were often greater than 2. Plumes from 23 November 2022 (top left), 26 December 2022 (top middle), 10 January 2023 (top right), 15 February 2023 (bottom left), 13 March 2023 (bottom middle), and 21 April 2023 (bottom right) that drifted SW, SW, W, SE, W, and SW, respectively. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

IGP reported that moderate activity during November and December 2022 continued; during November, an average number of explosions were reported each week: 30, 33, 36, and 35, and during December, it was 32, 40, 47, 52, and 67. Gas-and-ash plumes in November rose 3-3.5 km above the summit and drifted E, NE, SE, S, N, W, and SW. During December the gas-and-ash plumes rose 2-4 km above the summit and drifted in different directions. There were 1,259 volcanic earthquakes recorded during November and 1,693 during December. Seismicity also included volcano-tectonic-type events that indicate rock fracturing events. Slight inflation was observed in the N part of the volcano near Hualca Hualca (4 km N). Thermal activity was frequently reported in the crater at the active lava dome (figure 120).

Explosive activity continued during January and February 2023. The average number of explosions were reported each week during January (51, 50, 60, and 59) and February (43, 54, 51, and 50). Gas-and-ash plumes rose 1.6-2.9 km above the summit and drifted NW, SW, and W during January and rose 1.4-2.8 above the summit and drifted W, SW, E, SE, N, S, NW, and NE during February. IGP also detected 1,881 volcanic earthquakes during January and 1,661 during February. VT-type earthquakes were also reported. Minor inflation persisted near Hualca Hualca. Satellite imagery showed continuous thermal activity in the crater at the lava dome (figure 120).

During March, the average number of explosions each week was 46, 48, 31, 35, and 22 and during April, it was 29, 41, 31, and 27. Accompanying gas-and-ash plumes rose 1.7-2.6 km above the summit crater and drifted W, SW, NW, S, and SE during March. According to a Buenos Aires Volcano Ash Advisory Center (VAAC) notice, on 22 March at 1800 through 23 March an ash plume rose to 7 km altitude and drifted NW. By 0430 an ash plume rose to 7.6 km altitude and drifted W. On 24 and 26 March continuous ash emissions rose to 7.3 km altitude and drifted SW and on 28 March ash emissions rose to 7.6 km altitude. During April, gas-and-ash plumes rose 1.6-2.5 km above the summit and drifted W, SW, S, NW, NE, and E. Frequent volcanic earthquakes were recorded, with 1,828 in March and 1,077 in April, in addition to VT-type events. Thermal activity continued to be reported in the summit crater at the lava dome (figure 120).

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

Information Contacts: Instituto Geofisico del Peru (IGP), Centro Vulcanológico Nacional (CENVUL), Calle Badajoz N° 169 Urb. Mayorazgo IV Etapa, Ate, Lima 15012, Perú (URL: https://www.igp.gob.pe/servicios/centro-vulcanologico-nacional/inicio); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php); 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/); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard MD 20771, USA (URL: https://so2.gsfc.nasa.gov/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Sheveluch (Russia) — May 2023 Citation iconCite this Report

Sheveluch

Russia

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

All times are local (unless otherwise noted)


Significant explosions destroyed part of the lava-dome complex during April 2023

Sheveluch (also spelled Shiveluch) in Kamchatka, has had at least 60 large eruptions during the last 10,000 years. The summit is truncated by a broad 9-km-wide caldera that is breached to the S, and many lava domes occur on the outer flanks. The lava dome complex was constructed within the large open caldera. Frequent collapses of the dome complex have produced debris avalanches; the resulting deposits cover much of the caldera floor. A major south-flank collapse during a 1964 Plinian explosion produced a scarp in which a “Young Sheveluch” dome began to form in 1980. Repeated episodes of dome formation and destruction since then have produced major and minor ash plumes, pyroclastic flows, block-and-ash flows, and “whaleback domes” of spine-like extrusions in 1993 and 2020 (BGVN 45:11). The current eruption period began in August 1999 and has more recently consisted of lava dome growth, explosions, ash plumes, and avalanches (BGVN 48:01). This report covers a significant explosive eruption during early-to-mid-April 2023 that generated a 20 km altitude ash plume, produced a strong sulfur dioxide plume, and destroyed part of the lava-dome complex; activity described during January through April 2023 use information primarily from the Kamchatka Volcanic Eruptions Response Team (KVERT) and various satellite data.

Satellite data. Activity during the majority of this reporting period was characterized by continued lava dome growth, strong fumarole activity, explosions, and hot avalanches. According to the MODVOLC Thermal Alerts System, 140 hotspots were detected through the reporting period, with 33 recorded in January 2023, 29 in February, 44 in March, and 34 in April. Frequent strong thermal activity was recorded during January 2023 through April, according to the MIROVA (Middle InfraRed Observation of Volcanic Activity) graph and resulted from the continuously growing lava dome (figure 94). A slightly stronger pulse in thermal activity was detected in early-to-mid-April, which represented the significant eruption that destroyed part of the lava-dome complex. Thermal anomalies were also visible in infrared satellite imagery at the summit crater (figure 95).

Figure (see Caption) Figure 94. Strong and frequent thermal activity was detected at Sheveluch during January through April 2023, according to this MIROVA graph (Log Radiative Power). These thermal anomalies represented the continuously growing lava dome and frequent hot avalanches that affected the flanks. During early-to-mid-April a slightly stronger pulse represented the notable explosive eruption. Courtesy of MIROVA.
Figure (see Caption) Figure 95. Infrared (bands B12, B11, B4) satellite imagery showed persistent thermal anomalies at the lava dome of Sheveluch on 14 January 2023 (top left), 26 February 2023 (top right), and 15 March 2023 (bottom left). The true color image on 12 April 2023 (bottom right) showed a strong ash plume that drifted SW; this activity was a result of the strong explosive eruption during 11-12 April 2023. Courtesy of Copernicus Browser.

During January 2023 KVERT reported continued growth of the lava dome, accompanied by strong fumarolic activity, incandescence from the lava dome, explosions, ash plumes, and avalanches. Satellite data showed a daily thermal anomaly over the volcano. Video data showed ash plumes associated with collapses at the dome that generated avalanches that in turn produced ash plumes rising to 3.5 km altitude and drifting 40 km W on 4 January and rising to 7-7.5 km altitude and drifting 15 km SW on 5 January. A gas-and-steam plume containing some ash that was associated with avalanches rose to 5-6 km altitude and extended 52-92 km W on 7 January. Explosions that same day produced ash plumes that rose to 7-7.5 km altitude and drifted 10 km W. According to a Volcano Observatory Notice for Aviation (VONA) issued at 1344 on 19 January, explosions produced an ash cloud that was 15 x 25 km in size and rose to 9.6-10 km altitude, drifting 21-25 km W; as a result, the Aviation Color Code (ACC) was raised to Red (the highest level on a four-color scale). Another VONA issued at 1635 reported that no more ash plumes were observed, and the ACC was lowered to Orange (the second highest level on a four-color scale). On 22 January an ash plume from collapses and avalanches rose to 5 km altitude and drifted 25 km NE and SW; ash plumes associated with collapses extended 70 km NE on 27 and 31 January.

Lava dome growth, fumarolic activity, dome incandescence, and occasional explosions and avalanches continued during February and March. A daily thermal anomaly was visible in satellite data. Explosions on 1 February generated ash plumes that rose to 6.3-6.5 km altitude and extended 15 km NE. Video data showed an ash cloud from avalanches rising to 5.5 km altitude and drifting 5 km SE on 2 February. Satellite data showed gas-and-steam plumes containing some ash rose to 5-5.5 km altitude and drifted 68-110 km ENE and NE on 6 February, to 4.5-5 km altitude and drifted 35 km WNW on 22 February, and to 3.7-4 km altitude and drifted 47 km NE on 28 February. Scientists from the Kamchatka Volcanological Station (KVS) went on a field excursion on 25 February to document the growing lava dome, and although it was cloudy most of the day, nighttime incandescence was visible. Satellite data showed an ash plume extending up to 118 km E during 4-5 March. Video data from 1150 showed an ash cloud from avalanches rose to 3.7-5.5 km altitude and drifted 5-10 km ENE and E on 5 March. On 11 March an ash plume drifted 62 km E. On 27 March ash plumes rose to 3.5 km altitude and drifted 100 km E. Avalanches and constant incandescence at the lava dome was focused on the E and NE slopes on 28 March. A gas-and-steam plume containing some ash rose to 3.5 km altitude and moved 40 km E on 29 March. Ash plumes on 30 March rose to 3.5-3.7 km altitude and drifted 70 km NE.

Similar activity continued during April, with lava dome growth, strong fumarolic activity, incandescence in the dome, occasional explosions, and avalanches. A thermal anomaly persisted throughout the month. During 1-4 April weak ash plumes rose to 2.5-3 km altitude and extended 13-65 km SE and E.

Activity during 11 April 2023. The Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS) reported a significant increase in seismicity around 0054 on 11 April, as reported by strong explosions detected on 11 April beginning at 0110 that sent ash plumes up to 7-10 km altitude and extended 100-435 km W, WNW, NNW, WSW, and SW. According to a Tokyo VAAC report the ash plume rose to 15.8 km altitude. By 0158 the plume extended over a 75 x 100 km area. According to an IVS FEB RAS report, the eruptive column was not vertical: the initial plume at 0120 on 11 April deviated to the NNE, at 0000 on 12 April, it drifted NW, and by 1900 it drifted SW. KVS reported that significant pulses of activity occurred at around 0200, 0320, and then a stronger phase around 0600. Levin Dmitry took a video from near Békés (3 km away) at around 0600 showing a rising plume; he also reported that a pyroclastic flow traveled across the road behind him as he left the area. According to IVS FEB RAS, the pyroclastic flow traveled several kilometers SSE, stopping a few hundred meters from a bridge on the road between Klyuchi and Petropavlovsk-Kamchatsky.

Ashfall was first observed in Klyuchi (45 km SW) at 0630, and a large, black ash plume blocked light by 0700. At 0729 KVERT issued a Volcano Observatory Notice for Aviation (VONA) raising the Aviation Color Code to Red (the highest level on a four-color scale). It also stated that a large ash plume had risen to 10 km altitude and drifted 100 km W. Near-constant lightning strikes were reported in the plume and sounds like thunderclaps were heard until about 1000. According to IVS FEB RAS the cloud was 200 km long and 76 km wide by 0830, and was spreading W at altitudes of 6-12 km. In the Klyuchi Village, the layer of both ash and snow reached 8.5 cm (figure 96); ashfall was also reported in Kozyrevsk (112 km SW) at 0930, Mayskoye, Anavgay, Atlasovo, Lazo, and Esso. Residents in Klyuchi reported continued darkness and ashfall at 1100. In some areas, ashfall was 6 cm deep and some residents reported dirty water coming from their plumbing. According to IVS FEB RAS, an ash cloud at 1150 rose to 5-20 km altitude and was 400 km long and 250 km wide, extending W. A VONA issued at 1155 reported that ash had risen to 10 km and drifted 340 km NNW and 240 km WSW. According to Simon Carn (Michigan Technological University), about 0.2 Tg of sulfur dioxide in the plume was measured in a satellite image from the TROPOMI instrument on the Sentinel-5P satellite acquired at 1343 that covered an area of about 189,000 km2 (figure 97). Satellite data at 1748 showed an ash plume that rose to 8 km altitude and drifted 430 km WSW and S, according to a VONA.

Figure (see Caption) Figure 96. Photo of ash deposited in Klyuchi village on 11 April 2023 by the eruption of Sheveluch. About 8.5 cm of ash was measured. Courtesy of Kam 24 News Agency.
Figure (see Caption) Figure 97. A strong sulfur dioxide plume from the 11 April 2023 eruption at Sheveluch was visible in satellite data from the TROPOMI instrument on the Sentinel-5P satellite. Courtesy of Simon Carn, MTU.

Activity during 12-15 April 2023. On 12 April at 0730 satellite images showed ash plumes rose to 7-8 km altitude and extended 600 km SW, 1,050 km ESE, and 1,300-3,000 km E. By 1710 that day, the explosions weakened. According to news sources, the ash-and-gas plumes drifted E toward the Aleutian Islands and reached the Gulf of Alaska by 13 April, causing flight disruptions. More than 100 flights involving Alaska airspace were cancelled due to the plume. Satellite data showed ash plumes rising to 4-5.5 km altitude and drifted 400-415 km SE and ESE on 13 April. KVS volcanologists observed the pyroclastic flow deposits and noted that steam rose from downed, smoldering trees. They also noted that the deposits were thin with very few large fragments, which differed from previous flows. The ash clouds traveled across the Pacific Ocean. Flight cancellations were also reported in NW Canada (British Columbia) during 13-14 April. During 14-15 April ash plumes rose to 6 km altitude and drifted 700 km NW.

Alaskan flight schedules were mostly back to normal by 15 April, with only minor delays and far less cancellations; a few cancellations continued to be reported in Canada. Clear weather on 15 April showed that most of the previous lava-dome complex was gone and a new crater roughly 1 km in diameter was observed (figure 98); gas-and-steam emissions were rising from this crater. Evidence suggested that there had been a directed blast to the SE, and pyroclastic flows traveled more than 20 km. An ash plume rose to 4.5-5.2 km altitude and drifted 93-870 km NW on 15 April.

Figure (see Caption) Figure 98. A comparison of the crater at Sheveluch showing the previous lava dome (top) taken on 29 November 2022 and a large crater in place of the dome (bottom) due to strong explosions during 10-13 April 2023, accompanied by gas-and-ash plumes. The bottom photo was taken on 15 April 2023. Photos has been color corrected. Both photos are courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.

Activity during 16-30 April 2023. Resuspended ash was lifted by the wind from the slopes and rose to 4 km altitude and drifted 224 km NW on 17 April. KVERT reported a plume of resuspended ash from the activity during 10-13 April on 19 April that rose to 3.5-4 km altitude and drifted 146-204 km WNW. During 21-22 April a plume stretched over the Scandinavian Peninsula. A gas-and-steam plume containing some ash rose to 3-3.5 km altitude and drifted 60 km SE on 30 April. A possible new lava dome was visible on the W slope of the volcano on 29-30 April (figure 99); satellite data showed two thermal anomalies, a bright one over the existing lava dome and a weaker one over the possible new one.

Figure (see Caption) Figure 99. Photo showing new lava dome growth at Sheveluch after a previous explosion destroyed much of the complex, accompanied by a white gas-and-steam plume. Photo has been color corrected. Courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.

References. Girina, O., Loupian, E., Horvath, A., Melnikov, D., Manevich, A., Nuzhdaev, A., Bril, A., Ozerov, A., Kramareva, L., Sorokin, A., 2023, Analysis of the development of the paroxysmal eruption of Sheveluch volcano on April 10–13, 2023, based on data from various satellite systems, ??????????? ???????? ??? ?? ???????, 20(2).

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1,300 km3 andesitic volcano is one of Kamchatka's largest and most active volcanic structures, with at least 60 large eruptions during the Holocene. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes occur on its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large open caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Kamchatka Volcanological Station, Kamchatka Branch of Geophysical Survey, (KB GS RAS), Klyuchi, Kamchatka Krai, Russia (URL: http://volkstat.ru/); 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/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/); Kam 24 News Agency, 683032, Kamchatka Territory, Petropavlovsk-Kamchatsky, Vysotnaya St., 2A (URL: https://kam24.ru/news/main/20230411/96657.html#.Cj5Jrky6.dpuf); Simon Carn, Geological and Mining Engineering and Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA (URL: http://www.volcarno.com/, Twitter: @simoncarn).


Bezymianny (Russia) — May 2023 Citation iconCite this Report

Bezymianny

Russia

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

All times are local (unless otherwise noted)


Explosions, ash plumes, lava flows, and avalanches during November 2022-April 2023

Bezymianny is located on the Kamchatka Peninsula of Russia as part of the Klyuchevskoy volcano group. Historic eruptions began in 1955 and have been characterized by dome growth, explosions, pyroclastic flows, ash plumes, and ashfall. During the 1955-56 eruption a large open crater 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. The current eruption period began in December 2016 and more recent activity has consisted of strong explosions, ash plumes, and thermal activity (BGVN 47:11). This report covers activity during November 2022 through April 2023, based on weekly and daily reports from the Kamchatka Volcano Eruptions Response Team (KVERT) and satellite data.

Activity during November and March 2023 was relatively low and mostly consisted of gas-and-steam emissions, occasional small collapses that generated avalanches along the lava dome slopes, and a persistent thermal anomaly over the volcano that was observed in satellite data on clear weather days. According to the Tokyo VAAC and KVERT, an explosion produced an ash plume that rose to 6 km altitude and drifted 25 km NE at 1825 on 29 March.

Gas-and-steam emissions, collapses generating avalanches, and thermal activity continued during April. According to two Volcano Observatory Notice for Aviation (VONA) issued on 2 and 6 April (local time) ash plumes rose to 3 km and 3.5-3.8 km altitude and drifted 35 km E and 140 km E, respectively. Satellite data from KVERT showed weak ash plumes extending up to 550 km E on 2 and 5-6 April.

A VONA issued at 0843 on 7 April described an ash plume that rose to 4.5-5 km altitude and drifted 250 km ESE. Later that day at 1326 satellite data showed an ash plume that rose to 5.5-6 km altitude and drifted 150 km ESE. A satellite image from 1600 showed an ash plume extending as far as 230 km ESE; KVERT noted that ash emissions were intensifying, likely due to avalanches from the growing lava dome. The Aviation Color Code (ACC) was raised to Red (the highest level on a four-color scale). At 1520 satellite data showed an ash plume rising to 5-5.5 km altitude and drifting 230 km ESE. That same day, Kamchatka Volcanological Station (KVS) volcanologists traveled to Ambon to collect ash; they reported that a notable eruption began at 1730, and within 20 minutes a large ash plume rose to 10 km altitude and drifted NW. KVERT reported that the strong explosive phase began at 1738. Video and satellite data taken at 1738 showed an ash plume that rose to 10-12 km altitude and drifted up to 2,800 km SE and E. Explosions were clearly audible 20 km away for 90 minutes, according to KVS. Significant amounts of ash fell at the Apakhonchich station, which turned the snow gray; ash continued to fall until the morning of 8 April. In a VONA issued at 0906 on 8 April, KVERT stated that the explosive eruption had ended; ash plumes had drifted 2,000 km E. The ACC was lowered to Orange (the third highest level on a four-color scale). The KVS team saw a lava flow on the active dome once the conditions were clear that same day (figure 53). On 20 April lava dome extrusion was reported; lava flows were noted on the flanks of the dome, and according to KVERT satellite data, a thermal anomaly was observed in the area. The ACC was lowered to Yellow (the second lowest on a four-color scale).

Figure (see Caption) Figure 53. Photo showing an active lava flow descending the SE flank of Bezymianny from the lava dome on 8 April 2023. Courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.

Satellite data showed an increase in thermal activity beginning in early April 2023. A total of 31 thermal hotspots were detected by the MODVOLC thermal algorithm on 4, 5, 7, and 12 April 2023. The elevated thermal activity resulted from an increase in explosive activity and the start of an active lava flow. The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system based on the analysis of MODIS data also showed a pulse in thermal activity during the same time (figure 54). Infrared satellite imagery captured a continuous thermal anomaly at the summit crater, often accompanied by white gas-and-steam emissions (figure 55). On 4 April 2023 an active lava flow was observed descending the SE flank.

Figure (see Caption) Figure 54. Intermittent and low-power thermal anomalies were detected at Bezymianny during December 2022 through mid-March 2023, according to this MIROVA graph (Log Radiative Power). In early April 2023, an increase in explosive activity and eruption of a lava flow resulted in a marked increase in thermal activity. Courtesy of MIROVA.
Figure (see Caption) Figure 55. Infrared satellite images of Bezymianny showed a persistent thermal anomaly over the lava dome on 18 November 2022 (top left), 28 December 2022 (top right), 15 March 2023 (bottom left), and 4 April 2023 (bottom right), often accompanied by white gas-and-steam plumes. On 4 April a lava flow was active and descending the SE flank. Images using infrared (bands 12, 11, 8a). Courtesy of Copernicus Browser.

Geologic Background. The modern Bezymianny, much smaller than its massive neighbors Kamen and Kliuchevskoi on the Kamchatka Peninsula, was formed about 4,700 years ago over a late-Pleistocene lava-dome complex and an edifice built about 11,000-7,000 years ago. Three periods of intensified activity have occurred during the past 3,000 years. The latest period, which was preceded by a 1,000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large open 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: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Kamchatka Volcanological Station, Kamchatka Branch of Geophysical Survey, (KB GS RAS), Klyuchi, Kamchatka Krai, Russia (URL: http://volkstat.ru/); 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/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Chikurachki (Russia) — May 2023 Citation iconCite this Report

Chikurachki

Russia

50.324°N, 155.461°E; summit elev. 1781 m

All times are local (unless otherwise noted)


New explosive eruption during late January-early February 2023

Chikurachki, located on Paramushir Island in the northern Kuriles, has had Plinian eruptions during the Holocene. Lava flows have reached the sea and formed capes on the NW coast; several young lava flows are also present on the E flank beneath a scoria deposit. Reported eruptions date back to 1690, with the most recent eruption period occurring during January through October 2022, characterized by occasional explosions, ash plumes, and thermal activity (BGVN 47:11). This report covers a new eruptive period during January through February 2023 that consisted of ash explosions and ash plumes, based on information from the Kamchatka Volcanic Eruptions Response Team (KVERT) and satellite data.

According to reports from KVERT, an explosive eruption began around 0630 on 29 January. Explosions generated ash plumes that rose to 3-3.5 km altitude and drifted 6-75 km SE and E, based on satellite data. As a result, the Aviation Color Code (ACC) was raised to Orange (the second highest level on a four-color scale). At 1406 and 1720 ash plumes were identified in satellite images that rose to 4.3 km altitude and extended 70 km E. By 2320 the ash plume had dissipated. A thermal anomaly was visible at the volcano on 31 January, according to a satellite image, and an ash plume was observed drifting 66 km NE.

Occasional explosions and ash plumes continued during early February. At 0850 on 1 February an ash plume rose to 3.5 km altitude and drifted 35 km NE. Satellite data showed an ash plume that rose to 3.2-3.5 km altitude and drifted 50 km NE at 1222 later that day (figure 22). A thermal anomaly was detected over the volcano during 5-6 February and ash plumes drifted as far as 125 km SE, E, and NE. Explosive events were reported at 0330 on 6 February that produced ash plumes rising to 4-4.5 km altitude and drifting 72-90 km N, NE, and ENE. KVERT noted that the last gas-and steam plume that contained some ash was observed on 8 February and drifted 55 km NE before the explosive eruption ended. The ACC was lowered to Yellow and then Green (the lowest level on a four-color scale) on 18 February.

Figure (see Caption) Figure 22. Satellite image showing a true color view of a strong ash plume rising above Chikurachki on 1 February 2023. The plume drifted NE and ash deposits (dark brown-to-gray) are visible on the NE flank due to explosive activity. Courtesy of Copernicus Browser.

Geologic Background. Chikurachki, the highest volcano on Paramushir Island in the northern Kuriles, is a relatively small cone constructed on a high Pleistocene edifice. Oxidized basaltic-to-andesitic scoria deposits covering the upper part of the young cone give it a distinctive red color. Frequent basaltic Plinian eruptions have occurred during the Holocene. Lava flows have reached the sea and formed capes on the NW coast; several young lava flows are also present on the E flank beneath a scoria deposit. The Tatarinov group of six volcanic centers is located immediately to the south, and the Lomonosov cinder cone group, the source of an early Holocene lava flow that reached the saddle between it and Fuss Peak to the west, lies at the southern end of the N-S-trending Chikurachki-Tatarinov complex. In contrast to the frequently active Chikurachki, the Tatarinov centers are extensively modified by erosion and have a more complex structure. Tephrochronology gives evidence of an eruption around 1690 CE from Tatarinov, although its southern cone contains a sulfur-encrusted crater with fumaroles that were active along the margin of a crater lake until 1959.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far East Division, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Marapi (Indonesia) — May 2023 Citation iconCite this Report

Marapi

Indonesia

0.38°S, 100.474°E; summit elev. 2885 m

All times are local (unless otherwise noted)


New explosive eruption with ash emissions during January-March 2023

Marapi in Sumatra, Indonesia, is a massive stratovolcano that rises 2 km above the Bukittinggi Plain in the Padang Highlands. A broad summit contains multiple partially overlapping summit craters constructed within the small 1.4-km-wide Bancah caldera and trending ENE-WSW, with volcanism migrating to the west. Since the end of the 18th century, more than 50 eruptions, typically characterized by small-to-moderate explosive activity, have been recorded. The previous eruption consisted of two explosions during April-May 2018, which caused ashfall to the SE (BGVN 43:06). This report covers a new eruption during January-March 2023, which included explosive events and ash emissions, as reported by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) and MAGMA Indonesia.

According to a press release issued by PVMBG and MAGMA Indonesia on 26 December, primary volcanic activity at Marapi consisted of white gas-and-steam puffs that rose 500-100 m above the summit during April-December 2022. On 25 December 2022 there was an increase in the number of deep volcanic earthquakes and summit inflation. White gas-and-steam emissions rose 80-158 m above the summit on 5 January. An explosive eruption began at 0611 on 7 January 2023, which generated white gas-and-steam emissions and gray ash emissions mixed with ejecta that rose 300 m above the summit and drifted SE (figure 10). According to ground observations, white-to-gray ash clouds during 0944-1034 rose 200-250 m above the summit and drifted SE and around 1451 emissions rose 200 m above the summit. Seismic signals indicated that eruptive events also occurred at 1135, 1144, 1230, 1715, and 1821, but no ash emissions were visually observed. On 8 January white-and-gray emissions rose 150-250 m above the summit that drifted E and SE. Seismic signals indicated eruptive events at 0447, 1038, and 1145, but again no ash emissions were visually observed on 8 January. White-to-gray ash plumes continued to be observed on clear weather days during 9-15, 18-21, 25, and 29-30 January, rising 100-1,000 m above the summit and drifted generally NE, SE, N, and E, based on ground observations (figure 11).

Figure (see Caption) Figure 10. Webcam image of the start of the explosive eruption at Marapi at 0651 on 7 January 2023. White gas-and-steam emissions are visible to the left and gray ash emissions are visible on the right, drifting SE. Distinct ejecta was also visible mixed within the ash cloud. Courtesy of PVMBG and MAGMA Indonesia.
Figure (see Caption) Figure 11. Webcam image showing thick, gray ash emissions rising 500 m above the summit of Marapi and drifting N and NE at 0953 on 11 January 2023. Courtesy of PVMBG and MAGMA Indonesia.

White-and-gray and brown emissions persisted in February, rising 50-500 m above the summit and drifting E, S, SW, N, NE, and W, though weather sometimes prevented clear views of the summit. An eruption at 1827 on 10 February produced a black ash plume that rose 400 m above the summit and drifted NE and E (figure 12). Similar activity was reported on clear weather days, with white gas-and-steam emissions rising 50 m above the summit on 9, 11-12, 20, and 27 March and drifted E, SE, SW, NE, E, and N. On 17 March white-and-gray emissions rose 400 m above the summit and drifted N and E.

Figure (see Caption) Figure 12. Webcam image showing an eruptive event at 1829 on 10 February 2023 with an ash plume rising 400 m above the summit and drifting NE and E. Courtesy of PVMBG and MAGMA Indonesia.

Geologic Background. Gunung Marapi, not to be confused with the better-known Merapi volcano on Java, is Sumatra's most active volcano. This massive complex stratovolcano rises 2,000 m above the Bukittinggi Plain in the Padang Highlands. A broad summit contains multiple partially overlapping summit craters constructed within the small 1.4-km-wide Bancah caldera. The summit craters are located along an ENE-WSW line, with volcanism migrating to the west. More than 50 eruptions, typically consisting of small-to-moderate explosive activity, have been recorded since the end of the 18th century; no lava flows outside the summit craters have been reported in historical time.

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.esdm.go.id/v1).


Kikai (Japan) — May 2023 Citation iconCite this Report

Kikai

Japan

30.793°N, 130.305°E; summit elev. 704 m

All times are local (unless otherwise noted)


Intermittent white gas-and-steam plumes, discolored water, and seismicity during May 2021-April 2023

Kikai, located just S of the Ryukyu islands of Japan, contains a 19-km-wide mostly submarine caldera. The island of Satsuma Iwo Jima (also known as Satsuma-Iwo Jima and Tokara Iojima) is located at the NW caldera rim, as well as the island’s highest peak, Iodake. Its previous eruption period occurred on 6 October 2020 and was characterized by an explosion and thermal anomalies in the crater (BGVN 45:11). More recent activity has consisted of intermittent thermal activity and gas-and-steam plumes (BGVN 46:06). This report covers similar low-level activity including white gas-and-steam plumes, nighttime incandescence, seismicity, and discolored water during May 2021 through April 2023, using information from the Japan Meteorological Agency (JMA) and various satellite data. During this time, the Alert Level remained at a 2 (on a 5-level scale), according to JMA.

Activity was relatively low throughout the reporting period and has consisted of intermittent white gas-and-steam emissions that rose 200-1,400 m above the Iodake crater and nighttime incandescence was observed at the Iodake crater using a high-sensitivity surveillance camera. Each month, frequent volcanic earthquakes were detected, and sulfur dioxide masses were measured by the University of Tokyo Graduate School of Science, Kyoto University Disaster Prevention Research Institute, Mishima Village, and JMA (table 6).

Table 6. Summary of gas-and-steam plume heights, number of volcanic earthquakes detected, and amount of sulfur dioxide emissions in tons per day (t/d). Courtesy of JMA monthly reports.

Month Max plume height (m) Volcanic earthquakes Sulfur dioxide emissions (t/d)
May 2021 400 162 900-1,300
Jun 2021 800 117 500
Jul 2021 1,400 324 800-1,500
Aug 2021 1,000 235 700-1,000
Sep 2021 800 194 500-1,100
Oct 2021 800 223 600-800
Nov 2021 900 200 400-900
Dec 2021 1,000 161 500-1,800
Jan 2022 1,000 164 600-1,100
Feb 2022 1,000 146 500-1,600
Mar 2022 1,200 171 500-1,200
Apr 2022 1,000 144 600-1,000
May 2022 1,200 126 300-500
Jun 2022 1,000 154 400
Jul 2022 1,300 153 600-1,100
Aug 2022 1,100 109 600-1,500
Sep 2022 1,000 170 900
Oct 2022 800 249 700-1,200
Nov 2022 800 198 800-1,200
Dec 2022 700 116 600-1,500
Jan 2023 800 146 500-1,400
Feb 2023 800 135 600-800
Mar 2023 1,100 94 500-600
Apr 2023 800 82 500-700

Sentinel-2 satellite images show weak thermal anomalies at the Iodake crater on clear weather days, accompanied by white gas-and-steam emissions and occasional discolored water (figure 24). On 17 January 2022 JMA conducted an aerial overflight in cooperation with the Japan Maritime Self-Defense Force’s 1st Air Group, which confirmed a white gas-and-steam plume rising from the Iodake crater (figure 25). They also observed plumes from fumaroles rising from around the crater and on the E, SW, and N slopes. In addition, discolored water was reported near the coast around Iodake, which JMA stated was likely related to volcanic activity (figure 25). Similarly, an overflight taken on 11 January 2023 showed white gas-and-steam emissions rising from the Iodake crater, as well as discolored water that spread E from the coast around the island. On 14 February 2023 white fumaroles and discolored water were also captured during an overflight (figure 26).

Figure (see Caption) Figure 24. Sentinel-2 satellite images of Satsuma Iwo Jima (Kikai) showing sets of visual (true color) and infrared (bands 12, 11, 8a) views on 7 December 2021 (top), 23 October 2022 (middle), and 11 January 2023 (bottom). Courtesy of Copernicus Browser.
Figure (see Caption) Figure 25. Aerial image of Satsuma Iwo Jima (Kikai) showing a white gas-and-steam plume rising above the Iodake crater at 1119 on 17 January 2022. There was also green-yellow discolored water surrounding the coast of Mt. Iodake. Courtesy of JMSDF via JMA.
Figure (see Caption) Figure 26. Aerial image of Satsuma Iwo Jima (Kikai) showing white gas-and-steam plumes rising above the Iodake crater on 14 February 2023. Green-yellow discolored water surrounded Mt. Iodake. Courtesy of JCG.

Geologic Background. Multiple eruption centers have exhibited recent activity at Kikai, a mostly submerged, 19-km-wide caldera near the northern end of the Ryukyu Islands south of Kyushu. It was the source of one of the world's largest Holocene eruptions about 6,300 years ago when rhyolitic pyroclastic flows traveled across the sea for a total distance of 100 km to southern Kyushu, and ashfall reached the northern Japanese island of Hokkaido. The eruption devastated southern and central Kyushu, which remained uninhabited for several centuries. Post-caldera eruptions formed Iodake (or Iwo-dake) lava dome and Inamuradake scoria cone, as well as submarine lava domes. Recorded eruptions have occurred at or near Satsuma-Iojima (also known as Tokara-Iojima), a small 3 x 6 km island forming part of the NW caldera rim. Showa-Iojima lava dome (also known as Iojima-Shinto), a small island 2 km E of Satsuma-Iojima, was formed during submarine eruptions in 1934 and 1935. Mild-to-moderate explosive eruptions have occurred during the past few decades from Iodake, a rhyolitic lava dome at the eastern end of Satsuma-Iojima.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Japan Coast Guard (JCG) Volcano Database, Hydrographic and Oceanographic Department, 3-1-1, Kasumigaseki, Chiyoda-ku, Tokyo 100-8932, Japan (URL: https://www1.kaiho.mlit.go.jp/kaiikiDB/kaiyo30-2.htm); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Lewotolok (Indonesia) — May 2023 Citation iconCite this Report

Lewotolok

Indonesia

8.274°S, 123.508°E; summit elev. 1431 m

All times are local (unless otherwise noted)


Strombolian eruption continues through April 2023 with intermittent ash plumes

The current eruption at Lewotolok, in Indonesian’s Lesser Sunda Islands, began in late November 2020 and has included Strombolian explosions, occasional ash plumes, incandescent ejecta, intermittent thermal anomalies, and persistent white and white-and-gray emissions (BGVN 47:10). Similar activity continued during October 2022-April 2023, as described in this report based on information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, the Darwin Volcanic Ash Advisory Centre (VAAC), and satellite data.

During most days in October 2022 white and white-gray emissions rose as high as 200-600 m above the summit. Webcam images often showed incandescence above the crater rim. At 0351 on 14 October, an explosion produced a dense ash plume that rose about 1.2 km above the summit and drifted SW (figure 43). After this event, activity subsided and remained low through the rest of the year, but with almost daily white emissions.

Figure (see Caption) Figure 43. Webcam image of Lewotolok on 14 October 2022 showing a dense ash plume and incandescence above the crater. Courtesy of MAGMA Indonesia.

After more than two months of relative quiet, PVMBG reported that explosions at 0747 on 14 January 2023 and at 2055 on 16 January produced white-and-gray ash plumes that rose around 400 m above the summit and drifted E and SE (figure 44). During the latter half of January through April, almost daily white or white-and-gray emissions were observed rising 25-800 m above the summit, and nighttime webcam images often showed incandescent material being ejected above the summit crater. Strombolian activity was visible in webcam images at 2140 on 11 February, 0210 on 18 February, and during 22-28 March. Frequent hotspots were recorded by the MIROVA detection system starting in approximately the second week of March 2023 that progressively increased into April (figure 45).

Figure (see Caption) Figure 44. Webcam image of an explosion at Lewotolok on 14 January 2023 ejecting a small ash plume along with white emissions. Courtesy of MAGMA Indonesia.
Figure (see Caption) Figure 45. MIROVA Log Radiative Power graph of thermal anomalies detected by the VIIRS satellite instrument at Lewotolok’s summit crater for the year beginning 24 July 2022. Clusters of mostly low-power hotspots occurred during August-October 2022, followed by a gap of more than four months before persistent and progressively stronger anomalies began in early March 2023. Courtesy of MIROVA.

Explosions that produced dense ash plumes as high as 750 m above the summit were described in Volcano Observatory Notices for Aviation (VONA) at 0517, 1623, and 2016 on 22 March, at 1744 on 24 March, at 0103 on 26 March, at 0845 and 1604 on 27 March (figure 46), and at 0538 on 28 March. According to the Darwin VAAC, on 6 April another ash plume rose to 1.8 km altitude (about 370 m above the summit) and drifted N.

Figure (see Caption) Figure 46. Webcam image of Lewotolok at 0847 on 27 March 2023 showing a dense ash plume from an explosion along with clouds and white emissions. Courtesy of MAGMA-Indonesia.

Sentinel-2 images over the previous year recorded thermal anomalies as well as the development of a lava flow that descended the NE flank beginning in June 2022 (figure 47). The volcano was often obscured by weather clouds, which also often hampered ground observations. Ash emissions were reported in March 2022 (BGVN 47:10), and clear imagery from 4 March 2022 showed recent lava flows confined to the crater, two thermal anomaly spots in the eastern part of the crater, and mainly white emissions from the SE. Thermal anomalies became stronger and more frequent in mid-May 2022, followed by strong Strombolian activity through June and July (BGVN 47:10); Sentinel-2 images on 2 June 2022 showed active lava flows within the crater and overflowing onto the NE flank. Clear images from 23 April 2023 (figure 47) show the extent of the cooled NE-flank lava flow, more extensive intra-crater flows, and two hotspots in slightly different locations compared to the previous March.

Figure (see Caption) Figure 47. Sentinel-2 satellite images of Lewotolok showing sets of visual (true color) and infrared (bands 12, 11, 8a) views on 4 March 2022, 2 June 2022, and 23 April 2023. Courtesy of Copernicus Browser.

Geologic Background. The Lewotolok (or Lewotolo) stratovolcano occupies the eastern end of an elongated peninsula extending north into the Flores Sea, connected to Lembata (formerly Lomblen) Island by a narrow isthmus. It is symmetrical when viewed from the north and east. A small cone with a 130-m-wide crater constructed at the SE side of a larger crater forms the volcano's high point. Many lava flows have reached the coastline. Eruptions recorded since 1660 have consisted of explosive activity from the summit crater.

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.esdm.go.id/v1); 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/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Barren Island (India) — April 2023 Citation iconCite this Report

Barren Island

India

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

All times are local (unless otherwise noted)


Thermal activity during December 2022-March 2023

Barren Island is part of a N-S-trending volcanic arc extending between Sumatra and Burma (Myanmar). 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. Eruptions dating back to 1787, 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. Previous activity was detected during mid-May 2022, consisting of intermittent thermal activity. This report covers June 2022 through March 2023, which included strong thermal activity beginning in late December 2022, based on various satellite data.

Activity was relatively quiet during June through late December 2022 and mostly consisted of low-power thermal anomalies, based on the MIROVA (Middle InfraRed Observation of Volcanic Activity) graph. During late December, a spike in both power and frequency of thermal anomalies was detected (figure 58). There was another pulse in thermal activity in mid-March, which consisted of more frequent and relatively strong anomalies.

Figure (see Caption) Figure 58. Occasional thermal anomalies were detected during June through late December 2022 at Barren Island, but by late December through early January 2023, there was a marked increase in thermal activity, both in power and frequency, according to this MIROVA graph (Log Radiative Power). After this spike in activity, anomalies occurred at a more frequent rate. In late March, another pulse in activity was detected, although the power was not as strong as that initial spike during December-January. Courtesy of MIROVA.

The Suomi NPP/VIIRS sensor data showed five thermal alerts on 29 December 2022. The number of alerts increased to 19 on 30 December. According to the Darwin VAAC, ash plumes identified in satellite images captured at 2340 on 30 December and at 0050 on 31 December rose to 1.5 km altitude and drifted SW. The ash emissions dissipated by 0940. On 31 December, a large thermal anomaly was detected; based on a Sentinel-2 infrared satellite image, the anomaly was relatively strong and extended to the N (figure 59).

Figure (see Caption) Figure 59. Thermal anomalies of varying intensities were visible in the crater of Barren Island on 31 December 2022 (top left), 15 January 2023 (top right), 24 February 2023 (bottom left), and 31 March 2023 (bottom right), as seen in these Sentinel-2 infrared satellite images. The anomalies on 31 December and 31 March were notably strong and extended to the N and N-S, respectively. Images using “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Thermal activity continued during January through March. Sentinel-2 infrared satellite data showed some thermal anomalies of varying intensity on clear weather days on 5, 10, 15, 20, and 30 January 2023, 9, 14, 19, and 24 February 2023, and 21, 26, and 31 March (figure 59). According to Suomi NPP/VIIRS sensor data, a total of 30 thermal anomalies were detected over 18 days on 2-3, 7, 9-14, 16-17, 20, 23, 25, and 28-31 January. The sensor data showed a total of six hotspots detected over six days on 1, 4-5, and 10-12 February. During March, a total of 33 hotspots were visible over 11 days on 20-31 March. Four MODVOLC thermal alerts were issued on 25, 27, and 29 March.

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

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


Villarrica (Chile) — April 2023 Citation iconCite this Report

Villarrica

Chile

39.42°S, 71.93°W; summit elev. 2847 m

All times are local (unless otherwise noted)


Nighttime crater incandescence, ash emissions, and seismicity during October 2022-March 2023

Villarrica, located in central Chile, consists of a 2-km-wide caldera that formed about 3,500 years ago, located at the base of the presently active cone. Historical eruptions date back to 1558 and have been characterized by mild-to-moderate explosive activity with occasional lava effusions. The current eruption period began in December 2014 and has recently consisted of ongoing seismicity, gas-and-steam emissions, and thermal activity (BGVN 47:10). This report covers activity during October 2022 through March 2023 and describes Strombolian explosions, ash emissions, and crater incandescence. Information for this report primarily comes from the Southern Andes Volcano Observatory (Observatorio Volcanológico de Los Andes del Sur, OVDAS), part of Chile's National Service of Geology and Mining (Servicio Nacional de Geología y Minería, SERNAGEOMIN) and satellite data.

Seismicity during October consisted of discrete long-period (LP)-type events, tremor (TR), and volcano-tectonic (VT)-type events. Webcam images showed eruption plumes rising as high as 460 m above the crater rim; plumes deposited tephra on the E, S, and SW flanks within 500 m of the crater on 2, 18, 23, and 31 October. White gas-and-steam emissions rose 80-300 m above the crater accompanied by crater incandescence during 2-3 October. There was a total of 5 VT-type events, 10,625 LP-type events, and 2,232 TR-type events detected throughout the month. Sulfur dioxide data was obtained by the Differential Absorption Optical Spectroscopy Equipment (DOAS) installed 6 km in an ESE direction. The average value of the sulfur dioxide emissions was 535 ± 115 tons per day (t/d); the highest daily maximum was 1,273 t/d on 13 October. These values were within normal levels and were lower compared to September. During the night of 3-4 October Strombolian activity ejected blocks as far as 40 m toward the NW flank. Small, gray-brown ash pulses rose 60 m above the crater accompanied white gas-and-steam emissions that rose 40-300 m high during 4-5 October. In addition, crater incandescence and Strombolian explosions that ejected blocks were reported during 4-5 and 9-11 October. Based on satellite images from 12 October, ballistic ejecta traveled as far as 400 m and the resulting ash was deposited 3.2 km to the E and SE and 900 m to the NW.

Satellite images from 14 October showed an active lava lake that covered an area of 36 square meters in the E part of the crater floor. There was also evidence of a partial collapse (less than 300 square meters) at the inner SSW crater rim. POVI posted an 18 October photo that showed incandescence above the crater rim, noting that crater incandescence was visible during clear weather nights. In addition, webcam images at 1917 showed lava fountaining and Strombolian explosions; tourists also described seeing splashes of lava ejected from a depth of 80 m and hearing loud degassing sounds. Tephra deposits were visible around the crater rim and on the upper flanks on 24 October. On 25 October SERNAGEOMIN reported that both the number and amplitude of LP earthquakes had increased, and continuous tremor also increased; intense crater incandescence was visible in satellite images. On 31 October Strombolian explosions intensified and ejected material onto the upper flanks.

Activity during November consisted of above-baseline seismicity, including intensifying continuous tremor and an increase in the number of LP earthquakes. On 1 November a lava fountain was visible rising above the crater rim. Nighttime crater incandescence was captured in webcam images on clear weather days. Strombolian explosions ejected incandescent material on the NW and SW flanks during 1, 2, and 6-7 November. POVI reported that the width of the lava fountains that rose above the crater rim on 2 November suggested that the vent on the crater floor was roughly 6 m in diameter. Based on reports from observers and analyses of satellite imagery, material that was deposited on the upper flanks, primarily to the NW, consisted of clasts up to 20 cm in diameter. During an overflight on 19 November SERNAGEOMIN scientists observed a cone on the crater floor with an incandescent vent at its center that contained a lava lake. Deposits of ejecta were also visible on the flanks. That same day a 75-minute-long series of volcano-tectonic earthquakes was detected at 1940; a total of 21 events occurred 7.8 km ESE of the crater. Another overflight on 25 November showed the small cone on the crater floor with an incandescent lava lake at the center; the temperature of the lava lake was 1,043 °C, based data gathered during the overflight.

Similar seismicity, crater incandescence, and gas-and-steam emissions continued during December. On 1 December incandescent material was ejected 80-220 m above the crater rim. During an overflight on 6 December, intense gas-and-steam emissions from the lava lake was reported, in addition to tephra deposits on the S and SE flanks as far as 500 m from the crater. During 7-12 December seismicity increased slightly and white, low-altitude gas-and-steam emissions and crater incandescence were occasionally visible. On 24 December at 0845 SERNAGEOMIN reported an increase in Strombolian activity; explosions ejected material that generally rose 100 m above the crater, although one explosion ejected incandescent tephra as far as 400 m from the crater onto the SW flank. According to POVI, 11 explosions ejected incandescent material that affected the upper SW flank between 2225 on 25 December to 0519 on 26 December. POVI recorded 21 Strombolian explosions that ejected incandescent material onto the upper SW flank from 2200 on 28 December to 0540 on 29 December. More than 100 Strombolian explosions ejected material onto the upper W and NW flanks during 30-31 December. On 30 December at 2250 an explosion was detected that generated an eruptive column rising 120 m above the crater and ejecting incandescent material 300 m on the NW flank (figure 120). Explosions detected at 2356 on 31 December ejected material 480 m from the crater rim onto the NW flank and at 0219 material was deposited on the same flank as far as 150 m. Both explosions ejected material as high as 120 m above the crater rim.

Figure (see Caption) Figure 120. Webcam image of a Strombolian explosion at Villarrica on 30 December 2022 (local time) that ejected incandescent material 300 m onto the NW flank, accompanied by emissions and crater incandescence. Courtesy of SERNAGEOMIN (Reporte Especial de Actividad Volcanica (REAV), Region De La Araucania y Los Rios, Volcan Villarrica, 30 de diciembre de 2022, 23:55 Hora local).

During January 2023, Strombolian explosions and lava fountaining continued mainly in the crater, ejecting material 100 m above the crater. Gas-and-steam emissions rose 40-260 m above the crater and drifted in different directions, and LP-type events continued. Emissions during the night of 11 January including some ash rose 80 m above the crater and as far as 250 m NE flank. POVI scientists reported about 70 lava fountaining events from 2130 on 14 January to 0600 on 15 January. At 2211 on 15 January there was an increase in frequency of Strombolian explosions that ejected incandescent material 60-150 m above the crater. Some ashfall was detected around the crater. POVI noted that on 19 January lava was ejected as high as 140 m above the crater rim and onto the W and SW flanks. Explosion noises were heard on 19 and 22 January in areas within a radius of 10 km. During 22-23 January Strombolian explosions ejected incandescent material 60-100 m above the crater that drifted SE. A seismic event at 1204 on 27 January was accompanied by an ash plume that rose 220 m above the crater and drifted E (figure 121); later that same day at 2102 an ash plume rose 180 m above the crater and drifted E.

Figure (see Caption) Figure 121. Webcam image of an ash plume at Villarrica on 27 January rising 220 m above the crater and drifting E. Courtesy of SERNAGEOMIN (Reporte Especial de Actividad Volcanica (REAV), Region De La Araucania y Los Rios, Volcan Villarrica, 27 de enero de 2023, 12:35 Hora local).

Seismicity, primarily characterized by LP-type events, and Strombolian explosions persisted during February and March. POVI reported that three explosions were heard during 1940-1942 on 6 February, and spatter was seen rising 30 m above the crater rim hours later. On 9 February lava fountains were visible rising 50 m above the crater rim. On 17 February Strombolian explosions ejected material 100 m above the crater rim and onto the upper SW flank. Webcam images from 20 February showed two separate fountains of incandescent material, which suggested that a second vent had opened to the E of the first vent. Spatter was ejected as high as 80 m above the crater rim and onto the upper NE flank. A sequence of Strombolian explosions was visible from 2030 on 20 February to 0630 on 21 February. Material was ejected as high as 80 m above the crater rim and onto the upper E flank. LP-type earthquakes recorded 1056 and at 1301 on 27 February were associated with ash plumes that rose 300 m above the crater and drifted NE (figure 122). Crater incandescence above the crater rim was observed in webcam images on 13 March, which indicated Strombolian activity. POVI posted a webcam image from 2227 on 18 March showing Strombolian explosions that ejected material as high as 100 m above the crater rim. Explosions were heard up to 8 km away. On 19 March at 1921 an ash emission rose 340 m above the crater and drifted NE. On 21 and 26 March Strombolian explosions ejected material 100 and 110 m above the crater rim, respectively. On 21 March Strombolian explosions ejected material 100 m above the crater rim. Low-intensity nighttime crater incandescence was detected by surveillance cameras on 24 March.

Figure (see Caption) Figure 122. Photo of an ash plume rising 300 m above the crater of Villarrica and drifting NE on 27 February 2023. Courtesy of SERNAGEOMIN (Reporte Especial de Actividad Volcanica (REAV), Region De La Araucania y Los Rios, Volcan Villarrica, 27 de febrero de 2023, 11:10 Hora local).

Infrared MODIS satellite data processed by MIROVA (Middle InfraRed Observation of Volcanic Activity) detected an increase in thermal activity during mid-November, which corresponds to sustained Strombolian explosions, lava fountaining, and crater incandescence (figure 123). This activity was also consistently captured on clear weather days throughout the reporting period in Sentinel-2 infrared satellite images (figure 124).

Figure (see Caption) Figure 123. Low-power thermal anomalies were detected during August through October 2022 at Villarrica, based on this MIROVA graph (Log Radiative Power). During mid-November, the power and frequency of the anomalies increased and remained at a consistent level through March 2023. Thermal activity consisted of Strombolian explosions, lava fountains, and crater incandescence. Courtesy of MIROVA.
Figure (see Caption) Figure 124. Consistent bright thermal anomalies were visible at the summit crater of Villarrica in Sentinel-2 infrared satellite images throughout the reporting period, as shown here on 19 December 2022 (left) and 9 February 2023 (right). Occasional gas-and-steam emissions also accompanied the thermal activity. Images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Geologic Background. The glacier-covered Villarrica stratovolcano, in the northern Lakes District of central Chile, is ~15 km south of the city of Pucon. A 2-km-wide caldera that formed about 3,500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesite cone at the NW margin of a 6-km-wide Pleistocene caldera. More than 30 scoria cones and fissure vents are present on 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. Eruptions documented since 1558 CE 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/); 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).


Fuego (Guatemala) — April 2023 Citation iconCite this Report

Fuego

Guatemala

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

All times are local (unless otherwise noted)


Daily explosions, gas-and-ash plumes, avalanches, and ashfall during December 2022-March 2023

Fuego, one of three large stratovolcanoes overlooking the city of Antigua, Guatemala, has been vigorously erupting since January 2002, with recorded eruptions dating back to 1531 CE. Eruptive activity has included major ashfalls, pyroclastic flows, lava flows, and lahars. Frequent explosions with ash emissions, block avalanches, and lava flows have persisted since 2018. More recently, activity remained relatively consistent with daily explosions, ash plumes, ashfall, avalanches, and lahars (BGVN 48:03). This report covers similar activity during December 2022 through March 2023, based on information from the Instituto Nacional de Sismologia, Vulcanología, Meteorología e Hidrologia (INSIVUMEH) daily reports, Coordinadora Nacional para la Reducción de Desastres (CONRED) newsletters, and various satellite data.

Daily explosions reported throughout December 2022-March 2023 generated ash plumes to 6 km altitude that drifted as far as 60 km in multiple directions. The explosions also caused rumbling sounds of varying intensities, with shock waves that vibrated the roofs and windows of homes near the volcano. Incandescent pulses of material rose 100-500 m above the crater, which caused block avalanches around the crater and toward the Santa Teresa, Taniluyá (SW), Ceniza (SSW), El Jute, Honda, Las Lajas (SE), Seca (W), and Trinidad (S) drainages. Fine ashfall was also frequently reported in nearby communities (table 27). MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed frequent, moderate thermal activity throughout the reporting period; however, there was a brief decline in both power and frequency during late-to-mid-January 2023 (figure 166). A total of 79 MODVOLC thermal alerts were issued: 16 during December 2022, 17 during January 2023, 23 during February, and 23 during March. Some of these thermal evets were also visible in Sentinel-2 infrared satellite imagery at the summit crater, which also showed occasional incandescent block avalanches descending the S, W, and NW flanks, and accompanying ash plumes that drifted W (figure 167).

Table 27. Activity at Fuego during December 2022 through March 2023 included multiple explosions every hour. Ash emissions rose as high as 6 km altitude and drifted generally W and SW as far as 60 km, causing ashfall in many communities around the volcano. Data from daily INSIVUMEH reports and CONRED newsletters.

Month Explosions per hour Ash plume altitude (max) Ash plume distance (km) and direction Drainages affected by block avalanches Communities reporting ashfall
Dec 2022 1-12 6 km WSW, W, SW, NW, S, SE, NE, and E, 10-30 km Santa Teresa, Taniluyá, Ceniza, El Jute, Honda, Las Lajas, Seca, and Trinidad Panimaché I and II, Morelia, Santa Sofía, El Porvenir, Finca Palo Verde, Yepocapa, Yucales, Sangre de Cristo, La Rochela, Ceilán, San Andrés Osuna, and Aldea La Cruz
Jan 2023 1-12 5 km W, SW, NW, S, N, NE, E, and SE, 7-60 km Ceniza, Las Lajas, Santa Teresa, Taniluyá, Trinidad, Seca, Honda, and El Jute Panimaché I and II, Morelia, Santa Sofía, El Porvenir, Palo Verde, Yucales, Yepocapa, Sangre de Cristo, La Rochela, Ceylon, Alotenango, and San Andrés Osuna
Feb 2023 1-12 4.9 km SW, W, NW, and N, 10-30 km Santa Teresa, Taniluyá, Ceniza, Las Lajas, Seca, Trinidad, El Jute, and Honda Panimaché I and II, Morelia, Santa Sofía, Palo Verde, San Pedro Yepocapa, El Porvenir, Sangre de Cristo, La Soledad, Acatenango, El Campamento, and La Asunción
Mar 2023 3-11 5 km W, SW, NW, NE, N, S, SE, and E, 10-30 km Seca, Ceniza, Taniluyá, Las Lajas, Honda, Trinidad, El Jute, and Santa Teresa Yepocapa, Sangre de Cristo, Panimaché I and II, Morelia, Santa Sofía, El Porvenir, La Asunción, Palo Verde, La Rochela, San Andrés Osuna, Ceilán, and Aldeas
Figure (see Caption) Figure 166. Thermal activity at Fuego shown in the MIROVA graph (Log Radiative Power) was at moderate levels during a majority of December 2022 through March 2023, with a brief decline in both power and frequency during late-to-mid-January 2023. Courtesy of MIROVA.
Figure (see Caption) Figure 167. Frequent incandescent block avalanches descended multiple drainages at Fuego during December 2022 through March 2023, as shown in these Sentinel-2 infrared satellite images on 10 December 2022 (top left), 4 January 2023 (top right), 18 February 2023 (bottom left), and 30 March 2023 (bottom right). Gray ash plumes were also occasionally visible rising above the summit crater and drifting W, as seen on 4 January and 30 March. Avalanches affected the NW and S flanks on 10 December, the SW and W flanks on 18 February, and the NW, W, and SW flanks on 30 March. Images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Daily explosions ranged between 1 and 12 per hour during December 2022, generating ash plumes that rose to 4.5-6 km altitude and drifted 10-30 km in multiple directions. These explosions created rumbling sounds with a shock wave that vibrated the roofs and windows of homes near the volcano. Frequent white gas-and-steam plumes rose to 4.6 km altitude. Strombolian activity resulted in incandescent pulses that generally rose 100-500 m above the crater, which generated weak-to-moderate avalanches around the crater and toward the Santa Teresa, Taniluyá, Ceniza, El Jute, Honda, Las Lajas, Seca, and Trinidad drainages, where material sometimes reached vegetation. Fine ashfall was recorded in Panimaché I and II (8 km SW), Morelia (9 km SW), Santa Sofía (12 km SW), El Porvenir (8 km ENE), Finca Palo Verde, Yepocapa (8 km NW), Yucales (12 km SW), Sangre de Cristo (8 km WSW), La Rochela, Ceilán, San Andrés Osuna, and Aldea La Cruz. INSIVUMEH reported that on 10 December a lava flow formed in the Ceniza drainage and measured 800 m long; it remained active at least through 12 December and block avalanches were reported at the front of the flow. A pyroclastic flow was reported at 1100 on 10 December, descending the Las Lajas drainage for several kilometers and reaching the base of the volcano. Pyroclastic flows were also observed in the Ceniza drainage for several kilometers, reaching the base of the volcano on 11 December. Ash plumes rose as high as 6 km altitude, according to a special bulletin from INSIVUMEH. On 31 December explosions produced incandescent pulses that rose 300 m above the crater, which covered the upper part of the cone.

Activity during January 2023 consisted of 1-12 daily explosions, which produced ash plumes that rose to 4.2-5 km altitude and drifted 7-60 km in multiple directions (figure 168). Incandescent pulses of material were observed 100-350 m above the crater, which generated avalanches around the crater and down the Ceniza, Las Lajas, Santa Teresa, Taniluyá, Trinidad, Seca, Honda, and El Jute drainages. Sometimes, the avalanches resuspended older fine material 100-500 m above the surface that drifted W and SW. Ashfall was recorded in Panimaché I and II, Morelia, Santa Sofía, El Porvenir, Palo Verde, Yucales, Yepocapa, Sangre de Cristo, La Rochela, Ceylon, Alotenango, and San Andrés Osuna. Intermittent white gas-and-steam plumes rose to 4.5 km altitude and drifted W and NW.

Figure (see Caption) Figure 168. Webcam image showing an ash plume rising above Fuego on 15 January 2023. Courtesy of INSIVUMEH.

There were 1-12 daily explosions recorded through February, which generated ash plumes that rose to 4.2-4.9 km altitude and drifted 10-30 km SW, W, NW, and N. Intermittent white gas-and-steam emissions rose 4.5 km altitude and drifted W and SW. During the nights and early mornings, incandescent pulses were observed 100-400 m above the crater. Weak-to-moderate avalanches were also observed down the Santa Teresa, Taniluyá, Ceniza, Las Lajas, Seca, Trinidad, El Jute, and Honda drainages, sometimes reaching the edge of vegetated areas. Occasional ashfall was reported in Panimaché I and II, Morelia, Santa Sofía, Palo Verde, San Pedro Yepocapa, El Porvenir, Sangre de Cristo, La Soledad, Acatenango, El Campamento, and La Asunción. On 18 February strong winds resuspended previous ash deposits as high as 1 km above the surface that blew 12 km SW and S.

During March, daily explosions ranged from 3-11 per hour, producing ash plumes that rose to 4-5 km altitude and drifted 10-30 km W, SW, NW, NE, N, S, SE, and E. During the night and early morning, crater incandescence (figure 169) and incandescent pulses of material were observed 50-400 m above the crater. Weak-to-moderate avalanches affected the Seca, Ceniza, Taniluyá, Las Lajas, Honda, Trinidad, El Jute, and Santa Teresa drainages, sometimes reaching the edge of vegetation. Frequent ashfall was detected in Yepocapa, Sangre de Cristo, Panimaché I and II, Morelia, Santa Sofía, El Porvenir, La Asunción, Palo Verde, La Rochela, San Andrés Osuna, Ceilán, and Aldeas. Weak ashfall was recorded in San Andrés Osuna, La Rochela, Ceylon during 8-9 March. A lahar was reported in the Ceniza drainage on 15 March, carrying fine, hot volcanic material, tree branches, trunks, and blocks from 30 cm to 1.5 m in diameter. On 18 March lahars were observed in the Las Lajas and El Jute drainages, carrying fine volcanic material, tree branches and trunks, and blocks from 30 cm to 1.5 m in diameter. As a result, there was also damage to the road infrastructure between El Rodeo and El Zapote.

Figure (see Caption) Figure 169. Sentinel-2 infrared satellite image showing Fuego’s crater incandescence accompanied by a gas-and-ash plume that drifted SW on 25 March 2023. Images use bands 12, 11, 5. Courtesy of INSIVUMEH.

Geologic Background. Volcán Fuego, one of Central America's most active volcanoes, is also one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between Fuego and Acatenango to the north. 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 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: 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/ ); 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).


Santa Maria (Guatemala) — April 2023 Citation iconCite this Report

Santa Maria

Guatemala

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

All times are local (unless otherwise noted)


Active lava flows, explosions, ash plumes, and ashfall during December 2022-March 2023

The Santiaguito lava-dome complex of Guatemala's Santa María volcano has been actively erupting since 1922. The lava dome-complex formed within a large crater on the SW flank of Santa Maria that formed during the 1902 eruption. Ash explosions, pyroclastic flows, and lava flows have emerged from Caliente, the youngest of the four vents in the complex, for more than 40 years. The Caliente vent has an elevation of about 2.5 km, and the summit of Santa Maria is at about 3.7 km elevation. 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. Recent activity has included frequent explosions, ash plumes, and ashfall (BGVN 48:03) has persisted for this reporting period of December 2022 through March 2023, using information from Guatemala's INSIVUMEH (Instituto Nacional de Sismologia, Vulcanologia, Meterologia e Hidrologia) and satellite data.

Activity during December 2022 consisted of weak-to-moderate explosions and white-to-gray and blue gas-and-steam emissions that rose 200-800 m above the crater and drifted up to 15 km SW, NW, S, W, SSW, E, SE, and N. Explosions generated ash plumes that drifted as far as 6 km W and SW. Nighttime crater incandescence was often visible above the Caliente dome, accompanied by active lava flows that mainly traveled down the W, SW, and WSW flanks each day during December, also affecting the San Isidro (W) and El Tambor (SW) drainages. Frequent block-and-ash avalanches were detected on the W, WSW, S, and SE flanks, which sometimes resulted in ash plumes that drifted up to 10 km downwind. Ashfall was reported in Finca la Mosqueta and Santa Marta (5-6 km SW) on 2 December and in Las Marías (10 km S), Viejo Palmar, and the Palajunoj area on 9 December. On 11 December the active lava flow in the San Isidro and El Tambor drainages generated some block collapses, which resulted in ash clouds that rose several hundred meters high and drifted toward the Zanjón Seco drainage (SW flank). On 13, 18, 27, and 31 December block collapses from the lava flow generated ash clouds that rose several hundred meters high and drifted toward the San Isidro drainage. The smell of sulfur was reported on 13 December to the SE of the Caliente dome and on 14 December in the Las Marías area. Ashfall was recorded in Lotación Las Marías, Santa Marta, La Florida (6 km S), and El Faro (7 km S) on 22 December, which was accompanied by the smell of sulfur. Explosions on 27 and 31 December resulted in weak ashfall in El Faro, La Florida, Santa Marta, El Viejo (11 km S), El Palmar (12 km SSW), and Lotación Las Marías.

Daily white-to-gray gas-and-steam emissions continued during January 2023, rising 300-900 m above the crater, and drifting 3.5-8 km SW, W, S, SE, and E. Weak-to-moderate explosions persisted throughout the month, generating ash plumes that rose up to 900 m and drifted E, NE, and SW. Crater incandescence in the Caliente dome, on the S flank, and at the front of the lava flow on the W and SW flanks was visible. Lava flows were often observed on the W, SW, and WSW flanks in the San Isidro and El Tambor drainages; on 19 and 23 January the active lava flow was noted in the Zanjón Seco and San Isidro drainages and the longest part of the lava flow was 4.4 km on 15 January. Weak-to-moderate block collapses and block-and-ash avalanches were recorded at the middle and front of the lava flow on the W, SW, and WSW flanks of the Caliente dome, and on the S and SE flanks, which sometimes caused ash to rise as high as 1 km altitude and disperse 3 km to the W and S (figure 135). On 7 January explosions generated ash plumes that rose to 3 km altitude and drifted SW. On 9 January ashfall was recorded over Las Marías and El Viejo Palmar. The active lava flow in the San Isidro and El Tambor drainages generated some block collapses on 11 January, which produced ash plumes that rose several hundred meters high and caused weak ashfall in El Faro, La Florida, Santa Marta, El Viejo Palmar, and Las Marías. Ashfall was recorded at Monte Carlo on 13 January, weak ashfall was reported in El Faro, La Florida, Santa Marta, El Viejo Palmar, and Las Marías on 19 January, and weak ashfall was again reported on 23 January in Monte Claro, El Faro, La Florida, Santa Marta, and El Viejo Palmar.

Figure (see Caption) Figure 135. Image of gas-and-steam emissions rising above the Caliente dome at Santa María on 13 January 2023, accompanied by block avalanches descending the flanks. Photo has been color corrected. Courtesy of INSIVUMEH (BOLETÍN VULCANOLÓGICO ESPECIAL BESAN #001-2023, Guatemala 15 de enero de 2023, 18:30 horas (Hora Local)).

Similar activity persisted during February with frequent explosions that produced white gas-and-steam and ash emissions that rose 200-700 m above the crater and drifted SW, W, SE, E, and NW. During the night and early morning, constant crater incandescence at Caliente dome was observed, in addition to incandescence from the active lava flow on the W, SW, and WSW flanks. Weak-and-moderate avalanches were visible on the S, SW, W, SE, WSW, and E flanks and in the middle and front of the lava flow, sometimes generating ash clouds that rose several hundred meters high. Explosions on 3 February expelled gas-and-ash plumes that rose to 3.2 km altitude and drifted W. On 4 February explosions were accompanied by audible rumbles heard in El Palmar; gas-and-ash plumes rose several hundred meters above the lava dome and incandescent avalanches traveled W, S, and SE on the flanks. That same day, the lava flow was reported in the Zanjón Seco and San Isidro drainages; block collapses generated ash clouds that rose several hundred meters high. Weak ashfall was reported in Monte Claro, El Faro, La Florida, Santa Marta, and El Viejo Palmar. Seismic stations registered weak-to-moderate explosions that produced gray plumes that rose to 3.3 km altitude on 8, 11, and 19 February, which generally drifted W and SW. On 9 February ash plumes that rose 800 m above the crater and extended E. Explosions and block collapses on 12 February caused ashfall in Monte Claro, El Faro, La Florida, Santa Marta, and El Viejo Palmar. During the early morning of 15 February, four explosions were detected that generated gray plumes that rose to 2.9 km altitude. Nine explosions were recorded on 16 February, which produced gray plumes and generated weak avalanches on all flanks. On 20 February weak ashfalls from explosions and block collapses were reported in Monte Claro, El Faro, La Florida, Santa Marta, and El Viejo Palmar. Measurements taken on 23 February showed that the length of the lava flow was 4.3 km long.

During March, degassing 400-800 m above the crater dispersed W, SW, S, and SE, and nighttime crater and lava flow incandescence to the WSW continued. Weak-to-moderate avalanches were reported on the S, W, SE, E, and N flanks and from the middle and front of the lava flow. The lava flow remained active on the SW, W, and WSW flanks and in the Zanjón Seco and San Isidro drainages, occasionally accompanied by block collapses that generated ash clouds up to several hundreds of meters high. Weak-to-moderate explosions persisted throughout the month, producing gas-and-ash emissions rising 500-1,000 m above the crater and drifting SW. On 19 March a gas-and-ash plume rose to 3.2 km altitude and drifted S and SE; the lava flow remained at 4.3 km long on the SW flank, according to INSIVUMEH. Additionally, strong rains in the upper part of the volcanic complex caused a lahar to descend the Cabello de Ángel drainage on the SE flank, consisting of a cement-like mixture of volcanic material and transporting tree branches of varying sizes. Small pyroclastic flows were reported during 22-23 March. Explosions on 23 March generated an ash plume that rose to 3.5 km altitude and drifted W and on 24 March ash plumes rose to 4.3 km altitude and drifted W. On 31 March explosions produced ash plumes that rose to 3.5 km altitude and drifted W, accompanied by constant avalanches on the S, SW, E, and N flanks of the Caliente dome and small pyroclastic flows.

The MIROVA (Middle InfraRed Observation of Volcanic Activity) graph showed moderate-power thermal anomalies during the reporting period; the intensity gradually increased over January through March, and the frequency remained relatively high (figure 136). A total of 75 MODVOLC thermal alerts were issued on 40 days during December-March. Incandescent avalanches and active lava flows were also occasionally visible over the Caliente dome in Sentinel-2 infrared satellite imagery on clear weather days (figure 137).

Figure (see Caption) Figure 136. Moderate-power thermal anomalies were frequently detected at Santa María during 20 November 2022 through March 2023, as shown on this MIROVA graph (Log Radiative Power). Anomalies gradually increased in intensity beginning in January through March. Courtesy of MIROVA.
Figure (see Caption) Figure 137. Sentinel-2 infrared satellite imagery showing strong thermal activity at the Caliente dome of Santa María and incandescent avalanches and lava flows primarily on the SW and W flanks on 23 December 2022 (top left), 27 January 2023 (top right), 11 February 2023 (bottom left), and 3 March 2023 (bottom right). Clouds often covered the summit. Images rendered using bands 12, 11, 8a. Courtesy of Copernicus Browser.

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

Information Contacts: 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/); 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/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).


Reventador (Ecuador) — April 2023 Citation iconCite this Report

Reventador

Ecuador

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

All times are local (unless otherwise noted)


Daily explosions, gas-and-ash emissions, crater incandescence, and block avalanches during December 2022-March 2023

Volcán El Reventador, located in Ecuador, includes a 4-km-wide avalanche scarp open to the E. Recorded eruptions date back to the 16th century and have been characterized by explosive events, lava flows, ash plumes, and lahars. Frequent lahars in this region of heavy rainfall have built deposits on the scarp slope. The largest recorded 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. The current eruption began in July 2008 and more recently has consisted of daily explosions, ash plumes, lava flows, and block avalanches (BGVN 48:02). This report covers similar activity during December 2022 through March 2023 using daily reports from Ecuador's Instituto Geofisico (IG-EPN), the Washington Volcano Ash Advisory Center (VAAC), and satellite data.

During December 2022 through March 2023, IG-EPN reported daily explosions, gas-and-steam and ash plumes rising as high as 1,100 m above the crater, and frequent crater incandescence, often accompanied by incandescent block avalanches and lava flows that traveled down each of the flanks and lava flows that generally affected the NE and E flanks. On average, there were more daily explosions detected during December 2022 compared to January through March 2023, with 57 per day (table 17).

Table 17. Monthly summary of explosions and plume heights recorded at Reventador from December 2022 through March 2023. Data courtesy of IG-EPN (December 2022-March 2023 daily reports).

Month Average number of explosions per day Max plume height above the crater rim (m)
Dec 2022 57 1,000
Jan 2023 43 1,000
Feb 2023 30 1,000
Mar 2023 33 1,100

Activity during December 2022 consisted of daily explosions, ash plumes, crater incandescence, a lava flow, and occasional block avalanches, though cloudy weather often obscured clear views of the summit. There were 0-114 explosions recorded each day, in addition to long-period (LP) events and tremor emissions (TREMI). The Washington VAAC reported ash emissions that rose as high as 1.9 km above the crater during 5-6 and 12-13 December and drifted in different directions. IG-EPN also noted that gas-and-ash emissions rose 400-1,000 m above the summit and drifted S, W, NW, W, N, SW (figure 169). A lava flow was observed on the NE flank during 2-6 December and on the E flank during 9-11 December. There were six volcano-tectonic (VT) events detected during 7-8 December. Block avalanches frequently affected one, or multiple flanks, traveling 400-700 m below the crater. During 11-12 December a lava flow was reported on the NE flank.

Figure (see Caption) Figure 169. Webcam image of an ash plume rising 800 m above the crater of Reventador on 17 December 2022, accompanied by block avalanches on the flanks. Courtesy of IG-EPN (INFORME DIARIO DEL VOLCAN REVENTADOR No. 2022-351, 17 de diciembre de 2022).

Daily explosions and ash plumes continued during January 2023, with 12-96 explosions recorded each day. LP and TREMI-type events and crater incandescence were also frequently recorded on clear weather days, cloudy weather often obscured views of the summit. Gas-and-ash emissions rose 500-1,000 m above the crater and drifted W, NW, SW, N, and S. According to the Washington VAAC, ash emissions rose 688-3,750 m above the crater and drifted in multiple directions. During 31 December 2022 through 1 January 2023 nighttime crater incandescence was accompanied by block avalanches 500 m below the crater on all flanks. The lava flow continued to be observed on the NE flank during 31 December 2022 as well as during 1, 5-6, 7-9, 10-11, 16-17, 18-20, and 23-26 January. Block avalanches traveled 500-700 m from the crater throughout the month, affecting one or multiple flanks (figure 170). An ash plume was reported on 15 January that drifted S. A pyroclastic flow occurred during the morning of 29 January on the N flank.

Figure (see Caption) Figure 170. Thermal camera image showing the incandescent block avalanches (bright yellow) descending multiple flanks of Reventador on 22 January 2023. Courtesy of IG-EPN (INFORME DIARIO DEL VOLCAN REVENTADOR No. 2023-022, 22 de enero de 2023).

During February there were 12-100 daily explosions detected, along with LP and TREMI-type events. Crater incandescence persisted, in addition to block avalanches. Gas-and-ash emissions rose 200-1,000 m above the crater and drifted W, NW, NE, and N (figure 171). The Washington VAAC reported that ash emissions rose 400-2,200 m above the crater and drifted NE, NW, W, SW, SE, and N. During 1-6, 13-17, and 21-26 February incandescent block avalanches descended all the flanks 600-900 m below the crater. An active lava flow continued down the NE flank during 8-10, 14-15, 18-19, and 20-21 February. Block avalanches descended the E flank 900 m below the crater during 10-11 February. There were three VT-type events that were detected on 24 February.

Figure (see Caption) Figure 171. Webcam image of a gas-and-ash plume rising 1,000 m above the crater of Reventador on 25 February 2023. Photo has been color corrected. Courtesy of IG-EPN (INFORME DIARIO DEL VOLCAN REVENTADOR No. 2023-056, 25 de febrero de 2023).

Daily explosions, LP and TREMI-type events, crater incandescence, and block avalanches continued during March. There were 20-52 daily explosions recorded during the month. Cloudy weather often prevented clear views of the summit. Gas-and-ash emissions rose 600-1,100 m above the crater and drifted NW, W, N, NE, E, S, and SE. According to the Washington VAAC, ash emissions rose 688-1,300 m above the crater and drifted NW, W, NE, E, and SE. Block avalanches traveled down all the flanks 400-700 m below the crater during 2-3, 5-6, 8-12, 14-17, 23-24, and 30-31 March. During 6-7 March block avalanches descended all the flanks as far as 900 m below the crater, accompanied by ash emissions that rose 1,000 m above the summit that drifted W. IG-EPN reported that a lahar was detected on 6 March. During the nights of 12 and 15 March incandescent blocks moved down the S flank 400-500 m below the crater. During 20-21 March ash emissions rose 1 km above the crater and drifted S and SE (figure 172); reports from the Secretaría de Gestión de Riesgos (SGR) reported that light ashfall was observed in San Carlos and San Luis.

Figure (see Caption) Figure 172. Webcam image of a gas-and-ash plume rising Reventador on 20 March 2023. Courtesy of IG-EPN (INFORME DIARIO DEL VOLCAN REVENTADOR No. 2023-079, 20 de marzo de 2023).

Additional satellite data. MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed frequent thermal anomalies of moderate power during December 2022 through mid-January 2023, followed by a break in detected activity through late February (figure 173). During March, eight anomalies were detected intermittently throughout the month. The MODVOLC system identified a total of two thermal hotspots on 6 December 2022 and 20 March 2023. Although the summit was often obscured by weather clouds, Sentinel-2 infrared satellite images sometimes showed thermal activity at the summit crater (figure 174).

Figure (see Caption) Figure 173. Thermal activity at Reventador was more frequent during December 2022 through mid-January 2023, based on this MIROVA graph (Log Radiative Power). There was a short pause in detected activity during mid-January through late February. There were three anomalies detected during late February and eight during March. Courtesy of MIROVA.
Figure (see Caption) Figure 174. Sentinel-2 infrared satellite images of Reventador showed small thermal anomalies at the summit crater on 2 December 2022 (top left), 27 December 2022 (top right), 31 January 2023 (bottom left), and 25 February 2023 (bottom right). Though weather clouds often prevented clear views of the summit, gray ash emissions were sometimes visible above the clouds, as shown on 27 December and 25 February. Images with “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Geologic Background. Volcán El 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 stratovolcano has 4-km-wide avalanche scarp open to the E formed by edifice collapse. A young, unvegetated, cone rises from the amphitheater floor to a height comparable to the rim. It has been the source of numerous lava flows as well as explosive eruptions visible from Quito, about 90 km ESE. Frequent lahars in this region of heavy rainfall have left extensive deposits on the scarp slope. The largest recorded 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, Escuela Politécnica Nacional (IG-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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).

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Bulletin of the Global Volcanism Network - Volume 20, Number 11 (December 1995)

Managing Editor: Richard Wunderman

Aira (Japan)

Explosive eruptions continue to generate ash plumes

Akan (Japan)

Early November seismic swarm with two minutes of tremor

Arenal (Costa Rica)

Explosive activity increase from October; lava flows continue

Asosan (Japan)

Numerous isolated tremors

Barren Island (India)

Eruption apparently ends by late June, but aviation notice posted on 2 December

Erebus (Antarctica)

No significant activity from the active lava lake; gas measurements

Erta Ale (Ethiopia)

Lava lake still active with fountains as high as 15 m

Etna (Italy)

Six lava fountaining episodes from Northeast Crater

Fogo (Cabo Verde)

Eruption of 2 April through 28 May covered over 6 square kilometers of land

Fukutoku-Oka-no-Ba (Japan)

Discolored seawater

Galeras (Colombia)

Fumarolic and seismic activity continue at low levels

Irazu (Costa Rica)

Local seismicity detected

Kilauea (United States)

Surface lava flows, lava tubes, and ocean entries still active

Kujusan (Japan)

Seismically active with occasional lapilli and steam ejections

Langila (Papua New Guinea)

Ongoing eruptions lead to detectable ashfalls 10-15 km away

Lengai, Ol Doinyo (Tanzania)

Minor lava flows and projectile emission in December

Manam (Papua New Guinea)

Steam release with occasional minor ash and bombs

Monowai (New Zealand)

Earthquake swarm in late November detected acoustically

Negro, Cerro (Nicaragua)

Vigorous eruption produces a new cone, dome, lava flows, and large ash plumes

Niijima (Japan)

Seismic swarm on 4 December

Poas (Costa Rica)

Fumarolic and seismic activity

Rabaul (Papua New Guinea)

Small ash-bearing emissions from Tavurvur

Rincon de la Vieja (Costa Rica)

Additional details about the 6-10 November eruption

Shishaldin (United States)

Eruption sends ash plume above 10 km altitude

Soufriere Hills (United Kingdom)

Dome building, minor ash eruptions

St. Helens (United States)

Seismicity decreases without any explosive activity

Stromboli (Italy)

Low-level ash plumes and lava fountains during September-October

Suwanosejima (Japan)

Continued minor eruptive activity throughout much of 1995

Tokachidake (Japan)

Gradual increase in the number of seismic events

Ulawun (Papua New Guinea)

Modest degassing

Veniaminof (United States)

Minor steam and ash emissions in November

Whakaari/White Island (New Zealand)

Sub-crater divides collapse, but no eruptive activity



Aira (Japan) — December 1995 Citation iconCite this Report

Aira

Japan

31.5772°N, 130.6589°E; summit elev. 1117 m

All times are local (unless otherwise noted)


Explosive eruptions continue to generate ash plumes

Minami-dake crater was active throughout November-December 1995. Eruption totals for November and December were 19 and 42, respectively. Of these, explosive eruptions for the same months numbered 14 and 36, respectively. The local seismic station recorded 453 earthquakes and 446 tremors during November and 467 earthquakes and 83 tremors during December. The highest monthly ash plumes took place on 30 November (2,300 m above the crater), and on 9 December (1,700 m). Ashfall measured 10 km W of the crater was as follows: November, 5 g/m2; and December, 18 g/m2.

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 caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim and built an island that was joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4,850 years ago, after which eruptions took place at Minamidake. Frequent eruptions since the 8th century have deposited ash on the city of Kagoshima, located across Kagoshima Bay only 8 km from the summit. The largest recorded eruption took place during 1471-76.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


Akan (Japan) — December 1995 Citation iconCite this Report

Akan

Japan

43.384°N, 144.013°E; summit elev. 1499 m

All times are local (unless otherwise noted)


Early November seismic swarm with two minutes of tremor

On 1 November there were 46 earthquakes recorded, and small amplitude volcanic tremor continued for ~2 minutes. High seismicity continued through the 5th with 18-28 events/day. The November earthquakes totaled 643.

Geologic Background. Akan is a 13 x 24 km caldera located immediately SW of Kussharo caldera. The elongated, irregular outline of the caldera rim reflects its incremental formation during major explosive eruptions from the early to mid-Pleistocene. Growth of four post-caldera stratovolcanoes, three at the SW end of the caldera and the other at the NE side, has restricted the size of the caldera lake. Conical Oakandake was frequently active during the Holocene. The 1-km-wide Nakamachineshiri crater of Meakandake was formed during a major pumice-and-scoria eruption about 13,500 years ago. Within the Akan volcanic complex, only the Meakandake group, east of Lake Akan, has been historically active, producing mild phreatic eruptions since the beginning of the 19th century. Meakandake is composed of nine overlapping cones. The main cone of Meakandake proper has a triple crater at its summit. Historical eruptions at Meakandake have consisted of minor phreatic explosions, but four major magmatic eruptions including pyroclastic flows have occurred during the Holocene.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


Arenal (Costa Rica) — December 1995 Citation iconCite this Report

Arenal

Costa Rica

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

All times are local (unless otherwise noted)


Explosive activity increase from October; lava flows continue

October plumes rose as high as 1 km above Crater C. During the second week of November explosive activity increased, growing both in terms of the number of outbursts and the overall quantity of tephra emitted. Blocks and bombs landed above 1,000 m elevation. Ash columns rose over 1 km and blew over the NW, W, and SW flanks. Windows vibrated in buildings 6.5 km E (La Fortuna).

A lava flow first emitted in July remained mobile; one arm reached 860 m and another reached 900 m elevation. A new flow began at the end of the month, venting from a point S of the vent for the previous month's flow, and moving SW. Re-established vegetation in the zone of lava flows continued to degrade due to acid rain.

For the frequency range below 3.5 Hz, there were 765 events during October and 444 seismic events during November (figure 74). These events chiefly occurred associated with Strombolian eruptions; some were of sufficient amplitude to reach station JTS, 30 km from the active crater. The largest number recorded in a single day was 40 (on 5 November). During October and November, 2.1-3.5 Hz tremor took place for about 232 and 238 hours, respectively (figure 74). On 15 and 17 November tremor prevailed for 21 and 20 hours, respectively.

Figure (see Caption) Figure 74. Arenal seismicity and tremor for 1995 (recorded at station "VACR," 2.7 km NE of the main crater). Courtesy of OVSICORI-UNA.

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: E. Fernandez, E. Duarte, R. Saenz, W. Jimenez, and V. Barboza, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.


Asosan (Japan) — December 1995 Citation iconCite this Report

Asosan

Japan

32.8849°N, 131.085°E; summit elev. 1592 m

All times are local (unless otherwise noted)


Numerous isolated tremors

During November and December 1995 the floor of Naka-dake Crater 1 remained covered with hot water, yet there were few if any mud-and-water ejections. During November the number of isolated tremors reached 5,488; during December, 4,896. In addition, continuous tremor prevailed with amplitudes confined to 0.1-0.8 µm.

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: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


Barren Island (India) — December 1995 Citation iconCite this Report

Barren Island

India

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

All times are local (unless otherwise noted)


Eruption apparently ends by late June, but aviation notice posted on 2 December

Based on observations in late June 1995, the Indian Coast Guard reported on 1 July that explosive activity in the crater area had stopped, but gas emissions were still coming from the area near the coast. On 2 December an aviation Notice to Airmen (NOTAM) was issued from the United Kingdom for increased activity at Barren Island. However, no eruptive activity was seen on GMS satellite imagery over the area.

Landsat TM images from January 1995 (20:04) showed activity from a subsidiary vent on the S slope of the central crater. Subsequent images from 24 February, 13, 14, and 30 March, and 15 April 1995 also revealed activity from the central crater. Some of the images showed a lava or debris flow present in the WNW channel leading towards the sea. A thermal infrared image on 13 March showed a large hot central vent, and at least two subsidiary vents on the S slope; the image also revealed a lava passageway and the cooler plume.

Further Reference. Haldar, D., Chakraborty, S.C., and Chakraborty, P.P., 1996, The 1995 eruption of the Barren Island volcano in the Andaman Sea: Records, Geological Survey of India, v. 129(3), p. 59-62.

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: D. Haldar, Director, GSI Eastern Region, Calcutta; J. Lynch, SAB.


Erebus (Antarctica) — December 1995 Citation iconCite this Report

Erebus

Antarctica

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

All times are local (unless otherwise noted)


No significant activity from the active lava lake; gas measurements

Significant collapse of the Inner Crater was occurring in late 1995, although the lava lake remained fairly constant in size at ~20 m diameter and generally in the same location. No significant eruptions have occurred from the lava lake over the last 5 years and no bombs have been observed on the crater rim. Magma composition has shown no change over the last 20 years. A recent volume of 12 papers (Kyle, 1994) summarizes some aspects of the volcanic activity and environmental effects of Erebus through the 1980's and early 1990's.

Passive degassing from the lake contributes a small plume and the SO2 content has usually been monitored in December by COSPEC (see Kyle and others, 1994 for COSPEC data up to 1991). Since 1991 the SO2 emissions have ranged between 40 and 70 Mg/day (megagrams/day is the SI unit equivalent to metric tons/day); bad weather limited measurements in December 1995. FTIR (Fourier Transform Infrared) open-field spectrometry measurements in December confirmed the HCl/SO2 ratio of the emitted gases to be in agreement with measurements made by impregnated filters over the last 8 years. However, high CO levels significantly exceeded those of both HCl and SO2. Although CO2 in the plume has not been measured it is assumed to be high due to the alkalic nature of the magma. The high CO may be a function of the presumed high CO2 concentrations in the magma and its fairly low oxygen fugacity.

A network of eight seismic stations are operated as part of the Erebus Volcano Observatory by the New Mexico Institute of Mining and Technology. Seven stations have 1-Hz vertical single-component instruments, and the eighth is a 1-Hz three-component station. The stations have radio telemetry links to McMurdo Station where a digital event detection system and several analog helirecorders record the data, which are automatically transferred daily via the Internet to New Mexico for analysis and archiving. Details about the seismic network and associated seismicity can be accessed on the WWW Erebus page (see below).

Magmatic eruptive activity has been continuous since the discovery of a anorthoclase phonolite lava lake in 1972 (Giggenbach and others, 1973). Activity has been relatively uniform over the last 15 years with the exception of two significant events. In 1984 there was a 3-4 month period of larger and more frequent Strombolian eruptions which ejected bombs >2 km from the summit crater. On 19 October 1993 two moderate phreatic eruptions blasted a new crater ~80 m in diameter on the Main Crater floor and ejected debris over the northern Main Crater rim. These are the first known phreatic eruptions at Erebus, and probably resulted from steam build-up associated with melting snow in the crater.

References. Giggenbach, W.F., Kyle, P.R., and Lyons, G., 1973, Present volcanic activity on Erebus, Ross Island, Antarctica: Geology, v. 1, p. 135-136.

Kyle, P.R., Sybeldon, L.M., McIntosh, W.C., Meeker, K., and Symonds, R., 1994, Sulfur dioxide emissions rates from Mount Erebus, Antarctica, in Kyle (1994), p. 69-82.

Kyle, P.R., ed., 1994, Volcanological and Environmental Studies of Erebus, Antarctica: Antarctic Research Series, American Geophysical Union, v. 66.

Geologic Background. Mount Erebus, the world's southernmost historically active volcano, overlooks the McMurdo research station on Ross Island. It 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 3,200 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; other lava lakes are sometimes present. 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: Philip R. Kyle, Dept. of Earth and Environmental Sciences, New Mexico Institute of Mining and Technology, Socorro, NM 87801 USA.


Erta Ale (Ethiopia) — December 1995 Citation iconCite this Report

Erta Ale

Ethiopia

13.601°N, 40.666°E; summit elev. 585 m

All times are local (unless otherwise noted)


Lava lake still active with fountains as high as 15 m

Lava lakes have been present since 1967, and possibly 1906, although the N lava lake became inactive between 1988 and 1992. Recent ground observations were reported in September and November 1992. Observations have also been made using satellite imagery. New observations were made during 6-11 December 1995 by a team from Spele-Film and the Societe de Volcanologie Geneve while working for a French television network.

Only fumarolic activity was observed from the large crater (~300 m diameter) in the N part of the caldera. Fumaroles were concentrated SW of the pit within the crater, with some emissions coming from the inside wall and the slope of talus covering the pit floor. Almost all of the visible fumes came from the main pit, and seemed more abundant than in November 1992. A secondary pit crater with a diameter of ~15 m was seen in the SE part of the main pit.

Within the central part of the caldera, the S lava lake is located at the top of a small lava shield. The N and E flanks of this shield are partially covered by abundant lava flows originating from the N crater. The S flank of the shield is dominated by a large inactive cone. No fumes were visible, but the air near the pit-crater rim was very hot, frequently making it difficult to breathe without a mask. The diameter of the S pit-crater was ~140 m (based on a measured circumference of 446 +- 2 m), and the lake was 90 m below the W rim. The lava lake was similar in size and location to one observed in 1992, covering an area of ~60 x 100 m in the WSW part of the pit (figure 6). However, the level of the lake was believed to have risen ~5-6 m. Two slope breaks on the generally flat pit floor, not present in 1992, suggest that the entire floor may have subsided.

Figure (see Caption) Figure 6. Sketch showing a cross-sectional view of the central pit-crater (S lava lake) at Erta Ale, December 1995. Courtesy of P. Vetsch.

Lava lake activity was characterized by intermittent fountaining from as many as four locations at a time. No regular pattern was noted, but fountaining was more frequent near the SW border of the lake, and the more intense fountains (5-15 m high), started near the center of the lake and migrated to the border. During the stronger fountaining phases, a large raft of cooled surface lava moved towards the lake center. The lava lake was generally more active than in 1992. Pele's hair was frequently seen above the fountains, and some rose on the hot air out of the pit.

Geologic Background. The Erta Ale basaltic shield volcano in Ethiopia has a 50-km-wide edifice that rises more than 600 m from below sea level in the Danakil depression. The volcano includes a 0.7 x 1.6 km summit crater hosting steep-sided pit craters. Another larger 1.8 x 3.1 km wide depression elongated parallel to the trend of the Erta Ale range is located SE of the summit and is bounded by curvilinear fault scarps on the SE side. Basaltic lava flows from these fissures have poured into the caldera and locally overflowed its rim. The summit caldera usually also holds at least one long-term lava lake that has been active since at least 1967, and possibly since 1906. Recent fissure eruptions have occurred on the N flank.

Information Contacts: P. Vetsch, Societe de Volcanologie Geneve, B.P. 298, CH-1225 Chene-bourg, Switzerland; L. Cantamessa, Geo-Decouverte, 65 rue de Lausanne, CH-1202 Geneva, Switzerland; G. Farve and C. Rufi, Spele-Film, Borex, Switzerland; C. Peter, 14 Haupstrasse, D-82547 Eurasburg, Germany.


Etna (Italy) — December 1995 Citation iconCite this Report

Etna

Italy

37.748°N, 14.999°E; summit elev. 3357 m

All times are local (unless otherwise noted)


Six lava fountaining episodes from Northeast Crater

On 2 August 1995 explosive activity resumed at Northeast Crater (NEC) (BGVN 20:08). In August and September the activity was sporadic and low in intensity (BGVN 20:09), but after 2 October a vigorous Strombolian phase was observed (BGVN 20:10). Explosive activity occurred again during 19-22 October.

On 1 November there was vigorous spattering and bubbling of magma in a 15-m-wide pit on the NEC floor. Magma degassing formed large bubbles that burst, throwing spatter to the crater rim. In the following days the activity was discontinuous and less intense.

Lava fountaining episodes, 9-14 November. At 0014 on 9 November there was a sudden increase in volcanic tremor, but bad weather prevented summit observations. Between 0105 (at Trecastagni) and 0110 (at Catania, 30 km SSE) ash and lapilli fallout covered the SE flank (figure 61), eventually reaching as far as Siracusa, 75 km from the vent. The episode lasted only a few minutes and the material on the lower slope amounted to a few tens of grams per square meter, although rare dense lapilli broke some skylights and car windows. Fieldwork the next morning revealed that the NEC eruption produced a lava fountain followed by a strong phreatomagmatic blast. Part of the S rim collapsed inside the NEC and was later ejected. A welded spatter deposit several meters thick mantled the upper slope of the NEC cone and was overlain by a few centimeters of ash and lapilli. The bombs varied from 2-3 m close to the vent, to 25 cm at 2.5 km downwind. Several large accidental lithics (up to 1 m) occurred in the very proximal deposit. A large amount of spatter fell into the crater, raising its floor by several tens of meters. The crater appeared completely sealed, with wide red cracks on the crust of the spatter pile. The total volume of tephra from the 9 November eruption was ~1.5 x 106 m3.

Figure (see Caption) Figure 61. Map of the Etna area showing areas affected by ashfall on 9, 14, and 27 November, and 23 December 1995. Courtesy of IIV.

On 10 November a new lava fountain episode at NEC was observed from Catania around 0400-0530. Pulsating magma jets climbed up to 300 m above the crater rim; some were expelled up to 500 m. An ash-and-lapilli column ascended ~5,000 m and was blown SE. The spatter deposit was limited to the upper part of the volcano and in a narrow strip extending ~3 km SE; little ash fell on the middle slopes. The estimated volume of the pyroclastics was a few tens of thousands of cubic meters.

A third episode took place around 0600 on 14 November, and lasted ~3 hours. Between 0800 and 0900 the paroxysmal phase sent dense black ash columns through a white cloud covering the summit until they reached 5,000 m altitude. During the entire episode a non-continuous sustained eruptive column was observed and each ash puff contributed to a plume bent downwind that reached its buoyancy level at 6-7 km altitude. Ash and lapilli rained on the NE flank down to the coast (figure 61), leaving only a few grams of material per square meter on the middle and lower slopes. The proximal spatter deposits, mapped two days later, partially covered the previous ones on the cone and extended ~2 km NE in a band a few hundred meters wide. Lithic blocks and ash were less abundant than in deposits from the 9 November episode. The crater bottom was sealed by back-fallen welded spatter and was ~50 m below the crater rim, 100 m higher than before 9 November. The total volume of tephra from the 14 November eruptions was ~350,000 m3.

The volcano remained quiet after the 3rd episode. Within NEC, only a few large cracks on the welded spatter crust emitted fumes. Bocca Nuova crater showed a normal continuous degassing; Southeast and Voragine craters continued their steam emission.

Lava fountaining episodes, 22-27 November. Late on 22 November continuous glows were observed at NEC and some bangs were heard on the lower slopes. Beginning around midnight, two hours of fire fountaining and intense red glow was visible from Catania. The lava jets remained fairly low (~100 m above the crater rim) so the proximal spatter deposit mantled only the upper part of the cone, whereas the fine material fell on the SE flank as far as the coast. However, the total volume of the erupted material was limited to a few tens of thousand cubic meters, close to that of the second episode.

After the 22 November episode the vent was closed again by material that fell back into the crater. Three days later some bangs were heard at NEC and glow was observed during the night of 26-27 November. That morning seismic tremor rose suddenly and at 0715 an ash-and-lapilli column rose from the volcano. Cloud cover prevented direct observations. Ash and lapilli were carried by strong winds and fell on a narrow band of the N flank down to its foot (figure 61). Lapilli fallout ended around 1000, but the explosive activity continued for several hours. The thickness of the scoria-fall deposit varied from decimeters close to the vent to ~1 mm at 12 km away. The total tephra volume from this 5th eruptive episode was estimated at 0.4-0.5 x 106 m3.

Fieldwork two days later revealed that the proximal spatter deposits of the 22 and 26 November episodes were thinner than earlier ones. Lithic blocks were less abundant than in the 9 November deposits, but large ballistic scoriaceous bombs were found up to 500 m from the vent. The crater floor was completely sealed by fall-back spatter, but every 40-60 minutes a gas pocket broke the solid crust and a single lava bubble burst. These phenomena were observed for a few more days.

Activity during December. In the first half of December the summit craters were quiet, with continuous steam emissions, except for NEC, which had no open vent. A short explosive phase was reported on the night of 6 December. Poor weather conditions prevented observations until 16 December, when continuous Strombolian activity was seen at a small vent on the crater floor; a cone grew within a few days. The activity was characterized by the bursting of single magma bubbles alternating with degassing jets and spatter lasting from tens of seconds to a few minutes. This intense Strombolian activity continued for several days.

Around 1100 on 23 December strong bangs were heard from skiers on the upper slope. Very soon the bangs became frequent and black ash puffs were observed from NEC. Between 1215 and 1220 the first jet of magma rose above the crater rim, followed shortly by several pulses of magma jets and a large eruptive column. Between 1235 and 1305 the paroxysmal phase occurred, with jets of magma that rose 500-600 m (measured on the video record of the surveillance camera at La Montagnola, 2,700 m elevation on the S flank). Fragments from the top of the jets fed an eruptive column that reached 9.5 km altitude (6.2 km above the summit). Clear weather allowed observation of the column from many places on Sicily, as far as the city of Palermo 190 km away. Abundant ash and lapilli fell on a wide band of the NE flank down to the coast (figure 61). A brownish ash plume was emitted by Voragine during the entire paroxysmal phase of the eruption. Around 1330 the eruption quickly declined, but isolated explosions occurred until the evening. This episode was the most energetic among the six at NEC during November and December 1995.

The proximal deposit mantled the NEC cone with meters of welded spatter. In the W and E saddles between NEC and the Central Cone, spatter formed two thick lava flows a few hundred meters long. The E flow was still active during the night of 23-24 December; downslope movement of fluid material in the core produced continuous collapses of large incandescent blocks at the flow front. Crater modifications included the thick new scoria bank and widening and lowering of the S crater rim. Ballistic clasts had been thrown up to 600 m from the vent and landed as cow-pie bombs up to 2 m in diameter. The distal deposit from the eruptive column was made of scoriaceous bombs and lapilli up to 10-15 km from the vent, and from lapilli and a minor ash up to the shoreline, 22 km away. The bombs were very brittle, flat, and up to 30 cm in diameter at 6 km from the vent (observed while still in the air). The scoria-fall deposit formed a continuous band from the vent to the coast, damaging fruit plantations, vehicles, and buildings. The Messina-Catania freeway had to be cleared of a scoria deposit along a 4-km-long stretch. The deposit thickness along the dispersal axis was 6-7 cm at 6 km, 3-4 cm at 13 km, 3 cm at 16 km along the freeway, and 1-2 cm at 20 km near the coast. The estimated total volume of pyroclastics erupted on 23 December was ~3 x 106 m3.

On the days after 23 December eruption only a few blasts were heard from NEC, but on the nights of 27 and 28 December discontinuous glow was again seen, sometimes similar to those produced by mild Strombolian explosions. No further activity was reported at NEC or the other craters through the end of the year.

Tephra characteristics. Bombs and lapilli erupted during the November-December 1995 episodes are highly vesiculated and show glassy and smooth surfaces. Only in the volcanics erupted on 9 November are both vesicles and surfaces filled by reddish, fine-grained non-juvenile material. Juvenile ash consists of: 1) poorly vesiculated tachylitic (glassy) grains; 2) highly vesiculated clasts with glassy, smooth surfaces, and many Pele's hair and shards in the finer fraction; and 3) loose crystals covered in some cases by a thin film of glass.

Generally rounded grains with variable alteration form the non-juvenile fraction. In the ash fraction of all deposits, juvenile material is always the most abundant (60-100%), and preliminary investigation indicates that it increased with time. The juvenile fraction is ~60% of the 9 November ash, ~80% of the 14 November ash, and ~100% of the ash erupted during the following episodes (23 and 27 November, 23 December). The proportions of different juvenile components also changed during the eruptive sequence.

Scoria erupted during the November-December explosive episodes are, like most of Etna's historical volcanics, porphyritic hawaiites with phenocrysts of plagioclase, clinopyroxene, and olivine, and microphenocrysts of Ti-magnetite in a hyalopilitic groundmass. The scoria are more vesiculated and slightly less porphyritic than those erupted in October 1995. The chemical composition of November-December scoria is rather homogeneous even if the 9 and 14 November material is slightly more differentiated than those erupted after 23 November. Overall, the composition of the November-December volcanics is comparable to those of the Strombolian activity at NEC during the first half of October, and to the products erupted in the first days of the 1991-93 eruption.

Seismicity. Seismicity recorded by the permanent seismic network (12 stations; figure 62), during November-December 1995 was characterized by remarkable phases of increased volcanic tremor amplitude. Earthquake activity stayed at very low levels. A few tens of shocks took place and the only significant episode occurred on 24 December when a minor swarm (6 events; Mmax=3.2) was located near Mt. Maletto (NW slope of the volcano) at a depth of ~15 km.

Figure (see Caption) Figure 62. Map of Etna showing locations of seismic stations, tilt stations, and EDM networks maintained by the Istituto Internazionale di Vulcanologia as of December 1995. Courtesy of IIV.

Since the end of August 1995 volcanic tremor recorded at Pizzi Deneri (PDN: ~2 km from NEC, 2,820 m elevation) and Serra Pizzuta Calvarina (ESP: ~7 km from NEC, 1,590 m elevation) stations has shown an increasing trend. This pattern became more evident in late September, when some increases in tremor amplitude were recorded for durations ranging from tens of minutes to a few hours. The most relevant increases in tremor amplitude occurred on 22-23 September, 2, 3 and 21 October, 9, 10, 14, 22-23, and 27 November, and 23 December. This tremor amplitude pattern correlated with visually observed NEC eruptive activity.

The volcanic tremor spectral amplitude temporal pattern at PDN and ESP stations showed a clear amplitude increase. Spectral amplitude peaks were superimposed on the increased trend and corresponded to the episodes listed above. Dominant peaks in tremor spectra recorded at PDN and ESP stations showed a high-frequency (~3.5 Hz) trend coincident with the high tremor amplitude. Each amplitude increase showed similar characteristics.

Ground deformation. After the end of the 1991-93 eruption deformation was dominated by steady inflation, mostly affecting the W and NE slopes. Positive trends of areal dilatation, cumulating at ~14 ppm, were clearly apparent on the SW and NE flank EDM networks (figure 62) following the 1991-93 eruption, while the S network was characterized by a flat trend of areal dilatation for several years. Both the SW and NE networks followed comparable trends, only differing in the recent sharp positive gradient variation (10 ppm) shown by the latter between August and October.

The shallow bore-hole permanent tilt network (figure 62) indicated a progressive increase (starting by the second half of 1993) in the radial tilt component recorded at the stations on the W flank (MSC: 50 µrad) and on the N flank (MNR: 10 µrad), while the S slope showed no appreciable positive variation until July 1995. The eruptive activity resumed at the summit craters by late July-early August, and the renewed ejection of magma appeared to be strictly related in time to the positive variation of the radial tilt at SPC (~15 µrad) and the sharp increase of areal dilatation in the NE sector. Radial tilt at PDN was affected by a sharp negative variation (35 µrad) at almost the same time.

September EDM survey on the S flank. J. Moss noted that reoccupation of a different S-flank EDM network in September 1995 showed only minor line extension since eruptive activity resumed in August. Significant extensions of lines perpendicular to the Valle del Bove accompanied dike emplacement prior to the 1991-93 eruption. However, the July 1995 survey showed only minor changes since July 1994. Over 80% of the lines measured between those two surveys showed extension, suggesting a pattern of broad edifice inflation. The small strain rates suggest that no magma was intruded into this part of the S rift zone prior to September 1995.

Geologic Background. Mount Etna, towering above Catania on the island of Sicily, has one of the world's longest documented records of 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 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: M. Coltelli, M. Pompilio, E. Privitera, S. Spampinato, and S. Bonaccorso, CNR Istituto Internazionale di Vulcanologia (IIV), Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ingv.it/en/); Jane L. Moss, Cheltenham and Gloucester College of Higher Education, Francis Close Hall, Swindon Road, Cheltenham GL50 4AZ, United Kingdom.


Fogo (Cabo Verde) — December 1995 Citation iconCite this Report

Fogo

Cabo Verde

14.95°N, 24.35°W; summit elev. 2829 m

All times are local (unless otherwise noted)


Eruption of 2 April through 28 May covered over 6 square kilometers of land

The eruption that began on 2 April (BGVN 20:04 and 20:05) ended on or about 28 May, according to V. Martins. New lava flows covered ~6.3 km2 of land. The total volume of lava extruded was ~60-100 x 106 m3, assuming lava flow thicknesses of ~9-15 m; the known range was from 1 to >20 m. Based on six major-element XRF analyses, the lava flow erupted during the first night (3 April) was determined to be a differentiated kaersutite-bearing phonotephrite (IUGS system), whereas later lava flows and spatter were more primitive tephrite basanite.

Fogo Island consists of a single massive volcano with an 8-km-wide caldera breached to the E. The central cone was apparently almost continuously active from the time of Portuguese settlement in 1500 A.D. until around 1760. The June-August 1951 eruption from caldera vents S and NW of the central cone began with ejection of pyroclastic material.

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

Information Contacts: Richard Moore, U.S. Geological Survey, Mail Stop 903, Federal Center Box 25046, Denver, CO 80225 USA; Frank Trusdell, U.S. Geological Survey, Hawaiian Volcano Observatory, Hawaii National Park, HI 96718, USA; Veronica Carvalho Martins, U.S. Embassy, Rua Hoji Ya Henda 81, C.P. 201, Praia, Cape Verde; Arrigo Querido, INGRH Servicos Estudos Hidrologicos, C.P. 367, Praia, Cape Verde.


Fukutoku-Oka-no-Ba (Japan) — December 1995 Citation iconCite this Report

Fukutoku-Oka-no-Ba

Japan

24.285°N, 141.481°E; summit elev. -29 m

All times are local (unless otherwise noted)


Discolored seawater

An aviator flying over the waters of the southern Volcano Islands for Japan's Maritime Safety Agency reported seeing light-green seawater on 25, 27, and 28 November. Discolored seawater was last seen at this location in September 1993.

Geologic Background. Fukutoku-Oka-no-ba is a submarine volcano located 5 km NE of the island of Minami-Ioto. Water discoloration is frequently observed, and several ephemeral islands have formed in the 20th century. The first of these formed Shin-Ioto ("New Sulfur Island") in 1904, and the most recent island was formed in 1986. The volcano is part of an elongated edifice with two major topographic highs trending NNW-SSE, and is a trachyandesitic volcano geochemically similar to Ioto.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


Galeras (Colombia) — December 1995 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


Fumarolic and seismic activity continue at low levels

Volcanic activity remained low during November and December. No significant surface changes were detected during this period, in agreement with electronic tiltmeter measurements on the E flank. Gas emission was concentrated in the W part of the crater, and the El Paisita, Las Chavas, La Joya, and Las Deformes fumaroles remained active. During 2-22 November there were temperature increases at Las Deformes and Las Chavas of 28 and 14°C, respectively. Correlation spectrometer measurements of the SO2 flux remained low (<100 metric tons/day).

There were a few small seismic events associated with fluid movement in November, and sporadic seismicity associated with rock fracturing 2-4 km NNE of the active crater. During December, high-frequency seismicity consisted of small events (M <2.6) concentrated in the seismogenic region 6 km NE of the crater. Local residents felt events on 4 and 29 December that were M 2.5 and 2.6, respectively. The first of these events was centered in the NE region at 5 km depth, and the second at 7 km SW of the crater at 8 km depth. Only three small long-period events were recorded.

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 open 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 eruptions since the time of the Spanish conquistadors.

Information Contacts: Pablo Chamorro, INGEOMINAS - Observatorio Vulcanologico y Sismologico de Pasto, A.A. 1795, San Juan de Pasto, Narino, Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html).


Irazu (Costa Rica) — December 1995 Citation iconCite this Report

Irazu

Costa Rica

9.979°N, 83.852°W; summit elev. 3436 m

All times are local (unless otherwise noted)


Local seismicity detected

During October Irazú's seismic station (IRZ2), located 5 km SW of the active crater, registered 14 low-frequency events and an additional 19 microseisms that were only detected locally.

Geologic Background. The massive Irazú volcano in Costa Rica, immediately E of the capital city of San José, covers an area of 500 km2 and is vegetated to within a few hundred meters of its broad summit crater complex. At least 10 satellitic cones are located on its S flank. No lava effusion is known since the eruption of the 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 main crater, which contains a small lake. The first well-documented 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. Phreatic activity reported in 1994 may have been a landslide event from the fumarolic area on the NW summit (Fallas et al., 2018).

Information Contacts: E. Fernandez, E. Duarte, R. Saenz, W. Jimenez, and V. Barboza, OVSICORI-UNA.


Kilauea (United States) — December 1995 Citation iconCite this Report

Kilauea

United States

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

All times are local (unless otherwise noted)


Surface lava flows, lava tubes, and ocean entries still active

The East Rift Zone eruption continued in the last quarter of 1995 with lava erupting from the 780-m elevation flank vent next to the Pu`u `O`o cone (figure 98). The lava immediately entered subsurface tubes and traveled SE toward the coast, a distance of ~11 km.

Figure (see Caption) Figure 98. Map of recent lava flows from Kīlauea's east rift zone, October 1995. Contours are in meters and the contour interval is approximately 150 m. Courtesy of the USGS Hawaiian Volcano Observatory.

Activity during 10 October-6 November. Most surface flows broke out from the tubes on the steep slope of Pulama Pali and on the coastal plain. Some of these flows burned vegetation and extended the flow field at the base of Pulama Pali several hundred meters E. On the flats at the coast, surface flows occurred just upslope from the ocean entry at Kamokuna, and also 1 km farther W, near the old Kamoamoa campground. A major bench collapse at the Kamokuna entry on 16-17 October was accompanied by explosive activity that built two littoral cones.

A portion of the crater floor in the Pu`u `O`o cone collapsed, leaving a pit ~50 m in diameter that was partially filled by a large rockslide from the base of the W crater wall. The timing of the pit formation probably coincided with seismic events either on 19 and/or 29 October. The lava pond rose to ~75 m below the N spillway. On the upper slope above Pulama Pali, new skylights in the roof of the lava tubes continued to appear and crust over rapidly. Surface flows in this area and on the slope of Pulama Pali were small and infrequent. Most of the lava traveled via lava tubes to the coastal plain on the E side of the Kamoamoa flow field. Isolated breakouts occurred in the central part of the flow field, below Paliuli. The ocean entry at Kamokuna continued to produce a large acidic plume. Interaction between lava and seawater was occasionally explosive and formed two littoral cones on the bench.

Eruption tremor levels remained relatively low with amplitudes ~2x background. Long-period events from both shallow- and intermediate-depth sources continued at low-moderate rates. The number of short period microearthquakes was low beneath the summit and rift zones.

Activity during 7 November-4 December. A brief pause during the night of 10-11 November was immediately preceded by increased shallow seismic tremor and slight summit deflation. By the morning of 11 November lava was no longer entering the ocean at Kamokuna; however, activity at the eruption vent and the Pu`u `O`o cone had already resumed. During the afternoon, the lava pond was very active, its level fluctuating at least 10-15 m within 30 minutes, with spattering up to a height of 30 m. By the following day, lava was once again entering the ocean. Since this short pause, the lava pond has maintained a level ~75 m below the N rim. The floor of the large collapse pit was partially resurfaced by new lava flows after the pause.

Surface flows on the lower slope of Pulama pali and on the coastal plain continued to expand the Kamoamoa flow field E into forest and grasslands. At the shoreline, advancing pahoehoe flows filled the gap created by Kupaianaha eruptions in 1992, at the E edge of the current Kamoamoa flow field. These flows have produced a new ocean entry ~500 m E of the Kamokuna entry.

A large bench at the West Kamokuna entry collapsed on 23 November. Sustained explosive activity on 26 November built a new littoral cone (3-4 m high) on the bench. Lava was entering the ocean at 2-3 locations along a new East Kamokuna bench, located inside the W edge of the old Kupaianaha flow field. Breakouts from the relatively immature tube system were continuously active on the coastal plain near this entry. An older tube continued to feed isolated breakouts in the middle of the Kamoamoa flow field. The long-lived skylight at 735 m elevation finally crusted over in late November, leaving the tube system completely sealed off for the first 4 km from the vent. However, new skylights continued to appear and crust over near the top of Pulama Pali.

Eruption tremor was low and relatively steady, with a few isolated increases in amplitude in banded patterns. Shallow, long-period microearthquakes were slightly above average on 11, 12, and 16 November, with daily counts of nearly 100. Intermediate-depth, long-period counts were high on 2 and 3 December. Short-period summit and rift microearthquake counts were low.

Activity during 5 December-1 January. Small surface breakouts were observed high on Pulama Pali and on the coastal plain. The West Kamokuna entry occupied a large, mature bench; on 12 December, explosive activity at this entry built a new littoral cone. The East Kamokuna entry continued building a new bench. A pause in the eruption began at 1500 on 14 December and lasted until midnight on 15-16 December. The plume from the ocean entries stopped completely by 16 December. When the eruption resumed, lava again flowed through the existing tube system and reached the ocean at West Kamokuna bench on the afternoon of 17 December. The East Kamokuna entry was not reactivated after the pause.

Just prior to the 14-16 December pause, only a solid crust was visible where the Pu`u `O`o lava pond had been, at 80-90 m below the rim. By 19 December the lava pond had risen to ~68 m below the rim of the cone and was actively circulating. The pond level then subsided several meters and stabilized by 28 December. Surface flows occurred high on Pulama Pali, between 675 and 570 m elevation, and in the area from the 300-m elevation on Pulama Pali, down to the far eastern side of the flow field, to the coastal plain and ocean entry. Flows moved E into the grassland and brush near the base of Pulama Pali. A single ocean entry at West Kamokuna was active in late December, where a major collapse between 30 December and 1 January took out a section of the bench ~50-70 x 200-300 m in surface area, including several littoral cones. Explosive activity was observed at the ocean entry both before and after the collapse, but the most energetic and spectacular activity was reported on 1 January, immediately following the bench collapse. This activity included lava bubble burst and spatter and tephra ejections to heights estimated at 60 m. These explosions built a new littoral cone.

Eruption tremor levels remained low at ~2-3x the background. Shallow, long-period (LPC-A, 3-5 Hz) microearthquake counts were high on 5 December and again from 15-18 December. On the 15th and 16th, LPC-A counts were 200/day, gradually diminishing on the 17th and 18th. Shallow, long period (LPC-B, 1-3 Hz) microearthquakes were also high in number during 16-18 December, peaking on the 17th, with more than 150 events counted. Both types of LPC events are from a source 0-5 km in depth. They differ in frequency, suggesting a possible change in the condition of the source.

Shallow summit activity continued in the second half of December, with many hundreds of long-period (LPC-B, 0-3 Hz) events per day. The high counts peaked on 22 and 24 December with daily totals of 1,730 and 1,346, respectively. By 26 December, LPC-B counts appeared to be decreasing, while a slight increase of LPC-A was noted. The increase of shallow activity was coincident with the mid-December eruptive pause. Microearthquake counts were below average.

Geologic Background. Kilauea overlaps the E flank of the massive Mauna Loa shield volcano in the island of Hawaii. Eruptions are prominent in Polynesian legends; written documentation since 1820 records frequent summit and flank lava flow eruptions interspersed with periods of long-term lava lake activity at Halemaumau crater in the summit caldera until 1924. The 3 x 5 km caldera was formed in several stages about 1,500 years ago and during the 18th century; eruptions have also originated from the lengthy East and Southwest rift zones, which extend to the ocean in both directions. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1,100 years old; 70% of the surface is younger than 600 years. The long-term eruption from the East rift zone between 1983 and 2018 produced lava flows covering more than 100 km2, destroyed hundreds of houses, and added new coastline.

Information Contacts: Dave Clague, Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, Hawaii Volcanoes National Park, HI 96718, USA.


Kujusan (Japan) — December 1995 Citation iconCite this Report

Kujusan

Japan

33.086°N, 131.249°E; summit elev. 1791 m

All times are local (unless otherwise noted)


Seismically active with occasional lapilli and steam ejections

An aseismic phreatic eruption vented from the N flank (not E as previously reported) of Hosho dome on the evening of 11 October (BGVN 20:10). The eruption came from a 400-m-long E-W fissure that includes multiple sub-fissures and craters.

The Volcano Research Center (VRC) at the University of Tokyo reported that the estimated volume of tephra from the 11 October eruption was 22,000 m3. Violent steaming from the vents and craters along en-echelon cracks has reportedly continued since then. An image taken by the French SPOT-2 satellite on the morning of 13 October shows an ash plume extending SW.

JMA reported that on 12 and 13 November field observers saw steam vigorously escaping from Vent D. The steam carried volcanic lapilli up to 5 cm in diameter.

Another JMA field party witnessed a loud explosion on 13 December, but ejecta were not found. VRC reported that another phreatic eruption on the morning of 18 December produced ~20% of the tephra of the 11 October eruption. Associated tremor, local deflation, and earthquakes were noted. Small ash emissions continued until at least as late as the night of 13 January 1996. In material erupted since 20 December, clear juvenile rhyolite glass shards were recognized in the ash and comprised roughly 1% of its volume.

The highest plumes during November and December rose ~300 and 600 m above the vent. On 23 November, earthquakes increased and the daily total was 13; the monthly total was 69. During the most active days in December, the 2nd and 18th, daily totals were 22 and 29, respectively; the total for the month was 134.

Further Reference. Hiroki, H., and Tatsuro, C., 1995, Eruption of Iozan at Kuju volcano in October 1995: Journal of the Geological Society of Japan, v. 101, no. 12, p. 43-56.

Geologic Background. Kujusan is a complex of stratovolcanoes and lava domes lying NE of Aso caldera in north-central Kyushu. The group consists of 16 andesitic lava domes, five andesitic stratovolcanoes, and one basaltic cone. Activity dates back about 150,000 years. Six major andesitic-to-dacitic tephra deposits, many associated with the growth of lava domes, have been recorded during the Holocene. Eruptive activity has migrated systematically eastward during the past 5000 years. The latest magmatic activity occurred about 1600 years ago, when Kurodake lava dome at the E end of the complex was formed. The first reports of historical eruptions were in the 17th and 18th centuries, when phreatic or hydrothermal activity occurred. There are also many hot springs and hydrothermal fields. A fumarole on Hosho lava dome was the site of a sulfur mine for at least 500 years. Two geothermal power plants are in operation at Kuju.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan; Volcano Research Center, Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113 Japan (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html); Geological Survey of Japan, 1-1-3 Higashi, Tsukuba, Ibaraki 305 Japan (URL: http://www.aist.go.jp/ GSJ/dEG/sVOLC/kuju_E.html).


Langila (Papua New Guinea) — December 1995 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)


Ongoing eruptions lead to detectable ashfalls 10-15 km away

Throughout November-December, Crater 2 continued to emit white-to-gray ash and vapor, with plumes rising up to several hundred meters above the crater. During November, ashfalls reached 10-15 km on the N-NW flank; these eruptions were accompanied by audible explosions and rumbling. The eruptions threw incandescent projectiles during the first half of both November and December, and steady crater glow took place on most November nights and on 9-11 December. Crater 3 remained quiet. The greatest December activity, during the 23rd through the 26th, had emissions similar to those in November, but plumes rose somewhat higher (up to 1 km above the crater) and ash fell 10-15 km SE and SW.

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 E flank of the extinct Talawe volcano in the Cape Gloucester area of NW New Britain. A rectangular, 2.5-km-long crater is breached widely to the SE; Langila was constructed NE of the breached crater of Talawe. An extensive lava field reaches the coast on the N 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. The youngest and smallest crater (no. 3 crater) was formed in 1960 and has a diameter of 150 m.

Information Contacts: Ben Talai, H. Patia, D. Lolok, and C. McKee, RVO.


Ol Doinyo Lengai (Tanzania) — December 1995 Citation iconCite this Report

Ol Doinyo Lengai

Tanzania

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

All times are local (unless otherwise noted)


Minor lava flows and projectile emission in December

Summit visits by members of the Societe de Volcanologie Geneve during 15-19 December revealed low rates of intermittent effusive activity and some small explosions. Five episodes of lava emission were observed from hornito cluster T36 (BGVN20:10), each lasting

Figure (see Caption) Figure 37. Sketch map of part of the Ol Doinyo Lengai crater showing new features and lava flows, 15-19 December 1995. Modified from the January 1994 map in BGVN 19:04.

Almost continuous ejection of lava fragments occurred from a cinder cone T37 (~15-25 m high), and with less intensity from a hornito in a small collapse depression just W of T5/T9 (figure 37). A small lava pond, observed for ~3 hours on 16 December, inside the depression at the foot of the hornito exhibited splashing and small bubbles. Two major flank collapses of T37 released large quantities of very fast-moving (5-8 m/second) aa lava flows that were ~50 cm thick. The first flank failure, on 16 December, was a progressive event on the W side. However, the E-flank collapse on the 18th came without warning, quickly sending a lava flow NE between T5/T9 and F35, almost to the crater rim.

Fumarole temperature measurements were taken on the N crater rim, inside new cracks on the crater floor, and at the tops of T8 and T15. All temperatures were 70-80 degrees C.

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

Information Contacts: P. Vetsch, S. Haefli, and C. Peter, Societe de Volcanologie Geneve, B.P. 298, CH-1225 Chene-bourg, Switzerland.


Manam (Papua New Guinea) — December 1995 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)


Steam release with occasional minor ash and bombs

Throughout November, Manam's activity remained low and night glow from its craters was absent. On 8 December, weak projections of incandescent lava were seen, and steady glow took place on the nights of 9 and 10 December. During November and December, both summit craters chiefly released steam, but on 8, 17, and 19 November South Crater released wisps of blue vapor, and on 25 and 28 November it released gray ash. South Crater also made weak, low-frequency roaring sounds on 1 November. Except for 6-11 December, activity was low during most of the month.

Earthquakes increased at the end of October, but during November they took place at the moderate rate of 600-1,400/day. They remained moderate in December. In the first half of November a tiltmeter 4 km SW of the summit continued to register slight deflation followed during the latter half of the month by a 2 µrad inflation.

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 basaltic-andesitic stratovolcano to its lower flanks. These 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 observed eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent 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: Ben Talai, H. Patia, D. Lolok, and C. McKee, RVO.


Monowai (New Zealand) — December 1995 Citation iconCite this Report

Monowai

New Zealand

25.887°S, 177.188°W; summit elev. -132 m

All times are local (unless otherwise noted)


Earthquake swarm in late November detected acoustically

During November, Reseau Sismique Polynesien (RSP) stations on the islands of Tahiti, Rangiroa, Tubuai, and Rikitea registered acoustic T-waves. The waves were associated with a seismic swarm centered >2,500 km E of these islands. The swarm was located at 25.92 S, 177.15 W, essentially the coordinates of the Monowai seamount.

The T-wave swarm consisted of four episodes. The first, at 1751 on 27 November, lasted for 20 minutes and included seven separate explosions and other strong events. The second, 1403 on 28 November lasted 4 minutes and included small-amplitude events. The third, at 1842 on 30 November, prevailed for 7 minutes and included moderate-amplitude events. Ten minutes later, the fourth episode included 25 distinct explosions and other strong events.

The character of the T-wave signals was consistent with volcanism. T-waves are sound waves with paths that propagate through the sea; on reaching land the energy travels at the higher speed of ordinary seismic waves. Compared to earthquake-generated T-waves, volcanically generated ones are impulsive and of comparatively short duration.

Recent activity includes a possible eruption in 1944, and about seven documented eruptions during 1977-90 (BGVN 16:03). The seamount lies midway between the Kermadec and Tonga Islands, ~1,400 km NE of New Zealand. The adjacent trench is significantly shallower (~4 km) compared to the Tonga and Kermadec trenches (9-11 km deep).

Geologic Background. Monowai, also known as Orion seamount, is a basaltic stratovolcano that rises from a depth of about 1,500 to within 100 m of the ocean surface about halfway between the Kermadec and Tonga island groups, at the southern end of the Tonga Ridge. Small cones occur on the N and W flanks, and an 8.5 x 11 km submarine caldera with a depth of more than 1,500 m lies to the NNE. Numerous eruptions have been identified using submarine acoustic signals since it was first recognized as a volcano in 1977. A shoal that had been reported in 1944 may have been a pumice raft or water disturbance due to degassing. Surface observations have included water discoloration, vigorous gas bubbling, and areas of upwelling water, sometimes accompanied by rumbling noises. It was named for one of the New Zealand Navy bathymetric survey ships that documented its morphology.

Information Contacts: Francois Schindele, Laboratoire de Geophysique, B.P. 640, Papeete, Tahiti.


Cerro Negro (Nicaragua) — December 1995 Citation iconCite this Report

Cerro Negro

Nicaragua

12.506°N, 86.702°W; summit elev. 728 m

All times are local (unless otherwise noted)


Vigorous eruption produces a new cone, dome, lava flows, and large ash plumes

A significant eruption in November-December followed almost six months of unrest and minor eruptive activity. During a crater visit on 13 November no precursors were observed, and on 18 November only background seismicity was recorded by the CNGN station (500 m E of the crater).

Early phase of activity, 19-22 November. Local residents first noticed explosions about the time of the onset of 30 minutes of mildly increasing seismicity detected by the CNGN station at 1145 on 19 November. Following a pause, seismicity continued to gain strength. Increasing activity was reported that afternoon by residents in Malpaisillo (~10 km N). Observations on the night of 19-20 November indicated mild Strombolian activity, with vertically directed ejecta, that was gradually increasing in strength. A Notice to Airmen (NOTAM) was issued the next day warning aviators of the volcanic activity.

Eruption tremor amplitude increased continuously and saturated the CNGN station (60 dB gain) at 0200 on the 21st. Tremor was detected on short-period seismic stations within a 30 km radius (at San Cristóbal and Momotombo volcanoes, and near the city of León). Energy release increased continuously and tremor could be felt over 1 km away, when sitting down, as a smooth rocking motion.

At 2000 on 21 November incandescent bombs were being thrown up to 300-400 m above the 1992 crater rim. Ash content was low compared with the 1992 and May-August 1995 activity, and bombs were often very large (meters across), which deformed and broke up in flight. Because of near-vertical trajectories, few bombs fell outside the crater. The new cone being built within the 1992 crater (figure 8) had a steep (>45 degrees) basal scarp, 2-5 m high, followed by a level bench and then a less steep slope (25 degrees) to its crater. Ejecta pulses maintained a frequency of 20/minute, but the size and duration of each pulse varied. From 0255 to 0310 on 22 November ejecta heights were <150 m but ash content and degassing were much higher, emitting dark clouds with each explosion. A thick, white lower plume appeared to be escaping from a new lava dome in the 1992 crater, 50 m W of the new cone (figure 8). By 0500 the eruption had regained previous intensity levels and exhibited near-constant fire-fountain-like activity, bombs were larger, and pulse frequency increased to 22/minute. The eruption continued at this level for over 4 hours.

Figure (see Caption) Figure 8. Sketch of the crater at Cerro Negro, 0700 on 22 November 1995. Drawn from photographs taken by Pedro Perez; courtesy of INETER.

The new cone had almost reached the lip of the 1992 crater by 0700 on 22 November. At that time the lava dome emitted a small lava flow, 2-5 m wide and 50 m long, that followed the edge of the new cone towards the lowest part of the 1992 crater (figure 9). From 0930 to 1000 a series of explosions ejected material to the lower slopes of the new cone. Sand to gravel size ash fell W of the cone, but no large ejecta. Compared to the 1992 ejecta this material is highly vesicular with millimeter-size vesicles; olivine, pyroxene, and plagioclase are present, and some plagioclase crystals are 1 cm long. That evening the new cone overgrew the N rim of the 1992 crater and material began spilling towards Cerro La Mula. From 1900 to 2300 a tongue of lava spilled over the N rim of the 1992 crater. The front moved at less than 1 m/hour, but blocks constantly tumbled from the front down to the base of the main cone.

Figure (see Caption) Figure 9. Sketch map of Cerro Negro showing active lava flows, 2000 on 23 November 1995. Drawn by B. Van Wyk de Vries; courtesy of INETER.

Lava flows beyond the crater, 23 November. After 1400 on 23 November dark gray pulses observed from 25 km away formed a plume that rose faster and higher than on previous days, attaining several kilometers altitude. Observations were made from the seismic station after 1500. During about 1515-1525 the plume became less ash-rich, ejecta became less frequent, and strong degassing pulses were heard. When regular pulses resumed, some bombs were ejected laterally onto the flanks of the main cone. Periodic heavy falls of 1-3 cm scoria were encountered by the scientists walking under the plume 1.5 km from the cone. Red glow was visible at 1730 over Cerro La Mula, and there was a smell of burning vegetation, suggesting an active lava flow. The lava tongue was observed at 1800 between Cerro La Mula and Cerro Negro (figure 9). Later named the La Mula flow, it was ~20 m wide and 5 m thick, and advancing at ~2 m/hour.

At 1830 a 20-m-wide lava stream moved down the N flank through a small breach at a rate of ~150 m/minute from the crater rim to the base of the cone. A lava field spreading out from the base of the cone had reached ~1 km from the crater by 2000, advancing 10-30 m/hour along two 300-m-wide fronts (figure 9). To the E of the flow the volcano flank appeared to be bulging and was irregular with large blocks jutting out that occasionally fell downslope, revealing incandescent lava. It appeared to the scientists that a slow-moving 20-m-thick blocky lava flow was moving to the crater rim and collapsing down the flank; however, the shape of the flank also suggested outward bulging. The blocky lava extended at least 200 m NE from the base of the cone.

Continuous and voluminous pulses at 2000 created a fountain that sent bombs at least 600 m above the crater. Ash clouds accompanied each pulse and occasional flames of burning gas reached 100-200 m above the crater. This activity had decreased by 2045, and by 2115 pulses of bombs appeared only every 30 seconds, although continual noise suggested smaller pulses.

Of the four GPS stations set up in the vicinity of the cone, by 23 November one had been destroyed by lava and another was too dangerous to approach. Measurements at the remaining stations were within the error of the equipment (2 cm at best). However, two fresh fault scarps radial to the cone were observed on the W side with 5 cm of displacement. Tremor energy increased continuously until 1200 on 23 November, after which it maintained a constant level.

Continuing activity, 25-26 November.The eruption plume was again clearly visible on 25 November from Managua as a diffuse gray column turning horizontal at ~2,000 m. At 0900 distinct pulses of dark gray ash rose from the crater and formed mushroom shapes before drifting W and being incorporated into the plume; ashfall was reported in León and Corinto. At times only massive bombs were thrown out, while at others strong explosions sent up dense ash clouds. Ash and highly vesicular scoria

At 1100 on 25 November most bombs were still ejected vertically, but a significant number were exiting at low angles and falling low on the flanks. The new cone had grown to ~40 m across, and its top was ~30-50 m below the 1992 crater summit. Bombs fell mostly on the cone and rolled down to the base. The small breach where the 23 November lava flow exited was partly covered by a new blocky flow, which appeared to come straight N from the new cone, though no exit vent was visible. It may have been produced by accumulated, still liquid ejecta beginning to flow outwards, as seen on 22 November. The flow had advanced half way down the flank, covering another blocky flow. The dome in the crater had grown to ~100 m wide and 40 m high. Blocks were continually spalling off the dome, which also sustained a continuous rain of bombs from the new cone. Multiple small lava tongues originated from the dome. The crater dome was less pronounced on 26 November, and was blocky rather than spiny. The new cone had grown ~10 m overnight.

The two flows moving N on the 23rd had reached ~1-1.5 km from the volcano. The larger W lobe was ~400 m wide and 3-5 m thick at the front with a small lobe extending down the gully below Cerro La Mula, and another extending E into a depression in the old N lava field. The E lobe had extended into forest at the E side of the old N lava field. Over a three-hour period the flows advanced ~12 m. A low ash-covered area with a small old cinder cone separated the lobes. The sides of each flow were slowly (~1 m/hour) encroaching on this and thickening. The thick lava lobes below the dome were advancing, and many areas of the dome were glowing. The ~30-m-wide La Mula lava flow had advanced W ~500 m down a small valley and was moving at ~1 m/hour on 25 November; by 0600 on the 26th it had stopped. By 0645 the other lava fronts had advanced 20-50 m since the previous evening. The main W lobe had spread E and a large block in the middle of the flow had moved ~100 m.

Seismic tremor levels remained high through 26 November. Tremor was continuous and distinctly felt up to 1.5 km from the cone.

Satellite observations of the ash plume. Visible satellite imagery on 25 November indicated a possible low-level ash cloud at 1245 (figure 10). The height of the plume was estimated at 4,500 m altitude and was moving SW at ~30 km/hour. Another small low-level plume was seen on imagery at 0815 the next day at an estimated 2,750 m altitude and moving WSW at ~35 km/hour. Explosive activity increased on 1 December, when visible imagery at 1230 revealed a plume 18 km wide extending ~320 km W; it was estimated to be between 3,000 and 6,000 m altitude. By 0900 on 2 December, the plume extended at least 640 km W and was below 4,000 m.

Figure (see Caption) Figure 10. Map showing ash plumes from Cerro Negro detected on visible satellite imagery on 25-26 November, and 1-2 December 1995. Courtesy of the Synoptic Analysis Branch, NOAA/NESDIS.

End of the eruption, early December. Explosive and effusive activity ended on 6 December. However, a lava flow was still moving N on 8 December. Isopach maps of the ashfall through 2 December (figure 11) were constructed by Markus Kesseler based on 85 GPS control points (precision +- 30 m). The 0.1 cm isopach encloses an area of ~200 km2. An estimated 12,000 people were affected by this eruption, about 6,000 of whom had been evacuated from 15 rural communities. Farmland was significantly damaged by ashfall and lava flows during the harvesting season; most of those affected were farmers and their families.

Figure (see Caption) Figure 11. Isopach maps of ashfall from Cerro Negro, 19 November-2 December 1995. Isopachs within the 5.0 cm limit are at 10-cm intervals, up to 50 cm closest to the crater. The 2-5 June isopachs (BGVN 20:09) are shown for comparison. Courtesy of Markus Kesseler; base map courtesy of Brittain Hill.

Geologic Background. Nicaragua's youngest volcano, Cerro Negro, was created following an eruption that began in April 1850 about 2 km NW of the summit of Las Pilas volcano. It is the largest, southernmost, and most recent of a group of four youthful cinder cones constructed along a NNW-SSE-trending line in the central Marrabios Range. Strombolian-to-subplinian eruptions at intervals of a few years to several decades have constructed a roughly 250-m-high basaltic cone and an associated lava field constrained by topography to extend primarily NE and SW. Cone and crater morphology have varied significantly during its short eruptive history. Although it lies in a relatively unpopulated area, occasional heavy ashfalls have damaged crops and buildings.

Information Contacts: Wilfried Strauch, Virginia Tenorio, Rolf Schick, Helman Taleno, Leonel Urbina, Cristian Lugo, and Pedro Perez, Instituto Nicaraguense de Estudios Territorales, Managua, Nicaragua; Benjamin van Wyk de Vries, The Open University, Milton Keynes, United Kingdom; Markus Kesseler, Dept. of Mineralogy, Universite de Geneve, 13 rue des Maraichers, 1211 Geneve 4, Switzerland; Michael Conway and Brittain E. Hill, Center for Nuclear Waste Regulatory Analyses, Southwest Research Institute, 6220 Culebra Rd., San Antonio, TX 78238 USA; Jim Lynch, NOAA/NESDIS Synoptic Analysis Branch (SAB) , Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA; Department of Humanitarian Affairs, United Nations, Palais des Nations, 1211 Geneva 10, Switzerland.


Niijima (Japan) — December 1995 Citation iconCite this Report

Niijima

Japan

34.397°N, 139.27°E; summit elev. 432 m

All times are local (unless otherwise noted)


Seismic swarm on 4 December

On 4 December, many earthquakes occurred in and around the island, some of which were felt. The largest one was M 4.3.

Geologic Background. The elongated island of Niijima, SSW of Oshima, is 11 km long and only 2.5 km wide. Eight low rhyolitic lava domes are clustered in two groups at the northern and southern ends of the island, separated by an area of flat-topped domes and a low isthmus of pyroclastic deposits. The Mukaiyama complex on the south and the Atchiyama lava dome on the north were formed during eruptions in the 9th century CE, the last known activity. Shikineyama and Zinaito domes form small islands immediately to the SW and W, respectively, during earlier stages of volcanism. Earthquake swarms occurred during the 20th century.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


Poas (Costa Rica) — December 1995 Citation iconCite this Report

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2697 m

All times are local (unless otherwise noted)


Fumarolic and seismic activity

The surface of the sky-blue crater lake rose in November (20 cm higher than October); the lake's temperature was 26°C. A vigorous subaqueous fumarole appeared adjacent the lake's S shore. The W-terrace fumarole emitted yellow, sulfur-rich gases and particles; other fumaroles located on the NW-SW terrace emitted only low amounts of gases. Measured fumarole temperatures were in the range 94-96°C along the S and SE crater, an area that produced 100-m-tall gas columns. Gases escaping the pyroclastic cone had temperatures of 93°C.

During 1-22 November the local seismic station recorded 5,146 events (predominantly of low-frequency), significantly fewer than the number seen in the two previous months (figure 59).

Figure (see Caption) Figure 59. Poás seismicity for January-November 1995 recorded at station POA2 (2.7 km SW of the active crater). Courtesy of OVSICORI-UNA.

Geologic Background. The broad 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 are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the complex stratovolcano extends to the lower N flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, last erupted about 7,500 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 an eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Information Contacts: E. Fernandez, E. Duarte, R. Saenz, W. Jimenez, and V. Barboza, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA).


Rabaul (Papua New Guinea) — December 1995 Citation iconCite this Report

Rabaul

Papua New Guinea

4.2459°S, 152.1937°E; summit elev. 688 m

All times are local (unless otherwise noted)


Small ash-bearing emissions from Tavurvur

Throughout most of November 1995 the two recently active centers remained quiet, with Tavurvur emitting only steam and Vulcan not emitting any visible vapor (figure 24). Then on 28 November, Tavurvur suddenly began erupting, creating a parasitic crater. Vulcan continued to remain quiet throughout December.

Figure (see Caption) Figure 24. Index map of Rabaul and detail of soil CO2 transect. Elevation contours given in meters; base map after Johnson (1995).

The volume of Tavurvur's faint blue vapor emissions seemed to increase in the weeks prior to 28 November. On the morning of the eruption an impressive white steam cloud stood several hundred meters above Tavurvur's summit. The new eruption, which was preceded by weak roaring sounds, started at about 1020, and initially consisted of forceful emissions of gas and dark ash at 2-6 minute intervals. Those emissions lacked explosion sounds; they rose 400-800 m above the crater rim and blew over a broad arc between the SE and SW, resulting in fine ashfall both onshore and over the sea. No ashfall reached Kokopo, 25 km SE. The next day, 29 November, two intervals of stronger emission took place (at 1200-1300 and 1415-1430), sending columns ~1 km above the summit.

An aerial inspection on 30 November revealed a new crater on the 1994-95 crater's SSE rim. Although the 1994-95 crater displayed no new activity, fumaroles were particularly active along its E walls. An old explosion crater along the base of Tavurvur's S flank, in which 6 people were killed in 1990 by inhalation of carbon dioxide, was releasing weak-to-moderate emissions of white vapor from its N to E walls. Directly downslope and immediately offshore of this explosion crater a spring had become considerably more active since the 1994 eruption; during the 30 November aerial inspection it was prominent, giving off a strong stream of rusty brown water. During November and December, ground deformation remained low.

Tavurvur discharged dark ash clouds in December, typically at 3-6 minute intervals, that rose 400-1,000 m above the summit. On 2 December two ash clouds rose to 1.5-2 km. The second brought intense lightning causing minor damage to home appliances in Rabaul Town (figure 24). On 5 December, a particularly loud explosion, heard 30-40 km away, accompanied the discharge of an ash cloud that rose to 1.2 km. Additional loud explosions accompanied dense ash clouds that rose to 1-1.2 km; these took place during December as follows: 11th (1 time), 13th (1), 14th (4), 18th (1), 23rd (1), 24th (1), and 29th (2). Moderate-sized clouds blew SE, and very fine ash occasionally fell both in Kokopo and, due to shifting winds, in Rabaul Town. On December nights, observers saw incandescent fragments and during the second half of the month they heard occasional deep roaring noises.

Seismicity. November seismicity generally remained low, but was punctuated by 11 high- and 42 low-frequency events. Eight of the high-frequency events were located. Five occurred within the caldera's seismically active elliptical fault zone, in the NE (1 event), W (1), and S (3) quadrants. Although one of the extra-caldera events was centered S of the caldera, two events were located immediately to the caldera's NE, an area where the bulk of the high-frequency earthquakes have occurred in the past few months. One of these two events, ML 3.0 on 24 November, produced a felt intensity of MM III at Rabaul Town.

Of the 42 low-frequency earthquakes during November, 17 came from around Tavurvur volcano. Two of these occurred in late October, and 9 others in November prior to the 28 November eruption. The last time such events appeared was during the eruptive activity in March 1995. The other 25 low-frequency earthquakes not centered around Tavurvur were more difficult to locate accurately due to emergent waveforms and fewer stations outside the caldera. Many may have originated immediately N of the caldera. On 10 November a low-frequency earthquake centered 7-8 km outside of the caldera was strong enough to trigger aftershocks.

During December, seismic instruments detected 30 high-frequency earthquakes, 684 low-frequency earthquakes, and 488 explosion events. Instruments also recorded occasional discontinuous non-harmonic tremors. About 70% of the high frequency earthquakes occurred during 4-6 December. The five located events had epicenters in either the S part of the caldera's seismically active zone (the largest one, M 2.7), NE of the caldera (two events), or within the caldera. All of the seismic explosions and most low-frequency earthquakes originated at Tavurvur; the 20 exceptions originated farther NW and took place at the end of the month.

Fumarole and soil sampling. During 21-27 November, rainwater, water from hot springs, and gases from subaerial and submarine fumaroles were sampled at 13 sites (table 3). Compared to Vulcan, fumaroles at Tavurur displayed relatively high temperature, low pH, and high conductivity. Hot springs sampled near the shore of Greet Harbor were slightly acidic and comparatively conductive. All samples were more acid than those assessed prior to the 1994 eruption episode.

Table 3. Summary of fumarole and hot spring sampling at Rabaul Caldera, 21-27 November 1995. Courtesy of RVO.

Location Number of samples/type Temp (deg C) pH Electrical conductivity (mS/cm)
Tavurvur 3/fumarole 202-98.9 1.21-3.53 0.327-10.4
Vulcan 1/fumarole 99.8 5.28 0.0758
Rabalanakaia 1/fumarole 99.3 3.20 0.444
Vulcan 1/hot spring 99.2 5.98 73.3
Greet Harbor shore 4/hot spring 62.6-84.8 5.89-6.66 52.9-53.8
Sulphur Creek 1/hot spring N.D. 6.21 4.29
Rabaul 1/rainwater N.D. 6.06 N.D.

A soil CO2 survey E of Simpson Harbor (figure 24) showed that CO2 concentrations varied widely, 0.4-20% (figure 25). As reported by Mori and McKee in 1987, the CO2 concentrations peaked along the seismically active fault zone (near the old airport), some distance from either Tavurvur or Vulcan. Other anomalously high concentrations were seen at the Matupit causeway and Sulphur Creek. Low concentrations were seen at other places, including Matupit Island.

Figure (see Caption) Figure 25. Soil CO2 concentrations at Rabaul Caldera along transect A-A'. Courtesy of RVO.

Isotopic analysis of six selected samples along the profile found that 13C ranged from -29.8 to -18.4 per mil suggesting chiefly biogenic contributions. A mixing process with a minor contribution of volcanogenic CO2 might also account for the wide range of ratios seen. High soil CO2 levels could be related to the effects of a higher thermal gradient along active fractures and faults.

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 asymmetrical 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 1,400 years ago. An earlier caldera-forming eruption about 7,100 years ago is thought to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the N and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and W 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: Ben Talai, H. Patia, D. Lolok, and C. McKee, RVO; N. M. Perez and H. Wakita; University of Tokyo, Earth Chemistry, Bunkyo-ku, Tokyo 113 Japan.


Rincon de la Vieja (Costa Rica) — December 1995 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)


Additional details about the 6-10 November eruption

An eruption on 6 November 1995 followed increases in fumarolic activity and a several-month long increase in local earthquakes and tremor (figures 11 and 12). Park rangers who visited the summit at the start of October noted increased fumarolic activity and witnessed landslides down the main crater's walls. Strong sulfur smells were noted W-SW of the volcano on multiple occasions in the days prior to 6 November (figure 13).

Figure (see Caption) Figure 11. Rincón de la Vieja's monthly totals for tremor and low-frequency seismicity, January-September 1995. Courtesy of OVSICORI-UNA.
Figure (see Caption) Figure 12. Rincón de la Vieja's seismicity, 1-13 November 1995. An eruption began on 6 November. Courtesy of OVSICORI-UNA.
Figure (see Caption) Figure 13. Map of NW Costa Rica showing key features associated with Rincón de la Vieja's 6 November 1995 eruption. Courtesy of OVSICORI-UNA.

The seismic receiver (RIN3) sits 5 km SW of the active crater. Although the OVSCICORI-UNA seismic system failed on 29 October (and possibly other times during the month), it functioned reliably again after the 31st. Low-frequency events gradually increased during 1-6 November (figure 12), followed by a modest decline. High-frequency events were only registered after 3 November. Tremor was absent prior to the 6 November eruption.

OVSCICORI reported that the first phase of the eruption consisted of vapor with subordinate ash in a discharge lasting 2 minutes. Later, vigorous fumarolic activity led to many hours of constant tremor. Only two more clear eruptions followed in the initial 17 hours of venting, but others followed in subsequent days. The eruption climaxed on the morning of the 8th, when columns reached 3.5 km altitude. Fine ash blew W and NW; larger blocks and tephra were confined to within ~1 km and the area of heavy ashfall reached ~5 km away (figure 13).

During some phases of the eruption, lahars flowed down the Azul and Penjamo rivers and an interfluvial ravine called the Quebrada Azumicrorada (figure 13). Upper reaches of these drainages sustained up to 6 m of erosion. Lahars on the 7th were cooler and more water-rich than those on the 8th. In addition to previously reported damage, on 8 November lahars shut down some communications systems.

At 0900 and 1130 on 8 November OVSICORI scientists visited the summit area and saw impact craters as large as 2 m in diameter; the craters were produced by 0.5-1.0 m diameter blocks, some of which were still warm to the touch. The scientists also saw ongoing phreatic eruptions escaping from a vent adjacent to the crater lake.

At 0411 on the 9th a shock wave was felt 25 km SE in the city of Liberia; the related outburst was seen from the N flank, where residents witnessed incandescent block ejections.

Amplitudes on the seismic recorders regularly peaked at over 30 mm on 6-9 November. The highest amplitudes, on 7-9 November, reached nearly 60 mm. Amplitudes decreased the morning of 9 November; following the eruption (10-14 November) amplitudes generally remained under 10 mm with infrequent spikes to ~20 mm and a few rare spikes to 30 mm. Tremor decreased by an order of magnitude on 10 November and it dropped to <1 hour/day on 13 November.

During fieldwork in early December, G. Soto (ICE) and G. Boudon (IPG) inspected the near-source region. For a radial distance of ~1 km from the crater they saw a deposit consisting of muddy ash, lapilli, and blocks. These reached 40 cm thick on the crater's southern outer rim at a point 150 m from the inner rim. The deposit's thickness and grain size decreased rapidly with distance, such that at 600 m SW of the crater the deposit was only 7 cm thick. The deposit's basal zone was enriched in fine grained, muddy-looking material, but throughout the deposit there occurred lustrous black juvenile clasts. Over ~1 km2 of the upper surface of the deposit, there lay a blanket consisting of (a) dense, quenched blocks, (b) breadcrust bombs with notably vesicular cores, and (c) some highly vesiculated fragments. On 8 December at points 5 and 8 km from the summit, the Penjama and Blanco rivers, respectively, still ran milky and were slightly acidic in taste. That same day, the scientists saw only fumarolic activity. Although scientists looked for a lake in the depths of the crater, they failed to gain a clear view there.

Reference. Boudon, G., Rancon J.-P., Kieffer, G., Soto, G.J., Traineau, H., and Rossignol, J.-C., 1995, Estilio eruptivo actual del Volcan Rincón de la Vieja: evidencias de las productos de las erupciones de 1966-70 y 1991-92: Rothschildia, 2 (2): 10-13, Area de conservacion de Guanacaste, Costa Rica.

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 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 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 3,500 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: E. Fernandez, E. Duarte, R. Sáenz, W. Jimenez, and V. Barboza, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; Georges Boudon, Institut de Physique du Globe de Paris, 4, Place Jussieu, 75252, Paris Cedex 05, France.


Shishaldin (United States) — December 1995 Citation iconCite this Report

Shishaldin

United States

54.756°N, 163.97°W; summit elev. 2857 m

All times are local (unless otherwise noted)


Eruption sends ash plume above 10 km altitude

Based on satellite imagery and pilot reports received by the U.S. Federal Aviation Administration, an eruption began at 1830 on 23 December. Between 1830 and 2000 on 23 December, pilots reported an ash plume as high as 10.5 km altitude (35,000 feet); prevailing winds carried the plume primarily N and NW. Analysis of a satellite image from 1912 showed a possible small ash plume extending ~50 km NW. Possible very light ashfall was reported at approximately 0130 on 24 December in Cold Bay, 90 km NE; this ash would have been carried by westerly low-altitude winds.

Geologic Background. The symmetrical glacier-covered Shishaldin in the Aleutian Islands is the westernmost of three large stratovolcanoes in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." Constructed atop an older glacially dissected edifice, it is largely basaltic in composition. Remnants of an older edifice are exposed on the W and NE sides at 1,500-1,800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is covered by massive aa lava flows. Frequent explosive activity, primarily consisting of Strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century. A steam plume often rises from the summit crater.

Information Contacts: Alaska Volcano Observatory.


Soufriere Hills (United Kingdom) — December 1995 Citation iconCite this Report

Soufriere Hills

United Kingdom

16.72°N, 62.18°W; summit elev. 915 m

All times are local (unless otherwise noted)


Dome building, minor ash eruptions

Although there was relative quiet during October (20:10), during the first 10 days of November three large phreatic eruptions occurred. Each of these eruptions blanketed Plymouth, 4.5 km W of the active vent, with ~2 mm of ash (table 2). Dome growth within the crater started on 16 November, the estimated date when juvenile material first reached the surface, and continued through at least December. Estimates of the dome's rate of growth from 16 November to 6 December were on the order of 0.5 m3/sec.

Table 2. Summary of the daily behavior of Soufriere Hills, 1 November through 11 December 1995. The table omits most geophysical and geodedic observations, however, "eruption signal" refers to seismically determined eruptions, and "mudflow signal" refers to seismically determined mudflows. Courtesy of MVO.

Date Events and Comments (local time)
01 Nov 1995 Ashfall (1129).
02 Nov 1995 Ashfall in Trails, Brodericks, and surrounding areas (0118). Explosions accompanied by light ashfall in Upper Gages and Chances Peak (1923).
03 Nov 1995 Mudflow (0254); Steam-and-ash emissions resulting in light ashfall in Parson's-Amersham and Plymouth (1122). Continued enlargement of Vent 1. Steam-and- ash emission (1122). No major changes in Castle Peak.
04 Nov 1995 Eruption signal (0247), no reported ashfall. Eruption signal; one eruption generated an ash plume reaching 2.5-km high; several millimeters of ash fell in Amersham-Plymouth and S of Plymouth (1725).
05 Nov 1995 Eruption signal (0139), no reported ashfall. Mudflow toward Fort Ghaut (0214). Minor eruption without visible ash or steam (1307). Eruption signal (2030).
06 Nov 1995 Minor mudflow (0410). Increase in the size of Vent 1. Ashfall, light (0347) in crater area and steam plume, 1.5-km high. Eruption signals (1044, 1809), no ashfall.
07 Nov 1995 Eruption signal (0123), no ashfall. Ashfall (0815). Eruption signals (2018, 2358).
08 Nov 1995 Eruption signal (0935).
09 Nov 1995 Ashfall, several millimeters accumulated in areas to the W and SW of the vent (Kinsale, Amersham, Plymouth, and Richmond) (0419).
10 Nov 1995 Eruption signals (0145, 0420, 1348). Plume of ash and steam (1535), 1.5-km high, blown SW.
11 Nov 1995 Mudflows in Gages-Fort Ghaut areas (0548, 0743). Eruption signal (0733), no ash emission.
12 Nov 1995 Eruption signal (0247), no ash emission. Steam emission from several new vents SW of main activity area. Old vent reopened S of Vent 1.
13 Nov 1995 Eruption signal (0600). Minor ash and steam (1603), blown N.
14 Nov 1995 Minor ash-and-steam emission (1610). Continued steam emissions from vents first observed on 12 November. Vent closest to Castle Peak greatly increased in size, surrounded by fresh ash.
15 Nov 1995 Minor ash-and-steam emission (0900-1000). Noise of breaking rocks, small landslides, venting heard from crater.
16 Nov 1995 Poor visibility but felt earthquakes, loud venting, rock-impact sounds, and light ashfall at Chances Peak (1500), with some drifting SW into the Broderick's area.
17 Nov 1995 Episodes of light ashfall in Amersham. Landslides had partially filled the Vent 1 crater. The September dome grew in height and extended toward Chance's Peak. Vigorous steaming at the two vents between Castle Peak and the dome.
18 Nov 1995 Occasional landslides at the edge of Vent 1.
23 Nov 1995 Noises heard from crater (rock breaking and small landslides). CO2 detected in the summit area for the first time.
24 Nov 1995 Noises heard from crater (as above).
26 Nov 1995 Confirmed emergence of a new spine adjacent to the September spine and close to Castle Peak.
28 Nov 1995 Sound of breaking rocks heard from crater.
29 Nov 1995 Sound of breaking rocks heard from crater.
30 Nov 1995 Confirmed lava dome within Vent 1.
01 Dec 1995 Dome slowly growing in Vent 1 crater; attendant ash emission and rock avalanches. A second area of dome growth identified NW of September spine. Two small ash clouds drifted towards Plymouth.
05 Dec 1995 Rapid increase in the size of and the number of cracks within the new (26 November) spine. Increased emission of steam and light ash of reddish color.
06 Dec 1995 Lava dome glowing, visible from the airport.
07 Dec 1995 Reddish ashfall (0929) accompanied a small explosion. Continued slow growth of lava dome.
08 Dec 1995 Lava dome had broken along cracks. Deformation continued in the area around the September and November domes. Ash cloud (1025).
09 Dec 1995 About 20 minutes of mudflow signal recorded at Gages seismic station (0434). Explosion with light ashfall (1419, 1520). Dome growth rate slowed.
10 Dec 1995 Mudflow signal recorded at Gages seismic station (2240).
11 Dec 1995 Rusty brown ash eruptions, ashfall W of crater (0910, 1455, 1530, 1604). No major dome growth detected. Steam emitted with variable intensity at a vent close to Castle Peak.

Small rockfalls from the flanks of the new, locally incandescent dome were witnessed on several occasions. During early December, debris from a larger rock avalanche was seen in the moat of English's Crater. As of early January, neither local avalanches nor material liberated during the failure of spines escaped the crater area. The limited mobility of the rock avalanches suggested they were not propelled by gas explosions with great overpressures. Although floods and dilute mudflows were distinguished seismically, no significant debris avalanches or pyroclastic flows occurred.

Heavy rainfall after 11 December may have triggered several small ash emissions, depositing red-brown ash on the upper W-flanks. The ash presumably consisted of non-juvenile material, from rock avalanches sloughing off the new dome, and some hot juvenile ejecta from small explosions vented in or around the new dome.

Although quantitative SO2 flux measurements were lacking, as of early December related damage to vegetation extended ~3 km downwind and 1.5 km laterally. Tree damage was severe on the upper W flank. Gases sampled at three of the established fumaroles (soufrieres) around the volcano showed no change in composition. Although gas and acid aerosol production had been at enhanced levels from mid-November to early December, air sampled in Plymouth during early December contained very little SO2.

Dome growth.Beginning on 30 November, good visibility allowed observers to watch a single dome develop from two smaller bodies (figure 6). One body was NW of the September cryptodome (an intrusion that produces a surficial bulging), and the other at Vent 1. The evolving dome had a rough blocky carapace that initially had some small (

Figure (see Caption) Figure 6. Topographic map of the crater area at Soufriere Hills showing pre-eruption morphology (thin lines) and new features (bold lines) as of 10 December 1995. Contour interval is 50 feet, values shown are feet x 100 (3.28 feet = 1 m); coordinates shown are UTM. CH indicates Chances Peak; CA indicates Castle Peak. Courtesy of MVO.

A prominent spine on the new dome's E side grew in height until 7 December when it began to collapse. The spine's maximum vertical growth rate was estimated to be 5-8 m/day. Further dome growth at a slower rate occurred until 9-10 December, and slower growth, or a possible halt, continued as late as 13 December. On 13 December a small, radial crack on the N side of the new dome emitted steam and ash for most of the day. At least two columns reached in excess of 500 m above the crater rim.

A new batch of extruded material reached the surface on 15 December. On the 17th, in addition to widespread incandescence radiating from the new dome, observers saw a new ~ 40-m-tall spine. Between the 17th and 20th the spine grew vertically at 7 m/day, and the adjacent dome also rose, but at a slightly slower rate. The spine's growth rate during some undisclosed intervals reached up to 20 m/day. On 17 December observers also saw a narrow crack in the dome within Vent 1 that emitted glowing ejecta. Many small ash releases sent columns up to ~1.1 km above the summit.

During the week ending 27 December, several spines grew 5-10 m/day then subsequently collapsed. One spine had grown to ~15 m higher than Castle Peak (summit elevation ~910 m) prior to failing late on 25 December.

Explosions on 21 December produced a mildly convecting ash cloud that rose ~1.5 km above the volcano. Ash fell to the N, reaching the N portion of the island. Although apparently phreatic events took place in early- to mid-November, this was the most vigorous explosion since then and it may have been driven magmatically. Steam production remained constant during 21-27 December, feeding a plume that sometimes carried small amounts of ash. From 28 December to 3 January there was relative quiet and slow dome growth. Only 3 m of dome growth took place during the week, and for a least a few days after about 1 January, the dome may have ceased growing.

Deformation. Data from two electronic tiltmeters showed no significant changes during the crisis. Despite their stability, around 10 November deformation in the upper part of the volcanic edifice was recorded by EDM and GPS measurements at Castle Peak Dome and Chances Peak. Four days of significant deformation were followed on 15 November by intense seismic activity (see below). These were followed on 17 and 18 November by an upward extension of the dome that formed in September. The dome also appeared to have extended slightly towards Chance's Peak. Although visibility was poor for the next 10 days, glimpses through steam and cloud cover suggested further doming and rock avalanching. These processes influenced a wide area on the NW side of Castle Peak Dome, including the edge of Vent 1.

From mid-November until about mid-December, the rate of deformation remained very low, with daily shortening on the order of a few millimeters along most lines, even those aimed at the presumably less stable upper flanks.

The EDM data for 10-12 December showed lengthening of the lines to Castle Peak—a deflation of the edifice. Around this time, a longer interval of GPS data also showed their lines had lengthened by >1 cm overall (with some shorter-term variability). This rate was equal to or greater than the average rate during the month of October. Late December deformation measurements using GPS and EDM techniques suggested either a return to slight inflation (14-20 December) or stability (21-27 December).

Seismicity. Montserrat seismic activity falls into four categories: 1) tremor, 2) long-period events, 3) volcano-tectonic earthquakes, and 4) regional earthquakes.

After 15 November, elevated seismicity prevailed with relatively few quiet periods. The pattern appeared very similar to that seen in late September associated with the formation of a cryptodome and possibly associated with the later extrusion of a spine. The elevated seismicity was inferred to be due to a high-level magmatic intrusion.

After 27 November there was a loss of discreet, locatable events. Low-amplitude tremor became intermixed with intervals of intense, low-amplitude, long-period events; these arrived at rates of up to 5/minute but were recorded only on the closest seismic station (MGAT, Upper Gages, figure 7). In early December tremor increased somewhat at other stations farther from the crater (MLGT, Long Ground, and MBCT, Bethel); at this time amplitudes of events at Gages also increased and the RSAM seismic index rose as high as it has been since 15 November.

Figure (see Caption) Figure 7. Montserrat seismic stations and epicenters shown in map and cross-section views, 10 December 1995. The intersection of the two cross sections is indicated by an asterisk. Epicenters are shown with two symbols, indicating variations in data quality (square, A and B quality; cross, C and D quality). Stations MSAT and MPVF were off line; MVPZ and MSSZ were 3-component stations. Courtesy of MVO.

Until 9 December there were also small, frequent, long-period earthquakes. These were accompanied by low-to-variable amplitude tremor at the Gages station, but tremor disappeared from all other stations by 8 December. The number of locatable earthquakes dropped to 1-2/day, the lowest observed during this crisis. Located earthquakes were mostly volcano-tectonic and at slightly greater depths (0-5 km) than the long-period and hybrid-type earthquakes that had dominated since 24 November. High-amplitude, high-frequency tremor was recorded at station MGAT for several hours during 10-11 December; this was probably due to an increase in steam venting from several areas on Castle Peak.

The dome grew during the week ending on 13 December, with few accompanying earthquakes early on 6 December. In contrast, during 14-20 September there were 2-20 locatable earthquakes/day, many with epicenters along the N flanks at depths of 0-6 km. During the week ending on 20 December all stations registered earthquakes with emergent onsets and a dominant frequency of 2.2 Hz; these took place 5-15 times/day. Some of the earthquakes corresponded to small explosions. Heavy rains on 16-19 December triggered floods and dilute mudflows who's acoustic signals were detected by the seismic network.

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

Information Contacts: MVO, Plymouth; Seismic Research Unit, UWI.


St. Helens (United States) — December 1995 Citation iconCite this Report

St. Helens

United States

46.2°N, 122.18°W; summit elev. 2549 m

All times are local (unless otherwise noted)


Seismicity decreases without any explosive activity

During October-December there were no explosions or gas-and-ash emissions from the lava dome, and no explosion-like seismicity was detected. Surveys of the lava dome indicated that deformation rates have remained at background levels. No increase in deformation of the dome occurred as a consequence of the recent earthquake activity, but the NW side of the dome continued to move downward very slowly as it has since a series of small explosions between 1989 and 1991. Periods of intense rainfall in November generated several lahars from the crater. All of the lahars were detected by the USGS real-time acoustic-flow network and probably flowed into Spirit Lake. Such lahars are common during intense rainfall following the dry summer months.

The number of small-magnitude (M <1) earthquakes beneath the crater decreased slowly from nearly 100/month in September (BGVN 20:09) to ~25/month in December. Seismicity at the end of December was similar to the first 6 months of 1995. The gradual decrease in seismicity, combined with the lack of small explosions related to the September increase, has lowered the concern of scientists monitoring the volcano. Small dome explosions are still possible, but their likelihood is no greater early in 1995.

Geologic Background. Prior to 1980, Mount St. Helens was a conical volcano sometimes known as the Fujisan of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km breached crater now partially filled by a lava dome. There have been nine major eruptive periods beginning about 40-50,000 years ago, and it has been the most active volcano in the Cascade Range during the Holocene. Prior to 2,200 years ago, tephra, lava domes, and pyroclastic flows were erupted, forming the older edifice, but few lava flows extended beyond the base of the volcano. The modern edifice consists of basaltic as well as andesitic and dacitic products from summit and flank vents. Eruptions in the 19th century originated from the Goat Rocks area on the N flank, and were witnessed by early settlers.

Information Contacts: Dan Dzurisin, Cascades Volcano Observatory, U.S. Geological Survey, 5400 MacArthur Blvd., Vancouver, WA 98661 USA (URL: http://volcanoes.usgs.gov/); Steve Malone, Geophysics Program, University of Washington, Seattle, WA 98195 USA (URL: https://volcanoes.usgs.gov/observatories/cvo/ home.html).


Stromboli (Italy) — December 1995 Citation iconCite this Report

Stromboli

Italy

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

All times are local (unless otherwise noted)


Low-level ash plumes and lava fountains during September-October

In contrast to very intense activity seen in summer-autumn 1994, Boris Behncke noted that activity remained low from early 1995 through October. The low level of activity, also shown by seismic data acquired by the University of Udine (see recent Bulletins), was interpreted by some researchers as a possible precursor of a more powerful eruption in the near future, resulting in a warning and access restrictions in April-May.

Eruptions during August-October produced low lava fountains and ash plumes. Activity from vent 3/1 (figure 46) consisted of night glow and spatter ejections, at times throwing bombs outside the crater. Vent 1/1 had periods of vigorous lava fountaining, often dropping incandescent bombs on the Sciara del Fuoco, particularly in early September. During dry weather, a dense gas plume often formed a hazy layer at 850-900 m altitude that extended for tens of kilometers.

Figure (see Caption) Figure 46. Map of the crater terrace at Stromboli, 19-20 September 1995, showing active vents. The map was produced using EDM and triangulation measurements. Vent numbering is consistent with sketch maps from April 1995 (BGVN 20:04). Courtesy of Andy Harris and Nicki Stevens.

During a 19-20 September visit by Andy Harris and Nicki Stevens, activity was observed from five vents (figure 47). A 4-m-diameter vent in the side of a hornito (1/4), had incandescent walls and an internal temperature of 940°C, as measured with a Minolta/Land Cyclops 152 infrared (0.8-1.1 µm) thermometer. Gas-jet eruptions from this vent sent incandescent gas and minor ejecta ~50 m high. Regular explosions from vents 1/2 and 3/2 ejected bombs and brown ash clouds up to ~100 m. Seven eruptions during a 90-minute period from vent 2/1 sent bombs to a height of ~50 m. No explosions were seen from vent 3/1, but it exhibited continuous night glow and apparently quietly ejected a few bombs to no more than 10 m above the crater rim.

Observations by Behncke on 28-29 September showed that craters 2 and 3 had not changed significantly since a visit on 20 April (BGVN 20:04). Vent 3/1 showed fluctuating glow at night but had no ejections. Vent 3/2 had very weak emissions of reddish ash every 5-20 minutes. Crater 1 had been largely filled with small spatter cones during the summer of 1994, but their destruction began with a powerful phreatic explosion on 5 March 1995 (BGVN 20:04). However, the twin cones (1/4 & 5) in vent area 1/3 remained. Neither of them had erupted after September/October 1994, but an incandescent vent (~10 m wide) at the SE base of the SW cone (1/4) had brief noisy gas explosions that emitted a diffuse incandescent gas cloud.

Vigorous eruptions observed by Behncke from vent 1/1 ejected black ash plumes that occasionally rose >100 m. After dark, incandescent ejections were seen, and loud roaring noises were audible. Reports by other observers in early October disclosed continuing low-level eruptions from vents 1/1 and 3/2 and incandescence from vents 1/3 and 3/1. In addition to the vents active in September, a vent behind the twin cones in Crater 1 and a vent in the NW part of Crater 3 were active when observed by Open University geologists on 15 and 30 October.

Geologic Background. Spectacular incandescent nighttime explosions at Stromboli have long attracted visitors to the "Lighthouse of the Mediterranean" in the NE Aeolian Islands. This volcano has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent scarp that formed about 5,000 years ago due to a series of slope failures which extends 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: Boris Behncke and Giada Giuntoli, Department of Volcanology and Petrology, GEOMAR, Wischhofstr. 1-3, 24148 Kiel, Germany; Andy Harris, Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, United Kingdom; Nicki Stevens, ESSC, University of Reading, P.O. Box 227, Reading RG2 2AB, United Kingdom.


Suwanosejima (Japan) — December 1995 Citation iconCite this Report

Suwanosejima

Japan

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

All times are local (unless otherwise noted)


Continued minor eruptive activity throughout much of 1995

Eruptive activity took place from March to June and from August to December 1995. Some ashfalls were observed at a village 4 km SSW of the crater. The two historically active summit craters and typically have Strombolian eruptions.

Geologic Background. The 8-km-long island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two active summit craters. The summit is truncated by a large breached crater extending to the sea on the E flank that was formed by edifice collapse. One of Japan's most frequently active volcanoes, it was in a state of intermittent Strombolian activity from Otake, the NE summit crater, between 1949 and 1996, after which periods of inactivity lengthened. The largest recorded eruption took place in 1813-14, when thick scoria deposits covered 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 an open collapse scarp extending 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: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


Tokachidake (Japan) — December 1995 Citation iconCite this Report

Tokachidake

Japan

43.418°N, 142.686°E; summit elev. 2077 m

All times are local (unless otherwise noted)


Gradual increase in the number of seismic events

During the second half of December, the number of earthquakes gradually increased, totalling 103 for the month. Consisting of a NE-SW aligned group of stratovolcanoes, Tokachi has a record that includes a partial cone collapse in 1925 that led to ~144 deaths and 5,000 homes destroyed.

Geologic Background. Tokachidake volcano consists of a group of dominantly andesitic stratovolcanoes and lava domes arranged on a NE-SW line above a plateau of welded Pleistocene tuffs in central Hokkaido. Numerous explosion craters and cinder cones are located on the upper flanks of the small stratovolcanoes, with the youngest Holocene centers located at the NW end of the chain. Frequent historical eruptions, consisting mostly of mild-to-moderate phreatic explosions, have been recorded since the mid-19th century. Two larger eruptions occurred in 1926 and 1962. Partial cone collapse of the western flank during the 1926 eruption produced a disastrous debris avalanche and mudflow.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


Ulawun (Papua New Guinea) — December 1995 Citation iconCite this Report

Ulawun

Papua New Guinea

5.05°S, 151.33°E; summit elev. 2334 m

All times are local (unless otherwise noted)


Modest degassing

During October-December emissions generally consisted of moderate-to-high amounts of white vapor. Gray emissions were also reportedly observed on three days in October and a number of days in November. Seismic activity was very low in October-November and unreported for December.

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

Information Contacts: Ben Talai, H. Patia, D. Lolok, and C. McKee, RVO.


Veniaminof (United States) — December 1995 Citation iconCite this Report

Veniaminof

United States

56.17°N, 159.38°W; summit elev. 2507 m

All times are local (unless otherwise noted)


Minor steam and ash emissions in November

On 15 November, residents of Perryville, ~30 km S, heard rumblings and booms through the early evening. They also observed minor ash emission, as well as increased steaming. Minor steam and ash emission was again observed on 30 November. Veniaminof was obscured by clouds on satellite imagery of 15 November, and no hot spot was visible during the last week of the month. Low-level eruptive activity has been intermittent since July 1993 (BGVN 18:07).

Geologic Background. Veniaminof, on the Alaska Peninsula, is truncated by a steep-walled, 8 x 11 km, glacier-filled caldera that formed around 3,700 years ago. The caldera rim is up to 520 m high on the north, is deeply notched on the west by Cone Glacier, and is covered by an ice sheet on the south. Post-caldera vents are located along a NW-SE zone bisecting the caldera that extends 55 km from near the Bering Sea coast, across the caldera, and down the Pacific flank. Historical eruptions probably all originated from the westernmost and most prominent of two intra-caldera cones, which rises about 300 m above the surrounding icefield. The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

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


Whakaari/White Island (New Zealand) — December 1995 Citation iconCite this Report

Whakaari/White Island

New Zealand

37.52°S, 177.18°E; summit elev. 294 m

All times are local (unless otherwise noted)


Sub-crater divides collapse, but no eruptive activity

The following summarizes observations between August and December 1995 made by pilot R. Fleming and IGNS scientists. No significant eruptive activity has occurred since minor ash emissions on 28-29 June (BGVN 20:07).

A new 30-m-diameter crater was noted on 12 August in the area of the May '91 embayment. It had destroyed a large fumarole and was ejecting mud at intervals of 2-5 seconds. By 3 October, Wade, TV1, and Princess craters were joined in a single lake, following the failure of their divides. On 13 November the rising lake level was encroaching on the area of fumaroles and hot ground. Several new fumarolic vents were noted 20-30 m above the lake level. No more crater changes were observed through 12 December. Very little seismicity was recorded: low-frequency tremor accompanied the formation of the 12 August vent. Seismicity revealed no evidence of eruptive activity since 28-29 June.

Ground deformation and magnetic surveys continued to record trends indicative of future eruptive activity. Inflation was localized in the Donald Mound area, in contrast with the earlier pattern of crater-wide inflation between November 1994 and July 1995. Inflation is occurring at a much greater rate than that observed before the 1976 eruption. Magnetic decreases under Donald Mound and on the NE side of the 1978/90 Crater Complex indicate shallow heating. Other indicators like heatflow and gas chemistry do not suggest an incipient eruption. Fumarole temperatures remain relatively low, and gas samples from fumaroles were richer in water than in the past, consistent with the rise of the water table. However, the influence of the rising water level and its possible masking effects remain uncertain.

Geologic Background. The uninhabited Whakaari/White Island is the 2 x 2.4 km 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 SE side of the crater is open at sea level, with the recent activity centered about 1 km from the shore close to the rear crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of volcanism since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. The formation of many new vents during the 19th and 20th centuries caused 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. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities. The official government name Whakaari/White Island is a combination of the full Maori name of Te Puia o Whakaari ("The Dramatic Volcano") and White Island (referencing the constant steam plume) given by Captain James Cook in 1769.

Information Contacts: B.J. Scott, Institute of Geological & Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand.

Atmospheric Effects

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

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

Special Announcements

Special announcements of various kinds and obituaries.

Special Announcements  Obituaries

Misc 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 subject.

Additional Reports  False Reports