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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

Kuchinoerabujima (Japan) Eruption and ash plumes begin on 11 January 2020 and continue through April 2020

Soputan (Indonesia) Minor ash emissions during 23 March and 2 April 2020

Heard (Australia) Eruptive activity including a lava flow during October 2019-April 2020

Kikai (Japan) Ash explosion on 29 April 2020

Fuego (Guatemala) Ongoing ash explosions, block avalanches, and intermittent lava flows

Ebeko (Russia) Frequent moderate explosions, ash plumes, and ashfall continue, December 2019-May 2020

Piton de la Fournaise (France) Fissure eruptions in February and April 2020 included lava fountains and flows

Sabancaya (Peru) Daily explosions with ash emissions, large SO2 flux, ongoing thermal anomalies, December 2019-May 2020

Sheveluch (Russia) Lava dome growth and thermal anomalies continue through April 2020, but few ash explosions

Dukono (Indonesia) Numerous ash explosions continue through March 2020

Etna (Italy) Strombolian explosions and ash emissions continue, October 2019-March 2020

Merapi (Indonesia) Explosions produced ash plumes, ashfall, and pyroclastic flows during October 2019-March 2020



Kuchinoerabujima (Japan) — May 2020 Citation iconCite this Report

Kuchinoerabujima

Japan

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

All times are local (unless otherwise noted)


Eruption and ash plumes begin on 11 January 2020 and continue through April 2020

Kuchinoerabujima encompasses a group of young stratovolcanoes located in the northern Ryukyu Islands. All historical eruptions have originated from the Shindake cone, with the exception of a lava flow that originated from the S flank of the Furudake cone. The most recent previous eruptive period took place during October 2018-February 2019 and primarily consisted of weak explosions, ash plumes, and ashfall. The current eruption began on 11 January 2020 after nearly a year of dominantly gas-and-steam emissions. Volcanism for this reporting period from March 2019 to April 2020 included explosions, ash plumes, SO2 emissions, and ashfall. The primary source of information for this report comes from monthly and annual reports from the Japan Meteorological Agency (JMA) and advisories from the Tokyo Volcanic Ash Advisory Center (VAAC). Activity has been limited to Kuchinoerabujima's Shindake Crater.

Volcanism at Kuchinoerabujima was relatively low during March through December 2019, according to JMA. During this time, SO2 emissions ranged from 100 to 1,000 tons/day. Gas-and-steam emissions were frequently observed throughout the entire reporting period, rising to a maximum height of 1.1 km above the crater on 13 December 2019. Satellite imagery from Sentinel-2 showed gas-and-steam and occasional ash emissions rising from the Shindake crater throughout the reporting period (figure 7). Though JMA reported thermal anomalies occurring on 29 January and continuing through late April 2020, Sentinel-2 imagery shows the first thermal signature appearing on 26 April.

Figure (see Caption) Figure 7. Sentinel-2 thermal satellite images showed gas-and-steam and ash emissions rising from Kuchinoerabujima. Some ash deposits can be seen on 6 February 2020 (top right). A thermal anomaly appeared on 26 April 2020 (bottom right). Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

An eruption on 11 January 2020 at 1505 ejected material 300 m from the crater and produced ash plumes that rose 2 km above the crater rim, extending E, according to JMA. The eruption continued through 12 January until 0730. The resulting ash plumes rose 400 m above the crater, drifting SW while the SO2 emissions measured 1,300 tons/day. Ashfall was reported on Yakushima Island (15 km E). Minor eruptive activity was reported during 17-20 January which produced gray-white plumes that rose 300-500 m above the crater. On 23 January, seismicity increased, and an eruption produced an ash plume that rose 1.2 km altitude, according to a Tokyo VAAC report, resulting in ashfall 2 km NE of the crater. A small explosion was detected on 24 January, followed by an increase in the number of earthquakes during 25-26 January (65-71 earthquakes per day were registered). Another small eruptive event detected on 27 January at 0148 was accompanied by a volcanic tremor and a change in tilt data. During the month of January, some inflation was detected at the base on the volcano and a total of 347 earthquakes were recorded. The SO2 emissions ranged from 200-1,600 tons/day.

An eruption on 1 February 2020 produced an eruption column that rose less than 1 km altitude and extended SE and SW (figure 8), according to the Tokyo VAAC report. On 3 February, an eruption from the Shindake crater at 0521 produced an ash plume that rose 7 km above the crater and ejected material as far as 600 m away. As a result, a pyroclastic flow formed, traveling 900-1,500 m SW. The previous pyroclastic flow that was recorded occurred on 29 January 2019. Ashfall was confirmed in the N part of Yakushima Island with a large amount in Miyanoura (32 km ESE) and southern Tanegashima. The SO2 emissions measured 1,700 tons/day during this event.

Figure (see Caption) Figure 8. Webcam images from the Honmura west surveillance camera of an ash plume rising from Kuchinoerabujima on 1 February 2020. Courtesy of JMA (Weekly bulletin report 509, February 2020).

Intermittent small eruptive events occurred during 5-9 February; field observations showed a large amount of ashfall on the SE flank which included lapilli that measured up to 2 cm in diameter. Additionally, thermal images showed 5-km-long pyroclastic flow deposits on the SW flank. An eruption on 9 February produced an ash plume that rose 1.2 km altitude, drifting SE. On 13 February a small eruption was detected in the Shindake crater at 1211, producing gray-white plumes that rose 300 m above the crater, drifting NE. Small eruptive events also occurred during 20-21 February, resulting in gas-and-steam emissions that rose 200 m above the crater. During the month of February, some horizontal extension was observed since January 2020 using GNSS data. The total number of earthquakes during this month drastically increased to 1225 compared to January. The SO2 emissions ranged from 300-1,700 tons/day.

By 2 March 2020, seismicity decreased, and activity declined. Gas-and-steam emissions continued infrequently for the duration of the reporting period. The SO2 emissions during March ranged from 700-2,100 tons/day, the latter of which occurred on 15 March. Seismicity increased again on 27 March. During 5-8 April 2020, small eruptive events were detected, generating ash plumes that rose 900 m above the crater (figure 9). The SO2 emissions on 6 April reached 3,200 tons/day, the maximum measurement for this reporting period. These small eruptive events continued from 13-20 and 23-25 April within the Shindake crater, producing gray-white plumes that rose 300-800 m above the crater.

Figure (see Caption) Figure 9. Webcam images from the Honmura Nishi (top) and Honmura west (bottom) surveillance cameras of ash plumes rising from Kuchinoerabujima on 6 March and 5 April 2020. Courtesy of JMA (Weekly bulletin report 509, March and April 2020).

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

Information Contacts: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Soputan (Indonesia) — May 2020 Citation iconCite this Report

Soputan

Indonesia

1.112°N, 124.737°E; summit elev. 1785 m

All times are local (unless otherwise noted)


Minor ash emissions during 23 March and 2 April 2020

Soputan is a stratovolcano located in the northern arm of Sulawesi Island, Indonesia. Previous eruptive periods were characterized by ash explosions, lava flows, and Strombolian eruptions. The most recent eruption occurred during October-December 2018, which consisted mostly of ash plumes and some summit incandescence (BGVN 44:01). This report updates information for January 2019-April 2020 characterized by two ash plumes and gas-and-steam emissions. The primary source of information come from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) and the Darwin Volcanic Ash Advisory Center (VAAC).

Activity during January 2019-April 2020 was relatively low; three faint thermal anomalies were observed at the summit at Soputan in satellite imagery for a total of three days on 2 and 4 January, and 1 October 2019 (figure 17). The MIROVA (Middle InfraRed Observation of Volcanic Activity) based on analysis of MODIS data detected 12 distal hotspots and six low-power hotspots within 5 km of the summit during August to early October 2019. A single distal thermal hotspot was detected in early March 2020. In March, activity primarily consisted of white to gray gas-and-steam plumes that rose 20-100 m above the crater, according to PVMBG. The Darwin VAAC issued a notice on 23 March 2020 that reported an ash plume rose to 4.3 km altitude; minor ash emissions had been visible in a webcam image the previous day (figure 18). A second notice was issued on 2 April, where an ash plume was observed rising 2.1 km altitude and drifting W.

Figure (see Caption) Figure 17. Sentinel-2 thermal satellite imagery detected a total of three thermal hotspots (bright yellow-orange) at the summit of Soputan on 2 and 4 January and 1 October 2019. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 18. Minor ash emissions were seen rising from Soputan on 22 March 2020. Courtesy of MAGMA Indonesia.

Geologic Background. The Soputan stratovolcano on the southern rim of the Quaternary Tondano caldera on the northern arm of Sulawesi Island is one of Sulawesi's most active volcanoes. The youthful, largely unvegetated volcano is located SW of Riendengan-Sempu, which some workers have included with Soputan and Manimporok (3.5 km ESE) as a volcanic complex. It was constructed at the southern end of a SSW-NNE trending line of vents. During historical time the locus of eruptions has included both the summit crater and Aeseput, a prominent NE-flank vent that formed in 1906 and was the source of intermittent major lava flows until 1924.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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).


Heard (Australia) — May 2020 Citation iconCite this Report

Heard

Australia

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

All times are local (unless otherwise noted)


Eruptive activity including a lava flow during October 2019-April 2020

Heard Island is located on the Kerguelen Plateau in the southern Indian Ocean and contains Big Ben, a snow-covered stratovolcano with intermittent volcanism reported since 1910. Due to its remote location, visual observations are rare; therefore, thermal anomalies and hotspots detected by satellite-based instruments are the primary source of information. This report updates activity from October 2019 to April 2020.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed three prominent periods of strong thermal anomaly activity during this reporting period: late October 2019, December 2019, and the end of April 2020 (figure 41). These thermal anomalies were relatively strong and occurred within 5 km of the summit. Similarly, the MODVOLC algorithm reported a total of six thermal hotspots during 28 October, 1 November 2019, and 26 April 2020.

Figure (see Caption) Figure 41. Thermal anomalies at Heard from 29 April 2019 through April 2020 as recorded by the MIROVA system (Log Radiative Power) were strong and frequent in late October, during December 2019, and at the end of April 2020. Courtesy of MIROVA.

Six thermal satellite images ranging from late October 2019 to late March showed evidence of active lava at the summit (figure 42). These images show hot material, possibly a lava flow, extending SW from the summit; a hotspot also remained at the summit. Cloud cover was pervasive during the majority of this reporting period, especially in April 2020, though gas-and-steam emissions were visible on 25 April through the clouds.

Figure (see Caption) Figure 42. Thermal satellite images of Heard Island’s Big Ben showing strong thermal signatures representing a lava flow in the SW direction from 28 October to 17 December 2019. These thermal anomalies are located NE from Mawson Peak. A faint thermal anomaly is also captured on 26 March 2020. Satellite images with atmospheric penetration (bands 12, 11, and 8A), courtesy of Sentinel Hub Playground.

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

Information Contacts: 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).


Kikai (Japan) — May 2020 Citation iconCite this Report

Kikai

Japan

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

All times are local (unless otherwise noted)


Ash explosion on 29 April 2020

The Kikai caldera is located at the N end of Japan’s Ryukyu Islands and has been recently characterized by intermittent ash emissions and limited ashfall in nearby communities. On Satsuma Iwo Jima island, the larger subaerial fragment of the Kikai caldera, there was a single explosion with gas-and-steam and ash emissions on 2 November 2019, accompanied by nighttime incandescence (BGVN 45:02). This report covers volcanism from January 2020 through April 2020 with a single-day eruption occurring on 29 April based on reports from the Japan Meteorological Agency (JMA).

Since the last one-day eruption on 2 November 2019, volcanism at Kikai has been relatively low and primarily consisted of 107-170 earthquakes per month and intermittent white gas-and-steam emissions rising up to 1.3 km above the crater summit. Intermittent weak hotspots were observed at night in the summit in Sentinel-2 thermal satellite imagery and webcams, according to JMA (figures 14 and 15).

Figure (see Caption) Figure 14. Weak thermal hotspots (bright yellow-orange) were observed on 7 January (top) and 6 April 2020 (bottom) at Satsuma Iwo Jima (Kikai). Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 15. Incandescence at night on 10 January 2020 was observed at Satsuma Iwo Jima (Kikai) in the Iodake crater with the Iwanogami webcam. Courtesy of JMA (An explanation of volcanic activity at Satsuma Iwo Jima, January 2nd year of Reiwa [2020]).

Weak incandescence continued in April 2020. JMA reported SO2 measurements during April were 400-2000 tons/day. A brief eruption in the Iodake crater on 29 April 2020 at 0609 generated a gray-white ash plume that rose 1 km above the crater (figure 16). No ashfall or ejecta was observed after the eruption on 29 April.

Figure (see Caption) Figure 16. The Iwanogami webcam captured a brief gray-white ash and steam plume rising above the Iodake crater rim on Satsuma Iwo Jima (Kikai) on 29 April 2020 at 0609 local time. The plume rose 1 km above the crater summit. Courtesy of JMA (An explanation of volcanic activity at Satsuma Iwo Jima, April 2nd year of Reiwa [2020]).

Geologic Background. Kikai is 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 lava dome and Inamuradake scoria cone, as well as submarine lava domes. Historical 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 Tokara-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 Tokara-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); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Fuego (Guatemala) — April 2020 Citation iconCite this Report

Fuego

Guatemala

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

All times are local (unless otherwise noted)


Ongoing ash explosions, block avalanches, and intermittent lava flows

Fuego is a stratovolcano in Guatemala that has been erupting since 2002 with historical eruptions that date back to 1531. Volcanism is characterized by major ashfalls, pyroclastic flows, lava flows, and lahars. The previous report (BGVN 44:10) detailed activity that included multiple ash explosions, ash plumes, ashfall, active lava flows, and block avalanches. This report covers this continuing activity from October 2019 through March 2020 and consists of ash plumes, ashfall, incandescent ejecta, block avalanches, and lava flows. The primary source of information comes from the Instituto Nacional de Sismologia, Vulcanología, Meteorología e Hidrologia (INSIVUMEH), the Washington Volcanic Ash Advisory Center (VAAC), and various satellite data.

Summary of activity October 2019-March 2020. Daily activity persisted throughout October 2019-March 2020 (table 20) with multiple ash explosions recorded every hour, ash plumes that rose to a maximum of 4.8 km altitude each month drifting in multiple directions, incandescent ejecta reaching a 500 m above the crater resulting in block avalanches traveling down multiple drainages, and ashfall affecting communities in multiple directions. The highest rate of explosions occurred on 7 November with up to 25 per hour. Dominantly white fumaroles occurred frequently throughout this reporting period, rising to a maximum altitude of 4.5 km and drifting in multiple directions. Intermittent lava flows that reached a maximum length of 1.2 km were observed each month in the Seca (Santa Teresa) and Ceniza drainages (figure 128), but rarely in the Trinidad drainage. Thermal activity increased slightly in frequency and strength in late October and remained relatively consistent through mid-March as seen in the MIROVA analysis of MODIS satellite data (figure 129).

Table 20. Activity summary by month for Fuego with information compiled from INSIVUMEH daily reports.

Month Ash plume heights (km) Ash plume distance (km) and direction Drainages affected by avalanche blocks Villages reporting ashfall
Oct 2019 4.3-4.8 km 10-25 km, W-SW-S-NW Seca, Taniluyá, Ceniza, Trinidad, El Jute, Honda, and Las Lajas Panimaché I and II, Morelia, Santa Sofía, Porvenir, Finca Palo Verde, La Rochela, San Andrés Osuna, Sangre de Cristo, and San Pedro Yepocapa
Nov 2019 4.0-4.8 km 10-20 km, W-SW-S-NW Seca, Taniluyá, Trinidad, Las Lajas, Honda, and Ceniza Panimaché I and II, Morelia, Santa Sofía, Porvenir, Sangre de Cristo, Finca Palo Verde, and San Pedro Yepocapa
Dec 2019 4.2-4.8 km 10-25 km, W-SW-S-SE-N-NE Seca, Taniluya, Ceniza, Trinidad, and Las Lajas Morelia, Santa Sofía, Finca Palo Verde, El Porvenir, Sangre de Cristo, San Pedro Yepocapa, Panimaché I and II, La Rochela, and San Andrés Osuna
Jan 2020 4.3-4.8 km 10-25 km, W-SW-S-N-NE-E Seca, Ceniza, Taniluyá, Trinidad, Honda, and Las Lajas Morelia, Santa Sofía, Sangre de Cristo, San Pedro Yepocapa, Panimaché I and II, El Porvenir, Finca Palo Verde, Rodeo, La Rochela, Alotenango, El Zapote, Trinidad, La Reina, Ceilán
Feb 2020 4.3-4.8 km 8-25 km, W-SW-S-SE-E-NE-N-NW Seca, Ceniza, Taniluya, Trinidad, Las Lajas, Honda, La Rochela, El Zapote, and San Andrés Osuna Panimache I and II, Morelia, Santa Sofia, Sangre de Cristo, San Pedro Yepocapa, Rodeo, La Reina, Alotenango, Yucales, Siquinalá, Santa Lucia, El Porvenir, Finca Los Tarros, La Soledad, Buena Vista, La Cruz, Pajales, San Miguel Dueñas, Ciudad Vieja, San Miguel Escobar, San Pedro las Huertas, Antigua, La Rochela, and San Andrés Osuna
Mar 2020 4.3-4.8 km 10-23 km, W-SW-S-SE-N-NW Seca, Ceniza, Trinidad, Taniluyá, Las Lajas, Honda, La Rochela, El Zapote, San Andrés Osuna, Morelia, Panimache, and Santa Sofia San Andrés Osuna, La Rochela, El Rodeo, Chuchu, Panimache I and II, Santa Sofia, Morelia, Finca Palo Verde, El Porvenir, Sangre de Cristo, La Cruz, San Pedro Yepocapa, La Conchita, La Soledad, Alotenango, Aldea la Cruz, Acatenango, Ceilan, Taniluyá, Ceniza, Las Lajas, Trinidad, Seca, and Honda
Figure (see Caption) Figure 128. Sentinel-2 thermal satellite images of Fuego between 21 November 2019 and 20 March 2020 showing lava flows (bright yellow-orange) traveling generally S and W from the crater summit. An ash plume can also be seen on 21 November 2019, accompanying the lava flow. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 129. Thermal activity at Fuego increased in frequency and strength (log radiative power) in late October 2019 and remained relatively consistent through February 2020. In early March, there is a small decrease in thermal power, followed by a short pulse of activity and another decline. Courtesy of MIROVA.

Activity during October-December 2019. Activity in October 2019 consisted of 6-20 ash explosions per hour; ash plumes rose to 4.8 km altitude, drifting up to 25 km in multiple directions, resulting in ashfall in Panimaché I and II (8 km SW), Morelia (9 km SW), San Pedro Yepocapa (8 km NW), Sangre de Cristo (8 km WSW), Santa Sofía (12 km SW), El Porvenir (8 km ENE), Finca Palo Verde, La Rochela and San Andrés Osuna. The Washington VAAC issued multiple aviation advisories for a total of nine days in October. Continuous white gas-and-steam plumes reached 4.1-4.4 km altitude drifting generally W. Weak SO2 emissions were infrequently observed in satellite imagery during October and January 2020 (figure 130) Incandescent ejecta was frequently observed rising 200-400 m above the summit, which generated block avalanches that traveled down the Seca (W), Taniluyá (SW), Ceniza (SSW), Trinidad (S), El Jute, Honda, and Las Lajas (SE) drainages. During 3-7 October lahars descended the Ceniza, El Mineral, and Seca drainages, carrying tree branches, tree trunks, and blocks 1-3 m in diameter. During 6-8 and 13 October, active lava flows traveled up to 200 m down the Seca drainage.

Figure (see Caption) Figure 130. Weak SO2 emissions were observed rising from Fuego using the TROPOMI instrument on the Sentinel-5P satellite. Top left: 17 October 2019. Top right: 17 November 2019. Bottom left: 20 January 2020. Bottom right: 22 January 2020. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

During November 2019, the rate of explosions increased to 5-25 per hour, the latter of which occurred on 7 November. The explosions resulted in ash plumes that rose 4-4.8 km altitude, drifting 10-20 km in the W direction. Ashfall was observed in Panimaché I and II, Morelia, Santa Sofía, Porvenir, Sangre de Cristo, Finca Palo Verde, and San Pedro Yepocapa. Multiple Washington VAAC notices were issued for 11 days in November. Continuous white gas-and-steam plumes rose up to 4.5 km altitude drifting generally W. Incandescent ejecta rose 100-500 m above the crater, generating block avalanches in Seca, Taniluyá, Trinidad, Las Lajas, Honda, and Ceniza drainages. Lava flows were observed for a majority of the month into early December measuring 100-900 m long in the Seca and Ceniza drainages.

The number of explosions in December 2019 decreased compared to November, recording 8-19 per hour with incandescent ejecta rising 100-400 m above the crater. The explosions generated block avalanches that traveled in the Seca, Taniluya, Ceniza, Trinidad, and Las Lajas drainages throughout the month. Ash plumes continued to rise above the summit crater to 4.8 km drifting up to 25 km in multiple directions. The Washington VAAC issued multiple daily notices almost daily in December. A continuous lava flow observed during 6-15, 21-22, 24, and 26 November through 9 December measured 100-800 m long in the Seca and Ceniza drainages.

Activity during January-March 2020. Incandescent Strombolian explosions continued daily during January 2020, ejecting material up to 100-500 m above the crater. Ash plumes continued to rise to a maximum altitude of 4.8 km, resulting in ashfall in all directions affecting Morelia, Santa Sofía, Sangre de Cristo, San Pedro Yepocapa, Panimaché I and II, El Porvenir, Finca Palo Verde, Rodeo, La Rochela, Alotenango, El Zapote, Trinidad, La Reina, and Ceilán. The Washington VAAC issued multiple notices for a total of 12 days during January. Block avalanches resulting from the Strombolian explosions traveled down the Seca, Ceniza, Taniluyá, Trinidad, Honda, and Las Lajas drainages. An active lava flow in the Ceniza drainage measured 150-600 m long during 6-10 January.

During February 2020, INSIVUMEH reported a range of 4-16 explosions per hour, accompanied by incandescent material that rose 100-500 m above the crater (figure 131). Block avalanches traveled in the Santa Teresa, Seca, Ceniza, Taniluya, Trinidad, Las Lajas, Honda, La Rochela, El Zapote, and San Andrés Osuna drainages. Ash emissions from the explosions continued to rise 4.8 km altitude, drifting in multiple directions as far as 25 km and resulting in ashfall in the communities of Panimache I and II, Morelia, Santa Sofia, Sangre de Cristo, San Pedro Yepocapa, Rodeo, La Reina, Alotenango, Yucales, Siquinalá, Santa Lucia, El Porvenir, Finca Los Tarros, La Soledad, Buena Vista, La Cruz, Pajales, San Miguel Dueñas, Ciudad Vieja, San Miguel Escobar, San Pedro las Huertas, Antigua, La Rochela, and San Andrés Osuna. Washington VAAC notices were issued almost daily during the month. Lava flows were active in the Ceniza drainage during 13-20, 23-24, and 26-27 February measuring as long as 1.2 km.

Figure (see Caption) Figure 131. Incandescent ejecta rose several hundred meters above the crater of Fuego on 6 February 2020, resulting in block avalanches down multiple drainages. Courtesy of Crelosa.

Daily explosions and incandescent ejecta continued through March 2020, with 8-17 explosions per hour that rose up to 500 m above the crater. Block avalanches from the explosions were observed in the Seca, Ceniza, Trinidad, Taniluyá, Las Lajas, Honda, Santa Teresa, La Rochela, El Zapote, San Andrés Osuna, Morelia, Panimache, and Santa Sofia drainages. Accompanying ash plumes rose 4.8 km altitude, drifting in multiple directions mostly to the W as far as 23 km and resulting in ashfall in San Andrés Osuna, La Rochela, El Rodeo, Chuchu, Panimache I and II, Santa Sofia, Morelia, Finca Palo Verde, El Porvenir, Sangre de Cristo, La Cruz, San Pedro Yepocapa, La Conchita, La Soledad, Alotenango, Aldea la Cruz, Acatenango, Ceilan, Taniluyá, Ceniza, Las Lajas, Trinidad, Seca, and Honda. Multiple Washington VAAC notices were issued for a total of 15 days during March. Active lava flows were observed from 16-21 March in the Trinidad and Ceniza drainages measuring 400-1,200 m long and were accompanied by weak to moderate explosions. By 23 March, active lava flows were no longer observed.

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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Crelosa, 3ra. avenida. 8-66, Zona 14. Colonia El Campo, Guatemala Ciudad de Guatemala (URL: http://crelosa.com/, post at https://www.youtube.com/watch?v=1P4kWqxU2m0&feature=youtu.be).


Ebeko (Russia) — June 2020 Citation iconCite this Report

Ebeko

Russia

50.686°N, 156.014°E; summit elev. 1103 m

All times are local (unless otherwise noted)


Frequent moderate explosions, ash plumes, and ashfall continue, December 2019-May 2020

The current moderate explosive eruption of Ebeko has been ongoing since October 2016, with frequent ash explosions that have reached altitudes of 1.3-6 km (BGVN 42:08, 43:03, 43:06, 43:12, 44:12). Ashfall is common in Severo-Kurilsk, a town of about 2,500 residents 7 km ESE, where the Kamchatka Volcanic Eruptions Response Team (KVERT) monitor the volcano. During the reporting period, December 2019-May 2020, the Aviation Color Code remained at Orange (the second highest level on a four-color scale).

During December 2019-May 2020, frequent explosions generated ash plumes that reached altitudes of 1.5-4.6 km (table 9); reports of ashfall in Severo-Kurilsk were common. Ash explosions in late April caused ashfall in Severo-Kurilsk during 25-30 April (figure 24), and the plume drifted 180 km SE on the 29th. There was also a higher level of activity during the second half of May (figure 25), when plumes drifted up to 80 km downwind.

Table 9. Summary of activity at Ebeko, December 2019-May 2020. S-K is Severo-Kurilsk (7 km ESE of the volcano). TA is thermal anomaly in satellite images. In the plume distance column, only plumes that drifted more than 10 km are indicated. Dates based on UTC times. Data courtesy of KVERT.

Date Plume Altitude (km) Plume Distance Plume Directions Other Observations
30 Nov-05 Dec 2019 3 -- NE, E Intermittent explosions.
06-13 Dec 2019 4 -- E Explosions all week. Ashfall in S-K on 10-12 Dec.
15-17 Dec 2019 3 -- E Explosions. Ashfall in S-K on 16-17 Dec.
22-24 Dec 2019 3 -- NE Explosions.
01-02 Jan 2020 3 30 km N N Explosions. TA over dome on 1 Jan.
03, 05, 09 Jan 2020 2.9 -- NE, SE Explosions. Ashfall in S-K on 8 Jan.
11, 13-14 Jan 2020 3 -- E Explosions. Ashfall in S-K.
19-20 Jan 2020 3 -- E Ashfall in S-K on 19 Jan.
24-31 Jan 2020 4 -- E Explosions.
01-07 Feb 2020 3 -- E, S Explosions all week.
12-13 Feb 2020 1.5 -- E Explosions. Ashfall in S-K.
18-19 Feb 2020 2.3 -- SE Explosions.
21, 25, 27 Feb 2020 2.9 -- S, SE, NE Explosions. Ashfall in S-K on 22 Feb.
01-02, 05 Mar 2020 2 -- S, E Explosions.
08 Mar 2020 2.5 -- NE Explosions.
13, 17 Mar 2020 2.5 -- NE, SE Bursts of gas, steam, and small amount of ash.
24-25 Mar 2020 2.5 -- NE, W Explosions.
29 Mar-02 Apr 2020 2.2 -- NE, E Explosions. Ashfall in S-K on 1 Apr. TA on 30-31 Mar.
04-05, 09 Apr 2020 1.5 -- NE Explosions. TA on 5 Apr.
13 Apr 2020 2.5 -- SE Explosions.
18, 20 Apr 2020 -- -- -- TA on 18, 20 Apr.
24 Apr-01 May 2020 3.5 180 km SE on 29 Apr E, SE Explosions all week. Ashfall in S-K on 25-30 Apr.
01-08 May 2020 2.6 -- E Explosions all week. Ashfall in S-K on 3-5 May. TA on 3 May.
08-15 May 2020 4 -- E Explosions. Ashfall in S-K on 8-12 May. TA during 12-14 May.
14-15, 19-21 May 2020 3.6 80 km SW, S, SE during 14, 20-21 May -- Explosions. TA on same days.
22-29 May 2020 4.6 60 km SE E, SE Explosions all week. Ashfall in S-K on 22, 24 May.
29-31 May 2020 4.5 -- E, S Explosions. TA on 30 May.
Figure (see Caption) Figure 24. Photo of ash explosion at Ebeko at 2110 UTC on 28 April 2020, as viewed from Severo-Kurilsk. Courtesy of KVERT (L. Kotenko).
Figure (see Caption) Figure 25. Satellite image of Ebeko from Sentinel-2 on 27 May 2020, showing a plume drifting SE. Image using natural color rendering (bands 4, 3, 2) courtesy of Sentinel Hub Playground.

Geologic Background. The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion craters.

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


Piton de la Fournaise (France) — May 2020 Citation iconCite this Report

Piton de la Fournaise

France

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

All times are local (unless otherwise noted)


Fissure eruptions in February and April 2020 included lava fountains and flows

Piton de la Fournaise is a massive basaltic shield volcano on the French island of Réunion in the western Indian Ocean. Recent volcanism is characterized by multiple fissure eruptions, lava fountains, and lava flows (BGVN 44:11). The activity during this reporting period of November 2019-April 2020 is consistent with the previous eruption, including lava fountaining and lava flows. Information for this report comes from the Observatoire Volcanologique du Piton de la Fournaise (OVPF) and various satellite data.

Activity during November 2019-January 2020 was relatively low; no eruptive events were detected, according to OVPF. Edifice deformation resumed during the last week in December and continued through January. Seismicity significantly increased in early January, registering 258 shallow earthquakes from 1-16 January. During 17-31 January, the seismicity declined, averaging one earthquake per day.

Two eruptive events took place during February-April 2020. OVPF reported that the first occurred from 10 to 16 February on the E and SE flanks of the Dolomieu Crater. The second took place during 2-6 April. Both eruptive events began with a sharp increase in seismicity accompanied by edifice inflation, followed by a fissure eruption that resulted in lava fountains and lava flows (figure 193). MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed the two eruptive events occurring during February-April 2020 (figure 194). Similarly, the MODVOLC algorithm reported 72 thermal signatures proximal to the summit crater from 12 February to 6 April. Both of these eruptive events were accompanied by SO2 emissions that were detected by the Sentinel-5P/TROPOMI instrument (figures 195 and 196).

Figure (see Caption) Figure 193. Location maps of the lava flows on the E flank at Piton de la Fournaise on 10-16 February 2020 (left) and 2-6 April 2020 (right) as derived from SAR satellite data. Courtesy of OVPF-IPGP, OPGC, LMV (Monthly bulletins of the Piton de la Fournaise Volcanological Observatory, February and April 2020).
Figure (see Caption) Figure 194. Two significant eruptive events at Piton de la Fournaise took place during February-April 2020 as recorded by the MIROVA system (Log Radiative Power). Courtesy of MIROVA.
Figure (see Caption) Figure 195. Images of the SO2 emissions during the February 2020 eruptive event at Piton de la Fournaise detected by the Sentinel-5P/TROPOMI satellite. Top left: 10 February 2020. Top right: 11 February 2020. Bottom left: 13 February 2020. Bottom right: 14 February 2020. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.
Figure (see Caption) Figure 196. Images of the SO2 emissions during the April 2020 eruptive event at Piton de la Fournaise detected by the Sentinel-5P/TROPOMI satellite. Left: 4 April 2020. Middle: 5 April 2020. Right: 6 April 2020. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

On 10 February 2020 a seismic swarm was detected at 1027, followed by rapid deformation. At 1050, volcanic tremors were recorded, signaling the start of the eruption. Several fissures opened on the E flank of the Dolomieu Crater between the crater rim and at 2,000 m elevation, as observed by an overflight during 1300 and 1330. These fissures were at least 1 km long and produced lava fountains that rose up to 10 m high. Lava flows were also observed traveling E and S to 1,700 m elevation by 1315 (figures 197 and 198). The farthest flow traveled E to an elevation of 1,400 m. Satellite data from HOTVOLC platform (OPGC - University of Auvergne) was used to estimate the peak lava flow rate on 11 February at 10 m3/s. By 13 February only one lava flow that was traveling E below the Marco Crater remained active. OVPF also reported the formation of a cone, measuring 30 m tall, surrounded by three additional vents that produced lava fountains up to 15 m high. On 15 February the volcanic tremors began to decrease at 1400; by 16 February at 1412 the tremors stopped, indicating the end of the eruptive event.

Figure (see Caption) Figure 197. Photo of a lava flow and degassing at Piton de la Fournaise on 10 February 2020. Courtesy of OVPF-IPGP.
Figure (see Caption) Figure 198. Photos of the lava flows at Piton de la Fournaise taken during the February 2020 eruption by Richard Bouchet courtesy of AFP News Service.

Volcanism during the month of March 2020 consisted of low seismicity, including 21 shallow volcanic tremors and near the end of the month, edifice inflation was detected. A second eruptive event began on 2 April 2020, starting with an increase in seismicity during 0815-0851. Much of this seismicity was located on the SE part of the Dolomieu Crater. A fissure opened on the E flank, consistent with the fissures that were active during the February 2020 event. Seismicity continued to increase in intensity through 6 April located dominantly in the SE part of the Dolomieu Crater. An overflight on 5 April at 1030 showed lava fountains rising more than 50 m high accompanied by gas-and-steam plumes rising to 3-3.5 km altitude (figures 199 and 200). A lava flow advanced to an elevation of 360 m, roughly 2 km from the RN2 national road (figure 199). A significant amount of Pele’s hair and clusters of fine volcanic products were produced during the more intense phase of the eruption (5-6 April) and deposited at distances more than 10 km from the eruptive site (figure 201). It was also during this period that the SO2 emissions peaked (figure 196). The eruption stopped at 1330 after a sharp decrease in volcanic tremors.

Figure (see Caption) Figure 199. Photos of a lava flow (left) and lava fountains (right) at Piton de la Fournaise during the April 2020 eruption. Left: photo taken on 2 April 2020 at 1500. Right: photo taken on 5 April 2020 at 1030. Courtesy of OVPF-IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, April 2020).
Figure (see Caption) Figure 200. Photo of the lava fountains erupting from Piton de la Fournaise on 4 April 2020. Photo taken by Richard Bouchet courtesy of Geo Magazine via Jeannie Curtis.
Figure (see Caption) Figure 201. Photos of Pele’s hair deposited due to the April 2020 eruption at Piton de la Fournaise. Samples collected near the Gîte du volcan on 7 April 2020 (left) and a cluster of Pele’s hair found near the Foc-Foc car park on 9 April 2020 (right). Courtesy of OVPF-IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, April 2020).

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

Information Contacts: Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, 14 route nationale 3, 27 ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr); 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/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); GEO Magazine (AFP story at URL: https://www.geo.fr/environnement/la-reunion-fin-deruption-au-piton-de-la-fournaise-200397); AFP (URL: https://twitter.com/AFP/status/1227140765106622464, Twitter: @AFP, https://twitter.com/AFP); Jeannie Curtis (Twitter: @VolcanoJeannie, https://twitter.com/VolcanoJeannie).


Sabancaya (Peru) — June 2020 Citation iconCite this Report

Sabancaya

Peru

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

All times are local (unless otherwise noted)


Daily explosions with ash emissions, large SO2 flux, ongoing thermal anomalies, December 2019-May 2020

Although tephrochronology has dated activity at Sabancaya back several thousand years, renewed activity that began in 1986 was the first recorded in over 200 years. Intermittent activity since then has produced significant ashfall deposits, seismic unrest, and fumarolic emissions. A new period of explosive activity that began in November 2016 has been characterized by pulses of ash emissions with some plumes exceeding 10 km altitude, thermal anomalies, and significant SO2 plumes. Ash emissions and high levels of SO2 continued each week during December 2019-May 2020. The Observatorio Vulcanologico INGEMMET (OVI) reports weekly on numbers of daily explosions, ash plume heights and directions of drift, seismicity, and other activity. The Buenos Aires Volcanic Ash Advisory Center (VAAC) issued three or four daily reports of ongoing ash emissions at Sabancaya throughout the period.

The dome inside the summit crater continued to grow throughout this period, along with nearly constant ash, gas, and steam emissions; the average number of daily explosions ranged from 4 to 29. Ash and gas plume heights rose 1,800-3,800 m above the summit crater, and multiple communities around the volcano reported ashfall every month (table 6). Sulfur dioxide emissions were notably high and recorded daily with the TROPOMI satellite instrument (figure 75). Thermal activity declined during December 2019 from levels earlier in the year but remained steady and increased in both frequency and intensity during April and May 2020 (figure 76). Infrared satellite images indicated that the primary heat source throughout the period was from the dome inside the summit crater (figure 77).

Table 6. Persistent activity at Sabancaya during December 2019-May 2020 included multiple daily explosions with ash plumes that rose several kilometers above the summit and drifted in many directions; this resulted in ashfall in communities within 30 km of the volcano. Satellite instruments recorded SO2 emissions daily. Data courtesy of OVI-INGEMMET.

Month Avg. Daily Explosions by week Max plume Heights (m above crater) Plume drift (km) and direction Communities reporting ashfall Min Days with SO2 over 2 DU
Dec 2019 16, 13, 5, 5 2,600-3,800 20-30 NW Pinchollo, Madrigal, Lari, Maca, Achoma, Coporaque, Yanque, Chivay, Huambo, Cabanaconde 27
Jan 2020 10, 8, 11, 14, 4 1,800-3,400 30 km W, NW, SE, S Chivay, Yanque, Achoma 29
Feb 2020 8, 11, 20, 19 2,000-2,200 30 km SE, E, NE, W Huambo 29
Mar 2020 14, 22, 29, 18 2,000-3,000 30 km NE, W, NW, SW Madrigal, Lari, Pinchollo 30
Apr 2020 12, 12, 16, 13, 8 2,000-3,000 30 km SE, NW, E, S Pinchollo, Madrigal, Lari, Maca, Ichupampa, Yanque, Chivay, Coporaque, Achoma 27
May 2020 15, 14, 6, 16 1,800-2,400 30 km SW, SE, E, NE, W Chivay, Achoma, Maca, Lari, Madrigal, Pinchollo 27
Figure (see Caption) Figure 75. Sulfur dioxide anomalies were captured daily from Sabancaya during December 2019-May 2020 by the TROPOMI instrument on the Sentinel-5P satellite. Some of the largest SO2 plumes are shown here with dates listed in the information at the top of each image. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.
Figure (see Caption) Figure 76. Thermal activity at Sabancaya declined during December 2019 from levels earlier in the year but remained steady and increased slightly in frequency and intensity during April and May 2020, according to the MIROVA graph of Log Radiative Power from 23 June 2019 through May 2020. Courtesy of MIROVA.
Figure (see Caption) Figure 77. Sentinel-2 satellite imagery of Sabancaya confirmed the frequent ash emissions and ongoing thermal activity from the dome inside the summit crater during December 2019-May 2020. Top row (left to right): On 6 December 2019 a large plume of steam and ash drifted N from the summit. On 16 December 2019 a thermal anomaly encircled the dome inside the summit caldera while gas and possible ash drifted NW. On 14 April 2020 a very similar pattern persisted inside the crater. Bottom row (left to right): On 19 April an ash plume was clearly visible above dense cloud cover. On 24 May the infrared glow around the dome remained strong; a diffuse plume drifted W. A large plume of ash and steam drifted SE from the summit on 29 May. Infrared images use Atmospheric penetration rendering (bands 12, 11, 8a), other images use Natural Color rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

The average number of daily explosions during December 2019 decreased from a high of 16 the first week of the month to a low of five during the last week. Six pyroclastic flows occurred on 10 December (figure 78). Tremors were associated with gas-and-ash emissions for most of the month. Ashfall was reported in Pinchollo, Madrigal, Lari, Maca, Achoma, Coporaque, Yanque, and Chivay during the first week of the month, and in Huambo and Cabanaconde during the second week (figure 79). Inflation of the volcano was measured throughout the month. SO2 flux was measured by OVI as ranging from 2,500 to 4,300 tons per day.

Figure (see Caption) Figure 78. Multiple daily explosions at Sabancaya produced ash plumes that rose several kilometers above the summit. Left image is from 5 December and right image is from 11 December 2019. Note pyroclastic flows to the right of the crater on 11 December. Courtesy of OVI (Reporte Semanal de Monitorio de la Actividad de la Volcan Sabancaya, RSSAB-49-2019/INGEMMET Semana del 2 al 8 de diciembre de 2019 and RSSAB-50-2019/INGEMMET Semana del 9 al 15 de diciembre de 2019).
Figure (see Caption) Figure 79. Communities to the N and W of Sabancaya recorded ashfall from the volcano the first week of December and also every month during December 2019-May 2020. The red zone is the area where access is prohibited (about a 12-km radius from the crater). Courtesy of OVI (Reporte Semanal de Monitorio de la Actividad de la Volcan Sabancaya, RSSAB-22-2020/INGEMMET Semana del 25 al 31 de mayo del 2020).

During January and February 2020 the number of daily explosions averaged 4-20. Ash plumes rose as high as 3.4 km above the summit (figure 80) and drifted up to 30 km in multiple directions. Ashfall was reported in Chivay, Yanque, and Achoma on 8 January, and in Huambo on 25 February. Sulfur dioxide flux ranged from a low of 1,200 t/d on 29 February to a high of 8,200 t/d on 28 January. Inflation of the edifice was measured during January; deformation changed to deflation in early February but then returned to inflation by the end of the month.

Figure (see Caption) Figure 80. Ash plumes rose from Sabancaya every day during January and February 2020. Left: 11 January. Right: 28 February. Courtesy of OVI (Reporte Semanal de Monitorio de la Actividad de la Volcan Sabancaya, RSSAB-02-2020/INGEMMET Semana del 06 al 12 de enero del 2020 and RSSAB-09-2020/INGEMMET Semana del 24 de febrero al 01 de marzo del 2020).

Explosions continued during March and April 2020, averaging 8-29 per day. Explosions appeared to come from multiple vents on 11 March (figure 81). Ash plumes rose 3 km above the summit during the first week of March and again the first week of April; they were lower during the other weeks. Ashfall was reported in Madrigal, Lari, and Pinchollo on 27 March and 5 April. On 17 April ashfall was reported in Maca, Ichupampa, Yanque, Chivay, Coporaque, and Achoma. Sulfur dioxide flux ranged from 1,900 t/d on 5 March to 10,700 t/d on 30 March. Inflation at depth continued throughout March and April with 10 +/- 4 mm recorded between 21 and 26 April. Similar activity continued during May 2020; explosions averaged 6-16 per day (figure 82). Ashfall was reported on 6 May in Chivay, Achoma, Maca, Lari, Madrigal, and Pinchollo; heavy ashfall was reported in Achoma on 12 May. Additional ashfall was reported in Achoma, Maca, Madrigal, and Lari on 23 May.

Figure (see Caption) Figure 81. Explosions at Sabancaya on 11 March 2020 appeared to originate simultaneously from two different vents (left). The plume on 12 April was measured at about 2,500 m above the summit. Courtesy of OVI-INGEMMET (Reporte Semanal de Monitorio de la Actividad de la Volcan Sabancaya, RSSAB-11-2020/INGEMMET Semana del 9 al 15 de marzo del 2020 and RSSAB-15-2020/INGEMMET Semana del 6 al 12 de abril del 2020).
Figure (see Caption) Figure 82. Explosions dense with ash continued during May 2020 at Sabancaya. On 11 and 29 May 2020 ash plumes rose from the summit and drifted as far as 30 km before dissipating. Courtesy of OVI-INGEMMET (Reporte Semanal de Monitorio de la Actividad de la Volcan Sabancaya , RSSAB-20-2020/INGEMMET Semana del 11 al 17 de mayo del 2020 and RSSAB-22-2020/INGEMMET Semana del 25 al 31 de mayo del 2020).

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: Observatorio Volcanologico del INGEMMET (Instituto Geológical Minero y Metalúrgico), Barrio Magisterial Nro. 2 B-16 Umacollo - Yanahuara Arequipa, Peru (URL: http://ovi.ingemmet.gob.pe); 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); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); 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).


Sheveluch (Russia) — May 2020 Citation iconCite this Report

Sheveluch

Russia

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

All times are local (unless otherwise noted)


Lava dome growth and thermal anomalies continue through April 2020, but few ash explosions

The eruption at Sheveluch has continued for more than 20 years, with strong explosions that have produced ash plumes, lava dome growth, hot avalanches, numerous thermal anomalies, and strong fumarolic activity (BGVN 44:05). During this time, there have been periods of greater or lesser activity. The most recent period of increased activity began in December 2018 and continued through October 2019 (BGVN 44:11). This report covers activity between November 2019 to April 2020, a period during which activity waned. The volcano is monitored by the Kamchatka Volcanic Eruptions Response Team (KVERT) and Tokyo Volcanic Ash Advisory Center (VAAC).

During the reporting period, KVERT noted that lava dome growth continued, accompanied by incandescence of the dome blocks and hot avalanches. Strong fumarolic activity was also present (figure 53). However, the overall eruption intensity waned. Ash plumes sometimes rose to 10 km altitude and drifted downwind over 600 km (table 14). The Aviation Color Code (ACC) remained at Orange (the second highest level on a four-color scale), except for 3 November when it was raised briefly to Red (the highest level).

Figure (see Caption) Figure 53. Fumarolic activity of Sheveluch’s lava dome on 24 January 2020. Photo by Y. Demyanchuk; courtesy of KVERT.

Table 14. Explosions and ash plumes at Sheveluch during November 2019-April 2020. Dates and times are UTC, not local. Data courtesy of KVERT and the Tokyo VAAC.

Dates Plume Altitude (km) Drift Distance and Direction Remarks
01-08 Nov 2019 -- 640 km NW 3 November: ACC raised to Red from 0546-0718 UTC before returning to Orange.
08-15 Nov 2019 9-10 1,300 km ESE
17-27 Dec 2019 6.0-6.5 25 km E Explosions at about 23:50 UTC on 21 Dec.
20-27 Mar 2020 -- 45 km N 25 March: Gas-and-steam plume containing some ash.
03-10 Apr 2020 10 km 526 km SE 8 April: Strong explosion at 1910 UTC.
17-24 Apr 2020 -- 140 km NE Re-suspended ash plume.

KVERT reported thermal anomalies over the volcano every day, except for 25-26 January, when clouds obscured observations. During the reporting period, thermal anomalies, based on MODIS satellite instruments analyzed using the MODVOLC algorithm recorded hotspots on 10 days in November, 13 days in December, nine days in January, eight days in both February and March, and five days in April. The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, also based on analysis of MODIS data, detected numerous hotspots every month, almost all of which were of moderate radiative power (figure 54).

Figure (see Caption) Figure 54. Thermal anomalies at Sheveluch continued at elevated levels during November 2019-April 2020, as seen on this MIROVA Log Radiative Power graph for July 2019-April 2020. Courtesy of MIROVA.

High sulfur dioxide levels were occasionally recorded just above or in the close vicinity of Sheveluch by the TROPOspheric Monitoring Instrument (TROPOMI) aboard the Copernicus Sentinel-5 Precursor satellite, but very little drift was observed.

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

Information Contacts: 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/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).


Dukono (Indonesia) — May 2020 Citation iconCite this Report

Dukono

Indonesia

1.693°N, 127.894°E; summit elev. 1229 m

All times are local (unless otherwise noted)


Numerous ash explosions continue through March 2020

The ongoing eruption at Dukono is characterized by frequent explosions that send ash plumes to about 1.5-3 km altitude (0.3-1.8 km above the summit), although a few have risen higher. This type of typical activity (figure 13) continued through at least March 2020. The ash plume data below (table 21) were primarily provided by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) and the Darwin Volcanic Ash Advisory Centre (VAAC). During the reporting period of October 2019-March 2020, the Alert Level remained at 2 (on a scale of 1-4) and the public was warned to remain outside of the 2-km exclusion zone.

Table 21. Monthly summary of reported ash plumes from Dukono for October 2019-March 2020. The direction of drift for the ash plume through each month was highly variable; notable plume drift each month was only indicated in the table if at least two weekly reports were consistent. Data courtesy of the Darwin VAAC and PVMBG.

Month Plume Altitude (km) Notable Plume Drift
Oct 2019 1.8-3 Multiple
Nov 2019 1.8-2.3 E, SE, NE
Dec 2019 1.8-2.1 E, SE
Jan 2020 1.8-2.1 E, SE, SW, S
Feb 2020 2.1-2.4 S, SW
Mar 2020 1.5-2.3 Multiple
Figure (see Caption) Figure 13.Satellite image of Dukono from Sentinel-2 on 12 November 2019, showing an ash plume drifting E. Image uses natural color rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

During the reporting period, high levels of sulfur dioxide were only recorded above or near the volcano during 30-31 October and 4 November 2019. High levels were recorded by the Ozone Mapping and Profiler Suite (OMPS) instrument aboard the Suomi National Polar-orbiting Partnership (NPP) satellite on 30 October 2019, in a plume drifting E. The next day high levels were also recorded by the TROPOspheric Monitoring Instrument (TROPOMI) aboard the Copernicus Sentinel-5 Precursor satellite on 31 October (figure 14) and 4 November 2019, in plumes drifting SE and NE, respectively.

Figure (see Caption) Figure 14. Sulfur dioxide emission on 31 October 2019 drifting E, probably from Dukono, as recorded by the TROPOMI instrument aboard the Sentinel-5P satellite. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Geologic Background. Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia's most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during 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/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Etna (Italy) — April 2020 Citation iconCite this Report

Etna

Italy

37.748°N, 14.999°E; summit elev. 3320 m

All times are local (unless otherwise noted)


Strombolian explosions and ash emissions continue, October 2019-March 2020

Mount Etna is a stratovolcano located on the island of Sicily, Italy, with historical eruptions that date back 3,500 years. The most recent eruptive period began in September 2013 and has continued through March 2020. Activity is characterized by Strombolian explosions, lava flows, and ash plumes that commonly occur from the summit area, including the Northeast Crater (NEC), the Voragine-Bocca Nuova (or Central) complex (VOR-BN), the Southeast Crater (SEC, formed in 1978), and the New Southeast Crater (NSEC, formed in 2011). The newest crater, referred to as the "cono della sella" (saddle cone), emerged during early 2017 in the area between SEC and NSEC. This reporting period covers information from October 2019 through March 2020 and includes frequent explosions and ash plumes. The primary source of information comes from the Osservatorio Etneo (OE), part of the Catania Branch of Italy's Istituo Nazionale di Geofisica e Vulcanologica (INGV).

Summary of activity during October 2019-March 2020. Strombolian activity and gas-and-steam and ash emissions were frequently observed at Etna throughout the entire reporting period, according to INGV and Toulouse VAAC notices. Activity was largely located within the main cone (Voragine-Bocca Nuova complex), the Northeast Crater (NEC), and the New Southeast Crater (NSEC). On 1, 17, and 19 October, ash plumes rose to a maximum altitude of 5 km. Due to constant Strombolian explosions, ground observations showed that a scoria cone located on the floor of the VOR Crater had begun to grow in late November and again in late January 2020. A lava flow was first detected on 6 December at the base of the scoria cone in the VOR Crater, which traveled toward the adjacent BN Crater. Additional lava flows were observed intermittently throughout the reporting period in the same crater. On 13 March, another small scoria cone had formed in the main VOR-BN complex due to Strombolian explosions.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows multiple episodes of thermal activity varying in power from 22 June 2019 to March 2020 (figure 286). The power and frequency of these thermal anomalies significantly decreased between August to mid-September. The pulse of activity in mid-September reflected a lava flow from the VOR Crater (BGVN 44:10). By late October through November, thermal anomalies were relatively weaker and less frequent. The next pulse in thermal activity reflected in the MIROVA graph occurred in early December, followed by another shortly after in early January, both of which were due to new lava flows from the VOR Crater. After 9 January the thermal anomalies remained frequent and strong; active lava flows continued through March accompanied by Strombolian explosions, gas-and-steam, SO2, and ash emissions. The most recent distinct pulse in thermal activity was seen in mid-March; on 13 March, another lava flow formed, accompanied by an increase in seismicity. This lava flow, like the previous ones, also originated in the VOR Crater and traveled W toward the BN Crater.

Figure (see Caption) Figure 286. Multiple episodes of varying activity at Etna from 22 June 2019 through March 2020 were reflected in the MIROVA thermal energy data (Log Radiative Power). Courtesy of MIROVA.

Activity during October-December 2019. During October 2019, VONA (Volcano Observatory Notice for Aviation) notices issued by INGV reported ash plumes rose to a maximum altitude of 5 km on 1, 17, and 19 October. Strombolian explosions occurred frequently. Explosions were detected primarily in the VOR-BN Craters, ejecting coarse pyroclastic material that fell back into the crater area and occasionally rising above the crater rim. Ash emissions rose from the VOR-BN and NEC while intense gas-and-steam emissions were observed in the NSEC (figure 287). Between 10-12 and 14-20 October fine ashfall was observed in Pedara, Mascalucia, Nicolosi, San Giovanni La Punta, and Catania. In addition to these ash emissions, the explosive Strombolian activity contributed to significant SO2 plumes that drifted in different directions (figure 288).

Figure (see Caption) Figure 287. Webcam images of ash emissions from the NE Crater at Etna from the a) CUAD (Catania) webcam on 10 October 2019; b) Milo webcam on 11 October 2019; c) Milo webcam on 12 October 2019; d) M.te Cagliato webcam on 13 October 2019. Courtesy of INGV (Report 42/2019, ETNA, Bollettino Settimanale, 07/10/2019 - 13/10/2019, data emissione 15/10/2019).
Figure (see Caption) Figure 288. Strombolian activity at Etna contributed to significant SO2 plumes that drifted in multiple directions during the intermittent explosions in October 2019. Top left: 1 October 2019. Top right: 2 October 2019. Middle left: 15 October 2019. Middle right: 18 October 2019. Bottom left: 13 November 2019. Bottom right: 1 December 2019. Captured by the TROPOMI instrument on the Sentinel 5P satellite, courtesy of NASA Global Sulfur Dioxide Monitoring Page.

The INGV weekly bulletin covering activity between 25 October and 1 November 2019 reported that Strombolian explosions occurred at intervals of 5-10 minutes from within the VOR-BN and NEC, ejecting incandescent material above the crater rim, accompanied by modest ash emissions. In addition, gas-and-steam emissions were observed from all the summit craters. Field observations showed the cone in the crater floor of VOR that began to grow in mid-September 2019 had continued to grow throughout the month. During the week of 4-10 November, Strombolian activity within the Bocca Nuova Crater was accompanied by gas-and-steam emissions. The explosions in the VOR Crater occasionally ejected incandescent ejecta above the crater rim (figures 289 and 290). For the remainder of the month Strombolian explosions continued in the VOR-BN and NEC, producing sporadic ash emissions. Isolated and discontinuous explosions in the New Southeast Crater (NSEC) also produced fine ash, though gas-and-steam emissions still dominated the activity at this crater. Additionally, the explosions from these summit craters were frequently accompanied by strong SO2 emissions that drifted in different directions as discrete plumes.

Figure (see Caption) Figure 289. Photo of Strombolian activity and crater incandescence in the Voragine Crater at Etna on 15 November 2019. Photo by B. Behncke, taken by Tremestieri Etneo. Courtesy of INGV (Report 47/2019, ETNA, Bollettino Settimanale, 11/11/2019 - 17/11/2019, data emissione 19/11/2019).
Figure (see Caption) Figure 290. Webcam images of summit crater activity during 26-29 November and 1 December 2019 at Etna. a) image recorded by the high-resolution camera on Montagnola (EMOV); b) and c) webcam images taken from Tremestieri Etneo on the southern slope of Etna showing summit incandescence; d) image recorded by the thermal camera on Montagnola (EMOT) showing summit incandescence at the NSEC. Courtesy of INGV (Report 49/2019, ETNA, Bollettino Settimanale, 25/11/2019 - 01/12/2019, data emissione 03/12/2019).

Frequent Strombolian explosions continued through December 2019 within the VOR-BN, NEC, and NSEC Craters with sporadic ash emissions observed in the VOR-BN and NEC. On 6 December, Strombolian explosions increased in the NSEC; webcam images showed incandescent pyroclastic material ejected above the crater rim. On the morning of 6 December a lava flow was observed from the base of the scoria cone in the VOR Crater that traveled toward the adjacent Bocca Nuova Crater. INGV reported that a new vent opened on the side of the saddle cone (NSEC) on 11 December and produced explosions until 14 December.

Activity during January-March 2020. On 9 January 2020 an aerial flight organized by RAI Linea Bianca and the state police showed the VOR Crater continuing to produce lava that was flowing over the crater rim into the BN Crater with some explosive activity in the scoria cone. Explosive Strombolian activity produced strong and distinct SO2 plumes (figure 291) and ash emissions through March, according to the weekly INGV reports, VONA notices, and satellite imagery. Several ash emissions during 21-22 January rose from the vent that opened on 11 December. According to INGV’s weekly bulletin for 21-26 January, the scoria cone in the VOR crater produced Strombolian explosions that increased in frequency and contributed to rapid cone growth, particularly the N part of the cone. Lava traveled down the S flank of the cone and into the adjacent Bocca Nuova Crater, filling the E crater (BN-2) (figure 292). The NEC had discontinuous Strombolian activity and periodic, diffuse ash emissions.

Figure (see Caption) Figure 291. Distinct SO2 plumes drifting in multiple directions from Etna were visible in satellite imagery as Strombolian activity continued through March 2020. Top left: 21 January 2020. Top right: 2 February 2020. Bottom left: 10 March 2020. Bottom right: 19 March 2020. Captured by the TROPOMI instrument on the Sentinel 5P satellite, courtesy of NASA Global Sulfur Dioxide Monitoring Page.
Figure (see Caption) Figure 292. a) A map of the lava field at Etna showing cooled flows (yellow) and active flows (red). The base of the scoria cone is outlined in black while the crater rim is outlined in red. b) Thermal image of the Bocca Nuova and Voragine Craters. The bright orange is the warmest temperature measure in the flow. Courtesy of INGV, photos by Laboratorio di Cartografia FlyeEye Team (Report 10/2020, ETNA, Bollettino Settimanale, 24/02/2020 - 01/03/2020, data emissione 03/03/2020).

Strombolian explosions continued into February 2020, accompanied by ash emissions and lava flows from the previous months (figure 293). During 17-23 February, INGV reported that some subsidence was observed in the central portion of the Bocca Nuova Crater. During 24 February to 1 March, the Strombolian explosions ejected lava from the VOR Crater up to 150-200 m above the vent as bombs fell on the W edge of the VOR crater rim (figure 294). Lava flows continued to move into the W part of the Bocca Nuova Crater.

Figure (see Caption) Figure 293. Webcam images of A) Strombolian activity and B) effusive activity fed by the scoria cone grown inside the VOR Crater at Etna taken on 1 February 2020. C) Thermal image of the lava field produced by the VOR Crater taken by L. Lodato on 3 February (bottom left). Image of BN-1 taken by F. Ciancitto on 3 February in the summit area (bottom right). Courtesy of INGV; Report 06/2020, ETNA, Bollettino Settimanale, 27/01/2020 - 02/02/2020, data emissione 04/02/2020 (top) and Report 07/2020, ETNA, Bollettino Settimanale, 03/02/2020 - 09/02/2020, data emissione 11/02/2020 (bottom).
Figure (see Caption) Figure 294. Photos of the VOR intra-crater scoria cone at Etna: a) Strombolian activity resumed on 25 February 2020 from the SW edge of BN taken by B. Behncke; b) weak Strombolian activity from the vent at the base N of the cone on 29 February 2020 from the W edge of VOR taken by V. Greco; c) old vent present at the base N of the cone, taken on 17 February 2020 from the E edge of VOR taken by B. Behncke; d) view of the flank of the cone, taken on 24 February 2020 from the W edge of VOR taken by F. Ciancitto. Courtesy of INGV (Report 10/2020, ETNA, Bollettino Settimanale, 24/02/2020 - 01/03/2020, data emissione 03/03/2020).

During 9-15 March 2020 Strombolian activity was detected in the VOR Crater while discontinuous ash emissions rose from the NEC and NSEC. Bombs were found in the N saddle between the VOR and NSEC craters. On 9 March, a small scoria cone that had formed in the Bocca Nuova Crater and was ejecting bombs and lava tens of meters above the S crater rim. The lava flow from the VOR Crater was no longer advancing. A third scoria cone had formed on 13 March NE in the main VOR-BN complex due to the Strombolian explosions on 29 February. Another lava flow formed on 13 March, accompanied by an increase in seismicity. The weekly report for 16-22 March reported Strombolian activity detected in the VOR Crater and gas-and-steam and rare ash emissions observed in the NEC and NSEC (figure 295). Explosions in the Bocca Nuova Crater ejected spatter and bombs 100 m high.

Figure (see Caption) Figure 295. Map of the summit crater area of Etna showing the active vents and lava flows during 16-22 March 2020. Black hatch marks indicate the crater rims: BN = Bocca Nuova, with NW BN-1 and SE BN-2; VOR = Voragine; NEC = North East Crater; SEC = South East Crater; NSEC = New South East Crater. Red circles indicate areas with ash emissions and/or Strombolian activity, yellow circles indicate steam and/or gas emissions only. The base is modified from a 2014 DEM created by Laboratorio di Aerogeofisica-Sezione Roma 2. Courtesy of INGV (Report 13/2020, ETNA, Bollettino Settimanale, 16/03/2020 - 22/03/2020, data emissione 24/03/2020).

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

Information Contacts: Sezione di Catania - Osservatorio Etneo, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/it/); Toulouse Volcanic Ash Advisory Center (VAAC), Météo-France, 42 Avenue Gaspard Coriolis, F-31057 Toulouse cedex, France (URL: http://www.meteo.fr/aeroweb/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/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Boris Behncke, Sonia Calvari, and Marco Neri, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: https://twitter.com/etnaboris, Image at https://twitter.com/etnaboris/status/1183640328760414209/photo/1).


Merapi (Indonesia) — April 2020 Citation iconCite this Report

Merapi

Indonesia

7.54°S, 110.446°E; summit elev. 2910 m

All times are local (unless otherwise noted)


Explosions produced ash plumes, ashfall, and pyroclastic flows during October 2019-March 2020

Merapi is a highly active stratovolcano located in Indonesia, just north of the city of Yogyakarta. The current eruption episode began in May 2018 and was characterized by phreatic explosions, ash plumes, block avalanches, and a newly active lava dome at the summit. This reporting period updates information from October 2019-March 2020 that includes explosions, pyroclastic flows, ash plumes, and ashfall. The primary reporting source of activity comes from Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG, the Center for Research and Development of Geological Disaster Technology, a branch of PVMBG) and Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM).

Some ongoing lava dome growth continued in October 2019 in the NE-SW direction measuring 100 m in length, 30 m in width, and 20 m in depth. Gas-and-steam emissions were frequent, reaching a maximum height of 700 m above the crater on 31 October. An explosion at 1631 on 14 October removed the NE-SW trending section of the lava dome and produced an ash plume that rose 3 km above the crater and extended SW for about 2 km (figures 90 and 91). The plume resulted in ashfall as far as 25 km to the SW. According to a Darwin VAAC notice, a thermal hotspot was detected in HIMAWARI-8 satellite imagery. A pyroclastic flow associated with the eruption traveled down the SW flank in the Gendol drainage. During 14-20 October lava flows from the crater generated block-and-ash flows that traveled 1 km SW, according to BPPTKG.

Figure (see Caption) Figure 90. An ash plume rising 3 km above Merapi on 14 October 2019.
Figure (see Caption) Figure 91. Webcam image of an ash plume rising above Merapi at 1733 on 14 October 2019. Courtesy of BPPTKG via Jaime S. Sincioco.

At 0621 on 9 November 2019, an eruption produced an ash plume that rose 1.5 km above the crater and drifted W. Ashfall was observed in the W region as far as 15 km from the summit in Wonolelo and Sawangan in Magelang Regency, as well as Tlogolele and Selo in Boyolali Regency. An associated pyroclastic flow traveled 2 km down the Gendol drainage on the SE flank. On 12 November aerial drone photographs were used to measure the volume of the lava dome, which was 407,000 m3. On 17 November, an eruption produced an ash plume that rose 1 km above the crater, resulting in ashfall as far as 15 km W from the summit in the Dukun District, Magelang Regency (figure 92). A pyroclastic flow accompanying the eruption traveled 1 km down the SE flank in the Gendol drainage. By 30 November low-frequency earthquakes and CO2 gas emissions had increased.

Figure (see Caption) Figure 92. An ash plume rising 1 km above Merapi on 17 November 2019. Courtesy of BPPTKG.

Volcanism was relatively low from 18 November 2019 through 12 February 2020, characterized primarily by gas-and-steam emissions and intermittent volcanic earthquakes. On 4 January a pyroclastic flow was recorded by the seismic network at 2036, but it wasn’t observed due to weather conditions. On 13 February an explosion was detected at 0516, which ejected incandescent material within a 1-km radius from the summit (figure 93). Ash plumes rose 2 km above the crater and drifted NW, resulting in ashfall within 10 km, primarily S of the summit; lightning was also seen in the plume. Ash was observed in Hargobinangun, Glagaharjo, and Kepuharjo. On 19 February aerial drone photographs were used to measure the change in the lava dome after the eruption; the volume of the lava had decreased, measuring 291,000 m3.

Figure (see Caption) Figure 93. Webcam image of an ash plume rising from Merapi at 0516 on 13 February 2020. Courtesy of MAGMA Indonesia and PVMBG.

An explosion on 3 March at 0522 produced an ash plume that rose 6 km above the crater (figure 94), resulting in ashfall within 10 km of the summit, primarily to the NE in the Musuk and Cepogo Boyolali sub-districts and Mriyan Village, Boyolali (3 km from the summit). A pyroclastic flow accompanied this eruption, traveling down the SSE flank less than 2 km. Explosions continued to be detected on 25 and 27-28 March, resulting in ash plumes. The eruption on 27 March at 0530 produced an ash plume that rose 5 km above the crater, causing ashfall as far as 20 km to the W in the Mungkid subdistrict, Magelang Regency, and Banyubiru Village, Dukun District, Magelang Regency. An associated pyroclastic flow descended the SSE flank, traveling as far as 2 km. The ash plume from the 28 March eruption rose 2 km above the crater, causing ashfall within 5 km from the summit in the Krinjing subdistrict primarily to the W (figure 94).

Figure (see Caption) Figure 94. Images of ash plumes rising from Merapi during 3 March (left) and 28 March 2020 (right). Images courtesy of BPPTKG (left) and PVMBG (right).

Geologic Background. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequently growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent eruptive activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities during historical time.

Information Contacts: Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG), Center for Research and Development of Geological Disaster Technology (URL: http://merapi.bgl.esdm.go.id/, Twitter: @BPPTKG); Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/, Twitter: https://twitter.com/BNPB_Indonesia); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Jamie S. Sincioco, Phillipines (Twitter: @jaimessincioco, Image at https://twitter.com/jaimessincioco/status/1227966075519635456/photo/1).

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Bulletin of the Global Volcanism Network - Volume 16, Number 06 (June 1991)

Managing Editor: Lindsay McClelland

Aira (Japan)

Explosions remain frequent; tephra from one explosion damages houses and cars

Ambrym (Vanuatu)

Ash plume extends 50 km

Arenal (Costa Rica)

Frequent explosions; new lava flow

Colima (Mexico)

Avalanching from summit dome; flank lava flow continues to advance; April tephra fall mapped

Galeras (Colombia)

Frequent tephra emissions; more long-period seismicity; small summit inflation

Gede-Pangrango (Indonesia)

Seismicity declines without eruption after April/May swarm

Iliboleng (Indonesia)

Vapor and ash emission

Irazu (Costa Rica)

Tectonic earthquake swarm; new fumaroles but temperatures remain <100°C

Karthala (Comoros)

Seismic swarm precedes phreatic explosion; press reports of ash/lava eruption incorrect

Kilauea (United States)

E rift lava continues to enter the ocean

Klyuchevskoy (Russia)

Small plume seen from satellite image

Langila (Papua New Guinea)

Frequent Vulcanian explosions

Lewotobi (Indonesia)

Strombolian activity; ash to 300 m height; several hundred explosion earthquakes weekly

Lokon-Empung (Indonesia)

Explosions eject small ash columns

Manam (Papua New Guinea)

Occasional ash emissions

Merapi (Indonesia)

Gas plumes and seismicity

Northern EPR at 9.8°N (Undersea Features)

Post-1989 lava flows and high turbidity seen from submersible; frequent microseismicity

Ontakesan (Japan)

Seismicity declines slightly; steam plumes

Pinatubo (Philippines)

Continued ash emission with pulses to 15 km; typhoons trigger large lahars, leaving thousands homeless

Poas (Costa Rica)

Continued gas emission; harmonic tremor

Rabaul (Papua New Guinea)

Seismicity remains low; no significant deformation

Ruiz, Nevado del (Colombia)

Ash emission and low seismicity; increased SO2 flux

Slamet (Indonesia)

Plume emission follows harmonic tremor episodes

Soputan (Indonesia)

Ash and vapor ejected but glow ends in late May; 50 m of new lava on crater floor

Stromboli (Italy)

Explosions eject glowing fragments and gas columns

Unzendake (Japan)

Continued lava dome growth; debris flows to 7.5 km destroy houses; evacuations prevent more casualties



Aira (Japan) — June 1991 Citation iconCite this Report

Aira

Japan

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

All times are local (unless otherwise noted)


Explosions remain frequent; tephra from one explosion damages houses and cars

Frequent explosive activity . . . continued through mid-July. Explosions . . . occurred 31 times in June . . . and 15 times by 24 July, bringing the year's total to 168. An explosion at 2345 on 29 June ejected blocks and lapilli that damaged house roofs and two car windshields, the second episode of explosion-related damage in 1991. The ash cloud rose to a maximum height of 3,200 m (on 27 June), and a monthly total of 20 g/m2 of ash was deposited 10 km W of the crater (compared to 209 g/m2 in May). Volcanic earthquake swarms, similar to previous months, were recorded on 7, 16, 24, and 28 June.

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

Information Contacts: JMA.


Ambrym (Vanuatu) — June 1991 Citation iconCite this Report

Ambrym

Vanuatu

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

All times are local (unless otherwise noted)


Ash plume extends 50 km

The control tower at Bauerfield airport (serving Port Vila, ~150 km SSE of Ambrym), reported a 2-km-high ash cloud stretching ~50 km from Marum Crater on 10 June.

Geologic Background. Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides Arc. A thick, almost exclusively pyroclastic sequence, initially dacitic then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major Plinian eruption with dacitic pyroclastic flows about 1,900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.

Information Contacts: C. Mortimer, Dept of Geology, Mines, and Rural Water Supply, Vanuatu.


Arenal (Costa Rica) — June 1991 Citation iconCite this Report

Arenal

Costa Rica

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

All times are local (unless otherwise noted)


Frequent explosions; new lava flow

Gas and vapor emission increased in June, as Strombolian activity decreased moderately from May. Seismometers recorded up to 65 explosions/day (on 22 June) and medium- and high-frequency tremor (>4 Hz) was recorded up to 24 hours/day (Univ Nacional network). Seismicity decreased from a daily average of 20 earthquakes in May, to 15 in June (Red Sismológica Nacional). Two lobes of lava continued down the S and SW flanks [but see July observations below], reaching and partially burning some of the upper forest. No serious mudflows had yet occurred, midway through the rainy season.

The following is from W. Melson, V. Barboza, and E. Fernández. "We monitored the activity of Arenal 24 hours/day, 7-17 July 1991. About 40 pyroclastic eruptions/day were heard, and their acoustic and seismic signals recorded at the Arenal Observatory lodge. This is the highest eruption frequency we have observed since 1-23 October 1989. The flows that advanced down the S slope during January-May 1991 have ceased moving, and a new flow sequence has begun spilling over the westernmost crater and moving down the WSW slope. Over 17 cm of rain and constant clouds prevented observations of the summit during most of this time."

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: J. Barquero, E. Fernández, V. Barboza, R. Van der Laat, and E. Malavassi, OVSICORI; R. Barquero, Guillermo Alvarado, Mario Fernández, Hector Flores, and Sergio Paniagua, ICE; W. Melson, SI.


Colima (Mexico) — June 1991 Citation iconCite this Report

Colima

Mexico

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

All times are local (unless otherwise noted)


Avalanching from summit dome; flank lava flow continues to advance; April tephra fall mapped

CICT personnel visited the N and W flanks of the upper cone (El Playón and Soma areas) on 15 June, to observe morphological changes on the N and NW sides of the summit lava dome, and check reports of incandescence seen 8 June from nearby Nevado de Colima. Despite rainy weather, it was evident that a landslide 200-300 m long had occurred from the N side of the dome. A high-frequency seismic signal, interpreted as continuous avalanches, began at 1306 on 15 June and continued for about 30 minutes on RESCO stations EZV7 (at Volcancito, ~1 km NE of the summit) and EZV4 (on the NW flank). At 1440, RESCO seismometers recorded a large avalanche that lasted about 20 minutes, and was similar to the seismicity associated with the partial dome collapse on 16 April. The geologists saw a large fumarole and big reddish and yellow-brown dust clouds at 1450, while small gray plumes emerged from the dome; similar activity had been observed by a CICT team on 16 April. Morphologic changes were evident to the SSW side of the dome, probably from the partial collapse on 15 June, and the dome had decreased in height. The lava flow, about 20 m thick, continued to advance (down the El Cordobán canyon), reaching 3 km length and 2,500 m altitude (figure 14). Weather had prevented aerial monitoring of the lava flow.

Figure (see Caption) Figure 14. Topographic map of the Colima area, showing lava and pyroclastic-flow deposits on the SW flank. Courtesy of the Universidad de Colima.

Mapping of 16-19 April airfall ash distribution showed that tephra volume was limited (figure 15). Unusual winds during the eruption carried ash to the SE. Small block-and-ash flows had been emplaced along the El Cordobán and Montegrande canyons; ashfall and block-and-ash flow deposits in the El Cordobán canyon area had been [significantly eroded] by the season's first rains.

Figure (see Caption) Figure 15. Isopach map showing ashfall from the 16-19 April activity at Colima. Courtesy of the Universidad de Colima.

During the last two weeks in June, seismicity remained relatively constant, with no additional large avalanche episodes detected. There was no strong seismic evidence of impending changes in the eruption, but geologists recommended increased monitoring, including COSPEC analysis, to allow more complete evaluation of the activity.

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

Information Contacts: Francisco Núñez-Cornú, Julián Flores, F. Alejandro Nava, R. Saucedo, C. Valencia, Ariel Ramírez-Vázquez, G.A. Reyes-Dávila, R. García, and J. Hernández, CICT, Univ de; Z. Jiménez, S. de la Cruz-Reyna, and I. Yokoyama, UNAM; P. Lesage (France); D. Córdoba, UCM, Spain.


Galeras (Colombia) — June 1991 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


Frequent tephra emissions; more long-period seismicity; small summit inflation

Frequent ash and lapilli emissions continued in June, as indicated by seismic signals and confirmed by periodic observations during clear weather (2, 17, 18, and 20 June). Gas plumes rose to 800-1,700 m height (1 and 17 June) during periodic pulses of activity. Significant increases in the incandescent area were noted near the crater floor and on the W wall. The SO2 flux fluctuated between low and moderate values.

Fewer low-frequency events but more long-period events were recorded in June than in May. The majority of high-frequency events were centered 6 km E of the crater at 0.9-2.3 km depths. Some tremor episodes and long-period events were associated with ash emissions and increases in plume height. Deformation measurements continued to show low levels of inflation (20 µrad in June) at the "Crater" tiltmeter, . . . .

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

Information Contacts: INGEOMINAS-OVP.


Gede-Pangrango (Indonesia) — June 1991 Citation iconCite this Report

Gede-Pangrango

Indonesia

6.77°S, 106.965°E; summit elev. 3008 m

All times are local (unless otherwise noted)


Seismicity declines without eruption after April/May swarm

High seismicity associated with the 29 April-1 May swarm activity has continuously declined since late May (figure 1). An average of one volcanic earthquake/day was recorded in June, compared to 43/day in April and 5/day in May. No surface activity was observed.

Figure (see Caption) Figure 1. Daily number of earthquakes at Gede, April-May 1991. Courtesy of VSI.

Geologic Background. Gede volcano is one of the most prominent in western Java, forming a twin volcano with Pangrango volcano to the NW. The major cities of Cianjur, Sukabumi, and Bogor are situated below the volcanic complex to the E, S, and NW, respectively. Gunung Pangrango, constructed over the NE rim of a 3 x 5 km caldera, forms the high point of the complex at just over 3000 m elevation. Many lava flows are visible on the flanks of the younger Gunung Gede, including some that may have been erupted in historical time. The steep-walled summit crater has migrated about 1 km NNW over time. Two large debris-avalanche deposits on its flanks, one of which underlies the city of Cianjur, record previous large-scale collapses. Historical activity, recorded since the 16th century, typically consists of small explosive eruptions of short duration.

Information Contacts: W. Modjo, VSI.


Iliboleng (Indonesia) — June 1991 Citation iconCite this Report

Iliboleng

Indonesia

8.342°S, 123.258°E; summit elev. 1659 m

All times are local (unless otherwise noted)


Vapor and ash emission

Vapor and ash were continuously emitted to 100-850 m height, beginning 8 May and continuing through June. Shallow volcanic earthquakes were recorded 15-25 times/week (figure 2), but no explosion earthquakes were recorded. Tectonic earthquakes averaged 14-24/week.

Figure (see Caption) Figure 2. Monthly number of earthquakes at Iliboleng, January 1990-May 1991. Courtesy of VSI.

Geologic Background. Iliboleng stratovolcano was constructed at the SE end of Adonara Island across a narrow strait from Lomblen Island. The volcano is capped by multiple, partially overlapping summit craters. Lava flows modify its profile, and a cone low on the SE flank, Balile, has also produced lava flows. Historical eruptions, first recorded in 1885, have consisted of moderate explosive activity, with lava flows accompanying only the 1888 eruption.

Information Contacts: W. Modjo, VSI.


Irazu (Costa Rica) — June 1991 Citation iconCite this Report

Irazu

Costa Rica

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

All times are local (unless otherwise noted)


Tectonic earthquake swarm; new fumaroles but temperatures remain <100°C

A swarm of tectonic earthquakes, centered near the summit at 0-8 km depth, began in late May (16:05) and continued through June. The swarm followed aftershocks of the 22 April earthquake (16:05), and has been interpreted as representing reactivation of a fault zone. A similar earthquake swarm in January (16:1-2) was interpreted as fault reactivation caused by an [M 5.7] earthquake on 22 December [50 km WSW] of Irazú.

During the second week of June, a group of new fumaroles formed in the NE, N, NW, and S parts of the crater. Temperatures of up to 94°C were measured during fieldwork the next week, similar to NW-flank fumarole temperatures (80-90°C) since 1965. Temperatures and activity at other fumaroles remained unchanged. The seasonal crater lake, which began to fill the last week of June, remained at ambient temperature except around fumaroles, where the water was 30-48°C and had a pH of 5.9 (similar to pH measurements in 1986 and 1987). Small landslides occurred down the E, NE, and SW crater walls. Deformation measurements indicated no significant changes.

Several small tremor episodes (durations <=60 seconds) and low-frequency events were recorded during June. Univ Nacional scientists suggested that the tremor could be related to shallow hydrothermal activity and degassing beneath the crater.

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

Information Contacts: J. Barquero, E. Fernández, V. Barboza, R. Van der Laat, and E. Malavassi, OVSICORI; R. Barquero, Guillermo Alvarado, Mario Fernández, Hector Flores, and Sergio Paniagua, ICE.


Karthala (Comoros) — June 1991 Citation iconCite this Report

Karthala

Comoros

11.75°S, 43.38°E; summit elev. 2361 m

All times are local (unless otherwise noted)


Seismic swarm precedes phreatic explosion; press reports of ash/lava eruption incorrect

Widely distributed news reports of ash and lava emission during the evening of 2 July proved incorrect. As of mid-July, the only documented eruptive activity had been a phreatic explosion on the 11th. According to the press, some villages around the base of the volcano were evacuated, but many fewer residents fled than the tens of thousands initially reported [see 16:8]. The eruption followed three months of increasing seismicity monitored by a joint group from the Centre National de Documentation et de Recherche Scientifique des Comores (CNDRS), the Univ de la Réunion, and the IPGP. The following is from their report. [See 16:8 for additional details].

An average of 3-5 seismic events/month were recorded from the start of monitoring in June 1988 until April 1991. "At the beginning of April, a slight increase in seismicity was noticed, with events mainly centered under the summit caldera from 0-2 km below sea level [see also 16:8]. The rate of seismicity progressively increased from an average of 5-10 events/day in May to 20/day in June, reaching 40/day by the end of June. The earthquakes occurred along a roughly N-S axis below the summit caldera at 0-1 km below sea level. Deformation measurements, using a 10-station dry-tilt network in the summit caldera, indicated inflation of ~ 20 µrads.

"At 1645 on 30 June a seismic crisis began with events centered below the S part of the caldera and the volcano's S flank. During the night of 30 June, many shocks were felt by residents of the SW part of the island. Seismic activity continued 1-2 July, with both short- and long-period events occurring at average rates of 60-100/hour. Some of the short-period events reached M 2.5-3. One M 3.1 earthquake (at 0708 on 2 July) was felt in the SE part of the island (in the Foumbouni area; figure 1). This intense seismic activity has caused many people living in the SW to move to Moroni, the capital and island's largest city.

Figure (see Caption) Figure 1. Topographic map of Karthala, after Strong and Jacquot (1970).

"The seismic crisis continued until 10 July, with the number of earthquakes reaching 250/hour. After several hours of relative calm, a phreatic eruption occurred at 0330 on 11 July [but see 16:8], after which the number of earthquakes returned to ~100/hour. During overflights of Choungou Chahalé Crater (summit area), it was observed that the rim of the S half of the summit caldera was covered by ash and blocks of old material. The crater was filled with gas that stagnated in its bottom. A sound like a lava fountain [but see 16:8] was audible, but no lava fountain was visible. The same day, seismometers recorded ~40-60 earthquakes/hour, most of M <2. Some of M >3 were felt by the population."

Reference. Strong, D.F., and Jacquot, C., 1970, The Karthala Caldera, Grande Comore: BV, v. 34, p. 663-680.

Geologic Background. The southernmost and largest of the two shield volcanoes forming Grand Comore Island (also known as Ngazidja Island), Karthala contains a 3 x 4 km summit caldera generated by repeated collapse. Elongated rift zones extend to the NNW and SE from the summit of the Hawaiian-style basaltic shield, which has an asymmetrical profile that is steeper to the S. The lower SE rift zone forms the Massif du Badjini, a peninsula at the SE tip of the island. Historical eruptions have modified the morphology of the compound, irregular summit caldera. More than twenty eruptions have been recorded since the 19th century from the summit caldera and vents on the N and S flanks. Many lava flows have reached the sea on both sides of the island. An 1860 lava flow from the summit caldera traveled ~13 km to the NW, reaching the W coast to the N of the capital city of Moroni.

Information Contacts: P. Bachélery, Univ de la Réunion; J-L. Klein, CNDRS, RFI des Comores; J-L. Cheminée, IPGP; UPI; AP; Reuters.


Kilauea (United States) — June 1991 Citation iconCite this Report

Kilauea

United States

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

All times are local (unless otherwise noted)


E rift lava continues to enter the ocean

Lava . . . continued to flow into the ocean at two main entries through June. The W branch fed two active sites (at the Poupou entry). At the E Poupou site, lava continued to build the E edge of the lower bench, although its W edge had been eroded by waves. "Firehose"-like outflow of lava from truncated tubes occurred periodically at the E Poupou site, as on 7 June when the activity fed a tube in the surf zone. Frequent underwater explosions occurred along the tube, sometimes sending spatter several meters into the air. Firehose activity typically ended with the construction of a new lower lava bench. At the W Poupou site, parts of the 3-m-high littoral cone and the underlying sea cliff were eroding. A fissure developed just inland of the littoral cone in late May and additional large fissures appeared within a few meters of the sea cliff on 25 June.

Lava broke out from the main tube in mid-May and formed a new (E branch) tube, reaching the sea (at the Paradise entry) late in the month. Lava initially entered the ocean along a front 300-400 m wide, but within a few days the entry narrowed to <20 m across. The resulting bench sloped steeply and smoothly into the ocean, with none of the step-like changes in relief evident at the Poupou entry. Lava continued to pour into the ocean from the bench until the last week in June, when a large flow broke out and moved W across the beach behind the bench. The new entry was <500 m E of a 1988-89 bench where major collapses occurred after it extended no more than 45 m into the ocean. Only one significant collapse episode, which removed ~15 m of the new bench, had been noted at Paradise as of early July.

No changes were observed near the source (Kupaianaha) vent. Lava in a tube near the vent was flowing at ~0.9 m/s . . . on 20 June. A small lava lake persisted in the older Pu`u `O`o vent . . . . Overflows from the lava lake covered the crater floor, ~80 m below the rim. Some spattering was observed, concentrated in the S part of the lake.

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

Information Contacts: T. Moulds, HVO.


Klyuchevskoy (Russia) — June 1991 Citation iconCite this Report

Klyuchevskoy

Russia

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

All times are local (unless otherwise noted)


Small plume seen from satellite image

The NOAA 10 polar-orbiting weather satellite showed a plume ~20 km long, extending S from the summit then turning SW, on 24 June at 1024.

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

Information Contacts: W. Gould, NOAA/NESDIS.


Langila (Papua New Guinea) — June 1991 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)


Frequent Vulcanian explosions

"Crater 3 . . . produced 1 to >40 Vulcanian explosions/day in June. The explosions produced dark grey vapour and ash clouds or columns, resulting in light ashfalls over the NW flank of the volcano and to coastal villages (10-15 km distant). Villagers were also shaken by the airwaves of the strongest explosions. Night activity consisted of weak red glow, with the largest explosions producing a short-term brighter glow between 5 and 16 June.

"Crater 2 released weak to moderate white vapour emissions plus occasional grey ash and blue vapours. The crater produced one loud Vulcanian explosion on 28 June, accompanied by an ashfall. A steady weak night glow was visible over the crater for much the same period as at Crater 3 (3-17 June). After a 10-day absence, night glow reappeared at Crater 2 on 28 June, following its throat-clearing Vulcanian explosion. Two days later, night glow also returned to Crater 3.

"The daily number of Vulcanian explosions from Crater 3 reached its maximum level of >30 between the 15th and 19th, coinciding with the absence of night glow at both craters (figure 3). A seismograph 9 km away (CGA), which previously recorded ~10% of the explosion earthquakes detected by the summit station (LAN), started to record an increasing proportion of these events (to >50%)."

Figure (see Caption) Figure 3. Number of explosion earthquakes/day recorded at Langila's summit seismic station (LAN) and a second station (CGA) 9 km away, late May-early July 1991. Periods of glow at craters 2 and 3 are shown by shaded areas along the bars at bottom. Courtesy of RVO.

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

Information Contacts: P. de Saint-Ours, RVO.


Lewotobi (Indonesia) — June 1991 Citation iconCite this Report

Lewotobi

Indonesia

8.542°S, 122.775°E; summit elev. 1703 m

All times are local (unless otherwise noted)


Strombolian activity; ash to 300 m height; several hundred explosion earthquakes weekly

Explosions at the summit crater on 28 May at 1615, 1840, and 1911 produced ash clouds to 300 m, accompanied by thunder-like sounds heard 4 km SW of the crater (at Pos Observatory). Since then, activity has been dominated by gas emissions and explosion earthquakes (figure 1). Explosions emitted ash (12-19 times/week) to 100-300 m high. On 8 and 13 June, lapilli and bombs ejected by Strombolian activity covered the area surrounding the crater. Glow and lava fountaining then steadily diminished through the end of June. Explosion earthquakes were recorded 200-405 times/week, compared to 0-4 deep and shallow volcanic earthquakes, and 5-7 tectonic earthquakes/week. No tremor episodes were recorded.

Figure (see Caption) Figure 1. Daily number of earthquakes and explosion events at Lewotobi Lakilaki, May 1991. Arrows represent explosions. Courtesy of VSI.

Geologic Background. The Lewotobi "husband and wife" twin volcano (also known as Lewetobi) in eastern Flores Island is composed of the Lewotobi Lakilaki and Lewotobi Perempuan stratovolcanoes. Their summits are less than 2 km apart along a NW-SE line. The conical Lakilaki has been frequently active during the 19th and 20th centuries, while the taller and broader Perempuan has erupted only twice in historical time. Small lava domes have grown during the 20th century in both of the crescentic summit craters, which are open to the north. A prominent flank cone, Iliwokar, occurs on the E flank of Perampuan.

Information Contacts: W. Modjo, VSI.


Lokon-Empung (Indonesia) — June 1991 Citation iconCite this Report

Lokon-Empung

Indonesia

1.358°N, 124.792°E; summit elev. 1580 m

All times are local (unless otherwise noted)


Explosions eject small ash columns

Ash explosions occurred at 1537 on 27 May and 1000 on 28 May, producing columns 250 m high. Continued ash explosions were observed at a rate of 7-16/week, with column heights of 200-400 m. Seismic activity was characterized by explosion earthquakes, averaging 30-50 recorded events/week. Shallow and deep volcanic earthquakes were less frequent (2-8 and 3-9 events/week, respectively). Tectonic earthquakes ranged from 18 to 101 weekly.

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

Information Contacts: W. Modjo, VSI.


Manam (Papua New Guinea) — June 1991 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)


Occasional ash emissions

"Both craters released weak emissions of white vapour. However, some greyish, ash-laden clouds were also occasionally emitted. Between 5 and 9 June, deep roaring sounds were heard from Southern Crater and plumes of ash occasionally rose to 150-700 m above the crater rims. Similar activity recurred between 25 and 29 June. Although no night glow was observed, the seismicity was at a moderately high level and radial tilt measurements fluctuated by 3 µrad."

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

Information Contacts: P. de Saint-Ours, RVO.


Merapi (Indonesia) — June 1991 Citation iconCite this Report

Merapi

Indonesia

7.54°S, 110.446°E; summit elev. 2910 m

All times are local (unless otherwise noted)


Gas plumes and seismicity

Diffuse to dense gas plumes rose 475 m in June, with SO2 fluxes averaging 80 t/d. The weekly number of volcanic earthquakes fluctuated, briefly rising to 33 during the third week in June, of which 28 were recorded on the 22nd. Three volcanic earthquakes were recorded below the crater at 3.0-3.5 km depth. An average of two multiphase events and 10-12 tectonic earthquakes were recorded weekly.

Geologic Background. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequently growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent eruptive activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities during historical time.

Information Contacts: W. Modjo, VSI.


Northern EPR at 9.8°N (Undersea Features) — June 1991 Citation iconCite this Report

Northern EPR at 9.8°N

Undersea Features

9.83°N, 104.3°W; summit elev. -2500 m

All times are local (unless otherwise noted)


Post-1989 lava flows and high turbidity seen from submersible; frequent microseismicity

Evidence for a recent, possibly ongoing eruption on the axis of the East Pacific Rise was found between 31 March and 24 April during a series of 25 Adventure Program Alvin dives (led by Rachel Haymon and Dan Fornari). The following phenomena suggested eruptive activity:

1. Bottom waters were extremely murky. A high density of suspended particulate matter plus white biogenic particles swept from the bottom by strong hydrothermal flow created a turbid zone to 50 m above the sea floor.

2. Total flux of hydrothermal fluid over the area was very high and temperatures reached 403°C.

3. Animal communities documented by an ARGO survey in November-December 1989 (Haymon and others, 1991) had been buried by fresh lava flows, and the scorched soft tissues of partially buried biota had not yet attracted crabs and other bottom scavengers.

4. At one vent, temperature increased from 389 to 403°C and fluid composition changed during a two-week period.

5. Fresh, sulfate-bearing chimneys at the collapsed margin of the axial summit caldera were draped with new flows. At sites of black smoker chimneys seen from ARGO, [hydrothermal fluids or black smoke] poured directly from piles of collapse rubble.

6. At a number of sites, high-temperature fluids vented directly from the basaltic sea floor, probably because there had been insufficient time for chimneys to form.

7. Vent animal communities were absent (presumably had not yet developed) at many sites where H2S-rich effluents were sampled. Instead, basalts near the vents were extensively coated with unusual white bacterial mats, not seen during the 1989 survey, that appear different from those previously described at other sea-floor hot springs.

After a seismically detected eruption of the submarine volcano Kick-'em-Jenny (N of Grenada, West Indies) in December 1988, observations from a submersible in mid-April 1989 revealed bacterial mats at the eruption site, associated with upwelling hydrothermal fluid and an apparently anoxic environment. The mats were breaking up by the next dive in mid-May, and normal sea life was returning.

In mid-May, ocean bottom seismographs, deployed from the RV Thomas Washington to monitor the volcanic activity, detected frequent microseismicity. Of the seven instruments deployed (at 5-km spacing), five returned usable data, and two (on-axis at 9.808°N, 104.286°W, off-axis at 9.816°N, 104.243°W) were examined in detail. A total of 151 local events were recorded in 68 hours (figure 1). The data suggested swarm-like behavior, although the time series was too short to reveal a well-defined pattern. Time intervals between P, S, and interface waves indicated that the majority of events were at distances of 0.5-2 km. Many of the events recorded strongly on-axis were detected poorly if at all by the off-axis instrument; the best-recorded phases off-axis were often the water waves. Seismologists noted that these observations suggest that seismicity was centered near the ridge axis and was probably very shallow (0.5-2 km depth), since events at the depth of the instrument spacing (5 km) would be roughly equidistant from the two stations. It seemed likely that at least 10 km of the ridge axis was generating microseismicity.

Figure (see Caption) Figure 1. Number of seismic events detected in 2-hour periods by ocean bottom seismometers along the East Pacific Rise near 9.8°N, 12-15 May, 1991. The 24-hour gap in data represents airgun recording for local crustal structure inversion. Courtesy of J. Hildebrand.

Currently funded programs that will visit the site include: 1-2 dives by Nautile in October 1991 (D. Desbruyeres, CNEXO, Brest); Alvin dives in November-December 1991 (L. Mullineaux and C. van Dover, Woods Hole Oceanographic Institution), January 1992 (R. Haymon, Univ of California at Santa Barbara and R. Lutz, Rutgers), and April 1992 (J. Childress, UCSB). Ocean Drilling Program leg 142 will begin efforts to drill the ridge axis in late January 1992 (R. Batiza, Univ of Hawaii). A special session on studies at 9-10°N will be held at the fall 1991 American Geophysical Union meeting.

Reference. Haymon, R., Fornari, D., Edwards, M., Carbotte, S., Wright, D., and Macdonald, K.C., Hydrothermal vent distribution along the East Pacific Rise crest (9°9'-54'N) and its relationship to magmatic and tectonic processes on fast-spreading mid-ocean ridges: Earth and Planetary Science Letters, v. 104, p. 513-534.

Geologic Background. Evidence for a very recent, possibly ongoing eruption was detected during a series of dives in the submersible vessel Alvin in 1991 on the East Pacific Rise at about 9° 50' N. Hot-vent animal communities that had been documented during November to December 1989 imaging were observed to have been buried by fresh basaltic lava flows, and the scorched soft tissues of partially buried biota had not yet attracted bottom scavengers. Fresh black smoker chimneys were draped by new lava flows. This position south of the Clipperton Fracture Zone at a depth of about 2500 m, and about 1000 km SW of Acapulco, México. It coincided with a location where fresh lava flows previously estimated as less than roughly 50 years in age had been found. Later dating of very short half-life radionuclides from dredged samples confirmed the young age of the eruption and indicated that another eruptive event had taken place in late 1991 and early 1992. An eruption in 2005-2006 produced lava flows that entrapped previously emplaced seismometers. The south end of the Lamont Seamount chain is about 10 km NW.

Information Contacts: R. Haymon, Univ of California, Santa Barbara; J. Hildebrand, S. Webb, and L. Dohrman, Scripps Inst of Oceanography; T. Stroh, RIDGE, Univ of Washington.


Ontakesan (Japan) — June 1991 Citation iconCite this Report

Ontakesan

Japan

35.893°N, 137.48°E; summit elev. 3067 m

All times are local (unless otherwise noted)


Seismicity declines slightly; steam plumes

Seismicity has remained at high levels since April, with nine tremor episodes and 234 small earthquakes recorded in June (figure 9), down from 28 and 313, respectively, in May. Similar seismicity +continued as of 18 July. White steam plumes . . . rose to 200 m height.

Figure (see Caption) Figure 9. Daily number of earthquakes from the start of monitoring in July 1989 through June 1991.

Geologic Background. The massive Ontakesan stratovolcano, the second highest volcano in Japan, lies at the southern end of the Northern Japan Alps. Ascending this volcano is one of the major objects of religious pilgrimage in central Japan. It is constructed within a largely buried 4 x 5 km caldera and occupies the southern end of the Norikura volcanic zone, which extends northward to Yakedake volcano. The older volcanic complex consisted of at least four major stratovolcanoes constructed from about 680,000 to about 420,000 years ago, after which Ontakesan was inactive for more than 300,000 years. The broad, elongated summit of the younger edifice is cut by a series of small explosion craters along a NNE-trending line. Several phreatic eruptions post-date the roughly 7300-year-old Akahoya tephra from Kikai caldera. The first historical eruption took place in 1979 from fissures near the summit. A non-eruptive landslide in 1984 produced a debris avalanche and lahar that swept down valleys south and east of the volcano. Very minor phreatic activity caused a dusting of ash near the summit in 1991 and 2007. A significant phreatic explosion in September 2014, when a large number of hikers were at or near the summit, resulted in many fatalities.

Information Contacts: JMA.


Pinatubo (Philippines) — June 1991 Citation iconCite this Report

Pinatubo

Philippines

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

All times are local (unless otherwise noted)


Continued ash emission with pulses to 15 km; typhoons trigger large lahars, leaving thousands homeless

As of 26 July, the volcano was still emitting ash continuously to 3-6 km height, with occasional pulses to 15-16 km. Typhoon rains triggered large debris flows down rivers on all sides of the volcano, inundating many of the towns in figure 11. Preliminary estimates of the eruption's size suggest that it is larger than those of Mt. St. Helens (1980) and El Chichón (1982), the largest eruptions of the last decade, but smaller than those of Cerro Azul/Quizapú (1932), Katmai/Novarupta (1912) and Santa María (1902), the largest of the century.

Figure (see Caption) Figure 11. Map of Pinatubo and the surrounding area, showing towns, rivers, and roads. Preliminary pyroclastic-flow deposit distribution courtesy of Pinatubo Volcano Observatory. Contour interval is 1,000 m.

Paroxysmal activity, products and deposits. Damage from the eruption made evaluation of its products slow and difficult. The following preliminary information has been compiled over several weeks from our correspondents' visual observations, fieldwork, and airphoto/satellite image interpretation. Data on the paroxysmal phase supplement the report in 16:5.

Infrared video taken from the Clark Air Base control tower on 14 June suggests that the summit began to fail at 2320 as a fissure propagated tangentially across the summit. An explosion and apparent lateral blast, at 0555 the next day, removed the summit and produced a 25-km ash column. This event marked the onset of strong sustained activity that lasted until early 16 June.

The eruption's most violent explosive phase began at 1342 on 15 June and continued for more than 15 hours at full strength, with 30-40-km columns feeding a massive cloud. Intense seismicity began at 1440 and was felt continuously (at Mt. Arayat ~40 km E) by 1700. This seismicity lasted until about 0000 on 16 June, and was probably associated with the explosions or collapse that formed a nearly circular caldera, 2 km in diameter. The caldera was offset slightly N of the former summit, and the new summit was 145 m lower than before the eruption. The caldera wall ranged in height from 150-200 m at the highest point to 0 m on the E side. In the caldera's NE corner, a cone-shaped feature, ~75 m in diameter and 10 m high, was observed on satellite images. By 20 June, this feature was no longer visible, and the floor of the caldera appeared deeply ash-covered and relatively smooth. A conical depression developed in the SE corner of the caldera, reaching 800 m in diameter by 8 July and continuing to grow. No dome had been identified as of 26 July. No vegetation remained within 1-2 km of the caldera and trees 6-7 km away were defoliated.

Tephra fell primarily to the SE, S, and SW, but airfall distribution was complicated by the typhoon's winds. Pumice to roughly 7 cm fell 25 km E (at Clark Air Base) and particles to roughly 1.5 cm fell 33 km SSW (at Olongapo). Within 3 km of the caldera rim, ash thicknesses averaged 1-2 m. Eruption volume estimates and detailed isopach information were not available as of 26 July. The pumices are porphyritic biotite-hornblende quartz latite, and preliminary analyses indicate 66% SiO2, and 1.6% K2O.

The quoted material below is from Pinatubo Volcano Observatory reports.

"Pyroclastic flows reached radial distances of 12-18 km from the vent (figure 11) and were accompanied by ash clouds whose deposits ranged in thickness from a few to tens of centimeters. Thick pyroclastic-flow deposits (locally in excess of 200 m) occur in main valleys at distances of 5-15 km from the caldera, and have caused surface-drainage diversions that may have severe consequences as the monsoon and typhoon season gets into full swing. Blockage of the Sacobia River on the NE flank has raised the level of that drainage about 12 m above the level of the Abacan River capture point, potentially tripling the source drainage area for the modified Abacan River.

"Such factors as high velocity, high mobility, and low density allowed pyroclastic flows to drain off proximal slopes, which are covered by only a thin, discontinuous veneer. The flows removed vegetation and, in many places, soil and colluvium. Rugged highlands to the NE and SE, which are incised by narrow, steep canyons that head on high ridges separated from Pinatubo, have pyroclastic-flow fills several meters to perhaps 20 m thick locally. These deposits have been eroded extensively and occur as small patches in relatively protected areas along the canyons. Their distribution in such isolated valleys attests further to the great mobility of the pyroclastic flows. Pyroclastic-flow deposits downstream from the major fills were apparently formed by relatively dense flows, because vegetation along the margins of many was only slightly scorched. Conspicuous features include secondary explosion craters, fumaroles, breakaway scarps, and small ponds in blocked tributaries." Satellite data indicated that several lakes, up to 4 km x 350 m, were formed about 7 km W and NW of the caldera. Pyroclastic flows down the Sacobia River valley reached 3 km NW of housing on Clark Air Base, but did not reach the base itself. Numerous houses were swept away or buried by pyroclastic flows, 2-3 km SW of the caldera.

Activity, 16 June-mid July. Following the paroxysmal explosions on 14-16 June, tephra emission decreased and seismicity dropped dramatically (figure 12). With the strongest activity apparently ended, the radius of the official danger zone was reduced to 20 km on 17 June. Ash was emitted continuously to 3-6 km height, with periods of more intense explosions to 10 km height typically lasting several hours but separated by 5-7 hours. On 28 June, explosions were observed pulsating every 5 minutes from different points on the crater floor. Explosions were most frequently observed in the S and SE parts of the caldera.

Figure (see Caption) Figure 12. Hourly number of earthquakes at Pinatubo, 16 June-4 July 1991. No data are available for 15-late 16 June due to equipment saturation. Courtesy of PVO.

Periods of sustained high-amplitude tremor and large long-period earthquakes (15-20/hour), represented as spikes on Realtime Seismic Amplitude Measurement (RSAM) plots, often coincided with higher ash ejection. A rough 7-hour periodicity was recognized for these spikes beginning about 7 July (figure 13). Ash emission during inter-eruptive periods (between spikes) gradually decreased and the repose period increased, before the pattern finally became irregular around noon on 11 July. This episode was accompanied by a coincident increase in seismic energy release (figure 14).

Figure (see Caption) Figure 13. RSAM at Pinatubo, 5-11 July 1991. Arrows represent suspected lahar signals. Courtesy of PVO.
Figure (see Caption) Figure 14. Accumulated RSAM energy at Pinatubo, 16 June-14 July 1991. Courtesy of PVO.

Earthquakes were occasionally felt as far away as Manila. The largest of these (M 5.9) was at 1250 on 3 July, and was centered 6 km NE of the volcano at 6 km depth (in a previously near-aseismic location). Most earthquakes, however, were centered beneath the volcano, at depths ranging from 0 to >20 km, whereas focal depths before the cataclysmic activity did not exceed 8 km depth (figure 15).

Figure (see Caption) Figure 15. Depths of 2,080 earthquakes at Pinatubo, 6 May-9 July 1991. Data for 27-30 June are similar to those of early July. Courtesy of PVO.

Rains triggered debris flows, ranging from landslides to hyperconcentrated flows, on all flanks of the volcano. Several of these flows were recorded seismically (figure13). On 23 June, at 2240-2330, a "hot" lahar was observed NW of the volcano on the Balintawak River near Poonbato. Hyperconcentrated flows were reported on the nearby Maronut River the next day, and to the SE (on the Pasig, Porac, and Gumain Rivers) on 30 June. Houses in Porac and Floridablanca (SE of Pinatubo) were buried up to roof level with volcanic debris. A lahar occurred on the Balintawak River the night of 30 June-1 July.

Large explosive episodes ejected ash clouds to 16 km height on 2 July, and explosive activity again intensified slightly on 7 July, ejecting ash clouds to 14-15 km height. Intense activity continued the next day and weather satellites observed clouds 14 km high at 0230-0250, >15 km high at 0700, 16 km high at 0800-0900, and about 15 km high at 1604. Eruption cloud heights of 15 and 16 km were measured on 7 and 8 July, respectively. Small, low-energy pyroclastic flows were observed billowing from within the caldera and travelling only a few hundred meters from the rim. Ash emission between explosive episodes was very low. SO2 fluxes, determined by COSPEC, were 5,190 t/d on 5 July, and 1,243 t/d on 9 July. Clear weather enabled the installation of several telemetered rain gauges. Observers reported hundreds of small ash avalanches off steep ridges into valleys. Periodic ash emissions to 15 km continued on the 17th, when the prevailing wind carried ash SE to Manila, closing the airport for two days.

Debris-flow activity, 7-10 July. Information about W-flank lahars in the next two sections is abstracted from a report by Kelvin Rodolfo.

In response to a 9 July warning of possible heavy rains, geologists were stationed at two W-flank sites to monitor rivers and warn downstream residents if lahars were detected. The next morning, an intense cloudburst in the headwaters of the Bucao River triggered a minor, dilute lahar. One team (10 km E of Botolan on the N bank of the Bucao River) heard a strong noise of rushing water and rolling boulders for 15 minutes before the head of the flow came into view at 0557. Approximately 25% of the channel was occupied by the flow. Velocities averaged 3.5 m/s (12.6 km/hour). Numerous boulders to 1.5 m were intermittently rolled and pushed by the flow at rates comparable to its velocity.

From a hazards perspective, geologists noted that the flow's most significant characteristic was its capacity to erode laterally. Along a straight stretch of channel, cutting rates from 1.6 to 6 minutes per meter of horizontal bank erosion were documented. Lateral erosion was by undercutting and slumping of blocks 1-6 m long, 1.5 m thick, and 0.3 to 1 m wide (average width, 0.5 m) that were continuously incorporated into the flow. Bank erosion rates were faster along an outer bend, ranging between 0.2 and 1.2 min/m, and averaging 0.9 min/m over 2 hours of observation and measurement. The lahar deposits behaved like quicksand, especially those with a high content of fine ash, and crossing them before they had some time to drain caused people and animals to sink knee-deep. Mayor Doble of Botolan reported that some trapped animals had died from starvation.

Mountain slopes partially cleansed of ash by runoff from moderate rain were green, as were portions of grasslands on the plains that escaped total burial. Farmers were impressed by the health of surviving plants.

East of the volcano, the press reported that lahars travelling down the Chico River (NE flank) deposited knee-deep mud in several villages on 10 July. At a village near Porac, flows broke through sandbags for the second time in 13 days, causing people to flee. The next day, debris flows traveled down the Pasig, Porac, and Gumain Rivers on the SE flank, causing extensive erosion in small tributaries.

A lahar observed on the Marimla River (ENE flank) on 15 July, was up to 50 m wide, 4 m deep, and highly erosive. Post-15 June wingwall and channelization efforts proved ineffective as the lahar breached the N levee downstream on the Bamban River (NE flank) in 3 places.

Typhoon-related debris-flow activity, 20-26 July. The first typhoon after the paroxysmal eruption passed N of Luzon 18-19 July. At 0900 on 18 July, in response to weather forecasts, geologists recommended that Lahar Alert 2 be issued for the W flank's Zambales region. Teams were sent to the Bucao and Santo Tomas rivers. A minor dilute lahar occurred from 2300 until 0630 the following morning, but was hardly noticeable at Botolan, and caused no damage.

After the typhoon, the threat of lahars persisted, with continued scattered thunderstorms around Pinatubo. Large lahars along various rivers E of Pinatubo buried sections of some towns (such as Guagua). W of Pinatubo, monitoring stations were established on the Bucao River east of Botolan, and at the junction of the Marella and Santo Tomas Rivers (threatening San Marcelino and nearby towns). Small, dilute lahars were observed on two evenings, but none was large enough either to escape its channels or to reach the sea.

Geologists cited three reasons for expecting strong rainfall to trigger serious flooding in all of coastal Zambales province. First, ash deposited on the steeper mountain slopes has been washed into creeks and rivers by the first rains, seriously reducing capacities of the drainages to hold water. Second, to clear the national highway, much of its ash cover was dumped by the roadside, choking many ditches. Third, during typhoons, large waves or tidal surges will effectively raise sea level, making it harder for rivers to enter the sea.

Installation of a USGS computer that receives telemetered rainfall data from instruments on Pinatubo's W flank will help warn people in Botolan, San Marcelino, and other towns threatened by lahars. Watchers at stations on the Bucao and Santo Tomas Rivers are equipped with two-way radios with which to contact threatened towns.

On the E side of the volcano, the press reported that large lahars on 20 July (related to typhoon Amy) destroyed more than 400 houses in Floridablanca, and buried more than 130 houses in Concepcion, forcing the evacuation of at least 1,200 people. This event brought the total number of houses damaged during the eruption to more than 80,000. Two days later, heavy rains from typhoon Brendan caused additional large lahars travelling 10 m/s at the slope breaks and 3 m/s at distal locations. Lahars to 3 m deep caused the evacuation of parts of 13 towns in Zambales (W flank), Tarlac, and Pampanga (E flank) provinces, with 2,000 initially fleeing from Santa Rita (just S of Concepcion) where 4,000 more were left stranded, unable to leave until the following morning. Evacuees from Pampanga province numbered about 10,000. Channel infilling and dike ruptures resulted in lahars up to 4 km wide on the Bamban River E of Concepcion, with similar activity along the O'Donnell, Abacan, Pasig, Porac, and Santo Tomas Rivers.

By 23 July, more than 60,000 people had fled their homes, with at least five killed during the previous two days. Mudflows, 5 m high, traveled through Concepcion at 8-11 m/s, sweeping several people away. Further lahars buried 11 villages near Sexmoan and damaged fish ponds, buried almost half of Santa Rita, and had completely silted up the Abacan River at the town of Mexico.

Debris flows continued to form on 25-26 July, with the onset of typhoon Caitlin. About 10,000 people evacuated Mexico and 308 houses were buried in 1.2 m of mud from flows down the Abacan River. A 30-m section was removed from the Mexico-Concepcion road. Swelling of the Santa Rita River caused 300 to flee Olongapo when houses were flooded waist deep. Flooding also occurred in Manila.

The press reported that by the 26th, 1.2 million people had either lost their homes or their livelihoods, 100,000 houses had been crushed or buried, and about 90,000 people remained in evacuation camps. Casualty reports ranged from 323 (with 40 missing), to more than 435.

Medical impact. The following is from Peter Baxter. The paroxysmal phase of the eruption caused the collapse of numerous buildings, and in some towns W of the volcano, destruction was complete. An estimated 250,000 people were evacuated, many moving to temporary camps. Efforts have been made to determine the medical hazards presented by the eruption, by characterizing ash composition and leachates, and measuring exposure to humans. Epidemiology teams from the U.S. Centers for Disease Control collected information on health and medical conditions at hospitals and evacuation camps, establishing programs to monitor food/water contamination and changing ash compositions. Preliminary information showed that ashfall was not yet a serious health problem. Heavy rains that coincided with the paroxysmal activity alleviated some ash problems by washing the suspended material out of the air. There had been no outbreaks of respiratory ailments, and surface water contamination was not a major problem since residents generally drink ground water. Concern was expressed that malaria, endemic on the W side of the volcano, might increase. There was additional concern for the mental health of people who have been forced to relocate several times and are now threatened by large mudflows.

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

Information Contacts: PVO, PHIVOLCS-USGS, Clark Air Base, Philippines; Kelvin Rodolfo, Univ of Illinois; Peter Baxter, Dept of Community Medicine, Fenner's, England; John Ewert, Edward Wolfe, and Richard Hoblitt, CVO; T. Casadevall, USGS Denver; Ellen Limburg-Santistevan, USGS Reston; Harvey Miller, Pearl Harbor CINCPACFLT, HI, USA; SAB; Manila Far East Broadcasting Company; AP; Reuters; UPI.


Poas (Costa Rica) — June 1991 Citation iconCite this Report

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Continued gas emission; harmonic tremor

Gas emission continued from crater fumaroles (60-95°C) in June. The crater lake temperature was 73°C, similar to December-February values, while lake depth increased to 3 m, coinciding with heavy rainfall. Medium-frequency (2.5 Hz) harmonic tremor was recorded 6-17 June, occurring up to 24 hours/day (figure 38). Seismicity was dominantly low-frequency.

Figure (see Caption) Figure 38. Hours/day of tremor recorded at Poás by the Univ Nacional, June 1991.

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

Information Contacts: J. Barquero, E. Fernández, V. Barboza, R. Van der Laat, and E. Malavassi, OVSICORI; R. Barquero, G. Alvarado, M. Fernández, H. Flores, and S. Paniagua, ICE.


Rabaul (Papua New Guinea) — June 1991 Citation iconCite this Report

Rabaul

Papua New Guinea

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

All times are local (unless otherwise noted)


Seismicity remains low; no significant deformation

". . . In June . . . the seismicity remained at a very low level with only 99 events recorded, all ML <1. Only four events could be plotted and were distributed on the N and W sides of the caldera seismic zone. Levelling, tilt, and EDM measurements showed no significant change."

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

Information Contacts: P. de Saint-Ours, RVO.


Nevado del Ruiz (Colombia) — June 1991 Citation iconCite this Report

Nevado del Ruiz

Colombia

4.892°N, 75.324°W; summit elev. 5279 m

All times are local (unless otherwise noted)


Ash emission and low seismicity; increased SO2 flux

Activity was generally at low levels in June, although there were one large ash emission and a high-frequency seismic swarm. The ash emission was associated with low to moderate levels of tremor, and deposited material on Manizales (30 km WNW). One earthquake, located 2.5 km S of the summit crater, was felt during the swarm. The monthly average SO2 flux, measured by COSPEC, was 2,275 t/d, compared to 930 t/d in May and ~2,740 t/d in April. Deformation measurements did not show significant changes.

Geologic Background. Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.

Information Contacts: C. Carvajal, INGEOMINAS, Manizales.


Slamet (Indonesia) — June 1991 Citation iconCite this Report

Slamet

Indonesia

7.242°S, 109.208°E; summit elev. 3428 m

All times are local (unless otherwise noted)


Plume emission follows harmonic tremor episodes

Harmonic tremor episodes (average frequency 2.5 Hz) began at 1730 on 24 June and were continuing as of early July. A dense 200-m-high plume was observed on 28 June. COSPEC measurements, started on 29 June, yielded SO2 fluxes of 66-87 t/d, compared to 30 t/d in 1988.

Geologic Background. Slamet, Java's second highest volcano at 3428 m and one of its most active, has a cluster of about three dozen cinder cones on its lower SE-NE flanks and a single cinder cone on the western flank. It is composed of two overlapping edifices, an older basaltic-andesite to andesitic volcano on the west and a younger basaltic to basaltic-andesite one on the east. Gunung Malang II cinder cone on the upper E flank on the younger edifice fed a lava flow that extends 6 km E. Four craters occur at the summit of Gunung Slamet, with activity migrating to the SW over time. Historical eruptions, recorded since the 18th century, have originated from a 150-m-deep, 450-m-wide, steep-walled crater at the western part of the summit and have consisted of explosive eruptions generally lasting a few days to a few weeks.

Information Contacts: W. Modjo, VSI.


Soputan (Indonesia) — June 1991 Citation iconCite this Report

Soputan

Indonesia

1.112°N, 124.737°E; summit elev. 1785 m

All times are local (unless otherwise noted)


Ash and vapor ejected but glow ends in late May; 50 m of new lava on crater floor

Emissions of moderate to weak white-gray ash and vapor rose 100-300 m in June, but the weak red glow visible over the crater since 22 May, vanished on 29 May. During fieldwork on 18 June, the crater floor (50 m in diameter) was covered by ~50 m of lava (approximate volume 2.4 x 106 m3). Seismographs recorded 101 tectonic and 97 explosion earthquakes weekly, but no volcanic earthquakes were detected. An M 5.6 earthquake occurred on 20 June at 1319 in the Sulawesi Sea ~200 km NW of the volcano at 1.15°N, 122°E. The shock was felt (MM III) near Soputan.

Geologic Background. The Soputan stratovolcano on the southern rim of the Quaternary Tondano caldera on the northern arm of Sulawesi Island is one of Sulawesi's most active volcanoes. The youthful, largely unvegetated volcano is located SW of Riendengan-Sempu, which some workers have included with Soputan and Manimporok (3.5 km ESE) as a volcanic complex. It was constructed at the southern end of a SSW-NNE trending line of vents. During historical time the locus of eruptions has included both the summit crater and Aeseput, a prominent NE-flank vent that formed in 1906 and was the source of intermittent major lava flows until 1924.

Information Contacts: W. Modjo, VSI.


Stromboli (Italy) — June 1991 Citation iconCite this Report

Stromboli

Italy

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

All times are local (unless otherwise noted)


Explosions eject glowing fragments and gas columns

The number of recorded explosion shocks remained elevated through late June (figure 15), with mean rates relatively stable near the long-term "normal value" of 6/hour. Average tremor amplitude declined slightly at the beginning of June while the number of saturating earthquakes rose sharply (figure 16). Volcano guides reported that the activity was concentrated at Crater 3, where explosions ejected glowing fragments and white gas columns that rose 100-200 m in late June. Explosions were rare from other craters, but tephra built small cones in Crater 2. White gas emission was continuous.

Figure (see Caption) Figure 15. Average number of explosion events/hour at Stromboli, 18 May-21 June 1991. The mean value for the period is shown. At the end of May, the Mark L4 seismometer was replaced by a Willmore MK III set to a natural undamped frequency of 2 seconds, with the gain adjusted to keep the same overall amplitude response at 1 Hz. Courtesy of M. Riuscetti.
Figure (see Caption) Figure 16. Average number of seismometer-saturating events (lower curve) and average tremor amplitude (upper curve) at Stromboli, 18 May-21 June 1991. Courtesy of M. Riuscetti.

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

Information Contacts: M. Riuscetti, Univ di Udine.


Unzendake (Japan) — June 1991 Citation iconCite this Report

Unzendake

Japan

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

All times are local (unless otherwise noted)


Continued lava dome growth; debris flows to 7.5 km destroy houses; evacuations prevent more casualties

Lava extrusion from Jigoku-ato crater began on 20 May. As growth of the dome continued, its E side, advancing down the steep upper flank, became structurally unstable, and collapse episodes triggered pyroclastic flows that traveled E down the Mizunashi River beginning 24 May. Pyroclastic flows were frequent in June, and continued as of mid-July (table 7). A large pyroclastic flow on 3 June traveled 4.6 km, reaching Kita-Kamikoba (a district of Shimabara), where 41 people were killed, and many houses destroyed. On 8 June, a pyroclastic flow advanced 5.5 km (the largest as of 24 July; figure 23), reaching the coast highway (57) and destroying additional houses. Evacuations prevented any injuries. An explosion from the crater at 2359 on 11 June ejected pumice, up to 10 cm in diameter, that fell 10 km NE. Ashfall was reported 250 km NE (at Matsuyama, Shikoku Is.). No further explosions had occurred by 24 July.

Table 7. Volcanic activity at Unzen along with injuries and major damage, and actions taken by the Coordinating Committee for the Prediction of Volcanic Eruptions, November 1990-24 July 1991. Courtesy of D. Shimozuru.

Date Volcanic Activity and Action by Committee
17 Nov 1990 Minor phreatic eruption; Official statement issued.
early Dec 1990 Surface activity declines.
12 Dec 1990 Official statement issued, warning of future activity based on seismicity.
13 May 1991 Shallow earthquakes begin beneath crater.
17 May 1991 Official statement issued, warning of the appearance of lava.
20 May 1991 Lava appears in crater.
24 May 1991 First minor pyroclastic flow observed.
26 May 1991 Official statement issued, warning of debris flows and pyroclastic flows. One person injured by pyroclastic flow.
31 May 1991 Committee meeting held evaluating activity; setup of advanced HQ at Shimabara Volcano Obs. proposed to deal with rapid changes in activity.
03 Jun 1991 Pyroclastic flow kills 41 people, injures 11 people, and destroys 49 houses.
08 Jun 1991 Pyroclastic flow destroys 70 houses.
11 Jun 1991 Official statement issued from Shimabara. Block fall damages 11 houses and 53 cars.
mid-Jun 1991 Continuous ash emission.
19 Jun 1991 Increase in pyroclastic-flow rate for 2 hours.
30 Jun 1991 Heavy rainfall caused large debris flow, destroying 87 houses and injuring one person.
01-24 Jul 1991 Dome growth, partial collapse, and pyroclastic flows continued. Flows became smaller and less frequent. Continuous ash emission from crater since 13 July.
Figure (see Caption) Figure 23. Seismically-recorded durations of pyroclastic-flow events at Unzen, May-mid July 1991. Courtesy of JMA.

The pyroclastic-flow rate increased briefly on 19 June (between 1400 and 1600) with some of the larger flows traveling 2 km E. Larger pyroclastic flows were reported by the press on 26 and 27 June (~2.5 and 3.5 km in length, respectively). Ash elutriated from pyroclastic flows fell to the NE in June and July. By the end of June, the crater dome was about 150 x 250 m and 80 m thick, and pyroclastic flows were recorded seismically 10-20 times daily (figure 24).

Figure (see Caption) Figure 24. Daily number of earthquakes (bars), tremor episodes (lower curve), and pyroclastic-flow events (upper curve) at Unzen, May to mid-July 1991. Courtesy of JMA.

On 30 June, heavy rainfall caused a large debris flow down the Mizunashi River, injuring one person, and destroying 87 houses [a total of 202 were damaged] near the coast (7.5 km E). The area affected by the flow was entirely within the evacuation zone designated in early June (a 5 x 5 km zone E of the summit, including parts of Shimabara and Fukae), with a pre-evacuation population of 12,395.

The dome continued to grow E, reaching 150 x 530 m and 80 m thick by 21 July. The eruption rate calculated from dome and pyroclastic deposit volumes was 0.3 x 106 m3/day in June and July, although the rate of dome growth was higher in July. Continuous ash emission to 1,000 m height began 13 July, echoing a similar period in mid-June.

By mid-July, the month's longest pyroclastic flows had advanced

Summit seismicity was at lower levels in June and July than in May, with 230 earthquakes recorded in June, compared to 1959 in May. The monthly number of tremor episodes increased dramatically in June, apparently associated with small dome collapses.

An earthquake swarm, from 23 June to early July, was centered 18 km SW of the summit, at 10 km depth (figure 25). Nine of the earthquakes were felt. However, seismicity near the volcano and to its W (in Tachibana Bay) was lower in June and July than in previous months.

Figure (see Caption) Figure 25. Epicenters of earthquakes near Unzen, June-mid July, 1991. A triangle marks the summit. Courtesy of JMA.

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

Information Contacts: JMA; S. Nakada, Kyushu Univ; Kyodo News Service, Tokyo.

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