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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 07 (July 1991)

Managing Editor: Lindsay McClelland

Aira (Japan)

Frequent explosions; aircraft windshield damaged

Ambae (Vanuatu)

Caldera lake bubbling; burned vegetation

Ambrym (Vanuatu)

Ash emissions and lava lake activity continue

Arenal (Costa Rica)

Increased Strombolian activity; seismicity

Colima (Mexico)

Block lava flow advances; new dome lobe; seismicity

Etna (Italy)

Strombolian activity and continued strong degassing

Fournaise, Piton de la (France)

Brief lava production follows seismicity, deformation, and magnetic changes

Galeras (Colombia)

More small explosions; increased seismicity and deformation

Gaua (Vanuatu)

Increased fumarolic activity; vegetation killed

Hudson, Cerro (Chile)

SO2 circles globe; aircraft encounter ash over Australia; >1 km3 airfall on Argentina

Irazu (Costa Rica)

Seismicity remains high; crater lake level rises

Kavachi (Solomon Islands)

May-June submarine eruption ends; temporary island eroded away

Kilauea (United States)

Continued E rift lava production; summit earthquake swarm

Kuwae (Vanuatu)

Summit at 2-3 m depth; no visible fumarolic activity; sulfur odor

Langila (Papua New Guinea)

Tephra emission and seismicity

Lewotobi (Indonesia)

Strombolian activity

Lopevi (Vanuatu)

No fumarolic activity

Manam (Papua New Guinea)

Stronger ash emission

Mauna Loa (United States)

Summit earthquake swarm

Ontakesan (Japan)

Decreasing seismicity

Pacaya (Guatemala)

Explosive eruptions destroy cone and crater; crop damage; evacuations

Pinatubo (Philippines)

Ash emissions decreasing; typhoons trigger large lahars

Poas (Costa Rica)

Continued degassing; seismicity

Rincon de la Vieja (Costa Rica)

Seismicity and tremor

Ruiz, Nevado del (Colombia)

Seismicity remains at low levels; small ash emissions

Sabancaya (Peru)

Earthquake swarm damages towns and triggers mudslides; 20 people reported dead

Santa Maria (Guatemala)

Explosions and avalanches; plumes to 600 m height

Stromboli (Italy)

Continued explosions from two craters

Suretamatai (Vanuatu)

Fumarolic activity

Taal (Philippines)

Abnormal seismicity continues

Unzendake (Japan)

Continued dome growth and pyroclastic flow generation; dome history reviewed

Yasur (Vanuatu)

Continued block and ash emissions; small episodic lava lakes



Aira (Japan) — July 1991 Citation iconCite this Report

Aira

Japan

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

All times are local (unless otherwise noted)


Frequent explosions; aircraft windshield damaged

Eighteen explosions occurred . . . in July . . ., bringing the yearly total to 171. Ejecta from an explosion at 1057 on 5 August struck the windshield of a Boeing 737 airliner 13 minutes later as it flew at an altitude of 1.2 km, 10 km N of the volcano. A crack 50 cm long formed in the outer surface of the windshield, but the plane (domestic flight ANK 793) landed its 122 passengers and five crew safely. Dense weather clouds had prevented the pilot from seeing the eruption plume. This was the first incident of in-flight damage since 24 June 1986, and the 12th near the volcano since 1975. A car windshield a few kilometers from the crater was cracked by ejecta from another explosion (at 1249) the same day. These were the third and fourth cases of explosion-related damage in 1991.

On 23 July, the month's highest ash cloud rose 2,500 m. Prevailing wind directions prevented ash from being deposited at [KLMO]. Earthquake swarms, not unusual for Sakura-jima, were recorded on 1, 2, 9, 15, 18, 21, and 22 July.

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.


Ambae (Vanuatu) — July 1991 Citation iconCite this Report

Ambae

Vanuatu

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

All times are local (unless otherwise noted)


Caldera lake bubbling; burned vegetation

"Three anomalous 'boiling' areas with large bubbles and burned vegetation were observed at Lake Vui on 13 July, by P. Fogarty (Chief Pilot of VANAIR). This was the first time he had observed such a phenomenon, and he noted that the vegetation had still been green in May. An aerial survey of the two summit calderas was carried out (during a VANAIR flight) on 24 July. At that time, no strong degassing was visible, but 3 areas of discolored water (each several tens of meters in diameter) were noticeable in the crater lake. Burned vegetation was observed up to the crater rim, 120 m above the water. On 26 July, microseismicity in the caldera was very weak and without any volcanic characteristics.

"Although continuous weak solfataric activity occurs beneath Lake Vui (Warden, 1970), an anomalously strong SO2 degassing is believed to have occurred between May and July. This event was unnoticed by island residents, but since Aoba has been quiet for 300 years, vigilance for this kind of phenomenon must be improved. The existence of a summit caldera lake, numerous lahar deposits, and thick layers of ash (vesiculated and accretionary lapilli) demonstrate the hazards that would accompany renewed activity. Thus, as a precaution, a seismological station was installed in July on the SW flank of the volcano.

Reference. Warden, A.J., 1970, Evolution of Aoba caldera volcano, New Hebrides: BV, v. 34, p. 107-140.

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

Information Contacts: C. Robin and M. Monzier, ORSTOM, Nouméa, New Caledonia; M. Lardy and C. Douglas, ORSTOM, Vanuatu; C. Mortimer, Dept. of Geology, Mines, and Rural Water Supply, Vanuatu; J. Eissen, ORSTOM, France.


Ambrym (Vanuatu) — July 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 emissions and lava lake activity continue

"Aerial surveys on 13 and 24 July (VANAIR flights) showed puffs of gas and ash rising several hundred meters above Mbuelesu crater, and weak degassing from Benbow crater. Mbuelesu's lava lake, ~100 m in diameter and very deep in the crater, was still present. Activity has remained more or less constant since 1990, and no new lava flows have been observed since 1989."

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. Robin and M. Monzier, ORSTOM, New Caledonia; M. Lardy and C. Douglas, ORSTOM, Vanuatu; C. Mortimer, Dept of Geology, Mines, and Rural Water Supply, Vanuatu; J. Eissen, ORSTOM, France.


Arenal (Costa Rica) — July 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)


Increased Strombolian activity; seismicity

Strombolian activity, lava effusion, and seismicity all increased in July . . . . The number of volcanic earthquakes rose to a maximum of 59 recorded events/day on 11 July (figure 39). Seismometers recorded intermittent, vigorous tremor episodes, several hours long (6-hour average duration), especially at the beginning of the month.

Figure (see Caption) Figure 39. Daily number of earthquakes at Arenal, July 1991. Courtesy of the Instituto Costarricense de Electricidad.

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: R. Barquero and Guillermo Alvarado, ICE.


Colima (Mexico) — July 1991 Citation iconCite this Report

Colima

Mexico

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

All times are local (unless otherwise noted)


Block lava flow advances; new dome lobe; seismicity

Block lava continued to advance down the main cone's SW flank, generating small avalanches from the flow front and levees. Avalanches have also occurred from the summit area, similar to those that preceded the partial collapse of the newly extruded dome on 16 April. A new lobe was observed in the W part of the summit area on 28 July. Poor weather has severely limited observations of the summit, so the date of the new lobe's extrusion is not known.

On 3 August at about 0600, a NW-flank seismic station (EZV4) recorded the beginning of signals that formed a distinctive wave package with a periodicity of about 15-20 seconds. By 5 August at 1200, the amplitude of these signals had nearly doubled and the periodicity had dropped to 10 seconds. The next day at about 0100, seismicity decreased to nearly background levels, but at 0900 sustained harmonic tremor was registered by EZV4 and other nearby stations (EZV3, 5, and 6); heavy rain during the second week in July had damaged the seismic station about 1 km NE of the summit (EZV7, at Volcancito), and poor weather has prevented it from being re-established. Harmonic tremor continued until 8 August at about 0600. During the increased seismicity, the plume was vigorous and a dense white color.

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, G.A. Reyes-Dávila, Ariel Ramírez-Vázquez, J. Hernández, A. Cortés, and Hector Tamez, CICT, Universidad de Colima; Z. Jiménez and S. de la Cruz-Reyna, UNAM.


Etna (Italy) — July 1991 Citation iconCite this Report

Etna

Italy

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

All times are local (unless otherwise noted)


Strombolian activity and continued strong degassing

Strong degassing continued .. during fieldwork in June and July. Strombolian activity was reported at a vent in the NE part of Southeast Crater. Small explosions occurred almost continuously, with more powerful blasts ejecting material to the level of the crater rim occurring every 10-15 minutes (in July). Meanwhile, a vent in the center of the crater gently degassed. In June, occasional emissions of small (<20 cm) sublimate-covered lithic blocks and scoria occurred from a 20 x 10 m pit in Northeast Crater. Lava was visible within the vent, which continued to glow through July. The vent widened internally, giving the appearance of a large chamber inclined in the direction of La Voragine. The elliptical vent at La Voragine crater (reopened prior to a 24 May visit; 16:05) showed incandescence in July, but not in June. Degassing continued from numerous fumaroles within the crater. The floor of Bocca Nuova crater was hidden by large quantities of gas in June, but in July two scoria cones were seen gently emitting vapor. At night, a strongly degassing vent on the SE side of the crater emitted tongues of incandescent gas at 15-minute intervals. A fumarole (56°C) was observed on the October 1989 fracture where it crossed the Canalone Della Montagnola at an altitude of ~ 2,200 m.

The following is from Steve Saunders. "A resurvey, in July, of an EDM network (67 lines) on the upper S flank showed a shortening of the majority of the lines (56), suggesting that minor deflation had occurred since the previous survey in July 1990. At that time, length increases along most lines were interpreted as resulting from minor inflation of the upper flanks since November 1989."

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: H. Gaudru, EVS, Switzerland; T. De St. Cyr, Fontaines St. Martin, France; S. Saunders, West London Institute of Higher Education; W. McGuire, Cheltenham and Glouster College of Higher Education.


Piton de la Fournaise (France) — July 1991 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)


Brief lava production follows seismicity, deformation, and magnetic changes

A short eruption occurred on 19-20 July, following a slight increase in seismicity that began 24 June (figure 28), and immediately preceded by a shallow microearthquake swarm. Almost 80 earthquakes (M <1.5), located beneath the S flank of the summit cone at depths of <1 km, were recorded from 0256 to 0350 on 19 June. At 0350, the appearance of tremor signaled the start of lava outflow.

Figure (see Caption) Figure 28. Daily number of earthquakes (top), measured tilt at Dolomieu station 100 m S of the crater (middle), and difference of magnetic field from the reference station 3.5 km W of the fissure (bottom) at Piton de la Fournaise, 30 May-19 July 1991. Courtesy of J. Toutain.

EDM (sampled every 5 minutes) and radial tilt measurements (every minute) at a station (DOLO) ~200 m from the eruptive fissure (figure 29) showed relatively slow inflation beginning at 0310 (figure 30), believed associated with the beginning of intrusion from the magma reservoir. At 0340, radial tilt began to increase rapidly (up to 54 µrad/min), while EDM indicated a rapid decrease in the distance between the rims of the two summit craters. Inflation led to southward tilting (mean azimuth, 175°) of the DOLO station area. Rapid deflation began at 0350, corresponding with the start of tremor, and lasted until 0434. Deflation occurred at maximum rates of 48 µrad/min, causing DOLO to tilt roughly N (azimuth ~10°).

Figure (see Caption) Figure 29. Sketch map showing the summit area of Piton de la Fournaise and the 19 July 1991 lava flows. Courtesy of J.P. Toutain.
Figure (see Caption) Figure 30. Deformation at Piton de la Fournaise, 0140-0500 on 19 July 1991. Top: EDM, sampled every 5 minutes at Dolomieu. Middle: tilt measurements, sampled every minute at Dolomieu and Soufriere; bold lines=radial component, normal lines=tangential component. Bottom: measured strain, sampled every minute at Dolomieu; Z=vertical, X and Y= horizontal components. Arrow indicates start of eruption. Stations are shown in Figure 33. Courtesy of J. Toutain.

The magnetic field near the eruptive vents (station 6) showed a clear decreasing trend beginning on 16 June (figure 28). On 19 July, a rapid magnetic field increase was measured, corresponding with the onset of the eruption.

Lava was emitted from two vents along an eruptive fissure, one inside and one outside of the summit (Dolomieu) crater (figure 29). Lava fountains, 30 m high, were observed during the morning of the 19th and flow velocity was estimated at 3-4 m/sec that afternoon. Lava flowed E through the Grandes Pentes area, covering ~ 1 x 106 m2, with a total volume estimated at 5 x 106 m3. The eruption lasted until about 2000 on 20 July.

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: J. Toutain and P. Taochy, OVPDLF; P. Bachelery, Univ de la Réunion; J-L. Cheminée, P. Blum, A. Hirn, J. LePine, and J. Zlotnicki, IPGP; F. Garner and I. Appora, Univ Paris VI.


Galeras (Colombia) — July 1991 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


More small explosions; increased seismicity and deformation

Seismicity and emissions began to increase at the end of July, leading to the evacuation of 11 people working on the summit . . . in early August. Released seismic energy (see figure 52) and reduced displacement (figure 42) of long-period earthquakes reached the highest values since the start of monitoring in February 1989. Amplitudes and durations for long-period events showed slow increases, as well. Tremor was recorded in low-frequency bands and modulated packs, with small variations in amplitude and period.

Figure (see Caption) Figure 42. Daily reduced displacement of long-period earthquakes at Galeras, July-August 1991. Courtesy of INGEOMINAS.

Long-period events, shallow in origin and often associated with gas-and-ash emissions, increased to >100/day by mid-August. The number of gas-and-ash emissions increased correspondingly. Plume heights reached 2 km and ash was deposited to 8 km N and NW. Head-sized blocks, hot to the touch, were periodically ejected onto the crater rim.

Inflation, continuing since September 1990, increased dramatically during the first half of August, when 265.8 µrad tangential and -180.6 µrad radial deformation were measured (figure 43) 0.9 km E of the crater ("Crater" electronic tiltmeter). The resultant inflation vector was 321.35 µrad with an azimuth of 115.81°.

Figure (see Caption) Figure 43. Tangential (top curve) and radial (bottom curve) deformation at the Crater electronic tiltmeter at Galeras, January-August 1991. Courtesy of INGEOMINAS.

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; S. Williams and M. Calvache, Arizona State Univ.


Gaua (Vanuatu) — July 1991 Citation iconCite this Report

Gaua

Vanuatu

14.27°S, 167.5°E; summit elev. 797 m

All times are local (unless otherwise noted)


Increased fumarolic activity; vegetation killed

"An increase in fumarolic activity was noted by VANAIR pilots since April. On 13 July, a detailed aerial survey was conducted over the island during a VANAIR flight. Strong continuous degassing was observed, forming a dense white plume from the SE crater of Mt. Gharat cone. The NW slopes of the cone were largely denuded of vegetation, and the area of the caldera affected by the prevailing SE trade winds had burned vegetation. Due to this increasing activity, we plan to install a seismological station to monitor the volcano as soon as possible.

"Gaua is a composite volcano with a large (8 x 6 km) central caldera occupied by Lake Letas (428 m elev). Mt. Gharat (797 m elev) is an active basaltic cone located near the center of this caldera. Only solfataric activity was recorded from 1868 to 1962 (Mallick and Ash, 1975). Beginning in 1962, central crater explosions with frequent associated ash columns were reported nearly every year until 1977. Information on activity from 1977 to 1990 is scarce, but the volcano was probably quiet, with only minor steam emissions from the SE crater." [BVE reported strong gas emission in mid-1980, a black plume on 9 July 1981, and a brown plume with tephra on 18 April 1982.]

Reference. Mallick, D.I.J., and Ash, R.P., 1975, Geology of the southern Banks Islands: New Hebrides Geological Survey Regional Report, 33 p.

Geologic Background. The roughly 20-km-diameter Gaua Island, also known as Santa Maria, consists of a basaltic-to-andesitic stratovolcano with an 6 x 9 km wide summit caldera. Small parasitic vents near the caldera rim fed Pleistocene lava flows that reached the coast on several sides of the island; several littoral cones were formed where these lava flows reached the sea. Quiet collapse that formed the roughly 700-m-deep caldera was followed by extensive ash eruptions. Construction of the historically active cone of Mount Garat (Gharat) and other small cinder cones in the SW part of the caldera has left a crescent-shaped caldera lake. The symmetrical, flat-topped Mount Garat cone is topped by three pit craters. The onset of eruptive activity from a vent high on the SE flank in 1962 ended a long period of dormancy.

Information Contacts: C. Robin and M. Monzier, ORSTOM, Nouméa, New Caledonia; M. Lardy and C. Douglas, ORSTOM, Vanuatu; C. Mortimer, Dept. of Geology, Mines, and Rural Water Supply, Vanuatu; J. Eissen, ORSTOM, France.


Cerro Hudson (Chile) — July 1991 Citation iconCite this Report

Cerro Hudson

Chile

45.9°S, 72.97°W; summit elev. 1905 m

All times are local (unless otherwise noted)


SO2 circles globe; aircraft encounter ash over Australia; >1 km3 airfall on Argentina

On 12 August, the volcano entered a paroxysmal phase, after four days of lesser explosive activity. Tephra was ejected to 16-18 km height, falling up to 1,000 km SE on the Falkland Islands, and with estimates of >1 km3 deposited in Argentina [but see 16:8]. Ash leacheate analyses showed unusually high levels of fluorine. The SO2-rich plume produced by the eruption was rapidly transported around the world, returning to Chile within 7 days. Airline pilots reported sighting the plume as it passed near Melbourne, Australia (roughly 15,000 km from the volcano).

Initial strong explosive activity, 8-10 August. The following quoted material is from José A. Naranjo. "Just 20 years after the previous activity, Hudson started a new eruption on 8 August at 1820. Local inhabitants who were evacuated from the Huemules River (to the W) reported small precursory seismic activity 3-4 hours before the first explosion. The eruption started with a phreato-magmatic explosion that produced a column almost 7-10 km high. Immediately following the initial explosion, a dense, ash-laden column (light brown-greyish in color) formed, reaching ~12 km. Intense lightning discharged from the mushroom-shaped cloud. Activity steadily decreased through 11 August, when direct observation of the summit showed that the 8 August eruption vent was on the W side of the caldera (10 x 7 km; figure 1). The caldera floor was covered by glacial ice estimated to be at least 40 m thick, and having a volume of about 2.5 km3. In addition, a flank valley, extending 10 km NW from the summit to Huemules valley, is filled with a tongue of ice from the main summit glacier. This terminates at the Huemules Valley, which extends onward ~35 km W to the coast.

Figure (see Caption) Figure 1. Sketch map of the summit area of Hudson, 11 August 1991. Courtesy of José Naranjo.

"Prevailing winds during clear weather carried the column NNE (figure 2) over Puerto Chacabuco (50 km away), where 5-7 mm of ash was deposited. At Puerto Aisén (~ 65 km NNE), ash accumulations reached 5 mm in 16 hours. Lava was observed beneath glacial ice near the vent, flowing down to Ventisquero ('glacial tongue') Huemules. Between 3 and 4 hours after the main explosion, a jökullhaup flowed down the Huemules valley to the coast. A 2-m-thick deposit of ash- to lapilli-sized sand and 0.2-5-m-diameter ice blocks was randomly dispersed near the delta. These ice blocks probably floated in the mudflow." The press reported that the flow increased the river width from 80 m to 170 m.

Figure (see Caption) Figure 2. Map showing the location of Hudson and the direction of ash dispersal on 8-9 and 12-15 August 1991. Courtesy of José Naranjo.

Late on 9 August, a NOTAM reported the plume at 11-12 km altitude. Although the eruption remained nearly continuous, intensity declined. By 10 August, Ladeco (Chilean Airlines) pilots reported the plume at ~ 6 km altitude.

"Eleven people were evacuated from along the Huemules River on 11 August. Direct observations at 1250 showed an explosion from a new vent (Crater 2), about 2.5 km SSE of the first vent (Crater 1; figure 1). The new white-and-black explosion cloud was smaller and spread laterally, developing black, cold pyroclastic-ice flows around the vent, similar to the original. White-grey columns, reaching 3 km height, were observed up to the last direct observation at 1630 on 11 August.

Paroxysmal activity, 12-15 August. "A second, larger eruption started at about 1200 on 12 August. Bad weather prevented aerial observation, but heavy ashfall was reported at Río Murta (60 km SSE) at 1245, and 7 minutes later at Río Tranquilo, 20 km farther S. The ashfall was accompanied by intense lightning, and a sulfur odor. At 1300, ashfall was reported at Puerto Guadal (105 km S). The eruption was directly observed on a commercial flight at 1430. The dense, brown-grey cauliflower-shaped cloud, carried SE, was visible from 4 km altitude, but clearly reached >10 km, with more than a 5-km thickness. One explosion was observed rising at a rate of 1.9 km/min. Observations ended at 1440.

"Since 12 August the eruption has continued without variation, and the plume has been carried SE. On 13 August at 1415, a black ash-laden column was reported from a commercial airplane at >10 km altitude. Pumice fall was since reported beginning 14 August, and coarse lapilli up to 5 cm in diameter fell 55 km SE."

Although weather clouds obscurred the eruption plume to visible and infrared satellite images on the 12th and much of the 13th, preliminary data from the Nimbus-7 satellite (TOMS) indicated 250,000 metric tons of SO2, within a disconnected section of the eruption cloud near the Falkland Islands at about 1100 on the 13th. Beginning at about 2000, a continuous, narrow, eruption plume was visible on AVHRR (NOAA 9 and 11) and GOES satellite images, gradually extending 1200 km SE, beyond the Falkland Islands, at ~12 km altitude. The plume became disconnected from the volcano at about 1200 on 14 August, by which time, Naranjo reported, the eruptive column reached a stable altitude of 16 km. TOMS data from 1100 on the 14th revealed a segment of SO2-rich plume (probably the same as on the 13th) near South Georgia Island (2,600 km ESE of the volcano), and a second, smaller segment over the Falkland Islands. No other SO2-rich plume was visible.

Intense seismic activity was felt on 14 August at 1630, 60 km SSE, where 3-cm-diameter pumice was falling. A continuous eruption began again at about 2000, when satellite images (GOES and NOAA 9 and 11) showed that the plume was carried SE at 185 km/hr (100 knots) at stratospheric altitudes of 17-18 km (figure 3). Seismicity increased, with felt earthquakes at Coyhaique (80 km NE) beginning at 2200, and a series of five large earthquakes (M>5) detected near Hudson by the WWSSN beginning at 2238 (table 1). Early on the 15th, the plume extended 1,500 km SE, past the Falkland Islands, where it divided into two components, one travelling E, the other S, both quickly becoming diffuse. At its widest point (the Falkland Islands), the plume was 370 km wide. Infrared satellite imagery showed the plume before it disconnected from the volcano at 1130. TOMS data from 1100 on the 15th (figure 4) showed the plume already disconnected from the volcano, and containing roughly twice as much SO2 as on the 13th (missing data prevented more accurate determinations). No additional emissions have been reported as of 23 August.

Figure (see Caption) Figure 3. Infrared image from the NOAA 10 polar orbiting weather satellite on 15 August 1991 at about 0800, showing the ash plume extending SE from Hudson. Temperature estimates suggest that the plume is at aboout 17-18 km altitude. Courtesy of G. Stephens.

Table 1. Earthquakes near Hudson recorded by the Worldwide Standardized Seismic Net on 14-15 August 1991. Original, very preliminary data are replaced by information from the National Earthquake Information Center's Preliminary Determination of Epicenters.

Date Time Latitude Longitude Magnitude Depth
14 Aug 1991 2238:15 45.6°S 72.6°W 5.2 mb --
15 Aug 1991 0039:08.5 45.7°S 72.6°W 5.3 mb --
15 Aug 1991 0250:37.9 45.8°S 72.5°W 5.3 mb --
15 Aug 1991 0546:15.7 45.7°S 73.2°W 5.7 Ms 13 km
15 Aug 1991 0816:19.3 45.6°S 71.9°W 5.3 mb --

Eruption plume migration. The eruption plume of 14-15 August was rapidly carried E by the "Roaring Forties" winds as shown by TOMS data (figure 4), reaching Australia (15,000 km E) on 20 August. There the following report was compiled from airline information by Alfred Prata:

Figure (see Caption) Figure 4. Preliminary data from the TOMS on the Nimbus-7 satellite showing a polar view of an eruption cloud from Hudson on 20 August 1991 at about 1100 (local time). Each dot represents SO2 values above 10 milliatmosphere-cm (100 ppm-m), within an area 50 km across. The prominent concentration of SO2 to the left represents the cloud's position 24 hours after that to the right, but both are 20 August because they straddle the International Date Line. Envelopes surrounding the cloud's position at approximately 1100 (local time) on 15, 16, and 18 August have been added to illustrate its passage around the globe. Courtesy of Scott Doiron.

"On 20 August, Australian Airlines flight FL418 (Airbus) from Melbourne to Sydney reported an encounter with a strange hazy cloud 260 km NE of Melbourne at about 0230. The haze was faint grey, much like the material often trapped under a temperature inversion, and had a brownish-orange tinge. The haze appeared uniform (not wispy) and there was no evidence of any trace of debris. Associated with this was a strong smell of sulfurous gas which entered the aircraft and was noticed by the crew and passengers. The return flight departed Sydney at about 0400 and encountered the same haze in roughly the same place at 0445. The aircraft was in the haze for 5-10 minutes (75-150 km) and did not change their flight level (FL330, ~10 km altitude). A NOTAM was issued for the period of the evening of the 20th through the morning of the 22nd." The cloud was also reported by pilots from Qantas and Ansett, as late as 2000 on the 20th.

The Atmospheric Research Division of CSIRO were able to discriminate the plume, ~ 500 km long and 100 km wide, on an AVHRR image by ratioing bands 4 and 5. TOMS data showed the plume continuing its eastward path, reaching Chile on 21 August.

Deposits and post-eruptive activity. Intense fumarolic activity continued from a 2-km fissure (oriented N20°E) on the WNW caldera margin during a 23 August overflight. Weaker fumarolic activity was observed on the interior slopes of the 500-m-diameter Crater 1, located 400 m E of the fissure (figure 1). The fissure and Crater 1 were the site of activity 8-10 August.

A black flow (probably lava), with shades of reddish-brown, extended about 3.5 km from the extreme N end of the fissure, onto Ventisquero Huemules. The flow was 50-300 m wide, with several broader sections, and covered recent scoria (8-10 August) in places. Several weak vapor/gas emissions were visible. Scoriaceous pyroclastic flow deposits containing large quantities of ice and snow extended from the fissure toward the interior of the caldera, and in part, over Ventisquero Huemules toward the NW, and Huemules Valley.

Products of the 8-10 August activity were basaltic in composition. Ash samples (ranging to 0.1 mm in size) from Puerto Aisén contained abundant magnetite, pyroxene, plagioclase, and black glass shards. Silica contents of the ash were determined to be 50.98% (at Sernageomin Laboratory).

At Crater 2, believed to be the site of activity on 12-15 August, intense degassing occurred at 3 fumaroles along the S margin. Concentric cracks were visible in the thick ice surrounding the 800-m-wide Crater 2. Pumice from 12-15 August activity differed in composition from the earlier erupted material. Whole rock analyses (from Peter Bitschene) indicated a trachyandesitic composition, with ~ 60% SiO2 and 8-9% alkalies. The distal fallout ash was >98% vitric with predominant pumice and platy shards, and some entrained blocky basaltic shards.

Bitschene estimated that more than 1 km3 of tephra was deposited in Argentina's Santa Cruz province [but see 16:8]. Lakes near the volcano were highly turbid and had layers of floating pumice along their E shores. Increased sediment load resulted in the acceleration of delta growth in Lago Buenos Aires (SE; also called Lago General Carrera), and silting up of the mouth of Río Ibáñez near Puerto Ingeniero Ibáñez (75 km SE) creating a flood risk.

Roughly 50-60,000 sheep and cattle are located within the airfall zone. Extremely high values of fluorine (225 ppm water extractable) were obtained from the ash analyzed 4 days after the eruption. Alberto Villa (INTA, Univ de Chile) reported that grass samples collected at the same site had 280 ppm fluorine (on a dry basis). [but see 16:9-10]

Reference. Stern, C.R., 1991, Mid-Holocene Tephra on Tierro del Fuego (54°S) Derived from the Hudson Volcano (46°S): Evidence for a Large Explosive Eruption; Revista Geológica de Chile, v. 18, no. 2, in press.

Geologic Background. The ice-filled, 10-km-wide caldera of the remote Cerro Hudson volcano was not recognized until its first 20th-century eruption in 1971. It is the southernmost volcano in the Chilean Andes related to subduction of the Nazca plate beneath the South American plate. The massive volcano covers an area of 300 km2. The compound caldera is drained through a breach on its NW rim, which has been the source of mudflows down the Río de Los Huemeles. Two cinder cones occur N of the volcano and others occupy the SW and SE flanks. This volcano has been the source of several major Holocene explosive eruptions. An eruption about 6700 years ago was one of the largest known in the southern Andes during the Holocene; another eruption about 3600 years ago also produced more than 10 km3 of tephra. An eruption in 1991 was Chile's second largest of the 20th century and formed a new 800-m-wide crater in the SW portion of the caldera.

Information Contacts: J. Naranjo, SERNAGEOMIN; H. Moreno, Univ de Chile; G. Fuentealba and P. Riffo, Univ de La Frontera; P. Bitschene, Patagonia Volcanism Project, Argentina; N. Banks, USGS; SAB, NOAA; G. Stephens, NOAA/NESDIS; S. Doiron, GSFC; B. Presgrave, NEIC; C. Stern, Univ of Colorado, Boulder; A.J. Prata, CSIRO, Australia; ICAO; Radio Nacional de Chile; AP.


Irazu (Costa Rica) — July 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)


Seismicity remains high; crater lake level rises

In July, the turquoise-green crater lake continued to rise, eventually covering 2/3 of the crater floor, including several fumaroles that formed during early-mid June. Sulfur deposits had been observed at some of these fumaroles. On 17 July, the lake was 150 x 100 m, with a maximum depth of 2 m. Water temperatures increased with proximity to the bubbling springs (90°C), mud pots, and roaring fumaroles, ranging from 35°C to 55°C (compared to 30-48°C in late June). The lake had pH of 3.7.

Seismicity remained at high levels in July, but was decreased in comparison to late May-June (16:5-6). July's highest seismicity occurred on the 4th, when 75 earthquakes were recorded (seismic station IRZ2, 5 km WSW, Univ Nacional network; figure 3), 34 of which occurred in a NW-SE trend. The 4 July earthquakes (M 1.5-2.7) were centered 0.6-10 km from the crater at <10 km depth. Tremor episodes and B-type earthquakes continued to be recorded in July.

Figure (see Caption) Figure 3. Daily number of earthquakes at Irazú, July 1991. Courtesy of Universidad Nacional.

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: R. Barquero, Guillermo Alvarado, and Alain Creussot, ICE; Mario Fernández and Hector Flores, Sección de Sismología y Vulcanología, Univ de Costa Rica; J. Barquero, E. Fernández, V. Barboza, and J. Brenes, OVSICORI.


Kavachi (Solomon Islands) — July 1991 Citation iconCite this Report

Kavachi

Solomon Islands

8.991°S, 157.979°E; summit elev. -20 m

All times are local (unless otherwise noted)


May-June submarine eruption ends; temporary island eroded away

An eruption built a small temporary island . . . first observed on 4 May, but its location was initially uncertain. However, more precise navigational data from the chief pilot of Western Pacific Air Services placed the activity at 9.00°S, 157.97°E, roughly 3 km NE of Kavachi's summit.

Activity apparently had not changed when, during an overflight on 5 June, [John] Monroe observed a vigorously active lava fountain roughly 25 m high and a plume that rose >2,500 m. The island's dimensions were estimated at 150-200 m long and ~50 m high. Carl Rossiter reported that divers ~45 km NE of Kavachi (at Kicha Island) felt powerful explosions while underwater on 7-8 and 12-13 June. Individual explosions occurred a few seconds apart in groups of 12-20. Explosion groups generally lasted a total of 1-2 minutes, were typically preceded and followed by rumbling, and were separated by roughly 30 minutes of quiet. No explosions were felt at other dive sites, where islands were between the observers and Kavachi.

The eruption weakened in mid-June, and the island disappeared beneath the ocean surface later in the month. No additional activity has been reported.

Geologic Background. Named for a sea-god of the Gatokae and Vangunu peoples, Kavachi is one of the most active submarine volcanoes in the SW Pacific, located in the Solomon Islands south of Vangunu Island about 30 km N of the site of subduction of the Indo-Australian plate beneath the Pacific plate. Sometimes referred to as Rejo te Kvachi ("Kavachi's Oven"), this shallow submarine basaltic-to-andesitic volcano has produced ephemeral islands up to 1 km long many times since its first recorded eruption during 1939. Residents of the nearby islands of Vanguna and Nggatokae (Gatokae) reported "fire on the water" prior to 1939, a possible reference to earlier eruptions. The roughly conical edifice rises from water depths of 1.1-1.2 km on the north and greater depths to the SE. Frequent shallow submarine and occasional subaerial eruptions produce phreatomagmatic explosions that eject steam, ash, and incandescent bombs. On a number of occasions lava flows were observed on the ephemeral islands.

Information Contacts: R. Addison and A. Papabatu, Ministry of Natural Resources, Honiara; J. Monroe, San Jose, USA; C. Rossiter, See and Sea Travel Service, San Francisco, USA.


Kilauea (United States) — July 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)


Continued E rift lava production; summit earthquake swarm

The . . . eruption continued through July, as lava from Kupaianaha vent flowed into the sea. The surface of Kupaianaha's lava pond remained frozen, while lava was still active at the bottom of Pu`u `O`o crater. Nearly simultaneous earthquake swarms occurred in the summit areas of Kilauea and its larger neighbor Mauna Loa.

Eruptive activity. Lava from Kupaianaha was confined to tubes as it advanced down the upper slopes, where skylights at ~650 m (2,150-2,140 ft) elevation revealed an average velocity of ~1 m/s. Active surface flows were intermittently observed in a steeper area near 350 m (1,100 ft) elevation, and additional large surface flows emerged from the tube system between there and the coast through July. One large flow, active since June, advanced on top of the main (Wahaula) tube's E branch (figure 79). Its terminus was near 40 m (140 ft) elevation on 9 July. Although the flow front was wide with many active lobes, it did not reach the coast. Numerous small breakouts were active behind its front. Another flow emerged from a tube near 180 m (600 ft) elevation, moved downslope above the tube's W branch, and reached the coastal plain on 14 July. Two fluid pahoehoe lobes were advancing toward the coast on 16 July, moving past a kipuka at 35 m (120 ft) elevation. By the end of the month, the active flow front was > 400 m wide, and small breakouts from the flow were burning vegetation in Royal Gardens subdivision.

Despite the extensive surface activity, lava continued to pour into the sea from tubes at two main entries. The tube's W branch fed two active sites (at the Poupou entry). The littoral cone at the W Poupou site continued to erode, but erosion slowed toward the end of July as a bench growing outward below the littoral cone absorbed most of the waves' force. A cycle of bench erosion and rebuilding occurred repeatedly at the E Poupou site. Undercutting by wave action removed meter-sized blocks from the cliff face, and the resulting rapid collapse and erosion generated increased spatter activity, initiating construction of a new lower bench. At the entry fed by the E branch of the tube (Paradise), a prominent mid-bench scarp was noted on 4 July. Spatter was found draped over the scarp but none was evident on the lower portion of the bench, suggesting that the lower bench grew after the collapse episode. However, no seismic evidence of collapse was noted. The lower bench grew to within 1 m of the upper bench by 26 July. By the end of the month, the lava entry point shifted from the middle to the E side of the bench. Its W side began eroding and soon developed a cliff facing the ocean.

Seismicity. Continuous volcanic tremor persisted through July at the seismic stations nearest the eruption site and near the W ocean entry. Tremor amplitudes were generally low, although occasional brief bursts of higher amplitude tremor were recorded.

Earthquake activity beneath the summit appeared to have changed slightly since mid-late June. Shallow activity (0-5 km depth) had decreased, especially from the first 3 months of 1991. Daily visual scans of analog records since mid-June suggest that the dominant frequency content of shallow harmonic events had also changed, from 3-5 Hz to 1-3 Hz. The number of deeper (5-13 km) harmonic events fluctuated through July. Between 3 and 6 July, there were swarms of both shallow and deeper long-period events, then activity declined before a second, less intense swarm of intermediate-depth long-period events occurred on 11 July. This was followed first by an increase in shallower long-period activity, then a swarm of several hundred short-period microearthquakes on 13 July between 1400 and 2300, ~2 hours after the onset of a swarm under neighboring Mauna Loa. Almost all were too small for precise location. The 13 July seismicity was not associated with obvious eruptive changes, but geophysicists believe that it may indicate changes in magmatic activity or the state of stress beneath the summit.

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 and P. Okubo, HVO.


Kuwae (Vanuatu) — July 1991 Citation iconCite this Report

Kuwae

Vanuatu

16.829°S, 168.536°E; summit elev. -2 m

All times are local (unless otherwise noted)


Summit at 2-3 m depth; no visible fumarolic activity; sulfur odor

"Kuwae is a mainly submarine caldera (~10x5 km) that, according to C14 ages, Tongan folklore, and reconnaissance fieldwork (Garanger, 1972; Crawford, 1988), is probably very young (~1,500 A.D.). The caldera is located between Epi, Laika, and Tongoa islands in the central part of Vanuatu. During the ORSTOM-CALIS cruise in May 1991, detailed bathymetric and magnetic surveys of the collapse structure were made, and data are presently under analysis. August fieldwork was carried out on Tongoa and Laika Islands in order to study caldera eruption products, their composition, and their age. Several ignimbrite units, including non-welded ash and pumice flow deposits, and thick, complex sequences of poorly-welded to densely-welded tuffs, have been discovered. C14 ages will be determined for charcoal samples from these deposits.

"During the last century, the caldera's active Karua volcanic cone has emerged at least six times, in 1897, [1901], . . . 1948, [1949], 1959, and 1971. Each period of activity was accompanied by explosions. The ephemeral island reached a maximum size of 100 m tall and 1.5 km in diameter in 1949. On 6 August, during a visit by speedboat, the submerged summit area was 50-70 m large at 2-3 m depth. No fumarolic activity was observed despite a strong sulfur smell." [Turbulence and discolored sea water were observed in 1971-74 and 1977.]

References. Crawford, A.J., 1988, Circum-Pacific Council for Energy and Mineral Resources: Earth Science Series, v. 8.

Garanger, J., 1972, Publication de la Société Océanistes, no. 30.

Geologic Background. The largely submarine Kuwae caldera occupies the area between Epi and Tongoa islands. The 6 x 12 km caldera contains two basins that cut the NW end of Tongoa Island and the flank of the late-Pleistocene or Holocene Tavani Ruru volcano on the SE tip of Epi Island. Native legends and radiocarbon dates from pyroclastic-flow deposits have been correlated with a 1452 CE ice-core peak thought to be associated with collapse of Kuwae caldera; however, others considered the deposits to be of smaller-scale eruptions and the ice-core peak to be associated with another unknown major South Pacific eruption. The submarine volcano Karua lies near the northern rim of Kuwae caldera and is one of the most active volcanoes of Vanuatu. It has formed several ephemeral islands since it was first observed in eruption during 1897.

Information Contacts: C. Robin and M. Monzier, ORSTOM, New Caledonia; M. Lardy and C. Douglas, ORSTOM,Vanuatu; C. Mortimer, Dept of Geology, Mines, and Rural Water Supply, Vanuatu; J. Eissen, ORSTOM, France.


Langila (Papua New Guinea) — July 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)


Tephra emission and seismicity

"Activity of both craters remained moderately strong in July, as in June. Crater 3, which had resumed activity in mid-May, released white-to-grey vapor and ash clouds, and light ashfall occurred towards the NE of the volcano on the 6th and 8th. Occasional weak to loud explosions were heard throughout the month. Weak to bright red glow was observed on the 8th, 9th, 13th, and throughout the last week of the month.

"Activity at Crater 2 was characterized by the emission of moderate to thick pale grey ash clouds. Occasional loud to low explosions, some of which were accompanied by light ashfall, were heard during the second and last week of the month. Steady, weak night glow was visible throughout the second week and on the 22nd and 23rd.

"Seismicity remained high throughout the month, with the occurrence of explosion earthquakes and tremor. The daily number of Vulcanian explosions recorded by the summit station (LAN) reached a maximum of 40-60 between the 21st and 26th. Tremor, hardly noticeable in May, occurred almost daily in June-July (up to 100-200 minutes/day). Two types were recognized: high-frequency, discontinuous tremor periods, lasting 1-2 minutes; and lower-frequency harmonic tremor, continuous for periods of several (up to 10) minutes. The tremor became strong enough to be recorded at both the summit station (LAN) and the 9-km-distant CGA station."

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: C. McKee, RVO.


Lewotobi (Indonesia) — July 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

Press releases reported increased activity, with small eruptions occurring around 19 July. One eruption reportedly ejected incandescent material 100 m high, dropping hot ash (smelling of sulfur) onto nearby areas and causing residents to flee. At 1645 on 29 July, a 300-m-high ash cloud extending ~35 km W was reported by pilots on Qantas flight A61. By the week of 14-19 August the volcano was no longer exploding, and gas emissions, 50-100 m high, appeared to be decreasing.

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; ICAO; UPI.


Lopevi (Vanuatu) — July 1991 Citation iconCite this Report

Lopevi

Vanuatu

16.507°S, 168.346°E; summit elev. 1413 m

All times are local (unless otherwise noted)


No fumarolic activity

"The volcano was totally quiet during overflights (VANAIR) on 4 September 1990, and 13 and 24 July 1991. . . . As with Gaua, the scarcity of information from 1977 to 1989 prevents a precise description of its activity. Nevertheless, it seems that no major event occurred during this period."

[The Bulletin of Volcanic Eruptions (BVE) reports lava flows in November 1978, ash eruptions and lava flows February-March 1979, a black eruption column on 2 July 1979, minor ash emissions on 12 September 1979, vigorous ash eruptions in April and July 1980, and an eruption cloud and lava flow on 18-20 August 1980.]

Geologic Background. The small 7-km-wide conical island of Lopevi, known locally as Vanei Vollohulu, is one of Vanuatu's most active volcanoes. A small summit crater containing a cinder cone is breached to the NW and tops an older cone that is rimmed by the remnant of a larger crater. The basaltic-to-andesitic volcano has been active during historical time at both summit and flank vents, primarily along a NW-SE-trending fissure that cuts across the island, producing moderate explosive eruptions and lava flows that reached the coast. Historical eruptions at the 1413-m-high volcano date back to the mid-19th century. The island was evacuated following major eruptions in 1939 and 1960. The latter eruption, from a NW-flank fissure vent, produced a pyroclastic flow that swept to the sea and a lava flow that formed a new peninsula on the western coast.

Information Contacts: C. Robin and M. Monzier, ORSTOM, New Caledonia; M. Lardy and C. Douglas, ORSTOM,Vanuatu; C. Mortimer, Dept of Geology, Mines, and Rural Water Supply,Vanuatu; J. Eissen, ORSTOM, France.


Manam (Papua New Guinea) — July 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)


Stronger ash emission

"Activity . . . increased slightly in July, as shown by more voluminous vapour and ash emissions, stronger sounds, and the resumption of night glow over Main Crater. Emissions from Main Crater consisted of weak to moderate white-grey ash and vapour accompanied by thin blue vapour from 22 to 25 July. Occasional deep roaring noises were heard on the 4th-6th. A weak fluctuating night glow was visible 23-25 July for the first time since April. Southern Crater emitted thin to thick grey-brown ash clouds, occasionally rising to ~400-500 m above the crater rim. Booming and deep roaring noises were heard on most days throughout the month, but no night glow was observed. Seismicity was at a moderate level and tiltmeter measurements showed no change."

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: C. McKee, RVO.


Mauna Loa (United States) — July 1991 Citation iconCite this Report

Mauna Loa

United States

19.475°N, 155.608°W; summit elev. 4170 m

All times are local (unless otherwise noted)


Summit earthquake swarm

Surface deformation measurements indicate gradual reinflation of Mauna Loa's summit since its 1984 eruption. Earthquake counts have fluctuated, but have apparently increased since late 1990.

Two bursts of intermediate-depth volcanic tremor, beginning at about 1200 on 13 July, preceded a swarm of long-period earthquakes that continued for ~14 hours. Activity peaked between 2300 on 13 July and 0100 the next morning. As the long-period events gradually declined, shallow microearthquake activity increased, and continued for about 6 hours. All of the events were too small for precise location.

The 13 July activity began ~2 hours before an earthquake swarm under the summit of Kilauea. Seismicity at Mauna Loa has apparently returned to average background levels since mid-July.

Geologic Background. Massive Mauna Loa shield volcano rises almost 9 km above the sea floor to form the world's largest active volcano. Flank eruptions are predominately from the lengthy NE and SW rift zones, and the summit is cut by the Mokuaweoweo caldera, which sits within an older and larger 6 x 8 km caldera. Two of the youngest large debris avalanches documented in Hawaii traveled nearly 100 km from Mauna Loa; the second of the Alika avalanches was emplaced about 105,000 years ago (Moore et al. 1989). Almost 90% of the surface of the basaltic shield volcano is covered by lavas less than 4000 years old (Lockwood and Lipman, 1987). During a 750-year eruptive period beginning about 1500 years ago, a series of voluminous overflows from a summit lava lake covered about one fourth of the volcano's surface. The ensuing 750-year period, from shortly after the formation of Mokuaweoweo caldera until the present, saw an additional quarter of the volcano covered with lava flows predominately from summit and NW rift zone vents.

Information Contacts: P. Okubo, HVO.


Ontakesan (Japan) — July 1991 Citation iconCite this Report

Ontakesan

Japan

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

All times are local (unless otherwise noted)


Decreasing seismicity

Seismicity decreased in July, with 94 earthquakes and two tremor episodes recorded . . . (figure 10). Summit vents continued emitting white steam plumes but these rose weakly to ~ 100 m . . . .

Figure (see Caption) Figure 10. Daily number of earthquakes January-15 August 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.


Pacaya (Guatemala) — July 1991 Citation iconCite this Report

Pacaya

Guatemala

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

All times are local (unless otherwise noted)


Explosive eruptions destroy cone and crater; crop damage; evacuations

Fourteen eruptions occurred during the most recent phase of strong explosive activity, 6 June-1 August, with the strongest and most destructive activity occurring 27-31 July. Activity was at low levels as of 15 August.

The following report from Philippe Rocher describes activity through mid-June.

"During the first half of 1991, activity was continuous and relatively quiet, with several small eruptions and lava flows from the main crater. This last cycle of activity began in November 1990. The continuous ejection of material built a cone that reached 400-500 m height. Although seismicity showed no significant changes in May, occassional pulses of increased surface activity occurred. On 11-15 May, explosion counts ranged from 1,170 to 1,730/day and a new lava flow was emitted. The cone reached 500 m high and lava traveled down the SE slope.

"On 6 June, explosive activity increased again, with explosions every 10-40 seconds and ash reaching 100-500 m heights. The next pulse occurred on 11 June. On the following day, strong explosions sent material to 500 m height and triggered avalanches that destroyed the summit of the cone. Lava flowed down the SW slope. Ash emissions to 500 m height and short lava flows characterized the next increase, lasting 4.5 hours on 14 June. On 16 June, a 10-hour episode of strong explosions ejected a black plume to 600 m height and caused avalanches that traveled to the foot of the volcano. Between the different eruptions, strong degassing continued, accompanied by B-type earthquakes and small, low-amplitude (about 1 mm) tremor episodes."

The following is from Eddy Sánchez.

"The most explosive and destructive activity during the current phase of activity began at 0100 on 27 July. Strombolian activity destroyed the main crater, and ejected ash and lapilli to the SW, principally affecting Caracol, Rodeo, and Patrocinio, the same towns affected by the eruption on 25 January 1987. Activity decreased at 0230." The press reported that three people were injured and 2,000 left homeless.

"Intense activity resumed at 1330-2230 on 30 July, with four cycles of moderate explosions, each cycle lasting 1.5 hours. Similar activity occurred the next day, when columns of fine ash and gas rose 400-1,000 m above MacKenney Crater. The last strong episode of Strombolian activity began at 0230 on 1 August, when ash clouds reached 700-1,000 m heights, with pulses and pauses of 30-60 minutes, and blocks (>=5 m in diameter) were ejected onto the flanks of the volcano.

"Local agriculture was significantly damaged by airfall from this recent phase of explosive activity. Corn and bean fields were destroyed, as well as part of the coffee crop. Airfall thicknesses ranged from 0.5 to 26 cm, with up to 5 cm in Rodeo and 15 cm in Santa Lucía Cotzumalguapa (figure 8). The ash was deposited as far as 55 km WSW (Pueblo Nuevo Tiquisate).

Figure (see Caption) Figure 8. Isopach map of airfall deposits from activity on 27-31 July 1991 at Pacaya. Base Map is a portion of Guatemala 1:250,000 sheet (ND 15-8, Dirección General de Cartografía, Guatemala City, Guatemala). Contour interval, 100 m. Courtesy of E. Sánchez.

"During the last eruption, on 1 August, INSIVUMEH recommended to emergency agencies that the approximately 1,500 residents of Caracol, Rodeo, and Patrocinio be evacuated, due to the hazard of a new violent eruption. The next day, seismic and eruptive activity decreased considerably, allowing the evacuated people to return home. Activity continued to decrease quickly, with 40 B-type microearthquakes (frequency, 4-5 Hz, and amplitude, 2.0-2.5 mm) recorded daily on 7 August. Activity as of 15 August was considered at low levels."

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

Information Contacts: E. Sánchez, INSIVUMEH; Philippe Rocher, L.A.V.E., France; ACAN network, Panama City, Panama.


Pinatubo (Philippines) — July 1991 Citation iconCite this Report

Pinatubo

Philippines

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

All times are local (unless otherwise noted)


Ash emissions decreasing; typhoons trigger large lahars

Activity declined through the third week of August, although periodic explosions continued to eject material to >15 km height. Heavy rains triggered large mudflows that traveled down all major drainage systems, destroying houses and resulting in numerous casualties. The number of people killed by the eruption, mudflows, and disease (in evacuation camps) now exceeds 500. The stratospheric aerosol cloud produced by the paroxysmal activity on 15-16 June continued to disperse.

Continuing activity, to 20 August. Declining seismicity was interrupted by a M 4.5-5 volcano-tectonic earthquake at 1456 on 26 July and several felt aftershocks. Ash emission continued, often accompanied by tremor during periods of increased plume heights. Two pulses of emissions to >7.5 km at 0136 and 0203, and one to 16.4 km (as determined by radar at Clark Air Base) at 1212 on 27 July, were accompanied by low-amplitude tremor. Aviation officials were notified within 15 minutes of the onset of this more energetic activity. Relatively dry weather continued through early August.

Seismicity continued a gradual downward trend (figure 16), with a decrease in amplitude and number of long-period events, and a decrease in seismic energy released (figure 17). Small upsurges in amplitude (RSAM) corresponded to long-period earthquakes. Ash emissions were rare and did not exceed 8 km height during 8-10 August and had fewer accompanying long-period events. Occasional high-frequency earthquakes were felt at Clark Air Base with intensities up to II. Mudflow signals were seismically recorded on the 10th.

Figure (see Caption) Figure 16. Number of earthquakes per 4 hours (top) and Realtime Seismic Amplitude Measurement (bottom) at Pinatubo, 16 June-11 August 1991. Courtesy of PHIVOLCS.
Figure (see Caption) Figure 17. Accumulated RSAM energy at Pinatubo, 16 June-15 August 1991. Courtesy of PHIVOLCS.

Heavy rain triggered large mudflows on 11 August. The press reported that more than 13,000 people fled their villages, and more than 1,000 houses were destroyed. The Gumain (SE flank) and Sacobia (E flank) Rivers rose an average 1.2 m, and 300 houses were damaged along the Abacan near Mexico (~45 km E of the summit). Five large ash emissions (average height 5 km) occurred on 12 August. United Airlines pilots reported an ash cloud to >15 km altitude at about 1300 on the 12th and to 12 km the following day at 1426.

High ash emissions (maximum plume height about 13 km) and mudflows were reported on 14 August. About 5,000 people evacuated Tabon in the Pampanga region (E flank), as 96 houses were washed away. The press reported debris to 3 m deep. Mudflows on the 18th prompted another large evacuation, with 3,000 fleeing 6 towns in the Pampanga and Tarlac regions (E flank).

On 20 August, the press reported that the largest mudflows since the start of the eruption killed 31 people (primarily in Santa Rita, ~40 km NE), bringing the number of mudflow-related deaths to over 100. Flows 5 m high reportedly traveled down ten rivers, damaging more than 9,000 houses and destroying three bridges. Up to 55,000 people evacuated their homes. Ash clouds rose to 12 km high.

The press reported that by 6 August, more than 46 people (mostly children and infants) had died of various illnesses (primarily diarrhea, measles, and broncho-pneumonia) in evacuation camps. This number had increased to nearly 200 (mostly Aeta tribesmen) by 18 August, and it was reported that almost 1,500 people in the camps were suffering from disease. By 20 August, more than 500 people had died since the start of the eruption according to press reports.

Field geology. Fieldwork and evaluation of the deposits from the paroxysmal activity of 15-16 June continued. A preliminary airfall isopach map was prepared by the PHIVOLCS MGB Lahar Task Force (figure 18), and the volume of material within the 10-cm isopach was estimated to be 0.47 km3. Ash leachates indicated chloride contents to almost 1,000 ppm, and fluoride contents under 10 ppm (table 3). Petrographic analysis of pumice samples revealed the presence of anhydrite micro-phenocrysts scattered in the matrix groundmass (Bernard, and others, 1991). Pyroclastic-flow deposit volumes were estimated to total roughly 7 km3. The following report by Alain Bernard describes one of the pyroclastic-flow deposits.

Figure (see Caption) Figure 18. Preliminary isopach map of 12-16 June 1991 airfall deposits from Pinatubo. Isopachs are centimeters. Prepared by PHIVOLCS MGB Lahar Task Force.

Table 3. Preliminary fluoride and chloride contents in Pinatubo ash leachates, 12 June-4 July 1991. Ash was washed for 12 hours in a 4:1 ratio of water (distilled-deionized water, pH 5.5) to ash. The 12, 15, and 22 June samples were collected by PHIVOLCS and reported "fresh fallen," the other samples were collected shortly after falling, during dry weather. Courtesy of Alain Bernard and PHIVOLCS.

Date Location Distance from volcano F- (ppm) Cl- (ppm) pH
12 Jun 1991 San Marcelino 28 km 0.3 212 --
15 Jun 1991 Bacoor-Cavite 120 km 9.8 208 --
22 Jun 1991 O'Donnell 26.5 km 0.4 475 --
29 Jun 1991 Binoclutan 38 km 1.6 991 --
29 Jun 1991 Mapanuepe 19 km 0.05 67 3.83
30 Jun 1991 Botolan 39.5 km 0.4 803 --
03 Jul 1991 Iba 44 km 0.65 464 --
03 Jul 1991 Marella 1 10 km 0.06 11 7.9
03 Jul 1991 Marella 2 13 km 0.1 50 7.2
03 Jul 1991 Hot mudflow (on pyroclastic flow) 8 km 0.4 354 6.19
04 Jul 1991 Poonbato 23.5 km 0.5 604 --
03 Jul 1991 Burgos-Ugik 17 km 0.6 699 --

"A pyroclastic-flow deposit emplaced in the Marella River (reaching 15 km SW from the main crater) was visited on 3 July. It was still degassing, with numerous rootless fumaroles present even at low altitude at the end of the deposits. The gases emitted were mostly steam, but minor amounts of SO2 (and probably H2S) were present, since incrustations of native sulfur were observed at the mouths of these fumaroles. Strong odors of burned wood (charcoal) were also perceptible in some places, and associated with black-brown deposits at the surface of the pyroclastic-flow deposit resulting from some pyrolysis of wood buried at shallow depth beneath the deposit. Maximum temperatures of the fumarole were close to boiling, 98-99.5°C. The temperature inside of the pyroclastic-flow deposit measured at one location (~10 km from the crater) was 223°C at a depth of 70 cm.

"The surface of the deposit was a hard crust that was very easy to walk on. It looked like some recent pyroclastic-flow deposits observed on Augustine, with rounded pumice clasts (maximum size

"Numerous small cones (maximum diameter about 10 m, up to about 1-2 m high) were also present on the surface of the pyroclastic-flow deposit. These cones resulted from the activity of large steam fumaroles. At the time of the visit, two intermittent fumaroles were active in the upper portion of the deposit (~8 km from the crater) emitting a steam plume 3-4 m high mixed with fine-grained ash. A hot (88°C) stream of muddy water (65 cm wide), with the consistency of a mudflow, was also surging from the ground in the area close to these intermittent fumaroles. A water sample filtered from this stream showed a high chloride content compared to other streams and rivers travelling down the volcano (table 3). Many old tracks of other mudflows were observed on the surface of the pyroclastic flow deposit."

[Additional encounters between aircraft and ash clouds, frequent in the eruption's first days, were reported this month but included above in table 2.]

Reference. Bernard, A., Demaiffe, D., Mattielli, N., and Punongbayan, R.S., 1991, Anhydrite-bearing pumices from Mount Pinatubo: further evidence for the existence of sulphur-rich silicic magmas: Nature, v. 354, p. 139-140.

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

Information Contacts: R. Punongbayan, PHIVOLCS; A. Bernard, Univ Libre de Bruxelles, Belgium; T. Casadevall, USGS Denver; J. Lynch, SAB; Daily Inquirer, Manila, Philippines; AP; UPI; Reuters.


Poas (Costa Rica) — July 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 degassing; seismicity

An average of 239 microearthquakes, with a maximum of 485 (3 July), were recorded daily in July (figure 39), at a station 2 km SW of the crater. Of these, 29 were identified as A- and B-type earthquakes. Seismic frequencies ranged from 1.4 to 2.6 Hz. A total of 41 hours of continuous and discrete semi-harmonic tremor episodes were recorded, with durations of up to 6 hours.

Figure (see Caption) Figure 39. Daily number of earthquakes at Poás, July 1991. Courtesy of the Univ Nacional.

The crater lake's average temperature was 63°C. Fumaroles were covered as the lake level continued to rise. Area residents sporadically reported a sulfurous odor.

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, and J. Brenes, OVSICORI.


Rincon de la Vieja (Costa Rica) — July 1991 Citation iconCite this Report

Rincon de la Vieja

Costa Rica

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

All times are local (unless otherwise noted)


Seismicity and tremor

A total of 399 microearthquakes were recorded in July (figure 4) at a seismic station (RIN3) 6 km SW of the crater. Six hours of low- and medium-frequency tremor (1.3-3.2 Hz), were recorded in episodes 12 minutes to 3 hours long. Low-frequency earthquakes were also recorded, with durations that reached 175 seconds.

Figure (see Caption) Figure 4. Daily number of earthquakes at Rincón de la Vieja, July 1991. Courtesy of OVSICORI.

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

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


Nevado del Ruiz (Colombia) — July 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)


Seismicity remains at low levels; small ash emissions

Seismicity was at very low levels in July, although tremor reached slightly higher levels at the beginning of the month. Deformation measurements showed no significant changes. The SO2 flux continued to fluctuate, with a monthly average of ~1,220 t/d. Two small ash emissions, restricted to the summit region, were observed during July.

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.


Sabancaya (Peru) — July 1991 Citation iconCite this Report

Sabancaya

Peru

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

All times are local (unless otherwise noted)


Earthquake swarm damages towns and triggers mudslides; 20 people reported dead

A swarm of earthquakes, reported on 23-24 July, triggered mudslides that partly buried four villages. In towns within 20 km N of the volcano, the earthquakes caused many houses to collapse, especially in Maca (15 km N) which was almost completely destroyed. The press reported that 20 people were killed, 80 were injured, and 3,000 were left homeless. More than 20 earthquakes/day were reported felt (MM <=V) 75 km SE (in Arequipa). The largest of the shocks (Ms [4.7]), detected at [1444] on 23 July by the WWSSN, was centered [35] km [ENE] from the volcano at shallow depth.

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: NEIC; EFE network, Madrid, Spain; Agence France-Presse; Reuters; UPI; AP.


Santa Maria (Guatemala) — July 1991 Citation iconCite this Report

Santa Maria

Guatemala

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

All times are local (unless otherwise noted)


Explosions and avalanches; plumes to 600 m height

The volcano was in a moderate explosive phase in May, emitting gray ash clouds 300-500 m high. In June, the number of moderate to strong explosions increased daily, with plumes 400-600 m high, and ashfall on the area surrounding the volcano. Numerous collapses and large avalanches were observed on the SE slope.

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

Information Contacts: Philippe Rocher, L.A.V.E., France.


Stromboli (Italy) — July 1991 Citation iconCite this Report

Stromboli

Italy

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

All times are local (unless otherwise noted)


Continued explosions from two craters

The number and intensity of explosions has continued to fluctuate in recent months, with the average rate remaining slightly higher since mid-March. During a summit visit on the night of 31 July-1 August, >50 explosions were observed between 2100 and 0600. The strongest ejected incandescent material toward the edge of the summit area. Most of the explosions were from Crater 1, the rest from Crater 3, with only gas emission evident from Crater 2 and from a small cone. On this occasion and during other visits over the past several years, durations of precursory noises appeared linked to explosive vigor, with stronger explosions following noises lasting 3-5 seconds, whereas 1-2-second noises preceded weak explosions [see also 16:08].

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: H. Gaudru, SVE, Switzerland; T. De St. Cyr, Fontaines St. Martin, France.


Suretamatai (Vanuatu) — July 1991 Citation iconCite this Report

Suretamatai

Vanuatu

13.8°S, 167.47°E; summit elev. 921 m

All times are local (unless otherwise noted)


Fumarolic activity

"During our survey, no change in activity at the major geothermal areas (Frenchman's Solfataras and Hell's Gate) was noted, with respect to descriptions by Aubert de la Rue (1937) and Hochstein (1980). Slightly superheated fumaroles (with sulfur deposits), hot springs, and boiling ponds up to 3 m in diameter occurred over a 300-m strip along the Sulfur River (E flank) between 300 to 400 m elevation. The temperature of the Sulfur River at Hell's Gate remained stable at 50°C.

"Soretimeat . . . is a composite volcano built on an ancient Pleistocene edifice. Ash emissions reported in 1860 and 1965-66 are most likely to have been from hydrothermal explosions (Ash and others, 1980)." ["Flames" were observed during an apparent eruption in 1865 (Atkin, 1868).]

References. Ash, R.P., Carney, J.N., and MacFarlane, A., 1980, Geology of the northern Banks Islands: New Hebrides Geological Survey Regional Report, p. 1-47.

Atkin, J., 1868, On volcanoes in the New Hebrides and Banks Islands: Proceedings of the Geological Society of London, v. 24, p. 305-307.

Aubert de la Rue, E., 1937, La Volcanisme aux Nouvelles Hebrides (Melanesie): BV, v. 2, p. 79-142.

Hochstein, M.P., 1980, Geology of the Northern Banks Islands: New Hebrides Geological Survey Regional Report, p. 47-49.

Geologic Background. Suretamatai volcano (also known as Soritimeat) forms much of Vanua Lava Island, one of the largest of Vanuatu's Banks Islands. The younger lavas overlie a number of small older stratovolcanoes that form the island. In contrast to other large volcanoes of Vanuatu, the dominantly basaltic-to-andesitic Suretamatai does not contain a youthful summit caldera. A chain of small stratovolcanoes oriented along a NNE-SSW line gives the low-angle volcano an irregular profile. The youngest cone, near the northern end of the chain, is the largest and contains a lake of variable depth within its 900-m-wide, 100-m-deep summit crater. Activity reported during the 19th century consisted of moderate explosive eruptions.

Information Contacts: C. Robin and M. Monzier, ORSTOM, Nouméa, New Caledonia; M. Lardy and C. Douglas, ORSTOM, Vanuatu; C. Mortimer, Dept. of Geology, Mines, and Rural Water Supply, Vanuatu; J. Eissen, ORSTOM, France.


Taal (Philippines) — July 1991 Citation iconCite this Report

Taal

Philippines

14.002°N, 120.993°E; summit elev. 311 m

All times are local (unless otherwise noted)


Abnormal seismicity continues

Abnormally high levels of seismicity continued as of mid-August. Up to 5 small high-frequency earthquakes were recorded daily 9-12 August. No earthquakes were felt during this time. The main crater lake temperature remained at 31°C. Close monitoring of the volcano continued.

Geologic Background. Taal is one of the most active volcanoes in the Philippines and has produced some of its most powerful historical eruptions. Though not topographically prominent, its prehistorical eruptions have greatly changed the landscape of SW Luzon. The 15 x 20 km Talisay (Taal) caldera is largely filled by Lake Taal, whose 267 km2 surface lies only 3 m above sea level. The maximum depth of the lake is 160 m, and several eruptive centers lie submerged beneath the lake. The 5-km-wide Volcano Island in north-central Lake Taal is the location of all historical eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones that have grown about 25% in area during historical time. Powerful pyroclastic flows and surges from historical eruptions have caused many fatalities.

Information Contacts: R. Punongbayan, PHIVOLCS.


Unzendake (Japan) — July 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 dome growth and pyroclastic flow generation; dome history reviewed

The dome in Jigoku-ato crater continued to grow in an easterly direction in July, at a rate of 0.3 x 106 m3/day (figure 26). The magma supply rate remained unchanged in August, but the direction of growth became westerly. By 15 August, the dome was estimated to be 650 x 250 m and 130 m thick. On 19 July it had been 520 x 260 m, with a volume of 5.9 x 106 m3.

Figure (see Caption) Figure 26. Cumulative volumes of magma erupted from Unzen, May-July 1991. Courtesy of S. Nakada.

The number of seismically-detected pyroclastic flows and avalanches from the dome decreased in July (compared to June), showed a gradual increase late July-early August, then decreased suddenly on 12 August to only a few events/day. A total of 326 pyroclastic flows were recorded in July (down from 482 in June), and 155 during 1-15 August. Event durations were shorter than in previous months when flow signals occasionally lasted more than 300 seconds. The longest events lasted 140 seconds in July and 150 seconds in August.

Pyroclastic flows continued to travel as much as 2 km E down the Mizunashi River. None of the flows reached the evacuated areas of Shimabara and Fukae, which remained closed with 12,395 inhabitants relocated. Ash clouds from the larger pyroclastic flows rose 2 km, with ash falling mainly NE on Shimabara. Prevailing winds remained unchanged since May. Continuous ash emission from vents in the crater near the dome occurred in mid-July (16:06), and on 5-6, and 12 August, when the ash cloud rose 1.5 km. Explosive ejections of incandescent blocks to 100 m height were observed from midnight to 0200 on 12 August, presumably from a vent on the W end of the dome that continuously emitted ash throughout the day.

In contrast to the drop in pyroclastic flows on 12 August, the number of summit earthquakes and tremor episodes increased sharply on 11 August. This followed reduced seismic activity in June (230 recorded earthquakes) and July (133), compared to April (1959). More than 460 earthquakes had already been recorded in August by the 15th. Earthquake magnitudes were small and no shocks were felt, nor were changes in ground deformation detected by tiltmeters or EDM lines near the summit. Following the peak on 12 August, seismicity began to decrease. The increase in seismicity may be related to the incandescent ejections on 12 August, the active continuous ash emission, and the westward growth of the dome.

A man died on 8 August from burns suffered on 3 June, bringing the total casualties to 39 dead and three missing.

The following is a report from Setsuya Nakada on dome growth and morphology in June. "Large pyroclastic flows occurred on 3 and 8 June (figure 27), with volumes of about 0.7 x 106, and 1 x 106 m3, respectively. The E half of the lava dome collapsed during the eruption of the 3 June pyroclastic flow, leaving a 150-m-wide horseshoe-shaped depression opening to the E (figure 28). The volume of dome material left behind (referred to as W dome) was about 0.48 x 106 m3. A new lava dome formed within the depression by 8 June, obtaining pre-3 June volumes.

Figure (see Caption) Figure 27. Distribution of the 3 and 8 June 1991 pyroclastic flow deposits at Unzen. From Nakada and Kobayashi (1991).
Figure (see Caption) Figure 28. Growth pattern of the lava dome in Jigoku-ato Crater at Unzen, May-August, 1991. From Nakada and Kobayashi (1991).

"Some of the 8 June pyroclastic flows, which reached 5.5 km beyond the crater, resulted from the direct eruption of magma from the vent. An extensive area of trees was burnt by the accompanying ash clouds. Pyroclastic surge (ash-cloud surge) deposits, such as those in the deposits from 3 June, were not clearly identified. Breadcrust bombs 5 cm in diameter were ejected to 3 km NE of the crater. Half of the W dome and the entire E dome (post-3 June material) were destroyed, widening the horseshoe-shaped depression to 200 m. About 0.15 x 106 m3 of the W dome remained.

"Vulcanian explosions on 11 June ejected breadcrust and cauliflower bombs, up to 46 cm long, to 3 km distance. As a result, a depression 20-30 m in diameter formed within the crater, just above the former Jigoku-ato crater. On 17 June a continuous eruption column was observed rising from the W dome, for the first time since the start of lava extrusion.

"The E dome continued to grow and collapse along its E margin, filling a steep valley on the E slope of Jigoku-ato crater, then growing over the valley-fill deposits, a gentler surface than the original valley floor. The surface of the lava dome had the form of a petal with two lobes. These were created by extrusion near the summit of the E dome. After the middle of June, the lava surface traveled SE at a rate of 40 m/day, but the dome only lengthened a maximum of 10 m/day. By the end of June the horseshoe-shaped depression was filled with dome material, and lava blocks began to overflow NE onto the caldera floor."

Reference. Nakada, S., and Kobayashi, T., 1991, Lava dome and pyroclastic flows of the 1991 eruption at Unzen volcano: Bulletin of the Volcanological Society of Japan, v. 36, in press.

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.


Yasur (Vanuatu) — July 1991 Citation iconCite this Report

Yasur

Vanuatu

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

All times are local (unless otherwise noted)


Continued block and ash emissions; small episodic lava lakes

"Activity remained unchanged during 1990-91, with block and ash emissions and small episodic lava lakes."

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

Information Contacts: C. Robin and M. Monzier, ORSTOM, New Caledonia; M. Lardy and C. Douglas, ORSTOM, Vanuatu; C. Mortimer, Dept of Geology, Mines, and Rural Water Supply, Vanuatu; J. Eissen, ORSTOM, France.

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