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 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 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 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 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 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 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 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 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 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).

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 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 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 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 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.

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 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 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 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).

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.

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 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 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 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 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 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 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 197. Photo of a lava flow and degassing at Piton de la Fournaise on 10 February 2020. Courtesy of OVPF-IPGP.

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 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 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 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).

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.

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 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 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 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 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 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 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 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).

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 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.

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 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/).

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.

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 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).

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 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 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 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 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 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 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 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 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 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 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 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 90. An ash plume rising 3 km above Merapi on 14 October 2019.

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 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 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 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).

The rate of explosions from the summit crater of Minami-dake declined in early and mid-February, then increased late in the month. Frequent explosions continued through March. Recorded explosions numbered 15 in February, 47 in March.

On 26 February, an explosion at 1044 produced a 1,600-m-high eruption column, then a continuous ash cloud was observed until 1150, and from 1430 until sunset ended visual observation from the JMA's Kagoshima Observatory. A 1,500-m-high eruption column was ejected at 1731. On 28 February a continuous ash cloud was observed 0620-1230, and three explosions were recorded the next day. On 24 March a 100-m-high incandescent column was observed for 15 seconds, and on the 28th a 200-m-high incandescent column lasting 30 seconds was accompanied by rumbling. Local seismicity was active in the first half of February, when explosive activity had declined. JMA scientists have observed that a swarm of B-type earthquakes, which they interpret as possibly caused by magma rising to a shallower depth, is often followed by increased explosive activity. In March local seismic events and continuous ash clouds were frequently observed, but only rarely did an explosion with a large amount of ejecta occur. There was some damage to nearby farm products.

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, Tokyo.

On 21 March a strong (M 6.9) earthquake occurred near Urakawa, off the S coast of Hokkaido and 182 km SW of Akan. Local seismicity at Me-Akan increased after the earthquake, but the JMA has reported that there is no evidence of a causative relationship. The total number of seismic events recorded in March was 411 (table 1). The numbers of recorded seismic events at Me-Akan for 1977-81 are 97, 45, 491, 254, and 194.

Table 1. Number of seismic events recorded at Me-Akan during 19-31 March 1982. Courtesy of JMA.

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

Information Contacts: JMA, Tokyo.

Imagery from the GMS satellite revealed a narrow, linear eruption plume emerging from Alaid at 1100 on 29 March. The plume extended roughly 100 km to the ESE and was estimated to be roughly 2 hours old. Images returned 3 hours earlier and later showed no evidence of activity.

Geologic Background. The highest and northernmost volcano of the Kuril Islands, 2285-m-high Alaid is a symmetrical stratovolcano when viewed from the north, but has a 1.5-km-wide summit crater that is breached widely to the south. Alaid is the northernmost of a chain of volcanoes constructed west of the main Kuril archipelago. Numerous pyroclastic cones dot the lower flanks of this basaltic to basaltic-andesite volcano, particularly on the NW and SE sides, including an offshore cone formed during the 1933-34 eruption. Strong explosive eruptions have occurred from the summit crater beginning in the 18th century. Reports of eruptions in 1770, 1789, 1821, 1829, 1843, 1848, and 1858 were considered incorrect by Gorshkov (1970). Explosive eruptions in 1790 and 1981 were among the largest in the Kuril Islands during historical time.

Information Contacts: M. Matson, NOAA/NESS.

The widely-distributed volcanic aerosol cloud remained in the lower stratosphere through early April. Since 29 January, each lidar measurement at MLO has detected the cloud. As of 9 April, it was centered at about 18 km altitude (with a peak backscattering ratio of 1.6) and was about 2 km thick. A balloon flight the first week in April from Laramie, Wyoming showed a broad layer centered at 18 km altitude. From Hampton, Virginia, lidar data 8 April showed a 3-km-thick layer centered at about 17 km altitude (backscattering ratio about 1.6). The cloud has also been intermittently present over Toronto, Canada (43.6°N, 70.5°W) since early March.

A NASA sampling aircraft flew S from San Francisco 18 March, and collected about 20 times the normal concentration of H₂SO4 from a layer at the base of the stratosphere. Silicate particles about 0.25 µm in diameter were present both as discrete fragments and within the acid droplets. Chemical analysis of these particles showed that they contained no Na, and their Si/Al ratio was consistent with a basaltic composition. Additional sampling flights are planned in mid-April by NASA and LASL.

No eruption can be unequivocally identified as the source for the cloud. Careful inspection of satellite images has yielded no large eruption clouds that had gone unreported from the ground, but cloudy weather often obscured volcanically active areas of the world. The best candidate appears to be Pagan (18.13°N, 145.80°E), where moderate explosive activity was reported in early January. However, no ground observations are available between 6 January and 8 February, and the source eruption for the cloud probably occurred in mid-January. Careful inspection of images from the Japanese geostationary weather satellite by Yosihiro Sawada showed a possible volcanic cloud from Pagan 14 January at 1900 local time (0900 GMT), but interference from weather clouds made this impossible to confirm. Sawada observed a similar feature on an image returned at 2200 local time 19 January 1981, the same day that visiting islanders reported explosive activity.

[Unpublished data from NASA's Total Ozone Mapping Spectrometer (TOMS), which is sensitive to the SO₂ that is emitted by most eruptions, strongly suggest that this cloud was ejected by Nyamuragira (Zaire) during the initial explosive phase of its December 1981-January 1982 eruption.]

Geologic Background. 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 here.

Information Contacts: R. Chuan, Brunswick Corp.; Y. Sawada, Meteorological Research Inst., Japan; N. Banks, USGS-HVO, HI; K. Coulson, MLO; W. Fuller, NASA, VA; D. Hofmann, Univ. of Wyoming; B. Ragent, NASA, CA; W. Evans, ARPX-AES, Downsview, Canada.

After several weeks of local seismicity, explosions in late March and early April ejected a series of tephra columns, two of which penetrated well into the stratosphere. Officials reported that as many as 100 persons may have been killed by the eruption and associated seismic activity. Tephra falls were very heavy near the volcano, forcing tens of thousands of residents to flee their homes, and causing major damage to crops and livestock.

Activity during 28-29 March 1982. The eruption began 28 March at 2332 and NOAA geostationary weather satellite imagery showed that the eruption column was about 100 km in diameter 40 minutes later. Analysis of an infrared image returned at 0300 yielded a cloud top temperature of -75°C, corresponding to an altitude of 16.8 km, ~ 1 km above the tropopause. Surface and vault microbarographs and a KS36000 (SRO-type) seismograph operated by Teledyne Geotech near Dallas, Texas (1,797 km from El Chichón) received 22 minutes of infrasonic signals generated by explosive activity. Nine distinct signals were recorded, including a strong gravity wave, indicating that the eruption column struck the tropopause. Instruments at McMurdo, Antarctica, 11,865 km from El Chichón, recorded about 2 hours of infrasonic signals. Nine intensity peaks were detected, of which five were clearly from the eruption.

Vigorous feeding of the plume continued for several hours but had clearly ended by 0600. A dense tephra cloud drifted ENE from the volcano and a much more diffuse plume moved in roughly the opposite direction (figure 1). By 0530 the next morning, satellite images showed the main plume extending from the Yucatán Peninsula, S of Cuba, to Haiti, and remnants of the more diffuse plume over the E Pacific Ocean at about 15°N, and 118-119°W. The U. S. National Weather Service analyzed wind directions and speeds at different altitudes near the volcano, and concluded that the ENE drift of the dense cloud indicated that it was in the upper troposphere, whereas the diffuse plume blown to the WSW was in the middle troposphere at roughly 6-7.5 km altitude. Initially, none of the tephra appeared to be drifting in a direction consistent with the lower stratospheric circulation, but significant aerosol development in the stratosphere is indicated by the lidar measurements described in the next-to-last paragraph of this report.

Figure 1. NOAA geostationary weather satellite image returned 29 March at 1000, about 10.5 hours after El Chichón's initial explosion. A dense upper tropospheric eruption cloud drifts ENE, and a more diffuse cloud drifts WSW, probably in the mid-troposphere.

Heavy ashfall was reported from towns near the volcano. At Pichucalco, ~20 km NE of the summit, 15 cm of ash was reported, and 5 cm of ash fell at Villahermosa (population 100,000), 70 km NE of the volcano. Residents of Nicapa, a village on the NE flank, took refuge in a church that was toppled by a M 3.5 earthquake, killing 10 people and injuring about 200. Initial estimates of the number of additional deaths varied, ranging as high as 100, and many more were probably killed on the SW flank during this or subsequent eruptions (see 5 paragraphs below). Most of the casualties on the N flank were reportedly caused by fires started by incandescent airfall tephra. Tens of thousands of people fled the area. The heavy ashfall forced the closure of roads and the airports at Villahermosa and Tuxtla Gutiérrez (~ 70 km S of the volcano). Cocoa, coffee, and banana crops were destroyed, and the cattlemen's association requested that animals from a wide area be transported for butchering because ashfall had made grazing impossible.

Activity during 30 March-3 April 1982. A second but much smaller explosion was observed on the satellite imagery at about 0900 on 30 March. A thin plume drifted E about 120 km before dissipating. A somewhat larger explosion that was first visible at 1500 produced a cloud that rose into the mid-troposphere and moved about 350 km N. Activity was declining by 1900. Haze was widespread over central México, reducing visibility to about 8 km in México City ( ~ 650 km WNW of the volcano) and to only about 3 km in Tampico (~ 750 km NW of the volcano). A small explosion shortly before 1330 on 31 March produced a plume that reached the upper troposphere and blew to the E but dissipated quickly.

A small explosion during the early afternoon of 2 April ejected a mushroom-shaped cloud that rose to ~ 3.5 km altitude in 30 minutes. Satellite images showed renewed explosive activity early 3 April. An eruption column was emerging from the volcano by 0300 and blew to both the NE and SW. A series of gravity waves and acoustic signals from this activity were again recorded by Teledyne Geotech instruments near Dallas, Texas. The calculated start time for this activity was 0250 and signals continued for 14 minutes. As with the initial explosion 28 March, the powerful gravity waves generated by this event indicated that the eruption column struck the tropopause forcefully. Smaller explosions, calculated to have begun at 0312, generated acoustic waves and a single gravity wave that were received near Dallas for 10 minutes. During the next 5 hours, ash drifted over N Guatemala and Belize. At Nicapa, on the NE flank, 7.5 cm of new ash was reported and a haze of SO₂ was visible during the day. Explosive activity resumed about 2000. Acoustic data recorded by Teledyne Geotech indicated that explosions probably occurred every 2-3 minutes, generating a few initial gravity waves and a complex series of acoustic waves that continued for 48 minutes. The total acoustic energy of this activity was significantly greater than that produced by the early morning explosions, and the eruption plume was denser and probably rose somewhat higher. It was initially elongate NE-SW and drifted over S México, N Guatemala and Belize. By noon the next day, a faint plume extended to about 25°N, 79°W, almost to Cuba, and lower altitude material, probably at only ~ 1.5 km, was drifting directly northward along the 95°W meridian.

Activity during 4 April 1982. A stronger explosion, possibly larger than the initial event on 28 March, first appeared on the NOAA geostationary weather satellite image returned at 0530 on 4 April and was reported by ground observers to have started at 0522. An infrared image 3.5 hours later showed a temperature of -76°C at the top of the eruption cloud, corresponding to an altitude of 16.8 km, identical to the altitude measured from the 28 March plume. Wind speeds near the volcano apparently remained relatively low and most of the cloud remained over S México and N Guatemala more than 24 hours later. In Pichucalco (~ 20 km NE of the summit) incandescent tephra could be seen rising from the volcano and the ash cloud darkened the sky during the morning as though it were night. Felt earthquakes were also reported early 4 April. At Ixtacomitán, 18 km ENE of the summit, there was a heavy fall of tephra no larger than 4 cm in diameter and the army was sent to evacuate 3,000 residents. No casualties were reported. All villages within 15 km of the summit had previously been evacuated and tens of thousands of people had fled their homes. Government officials reported ashfall over an area of 24,000 km² and crop damage of $55,000,000.

A pumice flow deposit from the 4 April eruption extended ~ 5 km NE from the summit, terminating ~ 2 km from Nicapa. At its distal end, the deposit was about 100 m wide and 3 m thick and contained pumice blocks 1 m in diameter. Temperatures measured by a thermocouple at 40 cm depth on 8 April averaged 360°C, and were as high as 402°C. The pumice flow deposit appeared to have been emplaced as two separate events in rapid succession. Shortly afterward, an ash flow flattened trees in the valley surrounding the pumice flow deposit and left a relatively thin layer of ash that had a temperature of 94°C at 10 cm depth 3 days later.

Airfall tephra thickness in Nicapa, 7 km NE of the summit, totaled 25-40 cm [but see 7:4] after the 4 April eruption. Bombs as large as 50-60 cm in diameter had made numerous holes in the roofs of houses and many other roofs had collapsed. In hand specimen, the tephra appeared to be a crystal-rich andesite or dacite containing hornblende and considerable feldspar. In Ostuacán, 12.5 km NW of the summit, tephra was 15-20 cm thick after the 4 April eruption, including pumice as large as 15 cm in diameter. Many roofs had been destroyed. Extreme heat made it impossible to approach the village of Francisco León, 5 km SW of the summit. Midway between Ostuacán and Francisco León, a river was boiling and flattened trees could be seen upslope. Geologists thought it was likely that pyroclastic flows had moved through the area. Of the roughly 1,000 residents of Francisco León, about half had reportedly left before the eruption because of the many felt earthquakes in February and March, but the remainder were missing in early April. A helicopter flight over the village during the first week in April revealed no signs of life. Because of the danger of mudflows when the rainy season begins around the end of April, authorities established a prohibited zone extending outward 10 km from the summit.

By 5 April, the low-altitude plume from the second 3 April explosion had reached the S Texas coast and Brownsville reported visibility of only 6.5 km in haze. A few flights into small S Texas airports were cancelled, but winds initially forced most of this material into the Gulf of México. Low-altitude (1.5-2 km) ejecta from the 4 April explosion also moved northward, and a slight change in wind direction blew the ash cloud further N and inland over Texas by late 7 April. A light ashfall occurred in Houston during the night of 7-8 April and samples were collected for analysis by NASA geologists.

Activity during 5-11 April 1982. A plume generated by a smaller explosion was observed on satellite imagery at 1130 on 5 April. Ground observers reported that the comparatively minor activity lasted about 3 hours and that no incandescent tephra was ejected. A similar but possibly slightly larger explosion could be seen on the satellite image returned at 0930 on 6 April. Geologists reported that earthquakes as strong as magnitude 1.5 were recorded about every 3 minutes 6 April. Geologists working a few km NE of the summit reported that about 2 mm of wet ash fell at about 1000 on 8 April and 1130 on the 9th. Satellite images returned at 0728 on 9 April and 0238 on 10 April both showed small diffuse plumes, drifitng NNE and SSE respectively.

Data from laser radar (lidar) measurements at Mauna Loa Observatory, Hawaii (about 19.5°N, 155.6°W) during the nights of 9-10 and 10-11 April indicated that El Chichón had injected large quantities of volcanic material into the stratosphere. Several layers were detected, with strongest backscattering at an altitude of 25.7 km. Analysis of wind conditions at 25 km altitude in Hawaii and México indicated a likely drift of ~ 5-7 m/s (roughly 430-600 km/day) towards the W, which would carry volcanic debris from El Chichón to Hawaii in 1.5 to 2 weeks. Inspection of a satellite image returned late 11 April showed a moderately dense cloud extending from México to just W of Hawaii, spreading from roughly 300 km wide near the Mexican coast to nearly 850 km near its distal end.

No previous eruptions of El Chichón are known in historic time. Before the 1982 eruption, the volcano was heavily forested, with a shallow crater, 1,900 X 900 m, elongate NNW-SSE. Solfataras and hot springs were present in the crater and on the flanks. Müllerried (1933) describes voluminous airfall deposits from previous eruptions that he believed to be post-Pleistocene.

Reference. Müllerried, F.K.G., 1933, El Chichón, unico volcán en actividad en el sureste de México: Universidad de México, v. 5, no. 27, p. 156-170.

Geologic Background. El Chichón is a small, but powerful trachyandesitic tuff cone and lava dome complex that occupies an isolated part of the Chiapas region in SE México far from other Holocene volcanoes. Prior to 1982, this relatively unknown volcano was heavily forested and of no greater height than adjacent nonvolcanic peaks. The largest dome, the former summit of the volcano, was constructed within a 1.6 x 2 km summit crater created about 220,000 years ago. Two other large craters are located on the SW and SE flanks; a lava dome fills the SW crater, and an older dome is located on the NW flank. More than ten large explosive eruptions have occurred since the mid-Holocene. The powerful 1982 explosive eruptions of high-sulfur, anhydrite-bearing magma destroyed the summit lava dome and were accompanied by pyroclastic flows and surges that devastated an area extending about 8 km around the volcano. The eruptions created a new 1-km-wide, 300-m-deep crater that now contains an acidic crater lake.

Information Contacts: C. Lomnitz, S. de la Cruz-Reyna, F. Medina, UNAM, México; M. Krafft, Cernay; D. Haller, C. Kadin, M. Matson, NOAA/NESS; A. Krueger, NOAA/NWS; F. Mauk, Teledyne Geotech; C. Wilson, Univ. of Alaska; K. Coulson, T. DeFoor, MLO, HI; C. Wood, NASA, Houston; Notimex Radio, México; New York Times; UPI.

The following report from James Luhr supplements the report from Mexican scientists in 07:01.

"The andesitic block lava that began to flow from the summit crater dome in early December was the first to descend Colima's S flank for hundreds of years. Geologists from the Univ. of California at Berkeley observed the flow from the S side of the volcano starting 18 January, about the time of the report in 7:1. The new lava was moving down a polished avalanche chute with a slope of about 36°. On 20 January, the flow had a simple tongue shape and was some 600 m long. By 3 March, the lava had reached 1 km length. Block-and-ash flows were common from the uppermost margins of the lobe with surprisingly few from the flow front. In several instances, sizeable (2,000 m² ?) areas on the flow surface suddenly shifted downslope 5-10 m, accompanied by only small amounts of ash and steam. This may be a major process of downslope movement of the flow. The active scree deposit below the lava contained blocks several meters in diameter, grading into a new sand and conglomerate wedge flooding the upper reaches of the Barranca Playa de Montegrande.

"Since the early part of Colima's lava eruption of 1975-76, through several episodes of dome growth, the andesitic magma has become progressively more basic. The latest lava continues this trend."

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: J. Luhr, Univ. of California, Berkeley.

"A series of small steam and ash eruptions occurred from mid-January to mid-February. During flights over Concepción on 18 February and 4 March we saw a moderate-sized continuous white vapor plume being emitted from the crater."

Geologic Background. Volcán Concepción is one of Nicaragua's highest and most active volcanoes. The symmetrical basaltic-to-dacitic stratovolcano forms the NW half of the dumbbell-shaped island of Ometepe in Lake Nicaragua and is connected to neighboring Madera volcano by a narrow isthmus. A steep-walled summit crater is 250 m deep and has a higher western rim. N-S-trending fractures on the flanks have produced chains of spatter cones, cinder cones, lava domes, and maars located on the NW, NE, SE, and southern sides extending in some cases down to Lake Nicaragua. Concepción was constructed above a basement of lake sediments, and the modern cone grew above a largely buried caldera, a small remnant of which forms a break in slope about halfway up the N flank. Frequent explosive eruptions during the past half century have increased the height of the summit significantly above that shown on current topographic maps and have kept the upper part of the volcano unvegetated.

Information Contacts: S. Williams, R. Stoiber, Dartmouth College; I. Menyailov, V. Shapar, IVP, Kamchatka; D. Fajardo B., INETER.

Fumarolic activity was observed on the morning of 19 March. A white plume was rising from the summit crater during the 3 hours the observer was on Nevados de Chillán Volcano, 160 km to the S. The only recorded eruption at Descabezado Grande, in 1932, was from a crater at its NE foot. Weak fumarolic activity has been reported on the W slope at about 3,500 m, but none had previously been observed in the main crater.

Geologic Background. Volcán Descabezado Grande is a late-Pleistocene to Holocene andesitic-to-rhyodacitic stratovolcano with a 1.4-km-wide ice-filled summit crater. Along with Cerro Azul, only 7 km to the S, Descabezado Grande lies at the center of a 20 x 30 km volcanic field. A lateral crater, which formed on the upper NNE flank in 1932 shortly after the end of the major 1932 eruption from nearby Quizapu volcano on the N flank of Cerro Azul, was the site of the only historical eruption. The Holocene Alto de las Mulas fissure on the lower NW flank produced young rhyodacitic lava flows. Numerous small late-Pleistocene to Holocene volcanic centers are located N of the volcano. The northernmost of these, Lengua de Vulcano (or Mondaca), produced a very youthful rhyodacitic lava flow that dammed the Río Lentué.

Information Contacts: H. Moreno R., Univ. de Chile, Santiago.

"The summit crater was visited by New Zealand and U.S. scientists during late November and December 1981, and on one day in late January 1982. The anorthoclase phonolite lava lake was still present and the pattern of activity was similar to that observed over the last 5 years.

"The lake was undergoing simple convection. Small Strombolian explosions continued at a frequency of 4-6/day. The eruptions were believed to originate from the Active Vent, adjacent to the lava lake. Many fresh bomb were found on the crater rim, suggesting that the eruptions were the strongest observed in the last 3 years. This may reflect an increase in distance between the lip of the Active Vent and the underlying magma level.

"The lava lake grew from small hornitos in 1972 to a semi-circular lake ~100 m long by 1976. Since then there has been little change in surface area, but a slight lowering in the lake level has occurred. No measurements of the magma column withdrawal were available but it was small, perhaps 5-10 m over the last 3 years. The withdrawal was possibly equivalent to the amount of material ejected by the small Strombolian eruptions. A deformation survey pattern set up in December 1980 was remeasured in December 1981; . . . data indicate [little change in the width] of the crater rim, [despite the] lowering of the column. Withdrawal was [however] suggested by the development of a semi-radial fracture, on the main crater floor, that parallels the inner crater rim."

Further References. Dibble, R.R., Kienle, J., Kyle, P.R., and Shibuya, K., 1984, Geophysical studies of Erebus volcano, Antarctica, from 1974 December to 1982 January, in Lynch, R.P. (ed.), Tenth Antarctic Issue: New Zealand Journal of Geology and Geophysics, v. 27, no. 4, p. 425-455.

Wiesnet, D.R., and D'Aguanno, J., 1982, Thermal imagery of Mount Erebus from the NOAA-6 satellite: Antarctic Journal of the United States, v. 17, no. 5, p. 32-34.

Geologic Background. Mount Erebus, the world's southernmost historically active volcano, overlooks the McMurdo research station on Ross Island. It is the largest of three major volcanoes forming the crudely triangular Ross Island. The summit of the dominantly phonolitic volcano has been modified by one or two generations of caldera formation. A summit plateau at about 3,200 m elevation marks the rim of the youngest caldera, which formed during the late-Pleistocene and within which the modern cone was constructed. An elliptical 500 x 600 m wide, 110-m-deep crater truncates the summit and contains an active lava lake within a 250-m-wide, 100-m-deep inner crater; other lava lakes are sometimes present. The glacier-covered volcano was erupting when first sighted by Captain James Ross in 1841. Continuous lava-lake activity with minor explosions, punctuated by occasional larger Strombolian explosions that eject bombs onto the crater rim, has been documented since 1972, but has probably been occurring for much of the volcano's recent history.

Information Contacts: P. Kyle, New Mexico Inst. of Mining & Tech.; P. Otway, NZGS, Wairakei.

A brief explosive eruption began before dawn 5 April, ejecting incandescent tephra and "stones as big as a human head" according to press reports. An image returned at 0700 by the Japanese geostationary weather satellite showed an eruption column about 50 km in diameter. The next available image, at 1410, showed that feeding of the eruption column had stopped and the plume had drifted about 250 km to the N. As much as 25 cm of ash fell on the flanks and ashfalls were reported from as far away as Garut, 35 km to the NW. The activity was accompanied by strong felt seismicity, and felt events continued in midafternoon. Two persons were killed and as many as 31,000 were evacuated, but most of the evacuees returned home within a few hours.

A second explosive eruption occurred during the night of 8-9 April, associated with at least one felt earthquake. Hot mud flowed at 60 km/hour as far as 11 km down the SE flank, buried houses in at least six villages, and destroyed a bridge over the Cikunir River, which emerges from a large breach in the SE side of the crater (figure 1). Officials said that only about half of the 8.6 x 10⁶ m³ of material in the crater had been ejected and feared that the steady rain falling on the area could trigger more mudflows. AFP reported eight persons dead, three missing, and 22 injured. UPI reported that many were burned or suffering from the effects of toxic volcanic gases. Authorities have forbidden entry into several areas where gases were seeping from cracks in the ground. The rice crop, within a month of its harvest, was destroyed.

Figure 1. Sketch map of Galunggung crater and vicinity, showing the Gaunug Jadi lava dome, Walirang ridge, major drainages, and flank towns. A temporary volcano observatory was established in Cikasasah, 7 km SE of the crater. From Katili and Sudradjat, 1984.

Geologic Background. The forested slopes Galunggung in western Java are cut by a large horseshoe-shaped caldera breached to the SE that has served to channel the products of recent eruptions in that direction. The "Ten Thousand Hills of Tasikmalaya" dotting the plain below the volcano are debris-avalanche hummocks from the collapse that formed the breached caldera about 4,200 years ago. Historical eruptions have been infrequent and restricted to the central vent near the caldera headwall, but have caused much devastation. The first historical eruption in 1822 produced pyroclastic flows and lahars that killed over 4,000 people. A strong explosive eruption during 1982-1983 caused severe economic disruption to nearby populated areas.

Information Contacts: D. Haller, NOAA; C. Dan Miller, USGS; Jakarta DRS; AFP; UPI.

Summit seismicity had increased to nearly normal daily counts by late December 1981. Since January, several very small intrusions (occasionally seismic but generally aseismic) have been detected by changes in tilt, gas emission, and fumarole temperatures in the E and SW rifts. By late March, tiltmeters showed that the summit area had recovered most of the roughly 100 µrad of deflation recorded during the intrusion of magma into the S summit region and SW rift 10-12 August. The inflation center was in the S caldera-upper SW rift area. A 45-minute swarm of 400-500 earthquakes that started about 1430 on 23 March indicated that magma was forcing open a new channel (or reopening an old one). The seismic swarm was not accompanied by any detectable ground deformation. Overall seismicity in the SW rift remained high in early April but seismicity in the E rift was still relatively unchanged.

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: N. Banks, HVO.

"A fairly low level of activity prevailed in early March, but in the second half of the month activity at both craters intensified. Crater 3 erupted incandescent tephra 18-22 March, accompanied by frequent explosive detonations and loud rumbling. From 22 March until the end of the month glow and incandescent tephra ejections from Crater 2 were seen on most nights. Dark eruption clouds were occasionally seen, and loud explosions and rumblings were heard. Seismicity was stronger from 18 March, and correlated with the intensified visible activity."

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.

"Strong eruptive activity occurred in 2 intervals in March, the first during several days at the beginning of the month. Spearheaded projections of tephra from Southern crater were observed on 2 and 3 March. Tephra ejections were less intense 4-7 March, but instability of the rapidly accumulated tephra caused avalanches of this material to descend from the summit into the SW valley. Inspections by volcanologists on 10 and 11 March suggested these avalanches were small. No significant changes in tiltmeter readings accompanied this eruptive phase, but seismicity showed a marked intensification on 5 March.

"Much stronger activity occurred near the end of the month. A paroxysmal eruption was observed at 1207 on 27 March. The dark grey-brown Vulcanian eruption cloud ascended to 6-7 km. Lightning flashes were seen in parts of the cloud. Strong Strombolian explosive activity followed the paroxysmal eruption at about 1215. The E side of the island experienced a brief period of darkness and tephra falls were locally severe, but the maximum thickness of the tephra deposit was probably only a few mm. Fragments up to 7 cm in size were collected at one village. Vegetation was strongly affected by the tephra fall and water supplies were polluted, but no structural damage was done to houses. A pyroclastic flow descended the SE valley during the eruption, but stopped about halfway to the coast.

"Seismicity was very strong at the time of the eruption and was still high at month's end. Before and after the eruption discrete B-type earthquakes occurred at the rate of about 1 per minute. For about 15 hours from the commencement of visible activity, discontinuous seismic tremor was recorded. No significant changes were evident in tiltmeter readings."

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.

"Bright yellow incandescence was plainly visible at night in Santiago Crater in early March. No change had occurred except for a small collapse of the inner crater walls. The huge gas plume still poured out continuously."

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras caldera and is itself a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The Nindirí and Masaya cones, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6,500 years ago. Historical lava flows cover much of the caldera floor and there is a lake at the far eastern end. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals have caused health hazards and crop damage.

Information Contacts: S. Williams and R. Stoiber, Dartmouth College; I. Menyailov and V. Shapar, IVP, Kamchatka; D. Fajardo B., INETER.

Seismic activity that began in March 1981 ceased in December. Only a few low-energy events per month have been recorded since. Bathymetric reconnaissance around the island found evidence of an elliptical opening at 1,700 m below sea level on the SE flank, in the same location as the initial events of the earthquake swarm. RSP scientists interpreted the opening as a possible crater and the activity as a magmatic intrusion or eruption.

Geologic Background. The 1.5-km-wide, steep-sided island of Mehetia, the youngest and SE-most of the Society Islands, lacks a well-developed fringing coral reef. The ~400-m-high island (known as Meetia or Meketia in the Tahitian and Tuamotuan languages, respectively) is the summit of a large volcano that rises 4000 m from the sea floor. An older edifice is formed of a lava flow sequence overlain by hydromagmatic deposits and strombolian ejecta. A well-preserved Holocene crater, 150 m wide and 80 m deep, is located NW of the summit and has been the source of the youngest lava flows on the island (Binard et al., 1993). Polynesian legends mention "large fires," and the lack of vegetation on some lava flows suggests that the latest activity occurred within the last 2000 years (Talandier and Custer, 1976). Other recent activity originated from a submarine crater at 2500-2700 m depth on the SE flank.

Information Contacts: J.M. Talandier, Lab. de Géophysique, Tahiti.

"Paolo Pisani, a consultant to INE, reported finding four previously unknown low-temperature hot springs on the S side of Mombacho. These are not believed to be new, however."

Geologic Background. Mombacho is an andesitic and basaltic stratovolcano on the shores of Lake Nicaragua south of the city of Granada that has undergone edifice collapse on several occasions. Two large horseshoe-shaped craters formed by edifice failure cut the summit on the NE and S flanks. The NE-flank scarp was the source of a large debris avalanche that produced an arcuate peninsula and a cluster of small islands (Las Isletas) in Lake Nicaragua. Two small, well-preserved cinder cones are located on the volcano's lower N flank. The only reported historical activity was in 1570, when a debris avalanche destroyed a village on the south side of the volcano. Although there were contemporary reports of an explosion, there is no direct evidence that the avalanche was accompanied by an eruption. Fumarolic fields and hot springs are found within the two collapse scarps and on the upper N flank.

Information Contacts: S. Williams, R. Stoiber, Dartmouth College; I. Menyailov, V. Shapar, IVP, Kamchatka; D. Fajardo B., INETER.

"Temperatures of the crater fumaroles, measured on 13 March, were as high as 800°C. Heating has occurred since December 1981, but it was not apparent whether this was a result of dry-season effects or was a true increase in heat. A small gas plume was continuously emitted."

Further Reference. Menyailov, I.A., Nikitina, L.P., Shapar, V.N., Grinenko, V.A., Buachidze, G.I., Stoiber, R., and Williams, S., 1986, The chemistry, metal content, and isotope composition of fumarolic gases from Momotombo volcano, Nicaragua, in 1982: Volcanology and Seismology, no. 2, p. 60-70.

Geologic Background. Momotombo is a young stratovolcano that rises prominently above the NW shore of Lake Managua, forming one of Nicaragua's most familiar landmarks. Momotombo began growing about 4500 years ago at the SE end of the Marrabios Range and consists of a somma from an older edifice that is surmounted by a symmetrical younger cone with a 150 x 250 m wide summit crater. Young lava flows extend down the NW flank into the 4-km-wide Monte Galán caldera. The youthful cone of Momotombito forms an island offshore in Lake Managua. Momotombo has a long record of Strombolian eruptions, punctuated by occasional stronger explosive activity. The latest eruption, in 1905, produced a lava flow that traveled from the summit to the lower NE base. A small black plume was seen above the crater after a 10 April 1996 earthquake, but later observations noted no significant changes in the crater. A major geothermal field is located on the south flank.

Information Contacts: S. Williams and R. Stoiber, Dartmouth College; I. Menyailov and V. Shapar, IVP, Kamchatka; D. Fajardo B., INETER.

"A very small gas plume was being emitted from a group of fumaroles on the NW inner crater wall. Maximum fumarole temperatures of 505°C were measured on 3 March."

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

Information Contacts: S. Williams and R. Stoiber, Dartmouth College; I. Menyailov and V. Shapar, IVP, Kamchatka; D. Fajardo B., INETER.

Rodolfo Alvarado reported that as of 4 March lava continued to flow from a hornito on the upper SW flank.

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: R. Alvarado, Inst. Nacional de Electrificación; T. Casadevall, USGS.

Seismic activity, Crater Lake temperature, and strength and frequency of the lake's hydrothermal eruptions declined in February and early March, but increased again in mid-March.

Summit-area monitoring by NZGS personnel 11 February showed little change since the visit 6 days earlier. Only 4 small explosions from Crater Lake were noted in 8.5 hours. The largest, lasting about a minute, ejected three 30 m-high columns of muddy black water, which collapsed onto the lake surface to form small base surges. The temperature of the lake water had risen slightly, from 49° to 50.5°C. Distance-measuring and tilt surveys showed no significant changes. The next visit by geologists, on 5 March, lasted 4 hours, but no explosions were observed nor was there any evidence of new ash around the lake. However, climbers saw two very small explosions the next day. The lake temperature had dropped almost 10°C, to 41°C, in about 3 weeks. Only minor tilt changes were observed.

Park rangers received a report of an eruption at about 1215 on 16 March that generated a steam cloud filling the entire crater area to an estimated height of 1 km. NZGS personnel saw one steam explosion during a 2.5-hour visit 18 March. Continuous steaming of Crater Lake was reported during the early morning of 20 March. Geologists returned 23 March and observed 5 explosions from Crater Lake in 10 hours. Four were relatively small, producing columns of water 5-30 m high. However, a larger explosion at about 1430 produced large waves, and jets of black water that rose more than 100 m above the lake surface. Lake temperature had increased 6° since 5 March, to 47°C. No significant tilt changes were detected during surveys 23 and 26 March. A single Crater Lake explosion was observed during 5 hours of NZGS fieldwork 26 March.

The following is from reports by J.H. Latter. [For Latter's definitive analysis of this activity, see New Zealand Volcanological Record, no. 12, p. 31-37].

A period of higher-amplitude volcanic tremor began about 1600 on 14 January, climaxed 26 January and ended 30 January. Since then, strong tremor has been recorded only during an 8-hour period 10-11 February. Through 25 January, the tremor was dominantly high-frequency (3-4 Hz), suggesting that its origin was very shallow, but since then the strongest tremor has been mainly low-frequency (1-2 Hz). The focus of activity has evidently moved down to a lower level within the volcano. Latter notes that this could either be due to a process of withdrawal of magma, which up to now has been standing at a high level, or to the arrival of fresh magma from greater depths at the normal volcanic focus about 1 km below Crater Lake.

Only small volcanic earthquakes occurred between mid January and the end of February. A marked swarm of low-frequency volcanic earthquakes (B-type) took place, at about the normal focus, 20-22 February; activity peaked about 1200 on 20 February with several magnitude 2.1 earthquakes. This magnitude was relatively low, and it was not known whether the events were accompanied by eruptions. Latter notes that it was likely that the B-type swarm represented a minor stoppage in the volcano's conduits, but that the stoppage must have been rather weak since it was evidently overcome by quite small-magnitude earthquakes. Similar but smaller events took place 21-22 January (when no eruptions took place), and 3 and 14 February.

Shallower seismic activity peaked 23-25 January, when high-frequency tremor was fairly strong, preceded by the largest magnitude volcanic earthquakes at this level since 24 December (the so-called C-types, two ML 2.0 events). A smaller C-type earthquake (ML 1.8) occurred 28 January; since then there have been few, the largest only ML 1.6 (on 26 February). During the declining stages of activity 24-25 January, 31 January, and 24-26 February (after the B-type swarm mentioned above), high-frequency roof rock earthquakes with magnitudes between 1.6 and 1.9 have been detected.

Latter notes that "the best fit for B-type earthquake data suggests a mean depth of origin of 0.77 km beneath the floor of Crater Lake. Adopting an explosion model for the earthquakes, and equating the travel time (origin time of earthquake minus observed eruption time) of 8.5 seconds with upward movement of gas from this depth, gives an average velocity of the gas column of about 90 m/s. Applying the same velocity to the onsets of C-type earthquakes yields a depth of origin of about 250 m below the floor of the lake. This estimate, though crude, is probably of the right order, and suggests that magma had risen during the increased activity (since September 1981) by about 500 m.

"The decline in seismic activity at the end of January, and the change to tremor of deeper origin, appears more likely to have been due to withdrawal of magma than to a major blockage of conduits within the volcano. Although lake temperature has declined, partly no doubt because of the accelerated melt around Crater Lake during the long spell of fine weather, the volcano still gives the impression of being 'open vent.' The small magnitude (ML 2.1) of the largest earthquakes occurring since activity declined suggests that only minor blockages have formed, and have been fairly quickly overcome."

High-level (high-frequency) tremor continued 1-23 March, although none was recorded 4 or 7-10 March. Tremor was strong 11-16 March, peaking on the 13th, but remained much weaker than in late January. Occasional episodes of low-frequency tremor were recorded during the first 3 weeks in March, some lasting for several hours. These were interpreted by Latter as indicating movement at the base of the magma column, at least 500 m tall, that may extend from 200-300 to 700-800 m below Crater Lake. A swarm of B- and C-type earthquakes began on 15 March, culminating in a 6-minute B-type sequence 21 March that reached a magnitude of 2.7, the largest volcanic earthquake at Ruapehu since 2 January. Clouds obscured the volcano 21 March, so it was impossible to determine if an eruption accompanied this event. The swarm was continuing as of 23 March.

Geologic Background. Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The dominantly andesitic 110 km3 volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 ring plain of volcaniclastic debris, including the Murimoto debris-avalanche deposit on the NW flank. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. A single historically active vent, Crater Lake (Te Wai a-moe), is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene. Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent, and tephra characteristics suggest that the crater lake may have formed as early as 3,000 years ago. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys.

Information Contacts: J. Latter, DSIR, Wellington; I. Nairn and B. Scott, NZGS, Rotorua; P. Otway, NZGS, Wairakei; R. Beetham, NZGS, Turangi.

"During a crater visit 9 March we found that the small white vapor plume was almost entirely made up of water vapor, with little acid gas content. We were unable to reach the fumaroles, but Bruce Gemmell of Dartmouth College measured fumarole temperatures as high as 590°C in December 1981.

Geologic Background. The San Cristóbal volcanic complex, consisting of five principal volcanic edifices, forms the NW end of the Marrabios Range. The symmetrical 1745-m-high youngest cone, named San Cristóbal (also known as El Viejo), is Nicaragua's highest volcano and is capped by a 500 x 600 m wide crater. El Chonco, with several flank lava domes, is located 4 km W of San Cristóbal; it and the eroded Moyotepe volcano, 4 km NE of San Cristóbal, are of Pleistocene age. Volcán Casita, containing an elongated summit crater, lies immediately east of San Cristóbal and was the site of a catastrophic landslide and lahar in 1998. The Plio-Pleistocene La Pelona caldera is located at the eastern end of the complex. Historical eruptions from San Cristóbal, consisting of small-to-moderate explosive activity, have been reported since the 16th century. Some other 16th-century eruptions attributed to Casita volcano are uncertain and may pertain to other Marrabios Range volcanoes.

Information Contacts: S. Williams and R. Stoiber, Dartmouth College, I. Menyailov and V. Shaper, IVP, Kamchatka; D Fajardo, INETER.

The first explosive eruption in 17 months ejected a tephra cloud that briefly rose to more than 13.5 km altitude on 19 March. A directed blast from near the base of the lava dome spawned a multilobate avalanche that flowed several kilometers down the volcano's N flank. A mudflow moved down the N fork of the Toutle River, but caused only minor damage. Clouds produced by explosions 20-21 March were much smaller and contained only a little tephra. Lava extrusion began 21 March, adding a new lobe to the SE side of the crater's composite dome. No injuries resulted. Smaller explosions 4-5 April were followed by the extrusion of a second lobe onto the N side of the dome.

Premonitory activity during 26 February-18 March. Seismic activity began to increase 3 weeks before the March eruption and included a substantial number of deeper events, in contrast to previous dome extrusion episodes, which were typically preceded by only a few days of shallow seismicity. Earthquakes occurred in two zones, at about 1-3 and 4-12 km depth (below average seismic station elevation of about 1 km above sea level). An average of one event per day stronger than M 1.5 occurred in the shallow zone 26 February-12 March, with the rate of energy release remaining relatively constant. Most of the deeper events had negative magnitudes, and energy release from the deeper zone was about 2 orders of magnitude less than from the shallow zone. The end of deeper seismicity 12 March coincided with both an increase in the number of events (to an average of 3/day of m_b > 1.5 through 17 March) and a jump in the rate of energy release.

Deformation in the crater accelerated rapidly in mid-March. Between 17 and 18 March, uplift of an area near the SW base of the dome accompanied about 30 cm of movement along a nearby thrust, higher than any rate of crater-floor thrust movement previously measured at Mt. St. Helens. Outward displacement rate of the N-crater rampart reached 32 cm/day, and a portion of the dome itself expanded 42 cm in the 24 hours ending shortly before the eruption. However, no deformation of the edifice as a whole was detected by measurements outside the crater. For the first 18 days of March, the rate of SO₂ emission averaged 110 t/d, remaining at about the same level as it has since the lava extrusion episode of October-November 1981.

After remaining approximately constant for several days, the rate of seismic energy release increased again about noon 18 March, and 14 events larger than M 1.5 were recorded in the next 24 hours. A few brief (1-2 minutes or less) periods of low-level harmonic tremor were recorded during the afternoon of 19 March, as were 20 discrete events stronger than M 1.5. SO₂ emission doubled to about 230 t/d. Tilt measured about 300 m N of the dome reversed about 1900 and seismic data showed that explosions began at 1928. After 2 minutes of initial seismicity there was a brief hiatus, followed by about 40 minutes of activity that declined gradually.

Explosive eruption on 19 March. A vertical tephra column, probably ejected from a vent near the center of the dome, reached its maximum altitude of more than 13.5 km (as measured by radar at Portland airport) at 1933 on 19 March. By 1950, radar data indicated that the altitude of the top of the column had dropped to 10.5 km. An infrared image returned at 2003 by a NOAA geostationary weather satellite showed a cloud-top temperature of -35°C, yielding an altitude of about 7 km. According to radar data, the eruption column contained 20-60 times less tephra than the cloud produced by the last significant explosion, in October 1980 [but see SEAN 07:04]. Ash blew SE at about 30 km/hr. Light ashfalls were reported as much as 80 km away, but caused only minor disruptions to auto travel. Bombs up to 3 m across fell 200-300 m from the dome. Frothy pumice (density about 0.8) fell 8 km away. Smaller explosions occurred at 0135 the next morning, when radar detected a cloud, containing a little ash, that rose to about 5.5 km altitude, and a small steam-and-ash column was ejected at 0415 on 21 March.

[Further investigation revealed a more complex sequence of events than was originally reported in the Bulletin. The following has been modified by R. Waitt and D. Swanson. A detailed description can be found in Waitt and others, 1983.] The initial avalanche apparently resulted from a directed blast that emerged from near the SW base of the dome. This blast destroyed the dome's SW margin, and struck the S wall of the crater, removing snow cover and rock. The resulting mixture of snow granules (0.5-2 mm in diameter), hot pumice, and lithic material [descended] the [E and] S crater walls, [flowed around] the E and W sides of the dome, joined N of it, then flowed out through the breach in the N side of the crater and continued for several kilometers down the N flank. Fed by water from the avalanche . . . and a [transient] pond [behind the dome], a complex mudflow sequence moved down the N fork of the Toutle River, which flows W . . . at the N foot of the volcano. Upstream deposits showed evidence of two distinct pulses, but gauges downstream registered only one well-defined peak. About 70 families were evacuated from the Toutle valley, but no major damage was reported. The mudflow buried trucks at an earthen flood-control dam and breached its S side. Three storms earlier this winter had produced higher peak river stages at Castle Rock, roughly 70 km downstream. Floods produced by these storms had breached the N side of the dam and the combined damage has essentially destroyed the dam's effectiveness.

Lava extrusion on 20-24 March. Seismographs began to record rockfall events, probably associated with extrusion of a new lobe of lava, during the evening of 20 March. This activity slowly increased, and aerial observers first saw the new lobe during the night. It emerged from a vent at the top of the most recent lobe (extruded October-November 1981) and flowed down the SE side of the dome, barely reaching the crater floor. Growth was fairly rapid through 23 March, but there was little apparent increase in size between the 23rd and 24th, and the number of rockfall events was noticeably declining early 24 March. By the time growth slowed, the volume of new lava appeared to be greater than that for any previous lobe. SO₂ emission increased to 370 t/d 21 March, about 3.5 times background levels, but had dropped to 90 t/d by 24 March.

However, before dawn on 24 March new glowing radial cracks were observed in older portions of the dome. The N-crater rampart and the N side of the dome showed 12 cm of outward movement between the mornings of 23 and 24 March and 16-18 cm during field work 24 March. No unusual seismicity accompanied the movement, nor was any significant tilt measured N of the dome, but at similar stages of previous dome extrusion episodes, little or no deformation of any kind has been observed.

Poor weather prevented geologists from entering the crater again until early April. Seismicity remained at low levels through the end of March. SO₂ emission dropped to about background levels 24 March, but by the next measurement, on 28 March, had increased to about 200 t/d and reached a rate of 440 t/d during a small gas explosion. On 29 March, the rate was still high, at 180 t/d, but weather conditions prevented further measurements until a week later. Seismographs began to record a few very small, brief (20 seconds or less) harmonic events 1-2 April, and these became more numerous 3-4 April. Occasional low-frequency earthquakes began to appear on the seismic records 3 April. A few were recorded the next morning, then these events increased to about 2 per hour after 1400. A further increase in seismicity was noted in the early evening, and at about 2000, University of Washington seismologists alerted USFS and Washington state officials that an eruption was imminent.

Renewed explosions and dome growth during 3-12 April. [A large rock avalanche and] explosive activity began at 2052 on 3 April, and three seismic pulses occurred in 3 minutes. A plume containing a little ash rose to 8.5 km (altitude data from Portland airport radar) and drifted NE. Minor ashfall was reported in Packwood, 65 km away. Seismographs recorded pulsating activity for the next several hours, then a pair of stronger events at 0035 and 0039 that accompanied the ejection of an ash-poor cloud to almost 10 km altitude (as measured by Portland airport radar). A small mudflow emerged from the breach in the N side of the crater and flowed a short distance down the N flank. After 10-15 minutes, seismicity briefly dropped to background levels, but apparent harmonic tremor began about 0230 and continued for the next 14 hours. Gas and/or rockfall events began at roughly 0330 and became increasingly frequent during the next several hours.

Before dawn, geologists observed a new lobe of lava on the N side of the composite dome. Growth of this lobe continued through 8 April, but had slowed considerably by the 9th. The April lava, perched on the N side of the dome, looked very similar to the October 1981 lobe but appeared to be smaller than any previously extruded. Gas emission events, including one that sent a plume to 7 km altitude at 1719 on 5 April, could be seen on seismic records, as well as large avalanche events as large chunks fell off the dome. Seismicity declined gradually as lava extrusion continued and had dropped to low levels by 12 April. By 10 April, deformation in the crater had decreased to levels typical of periods between extrusion episodes. As lava extrusion was beginning early 5 April, the rate of SO₂ emission increased to 900 t/d, dropping to 500 t/d during the afternoon, and to 390 t/d, a typical value during dome extrusion episodes, on 6 April. No gas data were available 7 April but SO₂ emission had returned to background levels 8-10 April.

Further Reference. Waitt, R.B., Pierson, T.C., MacLeod, N.S., and Janda, R.J., 1983, Eruption-Triggered Avalanche, Flood, and Lahar at Mount St. Helens-Effects of Winter Snowpack: Science, v. 221, no. 4618, 1394-1396 p.

Geologic Background. Prior to 1980, Mount St. Helens formed a conical, youthful volcano sometimes known as the Fuji-san of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km horseshoe-shaped crater now partially filled by a lava dome. Mount St. Helens was formed during nine eruptive periods beginning about 40-50,000 years ago and has been the most active volcano in the Cascade Range during the Holocene. Prior to 2200 years ago, tephra, lava domes, and pyroclastic flows were erupted, forming the older St. Helens edifice, but few lava flows extended beyond the base of the volcano. The modern edifice was constructed during the last 2200 years, when the volcano produced basaltic as well as andesitic and dacitic products from summit and flank vents. Historical eruptions in the 19th century originated from the Goat Rocks area on the north flank, and were witnessed by early settlers.

Information Contacts: T. Casadevall, R. Janda, C. Newhall, D. Swanson, R. Waitt, USGS CVO, Vancouver, WA; C. Boyko, S. Malone, E. Endo, C. Weaver, University of Washington; O. Karst, NOAA/NESS; D. Harris, University of Alberta; R. Bailey, USGS, Reston, VA.

"The eruption sequence that began in mid-December 1981 appears to have drawn to a close. The last confirmed eruption occurred at approximately noon on 2 March, sending ash to Corinto and beyond. Since then the volcano has also been seismically quiet. A crater visit on 19 March revealed continued collapse of the crater walls. The vent was clogged with boulders and a ring of strongly jetting fumaroles was established around its margins."

Further Reference. Williams, S.N., 1985, La Erupción del Volcán Telica, Nicaragua, 1982; Boletín de Vulcanología (Universidad Nacional, Heredia, Costa Rica), no. 15, p. 10-19.

Geologic Background. Telica, one of Nicaragua's most active volcanoes, has erupted frequently since the beginning of the Spanish era. This volcano group consists of several interlocking cones and vents with a general NW alignment. Sixteenth-century eruptions were reported at symmetrical Santa Clara volcano at the SW end of the group. However, its eroded and breached crater has been covered by forests throughout historical time, and these eruptions may have originated from Telica, whose upper slopes in contrast are unvegetated. The steep-sided cone of Telica is truncated by a 700-m-wide double crater; the southern crater, the source of recent eruptions, is 120 m deep. El Liston, immediately E, has several nested craters. The fumaroles and boiling mudpots of Hervideros de San Jacinto, SE of Telica, form a prominent geothermal area frequented by tourists, and geothermal exploration has occurred nearby.

Information Contacts: S. Williams and R. Stoiber, Dartmouth College; I. Menyailov and V. N. Shapar, IVP, Kamchatka; D. Fajardo B., INETER.

"The crustal deformation and local seismicity at Usu continued through 1981. The monthly number of recorded seismic events, having gradually declined since the major 1977 eruption, dropped further to about 308/month in 1981 but remained at about this level through the year (figure 20 and table 4). Gradually weakening steam activity from the craters formed in 1978 has been observed. Around these craters, there have been many fumaroles that vigorously emitted white vapor; highest temperature was 643°C in August 1981. According to the data from the Usu Volcano Observatory (Hokkaido University) the rate of uplift of the Usu-Shinzan cryptodome decreased from about 2/cm per day in 1980 to about 0.8 cm/day in 1981. The northward lateral movement of the N flank continued at a similar rate."

Figure 20. Graph of monthly numbers of recorded (white bars) and felt (black bars) seismic events at Usu, August 1977-December 1981, supplied by I. Yokoyama. [Eruptive] activity during a particular month is indicated by arrows. Earthquakes in August 1977 numbered at least 25,000.

Geologic Background. Usuzan, one of Hokkaido's most well-known volcanoes, is a small stratovolcano located astride the southern topographic rim of the 110,000-year-old Toya caldera. The center of the 10-km-wide, lake-filled caldera contains Nakajima, a group of forested Pleistocene andesitic lava domes. The summit of the basaltic-to-andesitic edifice of Usu is cut by a somma formed about 20-30,000 years ago when collapse of the volcano produced a debris avalanche that reached the sea. Dacitic domes erupted along two NW-SE-trending lines fill and flank the summit caldera. Three of these domes, O-Usu, Ko-Usu and Showashinzan, along with seven crypto-domes, were erupted during historical time. The 1663 eruption of Usu was one of the largest in Hokkaido during historical time. The war-time growth of Showashinzan from 1943-45 was painstakingly documented by the local postmaster, who created the first detailed record of growth of a lava dome.

Information Contacts: I. Yokoyama, Hokkaido Univ.

The volcano's 17-km-long Bilchenok Glacier has begun to advance. The glacier, located in Plosky's caldera, has three large ice cascades on its NW flank. Previous surges of this glacier occurred in 1959, 1976, and 1977. Photo reconaissance flights over Kamchatkan glaciers 10-11 March revealed that Bilchenok's front was 1 km from its 1980 position and 500 m from the 1959 maximum surge. Its surface was broken into blocks, and rupture disturbances of the snow cover were observed.

Further Reference. Ovsyannikov, A.A., Khrenov, A.P., and Murav'yeva, Y.D., 1985, Recent activity of the Dal'nya Ploskaya volcano: Volcanology and Seismology, no. 5, p. 97-98.

Geologic Background. Ushkovsky volcano (formerly known as Plosky) is a large compound volcanic massif located at the NW end of the Kliuchevskaya volcano group. It consists of the flat-topped Ushkovsky (Daljny Plosky), which is capped by an ice-filled 4.5 x 5.5 km caldera, and the adjacent slightly higher peak of Krestovsky (Blizhny Plosky) volcano. Two glacier-clad cinder cones with large summit craters form a high point within the Ushkovsky caldera. Linear zones of cinder cones are found on the SW and NE flanks and on lowlands to the west. The younger caldera at the summit of Daljny was formed in association with the eruption of large lava flows and pyroclastic material from the Lavovy Shish cinder cones at the foot of the volcano about 8600 years ago. The only known historical activity was an explosive eruption from the summit cone in 1890.

Information Contacts: V. Vinogradov, IVP.