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).

Mt. Cameroon began erupting during the night of 28 May 2000. On 29 May, following a violent explosion, red-tinged fumaroles were observed at an elevation of 3,300 m. On May 30, an earthquake shook the provincial capital of Buea, located to the SE of the volcano. Volcanic ash and gases that were vented during the course of the eruption were blown to the W coast by NE winds.

The eruption occurred at two principle sites separated by 3 km. These sites lie on the central portion of the upper SE flank, upslope of the town of Buea and in the vicinity of vents active in 1904 and 1922. The first site, located at latitude 04°12'40" N and longitude 09°10'45" E and an elevation of 4,000 m, is composed of two craters aligned NE to SW. Juvenile material comprises less than 1% of the total volume of the pyroclastic material surrounding the vents. The larger pyroclasts were found farther away from the vent, while the finer material was deposited closest to the crater. The NE crater, with slopes that are fissured and unstable, showed relatively little activity compared with its neighbor to the SW. The eruption at the SW crater was characterized by sporadic explosions of gas and pyroclastic materials, including juvenile materials such as volcanic bombs, blocks, and scoria. There were no lava flows reported from this site.

The second vent lies at 04°11'15" N and 09°10' E at an elevation of 3,300 m. This site consists of a large open fissure oriented at N 40° E. The following features at the site run NE to SW along the fissure: two lava lakes surrounded by spatter cones, two craters in the process of forming cones with fluid lava, and several hectometer-sized (104 m²) fissure lava flows. The spatter cones are about 40 m from the associated lava lake.

The NE lava lake forms a 60 x 40 m ellipse. This lava lake was the source of the lava flows that moved towards the ocean to the S and away from many of the inhabited parts of the volcano's flanks. There were sporadic explosions at the lava lakes.

Contrary to some media reports that suggested the lava was advancing at rates up to 20-25 m/hour, a scientist from the Ministry of Territorial Administration reported that the lava moved at ~5 m/hour. The scientist also indicated that the lava flows were far from populated areas.

However, on 8 June, various news reports placed the lava flows within 5-7 km of the town of Buea. Reuters reported on 9 June that geologist Isaac Konifer Nijah, a member of a scientific team monitoring the volcano, considered the Buea area a high risk zone. Concern for the residents in this town prompted an evacuation plan for ~3,000 residents to the towns of Limbe to the SW and Tiko to the SE. However, the evacuation plan was not implemented because on 10 June the lava front halted its advance on the town.

The BBC reported that on 19 June, the Prime Minister of Cameroon, Peter Mafany Musonge, visited the village of Bokwango, which is on the outskirts of Buea. News reports stated that at this point the lava flows were 4 km from the edge of the village. However, no new activity had been reported by seismologists for several days preceding the visit.

Thanks to Pierre Vincent and the company ELF Aquitaine, an initially proprietary report on Mount Cameroon geology, eruptions, and hazards (including a geological map) were recently made available to the Smithsonian (Vincent, 1980). The same author has some earlier published work on this volcano (Vincent, 1971).

References. Vincent, Pierre M., 1980, GNL Project in Cameroon, geology and volcanology of Mount Cameroon: Report for ELF Aquitaine (in French), 11 p., appendices, and map (plate).

Vincent, Pierre M., 1971, New data about Cameroon Mountain volcano: 6th Colloquium on African Geology, Leicester, UK, April 1971, Jour. Geol. Soc. London 127, p. 414-415.

Geologic Background. Mount Cameroon, one of Africa's largest volcanoes, rises above the coast of west Cameroon. The massive steep-sided volcano of dominantly basaltic-to-trachybasaltic composition forms a volcanic horst constructed above a basement of Precambrian metamorphic rocks covered with Cretaceous to Quaternary sediments. More than 100 small cinder cones, often fissure-controlled parallel to the long axis of the 1400 km3 edifice, occur on the flanks and surrounding lowlands. A large satellitic peak, Etinde (also known as Little Cameroon), is located on the S flank near the coast. Historical activity was first observed in the 5th century BCE by the Carthaginian navigator Hannon. During historical time, moderate explosive and effusive eruptions have occurred from both summit and flank vents. A 1922 SW-flank eruption produced a lava flow that reached the Atlantic coast, and a lava flow from a 1999 south-flank eruption stopped only 200 m from the sea. Explosive activity from two vents on the upper SE flank was reported in May 2000.

Information Contacts: US State Department, 2201 C St., NW, Washington, DC 20520 USA (URL: http://www.state.gov/); BBC (URL: http://news.bbc.co.uk/); Reuters (URL: http://www.reuters.com).

The following summarizes activity at Colima during the period from August 1999 to May 2000. As previously mentioned (BGVN 24:08), outbursts occurred on 5 and 17 July 1999. However, in the months that followed, August 1999 through May 2000, little activity occurred on Colima. Microearthquakes, sporadic eruptions and lahars were the most common events during these months.

During August through December 1999 Colima maintained low levels of seismicity, with few explosions or mudflows. Due to heavy precipitation on 2 September a lahar traveled under the Cordoban bridge without causing damage. Residents of Yerbabuena, La Becerrera, and Rancho El Jabali were told to avoid activities on the S-flank stream beds of the Cordoban, La Lumbre, San Antonio, and Montegrande rivers.

Landslides and lahars on the S and SW flanks during 5-6 September were quickly dispersed into La Lumbre and Cordoban drainages due to intense rains. Other monitored parameters showed no significant changes. During the week of 10 September seismicity remained low, with no degassing events or important explosions noted.

On 6 October at about 0120, residents from the village La Yerbabuena (8 km SW of the summit) reported a very short and light ashfall. The ashfall lasted only a few minutes, and prior to the fall residents reportedly heard "jet" sounds coming from the crater. Before the described events, the telemetered seismic network alerted the civil protection authorities, who then notified nearby villages of the activity. At 1700 on 12 October there were ground reports of an eruption that sent an ash cloud ~6 km.

During the first two weeks of November Colima ejected steam-and-ash an average of once per day. The estimated height of the columns varied from 200 to 1,000 m above the summit. Neither ballistic ejecta nor pyroclastic flows were observed. On 17 December seismicity remained stable, but some fumarolic and explosive emissions took place.

Beginning in January and continuing through May, ash explosions and steam emissions became frequent. Seismicity on 18 March remained low, yet Colima continued to produce fumes and explosions that were considered to be a high risk to the surrounding population. The evacuation of populations within a radius of 6.5-8.5 km from the summit was maintained by the State Systems of Civil Protection and the Mexican Army. After some explosions on 25 May these evacuations were again enforced.

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: Colima Volcano Observatory, University of Colima, Ave. 25 de Julio 965, Colima 28045 México (URL: https://portal.ucol.mx/cueiv/).

An eruption of Copahue (figure 5) began on 1 July 2000. Ash-and-gas emissions, which have continued into late July, are considered to be Copahue's most vigorous activity in the past century. Reports were received from geologists in Argentina and Chile. Except where otherwise noted, Argentine geologists Adriana Bermúdez (CONICET) and Daniel Delpino (Civil Defense of Neuquén Province) reported information for 1-9 July, and Chilean geologists José Naranjo and Gustavo Fuentealba (both of SERNAGEOMIN) reported information from 10-13 July. The scientists submitted joint reports beginning on 13 July. All time references are to Argentina local time; Chilean time is one hour earlier (GMT - 4 hours).

Figure 5. Preliminary geologic map of Copahue, showing outlines of Pliocene and Pleistocene calderas and post-caldera lava flows. Contour interval, 100 m. Modified from a previous map in BGVN 17:10. Courtesy of A. Bermúdez and D. Delpino.

Initial explosions, 1-2 July. Although visibility was poor in late June, at 0030 and at 0430 on 1 July local Argentine police and gendarmerie (National Guard) reported ash mixed with heavy snowfall, as well as a strong sulfur smell. At around 1145, lapilli and ashfall became heavier, eventually covering the snow and the products of previous eruptions around the summit. At 1200 the gendarmerie reported lapilli falling 7.5 km NE of the volcano, in the village of Copahue, Argentina. The alert status was set at yellow; the village's emergency committee restricted tourist access and helped to evacuate 200 people.

Explosions continued throughout 2 July with increasing intensity. Lapilli, ash, and sporadic bombs (15 cm in diameter) fell 8-9 km E on the town of Caviahue, Argentina, with up to 15 cm of materials from the day's explosions eventually being deposited in some areas (figure 6). Until 2345 there were explosions of varying intensities. Preliminary results of an examination of the deposits revealed that they were composed of a very fine silica, sulfur particles, accidental rock fragments from the conduit, and juvenile materials. In Caviahue, visibility was practically zero due to ash particles in the air, and heavy ashfall cut off power for several hours. By midday, eruption plumes blowing SE reached Loncopué, a small village 50 km from the volcano.

Figure 6. Ashfall from the frequent eruptions that began [1 July] at Copahue and heavy snowfall have affected the reliability of power and potable water resources in the town of Caviahue, a popular ski area 8-9 km E of the volcano. Although the town is no longer under official evacuation, many inhabitants have not returned to battle current conditions. Courtesy of A. Bermúdez and D. Delpino.

Alert status was raised to orange on 2 July when ash was dispersed as far as 100 km away from the crater and the plume covered a total area of 2,000 km². Maximum ash accumulation of 3-5 cm occurred over an area of 6 km², including the town of Caviahue and the W sector of Lake Caviahue. Due to the ashfall, the surface of Lake Caviahue changed color from its normal deep blue to gray-green, and a water sample taken had a pH of 2.l.

Tests by Argentine geologists on ash samples deposited in Caviahue revealed a grain-size distribution of 15% coarse ash (> 1 mm), 80% fine ash (0.5-1.0 mm), and 5% fine ash dust (< 0.5 mm). The coarse ash contained a small quantity of juvenile and lapilli-sized (3-6 mm) accidental fragments; the juvenile materials were dark gray vitric scoria. Non-juvenile accessory materials accounted for 7-10% of the coarse ash and consisted primarily of white-gray silica from the bottom of the crater lake. The fine ash-sized particles had similar components and characteristics.

Irregularly shaped dark gray scoriae, 3-8 cm in size, were found as far as 12 km N of the crater; scoriae completely covered the area within a 1.0-1.5 km radius around the crater. The scoriae contained spherical vesicles 3-5 mm in diameter. Cooling cracks marked the scoriae's surfaces and their shapes had been modified during flight.

Ashfall was also reported 60 km SE of the volcano in the town of Loncopué, where the stream closest to the volcano had cloudy brown-gray waters.

Continuing activity through 25 July. Activity decreased after 2345 on 2 July. The only explosion of 3 July, at 1720 in the main crater, deposited tephra on the flanks and generated a dense, dark gray ash plume that blew NW and produced a local ashfall. According to the Buenos Aires Volcanic Ash Advisory Center, the ash plume reached an altitude of 10.6 km and blew NE. On 4 July there were explosions at 1030, 1830, and 2000. In the town of Caviahue, Delpino noted a strong sulfur smell and great booming sounds that caused windows to shake. A dark gray ash plume rose 2 km above the summit. Bermúdez and Delpino reported that at 0020 on 5 July a new cycle of rhythmic explosions began; by 1325 a total of 37 explosions had occurred. The biggest explosion, at 0515, generated a pyroclastic surge down the E and N slopes.

A report was received on 5 July from Ralco-Lepoy, a town 30 km SW of the volcano, indicating that dead fish had washed up along the banks of the Lomín river. The Lomín, as well as the Agrio river, which drain the acidic, active crater, were marked by a deep, dark-colored gully but there was no evidence of lahars. However, it is possible that ashfall covered up the evidence. The dead fish found along the Lomín River on 5 July confirmed that acidic mudflows from the crater had been channeled down this river. Chilean geologists Naranjo and Fuentealba recommended that states bordering the Lomín river (to the SW) and Queuco to Trapa-Trapa (to the N) be alerted that an acidic mudflow was moving down the river. Accordingly, authorities noted that inhabitants should be evacuated outside of an enforced safety radius. It was also recommended that professionals regularly measure the pH of affected Lomín drainages, meteorological reports be kept up to date, and that town officials periodically reevaluate the yellow alert.

Naranjo and Fuentealba also noted that at 2030 on 5 July a patrol of carabineros (Chilean National Guard) approached the volcano on horseback and observed small dark ash emissions moving SE from the volcano.

Observers in Argentina during the night of 5-6 July reported an incandescent pyroclastic emission flowing down the cone and, at one point, a white light emanating from the crater for ~15 seconds. In the same time interval, gendarmerie officers from Copahue village described "an orange-red light coming up from the crater." It is thought that the light was produced when magma rose to the surface but did not spill over the crater walls. They also noted the vertical ejection of large incandescent blocks that fell back into the crater, as well as smaller incandescent fragments that fell onto the volcano's slopes, rolled downhill, and broke up into smaller pieces.

On 6 July, Delpino reported to Naranjo and Fuentealba from Caviahue that the eruption was Strombolian with explosion pulses every 1-2 hours. Winds blew ash S of Caviahue without any ashfall in the town. There was no evidence of lahars or floods. Throughout the morning of 6 July snow continued, and there was zero visibility of the volcano.

Bermúdez and Delpino reported that during 0100-1020 on 7 July, loud explosions and ash emissions occurred at 15-minute intervals. At about 2000, the wind changed, blowing W, and ash began falling over Caviahue. About 1 mm of ashfall was observed from 20 km W of the crater.

The same day, ice blocks 15-20 cm in diameter, as well as ash and lapilli, were carried down the swollen Agrio river from the volcano's permanent ice cap. At 1300, a sample of the river water taken at the bridge near Caviahue had a pH of 2, and at 2000 a sample from the same location had a pH of 1.5. The Dulce stream source lies 4.5 km E of the cone and it flows 5.5 km W of the cone into Lake Caviahue. Ashfall altered the stream's typical pH of 7 to a pH of 2.5. Preliminary investigations by Argentina's Provincial Water Division also indicated an increased iron content.

A loud explosion summit at 0300 on 8 July awakened citizens of Caviahue; a day-long ash emission moved SE through clear skies. On 9 July at 0100 a glowing light was seen over the crater, but cloud cover obscured visual observations throughout the day.

Naranjo and Fuentealba reported that on 10 July, explosions were gray to dark brown and it is thought that the ash fell over a 25 km² area to the W, in the direction of Chile. Ash reached the summit of neighboring Callaqui volcano, covering it in gray ash. Samples from this ashfall taken 4 km W of the active crater were found to contain juvenile volcanic glass fragments, 0.3-0.5 mm in diameter.

During 1200-1230 on 12 July, a Chilean overflight revealed that explosions inside the active crater (El Agrio) occurred at 1- to 3-minute intervals, ejecting fine material up to 500 m above the crater. This material was dispersed via a plume of fine ash and gases moving NNE for more than 250 km. Observers reported that 1-2 mm of fine ash was deposited in the village of Copahue. Throughout the day, activity increased and, at 2300, there was an explosion heard in Caviahue that was thought to have deposited 1-2 cm of ash 5 km NNE of Copahue. On 12 July, scientists noted that Copahue was in an eruptive phase of lower intensity (a Volcano Explosivity Index, VEI, of 1) compared to that seen on 1-2 July (an inferred VEI of 2).

At 1100 on 13 July, explosions generated white-gray to bluish gas emissions rising 200-300 m over the crater. A gas cloud with a strong sulfur odor remained trapped in the Agrio valley over a 10 km² area; it later descended, and strong winds spread it over a 20 km² area. At 2310, an explosion produced a 1-km-high plume and incandescent fragments were ejected onto the flanks of the cone reaching up to 1 km from the crater. The plume covered Caviahue, obscuring the moon, but there was no ashfall on the town.

A Chilean helicopter flight on the morning of 13 July observed explosions emitting pale gray ash columns up to 300 m above the crater rim. Winds dispersed the ash ENE to Caviahue. Carabineros sampling water at the source of the Lomín river found it slightly acidic (pH = 5-6).

At 1250 on 13 July, an eruption plume that rose 3-5 km over the crater was reported by military and civilian pilots. The column dispersed to the NE and was a reddish-brown color. Reports from Caviahue stated that on 15 July the eruption stayed at the same intensity as previous days, and fine ash was dispersed to the N. Ash samples from 13 July were found to have an andesitic composition and to include juvenile fragments, the presence of which indicates the volcano's potential to produce even larger explosions. Water samples from the Lomín river on the same date revealed high fluorine and sulfate levels.

At 1700-1730 on 16 July, and also between 0300 and 0400 on 17 July, a dusting of ash fell over Caviahue and there was a strong sulfur smell in the air. At 0905 on 18 July, a civilian pilot reported a pale gray ash column at 3.5-4 km above sea level (just over the top of the cordillera) dispersed over 10 km to the volcano's NNW. At this time, the ongoing eruptions were considered to be of VEI 1. Ash from the weak explosions was dispersed by low winds as it escaped from the crater.

At 2206 on 19 July, members of the gendarmerie reported that a series of explosions continued to generate columns of ash and water vapor 0.5-1.0 km above the crater. The plumes dispersed to the NE depositing a fine dusting of ash over the village of Copahue. A strong sulfurous odor was reported at 2100 in Caviahue. On 20 July activity remained low, and no noises or odors were detected. Winds carried the gas-and-ash plume NNE, depositing a light ashfall over the N sector of Caviahue.

On 21 July, light ashfall dusted Caviahue and, although the crater was obscured, ash columns were sighted rising above the summit and through the clouds to heights of 700-1,000 m. At 1048 (Argentina), Caviahue residents heard a series of rhythmic explosions occurring every 2-5 minutes for one hour. The plume carried ash NNE toward Trapa-Trapa. The volcano was obscured by cloud cover on 22 July but intermittent explosions continued emitting ash plumes carried NE toward Trapa-Trapa.

A seismological team from the Southern Andes Volcanological Observatory (OVDAS) installed a portable seismic station on 21 July at a spot ~2 km NNW of the active crater in the vicinity of Trapa-Trapa, Chile. After taking 15 hours of readings, the team left on 23 July after cold temperatures had prematurely reduced battery power. These readings were fortunately during a time of elevated activity, and registered seismic events generally correlated with visual observations. Despite this similarity, it was impossible to establish an exact correlation between the periodicity of the explosions (occurring every 1-3 minutes) and their microseismic signals at distance.

During the stay of the seismic team, no ashfall was reported in the Queco river region and no correlation was established between seismicity and sporadic thundering sounds reported by villagers in the area. These sounds have been attributed to chunks of the ice cap breaking off and rolling down Copahue's flanks. Due to over 3 m of snowfall, access to the area is difficult.

Explosions of low to intermediate intensity continued emitting ash-and-gas plumes on 23 July. The clouds continued to partially obscure the volcano, but at 1930 an ash column blew E toward Caviahue. On 24 July, the active crater was producing small explosions and dark gray ash emissions; a dusting of ash fell over Caviahue. When the Argentina gendarmerie and the Chilean carabineros compared respective observations no discrepancies were found.

Two pilots reported a strong sulfur odor at 1.8-2.1 km altitude, ~250 km WSW of Copahue on 25 July. At 1000 another pilot reported an ash plume extending 200 km WNW from the summit; plume height was ~2 km and width was 10-15 km. Although this explosion was not seen from Caviahue, a light ashfall fell over the town.

Due to the continued frequent ashfalls over Caviahue, town officials decided to reestablish a yellow alert. The prolonged fall of fluorine-rich ash has posed a possible problem for grazing animals in the affected fields, but heavy snowfall has made it less likely that vegetation will absorb the fluorine.

Background. Volcan Copahue is a composite cone constructed along the Chile-Argentina border. The cone lies within an 8-km-wide caldera formed 0.6 million years ago at a spot near the NW rim of the Pliocene, 20 x 15 km Del Agrio caldera. Copahue's eastern summit crater, part of a 2-km-long, ENE-WSW line of nine craters, contains an acidic crater lake (also referred to as Del Agrio) and displays intense fumarolic activity. Infrequent explosive eruptions have been recorded since the 18th century. Eruptions in 1992 and 1995 produced several phreatic and phreatomagmatic explosions and emissions that contained higher levels of water vapor but lower ash particle content than the current eruption. The current eruption has been of longer duration than either of the previous two.

The Agrio river emerges from a crack in the edifice of the volcano 50 m below the active El Agrio crater. The river water is highly acidic and has a yellow color. Near Caviahue, the Agrio river enters the Caviahue lake basin. The lake is formed by 2 glacial finger lakes over a 9.2 km² area and is a reservoir of acidic water.

Most residents of Copahue village leave each winter, but Caviahue's population of 400 can grow to 10,000 during the ski season. Eruption-related damage has cut off power and potable water, and there remains an inability to keep ski slopes cleared of ash. In late July there were reportedly only about 419 people staying in Caviahue.

Geologic Background. Volcán Copahue is an elongated composite cone constructed along the Chile-Argentina border within the 6.5 x 8.5 km wide Trapa-Trapa caldera that formed between 0.6 and 0.4 million years ago near the NW margin of the 20 x 15 km Pliocene Caviahue (Del Agrio) caldera. The eastern summit crater, part of a 2-km-long, ENE-WSW line of nine craters, contains a briny, acidic 300-m-wide crater lake (also referred to as El Agrio or Del Agrio) and displays intense fumarolic activity. Acidic hot springs occur below the eastern outlet of the crater lake, contributing to the acidity of the Río Agrio, and another geothermal zone is located within Caviahue caldera about 7 km NE of the summit. Infrequent mild-to-moderate explosive eruptions have been recorded since the 18th century. Twentieth-century eruptions from the crater lake have ejected pyroclastic rocks and chilled liquid sulfur fragments.

Information Contacts: Adriana Bermúdez, National Council of Scientific and Technical Research (CONICET) and the National University of Comahue, Buenos Aires 1400, Neuquén Capital, Argentina; Daniel Delpino, Advisor to the Civil Defense of Neuquén Province, Argentina and the National University of Comahue, Buenos Aires 1400, Neuquén Capital, Argentina; José Naranjo, National Geology and Mining Service (SERNAGEOMIN), P.O. Box 10465, Avda. Santa Maria 0104, Providencia, Santiago, Chile; Gustavo Fuentealba, Southern Andes Volcanological Observatory (OVDAS), SERNAGEOMIN, P.O. Box 10465, Avda. Santa Maria 0104, Providencia, Santiago, Chile; Buenos Aires Volcanic Ash Advisory Center, Argentina (URL: http://www.ssd.noaa.gov/ VAAC/OTH/AG/messages.html).

Between March and June 2000, Etna's activity was characterized by several Strombolian eruptions and high gas emissions predominantly at the Southeast Crater (SEC). Sixty-four strong eruptive episodes have occurred since the new eruptive series began on 26 January 2000 (BGVN 25:03), with 19 episodes between March and June. The information for the following report is based on official weekly monitoring reports posted on the Poseidon website.

Activity during 29 March-April. Through March lava flows and ash emissions occurred frequently, and on 29 March at about 1900, lava flows were generated on the S sector of the SEC. Shortly after 0730 on 1 April intermittent ash emissions rose to ~3 km and fell on the E flank. An episode on 3 April produced strong rumblings that were felt in the area of Zafferana Etnea, with ashfall in the area of Giardini (NE sector). On 6 April, between 1010 and 1130, explosive activity produced a lava fountain and lava flows. Over the following days the only activity at the volcano was abundant emissions of steam from Bocca Nuova (BN).

On 10 and 11 April, modest Strombolian activity was observed at BN, which became more sporadic in the following days then quieted on the evening of 14 April. On 15 April, at about 1700, weak effusive activity resumed from the vent at the S foot of SEC. At 0928 explosive activity recommenced with abundant lava emission. Ash also erupted from SEC's summit and reached 2 km altitude. Intense but irregular explosive activity was also present at the BN. Activity peaked at 1235 with an eruptive column that enveloped the SEC and rose to an estimated height of 6 km; the column produced abundant fall of ash and lapilli on the E slope. The episode ended abruptly at 1250. During this time Voragine (VOR) exhibited slow steam emission.

At 0545 on 26 April, intense Strombolian activity began and was followed at 0637 by an ash emission that rose several kilometers. In addition, a series of lava flows occurred from the SEC. Beginning at 0723, explosive activity diminished and had ended by 0740. In the following days there were no further eruptive events except for occasional, and sometimes intense, gas emissions from the BN.

Activity during May 2000. During 1-7 May, there was strong gas emission. On 5 May, a strong new gas emission phase began at the SEC, representing the 52nd episode since 26 January 2000. A dense eruptive column rose several kilometers over the volcano's summit and deposited several centimeters of ash on local villages to the SE. At about 1800 the volcanic tremors and eruptive column waned, leaving weak Strombolian activity that ended around 1824. After 5 May, the SEC returned to a state of quiet. The Northeast Crater (NEC) showed intense gas emission, with varied ash content. Weak Strombolian activity persisted at the BN.

Eruptive activity during 8-14 May consisted of abundant steam emissions, mainly from BN and NEC. The BN was the most active crater, emitting copious amounts of steam from at least two vents. The NEC also had abundant steam emissions with varied ash content. Meanwhile, VOR emitted modest amounts of gas and SEC virtually nothing.

During 15-21 May there were four strong gas emissions from the SEC. During the first strong episode, on 15 May, tephra covered the E flank of the volcano. A second episode during the night of 15-16 May consisted of a violent emission of tephra from 2100-2150 that covered the SE flank. The third episode began with Strombolian activity at the SEC then changed rapidly to well-developed lava fountains between 2240 and 2300. Activity abruptly decreased and ended completely within the space of a few minutes. A fourth strong episode occurred about 2145 on 19 May with increased activity from the lava flow on the N flank of the SEC. Violent gas emissions occurred shortly after 2200 and ended within an hour. Significant eruptive activity continued from the NEC, though more discontinuous than during the preceding weeks. The abundant emissions of ash increased significantly beginning 17 May, continuing for several hours. The ash emissions from the NEC were independent of the concurrent increase of volcanic tremors and activity of the SEC, except for occasional temporal coincidence. Steam emissions from the BN were also intense, sometimes associated with weak Strombolian intracrater activity. Slow gas emissions appeared from the VOR.

Two strong episodes occurred at SEC on 23 and 27 May. Activity at the other craters consisted of above normal ash emissions from NEC, intense gas emissions at BN, and weak fumarolic activity at VOR. The 57th eruptive episode of the series began on 23 May with strong explosive activity between 0301 and 0329 accompanied by lava flows down the S flank of the volcano. An episode on 27 May was obscured by poor meteorological conditions.

Activity through June 2000. Two eruptive episodes occurred at SEC on 1 June. First, at 0814, sustained lava fountains began, with some reaching an altitude of 600-700 m before ending around 0832. The column of ash and steam rose for several thousands of meters over the summit and produced a fall of fine pyroclastic material over much of the countryside on Etna's S slope, as far as Catania. At 1930 on 1 June another episode began with a considerable increase in the flow of lava.

On 5 June a strong gas emission at SEC went on for about thirty minutes, during which an ash-and-steam cloud rose to ~3-4 km. The ashfall covered an ample sector of the SE and S region, extending to the Plain of Catania and creating difficulties in air traffic to and from Fonatanrossa and Sigonella airports. As with preceding episodes, the gas emissions were associated with lava flows, primarily on the N slope of the SEC. Just after 1230 on 8 June, an increase in this same lava flow announced another strong gas emission phase beginning with a Strombolian eruption. There was a progressive increase in the explosive activity which reached its peak between 1356 and 1426. The fallout from the eruptive cloud was distributed toward the N.

Another strong gas emission began on 14 June at about 0700 with Strombolian characteristics. Ash emissions reached a climax between 0920 and 0940. On 24 June the 64th episode of activity at SEC occurred when a strong gas emission issued from NEC and VOR. This episode began with an increase of lava flow activity from the fracture on the N flank of the SEC. Later, Strombolian activity at the SEC's summit crater made a transition at about 2130 to a more violent, continuous gas emission phase which reached a peak about 2144, before ending shortly thereafter. After the 24 June activity there were no eruptions the rest of the month, but sporadic ash emissions occurred at all summit craters, particularly at BN and VOR.

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: Sistema Poseidon, a cooperative project supported by both the Italian Government and the Sicilian Regional Government, and operated by several scientific institutions (URL: http://www.ct.ingv.it/en/chi-siamo/la-sezione.html).

This report discusses activity at Guagua Pichincha during the months of June and July 2000. A Washington Volcanic Ash Advisory Center (VAAC) advisory was issued at 1337 on 2 June after a minor ash explosion propelled a plume to 7.3 km altitude above the summit. Another small eruption occurred one week later at 0941 on 9 June. Emissions from this second eruption did not rise more than 5 km, but more earthquakes and rockfalls indicated increasing instability of the January 2000 lava dome.

At 0953 on 12 July the dome experienced a partial collapse on its W side. This is the area of the dome closest to the W opening of the horseshoe-shaped caldera. High on the slope of the volcano's W flank, just below the caldera's opening, is the origin of the Cristál river. A long-period (LP) earthquake with a reduced displacement of 14.5 cm² probably destabilized the dome and caused the partial collapse. Judging by seismic data, the ash plume may have risen ~12 km above the crater, but cloud cover inhibited visual observations. A strong wind blew most ash W, away from the city of Quito, and very fine ash blanketed the caldera. Seismicity remained low after the eruption, but a slight increase in the number of rockfalls indicated that the dome was still unstable.

Two other events occurred during July. An ash plume was also sighted at 0900 on 23 July at an estimated height of 6.1 km moving W. An aviation notice at 0900 on 24 July described ash from six emissions over the course of the previous night that reached 4.8 km altitude, a height comparable to the volcano's summit elevation.

Over 14,530 LP events were registered in the month of March and this number decreased to 6,892 in April; there was a reported average of 271 LP events daily for the year 2000. The number of monthly explosions dropped to almost zero during the period of January to April; this was the first time there have been so few explosions since the month of July 1998. Volcano-tectonic seismicity also dropped dramatically during January-July 2000, averaging approximately the same number of monthly events as seen prior to activity that began in October 1999. The number of rockfall events has remained high since dome growth began in January 2000; thus far in the year 2000 there has been an average of 72 daily rockfalls. Beginning around June 2000 these events have occurred 100-200 times per day. Two main seismic centers have been inferred at Guagua Pichincha from data; one center is less than 1 km below the crater surface and the second ~2-4 km deeper. Continued fumarolic activity has been moderate but variable.

Geologic Background. Guagua Pichincha and the older Pleistocene Rucu Pichincha stratovolcanoes form a broad volcanic massif that rises immediately to the W of Ecuador's capital city, Quito. A lava dome is located at the head of a 6-km-wide breached caldera that formed during a late-Pleistocene slope failure ~50,000 years ago. Subsequent late-Pleistocene and Holocene eruptions from the central vent in the breached caldera consisted of explosive activity with pyroclastic flows accompanied by periodic growth and destruction of the central lava dome. One of Ecuador's most active volcanoes, it is the site of many minor eruptions since the beginning of the Spanish era. The largest historical eruption took place in 1660, when ash fell over a 1000 km radius, accumulating to 30 cm depth in Quito. Pyroclastic flows and surges also occurred, primarily to then W, and affected agricultural activity, causing great economic losses.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch, NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ssd.noaa.gov/); Associated Press.

NASA's Dryden Flight Research Center (DFRC) advised that information concerning two flights of their DC-8 aircraft as reported in BGVN 25:02 contained errors and requested that the information be corrected with additional details as follows:

"For approximately seven minutes starting at 0510 during a transit flight on 29 February to Kiruna, Sweden, a NASA DC-8 aircraft with a payload of SOLVE (SAGE III Ozone Loss and Validation Experiment) sensors flew through the plume ~11.3 km NNE of Iceland at 76 °N and 5 °W, just off the Greenland coastline. The plume extended up to ~13 km altitude, well into the lower stratosphere. The aircraft passed thorough the volcanic ash far N and W, and at a flight level much higher, than the predictions reported by the Volcanic Ash Advisory Center (VAAC), London. Instruments measured many in situ trace gases, SO₂, HNO₃, NO, NOy, O₃, volatile and non-volatile aerosols, and aerosol size distribution. The scientific team reported substantial increases in CN, NOy, HNO₃, CO, and particle counts, O₃ went to nearly zero, H₂O increased, and strong scattering layers up to 13 km were detected.

"A flight on 5 March detected enhanced aerosols and SO₂ at 1301, but by that time the plume was so diluted that it represented no danger to the aircraft. During the three weeks following the initial encounter the DC-8 detected remnants of the plume trapped within the polar vortex. The resulting analysis concluded that volatile aerosols increased and the sizes of non-volatile large aerosols decreased."

NASA-DFRC also advised that the statement about the plume being a "very impressive, orange, airfoil-shaped feature in the pre-dawn sky" was erroneous. Post-flight interviews with the pilot indicated that there was no moon out, therefore pitch black sky conditions existed at the time of the encounter. The pilots had no visual evidence of flying into the plume.

Geologic Background. One of Iceland's most prominent and active volcanoes, Hekla lies near the southern end of the eastern rift zone. Hekla occupies a rift-transform junction, and has produced basaltic andesites, in contrast to the tholeiitic basalts typical of Icelandic rift zone volcanoes. Vatnafjöll, a 40-km-long, 9-km-wide group of basaltic fissures and crater rows immediately SE of Hekla forms a part of the Hekla-Vatnafjöll volcanic system. A 5.5-km-long fissure, Heklugjá, cuts across the 1491-m-high Hekla volcano and is often active along its full length during major eruptions. Repeated eruptions along this rift, which is oblique to most rifting structures in the eastern volcanic zone, are responsible for Hekla's elongated ENE-WSW profile. Frequent large silicic explosive eruptions during historical time have deposited tephra throughout Iceland, providing valuable time markers used to date eruptions from other Icelandic volcanoes. Hekla tephras are generally rich in fluorine and are consequently very hazardous to grazing animals. Extensive lava flows from historical eruptions, which date back to 1104 CE, cover much of the volcano's flanks.

Information Contacts: Gary Shelton, NASA, Dryden Flight Research Center, P.O. Box 273, Edwards, CA 93523-0273 USA.

This report covers January-June 2000. In January seismographic station IRZ2 (5 km SW of the active crater) recorded seven small-magnitude earthquakes. During February and March no activity was recorded. In April, May, and June, respectively, IRZ2 recorded 10, 12, and 30 earthquakes. The latter month included low-frequency events.

During May the level of the crater lake decreased by 50 cm. During the dry period, the lake's color was yellow/green, and a significant amount of algae covered its surface. On the lake's NE and S shore lines constant bubbling continued; the temperature of the lake was 18°C. The E, N, and W crater walls continued sliding toward the lake. Fumarolic activity on the NE flank continued at a low level.

In June the crater lake's surface rose 40 cm in comparison to May. The lake color was now green and its surface was still covered by abundant algae. The NE crater wall continued sliding, partly covering some fumaroles while others completely disappeared. Also, along the NE wall three new thermal features appeared with temperatures that fluctuated between 22 and 54°C. On the NE and S shore the bubbling stopped during June.

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

Information Contacts: Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.

The period from 1 May through 17 July 2000 was characterized by frequent surface flows and earthquakes. On 9 May a thick steam and sulfur dioxide fume formed SW of Pu`u `O`o; such fumes, or vog, have often obscured the crater for the past few months. The prominent fumes came from skylights (holes in roofs of lava tubes) along the active tubes leading to a narrow dark aa flow that emerged onto the surface on 6-7 May.

On 15 May lava broke frequently onto the surface, widening the active flow field toward the E. During 16-25 May very little activity took place. On 26 May at 0457, heavy vog hung over Pulama pali and slowly drifted downslope. The ocean entry at Waha`ula remained vigorous over the past several weeks, building a bench 40-45 m seaward of the former coastline (figure 147).

Figure 147. Map of Kilauea showing lava flows (black) on Pulama pali and the coastal plain active since October 1999 through 1 July 2000, as well as flows erupted earlier from Pu`u `O`o and Kupaianaha. Courtesy of the USGS Hawaiian Volcano Observatory.

On the afternoon of 29 May two successive earthquakes occurred on Kilauea's S flank. The earthquakes had a preliminary magnitude of 4 and were felt in the town of Hilo 45 km NW of Kilauea.

Observations of the Pu`u `O`o cone on 1 June revealed no significant changes in the crater or collapse pits on the S and W flanks (figure 148). On the E crater rim, gentle "sloshing" sounds were heard, indicating lava at a shallow level. Direct observation into the vent was prevented by heavy fume. The Pu`u `O`o crater contains three pond vents and two hornitos. Most of these originated during September-November 1999 intracrater activity. Since then the crater has often been obscured by fume, but occasionally HVO observers have witnessed active lava within these vents.

Figure 148. A diagram of the Pu`u `O`o cone and surroundings at Kilauea as of March 2000 showing the area covered by lava since February 1997 during episode 55 (light gray). Inside the crater of Pu`u `O`o, the "trough" is the drained lava pond of September-October 1999. The central portion of the trough was briefly filled with active lava in February 2000. Puka Nui is the prominent collapse pit on the SW flank of Pu`u `O`o, which was floored with lava during September-October 1999. Puka Nui is a slowly expanding collapse crater that has consumed part of the tephra cone and surrounding shield on Pu`u `O`o's SW flank. Flank vents active in 1997 have built the south shield, minishield, and 55 cone. Courtesy of Steven Brantley and Christina Heliker, USGS Hawaiian Volcano Observatory.

The S shield (figure 148) has about 20 m of relief; the minishield, less than 10 m. The episode 55 cone was about 10 m high; yet has subsided into a slowly expanding collapse crater. The cracks adjacent to the pit wall show the expansion of the 55 cone's pit. These cracks are as wide as 1-2 m and some have slight vertical offsets. Major subsidence occurs in abrupt stages. Entire collapse craters 10-30 m deep and 50 m across form in a few hours or less. The cracked ground then remains stable for weeks or months. The W gap, which formed in January 1997, is the result of the subsidence along the E-rift axis. An E-rift intrusion in September 1999 led to a temporary shutdown of volcanic activity at Pu`u `O`o. When activity resumed, new small spatter cones were active briefly, shedding the lava flows shown as 1999 flows on the sketch map.

Throughout the week of 11-17 June activity remained stable. Lava continued to flow to the sea from Waha`ula entry, and from the entry to its W. Surface lava flows were visible sporadically on Pulama pali and elsewhere. Volcanic tremor near Pu`u `O`o remained weak to moderate.

On 13 June rain cleared vog from Holei Pali and enabled good views of the flow field in the morning. Lava continued to enter the ocean, not only at the Waha`ula entry but also at other entries a few hundred meters to the W (figure 147). Surface flows were apparent several hundred meters inland, and visitors reported breakouts near the western edge of the present flow field for the past several days. Pulama pali remained dark, but the fumes rolling down the pali came from active lava tubes feeding the active ocean entries and surface breakouts. Due to rain clouds and volcanic gas in the crater center, Pu`u `O`o was dark on the morning of 14 June. Seismicity was low across the island. Volcanic tremor near Pu`u `O`o remained weak to moderate. Kilauea's summit tilt and the tilt near and on Pu`u `O`o and all along the E rift zone were flat and stable.

Two moderate steam plumes rose from coastal entries on the afternoon of 15 June. Summit and rift-zone tilt remained steady, volcanic tremor at Pu`u `O`o was moderate and continued, and there was no unusual earthquake activity. Apparently on 15 June the eruption continued through tubes, with relatively little entering the sea.

On 16-17 June the lava bench at the Waha`ula entry was 30-50 m wide. On top of Pulama pali lava moved through the tube at a speed of ~10 km/hour. On 17 June, from 1330 to 1415, observations during a helicopter flight revealed more lava on the flow field a few hundred meters inland of Waha`ula. As movement of lava continued in Waha`ula, for the first time in several weeks a surface breakout was visible on Pulama pali between 1830 and 2030 on the evening of 17 June. The lava appeared from a distance to be aa and moved slowly down the middle third of the pali, near the eastern edge of the flow field W of Royal Gardens. On the evening of 17 June the Waha`ula entry , and another entry ~800 m to the W became active for several hours.

No breakouts were visible on 20 June on Waha`ula, Pulama pali, or the coastal flat. Fume continued to blanket the flow path down the pali. Above Pulama pali a new ledge was observed on 25 June, only ~1 m below the surface, at 642 m elevation. The ledge indicated that the level of lava in the tube rose temporarily and then subsided, and a breakout was observed at 686 m elevation.

During July there were frequent surface flows. On 6 July a substantial new pahoehoe flow began from a breakout point at about 200 m elevation on Pulama pali. The flow was ~500 m long and 150-200 m wide. Lava continued to spill into the sea at three sites. The most vigorous entry remained at Waha`ula, which generated two steam plumes on 6 July. The Kamokuna entry, the westernmost active bench, was less vigorous than Waha`ula but created a substantially larger steam plume. During mid-day 16 July, several entries were active: Waha`ula was the most active and Kamokuna the second most active. Several moderate-size surface flows were active in the eastern part of the flow field, between Royal Gardens and the coast. Heavy fume continued to flow down Pulama pali above the lava tube system.

Overall the seismicity and volcanic tremor for the months of May through July remained moderate and stable in the area around Kilauea's summit. Within the summit of Kilauea activity has remained slightly elevated.

Background. Kilauea is one of five coalescing volcanoes that comprise the island of Hawaii. Historically its eruptions originate primarily from the summit caldera or along one of the lengthy E and SW rift zones that extend from the caldera to the sea. The latest Kilauea eruption began in January 1983 along the E rift zone. The eruption's early phases, or episodes, occurred along a portion of the rift zone that extends from Napau Crater on the uprift end (towards the summit) to ~8 km E on the downrift end (towards the sea). Activity eventually centered on the area and crater that was later named Pu`u `O`o.

Between July 1986 and January 1992, the Kupaianaha lava lake was active ~3 km NE of Pu`u `O`o. It was during this period that the town of Kalapana and a majority of the 181 homes lost were destroyed. In December 1991, one month prior to the shutdown of Kupaianaha, eruptive activity returned to Pu`u `O`o. More than 1 km³ of lava has erupted during the 14 years of activity (January 1983-January 1997).

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: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawaii National Park, HI 96718, USA (URL: https://volcanoes.usgs.gov/observatories/hvo/).

At about 1044 on 20 July 2000, an eruption began at Lascar volcano that lasted until 1509. The Washington VAAC reported an ash advisory at 1509 for an ash plume that extended 660 km to the E, stretching from N Chile across S Bolivia and N Argentina and into W central Paraguay. At that time, the plume was traveling at speeds of up to 130 km/hour, reached altitudes of 10.7-13.7 km, and was reported to be 103 km wide.

Residents of the village of Jama, located 60 km ENE of the volcano on the Argentina-Chile border, reported feeling an earthquake before seeing a white mushroom cloud that rose 4-5 km high and rapidly blew E, depositing 1-2 mm of ash over the village. Several explosions were felt and heard 160 km ESE in San Antonio de los Cobres, but there were no reports of any injuries or damage. Activity continued into 21 July with small explosions producing plumes 200-300 m above the summit. The volcano is in a sparsely populated area so no evacuations were necessary.

According to Matthews and others (1997) Lascar has undergone four recognized cycles between 1984 and 1993. In each of these cycles, a lava dome is extruded in the active crater accompanied by vigorous degassing through high-temperature, high-velocity fumaroles on and around the dome. The dome then subsides into the conduit while the velocity and gas output of the fumaroles decrease; the cycle ends with violent explosive activity. No new lava was immediately extruded after the dome collapsed in the explosive 1993 eruption, thus breaking the previous pattern.

Background. Lascar is the most active volcano of the northern Chilean Andes; it is characterized by its persistent fumarolic activity, steam eruptions, and occasional vulcanian eruptions. The andesitic-to-dacitic stratovolcano contains six overlapping summit craters along a NE-SW trend.

Matthews and others (1997) discussed Lascar's evolution in four phases starting at ~50 ka. During phase I, an edifice was established on the E side, and pyroxene andesite lavas erupted. Phase II saw the development of the W edifice with a subglacial andesitic eruption, and the destruction of a substantial dome, arguably the volcano's most explosive event. In Phase III, a stratocone was constructed and a major andesitic explosive eruption generated scoria flows, known as the Tumbres deposits, dated at 9.2 ka. Phase IV activity shifted back to the E, leaving pyroclastic deposits dated at 7.1 ka. Prominent Phase IV lava flows extended NW and were later truncated by the formation of three deep collapse craters that mark the W migration of the active center. The current active vent discharges in the deepest of these craters, which is 800 m in diameter and 300 m deep. Frequent explosive eruptions have been recorded since the mid-19th century.

Reference. Matthews, S.J., Gardeweg, M.C., and Sparks, R.S.J., 1997, The 1894 to 1996 cyclic activity of Lascar Volcano, northern Chile: cycles of dome growth, dome subsidence, degassing and explosive eruptions: Bulletin of Volcanology, v. 59, p. 72-82.

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

Information Contacts: José Viramonte, Universidad Nacional de Salta and CONICET, Buenos Aires 177 -4400 Salta, Argentina; George Stephens, NOAA Operational Significant Events Imagery Support Team, World Weather Bldg., 5200 Auth Road, Rm. 510, NOAA/NESDIS, Camp Springs, MD 20748 (URL: https://www.nnvl.noaa.gov/); Associated Press.

The 27 June 2000 water discoloration ~1 km off the W shore of the island of Miyake-jima (BGVN 25:05) prompted considerable investigation. Remote Operation Vehicle (ROV) work and multi-beam side-scan sonar revealed fractures and what appeared to be three ocean-floor craters around the area of discoloration. Crustal deformation found in this region implies that cracks have opened under the W flank of the volcano. Magma intrusion was confirmed to have occurred in the W flank of the volcano around the time of the 27 June event. The absence of scoria or other eruptive products makes it likely that the event was thermal water released due to intrusion.

Magma intrusion is also thought to be the cause of a series of earthquakes that began on 26 June. Hypocenters migrated from a central position under the island in a curve to the W, NW, and N, reaching a position ~70 km NNW of the island by 21 July (figure 5).

Figure 5. A map showing Miyake-jima (lower right-hand corner) and the NW migration of hypocenters, 26 June-21 July 2000. Hypocenters were centered under the summit when activity began and then migrated to a submarine location ~ 10 km NW. This movement was thought to be related to magma intruding to the W. Labels for the higher-magnitude events indicate the month/day, magnitude, and hypocenter depth. Courtesy of the Japan Meteorological Agency.

Miyake-jima's mayor, Naoyuki Hirose, lifted the evacuation order for the SE district of Tsubota on 29 June, permitting hundreds of the almost 2,000 evacuees to return home. Approximately half of the island's population of 4,000 had been evacuated on 26 June.

At 0414 on 7 July, an eruption from the summit crater sent ash and rock into the sky; plumes dispersed ash over wide areas of the island. The eruption continued until 1110 and about 140 residents had to be evacuated from the N sector of the island to protect them from heavy ashfall. A second eruption at 1550 sent an ash column 1 km above the crater, ejected rocks, and produced loud booming noises. On 8 July there was a weak yellow-colored emission. Closer inspection of this last eruption revealed that very little material had been ejected, but a pit crater ~200 m in diameter and 100-200 m deep had formed. It is thought that the pit crater marked an empty cavity left when magma progressed from the summit area and intruded to the W.

The month-long crisis (figure 5) involved more than 17,500 earthquakes, including 5,480 strong enough to be felt by humans. The Miyake-jima earthquake swarm included a 7 July, M 5.2 event centered 25 km NW of Miyake-jima under the young volcanic islands of Nii-jima and Kozu-shima at 10 km depth, and a 1 July, M 6.4 event that killed one man on Kozu-shima by rockfall.

Geologic Background. The circular, 8-km-wide island of Miyakejima forms a low-angle stratovolcano that rises about 1100 m from the sea floor in the northern Izu Islands about 200 km SSW of Tokyo. The basaltic volcano is truncated by small summit calderas, one of which, 3.5 km wide, was formed during a major eruption about 2500 years ago. Parasitic craters and vents, including maars near the coast and radially oriented fissure vents, dot the flanks of the volcano. Frequent historical eruptions have occurred since 1085 CE at vents ranging from the summit to below sea level, causing much damage on this small populated island. After a three-century-long hiatus ending in 1469, activity has been dominated by flank fissure eruptions sometimes accompanied by minor summit eruptions. A 1.6-km-wide summit caldera was slowly formed by subsidence during an eruption in 2000; by October of that year the crater floor had dropped to only 230 m above sea level.

Information Contacts: Geological Survey of Japan, Higashi 1-1-3, Tsukuba, Ibaraki 305 Japan; Japan Meteorological Agency, Tokyo, Japan; Associated Press; Reuters.

Seismicity remained stable between November 1999 and April 2000. In May 2000 a seismic swarm began near the volcano, and in June there was heightened seismicity.

During 9-11 June the INETER seismic network registered over 500 earthquakes near Momotombo, 100 of which were located. Many of the earthquakes were between M 3.4 and 4.1 (figure 8), and occurred at depths less than 5 km. The small epicentral area was directly under a geothermal plant on the S slope of the volcano, between Momotombo's crater and the coast of Lake Managua. A similar area was the site of seismic swarms in past years, with the most recent occurrence in May 2000. Some of the earthquakes on 9 June were felt by the personnel of the geothermal plant 5 km SW of the crater and one was felt by several people in the town of Nagarote. INETER stated that an eruption could affect the geothermal plant's 96 employees, as well as residents of towns bordering the volcano. Continuous seismic tremor was also observed at the volcano, which was attributed to volcanic processes rather than movements at tectonic faults. The number of seismic events began to decrease on 11 June. From 12 to 13 June, 60 earthquakes occurred with seven epicenters located. In comparison, 150 earthquakes occurred from 9 to 10 June with 38 epicenters located. After 13 June the number of earthquakes gradually decreased to normal levels.

Figure 8. Locations of earthquake epicenters at Momotombo with magnitudes less than 3.8 (circles), and magnitudes between 3.8 and 4.1 (stars) from 9 to 16 June 2000. Courtesy of INETER.

Julio Alvarez, Jorge Cross, Arming Saballos (all INETER/Vulcanología), and Eduardo Mayorga visited the volcano on 15 June to measure the temperature of fumaroles in the crater zone. Temperature measurements conducted at fumaroles in the volcano's dome yielded values between 255 and 933 °C (figure 9). The highest temperature was found near the N edge of the crater.

Figure 9. Sketch of Momotombo's active crater showing fumarole temperatures on 15 June 2000. Areas of fumarolic activity are gray. View is towards the S; the crater is ~ 150 m wide. Courtesy of INETER.

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: Wilfried Strauch and Virginia Tenorio, Dirección General de Geofísica, Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado 1761, Managua, Nicaragua (URL: http://www.ineter.gob.ni/).

A blocky lava flow fed from the Caliente vent, active since July 1999 (see BGVN 24:12), had advanced nearly 2.5 km by the end of January 2000. The thermal anomaly related to this flow as measured on the 23 January Landsat 7 Enhanced Thematic Mapper (ETM+) is ~2,370 m long and 60-120 m wide. The flow extended S down the flank of the Santiaguito dome complex before being deflected SW by a low ridge and moving over the top of the 1986-89 flow (figure 29). A ~50 m-wide axial zone of the flow was very steep with a front slope of 60-70°. This ~30-m high axial zone advanced downward and collapsed into the sheer-sided ravine that forms the upper reaches of the Río Nimá II. The marginal flow front is ~18 m thick and its slope is smaller (~32°). As 2- to 5-m-wide sections of the flow front moved, minor collapses occurred at a rate of 1 to 2 per minute. Ash clouds generated by these collapses had temperatures of 185°C, and flow temperatures as high as 531°C were measured at a freshly exposed section of the axial zone. Temperatures for the blocky crust capping the flow front were lower, typically 34-76°C.

Figure 29. Sketch map of Santiaguito showing the January 2000 location of the blocky lava flow that began in July 1999. Also marked are lava flows emplaced between 1990 and 1999, as identified from an analysis of a Thematic Mapper time-series of 13 images. Using this time series the blocky flow which breached the 1902 crater rim is believed to have occurred during 1996-97, where "a" indicates the new aggradation load supply to Río Nimá I. Courtesy of Eddie Sánchez, Otoniel Matías, Andy Harris, Luke Flynn, Bill Rose, James Vallance, Edouard Gegout.

On 23 January, the Caliente vent was full. The 23 January ETM+ image shows this zone as an intense, thermal anomaly, 120-150 m in diameter. Small ash eruptions occurred at a rate of 1-2 events per hour producing ash plumes that extended kilometers above the vent. More powerful events generated small pyroclastic flows as well as rock falls. Both the dome and upper flow area collapse frequently produced audible rock falls that could be heard from a distance of ~1.5 km. Thirty-seven (37) rockfalls were heard on 23 January; 7 of which were incandescent as hot blocks from the dome and upper flow bounced down the flank of the dome.

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

Information Contacts: Eddie Sánchez and Otoniel Matías, Instituto Nacional de Sismología, Vulcanología, Meteorología e Hydrología (INSIVUMEH), Ministerio de Communicaciones, Transporte y Obras Publicas, 7A Avenida 14-57, Zona 13, Guatemala City, Guatemala; Andy Harris and Luke Flynn, IGP/SOEST, University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA; Bill Rose, Department of Geological Engineering and Sciences, Michigan Technological University, Houghton, MI 49931, USA; James Vallance, Department of Civil Engineering and Applied Mechanics, McGill University, Montreal, Quebec H3A 2K6, Canada; Edouard Gegout, c/o European Volcanological Society, C.P.1-1211 Geneva 17, Switzerland.

During June-July 2000 seismicity was generally at background levels with occasional weak fumarolic activity; the hazard level was Green. However at 0447 on 30 June, visual reports indicated a short-lived explosive eruption and an ash-gas plume that rose to about 8 km altitude; in response, the hazard status was raised to Yellow. Similar reports indicated that a short-lived explosive eruption at 1644 on 1 July sent and an ash-gas plume to ~6 km altitude. The mushroom-shaped plume extended to the W and at 2034, satellite imagery showed the arched plume extending 70 km NW. At 1728 on 1 July seismic data indicated a less intensive short-lived explosion, and on 2 July several weak explosions occurred and a gas-steam plume rose 300-700 m extending 3-5 km to the W and E. On 3 July seismicity under the volcano returned to background levels and the hazard status was reduced to Green.

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: Olga Chubarova, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Tom Miller, Alaska Volcano Observatory (AVO), U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508, USA (URL: http://www.avo.alaska.edu/).

This report covers the period of 1 May to 3 July 2000. Tiltmeter readings from 1-3 May showed a decrease in both the x-axis (25 µrad) and y-axis (40 µrad on the SW side of the summit, indicating deformation due to magma rising towards the surface. Magma continued to rise, but there was no increase in earthquakes registered at the Soputan Post Observatory (SPO) in Maliku. Nevertheless, seismic data from both satellite-telemetered and SPO's instruments contained an increasing trend in cumulative energy that could have been the result of tectonic earthquakes. A 5 May MR 6.5 earthquake in Banggai, ~325 km SW of Soputan, is thought to have been a precursor to a 13 May eruption.

At 1250 on 13 May, an eruption began with the ejection of incandescent materials and the emission of a thick, black ash cloud that rose 1,000 m above the summit and drifted NE. There were reports of ashfall up to 2 cm thick in the towns of Malompar and Tombatu, ~9 km S of the summit.

In the weeks following this event, seismicity remained elevated, with tectonic earthquakes dominating activity. Sporadic emissions of thin, white ash-and-steam plumes rose up to 100 m, but no explosions were reported. By 22 June, scientists were reporting several small explosions and avalanches, as well as a significant increase in the number of volcanic tremors and avalanche earthquakes.

At 1200 on 1 July, continuous tremor earthquakes reached amplitudes of 20-50 mm. Later that day, at 2232, two loud booms were heard and at 2255, lava was seen flowing up to 200 m to the W of Soputan's summit, covering over 13-14 May lava flows. Lightning was also seen around the crater and the rising plume. At 0200 on 2 July, Strombolian lava fountains were seen spewing lava 10-50 m above the crater. Later in the day, a thick gray ash plume was seen as it reached ~1,000 m altitude and slowly changed color to a dark brown. The volcano continued to produce ash plumes and persistent booming that indicated explosions were taking place although they could not be seen. The number of earthquakes reached over 100 events per day, indicating that lava dome growth continued. Observations made at both SPO and the Lokon Post Observatory, ~30 km N in Tomohon, gave the government reason to have concern for inhabitants' safety and, on 3 July, the alert level was raised from 2 to 3 (on a scale of 4).

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: Dali Ahmad, Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).

This report covers activity from 26 May to 21 July 2000. During this interval, the lava dome continued to grow; however, between 26 May and 2 June, the direction of the dome's growth changed. Although it continued to grow vertically, the majority of growth appears to have redirected from the E and NE to the S and possibly the W.

Visual observations were severely limited due to clouds throughout the early part of this period. However, during the week of 23-30 June a "rough, spiny area" appeared high on the E face of the dome at the top of the Tar River Valley. The week of 9-16 June, the dome grew to about 914 m. By 25 June, the dome had surpassed the height attained prior to the 20 March 2000 collapse. During this event, instruments for measuring dome volume were damaged. Observations from 30 June through 7 July showed that the area of dome growth had changed to a more slab-like appearance. A new area of spiny growth was first seen on 10 July. This growth appeared on the NE flank at 940 m elevation, which was thought to be the highest point on the dome. On 17 July, a large area of new growth was reported on the S and W sectors of the dome, attaining a height of 950 m.

Pyroclastic flows were reported to the ENE in the Tar River, between 9 and 16 June. The following week, pyroclastic flows were reported in the Gages valley to the W. Additional pyroclastic flows during the week of 7 July went NE into the upper Tar valley; some, if not all, of the flow material originated from the remains of the 1995-98 dome. On 21 July at 0620, there was a small pyroclastic flow with an explosive start. During an observation flight later that day, evidence of pyroclastic flows was observed to the SW in the upper region of the White River valley.

Rockfalls occurred throughout the reporting period (table 34). However, the week of 23 to 30 June was characterized by nearly constant rockfalls and small pyroclastic flows. These rockfalls were concentrated on the E side of the dome and talus accumulated much more slowly to the S above the White River. Prior to this, during the week of 9 to 16 June, the rockfalls occurred almost exclusively in the Tar River valley. During 30 June to 14 July, rockfalls occurring to the E of the dome were infrequent despite the presence of large blocks at the top of the steep E slope. The majority of the rockfall events at this point were occurring to the S and to the W of the dome.

Table 34. Seismic data for Soufriere Hills during 26 May-21 July 2000. Courtesy of MVO.

Seismic records (table 1) revealed a sharp increase in the number of long-period (LP) earthquakes after 2 June. The frequency of LP events continued to increase until its peak during 23-30 June. This same week marked the low point in the number of hybrid earthquakes. The number of volcano-tectonic earthquakes increased towards the end of the reporting period.

A steady production of ash during the week of 9-16 June maintained a dilute ash plume that moved W towards Plymouth and off the coast. Neither this ash plume nor the smaller ash clouds produced by rockfalls during the preceding weeks affected the inhabited parts of the island. During the week of 30 June to 7 July, abundant steaming was observed on the W flanks of the dome. The following week, steaming occurred on the N side between the main masses of the old dome. During this same week, ash venting was also observed from the S side of the dome.

The sharp increase in the number of LP and hybrid earthquakes after 2 June was taken to indicate increasing pressure in the dome. In addition, the dome's filling in of the crater on all sides suggests that rockfalls and pyroclastic flows will increase in the future. These events are expected to affect not only the Tar River valley, but also several other surrounding valleys, particularly Tuitt's Ghaut, White River valley, and Gages valley. These observations also lead to increased concern over the possibility of a substantial dome collapse in the near future.

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

Information Contacts: Montserrat Volcano Observatory (MVO), Mongo Hill, Montserrat, West Indies (URL: http://www.mvomrat.com/).

Usu's multi-vent NW-flank eruption that began on 31 March 2000 continued until at least 10 July (see previous report and map in BGVN 25:03). By 10 July the eruption had lost considerable vigor. The last noteworthy ash fall took place on 6 April; a small one occurred on 7 April. Several excellent reports were published rapidly by the Geological Survey of Hokkaido (GSH, 2000a, b). This article provides a summary of those Japanese-language reports as well as excerpts from a formal statement discussing Usu's behavior through 10 July. Satellite imagery also provided ashfall data. The active dome and associated vent group was incorrectly spelled "Konpira-yama" in previous Bulletin reports. According to formal rules of translation this name should be "Kompira-yama."

Prior to the eruption, geological mapping and bore holes had delineated portions of Usu's edifice and surrounding subsurface, enabling workers to draw a generalized cross section (figure 22). In addition to these background studies, as Usu entered an eruptive phase on 31 March a comprehensive suite of monitoring instruments were in place.

Figure 22. A schematic cross section across the flank of Usu showing boreholes, subsurface rock units (unlabeled), and areas of the two active vent groups with their plumes. The schematic illustrates the inferred zone of phreatic eruptions, estimated at 200-1000 m in depth. The groundwater surface was drawn as the distinctly heavier line connecting to the Toya lake on the right and at a depth of a few tens of meters above the "0" datum on the left). Arrows show the idealized paths of groundwater moving through the rock. After GSH (2000a, b).

Four days prior to the eruption, groundwater levels in instrumented wells (the potentiometric surface) around the volcano began to change (figure 23). A day or two later, these perturbations escalated rapidly. Data from five wells (figure 23) show that at least four underwent roughly synchronous offsets that grew to reach the 2- to 10-m range. These dramatic offsets were inferred to have been driven by the influx of magma. Also, water temperatures increased at hot springs. The level of the groundwater surface in the instrumented wells peaked near the time the eruption started. For the wells with post-eruptive data on figure 23, the groundwater surface began a comparatively gradual steady decrease soon after the eruption started. Ancillary details on well locations and behavior appear in the cited reports.

Figure 23. Perturbations to the groundwater surface level in monitored water wells around the time of the initial Usu eruptions; common vertical scale bar at upper right shows relative magnitude of displacement with strong offset beginning around 27 March 2000. Small arrow labeled "3/31" indicates the point of initial eruption (31 March 2000). After GSH (2000a, b).

Global Positioning System (GPS) data helped predict the 31 March eruption. GPS station KMK is near Hokkaido's N coast and ~7 km E of Usu's active vent groups. KMK was compared with three other stations near Usu beginning around 30 March (figure 24). The comparison revealed large vertical motions-tens of centimeters per day- including some beginning on 29 March (not shown). Figure 24 shows how the rates of vertical motion declined in early April at all three close-in stations. The reports also noted horizontal motions measuring tens of centimeters per day.

Figure 24. Relative vertical position of the land surface near Usu during 30 March-9 May 2000. The comparison is between three close-in GPS stations with respect to station KMK, ~ 7 km E of the Kompira-yama and western Nishi-yama vent groups. After GSH (2000a, b).

Clear precursory seismicity appeared at Usu (figure 25). The maxima, ~150 earthquakes in a 2-hour interval (i.e., ~75 earthquakes/hour), occurred ~1 day prior to the eruption. The eruptive pulses on 1 April took place during an interval with comparatively low seismicity.

Figure 25. Seismic overview of Usu for 28 March to 7 April 2000 portraying multifold increases in the number of earthquakes prior to the 31 March eruption. Bars are for 2-hour intervals with the maximum values representing ~75 earthquakes/hour. The arrows indicate the date of the first three eruptions of the episode. For comparison, the perturbations of hydraulic head were strongest during 27-31 March. After GSH (2000a, b).

Figure 26 provides a graphical summary of the episode's eight modest but identifiable ash falls. Most of the ash blew E, but an eruption on 1 April blew SE and one on 4 April blew N. GSH (2000a) features a time line for the two vent groups in eruption, graphically portraying 31 March-7 April plume observation. Figure 27 presents a sample of this larger time line: the portion for 1 April 2000. Figures such as this provide a particularly apt summary of complex phenomena.

Figure 26. Limits of ash fall distribution seen for Usu's outbursts (31 March-7 April 2000). The date convention is month/day. After GSH, 2000a, b.

Figure 27. A time line of activity at Usu on 1 April 2000 portraying the character of eruptive plumes from the Kompira-yama (upper line) and western Nishi-yama (lower line) vent groups. Plume symbols are shown in two sizes and colors, representing larger (>1-km-tall), smaller (< 1-km-tall), black, and white plumes. The shaded area bracketed by a solid line above (about 1145-1545) indicates an interval of dominantly visual plume observations. The arrow at 11:30 represents the time of onset for an eruption. The given compass directions (eg., E~SE) indicate the direction of ashfall from the vent groups. The original full-length version (31 March-7 April, in Japanese) includes numerous other notes and comments. After GSH (2000a).

Committee's announcement. The Usu eruption committee chaired byYoshiaki Ida made a formal announcement on 10 July. They noted that on this date Usu's phreatic eruption continued at the Kompira-yama and western Nishi-yama vent groups, but the supply of magma from depth had almost ceased. Accordingly, they anticipated a gradual decrease in volcanism.

The committee indicated that the current eruption occurred due to upward movement of magma from depths of ~10 km reaching a shallow reservoir around 4-5 km. Portions of the shallow reservoir traveled NW and then to the vents where magma escaped. The committee noted that on 10 July uplift still continued at western Nishi-yama (~5 cm/day) but that its areal extent and rate were decreasing. The committee noted that by 10 July small faults associated with the eruption ceased moving. They appeared as visible fault traces cutting across roads and other infrastructure (see photos in GSH, 2000a, b).

The committee also noted that the early phases of the eruption had ejected portions of juvenile material, whereas by 10 July the eruptions mainly discharged steam. Similarly, with time, cloud height and explosive vigor decreased. On 10 July Nishi-yama still gave off intermittent weak ash; Kompira-yama still emitted loud blasts with glowing volcanic rocks. But by this time such activities had decreased and ballistic bombs continued to fall several hundred meters from the Kompira-yama vent group. Earthquakes continued on the SW flank of Usu, but by 10 July they became increasingly scarce. The committee suggested a pyroclastic surge was unlikely in the near future .

Satellite imagery. A satellite image from 3 April shows Usu's ash blanketing parts of the largely snow-covered landscape (figure 28). The image caption states that the team planned to image Usu every 3-4 days. The images were captured on ASTER (The Advanced Spaceborne Thermal Emission and Reflection Radiometer), a Japanese-built instrument that obtains high-resolution (15-90 m²/pixel) images at 14 wavelengths from visible to thermal infrared. ASTER registers land surface temperature, emissivity, reflectance, and elevation; it flies on the Terra platform where it serves as a zoom lens for the other Terra instruments. ASTER has the ability to change viewing angles, enabling it to make stereoscopic images and detailed terrain height models. NASA terms the Terra satellite the flagship of the EOS mission. The latter is an effort to better understand planet Earth's atmosphere, land, and oceans, as well as their interactions with solar radiation and with one another.

Figure 28. A false-color image taken on 3 April by the Terra satellite's ASTER instrument showing the ash-darkened snow resulting from complex eruptions at Usu volcano's multiple vents. N is towards the top of the image. Usu and many of the visible deposits lie immediately S of Lake Toya, a circular 10-km-diameter caldera lake with a central island. The Pacific Ocean lies towards the S (the image's lower left-hand corner) and in this region enters Uchiura-Wan bay. (ASTER record identification, 257). Courtesy of NASA.

References. Geological Survey of Hokkaido (GSH), 2000a, Observations of Usu's volcanic eruption, 2000, Preliminary Report (in Japanese), 53 p. (in color on the GSH website and available as a 47 M file.

Geological Survey of Hokkaido (GSH), 2000b, Usu eruption in 2000, GSH News, 2000, 5, vol. 16, (ISSN 1345-1138), (text and captions in Japanese), 4 p. (1 additional sheet with 8 color plates)

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: Masahiro Yahata, Geological Survey of Hokkaido, Kita 19, Nishi 12, Kita-Ku, Sapporo, 060-0819, Japan; Yoshiaki Ida, University of Tokyo, Earthquake Research Institute, Yayoi 1-1-1 Bunkyo-Ku, Tokyo 113, Japan; NASA Terra Project, NASA Goddard SFC, MC 613, Greenbelt, MD 20771 USA (URL: https://terra.nasa.gov/); Yasushi Yamaguchi, Japan Outreach Center for ASTER, Nagoya University, Earth & Planetary Sci Dept/Faculty Sci, Furou-cho Chikusa-ku, Nagoya 464-01; Usu Volcano Observatory, Institute of Seismology and Volcanology, Graduate School of Science, Hokkaido University, Sohbetsu-cho, Usu-gun, Hokkaido, 052-0103, Japan (URL: http://www.sci.hokudai.ac.jp/isv/english/).