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

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

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

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

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

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

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

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

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

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

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

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

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

Figure 17. Sentinel-2 thermal satellite imagery detected a total of three thermal hotspots (bright yellow-orange) at the summit of Soputan on 2 and 4 January and 1 October 2019. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

Figure 18. Minor ash emissions were seen rising from Soputan on 22 March 2020. Courtesy of MAGMA Indonesia.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

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

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

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

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

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

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

Information Contacts: MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

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

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

Figure 14. Weak thermal hotspots (bright yellow-orange) were observed on 7 January (top) and 6 April 2020 (bottom) at Satsuma Iwo Jima (Kikai). Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 15. Incandescence at night on 10 January 2020 was observed at Satsuma Iwo Jima (Kikai) in the Iodake crater with the Iwanogami webcam. Courtesy of JMA (An explanation of volcanic activity at Satsuma Iwo Jima, January 2nd year of Reiwa [2020]).

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

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

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

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

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

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

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

Figure 128. Sentinel-2 thermal satellite images of Fuego between 21 November 2019 and 20 March 2020 showing lava flows (bright yellow-orange) traveling generally S and W from the crater summit. An ash plume can also be seen on 21 November 2019, accompanying the lava flow. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 129. Thermal activity at Fuego increased in frequency and strength (log radiative power) in late October 2019 and remained relatively consistent through February 2020. In early March, there is a small decrease in thermal power, followed by a short pulse of activity and another decline. Courtesy of MIROVA.

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

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

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

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

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

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

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

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

Geologic Background. Volcán Fuego, one of Central America's most active volcanoes, is also one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between Fuego and Acatenango to the north. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at the mostly andesitic Acatenango. Eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); Crelosa, 3ra. avenida. 8-66, Zona 14. Colonia El Campo, Guatemala Ciudad de Guatemala (URL: http://crelosa.com/, post at https://www.youtube.com/watch?v=1P4kWqxU2m0&feature=youtu.be).

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

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

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

Figure 24. Photo of ash explosion at Ebeko at 2110 UTC on 28 April 2020, as viewed from Severo-Kurilsk. Courtesy of KVERT (L. Kotenko).

Figure 25. Satellite image of Ebeko from Sentinel-2 on 27 May 2020, showing a plume drifting SE. Image using natural color rendering (bands 4, 3, 2) courtesy of Sentinel Hub Playground.

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

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

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

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

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

Figure 193. Location maps of the lava flows on the E flank at Piton de la Fournaise on 10-16 February 2020 (left) and 2-6 April 2020 (right) as derived from SAR satellite data. Courtesy of OVPF-IPGP, OPGC, LMV (Monthly bulletins of the Piton de la Fournaise Volcanological Observatory, February and April 2020).

Figure 194. Two significant eruptive events at Piton de la Fournaise took place during February-April 2020 as recorded by the MIROVA system (Log Radiative Power). Courtesy of MIROVA.

Figure 195. Images of the SO2 emissions during the February 2020 eruptive event at Piton de la Fournaise detected by the Sentinel-5P/TROPOMI satellite. Top left: 10 February 2020. Top right: 11 February 2020. Bottom left: 13 February 2020. Bottom right: 14 February 2020. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Figure 196. Images of the SO2 emissions during the April 2020 eruptive event at Piton de la Fournaise detected by the Sentinel-5P/TROPOMI satellite. Left: 4 April 2020. Middle: 5 April 2020. Right: 6 April 2020. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

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

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

Figure 198. Photos of the lava flows at Piton de la Fournaise taken during the February 2020 eruption by Richard Bouchet courtesy of AFP News Service.

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

Figure 199. Photos of a lava flow (left) and lava fountains (right) at Piton de la Fournaise during the April 2020 eruption. Left: photo taken on 2 April 2020 at 1500. Right: photo taken on 5 April 2020 at 1030. Courtesy of OVPF-IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, April 2020).

Figure 200. Photo of the lava fountains erupting from Piton de la Fournaise on 4 April 2020. Photo taken by Richard Bouchet courtesy of Geo Magazine via Jeannie Curtis.

Figure 201. Photos of Pele’s hair deposited due to the April 2020 eruption at Piton de la Fournaise. Samples collected near the Gîte du volcan on 7 April 2020 (left) and a cluster of Pele’s hair found near the Foc-Foc car park on 9 April 2020 (right). Courtesy of OVPF-IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, April 2020).

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

Information Contacts: Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, 14 route nationale 3, 27 ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); GEO Magazine (AFP story at URL: https://www.geo.fr/environnement/la-reunion-fin-deruption-au-piton-de-la-fournaise-200397); AFP (URL: https://twitter.com/AFP/status/1227140765106622464, Twitter: @AFP, https://twitter.com/AFP); Jeannie Curtis (Twitter: @VolcanoJeannie, https://twitter.com/VolcanoJeannie).

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

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

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

Figure 75. Sulfur dioxide anomalies were captured daily from Sabancaya during December 2019-May 2020 by the TROPOMI instrument on the Sentinel-5P satellite. Some of the largest SO2 plumes are shown here with dates listed in the information at the top of each image. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Figure 76. Thermal activity at Sabancaya declined during December 2019 from levels earlier in the year but remained steady and increased slightly in frequency and intensity during April and May 2020, according to the MIROVA graph of Log Radiative Power from 23 June 2019 through May 2020. Courtesy of MIROVA.

Figure 77. Sentinel-2 satellite imagery of Sabancaya confirmed the frequent ash emissions and ongoing thermal activity from the dome inside the summit crater during December 2019-May 2020. Top row (left to right): On 6 December 2019 a large plume of steam and ash drifted N from the summit. On 16 December 2019 a thermal anomaly encircled the dome inside the summit caldera while gas and possible ash drifted NW. On 14 April 2020 a very similar pattern persisted inside the crater. Bottom row (left to right): On 19 April an ash plume was clearly visible above dense cloud cover. On 24 May the infrared glow around the dome remained strong; a diffuse plume drifted W. A large plume of ash and steam drifted SE from the summit on 29 May. Infrared images use Atmospheric penetration rendering (bands 12, 11, 8a), other images use Natural Color rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

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

Figure 78. Multiple daily explosions at Sabancaya produced ash plumes that rose several kilometers above the summit. Left image is from 5 December and right image is from 11 December 2019. Note pyroclastic flows to the right of the crater on 11 December. Courtesy of OVI (Reporte Semanal de Monitorio de la Actividad de la Volcan Sabancaya, RSSAB-49-2019/INGEMMET Semana del 2 al 8 de diciembre de 2019 and RSSAB-50-2019/INGEMMET Semana del 9 al 15 de diciembre de 2019).

Figure 79. Communities to the N and W of Sabancaya recorded ashfall from the volcano the first week of December and also every month during December 2019-May 2020. The red zone is the area where access is prohibited (about a 12-km radius from the crater). Courtesy of OVI (Reporte Semanal de Monitorio de la Actividad de la Volcan Sabancaya, RSSAB-22-2020/INGEMMET Semana del 25 al 31 de mayo del 2020).

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

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

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

Figure 81. Explosions at Sabancaya on 11 March 2020 appeared to originate simultaneously from two different vents (left). The plume on 12 April was measured at about 2,500 m above the summit. Courtesy of OVI-INGEMMET (Reporte Semanal de Monitorio de la Actividad de la Volcan Sabancaya, RSSAB-11-2020/INGEMMET Semana del 9 al 15 de marzo del 2020 and RSSAB-15-2020/INGEMMET Semana del 6 al 12 de abril del 2020).

Figure 82. Explosions dense with ash continued during May 2020 at Sabancaya. On 11 and 29 May 2020 ash plumes rose from the summit and drifted as far as 30 km before dissipating. Courtesy of OVI-INGEMMET (Reporte Semanal de Monitorio de la Actividad de la Volcan Sabancaya , RSSAB-20-2020/INGEMMET Semana del 11 al 17 de mayo del 2020 and RSSAB-22-2020/INGEMMET Semana del 25 al 31 de mayo del 2020).

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

Information Contacts: Observatorio Volcanologico del INGEMMET (Instituto Geológical Minero y Metalúrgico), Barrio Magisterial Nro. 2 B-16 Umacollo - Yanahuara Arequipa, Peru (URL: http://ovi.ingemmet.gob.pe); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

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

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

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

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

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

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

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

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

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

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

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

Figure 13.Satellite image of Dukono from Sentinel-2 on 12 November 2019, showing an ash plume drifting E. Image uses natural color rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

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

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

Geologic Background. Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia's most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

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

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

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

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

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

Figure 287. Webcam images of ash emissions from the NE Crater at Etna from the a) CUAD (Catania) webcam on 10 October 2019; b) Milo webcam on 11 October 2019; c) Milo webcam on 12 October 2019; d) M.te Cagliato webcam on 13 October 2019. Courtesy of INGV (Report 42/2019, ETNA, Bollettino Settimanale, 07/10/2019 - 13/10/2019, data emissione 15/10/2019).

Figure 288. Strombolian activity at Etna contributed to significant SO2 plumes that drifted in multiple directions during the intermittent explosions in October 2019. Top left: 1 October 2019. Top right: 2 October 2019. Middle left: 15 October 2019. Middle right: 18 October 2019. Bottom left: 13 November 2019. Bottom right: 1 December 2019. Captured by the TROPOMI instrument on the Sentinel 5P satellite, courtesy of NASA Global Sulfur Dioxide Monitoring Page.

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

Figure 289. Photo of Strombolian activity and crater incandescence in the Voragine Crater at Etna on 15 November 2019. Photo by B. Behncke, taken by Tremestieri Etneo. Courtesy of INGV (Report 47/2019, ETNA, Bollettino Settimanale, 11/11/2019 - 17/11/2019, data emissione 19/11/2019).

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

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

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

Figure 291. Distinct SO2 plumes drifting in multiple directions from Etna were visible in satellite imagery as Strombolian activity continued through March 2020. Top left: 21 January 2020. Top right: 2 February 2020. Bottom left: 10 March 2020. Bottom right: 19 March 2020. Captured by the TROPOMI instrument on the Sentinel 5P satellite, courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Figure 292. a) A map of the lava field at Etna showing cooled flows (yellow) and active flows (red). The base of the scoria cone is outlined in black while the crater rim is outlined in red. b) Thermal image of the Bocca Nuova and Voragine Craters. The bright orange is the warmest temperature measure in the flow. Courtesy of INGV, photos by Laboratorio di Cartografia FlyeEye Team (Report 10/2020, ETNA, Bollettino Settimanale, 24/02/2020 - 01/03/2020, data emissione 03/03/2020).

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

Figure 293. Webcam images of A) Strombolian activity and B) effusive activity fed by the scoria cone grown inside the VOR Crater at Etna taken on 1 February 2020. C) Thermal image of the lava field produced by the VOR Crater taken by L. Lodato on 3 February (bottom left). Image of BN-1 taken by F. Ciancitto on 3 February in the summit area (bottom right). Courtesy of INGV; Report 06/2020, ETNA, Bollettino Settimanale, 27/01/2020 - 02/02/2020, data emissione 04/02/2020 (top) and Report 07/2020, ETNA, Bollettino Settimanale, 03/02/2020 - 09/02/2020, data emissione 11/02/2020 (bottom).

Figure 294. Photos of the VOR intra-crater scoria cone at Etna: a) Strombolian activity resumed on 25 February 2020 from the SW edge of BN taken by B. Behncke; b) weak Strombolian activity from the vent at the base N of the cone on 29 February 2020 from the W edge of VOR taken by V. Greco; c) old vent present at the base N of the cone, taken on 17 February 2020 from the E edge of VOR taken by B. Behncke; d) view of the flank of the cone, taken on 24 February 2020 from the W edge of VOR taken by F. Ciancitto. Courtesy of INGV (Report 10/2020, ETNA, Bollettino Settimanale, 24/02/2020 - 01/03/2020, data emissione 03/03/2020).

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

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

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

Information Contacts: Sezione di Catania - Osservatorio Etneo, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/it/); Toulouse Volcanic Ash Advisory Center (VAAC), Météo-France, 42 Avenue Gaspard Coriolis, F-31057 Toulouse cedex, France (URL: http://www.meteo.fr/aeroweb/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Boris Behncke, Sonia Calvari, and Marco Neri, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: https://twitter.com/etnaboris, Image at https://twitter.com/etnaboris/status/1183640328760414209/photo/1).

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

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

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

Figure 91. Webcam image of an ash plume rising above Merapi at 1733 on 14 October 2019. Courtesy of BPPTKG via Jaime S. Sincioco.

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

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

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

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

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

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

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

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

The latest eruption of Barren Island began about 28 May 2005 (BGVN 30:05 and 30:07). The following additional information regarding this eruption was provided by Dhanapati Haldar (Presidency College). A photograph (figure 11) taken on 21 July by the Indian Coast Guard indicated that the lava pouring from the main crater had cascaded down to arrive at two points on the W shore. The seawater boiled profusely.

Figure 11. Photo taken on 21 July 2005 showing the Barren Island eruption continuing unabated. Lava cascaded down and into the sea along the island's W shore. It entered the sea at two points following the pre-existing lava routes of the 1991 and 1994-95 eruptions. Courtesy of the Indian Coast Guard.

On 28 August, a senior geologist with the Central Ground Water Board (CGWB), A. Kar, made observations from a ship (figure 12). Kar noted that Strombolian eruptive activity had increased, and was both explosive and effusive in nature. The main crater and a newly created vent on the N flank were active. Streams of hot lava flowed down the slope of the cinder cone at the main crater. This cinder cone was built during the eruption in 1787-1832 and modified during subsequent eruptive pulses in 1991, in 1994-95, and (the current episode) in 2005. Kar's observations on 28 August 2005 noted that the descending lava flows traveled to the W shore, entering the sea near the lone preexisting landing site and ~ 250 m S of it. The latter was where the lava stream had met the sea during the 1994-95 eruption. Gas columns rose to more than 2 km, and fire fountains attained a height of around 300 m.

Figure 12. Photo taken 26 August 2005 showing Barren Island in Strombolian eruption. The main crater was active, and both explosive and effusive activity had shifted N. Hot lava (seen as incandescent strips) was flowing down the slope of the cinder cone. As before, lava entered the sea at two points on the W shore. Courtesy of A. Kar.

Kar visited the island again on 2 September and noted that eruptive activity was continuing unabated. As before, a thick gas plume hovered over the N part of the island, and hot lava still flowed down into the sea. The lava coming in contact with sea water was immediately broken into fine particles that were forcefully thrown into the air to a height of nearly 100 m. Accompanying steam rose to a height of about 300-400 m before being drawn away by the prevailing wind. The eruption column's top formed a spectacular mushroom of gas and smoke, blowing to the N. Subsequent reports received from the Indian Coast Guard indicated that the eruption was continuous until at least 25 September.

All the active vents so far observed during 2005 eruption, including the S footwall vent, lie in a zone trending almost N-S. This zone conforms with a pre-existing surficial fracture. This alignment of the active vents had been noted during the 1991 and 1994-95 eruptions, and, as previously mentioned, the lava streams of the current eruption retraced the 1991 and 1994-95 lava routes.

According to Haldar, recent lava samples show large (to 5 mm) megacrysts and phenocrysts of plagioclase (An 93-57), olivine (Fo 85-70), and diopside (Mg 47-44, Fe 16-10). The samples also included a groundmass of glass charged with microlites of plagioclase (An 50-45), augite, olivine, titanomagnetite, and rare orthopyroxene. The 2005 lavas contain relatively few olivine megacrysts, but are rich in plagioclase megacrysts, similar to the 1994-95 lavas.

The bulk chemical composition of the lava falls within the basalt field (table 2), which was comparable with the compositions of the 1994-95 lava. In comparison, the 2005 lava is slightly richer in both MgO and Na₂O and slightly lower in SiO₂.

Table 2. Analysis of one lava sample (number B1/05) erupted in June 2005 from Barren Island volcano. EMPA stands for electron microprobe analysis. Courtesy of Dhanapati Haldar.

As this issue went to press Haldar noted that Barren Island continued to vigorously spew lava, gas, and ash at least as late as 10 November 2005. The eruption was unabated since the last week of May 2005.

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

Information Contacts: Dhanapati Haldar, Presidency College, Kolkata, 4/3K/2 Ho-Chi-Min Sarani, Shakuntala Park, Biren Roy Road (West), Kolkata-700 061, India; Geological Survey of India, 27 Jawaharlal Nehru road, Kolkata 700 016, India (URL: https://www.gsi.gov.in/); Indian Coast Guard, National Stadium Complex, New Delhi 110 001, India (URL: http://indiancoastguard.nic.in/indiancoastguard/).

Mount Cleveland produced significant ash plumes during March 2001 (BGVN 26:04). Volcanic unrest continued through 4 May 2001, and signals consistent with volcanic seismicity were detected by an Alaska Volcano Observatory (AVO) seismic network 230 km E. By the end of May, neither eruptive activity nor thermal anomalies were observed. Until July 2005, no alert level was assigned, and AVO monitoring produced no reports on Cleveland.

Cleveland lacks a real-time seismic network. Accordingly, even during times of perceived quiet there is an absence of definitive information that activity level is at background. AVO's policy for volcanoes without seismic networks is to not get assigned a color code of Green.

Satellite imagery of Cleveland taken during 24 June to 1 July 2005 showed increased heat flow from the volcano and a possible debris flow. AVO stated that although observations were inhibited by cloudy weather, they indicated the possibility of increased volcanic activity. AVO did not assign a Concern Color Code to Cleveland due to the lack of seismic monitoring and limited satellite observations.

Satellite images during 1-8 July showed increased heat flow, thin ash deposits, and possible debris flows extending ~ 1 km down the flanks from the summit crater. AVO assigned a Concern Color Code of Yellow on 7 July. On 18 July satellite imagery showed steam emanating from Cleveland's summit and evidence of minor ash emissions. Meteorological clouds obscured Cleveland during the third week of July. During 22-29 July satellite images showed minor steaming from the summit, possible fresh localized ash deposits, and a weak thermal anomaly.

On 4 August satellite images showed a thermal anomaly. On 27 August AVO reduced the Concern Color Code at Cleveland from Yellow to "Not Assigned" because there had been no evidence of activity since a thermal feature was observed on satellite imagery from 11 August. A thermal feature was detected on several satellite images obtained on 31 August, and one on 19 September, but there was no evidence of eruptive activity.

On 7 October, AVO raised the Concern Color Code to Orange after detecting a small drifting volcanic ash cloud. The cloud was seen in satellite data at a spot ~ 150 km ESE of Dutch Harbor at 1700 UTC. Based on data from a regional seismometer at Nikolski, AVO concluded that the ash came from a small Cleveland eruption at approximately 0145. AVO, in consultation with the National Weather Service, estimated the top of the ash cloud to be no more than 4,600 m altitude. The ash cloud dissipated and was not detected via satellite after 1800 UTC. Three days passed during which there were no new observations of eruptive activity at Cleveland from satellite data, pilots, or ground-based observers. Accordingly, on 10 October the Concern Color Code was reduced to Yellow.

Geologic Background. The beautifully symmetrical Mount Cleveland stratovolcano is situated at the western end of the uninhabited Chuginadak Island. It lies SE across Carlisle Pass strait from Carlisle volcano and NE across Chuginadak Pass strait from Herbert volcano. Joined to the rest of Chuginadak Island by a low isthmus, Cleveland is the highest of the Islands of the Four Mountains group and is one of the most active of the Aleutian Islands. The native name, Chuginadak, refers to the Aleut goddess of fire, who was thought to reside on the volcano. Numerous large lava flows descend the steep-sided flanks. It is possible that some 18th-to-19th century eruptions attributed to Carlisle should be ascribed to Cleveland (Miller et al., 1998). In 1944 Cleveland produced the only known fatality from an Aleutian eruption. Recent eruptions have been characterized by short-lived explosive ash emissions, at times accompanied by lava fountaining and lava flows down the flanks.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of the U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA; Washington Volcanic Ash Advisory Center (VAAC), Washington, DC, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/).

An eruption began on 26 September 2005 in the Afar triangle region of NW Ethiopia, near the Afar's W topographic margin, a spot ~ 330 km E of Lake Tan'a (the source of the Blue Nile river) and ~ 320 km NNW of the city of Djibouti. The venting took place on the flanks of Dabbahu (Boina), a volcano without previous historical eruptions. What follows is a brief synopsis of seismicity available from the USGS and some field observations from Gezahegn Yirgu, Dereje Ayalew, Asfawossen Asrat, and Atalay Ayele of Addis Ababa University (AAU). Shortly after the Bulletin editors received the AAU report, normal lines of communication were temporarily halted due to civil unrest. Consequently, this report was reviewed and augmented by Anthony Philpotts of the University of Connecticut, who had flown to Erta Ale and Dabbahu with them and other scientists on 16 October 2005.

Dabbahu, a stratovolcano, also goes by several other names, including Mount Dabbahu, Boina, Moina, and Boyna. The eruption occurred at least 5 km NE of Dabbahu's summit area, at a flat spot referred to by the names Da'Ure and Teru Boyna. The profusion of names and spellings for this region of Africa partly stems from widely dissimilar alphabets; the one used in the region has over 100 letters, complicating conversion into languages having only 26.

The Dabbahu eruption has been confusing. Initial news reports shed little light on the eruption's source, size, or impact. Several news reports stated that nearby earthquakes had caused an eruption at Erta Ale, which is 113 km N of Dabbahu, but that was not the critical eruption in this region during late September. (Seismicity, however, did appear associated with an elevated level of unrest at Erta Ale in October-see report in this issue.) The confusion propagated into the Smithsonian-USGS Weekly Report of 5-11 October 2005, which incorrectly attributed some details of the Dabbahu eruption to Erta Ale. A correction was issued and the report was withdrawn. Official sources and news reports also seem to have initially overstated the impact (e.g., statements like 50,000 nomads evacuated, almost 500 goats killed, etc.).

In a later, more measured report, The Ethiopian Herald posted a 6 October article on the web that noted the following.

"... the [Disaster Prevention and Preparedness Commission] has sent relief aid, household utensils and a tanker truck to areas affected by the natural disaster. A regional committee set up in charge of studying the magnitude of the disaster has already sent its report to the commission. According to the report, 1,215 quintals [121,500 kg] of food aid has been dispatched to 6,384 citizens displaced from Boya and Debawo ... and resettled in Debabo locality, 20 km from Teru. Some 18,234 various household utensils, 1,280 blankets as well as 119 roles of plastic sheets were being transported to the area."

According to faculty at Addis Ababa University, prior to the eruption and in addition to the earthquake swarm there was also volcanic tremor, as well as faulting, fracturing, and possible local landslides.

Earthquake swarm. During September-4 October 2005, an earthquake swarm consisting of 131 events occurred at and immediately surrounding Dabbahu (figure 1 and table 1). The swarm was sudden and comparatively intense, with magnitudes ranging from body-wave magnitude (mb) 3.9 to 5.2. Instruments registered earthquakes of both the highest number and magnitude during 24-26 September, just prior to the 26 September eruption. Seismicity in the area declined sharply on 27 September and stopped on 4 October. According to another data set, earthquakes occurred in the region during the 5 years prior to this swarm at an average rate of ~ 12 per year.

Figure 1. A map showing Dabbahu volcano in the Afar triangle, along with epicenters from the earthquake swarm of 14 September to 4 October 2005 The solid triangles indicate Holocene volcanoes, although the one for Dabbahu is swamped by the pattern of epicenters. The Alayta shield volcano (labeled "A") sits 32.7 km NNE of Dabbahu's summit and erupted several times in the early 1900's. Epicenters were compiled from the U.S. Geological Survey (USGS) National Earthquake Information Center website.

Table 1. Daily number and maximum magnitude of earthquakes located in the Dabbahu region during 14 September-4 October 2005 (up to 42 per day, with a total of 131 earthquakes). Mw stands for moment magnitude; mb stands for body-wave magnitude. Data courtesy of National Earthquake Information Center, USGS.

First-hand observations. Gezahegn Yirgu of AAU submitted a preliminary description of the eruption. He reported that people in the area noted that on 26 September at about 1300 a very strong earthquake occurred. That was followed by a dark column of "smoke" that rose high into the atmosphere and spread out to form an umbrella-shaped cloud. Emissions darkened the area for 3 days and 3 nights. On their first visit, provoked by the abnormal seismicity, his team departed the site just two hours before the 26 September eruption. He went back to Dabbahu for several more visits, some of which included geologists from overseas.

The visitors found that a minor explosive eruption had taken place from a fissure-vent system, producing a light-colored ash layer that extended over 500 m from the vent (figure 2). The eruption threw out pre-existing near-surface pyroclastic deposits (sediments) and felsic lavas, and redeposited them near the vent (figure 3). Some of the rocks that were thrown 20 m from the vent measured 2-3 m across. Fine white ash fell in the surrounding region as far as Teru village, 40 km SW of the eruption site.

Figure 2. An aerial view of the fissure vent at Da'Ure (Dabbahu) taken around 4-5 October 2005, showing the post-eruptive scene captured by a camera that was aimed down and toward the NW. The fissure vent, which extends ~500 m and trends nearly N-S, cuts across the photo diagonally (for sense of scale, see people in figure 4). The deepest part, ~100 m below the surface, lies along the vent's base at its widest point. It exposes dark material at the bottom (see figure 3). N of that wide segment lies a cauliflower-shaped pumice dome, a feature ~30 m in diameter. What appears as a short, narrow segment of the fissure vent continuing in the distance behind (to the N of) the dome is actually longer and more prominent than it appears, owing to foreshortening due to camera angle, surface topography, and perspective to the more distant location. This northernmost segment of the vent is roughly one-third as long as the segment in front of the dome. Photo taken by Asfawossen Asrat.

Figure 3. An aerial view of the fissure vent at Da'Ure (Dabbahu) taken around 4-5 October 2005, showing the post-eruptive scene captured by a camera aimed down and approximately NE. This image presents enlarged views of both the pumice dome and the fissure vent's lower portions. (For sense of scale, see figure 4). Photo taken by Asfawossen Asrat.

Roughly two-thirds of the way from the S end of the fissure vent, a 30-m-diameter pumice dome formed. From within the fractures in this dome, the team heard a sound from below resembling the sound of a helicopter engine or a boiling liquid.

The bulk of Yirgu's report on the second visit to the eruption site, on 4-5 October, follows.

"A team of three geologists and one geophysicist (Gezahegn Yirgu, Dereje Ayalew, Asfawossen Asrat, and Atalay Ayele) revisited the Da'Ure locality (at approximately 120° 43' 37" N, 40° 32' 55" E) immediately adjacent to the NE flank of the Quaternary Boina felsic complex. This locality is the southwestern extension of the area we visited a week earlier and where we observed a number of newly opened parallel fissures and a major reactivated normal fault.

"We first investigated the area where a volcanic eruption had been reported. Here we observed the presence of a wide and elongate fissure more than 500 m long and about 60 m deep [(figures 2-4)]. The elongate fissure attains a maximum width of about 100 m where a semi-circular pit has formed and from where the explosive eruption appears to have taken place. This elongate vent is oriented almost N-S [trending N10W] and has broken through felsic pyroclastic deposits and lavas. Two smaller pits were also observed farther N along the fissure [situated] to the N of the major pit. A very fine and light grey ash has been deposited on both sides of the elongate fissure with the ash cover extending more than 500 m away from the vent. Beneath the ash deposit lies a sequence of loose layers consisting of mixed volcanic ash and ejecta from pre-existing fissure wall rocks. These layers have a total thickness of about 20 m near the large pit."

Figure 4. A view taken from Da'Ure's (Dabbahu's) new pumice dome looking S down the fissure vent on 16 October 2005, with people for scale. Part of the outer flank of Dabbahu is visible on the right side of the photo; Dabbahu's central area lies farther to the right off the margin of the photo. Courtesy of Anthony Philpotts.

At the pumice dome Yirgu noted "... intense degassing is occurring with the production of SO₂ as evidenced by its smell as far as 500 m away. Degassing is also visible along the length of the vent as well as through nearby fissures. The local people have reported that on 26 September 2005 at about 1300 local time a very strong earthquake shook the area. This was followed by a dark column of 'smoke' that rose high into the atmosphere and spread out to form a cloud, which darkened the area for three days and three nights. Our field observations were consistent with . . . [a minor ejection] of volcanic ash from a small vent or vents along the opened fissure."

"In the same locality, we also studied the newly formed second-order fractures and fissures, most of which were located on the eastern side of the main eruptive fissure/vent. Here, the [roughly N- to S-trending] fractures and fissures were all parallel to each other .... They were better developed on unconsolidated pyroclastic deposits and sediments; they affected an area nearly 700 m away from the main eruptive vent/fissure; spacing is commonly between 10 and 20 m; some extend discontinuously along strike for over 500 m, as observed from the helicopter; open fissures in the pyroclastic deposits measure up to 20 cm wide with common elliptical pits or collapse structures between fissures up to 4 m wide and up to 4 m deep.

"We have also observed a major reactivation on a N- to S-trending normal fault located some 500 m to the E of the elongate eruptive vent/opening. This fault breaks through felsic lavas and unwelded pyroclastic deposits and has a reactivated displacement (down thrown to the W) reaching half a meter in places. This reactivated fault extends . . . discontinuously for at least three kilometers as observed from the helicopter. Degassing is occurring along some parts of this fault."

Yirgu also said that, according to the AAU Geophysical Observatory, seismicity continued in early October in the area affected by the eruption, faulting, and fissuring.

Other data from a 16 October visit. Anthony Philpotts accompanied a team who, along with AAU colleagues, were helicoptered to the eruption site, which had completely ceased by this time. At the eruption site and on the helicopter trip to and from it, he saw no dead nor injured livestock. The team also visited a refugee camp for displaced nomads.

In discussions with AAU colleagues who saw the fissure vent during multiple visits, and in comparing photographs, it appeared that material exposed at depth in the wall of the vent changed to a lighter color. Presumably, these color changes were linked to water, initially present but that had evaporated in the intense heat of the Afar day. Philpotts suggested that if the vent did provide a window into the water table, groundwater may have added to the explosive activity.

Philpotts said that when they arrived, on 16 October, the pumice dome (shown in close-up in figure 5) still yielded temperatures of 400°C in cracks. The pumice dome lacked any deposits on top of its upper surfaces, and thus clearly represented the last volcanic feature to form. Some post-eruptive faulting was noticed with offsets on the order of 10 m.

Figure 5. Curving fractures in the top of the new Da'Ure (Dabbahu) pumice dome; view looking N. Two people are visible in the photo, one immediately behind the large central fracture. It was from these fractures the boiling noise had been heard the previous week. No sound was heard during the visit on 16 October. Courtesy of Anthony Philpotts.

Philpotts made several thin sections of pumice dome samples, and found it to be almost totally aphyric. It contains a very few rounded (resorbed) sanidine phenocrysts (figure 6) and needle-shaped microlites with high refractive index (pyroxene?). He noted that "The microlites undoubtedly formed during emplacement of the dome, but the resorption of the sanidine phenocrysts must have occurred at depth prior to eruption and probably indicates heating of the source magma chamber with an influx of hotter (basaltic?) magma."

Figure 6. A rounded, twinned phenocryst of sanidine feldspar in pumice from the Da'Ure (Dabbahu) dome in the center of the vent. Dark circles are air bubbles trapped during preparation of the thin section. The photo was taken with partly crossed polarizing filters; the width of the entire field is 1.62 mm. Courtesy of Anthony Philpotts.

Geologic Background. Dabbahu (also known as Boina, Boyna, or Moina) is a Pleistocene-to-Holocene volcanic massif forming an axial range of the Afar depression SSW of the Alayta massif. Late-stage pantelleritic obsidian flows, lava domes, and pumice cones form the summit and upper flanks. The volcano rises above the Teru Plain and was built over a volumetrically dominant base of basaltic-to-trachyandesitic lava flows of a shield volcano. Late-stage basaltic fissure eruptions also occurred at the NW base of the volcano. Abundant fumaroles are located along the crest of the volcano and extend NE towards Alayta. The first historical eruption took place from a fissure vent on the NE flank in September 2005, producing ashfall deposits and a small pumice dome. More than 6000 people were evacuated from neighboring villages.

Information Contacts: Gezahegn Yirgu, Dereje Ayalew, Asfawossen Asrat, and Atalay Ayele, Department of Earth Sciences, Addis Ababa University, PO Box: 1176, Addis Ababa, Ethiopia; Anthony Philpotts, University of Connecticut, U-45, Beach Hall, Storres, CT 06269, USA; National Earthquake Information Center (NEIC), US Geological Survey, Geologic Hazards Team Office, Colorado School of Mines, 1711 Illinois St., Golden, CO 80401, USA (URL: https://earthquake.usgs.gov/); The Ethiopian Herald, Addis Ababa, Ethiopia.

In conjunction with their investigation of eruptive activity related to a swarm of earthquakes at Dabbahu/Boina, a team of geologists from Addis Ababa University (AAU) also undertook field observations at Erta Ale, with the aid of a military helicopter (see map in this issue of BGVN, the report on Dabbahu/Boina). What follows is their report combined with other information they gathered.

Between 21 and 24 September 2005, the local people saw, from a distance, red and glowing light shooting and rising into the air above Erta Ale. This was an indication that a Strombolian eruption probably occurred, emitting a significant volume of fresh magma within and possibly out of the pit.

The AAU team surveyed Erta Ale's craters at about 0930 on 26 September from the helicopter, as landing was not possible. Within the small southern pit crater of the main crater, they observed a new cone-shaped construct and the presence of an actively convecting lava lake in the center of the new cone. The lava lake occupied the entire lower/inner pit with hot red lava visibly overturning at the edges of the pit. Molten lava was breaking through the lake's solidified black crust. In the northern pit crater, there was a conspicuous solidified lava bulge with dark emissions along the crater walls. No incandescent lava was visible in this pit.

In addition to their direct observations, the AAU team studied videos taken by Walta Information Center of the southern pit on November 2004 and 26 September 2005. The comparison revealed significant changes, particularly in the morphology and activity of the southern pit crater. In the later videos the main crater/pit had widened significantly, with portions of the earlier crater walls having collapsed into the lava lake. There was a new cone-shaped construct within the crater in place of the previous platform that existed between the rim of the outer crater/pit and the lower pit. The new cone was estimated to be some 20 to 30 m from the top of the crater rim. The new cone apparently contained layers of basaltic scoria covered by fresh lava flows. The combined thickness of tephra and lava was estimated to be 20 to 30 m. The lava lake occupied the entire width of the inner crater/pit and was then bounded by steep sides. The lake's surface stood 20 to 30 m below the cone's top.

Anthony Philpotts accompanied Gezahegn Yirgu and colleagues from Addis Ababa University faculty on a helicopter visit to Erta Ale on 15 October. They found the lava lake incredibly active, much more so than when filmed by earlier visitors in March 2005.

A brief review of satellite thermal anomaly data from MODIS/MODVOLC revealed an absence of thermal activity between 12 October 2004 and 31 March 2005, with a renewal beginning on 31 March 2005, increasing substantially in mid-2005 and continuing vigorously through at least 2 November 2005.

Geologic Background. Erta Ale is an isolated basaltic shield that is the most active volcano in Ethiopia. The broad, 50-km-wide edifice rises more than 600 m from below sea level in the barren Danakil depression. Erta Ale is the namesake and most prominent feature of the Erta Ale Range. The volcano contains a 0.7 x 1.6 km, elliptical summit crater housing steep-sided pit craters. Another larger 1.8 x 3.1 km wide depression elongated parallel to the trend of the Erta Ale range is located SE of the summit and is bounded by curvilinear fault scarps on the SE side. Fresh-looking basaltic lava flows from these fissures have poured into the caldera and locally overflowed its rim. The summit caldera is renowned for one, or sometimes two long-term lava lakes that have been active since at least 1967, or possibly since 1906. Recent fissure eruptions have occurred on the N flank.

Information Contacts: Gezahegn Yirgu, Department of Earth Sciences, Addis Ababa University, P.O. Box: 1176, Addis Ababa, Ethiopia; Walta Information Centre, Woreda Kirkos, Kebele 05, House No. 095, PO Box 12918, Addis Ababa, Ethiopia (URL: http://www.waltainfo.com/); Anthony Philpotts, University of Connecticut, U-45, Beach Hall, Storrs, CT 06269, USA; MODIS/MODVOLC Thermal Alerts Team, Hawaii Institute of Geophysics and Planetology (HIGP), University of Hawaii, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

In a meeting abstract Gomez and others (2004) wrote, "Following 11 years of relatively low activity, Galeras . . . produced a sequence of ash eruptions in July and August 2004. . .. Initial evidence of the activity transition appeared in the gas measurements [of] early June, followed by a strong increase in the shallow seismic activity below the active cone on 27 June. As in many cases at other volcanoes, the most clear evidence for the transition came in the form of seismic swarms and tremor. The current activity has culminated in two brief episodes of ash emission, on 16 July and 21 July, followed by two longer episodes, [during] 27 July-8 August and 11-19 August. This last episode began with a large explosion and released more ash than any individual episode from 1989 to 1993. Sudden deformation, as well as changes in the electric and magnetic [EM] fields at the crater EM station, and [in] gas parameters such as CO₂ concentration and fumarole temperature accompanied the [16 and 21 July] ash emissions. Unfortunately, the EM and gas instruments were lost to ashfall shortly afterward."

The same abstract also noted that "Starting in March 1996, a multiparameter real-time monitoring system was installed at Galeras, as a part of a cooperative program between INGEOMINAS [Instituto Colombiano de Geología y Minería] (Colombia) and the BGR [Bundesanstalt f?r Geowissenschaften und Rohstoffe] (Germany). Broadband seismometers were installed first, with electromagnetic (EM) sensors, sensors for the chemistry and physics of the fumarole gases, and a weather station following later. The data from these instruments augment the short-period seismic network and tiltmeters of Observatorio Vulcanológico de Pasto (OVP). Additional spot measurements [relied upon] visual inspection from the ground or helicopter, a thermal camera[,] and regular geological forays onto Galeras' slopes."

Our previous report covered events through late July 2004 (BGVN 29:07); this report discusses events through mid-October 2005. Besides the eruptions of July through August 2004, another month with vigorous activity was November 2004. A sudden explosion on 21 November drove a plume to 9-10 km altitude. The latter portion of this report interval (June to mid-October 2005) typically involved ongoing though diminished intensity of volcanism and seismicity.

In response to the crisis, authorities produced engaging graphics, reminiscent of landscape paintings, but also containing risk assessments (figures 108 and 109), in the originals as color-coded lines. These graphics accompanied explanatory text. The authorities also produced a colorful poster. In addition, articles on Galeras hazards appeared in local papers, many along with clear graphics. The distance from the summit to central Pasto is only ~ 9 km.

Figure 108. A hazards map prepared for Galeras. The key (upper left) shows symbols for risk zones (high, medium, and low). The settlement Genoy is also spelled Jenoy. This map is slightly modified from one by Observatorio Vulcanológico y Sismológico de Pasto, INGEOMINAS.

Figure 109. A sample of Galeras hazards graphics available during the 2004-2005 crisis. Galeras and surroundings appear in a series of perspectives that also illustrate likely paths of destructive processes. The artwork emphasizes important geography, labels many settlements, and portrays familiar buildings and skylines. Hazard zones are shown by symbols (see key at the bottom). Views are as follows: A: NW-looking view (S-SE flanks, "Pasto"), B: NE-looking view (SW flanks, "Consaca-Yacuanquer"), C: SE-looking view, (NW flanks, "La Florida-Sandona"), and D: SW-looking view, (NE flanks, "Genoy-Nariño"). Copyrighted images courtesy of Observatorio Vulcanológico y Sismológico de Pasto, INGEOMINAS.

July-December 2004. INGEOMINAS noted that the July 2004 emissions came from El Pinta crater and from Deformes fumarolic field. Field observations on 19 July disclosed ash freshly vented from El Pinta crater, forming a deposit that ranged in thickness from 3 mm at the base of the cone to ~ 20 cm near the point of emission.

During the latter half of July 2004 INGEOMINAS noted that emissions rose ~ 600 m above the volcano's summit. Ash was not then visible on satellite imagery. On 21 July 2004 a seismic signal corresponded with a visible plume rising ~ 500 m above the volcano and seen from Pasto. According to a news report, a wide area around the volcano had been declared off limits to visitors. Several higher plumes followed.

According to the Washington VAAC, several ash plumes emitted were visible on satellite imagery during 7-10 August 2004. The highest rising plume reached ~ 6 km altitude.

INGEOMINAS reported that on 11 August at 2349 an eruption sent an ash-and-gas cloud to an unknown height and generated visible incandescence. According to the Washington VAAC, satellite imagery showed an ash plume that rose to ~ 10.7 km altitude. This plume spread in all directions, but mainly to the NE, E, and SW. Later, a thin plume reached a height of ~ 7.3 km altitude and drifted SW into northern Ecuador. A distinctly separate plume also occurred, drifting NW at an altitude of ~ 6.1 km.

Figure 110 shows a graphical depiction of the two plumes issued by the Washington VAAC, which incorporated GOES-12 satellite imagery as part of an advisory sent out at 0807 on 12 August 2004. The observations were from about an hour earlier. This following message was in the 'remarks' part of the advisory."Ash heading [NE] earlier in the night can no longer be seen in satellite imagery. A faint plume of ash is heading SW into northern Ecuador but is slowly becoming diffused in satellite imagery. The ash heading SW is estimated to FL240 [~ 7.3 km altitude]. An ash plume moving NW from the summit is estimated to FL200 [~ 6.1 km altitude]. We will continue to closely monitor and advise earlier than normal if needed."

Figure 110. The Galeras ash plumes were distributed in a Volcanic Ash Advisory (VAA) issued at 1307 UTC on 12 August 2004. When this image was taken at 1215 UTC, the two visible plumes had separated widely; one lingering slightly N of the volcano, the other, larger, reached a higher altitude and drifted over Ecuador. Plume top altitude estimates were 'flight level' (FL) 200 and 240, equivalent to 20,000 and 24,000 feet, ~ 6.1 and ~ 7.3 km altitude. Information sources listed included the GUAYAQUIL Meteorological Watch Office (MWO) and the GOES-12 satellite. (This VAA was issued under the header FVXX20 KNES 121307). Courtesy of the Washington VAAC; analysis by Jamie Kibler.

The next advisory noted that ash had ceased to be visible in the imagery after 0715 (1215 UTC) on 12 August 2004 (in other words, after the image associated with the graphic in figure 110).

Fine ash from the 11 August eruption was deposited in villages near the volcano, including La Florida (~ 10 km NW of the volcano), Nariño, Sandoná, and Consacá, and farther afield in Ancuya, Linares, and Sotomayor (~ 40 km NW of the volcano). News articles reported that during these episodes ~ 230 families were evacuated, mainly from the volcano's N flank. The village of La Florida on the volcano's NW flank was most strongly impacted by the eruption. Ash contaminated potable water in some villages, impacted farm animal's health, and left hundreds of dead fish floating in rivers. On 16 August, ash emissions continued, depositing ash in several villages.

INGEOMINAS reported that gas-and-ash emissions continued at Galeras as of 18 August. Ash fell in villages near the volcano, including La Florida, Sandoná, El Ingenio (within 15 km of the volcano), and farther afield in Samaniego and Sotomayor (between 20 and 40 km from the volcano). During 19 August to 1 September, there was a decrease in the level of seismicity and the number of ash emissions. But, gas-and-steam emissions continued.

During September 2004, tremor associated with ash-and-gas emissions was recorded at Galeras. On the 23rd, ash deposits were seen on the upper N flank. By the 27th, the amount of tremor had decreased significantly, a change that coincided with a decrease in ash emissions. During most of October 2004, emissions of gas and fine ash continued at Galeras. Plumes rose to a maximum height of ~ 1.5 km above the volcano. Instruments recorded small-amplitude tremor associated with gas-and-ash emissions.

INGEOMINAS reported that at 1544 on 21 November 2004 Galeras erupted explosively. A resulting shock wave was felt as far away as Cimarrones (18 km N of the volcano), Chachagui (17 km N of the volcano), and Laguna de La Cocha (20 km SW of the volcano). Effects of the shock wave varied from a loud roar, to the vibration of large windows, to the vibrating sensation of an earthquake. Hot ballistic blocks fell nearly 3 km from the volcano on its eastern flank, producing short-lived forest fires. The eruption produced an ash-and-gas column that rose to an estimated 9-10 km altitude and drifted to the S and W. The Washington VAAC reported that satellite imagery of 21 November at 1815 (i.e., 22 November at 0015 UTC) revealed two separate plumes, a situation somewhat analogous to 11-12 August (figure 110). One set of plumes from the 21 November eruption were estimated to reach 9 km altitude, and they blew to the W. Other plumes interpreted as low-level ash were estimated to be near 4-5 km altitude; these remained in the vicinity of the volcano and showed little motion.

January-September 2005. During January 2005, low-level relatively shallow seismicity continued, and a small amount of deformation towards the W portion of the volcanic cone occurred. On 30 January an emission of gas and ash rose ~ 800 m above the volcano. During the first week of February 2005, small gas-and-ash emissions continued. Ash was deposited in the sectors of Consacá (~ 15 km W of the volcano) and La Florida, and in the city of Pasto (~ 10 km E). Low-level seismicity and a small amount of deformation were recorded.

According to a news article, on 24 May 2005 the Colombian government ordered the evacuation of ~ 9,000 people living near Galeras due to an increase in volcanic activity. INGEOMINAS reported that during 16-23 May, small shallow earthquakes occurred beneath the volcano. Earthquakes believed associated with fracturing within the volcano increased during the night of 21 May to the morning of 22 May. Deformation continued to be recorded at the volcano's summit. There were no ash emissions. Galeras remained at alert level II ('probable eruption in terms of days or weeks') as it has since 19 April 2005.

During early June 2005, seismicity and deformation decreased in comparison to the previous week. On 6 June the alert level was decreased from II to III ('changes in the behavior of volcanic activity have been noted'). During July and August 2005, seismicity chiefly remained low. One exception, a M 2.5 volcano-tectonic earthquake on 4 July 2005, was felt in sections of some towns near the volcano. Generally, observers also noted small amounts of deformation and low rates of gas discharge, with continued emissions from the main and secondary craters. Thirty volcano-tectonic earthquakes were recorded at Galeras during 19-21 August 2005. The earthquakes occurred 3-4 km NW of the volcano's active cone, near the towns of Santa Bárbara, Nariño, and La Florida. About five earthquakes felt by nearby populations occurred at depths of 6-8 km, with the largest (M 4.7) occurring at a depth of 6 km on 21 August.

During September 2005, minor seismicity and minor deformation continued. Seismic signals included 365 minor events near the volcano at less than 6 km depth. The larger September record consisted of 179 volcano-tectonic events, 291 long-period events, 258 hybrid events, and 96 tremor episodes. Some of these earthquakes correlated with gas and fine ash discharges. Flyovers at the end of September confirmed that gas emissions were significantly reduced compared to August 2005.

October INGEOMINAS reports noted occasional steam plumes visible from Pasto, often correlated with and presumably related to increases in rainfall and infiltration of water into hot portions of the volcano. A 5 October 2005 overflight revealed a small increase in gas emissions compared to similar flights during September 2005. Seismicity fluctuated and some instrumentally measured deformation continued.

Reference. Gomez, D., Hellweg, M., Buttkus, B., Boker, F., Calvache, M. L., Cortes, Faber, E., Gil Cruz, F., Greinwald, S., Laverde, C , Narváez, L., Ortega, A., Rademacher, H., Sandmann, Seidl, D., Silva, B., and Torres, R., 2004, A Volcano Reawakens: Multiparameter Observations of Activity Transition at Galeras Volcano (Colombia), Transactions, American Geophysical Union, Fall meeting (session entitled "Sources of Oscillatory Phenomena in Volcanic Systems I; Posters"), December 2004, San Francisco, CA

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

Information Contacts: Diego Gomez Martinez, Observatorio Vulcanológico y Sismológico de Pasto (OVSP), INGEOMINAS, Carrera 31, 1807 Parque Infantil, PO Box 1795, Pasto, Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html; Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); El Spectador; El Pais (URL: http://elpais-cali.terra.com.co/paisonline/); Reuters.

The first recorded eruption of Mt. Belinda volcano (Montagu Island), which began around 20 October 2001, continued (as reported in BGVN 28:02, 29:01, 29:09, 29:10) until at least the latter part of 2005. Information for the following report was prepared and submitted by Matt Patrick of the Hawai'i Institute of Geophysics and Planetology (HIGP) and John Smelie of the British Antarctic Survey, with the assistance of the HIGP Thermal Alerts Team.

This eruption was detected by the MODVOLC automated satellite detection system, which scans for anomalous thermal activity in MODIS (Moderate Resolution Imaging Spectroradiometer) satellite data over the entire Earth approximately twice per day (Wright and others, 2004). Investigators acquired a recent, 23 Sept 2005, cloud-free ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) image (15-30 m pixel size), which provided valuable information on a new phase of activity. It revealed a larger effusive eruption than previously identified in satellite imagery of Montagu Island (figure 9).

Figure 9. ASTER image showing Montagu Island's Mount Belinda on 23 September 2005. Courtesy of HIGP Thermal Alerts Team.

Based on frequent MODVOLC alerts (figure 10) and occasional high-resolution satellite data (ASTER, IKONOS, and Quickbird), Mount Belinda has maintained persistent activity since the start of the eruption. Activity has consisted of continuous steaming and low-intensity explosive events at the summit (presumably Strombolian), producing low-level ash plumes and ubiquitous tephra deposits on the island's ice cover, and at least three distinct effusive events. Several satellite images were posted by HIGP on the National Aeronautics and Space Administration (NASA) Earth Observer website, 13 October 2004 and 19 October 2005.

Figure 10. (A) Chronological graph of radiant heat output from Mount Belinda measured from satellite sensors. The date range depicted along the x-axis of this graph is from late 2001 to September 2005. (B) A plot showing the distance of satellite-measured thermal anomaly pixels from the Mount Belinda vent during the period 2001 to September 2005. Courtesy of HIGP Thermal Alerts Team.

Scientists noted an intense shortwave-IR anomaly at the summit of Mt. Belinda in all cloud-free ASTER images acquired throughout the eruption. This suggested the presence of a lava lake in the summit crater (see Patrick and others, 2005, for more detailed information on the eruption).

Far from slowing down, the activity throughout 2005 marked the highest levels yet registered by MODVOLC (figure 10a). For the first time in 2005, radiant heat output exceeded 150 MW (see Wright and Flynn, 2004, and Wright and others, 2005, for calculation details).

By plotting the position of each anomalous MODVOLC pixel relative to the central vent (figure 10b) one can see that most pixels are within 1 km of the vent. This reflects the approximate scale of MODIS pixels and thus the inherent level of location ambiguity (note, however, these results fail to show the 2-km-long lava flow emplaced in mid-2003 — see BGVN 29:01).

For the first time during this eruption, anomalous pixels began appearing more than 2 km away from the central vent on the satellite image for 0100 UTC on 15 September 2005, some up to 3.3 km away (figure 10b). This suggested the presence of a ~ 3 km long lava flow. Corroborating this was the ASTER image from 23 September 2005 (figure 9), which indicated heightened activity and a 3.5-km long lava flow extending from the summit cone of Mt. Belinda into the sea. A steam plume originated in the vicinity of the ocean entry. Note that the steam plume appears to drift W from its origin (where the plume is whitest), while the ash plume from the summit of Mt. Belinda (1,370 m elev.) drifts E, indicating varying wind directions at different elevations.

The lava flow initially traveled NE from the vent, but farther on it ran into a rocky arete, which diverted its path to due N. A 90-m-wide lava channel is visible at a distance of 1 km from the summit. The flow appears to be covered (perhaps entering a tube) within its first kilometer, where no anomalous shortwave IR pixels exist. It is unlikely that the flow is subglacial in this first kilometer, as its path is coincident with emplacement of the previously mentioned lava flow of mid-2003, which was 2 km long and had already melted ice along this route.

At the request of the British Antarctic Survey, the Royal Air Force sent an airplane from the Falkland Islands on 11 October 2005. The plane encountered cloudy conditions but those on board recognized steam rising from the sea. This flight took place prior to study of the 23 September ASTER image and thus it marked the first observation that lava reached the sea.

References. Patrick, M., Smellie, J.L., Harris, A.J.L., Wright, R., Dean, K., Izbekov, P., Garbeil, H., and Pilger, E., 2005, First recorded eruption of Mount Belinda volcano (Montagu Island), South Sandwich Islands: Bulletin of Volcanology, v. 67, p. 415-422.

Wright, R., and Flynn, L.P., 2004, A space-based estimate of the volcanic heat flux into the atmosphere during 2001 and 2002: Geology, v. 32, p. 189-192.

Wright, R., Flynn, L.P., Garbeil, H., Harris, A.J.L., and Pilger, E., 2004, MODVOLC: near-real-time thermal monitoring of global volcanism: Journal of Volcanology and Geothermal Research, v. 135, p. 29-49.

Wright, R., Carn, S., and Flynn, L.P., 2005, A satellite chronology of the May-June 2003 eruption of Anatahan volcano: Journal of Volcanology and Geothermal Research, v. 146, p. 102-116.

Geologic Background. The largest of the South Sandwich Islands, Montagu consists of a massive shield volcano cut by a 6-km-wide ice-filled summit caldera. The summit of the 10 x 12 km wide island rises about 3000 m from the sea floor between Bristol and Saunders Islands. Around 90% of the island is ice-covered; glaciers extending to the sea typically form vertical ice cliffs. The name Mount Belinda has been applied both to the high point at the southern end of the summit caldera and to the young central cone. Mount Oceanite, an isolated 900-m-high peak with a 270-m-wide summit crater, lies at the SE tip of the island and was the source of lava flows exposed at Mathias Point and Allen Point. There was no record of Holocene or historical eruptive activity until MODIS satellite data, beginning in late 2001, revealed thermal anomalies consistent with lava lake activity that has been persistent since then. Apparent plumes and single anomalous pixels were observed intermittently on AVHRR images during the period March 1995 to February 1998, possibly indicating earlier unconfirmed and more sporadic volcanic activity.

Information Contacts: Matt Patrick, University of Hawaii, Hawaii Institute of Geophysics and Planetology (HIGP) Thermal Alerts Team, 2525 Correa Road, Honolulu, HI 96822 (URL: http://modis.higp.hawaii.edu/); John Smelie, British Antarctic Survey, Natural Environment Research Council, High Cross, Madingly Road, Cambridge CB3 0ET, United Kingdom (URL: https://www.bas.ac.uk/); NASA Earth Observer (URL: http://earthobservatory.nasa.gov/NaturalHazards/).

At about 1730 on 22 October 2005 Sierra Negra began erupting. This shield volcano with a large oval-shaped caldera is located at the S end of Isabela Island. Circumferential fractures define the northern edge of the caldera. Volcán Chico, noted for its 1963 and 1979 eruptions, is comprised of a series of scoria cones and other vents aligned along several prominent fractures on the outer slope of the N caldera rim. The present activity is not related to the Volcán Chico fracture system, but is venting from fractures along the N inner caldera wall. The most prominent fracture can be traced westward ~3 km where it lies along the rim. This initial report was provided by a scientific team from the Instituto Geofísico.

The eruption was preceded by a seismic event at 1438 on 22 October, felt in the coastal village of Villamil (20 km SE of the caldera border) and by Park Wardens on Cerro Azul. Others reported single earthquakes on 19 October and two weeks earlier. At 1730 the eruption began with an explosion heard by many people in the Villamil area. Hikers in the area of the subsequent lava emission in the mid-afternoon of both 21 and 22 October witnessed no unusual activity. By 1745 the eruption column had reached an estimated altitude of 5 km, and the setting sun illuminated the light gray eruption column. At 1815 the team observed the column after sunset from Point (Punto) Ayora, Santa Cruz Island (80 km E) and estimated its height at 10 km. The still-rising column was 4-6 km wide, not spreading laterally, and a small lenticular cloud was beginning to form a cap over the column. As night fell, the western sky above the caldera was a burgundy red, suggesting that lava had covered an extensive area of the caldera floor. Satellite imagery of the eruption at 1745 showed an eruption cloud at an estimated altitude of at least 15 km moving SW. A very large hotspot in the multispectral imagery was also observed and continued on 27 October.

Observations at 1945 from the Santa Cruz highlands (75 km away) employing a camcorder with night vision capabilities confirmed extensive lava fountaining estimated to be 200-300 m high along a segment of the caldera rim, as well as the incandescence from a lava flow several kilometers long descending the NW outer flank. Although the complete eruption column was not visible, it may have reached an altitude close to 20 km and had spread out. Tourist boats between Isabela and Fernandina Island reported seeing two lava flows descending the N flank.

During an overflight between 0715 and 0900 on 23 October the team did not witness active lava flows or evidence of lava having entered the sea. A thin khaki-colored ash cloud layer was observed, between about 1,200 and 1,500 m altitude, that had spread out laterally and extended E as far as St. Cruz Island and N to Santiago Island. Later in the day the plume was directed NNW in agreement with satellite information. From the plane the team confirmed that the main eruption was venting from four craters along a 500-m-long fracture at the base of the NNE inner caldera wall. The highest lava fountaining (up to 200 m high) was being generated at the two middle vents, while the end vents were feeding many lava flows S onto the caldera floor. The fracture apparently extended W along the inner wall, but then climbed to the caldera rim where its trace was not obvious. However, small vents with fountaining and incandescent lava were observed on the rim along this general fracture system, implying that the active fracture extended ~ 2 km W of the main vents.

During the mid-day hours of 23 October the team ascended the S flank, followed the E rim of the caldera, and reached a point ~ 800 m from the active vents, from which the following description was made. From the four principal vents the lava flowed S with exceptional force, volume, and speed downslope in three main channels (figures 3 and 4). Based on the apparent speed of the lava, and the more than 10-m height of the waves in the stream of passing lava, the team estimated that the main lava flow was traveling nearly 20 m/second as it left its vent. The W channels, some 30-50 m wide, maintained their red incandescent color and high speeds, albeit less than that near the vent.

Figure 3. View looking W from the NE rim of Sierra Negra's caldera (right) on 23 October 2005. The caldera floor is to the left. The four active vents are superimposed in this photo, aligned along the E-W fracture that lies at the base of the inner caldera wall. Numerous lava flows descended southwards to the left where they joined to form one single flow of a'a lava ~ 1 km wide and 7 km long that had already reached the southern inner wall of the caldera on 23 October. Courtesy of M. Hall.

Figure 4. A 150-m-high lava fountain rises on 23 October 2005 from one of four active vents that define the active fracture system at the base of the northern inner wall of Sierra Negra's caldera. From these four principal vents lava flows moved southwards at velocities estimated at close to 20 m/second on 23 October. Courtesy of M. Hall.

By 1500 the E channel was slowing and cooling to a gray surface color; this thin solid veneer was subsequently fragmented when the flow went over the edge of the bench and cascaded to the caldera floor. On the caldera floor the incandescent lavas of all three channels disappeared under the black solidified a'a lava that already covered about 12% of the caldera. In the 22 hours since the eruption had begun, the lavas had formed one large flow 1-1.5 km wide that traveled SE along the base of the E interior caldera wall, then W along the S wall reaching a point almost halfway across the caldera. As such it had traveled a total distance of 7 km and had started small brush fires on the floor and interior walls of the caldera. With an estimated thickness of no more than 3 m, the volume of the lava ejected by 1530 on 23 October was calculated at about 25 million cubic meters.

Along the trail leading to the vent area an increasing amount of scoria fragments was observed on the rim's edge. Fragments ~ 1 cm in size were first observed ~ 4 km SE of the active vents, and they increased in size (up to 15 cm) and abundance towards the vents. Very little fine ash was in the air or on the ground along the E caldera rim. The scoria was black, exceedingly vesiculated, with vesicles from millimeter to many centimeters in diameter; it seemed comparable in density to popcorn. No crystals were observed in the glassy scoria material. At their closest approach to the vent, scoria fragments formed a deposit 3-5 cm thick.

An explosion heard at 1900 on 25 October was accompanied by a dark eruptive column and minor ashfall along the E rim of the caldera and probably elsewhere. By early 26 October the Park Wardens were reporting that one of the four principal vents had shut down. Observations made late on 26 October indicated that the a'a flow on the caldera floor had slowed and was still several kilometers from the sulfur mine area. Civil Defense officials also reported that apparently less lava was leaving the vents and that lava extrusion might have shifted to the outer N flank, possibly to the Volcán Chico fracture system.

The only inhabited areas include the small town of Villamil, located 20 km SE of the caldera's border on the S coast, plus several other small populated areas about halfway between the caldera and Villamil. There was no immediate threat to those residents, given the fact that in order to spill out of the caldera and descend the S flanks the entire 100-m depth of the caldera would have to fill with lava. The southern caldera border has not been active in the recent geologic past.

Geologic Background. The broad shield volcano of Sierra Negra at the southern end of Isabela Island contains a shallow 7 x 10.5 km caldera that is the largest in the Galápagos Islands. Flank vents abound, including cinder cones and spatter cones concentrated along an ENE-trending rift system and tuff cones along the coast and forming offshore islands. The 1124-m-high volcano is elongated in a NE direction. Although it is the largest of the five major Isabela volcanoes, it has the flattest slopes, averaging less than 5 degrees and diminishing to 2 degrees near the coast. A sinuous 14-km-long, N-S-trending ridge occupies the west part of the caldera floor, which lies only about 100 m below its rim. Volcán de Azufre, the largest fumarolic area in the Galápagos Islands, lies within a graben between this ridge and the west caldera wall. Lava flows from a major eruption in 1979 extend all the way to the north coast from circumferential fissure vents on the upper northern flank. Sierra Negra, along with Cerro Azul and Volcán Wolf, is one of the most active of Isabela Island volcanoes.

Information Contacts: Minard Hall and Patricio Ramón, Instituto Geofísico, Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Tapia and Oscar Caravajal, Parque Nacional Galápagos, Pto. Ayora, Santa Cruz Island, Ecuador.

This report discusses a 1 October 2005 eruption at Santa Ana (also called Ilamatepec) that sent a plume to 14 km altitude and led to initial estimates cited in the press of two deaths (perhaps from landslides), several injuries, and the evacuation of over 2,000 people. Observations of glowing fumaroles and release of magmatic gas during 2000-2001 were previously reported at Santa Ana (BGVN 26:04). Servicio Nacional de Estudios Territoriales (SNET) scientists noticed that between the summer of 2000 and April 2001 there was increased venting of a well-developed hydrothermal system through the crater lake, hot springs, and fumaroles, but these changes were not accompanied by detected seismicity, which was then taken to suggest that the increase in hydrothermal activity was not driven by the arrival of new magma beneath the crater. An ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) image from 3 February 2001 shows the volcano's setting well before the eruption (figure 1).

Figure 1. An ASTER image of Santa Ana from 2001 featured in one of several Earth Observatory reports. N is to the top left of the image and Santa Ana is the large, blunt-topped edifice closest to the left side of the image. In the color version of this image can be seen a tiny blue spot in the center of the inner-most crater?a crater lake (often called the lagoon). Behind Santa Ana is a large (7-km-diameter) lake inside the Coatepeque caldera. In the center is Izalco volcano, with dark-colored historical lava flows. Courtesy of NASA's Earth Observatory.

SNET reported that a sudden eruption at Santa Ana took place around 0820 on 1 October 2005. They estimated that it produced an ash-and-gas plume to a height of ~ 10 km above the volcano. According to the Washington VAAC, ash was visible on satellite imagery at an altitude of ~ 14 km. The US Air Force Weather agency provided images of the plume (figure 2).

Figure 2. Two images of a Santa Ana eruptive plume on 1 October 2005. (top) The plume at 1516 UTC; (bottom) the plume at 1650 UTC. Note that the label 'FL 460,' stands for 'flight level 460,' which is equivalent to an altitude of 46,000 feet or 14 km. Courtesy of the US Air Force Weather Agency.

Ash fell in towns W of the volcano, including in Naranjos, Nahuizalco, Juayúa, Ahuachapán (NW), and La Hachadura (at the border, ~ 40 km W, figure 3). SNET produced a graphic similar to an isopach map that showed near-source thicknesses provisionally to over 10 cm. The 10 cm isopach stretched ~ 5 km W; the 1 mm isopach, ~ 20 km W. The outermost isopach, presumably where measurable ash fell, was not closed; instead it was cut off along the Guatemalan border (~ 40 km to W of Santa Ana) and the caption said that ash would fall into valleys in Guatemala and to the sea. Volcanic blocks up to a meter in diameter fell as far as 2 km S of the volcano's crater. Lahar deposits were seen SE of the volcano. The alert level within a 4-km radius around the volcano's central crater was raised to Red, the highest level.

Figure 3. Graphic from SNET showing ashfall distribution from Santa Ana that appeared in the newspaper, La Prensa Grafica, following the 1 October eruption. N is upwards; Santa Ana lies ~ 40 km E of the Guatemalan border. This clearly transmitted the message that the ashfall was variable and W-directed over parts of El Salvador and neighboring Guatemala. The bottom of the graphic discussed the impact of the ash fall, including damage to specialty coffee farms. Credit: Ricardo Orellana, La Prensa Grafica.

According to news reports, two people were killed by landslides (possibly caused by heavy rain in the area) in the town of Palo Campana, and thousands of residents near the volcano were evacuated. As many as 1,400 hectares of crops were damaged by ash (1 hectare = 10,000 m²). News also mentioned other processes such as a flood of boiling mud and water, and molten rocks, some the size of small automobiles, that will be discussed in later reports. A several-minute-long video from the LPG Television website appears as both a hyperlink and an active file on our website. In addition to numerous interviews with evacuees, it shows a host of features including what appear to be the swaths left by previously inflated mudflows passed down steep-sided valleys.

Prior to the eruption, no significant change in seismicity was observed. On 3 October, after the eruption, seismicity fluctuated and small explosions occasionally occurred. Earthquakes associated with explosions were recorded. In addition, there was a decrease in the amount of SO₂ emitted from the volcano.

Strong degassing had been measured at the volcano since June 2004. An ash emission occurred on 16 June 2005, and a slight increase in seismicity and a significant increase in gas emission were measured from 27 July until at least 30 August. SNET also reported a significant increase in seismic activity at Santa Ana on the night of 27 August. A cluster of 17 volcano-tectonic earthquakes were recorded, with four located S of the volcano. Afterwards, continuous high-frequency tremor was recorded until at least 30 August. Observations made on 29 August revealed incandescent rocks in the fumarole field, effects attributed to hot gases heating the rocks to sufficient temperature to glow. A significant increase in SO₂ emission was recorded, and gas-and-steam plumes rose 500-1,000 m above the volcano's crater. As a safety measure, access to the volcano's crater was restricted.

From 27 July until the eruption on 1 October, seismicity and gas emissions were above normal levels, and Santa Ana was at alert level yellow. During the first week of September, tremor continued to be recorded, and on 2 September a cluster of at least eight small earthquakes occurred, which were not felt by local residents. Gas plumes rose to ~ 500 m above the volcano, and the SO₂ flux was over 1,000 metric tons per day during the first two weeks of September. Satellite imagery from 5 September showed a thermal anomaly.

Microseismicity increased significantly on 12 September. During a visit to the volcano on 8 September, larger areas of incandescence were visible at a field of fumaroles than during a visit on 29 August. Satellite imagery showed a thermal anomaly at the volcano on several days during the second week of September.

During 15-19 September gas plumes rose to ~ 500 m above the volcano, and the SO₂ flux reached a maximum of 3,320 metric tons per day on 16 September. Microseismicity remained at relatively high levels. No significant changes were seen at the volcano's crater when observed on 19 September in comparison to 13 September. Intense degassing continued and the crater lake (lagoon) remained a dark coffee color. Incandescence was visible inside some cracks.

During a visit to the crater on 21 September, observers noted that the lagoon had become greener and small rock landslides occurred in the field of fumaroles. Gas plumes rose to ~ 1 km above the volcano on 26 September.

Following the eruption of 1 October, small explosions, degassing, and low-to-moderate seismicity occurred at Santa Ana during 5-11 October. Inclement weather prohibited ground and satellite observations, and sulfur-dioxide (SO₂) measurements during much of the report period. During an aerial inspection of the volcano on 11 October, no changes were observed at the crater. Around 11 October, SO₂ measurements were around 600-700 metric tons per day. The alert level within a 5-km radius around the volcano's central crater remained at Red.

Geologic Background. Santa Ana, El Salvador's highest volcano, is a massive, dominantly andesitic-to-trachyandesitic stratovolcano that rises immediately W of Coatepeque caldera. Collapse of Santa Ana (also known as Ilamatepec) during the late Pleistocene produced a voluminous debris avalanche that swept into the Pacific Ocean, forming the Acajutla Peninsula. Reconstruction of the volcano subsequently filled most of the collapse scarp. The broad summit is cut by several crescentic craters, and a series of parasitic vents and cones have formed along a 20-km-long fissure system that extends from near the town of Chalchuapa NNW of the volcano to the San Marcelino and Cerro la Olla cinder cones on the SE flank. Historical activity, largely consisting of small-to-moderate explosive eruptions from both summit and flank vents, has been documented since the 16th century. The San Marcelino cinder cone on the SE flank produced a lava flow in 1722 that traveled 13 km E.

Information Contacts: Servicio Nacional de Estudios Territoriales (SNET), Alameda Roosevelt y 55 Avenida Norte, Edificio Torre El Salvador, Quinta Planta, San Salvador, El Salvador (URL: http://www.snet.gob.sv); Washington Volcanic Ash Advisory Center (VAAC), NOAA/NESDIS Satellite Analysis Branch (SAB), 5200 Auth Road, Camp Springs, MD 20746, USA; Charles Holliday and Jenifer E. Piatt, U.S. Air Force Weather Agency (AFWA)/XOGM, Offutt Air Force Base, NE 68113, USA; NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/NaturalHazards/); La Prensa Grafica and La Prensa Grafica Television, Final bulevar Santa Elena, frente a embajada de EUA, Antiguo Cuscatlán, La Libertad, San Salvador, El Salvador.

During the week of 22-28 August 2005, Ulawun often remained quiet but also displayed continued restlessness. People from Tauke, on the S side of the volcano reported occasional low roaring, rumbling, and booming noises on 21-22 and 26-28 August. Emissions from the summit crater consisted of moderate volumes of thick grayish vapor released forcefully. Some traces of blue vapor were also visible, but no glow was observed. Seismicity fluctuated between low and moderate, marked by small low-frequency earthquakes and small sporadic volcanic tremors. Only one high-frequency earthquake was recorded. An earthquake was felt on 22 August by people from Tauke. Apparently the earthquake was not reported by the observer at Ulamona, NW of the volcano, suggesting it was local and focused on the S side of the volcano.

Ulawun remained quiet through mid-September 2005, with the summit crater releasing weak to moderate volumes of thick white vapor.

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

Information Contacts: Rabaul Volcano Observatory, Papua New Guinea.

During the observation interval 12-18 September 2005, Pago continued to be quiet. Very small volumes of thin white vapor were released from all vents. No noises were heard and no glow was observed. Seismic activity was low, with some small, high frequency earthquakes being recorded. The highest number of high frequency events on any given day was 3, recorded on 18 September.

Geologic Background. The 5.5 x 7.5 km Witori caldera on the northern coast of central New Britain contains the young historically active cone of Pago. The Buru caldera cuts the SW flank of Witori volcano. The gently sloping outer flanks of Witori volcano consist primarily of dacitic pyroclastic-flow and airfall deposits produced during a series of five major explosive eruptions from about 5600 to 1200 years ago, many of which may have been associated with caldera formation. The post-caldera Pago cone may have formed less than 350 years ago. Pago has grown to a height above that of the Witori caldera rim, and a series of ten dacitic lava flows from it covers much of the caldera floor. The youngest of these was erupted during 2002-2003 from vents extending from the summit nearly to the NW caldera wall.

Information Contacts: Ima Itikarai and Herman Patia, Rabaul Volcano Observatory (RVO), PO Box 386, Rabaul, Papua New Guinea.