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).

Explosive volcanism continued through September but caused no damage. Nine eruptions occurred . . ., including four explosive ones, a significant decrease from last month. The highest ash plume of September rose to 3,200 m on the morning of 12 September. No volcanic earthquake swarms were detected, but 438 distinct events were registered at a seismic station 2.3 km NW of Minami-dake crater. Ashfall was sometimes observed at [KLMO], where 425 g/m² was measured in September.

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

Information Contacts: JMA.

Strombolian eruptions and lava output from Crater C continued in August-September, while Crater D exhibited fumarolic activity. The new lava flow observed in July on the high W flank stopped in August. However, the composite lava flow active since 28 August 1993 formed two new lobes that overflowed levees around 1,200 m elev. In August-September a cone in Crater C, new lava flows, and pyroclastic materials had covered and filled the bulk of the amphitheater opened by the August 1993 event.

ICE scientists noted that explosive activity in August was similar to July, although volcano-seismic activity declined. On 11 and 15 August the number and size of explosions escalated, vibrating windows and other infrastructure at a settlement 4 km from the active crater. Some of these events were detected seismically 30 km away (station Las Juntas de Abangares).

In September, explosions were fewer in number, of lower magnitude, and they carried smaller amounts of pyroclastic material. The lobes of the 28 August 1993 lava flow remained active in September. Several flow-front collapses, resembling pyroclastic flows, were witnessed during September. The largest such witnessed event (1600, 29 September), resulted in a 500-m-high, reddish-brown ash cloud. In addition, some "noisy" seismic signals recorded by ICE may have been caused by similar unwitnessed collapse events. Summit fumarolic activity remained very vigorous. Explosive activity was similar to previous months. Volcano-seismic events decreased to an average of 55/day, and tremor declined slightly to 58 minutes/day. On the SE, E, and NE flanks the vegetation continued to recede because of the effects of acidic rain, rock falls, and other factors such as high rainfall, which had induced small cold avalanches (specifically down Calle de Arena, Guillermina, and Agua Caliente rivers).

On average, 76 daily seismic events were recorded by ICE during August, compared to 104 in July and 73 in June; daily number of tremor hours averaged ~1.3, similar to July. During September, 620 seismic events (1.5-2.5 Hz frequencies) were recorded by OVSICORI-UNA, and were thought to correlate chiefly to gas-dominated eruptions, or in some cases to gas-and-ash eruptions. Sounds associated with these eruptions were similar to a jet or steam locomotive. Sporadic tremor took place in the 1.3-3.0 Hz frequency range; total tremor duration for September was 99 hours. During August-September, distance and dry tilt measurements failed to show significant changes.

Geologic Background. Conical Volcán Arenal is the youngest stratovolcano in Costa Rica and one of its most active. The 1670-m-high andesitic volcano towers above the eastern shores of Lake Arenal, which has been enlarged by a hydroelectric project. Arenal lies along a volcanic chain that has migrated to the NW from the late-Pleistocene Los Perdidos lava domes through the Pleistocene-to-Holocene Chato volcano, which contains a 500-m-wide, lake-filled summit crater. The earliest known eruptions of Arenal took place about 7000 years ago, and it was active concurrently with Cerro Chato until the activity of Chato ended about 3500 years ago. Growth of Arenal has been characterized by periodic major explosive eruptions at several-hundred-year intervals and periods of lava effusion that armor the cone. An eruptive period that began with a major explosive eruption in 1968 ended in December 2010; continuous explosive activity accompanied by slow lava effusion and the occasional emission of pyroclastic flows characterized the eruption from vents at the summit and on the upper western flank.

Information Contacts: E. Fernandez, J. Barquero, V. Barboza, R. Van der Laat, T. Marino, F. de Obaldia, and L. Carvajal, OVSICORI; G. Soto, W. Taylor, F. Arias, G. Alvarado, and R. Barquero, ICE; M. Mora, Univ de Costa Rica.

Activity increased at Crater 1 during September. Tremor amplitude registered at a seismic station 800 m W of the crater was 4.8 µm at about 0800 on 11 September. Three hours later, the AWS (figure 24), issued a Volcanic Advisory noting that Aso was getting restless. Another tremor, which was large enough to be felt at AWS, occurred at 1148 later that day. The floor of Crater 1 was covered by a pool of water, and intermittent mud ejection took place. Several tens of volcanic stones were found outside of the crater rim within ~300 m from the center of the crater during a visit on the morning of 14 September. These rocks were ejected by an explosion on the evening of 12 September, based on seismic records. The area within 1 km of Crater 1 was placed off-limits on 11 September by local governments through the Board for Volcanic Disaster Reduction.

Figure 24. Summit area of Nakadake cone at Aso, showing numbered craters, the Aso Weather Station, and associated buildings (squares). Courtesy of JMA.

During the rest of September, mud ejection was intermittent and volcanic tremor was frequent. On 15 and 18 September, ejected mud rose 150 m above the bottom of the crater, almost to the crater rim. On 16 and 19 September, a plume rose to a height of 1,500 m above the crater rim. Tremor was felt by personnel at AWS on 11, 15, 21, 22, and 29 September, and 1 October. The 29 September event was registered 800 m W of the crater with an amplitude of 52 µm, which is the largest reading since tremor amplitude measurements began in 1969.

The 12 September ejection of stones beyond the crater rim was the first eruptive activity since February 1993; mud ejections have been reported since 2 May 1994.

Geologic Background. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Information Contacts: JMA.

The Deception Volcano Observatory (figure 9) was created in 1993, but the volcano has been monitored every summer since 1986. Seismicity remained stable during the austral summer of 1993-94. The decrease in seismic activity seen during 1992-93 from 1991-92 levels continued. Only a few small local seismic events (M 1.5-2) and some larger events (M 2.5, >100 km depth) were detected. Fumaroles emitted mainly CO₂ (94.7%) and H₂S (3.5%); no SO₂ was detected. Fumarole temperatures were similar to previous years near the Argentine Station (60.5°C), in Fumarole Bay (101.2°C), and at Steaming Hill (98.5°C).

Figure 9. Map of Deception Island during 1993-94 showing craters, ice cover, the volcano observatory, and locations of monitoring equipment. Equipment near the observatory includes an electronic clinometer, a gravimeter, a magnetometer, and a 3-component seismic station. Courtesy of the Instituto Antártico Argentino.

Geologic Background. Ring-shaped Deception Island, one of Antarctica's most well known volcanoes, contains a 7-km-wide caldera flooded by the sea. Deception Island is located at the SW end of the Shetland Islands, NE of Graham Land Peninsula, and was constructed along the axis of the Bransfield Rift spreading center. A narrow passageway named Neptunes Bellows provides entrance to a natural harbor that was utilized as an Antarctic whaling station. Numerous vents located along ring fractures circling the low, 14-km-wide island have been active during historical time. Maars line the shores of 190-m-deep Port Foster, the caldera bay. Among the largest of these maars is 1-km-wide Whalers Bay, at the entrance to the harbor. Eruptions from Deception Island during the past 8700 years have been dated from ash layers in lake sediments on the Antarctic Peninsula and neighboring islands.

Information Contacts: C. Risso, Instituto Antártico Argentino; R. Ortiz, Museo Nacional de Ciencias Naturales, Spain.

Long-period screw-type events (monochromatic and with a slow coda decay) continued during September. The current episode of screw-type events began on 9 August. Compared to the episodes that preceded five eruptions at Galeras during 1992-93, this episode was more intermittent, with periods of several days between events. From 9 August to 23 September there were 29 screw-type events, with frequencies of 2.4-8.5 Hz and durations of 20-180 seconds. These events were associated with pressurization phases in the volcanic system, and gas emission.

Distinct screw-type events took place until 23 September, when 100 minutes of 7.8 Hz tremor were recorded at the station 900 m NE of the crater. The tremor episode corresponded to an increase in the gas emission rate, according to aerial observations and mobile COSPEC SO₂ measurements. After the tremor, a small swarm of short-duration long-period events occurred, which in the past have been associated with gas emission. This behavior, although on a smaller scale, was similar to that during and after the July 1992 and January, March, April, and June 1993 eruptions. Seismic activity stayed at low levels through the end of September; superficial low-magnitude events were related to fracturing and fluid movement (butterfly events). Low rates of deformation and SO2 emission continued.

High-frequency seismicity was located in several sectors around the volcano; the most significant activity was from a source 3.3 km NNE of the active cone, where three earthquakes originated that were felt in Pasto (9 km E) and villages such as Jenoy, Nariño, and La Florida. An earthquake on 5 September had M 2.6 and a depth of ~8.6 km. Two earthquakes on the 28th had M 2.2 and 2.9 with depths of 7.1 and 8.8 km, respectively.

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

Information Contacts: INGEOMINAS, Pasto.

Eruptive activity continued in the second half of August with emissions of steam and minor amounts of ash on 20-21 August. A shift in wind direction produced light ashfall in Adak on 20 August and temporarily disrupted air traffic to Adak on the 22nd. Weather clouds frequently obscured Kanaga from late August through mid-September. Preliminary analysis suggests the ash is broadly similar in composition to other known tephras and lavas from Kanaga.

Observers reported white steam clouds rising to 600 m above the summit on 8 September; occasional low rumbling noises were also heard. Weather clouds obscured Kanaga for much of 16-30 September, but AVHRR satellite images indicated a steam plume extending ~50 km S of Kanaga on 22 September. . . . .

Geologic Background. Symmetrical Kanaga stratovolcano is situated within the Kanaton caldera at the northern tip of Kanaga Island. The caldera rim forms a 760-m-high arcuate ridge south and east of Kanaga; a lake occupies part of the SE caldera floor. The volume of subaerial dacitic tuff is smaller than would typically be associated with caldera collapse, and deposits of a massive submarine debris avalanche associated with edifice collapse extend nearly 30 km to the NNW. Several fresh lava flows from historical or late prehistorical time descend the flanks of Kanaga, in some cases to the sea. Historical eruptions, most of which are poorly documented, have been recorded since 1763. Kanaga is also noted petrologically for ultramafic inclusions within an outcrop of alkaline basalt SW of the volcano. Fumarolic activity occurs in a circular, 200-m-wide, 60-m-deep summit crater and produces vapor plumes sometimes seen on clear days from Adak, 50 km to the east.

Information Contacts: AVO.

Lava continued to enter the ocean in the Kamoamoa/Lae Apuki area during the first half of September. Flows from the tube extended the bench, stranding the littoral cone built in July. Activity appeared to diminish in early September, and by 5 September the only active entry was SE of the littoral cone. The entry was moderately explosive through 12 September. Small pahoehoe and 'a'a lava flows continued to break out on the E side of the flow field between 270 and 15 m elevation.

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

Information Contacts: T. Mattox, HVO.

During 15-19 September, gas-and-ash bursts rose 500-700 m above the crater. The eruption column reached 1.5-2.0 km above the crater and extended >50 km downwind to the SE. Lava flows extruding from two vents 200 m below the crater rim had moved down to 2,800 m elevation on the NW and SW flanks. Phreatic explosions were occurring at the contact of the NW lava flow and the glacier. Lava fountains in the central crater reached heights of 300-500 m. Continuous volcanic tremor, with a maximum amplitude of 6.1 µm, was recorded at the seismic station 11 km from the volcano.

From 20 to 23 September, gas-and-ash bursts increased in height to 800-1,000 m above the crater. The eruption column continued to reach ~2 km above the crater, but extended >100 km SE. Lava flows on the NW and SW flanks remained active, and fountains in the central crater increased to heights of 500-700 m. Volcanic tremor was continuous with a maximum amplitude of 8.2 µm.

Eruptive activity increased on the afternoon of 30 September. Ash bursts rose 3 km above the crater and the ash column reached an estimated altitude of 10 km and extended SE for >100 km. Lava flows on the NW and SW slopes of the volcano remained active, and mudflows were noted on the N slope. Continuous volcanic tremor had a maximum amplitude of 8.4 µm.

At 0600 on 1 October the eruption entered a paroxysmal stage with lava bursts rising 4,500 m above the crater rim. The ash column was estimated at 15-20 km altitude and extended >100 km SE. Phreatic explosions along the margin of the flank lava flows generated steam clouds >1 km high. Avalanches of incandescent blocks were observed descending the N slope. Between 0900 and 1100, ash and lava bursts produced a dark, ash-laden plume rising to a height of 15-18 km and moving ESE. GMS satellite imagery showed ash ~565 km SE moving at ~140 km/hour. By 1400 the dark ash plume reached 15 km altitude. Lava and ash explosions continued from the central crater at 1500, when the ash column rose to 12-14 km above sea level and moved ESE at an altitude of 10-11 km. Pilot reports indicated that the ash was at 9-11 km (FL300-370 = 30,000-37,000 feet). A 747 aircraft reported an ash encounter at 11 km altitude, but avoided the cloud by climbing to ~12 km (FL390). Helicopter observations at 1500-1700 revealed two lava flows on the N and NW slopes and lava fountaining to 900 m above the crater rim. The eruption appeared to reach its maximum intensity between 0600 and 1630. By 1900 the ash plume was at a maximum altitude of 9-11 km and drifting E for >100 km. Volcanic tremor was continuous with a maximum amplitude of 8.4 µm. Analysis of GMS infrared imagery at 2330 showed a thin concentrated plume extending generally SE, surrounded by areas of thinner ash.

After about 0530 on 2 October, layered weather clouds moving from the W had obscured the summit from GMS satellite observation, although the dissipating ash cloud could be seen SE of the volcano. At 0920 a dark ash plume rose to ~8.4-8.7 km altitude and drifted E, but by 1100 the plume was only rising to 6-7 km and drifting NNE. Areas of thick, moderate, and thin dispersing ash, E and S of the volcano beyond the obscuring weather clouds, continued to be tracked by satellite through 2030. By that time, the ash cloud was becoming more diffuse and harder to distinguish from underlying low-level clouds.

The volcano was obscured by clouds on 3 October. Volcanic tremor with a maximum amplitude of 1-2.5 Nm indicated that the eruption was continuing, but at a reduced rate. On 4 October, only fumarolic activity appeared to be occurring inside the summit crater and no incandescence could be seen at night. The gas-and-steam plume rose ~1 km above the crater and was directed S for ~5 km.

Meteor-3 TOMS overflew the eruption plume at 1347 on 1 October. Preliminary results showed an extended SO2 cloud ~800 km long to the SE, with an approximate area of 150,000 km². Estimated cloud mass was 90 kt SO₂ +- 50%. A pass at 1520 on 2 October did not find an SO₂ cloud.

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

Information Contacts: V. Kirianov, IVGG; J. Lynch, SAB; I. Sprod, GSFC.

A small eruption on 18 September 1994 was the first observed activity since July 1993. A new central depression ~20 m deep was emanating hot gas from a prominent ring fracture ~100 m in diameter. Virtually continuous booming and rushing noises indicated near-surface lava, but it was not possible to see over the dangerous overhang. The new depression within the existing crater overlapped the 1992-93 eruptive sites and caused partial subsidence of older hornitos. A separate new lava-filled central hornito (~30 m in diameter and 10 m high) was observed for ~6 hours. Highly vesicular brown lava erupted once to the brim and was sampled. Lava was generally a few meters below the surface of the hornito, but periodic surges ejected spatter to ~30 m away. These ejections were interspersed with jetting of colorless gas and occasional widespread lapilli emissions to ~50 m away. The new hornito lava, ~50 m above the base of the central depression, was very frothy, crystal-rich, non-incandescent, and appeared similar to the type seen in 1992.

Geologic Background. The symmetrical Ol Doinyo Lengai is the only volcano known to have erupted carbonatite tephras and lavas in historical time. The prominent stratovolcano, known to the Maasai as "The Mountain of God," rises abruptly above the broad plain south of Lake Natron in the Gregory Rift Valley. The cone-building stage ended about 15,000 years ago and was followed by periodic ejection of natrocarbonatitic and nephelinite tephra during the Holocene. Historical eruptions have consisted of smaller tephra ejections and emission of numerous natrocarbonatitic lava flows on the floor of the summit crater and occasionally down the upper flanks. The depth and morphology of the northern crater have changed dramatically during the course of historical eruptions, ranging from steep crater walls about 200 m deep in the mid-20th century to shallow platforms mostly filling the crater. Long-term lava effusion in the summit crater beginning in 1983 had by the turn of the century mostly filled the northern crater; by late 1998 lava had begun overflowing the crater rim.

Information Contacts: A. Jones, W. Taylor, A. Church, L. Johnson, and T. Allison, Univ College London.

A red incandescent area that opened in the inner crater during mid-June 1993 remained active at least through June 1994. An unbroken gas plume has often been observed extending several kilometers from the volcano. Average fumarole temperatures, measured with an infrared pyrometer, began increasing in May 1993 from around 50°C to almost 250°C by July 1993 (figure 9 and 18:07). Fumarole temperatures slowly increased to almost 400°C by May 1994, when they suddenly increased again, reaching almost 600°C by the end of July 1994. Measurement of SO₂ emissions at the summit were carried out using colorimetric and chemical techniques. An increase from background to ~5 mg/m³ was detected in June 1993 after the incandescent opening first appeared. SO₂ increased to ~15 mg/m³ between July and August, and again increased sharply during September-November 1993 to ~30 mg/m³. Steady increases in the SO₂ emission rate since then resulted in measurements of ~35 mg/m³ in May-July 1994.

Figure 9. Average fumarole temperatures in the summit crater of Masaya, January 1993-July 1994. Courtesy of INETER.

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

Information Contacts: H. Taleno, L. Urbina, C. Lugo, and O. Canales, INETER.

"The Office of Seismology and Volcanology of the Department of Geological Engineering, Costa Rican Institute of Electricity (ICE), has monitored the seismicity of the Miravalles Geothermal Field since 1977. The monthly number of recorded earthquakes at the Miravalles Caldera from April 1991 through July 1994 is shown on figure 1. Maximum magnitudes were 3.5; no high-magnitude local earthquakes occurred within the geothermal field during this study period. Previous seismological campaigns showed a similar level of activity.

Figure 1. Monthly number of earthquakes recorded within the Miravalles Caldera, April 1991-July 1994. Courtesy of R. Barquero, ICE.

"The 219 tectonic events located during this period were distributed within a radius of 15 km of the geothermal field. There were some clusters of events that from their location and alignment could be correlated to previously determined faults and structures in the area and they were cataloged in 8 groups. Earthquakes recorded during the monitoring campaign were mostly shallow, with depths of 0-15 km and predominantly 0-5 km. The distribution of earthquakes cannot be correlated with a magma chamber or any shallow magmatic body in the area, but it confirms that some seismic activity is taking place under and inside the caldera."

Geologic Background. Miravalles is an andesitic stratovolcano that is one of five post-caldera cones along a NE-trending line within the broad 15 x 20 km Guayabo (Miravalles) caldera. The caldera was formed during several major explosive eruptions that produced voluminous dacitic-rhyolitic pyroclastic flows between ~1.5 and 0.6 million years ago. Growth of post-caldera volcanoes in the eastern part of the caldera that overtopped much of the eastern and southern caldera rims was interrupted by edifice collapse which produced a major debris avalanche to the SW. Morphologically youthful lava flows cover the W and SW flanks of the post-caldera Miravalles complex, which rises above the town of Guayabo on the flat western caldera floor. The only reported historical activity was a small steam explosion on the SW flank in 1946. High heat flow remains, and it is the site of the largest developed geothermal field in Costa Rica.

Information Contacts: R. Barquero, ICE.

After the last eruption of Cerro Negro in April 1992 (BGVN 17:03 and 17:04), telemetry-equipped seismic instruments donated by the Japanese government were installed in November 1993. During the previous 10 months, seismic behavior has chiefly consisted of low-amplitude high-frequency events, but beginning on 7 September this changed. Tremor amplitudes increased, first to 2 mm but later reaching 10-12 mm, and tremor episodes lasted from minutes to hours. Field observers inspecting the summit on 15 September found neither steam nor fresh ash. Tremor and high-frequency seismicity continued through 30 September. Other recent fieldwork has investigated the extent of passive degassing and the chemical composition of the emissions (BGVN 19:06).

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

Information Contacts: H. Taleno, L. Urbina, C. Lugo, and O. Canales, INETER.

Activity increased at 0400 on 12 October with vigorous Strombolian explosions. Approximately 5 cm of ash was deposited in El Patrocinio, ~4 km W (figure 12). Ash drifted as far as Santa Lucia Cotzumalguapa, ~45 km WSW on the Pacific lowlands. Although apparently declining on 14 October, Strombolian activity was continuing, an ash plume to 300 m above the vent persisted, and tremor was still being detected by the seismometer at Pacaya. As of 14 October, five lava flows active on MacKenney cone had reached the base of the edifice, two on the N, two on the W, and one on the S flank. Flow velocities were reported to be 10 m/hour. Heavy rains and cloud cover since the start of the increased activity have prevented detailed observations. The Comite Nacional de Emergencias (CONE) evacuated 142 people from the towns of El Patrocinio, El Caracol (3 km SW), and other nearby areas, to San Vincente de Pacaya (5 km NW).

Pacaya is a complex volcano constructed on the S rim of the 14 x 16 km Pleistocene Amatitlan Caldera. In 1565, the first recorded historical eruption from Pacaya caused ashfall for three days in Guatemala City. Following explosions in July and October 1965, Strombolian activity was generally continuous until March 1989 when explosive activity removed ~75 m of the MacKenney cone summit and enlarged the crater. Strombolian activity began again in January 1990 and has continued intermittently since then. This latest episode of activity, although smaller in terms of area impacted by tephra, is similar to the activity during July-August 1991, which again destroyed part of the cone and damaged towns W of the volcano.

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

Information Contacts: Eddy Sanchez, INSIVUMEH.

Phreatic and strong fumarolic activity between 20 July and 5 August formed a pan-like structure in the bottom of the inner lake (figure 55). Following heavy rainfall on the summit area, this structure was filled with water and mud. In the active crater, fumaroles on the S and SE sides of the lake disappeared during August, and block-and-ash eruptions formed a new small crater. The majority of the blocks fell onto the crater floor, the largest seen was 1.2 m in diameter. These eruptions ceased 5 August, but smaller gas-column discharges followed, to heights of 600 m above the lake. These discharges were noteworthy because they were rich in sulfur particulates.

Figure 55. Perspective sketch looking W showing the active crater at Poás, mid-late August 1994. The dome is on the left, and the water-filled pan-like depression in the center is surrounded by active fumaroles (1-8) and a boiling mudpot (9). There is no scale, but the crater opening (rim-to-rim) is on the order of a kilometer across. Courtesy of Mauricio Mora, UCR.

The lake in the active crater rose 1.5 m in September, covering some fumaroles. The 60°C lake was gray, muddy-looking, and clouded with suspended sulfur. Fringed by mud pots, the lake occupied the pan-like structure formed during earlier phreatic and strong fumarolic activity. Owing to the lake's rise, fumaroles in its center appeared isolated; the fumaroles to the N, NW, and W generally maintained steam columns rising ~600 m above the crater. The sound produced resembled steam escaping from a pressure-release valve when heard from the overlook.

Fumaroles on the dome were unchanged in August and September. Fumarolic activity remained strong through late September in several locations on the crater bottom, including boiling mudpots. At the beginning of September the W fumarole converted into a pan-shaped source vent constantly releasing gas and phreatic emissions to heights of 5 m. In mid-September a new fumarole appeared on the W fringe of this source vent with a moderate gas output. Toward the end of the month the gas released at the source vent decreased.

During August and September, OVSICORI-UNA recorded 3,639 and 1,524 low-frequency events, respectively. Compared to tremor duration in August (97 hours), tremor duration in September increased by 42% (to 138 hours). August tremor amplitude was 4-11 mm, with a frequency range centered around 2.3 Hz. September tremor amplitude was 3-9 mm, its frequency range was largely 1.4-2.3 Hz. In addition, a contant, deep noise source (1-3 mm amplitude) was noted during August.

On 23 September seismic instruments recorded a swarm of 11 events, of which 10 were felt by the inhabitants close to the volcano. Four of these events were located (table 5). The located events had magnitudes between 2.1 and 3.0 and epicenters in the W sectors of the volcano. Deformation measurements showed an expansion of 14 ppm during the last week of September. The localized change was found along one of the measured lines inside the crater. Outside the crater there were no significant changes. Radial inclination at the summit was very low on the two precision leveling lines. The dry tilt meters also lacked significant changes.

Table 5. Four located Poás earthquakes that occurred in the swarm on 23 September 1994. Courtesy of OVSICORI-UNA.

Acidic atmospheric conditions were discussed for 1986-90 in an unpublished report by Fernandez and Barquero (1990). During this interval the active crater lake at Poás progressively rose in temperature from ~30 to 90°C. Compared to 1986, the lake's water also increased in dissolved sulfur (2- to 3.5-fold), chlorine (7-fold), and fluorine (~10-fold). Prevailing winds generally carried acidic gases S and SW. Measurements of total wet and dry deposition taken at both the crater rim overlook (El Mirador) and 2.3 km SW of the crater during 1986-90 indicated pH values as low as 3.5-4.1. Acidic rain disrupted strawberry, dairy, and coffee farms (2 x 10⁴ m² severely damaged), affecting 681 farmers. It also disturbed the trees in several reforestation projects, where losses reached 95%. Farm equipment rusted rapidly. At the time of the report, studies failed to clearly demonstrate health problems, although local inhabitants complained of respiratory, skin, and eye irritations. The National Park and villages adjacent to Poás sustained damage, especially to building roofs. Areas significantly affected by the acidic atmospheric conditions reached over 24.5 ha (245,000 m²). The report cited four references to Poás work, including a paper by Brown and others (1989) proposing that ". . . crater-lake and fumarole discharge variations may well occur before significant signals on seismic and tilt networks are detected."

They further stated that ". . . maintained power output and/or low water supply could culminate in a dramatic change in activity, possibly with devastating results." A final note makes this case by example: "After continued evaporation through the dry season, Poás lake disappeared in late April 1989 accompanied by several days of continuous phreatic geysering. A dry steam/'ash' plume . . . was erupted to 200 m height on 25 April; from 30 April to early May a continuous plume reached 2 km in height with fallout over 200 km²."

References. Brown, G., Rymer, H., Dowden, J., Kapadia, P., Stevenson, D., Barquero, J., and Morales, L.D., 1989, Energy budget analysis for Poás crater lake: implications for predicting volcanic activity: Nature, v. 339, no. 6223, p. 370-72.

Fernandez, E., and Barquero, J., 1990, Erupciones de gases y sus consecuencias en el volcan Poás, Costa Rica [Eruption of gases and their consequences at Poás volcano], Costa Rica: Observatorio Vulcanologico y Sismologico de Costa Rica, Univ Nacional, Heredia, Costa Rica, 4 p.

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

Information Contacts: E. Fernandez, J. Barquero, V. Barboza, R. Van der Laat, T. Marino, F. de Obaldia, and L. Carvajal, OVSICORI-UNA; G. Soto, W. Taylor, F. Arias, G. Alvarado, and R. Barquero, ICE; M. Mora, UCR.

New eruptions began on 19 September 1994, ending a repose period of ~51 years. Following the pattern of the last two eruptive episodes (1878 and 1937-43), there were almost simultaneous outbursts on opposite sides of the caldera as the intracaldera cones Tavurvur and Vulcan began erupting at 0605 and 0717, respectively. The eruption at Vulcan was the more powerful and included a brief phase of strong Plinian activity soon after its onset. Vulcan's eruption ended on 2 October. The eruption at Tavurvur, after peaking during the first five days of activity, exhibited a slow decline. However, moderate to weak activity continued as of 28 October. By mid-late October, eight new 3-component seismic stations and two tilt stations had been installed by volcanologists at RVO with the assistance of USGS scientists. Many stations had been damaged or destroyed by tsunami, vandalism, or heavy ashfall during the eruption. The following report is from RVO.

Precursory activity. "A levelling survey along the usual route from the Rabaul Town area to Matupit Island was completed on 15 September. Compared with the previous survey on 19 July (19:07), the greatest change was uplift of ~25 mm at the S extremity of the island. This rate of uplift is similar to the long-term rate observed during 1973-83, prior to the 'Rabaul Seismo-Deformational Crisis Period' of 1983-85.

"For most of the time in the preceeding few months, seismicity gave little or no warning of the coming eruptions. The normal (high-frequency) seismicity on the caldera ring-fault was at a low level. Some low-frequency events were recorded, but their origin and significance are not yet known.

"The eruptions were immediately preceded by 27 hours of vigorous and fluctuating seismicity, which was initiated by two caldera earthquakes (max M_L 5.1) at 0251 on 18 September. These earthquakes were located in the E part of the caldera seismic zone, near Tavurvur, at a depth of 1.2 km. The earthquakes were felt very strongly throughout the town and a small localized tsunami was generated. Seismicity over the following four hours took place near Vulcan and showed a general decline. Through this period, the pattern of seismicity appeared to be similar to many previous swarms of earthquakes on the caldera fault system. During the next ten hours (0600-1600), earthquakes continued at a steady rate, still concentrated near Vulcan. From about 1600 on 18 September, seismicity increased and reached a peak at about 0200 on 19 September; at this time, earthquakes were felt every few minutes. Seismicity then showed a slow decrease. Earthquake epicentres were concentrated in the Vulcan area until about 0430, when the focus shifted to Tavurvur.

"Soon after dawn on 19 September (0600), it was clear that an eruption was imminent because offshore areas had emerged. The most obvious uplift was at Vulcan, where a tide gauge was almost out of the water, indicating an estimated uplift of 6 m. The W and S coasts of Matupit Island had also been raised and the S shoreline was shifted ~70 m S.

Evacuation. "In consideration of the increased seismicity after about 1600 on 18 September, RVO recommended the declaration of a Stage 2 alert (eruption expected within weeks to months) around 1800. This was subsequently issued at 1815. Throughout the late afternoon a voluntary evacuation of the town had developed, but the release of the Stage 2 alert accelerated the process. At midnight, RVO advised the Provincial Disaster Committee that an eruption was imminent. By this time, people had congregated in Queen Elizabeth Park in the centre of Rabaul Town. Transport was mobilised, and during the next few hours people were ferried from the town area to beyond the caldera rim. RVO recommended a Stage 3 alert (eruption expected within days to weeks) in the early hours of the 19th, but the Disaster Committee refrained from a declaration because the evacuation appeared to be proceeding well. It was feared that announcement of a higher stage of alert might be counter-productive. The evacuation went smoothly and by around 0700 on the 19th, the town and high-risk areas were virtually deserted.

Outbreak of eruptions. "An aerial inspection had been arranged for early morning on the 19th. While waiting on the Rabaul airstrip, a small white emission cloud was noticed above the W rim of Tavurvur's summit crater at about 0603. Three minutes later, ash was seen in the emissions which appeared to originate from the SW part of Tavurvur's 1937 crater. The intensity of the emissions was low as billowing, grey, cauliflower-shaped ash clouds rose slowly and with little sound (figure 18). The ash clouds rose only a few hundred metres and were driven towards Rabaul Town by moderate SE winds. At about 0618, the ash plume had reached the S limits of the town. The strength of the eruption remained low over the next hour as darkness descended on Rabaul.

Figure 18. Photograph of Tavurvur taken from a helicopter at 0611 on 19 September 1994, just after the onset of activity. Note the 1878 cone (right foreground) being eaten away. View is approximately towards the ENE. Courtesy of Rod Stewart, RVO.

"The eruption of Vulcan commenced at 0717 on 19 September with relatively small explosions on the N flank of the Vulcan 1937 cone. However, activity intensified rapidly, and by 0737 low-density pyroclastic flows were being generated and the eruption column was rising rapidly. Run-out distances of ~2 km were common for these early pyroclastic flows. At 0743, ballistic ejecta were seen landing in the water up to 1 km from the E shore of Vulcan. At about 0745 a phase of very strong activity commenced. Continuous explosions generated a Plinian eruption column that attained a height of ~20 km. The sounds of this activity were of dull thudding, quite a contrast to the sharp, loud reports of electrical discharges around the eruption column. By 0830, Rabaul Town and surrounding areas were enveloped in darkness by the spreading ash canopy. The phase of Plinian activity had ended by about 0830, but strong ash emission continued.

"A number of tsunami were generated, probably by the Vulcan activity. The largest of these rose ~5 m above high water. The SW and W parts of Matupit Island were hit numerous times by tsunami, washing inland as far as several hundred metres. Small boats were carried inland ~60 m at the head of Rabaul Harbour.

Continuing eruptions. "The activity at Tavurvur increased through the 19th and the eruption column was estimated to have reached a maximum height of ~6 km. Only one vent was active. The eruption column was very dense and the moderate SE winds drove the ash plume directly over Rabaul. No pyroclastic flows were generated at Tavurvur. Over the next few days activity at Tavurvur waned slightly. The eruption column was usually ~1-2 km high. The dense dark grey-brown ash clouds fed a plume that continued to blanket Rabaul Town with fine ash.

"At Vulcan, at least four vents were active. The main vent was at the point of the eruption outbreak. Another vent slightly to the N was active briefly. A vent in the crater of the 1937 Vulcan cone and one on its SW flank also were active. Two more phases of Plinian activity took place at Vulcan in the evening of 19 September between about 1830 and 1930. The intensity of this activity was considerably weaker than the first Plinian phase. Pyroclastic flows were formed throughout the first few days of the eruption. The largest of these extended ~3 km. Pumice from Vulcan formed a large raft that covered most of Simpson Harbour.

Sequence of felt earthquakes and decline of eruption. "On 23 September, between about 1850 and 1900, there was a sequence of strongly felt caldera earthquakes. The largest of these had an estimated magnitude of 3.5. Most of the seismic stations had been lost during the first day of the eruption, so it was not possible to locate any of these earthquakes. However, most of them appeared to originate from the SE part of the caldera. These earthquakes may have been due to structural re-adjustment of the caldera to the eruptive removal of significant quantities of magma. On the morning of 24 September, a marked decline was evident in the activity at Vulcan, and a lesser decline was seen at Tavurvur. This may have been connected with the sequence of earthquakes the previous evening. The eruption at Vulcan ended on 2 October, but Tavurvur continued erupting, generating an eruption column 1-2 km high and a plume ~20 km long.

Lava flow at Tavurvur. "A small lava flow was first noticed in the summit crater of Tavurvur on 30 September. The aa lava was emerging from a sub-terminal vent on the W flank of the growing ejecta cone. The flow rate was extremely low as the lava slowly advanced towards the W rim of the summit crater. On 5 October, a new lava lobe was seen overriding the first lobe in the summit crater of Tavurvur. This lava lobe also advanced very slowly and eventually reached the nose of the first lobe. The length of these lobes was ~100 m. Lava continued to be fed into these lobes after they had stopped advancing, causing them to thicken. Eventually, on 8 October, a breakout occurred on the W side of the original lobe. A more fluid black lava emerged, ponding between the earlier lava flows and the W crater rim. On 12 October, following a considerable growth of the body of lava within the crater, lava began spilling over the crater rim and descending Tavurvur's W flank. A second lava breakout from the earlier bulky flows within the crater took place on 14 October. This became the main feeder for the slowly advancing lava flow on the W flank of the cone. It remained active until about 25 October.

Tephra from Vulcan and Tavurvur. "The tephra from Vulcan was pale grey-brown pumice and ash, probably of dacitic composition. In contrast, Tavurvur's tephra was dominated by very fine-grained ash. Accretionary lapilli were abundant throughout both sequences and a number of ash units were extremely hard, apparently having self-cemented on deposition. The base of the Tavurvur sequence was marked by a blue-grey very fine ash that appeared to be rich in sulphides. This material probably originated as a hydrothermal clay on the crater floor. Late in the Tavurvur sequence was a pumiceous unit that may be sub-Plinian. During 8-18 October, strong explosions ejected ballistic material as far as 1.5 km from Tavurvur's summit. Large blocks (to ~1 m size) were found partially buried in the road around the N and E foot of Tavurvur. These ejecta included a mixture of dense glassy lava blocks, porphyritic lava blocks, and pumiceous bombs.

Sulfur dioxide emissions. "SO₂ emission rates from Tavurvur were measured in the period from 29 September to 6 October by Stan Williams (Arizona State Univ). Preliminary results indicated a progressive decline from ~30,000 to ~3,000 t/d.

Ground deformation. "Tilt measurements, which started at Matupit Island on 24 September, indicated a large deflation (~930 µrad) of the central part of the caldera compared with pre-eruption values, and a slowly reducing rate of deflation during the eruption. The rate of deflation declined from ~10 to ~2 µrad/day between 24 September and 25 October. Sea-shore levelling measurements, which started in late September, indicated minor subsidence over most of the caldera compared with pre-eruption levels. The greatest subsidence was ~80 cm in the area of Rabaul Airport, between Matupit Island and the town. About 3 m of uplift was recorded at the E shore of Vulcan and slight uplift was recorded at the S end of Matupit Island. Geodetic levelling from outside the caldera, through Rabaul Town, and onto Matupit Island, confirmed these results.

Effects of the eruption. "The official death toll from the eruptions and associated events was five; four of which were due to house roofs collapsing. One person was killed by lightning. Over 50,000 people have been displaced by the eruptions and were in care centres in safe areas of the Gazelle Peninsula as of the end of October.

"The rapid accumulation of ash on Rabaul Town caused collapse of some buildings within a few hours of the onset of the eruptions. Ashfall from Tavurvur in the first few days of the eruption caused widespread damage in Rabaul Town; virtually every building in the S part of town collapsed. Serious structural damage was sustained by most buildings in the ashfall zone within 8 km of Tavurvur. All housing in the immediate area of Vulcan (to ~2 km) was destroyed within ~1 hour of the start of the Vulcan eruption by a combination of pyroclastic flows and heavy ashfall.

"Heavy rainfall during the first day and night of the eruption exacerbated the effects of heavy ashfall. Mudflows and floods were widespread in the Rabaul Town area, near Vulcan, and immediately outside the Rabaul Caldera to the NW. The most serious floods were NW of the caldera, where the heavy ashfall caused rapid runoff and eventual deep erosion and migration of stream channels. The obliteration of rainforest cover around Rabaul will present a serious risk of flash floods and mudflows at times of heavy rainfall. The wet season in Rabaul normally starts in early December.

Satellite imagery. "The westwards-spreading ash plume . . . was clearly visible from Earth-imaging satellites. A wide-angle plume (90°) was seen on a series of Japanese GMS images as a triangular area at 0903 of 19 September, spreading at different wind levels in a fan extending from Rabaul. The N edge of the plume trended NW, and the S edge to the SW, extending across the E Bismarck Sea and moving down the N coast of New Britain.

"A similar spreading pattern was seen on images (IR channel 4) from the NOAA-12 polar orbiting satellite (19:08). The SE margin of the cloud at 1800 on 19 September was seen curving S over the Solomon Sea and SE New Guinea, with the NE margin extending past Manus Island. All parts of Papua New Guinea to the W of these margins were covered by the eruption cloud. The strongly sheared cloud seen on subsequent images was being driven S and then E by high-level winds towards the Fiji region.

"AVHRR imagery from the Nimbus-7 satellite showed similar ash-cloud dispersal patterns. However, computation of the temperature differences recorded between AVHRR IR channels 4 and 5 at 1905 on 19 September and 0747 the next day yielded unexplained patterns in which negative temperature differences (T4-T5), thought to be indicative of ash-bearing clouds, were restricted to 1° of latitude W of Rabaul (F. Prata, pers. comm. to RVO). In addition, the SO₂ signature seen on TOMS images at 1520 on the 20th and 1503 on the 21st (19:08) were restricted to the E corner of the Bismarck Sea W of Rabaul, or over the general Rabaul area. Both of these aspects of the satellite imagery require further consideration and study."

Jim Lynch (NOAA Synoptic Analysis Branch) provided the following satellite interpretation. NOAA and GMS satellite imagery clearly depicted the volcanic plume during the first three days of the eruption (19-22 September). The size and shape of the plume during the first 18 hours is shown on figure 19. By correlating plume drift with available wind data, the maximum height of the original plume was estimated at 21-30 km altitude, well into the stratosphere. The eruption maintained the plume to this altitude for ~12 hours before tapering off to 12-18 km. After the first 56 hours of continuous activity there was apparently a 6-hour respite, after which the eruption resumed at a moderate intensity, generating a plume to 21 km) blew W and WNW toward Borneo and Southeast Asia; however, the plume became too diffuse to track beyond 1,300 km from the volcano. The upper tropospheric plume (12-18 km) tracked SW, then S, and finally SE for ~1,000 km around an upper-level ridge before it became too diffuse to track with standard infrared imagery. The denser, more opaque portion of the plume remained within ~400 km of the volcano. Analyses of visible, infrared, and multispectral imagery from NOAA-12 and GMS satellites definitively depicted an ash plume only within 1,000 km of the volcano. Analysis of TOMS data revealed a relatively small amount of SO₂ (80 kt) close to the volcano (19:08). The fact that a dense plume of ash and aerosols did not remain in the upper atmosphere suggests that the ash plume was composed mostly of large particulates that fell out of the atmosphere near and just downwind from the volcano.

Figure 19. Areal extent and propagation of ash from Rabaul by upper-level winds from 0830 on 19 September to 0230 on 20 September 1994. Isochrones are based on analysis of GMS infrared imagery. Courtesy of Jim Lynch, NOAA.

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

Information Contacts: C. McKee, with contributions fromRVO Staff and R. Johnson, RVO; J. Lynch, SAB; D. Dzurisin and C. Miller, CVO.

Fumarolic activity in the main crater remained vigorous during August and September. Preliminary processing of seismicity recorded by ICE with a portable digital station 2.2 km S of the crater during fieldwork in late August indicated several hundred low-frequency earthquakes beneath the crater, and background tremor-like activity. The preliminary interpretation is that the low-frequency seismicity is caused by hydrothermal circulation among a shallow magma body, aquifers, and the lake system. The OVSICORI-UNA seimic station (5 km SW of the active crater) registered 15 high-frequency low-magnitude events during September.

From the village of México (40 km NE), early morning observations during late September and early October by an ICE geologist revealed a steam-rich gas column rising up to 1 km above the crater. This is higher than the 300-400 m estimated in March.

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

Information Contacts: E. Fernandez, J. Barquero, V. Barboza, R. Van der Laat, T. Marino, F. de Obaldia, and L. Carvajal, OVSICORI; G. Soto, W. Taylor, F. Arias, G. Alvarado, and R. Barquero, ICE; Mauricio Mora, Univ. de Costa Rica.

Crater Lake has continued cooling since a minor heating event in early June, which occurred without eruptions. Observations through late August indicated a possible reversal of this cooling trend: minor convection, slightly enhanced acoustic signals, and an increase in volcanic tremor.

On 12 August the crater lake was pale gray with an indistinct slick over the central vent. The N vent area was not observed. Snow was present almost to the water's edge with no evidence of surging. Lake temperature at Logger Point was 16°C on 12 August. The battery for the ARGOS temperature logger was replaced on 12 August and a lake temperature of 18°C was recorded. The lake had a similar appearance on 27 August, but there was weak upwelling in the N vent area. Rafts of yellow sulfur were stranded on the shoreline. Lake temperature at Outlet was 17°C. In late August, ARGOS temperatures began displaying significant diurnal variation, and were not much higher than at Outlet. This may indicate that either the sensor had drifted closer to the surface or that surface temperature variations penetrated deeper into the lake. Outflow was ~25 l/s during both visits.

Volcanic tremor remained at slightly elevated levels during June, and during July the tremor levels varied. The dominant frequency remained at 2 Hz, implying only one source region but a periodic variation in output strength. Tremor levels were low in early August, but rose slightly during the month. Volcano-seismic activity was last reported on 7 July. . . .

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

Information Contacts: P. Otway, IGNS Wairakei.

The number of high-frequency seismic events increased from 46 in March to 897 in July. The number decreased again in August and September, but there were large tremors. For an unspecified time interval prior to 21 August the gas plume extended several kilometers from the volcano.

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

Information Contacts: H. Taleno, L. Urbina, C. Lugo, and O. Canales, INETER.

Extraordinarily intense activity was observed 21-22 August during an ascent and 8 hours on the summit (Pizzo sopra la Fossa). Significant morphologic changes had taken place in the crater area since March 1994 (19:03). Due to the vigorous activity, the craters could not be approached; however, the position and shape of eruptive vents were visible due to the filling of the craters. During the observation period, 10 boccas produced eruptions (compared with 4 in March), most of which were generally clustered and showed sympathetic to simultaneous activity. There were rarely any 10-minute intervals without eruptions, and for periods of up to several hours there was continuous lava fountaining from up to 3 vents at the same time. There was no regularity in the succession, size, or timing of the eruptions. Crater 2 was inactive.

Crater 1, the NE-most active crater, had 6 active boccas, most of which had formed spatter cones. None of these cones had been present during the crater visits in March; during the present visit, however, Crater 1 was filled almost to its rim with cones and erupted pyroclastics. Growth of these spatter cones since March had been much more vigorous than the formation of the earlier cones (1986-93), which were destroyed by explosions in October 1993. Only 5 months before this visit, Crater 1 had been a deep (>60 m) chasm, with no indication of incipient cones. The new cones were, after only 5 months of growth, larger than the pre-October 1993 cones.

The northernmost two vents, 1A and 1B, formed a broad, flat cone ~5 m high that displayed continuous incandescence. Vent 1A formed a crater 5-10 m wide on top of the cone and was the site of frequent brief lava fountains, but also had periods of quasi-continuous lava jetting and spraying. The focus of the explosions was apparently very close to the surface judging from the broad angle of the jets that sprayed large clumps of lava over a wide area, thus contributing to the broad, flat shape of the cone. The largest fountains from 1A rose higher than Pizzo sopra la Fossa, maybe to heights of 250 m. Vent 1B on the NE flank only became active towards the closing stages of the largest eruptions of 1A, ejecting a narrow fountain obliquely NE.

A cluster of vents was present in the central part of Crater 1, the most active among them (2A) was located on top of a tall, steep, spatter cone about 20-25 m high. Vent 2A (diameter <=3 m) was the site of activity ranging from continuous spattering to vigorous, long-lasting fountains that reached heights >250 m. There were at least four periods of continuous and vigorous fountaining, at 1930-2000, 2300-2400 (21 August), 0100-0200, and 0700-0800 (22 August), spraying rapid successions of lava 100 m above the vent and producing a continuous loud roaring sound. All fountains from 2A were vertical and relatively narrow. Frequently the entire cone was covered by cascading spatter forming small, rootless flows. Towards the morning of 22 August, the upper ~3 m of the cone was destroyed by vigorous gas emissions and explosive fountaining. Vent 2B, on the SE flank of cone 2A, was somewhat wider (<=5 m) and had formed a low, flat conelet. Its activity was restricted to minor oblique ejections of spatter towards the E that always preceded major activity from cone 2A. A very small incandescent vent (2C) was present on the S flank of 2A; it did not eject any solid material.

In the SW sector of Crater 1, two similarly shaped spatter cones (3A & 3B) were each ~10 m high. They were at the site of the twin boccas of March (labeled ##4 at that time). The activity of these boccas was stupendously symmetrical, producing a pair of equally shaped narrow, tall (> 100 m) vertical fountains of equal height, initially of bluish burning gas followed by the ejection of lava fragments. Magmatic eruptions lasted up to 15 seconds and were accompanied by very loud crashing noises.

Crater 3, largely filled with new pyroclastic material, had two principal eruptive sites that had not developed into cones due to the wide dispersal of ejecta beyond the crater. Vent 1 lay in the NE part of Crater 3, at the site of the pit containing the active lava pond 5 months earlier. The vent was very small (<=3 m diameter) and had built a low mound of very large agglutinated bombs to above the almost level surface of pyroclastics filling the crater. Activity from this bocca was highly irregular, with repose periods of >30 minutes, and continuous fountaining episodes up to 60 minutes long. Larger fountains every 10-45 minutes sprayed incandescent tephra up to 150 m high. During periods of continuous fountaining, the focus of the explosions migrated towards the surface, as evidenced by the increasingly wide angle of the fountains. The vent area was covered by a continuous sheet of incandescent spatter, but no lava outflow took place.

The most impressive eruptions took place from a cluster of three closely spaced, continuously incandescent vents (2) at the SW end of Crater 3, probably corresponding to vents 3 and 4 in March (19:03). Eruptions began instantaneously and sent very broad jets to heights of up to 300 m, covering an area far beyond the crater rim. During daylight, some of these eruptions produced spectacular plumes that rose up to 500 m above the vents (350 m above the summit). The eruptions made little noise, but sometimes produced heat waves that could be intensely felt on Pizzo sopra la Fossa. At times, two eruptions occurred within a 5-minute period, whereas others were separated by up to 60 minutes.

During the week preceding and 10 days after the visit, occasional large ash puffs (up to 350-400 m above the summit) were seen from neighboring islands, and frequent lava fountains were seen at night from N Lipari Island (26 August) and Alicudi Island (30-31 August), indicating that Stromboli was in a state of increased activity at least from mid-August until the end of the month.

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

Information Contacts: G. Giuntoli and B. Behncke, GEOMAR, Kiel, Germany.

A phreatic explosion on 12 August followed strong tremor two days earlier. Activity that began on 31 July produced a gas-and-ash column that rose ~800 m above the 1,060-m-high summit; detectable amounts of ash fell as far as ~17 km from the summit source vent (BGVN 19:07). Strong tremor again took place on 28 August. From that time until mid-September, weak tremor and few events of high or low frequency were recorded. Geochemical monitoring revealed decreases in SO₂, Cl, and F gases. The most significant morphological change in the inner crater was the joining of crater fumaroles A and B (figure 7).

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

Information Contacts: H. Taleno, L. Urbina, C. Lugo, and O. Canales, INETER.

Almost no advancement of the talus slopes took place from September to October. However, small pyroclastic flows and rockfalls occurred to the S during September and to the N during October (figure 76). These collapses resulted in the formation of small horseshoe-shaped craters on the talus slopes. The top of the dome decreased in elevation from 1,490 m in July, to 1,470 m in August, and to 1,460 m by October. The top of the endogenous dome, which was cone-shaped, exhibited a flat morphology by August with gentle depressions in some parts, including the E-W-trending ridges. These morphological changes were accompanied by a decrease in eruption rate to3/day.

Figure 76. Map showing distribution of pyroclastic-flow and debris-flow deposits at Unzen from 1991 through early October 1994. Directions of recent pyroclastic flows were limited to either N or S of the dome. The 1663 andesitic lava flow has been eroded and completely covered by new pyroclastic-flow deposits. Courtesy of Setsuya Nakada.

Pyroclastic flows caused by lava dome collapse, detected seismically ~1 km WSW of the dome, totaled 128 in September. Most of the pyroclastic flows occurred during 11-13 September, and none took place late in the month. The pyroclastic flows moved SW and SE, reaching the Akamatsu Valley; the longest of the month traveled 2.5 km SE.

On 1 September, 439 microearthquakes beneath the lava dome were registered at a seismic station ~3.6 km SW, but they gradually decreased in number throughout the month to 20/day. The total number of earthquakes for September was 3,260. Crest-line theodolite measurements from the UWS revealed that endogenous growth almost stopped in mid-September. EDM on the N flank by the JMA and GSJ indicated shortening of 10 mm/day during the second half of September.

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

Information Contacts: S. Nakada, Kyushu Univ; JMA.

During mid-July, observers in Perryville . . . reported a small steam plume over the volcano. Satellite imagery recorded a hot spot at the volcano on 10 August, but no additional reports were received until 12 August, when observers in Perryville saw low-level steam-and-ash emission. Snow on the upper S flank was gray, indicating a light ash cover. Observers in Port Heiden . . . were able to view Veniaminof on several days during 12-19 August, but no steam or ash clouds were visible. On 16 August, a pilot reported a plume, possibly containing small amounts of ash, rising 300 m above the volcano. During 19-26 August, observers in Port Heiden and Perryville could see Veniaminof and reported that no steam or ash clouds were visible.

Observers in Perryville noted a small steam plume over the volcano in late August and occasionally during the first half of September when weather conditions were favorable. Poor weather prevented visual observation of Veniaminof during 16-23 September. Residents of Port Heiden observed steam and ash bursts reaching ~600 m over Veniaminof on 28 September. On that day, AVHRR satellite imagery showed a "hot" spot at the volcano. Residents of Port Heiden reported no activity on 6 October, the one day they could see the volcano. Also, AVHRR satellite imagery showed overcast conditions during 1-7 October.

Geologic Background. Veniaminof, on the Alaska Peninsula, is truncated by a steep-walled, 8 x 11 km, glacier-filled caldera that formed around 3,700 years ago. The caldera rim is up to 520 m high on the north, is deeply notched on the west by Cone Glacier, and is covered by an ice sheet on the south. Post-caldera vents are located along a NW-SE zone bisecting the caldera that extends 55 km from near the Bering Sea coast, across the caldera, and down the Pacific flank. Historical eruptions probably all originated from the westernmost and most prominent of two intra-caldera cones, which rises about 300 m above the surrounding icefield. The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

Information Contacts: AVO.

A small eruption from Wade Crater on 28 July ejected mud and ballistic blocks. During a visit on 17 August, the floor of Princess Crater was occupied by a small green pond larger than on 28 June. The view of Wade Crater was restricted for most of the visit, but the gray lake was still present, and a small bench had formed on the E side of the lake. A mudflow deposit S of Wade Crater extended from the talus slope beneath the crater rim for 20-30 m towards The Sag. The deposit was ~20 cm thick, composed of fine mud with some small pebbles, and had a slightly yellow surface with a gray interior. The same deposit was seen on the divide between Wade and Princess craters, but thinned rapidly to the N, and disappeared before reaching TV1 Crater. Recent bombs and impact craters were observed SE of, but not within, the mudflow deposit. Additional bombs and impact craters were present N of TV1 Crater. The mud and block material was probably erupted at the same time from the lake bed of Wade Crater; the mud component was then remobilized and flowed down the talus slope. The blocks N of TV1 are assumed to be associated with the same eruption that formed the mudflow.

Leveling data showed a continuation of the uplift observed during January-June 1994. Total uplift at Peg M was 35 mm since January 1994. The uplift center was >100 m S of Donald Mound, although an area of relative subsidence persisted in the Donald Duck-TV1 Crater area to the N. Crater-wide inflation centered S of Donald Mound was clearly established. Inflation was also occurring N of Donald Mound, previously the most rapidly deflating area, but at a slower rate. The situation in mid-August was a significant reversal of the strong deflationary trend from 1987 to late 1993. These inflationary trends can be modelled as a doublet with a deep (500 m) source and a secondary shallow (200 m) source beneath Donald Mound, similar to the results observed in 1973-74 before the 1976-82 eruption. Volcanic seismicity continued at low levels during July-August compared to the April-June period, although volcanic tremor increased in late August.

Geologic Background. The uninhabited Whakaari/White Island is the 2 x 2.4 km emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes. The SE side of the crater is open at sea level, with the recent activity centered about 1 km from the shore close to the rear crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of volcanism since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. The formation of many new vents during the 19th and 20th centuries caused rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities. The official government name Whakaari/White Island is a combination of the full Maori name of Te Puia o Whakaari ("The Dramatic Volcano") and White Island (referencing the constant steam plume) given by Captain James Cook in 1769.

Information Contacts: S. Sherburn, IGNS, Wairakei.