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).

Gaua awoke in 2009 (BGVN 34:10) and has continued sporadic eruptions and seismic unrest into 2012. Our last Bulletin report discussed events at Gaua (and island of the same name) into late 2010, with some later seismic and thermal data (BGVN 35:05). A new report from the Vanuatu Geohazards Observatory (VGO) issued in October 2011 contains a new hazards map (figure 21).

Figure 21. An updated hazard map for Gaua ("Gaua Volkeno Denja Map" in local parlance). Note the crescent-shaped Lake Letas (blue, and overlain with other colors) wrapping around the N and E sides of the active center's ~800-m-tall summit (Mt. Garat). An earlier map appeared in BGVN 34:12. From the VGO Bulletin issued on 26 October 2011. [Note: This image is very low resolution; a higher resolution version of this map and explanation of symbols will be posted if it becomes available.]

In addition, a new geosciences publication, Globe Magazine, contained photos (figures 22 and 23) and a brief discussion of Gaua's behavior as late as early 2010 (Scott and others, 2010). The report included the following statements on events at the volcano and efforts to bolster instrumental observations.

Figure 22. Undated photo of Gaua in the course of a modest ash-bearing eruption at Mt. Garat. The water in the foreground is Lake Letas, which surrounds the N to SE flanks. From Scott and others (2010).

Figure 23. Vanuatu Geohazards Unit staff member Jimmy Loic checking one of the GNS Science seismic stations installed on Gaua. From Scott and others (2010).

"Mount Garet [Garat] on Gaua, a 20-km-diameter island 400 km N of the capital Port Vila, started erupting in September 2009, and by late November there were signs that eruptions might become larger and more explosive. Because of its remoteness and the vulnerability of its population of about 3,000 to volcanic ash, the Vanuatu government decided immediate action was needed. The main concerns are volcanic ash contaminating water supplies and anxiety caused by the erratic behaviour of the volcano.

"The volcano has been erupting mostly steam and fine ash. However, in early 2010 several more explosive eruptions threw scoria bombs up to 2 km from the crater. The ash has been falling mostly on villages and fields W and NW of the volcano, and more than 200 people living in those areas have been relocated.

"Based on their observations and the recent history of eruptions on Gaua, volcanologists from GNS Science and Vanuatu concluded that the eruptive activity is most likely to continue for some months at a level similar to that seen so far. The New Zealand government's international aid and development agency, NZAID, has funded the visits by GNS Science. NZAID has subsequently asked GNS Science to provide the Vanuatu government with three seismographs and to train local staff in their use, and in data analysis and interpretation."

2011 activity. VGO reported on 10 October 2011 that data collected by the Gaua monitoring system showed the existence of earthquakes caused by volcanic activity in August 2011. OMI satellite images clearly showed degassing during 17 and 27-28 September 2011, indicating ongoing activity. According to VGO, on 10 October local authorities reported ashfall on the NE and W sides of Gaua Island.

VGO issued a report on 26 October 2011 that described an activity assessment made during 17-18 October 2011. The report confirmed Gaua's ash emissions since September 2011, with ash distribution dictated by trade winds. Seismic data suggested eruptive activity since June 2011, but the intensity of the activity was lower than during 2009-2010.

VGO indicated that two scenarios were envisaged for Gaua. Activity could intensify with little or no warning and then cease. On the other hand, activity could continue more regularly, causing ashfall in the neighboring communities, especially those on the W side of the island that are exposed to trade winds. With this analysis, the Alert Level of Gaua remained at level 1 (on a scale from 0-4), meaning that activity had slightly increased, with the risk remaining near the volcano crater, within the red zone (see figure 21).

Reference. Scott, B., Jolly, A., Sherburn, S., and Jolly, G., 2010, Expert advice on Vanuatu volcano, Globe Magazine, Issue 1 (July 2010); pp. 12-13. Published by GNS Science (New Zealand; Editor, John Callan; Chief Executive, Alex Malahoff); ISSN 1179-7177 (Print); ISSN 1179-7185 (Online)

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

Information Contacts: Vanuatu Geohazards Observatory (VGO), Department of Geology, Mines and Water Resources (DGMWR), Vanuatu (URL: http://www.vmgd.gov.vu/vmgd/).

Since our last report covering Masaya's seismic activity and emissions from November 2011 through March 2012, the Instituto Nicaragüense de Estudios Territoriales (INETER) has maintained monitoring efforts including site visits in April and May 2012. Here we discuss regular gas emissions (SO₂ and CO₂) and seismic monitoring efforts and highlight events preceding the 30 April 2012 explosion from Santiago crater that ejected ash and incandescent blocks within the bounds of the National Park. That event began a series of explosions; more than 68 explosions occurred between 30 April and 17 May 2012.

On 21 April 2012 INETER conducted routine site visits and made field measurements at Masaya. Maximum temperatures recorded with an infrared sensor found temperatures between 98.7°C and 102°C within Santiago crater. Some jetting sounds were heard from the depths of the crater, cracks were observed on the E wall that emitted abundant gases, and the W interior wall showed signs of rockfalls. INETER field teams also visited Comalito cone, located on the NE flank, and measured maximum temperatures of 72°C to 77°C.

During field investigations on 25 April 2012, INETER volcanologists measured diffuse CO₂ emissions from Comalito cone. At night on 26 April, the National Park guards reported incandescence within the crater; the last report of incandescence was in October 2010 (BGVN 36:11). SO₂ was measured with Mobile DOAS on 27 April on a traverse between the towns Ticuantepe and La Concha (see map for location in figure 25 from BGVN 36:11).

INETER reported that, on 27 April 2012 at approximately 0500 volcanic tremor appeared in Masaya's seismic records (figure 34). Tremor slowly increased to 70 RSAM that day, and civil defense authorities released notices to officials that significant seismic unrest was detected at Masaya.

Figure 34. RSAM (averaged seismic amplitude) record from Masaya volcano during April 2012, an interval leading up to and including a 30 April eruption. Tremor drove a notable increase in RSAM on 27 April, diminishing slightly as monochromatic tremor prevailed over the following days. After an abrupt decrease in RSAM, the eruption occurred on 30 April. Courtesy of INETER.

On 28 April 2012, authorities, including the Masaya Volcano National Park, released a public announcement about the unusual seismic activity. Three hours following that announcement, the tremor signal became monochromatic near 15 Hz (figure 35). INETER suggested that this signal arose from magma moving beneath the edifice. RSAM reached 100 units with spectral analysis indicating frequencies oscillating between ~1.26 Hz and ~18.84 Hz. The strongest frequency during one particular time window (figure 35) was centered near 15.8 Hz, with a smaller peak at ~1.5 Hz.

Figure 35. (Upper panel) Seismic signal dominated by ongoing tremor recorded at Masaya on 28 April 2012 on a seismogram (amplitude, y-axis, and time (hours : minutes), x-axis). (Lower panel) A spectral analysis made for the interval shown above (frequency, in Hz, along x-axis). Courtesy of INETER.

INETER noted that before the onset of tremor on 27 April, an average of 35 seismic events per day were recorded. These were low frequency earthquakes that included signals reaching 16 Hz and interpreted as rupture events beneath Masaya. The depths of the earthquakes were determined by the P- and S-wave arrival times indicating a depth range between 3 and 4 km.

On 28 April, tremor continued at 70 RSAM and monochromatic tremor occurred again, reaching 90 RSAM. Up to 40 earthquakes were detected that day.

On 29 April, seismic tremor was slightly lower at 65 RSAM and monochromatic tremor was recorded. A total of 45 earthquakes were recorded. Signals were again monochromatic at peak frequencies of 15.8 Hz.

On 30 April at 0045, the tremor signal dramatically decreased to 30 RSAM. INETER commented that this was abnormal since tremor was often recorded between 40 and 50 RSAM during times of quiescence. Seven hours later, a strong explosion was recorded by seismic instruments and observers within the National Park witnessed a blast of gas and ash from Santiago crater (figure 36).

Figure 36. Ash explosions began on 30 April 2012 from Masaya's Santiago crater. (A) A large explosion occurred at 0829 on 30 April and was photographed by National Park staff. (B) Later in the day a smaller explosion released a small ash plume. Courtesy of INETER and the Masaya Volcano National Park.

Due to the explosions, the Plaza de Oviedo, an overlook at the edge of Santiago crater, was covered with sand-sized pink and yellow ash and lapilli with some rocks up to 10 cm in diameter. Some of the clasts were incandescent and damaged the roofs of structures near the crater and also burned the asphalt of the plaza (figure 37). Small brush fires were ignited on the N flank of the volcano due to hot blocks falling onto the dry plants. Local firefighters worked with the National Park and Civil Defense for most of the day in order to contain and extinguish the fires. The national park was closed due to the hazardous conditions.

Figure 37. (A) The roofs of several structures near Santiago crater were damaged by volcanic bombs during the 30 April 2012 explosions. (B) Some of the bombs ejected during the primary explosion were incandescent and burned the asphalt of the plaza when they landed. Courtesy of INETER.

INETER reported the explosion ejected a column of ash, gas, and blocks reaching 1,000 m above the summit and the initial explosion was followed by 24 smaller explosions that reached 500 m. Ballistic ejecta covered an area with a 300 m radius to the SSE of the crater and ash fell as far as 3 km to the SE of the crater. Blocks measured from this area had maximum dimensions of 50 x 40 x 30 cm. Ash fell to a thickness of 2 mm in some areas and INETER calculated a total volume of 736 cubic meters of ejecta.

INETER measured temperatures from Santiago crater on 30 April with an infrared thermal camera and detected a maximum of 165°C. During the night of 30 April, 23 explosions were recorded by the seismic network.

Between 30 April and 3 May, a collaborative effort among INETER, Civil Defense, local fire fighters, and the National Park succeeded in maintaining a 24-hour watch of Santiago crater. Over four days, the teams recorded observations and determined that 68 explosions had occurred and the maximum detected crater temperature was 162°C.

On 1 May 2012 at 0223 a small explosion was recorded by the INETER seismic network. This event produced ash and volcanic bombs that fell across the NE-SE sectors including the flanks of Nindirí cone (see figure 30 in BGVN 37:04 for site names). The dimensions of the largest blocks were 60 x 50 x 40 cm.

On 3 May there were two small explosions at 0008 and 0022 with abundant gas and ash emissions. Throughout these events, tremor was constant at 1.5 Hz. On 4 May no earthquakes were recorded but tremor remained between 45 and 50 RSAM; explosions of gas and light ash were observed. On 5 May a total of 19 earthquakes were recorded and RSAM varied between 45 and 58 RSAM; ash and gas explosions were reported by National Park staff. On 6 May between 0700 and 1030 a total of 45 earthquakes were recorded and RSAM increased to 70 units.

Sporadic explosions continued until mid-May (figure 38). INETER noted that in May, RSAM averaged 60 units and a significant increase occurred on 18 May. RSAM reached 120 units and was maintained at that level until 21 May. Low tremor was recorded up to 75 RSAM units after 21 May and two days later reached 85 RSAM units with frequencies in the range 1.5-3.0 Hz. Tremor decreased and remained between 65 and 70 RSAM units until the end of the month. A total of 266 earthquakes were recorded in May.

Figure 38. RSAM record from Masaya volcano during May 2012. Courtesy of INETER.

Long-term gas monitoring. Long-term records of Masaya's gas emissions (SO₂ and CO₂) and fumarole temperatures have been developed by INETER. On 2 May, SO₂ flux was measured during traverses between Ticuantepe and La Concha (table 5). INETER commented that they observed increasing SO₂ flux since December 2011 (648 tons per day) that peaked in March 2012 (1002 tons per day). Flux was decreasing at the time of the explosion on 30 April 2012. INETER noted that overall trends in SO₂ flux did not correlate with trends in seismicity, however, they emphasized that difficult-to-constrain variables such as wind speed and direction should be factored into the SO₂ data interpretations.

Table 5. SO₂ flux detected at Masaya from January 2011 through May 2012 during traverses with a Mobile DOAS. Courtesy of INETER.

Since 7 December 2008, INETER measured CO₂ emissions from Comalito cone, an active fumarolic site on the NE flank of Masaya. Diffuse CO₂ was measured from a 9 hectare sector of soil as recently as 1 May 2012 (table 6). INETER reported the highest CO₂ emissions were detected in 2008 and decreased between 2010 and 2011. Emissions recorded on 25 April 2012 (before the eruption) were considered low, however, there was a small peak on 1 May that may have been related to the explosive activity.

Table 6. The long-term record of diffuse CO₂ analyses from Comalito cone measured from September 2008 through May 2012. Courtesy of INETER.

On 17 May, INETER conducted fieldwork at Santiago crater and determined a maximum temperature of 162°C. While in the field, INETER staff observed two small explosions from the crater. Temperatures were also measured at Comalito cone (figure 39); the maximum recorded temperature was from Fumarole 2, 78.2°C, the highest temperature reading at Comalito cone since February 2012.

Figure 39. Temperatures measured at Comalito cone from January through May 2012. Courtesy of INETER.

New monitoring efforts and installations. Two seismic stations were installed in May 2012. One station, called La Azucena, was installed by INETER on 1 May. This site was located ~4 km N of the active crater and was considered temporary. A second station, called El Comalito, was installed on 15 May; located within the National Park at Comalito cone. INETER recognized potential contributions of background noise from the fumarolic sites close to the station and planned to reevaluate the location after reviewing the results from this station. Both stations transmitted realtime data through radio repeaters.

On 4 May a web camera was installed within the town of La Azucena on a short tower; the camera was programmed to send images through a wireless network every 5 minutes. A second camera was installed in the town of Masaya at the office building of the Center of Disaster Operations (CODE); this camera also captured images every 5 minutes. The camera at CODE suffered malfunctions after installation due to overexposure from direct sunlight. Future fieldwork was planned to fix these problems.

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: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); La Prensa (URL: http://www.laprensa.com.ni/).

Monowai volcano, located 1,000 km NE of New Zealand's North Island, is one of the most active submarine volcanoes identified in the Tonga-Kermadec arc, a 2,500-km-long chain of submarine volcanoes stretching from New Zealand to just N of Tonga (figure 22). Bradley Scott, a volcanologist at New Zealand's GNS Science, reported that seismic activity recorded by GeoNet on the seismograph at Rarotonga, Cook Islands, had shown there were several days of eruptive activity at Monowai starting on 3 August 2012. A large pumice raft, first spotted on 19 July 2012, was suspected to have a source in Monowai; however, that was later discounted (see a report on Havre seamount in a subsequent issue). The most recent previous eruptions of Monowai began on 8 February 2008 and 14 May 2011.

Figure 22. Regional bathymetric map of the Monowai Volcanic Centre (MVC), comprising the Monowai cone to the SW and the 10-km-wide Monowai caldera to the NE. Grey and red lines show the tracks of R/V Sonne on 14 May and during 1-2 June 2011, respectively. The yellow star with the red border shows the SW caldera hydrothermal site (from Leybourne and others, 2010). The letter 'V' indicates regions of active venting. The dashed black square around the cone shows the location of the maps in figure 23. The inset shows the location of the MVC in relation to historically active volcanoes in the Kermadec Trench area (red triangles; from Smithsonian Global Volcanism Program web site), Tonga and Kermadec Trench (blue lines), and the Louisville Ridge seamount chain (dashed black line). The depth scale along the right-hand side of the figure keys the colors in the figure to the appropriate depths, in meters. Courtesy of Watts and others (2012).

All previous Bulletin reports on Monowai, including most of the latest one in 2008 (BGVN 33:03), describe eruptive activity as measured remotely by the Polynesian Seismic Network (Réseau Sismique Polynésien, or RSP). In contrast, this report will emphasize recent oceanographic surveys conducted over the volcanic complex that help define the features of the area.

Background. According to a recent publication by Leybourne and others (2010), the MVC comprises a large, elongate caldera (7.9 x 5.7 km; 35 km²; floor depth = 1,590 m) to the NE, formed within an older caldera (84 km²). Associated is a large active stratovolcano to the SW, which rises to within ~100 m of the sea surface. Mafic rocks dominate MVC, with only rare andesites. Plume mapping shows at least four hydrothermal systems with venting from the summit of Monowai cone and its N flank. Monowai caldera has a major hydrothermal vent system associated with the SW wall of the caldera (figure 22).

Wright and others (2008) wrote that "The first recorded eruptions at Monowai date from between 1877 and 1928 (Mastin and Witter, 2000), and subsequently reported as a shoal in 1944 (Royal Australian Navy, written communication, 1944). More recent eruptions were first observed by maritime aircraft patrols in October 1977 (Davey, 1980). A bathymetric survey undertaken in July, 1978, and towed-sonar array surveys, undertaken in March and July 1978 and March, April, and June 1979, recorded periods of volcanic activity that included discolored water and vigorous gas emissions at the sea surface (Davey, 1980). A single-beam bathymetric survey recorded a conical edifice with a summit shoal of 117 m (velocity uncorrected) in September 1978 (Davey, 1980). A reconnaissance multibeam survey in 1986 by R/V Thomas Washington identified a shoal at a depth of 115 ± 5 m (Scripps Institute of Oceanography, unpublished data, 1986)."

Bathymetry. Multibeam surveys by RV Sonne in 1998 (SO-135 voyage) and RV Tangaroa in 2004 showed the Monowai stratovolcano cone (10-12 km in diameter, rising 965 m from the 1,100-m isobath) to be the largest of a number of postcollapse cones sited around the rim of the newly discovered Monowai caldera (part of the larger volcanic complex; Graham and others, 2008). The elongate caldera was 11 x 8.5 km in size and showed evidence of at least two phases of caldera formation. Monowai cone forms a relatively simple edifice on the S caldera rim, with near constant 13-18° slopes that were interpreted by the investigators of these cruises as angles of repose of volcaniclastic deposits generated at the summit. Prominent radial dikes and small aligned vents protruded up to 50 m above the edifice slopes, especially on the N and W flanks. The S flank showed evidence of repeated sector collapse. A single video-grab transect during the 1998 RV Sonne survey across the then-shallowest vent showed that it comprised coarse scoriaceous blocks with a lapilli sand matrix. Sampled rocks from Monowai cone comprise highly vesicular, plagioclase-clinopyroxene basalts (Brothers and others, 1980; Haase and othres, 2002).

Table 2 shows the various depths of the summit of the Monowai cone as measured by multiple bathymetyric surveys conducted since 1978. Figures 23 and 24 show regions of bathymetric changes.

Table 2. Summit depth measurements of Monowai cone since 1978. Courtesy of Watts and others (2012) and references listed.

Figure 23. Detailed bathymetric maps of Monowai cone as it appeared in September 2004, May 2007 and May-June 2011. The map area is outlined in figure 22 (dashed black square). 'SC' denotes sector collapses. (a) Swath bathymetry acquired by R/V Tangaroa in September 2004, contoured at 100 m intervals, with thick contours at 500 m intervals. (b) Swath bathymetry, R/V Sonne, May 2007. (c) Swath bathymetry, R/V Sonne, 14 May and 1-2 June 2011 merged into a single grid. The dashed black rectangle shows the view area in figure 24. (d) Difference in bathymetry between the 2007 and 2004 surveys colored to indicate depth changes from -125 to +125 m. Shades of blue indicate depth increase (collapse), and shades of red, depth decrease (growth). (e) Difference in bathymetry between the 2011 and 2007 surveys. Colors as in (d). Colored scales indicate depths as in (a)-(c) and differences in bathymetry (as in (e) and (f)) between two dated surveys. Courtesy of Watts and others (2012).

Figure 24. Perspective view from the SW (azimuth 240°, view angle 14° above horizontal) showing the bathymetry of the summit of Monowai cone in September 2004, May 2007, and May-June 2011. The view area is outlined by the dashed black rectangle in figure 23c. The bathymetry data have been artificially shaded by a sun located in the NW to enhance topography. The negative numbers in brackets to the right of each profile indicate the depth below sea level of the shallowest point on the summit. Colored scale shows key for bathymetry. Courtesy of Watts and others (2012).

Mid-May to early June 2011. Watts and others (2012) reported the results of two recent bathymetric surveys of MVC conducted within a period of 14 days (14 May and 1-2 June 2011). They found marked differences in bathymetry between the surveys. New growth structures, probably due to new lava cones and debris flows, caused decreases in depth of up to 71.9 m, while collapse of the volcano summit region caused increases in depth of up to 18.8 m.

Hydro-acoustic T-wave data revealed a 5-day-long swarm of seismic events with unusually high amplitude between the two 2011 surveys, which link the depth changes to explosive activity (figures MON4, MON5, and MON6). [Note: According to NOAA (Chadwick, 2001), "A 'T-phase' or 'T-wave' is an acoustic phase from an earthquake that travels through the ocean. The 'T' stands for 'tertiary', as in: P-waves are 'primary', S-waves are 'secondary', and T-waves are 'tertiary', because they travel the slowest and so arrive third. Basically, when an earthquake occurs in the earth's crust under the ocean, the usual crustal phases are generated (P and S waves), but in addition part of the energy goes into the ocean as acoustic energy, and that is the T-wave. Not all earthquakes generate T-waves (since they need to be near water)...T-waves are typically recorded by hydrophones, but on some islands seismometers sometimes record T-wave signals that have been converted to crustal phases when they hit the island."]

Figure 25. Time-series plots of hydro-acoustic T-wave data recorded at Rarotonga (IRIS station RAR, IU network) spanning the R/V Sonne repeat swath bathymetric surveys of 14 May and 1-2 June 2011. (a) Number of T-wave events per day (gray bars, left axis) and cumulative number of events (red line, right axis) versus time. An event is defined as one with a peak-to-peak amplitude in ground velocity >1,200 nm/s that is separated from another event by at least 1 min of quiescence. Note the abrupt increase in the number of events observed during the 5-day-long period between 17 to 22 May. (b) Peak-to-peak amplitude of individual events versus time. Red arrows mark the time of the 14 May and 1-2 June swath surveys. The full waveform of the event highlighted by the red circle is shown in the inset in (c). (c) Plot of ground velocity versus time. Courtesy of Watts and others (2012).

Figure 26. Swath bathymetry of the summit of Monowai cone as it appeared on 14 May and 1-2 June 2011. (a and b) Swath bathymetry acquired on R/V Sonne on 14 May (a) and 1-2 June (b) 2011. Open triangles with dates show the sequential position of the summit at selected times since 1978. 'SC3' indicates sector collapse 3 (see figures 23 and 24). Solid black lines show the profiles plotted in figure 27. The contour interval is 20 m. (c) Difference in the swath bathymetry between 14 May and 1-2 June colored to show depth decreases (blue) and increases (red). (d) Perspective view from the SSE (azimuth 168°, view angle 16° above horizontal) of the difference in swath bathymetry between 14 May and 1-2 June. Colored scales indicate depth (a, b, and d) and depth differences (c) in bathymetry between two dated surveys. Courtesy of Watts and others (2012).

Figure 27. Progressive southward growth of the S flank of Monowai cone and the rate of volcanism. (a and b) Bathymetry profiles 1 (a) and 2 (b) from figure 26 of the summit of Monowai cone, shown with no vertical exaggeration. Black arrows highlight the 14 May and 1-2 June summits. The S flank shows progressive southward growth since 1977, contrasting with the more stable N flank. (c) Plot of eruptive volume versus duration of magmatism at Monowai, compared to other selected oceanic volcanoes. Symbols: red/orange diamond, 2011 survey (filled, cone only; unfilled, all data); blue triangles, previous repeat surveys in 1998, 2004 and 2007; small blue filled circles, selected seamounts and ocean islands from Chrisp (1984); green square, Vailulu'u (Staudigel and others, 2006); large light blue circles, data from >9,000 seamounts (Watts and others, 2006) that formed during 0-30 Myr, 95-125 Myr, and 105-110 Myr; small open brown circles, Montserrat (Sparks and others, 1998). Courtesy of Watts and others (2012).

References. Brothers, R.N., Heming, R.F., Hawke, M.M., and Davey, F.J., 1980, Tholeiitic basalt from the Monowai seamount, Tonga-Kermadec ridge, New Zealand Journal of Geology and Geophysics, v. 23, no. 4, p. 537-539.

Chadwick, W.W., Jr., 2001, What is a T-phase?, URL: http://www.pmel.noaa.gov/vents/geology/tphase.html; posted 9 November 2001, accessed 14 August 2012.

Chadwick, W.W., Jr., Wright, I.C., Schwarz-Schampera, U., Hyvernaud O., Reymond, D., and de Ronde, C.E.J., 2008, Cyclic eruptions and sector collapses at Monowai submarine volcano, Kermadec arc: 1998-2007, GeochemistryGeophysicsGeosystemsG3, v. 9, p. 1-17 (DOI: 10.1029/2008GC002113).

Chrisp, J.A., 1984, Rates of magma emplacement and volcanic output, Journal of Volcanology and Geothermal Research, v. 20, pp. 177-211.

Davey, F.J., 1980, The Monowai seamount: An active submarine volcanic centre on the Tonga-Kermadec ridge (note), New Zealand Journal of Geology and Geophysics, v. 23, no. 4, p. 533-536.

Haase, K.M., Worthington, T.J., Stoffers, P., G-Schonberg, D., and Wright, I., 2002, Mantle dynamics, element recycling, and magma genesis beneath the Kermadec Arc-Havre Trough, GeochemistryGeophysicsGeosystemsG3, v. 3, no. 11. p. 1071 (DOI: 10.1029/2002GC000335).

Leybourne, M.I., de Ronde, C.E.J., Baker, E.T., Faure, K., Walker, S.L., Resing, J., and Massoth, G.J., 2010, Submarine magmatic-hydrothermal systems at the Monowai Volcanic Centre, Kermadec Arc, Goldschmidt Conference Abstracts 2010, Abstract A587.

Sparks, R.S.J., Young, S.R., Barclay, J., Calder, E.S., Cole, P., Darroux, B., Davies, M.A., Druitt, T.H., Harford, C., Herd, R., James, M., Lejeune, A.M., Loughlin, S., Norton, G., Skerrit, G., Stasiuk, M.V., Stevens, N.S., Toothill, J., Wadge, G., and Watts, R., 1998, Magma production and growth of the lava dome of the Soufriére Hills volcano, Montserrat, West Indies: November 1995 to December 1997, Geophysical Research Letters, v. 25, no. 18, pp. 3421-3424 (DOI: 10.1029/98GL00639).

Staudigel, H., Hart, S.R., Pile, A., Bailey, B.E., Baker, E.T., Brooke, S., Connelly, D.P., Haucke, L., German, C.R., Hudson, I., Jones, D., Koppers, A.A.P., Konter, J., Lee, R., Pietsch, T.W., Tebo, B.M., Templeton, A.S., Zierenberg, R., and Young, C.M., 2006, Vailulu'u Seamount, Samoa: Life and death of an active submarine volcano, Procedures of the National Academy of Science, USA, v. 103, pp. 6448-6453 (DOI: 10.1073/pnas.0600830103).

Watts, A.B., Sandwell, D.T., Smith, W.H.F., and Wessel, P., 2006, Global gravity, bathymetry, and the distribution of submarine volcanism through space and time, Journal of Geophysical Research, v. 111 (DOI: 10.1029/2005JB004083).

Watts, A.B., Peirce, C., Grevemeyer, I., Paulatto, M., Stratford, W., Bassett, D., Hunter, J.A., Kalnins, L.M., and de Ronde, C.E.J., 2012 (13 May), Rapid rates of growth and collapse of Monowai submarine volcano in the Kermadec Arc, Nature Geoscience, v. 5, p. 510-515 (DOI: 10.1038/ngeo1473).

Wright I.C., Chadwick, W.W., Jr, de Ronde, C.E.J., Reymond, D., Hyvernaud, O., Gennerich, H., Stoffers, P., Mackay, K., Dunkin, M.A., and Bannister, S.C., 2008, Collapse and reconstruction of Monowai submarine volcano, Kermadec arc, 1998-2004, Journal of Geophysical Research, v. 113, p. 1-13 (DOI: 10.1029/2007JB005138).

Geologic Background. Monowai, also known as Orion seamount, rises to within 100 m of the sea surface about halfway between the Kermadec and Tonga island groups. The volcano lies at the southern end of the Tonga Ridge and is slightly offset from the Kermadec volcanoes. Small parasitic cones occur on the N and W flanks of the basaltic submarine volcano, which rises from a depth of about 1500 m and was named for one of the New Zealand Navy bathymetric survey ships that documented its morphology. A large 8.5 x 11 km wide submarine caldera with a depth of more than 1500 m lies to the NNE. Numerous eruptions from Monowai have been detected from submarine acoustic signals since it was first recognized as a volcano in 1977. A shoal that had been reported in 1944 may have been a pumice raft or water disturbance due to degassing. Surface observations have included water discoloration, vigorous gas bubbling, and areas of upwelling water, sometimes accompanied by rumbling noises.

Information Contacts: Bradley J. Scott, GNS Science, Wainakel Research Centre, Taupo, New Zealand (URL: http://www.gns.cn.nz); GeoNet, New Zealand (URL: http://www.geonet.org.nz)

Minor seismic activity and fumarolic plumes at Papandayan occurred in July 2005, July and August 2007, and April 2008 (BGVN 33:06; figure 9). This report covers a seismic swarm reported in July and August 2011. According to the Center of Volcanology and Geological Hazard Mitigation (CVGHM), Papandayan is monitored by eight seismic stations (three permanent and five temporary).

Figure 9. A map showing the location of Papandayan relative to many other Indonesian volcanoes of Holocene age. Courtesy of USGS.

Since April 2008, reports on seismicity were sparse. Then, in July 2011, seismicity increased; several hundred earthquakes were detected per month, and the occurrence of deep earthquakes nearly tripled. (figure 10, table 4).

Figure 10. Papandayan crater as seen from the trail to Pondok Salada in August 2011. Courtesy of Daniel Quinn.

Table 4. The occurrence of various types of seismicity at Papandayan during July-24 August 2011. '--' indicates data not reported. Data from CVGHM.

According to CVGHM, sulfur-dioxide (SO₂) plumes rose 20-75 m above the vents between 1 June and at least 12 August 2011. Between 12-23 August, SO₂ emissions ranged from 3-8 tons per day. Carbon dioxide (CO₂) levels measured in the soil at 1 m depth in multiple areas did not increase. The temperature in the Manuk thermal area increased during 29 June to 12 August, and deformation measurements indicated inflation from 4 July to 10 August. On 13 August 2011, CVGHM announced that the Alert Level for Papandayan had been increased to 3 (on a scale of 1-4) based on seismicity, deformation, geochemistry, and visual observations. Visitors and residents were warned not to venture within 2 km of the active crater. The increase spurred multiple news reports.

On 14 August 2011, the Jakarta Globe reported that Sutopo Purwo Nugroho, a spokesman for the National Disaster Mitigation Agency, had stated that gas was emanating from three craters - Walirang, Manuk and Balagadama. The same report quoted Surono, who heads CVGHM, as saying: "For now, we are not too worried about a major eruption. We are more concerned by the toxic gas."

According to other news reports, by mid-August 2011 local officials had completed evacuation planning, especially for three vulnerable villages within 7 km of the active crater. The report also mentioned that as of 19 August, residents near the volcano were continuing their normal activities, but that tourist visitation had dropped sharply at the popular destination.

On 26 August 2011, CVGHM reported that Papandayan's activity had not increased during the previous few days. Seismicity remained high, but stable, and was dominated by shallow volcanic earthquakes. Deformation measurements (such as leveling and Electronic Distance Measurement - EDM) showed no change, and water temperatures in multiple fumarolic areas and lakes remained relatively constant.

On 31 January 2012, CVGHM lowered the Alert Level from 3 to 2, without indication of eruption details or reasons for the change. As of 30 June 2012, the Alert Level remained at 2.

Crater emission videos. Video clips of crater emissions taken at Papandayan in October 2009, and at an uncertain other date can be found on YouTube:

Pwarr3n, 2009, YouTube (URL: http://www.youtube.com/watch?feature=endscreen&NR=1&v=H_GIwMdkWT8).

Sweetmarias, undated, posted 13 August 2010, YouTube (URL: http://www.youtube.com/watch?v=tSFoybapqe0).

Geologic Background. Papandayan is a complex stratovolcano with four large summit craters, the youngest of which was breached to the NE by collapse during a brief eruption in 1772 and contains active fumarole fields. The broad 1.1-km-wide, flat-floored Alun-Alun crater truncates the summit of Papandayan, and Gunung Puntang to the north gives a twin-peaked appearance. Several episodes of collapse have created an irregular profile and produced debris avalanches that have impacted lowland areas. A sulfur-encrusted fumarole field occupies historically active Kawah Mas ("Golden Crater"). After its first historical eruption in 1772, in which collapse of the NE flank produced a catastrophic debris avalanche that destroyed 40 villages and killed nearly 3000 people, only small phreatic eruptions had occurred prior to an explosive eruption that began in November 2002.

Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Jakarta Globe (URL: http://www.thejakartaglobe.com).

Since our recent brief report on Tinakula (BGVN 37:02), the Bulletin received an informal report from Timothy McConachy of Neptune Minerals, Inc., containing observations of Tinakula volcano made 10 May 2012 (Cook and others, 2012). Most of the following information in the next few paragraphs was extracted from that report.

The location of Tinakula with respect to other islands in the Santa Cruz Islands is shown in figure 12; figure 13 shows geological details of the Tinakula volcanic island.

Figure 12. The location of Tinakula in the Santa Cruz Islands; inset area shows location of Santa Cruz Islands with respect to New Guinea and Australia. Courtesy of McCoy and Cleghorn (1988). This map previously appeared in BGVN 36:08.

Figure 13. Sketch map of Tinakula island based on work and publications by G.W. Hughes (1972) and colleagues, and summarized by Eissen and others (1991). This figure previously appeared in BGVN 28:01 and 36:08.

Visit to Tinakula. Cook and others (2012) twice circumnavigated Tinakula clockwise in a banana boat with a 40-horse-power engine in the afternoon on Thursday, 10 May 2012. The day was sunny and clear with minor clouds and a NE breeze which stiffened during the afternoon; cloud cover increased during the afternoon. During the 2 transits they observed recent land slides, the NW collapse area (shown on Figure 13), and steam/gas plumes. A highlight of the visit was when red incandescent boulders of lava bounced down the large scree slope (up to 200-m-wide and 600- to 800-m-long) in the NW collapse sector. As they bounced, the boulders broke into smaller fragments and puffs of stream/gas were seen making white dotted tracks, or 'vapour trails' (figure 14). A number of the fragments from the larger boulders made their way into the sea, and plumes of steam rose along with the splash. When the larger boulders rolled into the sea, the authors could hear thudding sounds as they hit the water, followed by a hissing sound. At times the splash would rise 2 m or higher when the boulders hit the sea. Some of the boulders and fragments did not roll into the sea, but sat on the edge of the water, steaming and hissing for some time (between 3-5 min) before they cooled off.

Figure 14. The main scree slope in the NW collapse sector of the volcano, photographed at 1416 hours on 10 May 2012. White patches of steam/gas ('vapour trails') were caused by boulders bouncing down the slope. Courtesy of Cook and others (2012).

To the naked eye, there appeared to be a steady cloud above Tinakula (figure 15), quite visible even from the town of Lata (~35 km S of Tinakula, located on Graciosa Bay, Nendö Island - aka Ndende Island, the provincial capital of Temotu Province in the far eastern Solomon Islands). It was difficult for Cook and others (2012) to photograph the incandescent color of the boulders and it only became apparent on the second time around the volcano in the later part of the afternoon when the area was backlit by the sun. The boulders originated from an area obscured by steam and gas. When the authors turned the outboard motor off, they could hear rumbling and small explosions at times. The size of the boulders was difficult to judge, but they thought that the larger ones were the size of a small car. They were surprised to see coconut palms growing up the slopes on most sides of the volcano, up to 50 m above sea level, possibly planted by locals.

Figure 15. Cloud covering the summit of Tinakula at 1358 on 10 May 2012. The top of the volcano is virtually deforested. Courtesy of Cook and others (2012).

Other comments. MODVOLC satellite thermal imagery continued to measure several thermal alerts almost daily.

References. Cook, H.J., Koraua, B.L., and McConachy, T.F., 2012, Observations of Tinakula Volcano, 10 May 2012, Solomon Islands (-10.38°S / 165.8°E), Informal report, 12 pp.

Eissen, J-P., Blot, C., and Louat, R., 1991, Chronology of the historic volcanic activity of the New Hebrides island arc from 1595 to 1991: Rapports Scientifiques et Technique, Sciences de la Terre, No. 2, ORSTOM, France.

Hughes, G.W., 1972, Geological map of Tinakula: Nendö sheet EOI 1, Soloman Geol. Survey, Honiara.

McCoy, P.C., and Cleghorn, 1988, Archaeological Excavations on Santa Cruz (Nendö), Southeast Solomon Islands: Summary Report, pp. 104-115; in Archaeology in Oceania.

Geologic Background. The small 3.5-km-wide island of Tinakula is the exposed summit of a massive stratovolcano at the NW end of the Santa Cruz islands. Similar to Stromboli, it has a breached summit crater that extends from the summit to below sea level. Landslides enlarged this scarp in 1965, creating an embayment on the NW coast. The satellitic cone of Mendana is located on the SE side. The dominantly andesitic volcano has frequently been observed in eruption since the era of Spanish exploration began in 1595. In about 1840, an explosive eruption apparently produced pyroclastic flows that swept all sides of the island, killing its inhabitants. Frequent historical eruptions have originated from a cone constructed within the large breached crater. These have left the upper flanks and the steep apron of lava flows and volcaniclastic debris within the breach unvegetated.

Information Contacts: Timothy F. McConachy, Neptune Minerals, Inc. (URL: http://www.neptuneminerals.com); Brent McInnes, Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia (URL: http://www.csiro.au); MODVOLC, Hawai’i Institute of Geophysics and Planetology (HIGP) 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/).

Turrialba is the eastern-most of Costa Rica's active volcanoes, located 65 km E of the capitol, San Jose. The previous Bulletin report discussed frequent degassing and occasional ashfall between March 2010-June 2011 (BGVN 36:09). This report discusses activity between July 2011 and May 2012.

A recent comprehensive report prepared by Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional (OVSICORI-UNA) provides an excellent background of activity at Turrialba: "Since May 1996, Turrialba volcano has shown an important increase in activity, which can possibly be interpreted as precursory of a new eruptive phase. The volcano-tectonic activity and degassing increase is particularly noticeable since 2007, and even more since the opening of the first fumarolic vent in the W crater [the main crater 'pLa Quemada'] in January 2010, which suggested a magmatic intrusion between 2005 and 2007 as well as the beginning of a new eruptive phase. A new vent opened on January 12th, 2012, (Boca 2012 or 2012 vent) on the southeast external flank of the W crater, with few hours of ash emission, followed by a second ash emission from the same vent on January 18th, 2012." A chronology of events leading up to the 12 January 2012 event is shown in table 6.

Table 6. Events since 1996 leading up to the 12 January 2012 vent opening event, and associated previous Bulletin coverage. Dates and event descriptions courtesy of OVSICORI-UNA.

Seismicity at Turrialba from early November through December 2011 was variable with event frequency ranging from as low as 20 events per day to an occasional high of 80 events per day. The frequency of events dropped significantly in early December to generally less than 60 per day until there was a dramatic increase on 31 December when 155 seismic events were recorded. Event frequency in early January 2012 showed a steady increase from 40 events per day reaching about 80-100 events per day between 6 and 13 January. This increase in seismic events was concurrent with emissions recorded on 5 January and 12 January (table 6).

On 5 January 2012 an eruption at Turrialba produced ashfall in local areas, particularly in areas to the SW, including areas near Irazú volcano (11 km SW). Later reporting suggested a new fumarolic vent may have opened in the main crater on 5 January. According to news articles, about 20 people evacuated the area.

2012 vent opens. After midnight on 9 January 2012, residents of the Central Valley heard booming and crashing sounds. Investigators at OVSICORI-UNA reviewed the seismic records but did not find associated seismic or volcanic activity. On 11 January, residents again reported several instances of rumbling. On 12 January, OVSICORI-UNA reported that a new vent, located on the SE flank of the volcano's W crater had opened. According to OVSICORI-UNA, the new vent exhibited "a vigorous output of bluish gas at high temperature (T > 592°C) that generated a jet-like sound audible from the visitor lookout." This activity included a few hours of ash emission. A second ash emission from the same vent occurred on 18 January (see subsection below). Seismic recordings, deformation, and diffused gas flux measurements allowed the conclusion that the opening of the 2012 fumarolic vent is not due to a change in the magmatic activity but to an excessive shallow accumulation of gas. This conclusion is substantiated by information obtained from a network of Electronic Distance Measurement (EDM) equipment using five reference points (prisms) which have been taking measurements since 2009. No significant variations of the distance relationships that would coincide with the ash emissions of 2010 and 2012 had been noted. EDM data after March 2011 showed a decrease in measured distances, mainly in the N direction with small variations in the other directions. This information is considered corroborated by Global Position System (GPS) data provided by two GPS stations which show a small but continuous trend of decreasing distance observed during April 2010-January 2012.

Similar vent openings occurred at Turrialba prior to the 1864-66 eruption and at Irazú volcano prior to its 1963-65 eruption. Hence, other openings of fumarolic vents can be expected in the future, especially along the fractures and weak zones aligned in a SW-NE direction that passes by the three upper craters of Turrialba.

The activity of 12 January was a pressure release on the SE flank of the W crater. OVSICORI-UNA considered the release to have penetrated weakened rock, not a magmatic or phreatic (steam-driven) eruption. (The rock at the summit of Turrialba is considered to be very weak due to the intense rainfall and the persistent hydrothermal activity at the summit. This weakness facilitates the development of vents.) An ash plume rose ~500 m above the crater and drifted NNE and NNW, rising to an altitude of ~4 km. Later that day residents reported a dark plume coming from the main crater and a white vapor plume that rose from the fumarolic vent which had formed in the main crater on 5 January 2010. The emissions caused OVSICORI-UNA to raise the Alert Level to Yellow in the communities of La Central (34 km SW), Santa Cruz (7 km SE), and around the perimeter of the crater. Towns of Jiménez (21 km N), Oreamuno (45 km SW), Alvarado (38 km SW), and Cartago (25 km SW) remained at Alert Level Green. Ashfall was reported in Tres Ríos (27 km SW).

Gas emission analysis the day before the opening of the 2012 vent (11 January) showed high values of CO₂ and H₂S over the entire E flank of the W crater. A 115-m-long liquid sulfur flow was observed in the main crater from the E side of W crater.

18 January eruption. During the evening of 18 January 2012, scientists observed gas emissions and ejection of tephra from the vent. They also observed reddish flames from combusting gas, estimated to be ~700°C. Degassing of Turrialba is considered a normal ongoing activity. An OVSICORI-UNA pilot observed an ash plume that rose to altitudes of ~4.3-6.1 km.

The seismogram from the 18 January eruption (figure 26) showed strong tremor coincident with the tephra and gas emissions. The tremor, which started at 1455, was most intense between 1502 and 1610 according to OVSICORI-UNA. Figure 26a shows >5,000 seconds of the most intense part of the tremor having significant variations in amplitude, especially at the beginning of the activity. Figure 26c shows the signal's frequency content over the same interval, with the highest normalized amplitudes having peaks between 5 and 15 Hz.

Figure 26. (a) A seismic recording for Turrialba on 18 January 2012 at station VTUN showing the most intense phase of the tremor that prevailed during the eruption that day. (b) Spectrogram of the seismicity shown in (a). (c) Normalized frequency spectrum of the seismic signal; the main peaks are between 5 and 15 Hz. Courtesy of OVSICORI-UNA.

A false color satellite image of Turrialba taken on 21 January 2012 highlights ongoing impacts to vegetation from high gas emissions (figure 27). One of the concerns of the government is the amount of acid rain that has fallen on the region surrounding Turrialba. The acid rain, with a pH as low as 3.2, has degraded the local agricultural and livestock economy.

Figure 27. A false-color satellite image of Turrialba (a combination of near infrared, red, and green light) acquired on 21 January 2012. Healthy vegetation appears bright red, while vegetation damaged by years of acidic gas emissions is brown. Bare ground in the summit craters is brown or gray. This image was acquired by NASA's Advanced Spaceborne Thermal Reflecton and Emission Radiometer (ASTER) instrument aboard the TERRA satellite. Courtesy of NASA Earth Observatory.

Vent incandescence in February 2012. A nocturnal visit to the W crater by volcanologists from OVSICORI-UNA on 2 February revealed several incandescent spots. Figure 28 (a view from the overlook taken on 9 February), shows a panoramic view of vent locations in relation to the West, Central, and East Craters.

Figure 28. A panoramic view of the relative locations of the three vents which have been the sites of activity since 2010. Courtesy of OVSICORI-UNA.

Each vent had different gas and vapor output, and different incandescence intensities. The 2012 vent, which opened on 12 January, registered temperatures above 700°C on 22 February. Continued degassing was noted in conjunction with incandescent spots at several locations on the W crater (figure 29).

Figure 29. A view of the 2012 vent from the overlook taken on 9 February 2012. The insert on the right is the second ash emission from the 2012 vent on 18 January. Courtesy of G. A. Avard, OVSICORI-UNA.

March-May 2012. Residents reported that two large steam-and-gas emissions (~90% water vapor) rose above the volcano on 27 March. The two gas columns rose ~1 km in height and drifted towards the N face of the volcano. A small phreatic eruption was noted on 12 April.

On 2 May 2012, following an increase in seismic and degassing activity with vigorous steaming, there were occasional phreatic explosions that produced ash. According to Tico Times, on 20 May the government raised the Alert Level to Yellow. Temperatures around some fumaroles had risen to as much as 800°C. High-temperature gas emissions (including SO₂) increased and caused incandescence in some of the fumaroles.

On 23 May, based on seismometers in Turrubares and Puntarenas, OVSICORI-UNA reported an earthquake with an epicenter ~84 km WSW of Turrialba. The M 3.9 earthquake was at a depth of ~14 km. The earthquake was reported to be a very brief jolt for residents of Esparza, Jaco Beach, and Puntarenas. Some residents of Monteverde, San Pedro, and Santa Ana reported having felt an earthquake of very slight intensity. It is not clear whether the earthquake and the earlier increased Turrialba activity were related.

Geologic Background. Turrialba, the easternmost of Costa Rica's Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazú volcano overlooking the city of Cartago. The massive edifice covers an area of 500 km2. Three well-defined craters occur at the upper SW end of a broad 800 x 2200 m summit depression that is breached to the NE. Most activity originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred during the past 3500 years. A series of explosive eruptions during the 19th century were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters.

Information Contacts: Avard G., Pacheco J., Fernández E., Martínez M., Menjívar E., Brenes J., van der Laat R., Duarte E., Sáenz W., Observatorio Vulcanológico y Sismológico de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Tico Times (URL: http://www.ticotimes.net/); Reuters (URL: http://www.reuters.com/); NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/).

After evaporating during 2011 and early 2012, White Island's crater lake rapidly rose on 28 July. Within two weeks, the first ash emissions from White Island in ~10 years occurred. This report summarizes GeoNet Alert Bulletins and provides selected photos of what "may represent the start of a new phase of activity at White Island."

Lake-level rise. During 2011-July 2012, White Island's crater lake slowly evaporated, exposing steam vents and leaving large mud pools on the lake floor (figure 52a). GeoNet reported intermittent volcanic tremor in early July 2012. One period of tremor lasted several hours in the early morning on 28 July; GeoNet stated that it may have been an indication than an eruption had occurred. Later that day, field observations revealed that the lake-level had rapidly risen 3-5 m sometime during the previous night or early morning (figure 52b). According to Brad Scott of GNS Science, rain and water derived from condensation within plumes were the sources of the lake-level rise.

Figure 52. Photos of White Island's crater lake taken on 6 March (a) and 28 July 2012 (b) illustrating the nearly dry lake floor during a period of evaporation in 2011-early 2012 and the newly refilled lake containing 3-5 m of water. The lake-level rose suddenly during 27-28 July 2012 (see text). The white asterisk marks the same location in each photograph. Courtesy of GeoNet.

The lake-level rise was accompanied by significant gas-and-steam emissions rising from the water. Gas measurements indicated an increase in SO₂ emissions compared to the last measurement three months prior, but CO₂ emissions were about the same. Ground surveys indicated that subsidence of the crater floor had stopped, and that the floor may have been slowly rising prior to the lake-level rise. Tremor was more continuous after 28 July 2012. As a result of the increased activity, the Aviation Colour Code was increased to Yellow (on a increasing scale of Green-Yellow-Orange-Red) on 2 August; the Alert Level remained at 1 (on a scale from 0-5).

First ash eruption in more than 10 years. An overnight episode of stronger tremor ended in a volcanic earthquake at 0454 on 5 August. Webcam images during the few minutes following revealed an accompanying plume rising from the crater lake (figure 53). As a result, the Alert Level/Aviation Colour Code was raised to 2/Orange.

Figure 53. An early morning webcam image of an eruptive plume at White Island on 5 August 2012. This was the first observed plume since the onset of the new episode of unrest in White Island's 1978/90 Crater Complex. Courtesy of GeoNet.

Two days later, on 7 August, tremor sharply decreased to levels seen prior to July 2012. A few hours later, however, the plume rising from the crater lake changed color from white to light brown, indicating the first observed ash erupted from White Island since February 2001 (BGVN 26:09). During a visit to the crater area, GeoNet volcanologists confirmed the ash emissions, and photographed the newly formed vent emerging in an area near the SW corner of the 1978/90 Crater Complex (figure 54). They described a 40-50-m-wide tuff cone forming around the vent and isolating the vent from the lake water. Impact craters around the tuff cone were the result of falling ejecta from explosions. The impact craters were confined to the 1978/90 Crater Complex.

Figure 54. A photograph of the new eruptive vent in the SW corner of White Island's 1978/90 Crater Complex. In this photograph, an ash laden plume is rising from the vent, and a 40-50-m-wide tuff cone is forming around the vent. Courtesy of GeoNet.

Through 13 August, weak volcanic tremor continued, along with steam-and-gas plumes that rose to 200-300 m above the crater and intermittently contained ash. A GeoNet Alert Bulletin released on the afternoon of 13 August announced the lowering of the Aviation Colour Code to Yellow "as a result of generally reduced ash emission." Four days later, on 17 August, the Alert Level was lowered to 1. GeoNet stated that "minor eruptive activity, which is required for Volcanic Alert Level 2, is no longer occurring and the Volcanic Alert Level is consequently reduced from 2 to 1." They noted that little-to-no ash was contained in steam-and-gas plumes, seismicity was low, and typical SO₂ levels were emitted during the previous week.

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: GeoNet, a collaboration between theEarthquake Commission and GNS Science (URL: http://www.geonet.org.nz/); Brad Scott, GNS Science, Wairakei Research Center, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Earthquake Commission (EQC), PO Box 790, Wellington, New Zealand (URL: http://www.eqc.govt.nz/).