Klyuchevskoy is part of the Klyuchevskaya volcanic group in northern Kamchatka and is one of the most frequently active volcanoes of the region. Eruptions produce lava flows, ashfall, and lahars originating from summit and flank activity. This report summarizes activity during October 2019 through May 2020, and is based on reports by the Kamchatkan Volcanic Eruption Response Team (KVERT) and satellite data.

There were no activity reports from 1 to 22 October, but gas emissions were visible in satellite images. At 1020 on 24 October (2220 on 23 October UTC) KVERT noted that there was a small ash component in the ash plume from erosion of the conduit, with the plume reaching 130 km ENE. The Aviation Colour Code was raised from Green to Yellow, then to Orange the following day. An ash plume continued on the 25th to 5-7 km altitude and extending 15 km SE and 70 km SW and reached 30 km ESE on the 26th. Similar activity continued through to the end of the month.

Moderate gas emissions continued during 1-19 November, but the summit was obscured by clouds. Strong nighttime incandescence was visible at the crater during the 10-11 November and thermal anomalies were detected on 8 and 10-13 November. Explosions produced ash plumes up to 6 km altitude on the 20-21st and Strombolian activity was reported during 20-22 November. Degassing continued from 23 November through 12 December, and a thermal anomaly was visible on the days when the summit was not covered by clouds. An ash plume was reported moving to the NW on the 13th, and degassing with a thermal anomaly and intermittent Strombolian activity then resumed, continuing through to the end of December with an ash plume reported on the 30th.

Gas-and-steam plumes continued into January 2020 with incandescence noted when the summit was clear (figure 33). Strombolian activity was reported again starting on the 3rd. A weak ash plume produced on the 6th extended 55 km E, and on the 21st an ash plume reached 5-5.5 km altitude and extended 190 km NE (figure 34). Another ash plume the next day rose to the same altitude and extended 388 km NE. During 23-29 Strombolian activity continued, and Vulcanian activity produced ash plumes up to 5.5 altitude, extending to 282 km E on the 30th, and 145 km E on the 31st.

Figure 33. Incandescence and degassing were visible at Klyuchevskoy through January 2020, seen here on the 11th. Courtesy of KVERT.

Figure 34. A low ash plume at Klyuchevskoy on 21 January 2020 extended 190 km NE. Courtesy of KVERT.

Strombolian activity continued throughout February with occasional explosions producing ash plumes up to 5.5 km altitude, as well as gas-and-steam plumes and a persistent thermal anomaly with incandescence visible at night. Starting in late February thermal anomalies were detected much more frequently, and with higher energy output compared to the previous year (figure 35). A lava fountain was reported on 1 March with the material falling back into the summit crater. Strombolian activity continued through early March. Lava fountaining was reported again on the 8th with ejecta landing in the crater and down the flanks (figure 36). A strong persistent gas-and-steam plume containing some ash continued along with Strombolian activity through 25 March (figure 37), with Vulcanian activity noted on the 20th and 25th. Strombolian and Vulcanian activity was reported through the end of March.

Figure 35. This MIROVA thermal energy plot for Klyuchevskoy for the year ending 29 April 2020 (log radiative power) shows intermittent thermal anomalies leading up to more sustained energy detected from February through March, then steadily increasing energy through April 2020. Courtesy of MIROVA.

Figure 36. Strombolian explosions at Klyuchevskoy eject incandescent ash and gas, and blocks and bombs onto the upper flanks on 8 and 10 March 2020. Courtesy of IVS FEB RAS, KVERT.

Figure 37. Weak ash emission from the Klyuchevskoy summit crater are dispersed by wind on 19 and 29 March 2020, with ash depositing on the flanks. Courtesy of IVS FEB RAS, KVERT.

Activity was dominantly Strombolian during 1-5 April and included intermittent Vulcanian explosions from the 6th onwards, with ash plumes reaching 6 km altitude. On 18 April a lava flow began moving down the SE flank (figures 38). A report on the 26th reported explosions from lava-water interactions with avalanches from the active lava flow, which continued to move down the SE flank and into the Apakhonchich chute (figures 39 and 40). This continued throughout April and May with sustained Strombolian and intermittent Vulcanian activity at the summit (figures 41 and 42).

Figure 38. Strombolian activity produced ash plumes and a lava flow down the SE flank of Klyuchevskoy on 18 April 2020. Courtesy of IVS FEB RAS, KVERT.

Figure 39. A lava flow descends the SW flank of Klyuchevskoy and a gas plume is dispersed by winds on 21 April 2020. Courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.

Figure 40. Sentinel-2 thermal satellite images show the progression of the Klyuchevskoy lava flow from the summit crater down the SE flank from 19-29 April 2020. Associated gas plumes are dispersed in various directions. Courtesy of Sentinel Hub Playground.

Figure 41. Strombolian activity at Klyuchevskoy ejects incandescent ejecta, gas, and ash above the summit on 27 April 2020. Courtesy of D. Bud'kov, IVS FEB RAS, KVERT.

Figure 42. Sentinel-2 thermal satellite images of Klyuchevskoy show the progression of the SE flank lava flow through May 2020, with associated gas plumes being dispersed in multiple directions. Courtesy of Sentinel Hub Playground.

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

Information Contacts: 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/); 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).

Nyamuragira (also known as Nyamulagira) is located in the Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo and consists of a lava lake that reappeared in the summit crater in mid-April 2018. Volcanism has been characterized by lava emissions, thermal anomalies, seismicity, and gas-and-steam emissions. This report summarizes activity during December 2019 through May 2020 using information from monthly reports by the Observatoire Volcanologique de Goma (OVG) and satellite data.

According to OVG, intermittent eruptive activity was detected in the lava lake of the central crater during December 2019 and January-April 2020, which also resulted in few seismic events. MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows thermal anomalies within the summit crater that varied in both frequency and power between August 2019 and mid-March 2020, but very few were recorded afterward through late May (figure 88). Thermal hotspots identified by MODVOLC from 15 December 2019 through March 2020 were mainly located in the active central crater, with only three hotspots just outside the SW crater rim (figure 89). Sentinel-2 thermal satellite imagery also showed activity within the summit crater during January-May 2020, but by mid-March the thermal anomaly had visibly decreased in power (figure 90).

Figure 88. The MIROVA graph of thermal activity (log radiative power) at Nyamuragira during 27 July through May 2020 shows variably strong, intermittent thermal anomalies with a variation in power and frequency from August 2019 to mid-March 2020. Courtesy of MIROVA.

Figure 89. Map showing the number of MODVOLC hotspot pixels at Nyamuragira from 1 December 2019 t0 31 May 2020. 37 pixels were registered within the summit crater while 3 were detected just outside the SW crater rim. Courtesy of HIGP-MODVOLC Thermal Alerts System.

Figure 90. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) confirmed ongoing thermal activity (bright yellow-orange) at Nyamuragira from February into April 2020. The strength of the thermal anomaly in the summit crater decreased by late March 2020, but was still visible. Courtesy of Sentinel Hub Playground.

Geologic Background. Africa's most active volcano, Nyamuragira, is a massive high-potassium basaltic shield about 25 km N of Lake Kivu. Also known as Nyamulagira, it has generated extensive lava flows that cover 1500 km2 of the western branch of the East African Rift. The broad low-angle shield volcano contrasts dramatically with the adjacent steep-sided Nyiragongo to the SW. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Historical eruptions have occurred within the summit caldera, as well as from the numerous fissures and cinder cones on the flanks. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Historical lava flows extend down the flanks more than 30 km from the summit, reaching as far as Lake Kivu.

Information Contacts: Information contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; 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/exp.

Nyiragongo is located in the Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo, part of the western branch of the East African Rift System and contains a 1.2 km-wide summit crater with a lava lake that has been active since at least 1971. Volcanism has been characterized by strong and frequent thermal anomalies, incandescence, gas-and-steam emissions, and seismicity. This report summarizes activity during December 2019 through May 2020 using information from monthly reports by the Observatoire Volcanologique de Goma (OVG) and satellite data.

In the December 2019 monthly report, OVG stated that the level of the lava lake had increased. This level of the lava lake was maintained for the duration of the reporting period, according to later OVG monthly reports. Seismicity increased starting in November 2019 and was detected in the NE part of the crater, but it decreased by mid-April 2020. SO₂ emissions increased in January 2020 to roughly 7,000 tons/day but decreased again near the end of the month. OVG reported that SO₂ emissions rose again in February to roughly 8,500 tons/day before declining to about 6,000 tons/day. Unlike in the previous report (BGVN 44:12), incandescence was visible during the day in the active lava lake and activity at the small eruptive cone within the 1.2-km-wide summit crater has since increased, consisting of incandescence and some lava fountaining (figure 72). A field survey was conducted on 3-4 March where an OVG team observed active lava fountains and ejecta that produced Pele’s hair from the small eruptive cone (figure 73). During this survey, OVG reported that the level of the lava lake had reached the second terrace, which was formed on 17 January 2002 and represents remnants of the lava lake at different eruption stages. There, the open surface lava lake was observed; gas-and-steam emissions accompanied both the active lava lake and the small eruptive cone (figures 72 and 73).

Figure 72. Webcam image of Nyiragongo in February 2020 showing an open lava lake surface and incandescence from the active crater cone within the 1.2 km-wide summit crater visible during the day, accompanied by white gas-and-steam emissions. Courtesy of OVG (Rapport OVG February 2020).

Figure 73. Webcam image of Nyiragongo on 4 March 2020 showing an open lava lake surface and incandescence from the active crater cone within the 1.2 km-wide summit crater visible during the day, accompanied by white gas-and-steam emissions. Courtesy of OVG (Rapport OVG Mars 2020).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data continued to show frequent strong thermal anomalies within 5 km of the summit crater through May 2020 (figure 74). Similarly, the MODVOLC algorithm reported multiple thermal hotspots almost daily within the summit crater between December 2019 and May 2020. These thermal signatures were also observed in Sentinel-2 thermal satellite imagery within the summit crater (figure 75).

Figure 74. Thermal anomalies at Nyiragongo from 27 July through May 2020 as recorded by the MIROVA system (Log Radiative Power) were frequent and strong. Courtesy of MIROVA.

Figure 75. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) showed ongoing thermal activity (bright yellow-orange) in the summit crater at Nyiragongo during January through April 2020. Courtesy of Sentinel Hub Playground.

Geologic Background. One of Africa's most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. The steep slopes of a stratovolcano contrast to the low profile of its neighboring shield volcano, Nyamuragira. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

Information Contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; 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).

Kavachi is a submarine volcano located in the Solomon Islands south of Gatokae and Vangunu islands. Volcanism is frequently active, but rarely observed. The most recent eruptions took place during 2014, which consisted of an ash eruption, and during 2016, which included phreatomagmatic explosions (BGVN 42:03). This reporting period covers December 2016-April 2020 primarily using satellite data.

Activity at Kavachi is often only observed through satellite images, and frequently consists of discolored submarine plumes for which the cause is uncertain. On 1 January 2018 a slight yellow discoloration in the water is seen extending to the E from a specific point (figure 20). Similar faint plumes were observed on 16 January, 25 February, 2 March, 26 April, 6 May, and 25 June 2018. No similar water discoloration was noted during 2019, though clouds may have obscured views.

Figure 20. Satellite images from Sentinel-2 revealed intermittent faint water discoloration (yellow) at Kavachi during the first half of 2018, as seen here on 1 January (top left), 25 February (top right), 26 April (bottom left), and 25 June (bottom right). Images with “Natural color” rendering (bands 4, 3, 2); courtesy of Sentinel Hub Playground.

Activity resumed in 2020, showing more discolored water in satellite imagery. The first instance occurred on 16 March, where a distinct plume extended from a specific point to the SE. On 25 April a satellite image showed a larger discolored plume in the water that spread over about 30 km2, encompassing the area around Kavachi (figure 21). Another image on 30 April showed a thin ribbon of discolored water extending about 50 km W of the vent.

Figure 21. Sentinel-2 satellite images of a discolored plume (yellow) at Kavachi beginning on 16 March (top left) with a significant large plume on 25 April (right), which remained until 30 April (bottom left). Images with “Natural color” rendering (bands 4, 3, 2); courtesy of Sentinel Hub Playground.

Geologic Background. Named for a sea-god of the Gatokae and Vangunu peoples, Kavachi is one of the most active submarine volcanoes in the SW Pacific, located in the Solomon Islands south of Vangunu Island about 30 km N of the site of subduction of the Indo-Australian plate beneath the Pacific plate. Sometimes referred to as Rejo te Kvachi ("Kavachi's Oven"), this shallow submarine basaltic-to-andesitic volcano has produced ephemeral islands up to 1 km long many times since its first recorded eruption during 1939. Residents of the nearby islands of Vanguna and Nggatokae (Gatokae) reported "fire on the water" prior to 1939, a possible reference to earlier eruptions. The roughly conical edifice rises from water depths of 1.1-1.2 km on the north and greater depths to the SE. Frequent shallow submarine and occasional subaerial eruptions produce phreatomagmatic explosions that eject steam, ash, and incandescent bombs. On a number of occasions lava flows were observed on the ephemeral islands.

Information Contacts: Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

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).

Shallow earthquakes that began 30 March (table 1) were felt and heard on Anatahan Island, and associated with an apparent increase in thermal activity from the younger E cone's crater lake. Felt seismicity remained frequent through 1 April. Observations limited to early morning and around noon yielded reports of 9 shocks, each lasting 5-7 seconds, 31 March-1 April. No felt events were reported 2-4 April. A helicopter overflight on 1 April revealed that the crater lake had become turbulent and had changed from its usual dirty green color to a bluish gray or whitish blue. Fumarolic activity had increased and a rotten egg smell was noted. A new landslide was visible on the SW wall of the active crater. The 23 residents of the island were evacuated 4 April, and had not returned as of mid-April.

Table 1. Earthquakes near Anatahan recorded by WWSSN stations, 30 March-1 April 1990. All events were shallow, but preliminary data did not allow precise depth determinations. Courtesy of the NEIC.

Geologic Background. The elongate, 9-km-long island of Anatahan in the central Mariana Islands consists of a large stratovolcano with a 2.3 x 5 km compound summit caldera. The larger western portion of the caldera is 2.3 x 3 km wide, and its western rim forms the island's high point. Ponded lava flows overlain by pyroclastic deposits fill the floor of the western caldera, whose SW side is cut by a fresh-looking smaller crater. The 2-km-wide eastern portion of the caldera contained a steep-walled inner crater whose floor prior to the 2003 eruption was only 68 m above sea level. A submarine cone, named NE Anatahan, rises to within 460 m of the sea surface on the NE flank, and numerous other submarine vents are found on the NE-to-SE flanks. Sparseness of vegetation on the most recent lava flows had indicated that they were of Holocene age, but the first historical eruption did not occur until May 2003, when a large explosive eruption took place forming a new crater inside the eastern caldera.

Information Contacts: N. Banks and J. Ewert, CVO; NEIC.

"Seismicity. . . continued throughout March, although at a milder level after the 5th. Following intense February seismicity that involved 83 earthquakes of M_L >=4.0, eight of M_L >=5.0, and one of M_L >=6.0, activity was strong again 3-5 March. More than 720 earthquakes (two of M_L = 5.0-5.1 and 10 of M_L >=4.5) were recorded before seismicity decreased to 20-50 events/day of small-moderate magnitude. The energy released by the February-March seismicity was relatively large, 1.22 x 10²¹ ergs (figure 1).

Figure 1. Daily number of earthquakes (bars) and cumulative energy release (circles) near Bamus, February-March 1990. Magnitudes (ML) of larger events are given over earthquake count bars. Courtesy of RVO.

"An inspection of the Bamus area was carried out on 6 March. Rockfalls had occurred at many places on the volcano and in the limestone ranges to the S. However, no change was observed in the temperatures of the solfataric areas on the summit tholoid (which remained at <=15°C).

"Temporary seismograph networks were operated in the area 13-16 February and 6-8 March. Earthquake locations defined a broad 15-km-long seismic zone trending NNE that extended from the Nakanai Mountains to the S flank of Bamus (figure 2). Within this zone was a concentration of locations trending ENE near the S foot of Bamus. Earthquake focal depths ranged from 0 to 23 km.

Figure 2. Epicenters of seismic events at Bamus, 13-16 February and 6-8 March 1990. Courtesy of RVO.

"Cross-sections . . . (figure 3) suggest that the main cluster of earthquakes defines an ENE-trending near-vertical fault. This orientation is consistent with the structural pattern evident in the Miocene limestone immediately S of, and underlying, Bamus.

Figure 3. Focal depths of seismic events near Bamus during 13-16 February and 6-8 March 1990 projected along lines A-B (top) and A-C (bottom). Horizontal scale (and thus vertical exaggeration) changes from A-B to A-C. Courtesy of RVO.

"The cause of this seismicity remains uncertain. Its ongoing fluctuating character, and the fact that its swarms include but do not occur in response to larger earthquakes, could be consistent with magmatic injection. On the other hand, M_L 5-6 earthquakes are uncommon for magmatic events. Analysis of the magnitude/frequency distribution of the earthquakes shows that the 'b' value is ~1, which is indicative of tectonic earthquake sequences. The seismicity was continuing in early April and was being monitored primarily by the permananent seismograph at Ulawun."

Geologic Background. Symmetrical 2248-m-high Bamus volcano, also referred to locally as the South Son, is located SW of Ulawun volcano, known as the Father. These two volcanoes are the highest in the 1000-km-long Bismarck volcanic arc. The andesitic stratovolcano is draped by rainforest and contains a breached summit crater filled with a lava dome. A satellitic cone is located on the southern flank, and a prominent 1.5-km-wide crater with two small adjacent cones is situated halfway up the SE flank. Young pyroclastic-flow deposits are found on the volcano's flanks, and villagers describe an eruption that took place during the late 19th century.

Information Contacts: I. Itikarai, P. de Saint-Ours, and C. McKee, RVO.

Steam jets from that rose 300-400 m from fumaroles on the SE flank, 200 m below the summit, were observed during dry weather at about noon on 9 and 16 March.

Geologic Background. The late-Pleistocene to Holocene Callaqui stratovolcano has a profile of an overturned canoe, due to its construction along an 11-km-long, SW-NE fissure above a 1.2-0.3 million year old Pleistocene edifice. The ice-capped, basaltic-andesite volcano contains well-preserved cones and lava flows, which have traveled up to 14 km. Small craters 100-500 m in diameter are primarily found along a fissure extending down the SW flank. Intense solfataric activity occurs at the southern portion of the summit; in 1966 and 1978, red glow was observed in fumarolic areas (Moreno 1985, pers. comm.). Periods of intense fumarolic activity have dominated; few historical eruptions are known. An explosive eruption was reported in 1751, there were uncertain accounts of eruptions in 1864 and 1937, and a small phreatic ash emission was noted in 1980.

Information Contacts: J. Naranjo, SERNAGEOMIN, Santiago; H. Moreno, Univ de Chile.

A group from CICBAS (Universidad de Colima) and CONMAR (Oregon State Univ) visited the volcano 15-17 February. Since their last visit, in May 1989, rockfall avalanches have occurred preferentially on the SW flank. Fumarolic activity persisted throughout their visit, forming a dense gray cloud. Poor weather conditions limited additional observations.

The geologists emplaced geoceivers for satellite communication, to determine geodetic positions of sites near the volcano for installation of two new telemetering seismographs. On 15 December 1989, the CICBAS seismology group had installed the 4th telemetric station of the Red Sismológica Telemétrica de Colima, 7 km from the volcano (at la Yerbabuena, site EZV6 on figure 6).

Geologic Background. The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the high point of the complex) on the north and the historically active Volcán de Colima at the south. A group of late-Pleistocene cinder cones is located on the floor of the Colima graben west and east of the complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, producing thick debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions have destroyed the summit (most recently in 1913) and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.

Information Contacts: Guillermo Castellanos, Gilberto Ornelas-Arciniega, C. Ariel Ramírez-Vazquez, G.A. Reyes-Dávila, and Hector Tamez, CICBAS, Universidad de Colima.

"Spanish scientists visited Deception Island in December 1989 and January-February 1990. A geophysical station is located on the island and the Spanish oceanographic vessel Las Palmas operated in the area. Geological, tectonic, and geophysical features on and near the island were investigated. A regional, higher precision GPS geodetic network spans the Deception section of the Bransfield Rift.

"During the 1989-90 field season, an array of six digital seismic stations was installed on Deception Island. More than 1,000 events (0.5-2.1 m_b) were digitally recorded. The major shocks were located in de Neptune Bowels (S of the island). The distribution of events shows a good correlation with tectonic features on and near the island (figure 2). A low seismic velocity, high-attenuation body was inferred under the NE sector of the island. A negative magnetic anomaly (-4,900 nT) is located in the same area.

Figure 2. Distribution of seismic events (circles) recorded by the Spanish Antarctic Program seismic array (triangles) on Deception Island, 20 January-20 February 1990.

"Chemical compositions of samples from fumaroles and thermal springs suggest a thermal anomaly related to an underlying magma body. Gas geothermometry shows a formation temperature >250°C, with an outflow temperature of about 100°C. The phreatomagmatic character of the recent episodes is hypothesized as the result of a magma intrusion into shallow and confined water-saturated layers.

"A permanent seismic station monitoring the seismic activity in the area has been established at Spain's Juan Carlos I facility (35 km from Deception)."

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

Information Contacts: R. Ortiz, Museo Nacional de Ciencias Naturales, Spain; Rafael Soto, Real Instituto y Observatorio de la Armada, Spain.

Scientists visited the summit of Mt. Erebus several times from mid-November 1989 through mid-January 1990. Activity was at a low level compared to that of the early 1980s. Anorthoclase phonolite lava in the summit inner crater was mainly confined to two small convecting lakes; one circular and about 20 m in diameter, and the other irregular and ~20 m long. This was the largest area of convecting lava seen at Mt. Erebus since late 1984, when eruptions buried an older, larger, lava lake system. Three hornitos were actively degassing around the lava lakes, and small fumaroles were present within the inner crater.

From mid-November to mid-December, infrequent small Strombolian explosions ejected bombs to a few tens of meters from the lava lakes. A small gas bubble burst was observed in one of the hornitos. In mid-December, an increase in the frequency and size of small Strombolian eruptions was recorded by Victoria University's remote video camera mounted on the crater rim 220 m above the lava lakes. Images transmitted to Scott base, 35 km from the volcano, showed bombs being ejected to more than 100 m height.

SO₂ emission, monitored by COSPEC, has increased substantially over the previous 5 years, commonly exceeding 100 t/d. This increase was consistent with previous observations suggesting that the surface area of the lava lakes correlates with SO₂ emission rates.

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

Information Contacts: P. Kyle and W. McIntosh, New Mexico Institute of Mining and Technology; R. Dibble, Victoria Univ.

Summit activity. (S. Calvari, M. Coltelli, O. Consoli, M. Pompilio, and V. Scribano.) February activity was characterized by a single strong eruptive episode at Southeast Crater. Summit-area craters generally remained quiet through the rest of February and March. The 1-2 February eruptive episode was similar to several in January. A gradual increase in Strombolian explosions was followed by lava fountaining, and lava flowed over the crater's E rim for 5 hours beginning at 2200 on 1 February. The flow turned toward the Valle del Bove, advancing to ~ 2,000 m altitude, near the terminus of the mid-January flow. During the morning of 2 February, discontinuous Strombolian activity was followed by ejection of scoria that seldom reached a few tens of meters from the rim. Activity changed at about 1330 to energetic, discontinuous explosions that generated rumbling heard at a considerable distance. Blocks more than a meter across fell within a few hundred meters of the crater; much of the slightly vesicular ash was non-juvenile. Similar activity continued until about midnight. After the eruptive episode, the crater was completely obstructed, without any gas emission, until 27 February, when sporadic ejection of dark tephra began from two vents on the crater floor. February activity at other summit-area craters was limited to vapor emission from floors and walls. Emissions were particularly strong from Northeast Crater, where the active vent's walls were strongly incandescent.

Degassing was continuous at the summit craters in March but was not accompanied by Strombolian activity. Degassing occurred from an elliptical vent on the W floor of La Voragine accompanied by sporadic rumbling. Gas was also emitted from two sites on the SE and NW floor of Bocca Nuova. Weak fumarolic activity, from collapse steps that have formed along concentric fractures in Southeast Crater, was strongest from the center of the crater. Degassing also continued in Northeast Crater. On 29 and 30 March, sporadic tephra ejection and incandescence were observed, apparently from a sudden rise in the magma column.

Seismic activity. (E. Privitera, C. Cardaci, O. Cocina, V. Longo, A. Montaldo, M. Patanè, A. Pellegrino, and S. Spampinato.) Volcanic tremor amplitude began a progressive increase on 1 February at 1239, probably associated with increased Strombolian activity at Southeast Crater. Amplitudes peaked at 1940 that day, and at 0048 the next morning as activity was changing from Strombolian to lava fountaining. Other substantial increases in tremor amplitude occurred at 0600-1100, 1855, and 1935. The first of two sequences of discrete earthquakes on 2 February began at 0352. Eight of the events, centered at ~15 km depth on the volcano's N sector, were larger than M 1, the strongest at M 2.6 between 0424 and 0619. The second series of shocks started at 1321, with the two largest events (M 2.8) at 1322 and 1337. Hypocenters were on the Valle del Bove at <1 km depth. From 3 February until the end of the month, seismic activity was at very low levels, with little variation in tremor amplitude or the number of low-frequency shocks. Nine fracturing events exceeded M 1, with a maximum magnitude of 2.5.

Seismic activity in March was characterized by a significant increase in the number of fracturing events. Swarms on 16 and 18 March totaled 124 shocks (M>=1) and brought the month's recorded earthquakes to 153, ~ 3 times as many as in January and February. The 16 March swarm began at 0530 and continued until 0050 the next day. Of the 107 shocks stronger than M 1, 28 were of M>=2 and three of M>=3. The bulk of the most energetic events originated from the central to W part of the edifice at 10-20 km depth, although one (at 1052) was located just NNW of the central crater at ~5 km depth. The strongest shock of the 18 March sequence, which included 17 events, occurred on the SW flank (a few kilometers S of Monte Nero) at ~10-15 km depth. An M 3.3 earthquake on 22 March at 1159 was ~15 km deep, roughly 6 km SSW of the summit (just S of Monte Vetore). The March seismicity was not accompanied by changes in volcanic tremor amplitude, which remained low throughout the month. The number and amplitude of low-frequency events showed little change after 3 February. A new seismic station (PZF) was installed on the lower NW flank (near Maletto), replacing station RCC, stolen in August 1989. With the new site, IIV's Etna network numbers 8 stations.

Ground deformation. (A. Bonaccorso, O. Campisi, G. Falzone, B. Puglisi, and R. Velardita.) Two tilt stations (SPC and CDV) operated during February, both on the S side of the volcano. Data from station SPC generally remained within resolution limits through February and March. A weak anomaly was recorded on the tangential component 18-20 February, then tangential data returned to the normal range. Radial values from recently installed station CDV remained within resolution limits through February, while tangential data began a (negative) excursion on 18 February that totalled 5 µrad by the end of the month. All instruments from this station were stolen on 1 March. Reoccupation of sites that form a triangle along the fracture zone between 1,800 and 1,500 m altitude on the S-SE flank (between benchmarks Bocche 1792, Serra Pizzuta Calvarina, and Mt. Stempato) did not show significant deformation since the previous measurements on 19 January.

Summit SO₂ flux. (T. Caltabiano and R. Romano.) Rates of SO₂ emission during Southeast Crater's eruptive episode on 2 February were three times mean values. Measurements 7, 14, and 21 February showed considerable variation. The five March measurements yielded SO₂ flux of 2,500-14,000 t/d, increasing at the end of the month.

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: R. Santacroce, IIV.

Overflights of Fuego were made on 15 and 16 February by volcanologists from INSIVUMEH and Michigan Tech. The following is from their report.

"Continuous gas emission was observed, with no evidence of any magma at the surface. The geometry of the summit crater and its surroundings (which influences the paths of pyroclastic flows during eruptive activity) was unchanged since 1980. COSPEC measurements of SO₂ emission rates were made from the air, yielding 265 ± 33 t/d on 15 February and 120 ± 30 t/d on 16 February (3 and 8 determinations respectively). These rates are very similar to the 100 t/d measured in February 1980 and much less than the rates measured in February 1978 (660-1,700 t/d) when Fuego was actively erupting (Stoiber et al., 1983; reference under Santiaguito)."

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: Otoniel Matías and Rodolfo Morales, Sección de Volcanología, INSIVUMEH; W.I. Rose, Jimmy Diehl, Robert Andres, Michael Conway, and Gordon Keating, Michigan Technological Univ, USA.

Small phreatic ash emissions continued in March, accompanied by spasmodic tremor and long-period seismicity (table 2). Incandescence was mainly observed in the W part of the crater. The number of low-frequency earthquakes increased 47% relative to February values, with an 86% increase in seismic energy release. However, the number of high-frequency events decreased 38% from February and energy release declined 28% (figures 17 and 18). Most earthquakes were centered in two zones under, W of, and S of the summit (figure 19). SO₂ emissions measured on 15 and 22 March by COSPEC were at low-moderate levels, ranging from 630 to 1,380 t/d.

Table 2. Phreatic ash emissions and associated seismicity at Galeras, March 1990. Courtesy of INGEOMINAS.

Figure 17. Number of seismic events at Galeras, February 1989-March 1990. Courtesy of INGEOMINAS.

Figure 18. Daily energy release of high-frequency (dashed line) and low-frequency (solid line) seismicity at Galeras, March 1990. Courtesy of INGEOMINAS.

Figure 19. Epicenters of 67 seismic events at Galeras, March 1990. Courtesy of INGEOMINAS.

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

Information Contacts: INGEOMINAS-OVP.

After 15 months of quiet, phreatic activity began on 16 April at 0221. The activity was confined to the phreatic crater formed in 1981-82, on the NE side of the 600-m-diameter dome that occupies most of the caldera floor. Activity began with spasmodic harmonic tremor of small to intermediate amplitude, accompanied by strong fumarolic emissions generating a vapor column that rose at least 800 m. Several explosions were heard and recorded by seismographs 1.5 km and (very weakly) 9 km from the crater. Seven new fumaroles were observed within the 1981 crater, but by 17 April had joined to form a single fumarole 4 m in diameter. Non-juvenile material, rocks, and mud were thrown outward to 250 m from the vent, forming a layer 4 cm thick. The explosions enlarged the 1981 crater by ~20 m.

Precursory activity began with a M 2.3 earthquake on 5 April and a M 2.2 shock on 13 April. Only a few small events, both A- and B-type, were detected during subsequent days. The tremor had a typical frequency of 1.7 Hz on 15-17 April. Periods of tremor lasted as much as 3 hours, separated by intervals of low-amplitude tremor or quiescence. Intermittent explosions were also recorded, always associated with tremor. Only a few very small B-type events have been recorded since the onset of phreatic activity. Fumarolic waters remained at their normal temperature of 87°C.

Given the shallow character of the activity, geologists believed that it was partly related to the previous week's increased precipitation. Stepped-up monitoring and re-deployment of the Instituto Geofísico's seismic net (dismantled following the 1988 activity) were begun 16-17 April, and tilt stations and EDM lines were being resurveyed. The Instituto's hazard map and previously planned preparedness exercises for a hypothetical eruption of Guagua Pichincha were helping civil defense authorities to prepare for the possibility of increased activity.

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

Information Contacts: M. Hall, Instituto Geofísico de la Escuela Politécnica Nacional.

December press reports in Bolivia of an eruption . . .[located 25 km NNW of Olca Volcano] remain unconfirmed, and attempts by Bolivian geologists to fly over the volcano in January were stymied by poor weather. State oil company (ENAP) geologist Patricio Sepulveda reported only normal fumarolic activity at Irruputuncu on 25 March.

Geologic Background. Irruputuncu is a small stratovolcano that straddles the Chile/Bolivia border. It is the youngest and most southerly of a NE-SW-trending chain of volcanoes. It was constructed within the collapse scarp of a Holocene debris avalanche whose deposit extends to the SW. Subsequent eruptions filled much of this scarp and produced thick, viscous lava flows down the W flank. The summit complex contains two craters, the southernmost of which is fumarolically active. The first unambiguous historical eruption took place in November 1995, when phreatic explosions produced dark ash clouds.

Information Contacts: J. Naranjo, SERNAGEOMIN.

The volcano was generally quiet during a 2 February overflight (figure 1). Pre-existing thermal areas were visible in the S and SW parts of the crater, although the vent was snow-covered. Slightly warm zones were also noted on the upper S flank.

Figure 1. Summit crater of Karymsky, looking roughly SW on 2 February 1990. Courtesy of B. Ivanov.

Geologic Background. Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

Information Contacts: B. Ivanov, IV.

Seismic stations along the Lesser Antilles arc began to record very strong acoustic (T-phase) signals, probably associated with an eruption of the . . . Kick-'em-Jenny . . . on 26 March at 1112. Overflights of the area during the period of vigorous seismicity did not reveal any water discoloration or other surface changes above the volcano, which had a summit depth of about 160 m in 1982.

Thirteen distinct seismic bursts, lasting up to 19 minutes, were recorded 26-27 March on instruments operated by the Seismic Research Unit, Univ of the West Indies. The IPGP's Mt. Pelée seismic network on Martinique, 250 km NNE of Kick-'em-Jenny, recorded strong T-waves on 26 March at 1117:22, 1502:30, 1723, and 2034 (the latter felt by residents of NW Martinique), and on 27 March at 0035:40 and 0424:25. T-waves reached IPGP's Soufrière de Guadeloupe net, 450 km N of Kick-'em-Jenny, on 26 March at 1118. The initial activity saturated the Grenada seismograph and the largest burst of seismicity, at about 1721 on 26 March, was felt on northern Grenada. After a single 14-minute episode that started at 0103 on 28 March, seismicity stopped on all but the Grenada instrument, which continued to record occasional low-frequency (0.5-2 Hz) signals for periods of about 30 seconds to more than 3 hours. The latest reported low-frequency episode occurred on 5 April between about 0500 and 0800.

Geologic Background. Kick 'em Jenny, a historically active submarine volcano 8 km off the N shore of Grenada, rises 1300 m from the sea floor. Recent bathymetric surveys have shown evidence for a major arcuate collapse structure, which was the source of a submarine debris avalanche that traveled more than 15 km W. Bathymetry also revealed another submarine cone to the SE, Kick 'em Jack, and submarine lava domes to its S. These and subaerial tuff rings and lava flows at Ile de Caille and other nearby islands may represent a single large volcanic complex. Numerous historical eruptions, mostly documented by acoustic signals, have occurred since 1939, when an eruption cloud rose 275 m above the sea. Prior to the 1939 eruption, which was witnessed by a large number of people in northern Grenada, there had been no written mention of the volcano. Eruptions have involved both explosive activity and the quiet extrusion of lava flows and lava domes in the summit crater; deep rumbling noises have sometimes been heard onshore. Historical eruptions have modified the morphology of the summit crater.

Information Contacts: W. Ambeh, K. Rowley, L. Lynch, and L. Pollard, UWI; A. Redhead, Office of the Prime Minister, Grenada; J.P. Viode and G. Boudon, Observatoire Volcanologique de la Montagne Pelée, Martinique; C. Antenor and M. Feuillard, Observatoire de la Soufrière, Guadeloupe; J.L. Cheminée, N. Girardin, and A. Hirn, IPGP Observatoires Volcanologiques, France.

Lava flows . . . remained active during the first half of March. The main (Quarry) and low-volume (Roberts) flows continued to enter the ocean, while a third (Keone) flow advanced slowly to within 600 m of a highway at 30 m elevation (figure 66). Activity was periodically observed at Pu`u `O`o. Crusted lava in Kupaianaha pond averaged 30 m below the rim and only overturned a few times/day, in contrast to vigorous past activity. On the 19th, the eruption stopped and the lava pond roofed over. Small collapse pits were found in the lava pond's crust the next day. Only residual lava from the Quarry and Roberts lava tubes drained into the ocean on the 21st.

Activity resumed on the night of the 21st, with glow reported from the East rift zone. By the next day, active lava was visible in Pu`u `O`o, had risen to 20 m below the rim at Kupaianaha, and had reoccupied the tube system to 550 m elevation. Surface lava breakouts at 550 and 600 m elevation fed two flows. Lava followed the course of the January 1990 flow between the December 1986 and 1977 aa flows, and by the end of the month had reached 200 m elevation. Lava also followed the course of the Keone flow, to within 500 m of the intersection of highways 130 and 137. Kupaianaha pond remained active through 23 March when it again began to roof over ~30 m below the rim, and by the 26th, only small pahoehoe lobes were periodically active around the pond's margins.

Seismic signals . . . marked the eruption's changes. From early to mid-March, sporadic gas pistoning was recorded, manifested as background volcanic tremor decreasing to an essentially quiet state for several minutes, generally ending with a sharp burst of energy followed by continued background tremor. This activity subsided after 17 March, succeeded by a marked increase in tremor and, on the afternoon of 18 March, brief summit deflation.

At Kilauea's summit, swarms of long-period tremor events occurred from late 16 March through midday 18 March and from the evening of 19 March through the early morning of the 21st (figure 67). A swarm of short-period microearthquakes began later that morning and continued until early 22 March. Five hours after the onset of the summit swarm, and several hours before eruptive activity resumed, a sudden increase in earthquakes occurred in the upper East rift zone between the summit and the active craters. The hypocenters were in two areas: near Makaopuhi (roughly midway between the summit caldera rim and Kupaianaha) and Pauahi (~5 km uprift from Makaopuhi). The swarm continued until the morning of 25 March.

Figure 67. Preliminary locations of earthquakes in the Hawaii Island region, including Kilauea and Loihi, 1-26 March 1990. Courtesy of R. Koyanagi.

After lava returned to Kupaianaha on 22 March, variations in seismicity became less obvious. Tremor near Pu`u `O`o increased gradually and was relatively steady from the 24th until the end of the month.

Addendum: Eruptive activity declined on 5 April [see also 15:4], but had resumed by the night of the 6th. Lava entered Kalapana Gardens subdivision on 3 April, and within three weeks had destroyed a dozen houses.

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

Information Contacts: C. Heliker, P. Okubo, and R. Koyanagi, HVO; AP.

During an overflight by geologists on 2 February, vigorous ash emission fed a large eruption column that rose to ~5 km height and had a basal diameter of ~400-600 m (figure 3). Individual ash bursts were visible at the base of the column, although ash emission appeared to be continuous. A new vent was noted at 4,500 m elev on the NE slope of the Apakhonchich valley, on the upper SE flank. Vapor jets 200-300 m high were distinctly visible above this vent. A subsidiary vent downslope (at 3,970 m elev) fed basaltic lava flows. An ash plume extended 60-80 km E. The ashfall area on 2 February was ~1,600 km².

Figure 3. Tephra cloud from Kliuchevskoi's summit crater on 2 February 1990, in photograph looking roughly E. Arrow 1 indicates the new vent at 4,600 m elev on the SE flank, arrow 2 the effusive vent at 3,970 m elev. Courtesy of B. Ivanov.

Images from the NOAA 10 and 11 polar orbiting satellites showed several plumes from Kliuchevskoi. On 22 February at 1548, a thin plume extended ~80 km SE. A plume was next visible on 10 March at 0956. Although obscured by weather clouds a short distance ENE of the volcano, it formed a distinct cold area on the infrared image, indicating that it was at relatively high altitude. On 12 March at 0335, a very thin plume stretched 15-20 km NE from the Kliuchevskoi area, and on 15 March at 0942, a small diffuse plume extended S from the volcano. A thin plume extended 250 km NE on 3 April at 0903. Weather clouds . . . may have obscured additional eruptive activity.

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

Information Contacts: B. Ivanov, IV; W. Gould, NOAA/NESDIS.

"Activity consisted of weak to moderate white-grey emissions from Crater 2. Weak, steady, red glow was observed 1-4 and 25-31 March. Rumbling noises were heard on the 28th and 29th. Crater 3 remained quiet throughout the month. Seismicity was at a low level."

Geologic Background. Langila, one of the most active volcanoes of New Britain, consists of a group of four small overlapping composite basaltic-andesitic cones on the lower eastern flank of the extinct Talawe volcano. Talawe is the highest volcano in the Cape Gloucester area of NW New Britain. A rectangular, 2.5-km-long crater is breached widely to the SE; Langila volcano was constructed NE of the breached crater of Talawe. An extensive lava field reaches the coast on the north and NE sides of Langila. Frequent mild-to-moderate explosive eruptions, sometimes accompanied by lava flows, have been recorded since the 19th century from three active craters at the summit of Langila. The youngest and smallest crater (no. 3 crater) was formed in 1960 and has a diameter of 150 m.

Information Contacts: I. Itikarai, P. de Saint-Ours, and C. McKee, RVO.

After the 20 February eruption, Lascar returned to its normal fumarolic activity with the generation of mainly white plumes that rise 300-500 m above the rim of the active central crater. Between 20 and 24 March, geologists from the SERNAGEOMIN and several British universities observed the volcano from the ground and from the active crater's rim, reached on the 23rd from the N slope and on the 24th from the S slope. The following is from their report.

"Examination of photographs taken by J.R. Gerneck (Chile Hunt Oil) during the 20 February eruption revealed three discrete plumes. The first, white in color, consisted mainly of steam, and was overtaken by two smaller, grayish, higher velocity clouds. Geologists interpreted this sequence as an initial steam explosion related to the partial destruction of the dome that fills the bottom of the active crater, followed by phreatomagmatic eruptions. The eruption products, primarily fragments of the dome, occurred as shattered, dark, dense blocks of porphyritic pyroxene andesite, ranging to white, semi-vesicular, largely disaggregated blocks of similar composition, with thin, darker, quenched rims. The blocks were composed of plagioclase, clinopyroxene, and orthopyroxene phenocrysts, small amounts of magnetite, and scarce reacted olivine and hornblende crystals in a glassy groundmass. They are enriched in crystals compared to bombs from the 1986 eruption, with larger phenocrysts (up to 2 mm), and a larger proportion of pyroxene. No olivine or hornblende were found in the 1986 bombs, which included occasional xenoliths of partially molten granite. The 20 February blocks were distributed almost symmetrically in a radius of 4 km around the crater, associated with asymmetrical impact craters, elongate parallel to block trajectories. The number of blocks increased dramatically close to the vent where they covered 70-90% of the surface. No fresh ash was observed close to the volcano.

"Preliminary calculations, based on the volume of ejecta and the size of the plume, indicate that between 10 and 30% of the dome was erupted on 20 February. This estimate is supported by 5 March airphotos of the interior of the crater and by observations made from the crater rim, where a large part of the dome can still be observed in the bottom of the crater. The dome has apparently continued deflating since our last observation in November 1989 (14:11). A hole appeared to be present in its center, produced by collapse into the vent. Fumaroles were located around the dome, along ring fractures as observed in April 1989. Gas was still venting at extremely high velocity, creating the same jet-like noise reported in November. The strongest fumaroles were on the dome's NE and SW edges. A strong smell of HCl and SO₂ was recorded from the N rim. Deposits of yellow sulfur are visible associated with the fumaroles. Temperatures were measured (by Clive Oppenheimer) using an infrared radiometer (after dark, to eliminate the effects of sunlight). The fumaroles were observed to be glowing red hot and bright spots were seen over the dome. Preliminary data show the largest fumarole to have a temperature of 700-800°C, while the surface of the dome had an average temperature of 100-200°."

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

Information Contacts: M. Gardeweg, SERNAGEOMIN, Santiago; S. Matthews, Univ College London; C. Oppenheimer, Open Univ; S. Sparks and M. Stasiuk, Univ of Bristol.

Airphotos taken between 16 and 18 October 1989 by Geoff Price and 7 March 1990 by Lester Eshelman suggest that no large-volume lava flows have been extruded since June 1989. Only minor changes appear to have occurred to cones in the crater since . . . 24 June-1 July and 22-25 November 1988.

During the October 1989 overflight, clouds partially obscured the crater floor, which appeared pale gray, with a slightly darker lava flow (F13), previously seen June-August 1989, near the W wall (figure 14). Cones and vents on the crater floor had changed little since June-August 1989. A vent (T12) seen in September 1989 was no longer visible at the base of the E crater wall. A new vent (T13) had been added to the old complex (T5/T9) which now appeared as several closely spaced cones joined at the base. A possible small hornito (H6) was observed between T5/T9 and T8. The width of the overflow across the former saddle (M2M1) had not changed, but the area of lava S of the saddle may have increased slightly, particularly on the W side of the southern depression.

Figure 14. View of the N crater and southern depression at Ol Doinyo Lengai, looking roughly S between 16 and 18 October, 1989. Traced from a photograph by Geoff Price; courtesy of C. Nyamweru.

On 7 March 1990, bright sunshine and clear visibility revealed small lava flows of varying colors on the crater floor. However, none were dark gray or black, suggesting that they were of different ages and probably more than a few days (but at most a few weeks) old. No new vents were recognized, and the area of lava in the southern depression had not increased. Flow F13 was white, but had been partially covered by younger brown flows from the W side of T5/T9T13 (figure 15). Many flows of different colors were seen on its W and N slopes, including a narrow white tongue of lava (roughly 4-5 m long and 50 cm wide) stretching from the vent down the flank of the cone complex. Similar features were observed forming on T4/T7 in 1988. Several dark grooves extending from the slopes of T5/T9 appear to be narrow channels formed when a lava flow built levees, restricting it to a narrow stream. The formation of similar features was observed . . . in June and November 1988.

Figure 15. View of the N crater and southern depression at Ol Doinyo Lengai, looking roughly S on 7 March 1990. Traced from a photograph by L. Eshelman; courtesy of C. Nyamweru.

Notes on individual vents and cones are as follows: T5/T9/T13: Probable center of activity since October 1989, with emission of small thin flows from very small vents, mostly on its W slopes. The top has merged into a single broad cone with several dark patches indicating cracks or vents near the top. T4/T7: Brown and buff colors dominate. Small black patches at the top of two mounds on the E side indicate vents still open. No sign of new material extruded from these vents. Generally smooth and weathered. Lava production from T4/T7 was last reported in November 1988 (13:12). T8: Brown and buff colors dominate. Top of pinnacle appears slightly less steep. No sign of new material. Lava spattering was seen in November 1988, but only gas emission has been observed since then. T10: Gray; part of ridge that joined this cone to the E crater wall may have collapsed. Bubbling lava was seen near T10 in May 1989 (14:06). T11: Pale gray; center of cone is flat and inactive. Possible collapse at N edge. No recent lava emission was apparent and none has been reported since November 1988.

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

Information Contacts: C. Nyamweru, Kenyatta Univ.

A small explosion on 25 February, followed by the ejection of a glowing column from the main crater, was reported by Conguillio National Park administrator Omar Toledo. He added that small sediment-laden streams of water had flowed down the E flank at times when thawing does not normally occur. Field observations by geologists 5-18 March revealed occasional increases in fumarolic activity from the main crater. On 10 March, vigorous 40-60-second puffs of gas were emitted every minute during the early evening. After a summit climb, Conguillio National Park rangers reported that intense fumarolic activity produced grayish gases and a strong sulfur odor. Rockslides occurred every 1-2 hours on the NE flank.

A portable seismograph was operated 19-22 March at the volcano's W foot (in Los Paraguas National Park) by Jaime Campos and Bertrad Delovis, Dept de Geofísica, Univ de Chile. Intense volcanic earthquakes and tremor were recorded. Another portable seismograph will be installed at the NE foot (near Conguillio Lake) by Univ de la Frontera scientists.

Geologic Background. Llaima, one of Chile's largest and most active volcanoes, contains two main historically active craters, one at the summit and the other, Pichillaima, to the SE. The massive, dominantly basaltic-to-andesitic, stratovolcano has a volume of 400 km3. A Holocene edifice built primarily of accumulated lava flows was constructed over an 8-km-wide caldera that formed about 13,200 years ago, following the eruption of the 24 km3 Curacautín Ignimbrite. More than 40 scoria cones dot the volcano's flanks. Following the end of an explosive stage about 7200 years ago, construction of the present edifice began, characterized by Strombolian, Hawaiian, and infrequent subplinian eruptions. Frequent moderate explosive eruptions with occasional lava flows have been recorded since the 17th century.

Information Contacts: H. Moreno, Univ de Chile; J. Naranjo, SERNAGEOMIN, Santiago.

A vigorous earthquake swarm occurred off the S flank of Hawaii 11-19 March 1990 (figure 4). More than 300 events were registered, about 15 of M 3-4, and some of M >4. Seismologists associated many of the events, including the larger ones, with processes at Loihi Seamount. No acoustic signals (T-waves) were reported.

Figure 4. Portion of a seismogram recorded during Loihi's 11 March 1990 earthquake swarm, by a station (AHU) 45 km from the epicentral area. Courtesy of R. Koyanagi.

Further Reference. Malahoff, A., 1987, Geology of the summit of Loihi submarine volcano, in Decker, R.W., Wright, T.L., and Stauffer, P.H., eds., Volcanism in Hawaii: USGS Professional Paper 1350, p. 133-144.

Geologic Background. Loihi seamount, the youngest volcano of the Hawaiian chain, lies about 35 km off the SE coast of the island of Hawaii. Loihi (which is the Hawaiian word for "long") has an elongated morphology dominated by two curving rift zones extending north and south of the summit. The summit region contains a caldera about 3 x 4 km wide and is dotted with numerous lava cones, the highest of which is about 975 m below the sea surface. The summit platform includes two well-defined pit craters, sediment-free glassy lava, and low-temperature hydrothermal venting. An arcuate chain of small cones on the western edge of the summit extends north and south of the pit craters and merges into the crests prominent rift zones. Deep and shallow seismicity indicate a magmatic plumbing system distinct from that of Kilauea. During 1996 a new pit crater was formed at the summit, and lava flows were erupted. Continued volcanism is expected to eventually build a new island; time estimates for the summit to reach the sea surface range from roughly 10,000 to 100,000 years.

Information Contacts: P. Okubo and R. Koyanagi, USGS Hawaiian Volcano Observatory.

Earthquake swarm activity in the caldera's S moat continued through March. A swarm of >300 events of magnitude greater than or equal to 2.8 occurred 3 March, followed by smaller swarms on 9, 18, 28, and 30 March. The swarm on the 30th included more than 100 events, all of which were smaller than M 2. Only a few isolated events occurred beneath Mammoth Mountain. Two-color geodimeter measurements indicate that extension across the S moat and resurgent dome continued through March at the 5 ppm/year rate that began in late September.

Geologic Background. The large 17 x 32 km Long Valley caldera east of the central Sierra Nevada Range formed as a result of the voluminous Bishop Tuff eruption about 760,000 years ago. Resurgent doming in the central part of the caldera occurred shortly afterwards, followed by rhyolitic eruptions from the caldera moat and the eruption of rhyodacite from outer ring fracture vents, ending about 50,000 years ago. During early resurgent doming the caldera was filled with a large lake that left strandlines on the caldera walls and the resurgent dome island; the lake eventually drained through the Owens River Gorge. The caldera remains thermally active, with many hot springs and fumaroles, and has had significant deformation, seismicity, and other unrest in recent years. The late-Pleistocene to Holocene Inyo Craters cut the NW topographic rim of the caldera, and along with Mammoth Mountain on the SW topographic rim, are west of the structural caldera and are chemically and tectonically distinct from the Long Valley magmatic system.

Information Contacts: D. Hill, USGS Menlo Park.

The following is a report from José A. Naranjo and Hugo Moreno R. Most field observations were made in collaboration with R.S.J. Sparks and Mark Stasiuk, Bristol Univ, and Clive Oppenheimer, Open Univ.

"Field evidence suggests that the eruption from Navidad Cone ended between 22 and 25 January 1990, after 13 months of activity. Explosions with pyroclastic ejections stopped between 29 December and 10 January. José Córdoba, a teacher from Malalcahuello, observed and photographed one of the last explosions, on 27 December at 1930-2000. Strong explosions ejected bombs, and white clouds consisting mainly of water vapor rose as much as 600 m above the crater. He also observed two small landslides that originated from the cone's flank (above the vent), followed by white steam clouds that rose along the scar left on the N flank (see below). These collapses may represent the early stages of the slumping observed on 20 January.

"Chlorine gases and minor water vapor fumaroles remained along concentric fractures within the main crater 3-17 March. Compared with previous observations on 21 November and 20 January, the innermost annular fractures exhibited clear evidence of collapse, leaving scarps 1.5-2 m high (figure 16). Fumes from the outermost fractures near the crater rim yielded temperatures of 86°C.

Figure 16. View N across the crater of Navidad scoria cone, Lonquimay volcano, from the highest (S) part of the rim. 21 November 1989 (top): Concentric fractures had formed on the W side of the innermost nested crater; intense water vapor fumaroles aligned with them, and a strong steam jet was emitted from a glowing vent on the inner wall. 20 January 1990 (middle): Vapor emission had ceased and collapse had occurred along the eastern inner wall, the southern fractures, and around the N wall-vent. A funnel-shaped crater about 120 m in diameter had clearly widened by collapse since November. 5 March 1990 (bottom): Only dry gases were emitted along the annular fractures, while no fumes were visible at the main crater vents. Fractures had widened on the S part of the cone, and collapse scars appeared on the E part. Sketched from photographs by J.A. Naranjo.

"By March, the source vent was completely covered by talus from the unstable flank material above it. Discontinuous slumping of this debris left a funnel-shaped scar about 90 m high and 30 m deep, with walls that project upward through the crater's inner concentric fractures. The channel was enlarged by successive collapses that were up to 30 m deep and 25 m wide near the vent.

"The lava surface remained almost completely covered by a 1-3-m-thick mantle of debris transported on it. Former arched transverse debris ridges were disturbed and a gash of fresher lava was formed along the debris mantle's front axis. The top parts of most ridges showed higher temperatures (up to 390°C at 30 cm depth) than the almost cool gullies between them. After 20 January, the debris-covered lava advanced 120 m before it stopped flowing. This smooth surface texture conspicuously contrasted with the spiny, jagged surface presented by the blocky/aa lava immediately downstream.

"The fumaroles aligned with the central vent and the flow to the ENE showed decreased activity when compared to April 1989, although their temperatures remained at 190° and 250-300°C, 600 and 300 m from Navidad Cone respectively.

"On 17 March, a 948°C thermocouple measurement was obtained ~7 m below the lava surface, 1.5-2 km downstream from the source vent. The main lobe in the Lolco River valley had not advanced since 20 November 1989, although it showed a front thickness that had increased slightly, from 45-50 m in November to 55-60 m in March."

Geologic Background. Lonquimay is a small, flat-topped, symmetrical stratovolcano of late-Pleistocene to dominantly Holocene age immediately SE of Tolguaca volcano. A glacier fills its summit crater and flows down the S flank. It is dominantly andesitic, but basalt and dacite are also found. The prominent NE-SW Cordón Fissural Oriental fissure zone cuts across the entire volcano. A series of NE-flank vents and scoria cones were built along an E-W fissure, some of which have been the source of voluminous lava flows, including those during 1887-90 and 1988-90, that extended out to 10 km.

Information Contacts: J. Naranjo, SERNAGEOMIN, Santiago; H. Moreno, Univ de Chile.

"Activity remained at a low level in March. The summit was obscured for long periods (4-9 and 11-23 March), but when weather cleared, emissions of white vapour in weak to moderate amounts were observed from both craters. Seismicity remained low, with daily totals of volcanic earthquakes ranging from 900 to 1,200. No significant changes were noted in seismic amplitudes and ground deformation."

Geologic Background. The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical 1807-m-high basaltic-andesitic stratovolcano to its lower flanks. These "avalanche valleys" channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island's shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most historical eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent historical eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Information Contacts: I. Itikarai, P. de Saint-Ours, and C. McKee, RVO.

The following observations, made by scientists from the USSR and New Zealand during a cruise of the RV Vulkanolog, were reported by W.F. Giggenbach and I. Menyailov.

"...Thermal activity manifests itself largely in areas of hydrothermally altered, steaming ground. The major thermal feature is a vigorously boiling pool near sea level in Sulphur Bay (Ramsay and Hayward, 1971). As indicated by the occurrence of bubble zones (Glasby, 1971), submarine thermal activity extends well SW of the island.

"During both the 1988 and 1990 cruises of the RV Vulkanolog, gas and water samples were collected from the main pool. The waters are essentially acid sulfate (4,000 mg/kg; Cl, 20 mg/kg), steam-heated, initially non-saline groundwater. Compositions of 1988 gases are compared in table 1 with those of 1974 samples from Sulphur Bay spring and the seafloor at 34 m depth (Lyon and others, 1977).

Table 1. Chemical composition of gases collected from vents on and near Whale Island (in mmol/mol of dry gas), March 1974 (Lyon and others, 1977) and during the September 1988 cruise of the RV Vulkanolog.

"All gases reflect a hydrothermal origin, and their major component is CO₂. The seafloor gases are contaminated with air, probably after sampling. Their higher CH4 and lower H₂ contents suggest longer residence at lower temperatures compared to the island samples. The composition of the latter has remained essentially unchanged over the last 14 years."

References. Glasby, G.P., 1971, Direct observation of columnar scattering associated with geothermal gas bubbling in the Bay of Plenty, New Zealand: New Zealand Journal of Marine and Freshwater Research, v. 5, p. 483-496.

Lyon, G.L., Giggenbach, W.F., Singleton, R.J., and Glasby, G.P., 1977, Isotopic and Chemical composition of submarine geothermal gases from the Bay of Plenty, New Zealand: New Zealand Department of Scientific and Industrial Research Bulletin, v. 218, p. 65-67.

Ramsay, W.R.H., and Hayward, B.W., 1971, Geology of Whale Island: Tane, v. 17, p. 9-32.

Geologic Background. Moutohora (Whale) Island forms the summit of a largely submerged Pleistocene dacitic-andesitic complex volcano that lies 11 km offshore from Whakatane in the Bay of Plenty. The island is 15 x 5 km wide and elongated E-W. The 354-m-high central dome complex is flanked by East Dome, which forms the eastern tip of the island and is the oldest of the domes, and Pa Hill lava dome, which forms the NW tip of the island. Acid hot springs, steaming ground, and fumaroles are located primarily between the central cone and East Dome. The central cone and east dome are both older than the roughly 42,000 before present (BP) Rotoehu Tephra, and Pa Hill dome is overlain by the 9000 years BP Rotoma Ash but may be considerably older. It was included in the Catalog of Active Volcanoes of the World (Nairn and Cole, 1975) based on its thermal activity.

Information Contacts: I. Menyailov and A. Ivanenko, IV, Petropavlovsk; W. Giggenbach, DSIR Chemistry, Petone.

Fumarolic activity, accompanied by low-intensity seismicity, was described by policemen from Ujina, 15 km SW of Olca, on 13 November 1989. Minor seismicity associated with Olca was noted in mid-March 1990 by state oil company (ENAP) geologist Patricio Sepulveda.

Geologic Background. A 15-km-long E-W ridge forming the border between Chile and Bolivia is comprised of several stratovolcanoes with Holocene lava flows. Andesitic-dacitic lava flows extend as far as 5 km N from the active crater of Volcán Olca and to the north and west from vents farther to the west. Olca is flanked on the west by Cerro Michincha and on the east by Volcán Paruma, which is immediately west of the higher pre-Holocene Cerro Paruma volcano. Volcán Paruma has been the source of conspicuous fresh lava flows, one of which extends 7 km SE, and has displayed persistent fumarolic activity. The only reported historical activity from the complex was a flank eruption of unspecified character between 1865 and 1867, which SERNAGEOMIN notes is based on unconfirmed records.

Information Contacts: J. Naranjo, SERNAGEOMIN.

Volcanologists from INSIVUMEH and Michigan Tech visited Pacaya on 13, 14, 17, 18, and 28 February and 1, 2, 3, and 4 March, and flew over the volcano on 16 February. The following is from their report.

"Activity at Pacaya continued at a low level, consisting of brief (10-60 second), weak (ejecta typically thrown 2-100 m), Strombolian explosions with reposes of <1 to several minutes. All activity was from a small cone, 6 m high and 8 m wide at its rim, within MacKenney crater. The explosions were accompanied by gas emission (with jet-like noise) and often by fine ash clouds.

"On 17 February, during activity that was typical of the observation period, 78 COSPEC scans were made from a ground observation site 1.25 km from MacKenney crater (at Cerro Chino). Pacaya was emitting SO₂ at an average rate of 30 t/d, with the measured range varying between 3 and 130 t/d. Higher fluxes were directly associated with observed small explosions. The new SO₂ observations at Pacaya were much lower than values measured several times from 1972 until 1980 (Stoiber et al., 1983; reference under Santiaguito), which were generally between 250 and 1,500 t/d."

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

Information Contacts: Otoniel Matias and Rodolfo Morales, Sección de Volcanología, INSIVUMEH; W.I. Rose, Jimmy Diehl, Robert Andres, Michael Conway, and Gordon Keating, Michigan Technological Univ.

"Activity remained at a low level in March. A total of 265 caldera earthquakes was recorded. Daily earthquake totals ranged from 0 to 24, with the highest daily total recorded in a small Greet Harbour swarm on 18 March that included two felt events (M_L 2.8 and 2.6). During the month, seismicity was broadly distributed within the caldera seismic zone. Levelling measurements on 26 March indicated deflation of 2 mm at the S tip of Matupit Island since previous measurements on 20 February."

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

Information Contacts: I. Itikarai, P. de Saint-Ours, and C. McKee, RVO.

The following observations, made by scientists from the USSR and New Zealand during a cruise of the RV Vulkanolog, were reported by W.F. Giggenbach and I. Menyailov. The island was visited on 30 January 1990.

"A considerable increase in microseismic activity to ~180 events/day, starting at the beginning of January 1990, was recorded by the Raoul Island seismic station. A similar swarm of minor shocks (Adams and Dibble, 1967) and an increase in hydrothermal activity (Healy et al., 1965) preceded the 1964 eruption. There were, however, no significant changes in the appearance and emission rate of thermal fluids from the main area of geothermal discharge along the W shore of Green Lake since the last visit of RV Vulkanolog in March 1988. Water and steam samples were collected in 1988 and 1990. The compositions of the 1988 samples are compared in table 1 with those reported by Weissberg and Sarbutt (1966) for samples collected shortly after the 1964 eruption. Gas compositions point to an essentially hydrothermal origin with insignificant contributions from high-temperature magmatic gases. Heavy seas prevented landing on Curtis Island, the other island in the Kermadecs showing thermal activity."

Table 1. Chemical composition (in mmol/mol of dry gas) of steam samples collected from the main fumarolic vents on Raoul Island in December 1964 (shortly after the 1964 eruption; Weissberg and Sarbutt, 1966) and during the March 1988 cruise of the RV Vulkanolog.

References. Adams, R.D., and Dibble, R.R., 1967, Seismological studies of the Raoul Island eruption, 1964: New Zealand Journal of Geology and Geophysics, v. 10, p. 1,348-1,361.

Weissberg, B.G., and Sarbutt, J., 1966, Chemistry of the hydrothermal waters of the volcanic eruption on Raoul Island, November 1964: New Zealand Journal of Science; v. 9, p. 426-432.

Geologic Background. Anvil-shaped Raoul Island is the largest and northernmost of the Kermadec Islands. During the past several thousand years volcanism has been dominated by dacitic explosive eruptions. Two Holocene calderas exist, the older of which cuts the center the island and is about 2.5 x 3.5 km wide. Denham caldera, formed during a major dacitic explosive eruption about 2200 years ago, truncated the W side of the island and is 6.5 x 4 km wide. Its long axis is parallel to the tectonic fabric of the Havre Trough that lies W of the volcanic arc. Historical eruptions during the 19th and 20th centuries have sometimes occurred simultaneously from both calderas, and have consisted of small-to-moderate phreatic eruptions, some of which formed ephemeral islands in Denham caldera. An unnamed submarine cone, one of several located along a fissure on the lower NNE flank, has also erupted during historical time, and satellitic vents are concentrated along two parallel NNE-trending lineaments.

Information Contacts: I. Nairn, P. Otway, B. Scott, and C. Wood, NZGS Rotorua; W. Giggenbach, DSIR Chemistry, Petone.

Quoted material is from the AVO staff. Information about the 4, 9, and 14 March explosive episodes supplements the initial reports in 15:02.

"Lava dome growth disrupted by moderate explosions and gravitational collapse continued. Since 15 February, explosive episodes have occurred at average intervals of 3-9 days (table 1). Explosive episodes were associated with pyroclastic flows and surges that triggered floods and lahars in the Drift River valley, which drains the volcano's N flank (figure 8). Seismicity remained centered on Redoubt from the surface to a depth of about 10 km, but earthquakes of M >= 2.0 have not occurred since 9 March. The summit seismometer that was damaged during the 15 February event was removed in March and three new seismometers were placed on the volcano's summit and flanks. COSPEC measurements began on 20 March; data are collected as weather permits. SO₂ emission rates have ranged from 1,600 to 6,000 t/d."

Figure 8. Sketch map of the Drift River valley and related drainages on the NE flank of Redoubt. The Drift River oil facility is between the mouth of the Drift River and Rust Slough. Courtesy of AVO.

Since early January, deposition in the Drift River's main channel has diverted significant amounts of flood water and debris into Rust Slough, S of the Drift River oil facility. An L-shaped 4-m-high levee upstream from the oil facility was designed to protect it from Drift River floods, but neither levees nor topography protect its S side. Beginning on 4 March, deposition in Rust Slough has diverted floodwater farther southward into Cannery Creek, just upstream of the Drift River facility. None of the subsequent floods associated with March-mid April explosive episodes have affected the oil facility.

Explosive episode, 4 March. "An explosive event that occurred at 2039 was recorded for 8 minutes at the Spurr station (a regional seismometer about 100 km NNE of Redoubt that has been operating since the onset of the eruption). By 2110, an ash plume was reported to an altitude of 12 km; the plume moved N20°E and ashfall occurred 225 km away. Moderate flooding occurred in the Drift River. A new diversion upstream of the Drift River oil facility caused much of the flow to be diverted S of the facility (from Rust Slough into Cannery Creek).

Explosive episode, 9 March. "An explosive event occurred at 0951 and was recorded for 10 minutes at the Spurr station. Tephra fell primarily W of the volcano; Port Alsworth, 95 km SW of the volcano, received a light dusting from the southern margin of the plume. Floodwater reached the Drift River oil facility about 2 3/4 hours after the onset of the event.

Explosive episode, 14 March. "Explosive activity that began at 0947 was recorded for 14 minutes at the Spurr station. Tephra fell E of the volcano; the Drift River oil facility reported heavy ashfall from 1057 to 1247. Oil facility crews were evacuated because of the heavy ashfall. Traces of ash were reported on the Kenai Peninsula and in the Anchorage area." Satellite images (figure 9) showed the plume moving ENE. The temperature at the top of the dense portion of the plume was -40°C at 1030, corresponding to an altitude of about 7 km. Winds were relatively light, and by 1230, the plume extended less than 150 km N and about 100 km E of the volcano.

Figure 9. Image from the NOAA 10 polar orbiting satellite, 14 March at 1054, about an hour after the onset of the eruptive episode. An elongate plume extends ENE of Redoubt. Courtesy of G. Stephens.

"Moderate flooding occurred in the lower Drift River valley. Peak flow velocity was about 6 m/sec. The flood reached the oil facility about 2 1/4 hours after the onset of the explosive episode. The flood carried numerous ice blocks and hot angular dome rocks 16 km from the glacier, where peak discharge was estimated at 1200 m³/sec.

"On 15 March, after a vigorous 2.5-minute seismic event was recorded at all seismic stations, an AVO field crew was warned about a possible explosion. They reported no changes in steam plume activity and did not hear any noises. However, 20 minutes later, they noted an approximate doubling of the Drift River's discharge 4 km downstream from the glacier. The increased discharge was accompanied by large quantities of cobble-sized ice.

"A small dome in the summit area was observed by field crews on 16, 18, 20, and 21 March. The dome appeared to be growing slowly between observations.

Explosive episode, 23 March. "Seismicity indicating the onset of explosive activity began at 0404 and was recorded for 8 minutes at the Spurr station. Seismic activity at the summit stations had increased around 0000 on 22 March and had stayed at elevated levels for most of the day. Seismic activity then decreased several hours before the 23 March explosive episode. A plume was reported to 10.5 km but appeared to be mostly steam. Light ashfall was observed W of the mountain, but ash did not fall on any community. Discharge increased in the Drift River."

An image from the NOAA 11 polar orbiting satellite at 0430 (figure 10), 26 minutes after the onset of the explosive episode, showed a plume extending WNW from the volcano. The top of the dense portion of the plume had a temperature of -39°C, yielding an altitude estimate of slightly less than 9 km based on the radiosonde temperature/altitude profile over Anchorage 1.5 hours earlier. The plume continued to move rapidly WNW, and by 1430, 10.5 hours after the explosion, its center was about 850 km from the volcano.

Figure 10. Image from the NOAA 11 polar orbiting satellite, 23 March at 0430, about 30 minutes after the start of the eruptive episode. The nearly circular plume is just WNW of Redoubt. Courtesy of G. Stephens.

"Pyroclastic flow deposits covered the lower Canyon (below 825 m) and the upper piedmont area (above 500 m) of the Drift glacier. The deposits were generally hot, dry, and friable; where they rested on snow, the basal part of thick deposits, and those less than 50 cm thick, were wet and warm to the touch. Pyroclastic deposits were still hot (325°C) when measured on 26 March.

"Views into the crater on 23 March were largely obscured by steam but much of the dome appeared missing from the summit area. Poor weather obscured observations of the summit area from 26 March until 6 April.

Explosive episode, 29 March. "Seismic activity indicated that an explosive event began at 1033 and was recorded for 7 minutes at the Spurr station. An increase in discharge of the Drift River was reported, reaching the oil facility by 1307. Pilots reported a plume, consisting chiefly of steam, to 15 km. Tephra fallout appears to have been similar to that of 4 March; light ashfall was reported to 225 km N-NE of the volcano.

"Poor weather prevented ground observations or views of the glacier. Deposits from a debris flow or hyperconcentrated flow were observed in the upper valley and flooding appeared similar to 23 March. No hot debris or ice blocks were observed in the upper valley.

Explosive episode, 6 April. "Seismicity increased throughout the morning of 6 April. An explosive event began at 1723 and was recorded for 7-8 minutes at the Spurr station. Seismicity declined after the explosive event. An ash plume was reported to 9 km; wind shear caused the lower part of the plume to drift NW and the upper part to drift E. The ash plume reached the W coast of the Kenai Peninsula by 1808, but only light ashfall was reported in Kenai during the evening.

"Pyroclastic flow deposits overlay the glacier down to about the 610 m level. A debris flow of dome-rock material and ice boulders flowed onto the Drift River valley, and peak flow velocity was estimated at 22 m/s. Peak discharge attenuated quickly downvalley.

Dome growth and hydrologic events 7-13 April. "A dome was first observed in the summit area on 7 April. This dome appeared to be larger when observed on 10 and 13 April and was greatly oversteepened on the N face.

"On 7 April, discharge near the E canyon mouth of the Drift River glacier fluctuated by 30-50% several times during a 1/2-hour observation period. A flood of ice blocks up to 1 m across caused a 4-fold discharge increase in one of the large glacier canyons. Repeated increases in discharge were noted over a 15-minute observation period. An iceslide blocked the entire width of the canyon bottom upstream of the increased discharge area. Episodic release through a tunnel at the base of the ice jam may explain the surges observed at the canyon mouth.

"On 10 April a rootless phreatic eruption was noted on the Drift Glacier at the 890 m level, causing a vigorous ash and steam plume to rise 1,000 m. A series of explosions migrated N and S of this area along a glacier bed stream, producing an elongate crater perhaps 300 m long. Numerous small pyroclastic flows emanated from the explosion area and formed a small pyroclastic flow fan that dammed the main water flow from the dome area for about an hour. Failure of the dam caused a flood with an estimated discharge of 10 m³/s.

Explosive event, 15 April. "A moderate explosive event occurred at 1440 and lasted about 8 minutes at the Spurr station. The ash plume reached elevations between 9 and 12 km and the plume moved N-NW. There were no clearly identifiable seismic precursors. Seismic activity before and after the event appeared unchanged." [See also 15:04].

Geologic Background. Redoubt is a glacier-covered stratovolcano with a breached summit crater in Lake Clark National Park about 170 km SW of Anchorage. Next to Mount Spurr, Redoubt has been the most active Holocene volcano in the upper Cook Inlet. The volcano was constructed beginning about 890,000 years ago over Mesozoic granitic rocks of the Alaska-Aleutian Range batholith. Collapse of the summit 13,000-10,500 years ago produced a major debris avalanche that reached Cook Inlet. Holocene activity has included the emplacement of a large debris avalanche and clay-rich lahars that dammed Lake Crescent on the south side and reached Cook Inlet about 3,500 years ago. Eruptions during the past few centuries have affected only the Drift River drainage on the north. Historical eruptions have originated from a vent at the north end of the 1.8-km-wide breached summit crater. The 1989-90 eruption had severe economic impact on the Cook Inlet region and affected air traffic far beyond the volcano.

Information Contacts: AVO Staff; SAB.

Phreatic eruptions had apparently stopped by 1 February. A possible eruption cloud was reported on 19 March, but a field inspection that day revealed only steam rising from the lake surface. There was no evidence of recent surging associated with small eruptions. Crater Lake was battleship gray with yellow and gray sulfur slicks. No convection was observed over the main vent, and only faint upwelling could be detected over the N vents. The lake temperature had cooled to 34.1°C from 46.5°C on 6 February. A sizeable lake had formed in an area of ice collapse in the valley draining Crater Lake to the S. Since 1 February, the lake had grown from ~60 ± 15 m to 100 ± 30 m. Sudden release of the lake could cause flooding in the Whangaehu River.

Volcanic tremor gradually declined in February, nearing background levels by 8 March. Continuous tremor with fairly uniform amplitude changed to bursts of tremor alternating with periods of quiet, similar to small volcanic earthquakes. On 8 March, tremor increased to high levels and broadened its frequency range, with 1 and 1.5 Hz tremor in addition to the usual 2 Hz signal. Tremor remained strong for 2-3 days before declining to more moderate amplitude. During the period of strongest activity, 6-hour energy release reached 400-1,400 x 10⁴ joules, exceeding levels that accompanied the January 1982 eruptions, but less than in September 1982, when there were no eruptions and declining lake temperature. Tremor increased again on 16 March, almost to the level of 8 March, but by the 22nd had decreased to moderate-strong amplitude. EDM measurements on four lines across the N portion of the crater detected only small (<7mm) changes since the 1 February survey.

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

Information Contacts: P. Otway, DSIR Wairakei.

The number of earthquakes and seismic energy release remained low in March. Located events were centered W and SW of the crater. The strongest recorded earthquake (M 2.1) occurred 21 March. Only a few short pulses of low-energy tremor were recorded, except for a high-energy episode on 12 March at 2301, associated with a small ash emission. Five COSPEC measurements yielded an average SO₂ flux of 1,540 t/d, similar to the previous month. Deformation measurements showed no significant changes.

Geologic Background. Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.

Information Contacts: C. Carvajal, INGEOMINAS, Manizales.

The following observations, made by scientists from the USSR and New Zealand during a cruise of the RV Vulkanolog, were reported by W.F. Giggenbach and I. Menyailov.

"Considerable uncertainty remains about the minimum depth to the summit of Rumble III seamount. Early bathymetric measurements place it at 117 m depth (Kibblewhite and Denham, 1967), while later data and surveys by the RV Vulkanolog in March 1988 suggest a depth of 200 m. A special effort was therefore made to locate its highest point and to determine its depth.

"From echograms, it appears that the uncertainty may largely be due to the production of gas-rich, probably volcanic fluids from the summit area (Kibblewhite, 1966). Close inspection of the echograms shows that reflections above 200 m are probably caused by a plume of expanding bubbles, as they are invariably Separated from the solid reflector (the true summit) by a non-reflecting zone. There, the bubbles are either too small or the prevailing pressures keep the gases in solution.

"In contrast to March 1988, when echograms suggested that some of the bubble swarms reached the surface and gas bubbles were observed from the RV Vulkanolog, in January 1990 the plumes terminated at 150-120 m depth and no bubbles were observed at the surface. The disappearance of bubbles at depths <120 m is likely to be due to re-dissolution of soluble, probably volcanic gases (CO₂ and SO₂). The decrease in extent of the bubble zones may reflect a decrease in the production rate of thermal fluids and, therefore, of volcanic activity. There were no obvious signs of volcanic activity in either March 1988 or January 1990.

"Several large samples of ferro-magnesian, basaltic pillow lavas were dredged from the slopes of the seamount at depths of 400-1,200 m."

References. Kibblewhite, A.C., 1966, The acoustic detection and location of an underwater volcano: New Zealand Journal of Science, v. 9, p. 178-199.

Kibblewhite, A.C. and Denham, R.N., 1967, The Bathymetry and total magnetic field of the south Kermadec Ridge seamounts: New Zealand Journal of Science, v. 10, p. 52-69.

Geologic Background. The Rumble III seamount, the largest of the Rumbles group of submarine volcanoes along the South Kermadec Ridge, rises 2300 m from the sea floor to within about 200 m of the sea surface. Collapse of the edifice produced a horseshoe-shaped caldera breached to the west and a large debris-avalanche deposit. Fresh-looking andesitic rocks have been dredged from the summit and basaltic lava from its flanks. Rumble III has been the source of several submarine eruptions detected by hydrophone signals.

Information Contacts: I. Menyailov and A. Ivanenko, IV, Petropavlovsk; W. Giggenbach, DSIR Chemistry, Petone.

Santiaguito was visited by volcanologists from INSIVUMEH, Michigan Tech, and Arizona State 20-26 February. The following is from their report.

"Eruptive activity was still focused on Caliente vent, capped by a cone-shaped exogenous domal mass of lava that feeds a viscous flow directed toward the SSW. The flow extended about 500 m, dropping about 250 m in elevation below the top of the vent (about 2,500 m above sea level) and terminating on a talus slope at the angle of repose. Rockfalls were frequent, resulting in ash clouds. The frequency of vertical ash eruptions from Caliente vent was only a few/day. The rate of SO₂ emission was measured on 22 February at 48 ± 15 t/d, with a range of 21-76 t/d (24 determinations). This emission rate was slightly less than the average of about 100 t/d (range 40-1,600 t/d) determined in July 1976, when there were many more vertical ash eruptions that had higher values, but was identical to the emission rates measured then between eruptions (Stoiber and others, 1983; especially Table 29.4).

"Figure 12 shows the pattern of Santiaguito's activity from June 1988 until 10 January 1990, five weeks before the dates of the most recent field surveys, as revealed from interpretation of telemetered seismic data by INSIVUMEH. The data demonstrate a good correlation between the frequency of avalanche events and vertical explosions. They also demonstrate that the February field observation dates represented a time of very few vertical explosions compared to the past year's record.

Figure 12. Mean daily number of explosions (crosses) and avalanches (squares) during 2-week periods at Santiaguito, as interpreted from telemetered data by INSIVUMEH, June 1988-January 1990. The 19 June 1989 eruption is marked by an arrow.

"Significant changes have occurred on the N side of Santiaguito since July 1989 (figure 13). The El Monje dome, mostly extruded between 1947 and 1952, had developed a talus slope on its N side that was stabilized and had developed a strong moss coating that prevented rockfalls. This slope allowed access to the summit of Santiaguito throughout a long period (1964-88) and also to the 1902 crater of Santa María. Deep barrancas (canyons) have formed on the N side of the El Monje dome, cutting steep barriers into the talus slopes. These have coalesced at the edge of the talus slope, forming a large barranca between Santiaguito and Santa María that feeds an enormous amount of material into the (Isla) area farther W, and caused another deep barranca to form at the end of the Loma trail. The barrancas on the El Monje dome have deepened and migrated headward until they intersect the top of the dome. They could reflect fracturing of the El Monje dome, perhaps the weakest of three dome units that buttress the N side of the Caliente Vent. If viewed in this way the new barrancas could forecast the site of new dome extrusion from a lateral vent. The increased sediment load from this barranca system is likely to affect the Río Concepción and the Río Tambor to the south when the next rainy season arrives in April or May.

Figure 13. Simplified geologic map of Santiaguito Dome, 1922-February 1990. Streams near Santiaguito are approximately located. Unit dates, such as Rc (1922-90), represent periods of discontinuous activity at each vent. Patterned areas represent very recent activity: Rl - area of active laharic and stream deposition, and very high aggradation rates; Rd - area of recently initiated extensive mass wasting indicating inflation of the El Monje vent area and potential reactivation of the vent; Rc (v pattern) - active block lava flows on Caliente's summit, with very common (hourly) collapse of the broad toe resulting in hot rock avalanches; Rc (dotted pattern) - extent of the 1986-88 block lava flow from Caliente.

"Fieldwork was also directed at examination of the areas affected by the 19 July 1989 eruption (figure 14). The outline of a distinct blast zone, marked by tree blowdown, was mapped. A collapse scarp facing the blast zone was observed. This shows conclusively that partial domal collapse accompanied the 19 July 1989 eruption (14:07)."

Figure 14. Map of Santiaguito and vicinity, showing the zones affected by the 1929, 1973, and 1989 pyroclastic flows. The 1989 and April 1973 deposits have similar areas but different sources. Modified from Rose, 1987.

Reference. Stoiber, R.E., Malinconico, L.L. Jr., and Williams, S.N., 1983, Use of the correlation spectrometer at volcanoes, in Tazieff, H. and Sabroux, J.C., eds., Forecasting Volcanic Events; Elsevier, Amsterdam, p. 425-444.

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

Information Contacts: O. Matías and R. Morales, INSIVUMEH; W.I. Rose, J. Diehl, R. Andres, F.M. Conway, and G. Keating, Michigan Technological Univ; J. Fink and S. Anderson, Arizona State Univ.

During a 2 February overflight, an explosion vent more than 100 m in diameter was observed in the center of the [extrusive] hornblende andesite lava dome (figure 1). Minor fumarolic activity was occurring.

Figure 1. Crater and lava dome at Shiveluch, looking roughly N on 2 February 1990, showing explosion vents. Courtesy of B.V. Ivanov.

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: B. Ivanov, IV.

"Activity remained at a low level in March. Summit crater emissions consisted of thick white vapour. Seismicity was low throughout the month."

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

Information Contacts: I. Itikarai, P. de Saint-Ours, and C. McKee, RVO.

Fumarolic activity at Vulcano remained at a very high level in 1989. The temperature of a fumarole (F5) on the crater rim (figure 6) has remained stable at 310 ± 5°C; more than 90 samples have been collected since July 1987. In contrast, a fumarole (FF) inside the crater showed very high temperatures, reaching a maximum of 550°C in August-September 1989, 100° hotter than in 1988. February 1990 temperatures were 515° and 312° at FF and F5 respectively.

Figure 6. Map of Vulcano, showing locations of F5 and FF fumaroles.

Major chemical species (H₂O, CO₂, H₂S, and SO₂) showed large variations in concentration (figure 7). ³He/4He ratios were very high for all crater fumaroles (~60% mantle-derived He), remaining stable during 1989 at ~ 7.5-8.0 x 10^-6. The 13C/12C ratio followed a similar trend to that of CO₂, with very wide oscillations from about d13C 0.00 to -2.20+. Geologists noted that the chemical and isotopic trends suggest mixing of different sources.

Figure 7. Variations in concentrations of H2O (top), CO2, (center) and SO2 and H2S (bottom) at Vulcano's fumarole F5, 1987-90. Courtesy of OV.

Seismic activity was monitored by a permanent network installed by IIV, and a digital mobile seismic network operated by OV since 1987. Seismicity was at a low level and characterized by low-energy earthquakes occurring in swarm sequences. On the basis of their wave shapes and spectral characteristics, the earthquakes were divided into "Volcano-tectonic" and "Volcanic" events (figure 8) using the classification of Latter (1981). Volcano-tectonic earthquakes outside the Fossa cone and around the island showed clear P and S phases, high frequency contents, and represented the most energetic events (M < 1.6). Volcanic-type events showed very regular wave trains that were sometimes sharply monochromatic, and were characterized by low dominant frequencies and an absence of clearly identifiable phases. Their energy reached 1011-1012 ergs and their magnitudes were negative. Particle motion analysis revealed the presence of Rayleigh and Rayleigh-like waves with a prograde rotation; the arrivals of these two phases followed one another during such earthquakes. Geologists interpreted these events, centered in the Fossa crater, as being related to fumarolic gas flow at shallow depth.

Figure 8. Seismograms showing events classified as "Volcano-tectonic" (top) and "Volcanic" (bottom) at Vulcano.

Reference. Latter, J.H., 1981, Volcanic earthquakes and their relationship to eruptions at Ruapehu and Ngauruhoe volcanoes: JVGR, v. 9, p. 293-310.

Geologic Background. The word volcano is derived from Vulcano stratovolcano in Italy's Aeolian Islands. Vulcano was constructed during six stages during the past 136,000 years. Two overlapping calderas, the 2.5-km-wide Caldera del Piano on the SE and the 4-km-wide Caldera della Fossa on the NW, were formed at about 100,000 and 24,000-15,000 years ago, respectively, and volcanism has migrated to the north over time. La Fossa cone, active throughout the Holocene and the location of most of the historical eruptions, occupies the 3-km-wide Caldera della Fossa at the NW end of the elongated 3 x 7 km island. The Vulcanello lava platform forms a low, roughly circular peninsula on the northern tip of Vulcano that was formed as an island beginning in 183 BCE and was connected to Vulcano in about 1550 CE. Vulcanello is capped by three pyroclastic cones and was active intermittently until the 16th century. The latest eruption from Vulcano consisted of explosive activity from the Fossa cone from 1898 to 1900.

Information Contacts: D. Tedesco, S. Vulcano, and G. Luongo, OV.

January 1990 fieldwork revealed no fumarolic ice towers or other signs of recent activity. A thick (<=4 m) sequence of tephra was found in blue ice at the foot of the volcano, but its vertical attitude suggested eruptions thousands of years ago.

Geologic Background. Mount Waesche is the southernmost of a N-S-trending chain of volcanoes in central Marie Byrd Land. It is located 20 km SW of Pliocene Mount Sidley, Antarctica's highest volcano, and was constructed on the SE rim of the 10-km-wide Chang Peak caldera. Pre-caldera Chang Peak lavas were erupted about 1.6 million years ago (Ma) and the Waesche shield formed about 1.0 Ma. Waesche may have been active during the Holocene and is a possible source of ash layers in the Byrd Station ice core that were deposited during the past 30,000 years. The youngest lavas are too young to date by Potassium-Argon. Satellitic cinder cones, some aligned along radial fissures, are located on the SW flank.

Information Contacts: P. Kyle and W. McIntosh, New Mexico Institute of Mining and Technology; R. Dibble, Victoria Univ.

Little eruptive activity has occurred since 29 November fieldwork revealed a new vent and fresh tephra on the main crater floor. Seismic activity has been at low levels, fumarole temperatures have decreased, and deflation on the main crater floor (centered in the Donald Duck area) suggests that heatflow has been redirected from Noisy Nellie fumarole westward to 1978 Crater. R. Fleming reported a small eruption of lithic accessory ejecta from Noisy Nellie in late January 1990, and further collapse of Corporate and Congress Craters.

Geologists from the RV Vulkanolog visited White Island 2-3 March. Only blue "flames" associated with fumarolic discharge were seen over fumaroles E of 1978 Crater (Donald Mound, Blue Duck, and Noisy Nellie) during the night of 2 March. The three most vigorous vents along a small cone on R.F. crater's floor glowed pale red (500-550°C) and a small eruptive episode on 3 March added pebble-sized material to the cone. A shallow green pond that occupied the rest of the crater floor was surrounded by yellow to orange precipitates.

On 6 March geologists found only 4 mm of fine green ash that had fallen since 29 November at a site 35 m E of 1978 Crater. No new ash was found on the 1978 Crater rim or to the SE (S of Donald Mound). Donald Duck emitted white gas/steam clouds, and low-pressure gas emerged from Noisy Nellie. Accessory blocks and smaller ejecta, first seen about a month earlier, extended 30 m SE from Noisy Nellie. Emissions from 1978 Crater obscured R.F. and Corporate craters, but small detonations from R.F. Crater were frequently heard.

Only ~10 small B-type events/day and an average of ~3 A-types/day were recorded in December, with small E-types recorded on the 7th and 21st. About 3-6 B-type events/day plus rare A-types were recorded during January and February, with tremor nearly absent.

A March deformation survey showed strong subsidence of the Donald Mound area following a period of brief uplift measured 29 November. Subsidence since then was centered E of 1978 Crater (between Noisy Nellie and Donald Mound), reaching 30 mm near Donald Duck vent, with a trough extending NW along the line of fumaroles. Noisy Nellie, near the apparent center of the 15+ mm uplift prior to 29 November, lies on the edge of this trough. The recent subsidence of 9 mm/month is similar to the rate observed since mid-1987.

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: I. Nairn, P. Otway, B. Scott, and C. Wood, NZGS Rotorua; W. Giggenbach, DSIR Chemistry, Petone.

The following observations, made by scientists from the USSR and New Zealand during a cruise of the RV Vulkanolog, are reported by W.F. Giggenbach and I. Menyailov.

"Calypso Mound is a white anhydrite cone some 6-8 m high, formed at 167 m depth by discharge of thermal waters at the ocean floor. It was discovered in February 1987 using the diving vessel Soucoup carried on the RV Calypso (Sarano and others, 1989). It lies within one of the 'bubble zones' extending in a line from White Island to Whale Island in the Bay of Plenty (Duncan and Pantin, 1969) [around 37.64°S, 177.10°E].

"The echograms indicated strong hydrothermal activity with a number of vents producing bubble curtains. However, an extended visual search under calm conditions from both the RV Vulkanolog and a rubber dinghy detected no bubbles at the surface. A possible explanation is re-dissolution of the gas in seawater. Similar gases, collected from more shallow submarine springs in the Bay of Plenty, S of Whale Island, and from Whale Island itself (see below), consisted predominantly of CO₂, which has a comparatively high solubility in water. Re-dissolution is also supported by the distribution of reflections recorded during a slow pass over the area. Most of the individual bubble swarms, now clearly separated, appeared to terminate at ~20 m depth.

"Close inspection of a video recording shows that the fluid discharged from two vents on Calypso Mound is very likely to contain a considerable free vapor phase, indicated by flame-like tongues of free vapor, rapidly quenched on contact with cold seawater. Water leaving the vapor-seawater interaction zone appeared clear and colorless except for schlieren indicating a density difference from seawater.

"The existence of free vapor at 167 m depth and about 18 bars pressure suggests that the temperature of the fluid discharged from Calypso Mound is close to 207°C. The high proportion of vapor, apparently present in the fluid mixture leaving the vents, would indicate high corresponding enthalpies of the fluid feeding Calypso Mound. The temperature of any initial single phase liquid, before flashing and possibly present at greater depth, may therefore be considerably higher. However, Sarano et al. (1989) consider it unlikely that the waters emitted from Calypso Mound were as hot as 160°C. The 'hydrothermal' nature indicated for the Calypso Mound system may also explain the enrichment in typically 'epithermal' elements such as As, Sb, Hg, and Tl, and the absence of a 'volcanic' trace metal signature (Giggenbach and Glasby, 1977) in clays recovered from near the main cone."

References. Duncan, A.R., and Pantin, H.M., 1969, Evidence for submarine geothermal activity in the Bay of Plenty: New Zealand Journal of Marine and Freshwater Research, v. 3, p. 602-606.

Giggenbach, W.F., and Glasby, G.P., 1977, The influence of thermal activity on the trace metal distribution in marine sediments around White Island, New Zealand: New Zealand Department of Scientific and Industrial Research Bulletin, v. 218, p. 121-126.

Sarano, F., Murphy, R.C., Houghton, B.F., and Hedenquist, J.W., 1989, Preliminary observations of submarine geothermal activity in the vicinity of White Island, Taupo Volcanic Zone, New Zealand: Journal of the Royal Society of New Zealand, v. 19, p. 449-459.

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: I. Menyailov and A. Ivanenko, IV, Petropavlovsk; W. Giggenbach, DSIR Chemistry, Petone.

On 2 February, fumarolic activity was noted in two vents inside the active crater and two vents to the W (figure 1).

Figure 1. Active fumarolic vents at Zhupanovsky, looking roughly E on 2 February 1990. Courtesy of B. Ivanov.

Geologic Background. The Zhupanovsky volcanic massif consists of four overlapping stratovolcanoes along a WNW-trending ridge. The elongated volcanic complex was constructed within a Pliocene-early Pleistocene caldera whose rim is exposed only on the eastern side. Three of the stratovolcanoes were built during the Pleistocene, the fourth is Holocene in age and was the source of all of Zhupanovsky's historical eruptions. An early Holocene stage of frequent moderate and weak eruptions from 7000 to 5000 years before present (BP) was succeeded by a period of infrequent larger eruptions that produced pyroclastic flows. The last major eruption took place about 800-900 years BP. Historical eruptions have consisted of relatively minor explosions from the third cone.

Information Contacts: B. Ivanov, IV.