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).

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

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

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

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

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

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

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

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

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

A team of scientists from India and Italy carried out detailed geological, volcanological, geochemical, and geothermal investigations on Barren Island (figures 4 and 5) during 3-6 February 2003. The scientific team, led by Dornadula Chandrasekharam, included Piero Manetti, Orlando Vaselli, Bruno Capaccioni, and Mohammad Ayaz Alam. The Indian Coast Guard vessel CGS Lakshmi Bai carried the team from Port Blair on 3 February 2003; the journey takes ~5-6 hours depending on sea conditions. Because of the great depths around the island, it is not possible to anchor, so the team was ferried to the island in a small rubber boat. After the ship returned on the morning of 6 February, a trip around the island was made to see the steep seaward face of the prehistoric caldera wall.

Figure 4. Barren Island as seen from the vessel CGS Lakshmi Bai on 3 February 2003. Courtesy of D. Chandrasekharam and others.

Figure 5. Preliminary sketch map of Barren Island. Courtesy of D. Chandrasekharam and others.

The volcano consists of a caldera, which opens towards the W, with a central polygenetic vent enclosing at least five nested tuff cones. Two spatter cones are located on the W and SE flanks of the central cone (figure 6).

Figure 6. A spatter cone on the SW flank of the central cinder cone at Barren Island around 3 February 2003. Courtesy of D. Chandrasekharam and others.

An eruption in 1991 ended more than 200 years of quiescence. Another eruption in 1994-95 left two spatter cones on its SE and W flanks. From these vents two aa lava flows poured out, both reaching the sea, during two distinct eruptive phases separated by ashfall. The lava flow created a delta into the sea (figure 7). There has been no documented eruptive activity since 1995, but Indian Coast Guards informed the team of renewed activity (strong gas and possible lava emission) in January 2000. The volcano currently exhibits continuing fumarolic activity. Steaming ground was visible at numerous places on the island.

Figure 7. Lava from the 1994-95 eruptions on Barren Island formed a tongue that reached the sea. Courtesy of D. Chandrasekharam and others.

On 5 February the team climbed the summit of the central cinder cone that showed strongly fumarolic (but not presently active) areas with layers of sulfur deposits (figure 8). The ascent to the crater was relatively difficult since the material on the very steep slope was loose (figure 9). Neither magma nor gas emissions were observed within the craters of the different cones. From the middle to the upper part of the W cone, the ground temperature was relatively high (>40°C), and steaming ground was visible at different sites. Fumarolic activity, with temperatures up to 101°C, was mainly concentrated along the upper crater wall of the SW cone. Blue fumes (indicative of SO₂) and the aroma of acidic gases such as HCl were not recorded.

Figure 8. Fumarolic deposit on top of the central cinder cone at Barren Island on 5 February 2003. Courtesy of D. Chandrasekharam and others.

Figure 9. Central cinder cone showing steep slopes at Barren Island on 5 February 2003. Courtesy of D. Chandrasekharam and others.

The pre-caldera deposits were characterized by more than five lava flows (prehistoric?) separated by scoria-fall beds and minor ash, tuff, and cinder deposits. The lava flows varied in thickness from 2 to 3 m, whereas the pyroclastic layers vary in thickness from 1 to 4 m. These lava flows could be clearly seen towards the N part of the main caldera. Towards the SE part of the inner caldera a 5-m-wide, NNE-SSW trending dike was observed. This feeder dike was fine-to-medium grained and contains buff-colored olivine, green pyroxene, and plagioclase phenocrysts. The N and NW part of the caldera has been mantled by a ~50-m-thick sequence of breccias and tuff representing syn/post-caldera phreatic and hydromagmatic activity, whereas the products of a small littoral cone occured mainly towards the W side. The lava flows of the main caldera were highly porphyritic with phenocrysts of green pyroxene (~3 cm) and plagioclase feldspars. Several steam vents could be seen within the 1994-95 lava flows. Some of these vents exhibited a lack of steam emanations at the time of the visit.

The outer and part of the inner caldera contains thick vegetation, which escaped the fury of the recent eruptions. Feral goats and rats dominate the island. Two fresh-water springs were discovered towards the SE part of the caldera. This is possibly the fresh water source for the goats living in this island. Chemical analysis indicates that the water from the springs is potable.

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

Information Contacts: Dornadula Chandrasekharam, Department of Earth Sciences, Indian Institute of Technology, Bombay 400076, India (URL: http://www.geos.iitb.ac.in/index.php/dc); Piero Manetti, Italian National Science Council (CNR), Institute of Geosciences and Earth Resources (CNR-IGG), Viale Moruzzi, 1, 56124 Pisa, Italy; Orlando Vaselli, Department of Earth Sciences, University of Florence, Via G. La Pira, 4 - 50121 Florence, Italy; Bruno Capaccioni, Institute of Volcanology and Geochemistry, University of Urbino, Loc. La Crocicchia, 61029 Urbino, Italy; Mohammad Ayaz Alam, Research Scholar, Department of Earth Sciences, Indian Institute of Technology, Bombay 400076, India.

The Deception Volcano Observatory has monitored the volcano every austral summer since 1993. Investigations of fumarole geochemistry, thermal anomalies, and volcanic activity were made during the summer survey of 2000 and 2002 by the Argentina Research Group. Compared to measurements made during the latest surveys, temperatures of fumaroles and hot soils remained stable at 99-101°C in Fumarole Bay, 97°C on Caliente Hill, 65°C in Whalers Bay, 41°C in Telefon Bay, and 70°C in Pendulum Cove (figure 18).

Figure 18. Map of Deception Island showing the area of geothermal anomalies during austral summer 2002. Courtesy of A.T.Caselli, M. dos Santos Afonso, and M. Agusto.

Following a possible magma intrusion during the summer of 1999 (BGVN 24:05), the composition of gases from fumarolic vents at Fumarole Bay changed compared to previous surveys. The chemical composition of the fumarolic gases was mainly H₂O (70-95 vol. %), CO₂ (5-30%), H₂S (0.1-0.3%), and SO₂ (0.01-0.08%). For the first time, SO₂ was detected. Elemental sulfur and iron sulfide coatings on lapilli were found around the vent outlets and at a few centimeters of depth, respectively. Elemental sulfur and iron sulfide occurrences were intermittent during the 2000 and 2002 summer surveys.

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: A.T.Caselli, M. dos Santos Afonso, and M. Agusto, Universidad de Buenos Aires, Instituto Antártico Argentino, Ciudad Universitaria, Pabellón 2, C1428EHA Buenos Aires, Argentina.

On 27 October 2002 Mount Etna opened on both its northern and southern sides (BGVN 27:10-27:12), erupting lava from vents about 2,500-1,800 m elevation on the NNE flank and 2,800-2,700 m on the S flank. The N vents emitted two flows that stopped after a few days, the longer of which stretched ~5 km. The S vents erupted lighter intermittent lava flows, but showed much stronger and sustained explosive activity that developed two large cinder cones at 2,750 and 2,850 m elevation.

The northern lavas are similar to the tephra erupted from Northeast Crater during the summer of 2002 and, more generally, to the trachybasalts that characterized Etna's activity during the past centuries (Tanguy and others 1997, and references therein). They are typically porphyritic (30-40% phenocryts), containing numerous millimeter-sized crystals of plagioclase (An 86-65/Or 0.4-2.1), clinopyroxene (En 42.3-37/Fs 11.7-15.5), and fewer ones of olivine (Fo 76-71) and titanomagnetite (Usp 35-43). The silica content is about 47-48% with a "normal" MgO content of about 5% and "low" CaO/Al₂O₃.

The southern lavas are significantly higher in MgO (~6.5%) and CaO/Al₂O₃ with fewer phenocrysts that comprise barely 10% of the rock. Olivine crystals are decidedly more magnesian (Fo 82-76), although other minerals are much like those described above, with plagioclase An 80.8-63.8/Or 0.8-1.3, clinopyroxene En 42-34/Fs 12-15.7, and titanomagnetite Usp 37-42.7. It must be pointed out, however, that plagioclase and titanomagnetite are here almost entirely confined within the groundmass, a characteristic that is uncommon in Etnean lavas and characterizes some of the most basaltic samples.

A particularity of the southern 2002 lavas is the presence of destabilized amphibole crystals, together with quartz-bearing inclusions (sandstones) surrounded by a reaction rim of pyroxene and embedded in a rhyolitic matrix. These characteristics are quite similar to those already found in the 2001 lavas emitted at 2,100 m elevation on this same flank (BGVN 26:10). The 2002 amphibole is present in rarer and smaller "megacrysts" that do not exceed 2 cm in length and display a reaction rim composed of rhonite, anorthitic plagioclase, and olivine within a silicic and potassic glass. Its chemical composition is similar to that of the 2001 amphibole.

Orthopyroxene was found in a southern flow emitted at the very beginning of the eruption (27 October). The average of 16 microprobe analyses is as follows (Centre de microanalyse Camparis, University of Paris 6): SiO₂, 53.18; TiO₂, 0.23; Al₂O₃, 0.79; Cr₂O₃, 0.04; FeO, 19.43; MnO, 0.80; MgO, 23.52; CaO, 1.72; Na₂O, 0.05; Total, 99.75. The composition is thus hypersthene close to bronzite, typical of basalts or basaltic andesites. Hypersthene here occurs as crystals 0.5-0.7 mm in length, always surrounded by clinopyroxene. The two minerals are not in equilibrium as indicated by their different Mg values (0.69 for Opx, 0.71 to 0.78 for Cpx). This is the first time that such large crystals of orthopyroxene have been observed in lavas of the last tens of thousand years. Orthopyroxene is very rare at Etna, being previously found on only two or three occasions in pre-Etnean basalts about 200,000 years old.

Olivine separates from both N and S lavas (~100 crystals each) were microprobed, showing a single distribution for the N flank of Fo 69-70 for 65% of the crystals. The S lavas have a twofold behavior with Fo 78-81 for 37% of the crystals and Fo 73-75 for 45% of them. These results are similar to what was found between the upper southern 2001 lavas (including the NE flank below Pizzi Deneri) and those emitted at lower elevation (S 2,600 m and S 2,100 m). It is worth noting that the 2,600 m S vent of the 2001 eruption is close (~1 km) to the 2,700 m S vent of the 2002 eruption.

Based on these preliminary results, the low porphyritic index added to the whole rock chemical composition and that of the olivine crystals, a common origin is suggested for the southern 2002 lavas and those emitted low on the S flank during the 2001 eruption.

Reference. Tanguy, J.C., Condomines, M., and Kieffer, G., 1997, Evolution of the Mount Etna magma: Constraints on the present feeding system and eruptive mechanism: Journal of Volcanology and Geothermal Research, v. 75, p. 221-250.

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: Roberto Clocchiatti, CNRS-CEN Saclay, Lab. Pierre Süe, 91191 Gif sur Yvette, France; Jean-Claude Tanguy, Univ. Paris 6 & Institut de Physique du Globe de Paris, Observatoire de St. Maur, 94107 St. Maur des Fossés, France.

Following the 16 November-3 December 2002 eruption (BGVN 27:11), the Observatoire volcanologique du Piton de la Fournaise reported on 19 December that very strong seismicity had continued at a rate of more than 1,000 earthquakes per day. The earthquakes were located a few hundred meters below Dolomieu crater.

MODIS tracking of effusive activity during 2000-2002. The November-December 2002 eruption was detected by the Hawai'i Institute of Geophysics and Planetology MODIS thermal alert system (http://modis.higp.hawaii.edu/). The eruption was apparent as a major hot spot in the SW sector of Reunion (figure 66). The first image on which activity was flagged was that of 1030 (0630 UTC) on 16 November 2002. At that point the flagged anomaly was six 1-km pixels (E-W) by 2-3 pixels (N-S). The hot spot attained roughly the same locations and dimensions on all subsequent images, where hot pixels were flagged on 16 images during November 16-3 December 2002. The exception was an image acquired at 2255 (1855 UTC) on 30 November (figure 66), on which the hot spot attained its largest dimensions of ~12 x 5 pixels. The increase in hot spot dimensions towards the end of November is also apparent in the radiance trace (figure 67). However, without examination of the raw images HIGP scientists cannot determine from the hot spot data alone whether this recovery was due to an increase in activity or an improvement in cloud conditions. This was the 6th eruption of Piton de la Fournaise tracked by the MODIS thermal alert (Flynn et al., 2002; Wright et al., 2002) since its inception during April 2000 (figure 68).

Figure 66. Hot-spot pixels flagged at Piton de la Fournaise by the MODIS thermal alert at 0630 UTC on 16 November 2002 (top) and 1855 UTC on 30 November 2002 (bottom). Courtesy of the HIGP Thermal Alerts Team.

Figure 67. Piton de la Fournaise hot spot radiance detected by MODIS during 15 November-5 December 2002. Courtesy of the HIGP Thermal Alerts Team.

Figure 68. Piton de la Fournaise hot spot radiance detected by MODIS during April 2000-December 2002. Courtesy of the HIGP Thermal Alerts Team.

References. Wright, R., Flynn, L.P., Garbeil, H., Harris, A.J.L., and Pilger, E., 2002, Automated volcanic eruption detection using MODIS: Remote Sensing of Environment, v. 82, p. 135-155.

Flynn, L.P., Wright, R., Garbeil, H., Harris, A.J.L., and Pilger, E, 2002, A global thermal alert using MODIS: initial results from 2000-2001: Advances in Environmental Monitoring and Modeling (http://www.kcl.ac.uk/kis/ schools/hums/geog/advemm.html), v. 1, no. 3, p. 5-36.

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, 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France; Andy Harris, Luke Flynn, Harold Garbeil, Eric Pilger, Matt Patrick, and Robert Wright, HIGP Thermal Alerts Team, Hawai'i Institute of Geophysics and Planetology (HIGP) / School of Ocean and Earth Science and Technology (SOEST), University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

A slight increase in the number of volcano-tectonic (VT) and long-period (LP) events occurred during April through September 2002, although the energy levels diminished. Between October and December 2002, scientists noted a small decrease in VT seismicity and a considerable increase in seismic activity related to fluid-movement. An increase in LP signals, difficult to classify due to their non-typical signatures, coincided with strong rainfall over Pasto and the volcano. The geothermal system at Galeras, with fumarolic zones having temperatures between 100 and 370°C, easily interacts with rainwater, producing exothermic reactions with seismic and near-surface manifestations.

During April-June, there were 191 VT events with a seismic energy release of 1.08 x 10¹⁶ erg. Both the number of events and the total energy increased during July-September, when 209 VT events with a seismic energy release of 5.64 x 10¹⁵ erg were recorded. In comparison, there were 197 VT events with an energy release of 2.86 x 10¹⁵ erg during October-December. The vast majority of the events occurred close to the active crater and in the volcanic edifice. Other earthquakes occurred at depths of 0.2-16 km beneath the summit throughout the second half of 2002.

Volcano-tectonic earthquakes were felt in Pasto on 8 April (2 km deep, ML 3.6), 17 April (2 km deep, ML 4.2), 28 April (12 km deep, ML 3.2), 24 May (8 km deep, ML 2.3), 21 June (9 km deep, ML 3.0), 22 July (5 km deep, ML 2.7), and 1 November (5 km depth, ML 3.2, 3.8 km from the crater). The 17 April event was followed by 12 aftershocks from the main crater area; the strongest was ML 2.6. In Consacá, two events were felt on 12 August within 4 minutes of each other (5 km deep, ML 2.9 and 3.4). The strongest 12 August earthquake was located ~6 km SW of the crater. A strong event on 20 December (4 km deep, ML 3.6) was felt in the town of Yacuanquer and was centered ~5 km SW of the active crater.

During April-June, 111 LP events and 82 spasmodic tremor episodes were registered with a total energy release of 2.89 x 10¹⁴ erg. Some spasmodic tremor episodes were harmonic, with dominant frequencies of 2.5-2.7 Hz. Seismic events related to fluid movements during July through September had low frequencies between 2 and 3 Hz and high frequencies of 10.5, 12.1, 13.7, and 14.1 Hz. These frequencies appeared all over the local reporting stations. In total, there were 161 registered LP events and 17 spasmodic tremor episodes with a total energy release of 1.1 x 10¹⁴ erg. In addition, some spasmodic tremor episodes were of the harmonic type with dominant frequencies of 2.5 and 3.0 Hz. During October-December the frequencies exhibited spikes between 10 and 16 Hz. Sometimes these events showed one or more precursor signals with very short amplitude and appeared in doubles or triplets. The frequencies kept on time over many stations indicating a processes more directly related to the source rather than the path or station site. Overall, there were 1,541 LP events and 209 spasmodic tremor episodes in October-December with a total energy release of 2.65 x 10¹⁵ erg.

Reactivation of El Pinta Crater. Slight gas emissions were observed at the end of May from the El Pinta crater (E of the main crater), inactive since 1991. On 5 June 2002 began the number of daily seismic events increased. A team visiting the summit on 7 June noted an increase in the quantity and pressure of gas emissions at different points of the main crater and in El Pinta. However, temperatures did not show significant variations compared to previous months. Elevated temperatures were observed toward the SW sector of the active cone with values of 340°C at the Las Chavas fumarole field. Also on 7 June spasmodic tremor was registered at the observatory that signified a hydrothermal event. A subsequent field inspection observed a fine layer of ash and precipitate sulfur, besides great gas emission from El Pinta. The material emitted by El Pinta consisted of lapilli, ash, and clay; a high percentage of the sample was pre-existing material. Some reports of gas emissions coincide with spasmodic tremor records at the Galeras observatory site. After 11 June this activity began to decrease. The VT earthquakes that accompanied this activity were located in the main crater zone with depths to 3 km.

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: Marta Calvache, Observatorio Vulcanológico y Sismológico de Pasto (OVSP), INGEOMINAS, Carrera 31, 18-07 Parque Infantil, P.O. Box 1795, Pasto, Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html).

Seismicity was above background levels at Kliuchevskoi during 29 November 2002 through at least 4 March 2003. Tens of earthquakes per day were recorded, mostly at depths of ~30 km (table 8), and intermittent spasmodic volcanic tremor occurred. During December through February, gas-and-steam plumes generally rose up to 2 km above the crater. The Concern Color Code fluctuated between Yellow and Orange, but by the end of the report period remained at Yellow.

Table 8. Earthquakes recorded at Kliuchevskoi during 29 November 2002-28 February 2003. Courtesy KVERT.

Visual observations and video recordings from the town of Klyuchi revealed that a plume from an explosion on 24 December 2002 rose 4 km above the crater and drifted WSW. On 5 January 2003 a faint thermal anomaly, and probable mud flow down the SSE slope were visible on satellite imagery. According to KVERT, the thermal anomaly and mud flow indicated that a lava flow may have begun to travel down the SSE slope. A probable mudflow, seen on the SE slope on 7 January, may have emerged after a short explosion to the SE or E, or after powerful fumarolic activity in the crater. During the week of 26 February-4 March, gas-and-steam plumes rose to low levels and possible ash deposits on the volcano's SE summit were visible on satellite imagery.

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), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological and Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.

Claude Grandpey visited Ol Doinyo Lengai on 29-30 December 2002 during a trip organized by the French agency Aventure et Volcans. The group arrived on the crater rim late in the morning and noted a very active lava lake in the T49 vent that began to overflow a few minutes later. The resulting lava flow was ~10-15 m wide and reached a length of ~50 m before stopping when the overflow ended after a few minutes. The temperature inside the solid flow, measured some 2 hours after it had stopped, was 462°C.

The T49 lake, roughly circular and ~5 m in diameter, was extremely active and noisily ejecting blobs of fluid lava (figure 77). This type of activity lasted all day, without additional lava flows. After several hours of careful observations, Grandpey climbed the cone and stood a few meters from the lava lake. He noted that the lake was being fed in an oblique way from a vent on its SW side; the lava would flow to the E inner side before being projected back to the W and splashing out. The pressure of the lava as it splashed against the E side could be felt, and the whole cone was vibrating. In the evening the activity decreased at the lake, and a small vent opened a few meters to the E, emitting occasional vertical squirts of lava. All the time they stayed in the crater, cone T40 kept roaring, but no lava emissions were seen.

Figure 77. Photograph of activity at Ol Doinyo Lengai vent T49, 29 December 2002. Courtesy of Claude Grandpey.

After a night of heavy rain, the group visited the crater one more time. No lava flow had occurred during the night. Another lake was still bubbling at T49, at the exact spot were lava was squirting vertically the day before. It was violently throwing blobs of lava on its outer slopes.

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: Claude Grandpey, L'Association Volcanologique Européenne (LAVE), 7, rue de la Guadeloupe, 75018, Paris, France.

Numerous eruptions of Monowai Seamount (also known as Orion Seamount), an active volcano located in the Kermadec Island arc, were detected by the Polynesian Seismic Research (Reseau Sismique Polynesien, RSP) seismic network in Tahiti (figure 8). Strong T-phase waves were recorded at all of the stations in the RSP network (figure 9). The last reports of Monowai eruption activities were in January 1998 (BGVN 23:01), June 1999 (BGVN 24:06), and May 2002 (BGVN 27:05).

Figure 8. Map of the South Pacific Ocean showing the location of some RSP (Reseau Sismique Polynesien) seismic network stations (circles indicate area of island group with labeled stations) and Monowai Seamount (star). All seismic stations are inland; there are no hydrophones in the network. Stations shown include VAH and PMOR (Tuamotu archipelago), PAE, PPT, TVO, and TIAR (Society Islands), TBI (Austral Islands), and RKT (Gambier archipelago). Courtesy of Laboratoire de Geophysique, Tahiti.

Figure 9. Example of strong T-phase waves detected by the RSP from Monowai, 18 November 2002 (times are UTC). All the seismic stations in the network recorded the wave generated during eruption of the volcano. Note the good signal coherency between most stations. The record at the PMOR station, located in the north of Rangiroa, was masked for the T waves. Courtesy of Laboratoire de Geophysique, Tahiti.

Geophysical network. The Polynesian Seismic Network is composed of short-period seismic stations on Rangiroa atoll in the Tuamotu archipelago (stations VAH and PMOR), on Tahiti in the Society Islands (stations PAE, PPT, TVO, and TIAR), on Tubuai in the Austral Islands (station TBI), and on Rikitea in the Gambier archipelago (station RKT). There are also three long-period seismic stations in Tahiti, Tubuai, and Rikitea. In addition, Comprehensive Test Ban Treaty (CTBT) instruments located in Tahiti include a mini-array of micro-barographs, a primary seismic station (station PS18 at Papeete), and a radionuclide station.

Earthquake swarm. A volcanic earthquake swarm started on 1 November 2002 at 1200 UTC with strong explosive T-phase waves recorded by the RSP network (figure 10). The swarm stopped temporarily between 8 and 17 November; a second, very intense swarm started on 17 November (figure 11) and ended on 24 November. From inversion of T-phase wave arrival times, it was deduced that the swarm was located around Monowai Seamount. Because of the small aperture of the RSP network, the location is poorly constrained in longitude, but well constrained in latitude (figure 12). The source of the T-phase waves is most probably at Monowai.

Figure 10. Daily history of the Monowai swarm. The maximum number of daily events was on 21 November, but the higher amplitude T-phase waves were detected during 17-19 November. Courtesy of Laboratoire de Geophysique, Tahiti.

Figure 11. Daily history of amplitude (in nanometers) of Monowai swarm T-phase waves recorded at TVO station on Tahiti. The maximum intensity was between 17 and 19 November. These amplitudes should correlate to ground vibrations generated by the volcanic eruptions. Courtesy of Laboratoire de Geophysique, Tahiti.

Figure 12. Map showing the best source locations of the swarms using the entire seismic network. The star is Monowai Seamount, and the dots are possible source epicenters. The effect of linearity observed on the epicenters is due essentially to the aperture size of the network, but note that the latitude is well constrained. Courtesy of Laboratoire de Geophysique, Tahiti.

Regarding T-Phase waves. A short-period wave group from a seismic source that has propagated in part through the ocean is called T-phase or T(ertiary)-wave (Linehan, 1940; Tolstoy and Ewing, 1950; Walker and Hammond, 1998). The wave group propagates with low attenuation as hydro-acoustic (compressional) waves in the ocean, constrained within a low sound speed wave guide (the sound fixing and ranging - SOFAR - channel) formed by the sound speed structure in the ocean. The T-phase signal may be picked up by hydrophones in the ocean or by land seismometers. Upon incidence with the continental shelf/slope, the wave group is transformed into ordinary seismic waves that arrive considerably later than seismic wave groups from the same source that propagated entirely through the solid earth.

References. Brothers, R.N., Heming, R.F., Hawke, M.M., and Davey, F.J., 1980, Tholeiitic basalt from the Monowai seamount, Tonga-Kermadec ridge (Note): New Zealand Journal of Geology and Geophysics, v. 23, p. 537-539.

Davey, F.J., 1980, The Monowai Seamount: an active submarine volcanic centre of the Tonga-Kermadec Ridge (Note): New Zealand Journal of Geology and Geophysics, v. 23, p. 533-536.

Linehan, D, 1940, Earthquakes in the West Indian region: Transactions, American Geophysical Union, Pt. II, p. 229-232.

Tolstoy, I., and Ewing, M., 1950, The T phase of shallow-focus earthquakes: Bulletin of the Seismological Society of America, v. 40, p. 25-51.

Walker, D.A., and Hammond, S.R., 1998, Historical Gorda Ridge T-phase swarms; relationships to ridge structure and the tectonic and volcanic state of the ridge during 1964-1966: Deep-Sea Research Part II, v. 45, n. 12, p. 2531-2545.

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

Information Contacts: Dominique Reymond and Olivier Hyvernaud, Laboratoire de Geophysique, CEA/DASE/LDG, Tahiti, PO Box 640, Papeete, French Polynesia.

Although previous eruptions have been recorded elsewhere in the South Sandwich Islands (Coombs and Landis, 1966), ongoing volcanic activity has only recently been detected and studied. These islands (figure 1) are all volcanic in origin, but sufficiently distant from population centers and shipping lanes that eruptions, if and when they do occur, currently go unnoticed. Visual observations of the islands probably do not occur on more than a few days each year (LeMasurier and Thomson, 1990). Satellite data have recently provided observations of volcanic activity in the group, and offer the only practical means to regularly characterize activity in these islands. These observations are especially significant because there has previously been no evidence of Holocene activity on Montagu Island (LeMasurier and Thomson, 1990).

Figure 1. The South Sandwich Island archipelago, located in the Scotia Sea. The South Sandwich Trench lies approximately 100 km E, paralleling the trend of the islands, where the South American Plate subducts westward beneath the Scotia Plate. Courtesy Hawaii Institute of Geophysics and Planetology and British Antarctic Survey.

Using Advanced Very High Resolution Radiometer (AVHRR) data, Lachlan-Cope and others (2001) observed apparent plumes and unreported single anomalous pixels intermittently on images of Montagu Island during March 1995 to February 1998. However, field investigations in January 1997 revealed that Montagu Island, as viewed from Saunders Island, was apparently inactive, with the summit region entirely covered in snow and ice. Hand-held photographs of the island obtained in September 1992 also showed the summit to be wholly inactive.

Significant volcanic activity may have begun on Montagu Island in late 2001 based upon analysis of thermal satellite imagery (1 km pixel size) from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instrument. Using the automated MODIS Thermal Alert system (Wright and others, 2002), image pixels containing volcanic activity were detected and analyzed to characterize the eruption. From its location, the erupting center may be associated with a small hill on the NW edge of the ice-filled summit caldera, ~6 km from Mount Belinda (figure 2).

Figure 2. Map of Montagu Island with circles showing the location of all anomalous MODIS pixels detected since October 2001. Stippled areas show rock outcrop, the remainder is snow or ice covered. Relief is shown by form lines that should not be interpreted as fixed-interval contours. Map adapted from Holdgate and Baker (1979); courtesy Hawaii Institute of Geophysics and Planetology and British Antarctic Survey.

The first thermal alert on Montagu occurred on 20 October 2001 with a single anomalous pixel on the N side of the island. Subsequent anomalies generally involved 1-2 pixels, with the exception of several images in August and September 2002 that peaked at four pixels in size (figures 3 and 4). Visual inspection of the images revealed that the anomalies were all located between the summit of Mount Belinda and the N shore, changing in position either due to satellite viewing geometry or actual migration of hot material. We can generally discount other possible explanations for the anomalies, the most likely being solar reflectance influencing the short-wave bands, due to the presence of clear anomalies in nighttime imagery and the concomitance of apparent low-level ash plumes in several of the images. The persistence of the anomaly, and the lack of large ash plumes, suggests that activity here may involve a lava lake.

Figure 3. Selected MODIS images showing thermal anomalies on Montagu Island. Band 20 (3.7 µm) is shown here. The thermal anomalies appear to be located between the summit of Mount Belinda and the N shore. Images are not georeferenced for purposes of radiance integrity, therefore coastlines are approximate. Courtesy Hawaii Institute of Geophysics and Planetology and British Antarctic Survey.

Figure 4. Summed radiance of anomalous pixels in each image. Band 21 (3.9 µm) was used for these plots. Points show the result for each image, and the line is a three point running mean of values. Courtesy Hawaii Institute of Geophysics and Planetology and British Antarctic Survey.

References. Coombs, D.S., and Landis, C.A., 1966, Pumice from the South Sandwich eruption of March 1962 reaches New Zealand: Nature, v. 209, p. 289-290.

Holdgate, M.W., and Baker, P.E., 1979, The South Sandwich Islands, I, General description: British Antarctic Survey Science Report, v. 91, 76 p.

Lachlan-Cope, T., Smellie, J.L., and Ladkin, R., 2001, Discovery of a recurrent lava lake on Saunders Island (South Sandwich Islands) using AVHRR imagery: Journal of Volcanology and Geothermal Research, v. 112, p. 105-116.

LeMasurier, W.E., and Thomson, J.W. (eds), 1990, Volcanoes of the Antarctic Plate and Southern Oceans: American Geophysical Union, Washington, D.C., AGU Monograph, Antarctic Research Series, v. 48.

Wright, R., Flynn, L.P., Garbeil, H., Harris, A.J.L., and Pilger, E, 2002, Automated volcanic eruption detection using MODIS: Remote Sensing of Environment, v. 82, p. 135-155.

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

Information Contacts: Matt Patrick, Luke Flynn, Harold Garbeil, Andy Harris, Eric Pilger, Glyn Williams-Jones, and Rob Wright, HIGP Thermal Alerts Team, Hawai'i Institute of Geophysics and Planetology (HIGP) / School of Ocean and Earth Science and Technology (SOEST), University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); John Smellie, British Antarctic Survey, Natural Environment Research Council, High Cross, Madingly Road, Cambridge CB3 0ET, United Kingdom (URL: https://www.bas.ac.uk/).

Nyiragongo was last reported on through late October 2002 (BGVN 27:10). This report covers through 21 December, an interval in which the hazard status remained high, with the population asked to exercise vigilance (code Yellow). Included here are reports from the Goma Volcano Observatory (GVO), and from Dario Tedesco and Simon Carn on geochemistry and atmospheric SO₂. Several episodes of strong SO₂ outgassing and unfavorable wind directions caused elevated concentrations of the gas to enter cities and acid rain to damage vegetation and water supplies. High fluorine was found in some rainwater samples. The 24 October 2002 earthquake's aftershocks and the state of the volcano led to significant stress on the regional inhabitants, including those in Goma.

During the October-December reporting interval, the GVO reports noted that their roughly weekly Nyiragongo observational climbs disclosed considerable changes on the crater's floor, a spot ~700 m down inside the summit crater. Comparisons between photos taken on 24 November and 9 December 2002 revealed the merging of two adjacent molten-surfaced lakes and the birth of another similar, though smaller, lava lake at a point well over 100 m away from the merged ones. The deep crater is often filled with fumes too dense to clearly see the crater floor, and in the above-mentioned cases photographers had just 5 to 10 seconds of moderate visibility to capture their photos. This helps explain why the status and behavior of the lava lakes is often ambiguous (see BGVN 26:03). Adequate visibility during a climb on 18 December revealed that the sole lava lake seen then stood ~45 m in diameter, its surface restless and agitated.

In accord with one or more dynamic and molten-surfaced lava lakes on 20 December, SO₂ gas blew into Goma, causing residents to panic. Scoria falls were noted in late October, and in one particular case by residents of the SW-flank settlement of Rusayo at around 1100 on 15 November. It was noted in October that vegetation surrounding the crater's perimeter, particularly on the W flank, had sustained acid burns from abundant degassing. During October-21 December vapors over the crater frequently glimmered red at night. The 15 November visit disclosed the escape of high-temperature gases and the existence of fissures cutting across the residual platform of 17 January 2002 deposits. Fumaroles along fissures discharged gases. SW-flank fissures were also seen.

GVO summarized the volcano observations for the interval 15-28 December 2002, noting a permanent strong gas plume at 4,200-6,000 m altitudes. They again confirmed a permanent small lava lake, about 50 m in diameter with a central active lava fountain sending molten material to ~40 m heights. Minor amounts of Pelé's-hair ash fell in both Rusayo and Kibati villages. Residents of those villages and Kibumba reported seeing incandescence in the crater.

Residents of Kibati and Kibumba were greatly concerned the night of 27-28 November due to visible glimmer that appeared be coming toward them from Nyiragongo. The glimmer was benign activity in the crater rather than lava flows descending the flanks. This behavior was associated with lava-lake degassing.

Other observatory projects in late October to late December included the installation and maintenance of lake-level sensors on Lake Kivu, installation of thermal sensors at selected spots, and improved seismic telemetry.

Deformation surveys on 31 October, 2 November, and 13 November 2002 measured the distance between cross-fracture survey points (nails) along the scarps of Monigi, Lemera, and Shaheru. The results indicated that offsets remained comparatively stable, with little change compared to previous measurements (table 6). New cross-fracture measurements were also initiated at the Mapendo station. Data collected in late December continued to lack evidence of new deformation.

Table 6. Nyiragongo deformation measured along scarps on 2 and 13 November. These reportedly showed strong consistency with preceding measurements. New measurements were initiated at newly established survey points on 13 November. These were in the Mapendo neighborhood (a site towards Gift Bosco) on a revived fracture there. Courtesy of OVG.

Geochemistry. SO₂ fluxes increased during October and November 2002, rising from below detection limits to a few thousands metric tons per day (t/d), then to up to ~20,000 t/d. Dario Tedesco suggested that the increase might be due to a more efficient conduit geometry allowing gases access to the surface. The process may have accompanied upward movement of magma or its arrival at the surface.

During the last half of November through 2 December the TOMS SO₂ estimates were under reliable detection limits due low concentrations. After that, on 7 and 11 December, respectively, TOMS data measured considerable SO₂, ~12,000 and ~11,000 metric tons per day (t/d) (table 7).

Table 7. SO₂ fluxes at Nyiragongo based on the TOMS instrument. Courtesy of Simon Carn.

Thus the degassing had not risen to peak October-November levels, but increased since early December, either in terms of plume altitude, SO₂ concentration, or both. Simon Carn noted that "We are also sometimes seeing discrete SO₂ clouds to the W of the volcano, rather than SO₂ plumes emerging from the volcano, perhaps suggesting discontinuous degassing."

Tedesco also pointed out that the higher SO₂ fluxes accompanied acid rain falling on Goma and surroundings, with some rain samples also containing up to 15 parts per million (ppm) fluorine ion. (For comparison, the U.S. Centers for Disease Control and Prevention recommended a standard in drinking water at 0.7-1.2 ppm, a level that provides a means of preventing tooth decay without compromising public safety.) In December 2002, Goma residents complained about the acid rain, which besides affecting drinking water, put area crops in danger. Accordingly, scientists began collecting rainwater samples with the intent of carrying out regular analyses.

SO₂ blew towards the S on 4 and 5 November exposing people on the upper S flanks. Researchers measured gas concentrations in Goma on 20 November at 20 selected points. They found CO₂ concentrations of 0-4%, and much lower concentrations of CH4, H₂S, and CO. On 4-5 December the wind carried SO₂ gas into S-flank settlements. During the December, analysis of fumaroles at Sake, Mupambiro, Bulengo, and Himbi revealed similar concentrations to those seen in earlier visits (including the elevated values at Sake/Birere, which in October 2002 measured 35.1% CO₂, and Mupambiro, which on 7 December measured 63.1% CO₂). It was expected that the current rainy season favored enhanced CO₂ flow from the ground.

Nyiragongo summit geochemical surveys in mid-November found temperature elevations of 1°C (except one summit site with a 5.7°C rise). CO₂ concentrations had then risen to 3%. In a fissure called Shaheru, CO₂ concentrations stood at 53%. Methane was found at all sites in dilute concentrations, ~0.1 %. H₂S was below the limit of detection at all the visited sites.

The human side of January 2002 volcanism and the 24 October earthquake. Aftershocks to the unusually large earthquake of 24 October 2002 continued to be felt in the epicentral area through December. For example, Goma residents felt an M 4 tectonic earthquake with a 13 km focal depth on 13 December.

Field excursions in the reporting period revealed that the 24 October 2002 earthquake and aftershocks damaged towns in the Kitembo and Minova areas (including the towns Lwiro and Nyabibwe). The visits suggested that no lives were lost but about ten houses sustained cracks. Residents there still remained in need of humanitarian assistance, including safe housing, food, and medicine.

The December aftershocks were not reported to have caused significant damage; however, an earlier Reuters news article, published on 24 January 2002, described how about six days after the volcanism ceased in Goma, residents there had "flocked to receive aid" at distribution points, many having then gone about a week without food supplies. The news article went on to say, "the UN aims to distribute about 260 tonnes of food, which it says is enough to feed 70,000 people for a week. Each family-of an assumed seven people on average-will receive 26 kg of highly nutritious supplies including maize meal, beans, vegetable oil, and corn soya blend." The aid groups also distributed clean drinking water. The intensity of the volcanic and earthquake disasters had clearly left residents weakened and with reduced food security.

Previous Bulletin reports have included relatively few photographs of the scene in Goma due to the January 2002 eruption when lava flows overran the city. Figures 23-26, all sent to us by Wafula Mifundi, are intended to help make up for this deficiency. In many cases within Goma intense fires accompanied the lava flows. Several of the photos provided by Wafula captured these fires, including a devastating fire at a fuel depot, which accompanied an explosion that was widely discussed in the news. The photos presented here omit those of the larger fires and instead illustrate other important aspects of the crisis and its aftermath.

Figure 23. During Nyiragongo's January 2002 eruption lavas transected Goma, a city of about a half-million people. The summit of Nyiragongo lies ~ 20 km to the N. In the foreground, middle-ground, and central background lie destroyed buildings and gardens, and what has now become a field of rubble atop the rapidly cooled, thin lava flows of the January eruption. Note that the rubble contains abundant light-colored building material, such as concrete chunks dispersed from downed buildings. Unburned wood and some leaves may represent unburned portions of trees that came into contact with cooler lava surfaces at temperatures below their kindling point. Leaves and other fallen and wind-blown plant debris may have accumulated later. Date of photo is undisclosed. Courtesy of Wafula.

Figure 24. Nyiragongo lavas inundated these structures on 17 January 2002. A family took refuge in the lower portion of the building in the center. Trapped there by lava flows, one or more people died, including an infant. Provided courtesy of Wafula.

Figure 25. This photo shows some of the remarkably thin and mobile lava flows pouring through a narrow chute (behind the car and in line with the left-most opening in the low structure's wall). Below that, the lava spreads and descends across a lawn. Provided courtesy of Wafula.

Figure 26. Nyiragongo's January 2002 lavas slowly advancing across a road at an intersection. This area of Goma is called Signers rotary point. The sign advertises the Ishango Guest House. Note the lava-immersed but still-standing tree, which at this stage, may have only had substantial burns near the base of its trunk. Provided courtesy of Wafula.

Seismicity. The late October-early November 2002 earthquakes that were interpreted as magmatic, were relatively deep, at 10-25 km. Most of these earthquakes occurred in an elliptical area, although some struck ten's of kilometers W of Goma beneath the Bay of Sake in Lake Kivu, an area where previous earthquakes have sometimes occurred.

During the first half of November seismicity dropped significantly. It was noted that the operational seismic network then consisted of seven stations (table 8); an eighth station was not functioning. During November tectonic seismicity returned to normal; however, magmatic seismicity continued. In the week ending on the 9th, magmatic seismicity centered on the N side of Nyamuragira, a zone adjacent its recent eruption. In contrast, during this same interval earthquakes were rare at Nyiragongo, although gas escaping the crater remained visible from Goma, certifying ongoing intra-crater activity. During the week ending on the 16th, some earthquakes were centered about Nyiragongo. During the latter half of December most of the region's high-frequency and volcano- tectonic earthquakes were associated with an epicentral zone stretching from the 24 October major earthquake near Kalehe to W of Nyamuragira. Some HF events also occurred in the Nyiragongo vicinity too.

Table 8. Nyiragongo and Nyamuragira earthquakes and tremor recorded at Katale and Rusayo stations during November-December 2002. The Katale station sits on the E flank of Nyamuragira; the Rusayo station, on the SW flank of Nyiragongo. The dates on the left are for weekly intervals, except the last entry, which is for a 2-week interval (a fortnight). In the last entry, the elevated high-frequency earthquake count at Katale station was due to a swarm to N of Nyamuragira on 27-28 December. Courtesy of GVO.

The seismic reference stations Katale and Rusayo both registered sub-continuous volcanic tremor during much of the reporting interval (table 8). Rusayo station's tremor was attributed primarily to Nyiragongo, and except for one week in November, it registered the larger share of tremor.

During the week ending 23 November seismicity stayed about the same and tremor dropped considerably, particularly at neighboring volcano Nyamuragira where it was described as feeble (table 8). Banded tremor registered 29 November at the stations of Kunene, Rusayo, Bulengo, Kibumba, and Katale (during 0630-0745 UTC), with the highest amplitude at Katale station, implying Nyamuragira as their source, plausibly a reactivation associated with the 24 October earthquake. Many epicenters also concentrated in the vicinity of that neighboring volcano. On the other hand, epicenters for long-period earthquakes appeared to come from Nyiragongo. The epicenters were determined to a margin of error of ± 2 km.

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: Kasereka Mahinda, Kavotha Kalendi Sadaka, Celestin Kasereka, Jean-Pierre Bajope, Mathieu Yalire, Arnaud Lemarchand, Jean-Christophe Komorowski, and Paolo Papale, Goma Volcano Observatory (GVO), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; Dario Tedesco, Environmental Sciences Department, Via Vivaldi 43, 81100 Caserta, Italy; Jacques Durieux, Groupe d'Etude des Volcans Actifs (GEVA), 6, Rue des Razes 69320 Feyzin, France; Simon Carn, TOMS Volcanic Emissions Group, Joint Center for Earth Systems Technology (NASA/UMBC), University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250 USA (URL: https://so2.gsfc.nasa.gov/); Reuters News Service; BBC News (URL: http://news.bbc.co.uk/).

From November 2002 through mid-February 2003, volcanic activity at Popocatépetl was similar to that during July-October 2002 (BGVN 27:10). Activity consisted principally of small-to-moderate eruptions of steam, gas, and minor amounts of ash, and occasional explosions that ejected incandescent fragments for short distances. Larger explosions on 6 November, 18 and 23 December 2003, 9 January, and during 4-10 February 2003 produced ash plumes that reached approximate heights of 4, 2, 2, 3, and 2 km above the crater, respectively. Volcano-tectonic (VT) earthquakes (M 2.0-3.2) occurred frequently, most located to the SE, N, and E at depths up to 7.5 km beneath the crater. Episodes of harmonic and low-amplitude tremor were registered almost daily, typically for a few hours.

Until November, the daily emissions reported by the Centro Nacional de Prevencion de Desastres (CENAPRED) typically numbered from as few as 5 to as many as 20. In late November, this number increased markedly with 78 detected on 24 November and 40 the following day. Subsequently the daily number of these small-to-moderate emissions occasionally exceeded 30 through mid-February 2003.

New episodes of low-frequency tremor, beginning on 19 November, signaled the growth of a new lava dome within the crater. Aerial photographs obtained by the Mexican Ministry of Communications and Transportation on 2 December confirmed the presence of a fresh lava dome with a base diameter of 180 m, and a height of ~52 m. CENAPRED reported that the explosive activity reported on 18 and 23 December was related to the destruction of the lava dome. Photographs of the lava dome taken on 9 January revealed that the dome's inner crater had subsided. The volume of dome material ejected during the December explosions was calculated to be ~500,000 m³.

CENAPRED stated that explosive activity beginning in mid-January was related to the growth of a new lava dome in the crater. On 22 January a significant increase in volcanic microseismicity was recorded. According to the Washington Volcano Ash Advisory Center, on 25 January an ash emission reached ~10.7 km altitude. The explosion on 4 February ejected incandescent volcanic material that fell as far as ~2 km down the volcano's flanks. Similar emissions continued and were related to partial destruction of the lava dome. According to CENAPRED, as long as there are remains of a lava dome in the crater, a significant chance of further explosive activity remains, including ash emissions and incandescent ejections around the crater. The Alert Level remained at Yellow (second on a scale of three colors) and CENAPRED recommended that people avoid entering the restricted zone that extends 12 km from the crater. However, the road between Santiago Xalitzintla (Puebla) and San Pedro Nexapa (Mexico State), including Paso de Cortés, remained open for controlled traffic.

Geologic Background. Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Information Contacts: Alicia Martinez Bringas, Angel Gómez Vázquez, Roberto Quass Weppen, Enrique Guevara Ortiz, Gilberto Castelan, Gerardo Jímenez and Javier Ortiz, Centro Nacional de Prevención de Desastres (CENAPRED), Av. Delfín Madrigal No.665. Coyoacan, México D.F. 04360, Mexico (URL: https://www.gob.mx/cenapred/); Servando De la Cruz-Reyna, Instituto de Geofísica, UNAM. Cd. Universitaria. Circuito Institutos. Coyoácan. México, D.F. 04510 (URL: http://www.geofisica.unam.mx/); Washington Volcano Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Associated Press.

On 3 November 2002, an unexpected eruption occurred at Reventador (BGVN 27:11). The following report provides an update on recent activity and additional information about the November eruption, including discussion of a site visit after the eruption and satellite data.

Recent activity. Seismicity was low during mid-December 2002. On 10 January, Instituto Geofísico (IG) reported that several lahars occurred that day in the Marquer and Reventador rivers. Ashfall was reported in the N sector of Quito, ~90 km to the WSW. In the afternoon a bluish gas column was observed exiting the crater. IG personnel stated that lava was slowly advancing and that 80-90% of the 3 November 2002 pyroclastic-flow deposits were covered by lahars.

During late February, rain generated mudflows that ended near the Montana River and disrupted traffic on a highway. White steam exited the volcano. Seismicity remained low, and was characterized by bands of harmonic tremor and volcano-tectonic (VT) earthquakes.

Intense rains during the first few days of March caused mudflows and again disrupted traffic. A gas column reached 300-500 m above the summit. Low-level seismicity was characterized by bands of harmonic tremor and a few isolated earthquakes. The seismic station in Copete registered high-frequency signals associated with lahars.

Site visit during 17-19 November 2002. The following report of an investigation of the 3 November 2002 explosion (BGVN 27:11) was submitted by Claus Siebe (Instituto Geofísico (IG), UNAM). Siebe, Jesús Manuel Macías, and Aurelio Fernández were able to fly to Quito on 17 November. On 18 November they interviewed Ing. Marcelo Riaño (general manager of the Trans-Equatorian Oil-Pipeline) as well as Patricia Mothes, Minard Hall, and Hugo Yepes (IG).

On 19 November they arrived in El Chaco (~34 km from Reventador) and traveled to the confluences of the Ríos Marker and Montana with the Río Coca (both are located 8 km from the crater). A small apron of fresh lahar deposits ~300 m wide covered the area adjacent to the Río Marker where the road had been before the 3 November eruption. Several dozens of workers with heavy machinery were trying to make a temporary passage over the gravel and boulder surface for the waiting trucks. For a few minutes they could see for the first and only time a ~1-km-high brownish ash column rising from the crater before incoming clouds hindered further visual contact.

"At the time of our visit, the Río Marker was diminished to such an extent that we could jump from boulder to boulder from one side to the other of the stream without getting wet. The vegetation around the confluence of the rivers was completely destroyed, and surviving trees were scorched and defoliated. The base layer of the fresh deposits consisted of up to 2.5-m-thick, partly matrix-supported, partly clast-supported pyroclastic-flow deposit with abundant wood and charcoal fragments (abundant scoriaceous boulder- and gravel-sized clasts were subrounded while dense clasts were angular). This was overlain by a sequence of several sandy-gravelly lahar units with abundant charcoal supporting larger boulders as well as clasts from the underlying pyroclastic-flow deposit.

About 400 m from the Río Marker, after passing a narrow zone of unaffected vegetation, we were able to reach the Río Montana, where a similar situation was encountered (figure 7). Here, at places the lahar deposits were still steaming with a sulfurous smell. The bridge over the river was destroyed, but the oil pipeline was still basically intact (figure 8). Since the area did not seem safe (the last lahar had been emplaced less than 24 hours prior) the team returned to El Chaco, where they interviewed several people and obtained photographs of the pyroclastic flow and its deposits taken on 3 November 2002 (figures 9-11).

Figure 7. Fresh lahar deposits at Reventador near the confluence of Río Montana with Río Coca on 19 November 2002. According to workers trying to repair the road the still-warm and steaming surface of the lahar deposit shown in the photo was produced during the afternoon of 18 November after heavy rain. This was the 10th lahar event since 3 November. Courtesy of Claus Siebe.

Figure 8. Photo looking downstream near the confluence of Río Montana with Río Coca on the ESE flank of Reventador. In the foreground are the fresh lahar deposits. In the middle ground is the destroyed concrete bridge over the Río Montana as well as the oil-pipeline immediately behind. The bulldozer is trying to built a temporary passage for hundreds of trucks waiting on both sides of the road. In the background is the Río Coca with distal-debris avalanche deposit (19,000 Y BP) forming the vegetated hills behind the river. Photo taken on 19 November shortly after 1300 by Claus Siebe. Courtesy of Claus Siebe.

Figure 9. Pyroclastic flow descending Reventador's SE slopes during the morning of 3 November 2002. Photo was taken from the E (Transoceanic road in the foreground). This anonymous photo was purchased at a small hotel in El Chaco. Courtesy of Claus Siebe.

Figure 10. Fresh pyroclastic-flow deposits from Reventador, produced on 3 November 2002, ponding against the bridge over the Río Montana. This anonymous photo was purchased at a small hotel in El Chaco. Courtesy of Claus Siebe.

Figure 11. Distal pyroclastic-flow deposits from Reventador and scorched vegetation along the Transandean oil-pipeline near the confluence of the Río Montana with the Río Coca. This anonymous photo was purchased at a small hotel in El Chaco. Courtesy of Claus Siebe.

At about 2200 we drove to the summit of a hill (2,959 m elevation) N of Sta. Rosa, 27.5 km from the summit of Reventador. Although the night was clear and we had a good view, the summit was covered by clouds and no incandescence from an advancing lava flow could be seen.

From conversations with personnel from PETROECUADOR, road workers, peasants, etc., the team obtained the following information. Workers from TECHINT, an Argentinian company building a second pipeline parallel to the existing one, were at their campsite near the Río Montana when the eruption started in the early hours of 3 November (it was still dark). The eruption came without prior warning, but they were able to evacuate before strong explosions around 0900 sent pyroclastic flows along the Ríos Montana and Marker. These flows destroyed the road and parts of the new pipeline still under construction. The old pipeline was displaced several meters horizontally but never broke. At places the pyroclastic-flow deposits came to rest in direct contact with the tube. Temperature measurements at points of contact yielded values of 80°C. In subsequent days several lahars came down the Ríos Montana and Marker after heavy rains, further damaging the road (but not the pipeline). The pipeline has continued its operation; it delivers more than 400,000 barrels of oil per day to the Pacific coast.

Inhabitants of the small village of El Reventador, located ~12 km downstream from the confluence of the Ríos Montana and Coca voluntarily evacuated their homes when they heard the explosions around 0900.

One of the scoriaceous juvenile rock samples collected near the confluence of Río Marker with Río Coca was analyzed by X-ray fluorescence and thin sections were made of the same sample. The results revealed that the rock is an andesite (SiO₂= 58.1%) similar in composition to those erupted in 1976 (55-58% SiO₂).

Satellite data. Simon Carn (NASA/UMBC) reported that TOMS observations of the Reventador eruption clouds during 3-4 November suggest modest SO₂ burdens and spatial separation of the emitted SO₂ and ash. Carn, with input from Andy Harris, also constructed a timeline of notable events during 3-6 November along with potentially useful satellite images and overpasses (table 2).

Table 2. Preliminary timeline of the November 2002 eruption of Reventador, compiled using satellite imagery and information from IG and the Washington VAAC. Courtesy of Simon Carn and Andy Harris.

The TOMS overpass at 1543 UTC on 3 November captured the early phase of the eruption. An ash signal was localized over the volcano and a more extensive SO₂ cloud containing ~12 kilotons SO₂ was spreading E and W.

At 1632 UTC on 4 November, TOMS detected several distinct cloud masses. A cloud containing no detectable ash and ~11 kilotons SO₂ was situated E of Ecuador on the Perú/Colombia border, a maximum distance of ~600 km from Reventador beyond which a data gap intervened. A second cloud containing ~42 kilotons SO₂ and a weak ash signal was observed over the Pacific Ocean around 700 km from the volcano. The highest ash concentrations were detected in a cloud straddling the coast of Ecuador ~260 km W of the volcano that covered ~70,000 km². This cloud contained little SO₂. It is assumed that these clouds (total ~53 kilotons SO₂) were erupted on 3 November.

A plume was also detected extending ~200 km W of Reventador, containing ~10 kilotons SO₂. Based on high temporal resolution GOES imagery this plume first appeared sometime between 1045 UTC and 1115 UTC on 4 November. Nearby Guagua Pichincha was also reported active at this time by the Washington VAAC, and may have contributed some SO₂; the highest SO₂ concentrations in the Reventador plume were measured in the TOMS pixel covering Guagua Pichincha.

On 5 November neither SO₂ nor ash were detected by TOMS, although a ~700-km-wide data gap occurred off the coast of Ecuador. The TOMS orbit was better placed on 6 November but no SO₂ or ash were apparent. However, renewed SO₂ emissions were detected on 7 November.

Geologic Background. Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well east of the principal volcanic axis. The forested, dominantly andesitic Volcán El Reventador stratovolcano rises to 3562 m above the jungles of the western Amazon basin. A 4-km-wide caldera widely breached to the east was formed by edifice collapse and is partially filled by a young, unvegetated stratovolcano that rises about 1300 m above the caldera floor to a height comparable to the caldera rim. It has been the source of numerous lava flows as well as explosive eruptions that were visible from Quito in historical time. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the caldera. The largest historical eruption took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.

Information Contacts: P. Ramon, M. Hall, P. Mothes, and H. Yepes, Instituto Geofísico (IG), Escuela Politécnica Nacional, Quito (URL: http://www.igepn.edu.ec/); Simon A. Carn, Joint Center for Earth Systems Technology (NASA/UMBC), University of Maryland-Baltimore County, 1000 Hilltop Circle, Baltimore, MD (URL: https://jcet.umbc.edu/); Andy Harris, HIGP/SOEST, University of Hawaii at Manoa, HI 96822 USA (URL: http://goes.higp.hawaii.edu/); Claus Siebe and Gabriel Valdez Moreno, Instituto de Geofísica, UNAM, Mexico, D.F.; Jesús Manuel Macías, CIESAS-Mexico, Juarez 87, Tlalpan, DF. CP14000; Aurelio Fernández Fuentes, Centro Universitario de Prevencion de Desastres, Universidad de Puebla, Mexico; Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/).

Between 6 and 16 September 2002 the Institute of Geological & Nuclear Sciences (IGNS) reported that there were four short-lived episodes of volcanic tremor at Ruapehu. The duration of these episodes ranged from 8 to more than 40 hours. Episodes with similar characteristics were recorded previously in 2002 on 21 February (~12 hours duration), 17 May (~24 hours), 29 May (~18 hours), 17 June (~24 hours), and 15 July (~8 hours). The September events were unusual because there were four tremor episodes in a ten-day period. Another IGNS report on 8 October noted that there had been five short-lived episodes of moderate-strong volcanic tremor since 6 September, with durations of 8 hours to more than 2 days (figure 25). Tremor levels were generally higher than normal background levels starting on 22 September.

Figure 25. Plot of volcanic tremor amplitudes at Ruapehu, 10 September-8 October 2002. Courtesy of IGNS.

The temperature of Crater Lake during two visits between 16 September and 8 October remained around 19°C, similar to the 19.4°C value measured on 30 August. Intermittent weak seismic tremor continued during November, along with a small number of volcanic earthquakes early in the month. Water temperature of Crater Lake measured during 22-29 November was 24°C, an increase of 5°C from the previous month. Weak tremor continued as of 13 December, accompanied by a small number of minor volcanic earthquakes. Volcanic tremor and earthquakes continued through 19 December, and the water temperature of Crater Lake was reported to be 35°C.

The water temperature measured at Crater Lake at the end of January was 32°C, down 8°C from two weeks earlier (40°C). Minor volcanic tremor continued through February, then steadily declined during 21-28 February to low background levels. On 5 March the temperature measured at Crater Lake had decreased another 2°C to 30°C. The lake was a uniform light gray color with some surface sulfur slicks. Seismic tremor remained at normal levels as of 21 March, but there were periods of moderate tremor on the nights of 14 and 15 March. The temperature of Crater Lake rose to 35°C on 15 March; there were sulfur slicks on the lake surface.

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: Institute of Geological & Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

Although previous eruptions have been recorded in the South Sandwich Islands (Coombs and Landis, 1966), ongoing volcanic activity has only recently been detected and studied. These islands (figure 1) are all volcanic in origin, but sufficiently distant from population centers and shipping lanes that eruptions, if and when they do occur, currently go unnoticed. Visual observations of the islands probably do not occur on more than a few days each year (LeMasurier and Thomson, 1990). Satellite data have recently provided observations of volcanic activity in the group, and offer the only practical means to regularly characterize activity in these islands.

Figure 1. The South Sandwich Island archipelago, located in the Scotia Sea. The South Sandwich Trench lies approximately 100 km E, paralleling the trend of the islands, where the South American Plate subducts westward beneath the Scotia Plate. Courtesy Hawaii Institute of Geophysics and Planetology and British Antarctic Survey.

Using Advanced Very High Resolution Radiometer (AVHRR) data, Lachlan-Cope and others (2001) discovered and analyzed an active lava lake on the summit of Saunders Island (figure 2) that was continuously present for intervals of several months between March 1995 and February 1998; plumes originating from the island were observed on 77 images during April 1995-February 1998. J.L. Smellie noted that during helicopter overflights on 23 January 1997 (Lachlan-Cope and others, 2001) "dense and abundant white steam was emitted from the crater in large conspicuous puffs at intervals of a few seconds alternating with episodes of less voluminous, more transparent vapour." Smellie also observed that the plume commonly extended ~8-10 km downwind.

Figure 2. Map of Saunders Island, adapted from Holdgate and Baker (1979). Lighter shaded stippled areas show rock outcrop, the remainder is snow or ice covered. Relief is shown by form lines that should not be interpreted as fixed-interval contours. Courtesy Hawaii Institute of Geophysics and Planetology and British Antarctic Survey.

The MODIS Thermal Alert system also detected repeated thermal anomalies throughout 2000-2002 in the summit area (figure 3), indicating that activity at the lava lake has continued. Anomalous pixels (1 km pixel size) were detected intermittently and were all 1-2 pixels in size, consistent with the relatively small confines of the crater. The timing of anomalous images in this study likely has more to do with the viewing limitations imposed by weather (persistent cloud cover masks any emitted surface radiance in the majority of images) than it has to do with fluctuations in activity levels, so this plot of radiance (figure 4) should not be used as a proxy for lava lake vigor.

Figure 3. Selected MODIS images showing thermal anomalies on Saunders Island. Band 20 (3.7 µm) is shown here. Anomalous pixels on Saunders Island correspond to the lava lake in the summit crater of Mt. Michael volcano. Images are not georeferenced for purposes of radiance integrity, therefore coastlines are approximate. Courtesy Hawaii Institute of Geophysics and Planetology and British Antarctic Survey.

Figure 4. Summed radiance of anomalous pixels in each image. Band 21 (3.9 µm) was used for these plots. Points show the result for each image, and the line is a three point running mean of values. Courtesy Hawaii Institute of Geophysics and Planetology and British Antarctic Survey.

References. Coombs, D.S., and Landis, C.A., 1966, Pumice from the South Sandwich eruption of March 1962 reaches New Zealand: Nature, v. 209, p. 289-290.

Holdgate, M.W., and Baker, P.E., 1979, The South Sandwich Islands, I, General description: British Antarctic Survey Science Report, v. 91, 76 p.

Lachlan-Cope, T., Smellie, J.L., and Ladkin, R., 2001, Discovery of a recurrent lava lake on Saunders Island (South Sandwich Islands) using AVHRR imagery: Journal of Volcanology and Geothermal Research, v. 112, p. 105-116.

LeMasurier, W.E., and Thomson, J.W. (eds), 1990, Volcanoes of the Antarctic Plate and Southern Oceans: American Geophysical Union, Washington, D.C., AGU Monograph, Antarctic Research Series, v. 48.

Wright, R., Flynn, L.P., Garbeil, H., Harris, A.J.L., and Pilger, E, 2002, Automated volcanic eruption detection using MODIS: Remote Sensing of Environment, v. 82, p. 135-155.

Geologic Background. Saunders Island is a volcanic structure consisting of a large central edifice intersected by two seamount chains, as shown by bathymetric mapping (Leat et al., 2013). The young constructional Mount Michael stratovolcano dominates the glacier-covered island, while two submarine plateaus, Harpers Bank and Saunders Bank, extend north. The symmetrical Michael has a 500-m-wide summit crater and a remnant of a somma rim to the SE. Tephra layers visible in ice cliffs surrounding the island are evidence of recent eruptions. Ash clouds were reported from the summit crater in 1819, and an effusive eruption was inferred to have occurred from a N-flank fissure around the end of the 19th century and beginning of the 20th century. A low ice-free lava platform, Blackstone Plain, is located on the north coast, surrounding a group of former sea stacks. A cluster of parasitic cones on the SE flank, the Ashen Hills, appear to have been modified since 1820 (LeMasurier and Thomson, 1990). Analysis of satellite imagery available since 1989 (Gray et al., 2019; MODVOLC) suggests frequent eruptive activity (when weatehr conditions allow), volcanic clouds, steam plumes, and thermal anomalies indicative of a persistent, or at least frequently active, lava lake in the summit crater. Due to this observational bias, there has been a presumption when defining eruptive periods that activity has been ongoing unless there is no evidence for at least 10 months.

Information Contacts: Matt Patrick, Luke Flynn, Harold Garbeil, Andy Harris, Eric Pilger, Glyn Williams-Jones, and Rob Wright, HIGP Thermal Alerts Team, Hawai'i Institute of Geophysics and Planetology (HIGP) / School of Ocean and Earth Science and Technology (SOEST), University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); John Smellie, British Antarctic Survey, Natural Environment Research Council, High Cross, Madingly Road, Cambridge CB3 0ET, United Kingdom (URL: https://www.bas.ac.uk/).

During mid-September 2002 through February 2003 at Shiveluch, a lava dome continued to grow in the active crater. Short-lived explosions generally sent gas-steam plumes tens of meters to ~3 km above the dome. Seismicity remained above background levels. Earthquakes with magnitudes of ~2-2.7, as well as many smaller ones, occurred at depths of 0-6 km (table 5). Thermal anomalies were visible on satellite imagery (table 6). Intermittent spasmodic tremor with amplitudes of 0.3-1.3 x 10⁶ mps occurred throughout the report period.

Table 5. Earthquakes, explosions, and plumes at Shiveluch during 26 September 2002 through February 2003. Courtesy KVERT.

Table 6. Plumes at Shiveluch visible on satellite imagery during October 2002 through February 2003. Courtesy KVERT.

Incandescence was observed at the lava dome on 6 October. On 11 November, seismic data indicated possible hot avalanches sending clouds up to 5.5 km above the dome.

During late November and early December, gas-and-steam plumes extended >10 km to the E and W. On 19 December, short-lived explosions at 1238 and 1514 sent gas-ash plumes to ~5.5 km and 5.0 km altitude, respectively. In the first case, pyroclastic flows moved to the SE; in the second, to the S, inside the Baidarnaya river. The runout of both pyroclastic flows was 3 km.

On 28 December 2002, a small amount of light-gray ash was observed on the surface of snow. During early January 2003, plumes extended >5-10 km to the W and NW. During late February, plumes extended 10-40 km to the SW, S, and SE. Ash was noted in plumes on 24 October, 1, 11, 15, 19, and 20 November, 1, 19, and 24 December, 4 and 25 January, and 15, 17, 25, and 26 February. The Concern Color Code remained at Yellow.

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

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia; Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological and Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.

During mid-September 2002 through February 2003 at Soufrière Hills, the dome continued to grow, producing numerous rockfalls and small-to-moderate pyroclastic flows. Most of the activity was concentrated on the NE and N flanks, producing numerous pyroclastic flows in White's Ghaut, the Tar River Valley, and Tuitt's Ghaut. Pyroclastic flows and rockfalls also traveled down the W and NW flanks. Ashfall affected surrounding areas, accumulating in thicknesses up to 9 mm. The Washington VAAC issued notices to the aviation community almost daily. Seismicity was dominated by rockfalls (table 42).

Table 42. Seismicity at Soufrière Hills during 13 September 2002-28 February 2003. *During some weeks, the number of seismic events was under-represented because of problems with the seismic stations. Courtesy MVO.

Activity during September 2002. Lava-dome growth was directed to the NE during 13-20 September, with frequent rockfalls and small pyroclastic flows sending material to a sector extending from the central Tar River Valley on the E flank to the NE flanks above Tuitt's Ghaut. Some material tumbled through a notch onto the N flank. A major change in direction of extrusion followed a hybrid earthquake swarm between 0703 and 1515 on 19 September. Growth of the previously active NE lobe stagnated during 21-22 September. A near-vertical spine was extruded in the central area around the 21st, possibly indicating a switch in growth direction. On 26 September a swarm of 36 hybrid events occurred between 0330 and 1112. The same day observations revealed a large new dome lobe that had extruded towards the W in the area previously known as Gages Wall. Material spalling off of this lobe produced rockfalls and small pyroclastic flows down Gages Valley that reached up to 1 km.

Notable pyroclastic flows occurred on the evening of 25 September and the morning of the 27th. Growth and rockfall activity then changed towards the N flanks, suggesting a possible stagnation of the recently extruded western lobe. Spectacular incandescence and semi-continuous rockfall activity were observed on the NE and N flanks of the dome on the night of 26-27 September.

On 27 September a 4-hour-period of heightened activity occurred in the afternoon and evening, with small semi-continuous pyroclastic flows traveling down the N flanks and eastwards into the upper portions of Tuitt's Ghaut and then into White's Bottom Ghaut. A newly extruded lobe was visible on 28 September almost directly to the NW with a broad headwall over the N, NW, and W flanks. On the evening of 29 September there was another period of heightened activity on the N flanks that lasted 1.5 hours, with pyroclastic flows just reaching the sea along White's Bottom Ghaut. It was estimated that during this event only 2-3 x 10⁶ m³ of the N edge of the active NW lobe was shed.

The Washington VAAC reported that a low-level ash cloud from an emission at 1510 on 29 September was visible over eastern Puerto Rico on satellite imagery through the following day. On 30 September a light dusting of white ash fell in eastern Puerto Rico at Roosevelt Roads Naval Air Station.

Activity during October 2002. Observations on 1 October revealed that re-growth of the collapsed area had occurred. A brief period of heavy rain on 2 October triggered a moderate-sized mudflow down the Belham Valley. Analysis of seismic data suggested that pyroclastic-flow activity on 2 October began at 1310, and sustained dome collapse continued for 6 hours. Low-energy pyroclastic flows were observed reaching the sea on the Tar River's flanks throughout the collapse, and ash clouds were produced that drifted to the NW. Heavy ashfall occurred in the residential areas of Salem, Old Towne, and Olveston, with deposits up to 9 mm thick. Subsequent observations revealed that this collapse was confined to the E flanks, and that this was again a relatively small event (less than 5 x 10⁶m³ of material was shed off of the E side of the dome complex).

According to the Washington VAAC, after daybreak on 3 October there were several reports of ashfall in Puerto Rico, and visible satellite imagery at 1115 confirmed that an ash cloud around 2.4 km altitude covered most of the island. At 1615 the area of very thin ash was not visible on satellite imagery. By the next day, ash from the previous day's emissions had drifted W, and around 0902 it was located over southern Puerto Rico. A thin plume of ash also extended SSW of St. Croix island.

Early in October the NW extrusion lobe of the lava dome grew to the NW, but later growth remained more centralized and there was noticeable bulking up of the lobe's summit area. Talus continued to accumulate behind the NW buttress and in the head of Tyre's Ghaut. Minor mudflow activity occurred on 9 October. The growth of the lava dome towards the NW prompted the evacuation of populated areas along the fringes of the lower part of the Belham Valley (~300 people) on 8 and 9 October, and the area was declared part of the Exclusion Zone. A relatively small pyroclastic flow traveled NNE down the flanks on 13 October.

On the afternoon of 22 October intense rainfall at midday produced large mudflows NW in the Belham Valley. At the peak of flow, the entire width of the valley floor at Belham Bridge was flooded and standing waves up to 2.5 m high were observed. By 1430, pyroclastic-flow activity began. For several hours, pyroclastic flows from the N flank of the dome were channeled NE into the upper parts of Tuitt's Ghaut, from where they crossed over into White's Bottom Ghaut. Flows also occurred on the dome's E flank in the Tar River Valley.

The volcano was observed using a remote camera and during a flight on 31 October. The active extruded lobe in the NW continued to steadily grow, bulking out on the N and W sides. Rockfalls and pyroclastic flows traveled down the E and N flanks, particularly within Tuitt's Ghaut and the Tar River Valley. A considerable amount of debris also spalled off the W flank of the active extruded lobe and accumulated in the upper parts of Fort Ghaut.

Activity during November 2002. During early November lava-dome growth on the N part of the dome was less directed, with rockfalls dispersed over the summit and flanks. The lobe shed rockfall debris predominately down Tuitt's Ghaut and Tar River Valley, although also onto the NW flank and into the top of Gage's Valley. According to the Washington VAAC, on 8 November strong pyroclastic flows produced ash-and-gas clouds to a height of ~1.5 km.

On 8 and 9 November pyroclastic flows traveled 900-1,000 m NW into Tyer's Ghaut at the headwaters of the Belham Valley. During 12-15 November, the size and energy of the pyroclastic flows increased slightly. During 15-19 November, small pyroclastic flows traveled 1-1.5 km from the dome every few hours in Tuitt's Ghaut to the NE and in the Tar River Valley to the E. On 29 November the active lobe had a broad whaleback-shaped upper surface, which was oriented towards the NNE.

During 29 November-6 December a number of small, short-lived spines formed at the base of the active lobe in the N part of the dome complex, shedding material E into White's Ghaut and the Tar River Valley. Lava blocks continued to spall off the front of the lobe, shedding material NE into Tuitt's Ghaut and onto the northern talus slope. An average of one moderate-sized pyroclastic flow occurred per day and traveled no farther than 1-1.5 km from the lava dome into Tuitt's and White's ghauts and into the Tar River Valley. During 5-6 December, rockfalls and small pyroclastic flows occurred more frequently on the northern talus slope and on the NW, at the top of Tyer's Ghaut.

Activity during December 2002. A sustained dome collapse began on 8 December at 2045, producing energetic pyroclastic flows down White's Ghaut to the sea at Spanish Point. Ash clouds rose to ~3 km altitude and drifted WNW. In Plymouth and Richmond Hill 4 mm of ash was deposited. Seismicity returned to background levels on 9 December by 0045, and several days of weak tremor occurred.

The collapse scar on the dome's NNE flank, estimated to have had a volume of 4-5 x 10⁶ m³, was being filled rapidly with freshly extruded lava. Observations on 13 December revealed a large amount of fragmental lava extruded in a northerly direction on the summit. A large spine was also extruded on the NW side of the summit.

During late December spectacular incandescence of the dome was observed on most nights. Activity increased during 18-20 December, and on 19 December mudflows occurred in White River, Tar River Valley, and Fort Ghaut. During 20-27 December extrusion occurred on the N, and occassionally NW, sides of the summit. A large spine was pushed up at the back of the active extruded lobe during the night of 26-27 December, but was not visible by 2 January. The Washington VAAC reported that on 28 December around 1130 a 3-km-high ash cloud generated from pyroclastic flows drifted over the islands of St. Kitts and Nevis.

Activity during January-February 2003. Activity escalated to very high levels on the night of 27 December. During 27 December-10 January continuous rockfalls and numerous pyroclastic flows spalled off the active extruded lobe on the NNE side of the lava dome. Activity decreased on the night of 2 January to moderate levels on the 3rd.

During mid-January, activity generally declined to a moderate level. During 15-17 January almost all pyroclastic flows occurred in the Tar River Valley, with only minor rockfalls traveling down the dome's NE and N sides. Lava extrusion occurred NE of the lava-dome complex that was associated with rockfalls and small pyroclastic flows down Tar River Valley, White's Ghaut, Tuitt's Ghaut, and on the northern talus slopes. On 18, 20, and 24 January small pyroclastic flows traveled ~1 km down Tyer's Ghaut.

Activity increased during late January. Growth of the active extrusion lobe continued on the N side of the lava dome. The direction of growth was generally towards the NNE, although the focus of rockfall and pyroclastic-flow activity varied from day to day. A pulse of activity occurred at midday on 30 January, during which pyroclastic flows simultaneously descended several flanks of the lava dome traveling to the Tar River Valley, White's Ghaut, Tuitt's Ghaut, and W to Fort Ghaut.

During 31 January-14 February activity remained moderate. Growth of the lava dome was focused on a large, steep lobe directed to the NE. A small amount of rockfall material was directed W towards Fort Ghaut. Rockfalls and small pyroclastic flows also occurred off the N flank of the dome onto the area of Riley's Estate.

During 19-25 February pyroclastic flows and rockfalls were concentrated more on the E flank of the lava dome and in the Tar River Valley, although there were several periods of activity on the N flank, with pyroclastic flows in Tuitt's Ghaut and at the top of Farrell's Plain.

Activity increased slightly during 21-28 February. During an observation flight on 27 February lava-dome growth was concentrated towards the NE. Pyroclastic flows and rockfalls traveled down the lava dome's E and NE flanks via the Tar River Valley and Tuitt's Ghaut. There were also several periods of activity on the N flank, with pyroclastic flows at the top of Farrell's Plain.

SO₂ emission rates varied throughout the report period (table 43), and were especially high following the dome-collapse event on 9 December (2,350 tons per day average).

Table 43. SO₂ emission rates at Soufrière Hills during 13 September 2002 through 28 February 2003. Courtesy MVO.

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

Information Contacts: Montserrat Volcano Observatory (MVO), Mongo Hill, Montserrat, West Indies (URL: http://www.mvo.ms/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Associated Press.

Minor volcanic tremor continued, and the plume of steam and gases from the vent remained unchanged through the end of November 2002, according to the Institute of Geological & Nuclear Sciences (IGNS). The output of SO₂ measured on 10 December was 112 ± 36 metric tons per day (t/d); in October the value was 63 t/d. Volcanic tremor continued and was accompanied by minor booming and explosions in the second week of December. After a brief period of increased activity at the start of the next week, volcanic tremor dropped to the weaker levels of tremor observed previously. Weak steam and gas emissions continued through 19 December, along with weak volcanic tremor.

An IGNS report on 7 February 2002 noted continuing minor volcanic tremor and a weak plume of steam and gases from the active vent. Activity increased slightly during 9-16 February. On 12 February mud was being thrown some tens of meters in the air, and ground vibrations could be felt. This corresponded to a period of slightly stronger volcanic tremor. Seismograph readings returned to normal by the 13th. Minor hydrothermal activity continued as of 21 February, and the output of SO₂ had increased to 269 t/d. Seismic tremor steadily declined to low background levels in the last week of the month, though a weak plume of steam and gases was still being emitted.

Seismic tremor levels at White Island remained low on 7 March, but mud was being ejected to low levels around the active vent and a steam plume remained. There were intermittent periods of weak tremor the next week, and SO₂ output was reported to be 267 t/d. Seismic tremor was at a very low level during the week ending on 21 March.

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: Institute of Geological & Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).