Sabancaya is an andesitic stratovolcano located in Peru. The most recent eruptive episode began in early November 2016, which is characterized by gas-and-steam and ash emissions, seismicity, and explosive events (BGVN 44:06). The ash plumes are dispersed by wind with a typical radius of 30 km, which occasionally results in ashfall. Current volcanism includes high seismicity, gas-and-steam emissions, ash and SO₂ plumes, numerous thermal anomalies, and explosive events. This report updates information from June through November 2019 using information primarily from the Instituto Geofisico del Peru (IGP) and Observatorio Volcanologico del INGEMMET (Instituto Geológical Minero y Metalúrgico) (OVI-INGEMMET).

Table 5. Summary of eruptive activity at Sabancaya during June-November 2019 based on IGP weekly reports, the Buenos Aires VAAC advisories, the HIGP MODVOLC hotspot monitoring algorithm, and Sentinel-5P/TROPOMI satellite data.

Explosions, ash emissions, thermal signatures, and high concentrations of SO₂ were reported each week during June-November 2019 by IGP, the Buenos Aires Volcanic Ash Advisory Centre (VAAC), HIGP MODVOLC, and Sentinel-2 and Sentinel-5P/TROPOMI satellite data (table 5). Thermal anomalies were visible in the summit crater, even in the presence of meteoric clouds and ash plumes were occasionally visible rising from the summit in clear weather (figure 68). The maximum plume height reached 4.5 km above the crater drifting NW, W, and S the week of 29 July-4 August, according to IGP who used surveillance cameras to visually monitor the plume (figure 69). This ash plume had a radius of 30 km, which resulted in ashfall in Colca (NW) and Huambo (W). On 27 July the SO₂ levels reached a high of 12,814 tons/day, according to INGEMMET. An average of 58 daily explosions occurred in early November, which is the largest average of this reporting period.

Figure 68. Sentinel-2 satellite imagery detected ash plumes, gas-and-steam emissions, and multiple thermal signatures (bright yellow-orange) in the crater at Sabancaya during June-November 2019. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

Figure 69. A webcam image of an ash plume rising from Sabancaya on 1 August 2019 at least 4 km above the crater. Courtesy of IGP.

Seismicity was also particularly high between August and September 2019, according to INGEMMET. On 14 August, roughly 850 earthquakes were detected. There were 280 earthquakes reported on 15 September, located 6 km NE of the crater. Both seismic events were characterized as seismic swarms. Seismicity decreased afterward but continued through the reporting period.

In February 2017, a lava dome was established inside the crater. Since then, it has been growing slowly, filling the N area of the crater and producing thermal anomalies. On 26 October 2019, OVI-INGEMMET conducted a drone overflight and captured video of the lava dome (figure 70). According to IGP, this lava dome is approximately 4.6 million cubic meters with a growth rate of 0.05 m3/s.

Figure 70. Drone images of the lava dome and degassing inside the crater at Sabancaya on 26 (top) and 27 (bottom) October 2019. Courtesy of INGEMMET (Informe Ténico No A6969).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows strong, consistent thermal anomalies occurring all throughout June through November 2019 (figure 71). In conjunction with these thermal anomalies, the October 2019 special issue report by INGEMMET showed new hotspots forming along the crater rim in July 2018 and August 2019 (figure 72).

Figure 71. Thermal anomalies at Sabancaya for 3 January through November 2019 as recorded by the MIROVA system (Log Radiative Power) were frequent, strong, and consistent. Courtesy of MIROVA.

Figure 72. Thermal hotspots on the NW section of the crater at Sabancaya using MIROVA images. These images show the progression of the formation of at least two new hotspots between February 2017 to August 2019. Courtesy of INGEMMET, Informe Técnico No A6969.

Sulfur dioxide emissions also persisted at significant levels from June through November 2019, as detected by Sentinel-5P/TROPOMI satellite data (figure 73). The satellite measurements of the SO₂ emissions exceeded 2 DU (Dobson Units) at least 20 days each month during this time. These SO₂ plumes sometimes occurred for multiple consecutive days (figure 74).

Figure 73. Consistent, large SO2 plumes from Sabancaya were seen in TROPOMI instrument satellite data throughout June-November 2019, many of which drifted in different directions based on the prevailing winds. Courtesy of NASA Goddard Space Flight Center.

Figure 74. Persistent SO2 plumes from Sabancaya appeared daily during 13-16 September 2019 in the TROPOMI instrument satellite data. Courtesy of NASA Goddard Space Flight Center.

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: Instituto Geofisico del Peru (IGP), Calle Badajoz N° 169 Urb. Mayorazgo IV Etapa, Ate, Lima 15012, Perú (URL: https://www.gob.pe/igp); 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); 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/); 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); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Karangetang (also known as Api Siau), located on the island of Siau in the Sitaro Regency, North Sulawesi, Indonesia, has experienced more than 40 recorded eruptions since 1675 in addition to many smaller undocumented eruptions. In early February 2019, a lava flow originated from the N crater (Kawah Dua) traveling NNW and reaching a distance over 3 km. Recent monitoring showed a lava flow from the S crater (Kawah Utama, also considered the "Main Crater") traveling toward the Kahetang and Batuawang River drainages on 15 April 2019. Gas-and-steam emissions, ash plumes, moderate seismicity, and thermal anomalies including lava flow activity define this current reporting period for May through November 2019. The primary source of information for this report comes from daily and weekly reports by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), the Darwin Volcanic Ash Advisory Center (VAAC), and satellite data.

PVMBG reported that white gas-and-steam emissions were visible rising above both craters consistently between May through November 2019 (figures 30 and 31). The maximum altitude for these emissions was 400 m above the Dua Crater on 27 May and 700 m above the Main Crater on 12 June. Throughout the reporting period PVMBG noted that moderate seismicity occurred, which included both shallow and deep volcanic earthquakes.

Figure 30. A Sentinel-2 image of Karangetang showing two active craters producing gas-and-steam emissions with a small amount of ash on 7 August 2019. Courtesy of Sentinel Hub Playground.

Figure 31. Webcam images of gas-and-steam emissions rising from the summit of Karangetang on 14 (top) and 25 (bottom) October 2019. Courtesy of PVMBG via Øystein Lund Andersen.

Activity was relatively low between May and June 2019, consisting mostly of gas-and-steam emissions. On 26-27 May 2019 crater incandescence was observed above the Main Crater; white gas-and-steam emissions were rising from both craters (figures 32 and 33). At 1858 on 20 July, incandescent avalanches of material originating from the Main Crater traveled as far as 1 km W toward the Pangi and Kinali River drainages. By 22 July the incandescent material had traveled another 500 m in the same direction as well as 1 km in the direction of the Nanitu and Beha River drainages. According to a Darwin VAAC report, discreet, intermittent ash eruptions on 30 July resulted in plumes drifting W at 7.6 km altitude and SE at 3 km, as observed in HIMAWARI-8 satellite imagery.

Figure 32. Photograph of summit crater incandescence at Karangetang on 12 May 2019. Courtesy of Dominik Derek.

Figure 33. Photograph of both summit crater incandescence at Karangetang on 12 May 2019 accompanied by gas-and-steam emissions. Courtesy of Dominik Derek.

On 5 August 2019 a minor eruption produced an ash cloud that rose 3 km and drifted E. PVMBG reported in the weekly report for 5-11 August that an incandescent lava flow from the Main Crater was traveling W and SW on the slopes of Karangetang and producing incandescent avalanches (figure 34). During 12 August through 1 September lava continued to effuse from both the Main and Dua craters. Avalanches of material traveled as far as 1.5 km SW toward the Nanitu and Pangi River drainages, 1.4-2 km to the W of Pangi, and 1.8 km down the Sense River drainage. Lava fountaining was observed occurring up to 10 m above the summit on 14-20 August.

Figure 34. Photograph of summit crater incandescence and a lava flow from Karangetang on 7 August 2019. Courtesy of MAGMA Indonesia.

PVMBG reported that during 2-22 September lava continued to effuse from both craters, traveling SW toward the Nanitu, Pangi, and Sense River drainages as far as 1.5 km. On 24 September the lava flow occasionally traveled 0.8-1.5 km toward the West Beha River drainage. The lava flow from the Main Crater continued through at least the end of November, moving SW and W as far as 1.5 km toward the Nanitu, Pangi, and Sense River drainages. In late October and onwards, incandescence from both summit craters was observed at night. The lava flow often traveled as far as 1 km toward the Batang and East Beha River drainage on 12 November, the West Beha River drainage on 15, 22, 24, and 29 November, and the Batang and West Beha River drainages on 25-27 November (figure 35). On 30 November a Strombolian eruption occurred in the Main Crater accompanied by gas-and-steam emissions rising 100 m above the Main Crater and 50 m above the Dua Crater. Lava flows traveled SW and W toward the Nanitu, Sense, and Pangi River drainages as far as 1.5 km, the West Beha and Batang River drainages as far as 1 km, and occasionally the Batu Awang and Kahetang River drainages as far as 2 km. Lava fountaining was reported occurring 10-25 m above the Main Crater and 10 m above the Dua Crater on 6, 8-12, 15, 21-30 November.

Figure 35. Webcam image of gas-and-steam emissions rising from the summit of Karangetang accompanied by incandescence and lava flows at night on 27 November 2019. Courtesy of MAGMA Indonesia via Øystein Lund Andersen.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed consistent and strong thermal anomalies within 5 km of the summit craters from late July through November 2019 (figure 36). Satellite imagery from Sentinel-2 corroborated this data, showing strong thermal anomalies and lava flows originating from both craters during this same timeframe (figure 37). In addition to these lava flows, satellite imagery also captured intermittent gas-and-steam emissions from May through November (figure 38). MODVOLC thermal alerts registered 165 thermal hotspots near Karangetang's summit between May and November.

Figure 36. Frequent and strong thermal anomalies at Karangetang between 3 January through November 2019 as recorded by the MIROVA system (Log Radiative Power) began in late July and were recorded within 5 km of the summit craters. Courtesy of MIROVA.

Figure 37. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) confirmed ongoing thermal activity (bright orange) at Karangetang from July into November 2019. The lava flows traveled dominantly in the W direction from the Main Crater. Courtesy of Sentinel Hub Playground.

Figure 38. Sentinel-2 satellite imagery showing gas-and-steam emissions with a small amount of ash (middle and right) rising from both craters of Karangetang during May through November 2019. Courtesy of Sentinel Hub Playground.

Sentinel-5P/TROPOMI satellite data detected multiple sulfur dioxide plumes between May and November 2019 (figure 39). These emissions occasionally exceeded 2 Dobson Units (DU) and drifted in different directions based on the dominant wind pattern.

Figure 39. SO2 emissions from Karangetang (indicated by the red box) were seen in TROPOMI instrument satellite data during May through November 2019, many of which drifted in different directions based on the prevailing winds. Top left: 27 May 2019. Top middle: 26 July 2019. Top right: 17 August 2019. Bottom left: 27 September 2019. Bottom middle: 3 October 2019. Bottom right: 21 November 2019. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi island. The stratovolcano contains five summit craters along a N-S line. It is one of Indonesia's most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented in the historical record (Catalog of Active Volcanoes of the World: Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts have produced pyroclastic flows.

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/); 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); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: https://www.oysteinlundandersen.com); Dominik Derek (URL: https://www.facebook.com/07dominikderek/).

Ulawun is a basaltic-to-andesitic stratovolcano located in West New Britain, Papua New Guinea, with typical activity consisting of seismicity, gas-and-steam plumes, and ash emissions. The most recent eruption began in late June 2019 involving ash and gas-and-steam emissions, increased seismicity, and a pyroclastic flow (BGVN 44:09). This report includes volcanism from September to October 2019 with primary source information from the Rabaul Volcano Observatory (RVO) and the Darwin Volcanic Ash Advisory Centre (VAAC).

Activity remained low through 26 September 2019, mainly consisting of variable amounts of gas-and-steam emissions and low seismicity. Between 26 and 29 September RVO reported that the seismicity increased slightly and included low-level volcanic tremors and Real-Time Seismic Amplitude Measurement (RSAM) values in the 200-400 range on 19, 20, and 22 September. On 30 September small volcanic earthquakes began around 1000 and continued to increase in frequency; by 1220, they were characterized as a seismic swarm. The Darwin VAAC advisory noted that an ash plume rose to 4.6-6 km altitude, drifting SW and W, based on ground reports.

On 1 October 2019 the seismicity increased, reaching RSAM values up to 10,000 units between 0130 and 0200, according to RVO. These events preceded an eruption which originated from a new vent that opened on the SW flank at 700 m elevation, about three-quarters of the way down the flank from the summit. The eruption started between 0430 and 0500 and was defined by incandescence and lava fountaining to less than 100 m. In addition to lava fountaining, light- to dark-gray ash plumes were visible rising several kilometers above the vent and drifting NW and W (figure 21). On 2 October, as the lava fountaining continued, ash-and-steam plumes rose to variable heights between 2 and 5.2 km (figures 22 and 23), resulting in ashfall to the W in Navo. Seismicity remained high, with RSAM values passing 12,000. A lava flow also emerged during the night which traveled 1-2 km NW. The main summit crater produced white gas-and-steam emissions, but no incandescence or other signs of activity were observed.

Figure 21. Photographs of incandescence and lava fountaining from Ulawun during 1-2 October 2019. A) Lava fountains along with ash plumes that rose several kilometers above the vent. B) Incandescence and lava fountaining seen from offshore. Courtesy of Christopher Lagisa.

Figure 22. Photographs of an ash plume rising from Ulawun on 1 October 2019. In the right photo, lava fountaining is visible. Courtesy of Christopher Lagisa.

Figure 23. Photograph of lava fountaining and an ash plume rising from Ulawun on 1 October 2019. Courtesy of Joe Metto, WNB Provincial Disaster Office (RVO Report 2019100101).

Ash emissions began to decrease by 3 October 2019; satellite imagery and ground observations showed an ash cloud rising to 3 km altitude and drifting N, according to the Darwin VAAC report. RVO reported that the fissure eruption on the SW flank stopped on 4 October, but gas-and-steam emissions and weak incandescence were still visible. The lava flow slowed, advancing 3-5 m/day, while declining seismicity was reflected in RSAM values fluctuating around 1,000. RVO reported that between 23 and 31 October the main summit crater continued to produce variable amounts of white gas-and-steam emissions (figure 24) and that no incandescence was observed after 5 October. Gas-and-steam emissions were also observed around the new SW vent and along the lava flow. Seismicity remained low until 27-29 October; it increased again and peaked on 30 October, reaching an RSAM value of 1,700 before dropping and fluctuating around 1,200-1,500.

Figure 24. Webcam photo of a gas-and-steam plume rising from Ulawun on 30 October 2019. Courtesy of the Rabaul Volcano Observatory (RVO).

In addition to ash plumes, SO₂ plumes were also detected between September and October 2019. Sentinel-5P/TROPOMI data showed SO₂ plumes, some of which exceeded 2 Dobson Units (DU) drifting in different directions (figure 25). MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed strong, frequent thermal anomalies within 5 km of the summit beginning in early October 2019 and throughout the rest of the month (figure 26). Only one thermal anomaly was detected in early December.

Figure 25. Sentinel-5P/TROPOMI data showing a high concentration of SO2 plumes rising from Ulawun between late September-early October 2019. Top left: 11 September 2019. Top right: 1 October 2019. Bottom left: 2 October 2019. Bottom right: 3 October 2019. Courtesy of the NASA Space Goddard Flight Center.

Figure 26. Frequent and strong thermal anomalies at Ulawun for February through December 2019 as recorded by the MIROVA system (Log Radiative Power) began in early October and continued throughout the month. Courtesy of MIROVA.

Activity in November was relatively low, with only a variable amount of white gas-and-steam emissions visible and low (less than 200 RSAM units) seismicity with sporadic volcanic earthquakes. Between 9-22 December, a webcam showed intermittent white gas-and-steam emissions were observed at the main crater, accompanied by some incandescence at night. Some gas-and-steam emissions were also observed rising from the new SW vent along the lava flow.

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

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; 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/); 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/); Christopher Lagisa, West New Britain Province, Papua New Guinea (URL: https://www.facebook.com/christopher.lagisa, images posted at https://www.facebook.com/christopher.lagisa/posts/730662937360239 and https://www.facebook.com/christopher.lagisa/posts/730215604071639).

Nyamuragira (also known as Nyamulagira) is a high-potassium basaltic shield volcano located in the Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo. Previous volcanism consisted of the reappearance of a lava lake in the summit crater in mid-April 2018, lava emissions, and high seismicity (BGVN 44:05). Current activity includes strong thermal signatures, continued inner crater wall collapses, and continued moderate seismicity. The primary source of information for this June-November 2019 report comes from the Observatoire Volcanologique de Goma (OVG) and satellite data and imagery from multiple sources.

OVG reported in the July 2019 monthly that the inner crater wall collapses that were observed in May continued to occur. During this month, there was a sharp decrease in the lava lake level, and it is no longer visible. However, the report stated that lava fountaining was visible from a small cone within this crater, though its activity has also decreased since 2014. In late July, a thermal anomaly and fumaroles were observed originating from this cone (figure 85). Seismicity remained moderate throughout this reporting period.

Figure 85. Photograph showing the small active cone within the crater of Nyamuragira in late July 2019. Fumaroles are also observed within the crater originating from the small cone. Courtesy of Sergio Maguna.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows strong, frequent thermal anomalies within 5 km of the summit between June through November (figure 86). The strength of these thermal anomalies noticeably decreases briefly in September. MODVOLC thermal alerts registered 54 thermal hotspots dominantly near the N area of the crater during June through November 2019. Satellite imagery from Sentinel-2 corroborated this data, showing strong thermal anomalies within the summit crater during this same timeframe (figure 87).

Figure 86. The MIROVA graph of thermal activity (log radiative power) at Nyamuragira during 30 January through November 2019 shows strong, frequent thermal anomalies through November with a brief decrease in activity in late April-early May and early September. Courtesy of MIROVA.

Figure 87. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) confirmed ongoing thermal activity at Nyamuragira into November 2019. 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: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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/); Sergio Maguna (Facebook: https://www.facebook.com/sergio.maguna.9, images posted at https://www.facebook.com/sergio.maguna.9/posts/1267625096730837).

Bagana volcano is found in a remote portion of central Bougainville Island in Papua New Guinea. The most recent eruptive phase that began in early 2000 has produced ash plumes and thermal anomalies (BGVN 44:06, 50:01). Activity has remained low between January-July 2019 with rare thermal anomalies and occasional steam plumes. This reporting period updates information for June-November 2019 and includes thermal anomalies and intermittent gas-and-steam emissions. Thermal data and satellite imagery are the primary sources of information for this report.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed an increased number of thermal anomalies within 5 km from the summit beginning in late July-early August (figure 38). Two Sentinel-2 thermal satellite images showed faint, roughly linear thermal anomalies, indicative of lava flows trending EW and NS on 7 July 2019 and 6 August, respectively (figure 39). Weak thermal hotspots were briefly detected in late September-early October after a short hiatus in September. No thermal anomalies were recorded in Sentinel-2 past August due to cloud cover; however, gas-and-steam emissions were visible on 7 July and in September (figures 39, 40, and 41).

Figure 38. Thermal anomalies near the crater summit at Bagana during February-November 2019 as recorded by the MIROVA system (Log Radiative Power) increased in frequency and power in early August. A small cluster was detected in early October after a brief pause in activity in early September. Courtesy of MIROVA.

Figure 39. Sentinel-2 thermal satellite imagery showing small thermal anomalies at Bagana between July-August 2019. Left: A very faint thermal anomaly and a gas-and-steam plume is seen on 7 July 2019. Right: Two small thermal anomalies are faintly seen on 6 August 2019. Both Sentinel-2 satellite images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 40. A gas-and-steam plume rising from the summit of Bagana on 18 September 2019. Courtesy of Brendan McCormick Kilbride (University of Manchester).

The Deep Carbon Observatory (DCO) scientific team partnered with the Rabaul Volcano Observatory and the Bougainville Disaster Office to observe activity at Bagana and collect gas data using drone technology during two weeks of field work in mid-September 2019. For this field work, the major focus was to understand the composition of the volcanic gas emitted at Bagana and measure the concentration of these gases. Since Bagana is remote and difficult to climb, research about its gas emissions has been limited. The recent advancements in drone technology has allowed for new data collection at the summit of Bagana (figure 41). Most of the emissions consisted of water vapor, according to Brendan McCormick Kilbride, one of the volcanologists on this trip. During 14-19 September there was consistently a strong gas-and-steam plume from Bagana (figure 42).

Figure 41. Degassing plumes seen from drone footage 100 m above the summit of Bagana. Top: Zoomed out view of the summit of Bagana degassing. Bottom: Closer perspective of the gases emitted from Bagana. Courtesy of Kieran Wood (University of Bristol) and the Bristol Flight Laboratory.

Figure 42. Photos of gas-and-steam plumes rising from Bagana between 14-19 September 2019. Courtesy of Brendan McCormick Kilbride (University of Manchester).

Geologic Background. Bagana volcano, occupying a remote portion of central Bougainville Island, is one of Melanesia's youngest and most active volcanoes. This massive symmetrical cone was largely constructed by an accumulation of viscous andesitic lava flows. The entire edifice could have been constructed in about 300 years at its present rate of lava production. Eruptive activity is frequent and characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although explosive activity occasionally producing pyroclastic flows also occurs. Lava flows form dramatic, freshly preserved tongue-shaped lobes up to 50 m thick with prominent levees that descend the flanks on all sides.

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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Brendan McCormick Kilbride, University of Manchester, Manchester M13 9PL, United Kingdom (URL: https://www.research.manchester.ac.uk/portal/brendan.mccormickkilbride.html, Twitter: https://twitter.com/BrendanVolc); Kieran Wood, University of Bristol, Bristol BS8 1QU, United Kingdom (URL: http://www.bristol.ac.uk/engineering/people/kieran-t-wood/index.html, Twitter: https://twitter.com/DrKieranWood, video posted at https://www.youtube.com/watch?v=A7Hx645v0eU); University of Bristol Flight Laboratory, Bristol BS8 1QU, United Kingdom (Twitter: https://twitter.com/UOBFlightLab).

Kerinci, located in Sumatra, Indonesia, is a highly active volcano characterized by explosive eruptions with ash plumes and gas-and-steam emissions. The most recent eruptive episode began in April 2018 and included intermittent explosions with ash plumes. Volcanism continued from June-November 2019 with ongoing intermittent gas-and-steam and ash plumes. The primary source of information for this report comes from Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), the Darwin Volcanic Ash Advisory Centre (VAAC), and MAGMA Indonesia.

Brown- to gray-colored ash clouds drifting in different directions were reported by PVMBG, the Darwin VAAC, and MAGMA Indonesia between June and early November 2019. Ground observations, satellite imagery, and weather models were used to monitor the plume, which ranged from 4.3 to 4.9 km altitude, or about 500-1,100 m above the summit. On 7 June 2019 at 0604 a gray ash emission rose 800 m above the summit, drifting E, according to a ground observer. An ash plume on 12 July rose to 4 km altitude and drifted SW, as determined by satellite imagery and weather models. An eruption produced a gray ash cloud on 31 July that rose to 4.6 km altitude and drifted NE and E, according to PVMBG and the Darwin VAAC (figure 17). Another ash cloud rose up to 4.3 km altitude on 3 August. On 2 September a possible ash plume rose to a maximum altitude of 4.9 km and drifted WSW, according to the Darwin VAAC advisory.

Figure 17. A gray ash plume at Kerinci rose roughly 800 m above the summit on 31 July 2019 and drifted NE and E. Courtesy of MAGMA Indonesia.

Brown ash emissions rose to 4.4 km altitude at 1253 on 6 October, drifting WSW. Similar plumes reached 4.6 km altitude twice on 30 October and moved NE, SE, and E at 0614 and WSW at 1721, based on ground observations. On 1-2 November, ground observers saw brown ash emissions rising up to 4.3 km drifting ESE. Between 3 and 5 November the brown ash plumes rose 100-500 m above the summit, according to PVMBG.

Gas emissions continued to be observed through November, as reported by PVMBG and identified in satellite imagery (figure 18). Seismicity that included volcanic earthquakes also continued between June and early November, when the frequency decreased.

Figure 18. Sentinel-2 thermal satellite imagery showing a typical white gas-and-steam plume at Kerinci on 9 August 2019. Sentinel-2 satellite image with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Geologic Background. Gunung Kerinci in central Sumatra forms Indonesia's highest volcano and is one of the most active in Sumatra. It is capped by an unvegetated young summit cone that was constructed NE of an older crater remnant. There is a deep 600-m-wide summit crater often partially filled by a small crater lake that lies on the NE crater floor, opposite the SW-rim summit. The massive 13 x 25 km wide volcano towers 2400-3300 m above surrounding plains and is elongated in a N-S direction. Frequently active, Kerinci has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

The long-term activity at Bezymianny has been dominated by almost continuous thermal anomalies, moderate gas-steam emissions, dome growth, lava flows, and an occasional ash explosion (BGVN 44:06). The volcano is monitored by the Kamchatka Volcanic Eruptions Response Team (KVERT. Throughout the reporting period of June to November 2019, the Aviation Colour Code remained Yellow (second lowest of four levels).

According to KVERT weekly reports, lava dome growth continued in June through mid-July 2019. Thereafter the reports did not mention dome growth, but indicated that moderate gas-and-steam emissions (figure 32) continued through November. The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, based on analysis of MODIS data, detected hotspots within 5 km of the summit almost every day. KVERT also reported a thermal anomaly over the volcano almost daily, except when it was obscured by clouds. Infrared satellite imagery often showed thermal anomalies generated by lava flows or dome growth (figure 33).

Figure 32. Photo of Bezymianny showing fumarolic activity on 4 July 2019. Photo by O. Girina (IVS FEB RAS, KVERT); courtesy of KVERT.

Figure 33. Typical infrared satellite images of Bezymianny showing thermal anomalies in the summit crater, including a lava flow to the WNW. Top: 21 August 2019 with SWIR filter (bands 12, 8A, 4). Bottom: 17 September 2019 with Atmospheric Penetration filter (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Geologic Background. Prior to its noted 1955-56 eruption, Bezymianny had been considered extinct. The modern volcano, much smaller in size than its massive neighbors Kamen and Kliuchevskoi, was formed about 4700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7000 years ago. Three periods of intensified activity have occurred during the past 3000 years. The latest period, which was preceded by a 1000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large horseshoe-shaped crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

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/); 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).

Mayon, located in the Philippines, is a highly active stratovolcano with recorded historical eruptions dating back to 1616. The most recent eruptive episode began in early January 2018 that consisted of phreatic explosions, steam-and-ash plumes, lava fountaining, and pyroclastic flows (BGVN 43:04). The previous report noted small but distinct thermal anomalies, gas-and-steam plumes, and slight inflation (BGVN 44:05) that continued to occur from May into mid-October 2019. This report includes information based on daily bulletins from the Philippine Institute of Volcanology and Seismology (PHIVOLCS) and Sentinel-2 satellite imagery.

Between May and October 2019, white gas-and-steam plumes rose to a maximum altitude of 800 m on 17 May. PHIVOLCS reported that faint summit incandescence was frequently observed at night from May-July and Sentinel-2 thermal satellite imagery showed weaker thermal anomalies in September and October (figure 49); the last anomaly was identified on 12 October. Average SO₂ emissions as measured by PHIVOLCS generally varied between 469-774 tons/day; the high value of the period was on 25 July, with 1,171 tons/day. Small SO₂ plumes were detected by the TROPOMI satellite instrument a few times during May-September 2019 (figure 50).

Figure 49. Sentinel-2 thermal satellite imagery of Mayon between May-October 2019. Small thermal anomalies were recorded in satellite imagery from the summit and some white gas-and-steam plumes are visible. Top left: 30 May 2019. Top right: 9 June 2019. Bottom left: 22 September 2019. Bottom right: 12 October 2019. Sentinel-2 satellite images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 50. Small SO2 plumes rising from Mayon during May-September 2019 recorded in DU (Dobson Units). Top left: 28 May 2019. Top right: 26 July 2019. Bottom left: 16 August 2019. Bottom right: 23 September 2019. Courtesy of NASA Goddard Space Flight Center.

Continuous GPS data has shown slight inflation since June 2018, corroborated by precise leveling data taken on 9-17 April, 16-25 July, and 23-30 October 2019. Elevated seismicity and occasional rockfall events were detected by the seismic monitoring network from PHIVOLCS from May to July; recorded activity decreased in August. Activity reported by PHIVOLCS in September-October 2019 consisted of frequent gas-and-steam emissions, two volcanic earthquakes, and no summit incandescence.

Geologic Background. Beautifully symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the Philippines' most active volcano. The structurally simple edifice has steep upper slopes averaging 35-40 degrees that are capped by a small summit crater. Historical eruptions date back to 1616 and range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); 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/).

Merapi is an active volcano north of the city of Yogyakarta (figure 79) that has a recent history of dome growth and collapse, resulting in block-and-ash flows that killed over 400 in 2010, while an estimated 10,000-20,000 lives were saved by evacuations. The edifice contains an active dome at the summit, above the Gendol drainage down the SE flank (figure 80). The current eruption episode began in May 2018 and dome growth was observed from 11 August 2018-onwards. This Bulletin summarizes activity during April through September 2019 and is based on information from Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG, the Center for Research and Development of Geological Disaster Technology, a branch of PVMBG), Sutopo of Badan Nasional Penanggulangan Bencana (BNPB), MAGMA Indonesia, along with observations by Øystein Lund Andersen and Brett Carr of the Lamont-Doherty Earth Observatory.

Figure 79. Merapi volcano is located north of Yogyakarta in Central Java. Photo courtesy of Øystein Lund Andersen.

Figure 80. A view of the Gendol drainage where avalanches and block-and-ash flows are channeled from the active Merapi lava dome. The Gendol drainage is approximately 400 m wide at the summit. Courtesy of Brett Carr, Lamont-Doherty Earth Observatory.

At the beginning of April the rate of dome growth was relatively low, with little morphological change since January, but the overall activity of Merapi was considered high. Magma extrusion above the upper Gendol drainage resulted in rockfalls and block-and-ash flows out to 1.5 km from the dome, which were incandescent and visible at night. Five block-and-ash flows were recorded on 24 April, reaching as far as 1.2 km down the Gendol drainage. The volume of the dome was calculated to be 466,000 m3 on 9 April, a slight decrease from the previous week. Weak gas plumes reached a maximum of 500 m above the dome throughout April.

Six block-and-ash flows were generated on 5 May, lasting up to 77 seconds. Throughout May there were no significant changes to the dome morphology but the volume had decreased to 458,000 by 4 May according to drome imagery analysis. Lava extrusion continued above the Gendol drainage, producing rockfalls and small block-and-ash flows out to 1.2 km (figure 81). Gas plumes were observed to reach 400 m above the top of the crater.

Figure 81. An avalanche from the Merapi summit dome on 17 May 2019. The incandescent blocks traveled down to 850 m away from the dome. Courtesy of Sutopo, BNPB.

There were a total of 72 avalanches and block-and-ash flows from 29 January to 1 June, with an average distance of 1 km and a maximum of 2 km down the Gendol drainage. Photographs taken by Øystein Lund Andersen show the morphological change to the lava dome due to the collapse of rock and extruding lava down the Gendol drainage (figures 82 and 83). Block-and-ash flows were recorded on 17 and 20 June to a distance of 1.2 km, and a webcam image showed an incandescent flow on 26 June (figure 84). Throughout June gas plumes reached a maximum of 250 m above the top of the crater

Figure 82. The development of the Merapi summit dome from 2 June 2018 to 17 June 2019. Courtesy of Øystein Lund Andersen.

Figure 83. Photos taken of the Merapi summit lava dome in June 2019. Top: This nighttime time-lapse photograph shows incandescence at the south-facing side of the dome on the 16 June. Middle: A closeup of a small rockfall from the dome on 17 June. Bottom: A gas plume accompanying a small rockfall on 17 June. Courtesy of Øystein Lund Andersen.

Figure 84. Blocks from an incandescent rockfall off the Merapi dome reached out to 1 km down the Gendol drainage on 26 June 2019. Courtesy of MAGMA Indonesia.

Analysis of drone images taken on 4 July gave an updated dome volume of 475,000 m3, a slight increase but with little change in the morphology (figure 85). Block-and-ash flows traveled 1.1 km down the Gendol drainage on 1 July, 1 km on the 13th, and 1.1 km on the 14th, some of which were seen at night as incandescent blocks fell from the dome (figure 86). During the week of 19-25 July there were four recorded block-and-ash flows reaching 1.1 km, and flows traveled out to around 1 km on the 24th, 27th, and 31st. The morphology of the dome continued to be relatively stable due to the extruding lava falling into the Gendol drainage. Gas plumes reached 300 m above the top of the crater during July.

Figure 85. The Merapi dome on 30 July 2019 producing a weak plume. Courtesy of MAGMA Indonesia.

Figure 86. Incandescent rocks from the hot lava dome at the summit of Merapi form rockfalls down the Gendol drainage on 14 July 2019. Courtesy of Øystein Lund Andersen.

During the week of 5-11 August the dome volume was calculated to be 461,000 m3, a slight decrease from the week before with little morphological changes due to the continued lava extrusion collapsing into the Gendol drainage. There were five block-and-ash flows reaching a maximum of 1.2 km during 2-8 August. Two flows were observed on the 13th and 14th reaching 950 m, out to 1.9 km on the 20th and 22nd, and to 550 m on the 24th. There were 16 observed flows that reached 500-1,000 m on 25-27 August, with an additional flow out to 2 km at 1807 on the 27th (figure 87). Gas plumes reached a maximum of 350 m through the month.

Figure 87. An incandescent rockfall from the Merapi dome that reached 2 km down the Gendol drainage on 27 August 2019. Courtesy of BPPTKG.

Brett Carr was conducting field work at Merapi during 12-26 September. During this time the lava extrusion was low (below 1 m3 per second). He observed small rockfalls with blocks a couple of meters in size, traveling about 50-200 m down the drainage every hour or so, producing small plumes as they descended and resulting in incandescence on the dome at night. Small dome collapse events produced block-and-ash flows down the drainage once or twice per day (figure 88) and slightly larger flows just over 1 km long a couple of times per week.

Figure 88. A rockfall on the Merapi dome, towards the Gendol drainage at 0551 on 20 September 2019. Courtesy of Brett Carr, Lamont-Doherty Earth Observatory.

The dome volume was 468,000 m3 by 19 September, a slight increase from the previous calculation but again with little morphological change. Two block-and-ash flows were observed out to 600 m on 9 September and seven occurred on the 9th out to 500-1,100 m. Two occurred on the 14th down to 750-900 m, three occurred on 17, 20, and 21 September to a maximum distance of 1.2 km, and three more out to 1.5 km through the 26th. A VONA (Volcano Observatory Notice for Aviation) was issued on the 22nd due to a small explosion producing an ash plume up to approximately 3.8 km altitude (about 800 m above the summit) and minor ashfall to 15 km SW. This was followed by a block-and-ash flow reaching as far as 1.2 km and lasting for 125 seconds (figure 89). Preceding the explosion there was an increase in temperature at several locations on the dome. Weak gas plumes were observed up to 100 m above the crater throughout the month.

Figure 89. An explosion at Merapi on 22 September 2019 was followed by a block-and-ash flow that reached 1.2 km down the Gendol drainage. Courtesy of BPPTKG.

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

Information Contacts: Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG), Center for Research and Development of Geological Disaster Technology (URL: http://merapi.bgl.esdm.go.id/, Twitter: @BPPTKG); Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/, Twitter: https://twitter.com/BNPB_Indonesia); Øystein Lund Andersen? (Twitter: @OysteinLAnderse, URL: http://www.oysteinlundandersen.com); Sutopo Purwo Nugroho, BNPB (Twitter: @Sutopo_PN, URL: https://twitter.com/Sutopo_PN); Brett Carr, Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY, USA (URL: https://www.ldeo.columbia.edu/user/bcarr).

Manam is a frequently active volcano forming an island approximately 10 km wide, located 13 km north of the main island of Papua New Guinea. At the summit are the Main Crater and South Crater, with four valleys down the NE, SE, SW, and NW flanks (figure 57). Recent activity has occurred at both summit craters and has included gas and ash plumes, lava flows, and pyroclastic flows. Activity in December 2018 prompted the evacuation of nearby villages and the last reported activity for 2018 was ashfall on 8 December. Activity from January through September 2019 summarized below is based on information from the Rabaul Volcano Observatory (RVO), the Darwin Volcanic Ash Advisory Center (VAAC), the University of Hawai'i's MODVOLC thermal alert system, Sentinel-5P/TROPOMI and NASA Aqua/AIRS SO₂ data, MIROVA thermal data, Sentinel-2 satellite images, and observations by visiting scientists. A significant eruption in June resulted in evacuations, airport closure, and damage to local crops and infrastructure.

Figure 57. A PlanetScope image of Manam showing the two active craters with a plume emanating from the South Crater and the four valleys at the summit on 29 August 2019. Image copyright 2019 Planet Labs, Inc.

Activity during January-May 2019. Several explosive eruptions occurred during January 2019 according to Darwin VAAC reports, including an ash plume that rose to around 15 km and dispersed to the W on the 7th. RVO reported that an increase in seismic activity triggered the warning system shortly before the eruption commenced (figure 58). Small explosions were observed through to the next day with ongoing activity from the Main Crater and a lava flow in the NE valley observed from around 0400. Intermittent explosions ejected scoria after 0600, depositing ejecta up to 2 cm in diameter in two villages on the SE side of the island. Incandescence at both summit craters and hot deposits at the terminus of the NE valley are visible in Sentinel-2 TIR data acquired on the 10th (figure 59).

Figure 58. Real-Time Seismic-Amplitude Measurement graph representing seismicity at Manam over 7-9 January 2019, showing the increase during the 7-8 January event. Courtesy of RVO.

Figure 59. Sentinel-2 thermal infrared (TIR) imagery shows incandescence in the two Manam summit craters and at the terminus of the NE valley near the shoreline on 10 January 2019. Courtesy of Sentinel-Hub Playground.

Another explosion generated an ash plume to around 15 km on the 11th that dispersed to the SW. An explosive eruption occurred around 4 pm on the 23rd with the Darwin VAAC reporting an ash plume to around 16.5 km altitude, dispersing to the E. Activity continued into the following day, with satellites detecting SO₂ plumes on both 23 and 24 January (figure 60). Activity declined by February with one ash plume reported up to 4.9 km altitude on 15 February.

Figure 60. SO2 plumes originating from Manam detected by NASA Aqua/AIRS (top) on 23 January 2019 and by Sentinel-5P/TROPOMI on 24 January (bottom). Images courtesy of Simon Carn, Michigan Technological University.

Ash plumes rose up to 3 km between 1 and 5 March, and dispersed to the SE, ESE, and E. During 5-6 March the plumes moved E, and the events were accompanied by elevated seismicity and significant thermal anomalies detected in satellite data. During 19-22 March explosions produced ash plumes up to 4.6 km altitude, which dispersed to the E and SE. Simon Carn of the Michigan Technological University noted a plume in Aqua/AIRS data at around 15 km altitude at 0400 UTC on 23 January with approximately 13 kt measured, similar to other recent eruptions. Additional ash plumes were detected on 29 March, reaching 2.4-3 km and drifting to the E, NE, and N. Multiple SO₂ plumes were detected throughout April (figure 61).

Figure 61. Examples of elevated SO2 (sulfur dioxide) emissions from Manam during April 2019, on 9 April (top left), 21 April (top right), 22 April (bottom left), 28 April (bottom right). Courtesy of the NASA Space Goddard Flight Center.

During 19-28 May the Deep Carbon Observatory ABOVE (Aerial-based Observations of Volcanic Emissions) scientific team observed activity at Manam and collected gas data using drone technology. They recorded degassing from the South Crater and Main Crater (figure 63 and 64), which was also detected in Sentinel-5P/TROPOMI data (figure 65). Later in the day the plumes rose vertically up to 3-4 km above sea level and appeared stronger due to condensation. Incandescence was observed each night at the South Crater (figure 66). The Darwin VAAC reported an ash plume on 10 May, reaching 5.5 km altitude and drifting to the NE. Smaller plumes up to 2.4 km were noted on the 11th.

Figure 62. Degassing plumes from the South Crater of Manam, seen from Baliau village on the northern coast on 24 May 2019. Courtesy of Emma Liu, University College London.

Figure 63. A strong gas-and-steam plume from Manam was observed moving tens of kilometers downwind on 19 May 2019, viewed here form the SSW at dusk. Photo courtesy of Julian Rüdiger, Johannes Gutenberg University Mainz.

Figure 64. Sentinel-5P/TROPOMI SO2 data acquired on 22 May 2019 during the field observations of the Deep Carbon Observatory ABOVE team. Image courtesy of Simon Carn, Michigan Technological University.

Figure 65. Incandescence at the South Crater of Manam was visible during 19-21 May 2019 from the Baliau village on the northern coast of the island. Photos courtesy of Tobias Fischer, University of New Mexico (top) and Matthew Wordell (bottom).

Activity during June 2019. Ash plumes rose to 4.3 km and drifted SW on 7-8 June, and up to 3-3.7 km and towards the E and NE on 18 June. Sentinel-2 thermal satellite data show hot material around the Main Crater on 24 June (figure 66). On 27 June RVO reported that RSAM (Real-time Seismic Amplitude Measurement, a measure of seismic activity through time) increased from 540 to over 1,400 in 30 minutes. "Thundering noise" was noted by locals at around 0100 on the 28th. An ash plume drifting SW was visible in satellite images acquired after 0620, coinciding with reported sightings by nearby residents (figure 67). The Darwin VAAC noted that by 0910 the ash plume had reached 15.2 km altitude and was drifting SW. When seen in satellite imagery at 1700 that day the large ash plume had detached and remained visible extending SW. There were 267 lightning strokes detected within 75 km during the event (figure 68) and pyroclastic flows were generated down the NE and W flanks. At 0745 on 29 June an ash plume reached up to 4.8 km.

Villages including Dugulava, Yassa, Budua, Madauri, Waia, Dangale, and Bokure were impacted by ashfall and approximately 3,775 people had evacuated to care centers. Homes and crops were reportedly damaged due to falling ash and scoria. Flights through Madang airport were also disrupted due to the ash until they resumed on the 30th. The Office of the Resident Coordinator in Papua New Guinea reported that as many as 455 homes and gardens were destroyed. Humanitarian resources were strained due to another significant eruption at nearby Ulawun that began on 26 June.

Figure 66. Sentinel-2 thermal satellite data show hot material around the Main Crater and a plume dispersing SE through light cloud cover on 24 June 2019. Courtesy of Sentinel Hub Playground.

Figure 67. Himawari-8 satellite image showing the ash plume rising above Manam and drifting SW at 0840 on 28 June. Satellite image courtesy of NCIT ScienceCloud.

Figure 68. There were 267 lightning strokes detected within 75 km of Manam between 0729 on 27 June and 0100 on 29 June 2019. Sixty of these occurred within the final two hours of this observation period, reflecting increased activity. Red dots are cloud to ground lightning strokes and black dots are in-cloud strokes. Courtesy of Chris Vagasky, Vaisala Inc.

Activity during July-September 2019. Activity was reduced through July and September. The Darwin VAAC reported an ash plume to approximately 6 km altitude on 6 July that drifted W and NW, another plume that day to 3.7 km that drifted N, and a plume on the 21st that rose to 4.3 km and drifted SW and W. Diffuse plumes rose to 2.4-2.7 km and drifted towards the W on 29 September. Thermal anomalies in the South Crater persisted through September.

Fresh deposits from recent events are visible in satellite deposits, notably in the NE after the January activity (figure 69). Satellite TIR data reflected elevated activity with increased energy detected in March and June-July in MODVOLC and MIROVA data (figure 70).

Figure 69. Sentinel-2 thermal infrared images acquired on 12 October 2018, 20 May 2019, and 12 September 2019 show the eruption deposits that accumulated during this time. A thermal anomaly is visible in the South Crater in the May and September images. Courtesy of Sentinel Hub Playground.

Figure 70. MIROVA log radiative power plot of MODIS thermal infrared at Manam during February through September 2019. Increases in activity were detected in March and June-July. Courtesy of MIROVA.

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

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; 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); 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/); Office of the Resident Coordinator, United Nations, Port Moresby, National Capital District, Papua New Guinea (URL: https://papuanewguinea.un.org/en/about/about-the-resident-coordinator-office, https://reliefweb.int/report/papua-new-guinea/papua-new-guinea-volcanic-activity-office-resident-coordinator-flash-2); Himawari-8 Real-time Web, developed by the NICT Science Cloud project in NICT (National Institute of Information and Communications Technology), Japan, in collaboration with JMA (Japan Meteorological Agency) and CEReS (Center of Environmental Remote Sensing, Chiba University) (URL: https://himawari8.nict.go.jp/); Simon Carn, Geological and Mining Engineering and Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931, USA (URL: http://www.volcarno.com/, Twitter: @simoncarn); Chris Vagasky, Vaisala Inc., Louisville, Colorado, USA (URL: https://www.vaisala.com/en?type=1, Twitter: @COweatherman, URL: https://twitter.com/COweatherman); Emma Liu, University College London Earth Sciences, London WC1E 6BS (URL: https://www.ucl.ac.uk/earth-sciences/people/academic/dr-emma-liu); Matthew Wordell, Boise, ID, USA (URL: https://www.matthhew.com/biocontact); Julian Rüdiger, Johannes Gutenberg University Mainz, Saarstr. 21, 55122 Mainz, Germany (URL: https://www.uni-mainz.de/).

Tangkuban is located in the West Bandung and Subang Regencies in the West Java Province and has two main summit craters, Ratu and Upas (figure 3). Recent activity has largely consisted of phreatic explosions and gas-and-steam plumes at the Ratu crater. Prior to July 2019, the most recent activity occurred in 2012-2013, ending with a phreatic eruption on 5 October 2013 (BGVN 40:04). Background activity includes geothermal activity in the Ratu crater consisting of gas and steam emission (figure 4). This area is a tourist destination with infrastructure, and often people, overlooking the active crater. This report summarizes activity during 2014 through September 2019 and is based on official agency reports. Monitoring is the responsibility of Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM).

Figure 3. Map of Tangkuban Parahu showing the Sunda Caldera rim and the Ratu, Upas, and Domas craters. Basemap is the August 2019 mosaic, copyright 2019 Planet Labs, Inc.

Figure 4. Background activity at the Ratu crater of Tangkuban Parahu is shown in these images from 1 May 2012. The top image is an overview of the crater and the bottom four images show typical geothermal activity. Copyrighted photos by Øystein Lund Andersen, used with permission.

The first reported activity in 2014 consisted of gas-and-steam plumes during October-December, prompting PVMBG to increase the alert level from I to II on 31 December 2014. These white plumes reached a maximum of 50 m above the Ratu crater (figure 5) and were accompanied by elevated seismicity and deformation. This prompted the implementation of an exclusion zone with a radius of 1.5 km around the crater. The activity decreased and the alert level was lowered back to I on 8 January 2015. There was no further reported activity from January 2015 through mid-2019.

Figure 5. Changes at the Ratu crater of Tangkuban Parahu during 25 December 2014 to 8 January 2015. Rain water accumulated in the crater in December and intermittent gas-and-steam plumes were observed. Courtesy of PVMBG (8 January 2015 report).

From 27 June 2019 an increase in activity was recorded in seismicity, deformation, gas chemistry, and visual observations. By 24 July the responsible government agencies had communicated that the volcano could erupt at any time. At 1548 on 26 July a phreatic (steam-driven) explosion ejected an ash plume that reached 200 m; a steam-rich plume rose to 600 m above the Ratu crater (figures 6, and 7). People were on the crater rim at the time and videos show a white plume rising from the crater followed by rapid jets of ash and sediment erupting through the first plume. Deposition of eruption material was 5-7 cm thick and concentrated within a 500 m radius from the point between the Rata and Upas craters, and wider deposition occurred within 2 km of the crater (figures 8 and 9). According to seismic data, the eruption lasted around 5 minutes and 30 seconds (figure 10). Videos show several pulses of ash that fell back into the crater, followed by an ash plume moving laterally towards the viewers.

Figure 6. These screenshots are from a video taken from the Ratu crater rim at Tangkuban Parahu on 26 July 2019. Initially there is a white gas-and-steam plume rising from the crater, then a high-velocity black jet of ash and sediment rises through the plume. This video was widely shared across multiple social media platforms, but the original source could not be identified.

Figure 7. The ash plume at Tangkuban Parahu on 26 July 2019. Courtesy of BNPB.

Figure 8. Volcanic ash and lapilli was deposited around the Ratu crater of Tangkuban Parahu during a phreatic eruption on 26 July 2019. Note that the deposits have slumped down the window and are thicker than the actual ashfall. Courtesy of BNPB.

Figure 9. Ash was deposited on buildings that line the Ratu crater at Tangkuban Parahu during a phreatic eruption on 26 July 2019. Photo courtesy of Novrian Arbi/via Reuters.

Figure 10. A seismogram showing the onset of the 26 July 2019 eruption of Tangkuban Parahu and the elevated seismicity following the event. Courtesy of PVMBG via Øystein Lund Andersen.

On 27 July, the day after the eruption, Øystein Lund Andersen observed the volcano using a drone camera, operated from outside the restricted zone. Over a period of two hours the crater produced a small steam plume; ashfall and small blocks from the initial eruption are visible in and around the crater (figure 11). The ashfall is also visible in satellite imagery, which shows that deposition was restricted to the immediate vicinity to the SW of the crater (figure 12).

Figure 11. Photos of the Ratu crater of Tangkuban Parahu on 27 July 2019, the day after a phreatic eruption. A small steam plume continued through the day. Courtesy of Øystein Lund Andersen.

Figure 12. PlanetScope satellite images showing the Ratu crater of Tangkuban Parahu before (17 July 2019) and after (28 July 2019) the explosion that took place on 26 July 2019. Natural color PlanetScope Imagery, copyright 2019 Planet Labs, Inc.

Another eruption occurred at 2046 on 1 August 2019 and lasted around 11 minutes, producing a plume up to 180 m above the vent. Additional explosions occurred at 0043 on 2 August, lasting around 3 minutes according to seismic data, but were not observed. Explosions continued to be recorded at 0145, 0357, and 0406 at the time of the PVMBG report when the last explosion was ongoing, and a photo shows an explosion at 0608 (figure 13). The explosions produced plumes that reached between 20 and 200 m above the vent. Due to elevated activity the Alert Level was increased to II on 2 August. Ash emission continued through the 4th. During 5-11 August events ejecting ash continued to produce plumes up to 80 m, and gas-and-steam plumes up to 200 m above the vent. Ashfall was localized around Ratu crater. The following week, 12-18 August, activity continued with ash and gas-and-steam plumes reaching 100-200 m above the vent. During 19-25 August, similar activity sent ash to 50-180 m, and gas-and-steam plumes to 200 m. A larger phreatic explosion occurred at 0930 on 31 August with an ash plume reaching 300 m, and a gas-and-steam plume reaching 600 m above the vent, depositing ash and sediment around the crater.

Figure 13. A small ash plume below a white gas-and-steam plume erupting from the Ratu crater of Tangkuban Parahu on 2 August 2019 at 0608. Courtesy of PVBMG (2 August 2019 report).

In early September activity consisted of gas-and-steam plumes up to 100-180 m above the vent with some ash plumes observed (figure 14). Two larger explosions occurred at 1657 and 1709 on 7 September with ash reaching 180 m, and gas-and-steam up to 200 m above the vent. Ash and sediment deposited around the crater. Due to strong winds to the SSW, the smell of sulfur was reported around Cimahi City in West Bandung, although there was no detected increase in sulfur emissions. A phreatic explosion on 17 September produced an ash plume to 40 m and a steam plume to 200 m above the crater. Weak gas-and-steam emissions reaching 200 m above the vent continued through to the end of September.

Figure 14. A phreatic explosion at Tangkuban Parahu in the Ratu crater at 0724 on 4 September 2019, lasting nearly one minute. The darker ash plume reached around 100 m above the vent. Courtesy of PVGHM (4 September 2019 report).

Geologic Background. Gunung Tangkuban Parahu is a broad shield-like stratovolcano overlooking Indonesia's former capital city of Bandung. The volcano was constructed within the 6 x 8 km Pleistocene Sunda caldera, which formed about 190,000 years ago. The volcano's low profile is the subject of legends referring to the mountain of the "upturned boat." The Sunda caldera rim forms a prominent ridge on the western side; elsewhere the rim is largely buried by deposits of the current volcano. The dominantly small phreatic eruptions recorded since the 19th century have originated from several nested craters within an elliptical 1 x 1.5 km summit depression.

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/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: https://www.oysteinlundandersen.com/tangkuban-prahu/tangkuban-prahu-volcano-west-java-one-day-after-the-26th-july-phreatic-eruption/); Reuters (URL: https://www.reuters.com/news/picture/editors-choice-pictures-idUSRTX71F3E).

After a lull in activity at Sheveluch, levels intensified again in mid-December 2018 and remained high through April 2019, with lava dome growth, strong explosions that produced ash plumes, incandescent lava flows, hot avalanches, numerous thermal anomalies, and strong fumarolic activity (BGVN 44:05). This report summarizes activity between May and October 2019. The volcano is monitored by the Kamchatka Volcanic Eruptions Response Team (KVERT).

According to KVERT, explosive activity continued to generate ash plumes during May-October 2019 (table 13). Strong fumarolic activity, incandescence and growth of the lava dome, and hot avalanches accompanied this process. There were also reports of plumes caused by re-suspended ash rather than new explosions. Plumes frequently extended a few hundred kilometers downwind, with the longest ones remaining visible in imagery as much as 1,000-1,400 km away. One of the larger explosions, on 1 October (figure 52), also generated a pyroclastic flow. Some of the stronger explosions sent the plume to an altitude of 10-11 km, or more than 7 km above the summit. The Aviation Color Code remained at Orange (the second highest level on a four-color scale) throughout the reporting period, except for several hours on 6 October when it was raised to Red (the highest level).

Table 13. Explosions and ash plumes at Sheveluch during May-October 2019. Dates and times are UTC, not local. Data courtesy of KVERT.

Figure 52. An explosion of Sheveluch on 1 October 2019. A pyroclastic flow was also reported by KVERT this day. Courtesy of Yu. Demyanchuk, IVS FEB RAS, KVERT.

Numerous thermal anomalies, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, were observed every month. Consistent with this, the MIROVA (Middle InfraRed Observation of Volcanic Activity) system recorded thermal anomalies almost daily. According to KVERT, a thermal anomaly over Sheveluch was identified in satellite images during the entire reporting period, although cloudy weather sometimes obscured observations.

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/); 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/).

The southern-most cone at Sakura-jima, Minami-dake, manifested increased eruptivity from late October to early November 1999. Following a lull in the second half of November, vigorous activity in December was marked by incandescent columns, large amounts of bomb ejections, and ballistics falling as far as 4 km from the crater.

High eruptive activity occurred in late October and early November 1999. On 31 October the JMA issued a Volcanic Advisory. In early November, 19 eruptions (including 18 explosions) occurred at Minami-dake before activity declined to lower levels later in the month. Activity increased again in early December with a few explosions each day and small numbers of ballistic clasts falling onto the upper slopes. On the afternoon of 10 December JMA issued another Volcanic Advisory. At 0555 this day, Sakura-jima issued a large amount of bombs. Incandescent columns as high as 100 m were accompanied 116 times by volcanic lightning. According to a JMA field inspection, ballistics were scattered 3-4 km away from the Minami-dake crater; the maximum size was 4 cm across. Incandescent columns rose as high as 300 m at 0554 on 24 December and were accompanied by volcanic lightning six times.

Daily numbers of eruptions ranged from 2 to 8 during early- to mid-December; eruptions were mostly explosive. The maximum amplitude of explosion earthquakes recorded at JMA observation point A, 4.6-km WNW of the crater, reached up to 28 µm; the largest value was caused by an explosion at 1301 on 12 December. The plume heights of December explosions ranged from 1,500 m to 2,000 m. Explosions took place on 23 consecutive days between 3 and 25 December. This is the longest record of daily explosions since JMA started observing Sakura-jima in 1955; the previous record was 21 days in 1960. Explosions began again late in the month, with six more on 31 December.

The total of 88 explosions during December 1999 was the second highest monthly count since 1955; the highest was 93 explosions in June 1974. According to the JMA, the total number of eruptions in 1999 was 386, including 237 explosions.

Frequent explosive eruptions continued in early January (figure 21). Explosions on 2 January sent an eruption column to 2,200 m above the crater rim and emitted abundant cinders, as well as bombs that fell midway down the flanks of the volcano. Nine explosive eruptions occurred on 5 January, one of which again ejected cinders and bombs as far as the middle flank of the volcano. The highest plumes in early January reached 2,200 m above the crater rim during explosions at 0821 on 5 January and at 0746 on 14 January. The maximum amplitude of explosion seismic signals at JMA observation point A (4.6 km WNW of the active crater) was 17 µm for the 0513 explosion on 14 January.

Figure 21. Eruption at Sakura-jima at 0900 on 8 January 2000 from 3.5 km SW of the Minami-dake crater. Courtesy of Tatsuro Chiba.

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

Information Contacts: JMA-Fukuoka, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan; Setsuya Nakada, Volcano Research Center, ERI, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html); Tatsuro Chiba, Nihon University, Japan (URL: http://www.nihon-u.ac.jp/en/).

Eruptive activity continued at Ambrym in late 1999 and through January 2000. A volcanic ash advisory regarding this volcano was issued to aviators on 1 November 1999 reporting "smoke and ash" rising to ~1,500 m altitude. Similar notices were issued on 5 and 6 November. [Aviation reports on 9-10 December] described an ash cloud up to 2,700 m altitude.

John Search and Geoff Mackley investigated Ambrym caldera during a 19-28 January 2000 climb. Lava lakes had disappeared from both Benbow and Mbwelesu craters and a new vent had opened inside the previously inactive 1953 crater. A series of earthquakes were registered around Ambrym Island on 27 November 1999. The largest of these was magnitude 7.1. The earthquakes were followed by a month of reduced activity during which there were no reported observations of lava lakes. Landslides were visible in the caldera and ground cracking visible at Benbow, Mbwelesu, and Niri Mbwelesu craters.

Activity at Benbow Crater. Four vents were active inside Benbow. On 19 January a white plume tinged with blue and yellow rose 1,000 m above the crater rim. Twin plumes were visible the next day rising from the S end of the crater at 15 m/s and from the N end of the crater, where they were tinged with brown. Each time the crater was climbed from the S on 22, 23, and 24 January the pit was full of vapor and no sounds were heard. On 25 January the observers lowered themselves into Benbow using 200 m of rope. The floor of the first level was covered with fine brown ash and a shallow brown pond was present in the SW end of the crater. The inner crater was climbed and observations made from its rim. Below the observers was a ledge 120-140 m down covered with ash and containing a 10-m circular vent emitting white vapor. The main vent was 50 m farther down and 40 m in diameter. This was the vent that contained the lava lake in January 1999 (BGVN 24:02). No lava was observed inside this vent and it made no sound. At 1300 a large roar from the vent was followed by brown ash emission. At the NE end of the inner crater was a plume emission from an unseen vent.

The N end of Benbow crater (on the first level) contained another vent that could not be directly observed but regularly emitted light brown ash. On 26 January a loud continuous 30-second degassing heard from the N vent was followed by brown ash emission and rain of small cinders on observers at the S crater edge. From the central pit the vapor was rising at 5 m/s. During the late afternoon two visible atmospheric perturbations were observed above the main vent. The first followed a loud degassing sound and rose at 40 m/s to a height of 200 m above the vent. Rockfalls were also heard during the afternoon. During the night of 26 January twin skyglows of fluctuating intensity were visible above Benbow followed by a large brown ash emission that rose 1,400 m above the crater in 3 minutes.

Activity at Niri Mbwelesu Taten. On both 19 and 20 January light brown or red/brown ash was emitted from the collapse pit and rose 200-250 m. On 21 January a brown pond of water 150 m NE of the pit was bubbling from both fixed and random locations. Active fumaroles were present on a ledge 60 m down. There were large cracks on the SE side and evidence of wall collapse since August 1999. Ash fell on observers in the area N of the pit. On 23 January larger ash emissions occurred about every hour.

On 24 January the collapse pit was entered using ropes. Fumaroles on the ledge 60 m down averaged 64°C. The pit bottom was 120-140 m below the ledge covered in brown ash. Small clouds of ash were emitted occasionally from two large fissures. Bubbles of hot blue vapors, 6 m in diameter, rose past the observer. Continual degassing sounds were heard in the pit, like the sound of waves crashing on the beach. On 26 January from 0600 to 1100 dark gray ash clouds were continually being emitted from the pit. Plumes rose at 8 m/s to a height of 200 m above the pit, filling the caldera in all directions. During the afternoon the pit returned to a low level of activity. On 27 January a continuous emission of brown ash occurred all day to a height of 800 m above the pit.

Activity at Niri Mbwelesu. On 20 January white vapor tinged with blue was constantly emitted to 600 m above crater. During the evening a very intense pulsating night glow was visible. The glow would brighten (sometimes flicker), then rapidly drop to a lower level of illumination. The bright/dim cycle would repeat every 10-15 seconds. On 21 January in the afternoon degassing was heard from the crater rim and during the evening clouds were illuminated 250 m above the crater. Observers on the crater edge felt hot vapor. When the crater was climbed on the evening of 25 January a clearing of the vapor enabled the bottom to be seen 280 m down. A 40-m-diameter vent was visible emitting bright yellow burning gas, radiant heat was felt on the faces of observers, and moderate degassing was heard.

Activity at Mbwelesu. Observations were made of Mbwelesu crater on 21 January. The two lava lakes observed in August 1999 had disappeared (BGVN 24:08). A brown pond surrounded by fumaroles was in the Vent B location, with large amounts of ash and rock to the SE. The sill on the SE edge of the crater had large craters and several large sections (over 10 m) that had broken off and fallen into the crater. The fumarole field 40 m SE of the crater rim had a temperature of 72.7°C. Heavy rains caused waterfalls and rockfalls inside the crater. The crater was otherwise quiet with some vapor emissions from many fumaroles on the floor. Fumaroles were also present in the location of the former lava lake at Vent C.

Activity in the 1953 Crater. The 1953 crater contained two levels. The higher (W half) contained a brown pond. The lower (E half) had developed a deep smoking vent. This was in the location of the green pond observed in August 1999.

Geologic Background. Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides Arc. A thick, almost exclusively pyroclastic sequence, initially dacitic then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major Plinian eruption with dacitic pyroclastic flows about 1,900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.

Information Contacts: John Seach, PO Box 16, Chatsworth Island, N.S.W. 2469, Australia; Wellington Volcanic Ash Advisory Center (VAAC), MetService, PO Box 722, Wellington, New Zealand (URL: http://www.metservice.co.nz/).

Starting around dawn on 23 December, INETER registered low-amplitude seismic tremor at the seismic station located at the foot of Concepción. The seismic signal grew gradually and every few minutes small earthquakes were observed. Due to the increasing seismicity, at 1315 on 24 December INETER informed Civil Defense in Managua of the activity and recommended taking precautions for volcanic gases, ashfall, and, in the event of rain, for lahars or mudflows.

On the morning of 27 December INETER received reports from Lacsa and Aviateca airlines that their pilots had observed emission of material from Concepción rising ~300 m above the crater. Residents of Moyogalpa (at the W foot of the volcano) confirmed moderate activity. Minor amounts of gas and volcanic ash blew towards Moyogalpa.

INETER specialists conducted fieldwork around the volcano on 28 December and confirmed the occurrence of low-level eruptive activity based on their own observations and descriptions by local residents. Activity was characterized by sporadic gas explosions from the crater that ejected small amounts W-blown ash. The seismic instrumentation indicated constant tremor with rare volcanic earthquakes related to the crater explosions.

The level of seismicity had decreased by the morning of 29 December, and continued to decline through 1000 on the 30th. Although volcanic activity had also diminished, an explosion at 1600 on 29 December caused ashfall as far as San Jorge (also known as Rivas, a town 25 km SW of Concepción).

Some pilot reports received on 27 December also indicated possible activity from the adjacent Maderas volcano, which has no known historical activity. INETER observers were unable to confirm these reports during fieldwork in the area. However, another seismic station was installed on Ometepe Island in the SW zone of Maderas, which should help to confirm or refute any future reports of Maderas activity.

Geologic Background. Volcán Concepción is one of Nicaragua's highest and most active volcanoes. The symmetrical basaltic-to-dacitic stratovolcano forms the NW half of the dumbbell-shaped island of Ometepe in Lake Nicaragua and is connected to neighboring Madera volcano by a narrow isthmus. A steep-walled summit crater is 250 m deep and has a higher western rim. N-S-trending fractures on the flanks have produced chains of spatter cones, cinder cones, lava domes, and maars located on the NW, NE, SE, and southern sides extending in some cases down to Lake Nicaragua. Concepción was constructed above a basement of lake sediments, and the modern cone grew above a largely buried caldera, a small remnant of which forms a break in slope about halfway up the N flank. Frequent explosive eruptions during the past half century have increased the height of the summit significantly above that shown on current topographic maps and have kept the upper part of the volcano unvegetated.

Information Contacts: Wilfried Strauch and Virginia Tenorio, Dirección General de Geofísica, Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado 1761, Managua, Nicaragua (URL: http://www.ineter.gob.ni/).

On 26 February 2000 the WSW-trending, elongated Hekla volcano erupted. A fissure 6-7 km long opened along the SW flank of the Hekla ridge, from which a discontinuous curtain of lava erupted starting at 1819. Just a few minutes later, at 1825, an ash plume reached a height of 11 km and was carried N by light winds. Based on the tremor amplitude the eruption reached peak intensity in the first hour of activity, then gradually declined.

Seismic networks maintained by the Science Institute at the University of Iceland and the Icelandic Meteorological Office recorded short-term precursors. Small earthquakes were first detected by seismographs at various locations during 1655-1707. These gradually increased and the first well-located earthquakes (M 1-2) started at 1729, centered 1-2 km SE of the summit at depths of a few kilometers. A network of borehole strainmeters operated by the Meteorological Office also detected precursory changes associated with magma movements. A decrease in strain build-up rate, signaling a release of magma pressure, was recorded by a strainmeter in a borehole ~15 km from the summit at 1817.

Notice was given to the National Civil Defense and the Civil Aviation Administration about 40 minutes before the eruption, and the public was alerted about the imminent eruption about 15 minutes before it began through national radio broadcasts. Continuous low-frequency tremor began at 1819, at the same time the eruptive cloud was spotted.

Ashfall was reported on 26 February from Grimsey Island, ~70 km off the N coast of Iceland and 300 km N of Hekla. Although small amounts of ash fell in inhabited areas of N Iceland, most fell in uninhabited areas of the island's interior. Seven hours after the eruption's onset the ash deposit 21 km N had a maximum thickness of 4-5 cm.

Lava flows on 27 February covered a large part of the SE flank. That evening a lava stream flowed N from the erupting fissure at a rate of several meters per hour. Another more active lava stream emanated from three craters near the S end of the fissure; the stream was several kilometers long and advancing at ~1 m/minute.

On 28 February an eruption cloud was deflected towards the S by northerly winds. However weather conditions precluded direct observations. Tremor amplitude continued to slowly decline, and the strength of the eruption was decreasing (figure 1). Two eruption clouds were seen at 0500, confirming that activity was ongoing. Although the craters were not visible in the daylight, the most active crater just S of the summit produced three lava streams down the S flanks. Activity in the N declined during the day on 28 February. At 0630 one lava flow had reached the Vatnafjoll mountains at Lambafell, 5 km S of the summit. Advancing at ~2-3 m/hour, the lava front was estimated to be 8-10 m wide. That evening observers watched Strombolian activity in three craters at the southernmost part of the fissure.

Figure 1. Tremor at Hekla during 26-28 February 2000 recorded at Haukadalur, 10 km W. At the beginning of the eruption, 1819 on 26 February, the tremor increased rapidly and reached a maximum at 1850. Tremor then decreased until about 0700 on 27 February and became steady. The tremor was approximately 10 % of the maximum value, on 28 February, but over 10 times greater than the normal value. Courtesy of Páll Halldórsson, Science Institute at the University of Iceland.

Ashfall was reported on the morning of 29 February 35-40 km S in Fljótshlíð. At 0500 volcanic tremor had started to increase and continued until 1000-1100. By about 0800 all activity in the summit had ceased. During the afternoon of 29 February activity at the southernmost end of the fissure increased again, producing eruption clouds ascending above the summit. In the darkness of the evening, three craters at the southernmost end of the fissure produced lava flowing SW. People watching the lava on the NE flanks reported that they could walk on the stopped flow there.

Vigorous Strombolian eruptions and lava flows on the fissure that cuts the SW slopes were seen during a reconnaissance flight on 1 March during 1100-1230. Four main vents and three smaller vents produced explosions at intervals of 4-5 minutes. At the base of the fissure a large tumuli had developed. The lava streams coming out through the opening of the tumuli joined a stream coming from overflows of the uppermost craters. The S-directed lava flows were fed by the crater closest to the summit. The lava field in the S had only advanced ~100 m since 28 February, but on 1 March it was growing toward the E. By 1 March lava had covered approximately 17 km².

Increased activity was observed in the upper craters on 2 March, although bad weather persisted from 1200 on 1 March until midday on 3 March. There was also constant steaming from the SW craters, and, compared to 1 March, much larger steam clouds rising from the upper craters. At nightfall explosions were observed at ~30-minute intervals. Glowing lava streams were noted on the flank of the mountain on 2 March.

On 3 March a group of scientists reached the SW lava flow at 1300 and found that the lava front was ~10 m wide and advancing very slowly, ~1-2 m/day. While tracing the lava to the W the group noted that at some places the flow was spreading much faster, up to ~1 m/hour. Following the lava flow along its W side, the group reached its origin at the foot of the volcano, where it emerged from the end of the erupting fissure. At the origin, the estimated flow rate was 0.06 m/s, producing about 10 m³/s of lava. Due to the continuous degassing along the lava stream a blue mist was formed. The blue mist was also observed farther E along the flank of the volcano, indicating that lava was still flowing from the crater close to the summit area. The craters in this region fed the lava flow that moved S toward the Vatnafjoll glacier 10 km SE from Hekla. Later in the evening observers reported that lava was still flowing slowly towards Vatnafjoll. Explosive activity in the uppermost crater of the SW-fissure was characterized by small explosions at 10-20 minute intervals that produced white steam clouds with only trace amounts of ash.

Due to bad weather conditions on 4 March, no direct observations could be made of the eruption. Decreasing eruption tremor was detected. On 5 March the lava flow to the SW was still ongoing according to observations made in the afternoon. At sunset, a red pulsing glow was observed in the uppermost craters of the SW-fissure from the town of Selsundsfjall, 15 km SW. Small eruption clouds were observed on 6 March penetrating the weather clouds covering the summit of Hekla.

During a reconnaissance flight between 1730 and 1830 on 6 March the whole fissure was steaming vigorously and all of the lava flows appeared to have stopped. The lava stream in the SW had left behind an empty channel. Neither incandescence nor explosive activity were observed from the craters. Minor tremors continued on 6-7 March, but may have been related to lava degassing in the feeder dike.

At 0844 on 8 March the last eruptive tremor was detected on seismometers. Based on the end of detectable tremor, and with no signs of new eruptive products since 5 March, it was determined that the eruption ended on the morning of 8 March. Lava covered approximately 18 km²; the preliminary estimate of lava production was 0.11 km³.

Plume investigation. Sulfur dioxide (SO₂) contained in plumes from Hekla was detected by the Earth Probe TOMS (Total Ozone Mapping Spectrometer) instrument. TOMS imagery at 1154 on 27 February showed that the volcanic cloud was a narrow plume arcing from the volcano in southern Iceland, then N to Greenland, and finally E towards Norway. The plume primarily contained SO₂ because almost all of the ash fell out locally. On 28 February the TOMS imagery indicated that plume stretched out over the Barents Sea and possibly into eastern Russia. By 29 February the SO₂ cloud had drifted E in a band along the Norwegian and Russian coasts of the Barents Sea.

During a transit flight on 28 February a SOLVE (SAGE III Ozone Loss and Validation Experiment) mission with an instrument-laden DC-8 aircraft flew through the plume shortly after the eruption ~11.3 km NNE of Iceland at 76°N and 5°W, just off the Greenland coastline. The plume extended up to ~13 km altitude, well into the lower stratosphere. Instruments also measured many in situ trace gases, SO₂, HNO₃, NO, NOy, O₃, and aerosols (volatile and non-volatile), including their size distribution. From about 0508 until 0518 on 29 February the SOLVE aircraft again entered the volcanic cloud. The scientific team reported large enhancements in CN, NOy, HNO₃, CO, and particle counts, ozone went to nearly zero, H₂O jumped up, and there were strong scattering layers up to 13 km. The plume was a very impressive, orange, airfoil-shaped feature in the pre-dawn sky. The DC-8 engines needed an oil change and new filters after passing through the plume. A flight on 5 March detected enhanced aerosols and SO₂ at 1301, but by that time the plume was so diluted that it represented no danger to the aircraft. During the three weeks following the initial encounter the DC-8 detected remnants of the plume trapped within the polar vortex. The resulting analysis concluded that volatile aerosols increased and the sizes of non-volatile large aerosols decreased.

Fluoride analysis. Ash from previous Hekla eruptions has often been the cause of fluorosis in grazing animals. However, during this time of the year most domestic animals are kept indoors, so fluorosis is not expected to become a problem. Freshly fallen ash was measured for soluble fluoride ions (F-). The result was 800-900 mg F/kg. Snow melted by the ash contained about 2,200 mg/l (ppm) of fluoride.

Geologic Background. One of Iceland's most prominent and active volcanoes, Hekla lies near the southern end of the eastern rift zone. Hekla occupies a rift-transform junction, and has produced basaltic andesites, in contrast to the tholeiitic basalts typical of Icelandic rift zone volcanoes. Vatnafjöll, a 40-km-long, 9-km-wide group of basaltic fissures and crater rows immediately SE of Hekla forms a part of the Hekla-Vatnafjöll volcanic system. A 5.5-km-long fissure, Heklugjá, cuts across the 1491-m-high Hekla volcano and is often active along its full length during major eruptions. Repeated eruptions along this rift, which is oblique to most rifting structures in the eastern volcanic zone, are responsible for Hekla's elongated ENE-WSW profile. Frequent large silicic explosive eruptions during historical time have deposited tephra throughout Iceland, providing valuable time markers used to date eruptions from other Icelandic volcanoes. Hekla tephras are generally rich in fluorine and are consequently very hazardous to grazing animals. Extensive lava flows from historical eruptions, which date back to 1104 CE, cover much of the volcano's flanks.

Information Contacts: Freysteinn Sigmundsson, Nordic Volcanological Institute, Grensásvegur 50, IS-108 Reykjavik, Iceland (URL: http://nordvulk.hi.is); Páll Einarsson, Science Institute, University of Iceland, Hofsvallagata 53, IS-107 Reykjavík, Iceland; Ragnar Stefánsson, Icelandic Meteorological Office, Bustadavegur 9, 150 Reykjavík, Iceland (URL: http://www.vedur.is/); Mark Schoeberl, Code 910, NASA/GSFC, Greenbelt, MD, 20771 USA; Michael Fromm, Computational Physics, Inc., 2750 Prosperity Ave., Suite 600, Fairfax, VA 22031 USA (URL: http://cloud1.arc.nasa.gov/solve/); Arlin Krueger, Code 916, NASA/GSFC, Greenbelt, MD, 20771 USA.

At 1800 on 18 October 1999, the National Coordination Committee for Prediction of Volcanic Eruptions reported that the volcano's fumarolic area had expanded and the amount of steam had increased in the western part of Iwate volcano. New fumaroles have been observed since May on the N slopes of Mts. Ubakura-yama and Kurokura-yama and in the western stream of Ojigokudani (inside the erosion caldera). This fumarolic activity has intermittently increased since July, and ground temperatures between Mts. Kurokura-yama and Ubakura-yama also increased with time. Analyses of fumarolic gas collected between Ojigokudani and Mt. Ubakura-yama in August and October revealed a magmatic component. Although GPS measurements showed the end of the elongation trend observed since July, relatively large volcanic earthquakes occurred during May and June. Deep-seated (~30 km depth) low-frequency earthquakes, relatively deep-seated (6-13 km depth) low-frequency earthquakes, and shallow high-frequency earthquakes occurred under the eastern cone of Iwate. However, the overall level of seismicity has decreased compared to 1998 (figure 5).

Figure 5. Daily numbers of earthquakes at Iwate (recorded at the Matsukawa station) during 1 January 1998-13 November 1999. Courtesy of JMA.

On the evening of 12 November JMA issued a Volcano Advisory on Iwate after a 4-minute volcanic tremor (M 2.1) saturated local instruments starting at 2054. The event hypocenter was located 2-3 km below the Ubakura-yama and Kurokura-yama areas of western Iwate (figure 6). An earthquake swarm continued for 2 hours after the tremor event at a rate of 16-20 events/hour. Inspection from the air the following day did not show any major change in fumarolic activity or any deposition of new volcanic ash.

Figure 6. Hypocenters of earthquakes under the western section of Iwate during 11-12 November 1999. Courtesy of JMA.

On the evening of 16 November, the extended National Coordination Committee for Prediction of Volcanic Eruptions met in the city of Morioka, Iwate Prefecture, to review the events that occurred on the 12th. They noted that the tremor was similar in shape, amplitude, and duration to one (M 2.4) that occurred on 10 July 1999; hence it was considered likely that the two events occurred in the same place. Changes detected in tilt- and strain-meters located on the flank during the tremor were probably caused by subsurface ground faulting or fluid movement. After the tremor, however, no subsequent changes were observed. Neither the GPS-based, N-S traverse distance across the volcano nor the fumarole temperatures in the Ubakura-yama to Kurokura-yama region changed before or after the event. Fumarolic activity in western Iwate had increased since May as had the number of shallow earthquakes in the Ojigokudani area (erosion caldera). The tremor event on 12 November suggested a continuing possibility of a phreatic explosions in western Iwate.

Geologic Background. Viewed from the east, Iwatesan volcano has a symmetrical profile that invites comparison with Fuji, but on the west an older cone is visible containing an oval-shaped, 1.8 x 3 km caldera. After the growth of Nishi-Iwate volcano beginning about 700,000 years ago, activity migrated eastward to form Higashi-Iwate volcano. Iwate has collapsed seven times during the past 230,000 years, most recently between 739 and 1615 CE. The dominantly basaltic summit cone of Higashi-Iwate volcano, Yakushidake, is truncated by a 500-m-wide crater. It rises well above and buries the eastern rim of the caldera, which is breached by a narrow gorge on the NW. A central cone containing a 500-m-wide crater partially filled by a lake is located in the center of the oval-shaped caldera. A young lava flow from Yakushidake descended into the caldera, and a fresh-looking lava flow from the 1732 eruption traveled down the NE flank.

Information Contacts: Kazuo Sekine, Sendai District Meteorological Observatory, Japan Meteorological Agency, 1-3-15 Gorin, Miyagino-ku, Sendai 983, Japan; Hiroyuki Hamaguchi, Faculty of Science, Tohoku University, Sendai 980-8578 Japan (URL: http://www.sci.tohoku.ac.jp/); Setsuya Nakada, Volcano Research Center, ERI, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html); Jun-ichi Hirabayashi, Kusatsu-Shirane Volcano Observatory, Tokyo Institute of Technology, Kusatsu, Agatsuma-gun, Gunma 377-17 Japan.

A Volcanic Advisory on Kirishima volcano (figure 4) was issued on 10 November 1999 by the Japan Meteorological Agency (JMA) after seismicity began increasing on 6 November. This is the first advisory at Kirishima since 27 August 1995 (BGVN 20:08 and 20:09). Earthquakes detected at a site 1.7 km SW of Shinmoe-dake totaled 666 during 6-15 November (table 1), peaking at 192 events on the 10th. No volcanic tremor was observed.

Figure 4. Steam from Shinmoe-dake at Kirishima looking towards the SE in 1991. Naka-dake is the adjacent cone with a flat top, and in the background is Ohachi (crater to the right), Takachiho-no-mine (the highest peak in the center), and Futatsuishi (left). Courtesy of T. Kagiyama, ERI.

Table 1. Daily numbers of volcanic earthquake events at Kirishima, 5-15 November 1999. Courtesy of JMA.

Geologic Background. Kirishimayama is a large group of more than 20 Quaternary volcanoes located north of Kagoshima Bay. The late-Pleistocene to Holocene dominantly andesitic group consists of stratovolcanoes, pyroclastic cones, maars, and underlying shield volcanoes located over an area of 20 x 30 km. The larger stratovolcanoes are scattered throughout the field, with the centrally located Karakunidake being the highest. Onamiike and Miike, the two largest maars, are located SW of Karakunidake and at its far eastern end, respectively. Holocene eruptions have been concentrated along an E-W line of vents from Miike to Ohachi, and at Shinmoedake to the NE. Frequent small-to-moderate explosive eruptions have been recorded since the 8th century.

Information Contacts: JMA-Fukuoka, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan; Setsuya Nakada and Tsuneomi Kagiyama, Volcano Research Center, Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html).

Volcanic unrest that began in May 1999, and intermittent explosive eruptions beginning in June 1999, eventually led to growth of a lava dome on 12 February 2000. By 23 February PHIVOLCS had recommended evacuation to 7 km from the summit in the SE and to 6 km for the rest of the volcano. The latter is a permanent danger zone.

At 2206 on 23 February the seismic network detected an explosion-type earthquake that coincided with rumbling and minor ejection of lava fragments from the summit. This earthquake was followed shortly by bright incandescence, indicating that lava emission and ejection had intensified. Low-frequency volcanic earthquakes then occurred beginning at 2217 and lasting until about 2326 when the seismographs began to record harmonic tremor. The tremor became pronounced at about 0034 on 24 February and was accompanied by minor lava fountaining to 50 m above the summit lava dome. The hazard status was raised to Alert Level 4 (hazardous eruption imminent, possible within days) at 0300 on 24 February. No additional evacuation was recommended, but residents within 8 km of the summit were advised to prepare for evacuation.

At 0826 on 24 February another explosion-type earthquake was recorded by the seismographs at Anoling, Sta. Misericordia, and Mayon Resthouse Observatory. The summit was obscured, but at 0829 a pyroclastic flow descended SE towards the Bonga Gully with a run-out distance of ~7.2 km, reaching the distal end of the Bonga fan. The hazard status was then raised to Alert Level 5, (hazardous eruption in progress). Because pyroclastic flows could continue to sweep down along well-incised gullies and channels, especially the Bonga Gully, PHIVOLCS recommended extension of the danger zone to 8 km along the SE sector of Mayon Volcano. Likewise, ashfall was expected mainly W, SW, and NW of the crater.

The SO₂ emission rate increased on 24 February to 4,070-5,700 metric tons/day (t/d). Ground deformation measurements showed that the volcanic edifice swelled significantly in the previous two days, consistent with the growth of the lava dome.

By the morning of 25 February activity was mainly lava extrusion, with a flow channeled along the Bonga Gully. COSPEC readings conducted on 24 February reached 13,500 t/d. The abrupt increase in this value may be attributed to the series of highly gas-charged ash ejections comprising the volcanic plume.

Following a quiet interval that started at 1420 on 26 February, more vigorous activity resumed on the evening of the 27th. Seven ash-and-gas explosions occurred between 1950 and 2237, the most significant of which (at 2144 and 2237) were accompanied by lava fountaining with ejection of volcanic bombs. Large incandescent fragments were ejected to ~500 m above the crater rim. Ground deformation measurements showed that the edifice remained inflated. COSPEC readings of SO₂ flux remained significantly above normal at 4,900 t/d. Explosion earthquakes and harmonic tremor accompanied the lava fountaining and persisted even when the activity had apparently subsided.

Explosive eruptions during 28 February-1 March. Mayon had another series of explosive eruptions during 0700 to 2100 on 28 February, with the most significant eruptions occurring at 1641, 1732, and 1940. The first explosion produced a 5-6-km-high eruption column and generated a large pyroclastic flow that descended the W portion of the Bonga Gully on the SE flank and entered the Mabinit channel to the S. This was followed by voluminous eruption clouds beginning at 1732 that rose to ~10 km above the summit and generated multiple pyroclastic flows to the SW, S, and SE. Vigorous explosions sustained the eruption column and discharged large volcanic fragments that splattered the upper portions of the cone. Thick ash clouds hovered around the volcano and created frequent lightning discharges.

Most of the ash clouds were eventually carried to the SW and W, affecting Ligao, Guinobatan, and Camalig. However, the pyroclastic flows did not travel beyond the present danger zones. The ash clouds contained high concentrations of sulfur dioxide, with COSPEC-recorded emission rates of 13,000 t/d, as expected for an eruption cloud. Aircraft were warned to avoid lingering ash clouds to the W of the volcano. The E side, towards the Legaspi airport, remained free from volcanic ash, debris, and SO₂ emissions.

Electronic distance measurements revealed that the volcano's edifice remained inflated. Such inflation was thought to be caused by the ascent of magma as indicated by the near-continuous seismic tremor associated with active magma transport.

The series of major ash ejections and subsequent pyroclastic flows that occurred along Bonga Gully, Mabinit, and Miisi Channels started at 1641 on 28 February 2000. The maximum height estimated for the vertical ash plume was 12 km during the 1732 event. The approximate runout of the pyroclastic flows reached to ~5-6 km downslope. Severe ashfall occurred in the SW sector of the volcano, especially at Barangay Tumpa in Camalig and Barangays Maninila and Masarawag in Guinobatan. Lava fountaining with ballistic bombs was also frequently observed starting at 1732 with maximum heights estimated at 1 km.

After the vigorous activities late in the afternoon to early evening on 28 February, only quiet effusion of lava was noted during times when the summit was not obscured through the morning of 29 February.

Another series of ash ejections began at 1211 on 29 February. The largest event occurred at 1501 and produced a 14-km-high eruption column. This event also generated several pyroclastic flows that descended all sides of the volcano. Pyroclastic flows that were channeled by gullies in the SW, S, and SE reached up to 5-6 km from the summit. Smaller pyroclastic flows that followed gullies in other sectors stopped ~2-3 km from the crater. Ash from the tall eruption column and from pyroclastic flows drifted to the W and SW. The ash ejections were generally accompanied by rumbling sounds. Vigorous lava fountaining began at 1531 and ballistic projectiles fell within 1.5 km of the crater. Lava flows were observed on 1 March to have reached the 1,000 m elevation, or about 2.3 km from the summit.

COSPEC measurements on 29 February were hampered by thick ash cover. Ground deformation measurements made the morning of 29 February along the Buang and Masarawag EDM lines showed that the volcano edifice remain inflated. Significant potential was noted for lahars along major tributaries draining from the NW due to the presence of ash and pyroclastic-flow deposits, which could be eroded and remobilized during heavy rainfall.

Mayon exhibited another series of eruptions that began on 1 March and produced dense and highly convective ash columns that rose up to 7 km above the summit. Part of the eruption column would occasionally collapse to produce pyroclastic flows that traveled along major gullies around the volcano. Pyroclastic flows were observed along the main gullies facing Anoling. The largest of these pyroclastic flows occurred along Bonga Gully and traveled ~6 km from the crater, while smaller flows at other gullies descended some 4 km downslope. Explosive eruptions produced lava fountaining with discrete ballistic volcanic fragments hurled out to ~500 m above the crater rim. Frequent rumbling accompanied the explosions, which lasted until 1609. By the end of this episode of explosive activity, quiet lava extrusion followed and continued to be observed up to the present. Areas SW and W of the volcano were severely affected by ashfall with the most significant deposition in Camalig, Guinobatan, and Ligao. Minor ash and steam were continuously being generated by lava deposits from the summit crater and Bonga Gully and drifted to the SW and W areas by prevailing winds.

Lava emission phase. Mayon was relatively quiet during 2 March as the seismic network recorded short-duration harmonic tremors and some discrete low-frequency volcanic earthquakes. This departs from the continuous tremor recorded in the past days during periods of relative quiet. The volcano has apparently entered a phase of lava emission with sporadic episodes of minor ash puffs. Ash and steam emission from both the summit crater and new lava flow deposits produced a haze over the SW sector, particularly in the municipalities of Camalig, Guinobatan, and Ligao. SO₂-flux measurements on 2 March yielded a value of 14,500 t/d. Ash clouds derived from the new lava flow deposits apparently produced a significant portion of this emission rate. Ground deformation measurements indicated that the volcano deflated slightly following the 1 March ash ejections.

Lava emission with sporadic episodes of minor ash puffs dominated the eruptive activity on 3 March. This relatively quiet state was reflected in the low-level but significant seismicity comprised by short-duration harmonic tremors and some discrete low-frequency volcanic earthquakes. Thick clouds covered the summit area, but below the cloud line and on the middle and lower slopes of the volcano ash clouds and steam emanated from the new lava flows and pyroclastic-flow deposits. A high emission rate of 8,900 t/d SO₂ was measured by COSPEC. Much of the ash and steam clouds resulting from this degassing drifted to the W and SW sections of the volcano due to prevailing winds. The haze produced by fine ash suspended in the air temporarily precluded ground deformation measurements.

Potential exists for hot lahar flows due to the presence of highly erodible pyroclastic deposits, which may be remobilized during heavy rainfall. Gullies with confirmed pyroclastic-flow deposits in their headwaters, which may therefore be sites for future lahars, are the Mabinit and Matanag river channels in Legaspi City, Miisi channel in Daraga, Basud-Lidong channel in Sto. Domingo, San Vicente and Buang channels in Tabaco, and the Bulawan channel in Malilipot.

Short-duration harmonic tremors and low-frequency volcanic earthquakes continued on 4 March. This type of seismicity indicated that eruptive activity was limited to quiet lava emission. Ground deformation measurements showed that the volcano was still inflated in its lower portion, while the SO₂ emission rate was determined to be at a minimum of 12,100 t/d. Preliminary estimates of the volume of deposits emplaced by the eruptions yielded at least 40 million cubic meters of lava flow and pyroclastic flow deposits. Lava flow deposits account for the major proportion of this estimate.

Activity for the next day was mainly characterized by gentle outpouring of lava. During cloudbreaks the night of 5-6 March, intense glow from the crater and from some portions of the advancing lava flow along the upper and middle Bonga gully were evident. Rockfalls and minor collapses along the length of the flow contributed to some localized ash and steam emission. However, the majority of the thick volcanic plume came from the summit crater which emitted about 8,300 t/d of SO₂. The PHIVOLCS seismic network continued to record short-duration harmonic tremors and low-frequency volcanic earthquakes. Ground deformation measurements showed some slight inflation of the volcano on the lower NW flank. The very high sulfur dioxide emission rate, occurrence of tremor and volcanic earthquakes associated with magma ascent, and slight swelling of the Mayon edifice indicate that some ascent of magma is still ongoing. Due to cessation of explosive eruptions, the sky W and SW of the volcano was generally clear of ash.

During 6 March the volcano exhibited quiet lava effusion accompanied by intense crater glow and rolling incandescent materials along the upper and middle reaches of the Bonga Gully. Moderate to strong emission of steam drifted generally to the N from the summit crater. The high steam output also yielded an elevated SO₂ emission rate of at least 8,800 t/d. Seismic activity consisted of 11 low-frequency volcanic earthquakes and 25 episodes of short-duration tremors. Slight inflation of the lower NW flank of the volcano continued.

At 0746 on 7 March, a parallel collapse of the new lava flow deposit in the upper middle slopes produced a voluminous secondary pyroclastic flow. The billowing ash cloud descended the Bonga Gully to the SE.

The seismic network recorded low-frequency volcanic earthquakes and short-duration harmonic tremors on 7 March. The measured SO₂ gas emission rate of 3,900 t/d, although low compared to recent measurements, was still well above the volcano's baseline level. Likewise, ground deformation surveys showed that the edifice was slightly inflated. At night on 7-8 March, when the volcano's summit area was visible, intense crater glow continued.

A PHIVOLCS report on the morning of 9 March noted that since the last eruption of 1 March, a waning trend in Mayon's overall activity has been evident. The number of volcanic earthquakes decreased and remained at unremarkable levels. In addition, tremor associated with emission of lava from the crater ceased. Seismic activity only reflected sporadic surface disturbances such as occasional rockfalls caused by oversteepened slopes. The Electronic Distance Meter (EDM) and precise leveling surveys also showed a return to the baseline levels, indicating a probable deflation of the edifice. Mayon continued to vent a large amount of steam, but the SO₂ component measured by COSPEC had decreased. Although the summit and isolated spots on the new lava flow deposits continued to glow at night, this incandescence was attributed to residual heat.

In view of these recent developments at Mayon, PHIVOLCS lowered the volcano status to Alert Level 4. On 9 March the 8-km-radius extended danger zone in the SE quadrant was reduced to 7 km. PHIVOLCS emphasized that the 6-km radius Permanent Danger Zones should remain evacuated at all times because of instability of new pyroclastic and lava deposits that may be dislodged towards the lower slopes with resultant secondary explosions and life-threatening secondary pyroclastic flows.

Geologic Background. Beautifully symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the Philippines' most active volcano. The structurally simple edifice has steep upper slopes averaging 35-40 degrees that are capped by a small summit crater. Historical eruptions date back to 1616 and range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.

Information Contacts: Raymundo S. Punongbayan and Ernesto Corpuz, Philippine Institute of Volcanology and Seismology (PHIVOLCS), C.P. Garcia St. Diliman, Quezon City Philippines (URL: http://www.phivolcs.dost. gov.ph/).

A new eruption began at about 2200 on 20 November 1999 (figure 4) with a series of explosions that caused ashfall near the volcano. More than 100 people were evacuated from the Hacienda Las Rojas. A commercial airline pilot reported that the ash plume reached about 2.4-3 km altitude. As of the start of this increased activity, the Nicaraguan Institute of Territorial Studies (INETER) reported that volcanic tremor and sporadic minor ash emissions had occurred for more than a year.

Figure 4. Photograph showing ash emissions from San Cristóbal on the afternoon of 21 November 1999. The view is from the top of Casita volcano, 4 km away. The dark part in the foreground is the edge of the Casita crater. Courtesy of Wilfried Strauch, INETER.

The last previous significant eruptive activity at San Cristóbal began on the night of 19-20 May 1997 and spread fine ash on Chinandega, 18 km W (BGVN 22:05 and 22:06). On 30 October 1998 earth movements on the S flank of Casita volcano (4 km ESE of San Cristóbal) resulted from heavy hurricane rains, killing an estimated 1,560-1,680 people, with hundreds more displaced and several towns and settlements destroyed (BGVN 23:10). The following is based on INETER reports from November through the end of February 2000, with additional information based on crater visits in January and February and satellite imagery of a large eruption plume on 21 February.

Seismic tremor increased during the night of 19-20 November and quickly reached a maximum that was not matched at least through the end of December (figure 5). Tremor amplitude declined throughout 20 November, and then remained at levels of ~25-60% of the 20 November peak until a volcano-tectonic earthquake on 27 November.

Figure 5. RSAM (real-time seismic amplitude measurement) data showing the relative amplitude of seismic tremor at San Cristóbal recorded at the seismic station near the Hacienda Las Rojas, at the foot of the volcano, 19-28 November 1999. Seismicity began during the night of 19-20 November, although volcanic activity at the surface was not reported until the following night of 20-21 November. Ashfall was reported at dawn on the 21st near the volcano. The high peak at 1520 on 27 November was caused by a volcano-tectonic earthquake. Courtesy of INETER.

Small explosions preceded emissions on 22 November. Activity decreased after the initial eruptions, but a lack of winds caused the ash and gases to remain near the volcano. Concentrations of CO₂ and SO₂ measured on 22 November at three different sites exceeded the permissible limits established by the World Health Organization (WHO). INETER inspections showed that expelled gas and ash have been accumulating in local communities. However, on 23 November a slight increase in the wind speed facilitated the transport of volcanic material as far as the city of Chinandega 10 km to the SW. That day an observation post was established near the summit of Casita, where INETER staff could make visual observations and measurements of eruption column heights.

Ash emanations during 24-27 November varied in frequency, and the observer at Casita saw ash columns to heights of 100-300 m above the crater during the same period. At 0920 on 27 November a small earthquake (M 2.3) occurred ~2 km underneath the volcano. Volcanic gas monitoring on 24 November showed a significant increase in the concentrations of SO₂ in the San Rafael and Las Rojas areas. However, the concentration of CO₂ showed a diminution compared to 23 November. Concentrations of SO₂ and CO₂ decreased again on the 25th, although in some communities the level of SO₂ remained unchanged. A correlation spectrometer (COSPEC) for measuring SO₂ flux was brought from the INSIVUMEH of Guatemala on 26 November, with the support of the Coordination Center for the Prevention of Natural Disasters in Central America (CEPREDENAC).

Seismic tremor amplitude remained fairly stable, around 30-50% of the 20 November peak, during 26 November through 13 December. Seismicity fluctuated, with periods of higher and lower amplitude; a corresponding fluctuation in the ash-and-gas emissions was noted. The amounts of gases emitted by the volcano also showed this correlation, with SO₂-flux values that oscillated between 100 and 1,000 tons/day.

By 2 December ash emissions had decreased considerably, although low-level gas emissions remained continuous. There was a slight increase in emissions on 4 December, but activity remained low through the 13th. Higher wind speeds during this period helped keep gas concentrations low in local towns. Seismic tremor began to rise the night of 12-13 December to a high of 70% of the previous peak. On 14 December small amounts of volcanic ash fell in Chinandega. Tremor amplitude returned to ~40% of the peak on 15 December, then decreased to 20-30% of the peak by dawn on the 16th.

Lahars on 16 December 1999. The Civil defense and local residents reported that a mass-flow on the NW side of the volcano on 16 December stopped ~2 km from populated areas. On 21 December, two specialists visited the affected Rancherías region NW of San Cristóbal in the Municipality of Chinandega (Dpto. Chinandega) to investigate the event. According to the meteorological station of Chinandega, 7.9 mm of rain fell from 1824 until 2012; in the first hour strong rains were reported, and from 1920 there were light to moderate rains. Previous strong rains have produced erosion gullies on the slopes of the volcano.

Due to the recent eruptive activity, large amounts of ash and lapilli had accumulated in these gullies; these were mobilized by the rains into lahars. Several sources were identified between 1,400 and 1,500 m elevation. The mobilized material formed a debris flow containing ash and lapilli that carried blocks varying from centimeters to meters in size. The flow quickly cemented into an extremely hard deposit. The material eroded from the highest slopes of San Cristóbal moved along one main gully, leaving a very deep channel and, below 500 m elevation, an extended lobate deposit that reached within ~2 km of the community of Ranchería. The main flow had a length of ~7 km and variable widths between 10 and 150 m; deposit thickness varied from less than 10 cm up to 2 m at the terminus.

Similar events happened on the S slope of the volcano that same day. At least five lahars were visible from the Leon-Chinandega highway.

Minor ash emissions continue. Activity remained consistently low and unchanged until noon on 28 December when earthquakes began. These were centered SE of Casita with magnitudes between 2 and 3.5 and depths of a few kilometers. The occurrence of earthquakes near San Cristóbal is a new phenomenon in the current eruption. Ash emission also increased and small amounts fell in Chinandega.

Seismic tremor on 29 December increased to as high as 40% of the 20 November peak. Small amounts of ash fell in Chinandega and El Viejo. No significant changes in activity were noted on 30 December. Moderate ashfalls were reported near the volcano and in Chinandega. Depending on the wind direction, ashfall sporadically reached the communities of Higueral, 10.5 km NE, and Pelona, 9 km E.

Activity during January-February 2000. Small explosions continued during January with ash and gas emissions (figure 6) and 4,444 registered volcanic earthquakes. Seismicity was higher in the first 17 days of January, but the seismic tremor (RSAM) stayed constant. Between 17 and 23 February activity increased, causing significant ashfall in Chinandega. The number of registered volcanic earthquakes in February was of 1,784.

Figure 6. Ash emissions from San Cristóbal on 13 January 2000. The view is from the summit of Telica volcano. Courtesy of INETER.

Alain Creusot visited the crater on 10 January and observed rhythmic, phreatic explosions, which included rock ejections and ash columns from three vents. At 0600 that day, a violent explosion threw bombs high above the crater rim. Creusot visited the crater again on 4 February and observed a 50-cm-deep ash layer over the crater area and 30-cm depths over the entire summit. Rhythmic phreatic explosions continued and new bombs were observed and sampled on the E crater rim (figure 7). These bombs apparently originated from a Strombolian explosion on 30 January. A third visit on 20 February showed a 1-m-deep ash layer in the crater area and 50-cm depths elsewhere in the summit area. Rocks 50 cm in size had been ejected.

Figure 7. Sketch map of the San Cristóbal summit area showing the new vents within the crater and locations of bombs deposited following an explosion on 30 January 2000. Courtesy of Alain Creusot.

Benjamin van Wyk de Vries noted that GOES images on 21 February showed a long plume extending from San Cristóbal to ~100 km over the Pacific Ocean. He also reported that this was the strongest ash eruption at San Cristóbal since the 1997 eruption. At 1100 on 24 February, a violent explosion threw bombs over the entire summit. A similar explosion and effects occurred at 0900 on the 25th.

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

Information Contacts: Wilfried Strauch and Virginia Tenorio, Dirección General de Geofísica, Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado 1761, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); Alain Creusot, Instituto Nicaraguense de Energía, Managua, Nicaragua (URL: http://www.ine.gob.ni/); Benjamin van Wyk de Vries, Departement des Sciences de la Terre, Universite Blaise Pascal, 63038 Clermont-Ferrand, France.

The Alaska Volcano Observatory (AVO) reported on 21 January 2000 that investigations of recent seismic data had revealed evidence for small explosions at Shishaldin. Later detailed study of the seismic records showed that the activity may have begun in as early as late September. The numbers of explosions varied from several to over 200/day, but no steam or ash plumes were observed by airborne or ground observers. Also, no thermal anomaly was observed in satellite imagery, indicating that lava had not reached the surface. It was thought that the explosions were phreatic, caused by the flashing of water to steam; these events may represent a local hazard within a few hundred meters of the vent but do not pose a hazard to aircraft. Small explosions continued at a similar rate through 28 January.

Small low-frequency seismic events, present at Shishaldin since June 1999, gradually increased in amplitude after 28 January, with a noticeable increase during 2-3 February. Seismic data continued to show the presence of small phreatic explosions. Reports of steam plumes were received during the week ending on 2 February, with heights reaching as high as ~900 m above the summit. However, no thermal anomaly was observed in satellite imagery and no seismic tremor was identified; both were seen prior to the last eruptive episode in April and May 1999 (BGVN 24:03, 24:04, 24:08). Due to the increased activity, AVO raised the Level of Concern Color Code to Yellow on 3 February, indicating that the volcano is restless and an eruption may occur.

No appreciable number of seismic events were detected after 4 February; that was also the last day that small explosions were observed. Small low-frequency seismic events continued through 11 February, but at a slower rate and slightly lower amplitude. By 18 February seismic activity had declined significantly with no thermal anomalies or observations of unusual activity, so the hazard status was changed back to Green, indicating normal seismicity and surface activity.

Small low-frequency seismic events and very low-level tremor was recorded through 3 March, although at or below the levels observed in the months prior to the 19 April 1999 eruption. Low-level seismicity continued through the end of March. Vigorous steaming was reported in the second half of March, but no thermal anomaly observed in satellite imagery.

Geologic Background. The beautifully symmetrical Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The glacier-covered volcano is the westernmost of three large stratovolcanoes along an E-W line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." A steam plume often rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the W and NE sides at 1,500-1,800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of Strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century.

Information Contacts: 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 & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA.

As of late November 1999, microseismic activity had been occurring at Telica for more than a year. There were phreatic explosions in May and June 1999 (BGVN 24:06). An eruptive phase began in August 1999, generally producing only sporadic small and local ash falls. Intermittent gas-and-ash emissions continued to be reported through December 1999. One of the more vigorous events took place on 29 December, sending ash to several kilometers altitude and inducing falls detected 45 km away.

A noteworthy event began around 0200 on 10 August. Tremor and earthquakes increased abruptly. Small explosions took place in the crater, expelling gas and volcanic ash. Ash fell ~20 km WSW of Telica in the city of Chichigalpa. An interval of relative calm on 12 August lasted approximately one hour. It ended with the gas explosions and ash outbursts starting again at 1315 and continuing until 1515 with ongoing degassing afterwards. According to the summed seismic amplitudes (RSAM values), the greatest activity was between 2000 on 10 August until the morning of 11 August.

Observers saw a lava lake in the crater on 18 August. On that day, INETER's Wilfried Strauch and Armando Saballos, along with visiting North American specialists, climbed Telica to install GPS equipment. Taking advantage of periods of low degassing, they managed to observe the bottom of the new inner crater that had formed in the last few months (figure 11). To their surprise, they saw a lava lake there. In addition they listened to forceful jetting noises probably generated by the water contact with heated material.

Figure 11.Photograph from the crater rim at Telica showing the new inner crater, 18 August 1999. Courtesy of Wilfried Strauch, INETER.

On 21 August INETER's Virginia Tenorio and Julio Alvarez climbed the volcano and saw that the inner crater had enlarged; and, in addition they again heard jet-engine-like noises. Abundant escaping gases thwarted views into the inner crater so the visitors could not assess whether a lava lake remained. The same day between 0800 and 0900, residents who live on the SE flank of the volcano felt two rumblings from the volcano. Possibly, this caused the inner crater to enlarge even more.

Several days later seismic tremor increased, but the number of microearthquakes fluctuated, first dropping, then increasing again on the 25th. On 29 August seismic tremor began to drop substantially. Then, however, the number of microearthquakes increased. Telica's eruptive activity is typically associated with slightly increased tremor and over 200 to 300 microearthquakes per day.

During September, a month with 2,116 microearthquakes, gas emanations prevailed until the 10th. A seismic swarm at the beginning of October was followed by a series of explosions with tephra expulsions during 3-15 October. On the 5th, INETER staff on the crater's edge witnessed the discharge of both ash and lava (presumably in the form of bombs). The last similar lava-bearing explosion of this type was in 1988 (SEAN 13:01). On the 12th, W-flank residents reported that on the previous day (at about 1400 on the 11th) they had felt an unusually strong explosion shaking their houses. Later, they witnessed the fall of very fine gray ash. Observers also saw that the inner crater had grown wider than when seen in September. By 12 October the seismic amplitude had decreased to background levels. The number of earthquakes registered for October was 888.

During November the earthquake sum was comparatively low, 144, but that did not signify volcanic quiet. On 19 November, INETER's Julio Alvarez and Virginia Tenorio skirted the volcano along the León-Chinandega highway where they saw an ash column. Erminio Rojas, a farmer on Telica's S flank, told them that in the past few weeks the volcano had almost constantly been expelling gray ash. On 17 November he witnessed a very large explosion that caused an ashfall deposit reaching 2.5 cm thickness near his house, damaging his apples and beans. The observers further noticed that on the crater's SW a possible collapse feature had developed. Burned ash-covered plants lay in the area near the edge of the crater. Ash discharges on 17 November occasionally emitted a noise similar to a gunshot.

On 24 November, Civil defense of León reported a black cloud above Telica. An unusual seismic signal on 28 November prompted a visit to Telica by Tenorio and Strauch, along with Rafael Abelia of the Institute of Geomineras Investigations of Madrid, Spain. When they arrived at the volcano, the group found that a zone of disruption had spread over a great part of the N crater wall, and the edge of the crater was covered with a thick layer of fine dust. This indicated to them that there was no explosion and the cloud that the Civil Defense observed was due to the collapse of the N crater wall. COSPEC measurements conducted on 29 November indicated that the volcano was producing between 50 and 500 metric tons/day of SO₂ per day.

During December 1999 there were 1,085 volcanic earthquakes, of which, four were located. INETER's seismic network located several earthquakes that took place underneath the volcano on 14 December with magnitudes between 2 and 2.5. During December, tremor stayed low until the 24th, when it was punctuated by sporadic degassing and smaller ash-bearing discharges. On the 25th, tremor began to rise slowly; on the 28th there occurred an abrupt increase in the seismic signal, four-fold larger than seen during previous days. The morning of 29 December seismicity was high. The same day reports were received describing almost continuous ash-bearing explosions, with WSW-directed tephra falls.

Two large explosions at 0900 on 29 December sent ash to heights of more than 1,000 m above the crater. Besides affecting cities adjacent the volcano, ash was later known to have affected the cities of Posoltega (~16 km SW), Chichigalpa (20 km WSW), Quezalguaque (20 km SSW), Chinandega (35 km WSW), and Corinto (~45 km SW). INETER noted that civil-aviation pilots reported that ash rose up to 5 km, although whether this was an altitude or the height over the 1-km-tall volcano remained undisclosed. Tremor initially stayed high on 30 December but dropped on 31 December. Activity continued into January 2000.

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

Information Contacts: Wilfried Strauch and Virginia Tenorio, Dirección General de Geofísica, Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado 1761, Managua, Nicaragua (URL: http://www.ineter.gob.ni/).

The submarine eruption that started on December 1998 (BGVN 24:01 and 24:03) from multiple vents along the Serreta Volcanic Ridge, about 10 km W of Terceira Island, Azores, continued through March 2000. Vents along the ridge were very active between December 1998 and September 1999. Activity then declined to very low levels with rare surface manifestations through December 1999. Activity increased again in late January 2000.

Several times during 1999 basaltic lava balloons were observed floating in the eruptive area. These "balloons" are very hot, gas-rich, lava fragments produced from small submarine lava lakes/fountains. During ascent to the surface, magmatic gas exsolves from the hot fragments, increasing the volume of the balloon while the crust is glassy and expansible. Once at the surface, interaction between the hot blocks and seawater produce white steam columns that can be seen from land when meteorological conditions are favorable (figure 5). The blocks eventually sink after the gas escapes.

Figure 5. Lava balloon from the Serreta Ridge off Terciera floating on the sea surface and producing white steam column. Courtesy of CVUA.

An oceanographic mission supported by the national Foundation for Science and Technology was carried out in April 1999 to study the geological/geophysical characteristics of the eruption and its impact on local ecosystems. Scientists from the University of Azores, University of Lisbon, University of Algarve, Instituto do Mar, and Instituito Hidrográfico used a remotely operated vehicle that crossed an impressive submarine volcanic plume just above an active eruptive center at about 380 m depth. This plume was formed by volcanic particles of ash and lapilli size along with gas bubbles and lava balloons up to 2 m in diameter.

On 28 January 2000 a yellowish spot was observed at the sea surface above the eruptive area due to the dispersion of a volcanic plume that rose from a new vent located at about 250 m depth (figure 6). The area of water discoloration caused by the plume was visible almost continuously for about a month, reaching a maximum diameter of 8 km on 24 February. The plume was generated by multiple eruptive pulses from different eruptive centers located within a few hundred meters of each other.

Figure 6. Aerial view of the edge of a submarine volcanic ash plume spreading at the sea surface. Courtesy of CVUA.

Seismicity along the ridge related to the eruption continued through the end of March, but at low levels. Since the beginning of this volcanic crisis the physical and chemical parameters of waters and fumarolic gases from Terceira Island have been monitored, with no changes detected. Another submarine eruption took place in this general location in June 1867. At that time five months of strong seismicity destroyed about 200 houses at Serreta.

Geologic Background. Terceira Island contains four stratovolcanoes constructed along a prominent ESE-WNW-trending fissure zone that cuts across the island. Historically active Santa Barbara volcano at the western end of the island is truncated by two calderas. The youngest of these formed about 15,000 years ago. Comenditic lava domes fill and surround the caldera. Pico Alto lies north of the fissure zone in the north-central part of the island and contains a Pleistocene caldera largely filled by lava domes and lava flows. Guilherme Moniz caldera lies along the fissure zone immediately to the south, and 7-km-wide Cinquio Picos caldera at the SE end of the island is the largest in the Azores. Historical eruptions have occurred from Pico Alto, the fissure zone between Pico Alto and Santa Barbara, and from submarine vents west of Santa Barbara. Most Holocene eruptions have produced basaltic-to-rhyolitic lava flows from the fissure zone transecting the island.

Information Contacts: J.L. Gaspar, G. Queiroz, J.M. Pacheco, T. Ferreira, R. Coutinho, M.H. Almeida, and N. Wallenstein, Centre of Volcanology of the Azores University (CVUA), Departamento de Geociencias, Rua da Mae de Deus, 9502 Ponta Delgada, Azores, Portugal (URL: http://www.uac.pt/).

In discussing the week ending on 12 September, "Earthweek" (Newman, 1997) incorrectly claimed that a volcano named "Mount Pinukis" had erupted. Widely read in the US, the dramatic Earthweek report described terrified farmers and a black mushroom cloud that resembled a nuclear explosion. The mountain's location was given as "200 km E of Zamboanga City," a spot well into the sea. The purported eruption had received mention in a Manila Bulletin newspaper report nine days earlier, on 4 September. Their comparatively understated report said that a local police director had disclosed that residents had seen a dormant volcano showing signs of activity.

In response to these news reports Emmanuel Ramos of the Philippine Institute of Volcanology and Seismology (PHIVOLCS) sent a reply on 17 September. PHIVOLCS staff had initially heard that there were some 12 alleged families who fled the mountain and sought shelter in the lowlands. A PHIVOLCS investigation team later found that the reported "families" were actually individuals seeking respite from some politically motivated harassment. The story seems to have stemmed from a local gold rush and an influential politician who wanted to use volcanism as a ploy to exclude residents. PHIVOLCS concluded that no volcanic activity had occurred. They also added that this finding disappointed local politicians but was much welcomed by the residents.

PHIVOLCS spelled the mountain's name as "Pinokis" and from their report it seems that it might be an inactive volcano. There is no known Holocene volcano with a similar name (Simkin and Siebert, 1994). No similar names (Pinokis, Pinukis, Pinakis, etc.) were found listed in the National Imagery and Mapping Agency GEOnet Names Server (http://geonames.nga.mil/gns/html/index.html), a searchable database of 3.3 million non-US geographic-feature names.

The Manila Bulletin report suggested that Pinokis resides on the Zamboanga Peninsula. The Peninsula lies on Mindanao Island's extreme W side where it bounds the Moro Gulf, an arm of the Celebes Sea. The mountainous Peninsula trends NNE-SSW and contains peaks with summit elevations near 1,300 m. Zamboanga City sits at the extreme end of the Peninsula and operates both a major seaport and an international airport.

[Later investigation found that Mt. Pinokis is located in the Lison Valley on the Zamboanga Peninsula, about 170 km NE of Zamboanga City and 30 km NW of Pagadian City. It is adjacent to the two peaks of the Susong Dalaga (Maiden's Breast) and near Mt. Sugarloaf.]

References. Newman, S., 1997, Earthweek, a diary of the planet (week ending 12 September): syndicated newspaper column (URL: http://www.earthweek.com/).

Manila Bulletin, 4 Sept. 1997, Dante's Peak (URL: http://www.mb.com.ph/).

Simkin, T., and Siebert, L., 1994, Volcanoes of the world, 2nd edition: Geoscience Press in association with the Smithsonian Institution Global Volcanism Program, Tucson AZ, 368 p.

Information Contacts: Emmanuel G. Ramos, Deputy Director, Philippine Institute of Volcanology and Seismology, Department of Science and Technology, PHIVOLCS Building, C. P. Garcia Ave., University of the Philippines, Diliman campus, Quezon City, Philippines.

Xinhua News Agency filed a news report on 27 February under the headline "Volcano erupts in Somalia" but the veracity of the story now appears doubtful. The report disclosed the volcano's location as on the W side of the Gedo region, an area along the Ethiopian border just NE of Kenya. The report had relied on the commissioner of the town of Bohol Garas (a settlement described as 40 km NE of the main Al-Itihad headquarters of Luq town) and some or all of the information was relayed by journalists through VHF radio. The report claimed the disaster "wounded six herdsmen" and "claimed the lives of 290 goats grazing near the mountain when the incident took place." Further descriptions included such statements as "the volcano which erupted two days ago [25 February] has melted down the rocks and sand and spread . . . ."

Giday WoldeGabriel returned from three weeks of geological fieldwork in SW Ethiopia, near the Kenyan border, on 25 August. During his time there he inquired of many people, including geologists, if they had heard of a Somalian eruption in the Gedo area; no one had heard of the event. WoldeGabriel stated that he felt the news report could have described an old mine or bomb exploding. Heavy fighting took place in the Gedo region during the Ethio-Somalian war of 1977. Somalia lacks an embassy in Washington DC; when asked during late August, Ayalaw Yiman, an Ethiopian embassy staff member in Washington DC also lacked any knowledge of a Somalian eruption.

A Somalian eruption would be significant since the closest known Holocene volcanoes occur in the central Ethiopian segment of the East African rift system S of Addis Ababa, ~500 km NW of the Gedo area. These Ethiopian rift volcanoes include volcanic fields, shield volcanoes, cinder cones, and stratovolcanoes.

Information Contacts: Xinhua News Agency, 5 Sharp Street West, Wanchai, Hong Kong; Giday WoldeGabriel, EES-1/MS D462, Geology-Geochemistry Group, Los Alamos National Laboratory, Los Alamos, NM 87545; Ayalaw Yiman, Ethiopian Embassy, 2134 Kalorama Rd. NW, Washington DC 20008.

Following the Ms 7.8 earthquake in Turkey on 17 August (BGVN 24:08) an Email message originating in Turkey was circulated, claiming that volcanic activity was observed coincident with the earthquake and suggesting a new (magmatic) volcano in the Sea of Marmara. For reasons outlined below, and in the absence of further evidence, editors of the Bulletin consider this a false report.

The report stated that fishermen near the village of Cinarcik, at the E end of the Sea of Marmara "saw the sea turned red with fireballs" shortly after the onset of the earthquake. They later found dead fish that appeared "fried." Their nets were "burned" while under water and contained samples of rocks alleged to look "magmatic."

No samples of the fish were preserved. A tectonic scientist in Istanbul speculated that hot water released by the earthquake from the many hot springs along the coast in that area may have killed some fish (although they would be boiled rather than fried).

The phenomenon called earthquake lights could explain the "fireballs" reportedly seen by the fishermen. Such effects have been reasonably established associated with large earthquakes, although their origin remains poorly understood. In addition to deformation-triggered piezoelectric effects, earthquake lights have sometimes been explained as due to the release of methane gas in areas of mass wasting (even under water). Omlin and others (1999), for example, found gas hydrate and methane releases associated with mud volcanoes in coastal submarine environments.

The astronomer and author Thomas Gold (Gold, 1998) has a website (Gold, 2000) where he presents a series of alleged quotes from witnesses of earthquakes. We include three such quotes here (along with Gold's dates, attributions, and other comments):

(A) Lima, 30 March 1828. "Water in the bay 'hissed as if hot iron was immersed in it,' bubbles and dead fish rose to the surface, and the anchor chain of HMS Volage was partially fused while lying in the mud on the bottom." (Attributed to Bagnold, 1829; the anchor chain is reported to be on display in the London Navy Museum.)

(B) Romania, 10 November 1940. ". . . a thick layer like a translucid gas above the surface of the soil . . . irregular gas fires . . . flames in rhythm with the movements of the soil . . . flashes like lightning from the floor to the summit of Mt Tampa . . . flames issuing from rocks, which crumbled, with flashes also issuing from non-wooded mountainsides." (Phrases used in eyewitness accounts collected by Demetrescu and Petrescu, 1941).

(C) Sungpan-Pingwu (China), 16, 22, and 23 August 1976. "From March of 1976, various large anomalies were observed over a broad region. . . . At the Wanchia commune of Chungching County, outbursts of natural gas from rock fissures ignited and were difficult to extinguish even by dumping dirt over the fissures. . . . Chu Chieh Cho, of the Provincial Seismological Bureau, related personally seeing a fireball 75 km from the epicenter on the night of 21 July while in the company of three professional seismologists."

Yalciner and others (1999) made a study of coastal areas along the Sea of Marmara after the Izmet earthquake. They found evidence for one or more tsunamis with maximum runups of 2.0-2.5 m. Preliminary modeling of the earthquake's response failed to reproduce the observed runups; the areas of maximum runup instead appeared to correspond most closely with several local mass-failure events. This observation together with the magnitude of the earthquake, and bottom soundings from marine geophysical teams, suggested mass wasting may have been fairly common on the floor of the Sea of Marmara.

Despite a wide range of poorly understood, dramatic processes associated with earthquakes (Izmet 1999 apparently included), there remains little evidence for volcanism around the time of the earthquake. The nearest Holocene volcano lies ~200 km SW of the report location. Neither Turkish geologists nor scientists from other countries in Turkey to study the 17 August earthquake reported any volcanism. The report said the fisherman found "magmatic" rocks; it is unlikely they would be familiar with this term.

The motivation and credibility of the report's originator, Erol Erkmen, are unknown. Certainly, the difficulty in translating from Turkish to English may have caused some problems in understanding. Erkmen is associated with a website devoted to reporting UFO activity in Turkey. Photographs of a "magmatic rock" sample were sent to the Bulletin, but they only showed dark rocks photographed devoid of a scale on a featureless background. The rocks shown did not appear to be vesicular or glassy. What was most significant to Bulletin editors was the report author's progressive reluctance to provide samples or encourage follow-up investigation with local scientists. Without the collaboration of trained scientists on the scene this report cannot be validated.

References. Omlin, A, Damm, E., Mienert, J., and Lukas, D., 1999, In-situ detection of methane releases adjacent to gas hydrate fields on the Norwegian margin: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Yalciner, A.C., Borrero, J., Kukano, U., Watts, P., Synolakis, C. E., and Imamura, F., 1999, Field survey of 1999 Izmit tsunami and modeling effort of new tsunami generation mechanism: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Gold, T., 1998, The deep hot biosphere: Springer Verlag, 256 p., ISBN: 0387985468.

Gold, T., 2000, Eye-witness accounts of several major earthquakes (URL: http://www.people.cornell.edu/ pages/tg21/eyewit.html).

Information Contacts: Erol Erkmen, Tuvpo Project Alp.

In December 2002 information appeared in Mongolian and Russian newspapers and on national TV that a volcano in Central Mongolia, the Har-Togoo volcano, was producing white vapors and constant acoustic noise. Because of the potential hazard posed to two nearby settlements, mainly with regard to potential blocking of rivers, the Director of the Research Center of Astronomy and Geophysics of the Mongolian Academy of Sciences, Dr. Bekhtur, organized a scientific expedition to the volcano on 19-20 March 2003. The scientific team also included M. Ulziibat, seismologist from the same Research Center, M. Ganzorig, the Director of the Institute of Informatics, and A. Ivanov from the Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences.

Geological setting. The Miocene Har-Togoo shield volcano is situated on top of a vast volcanic plateau (figure 1). The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Pliocene and Quaternary volcanic rocks are also abundant in the vicinity of the Holocene volcanoes (Devyatkin and Smelov, 1979; Logatchev and others, 1982). Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Figure 1. Photograph of the Har-Togoo volcano viewed from west, March 2003. Courtesy of Alexei Ivanov.

Observations during March 2003. The name of the volcano in the Mongolian language means "black-pot" and through questioning of the local inhabitants, it was learned that there is a local myth that a dragon lived in the volcano. The local inhabitants also mentioned that marmots, previously abundant in the area, began to migrate westwards five years ago; they are now practically absent from the area.

Acoustic noise and venting of colorless warm gas from a small hole near the summit were noticed in October 2002 by local residents. In December 2002, while snow lay on the ground, the hole was clearly visible to local visitors, and a second hole could be seen a few meters away; it is unclear whether or not white vapors were noticed on this occasion. During the inspection in March 2003 a third hole was seen. The second hole is located within a 3 x 3 m outcrop of cinder and pumice (figure 2) whereas the first and the third holes are located within massive basalts. When close to the holes, constant noise resembled a rapid river heard from afar. The second hole was covered with plastic sheeting fixed at the margins, but the plastic was blown off within 2-3 seconds. Gas from the second hole was sampled in a mechanically pumped glass sampler. Analysis by gas chromatography, performed a week later at the Institute of the Earth's Crust, showed that nitrogen and atmospheric air were the major constituents.

Figure 2. Photograph of the second hole sampled at Har-Togoo, with hammer for scale, March 2003. Courtesy of Alexei Ivanov.

The temperature of the gas at the first, second, and third holes was +1.1, +1.4, and +2.7°C, respectively, while air temperature was -4.6 to -4.7°C (measured on 19 March 2003). Repeated measurements of the temperatures on the next day gave values of +1.1, +0.8, and -6.0°C at the first, second, and third holes, respectively. Air temperature was -9.4°C. To avoid bias due to direct heating from sunlight the measurements were performed under shadow. All measurements were done with Chechtemp2 digital thermometer with precision of ± 0.1°C and accuracy ± 0.3°C.

Inside the mouth of the first hole was 4-10-cm-thick ice with suspended gas bubbles (figure 5). The ice and snow were sampled in plastic bottles, melted, and tested for pH and Eh with digital meters. The pH-meter was calibrated by Horiba Ltd (Kyoto, Japan) standard solutions 4 and 7. Water from melted ice appeared to be slightly acidic (pH 6.52) in comparison to water of melted snow (pH 7.04). Both pH values were within neutral solution values. No prominent difference in Eh (108 and 117 for ice and snow, respectively) was revealed.

Two digital short-period three-component stations were installed on top of Har-Togoo, one 50 m from the degassing holes and one in a remote area on basement rocks, for monitoring during 19-20 March 2003. Every hour 1-3 microseismic events with magnitude <2 were recorded. All seismic events were virtually identical and resembled A-type volcano-tectonic earthquakes (figure 6). Arrival difference between S and P waves were around 0.06-0.3 seconds for the Har-Togoo station and 0.1-1.5 seconds for the remote station. Assuming that the Har-Togoo station was located in the epicentral zone, the events were located at ~1-3 km depth. Seismic episodes similar to volcanic tremors were also recorded (figure 3).

Figure 3. Examples of an A-type volcano-tectonic earthquake and volcanic tremor episodes recorded at the Har-Togoo station on 19 March 2003. Courtesy of Alexei Ivanov.

Conclusions. The abnormal thermal and seismic activities could be the result of either hydrothermal or volcanic processes. This activity could have started in the fall of 2002 when they were directly observed for the first time, or possibly up to five years earlier when marmots started migrating from the area. Further studies are planned to investigate the cause of the fumarolic and seismic activities.

At the end of a second visit in early July, gas venting had stopped, but seismicity was continuing. In August there will be a workshop on Russian-Mongolian cooperation between Institutions of the Russian and Mongolian Academies of Sciences (held in Ulan-Bator, Mongolia), where the work being done on this volcano will be presented.

References. Devyatkin, E.V. and Smelov, S.B., 1979, Position of basalts in sequence of Cenozoic sediments of Mongolia: Izvestiya USSR Academy of Sciences, geological series, no. 1, p. 16-29. (In Russian).

Logatchev, N.A., Devyatkin, E.V., Malaeva, E.M., and others, 1982, Cenozoic deposits of Taryat basin and Chulutu river valley (Central Hangai): Izvestiya USSR Academy of Sciences, geological series, no. 8, p. 76-86. (In Russian).

Geologic Background. The Miocene Har-Togoo shield volcano, also known as Togoo Tologoy, is situated on top of a vast volcanic plateau. The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Information Contacts: Alexei V. Ivanov, Institute of the Earth Crust SB, Russian Academy of Sciences, Irkutsk, Russia; Bekhtur andM. Ulziibat, Research Center of Astronomy and Geophysics, Mongolian Academy of Sciences, Ulan-Bator, Mongolia; M. Ganzorig, Institute of Informatics MAS, Ulan-Bator, Mongolia.

An eruption at Mount Elgon was mistakenly inferred when fumes escaped from this otherwise quiet volcano. The fumes were eventually traced to dung burning in a lava-tube cave. The cave is home to, or visited by, wildlife ranging from bats to elephants. Mt. Elgon (Ol Doinyo Ilgoon) is a stratovolcano on the SW margin of a 13 x 16 km caldera that straddles the Uganda-Kenya border 140 km NE of the N shore of Lake Victoria. No eruptions are known in the historical record or in the Holocene.

On 7 September 2004 the web site of the Kenyan newspaper The Daily Nation reported that villagers sighted and smelled noxious fumes from a cave on the flank of Mt. Elgon during August 2005. The villagers' concerns were taken quite seriously by both nations, to the extent that evacuation of nearby villages was considered.

The Daily Nation article added that shortly after the villagers' reports, Moses Masibo, Kenya's Western Province geology officer visited the cave, confirmed the villagers observations, and added that the temperature in the cave was 170°C. He recommended that nearby villagers move to safer locations. Masibo and Silas Simiyu of KenGens geothermal department collected ashes from the cave for testing.

Gerald Ernst reported on 19 September 2004 that he spoke with two local geologists involved with the Elgon crisis from the Geology Department of the University of Nairobi (Jiromo campus): Professor Nyambok and Zacharia Kuria (the former is a senior scientist who was unable to go in the field; the latter is a junior scientist who visited the site). According to Ernst their interpretation is that somebody set fire to bat guano in one of the caves. The fire was intense and probably explains the vigorous fuming, high temperatures, and suffocated animals. The event was also accompanied by emissions of gases with an ammonia odor. Ernst noted that this was not surprising considering the high nitrogen content of guano—ammonia is highly toxic and can also explain the animal deaths. The intense fumes initially caused substantial panic in the area.

It was Ernst's understanding that the authorities ordered evacuations while awaiting a report from local scientists, but that people returned before the report reached the authorities. The fire presumably prompted the response of local authorities who then urged the University geologists to analyze the situation. By the time geologists arrived, the fuming had ceased, or nearly so. The residue left by the fire and other observations led them to conclude that nothing remotely related to a volcanic eruption had occurred.

However, the incident emphasized the problem due to lack of a seismic station to monitor tectonic activity related to a local triple junction associated with the rift valley or volcanic seismicity. In response, one seismic station was moved from S Kenya to the area of Mt. Elgon so that local seismicity can be monitored in the future.

Information Contacts: Gerald Ernst, Univ. of Ghent, Krijgslaan 281/S8, B-9000, Belgium; Chris Newhall, USGS, Univ. of Washington, Dept. of Earth & Space Sciences, Box 351310, Seattle, WA 98195-1310, USA; The Daily Nation (URL: http://www.nationmedia.com/dailynation/); Uganda Tourist Board (URL: http://www.visituganda.com/).