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/).

Activity at Arenal since May 1999 (BGVN 24:06) has been comparatively quiet, a condition which has generally prevailed since an energetic outburst in May 1998 (BGVN 23:06), continued during July 1999 through January 2000. However, this relative quiet was broken in October 1999 by an anomalous pyroclastic flow, discussed below. Elevated activity occurred in November as well. In addition to lava flows traveling N and NE during this interval, in July a new, N-directed lava flow was emitted. Another during September traveled NE spawning occasional rockfalls off its front. Few eruptions produced plumes rising more than a kilometer above crater C, and crater D remained fumarolic in nature. Cold avalanches continued to occur down local valleys (including the Calle de Arenas, Manolo, Guillermina, and Agua Caliente). During June-August electronic distance measuring disclosed that the survey points underwent an average of 2 cm expansion.

A pyroclastic flow at 1721 on 26 October descended the W flank as far as the ~900 m contour and left an eroded swath. It was smaller and its path differed from the May 1998 pyroclastic flow down the N-NW flank along the Tabacón river (BGVN 23:04). In the 26 October event, fine tephra accumulated in an area ~200 m wide. This pyroclastic flow may have consisted of a series of several distinct events. The column height was ~1 km above the vent.

The 26 October event's precursors included heightened explosive activity and increased seismicity beginning on 8 October, and a decrease in tremor. A precursory seismic swarm may have also been related. Although high-frequency earthquake swarms are generally rare at Arenal, a modest one began in August 1999 and reached a maximum on 17 September (5 events per day). The swarm ceased after 1 October; it consisted of 55 registered events with 13 of these located. The earthquakes comprising the swarm had amplitudes below Mc 2.3. Hypocenters for the located earthquakes typically occurred at depths of 2-4 km. After the pyroclastic flow, the energy transmitted in explosions and the amplitude of tremors dropped considerably.

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

Information Contacts: E. Fernandez, E. Duarte, V. Barboza, R. Sáenz, E. Malavassi, R. Van der Laat, T. Marino, J. Barquero, and E. Hernández, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; M. Martinez and J. Valdez; Laboratorio de Quimica de la Atmosfera, Universidad Nacional; R. Barquero, Instituto Costarricense de Electricidad (I.C.E.), Departamento de Geologia, Apdo. 10032-1000, San José, Costa Rica; I. Arroyo and G. Alvarado, Observatorio Sismológico Vulcanológico Arenal y Miravalles (OSIVAM), Instituto Costarricense de Electricidad (ICE), Apartado 10032-1000, San José, Costa Rica.

Etna showed relatively low levels of activity during December 1999 and through 25 January 2000. In contrast, on 26 January, Southeast Crater (SEC) started a new series of strong eruptive episodes, and from then until the end of March, 46 episodes occurred at that crater (table 7). Episodic eruptive activity continued into April. The information for the following report, covering December 1999 to March 2000, was compiled by Boris Behncke at the University of Catania, with additional information from Marco Fulle, Roberto Carniel, and Jürg Alean of Stromboli On-Line. The compilation is based on personal visits to the summit, observations from Catania, and other sources cited in the text.

Table 7. Chronology of eruptive episodes from the Southeast Crater at Etna, 26 January-24 March 2000. Courtesy of Boris Behncke.

Activity at Southeast Crater, 26 January-29 February 2000. Eruptive activity resumed early on 26 January at the summit vent of SEC (figure 83), after 4.5 months of quiet, and 2.5 months after the cessation of lava emission from fissures at its SE base. Initially the activity was Strombolian, but at about 0500 the activity changed to fire-fountaining, followed by the opening of a fissure on the S flank of the cone. Fountaining continued intermittently until about noon, but lava continued to flow from the lower end of the fissure until the late evening, advancing ~2.5 km into the Valle del Bove along the S margin of the 1999 lava field. Field inspections later revealed that numerous blocks of older lava and welded scoriae from the upper part of the cone fell up to 500 m from the summit of the cone.

Figure 83. Map of the summit area of Etna showing the approximate extent of lavas erupted from the Southeast Crater (SEC) between late January and March 2000. Flows terminating in arrows indicate the flow direction rather than its length. Lavas erupted from fissures near SEC between February and November 1999 and from Bocca Nuova in October-November 1999 are shown for comparison. The broken line extending from TDF (Torre del Filosofo) to the W is the margin of the Piano caldera, presumably formed during a powerful explosive eruption in 122 BC. V is the Voragine and BN is the Bocca Nuova. Courtesy of Boris Behncke.

The second eruptive episode, on the morning of 29 January, lasted about 15 minutes. As during the preceding episode, the cone fractured on the S side, and lava flowed for a few hundred meters to the SSE and SE. After the cessation of lava fountaining, lava continued to trickle from the fissure until the evening.

Beginning on 1 February, eruptive episodes occurred at ever shorter intervals. For the next four days, these events were separated by quiet intervals of 20-24 hours. They essentially resembled the second episode, with initial mild Strombolian activity followed by lava fountaining at the summit vent. Fountaining continued for a few minutes before the S flank of the cone fractured and small fountains rose along the fracture, while lava flowed from its lower end. Activity continued for up to 10 minutes and then ceased.

During these days intermittent minor lava effusion occurred from vents on the lower N flank of the SEC cone, feeding short flows. On the evening of 4 February the lava output gradually increased. Mild Strombolian activity began sometime before 2330 from a vent high on the SSW flank. By this time lava apparently spilled over the N rim of the crater. The volume of lava running down the N flank increased, and explosive activity at the summit vent (and possibly at the SSW flank vent) became increasingly vigorous. Shortly after 0010 on 5 February the activity culminated with lava fountains and voluminous lava emission. After only ten minutes the activity began to diminish.

Between 5 and 18 February, eruptive episodes occurred at a rate of 2-3 events/day, separated by quiet intervals of 5.5-26 hours. During the first ten days of this period, lava slowly issued from the vents on the N flank of the SEC cone. Before each episode the volume of lava output gradually increased, followed by the onset of lava spattering at the same vents and increasing gas emission from the summit vent. The spattering soon graded into a continuous fountain of very fluid lava, jetting obliquely from the N-flank vents, and then the activity would extend to one or more vents at and near the SEC summit. At the height of the activity, an eruption column mainly consisting of white vapor rose several kilometers, and ash fell up to 40 km downwind. Towns at the base of the volcano, mostly in the E and SE sectors, received light rains of ash and lapilli.

During several episodes a fracture opened progressively across the N flank from the base up to the summit vent, with small fountains, while Strombolian bursts began at the summit vent. This activity rapidly culminated in high lava fountains from one or more summit vents. During an eruption late on 11 February, four fountains rose up to 400 m high, while a continuous line of smaller fountains played along the N-flank fracture. Lava flowed copiously from the lower end of that fracture, while a new vent high on the S flank fed a lava flow which reached the base of the cone. The activity became intermittent after 10 minutes of fountaining and ended shortly thereafter, while lava continued to flow at diminishing rate from the lower end of the N-flank fissure.

An eruptive episode on the afternoon of 14 February was observed from less than 1 km away by Behncke and Giuseppe Scarpinati (Italian delegate of the Association Européenne Volcanologique), who had arrived shortly before the onset at a spot SE of the cone. Like on other occasions, the activity started with increasing gas emission from the vents on the lower N flank. By 1600 a broad, dull red fountain roared to a height of ~100 m, and gas emissions increased rapidly on the upper N flank. Small rockfalls occurred on the SE flank.

Soon after 1605 a huge jet of glowing bombs from the summit formed a rapidly expanding eruption column. Shortly thereafter, a densely tephra-charged, cauliflower-shaped plume burst obliquely upwards from the S side of the summit. At the same time, incandescent pyroclastics fell far beyond the base of the cone, but none hit the area from where Behncke and Scarpinati were located. Instead, the curtain of falling ash and scoriae rapidly extended southwards, towards Torre del Filosofo, a mountain hut ~1 km S of the SEC. Scoria clasts up to 30 cm long fell around the building. Lapilli-sized scoriae fell abundantly up to 5 km to the S, and ash fell up to 50 km away. The continuous loud rumbling of the fountains mixed with the pattering noise of large clasts impacting the snow near Torre del Filosofo. Lava could be seen flowing down the S flank in a broad stream a few minutes after the onset of explosive activity. At about 1620, the activity began to wane, although lava trickled from a vent high on the S flank for several hours.

The next day, after 26 hours of quiet, the most powerful episode of the sequence was observed from Torre del Filosofo by a group including Marco Fulle of the Astronomical Observatory of Trieste, Italy. The event was heralded by increased gas emission from the summit vent shortly before 1800, followed by mild Strombolian activity. For about 10 minutes there was a gradual buildup of the activity, with Strombolian bursts from at least two vents. As the activity became more continuous, incandescent pyroclastics were thrown to ever greater distances, mainly onto the E flank. Shortly after 1800, a glowing spot appeared immediately below the S lip of the summit vent in a deep notch. A small pulsating fountain from this new vent gained rapidly in height and vigor. Eruption noises began to change from the intermittent gushing of the Strombolian activity to a continuous loud noise similar to heavy surf.

Within 1-2 minutes after the appearance of the S-flank vent, huge jets of fluid lava rose from that vent and from vents at the summit. The volume of lava from the S vent increased rapidly, at times generating surges overriding earlier flows. The upper part of the cone was soon covered by incandescent pyroclastics; most fallout occurred on the E side due to a strong wind from the W. Activity escalated when a huge incandescent jet burst obliquely from the S vent in the direction of the Torre del Filosofo, and within a few seconds it rose to a height of ~1,000 m. The noise soon became dominated by thousands of bombs crashing on the ground at rapidly growing distance from the cone. The observers fled under a side roof of the Torre del Filosofo building a few seconds before bombs began falling around and beyond the building. Some of them had diameters of tens of centimeters, and many were seen bouncing and bursting into fragments. This rain of bombs lasted about 20 seconds, after which activity stabilized with lava jetting vertically from S-flank and the summit vents.

As was evident from video filmed by British cameraman David Bryant, the largest fountain came from the summit, and from the video as well as from estimates made by other observers, including Behncke (in Catania) and Scarpinati (in Acireale), the fountain height was consistently 500-600 m with bursts reaching 800 m above the summit. The entire cone was covered with incandescent material, some of which developed secondary flowage, while a broad lava flow ran down the S flank.

About 10 minutes after the onset of violent fountaining, the fountains from the cone appeared slightly weaker, although the continuous uprush continued for some time. Then the fountains stopped abruptly, while thousands of incandescent projectiles continued to fall onto the cone. After a few seconds, new lava jets appeared that were short-lived and much weaker. At the end of the activity, dense ash from the summit vent blew E as far as Acireale. Lava continued to run out of a fracture on the S flank, and the gradual sinking of the lava level in the fracture indicated that the conduit was subsiding.

On the afternoon of 16 February, Fulle observed another eruptive episode from the Torre del Filosofo. This event included lava fountaining from a vent about halfway down the S flank of the SEC cone. The activity then extended to the summit vent, continued vigorously for about 10 minutes and ended abruptly.

Eruptive episodes began to diminish in frequency and intensity after 18 February. The near-continuous effusive activity at the N-flank vents stopped. During the last 10 days of the month, five episodes occurred. On the early morning of 23 February, an episode lasted more than 1 hour, but consisted mainly of strong Strombolian explosions. The last two episodes of February, on the 27th and 28th, involved significant activity from vents near the S base of the cone. In both events the activity lasted for several hours, and erupted more lava from the S vents than during earlier episodes. During some of the episodes lava was apparently also produced from N-flank vents.

Activity at Southeast Crater during March. Episodic eruptive activity at the SEC continued in March and became more focused at the vents at the S base of the SEC cone, where a cone began to grow. This cone was informally named "Sudestino" (little Southeast), following the example of the "Nordestino," a lava shield crowned by a large hornito that formed in 1970 at the NE base of the Northeast Crater. In late March, the main focus of activity returned to the SEC, and episodes became very similar to those of early- to mid-February, with lava emission mostly from fractures on the N and S flanks of the SEC cone.

The initial March activity began on the late afternoon of 3 March. At first the activity consisted of slow lava effusion from Sudestino. Loud detonations became audible in Acireale and other towns in the SE and E sectors around 0400 on 4 March, marking the period of strongest explosive activity. Scarpinati, who observed the activity from his home in Acireale, noted that even in the moments of strongest activity, no sustained lava fountaining occurred, but all activity consisted of discrete powerful explosions. When the activity began to diminish (at about 0430), a fountain of very fluid lava in the area of the Sudestino rose ~30 m. The episode ended at about 0500, but after 0430 most activity appears to have come from Sudestino. Minor outflow of lava continued for about two days from Sudestino. Another episode on 8 March was preceded by slow lava effusion from Sudestino. During a summit visit by Behncke and others on 11 March, the SEC and Sudestino were quiet.

Sudestino erupted again shortly after noon on 12 March. The activity began with increased gas emission, and by about 1300 a lava fountain rose to a height of several tens of meters. Ash was expelled from the crater lying a short distance further up the S flank. Later a densely ash-laden plume was emitted from the summit. Lava flowed abundantly from Sudestino, mainly to the S and SW. A lava flow passed only a few tens of meters W of the Torre del Filosofo and extended ~100 m down the steep slope, burying a section of the dirt road that leads to the building.

The Sudestino vent erupted once more on 14 March with a brightly incandescent lava fountain and emission of a voluminous lava flow that advanced to the S with a front hundreds of meters wide, reaching Torre del Filosofo sometime after 1100. Eyewitnesses reported that by about 1100 the lava front was still ~50 m from the building, but presumably the lava reached and encircled it on two sides shortly afterwards. The wooden shack next to the building, used as a souvenir shop by mountain guides during the summer, was burnt by the lava, melting the snow which had covered the shack. Lava flowed ~100 m further down the slope to the W of Torre del Filosofo. A new dirt road built on this flow two days later allowed monitoring and communication equipment to be salvaged prior to the building's destruction.

Lava fountains were visible at the Sudestino around 0130 on 19 March, by which time lava had already begun extending down the flanks. The activity continued vigorously until about 0300, and generated significant ash that fell in Catania and surrounding areas. A large volume of lava was emplaced on the plain SW of the SEC, and several flow lobes extended as far as the N base of Monte Frumento Supino, a prehistoric cinder cone (figure 83).

Sometime after 1800 on 22 March, mild Strombolian activity began at the summit vent, and by 1945 there was a pulsating lava fountain. A new vent burst open high on the SSW flank at about 2010, emitting a lava flow and producing a small fountain. The activity progressively increased at both vents until another vent opened at about 2025 near the NE base of the cone. At this vent, a lava fountain rapidly began to rise several tens of meters high, while two lava flows spilled into the adjacent Valle del Bove. The lava fountain from the summit began to diminish, and ceased shortly before 2100. Lava continued for some time from the flank vents. The southern flow rapidly reached the WSW base of the cone and turned W or WSW, in the direction of the 1971 "Observatory cone." About 500 m NW of Torre del Filosofo the flow turned SW and reached the slope near Monte Frumento Supino, where it advanced up to 100 m. On the NE side of the SEC cone, the two lava flows advanced several hundred meters into the Valle del Bove.

Lava effusion from the vents on the NE side of the SEC cone increased during the late afternoon of 24 March. Mild spattering and intermittent glow at the summit indicated the onset of Strombolian activity. This activity graded into a lava fountain shortly before the new year (2000), and a second, smaller fountain played at the effusive vent on the NE side of the cone. Lava flowed into the Valle del Bove, reaching a length of possibly more than 1 km. Sometime after the new year began, a vent opened on the upper S flank of the SEC cone, feeding a minor flow. The activity was still vigorous at around 2030, when loud rumbling noises could be heard in Catania, and windows were vibrating in Acireale and other towns nearer to the volcano. The strongest activity apparently ceased by 2100, but at 2230 there was still vigorous effusive activity.

The last significant activity of the reporting period occurred on the evening of 29 March, after five days of quiet, the longest repose period of the eruptive sequence. Lava effusion from vents on the NE side of the cone became evident after nightfall and gradually increased, accompanied by the weak Strombolian activity at the summit vent. By 2000, the Strombolian bursts had become more frequent, and soon blended into a continuous pulsating fountain. A new vent high on the S flank emitted a lava flow that rapidly spilled to the base of the cone, then was deflected to the SW by the Sudestino. During the following 30 minutes, at least three smaller vents opened at progressively lower elevations on the S flank in the direction of Sudestino. After the opening of the first S-flank vent, activity at the summit became weaker and discontinuous. Sometime around 2120 large fountains from vents on the N flank sent lava flows NE towards the Valle del Leone. Fountaining ceased at around 2200, but lava continued to flow from the N vents, feeding several lobes, the longest of which advanced ~2 km into the Valle del Leone. On the S side, lava extended ~1-1.5 km SW to the N base of Monte Frumento Supino.

Activity at Bocca Nuova, Voragine, and Northeast Crater. During December 1999-25 January 2000 Bocca Nuova produced intermittent mild Strombolian activity that at times ejected bombs outside the crater. Ash emissions were frequent in late December and early January.

Activity at Bocca Nuova during the eruptive episodes at SEC continued at relatively low levels. During a summit visit on 2 February, Behncke and Scarpinati observed frequent small explosions from the E part of the crater, but all ejecta fell back into the vent. Six days later, Behncke and Scarpinati entered the crater from the SW – this had become possible due to the filling of the crater in October-November 1999 – and approached the vent which was the source of intermittent night glow for most of February. Activity consisted of vigorous gas emission, punctuated by strong blasts of incandescent gas, but no pyroclastic ejections. When standing on the edge of the vent, Behncke and Scarpinati saw an incandescent hole ~2 m across on the floor of the funnel-shaped vent which was the source of the gas ejections. Scarpinati noted that the activity was similar to that observed during the first year of the life of the Bocca Nuova, when it was only a small vent ~8 m wide.

The same activity was observed in early March by Charles Rivière (from Tremblay-en-France, France). In late March activity was the same as in early February, consisting of jets of incandescent gas without pyroclastic ejections. A small amount of strongly altered, fine-grained lithics were sometimes contained in the gas jet. It appeared that no ejections of fresh magmatic material had occurred within the Bocca Nuova since at least early February.

The other two summit craters remained essentially quiet during the reporting period. Northeast Crater occasionally produced emissions of thick gas plumes, at times charged with a little lithic ash. No eruptive activity is known to have occurred at the Voragine. When seen by Behncke on 8 February, the crater emitted only wisps of vapor from the large pit formed during the 4 September 1999 eruption.

Geologic Background. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km horseshoe-shaped caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Information Contacts: Boris Behncke, Dipartimento di Scienze Geologiche, Palazzo delle Scienze, Universitá di Catania, Corso Italia 55, 95129 Catania, Italy; Roberto Carniel, Dipartimento di Georisorse e Territorio, Universitá di Udine, Via Cotonificio 114, 33100 Udine (URL: http://www.swisseduc.ch/stromboli/); Jürg Alean, Kantonsschule Zürcher Unterland, CH-8180 Bülach, Switzerland; Marco Fulle, Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34131 Trieste, Italy.

During 1 January-15 April 2000 there were two small eruptive episodes preceded by 24 tornillo ("screw-type") seismic events which showed dominant frequencies around 2.0 Hz and other peaks from 5 to 18 Hz. Volcano-tectonic events centered NE of the crater were also felt by local residents.

The first eruptive episode occurred on 21 March at 1628. The seismic signal associated with this activity was characterized by long-period events followed by 30 minutes of spasmodic tremor, and then 17 small long-period events registered in the following three hours. The dominant frequency of the main event was around 2.0 Hz, but at the nearest station to the crater other frequencies between 5 and 13 Hz were recorded. Field inspections before and after the 21 March eruption revealed fluctuations in the output pressure and in the quantity of gas emitted from the active vents; emissions were generally gray and white in color. Temperature measurements taken during March at Las Deformes fumarole (SSW border of the main crater) registered values of 124-127°C, which are similar to those observed in recent years. However, Las Chavas fumarole (WSW border of the main crater) showed a significant temperature increase one day before the 21 March eruption.

The second eruptive episode, on 5 April at 1738, was smaller than the 21 March event. Its associated seismicity was characterized by spasmodic tremor. The dominant frequency was around 2.4 Hz, but again at the nearest station to the active crater other frequencies between 6 to 17 Hz were observed.

Radon-222 soil emissions measured at stations around the volcano showed values between 98 and 8,619 pCi/l. Most of them were unchanged from previous measurements. The highest peak correspond to the Sismo5 station, located 7 km N of the summit.

Two volcano-tectonic events during this period were felt in some areas of Pasto city and Nariño town; a maximum Modified Mercalli Intensity of III was estimated in these regions. The first event occurred on 10 January centered 10 km NE of the summit at a depth of 8 km and with a magnitude of 3.2. The second event occurred 5 km NE of the summit on 6 April, with a depth of 9 km and a magnitude of 2.4.

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

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

This report covers the interval from 16 January to 28 February 2000 (table 10). This interval was marked by poor visibility and small emissions, some with and some without visible ash. These rose on the order of a few tens of meters to 2 km. Besides small ash emissions, evidence of the ongoing gradual growth of the dome (locally termed "dome 8") was provided by abundant rockfalls in the W crater, sulfurous odors, minor local ashfalls, and infrequent glimpses of extrusions and various changes within the crater. Several intervals of near-quiet also occurred.

Table 10. Seismic observations at Guagua Pichincha, 16 January-28 February 2000. The table shows the daily tally of these categories of earthquakes: long-period (LP), volcano-tectonic (VT), hybrid, rockfall, and emissions. Explosions were only recorded on 20 January (4) and 17 February (1). Dashes indicate a lack of (essentially zero) reported events. Courtesy of the Geophysical Institute.

The daily reports noted that small emissions occurred on many days in the reporting interval, which is also clear from the seismically based tallies shown on table 3. On the morning 19 January, the atmosphere was clear enough to see incandescent lava glowing through fractures in the dome. Observers noted lulls in fumarolic activity on 19 and 20 January, as well as on 22 and 23 January; in some cases they saw small, blue-tinged (sulfur-bearing) plumes that only rose 20-100 m. On 22 January observers looked into the small inner crater formed in 1999 (termed the "Herradura crater" or the "1999 crater") and noted a recent accumulation of fallen rocks there, including about twelve that stood ~10-12 m above the floor. Although the daily report noted that these rockfalls traveled in the direction of the head of the Río Cristal, their source was not made clear.

Starting at 1521 on 26 January a seismic emission signal with a small-to-moderate reduced displacement persisted for 120 minutes. Ash then fell W of the volcano. This emission followed a high-frequency seismic signal that possibly stemmed from a partial dome collapse. The possibility of a collapse appeared confirmed when observers noted the 26 January collapse of the crater's W zone. The latter event spawned a pyroclastic flow in the Río Cristal; associated deposits there exceeded 10 m in thickness.

In the morning on 1 February police reported the newly ash-covered Herradura crater generated white fumarolic columns that rose between 300 to 500 m. Blue vapors also hung in the air, indicating the presence of sulfur gases. On 2, 3, 12, 20, and on 28 February plumes rose to 1-2 km. In several cases the plumes carried noticeable ash, and a few ash falls were seen near the vent. The 12 February ash plume rose 1.3 km high; the plume's lower margins extended to engulf all sides of the caldera.

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

Information Contacts: Geophysical Institute (Instituto Geofísico), Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador.

Seismic monitoring disclosed many days during June-November 1999 without any detectable microseisms. Monthly averages for July-November 1999 (table 6) tallied 12 to 61 microseisms a month, an average of roughly 0.5-2 microseisms per day. Other monitoring data were absent. The last eruption at Irazú consisted of a small phreatic explosion in December 1994 (BGVN 19:12).

Table 6. Monthly microseisms at Irazú as recorded at station IRZ2, located 5 km SW of the active crater, July-November 1999. The two months with available RSAM data show the range of computed values (e.g., October estimates of 7 to 101 units). Courtesy of OVSICORI-UNA.

Geologic Background. Irazú, one of Costa Rica's most active volcanoes, rises immediately E of the capital city of San José. The massive volcano covers an area of 500 km2 and is vegetated to within a few hundred meters of its broad flat-topped summit crater complex. At least 10 satellitic cones are located on its S flank. No lava flows have been identified since the eruption of the massive Cervantes lava flows from S-flank vents about 14,000 years ago, and all known Holocene eruptions have been explosive. The focus of eruptions at the summit crater complex has migrated to the W towards the historically active crater, which contains a small lake of variable size and color. Although eruptions may have occurred around the time of the Spanish conquest, the first well-documented historical eruption occurred in 1723, and frequent explosive eruptions have occurred since. Ashfall from the last major eruption during 1963-65 caused significant disruption to San José and surrounding areas.

Information Contacts: E. Fernandez, E. Duarte, V. Barboza, R. Sáenz, E. Malavassi, R. Van der Laat, T. Marino, J. Barquero, and E. Hernández, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.

Activity remained at a low level during 1-20 January and no unusual volcanism was reported for February or March. Reports were absent for 21-31 January, but earlier in the month Crater 2 released weak thin-to-thick white vapor in moderate volumes. On 3-6, 19, and 20 January the emissions included weak gray and brown ash clouds. Crater 3 released weak white vapor throughout the month. The seismograph remained non-operational.

Langila, one of the most active volcanoes of New Britain, consists of a group of four small overlapping composite cones on the lower eastern flank of the extinct Talawe volcano. Talawe is the highest volcano in the Cape Gloucester area of NW New Britain. A rectangular, 2.5-km-long crater is breached widely to the SE; Langila volcano sits NE of the breached crater of Talawe. An extensive lava field reaches the coast on the north and NE sides of Langila. Frequent mild-to-moderate explosive eruptions, sometimes accompanied by lava flows, have been recorded since the 19th century from three active craters at the summit of Langila. The youngest and smallest crater (Crater 3) was formed in 1960 and has a diameter of 150 m. The Cape Gloucester observation post, airstrip, and seismometer is 9 km N of the volcano.

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

Information Contacts: I. Itikarai, D. Lolok, K. Mulina, and F. Taranu, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.

Weak activity at Manam continued during 1-16 January, and the months of February and March 2000. (Reports for the second half of the month were not received.) During 1-16 January Main and Southern craters both issued weak white vapor. By the end of the second week of January seismicity had reached a trough similar to that in mid-December. Still, the average number of daily earthquakes was over 1,000 (specifically, 1,160-1,470 except on 3 and 4 January, when they were 820 and 300). The wet tilt readings (available until 5 January) showed minor fluctuations.

Seismicity remained low, with amplitude measurements at normal background level until 18 March, when amplitudes increased slightly but remained within the background range. The higher level continued through March. Event counts were also steady through this period, averaging ~1,200/day, although several days in March had only 500-600. The water-tube tiltmeter ~4 km SW of the summit area measured ~14 µrad of inflation in March. The inflation began sometime in late January 2000.

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

Information Contacts: I. Itikarai, D. Lolok, K. Mulina, and F. Taranu, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.

Seismic activity registered at Momotombo stayed at consistently low levels during the seven months of April-November 1999, with a total of 81 small earthquakes, 30 of them in May and 26 in August. Only a few of these events were able to be located. RSAM (real-time seismic amplitude measurement) values never rose above two units. Starting in December, and continuing through March 2000, the seismic station only worked intermittently. Very few events were detected during this period, including two earthquakes when the station worked during 1-15 March.

Geologic Background. Momotombo is a young stratovolcano that rises prominently above the NW shore of Lake Managua, forming one of Nicaragua's most familiar landmarks. Momotombo began growing about 4500 years ago at the SE end of the Marrabios Range and consists of a somma from an older edifice that is surmounted by a symmetrical younger cone with a 150 x 250 m wide summit crater. Young lava flows extend down the NW flank into the 4-km-wide Monte Galán caldera. The youthful cone of Momotombito forms an island offshore in Lake Managua. Momotombo has a long record of Strombolian eruptions, punctuated by occasional stronger explosive activity. The latest eruption, in 1905, produced a lava flow that traveled from the summit to the lower NE base. A small black plume was seen above the crater after a 10 April 1996 earthquake, but later observations noted no significant changes in the crater. A major geothermal field is located on the south flank.

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/).

Comparative quiet continued at Poás; however, in addition to the fumarolic degassing often seen, seismicity was relatively high during the reporting period, June 1999-January 2000, when low-frequency earthquakes typically registered over 4,000 times per month (table 9). For comparison, a relative high in 1999 occurred in May when low-frequency events occurred ~1,400 times, and during a high in January 1998, when there were over 2,500 events. On 18 July 1999 an MR 3.1 earthquake occurred with 6 km focal depth and an epicenter 5 km NW of the active crater.

Table 9. A summary of seismic, temperature, and lake height data for Poás during July 1999-January 2000. Lake heights are with respect to the previous month and positive upwards (rising lake levels). The stated temperature for the pyroclastic cone's degassing refers to the value at an accessible point where the measurements are taken regularly. The seismic station POA2 lies 2.8 km SW of the active crater. "NR" indicates information absent and not reported. Courtesy of OVSICORI-UNA.

Tremor, which was seldom reported in 1999, took place for less than about 0.5 hours a day during October-November 1999. In contrast, tremor averaged only 0.1 hours a day during December 1999. In contrast, tremor durations of 20 to 70 hours were common in early 1998. Also appearing in the month of October 1999 were 5 unusual low-frequency events in conjunction with tremor; these low-frequency earthquakes had periods of 40-175 seconds.

During August -October, the pyroclastic cone's degassing led to unusually high plumes reaching 0.7 to 2 km above the crater floor. December plume heights ranged between 0.7 and 1 km. Some of the hottest temperatures were measured near the pyroclastic cone: up to 95°C during December-January and often over 92°C when reported during other months in late 1999.

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

Information Contacts: E. Fernandez, E. Duarte, V. Barboza, R. Sáenz, E. Malavassi, R. Van der Laat, T. Marino, J. Barquero, and E. Hernández, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.

After the emissions of dark gray ash clouds from the 1941 vent on 30 December 1999, through 16 January 2000 activity consisted mostly of thin white and grayish clouds. Occasional pale gray to dark gray ash clouds of moderate volumes were interspersed among the ongoing thin white vapor emissions.

The 1995 lava-producing vent reactivated on 16 January at 1532 with emissions of dark gray ash clouds until the 18th, before going quiet again at month's end. The initial emissions on 16 January occurred frequently (4/minute) during the first 30-45 minutes before decreasing to 1/minute thereafter. The ash clouds rose ~500-1,000 m above the summit and were later blown by high-altitude winds to the N and low-altitude winds to the SE, resulting in ashfalls in those directions.

Seismicity associated with the ongoing activity at Tavurvur was very low in January. A total of 66 low-frequency events were detected, of which most were associated with surface activity. The only harmonic tremor was recorded on the 30th. Nine high-frequency events were recorded during the month. Only two of these events which originated NE of the volcano, were located outside of the caldera. The other seven were too small to locate; however, their arrival times indicated an azimuth of NE.

The eruptive activity remained low throughout February. Gentle emissions of very thin volumes of white vapor continued for most of the period. However, between 7 and 14 February small volumes of pale gray ash clouds were produced at irregular intervals, and seismicity fluctuated. Again between 21st and 22nd small amounts of white-to-brownish ash clouds were produced. Most of the ash emissions during both periods rose to several hundred meters above the summit before they were blown to the SE and occasionally to the N, NW, and SW by variable winds. Very fine ash fell in the same areas.

Event trigger counts were similar to December 1999 and January 2000, with a total of 78 low-frequency events detected. Most of these were associated with the summit activity of Tavurvur. Three high-frequency earthquakes were detected in February. Two were located to the S and NE, outside of the caldera. The other was too small to locate, however, arrival times on the few stations that detected it indicated a NE azimuth.

A slight increase in ash emission associated with sub-continuous non-harmonic tremor was observed in March. Bands of such tremor were recorded on 8, 14-20, and 30-31 March. The tremor occurred only once each day, but at different times of the day. The duration for each episode of tremor ranged from an hour to about 5 hours. During the corresponding period of 15-20 March, Tavurvur's 1995 vent produced occasional gentle puffs of thick gray ash clouds that were blown SE by low-altitude winds and later to the W by high-altitude winds. Similar ash emission was observed on 31st. On that day the ash clouds rose only a few hundred meters at the highest and were later blown N and NW. The 1941 vent remained quiet, releasing only very small volumes of thin white vapor.

March's low-frequency earthquakes continued to fluctuate around normal background. Trigger counts for March were 90. Most of these events were associated with the summit activity of Tavurvur. Seven high-frequency earthquakes were detected in March. Three were locatable. The others occurred outside of the caldera. Ground deformation measurements by the electronic and water-tube tilt instrumentation showed an inflationary trend which began in late February.

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

Information Contacts: I. Itikarai, D. Lolok, K. Mulina, and F. Taranu, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.

The noisy escape of fumarolic gases continued at Rincón de la Vieja during June-November 1999. A summary of monitoring data appears in table 3. During August the crater floor became covered with a shallow ephemeral lake, covering the fumaroles there. Plumes then rose less than 100 m above their fumarolic sources. The active crater lake, with a sky-blue color, had a temperature of 36°C; the maximum measured fumarole temperature was 70°C.

Table 3. Geotechnical data at Rincón de la Vieja, July-November 1999. Seismic data recorded at station RIN3, 5 km SW of the active crater, includes microseisms who's amplitudes were under 5 mm, and those volcano-tectonic (VT) earthquakes with S minus P arrival times under 1.5 seconds (i.e. focused near the volcano). The reported tremor durations were sums of discontinuous segments, and were low-frequency (below 2 Hz). Courtesy of OVSICORI-UNA.

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

Information Contacts: E. Fernandez, E. Duarte, V. Barboza, R. Sáenz, E. Malavassi, R. Van der Laat, T. Marino, J. Barquero, and E. Hernández, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.

Seismic and eruptive activity consisting of gas-and-ash explosions continued during January. Observations from the León-Chinandega highway during fieldwork on 13 January showed that constant strong ash-and-gas emissions were continuing (figures 12 and 13). A resident on the S flank informed the scientists that strong rumblings had been heard at dawn on the 12th. The observers remained near the summit for several hours and witnessed moderate explosions every five minutes, with occasional periods of more frequent explosions (3/minute). The bottom of the crater could not be seen through the ash, but it appeared that the explosions did not come from the intercrater that formed in May 1999, but from a new vent in the NNW part of the crater. Evidence of collapses were present along all sides of the crater. In January the number of volcanic earthquakes was 3,950, and the RSAM (real-time seismic amplitude measurement) signal oscillated between the 40 and 120 units.

Figure 12. Photograph of the active crater during an ash explosion at Telica, 13 January 2000. View is from the south. Courtesy of INETER.

Figure 13. Photograph of Telica, 13 January 2000. View is from the north. Courtesy of INETER.

Low-intensity eruptive activity with ash-and-gas emanations continued through 17 February, after which the activity began to gradually decline. However, seismicity stayed high with 3,670 earthquakes detected in February. The volcano maintained constant tremor during March, but despite the continued high number of registered earthquakes (2,892) there were no gas or ash expulsions.

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/).

Following several days of increased seismicity, an eruption of Usu volcano began on 31 March. The eruption, the first at Usu since 1977-82, was continuing in April. This report is based on information compiled from a wide variety of sources cited in the text by Setsuya Nakada at the Volcano Research Center, University of Tokyo. Vigorous activity continued through April, and by the end of the month there were more than 50 craters; details will be provided in the next Bulletin.

Precursory activity. The number of volcanic earthquakes around Usu began increasing after 0800 on 27 March, prompting a series of Volcano Advisory notices from the Japan Meteorological Agency (JMA). At the site of the seismic station, ~2 km S of the summit, there were 16 earthquakes recorded on 27 March, followed by 599 (including 68 felt earthquakes) on the 28th (table 5). Neither volcanic tremor nor visible change in fumarolic gas had been observed by the night of 28 March.

Table 5. Numbers of earthquake events at Usu during 27 March-4 April 2000. The JMA seismometer is located ~2 km S of the summit. Courtesy of JMA.

On the evening of 28 March the National Coordination Committee of Volcanic Eruption Prediction (chaired by Yoshiaki Ida, Univ. of Tokyo) warned about the high possibility of an imminent eruption. JMA also called resident's attention to the hazard of mudflows triggered due to snow melting during an eruption. A hot spring resort at the N foot of the volcano had about 1,600 guests this night. However, more than 400 persons living around the volcano voluntarily evacuated by the night of 28 March.

A Volcano Alert was issued by JMA on the morning of 29 March. That day the number of volcanic earthquakes totaled 1,629 (600 of them felt), including low-frequency earthquakes whose number increased with time. At 0708 on 29 March a M 3.4 had a hypocenter on the N slope. Later that day, at 1722, one of M 4.2 was centered on the NW slope; analysis indicated faulting along a nearly vertical slip plane. The GPS network around the volcano, maintained by the Geographical Survey Institute (GSI), detected inflation. Neither volcanic tremor nor visible changes in fumarolic gas had been observed yet. People living in a city and two towns around the volcano were required to evacuate on the afternoon of 29 March. By that night, more than 9,000 people evacuated, including all tourists in resorts at the N foot of the volcano.

The number of volcanic earthquakes continued to increase on 30 March, to a total of 2,454, including 326 low-frequency earthquakes and 537 felt events. During a helicopter flight, Yoshio Katsui and Hiromu Okada (Hokkaido University) found chains of cracks as long as 100 m along the NW part of the caldera rim, just above the hypocenters of the volcanic earthquakes. A group of geologists from the same university, the Geological Survey of Japan (GSJ), and the Geological Survey of Hokkaido also found small cracks and signs of ground deformation at the N-NW foot of the volcano. The hot-spring resort on the S shore of Lake Toya, Toyako-Onsen, lies within the area that these phenomena were observed. The Usu Volcano Observatory of Hokkaido University, at the N foot of the volcano, was moved ~8 km S to the western part of Date City. Frequency and magnitude of earthquakes changed in a manner similar to that seen in the 1910 eruption; that event started with a phreatic eruption after 5 days of precursory phenomena. This was followed by explosions from 45 craters aligned along a 2.7-km-long, EW-trending zone. The 1910 eruption ended with a 3-month period of cryptodome emplacement.

Eruptions begin on 31 March. At 1310 on 31 March a phreatic eruption ~4 km NW of the summit and ~2 km NE of the epicenters of the volcanic earthquakes sent ash 3,200 m above the crater. Ash and cinders from the newly formed craters fell on nearby houses. After about 2 hours of strong ash emissions the eruption declined. No injuries were reported. According to Yoshio Katsui, who did a helicopter inspection, five craters formed successively that joined into one larger crater (roughly 200 m long and 60 m wide) during this eruptive episode.

According to the Joint University Research Group (JURG) on the morning of 31 March, additional cracks were observed in the W flank of the volcano, and on the summit of the old lava dome within the caldera. Cracks found the previous day on the NW flank and foot of the volcano became wider. Seismicity had decreased from the previous day.

According to a Volcano Advisory at 0312 on 1 April, a M 4.8 earthquake occurred, the largest so far during this eruption. Observations using a JMA camera indicated that another phase of the eruption started at the W foot around 0250, when explosions formed new craters near the previous craters W of Nishi-yama and also 1.5 km NE, on Konpira-yama. The latter were close to houses in the resort on the shore of Lake Toya. Cock's-tail-shaped jets were frequently observed from the active craters. Sometimes eruption clouds rose more than 2 km above the vents. According to Tadahide Ui, petrological work in Hokkaido University identified a few juvenile fragments in the products of the first eruption. Takayuki Kaneko (VRC, U. Tokyo) inspected the craters from the Asahi Shinbun news helicopter on 1 April (figure 21 and table 6).

Figure 21. Topographic map of the NW sector of Usu, showing the distribution of new craters in the Nishi-yama and Konpira-yama dome areas, 1 April 2000. The summit, on the O-Usu dome, is at the lower right. Craters are numbered in the order of their opening. Courtesy of Takayuki Kaneko.

Table 6. Venting from west of Nishi-yama dome (craters A1-A6) and near Konpira-yama dome (craters B1-B2) at stated times on 1 April 2000, as seen from helicopter by Takayuki Kaneko (VRC, U. Tokyo). Craters formed in the same order as their numbers, but the opening sequence of A4 and A5 was unclear.

According to the JURG and the GSJ, deformation on the NW part of the volcano continued. During 31 March to 1 April, with respect to the volcano's foot, the NW caldera rim uplifted by as much as 30 cm a day and migrated NE by 25 cm over a period of 19 hours. Small crack systems observed in the N foot also supported some slow but continual migration on the NW part of the volcano.

The GSJ and Hokkaido University noted that on 2 April fresh pumice fragments floated in Toya Lake, ~3.7 km ENE of the 31 May eruption vent. Three faults extending E-W for a few hundred meters were seen on 3 April near the explosion craters (NW of Nishi-yama). The maximum throw of the faults was ~10 m. They form a normal fault system with subsidence in the N side according to Kiyoaki Niida of Hokkaido University. A new fault system was found on 4 April a few hundred meters N of the one near the craters NW of Nishi-yama, according to Okada, and the area between the two fault systems was subsiding to form a graben. In early April, the fracture, which formed near the NW part of the summit caldera rim on 30 March, widened to ~4-5 m. The eruptive activity continued and the Asahi newspaper reported that at 1700 on 4 April at least one new crater lying between the two existing groups of craters sent a white plume 600 m high.

A new crater formed on the morning of 5 April on Konpira-yama near the previous two craters and sent a grayish plume to ~400 m height, according to JMA. On the W slope of Konpira-yama, a mudflow moved down slowly toward the spa, raising steam.

The main edifice consists of basaltic to basaltic-andesites (49-53% SiO₂) with a small summit caldera. Ten dacitic lava or cryptodomes (68-73 % SiO₂) lie on the summit and N slope arranged in two lines trending NW-SE. The eruptions that occurred at the summit (in 1663, 1769, 1822, 1853 and 1977-82) commenced with a strong Plinian phase and, apart from 1977-82, were accompanied by pyroclastic flows. All but perhaps the 1769 eruption also involved the growth of lava or cryptodomes in the middle to final stages. Both summit (O-Usu and Ko-Usu) and flank (Showa-Shinzan) lava domes, along with seven cryptodomes, were erupted in historical time. The war-time growth of Showa-Shinzan was painstakingly documented by the local postmaster, who created the first detailed record of lava-dome growth.

During the flank eruptions (in 1910 and 1943-45) the building of lava or cryptodomes was preceded by phreatic explosions in the initial stage. Each eruption lasted from one month to two years, with between thirty and one hundred years of repose between them. According to Akihiko Tomiya (Geological Survey of Japan), precursory seismicity of the historical eruptions (mainly volcanic earthquakes) lasted from 32 hours (1977-82) to 6 months (1943-45).

Geologic Background. Usuzan, one of Hokkaido's most well-known volcanoes, is a small stratovolcano located astride the southern topographic rim of the 110,000-year-old Toya caldera. The center of the 10-km-wide, lake-filled caldera contains Nakajima, a group of forested Pleistocene andesitic lava domes. The summit of the basaltic-to-andesitic edifice of Usu is cut by a somma formed about 20-30,000 years ago when collapse of the volcano produced a debris avalanche that reached the sea. Dacitic domes erupted along two NW-SE-trending lines fill and flank the summit caldera. Three of these domes, O-Usu, Ko-Usu and Showashinzan, along with seven crypto-domes, were erupted during historical time. The 1663 eruption of Usu was one of the largest in Hokkaido during historical time. The war-time growth of Showashinzan from 1943-45 was painstakingly documented by the local postmaster, who created the first detailed record of growth of a lava dome.

Information Contacts: Volcano Research Center, Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-0032, Japan (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html); Geological Survey of Japan, 1-1-3 Higashi, Ibaraki, Tsukuba 305, Japan (URL: https://www.gsj.jp/); Usu Volcano Observatory, Institute of Seismology and Volcanology, Graduate School of Science, Hokkaido University, Sohbetsu-cho, Usu-gun, Hokkaido, 052-0103, Japan (URL: http://www.sci.hokudai.ac.jp/isv/english/); Japan Meteorological Agency, Volcanological Division, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100, Japan.

Mass wasting and elevated seismicity continued at Turrialba during July-November 1999 (table 4). The seismicity has appeared anomalously high since it increased suddenly during May 1996, escalating to 540 such events in September 1996. Microseisms have dropped since then, although they still remained at over 100 per month during September and October 1999. Between April and August 1999 scientists made surveys of the distance to a reflector 500 m from the active crater on the SW flank; these failed to show significant changes in length. After 18 September three new seismic receivers helped detect and locate three earthquakes, M 1.7-2.8, at depths of 3-11 km centered 2.5-10 km E, SE, and SW of the volcano.

Table 4. Monthly seismicity at Turrialba as recorded at station VTU, ~ 0.5 km E of the active crater. Microseisms were defined as earthquakes registered on the local seismic system with amplitudes under 15 mm. NR indicates information not reported. Courtesy of OVSICORI-UNA.

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

Information Contacts: E. Fernandez, E. Duarte, V. Barboza, R. Sáenz, E. Malavassi, R. Van der Laat, T. Marino, J. Barquero, and E. Hernández, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.

Low-level activity continued in January with weak emissions of thin white vapor throughout the month. Slightly stronger emissions occurred on 17 and 26 January. Emissions from the summit crater during February consisted of fluctuating volumes of thin-to-thick white vapor being released gently. March emissions consisted of thin white vapor. The seismograph remained out of operational.

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

Information Contacts: I. Itikarai, D. Lolok, K. Mulina, and F. Taranu, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.

Minor eruptive activity recommenced on 7 March when a vent on the ridge SW of PeeJay vent began producing very weak ash emissions. Following reports from tour operators of ash emissions and the progressive failure of the transmission signal from the island, a visit by IGNS scientists was made on 9 March to ascertain the status of the eruptive activity and repair the seismic system.

When they arrived on the island, a weak, ash-charged gas plume rose ~1,500 m above the vent before being blown downwind >40 km. Viewing conditions within the Main Crater area were excellent. The steam-and-ash cloud was being fed from four vents on the ridge SW of the May 1991 embayment. PeeJay vent also was active in this area during 1999. Two of the vents on the ridge continuously emitted light brown ash while the other two emitted vivid white gas plumes. There was no evidence of ash accumulating on the Main Crater floor or on the outer flanks of the cone, indicating insignificant total ash emission; there was also no evidence of impact craters. Moderate convection was present in the crater lake, although there was no discoloration of the lake, which remained a bright green color with light gray surface slicks.

COSPEC flights were conducted on 10 and 17 March to measure the SO₂ flux within the gas plume. The results indicated an average estimated flux of 2,256 metric tons/day, the highest SO₂ values ever recorded from White Island. Despite a significant change in SO₂ flux, a prominent 1,500-m-high gas plume, and a phase of sustained but very minor ash discharge, there had not been any associated seismic activity or visible escalation of activity as of 21 March.

Geologic Background. The uninhabited White Island, also known as Whakaari in the Maori language, is the 2 x 2.4 km emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes. The summit crater appears to be breached to the SE, because the shoreline corresponds to the level of several notches in the SE crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of eruptions since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. Formation of many new vents during the 19th and 20th centuries has produced rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities.

Information Contacts: Brad Scott and Brent Alloway, Wairakei Research Center, Institute of Geological and Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

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/).