Short pulses of intermittent eruptive activity have characterized Piton de la Fournaise, the large basaltic shield volcano on La Réunion Island in the western Indian Ocean, for several thousand years. For the last 20 years, frequent effusive basaltic eruptions have occurred on average twice per year. The activity is characterized by lava fountains and lava flows, and occasional explosive eruptions that shower blocks over the summit area and produce ash plumes. Almost all of the recent activity has occurred within the Enclos Fouqué caldera, although past eruptions in 1977, 1986, and 1998 have occurred at vents outside of the caldera. Four separate eruptive episodes were reported during 2018; from 3-4 April, 27 April-1 June, 13 July, and 15 September-1 November (BGVN 43:12, 43:09). Two episodes from 2019 during February-March and June are covered in this report, with information provided primarily by the Observatoire Volcanologique du Piton de la Fournaise (OVPF) as well as satellite instruments.

Piton de la Fournaise experienced two eruptions during November 2018-June 2019. The first lasted from 18 February to 10 March 2019, and the second episode was 11-13 June. The episode in February-March started consisted of multiple fissures opening on the E flank of the Dolomieu crater on 18 February with lava flows that traveled several hundred meters. After a brief pause, one new fissure opened nearby on 19 February and produced up to 3 million m³ of lava in a little over four days. Although the flow rate then declined, the eruption continued until 10 March. During the last three days, 7-10 March, two new fissures opened nearby and produced large volumes of lava, bringing the total eruptive volume to about 14.5 million m³. After little activity during April and May, a small eruption occurred on the SSE outer slope of Dolomieu crater that lasted for about 48 hours on 11-13 June; multiple small flows traveled about 1,000 m down the steep flank before ceasing. The MIROVA thermal anomaly graph of log radiative power clearly showed the abruptness of the beginning and ends of the last three eruptive episodes at Piton de la Fournaise from August 2018 through June 2019 (figure 165).

Figure 165. The MIROVA graph of thermal energy from Piton de la Fournaise from 30 July 2018 through June 2019 shows the last three eruptive episodes at the volcano. From 15 September through 1 November 2018 fissures and flows were active on the SW flank of Dolomieu crater near Rivals crater (BGVN 43:12). Fissures opened on the E flank of the crater on 18 February 2019, and after a brief pause resumed on 19 February at the foot of Piton Madoré. Lava flows remained active until 10 March 2019. A short episode of lava effusion occurred on 11-12 June 2019 on the SSE outer slope of Dolomieu crater. Courtesy of MIROVA.

Activity during November 2018-March 2019. Following the end of the 15 September-1 November 2018 eruption, seismic activity immediately below the summit remained low (with only 20 shallow and two deep earthquakes during November). The inflationary signal recorded since the beginning of September stopped, and the OVPF deformation networks did not record any significant deformation. There were 35 shallow earthquakes (0-2 km depth) below the summit crater during December, and one deep earthquake. Only 12 shallow earthquakes and one deep earthquake (greater than 2 km below the surface) were reported in January.

OVPF reported an increase in CO₂ concentrations beginning in December 2018, and noted the beginning of inflation on 13 February 2019. A seismic swarm of 379 earthquakes accompanied by minor but rapid deformation (less than 1 cm) was reported on 16 February 2019. A new seismic swarm of 208 earthquakes began early on 18 February with a much larger ground deformation (10 cm of elongation of the summit zone). A volcanic tremor indicative of the arrival of magma near the surface began at 0948 that morning. Webcams indicated that eruptive fissures had opened in the NE part of the Enclos Fouqué caldera. The onset of the eruption was marked by a sudden drop in CO₂ flux which then stabilized. The eruptive sites were confirmed visually around 1130. Three fissures with actively flowing lava opened on the E flank of Dolomieu Crater; the fountains of lava were less than 30 m high. The front of the longest flow had reached 1,900 m elevation after one hour. The eruption lasted a little over 12 hours and was over by 2200 that evening; it covered about 150-200 m of the hiking trail to the summit.

Seismicity remained high after the event ended, and at 1500 on 19 February 2019 another seismic swarm of 511 deep earthquakes located under the E flank at about 2.5 km depth occurred. It was not accompanied by a significant amount of deformation. At 1710 tremor signals appeared on the observatory seismographs and the first gas plumes and lava ejection were observed at 1750 and 1912, respectively. During an overflight the next day (20 February), OVPF team members observed the new eruptive site at an elevation of 1,800 m at the foot of Piton Madoré. One fissure and one fountain were active at 0620 on 20 February and the flow front was at 1,300 m elevation (figure 166). During the night of 20-21 February the flow front crossed over the "Grandes Pentes" area in the eastern half of the Enclos Fouque (figure 167).

Figure 166. The eruption which began on 19 February 2019 on the E flank of Dolomieu crater at Piton de la Fournaise produced a lava fountain and flow which traveled down at least 500 m of elevation by the next morning when this photo was taken at 0620 local time. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du mercredi 20 février 2019 à 11h00, Heure locale).

Figure 167. The active fissure at Piton de la Fournaise was producing lava fountains and an active flow during the evening of 20 February 2019. Overnight the flow crossed over the "Grandes Pentes" area of the caldera. Photo courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du jeudi 21 février 2019 à 14H00, Heure locale).

OVPF reported on 22 February 2019 that 22 shallow earthquakes had been reported since the eruption began on 19 February. Surface flow rates estimated from satellite data, via the HOTVOLC system (OPGC - University of Auvergne), were between 2.5 and 15 m³/s. The quantity of lava emitted between 19 and 22 February was between 1 and 3 million m³. OVPF observed the growth of an eruptive cone that was filled with a small lava lake producing ejecta during a morning overflight on 22 February. A channelized flow moved downstream from the cone and split into two lobes about 1 km from (and 200 m below) the cone (figure 168). The split in the flow occurred near the Guyanin crater. The N flowing lobe, about 50 m wide, had an actively flowing front located at 1,320 m elevation; the incandescent flow was travelling over a recent flow (likely from the previous night). The S-flowing lobe spread to 200 m wide and split into two tongues 300 m SE of Guyanin crater.

Figure 168. During an overflight on the morning of 22 February 2019 scientists from OVPF observed a growing spatter cone with a small lava lake at Piton de la Fournaise. A channelized flow moved downstream from the fissure and split into two flows. Photo courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du vendredi 22 février 2019 à 13h30, Heure locale).

Incandescent ejecta from the cone was captured in a webcam image overnight on 22-23 February 2019 (figure 169). The rate of advance of the flow slowed significantly by 24 February, but the intensity of the eruptive tremor remained relatively constant. Mapping of the lava flow on 28 February carried out by the OI2 platform (OPGC - University Clermont Auvergne) from satellite data confirmed the slow progress of the flow after 24 February (300 m in 5 days) (figure 170). The flow front was located at 1,200 m elevation, and only the N arm was active; the lava had traveled about 2.2 km from the vent by 28 February.

Figure 169. Incandescent ejecta from the eruptive cone at Piton de la Fournaise was captured in the webcam in the early hours of 23 February 2019. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du samedi 23 février 2019 à 13h30, Heure locale).

Figure 170. Contours of the lava flows at Piton de la Fournaise from 18-28 February 2019 were determined from satellite data by the OI2 platform (Université Clermont Auvergne), dated 18 (red) and 19 (blue) February (top image); 20 (green), 21 (red), 22 (blue), 27 (turquoise), and 28 (pink) February (bottom image). Courtesy of and copyright by OVPF/IPGP. Top: Bulletin d'activité du vendredi 22 février 2019 à 13h30 (Heure locale); bottom: Bulletin d'activité du jeudi 28 février 2019 à 16h30 (Heure locale).

Between 28 February and 1 March 2019 a third lobe of lava appeared flowing NE from the vent on the N side of the new flow area; it split into two lobes sometime on 1 March. Very little new lava was recorded on the other lobes. By 4 March the flow rate estimated by satellite data was about 7.5 m³/s. During a site visit on the morning of 5 March OVPF scientists sampled the N lobe of the flow and bombs and tephra near the cone, and acquired infrared and visible images. They noted the continued growth of the cone which still had an open vent at the summit and a base 100 m in diameter. It was 25 m high with a 50-m-wide eruptive vent at the top (figure 171). High-temperature gas emissions and strong Strombolian activity issued from the vent. Steam emissions were present around the base of the cone, suggesting the presence of lava tunnels. A single lobe of lava flowed N from the cone.

Figure 171. The eruptive cone at Piton de la Fournaise on 5 March 2019 had a 100-m-diameter base, 25 m of vertical height, and 50-m-wide vent at the summit. Courtesy of and copyright by OVPF/IPGP, (Bulletin d'activité du mardi 5 mars 2019 à 17h30, Heure locale).

A new fissure that opened about 150 m from the main vent on the NW flank of Piton Madoré was first observed on the morning of 6 March (figure 172); OVPF concluded that it had opened late on 5 March. A small cone was forming and a new flow traveled N from the main eruptive site. At least six new emission points were noted the following morning (7 March) around the Piton Madoré. Poor weather prevented confirmation by aerial reconnaissance that day, but in a site visit on 8 March OVPF scientists determined that the new fissure from 5 March remained active; a small cone about 10 m high had two flow lobes on the W and N sides (figure 173). A fissure that opened on 7 March was located 300 m S of the 19 February vent and oriented E-W. It was very active on the morning of 8 March with two 50-m-high lava fountains (figure 174). Samples collected by OVPF indicated that the vents of 5 and 7 March produced lava of different compositions.

Figure 172. A new fissure that opened about 150 m from the main vent on the NW flank of Piton Madoré at Piton de la Fournaise was first observed on the morning of 6 March 2019; OVPF concluded that it had opened late on 5 March. A small cone was forming on the flank of an old one and a new flow traveled N from the main eruptive site. Courtesy of OVPF/IPGP, copyright by Helicopter Coral (Bulletin d'activité du jeudi 7 mars 2019 à 15h00 Heure locale).

Figure 173. The 5 March 2019 fissure at Piton de la Fournaise on the NW flank of Piton Madoré still had two active flow lobes emerging from it and heading N and W on 8 March 2019. Courtesy of and copyright by OVPF/IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, March 2019).

Figure 174. A fissure that opened on 7 March 2019 at Piton de la Fournaise was located 300 m S of the 19 February vent and oriented E-W. It was very active on the morning of 8 March 2019 with two 50-m-high lava fountains. Courtesy of and copyright by OVPF/IPGP (Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, March 2019).

There was a strong increase in the eruptive tremor intensity on 7 March, related to the opening of the two new fissures on 5 and 7 March (figure 175). As a result, the surface flow estimates made from satellite data increased significantly to high values greater than 50 m³/s, with the average values on 7-8 March of around 20-25 m³/s. The increased flow rates resulted in the flows traveling much greater distances. By the morning of 9 March the active flow had reached 650-700 m above sea level. The flow front had traveled about 1 km in 24 hours. Strong seismicity had been increasing under the summit zone for the previous 48 hours. After a phase of very strong surface activity observed overnight on 9-10 March that included lava fountains 50-100 m high (figure 176), surface activity ceased around 0630 on 10 March, and seismic activity decreased significantly. OVPF noted that sudden increases in seismicity and flow rates near the end of an eruption have occurred at about half of the eruptions at Piton de la Fournaise in recent years. Lava volumes emitted on the surface between 18 February and 10 March 2019 were estimated at about 14.5 million m³ (figure 177).

Figure 175. An infrared view of the eruptive site on the E flank of Dolomieu crater at Piton de la Fournaise on 8 March 2019 clearly showed the original fissure from 19 February (bottom right of center), the fissure on Piton Madore that opened on 5 March (right) and the fissures that opened on 7 March (upper, right of center). The combined activity produced significant thermal and seismic activity at the volcano. Courtesy of and copyright by OVPF/IPGP (Bulletin d'activité du vendredi 8 mars 2019 à 17h00, Heure locale).

Figure 176. Lava fountains 50-100 m high were the result of very strong surface activity observed overnight on 9-10 March 2019 at Piton de la Fournaise. Surface activity ceased around 0630 on 10 March, and seismic activity decreased significantly. Photo taken on 9 March 2019 around midnight from the RN2. Courtesy of OVPF/IPGP, copyright by A. Finizola LGSR/IPGP (Bulletin d'activité du dimanche 10 mars 2019 à 19h30 Heure locale).

Figure 177. A sudden increase in the flow rate at the end of the 18 February-10 March 2019 eruption at Piton de la Fournaise was recorded by researchers at the Université Clermont Auvergne. OVPF noted this was typical of about half of the eruptions at Piton de la Fournaise. Courtesy of OVPF/IPGP, copyright by HOTVOLC, Université Clermont Auvergne (OVPF Monthly bulletin of the Piton de la Fournaise Volcanological Observatory, March 2019).

Significant SO₂ plumes were captured by the TROPOMI instrument on the Sentinel 5-P satellite throughout the 18 February-10 March eruption (figure 178). After the surface eruption ceased, shallow seismicity continued at a lower rate of about 12 earthquakes per day. The end of the eruption (7-10 March) was accompanied by a marked deflation, interpreted by OVPF as the rapid emptying of the magma reservoir. Following the end of the eruption, inflation resumed for the rest of March but then ceased. Seismicity continued at a lower level during April with an average of six shallow earthquakes per day.

Figure 178. Multiple days of high DU value SO2 plumes were recorded by the TROPOMI instrument on the Sentinel 5-P satellite during the 18 February-10 March 2019 eruption at Piton de la Fournaise. Top row: during 18, 21, and 22 February SO2 plumes drifted SE. Middle row: during 23, 24, and 25 February the wind direction changed from SE through S to SW and left a curling trail of SO2. Bottom row: 5, 7, and 8 March showed an increase in SO2 emissions that corresponded with increased seismicity and lava flow output before the eruption ceased.

Activity during May-June 2019. OVPF reported slight inflation near the summit beginning in early May, and an increase in CO₂ concentration in the soil near Plaine des Cafres and Plaine des Palmistes. Strong shallow seismicity reappeared on 27 May 2019 and recurred on 30 and 31 May. Two small seismic swarms were measured on 31 May in the early morning. A new seismic swarm beginning at 0603 on 11 June accompanied by rapid deformation suggested a new eruption was imminent. A tremor near the summit area was first noted at 0635 local time; the webcams indicated a plume of gas, but poor visibility prevented evidence of fresh lava. Around 0930 that morning OVPF confirmed that five fissures had opened on the outer SSE slope of Dolomieu crater at elevations ranging from 2480 to 2025 m (figure 179). The flow fronts were not visible due to weather. Lava fountains under 30 m in height and lava flows were present in the three lowest fissures. The flows traveled rapidly down the steep flank of the crater (figure 180).

Figure 179. Around 0930 on the morning of 11 June 2019 OVPF confirmed that five fissures had opened on the outer SSE slope of Dolomieu crater at Piton de la Fournaise at elevations ranging from 2480 to 2025 m. Courtesy of and copyright by OVPF-IPGP and Imazpress (Bulletin d'activité du mardi 11 juin 2019 à 11h00).

Figure 180. Thermal imaging of the 11-12 June 2019 eruptive site at Piton de la Fournaise showed multiple streams of lava traveling rapidly down the steep flank from several fissures on 11 June 2019. Courtesy of and copyright by OVPF-IPGP (Bulletin d'activité du mardi 11 juin 2019 à 11h00).

The intensity of the eruptive tremor decreased throughout the day, and by 1530 only the lowest elevation fissure was still active (figure 181). The next afternoon (12 June) images in the OVPF webcam located in Piton des Cascades indicated the flow front was at about 1,200-1,300 m elevation. Seismographs indicated that the eruption stopped around 1200 on 13 June. Poor weather obscured visibility of the flow activity. Seismic activity decreased following the eruption, but appeared to increase again beginning on 21 June, with 10 events detected on 30 June. SO₂ plumes were recorded in satellite data on 11 and 12 June 2019.

Figure 181. The intensity of the eruptive activity at Piton de la Fournaise on 11 June 2019 decreased throughout the day, and by 1530 only the lowest elevation fissure was still active. Courtesy of and copyright by OVPF-IPGP (Bulletin d'activité du mardi 11 juin 2019 à 17h45 Heure locale).

Geologic Background. The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.

Information Contacts: Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, 14 route nationale 3, 27 ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

The ongoing eruption at Semeru has been characterized by numerous ash explosions and thermal anomalies, but activity apparently diminished in 2018 (BGVN 43:01 and 43:09); this decreased activity continued through at least February 2019. The current report summarizes activity from 24 August 2018 to 28 February 2019.

The Indonesian volcano monitoring agency, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), reported ongoing daily seismicity, dominated by explosion earthquakes and emission-related events from late November through February (figure 35). Ash plumes resulting in aviation advisories by the Darwin Volcanic Ash Advisory Centre (VAAC) were reported on 4, 6-7, and 19 September, and 12 October 2018. The next significant ash plume reported by the VAAC wasn't until 24 February 2019 (table 23).

Figure 35. Seismicity recorded at Semeru during 28 November 2018-26 February 2019. Plot shows explosion earthquakes ('Letusan'), emission-related events ('Hembusan'), felt earthquakes ('Gempa Terasa'), local tectonic events ('Tektonic Lokal'), and distant tectonic events ('Tektonic Jauh'). Courtesy of PVMBG and MAGMA Indonesia.

Table 23. Summary of ash plumes at Semeru during 25 August 2018 through February 2019. The summit is at 3,657 m elevation. Data courtesy of Darwin VAAC.

Thermal anomalies using MODIS satellite instruments processed by the MODVOLC algorithm were only recorded on 26, 28, and 30 August 2018, and 22 and 31 October 2018. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected numerous hotspots within 5 km of the volcano during August and early September, with a significant decrease in frequency through October (figure 36); only a few scattered hotspots were recorded from November 2018 through February 2019.

Figure 36. MIROVA plot of thermal anomalies (Log Radiative Power) at Semeru during July 2018-February 2019. Courtesy of MIROVA.

Geologic Background. Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano.

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/).

Heard Island, in the Southern Indian Ocean, includes the large Big Ben stratovolcano and the smaller, apparently inactive, Mt. Dixon. Because of the island's remoteness, satellites are the primary monitoring tool. Big Ben has been active intermittently since 1910, and was active during October 2017-September 2018 (BGVN 43:10). Activity continued during October 2018-March 2019.

Satellite photos using Sentinel Hub showed hotspots every month between October 2018 and March 2019. Because the area was frequently covered by a heavy cloud layer, most of the hotspot signals were partially obscured. Though thermal anomalies are usually seen at summit vents, on 18 October 2018 an anomaly was present about 300 m down the E flank. Similarly, on 1 January 2019, a weak anomaly beginning about 200 m down the NW flank was about 300 m long (figure 40).

The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected three hotspots, two in October and one in early November 2018, all of low radiative power. There were no MODVOLC alert pixels during this period.

Figure 40. Sentinel-2 L1C image of Heard Island's Big Ben volcano on 1 January 2019 one summit hotspot and an elongated thermal anomaly to the NW. Scale bar (bottom right) is 200 m. The photo was taken in atmospheric penetration view (bands 12, 11, and 8A), courtesy of Sentinel Hub Playground.

Geologic Background. Heard Island on the Kerguelen Plateau in the southern Indian Ocean consists primarily of the emergent portion of two volcanic structures. The large glacier-covered composite basaltic-to-trachytic cone of Big Ben comprises most of the island, and the smaller Mt. Dixon volcano lies at the NW tip of the island across a narrow isthmus. Little is known about the structure of Big Ben volcano because of its extensive ice cover. The historically active Mawson Peak forms the island's 2745-m high point and lies within a 5-6 km wide caldera breached to the SW side of Big Ben. Small satellitic scoria cones are mostly located on the northern coast. Several subglacial eruptions have been reported in historical time at this isolated volcano, but observations are infrequent and additional activity may have occurred.

Information Contacts: Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

The eruption at Dukono that began in 1933 has showered the area with ash from frequent explosions (BGVN 43:04, 43:12). The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Center for Volcanology and Geological Hazard Mitigation (CVGHM), is responsible for monitoring this volcano.

This long-term pattern of intermittent ash explosions continued during October 2018-March 2019, with ash plumes rising to between 1.5 and 2.7 km altitude, or about 300-1,500 m above the summit (table 19). Although meteorological clouds often obscured views, satellite imagery captured typical ash plumes on 28 September 2018 (figure 10) and 5 February 2019 (figure 11). Instruments aboard NASA satellites (TROPOMI and OMPS) detected high levels of sulfur dioxide near or directly above the volcano on multiple days during January-March 2019. The Alert Level remained at 2 (on a scale of 1-4), and visitors were warned to remain outside of the 2-km exclusion zone.

Table 19. Monthly summary of reported ash plumes from Dukono for October 2018-March 2019. The direction of drift for the ash plume through each month was highly variable. Data courtesy of the Darwin VAAC and PVMBG.

Figure 10. Satellite image from Sentinel-2 (LC1 natural color) of an ash plume at Dukono on 28 September 2018 with the plume blowing towards the NE. Courtesy of Sentinel Hub Playground.

Figure 11. Satellite image from Sentinel-2 (LC1 natural color) of an ash plume at Dukono on 5 February 2019, with the plume blowing SW. Courtesy of Sentinel Hub Playground.

Geologic Background. Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia's most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Intermittent small phreatic explosions from the acid lake of Rincón de la Vieja's active crater has most recently occurred since 2011 (BGVN 42:08, 43:03, and 43:09). This activity continued through at least February 2019. The volcano is monitored by the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), and the information below comes from its weekly bulletins between 18 August 2018 and 28 February 2019. Weather conditions often prevented webcam views and estimates of plume heights. The volcano was in Activity Level 3 throughout the reporting period (volcano erupting, steady state).

According to OVSICORI-UNA, two distinct, 2-minute-long explosions occurred on 31 August 2018 beginning at 0434 and 1305. Several hours after the eruption tremor became continuous but low-frequency long-period (LP) earthquakes ceased. OVSICORI-UNA reported a gas emission late on 7 September. An unconfirmed small phreatic explosion occurred on 11 September at 0634, and another on 17 September at 1014. The seismic record showed continuous background tremor and very sporadic LP earthquakes.

Intermittent background tremor was recorded during the first half of October, along with a few emissions and phreatic explosions. Deformation measurements during October showed a contraction between the N and S of the volcano, with subsidence. On 17 October there was another phreatic explosion, and thereafter tremor disappeared and seismicity decreased. On 23 and 27 October seismic stations signaled additional possible phreatic explosions.

OVSICORI-UNA reported that a series of explosions began at 1945 on 4 November and consisted of at least three 2-minute-long episodes. The next day at 1511 a plume of water vapor and diffuse gas, recorded by a webcam and visible to residents to the N, rose about 100 m above the crater rim and drifted W. On 9 November a 2-minute-long explosion began at 1703. Another explosion on 27 November at 0237 produced a plume of water vapor and gas that rose 600 m above the crater rim and drifted SW. A short 1-minute explosion began at 1054 on 3 December.

Based on OVSICORI-UNA weekly bulletins, activity remained stable in January 2019 with small-amplitude phreatic explosions on 11, 12, and 14 January. More energetic phreatomagmatic explosions on 17 and 20 January produced lahars. Several small-amplitude explosions were detected at the end of the month. During January, a few LPs, no VTs, and intermittent tremor were recorded.

OVSICORI-UNA reported that two small-scale explosions occurred on 1 February, along with possible events at 1906 and 1950 on 5 February and at 0120 on 6 February. An event at 0000 on 6 February was also recorded; the report noted that poor weather conditions prevented visual observations of the crater. On 16 and 17 February strong degassing was observed. No LPs were recorded, but two significant VTs were detected on 17 and 22 February near or under the crater.

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: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/).

This report summarizes activity at Turrialba during September 2018-February 2019. During this period there was similar activity as described earlier in 2018 (BGVN 43:09), with occasional ash explosions and numerous, sometimes continuous, periods of gas-and-ash emissions (table 8). Data were provided by the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA).

Table 8. Ash emissions at Turrialba, September 2018-February 2019. Cloudy weather sometimes obscured observations. Maximum plume height is above the crater rim. Information courtesy of OVSICORI-UNA.

According to OVSICORI-UNA's annual summary for 2018, a slow decline in activity occurred after the volcano reached its highest emission rate during 2016. Activity during 2018 was consistent with an open system, generating frequent passive ash emissions. The volcano emitted ash on 58% of the days during the year. Some explosions were large enough to eject ballistics more than 400 m around the crater. Typical activity can be seen in a photo from 11 September 2018 (figure 50) and satellite imagery on 7 November 2018 (figure 51).

Figure 50. Photo of an ash explosion at Turrialba taken on 11 September 2018. Courtesy of Red Sismologica Nacional (RSN: UCR-ICE), Universidad de Costa Rica.

Figure 51. Sentinel-2 satellite image of an ash emission from Turrialba on 7 November 2018, taken in natural color (gamma adjusted). Courtesy of Sentinel Hub Playground.

During January into early February 2019, passive ash emissions continued irregularly and with less intensity and duration. Emissions sometimes lacked ash. In their report of 4 February 2019, OVSICORI-UNA indicated that passive ash emissions were weak and slow. For the rest of February, they characterized ash emissions as frequent, but of low intensity.

Seismic activity. On 1 November 2018 OVSICORI-UNA reported that seismicity remained high, and involved low-amplitude banded volcanic tremor along with long-period (LP) and volcano-tectonic (VT) earthquakes. In late January-early February 2019, OVSICORI-UNA reported that seismicity remained relatively stable, although a small increase was associated with the hydrothermal system. VT earthquakes were absent, and tremors had decreased in both energy and duration. The number of low-frequency LP volcanic earthquakes remained stable, although they had decreasing amplitudes. No explosions were documented, and emissions were weak and had short durations and very dilute ash content.

Thermal anomalies. No thermal anomalies were recorded during the reporting period using MODIS satellite instruments processed by MODVOLC algorithm. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected five scattered hotspots during September-October 2018, none during November-December 2018, and two during January-February 2019. All were within 2 km of the volcano and of low radiative power.

Gas measurements. Significant sulfur dioxide levels near the volcano were recorded by NASA's satellite-borne ozone instruments only on 29 September 2018 (both NPP/OMPS and Aura/OMI instruments) and on 11 February 2019 (Sentinel 5P/TROPOMI instrument). OVSICORI-UNA's gas measuring instruments were compromised in September 2018 through January 2019 due to vandalism. In early February, however, they detected hydrogen sulfide for the first time since 2016.

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: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/); Red Sismologica Nacional (RSN) a collaboration between a) the Sección de Sismología, Vulcanología y Exploración Geofísica de la Escuela Centroamericana de Geología de la Universidad de Costa Rica (UCR), and b) the Área de Amenazas y Auscultación Sismológica y Volcánica del Instituto Costarricense de Electricidad (ICE), Costa Rica (URL: https://rsn.ucr.ac.cr/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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://hotspot.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/); 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/); Costa Rica Star (URL: https://news.co.cr); The Tico Times (URL: https://ticotimes.net).

San Cristóbal has produced occasional weak explosions since 1999, with intermittent gas-and-ash emissions. The only reported explosion during the first half of 2018 was on 22 April, the first since November 2017 (BGVN 43:03). The current report covers activity between 1 August 2018 and 1 May 2019. The volcano is monitored by the Instituto Nicaragüense de Estudios Territoriales (INETER).

According to INETER, a series of explosions occurred on 9 January 2019 that lasted several hours. INETER stated that one explosion occurred at 1643; the Washington VAAC's first advisory stated that an explosion occurred at 1145 (local time). The weak explosions, which occurred after a period of heightened seismic activity, generated an ash plume that reached 200 m above the edge of the crater and drifted W. The Washington VAAC reported volcanic ash plumes on 10-11 January extending about 92 km SW, and on 24-25 January extending about 185 km WSW. A low-energy explosion was detected by the seismic network at 1550 on 4 March 2019. The event produced a gas-and-ash plume that rose 400 m above the crater rim and drifted SW.

Monitoring data reported by INETER (table 6) showed elevated levels of seismicity during October 2018 through January 2019. Sulfur dioxide was also measured at higher levels in January 2019.

Table 6. Monthly sulfur dioxide measurements and seismicity reported at San Cristóbal during August 2018-March 2019. "Most" indicates that type of seismicity was dominant that month. Data courtesy of INETER.

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

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://webserver2.ineter.gob.ni/vol/dep-vol.html); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html).

The remote Semisopochnoi comprises the uninhabited volcanic island of the same name, ~20 km in diameter, in the Rat Islands group of the western Aleutians (figure 1). Plumes had been reported several times in the 18th and 19th centuries, and most recently observed in April 1987 from Sugarloaf Peak (SEAN 12:04). The volcano is dominated by an 8-km diameter caldera that contains a small lake (Fenner Lake) and a number of post-caldera cones and craters. Monitoring is done by the Alaska Volcano Observatory (AVO) using an on-island seismic network along with satellite observations and lightning sensors. An infrasound array on Adak Island, about 200 km E, may detect explosive emissions with a 13 minute delay if atmospheric conditions permit.

On 16 September 2018 increased seismicity was detected at 0831, prompting AVO to raise the Aviation Color Code (ACC) to Yellow and Volcano Alert Level (VAL) to Advisory. Retrospective analysis of satellite data acquired on 10 September revealed small ash deposits on the N flank of Mount Cerberus, possibly associated with two bursts of tremor recorded on 8 September (figure 5). This new information, coupled with intensifying seismicity and a strong tremor signal recorded at 1249 on 17 September, resulted in AVO raising the ACC to Orange and the VAL to Watch. Seismicity remained elevated on 18 September with nearly constant tremor recorded by local sensors. At the same time, no ash emissions were observed in cloudy satellite images and no eruptive activity was recorded on regional pressure sensors at Adak.

Figure 1. Minor ash deposits can be seen on the south and west flanks of the N cone of Mount Cerberus, Semisopochnoi Island, in this ESA Sentinel-2 image from 1200 on 10 September 2018. Also note probable minor steam emissions obscuring the crater of the N cone. Image courtesy of AVO.

During 19-25 September 2018 seismicity remained elevated, alternating between periods of continuous and intermittent bursts of tremor. Tremor bursts at 1319 on 21 September and at 1034 on 22 September produced airwaves detected on a regional infrasound array on Adak Island; no ash emissions were identified above the low cloud deck in satellite data, and the infrasound detections likely reflected an atmospheric change instead of volcanic activity.

Seismicity remained elevated during 3-9 October 2018, with intermittent bursts of tremor. No volcanic activity was detected in infrasound or satellite data. On 11 October satellite data indicated partial erosion of a tephra cone in the crater of Cerberus's N cone. A crater lake about 90 m in diameter filled the vent. The data also suggested that the vent had not erupted since 1 October. Seismicity remained elevated and above background levels. The next day AVO lowered the Aviation Color Code to Yellow and the Volcano Alert Level to Advisory, noting the recent satellite data results and lack of tremor recorded during the previous week. AVO reported that unrest continued during 11-24 October.

An eruptive event began at 2047 on 25 October 2018, identified based on seismic data; strong volcanic tremor lasted about 20 minutes and was followed by 40 minutes of weak tremor pulses. A weak infrasound signal was detected by instruments on Adak Island. The Aviation Color Code was raised to Orange (the second highest level on a four-color scale) and Volcano Alert Level was raised to Watch (the second highest level on a four-level scale). A dense meteorological cloud deck prevented observations below 3 km, but a diffuse cloud was observed in satellite data rising briefly above the cloud deck, though it was unclear if it was related to eruptive activity. Tremor ended after the event, and seismicity returned to low levels.

Small explosions were detected by the seismic network at 2110 and 2246 on 26 October 2018, and 0057 and 0603 on 27 October. No ash clouds were identified in satellite data, but the volcano was obscured by high meteorological clouds. Additional small explosions were detected in seismic and infrasound data during 28-29 October; no ash clouds were observed in partly-cloudy-to-cloudy satellite images.

AVO reported on 31 October 2018 that unrest continued. Two small explosions were detected, one just before 0400 and the other around 1000. Satellite views were obscured by clouds at the time, and no ash clouds were observed. Unrest continued through 1 November, at which time the satellite link and the seismic line failed. On 21 November the ACC was lowered to Yellow and the VAL was lowered to Advisory.

Geologic Background. Semisopochnoi, the largest subaerial volcano of the western Aleutians, is 20 km wide at sea level and contains an 8-km-wide caldera. It formed as a result of collapse of a low-angle, dominantly basaltic volcano following the eruption of a large volume of dacitic pumice. The high point of the island is 1221-m-high Anvil Peak, a double-peaked late-Pleistocene cone that forms much of the island's northern part. The three-peaked 774-m-high Mount Cerberus volcano was constructed during the Holocene within the caldera. Each of the peaks contains a summit crater; lava flows on the northern flank of Cerberus appear younger than those on the southern side. Other post-caldera volcanoes include the symmetrical 855-m-high Sugarloaf Peak SSE of the caldera and Lakeshore Cone, a small cinder cone at the edge of Fenner Lake in the NE part of the caldera. Most documented historical eruptions have originated from Cerberus, although Coats (1950) considered that both Sugarloaf and Lakeshore Cone within the caldera could have been active during historical time.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.gov/).

Japan's 24-km-wide Asosan caldera on the island of Kyushu has been active throughout the Holocene. Nakadake has been the most active of 17 central cones within the caldera for 2,000 years. Historical eruptions have been primarily basaltic to basaltic-andesitic ash eruptions, with periodic Strombolian activity, all from Nakadake Crater 1. The most recent major eruptive episode began in late November 2014 and continued through 1 May 2016. Another eruption, with the largest ash plume in 20 years, occurred on 8 October 2016. Asosan remained quiet until renewed activity from Crater 1 began in mid-April 2019; it is covered in this report, through the end of June 2019. The Japan Meteorological Agency (JMA) provides monthly reports of activity; the Tokyo Volcanic Ash Advisory Center (VAAC) issues aviation alerts reporting on possible ash plumes.

Asosan remained quiet during 2017 and 2018 with steam plumes rising a few hundred meters from Crater 1 and low levels of SO₂ emissions; a warm acidic lake was present within the crater. Fumarolic activity from two areas on the S and SW wall of the crater rim generated occasional thermal anomalies in satellite data and incandescence at night. A brief period of increased seismicity was reported in mid-March 2019. An increase in seismic amplitude on 14 April 2019 preceded a small explosion on 16 April; it produced an ash plume which rose 200 m above the crater rim and drifted NW. It was followed by additional small explosions on 19 April. A new explosion on 3 May produced minor ashfall in adjacent communities; ash emissions were reported multiple times during May with plumes reaching 1,400 m above the crater rim. No additional ash emissions were reported in June.

Activity during 2017 and 2018. JMA reported that no eruptions occurred during 2017. Amplitudes of volcanic tremor increased somewhat during March but were generally low for the rest of the year. The earthquake hypocenters were mostly located near the active crater at around sea level. SO2 emissions were slightly less than 1,000 tons per day (t/d) from January through April; for the rest of the year they ranged from 600 to 2,500 t/d. The Alert Level had been lowered from 2 to 1 on 7 February 2017 where it remained throughout the year. Steam plumes generally rose no more than 600 m above the active crater rim (figure 42). JMA noted that from January to June they often observed crater incandescence at night with a high-sensitivity surveillance camera; Sentinel-2 satellite images also captured thermal anomalies a few times (figure 43). The green lake inside the crater persisted throughout the year with water temperatures of 50-60°C. Two fumaroles were present with high-temperature gas emissions on the SW and S crater walls. Temperatures at the S crater wall were over 600°C from February to May; they decreased to 320-560°C during the rest of the year (figure 44). Sulfur deposits were visible around the SW crater wall fumarole during July.

Figure 42. Steam plumes that rose around 600 m above Nakadake Crater 1 at Asosan were typical activity throughout 2017. Images taken with JMA webcam on 9 June (top left), 22 August (top right), 12 November (bottom left), and 20 December (bottom right) 2017. Courtesy of JMA (Aso volcano monthly activity reports, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 43. Sentinel-2 images captured thermal anomalies at the S rim of the green lake at Asosan's Nakadake Crater 1 on 16 February (left) and 27 May 2017 (right). JMA reported that incandescence was occasionally visible during the night from January-June from the same area. Courtesy of Sentinel Hub Playground.

Figure 44. High-temperature gas and steam from fumaroles on the S wall of the Nakadake Crater 1 at Asosan on 24 August (top) and 17 November 2017 (bottom) were persistent all year, with temperatures ranging from 300 to over 600°C. The green lake inside the crater persisted throughout the year as well with water temperatures of 50-60°C. Courtesy of JMA (Aso volcano monthly activity reports, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

The Alert Level did not change at Asosan during 2018, and no eruptions were reported. Sulfur dioxide emissions fluctuated between 400 and 1,800 t/d throughout the year. Steam plumes generally rose less than 500 m above the active crater (figure 45); incandescence was observed at night during May-October and sometimes observed in satellite imagery as thermal anomalies (figure 46). The temperature of the green lake inside the crater ranged from 58 to 75°C throughout the year. The thermal anomaly on the S wall of the crater was consistently in the 300-500°C range, and had a high temperature in April of 580°C; in December the high temperature had risen to 738°C (figure 47). A brief increase in the number of isolated tremors occurred during March, with 1,044 reported on 4 March, exceeding the previous maximum of 1,000 on 27 October 2014. Seismicity also increased briefly during June, with more than 400 events reported each day on 8, 18, and 20 June. The Minami Aso village Yoshioka fumarole zone, located about 5 km W of Nakadake Crater 1, continued to produce modest steam plumes throughout 2017 and 2018 (figure 48).

Figure 45. Typical steam plumes at Asosan during 2018 rose around 500 m above the Nakadake Crater 1. Images are from 4 March (top left), 22 July (top right), 17 August (lower left), and 13 September 2018 (lower right). Courtesy of JMA (Aso volcano monthly activity reports, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 46. Nighttime incandescence was reported by JMA during May-October 2018 from the S rim of Nakadake Crater 1 at Asosan; Sentinel-2 satellite images (bands 12, 4, 2) captured thermal anomalies from the same area numerous times during 2018 including on 16 June (top left), 26 July and 19 September (middle row), and 18 and 23 November (bottom row). JMA photographed incandescence at night on 17 July 2018 at the S fumarole area (top right). Courtesy of Sentinel Hub Playground and JMA (Aso volcano Monthly Report for July 2018).

Figure 47. The "Green Tea Pond" inside Nakadake Crater 1 at Asosan had temperatures that ranged from 58 to 75°C during 2018 (top row, 26 March 2018); the thermal anomaly on the S wall of the crater consistently had temperatures measured in the 300-500°C range and the SW fumarole area had somewhat lower temperatures (bottom row, 22 June 2018). Courtesy of JMA (monthly Asosan reports for March, May, and June 2018).

Figure 48. The Minami Aso village Yoshioka fumarole zone, located about 5 km W of Nakadake Crater 1 at Asosan, continued to produce modest steam plumes throughout 2017 and 2018. It is shown here on 20 December 2017 (top) and 12 March 2018 (bottom). Courtesy of JMA (December 2017 and March 2018 monthly volcano reports).

Activity during 2019. Steam plumes rose to 800 m above the crater rim during January 2019. Overall activity increased slightly during February; SO₂ emissions peaked at 2,200 t/d early in the month; they ranged from 800 to 1,800 t/d for most of the month. The amplitude of volcanic tremor also increased slightly during February. A further increase in tremor amplitude on 11 March 2019 prompted JMA to raise the Alert Level from 1 to 2 the following morning. Volcanic tremor amplitude decreased on 15 March; JMA determined that activity had decreased, and the Alert Level was lowered back to 1 on 29 March 2019. The amount of water in the crater decreased significantly between 27 February and 20 March, exposing part of the crater floor.

The surface temperature of the lake rose during the first part of 2019; it was 78°C in February and 84°C in March. Steam plumes rose to 1,200 m above the crater rim during March and April. SO₂ emissions rose to 4,500 t/d on 12 March but dropped to a lower range of 1,300-2,400 for the rest of the month. Another surge in SO₂ emissions on 12 April 2019 to 3,600 t/d prompted a special report from JMA the following day. SO₂ emissions varied from about 1,700 to 4,100 t/d during the month; values remained high during the second half of the month. JMA noted that the color of the water in the lake inside Nakadake Crater 1 changed from green to gray after 4 April. Fountains of muddy water were periodically observed; they reached 15 m high on 9 April. The temperatures of both the lake (82°C) and around the two fumarole areas (S area about 530°C, SW area about 310°C) remained constant during April and similar to March.

A large increase in the amplitude of volcanic tremor early on 14 April 2019 prompted JMA to raise the Alert Level from 1 to 2 later in the day. The epicenters of the earthquakes were very shallow, located within 1 km beneath the crater. A small eruption occurred at 1828 on 16 April at Nakadake Crater 1; it produced a gray and white plume that rose 200 m above the crater rim and was the first eruption since 8 October 2016 (figure 49). Incandescence was observed inside the crater on 3 and 17 April. The amplitude of seismic tremors decreased on 18 April. Three very small eruptions on 19 April produced ash and steam plumes that rose 500 m above the crater rim. During a site visit that day JMA measured a high-temperature area that produced incandescence from the bottom of the crater at night (figure 50).

Figure 49. The first eruption since October 2016 at Nakadake Crater 1 at Asosan on 16 April 2019 sent an ash plume 200 m above the crater rim (top). Incandescent gas appeared on the crater floor the next day (bottom). Courtesy of JMA (Aso volcano monthly activity reports, April 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 50. Three small explosions on 19 April 2019 at Asosan's Nakadake Crater 1 produced small ash emissions that rose 500 m above the crater rim (top). A strong thermal signal also appeared from the bottom of the crater. Courtesy of JMA (Aso volcano monthly activity reports, April 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

A new eruption began at 1540 on 3 May that lasted until 0620 on 5 May (figure 51). Initially the ash plume rose 600 m above the crater rim, but a few hours later the volume of ash increased, and the plume reached 2 km above the crater rim for a brief period. Incandescence was visible from the webcam. The Tokyo VAAC reported the ash plume at 3 km altitude drifting SE on 3 May. Later in the day it rose to 3.7 km altitude and drifted SW. During a field survey the following day (4 May) JMA reported a steam and ash plume rising from the center of the active crater. The infrared thermal imaging camera recorded the temperature of the plume at about 500°C (figure 52).

Figure 51. An explosion at Asosan's Nakadake Crater 1 on 3 May 2019 produced an ash plume that reached 2 km above the crater rim (top) and incandescence visible from the webcam (bottom). Courtesy of JMA (Aso volcano monthly activity reports, April 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 52. During a site visit on 4 May 2019, staff from JMA witnessed an ash and steam plume rising from the bottom of Nakadake Crater 1 at Asosan (top). The infrared thermal imaging camera recorded the temperature of the plume at about 500°C (bottom). Courtesy of JMA (Aso volcano monthly activity reports, May 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Ash fell on the S flank, and a small amount of ashfall on 4 May was confirmed by evidence on a car windshield in Takamori Town (6 km S), Kumamoto Prefecture (figure 53). Ashfall was also reported in Takamori-machi, Minami Aso village (9 km SW), and part of Yamato-cho (25 km SW), also in the Kumamoto Prefecture. SO₂ emissions were measured as high as 4,000 t/d on 4 May. Additional explosions with ash plumes were reported from Asosan on 9, 12-16, 29, and 31 May; the plumes rose from 200 to 1,400 m above the crater rim but were not visible in satellite imagery. The TROPOMI instrument on the Sentinel-5 satellite captured SO₂ plumes on 3 and 26 May 2019 (figure 54).

Figure 53. Ashfall was reported on 4 May 2019 in Takamori Town, Kumamoto Prefecture, from the eruption at Asosan's Nakadake Crater 1 on 3 May 2019. Courtesy of JMA (Aso volcano monthly activity reports, May 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 54. Plumes of SO2 from Asosan were recorded by the TROPOMI instrument on the Sentinel-5P satellite on 3 (left) and 26 (right) May 2019. Courtesy of NASA Goddard Space Flight Center.

Steam plumes rose to 1,700 m above the crater rim during June 2019 (figure 55). During field visits on 6 and 25 June diffuse ash emissions were observed rising from the center of the active crater, but they did not extend significantly above the crater rim (figure 56). The maximum temperature of the plume was measured at about 340°C with a thermal imaging camera. Almost all of the water in the crater bottom had evaporated since early May; incandescence continued to be observed within the crater at night with the high-resolution webcam (figure 57).

Figure 55. Steam plumes rose to 1,700 m above the crater rim at Asosan's Nakadake Crater 1 on 10 June 2019. Courtesy of JMA (Aso volcano monthly activity reports, June 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 56. Plumes of gas and minor ash were visible at Asosan's Nakadake Crater 1 during site visits by JMA on 6 (left) and 25 (right) June 2019. Courtesy of JMA (Aso volcano monthly activity reports, June 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Figure 57. Incandescent gas was visible from the vent at Asosan's Nakadake Crater 1 on 18 (left) and 25 (right) June 2019. Courtesy of JMA (Aso volcano monthly activity reports, June 2019, Fukuoka District Meteorological Observatory, Regional volcano monitoring and warning center).

Geologic Background. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

The Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo is part of the western branch of the East African Rift System. Nyamuragira (or Nyamulagira), a high-potassium basaltic shield volcano on the W edge of VVP, includes a lava field that covers over 1,100 km² and contains more than 100 flank cones in addition to a large central crater (see figure 63, BGVN 42:06). A lava lake that had been active for many years emptied from the central crater in 1938. Numerous flank eruptions were observed after that time, the most recent during November 2011-March 2012 on the NE flank. This was followed by a period of degassing with unusually SO₂-rich plumes from April 2012 through April 2014 (BGVN 42:06). The lava lake reappeared during July 2014-April 2016 and November 2016-May 2017, producing a strong thermal signature. After a year of quiet, a new lava lake appeared in April 2018, reported below (through May 2019) with information provided by the Observatoire Volcanologique de Goma (OVG), MONUSCO (the United Nations Organization working in the area), and satellite data and imagery from multiple sources.

Fresh lava reappeared inside the summit crater in mid-April 2018 from a lava lake and adjacent spatter cone. Satellite imagery and very limited ground-based observations suggested that intermittent pulses of activity from both sources produced significant lava flows within the summit crater through April 2019 when the strength of the thermal signal declined significantly. Images from May 2019 showed a smaller but persistent thermal anomaly within the crater.

Activity from October 2017-May 2019. Indications of thermal activity tapered off in May 2017 (BGVN 42:11). On 20 October 2017 OVG released a communication stating that a brief episode of unspecified activity occurred on 17 and 18 October, but the volcano returned to lower activity levels on 20 October. There was no evidence of thermal activity during the month. The volcano remained quiet with no reports of thermal activity until April 2018 (figure 73).

Figure 73. Sentinel-2 satellite images (bands 12, 4, 2) indicated no thermal activity at Nyamuragira on 19 November (top left), 14 December 2017 (top right) and 18 January 2018 (bottom). However, Nyiragongo (about 13 km SE) had an active lava lake with a gas plume drifting SW on 18 January 2018 (bottom right). Courtesy of Sentinel Hub Playground.

OVG reported the new lava emissions beginning on 14 April 2018 as appearing from both the lava lake and a small adjacent spatter cone (figure 74). The first satellite image showing thermal activity at the summit appeared on 18 April 2018 (figure 75) and coincided with the abrupt beginning of strong MIROVA thermal signals (figure 76). MODVOLC thermal alerts also first appeared on 18 April 2018. An image of the active crater taken on 9 May 2018 showed the lake filled with fresh lava and two adjacent incandescent spatter cones (figure 77).

Figure 74. Fresh lava reappeared at Nyamuragira's crater during April 2018 from the lava lake (left) and the adjacent small spatter cone (right). Courtesy of OVG (Republique Democratique du Congo, Ministere de la Recherche Scientifique, Observatoire Volcanologique de Goma, Direction Generale Goma, Rapport Avril 2018).

Figure 75. The first satellite image (bands 12, 4, 2) indicating renewed thermal activity at the Nyamuragira crater appeared on 18 April 2018; the signal remained strong a few weeks later on 3 May 2018. Courtesy of Sentinel Hub Playground.

Figure 76. A strong thermal signal appeared in the MIROVA graph of Log Radiative Power on 18 April 2018 for Nyamuragira, indicating a return of the lava lake at the summit crater. Courtesy of MIROVA.

Figure 77. Fresh lava filled the lake inside the crater at Nyamuragira on 9 May 2018. Two spatter cones were incandescent with gas emissions. Courtesy of OVG (Republique Democratique du Congo, Ministere de la Recherche Scientifique, Observatoire Volcanologique de Goma, Direction Generale Goma, Rapport Mai 2018).

Satellite images confirmed that ongoing activity from the lava lake remained strong during June -September 2018 (figure 78). A mission to Nyamuragira was carried out by helicopter provided by MONUSCO on 20 July 2018; lava lake activity was observed along with gas emissions from the small spatter cone (figure 79). OVG reported increased volcanic seismicity during 1-3 and 10-17 September 2018, and also during October, located in the crater area, mostly at depths of 0-5 km.

Figure 78. Sentinel-2 satellite images (bands 12, 4, 2) confirmed that ongoing activity from the lava lake at Nyamuragira remained strong during June-September 2018, likely covering the crater floor with a significant amount of fresh lava. Image are from 12 June (top left), 7 July (top right), 17 July (middle left), 22 July (middle right), 11 August (bottom left), and 20 September (bottom right). Courtesy of Sentinel Hub Playground.

Figure 79. The crater at Nyamuragira on 20 July 2018 had an active lava lake and adjacent incandescent spatter cone with gas emissions. Courtesy of OVG (Republique Democratique du Congo, Ministere de la Recherche Scientifique, Observatoire Volcanologique de Goma, Direction Generale Goma, Rapport Juillet 2018).

Personnel from OVG and MONUSCO (United Nations Organization Stabilization Mission in DR Congo) made site visits on 11 October and 2 November 2018 and concluded that the level of the active lava lake had increased during that time (figure 80). On 2 November OVG measured the height from the base of the active cone to the W rim of the crater as 58 m (figure 81).

Figure 80. OVG scientists reported a rise in the lake level between site visits to the Nyamuragira crater on 11 October (top) and 2 November 2018 (bottom). Top image courtesy of MONUSCO and Culture Vulcan, bottom image courtesy of OVG (Republique Democratique du Congo, Ministere de la Recherche Scientifique, Observatoire Volcanologique de Goma, Direction Generale Goma, Rapport Octobre 2018).

Figure 81. On 2 November 2018 scientists from OVG measured the height from the base of the active cone to the W rim of the crater as 58 m. Courtesy of OVG (Republique Democratique du Congo, Ministere de la Recherche Scientifique, Observatoire Volcanologique de Goma, Direction Generale Goma, Rapport Octobre 2018).

Seismicity remained high during November 2018 but decreased significantly during December. Instrument and access issues in January 2019 prevented accurate assessment of seismicity for the month. The lava lake remained active with periodic surges of thermal activity during November 2018-March 2019 (figure 82). Multiple images show incandescence in multiple places within the crater, suggesting significant fresh overflowing lava.

Figure 82. The active lava lake at Nyamuragira produced strong thermal signals from November 2018 through March 2019 that were recorded in Sentinel-2 satellite images (bands 12, 4, 2). Several images suggest fresh lava cooling around the rim of the crater in addition to the active lake. A relatively cloud-free day on 19 November 2018 (top left) revealed no clear thermal signal, but a strong signal was recorded on 29 November (top right) despite significant cloud cover. Images from 13 and 28 January 2019 (second row) both showed evidence of incandescent lava in multiple places within the crater. The thermal signal was smaller and focused on the center of the crater on 12 and 27 February 2019 (third row). Images taken on 9 and 19 March 2019 clearly showed incandescent material at the center of the crater and around the rim (bottom row). Courtesy of Sentinel Hub Playground.

On 12 April 2019 a Ukrainian Aviation Unit supported by MONUSCO provided support for scientists visiting the crater for observations and seismic analysis. Satellite data confirmed ongoing thermal activity into May, although the strength of the signal appeared to decrease (figure 83). MODVOLC thermal alerts ceased after 8 April, and the MIROVA thermal data also confirmed a decrease in the strength of the thermal signal during April 2019 (figure 84).

Figure 83. Sentinel-2 satellite data (bands 12, 4, 2) confirmed ongoing thermal activity at Nyamuragira into May 2019. The thermal anomalies on 18 April (left) and 3 May (right) 2019 were smaller than those recorded during previous months. Courtesy of Sentinel Hub Playground.

Figure 84. The MIROVA graph of thermal activity (log radiative power) at Nyamuragira from 16 July 2018 through April 2019 showed near-constant levels of high activity through April 2019 when it declined. This corresponded well with satellite and ground-based observations. Courtesy of MIROVA.

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; Katcho Karume, Director; 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/); MONUSCO, United Nations Organization Stabilization Mission in the DR Congo (URL: https://monusco.unmissions.org/en/, Twitter: @MONUSCO); Cultur Volcan, Journal d'un volcanophile (URL: https://laculturevolcan.blogspot.com), Twitter: @CultureVolcan).

The 16-km-wide Tengger Caldera in East Java, Indonesia is a massive volcanic complex with numerous overlapping stratovolcanos (figure 11). Mount Bromo is a pyroclastic cone that lies within the large Sandsea Caldera at the northern end of the complex (figure 12) and has erupted more than 20 times during each of the last two centuries. It is part of the Bromo Tengger Semeru National Park (also a UNESCO Biosphere Reserve) and is frequently visited by tourists. The last eruption from November 2015 to November 2016 produced hundreds of ash plumes that rose as high as 4 km altitude; some of them drifted for hundreds of kilometers before dissipating and briefly disrupted air traffic. Only steam and gas plumes were observed at Mount Bromo from December 2016 to February 2018 when a new series of explosions with ash plumes began; they are covered in this report with information provided by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC). Copyrighted ground and drone-based images from Øystein Lund Andersen have been used with permission of the photographer.

Figure 11. The Tengger Caldera viewed from the north Mount Bromo issuing steam in the foreground and Semeru volcano in the background on 30 September 2018. Courtesy of Øystein Lund Andersen, used with permission.

Figure 12. Aerial view of the Bromo Cone in Tengger Caldera seen from the west on 30 September 2018. Courtesy of Øystein Lund Andersen, used with permission.

PVMBG lowered the Alert Level at Bromo on 21 October 2016 from III to II near the end of an eruptive episode lasting nearly a year. The last VAAC report was issued on 12 November 2016 (BGVN 41:12) noting that the last ash emission had been observed the previous day drifting NW at 3 km altitude. Throughout 2017 and 2018 Bromo remained at Alert Level II, with no unusual activity described by PVMBG. During 1-2 September 2018, a wildfire in the Bromo Tengger Semeru National Park burned 65 hectares of savannah (figure 13); the fire produced 12 MODVOLC thermal alerts around the Tengger Caldera rim. No reports of increased volcanic activity were issued by PVMBG during the period.

Figure 13. A wall of fire in the Bromo Tengger Semeru National Park savanna during 1-2 September 2018 produced thermal alerts that were not related to volcanic activity at the Bromo Cone in Tengger Caldera. Image courtesy of the park authority, reported by Mongabay. MODVOLC thermal alerts courtesy of Hawai'i Institute of Geophysics and Planetology (HIGP).

After slightly more than two years of little activity other than gas and steam plumes, ash emissions resumed from the Bromo Cone on 18 February 2019. After a brief pause, a new explosion on 10 March marked the beginning of a series of near-daily ash emissions that lasted for the rest of March, producing ash plumes that rose to altitudes ranging from 3.0 to 5.2 km and drifted in many different directions. A new series of ash emissions began on 6 April, rising to 3 km and also drifting in multiple directions. Ash emission density decreased during the month; plumes were only rising a few hundred meters above the summit by the end of April and consisted of mostly steam and moderate amounts of ash.

Activity during February-April 2019. PVMBG reported that at 0600 on 18 February 2019 an eruption at Tengger Caldera's Bromo Cone generated a dense white-and-brown ash plume that rose 600 m and drifted WSW. The plume was not visible in satellite imagery, according to the Darwin VAAC. The Alert Level remained at 2 (on a scale of 1-4). After a few weeks of quiet a new explosion on 10 March (local time) produced a white, brown, and gray ash plume that rose 600 m above the summit; the plume was visible in satellite imagery extending SW. Increased tremor amplitude was also reported on 10 March. A new emission the next morning produced similar ash plumes that drifted S, SW, and W at 3 km altitude. On the morning of 12 March (local time) a continuous ash plume was observed in satellite imagery at 3.4 km altitude drifting SW. The plume drifted counterclockwise towards the S, E, and NE throughout the day and continued to drift NE and SE on 13 March. The altitude of the plume was reported at 4.3 km later that day based on a pilot report.

Continuous brown, gray, and black ash emissions were reported by PVMBG during 14-19 March at altitudes ranging from 3 to 3.9 km; they drifted generally NE to NW. Ashfall was noted around the crater and downwind a short distance. The Darwin VAAC reported continuous ash emissions to 5.2 km altitude drifting SE on 20 March. It was initially reported by a pilot and partially discernable in satellite imagery before dissipating. Ongoing ash emissions of variable densities and colors ranging from white to black were intermittently visible in satellite imagery and confirmed in webcam and ground reports at around 3.0 km altitude during 21-25 March (figures 14-17). Ashfall impacted the closest villages to Bromo, including Cemara Lawang (30 km NW), which was covered by a thin layer of ash. A few trees in the area were toppled over by the weight of the ash. The plume altitude increased slightly on 26 March to 3.7-3.9 km, drifting N and NE. The higher altitude plume dissipated early on 28 March, but ash emissions continued at 3.0 km for the rest of the day.

Figure 14. Ash drifted NNE from the Bromo Cone in Tengger Caldera on 23 March 2019. Courtesy of Øystein Lund Andersen (drone image), used with permission.

Figure 15. Ash drifted N from the Bromo Cone in Tengger Caldera on 23 March 2019. The Batok Cone is on the right, Segera Wedi is behind Bromo, and Semeru is in the far background. Courtesy of Øystein Lund Andersen, used with permission.

Figure 16. A few trees toppled from ashfall in the vicinity of the Bromo Cone in Tengger Caldera on 24 March 2019. Courtesy of Øystein Lund Andersen, used with permission.

Figure 17. Ash plumes from the Bromo Cone in Tengger Caldera on 24 March 2019 caused ashfall in communities as far as 30 km away. View is from the floor of the Sandsea Caldera. Courtesy of Øystein Lund Andersen, used with permission.

After just a few days of quiet, new ash emissions rising to 3.0 km altitude and drifting SE were reported by both PVMBG (from the webcam) and the Darwin VAAC on 6 April 2019. By the next day the continuous ash emissions were drifting N, then E during 8-10 April, and S during 11 and 12 April. A new emission seen in the webcam was reported by the Darwin VAAC on 15 April (UTC) that rose to 3.0 km and drifted W. Ash plumes were intermittently visible in either webcam or satellite imagery until 17 April rising 500-1,000 m above the crater; from 19-25 April only steam plumes were reported rising 300-500 m above the summit. A minor ash emission was reported from the webcam on 26 April that rose to 3.0 km altitude and drifted NE for a few hours before dissipating. PVMBG reported medium density white to gray ash plumes that rose 400-600 m above the crater for the remainder of the month.

Geologic Background. The 16-km-wide Tengger caldera is located at the northern end of a volcanic massif extending from Semeru volcano. The massive volcanic complex dates back to about 820,000 years ago and consists of five overlapping stratovolcanoes, each truncated by a caldera. Lava domes, pyroclastic cones, and a maar occupy the flanks of the massif. The Ngadisari caldera at the NE end of the complex formed about 150,000 years ago and is now drained through the Sapikerep valley. The most recent of the calderas is the 9 x 10 km wide Sandsea caldera at the SW end of the complex, which formed incrementally during the late Pleistocene and early Holocene. An overlapping cluster of post-caldera cones was constructed on the floor of the Sandsea caldera within the past several thousand years. The youngest of these is Bromo, one of Java's most active and most frequently visited volcanoes.

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/); 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/); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: http://www.oysteinlundandersen.com); Mongabay, URL: https://news.mongabay.com/2018/09/fires-tear-through-east-java-park-threatening-leopard-habitat/.

Karangetang (also referred to as Api Siau) is an active volcano on the island of Siau in the Sitaro Regency, North Sulawesi, Indonesia. It produces frequent small eruptions that include gas-and-steam plumes, ash plumes, avalanches, lava flows, incandescent ballistic ejecta, and pyroclastic flows. This report covers May 2018-May 2019 and summarizes reports by Indonesia's Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), and the Darwin VAAC (Volcanic Ash Advisory Center), and satellite data. During this time, increased activity resulted in a lava flow that reached the ocean and cut road access to communities.

No activity was reported during May through October 2018. During this time, Sentinel-2 thermal images showed elevated temperatures in the main active crater and gas-and-steam plumes dispersing in different directions (figure 17). On 4 July, the Darwin VAAC reported a "weak" ash plume to an altitude of 3 km that drifted NE, only based on satellite imagery. There were few thermal signatures detected by the MIROVA algorithm from May through November (figure 18).

Figure 17. Incandescence and weak steam-and-gas plumes at the southern crater of Karangetang on 9 May and 17 August 2018. This was common in cloud-free images acquired during this time. Sentinel-2 false color (bands 12, 11, 4) images courtesy of Sentinel Hub Playground.

Figure 18. MIROVA log radiative power plot of MODIS infrared data for June 2018 through April 2019. There was little thermal energy detected before December, after which levels remained high until they began declining in March 2019. Courtesy of MIROVA.

Steam plumes were observed from two craters during November 2018 (figures 19 and 20). There was a significant increase in seismicity on 22 to 23 November, followed by a sharp decline on the 24th. The first MODVOLC thermal alert was issued on 25 November. At 1314 on 25 November an ash plume rose to at least 500 m above the N crater and the Aviation Color Code was raised to Orange. A Sentinel-2 thermal image acquired on this day showed elevated temperatures at both south and north craters, with accompanying gas-and-steam plumes. After the increase in seismicity and detected thermal energy, activity progressed to lava flow extrusion, avalanches, and pyroclastic flows triggered from the lava flow. The lava flow originated from the north crater (Kawah Dua) and moved towards the NNW. Avalanches accompanied the flow from the crater and down the lava flow surface. The Volcano Alert level was increased from II to III on 20 December at 1800 (on a scale of I to IV).

Figure 19. White gas-and-steam plumes emanating from two craters at Karangetang at 0630 on 16 November 2018. Courtesy of MAGMA Indonesia via Øystein Lund Andersen.

Figure 20. An ash plume from the N crater (left) and a gas-and-steam plume from the S crater (right) of Karangetang at 0703 on 26 November 2018. Courtesy of MAGMA Indonesia via Øystein Lund Andersen.

Throughout January 2019 activity consisted of small ash plumes up to 600 m above the N crater (figure 21) and continued lava flow activity. On 17 January Kompas TV reported that heavy ashfall impacted several villages. Lava and avalanches traveled as far as 0.7-1 km W towards the Sumpihi River and 1-2 km NE down the Kali Batuare throughout the month.

Figure 21. A small ash plume on 31 January 2019 at Karangetang. Courtesy of MAGMA Indonesia via Øystein Lund Andersen.

Video taken on 3 February 2019 shows the lava flow covering the road and continuing down the steep slope with multi-meter-scale incandescent blocky lava fragments on the surface dislodging and triggering small avalanches. By 5 February the lava flow reached over 3.5 km down the Malebuhe River drainage on the NW flank and into the ocean where a lava delta was growing with dense steam plume rising above by the 11th (figures 22-26). Drone footage from 9 February shows the lava flow across the section of road had a width of about 160 m and a width of about 140 m at the coast. Gas-and-steam and ash plumes were noted most days, reaching up to 600 m above the crater and dominantly dispersing to the E (figure 27). By 11 February there had been 190 people evacuated.

Figure 22. The lava flow front at Karangetang nearing the ocean on 5 February 2019. Courtesy of MAGMA Indonesia.

Figure 23. The lava flow entering the ocean at Karangetang in early February 2019. Photos posted on 11 February; courtesy of BNPB.

Figure 24. Locations of activity observations at Karangetang in November 2018 and February 2019. 27 November 2018: the descent of lava from the Kawah Dua crater (N crater) to about 700-1000 m away, towards the Sumpihi River and Kinali Village. 2 February 2019: the descent of lava 2.5 km NW, 500 m from the highway. 5 February 2019: the lava flow reached the sea. Courtesy of BNPB.

Figure 25. Sentinel-2 thermal satellite images of Karangetang during November 2018 through February 2019 showing elevated temperatures at two craters, gas-and-steam plumes, and a lava flow moving to the NW (bright yellow-orange). Sentinel-2 false color (bands 12, 11, 4) images courtesy of Sentinel Hub Playground.

Figure 26. View of the active lava flow on Karangetang at the ocean entry in early February 2019. Photo posted on 12 February; taken by Ungke Pepotoh, courtesy of Agence France-Presse.

Figure 27. Ashfall from Karangetang on Siau Island as seen from Pehe port on 7 February 2019. Photo courtesy of The New Indian Express, AFP / Ungke Pepotoh.

On 13 February 2019 avalanches continued from the northern crater to 700-1000 m W towards the Sumpihi River and 1-2 km NE towards Kali Batuare. KOMPAS TV reported a statement by PVMBG describing a decrease in activity, including lava avalanches, but with elevated seismicity on the 12 February. Throughout this period of elevated activity both seismicity (figure 28), along with plume heights and directions (figure 29), were variable. On 22 February the Darwin VAAC reported an ash plume, due to a pyroclastic flow, rising to an altitude of 3.7 km.

Figure 28. Graph showing the variable seismicity at Karangetang during 1 November 2018 to 8 February 2019. Courtesy of PVMBG.

Figure 29. Graph showing gas-and-steam plume heights in meters above the crater from 1 November 2018 to 8 February 2019, with the plume dispersal directions indicated in the box. Modified from data courtesy of PVMBG.

Throughout March 2019 PVMBG reported the continuation of a low rate of lava effusion at the north crater, avalanches, and gas-and-steam plumes rising up to 500 m above the crater. The Darwin VAAC reported an ash plume on 7 March that rose to an altitude of 2.7 km that dispersed to the SW. Minor ash emissions were reported by the Darwin VAAC on 6 April that rose to 2.1 km altitude and drifted SE. In mid-April, activity increased in the southern crater and on 15 April a pyroclastic flow traveled 2 km towards the Kahetang and Batuawang rivers. Another ash advisory was issued for an ash plume up to 2.4 km altitude on 16 April. Small gas-and-steam plumes continued through the month.

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/); 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/); 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/); 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/); Agence France-Presse (URL: http://www.afp.com/); Kompas TV, Menara Kompas Lt. 6, Jl. Palmerah Selatan No.21, Jakarta Pusat 10270 Indonesia (URL: https://www.kompas.tv/article/39190/abu-gunung-karangetang-tutup-permukiman-warga); The New Indian Express (URL: http://www.newindianexpress.com/world/2019/feb/08/emergency-declared-on-indonesian-island-after-volcanic-eruption-1936173.html); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: https://www.oysteinlundandersen.com).

Our last report covered generally low-level activity at Arenal through September 2007 (BGVN 32:09). Behavior then included pyroclastic flows to a runout distance of ~ 1 km and a new lava flow emerging from Crater C. This report covers the interval October 2007?June 2008 and originated from those of both the Observatorio Vulcanologico Sismologica de Costa Rica- Universidad Nacional (OVSICORI-UNA) and (ICE).

Impressive incandescent avalanches (block-and-ash flows or pyroclastic flows) traveled down several flanks during June 2008. At least portions of those avalanches broke off from a cone in Crater C and active lava flows high on the edifice.

During the reporting interval, Crater C continued to produce lava flows, gases, sporadic Strombolian eruptions, and avalanches from the lava flow fronts. Observers noticed acid rain and small amounts of ejected pyroclastic material impacting the NE, E, and SE flanks. They also cited loss of vegetation, steep slopes, poorly consolidated material, and high precipitation as factors that triggered small cold avalanches in Calle de Arenas, Manolo, Guillermina, and the river Agua Caliente. Crater D remained fumarolic. Except for the June avalanches, eruptive activity generally remained modest. Some reports noted that the eruptive vigor continued to drop both in terms of the number of eruptions and the amount of ejected pyroclastic material.

OVSICORI-UNA reported that by March 2008, the flow of lava down the S flank had stopped, but a new flow that had begun in February 2008 toward the SW flank was still active. A few eruptions produced ash columns that exceeded 500 m above the vent.

During April 2008, lava moving toward the S flank descended to about 1,400 m elevation. Some blocks had detached near the border of the crater. Sporadically small avalanches occurred and some blocks managed to reach vegetation below, igniting small fires. Some April eruptions produced dark gray ash columns.

Glowing avalanches of June. Jorge Barquero sent us a report on Arenal's behavior during June 2008. Prior to the June events a distinct cone had appeared in Crater C. Its steep sides generated small avalanches of loosened rocks. At about 1000 on 6 June, that cone collapsed, causing a pyroclastic (block-and-ash) flow that descended SE, forming a gully or channel, and laying down a deposit that fanned out at the base of Arenal. Lava also descended into or towards the gully, causing small avalanches.

Some residents heard noises and felt ashfall starting at 0600 on 10 June. At about 0800 these block-and-ash flows became larger. The wind blew ash NW to 4 km from the crater.

After 1730 on 14 June, the failure of the lava flow front sent down an avalanche more violent than those earlier. An hour later the largest block-and-ash flow of the month descended. It descended the channel and produced a large quantity of ash that blew SE and W to distances of 6 km. The area of greatest impact was in the SW portion of the Arenal National Park, where the branches of some vegetation cracked under the weight of the ash. More block-and-ash flows were also observed on 15 and 18 June.

On 11 June Eliecer Duarte and E. Fernández (OVSICORI-UNA) visited the distal parts of the new deposits, documenting the new flow field (figures 102 and 103). The distal area occurred at ~ 900 m elevation on Arenal's outer margins where the slope changes abruptly. A series of alternating lobes contained deposits that were 500°C on 11 June. The individual lobe's thickness reached up to about 3-4 m. The heterogeneous nature of the often angular blocks contrasted with a gray and quite sandy matrix, and included both pre-existing material eroded from the valley walls and more recent juvenile material from the summit. Conspicuous blocls from the block-and-ash flow (10% were 2-3 m in diameter and ~ 20% were ~ 1 m in diameter) are mostly juvenile material from the lava flow. The margins of the fan were covered by a fine dust layer several centimeters thick. On the S flanks, the block-and-ash deposit barely reached a few meters thick. On the N flanks, the deposit reached many tens of meters thick, the result of wind carrying the abundant fine materials in that direction.

Figure 102. A view of the early June 2008 incandescent avalanche deposits on Arenal's S flanks. Courtesy of OVSICORI-UNA.

Figure 103. Previously incandescent avalanche deposits at Arenal seen on 11 June 2008. Courtesy of OVSICORI-UNA.

Major S-flank avalanches reported on 6 and 10 June 2008 eroded a radially oriented gully (an avalanche chute). Later avalanches down this direction tended to form channelized deposits. A dark colored thick lava flow present at the summit (figure 104) provided an important source of materials in the deposits. The S-flank avalanches funneled through the gully, fracturing particles into finer grain sizes and generating columns of ash. During the visit, the team observed several avalanches containing large blocks that were similarly reduced in volume as they bounced through the gully. Some of these blocks arrived at the lower part of the fan with temperatures between 800 and 1,000°C. The large blocks seemingly cracked as the result of thermal shock, a process accelerated during a strong rainstorm.

Figure 104. Arenal's summit as seen looking up the new avalanche chute (steaming). At the head of the chute lies a thick black lava flow (labeled lava front "Frente de colada"). Courtesy of OVSICORI-UNA.

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. Fernández, E. Duarte, W. Sáenz, V. Barboza, M. Martinez, E. Malavassi, and R. Sáenz, Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/); Jorge Barquero Hernandez, Instituto Costarricense de Electricidad (ICE), Apartado 5 -2400, Desamparados, San José, Costa Rica.

A scientific expedition in February 2008 observed that the morphology of the volcano had changed considerably since 2005. The eruption that began in May 2005 (BGVN 30:05) ejected lava and tephra that built a new scoria cone NE of the previous central cone. Lava flows covered all of the earlier flows, and several new spatter cones were formed. Fumarolic activity was continuing in February, with a large amount of steam from the central cone.

Activity seemingly decreased in late March 2006, as shown by a significant decline in the number and frequency of thermal anomalies (BGVN 32:07). However, intermittent anomalies continued until 5 October 2007, and ash plumes were seen in satellite imagery on 23 December 2007 (BGVN 33:02). Thermal anomalies detected by MODIS instruments began to be detected again on 12 May 2008 at 1935 (UTC), suggesting a renewal of eruptive activity. Anomalies continued to be identified on 19 days through the end of June.

During 15-30 June 2008 observers on an Indian Coast Guard patrol boat could see red glow from the central cone summit at night from a distance of about 10 km. There were also twelve earthquakes between 27 and 29 June, centered SW of Port Blair (140 km SW of Barren Island) in the Andaman Islands.

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

Information Contacts: Dornadula Chandrasekharam, Dept. Earth Sciences, Centre of Studies in Resources Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India (URL: http://www.geos.iitb.ac.in/index.php/dc); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

Follow previous reports of May 2008 activity (BGVN 33:04, 33:05), this report summarizes Chaitén's behavior from 31 May through 25 July 2008. The bulk of this report came from SERNAGEOMIN (Servicio Nacional de Geología y Minería) and to some extent ONEMI (Oficina Nacional de Emergencia - Ministerio del Interior). A web camera located on a tower in Chaitén town and aimed upstream along the Blanco (Chaitén) river has helped authorities assess both the state of the volcano's plumes and the river (see URL in Information Contacts). In a later section are included some descriptions and photos by Richard Roscoe taken on 9 July.

On 3 June it was reported that lateral blasts or surges (or related processes) had devastated ~ 25 km² of native forest. Other behavior during this interval included consistent ash plumes, which were generally present when the volcano was visible, and continued growth of the intracrater dome and tephra cone. Vent areas and the dome and tephra cone's morphology changed as the dome grew more elongate.

The late May to early June behavior included a short-term seismic decrease, and a weakened eruptive column. During the reporting interval, the column was often noticeably weaker than in early May, but the seismicity was still relatively high. The two main seismic instruments monitoring the volcano (figure 13) registered numerous sustained events through late July, which began to cluster NNE of Chaitén. Some of the earthquakes were up to M 2.6.

Figure 13. Monitoring instrumentation includes two telemetered seismic stations, PUMA (short for Pumalín) and STAB (short for Santa Barbara), which sit adjacent the coast and monitor Chaitén volcano (Cv). On 12 July the stations detected two earthquakes centered NE of the volcano along a major fault trace there (the Liquiñe-Ofqui fault system). The colored versions of the map distinguish second-order faults, which mostly have left-lateral kinematics (red lines), and eroded scarps (yellow lines). Snow-covered Michinmahuida stratovolcano is also a prominent feature (M, along the E margin of map), as is the town of Chaitén (Ct). Courtesy of Luis E. Lara.

SERNAGEOMIN repeatedly interpreted the earthquakes to signify magma ascending from depth. If this magma reached the surface, they noted, vigorous eruptions might return. The high-viscosity of rhyolitic magmas seen here increases potential explosivity. This rhyolitic eruption at Chaitén is the first historically at a monitored volcano. The last significant rhyolitic eruption was at Novarupta volcano in Alaska in 1912.

Chaitén town has largely survived the lahars thus far. A deeper concern is that the growing dome and tephra cone sent bouncing rocks and smaller debris into the caldera's moat. In an early July SERNAGEOMIN report, the authors noted that the caldera's breach, located on the S, appeared blocked by recently eroded products. Small lakes were also then seen on the crater floor. Since the moat area drains to the S through this breach and feeds into the Blanco river, temporary dams in the moat area might seal the caldera's outflow, only to suddenly fail and release large volumes of debris towards the town. Despite this concern, as of 25 July such an event had been absent; however, on 12 July a sudden flood struck Chaitén town (see below).

Activity during June 2008. On 1 June, Chaitén's plume blew W, affecting Chiloé island (including the towns of Queilen, Lebjn, Chonchi, Dalcahue, and Castro, the island's capital). These conditions thwarted work on the seismic network. On 2 June dense fog affected the Gulf of Corcovado, especially adjacent Chiloé island, an atmosphere attributed to remobilization of air-fall ash by wind. That day, a helicopter managed to take off and the view enabled scientists to see an eruptive column to no higher than 3.0 km altitude dispersing SSE.

Seismicity on 2 July was higher than the previous days. Abundant were VT earthquakes, followed by long- period (LP) earthquakes. Between 1 and 2 July, seismic stations registered an average of 5 VT earthquakes per hour (below M 2). At some stations, some of the LP signals were sporadic, lasting less than a minute.

A 5 June SERNAGEOMIN report noted that explosions diminished gradually. Although ash was present, vapor dominated the emissions. A 3 June aerial inspection revealed that the dome's volume and footprint had increased, although it still had not reached the caldera's N wall.

The effects of N and NE flank blasts (or surges, pyroclastic flows, or related processes) were noted during aerial observations from the 3 June flight. The surges had scorched and burned an area of native forest. On this day observers computed an estimate of the damaged area, ~ 2,500 hectares (~ 25 km²). An undated photo looking down on part of the destruction appeared in BGVN 33:05 and more photos appear below. Several SERNAGEOMIN reports mentioned small pyroclastic flows during early and mid-May (12 May in particular, BGVN 33:05). Bulletin editors take the 3 June estimate as reflecting the sum of all devastation to that point in time.

On 3 and 4 June the plume's top stood below 3 km altitude. A 10 June SERNAGEOMIN report noted the continued lowered eruptive and seismic intensity through that time. Plumes continued to remain under 3 km altitude and they still affected air travel.

On 12 June observers at Chaitén town noticed tephra-bearing emissions. Noises had emanated from the volcano that day and the previous one. The SERNAGEOMIN report associated these emissions with two new vents seen on the S flank of the old dome, where craters had developed. Vapor-rich plumes had emerged from these areas and the observers inferred that the vents were possibly due to magma-water interactions. In addition, sudden floods swept into Chaitén town in the afternoon on 12 June, despite a lack of evidence for greater rains across the region. They were inferred as related to the emissions the same day.

Seismicity beneath the volcano on 12 June increased in the morning both in terms of the number of earthquakes and their magnitudes. Most of these events were less than M 2. Two prominent earthquakes struck ~ 5 km farther NE of the volcano, along the Liquiñe-Ofqui fault zone.

The 22 June report noted that observers looking at the contact between the old and new domes had seen two craters there that emitted ash plumes. The observers also noted near-source falls of both blocks and ash.

The same report said that a 17 June aerial inspection documented an ash plume to over 2 km over the volcano's summit that blew N and NW. Roars and associated noise from the eruption included the sound of an explosion at 1430 on 17 June. The resulting column rose to a height above the summit of over 3 km but later dropped to 2 km. Emissions continued from a crater S of the contact between the old and new domes. Immediately to the W of this crater, a new and growing crater issued increasingly large emissions of ash and gas. Numerous smaller vents were also apparent, chiefly emitting steam. Loose material covered parts of the old dome, forming a ring-shaped structure (a tephra cone). That structure's steep sides and inner and outer walls occasionally underwent mass wasting. Poor weather during 19-25 June halted aerial inspections then, but ash fell in Chaitén town and to the W and SE, as well as Queilen and other portions of E Chiloé island.

Following 20 June, seismicity remained stable with ~ 40-45 earthquakes per day. Sporadic numbers of VT earthquakes took place; there was no change in the number of LP earthquakes. Investigators inferred a lack of pressure increase in the volcanic system. During bad weather on 23-25 June some earthquakes again occurred on the Liquiñe-Ofqui fault zone, with epicenters in an area 2-3 km E of the volcano. A power outage struck midday on 25 June. A back-up power supply (UPS) worked for a while, but ultimately the outage caused several hours of lost seismic data at the Queilen processing center. Available data suggested a small increase in both the number and amplitudes of earthquakes during 24-25 June. During 0000-1200 on 25 June, instruments recorded 35 VT earthquakes, and four of those were M 2.2; LP earthquakes were absent.

Seismicity during the days leading up the SERNAGEOMIN report issued on 27 June reflected VT earthquakes generally below M 2, reaching 50 per day. An exception was on the 25th when four earthquakes exceeded M 2.0.

July 2008. On 1 July an ash column rose ~ 3 km above the top of the new dome. It blew N and NE. An aerial observation at close hand discerned two roughly vertical, sub-parallel eruption plumes issuing from vents in the crater. One plume, most active in recent weeks, came from a sector S of the new dome. The second plume came from a sector more to the W of the new dome. A photo of the scene in the 3 July SERNAGEOMIN report also depicted the area of eruption largely engulfed in white clouds from numerous fumaroles on the dome. On 3 July SERNAGEOMIN began a series of reports on unrest at Llaima stratovolcano (which went to Red alert on 10 July). Around 16 July a weather front also moved in across the Chiloé island region. Consecutive SERNAGEOMIN reports discussing Chaitén were only issued on 3 and 21 July, with a lack of much discussion on that volcano for the interval 3-15 July.

During 15-20 July seismicity stood relatively high, with an average of 350-400 VT earthquakes per day. On 20 July more than 20 earthquakes surpassed M 2.6. The next reports noted that on 21 and 22 July VT earthquakes occurred 330 times per day; 60 of those were near M 2.6, and that the number of earthquakes decreased on 24 July. Still, some of the minor earthquakes reached M 2.6 and were detected up to 300 km away. Seismic data around this time were interpreted to reflect magma at depth moving towards the surface, possibly implying a reactivation of the system, although the earthquake's depth was poorly constrained.

Chaitén's plume blew E at ~ 2 km altitude above the summit and appeared weaker than usual when seen as the weather cleared after 1500 on 23 July. During 22-24 July, earthquakes had increased both in number and magnitude, with the largest M ~ 2.6.

A new area of epicenters appeared during 22 and 23 July at a location 6 km ENE of the volcano. Seismic stations located 176 and 296 km from Chaitén, respectively monitoring the volcanoes Calbuco and Puyehue-Cordón Caulle, recorded these events, the first such occurrence since the eruption began. Previously, conspicuous epicenters had mainly occurred to the S and SE. Preliminary hypocenter calculations suggested the larger earthquakes in this NNE area were deeper, at 10-15 km depth.

Arrival times of S- and P-waves at stations Pumalín and Santa Bárbara indicated that the smaller magnitude earthquakes still occurred S and SE of Chaitén, whereas the larger magnitude earthquakes struck in the area 6 km ENE. An inspection flight carried viewers to the N and NE of the volcano on 24 July where they saw that the single active central vent sat to the S of the new dome. The emissions then were intermittent, white, and ash poor. When strongest, a thin plume rose to under 2 km altitude, with strong winds causing dispersion to the S and SE. When viewed on 24 July, the new dome also contained a significant depression in the S sector, at a point immediately N of the main active vent mentioned above. This depression emitted steam and gases. The new dome seemed to have decreased its growth rate, at least in the N sector. Strong steaming emerged from base of the dome's E sector. The observers looked around the new dome on the NW, N and NE sides, and they saw neither ponded areas nor lakes. During 24-27 July, the ash column rose to 2.5 km and occasionally 3.0 km altitude. The most active vent was the previously mentioned one located S of the new dome. The plume blew N and NW where it affected various localities along the coast.

Floating pumice. By early June, the white pumice from the eruption accumulated at river mouths to the volcano's W. Some fragments of pumice were as large as 40 cm in diameter. In addition to the Blanco river, those carrying the pumice included the Yelcho and Negro (respectively entering the sea 2 km and 5 km S of Chaitén town). Pumice rafts in the Gulf were seen in May (BGVN 33:05). During June and at least early July, along beaches of Chiloé (and particularly at Lelbjn, 12 km N of Queilen, a town almost directly W of Chaitén town) floating pumice continued to arrive. This area lies 60-100 km across Corcorvado gulf from the mouth of the Blanco river at Chaitén town. The pumice deposits, which included tree trunks and other debris, covered a thin zone along the shoreline stretching ~ 20 m from the sea's edge when photographed the afternoon of 1 July.

Roscoe's July 2008 photos. One of the subjects Roscoe presented on his PhotoVolcanica website was Chaitén's N devastated area, and some of those photos appear here (figures 14 and 15). The captions were brief and omitted the direction the camera was aimed. He visited the devastated area on 9 July 2008.

Figure 14. One of the parts of the devastation zone containing large lithic blocks (~ 1 m across), the most conspicuous being the one at left, which may have been perched above fallen timber. Trees here fell away from the viewer. Courtesy of Richard Roscoe, PhotoVolcanica.com.

Figure 15. Drainages redirected by Chaitén's eruption caused erosion of this road to the volcano's N. Courtesy of Richard Roscoe, PhotoVolcanica.com.

Roscoe noted that in the area he photographed, "Most trees were snapped off a couple of meters above the ground. The [pyroclastic] flow does not appear to have been hot enough to burn the leaves off the trees at the point we visited at the base of the volcano. Many branches with brown leaves were lying around. Very little pumice was found in the area although much of it may have been swept away during subsequent heavy rainfall."

In Chaitén town, Roscoe documented damage-mitigation and salvaging efforts (figure 16). Two of Roscoe's photos showed heavy equipment (a large backhoe and a bulldozer) reshaping the lahar deposits in an attempt to control encroaching lahars. Other scenes included people retrieving belongings, excavating lahar deposits covering the floor and lower shelves of a grocery store, and improving drainage from and access to their homes.

Figure 16. Work in Chaitén town to strengthen river banks to protect town from lahars. Although laden with tree trunks, the lahars appear quite uniform in color and character, devoid of coarse lithics or large rafted pumices. Courtesy of Richard Roscoe, PhotoVolcanica.com.

Geologic Background. Chaitén is a small, glacier-free caldera with a compound Holocene lava dome located 10 km NE of the town of Chaitén on the Gulf of Corcovado. Early work had identified only a single explosive eruption during the early Holocene prior to the major 2008 eruption, but later work has identified multiple explosive eruptions throughout the Holocene. A rhyolitic obsidian lava dome occupies much of the caldera floor. Obsidian cobbles from this dome found in the Blanco River are the source of prehistorical artifacts from archaeological sites along the Pacific coast as far as 400 km from the volcano to the N and S. The caldera is breached on the SW side by a river that drains to the bay of Chaitén. The first historical eruption, beginning in 2008, produced major rhyolitic explosive activity and growth of a lava dome that filled much of the caldera.

Information Contacts: Servicio Nacional de Geología y Minería(SERNAGEOMIN), Avda Sta María No 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); Oficina Nacional de Emergencia - Ministerio del Interior (ONEMI), Beaucheff 1637 / 1671, Santiago, Chile (URL: http://www.onemi.cl/); Luis E. Lara, Departamento de Geología Aplicada, SERNAGEOMIN; Richard Roscoe, Photovolcanica.com (URL: http://www.photovolcanica.com/).

Around 2-3 February 2008, a Volcano Discovery tour visited Erta Ale (figures 18-21). Tom Pfeiffer reported that the northern pit crater contained a lake of molten lava ~ 75 m across. Strong spattering and bursting bubbles were seen. At times, the lava lake rose and flooded the lower terrace. During this phase the usual fountains ceased. Richard Roscoe, who also visited during February 2008, presents animations of the flooding on his Photovolcanica website. He also shows photos of strong fountaining associated with falling lava lake levels.

Figure 18. Wide-angle photo showing the lava lake at Erta Ale, February 2008. Taken with fisheye-lens and a digital reflex camera. Courtesy Marco Fulle.

Figure 19. Folds developed in the crust of the lava lake at Erta Ale, February 2008. Courtesy of Tom Pfeiffer (Volcano Discovery).

Figure 20. Rising magmatic gases drove fountains like this one emerging above the surface of the lava lake at Erta Ale, February 2008. Courtesy of Tom Pfeiffer (Volcano Discovery).

Figure 21. Unusual egg-like sulfate structures at Erta Ale in February 2008. The delicate-looking incrustations cover an area of wet fumaroles on the rim of the North crater. Courtesy of Tom Pfeiffer (Volcano Discovery).

Occasionally, magmatic gas released in the middle of the lake created a zone a few meters in diameter where fountains typically lasted ~ 1 minute (figure 20). Thin threads of lava (Pelee's hair) are visible in some lava-fountain photographs. Richard Roscoe also features similar photos. Marco Fulle noted strong spattering when lava was drawn down (subducted) into the lake.

A Volcanologique de Genève (SVG) trip on 8-9 February 2008 noted extensions of ropy lava in the N crater. The lake was little changed from the group's last visit in 2005. The group visited the N Crater, and, given its constant degassing, was able to take gas samples. They also measured the lake's surface temperature (700°C). The descent into this crater, seemingly easy, was made difficult by a mantle of very unstable lava scoria. An elevated level of the lava lake halted a subsequent descent.

References. Rivallin, P., and Mougin, D., 2008, Trip report of Pierrette Rivallin and Dédé Mougin: LAVE Bulletin, no. 79, May 2008.

Geologic Background. Erta Ale is an isolated basaltic shield that is the most active volcano in Ethiopia. The broad, 50-km-wide edifice rises more than 600 m from below sea level in the barren Danakil depression. Erta Ale is the namesake and most prominent feature of the Erta Ale Range. The volcano contains a 0.7 x 1.6 km, elliptical summit crater housing steep-sided pit craters. Another larger 1.8 x 3.1 km wide depression elongated parallel to the trend of the Erta Ale range is located SE of the summit and is bounded by curvilinear fault scarps on the SE side. Fresh-looking basaltic lava flows from these fissures have poured into the caldera and locally overflowed its rim. The summit caldera is renowned for one, or sometimes two long-term lava lakes that have been active since at least 1967, or possibly since 1906. Recent fissure eruptions have occurred on the N flank.

Information Contacts: Tom Pfeiffer, Volcano Discovery (URL: http://www.VolcanoDiscovery.com/); Marco Fulle, Osservatorio Astronomico, Trieste, Italy; Richard Roscoe (URL: http://www.photovolcanica.com/).

According to government authorities in the Ngorongoro district of Tanzania and the 22 March 2008 edition of Arusha Times, nine months after the mountain began continuous eruptive activity (BGVN 33:02), many residents had moved to other villages at a safe distance. Ngorongoro district member of parliament Saning'o Ole Telele told reporters that up to 5,000 people may have moved out of the area. The last major eruption was in August 1966. Since then there had not been an eruption of such magnitude, although notable ones were recorded in 1983, 1993, 2002 and 2006.

Recent observations. Table 19 lists recent observations from April through early July 2008.

On 2 April 2008, Chris Daborn of Tropical Veterinary Services Ltd reported that the color of ash plumes changed from "salty" white to a more inert black, and eruptions were much smaller, barely rising above the mountain. Heavy rains made movement in the area difficult, washing away ash.

Table 19. Summary of visitors to Ol Doinyo Lengai and their brief observations (from a climb, aerial overflight, flank, or satellite) April-early July 2008 (continued from BGVN 33:02). Most of this list is courtesy of Frederick Belton.

Ben Wilhelmi flew over on 7 and 8 April 2008 just prior to an eruption on the 7th and following the start of an eruption on the 8th. The flanks showed newly formed erosion gullies in the recently deposited ash (figure 111). Pilots Wilhelmi and Michael Dalton-Smith observed little activity during early April, although visibility was hampered by atmospheric clouds on several occasions; aerial photos showed no activity on 11 April.

Figure 111. Aerial photographs of Ol Doinyo Lengai crater on (a, top) 7 April and (b, bottom) 8 April 2008. Photos courtesy Ben Wilhelmi.

On 14-16 May 2008, Chris Weber and Marc Szeglat visited. Weber noted that only minor ash eruptions were reported by local Masaai after the eruptions on 8 and 17 April 2008. Some of the evacuated Masaai had returned to their settlements, but part of the livestock had not returned by the middle of May. The fall-out of pyroclastics was still visible around the volcano. Due to a heavy rain season, vegetation damage was not as severe as it could have been. Up to an altitude of ~ 1,000 m the vegetation (mostly 'Elephant grass', normal grass, and some Akazia trees) was undamaged except for the W side, where severe damage occurred as far as 10 km from the summit. Some lahars had occurred on the N and NE sides. The former trekking route was not recommended because of rockfalls and poor conditions. Weber and Szeglat used a very steep route on the SE side (named "simba route"). From ~ 1,000 m altitude ash layers were clearly visible on the ground, but new grass had grown since the eruption. Above ~ 1,500 m on the SE flank all vegetation was covered by pyroclastic material. From an altitude of ~ 2,500 m, additional impacts of volcanic bombs were visible. In the inactive S crater, at their campsite, all vegetation was destroyed, and volcanic bomb impacts from the explosive events on April 2008 were quite impressive.

The active N crater had a new morphology (figure 112). The N-S diameter of the crater was 300 m and it was 283 m E-W. The crater floor was at ~ 2,740 m elevation, ~ 130 m deep below the W crater rim. Two vents, designated as c1 and c2, were present inside the crater (figure 112). Both vents were strongly degassing. On 15 May 2008, fine powdered ash was ejected until midday. It was not possible to determine which vent was responsible for this. After descent, Weber and Szeglat visited an abandoned Masaai boma (hut) a few kilometers W of the summit where ashfall had forced a family to flee.

Figure 112. (a) Sketch map of Lengai, May 2008, and (b) cross section AB. Two vents were located as c1 and c2 inside the crater; older hornito locations are marked as Txx on the map (see hornitos on sketch map of Lengai as of 23 August 2007 in BGVN 32:11). Courtesy of Chris Weber.

On 8 June Wilhelmi saw a small eruption during a flyover. Photos made by Wilhelmi during overflights on 3, 10, and 12 June showed no activity. However, an ash-poor plume was seen by Fred Belton on 12 June.

On 17 June 2008 a group of Masaai from Engare Sero climbed via the W route through the Pearly Gates, which has been closed for several months. Fred Belton and Paul Hloben climbed on 18 June with a Masaai guide, Peter, and two other Tanzanians Paul Mongi and Mweena Hosa, following the route of the group from the previous day, which was covered by thick ash deposits. The route is subject to danger should there be a significant eruption. Belton's group spent about an hour on the rim of the active cone.

The new active cone covered the former crater floor entirely except for a region just N of the summit. The W, N, and E sides of the former crater were ~ 30 m higher than before and enclosed a deep pit crater with a couple of small vents. To the S, the rim of the new cone rested on the crater floor. To the E and W the new cone merged with and covered up the old rim at the points where it intersects the arc formed by the summit ridge. Thus, there was a section of the former crater floor which was bounded to the N by the new cone's S rim and to the E, S, and W by the original curving summit ridge.

From approximately 0920-1020 the pit crater frequently emitted an ash-poor plume from the SW part of its floor, and there was light ashfall on the rim. Loud rumbling was continuous and occasional sounds of gas jetting and rockfalls were heard amid other noises. Occasionally there was a sloshing/hissing noise resembling the sound of 'lava at depth' often heard in the past, but there was no evidence of lava in the crater. The summit and S crater were not visited due to atmospheric clouds around the summit.

On 18 June, Ben Wilhelmi photographed the climbers with Belton during a flyover (figure 113). No activity was seen the next day, but on 30 June Wilhelmi saw gray plumes emerging. A small crater rim collapse was seen on the S part of the crater wall on 1 July 2008.

Figure 113. View of the crater rim on 18 June 2008 showing four climbers at left center just below the rim. Photo courtesy of Ben Wilhelmi.

Satellite thermal anomalies. Table 20 lists MODIS/MODVOLC thermal anomalies measured between November 2007 through July 2008; MODVOLC is the algorithm for identifying thermal anomalies used by the HIGP Thermal Alerts System Group. On 17 April 2008, as noted in table 19, MODIS data analyzed by Matthieu Kervyn's algorithm MODLEN (sensitive to lower temperature anomalies than MODVOLC) indicated a significant hotspot, showing that activity, although intermittent, continued.

Table 20. MODVOLC thermal anomalies measured by MODIS satellite at Ol Doinyo Lengai from November 2007 through July 2008. Courtesy of the MODIS Thermal Alerts System Group at the Hawai'i Institute of Geophysics and Planetology (HIGP).

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

Information Contacts: Frederick Belton, Developmental Studies Department, PO Box 16, Middle Tennessee State University, Murfreesboro, TN 37132, USA (URL: http://oldoinyolengai.pbworks.com/); Christoph Weber, Volcano Expeditions International (VEI), Muehlweg 11, 74199, Entergruppenbach, Germany (URL: http://www.volcanic-hazards.de/); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Matthieu Kervyn De Meerendre, Dept of Geology and Soil Science, Gent University, Krijgslaan 281, S8/A.310, B-9000 Ghent, Belgium (URL: http://homepages.vub.ac.be/~makervyn/).

A report from OVDAS-SERNAGEOMIN (Volcanological Observatory of the Southern Andes ? National Service of Geology and Mining) by Naranjo, Peña, and Moreno (2008) summarized the eruption at Llaima of January through February 2008. This and other reports from OVDAS-SERNAGEOMIN supplements earlier reports (BGVN 33:01) and extends observations through late April 2008..

Summary of January-February 2008 eruption. Shortly after 1730 (local time) on 1 January 2008, Llaima began a new eruptive cycle that was very similar in character to a large eruption that had occurred in February 1957. The 2008 activity was centered at the principal crater, a feature 350 x 450 m in diameter with the major axis trending NW-SE. This new continuous eruptive phase began with strong Strombolian eruptions. Strong ejections of lava fragments fell on the glaciers on the high flanks NE and W of the principal cone (figure 18), generating lahars that flowed ~15 km to reach the Captrén River to the N and the Calbuco River to the W (figure 19). The eruptive plume rose to an altitude of ~ 11 km and blew ESE; ash accumulated to a depth of ~11 cm at a distance of 7 km from the crater.

Figure 18. Satellite images depicting Llaima before and after the recent eruptions. The left image shows Llaima on 17 September 2006 covered with a white blanket of snow and ice; the right image shows Llaima on 22 February 2008 after numerous eruptions, with ash covering the remnants of the glacier. Courtesy of the Japan Aerospace Exploration Agency-Earth Observation Research Center (JAXA-EORC) Advanced Land-Observing Satellite (ALOS) website.

Figure 19. Map showing areas of principal effects of the eruption at Llaima on 1 January 2008. Courtesy of OVDAS-SERNAGEOMIN.

The 1 January 2008 phase was preceded by a slight increase in tremor and a swarm of low frequency earthquakes, but with an absence of volcano-tectonic (VT) or hybrid (HB) events. On 2 January 2008, the activity began to decline. However, a plume of sulfur dioxide (SO₂) was tracked by satellite (figure 20).

Figure 20. A plume of sulfur dioxide (SO2) was released on 2 January 2008. The initially intense plume thinned as it moved E. On 4 January 2008, the plume passed over Tristan da Cunha. This image, acquired by the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite, shows the progress of that plume from 2-4 January 2008. OMI measures the total column amount of SO2 in Dobson Units. (If all the SO2 in a column of atmosphere is compressed into a flat layer at standard temperature (0°C) and pressure (1 atmosphere), a single Dobson Unit of SO2 would measure 0.01 mm in thickness and would contain 0.0285 grams of SO2/m2.) Courtesy, NASA Earth Observatory website.

An explosion on 7 January 2008 resulted in an ash plume that rose 5 km above the crater and traveled E toward Argentina. This explosion was associated with a low frequency, large magnitude event.

On 9 January, a series of explosions occurred. The seismicity included a swarm of low frequency, high-amplitude events and an abrupt increase in microseismicity that decreased gradually until 14 January and more slowly thereafter. On 18 January, after discrete low frequency tremors, explosions from the crater resulted in a pyroclastic flow on the upper E flank (figure 21).

Figure 21. Pyroclastic flow on Llaima's E flank on 18 January 2008. Courtesy, OVDAS-SERNAGEOMIN and Gentileza M. Yarur.

On 21 January seismic activity increased. This was followed on 25 January by continuous Strombolian activity in the main crater. During the night of 26 January, a significant increase in activity occured. Pyroclastic-flow deposits were noted during 28 January on the E flank.

A lava lake that had formed in the main crater began to overflow the W rim on 3 February and a lava flow descended for 2.5 km, making channels in the ice tens of meters deep. The 'a'a lava flow, which was 30-40 m wide and 10 m thick, lasted until 13 February.

Between 8-13 February, explosions in the main crater propelled incandescent material 200-500 m in the air. Explosions occasionally alternated between N and S cones in the main crater. On 9 February, the Calbuco River was about 1 m higher than the normal level, likely due to melt water from the lava and glacier interaction. Strombolian eruptions from the main crater were observed during an overflight on 10 February. A strong explosion ejected bombs onto the E and NE flanks of the volcano on 12 February. Then, on 13 February, incandescence at the summit was noted. Thereafter seismic activity decreased, with only sporadic low frequency signals. The volcano was quiet until 21 February, when a small explosion occurred. Pyroclastic flows were also observed on 21 February descending the E and possibly the W flanks.

During the January-February eruptive phase, various types of plumes were observed, including steam plumes, sulfur dioxide plumes, small ash plumes, and ash-and-gas plumes. The Alert Level remained at Yellow.

March-April 2008. Fumarolic activity from the central pyroclastic cone in Llaima's main crater reactivated on 13 March and intensified during 15-17 March. SO₂ plumes rose to an altitude of 3.6 km and drifted E. During 20-21 March, incandescent material propelled from the crater was observed at night.

During 28 March-4 April, fumarolic plumes from Llaima drifted several tens of kilometers, mainly to the SE. Explosions produced ash and gas emissions, and on 4 April, incandescence was reflected in a gas-and-ash plume. An overflight of the main crater on 2 April revealed pyroclastic material and ash and gas emissions, accompanied by small explosions, that originated from three cones.

On 24 April 2008, seismicity from Llaima again increased. Bluish gas (SO₂) rose from the main crater, and ash-and-gas plumes associated with explosions rose to an altitude of 4.6 km. No morphological changes to the summit were observed during an overflight on 25 April except for a small increase of the diameter of the SE crater.

Thermal anomalies. Thermal anomalies measured by MODIS in 2008 began with an eruption on 1 January 2008 (BGVN 33:01) and continued almost daily through 13 February (table 3). Following a brief period of no measured anomalies, a new group occurred 30 March through 4 April, after which none were recorded through 1 June 2008. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images and reports by ground observers from Projecto Observación Visual Volcán Llaima (POVI) indicated incandescence at the volcano during periods when no anomalies were measured by the MODIS satellites (19-21 March and 24 April 2008), perhaps due to cloud cover. All periods of reported incandescence by ground observers during January 2008 were substantiated by MODIS measured thermal anomalies.

Table 3. MODIS thermal anomalies over Llaima from February through 1 June 2008; data processed by MODVOLC analysis. Daily anomalies were measured from 1-13 February 2008, followed by no anomalies through 29 March. After a period of anomalies from 30 March through 4 April 2008, none were measured through 1 June 2008. Some absences may be due to weather. Courtesy of HIGP Thermal Alerts System.

Reference. Naranjo, J.A., Peña, P., and Moreno, H., 2008, Summary of the eruption at Llaima through February 2008: National Service of Geology and Mining (Servico Nacional de Geologia y Mineria - SERNAGEOMIN).

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

Information Contacts: OVDAS-SERNAGEOMIN (Observatorio Volcanológico de los Andes del Sur-Servico Nacional de Geologia y Mineria) (Southern Andes Volcanological Observatory-National Geology and Mining Service), Avda Sta María 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); 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/productos.php); POVI (Projecto Observación Visual Volcán Llaima) (Project of Visual Observation of Llaima Volcano) (URL: http://www.povi.cl/llaima/); Japan Aerospace Exploration Agency-Earth Observation Research Center (JAXA-EORC) (URL: http://www.eorc.jaxa.jp/); ONEMI (Oficina Nacional de Emergencia - Ministerio del Interior) (National Bureau of Emergency - Ministry of Interior), Chile (URL: http://www.onemi.cl/).

The Alaska Volcano Observatory (AVO) reported that on 12 July 2008 at 1143 a strong explosive eruption at Okmok began abruptly after about an hour of rapidly escalating earthquake activity. The Volcano Alert Level was raised to Warning and the Aviation Color Code was raised to Red from the previous Alert Level of Normal/Green. The last explosive eruption began on 13 February, 1997 (BGVN 22:01) from a cone on the south side of the caldera floor. Lava flowed across the caldera floor until 9 May. Ash plumes generally rose to altitudes of 1.5-4.9 km from 13 February to about 23 May, when thermal anomalies and plumes were no longer seen on satellite imagery. One ash plume rose to an altitude of 10.5 km on 11 March. In May 2001 a small seismic swarm (BGVN 26:08) was detected in the vicinity of the volcano. The earthquake locations could not be pinpointed because Okmok is not monitored by a local seismic network.

The initial phase of the 2008 eruption was very explosive, with high levels of seismicity that peaked at 2200 then began to decline. A wet gas-and-ash-rich plume was estimated to have risen to altitudes of 10.7-15.2 km or greater. Wet, sand-sized ash fell within minutes of the onset of the eruption in Fort Glenn, about 10 km WSW. Heavy ashfall occurred on the eastern portion of Umnak Island; a dusting of ash that started at 0345 also occurred for several hours about 105 km NE in Unalaska/Dutch Harbor. News media reported that residents of Umnak Island heard thundering noises the morning of 12 July and quickly realized an eruption had begun. After calling the US Coast Guard for assistance, they began to evacuate to Unalaska using a small helicopter. A fishing boat evacuated the remaining residents after heavy ashfall made further flights impossible.

On 13 July, reports from Unalaska indicated no ashfall had occurred in Unalaska/Dutch Harbor since the previous night. The National Weather Service reported that the ash plume rose to an altitude of 13.7 km (figure 1). Plumes drifted SE and E. Based on observations of satellite imagery, the ash plume altitude was 9.1 km and drifted SE. However, satellite tracking of the ash cloud by traditional techniques was hampered by the high water content due to interaction of rising magma with very shallow groundwater and surficial water inside the caldera.

Figure 1. Photograph of Okmok by flight attendant Kelly Reeves during Alaska airlines flight on 13 July 2008. Image courtesy of Alaska Airlines.

Ash erupted from a vent or vents near composite cinder cone called Cone D in the eastern portion of the 9.7-km wide caldera. Activity during the past three significant eruptions (1945, 1958, and 1997) occurred from Cone A, a cinder cone on the far western portion of the caldera floor. Each of the three previous eruptions was generally mildly to moderately explosive with most ash clouds produced rising to less than 9.1 km altitude. Each eruption also produced a lava flow that traveled about 5 km across the caldera floor.

AVO reported that during 15-16 July seismicity changed from nearly continuous to episodic volcanic tremor, and the overall seismic intensity declined. Little to no ash was detected by satellite, but meteorological clouds obscured views. Satellite imagery from 0533 on 16 July indicated elevated surface temperatures in the NE sector of the caldera. On 16 July, a light dusting of ash was reported in Unalaska/Dutch Harbor. A plume at an altitude of 9.1 km was visible on satellite imagery at 0800. On 17 July, a pilot reported that an ash plume rose to altitudes of 4.6-6.1 km and drifted E and NE. The sulfur dioxide plume had drifted at least as far as eastern Montana (figure 2). On 18 July, the eruption was episodic, with occasional ash-producing explosions occurring every 15 to 30 minutes. The plumes from these explosions were limited to about 6.1 km.

Figure 2. OMI composite image from NOAA showing the extent of the sulfur dioxide gas cloud from the eruption of Okmok imaged at about 1200 AKDT on 17 July, 2008. The large mass shows the location of the high altitude sulfur dioxide cloud from the main explosive phase on 12 July 2008. Image created by Rick Wessels (AVO); courtesy of the OMI near-real-time decision support project funded by NASA.

Geologic Background. The broad, basaltic Okmok shield volcano, which forms the NE end of Umnak Island, has a dramatically different profile than most other Aleutian volcanoes. The summit of the low, 35-km-wide volcano is cut by two overlapping 10-km-wide calderas formed during eruptions about 12,000 and 2050 years ago that produced dacitic pyroclastic flows that reached the coast. More than 60 tephra layers from Okmok have been found overlying the 12,000-year-old caldera-forming tephra layer. Numerous satellitic cones and lava domes dot the flanks of the volcano down to the coast, including 1253-m Mount Tulik on the SE flank, which is almost 200 m higher than the caldera rim. Some of the post-caldera cones show evidence of wave-cut lake terraces; the more recent cones, some of which have been active historically, were formed after the caldera lake, once 150 m deep, disappeared. Hot springs and fumaroles are found within the caldera. Historical eruptions have occurred since 1805 from cinder cones within the caldera.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of the U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA; Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA; and Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://www.avo.alaska.edu/); Associated Press (URL: http://www.ap.org/).

Our last report on Papandayan (BGVN 29:08) described a modest surge in seismicity that began in July 2004, which rose for a short time but began to subside in mid-August 2004. We received no subsequent reports until June 2005. This report discusses non-eruptive restlessness from early June 2005 through the middle of April 2008, including wide fumarolic temperature variations, seismicity, and occasional minor steam plumes.

Beginning in early June 2005, the number of volcanic earthquakes increased in comparison to the previous months, and fumarole temperatures increased 3-9°C above normal levels. People were not permitted to visit Mas and Baru craters. On 16 June 2005, the Center of Volcanology and Geological Hazard Mitigation (CVGHM) in Indonesia raised the Alert Level at Papandayan from 1 to 2 (on a scale of 1-4) due to increased activity at the volcano. The Alert Level remained at 2 at least through 13 December 2005.

No subsequent reports were received until July 2007. On 15 July there was one volcanic earthquake; the next day 2-10 volcanic earthquakes were recorded. By 31 July, fumarole temperatures had increased 10°C above normal levels in Mas crater. On 1 August up to 53 volcanic earthquakes were recorded and a diffuse white plume rose to an altitude of 2.7 km. Residents and tourists were not permitted within a 1 km radius of the active craters.

On 2 August 2007, CVGHM raised the Alert Level from 1 to 2 (on a scale of 1-4) due to increased seismic activity at the volcano. Seismic events decreased in number after 2 August; earthquake tremors were not recorded after 14 November 2007, and on 7 January 2008, CVGHM lowered the Alert Level at Papandayan from 2 to 1 due to the decrease in activity during the previous four months. Data from deformation-monitoring instruments indicated deflation. White fumarolic plumes rose to an altitude of 2.9 km.

No subsequent reports were received until April 2008. According to the CVGHM, on 15 April the seismic network recorded one tremor signal. On 16 April, measurements of summit fumaroles revealed that the temperature had increased and water chemistry had changed since 7 April. White plumes continued to rise to an altitude of 2.7 km. CVGHM again increased the Alert Level to 2 and warned people not to venture within 1 km of the active crater.

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

Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://vsi.esdm.go.id/).

In an Antara News report, Balok Suryadi, an observer at the Center of Volcanology and Geological Hazard Mitigation (CVGHM) Raung monitoring post at Sumber Arum village, described clouds of "smoke and ash" that occurred on 12 and 13 June. He was also quoted in the 19 June article as saying that activity was "likely" continuing but that it could not be clearly monitored from the observation post.

Another ash eruption was seen rising through the clouds on 17 June 2008 around 1500. This event was photographed by Karim Kebaili while flying from Bali to Jakarta approximately 30 minutes after take-off (figure 4). The same eruption was seen at 1430 by pilot Nigel Demery, who stated that the ash cloud initially rose to about 4.5 km altitude but had dissipated on his return flight about two hours later. The Darwin VAAC was unable to identify the plume in satellite imagery due to meteorological clouds.

Figure 4. Ash plume rising from Raung at about 1500 on 17 June 2008. Courtesy of Karim Kebaili.

Thermal anomalies were detected by the MODIS instrument aboard the Terra satellite on 23 July 2005 and 15 August 2005. No additional thermal anomalies were detected through the end of June 2008. However, ash plumes were reported by pilots on 26 July 2007 and seen in satellite imagery on 26 August 2007 (BGVN 32:09).

Geologic Background. Raung, one of Java's most active volcanoes, is a massive stratovolcano in easternmost Java that was constructed SW of the rim of Ijen caldera. The unvegetated summit is truncated by a dramatic steep-walled, 2-km-wide caldera that has been the site of frequent historical eruptions. A prehistoric collapse of Gunung Gadung on the W flank produced a large debris avalanche that traveled 79 km, reaching nearly to the Indian Ocean. Raung contains several centers constructed along a NE-SW line, with Gunung Suket and Gunung Gadung stratovolcanoes being located to the NE and W, respectively.

Information Contacts: Rebecca Patrick, Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, Northern Territory 0811, Australia (URL: http://www.bom.gov.au/info/vaac); Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Nigel Demery, Indonesia; Karim Kebaili, Indonesia; Antara News (URL: http://www.antara.co.id/); Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

Our previous report on Tungurahua (BGVN 32:08) discussed the volcano's activity during March-July 2007. During that period, Ecuador's Instituto Geofisico (IG) reported significant, but variable eruptive behavior, along with many lahars, ash plumes that reached 4 km above the summit, and semi-continuous ashfall.

Table 15 presents a brief summary of the weekly activity at Tungurahua between 18 July 2007 and 19 February 2008. The plumes were described variously as ash, ash-and-gas, steam-and-gas, steam, or steam-and-ash. They rose up to 13 or 14 km altitude (25-26 October 2007 and 7 February 2008, respectively) but more typically, for many weeks, to below 8 km altitude. Around December 2007 IG stated a caution. They likened Tungurahua's behavior as similar to after its explosive phase of 14 July 2006. In that case, volcanic activity kept going, and this lead to the most explosive phase on 16 August 2006. That dramatic pattern was not repeated the next month, but the pace of volcanism kept up and led to the vigorous 7 February eruption.

Table 15. Summary of weekly activity at Tungurahua between 18 July 2007 and 19 February 2008. Courtesy of IG.

Geologic Background. Tungurahua, a steep-sided andesitic-dacitic stratovolcano that towers more than 3 km above its northern base, is one of Ecuador's most active volcanoes. Three major edifices have been sequentially constructed since the mid-Pleistocene over a basement of metamorphic rocks. Tungurahua II was built within the past 14,000 years following the collapse of the initial edifice. Tungurahua II itself collapsed about 3000 years ago and produced a large debris-avalanche deposit and a horseshoe-shaped caldera open to the west, inside which the modern glacier-capped stratovolcano (Tungurahua III) was constructed. Historical eruptions have all originated from the summit crater, accompanied by strong explosions and sometimes by pyroclastic flows and lava flows that reached populated areas at the volcano's base. Prior to a long-term eruption beginning in 1999 that caused the temporary evacuation of the city of Baños at the foot of the volcano, the last major eruption had occurred from 1916 to 1918, although minor activity continued until 1925.

Information Contacts: Geophysical Institute (IG), Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center, Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Reuters (URL: http://www.reuters.com/); Associated Press (URL: http://www.ap.org/); Pan American Health Organization (PAHO), 525 23rd St. NW, Washington, DC 20037, USA (URL: http://www.paho.org/).

Our most recent report on Ubinas (BGVN 33:01) discussed ongoing eruptions with continuous emissions of volcanic ash, rock, and gases during 2006-2007. During that previously discussed interval, ash plumes sometimes reached ~ 9 km altitudes at times, posing a hazard to aviation, ashfall was heavy. The current report discusses activity from the end of the previous report (17 December 2007) through 15 July 2008. During this period, ash plumes were frequent, as indicated in table 4. No thermal alerts have been detected by the University of Hawaii's Institute of Geophysics and Planetology (HIGP) MODIS satellite-based thermal alert system since 27 December 2006.

Table 4. Compilation of Volcanic Ash Advisories for aviation from Ubinas during 19 December 2007 through July 1, 2008. Courtesy of the Buenos Aires Volcanic Ash Advisory Center (VAAC) and the Instituto Geológical Minero y Metalúrgico (INGEMMET).

According to the ash advisories issued from the Buenos Aires VAAC, the aviation warning color code for Ubinas during the reporting period was variously orange or red. In terms of hazard status on the ground, a news article on 30 June 2008 indicated that local civil defense officials had maintained the Alert level at Yellow. They noted that small explosions and ash-and-gas emissions had continued during the previous two months. Families at immediate risk from the village of San Pedro de Querapi in the vicinity of the volcano have been relocated but have returned to their fields to pursue their agacultural activities. The population of local communities and their livestock had suffered the effects of gas and ash emissions, and local authorities had begun to discuss the possible relocation of about 650 affected families from six towns (Escacha, Tonoaya, San Migues, San Pedro de Querapi, Huataga and Ubinas). The article noted that officials recognized that the relocation process could take several years and should be the villager's decision and not one forced on them.

Geologic Background. A small, 1.4-km-wide caldera cuts the top of Ubinas, Peru's most active volcano, giving it a truncated appearance. It is the northernmost of three young volcanoes located along a regional structural lineament about 50 km behind the main volcanic front of Perú. The growth and destruction of Ubinas I was followed by construction of Ubinas II beginning in the mid-Pleistocene. The upper slopes of the andesitic-to-rhyolitic Ubinas II stratovolcano are composed primarily of andesitic and trachyandesitic lava flows and steepen to nearly 45 degrees. The steep-walled, 150-m-deep summit caldera contains an ash cone with a 500-m-wide funnel-shaped vent that is 200 m deep. Debris-avalanche deposits from the collapse of the SE flank about 3700 years ago extend 10 km from the volcano. Widespread plinian pumice-fall deposits include one of Holocene age about 1000 years ago. Holocene lava flows are visible on the flanks, but historical activity, documented since the 16th century, has consisted of intermittent minor-to-moderate explosive eruptions.

Information Contacts: Instituto Geológical Minero y Metalúrgico (INGEMMET), Av. Canadá 1470, San Borja, Lima 41, Perú (URL: http://www.ingemmet.gob.pe/); Buenos Aires Volcanic Ash Advisory Center (VAAC), Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/productos.php); La República Online (URL: http://www.larepublica.com.pe).

Reports about Pago early in 2006 (BGVN 31:02) noted small vapor emissions, but no noises or glow, and low levels of seismicity. Similar observations were reported by the Rabaul Volcano Observatory (RVO) for December 2006. A local security company reported that sometime during 27-31 October 2006 there was a single booming noise accompanied by a white-gray emissions above the summit. Volcanologists were sent to verify the activity, but no report about the event was received. A March 2007 report only noted diffuse white vapor emissions and low seismicity.

On 28 August 2007 lava fragments were observed being ejected during the daytime from one of the Upper vents (2nd Crater). People in a nearby village heard only a single booming noise in the early hours of 27 August. The residents also indicated increased white vapor emissions from 2nd Crater on the 27th that returned to normal levels the following day. Seismic activity had increased on 27-28 August, and the Real-Time Seismic Amplitude Measurement (RSAM) increased from background level (around 100 units) to a peak of about 400 units. RSAM levels began to decline on the 29th, returning to background levels on 30 August. An inspection on 1 October revealed that only the 2nd Crater of the Upper Vents was releasing diffuse white vapor, and that there were no noises or glow.

Pago remained quiet during September-November 2007. When observations were made, only diffuse white vapor was being released from the Upper Vents. A handful of high-frequency earthquakes and 18 low-frequency events were recorded during September. The daily number of earthquakes ranged from 1 to 4 from 1 to 24 September, with none after through the end of the month. There was a slight increase in gas emission during 9-11 November. The vapor plume was blown N, where villagers reported nose and windpipe irritation, and watery eyes. The daily number of high-frequency earthquakes ranged from 1 to 3, while low-frequency earthquakes ranged from 1 to 9. During January 2008 Pago was still quiet with diffuse white vapor from the upper vents and very occasional low-frequency seismic events.

Geologic Background. The 5.5 x 7.5 km Witori caldera on the northern coast of central New Britain contains the young historically active cone of Pago. The Buru caldera cuts the SW flank of Witori volcano. The gently sloping outer flanks of Witori volcano consist primarily of dacitic pyroclastic-flow and airfall deposits produced during a series of five major explosive eruptions from about 5600 to 1200 years ago, many of which may have been associated with caldera formation. The post-caldera Pago cone may have formed less than 350 years ago. Pago has grown to a height above that of the Witori caldera rim, and a series of ten dacitic lava flows from it covers much of the caldera floor. The youngest of these was erupted during 2002-2003 from vents extending from the summit nearly to the NW caldera wall.

Information Contacts: Ima Itikarai and Herman Patia, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.

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/).