Manam is a basaltic-andesitic stratovolcano that lies 13 km off the northern coast of mainland Papua New Guinea; it has a 400-year history of recorded evidence for recurring low-level ash plumes, occasional Strombolian activity, lava flows, pyroclastic avalanches, and large ash plumes from Main and South, the two active summit craters. The current eruption, ongoing since June 2014, produced multiple large explosive eruptions during January-September 2019, including two 15-km-high ash plumes in January, repeated SO₂ plumes each month, and another 15.2 km-high ash plume in June that resulted in ashfall and evacuations of several thousand people (BGVN 44:10).

This report covers continued activity during October 2019 through March 2020. Information about Manam is primarily provided by Papua New Guinea's Rabaul Volcano Observatory (RVO), part of the Department of Mineral Policy and Geohazards Management (DMPGM). This information is supplemented with aviation alerts from the Darwin Volcanic Ash Advisory Center (VAAC). MODIS thermal anomaly satellite data is recorded by the University of Hawai'i's MODVOLC thermal alert recording system, and the Italian MIROVA project; sulfur dioxide monitoring is done by instruments on satellites managed by NASA's Goddard Space Flight Center. Satellite imagery provided by the Sentinel Hub Playground is also a valuable resource for information about this remote location.

A few modest explosions with ash emissions were reported in early October and early November 2019, and then not again until late March 2020. Although there was little explosive activity during the period, thermal anomalies were recorded intermittently, with low to moderate activity almost every month, as seen in the MODIS data from MIROVA (figure 71) and also in satellite imagery. Sulfur dioxide emissions persisted throughout the period producing emissions greater than 2.0 Dobson Units that were recorded in satellite data 3-13 days each month.

Figure 71. MIROVA thermal anomaly data for Manam from 17 June 2019 through March 2020 indicate continued low and moderate level thermal activity each month from August 2019 through February 2020, after a period of increased activity in June and early July 2019. Courtesy of MIROVA.

The Darwin VAAC reported an ash plume in visible satellite imagery moving NW at 3.1 km altitude on 2 October 2019. Weak ash emissions were observed drifting N for the next two days along with an IR anomaly at the summit. RVO reported incandescence at night during the first week of October. Visitors to the summit on 18 October 2019 recorded steam and fumarolic activity at both of the summit craters (figure 72) and recent avalanche debris on the steep slopes (figure 73).

Figure 72. Steam and fumarolic activity rose from Main crater at Manam on 18 October 2019 in this view to the south from a ridge north of the crater. Google Earth inset of summit shows location of photograph. Courtesy of Vulkanologische Gesellschaft and Claudio Jung, used with permission.

Figure 73. Volcanic debris covered an avalanche chute on the NE flank of Manam when visited by hikers on 18 October 2019. Courtesy of Vulkanologische Gesellschaft and Claudio Jung, used with permission.

On 2 November, a single large explosion at 1330 local time produced a thick, dark ash plume that rose about 1,000 m above the summit and drifted NW. A shockwave from the explosion was felt at the Bogia Government station located 40 km SE on the mainland about 1 minute later. RVO reported an increase in seismicity on 6 November about 90 minutes before the start of a new eruption from the Main Crater which occurred between 1600 and 1630; it produced light to dark gray ash clouds that rose about 1,000 m above the summit and drifted NW. Incandescent ejecta was visible at the start of the explosion and continued with intermittent strong pulses after dark, reaching peak intensity around 1900. Activity ended by 2200 that evening. The Darwin VAAC reported a discrete emission observed in satellite imagery on 8 November that rose to 4.6 km altitude and drifted WNW, although ground observers confirmed that no eruption took place; emissions were only steam and gas. There were no further reports of explosive activity until the Darwin VAAC reported an ash emission in visible satellite imagery on 20 March 2020 that rose to 3.1 km altitude and drifted E for a few hours before dissipating.

Although explosive activity was minimal during the period, SO₂ emissions, and evidence for continued thermal activity were recorded by satellite instruments each month. The TROPOMI instrument on the Sentinel-5P satellite captured evidence each month of SO₂ emissions exceeding two Dobson Units (figure 74). The most SO₂ activity occurred during October 2019, with 13 days of signatures over 2.0 DU. There were six days of elevated SO₂ each month in November and December, and five days in January 2020. During February and March, activity was less, with smaller SO₂ plumes recording more than 2.0 DU on three days each month. Sentinel-2 satellite imagery recorded thermal anomalies at least once from one or both of the summit craters each month between October 2019 and March 2020 (figure 75).

Figure 74. SO2 emissions at Manam exceeded 2 Dobson Units multiple days each month between October 2019 and March 2020. On 3 October 2019 (top left) emissions were also measured from Ulawun located 700 km E on New Britain island. On 30 November 2019 (top middle), in addition to a plume drifting N from Manam, a small SO2 plume was detected at Bagana on Bougainville Island, 1150 km E. The plume from Manam on 2 December 2019 drifted ESE (top right). On 26 January 2020 the plume drifted over 300 km E (bottom left). The plumes measured on 29 February and 4 March 2020 (bottom middle and right) only drifted a few tens of kilometers before dissipating. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Figure 75. Sentinel-2 satellite imagery with Atmospheric penetration rendering (bands 12, 11, and 8a) showed thermal anomalies at one or both of Manam’s summit craters each month during October 2019-March 2020. On 17 October 2019 (top left) a bright anomaly and weak gas plume drifted NW from South crater, while a dense steam plume and weak anomaly were present at Main crater. On 25 January 2020 (top right) the gas and steam from the two craters were drifting E; the weaker Main crater thermal anomaly is just visible at the edge of the clouds. A clear image on 5 March 2020 (bottom left) shows weak plumes and distinct thermal anomalies from both craters; on 20 March (bottom right) the anomalies are still visible through dense cloud cover that may include steam from the crater vents as well. Courtesy of Sentinel Hub Playground.

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

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Vulkanologische Gesellschaft (URL: https://twitter.com/vulkanologen/status/1194228532219727874, https://twitter.com/vulkanologen/status/1193788836679225344); Claudio Jung, (URL: https://www.facebook.com/claudio.jung.1/posts/10220075272173895, https://www.instagram.com/jung.claudio/).

Near-constant fountains of lava at Stromboli have served as a natural beacon in the Tyrrhenian Sea for at least 2,000 years. Eruptive activity at the summit consistently occurs from multiple vents at both a north crater area (N area) and a southern crater group (CS area) on the Terrazza Craterica at the head of the Sciara del Fuoco, a large scarp that runs from the summit down the NW side of the volcano-island (figure 168). Periodic lava flows emerge from the vents and flow down the scarp, sometimes reaching the sea; occasional large explosions produce ash plumes and pyroclastic flows. Thermal and visual cameras that monitor activity at the vents are located on the nearby Pizzo Sopra La Fossa, above the Terrazza Craterica, and at multiple locations on the flanks of the volcano. Detailed information for Stromboli is provided by Italy's Istituto Nazionale di Geofisica e Vulcanologia (INGV) as well as other satellite sources of data; September-December 2019 is covered in this report.

Figure 168. This shaded relief map of Stromboli’s crater area was created from images acquired by drone on 9 July 2019 (In collaboration with GEOMAR drone group, Helmholtz Center for Ocean Research, Kiel, Germany). Inset shows Stromboli Island, the black rectangle indicates the area of the larger image, the black curved and the red hatched lines indicate, respectively, the morphological escarpment and the crater edges. Courtesy of INGV (Rep. No. 50/2019, Stromboli, Bollettino Settimanale, 02/12/2019 - 08/12/2019, data emissione 10/12/2019).

Activity was very consistent throughout the period of September-December 2019. Explosion rates ranged from 2-36 per hour and were of low to medium-high intensity, producing material that rose from less than 80 to over 150 m above the vents on occasion (table 7). The Strombolian activity in both crater areas often sent ejecta outside the crater rim onto the Terrazza Craterica, and also down the Sciara del Fuoco towards the coast. After the explosions of early July and late August, thermal activity decreased to more moderate levels that persisted throughout the period as seen in the MIROVA Log Radiative Power data (figure 169). Sentinel-2 satellite imagery supported descriptions of the constant glow at the summit, revealing incandescence at both summit areas, each showing repeating bursts of activity throughout the period (figure 170).

Table 7. Monthly summary of activity levels at Stromboli, September-December 2019. Low-intensity activity indicates ejecta rising less than 80 m, medium-intensity is ejecta rising less than 150 m, and high-intensity is ejecta rising over 200 m above the vent. Data courtesy of INGV.

Figure 169. Thermal activity at Stromboli was high during July-August 2019, when two major explosions occurred. Activity continued at more moderate levels through December 2019 as seen in the MIROVA graph of Log Radiative Power from 8 June through December 2019. Courtesy of MIROVA.

Figure 170. Stromboli reliably produced strong thermal signals from both of the summit vents throughout September-December 2019 and has done so since long before Sentinel-2 satellite imagery was able to detect it. Image dates are (top, l to r) 5 September, 15 October, 20 October, (bottom l to r) 14 November, 14 December 2019, and 3 January 2020. Sentinel-2 imagery uses Atmospheric penetration rendering with bands 12, 11, and 8A, courtesy of Sentinel Hub Playground.

After a major explosion with a pyroclastic flow on 28 August 2019, followed by lava flows that reached the ocean in the following days (BGVN 44:09), activity diminished in early September to levels more typically seen in recent times. This included Strombolian activity from vents in both the N and CS areas that sent ejecta typically 80-150 m high. Ejecta from the N area generally consisted of lapilli and bombs, while the material from the CS area was often finer grained with significant amounts of lapilli and ash. The number of explosive events remained high in September, frequently reaching 25-30 events per hour. The ejecta periodically landed outside the craters on the Terrazza Craterica and even traveled partway down the Sciara del Fuoco. An inspection on 7 September by INGV revealed four eruptive vents in the N crater area and five in the S crater area (figure 171). The most active vents in the N area were N1 with mostly ash emissions and N2 with Strombolian explosions rich in incandescent coarse material that sometimes rose well above 150 m in height. In the S area, S1 and S2 produced jets of lava that often reached 100 m high. A small cone was observed around N2, having grown after the 28 August explosion. Between 11 and 13 September aerial surveys with drones produced detailed visual and thermal imagery of the summit (figure 172).

Figure 171. Video of the Stromboli summit taken with a thermal camera on 7 September 2019 from the Pizzo sopra la Fossa revealed four active vents in the N area and five active vents in the S area. Images prepared by Piergiorgio Scarlato, courtesy of INGV (Rep. No. 37.2/2019, Stromboli, Bollettino Giornaliero del 10/09/2019).

Figure 172. An aerial drone survey on 11 September 2019 at Stromboli produced a detailed view of the N and CS vent areas (left) and thermal images taken by a drone survey on 13 September (right) showed elevated temperatures down the Sciara del Fuoco in addition to the vents in the N and CS areas. Images by E. De Beni and M. Cantarero, courtesy of INGV (Rep. No. 37.5/2019, Stromboli, Bollettino Giornaliero del 13/09/2019).

Strombolian activity from the N crater on 28 September and 1 October 2019 produced blocks and debris that rolled down the Sciara del Fuoco and reached the ocean (figure 173). Explosive activity from the CS crater area sometimes produced ejecta over 150 m high (figure 174). A survey on 26 November revealed that a layer of ash 5-10 cm thick had covered the bombs and blocks that were deposited on the Pizzo Sopra la Fossa during the explosions of 3 July and 28 August (figure 175). On the morning of 27 December a lava flow emerged from the CS area and traveled a few hundred meters down the Sciara del Fuoco. The frequency of explosive events remained relatively constant from September through December 2019 after decreasing from higher levels during July and August (figure 176).

Figure 173. Strombolian activity from vents in the N crater area of Stromboli produced ejecta that traveled all the way to the bottom of the Sciara del Fuoco and entered the ocean. Top images taken 28 September 2019 from the 290 m elevation viewpoint by Rosanna Corsaro. Bottom images captured on 1 October from the webcam at 400 m elevation. Courtesy of INGV (Rep. No. 39.0/2019 and Rep. No. 40.3, Stromboli, Bollettino Giornaliero del 29/09/2019 and 02/10/2019).

Figure 174. Ejecta from Strombolian activity at the CS crater area of Stromboli rose over 150 m on multiple occasions. The webcam located at the 400 m elevation site captured this view of activity on 8 November 2019. Courtesy of INGV (Rep. No. 45.5/2019, Stromboli, Bollettino Giornaliero del 08/11/2019).

Figure 175. The Pizzo Sopra la Fossa area at Stromboli was covered with large blocks and pyroclastic debris on 6 September 2019, a week after the major explosion of 28 August (top). By 26 November, 5-10 cm of finer ash covered the surface; the restored webcam can be seen at the far right edge of the Pizzo (bottom). Courtesy of INGV (Rep. No. 49/2019, Stromboli, Bollettino Settimanale, 25/11/2019 - 01/12/2019, data emissione 03/12/2019).

Figure 176. The average hourly frequency of explosive events at Stromboli captured by surveillance cameras from 1 June 2019 through 5 January 2020 remained generally constant after the high levels seen during July and August. The Total value (blue) is the sum of the average daily hourly frequency of all explosive events produced by active vents.

Geologic Background. Spectacular incandescent nighttime explosions at this volcano have long attracted visitors to the "Lighthouse of the Mediterranean." Stromboli, the NE-most of the Aeolian Islands, has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent horseshoe-shaped scarp formed about 5,000 years ago due to a series of slope failures that extend to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy, (URL: http://www.ct.ingv.it/en/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Semeru is a stratovolcano located in East Java, Indonesia containing an active Jonggring-Seloko vent at the Mahameru summit. Common activity has consisted of ash plumes, pyroclastic flows and avalanches, and lava flows that travel down the SE flank. This report updates volcanism from September 2019 to February 2020 using primary information from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC).

The dominant activity at Semeru for this reporting period consists of ash plumes, which were frequently reported by the Darwin VAAC. An eruption on 10 September 2019 produced an ash plume rising 4 km altitude drifting WNW, as seen in HIMAWARI-8 satellite imagery. Ash plumes continued to rise during 13-14 September. During the month of October the Darwin VAAC reported at least six ash plumes on 13, 14, 17-18, and 29-30 October rising to a maximum altitude of 4.6 km and moving primarily S and SW. Activity in November and December was relatively low, dominated mostly by strong and frequent thermal anomalies.

Volcanism increased in January 2020 starting with an eruption on 17 and 18 January that sent a gray ash plume up to 4.6 km altitude (figure 38). Eruptions continued from 20 to 26 January, producing ash plumes that rose up to 500 m above the crater that drifted in different directions. For the duration of the month and into February, ash plumes occurred intermittently. On 26 February, incandescent ejecta was ejected up to 50 m and traveled as far as 1000 m. Small sulfur dioxide emissions were detected in the Sentinel 5P/TROPOMI instrument during 25-27 February (figure 39). Lava flows during 27-29 February extended 200-1,000 m down the SE flank; gas-and-steam and SO₂ emissions accompanied the flows. There were 15 shallow volcanic earthquakes detected on 29 February in addition to ash emissions rising 4.3 km altitude drifting ESE.

Figure 38. Ash plumes rising from the summit of Semeru on 17 (left) and 18 (right) January 2020. Courtesy of MAGMA Indonesia and via Ø.L. Andersen's Twitter feed (left).

Figure 39. Small SO2 plumes from Semeru were detected by the Sentinel 5P/TROPOMI instrument during 25 (left) and 26 (right) February 2020. Courtesy of NASA Goddard Space Flight Center.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed relatively weak and intermittent thermal anomalies occurring during May to August 2019 (figure 40). The frequency and power of these thermal anomalies significantly increased during September to mid-December 2019 with a few hotspots occurring at distances greater than 5 km from the summit. These farther thermal anomalies to the N and NE of the volcano do not appear to be caused by volcanic activity. There was a brief break in activity during mid-December to mid-January 2020 before renewed activity was detected in early February 2020.

Figure 40. Thermal anomalies were relatively weak at Semeru during 30 April 2019-August 2019, but significantly increased in power and frequency during September to early December 2019. There was a break in activity from mid-December through mid-January 2020 with renewed thermal anomalies around February 2020. Courtesy of MIROVA.

The MODVOLC algorithm detected 25 thermal hotspots during this reporting period, which took place during 25 September, 18 and 21 October 2019, 29 January, and 11, 14, 16, and 23 February 2020. Sentinel-2 thermal satellite imagery shows intermittent hotspots dominantly in the summit crater throughout this reporting period (figure 41).

Figure 41. Sentinel-2 thermal satellite imagery detected intermittent thermal anomalies (bright yellow-orange) at the summit of Semeru, which included some lava flows in late January to early February 2020. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

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/); 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/); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: http://www.oysteinlundandersen.com).

Frequent historical eruptions have been reported from Mexico's Popocatépetl going back to the 14th century. Activity increased in the mid-1990s after about 50 years of quiescence, and the current eruption, ongoing since January 2005, has included numerous episodes of lava-dome growth and destruction within the 500-m-wide summit caldera. Multiple emissions of steam and gas occur daily, rising generally 1-3 km above the summit at about 5,400 m elevation; many contain small amounts of ash. Larger, more explosive events with ash plumes and incandescent ejecta landing on the flanks occur frequently. Activity through August 2019 was typical of the ongoing eruption with near-constant emissions of water vapor, gas, and minor ash, as well as multiple explosions with ash plumes and incandescent blocks scattered on the flanks (BGVN 44:09). This report covers similar activity from September 2019 through February 2020. Information comes from daily reports provided by México's Centro Nacional de Prevención de Desastres (CENAPRED); ash plumes are reported by the Washington Volcanic Ash Advisory Center (VAAC). Satellite visible and thermal imagery and SO₂ data also provide helpful observations of activity.

Activity summary. Activity at Popocatépetl during September 2019-February 2020 continued at the high levels that have been ongoing for many years, characterized by hundreds of daily low-intensity emissions that included steam, gas, and small amounts of ash, and periods with multiple daily minor and moderate explosions that produce kilometer-plus-high ash plumes (figure 140). The Washington VAAC issued multiple daily volcanic ash advisories with plume altitudes around 6 km for many, although some were reported as high as 8.2 km. Hundreds of minutes of daily tremor activity often produced ash emissions as well. Incandescent ejecta landed 500-1,000 m from the summit frequently. The MIROVA thermal anomaly data showed near-constant moderate to high levels of thermal energy throughout the period (figure 141).

Figure 140. Emissions continued at a high rate from Popocatépetl throughout September 2019-February 2020. Daily low-intensity emissions numbered usually in the hundreds (blue, left axis), while less frequent minor (orange) and moderate (green) explosions, plotted on the right axis, occurred intermittently through November 2019, and increased again during February 2020. Data was compiled from CENAPRED daily reports.

Figure 141. MIROVA log radiative power thermal data for Popocatépetl from 1 May 2019 through February 2020 showed a constant output of moderate energy the entire time. Courtesy of MIROVA.

Sulfur dioxide emissions were measured with satellite instruments many days of each month from September 2019 thru February 2020. The intensity and drift directions varied significantly; some plumes remained detectable hundreds of kilometers from the volcano (figure 142). Plumes were detected almost daily in September, and on most days in October. They were measured at lower levels but often during November, and after pulses in early and late December only small plumes were visible during January 2020. Intermittent larger pulses returned in February. Dome growth and destruction in the summit crater continued throughout the period. A small dome was observed inside the summit crater in late September. Dome 85, 210-m-wide, was observed inside the summit crater in early November. Satellite imagery captured evidence of dome growth and ash emissions throughout the period (figure 143).

Figure 142. Sulfur dioxide emissions from Popocatépetl were frequent from September 2019 through February 2020. Plumes drifted SW on 7 September (top left), 30 October (top middle), and 21 February (bottom right). SO2 drifted N and NW on 26 November (top right). On 2 December (bottom left) a long plume of sulfur dioxide hundreds of kilometers long drifted SW over the Pacific Ocean while the drift direction changed to NW closer to the volcano. The SO2 plumes measured in January (bottom center) were generally smaller than during the other months covered in this report. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Figure 143. Sentinel-2 satellite imagery of Popocatépetl during November 2019-February 2020 provided evidence for ongoing dome growth and explosions with ash emissions. Top left: a ring of incandescence inside the summit crater on 8 November 2019 was indicative of the growth of dome 85 observed by CENAPRED. Top middle: incandescence on 8 December inside the summit crater was typical of that observed many times during the period. Top right: a dense, narrow ash plume drifted N from the summit on 17 January 2020. Bottom left: Snow cover made ashfall on 6 February easily visible on the E flank. On 11 February, the summit crater was incandescent and nearly all the snow was covered with ash. Bottom right: a strong thermal anomaly and ash emission were captured on 21 February. Bottom left and top right images use Natural color rendering (bands 4, 3, 2); other images use Atmospheric penetration rendering to show infrared signal (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Activity during September-November 2019. On 1 September 2019 minor ashfall was reported in the communities of Atlautla, Ozumba, Juchitepec, and Tenango del Aire in the State of Mexico. The ash plumes rose less than 2 km above the summit and incandescent ejecta traveled less than 100 m from the summit crater. Twenty-two minor and three moderate explosions were recorded on 4-5 September along with minor ashfall in Juchitepec, Tenango del Aire, Tepetlixpa, and Atlautla. During a flyover on 5 September, officials did not observe a dome within the crater, and the dimensions remained the same as during the previous visit (350 m in diameter and 150 m deep) (figure 144). Ashfall was reported in Tlalmanalco and Amecameca on 6 September. The following day incandescent ejecta was visible on the flanks near the summit and ashfall was reported in Amecameca, Ayapango, and Tenango del Aire. The five moderate explosions on 8 September produced ash plumes that rose as high as 2 km above the summit, and incandescent ejecta on the flanks. Explosions on 10 September sent ejecta 500 m from the crater. Eight explosions during 20-21 September produced ejecta that traveled up to 1.5 km down the flanks (figure 145). During an overflight on 27 September specialists from the National Center for Disaster Prevention (CENAPRED ) of the National Coordination of Civil Protection and researchers from the Institute of Geophysics of UNAM observed a new dome 30 m in diameter; the overall crater had not changed size since the overflight in early September.

Figure 144. CENAPRED carried out overflights of Popocatépetl on 5 (left) and 27 September (right) 2019; the crater did not change in size, but a new dome 30 m in diameter was visible on 27 September. Courtesy of CENAPRED (Sobrevuelo al volcán Popocatépetl, 05 y 27 de septiembre).

Figure 145. Ash plumes at Popocatépetl on 19 (left) and 20 (right) September 2019 rose over a kilometer above the summit before dissipating. Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl 19 y 20 de septiembre).

Fourteen explosions were reported on 2 October 2019. The last one produced an ash plume that rose 2 km above the summit and sent incandescent ejecta down the E slope (figure 146). Ashfall was reported in the municipalities of Atlautla Ozumba, Ayapango and Ecatzingo in the State of Mexico. Explosions on 3 and 4 October also produced ash plumes that rose between 1 and 2 km above the summit and sent ejecta onto the flanks. Additional incandescent ejecta was reported on 6, 7, 15, and 19 October. The communities of Amecameca, Tenango del Aire, Tlalmanalco, Cocotitlán, Temamatla, and Tláhuac reported ashfall on 10 October; Amecameca reported more ashfall on 12 October. On 22 October slight ashfall appeared in Amecameca, Tenango del Aire, Tlalmanalco, Ayapango, Temamatla, and Atlautla.

Figure 146. Incandescent ejecta at Popocatépetl traveled down the E slope on 2 October 2019 (left); an ash plume two days later rose 2 km above the summit (right). Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl 2 y 4 de octubre).

During 2-3 November 2019 there was 780 minutes of tremor reported in four different episodes. The seismicity was accompanied by ash emissions that drifted W and NW and produced ashfall in numerous communities, including Amecameca, Juchitepec, Ozumba, Tepetlixpa, and Atlautla in the State of México, in Ayapango and Cuautla in the State of Morelos, and in the municipalities of Tlahuac, Tlalpan, and Xochimilco in Mexico City. A moderate explosion on 4 November sent incandescent ejecta 2 km down the slopes and produced an ash plume that rose 1.5 km and drifted NW. Minor ashfall was reported in Tlalmanalco, Amecameca, and Tenango del Aire, State of Mexico. Similar ash plumes from explosions occurred the following day. Scientists from CENAPRED and the Institute of Geophysics of UNAM observed dome number 85 during an overflight on 5 November 2019. It had a diameter of 210 m and was 80 m thick, with an irregular surface (figure 147). Multiple explosions on 6 and 7 November produced incandescent ejecta; a moderate explosion late on 11 November produced ejecta that traveled 1.5 km from the summit and produced an ash plume 2 km high (figure 148). A lengthy period of constant ash emission that drifted E was reported on 18 November. A moderate explosion on 28 November sent incandescent fragments 1.5 km down the slopes and ash one km above the summit.

Figure 147. A new dome was visible inside the summit crater at Popocatépetl during an overflight on 5 November 2019. It had a diameter of 210 m and was 80 m thick. Courtesy of CENAPRED (Sobrevuelo al volcán Popocatépetl, 05 de noviembre).

Figure 148. Ash emissions and explosions with incandescent ejecta continued at Popocatépetl during November 2019. The ash plume on 1 November changed drift direction sharply a few hundred meters above the summit (left). Incandescent ejecta traveled 1.5 km down the flanks on 11 November (right). Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl 1 y 12 de noviembre).

Activity during December 2019-February 2020. Throughout December 2019 weak emissions of steam and gas were reported daily, sometimes with minor amounts of ash, and minor explosions were only reported on 21 and 27 December. On 21 December two new high-resolution webcams were installed around Popocatépetl, one 5 km from the crater at the Tlamacas station, and the second in San Juan Tianguismanalco, 20 km away. Ash emissions and incandescent ejecta 800 m from the summit were observed on 25 December (figure 149). Incandescence at night was reported during 27-29 December.

Figure 149. Incandescent ejecta moved 800 m down the flanks of Popocatépetl during explosions on 25 December 2019 (left); weak emissions of steam, gas, and minor ash were visible on 27 December and throughout the month. Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl 25 y 27 de diciembre).

Continuous emissions of water vapor and gas with low ash content were typical daily during January 2020. A moderate explosion on 9 January produced an ash plume that rose 3 km from the summit and drifted NE. In addition, incandescent ejecta traveled 1 km from the crater rim. A minor explosion on 21 January produced a 1.5-km-high plume with low ash content and incandescent ejecta that fell near the crater (figure 150). The first of two explosions late on 27 January produced ejecta that traveled 500 m and a 1-km-high ash plume. Constant incandescence was observed overnight on 29-30 January.

Figure 150. Although fewer explosions were recorded at Popocatépetl during January 2020, activity continued. An ash plume on 19 January rose over a kilometer above the summit (top left). A minor explosion on 21 January produced a 1.5-km-high plume with low ash content and incandescent ejecta that fell near the crater (top right). Smaller emissions with steam, gas, and ash were typical many days, including on 22 (bottom left) and 31 (bottom right) January 2019. Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl 19, 21, 22 y 31 de enero).

A moderate explosion on 5 February 2020 produced an ash plume that rose 1.5 km and drifted NNE. Explosions on 10 and 13 February sent ejecta 500 m down the flanks (figure 151). During an overflight on 18 February scientists noted that the internal crater maintained a diameter of 350 m and its approximate depth was 100-150 m; the crater was covered by tephra. For most of the second half of February the volcano had a continuous emission of gases with minor amounts of ash. In addition, multiple explosions produced ash plumes that rose 400-1,200 m above the crater and drifted in several different directions.

Figure 151. Ash emissions and explosions continued at Popocatépetl during February 2020. Dense ash drifted near the snow-covered summit on 6 February (top left). Incandescent ejecta traveled 500 m down the flanks on 13 February (top right). Ash plumes billowed from the summit on 18 and 22 February (bottom row). Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl, 6, 15, 18 y 22 de febrero).

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

Information Contacts: Centro Nacional de Prevención de Desastres (CENAPRED), Av. Delfín Madrigal No.665. Coyoacan, México D.F. 04360, México (URL: http://www.cenapred.unam.mx/), Daily Report Archive http://www.cenapred.unam.mx:8080/reportesVolcanGobMX/BuscarReportesVolcan); 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); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

The dacitic Santiaguito lava-dome complex on the W flank of Guatemala's Santa María volcano has been growing and actively erupting since 1922. Ash explosions, pyroclastic, and lava flows have emerged from Caliente, the youngest of the four vents in the complex, for more than 40 years. A lava dome that appeared within the summit crater of Caliente in October 2016 has continued to grow, producing frequent block avalanches down the flanks. Daily explosions with ash plumes and block avalanches continued during September 2019-February 2020, the period covered in this report, with information primarily from Guatemala's INSIVUMEH (Instituto Nacional de Sismologia, Vulcanologia, Meterologia e Hidrologia) and the Washington VAAC (Volcanic Ash Advisory Center).

Constant fumarolic activity with steam and gas persisted from the Caliente dome throughout September 2019-February 2020. Explosions occurred multiple times per day, producing ash plumes that rose to altitudes of 3.1-3.5 km and usually drifted a few kilometers before dissipating. Several lahars during September and October carried volcanic blocks, ash, and debris down major drainages. Periodic ashfall was reported in communities within 10 km of the volcano. An increase in thermal activity beginning in November (figure 101) resulted in an increased number of observations of incandescence visible at night from the summit of Caliente through February 2020. Block avalanches occurred daily on the flanks of the dome, often reaching the base, stirring up small clouds of ash that drifted downwind.

Figure 101. The MIROVA project graph of thermal activity at Santa María from 12 May 2019 through February 2020 shows a gradual increase in thermal energy beginning in November 2019. This corresponds to an increase in the number of daily observations of incandescence at the summit of the Caliente dome during this period. Courtesy of MIROVA.

Constant steam and gas fumarolic activity rose from the Caliente dome, drifting W, usually rising to 2.8-3.0 km altitude during September 2019. Multiple daily explosions with ash plumes rising to 2.9-3.4 km altitude drifted W or SW over the communities of San Marcos, Loma Linda Palajunoj, and Monte Claro (figure 102). Constant block avalanches fell to the base of the cone on the NE and SE flanks. The Washington VAAC reported an ash plume visible in satellite imagery on 10 September at 3.1 km altitude drifting W. On 14 September another plume was spotted moving WSW at 4.6 km altitude which dissipated quickly; the webcam captured another plume on 16 September. Ashfall on 27 September reached about 1 km from the volcano; it reached 1.5 km on 29 September. Lahars descended the Rio Cabello de Ángel on 2 and 24 September (figure 102). They were about 15 m wide, and 1-3 m deep, carrying blocks 1-2 m in diameter.

Figure 102. A lahar descended the Rio Cabello de Ángel at Santa Maria and flowed into the Rio Nima 1 on 24 September 2019. Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo: Volcán Santiaguito (1402-03), Semana del 21 al 27 de septiembre de 2019).

Througout October 2019, degassing of steam with minor gases occurred from the Caliente summit, rising to 2.9-3.0 km altitude and generally drifting SW. Weak explosions took place 1-5 times per hour, producing ash plumes that rose to 3.2-3.5 km altitude. Ashfall was reported in Monte Claro on 2 October. Nearly constant block avalanches descended the SE and S flanks, disturbing recent layers of fine ash and producing local ash clouds. Moderate explosions on 11 October produced ash plumes that rose to 3.5 km altitude and drifted W and SW about 1.5 km towards Río San Isidro (figure 103). The following day additional plumes drifted a similar distance to the SE. The Washington VAAC reported an ash emission visible in satellite imagery at 4.9 km altitude on 13 October drifting NNW. Ashfall was reported in Parcelamiento Monte Claro on 14 October. Some of the block avalanches observed on 14 October on the SE, S, and SW flanks were incandescent. Ash drifted 1.5 km W and SW on 17 October. Ashfall was reported near la finca Monte Claro on 25 and 28 October. A lahar descended the Río San Isidro, a tributary of the Río El Tambor on 7 October carrying blocks 1-2 m in diameter, tree trunks, and branches. It was about 16 m wide and 1-2 m deep. Additional lahars descended the rio Cabello de Angel on 23 and 24 October. They were about 15 m wide and 2 m deep, and carried ash and blocks 1-2 m in diameter, tree trunks, and branches.

Figure 103. Daily ash plumes were reported from the Caliente cone at Santa María during October 2019, similar to these from 30 September (left) and 11 October 2019 (right). Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo: Volcán Santiaguito (1402-03), Semana del 28 de septiembre al 04 de octubre de 2019; Reporte Semanal de Monitoreo: Volcán Santiaguito (1402-03), Semana del 05 al 11 de octubre de 2019).

During November 2019, steam plumes rose to 2.9-3.0 km altitude and generally drifted E. There were 1-3 explosions per hour; the ash plumes produced rose to altitudes of 3.1-3.5 km and often drifted SW, resulting in ashfall around the volcanic complex. Block avalanches descended the S and SW flanks every day. On 4 November ashfall was reported in the fincas (ranches) of El Faro, Santa Marta, El Viejo Palmar, and Las Marías, and the odor of sulfur was reported 10 km S. Incandescence was observed at the Caliente dome during the night of 5-6 November. Ash fell again in El Viejo Palmar, fincas La Florida, El Faro, and Santa Marta (5-6 km SW) on 7 November. Sulfur odor was also reported 8-10 km S on 16, 19, and 22 November. Fine-grained ash fell on 18 November in Loma Linda and San Marcos Palajunoj. On 29 November strong block avalanches descended in the SW flank, stirring up reddish ash that had fallen on the flanks (figure 104). The ash drifted up to 20 km SW.

Figure 104. Ash plumes rose from explosions multiple times per day at Santa Maria’s Santiaguito complex during November 2019, and block avalanches stirred up reddish clouds of ash that drifted for many kilometers. Courtesy of INSIVUMEH. Left, 11 November 2019, from Reporte Semanal de Monitoreo: Volcán Santiaguito (1402-03), Semana del 09 al 15 de noviembre de 2019. Right, 29 November 2019 from BOLETÍN VULCANOLÓGICO ESPECIAL BESTG# 106-2019, Guatemala 29 de noviembre de 2019, 10:50 horas (Hora Local).

White steam plumes rising to 2.9-3.0 km altitude drifted SE most days during December 2019. One to three explosions per hour produced ash plumes that rose to 3.1-3.5 km altitude and drifted W and SW producing ashfall on the flanks. Several strong block avalanches sent material down the SW flank. Ash from the explosions drifted about 1.5 km SW on 3 and 7 December. The Washington VAAC reported a small ash emission that rose to 4.9 km altitude and drifted WSW on 8 December, and another on 13 December that rose to 4.3 km altitude. Ashfall was reported up to 10 km S on 24 December. Incandescence was reported at the dome by INSIVUMEH eight times during the month, significantly more than during the recent previous months (figure 105).

Figure 105. Strong thermal anomalies were visible in Sentinel-2 imagery at the summit of the Caliente cone at Santa María’s Santiaguito’s complex on 19 December 2019. Image uses Atmospheric Penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Activity during January 2020 was similar to that during previous months. White plumes of steam rose from the Caliente dome to altitudes of 2.7-3.0 km and drifted SE; one to three explosions per hour produced ash plumes that rose to 3.2-3.4 km altitude and generally drifted about 1.5 km SW before dissipating. Frequent block avalanches on the SE flank caused smaller plumes that drifted SSW often over the ranches of San Marcos and Loma Linda Palajunoj. On 28 January ash plumes drifted W and SW over the communities of Calaguache, El Nuevo Palmar, and Las Marías. In addition to incandescence observed at the crater of Caliente dome at least nine times, thermal anomalies in satellite imagery were detected multiple times from the block avalanches on the S flank (figure 106).

Figure 106. Incandescence at the summit and in the block avalanches on the S flank of the Caliente cone at Santa María’s Santiaguito’s complex was visible in Sentinel-2 satellite imagery on 8 and 13 January 2020. Atmospheric penetration rendering images (bands 12, 11, 8A) courtesy of Sentinel Hub Playground.

The Washington VAAC reported an ash plume visible in satellite imagery at 4.6 km altitude drifting W on 3 February 2020. INSIVUMEH reported constant steam degassing that rose to 2.9-3.0 km altitude and drifted SW. In addition, 1-3 weak to moderate explosions per hour produced ash plumes to 3.1-3.5 km altitude that drifted about 1 km SW. Small amounts of ashfall around the volcano’s perimeter was common. The ash plumes on 5 February drifted NE over Santa María de Jesús. On 8 February the ash plumes drifted E and SE over the communities of Calaguache, El Nuevo Palmar, and Las Marías. Block avalanches on the S and SE flanks of Caliente dome continued, creating small ash clouds on the flank. Incandescence continued frequently at the crater and was also observed on the S flank in satellite imagery (figure 107).

Figure 107. Incandescence at the summit and on the S flank of the Caliente cone at Santa María’s Santiaguito’s complex was frequent during February 2020, including on 2 (left) and 17 (right) February 2020 as seen in Sentinel-2 imagery. Atmostpheric Penetration rendering imagery (bands 12, 11, 8A) courtesy of Sentinel Hub Playground.

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

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/ ); 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); 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/).

Historical eruptions at Chile's Villarrica, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. An intermittently active lava lake at the summit has been the source of Strombolian activity, incandescent ejecta, and thermal anomalies for several decades; the current eruption has been ongoing since December 2014. Continuing activity during September 2019-February 2020 is covered in this report, with information provided by the Southern Andes Volcano Observatory (Observatorio Volcanológico de Los Andes del Sur, OVDAS), part of Chile's National Service of Geology and Mining (Servicio Nacional de Geología y Minería, SERNAGEOMIN), and Projecto Observación Villarrica Internet (POVI), part of the Fundacion Volcanes de Chile, a research group that studies volcanoes across Chile.

A brief period of heighted explosive activity in early September 2019 caused SERNAGEOMIN to raise the Alert Level from Yellow to Orange (on a four-color scale of Green-Yellow-Orange-Red) for several days. Increases in radiative power were visible in the MIROVA thermal anomaly data during September (figure 84). Although overall activity decreased after that, intermittent explosions were observed at the summit, and incandescence continued throughout September 2019-February 2020. Sentinel-2 satellite imagery indicated a strong thermal anomaly from the summit crater whenever the weather conditions permitted. In addition, ejecta periodically covered the area around the summit crater, and particulates often covered the snow beneath the narrow gas plume drifting S from the summit (figure 85).

Figure 84. Thermal activity at Villarrica from 28 May 2019 through February 2020 was generally at a low level, except for brief periods in August and September 2019 when larger explosions were witnessed and recorded in seismic data and higher levels of thermal activity were noted by the MIROVA project. Courtesy of MIROVA.

Figure 85. Natural-color (top) and Atmospheric penetration (bottom) renderings of three different dates during September 2019-February 2020 show typical continued activity at Villarica during the period. Dark ejecta periodically covered the snow around the summit crater, and streaks of particulate material were sometimes visible on the snow underneath the plumes of bluish gas drifting S from the volcano (top images). Persistent thermal anomalies were recorded in infrared satellite data on the same dates (bottom images). Dates recorded are (left to right) 28 September 2019, 20 December 2019, and 1 January 2020. Natural color rendering uses bands 4,3, and 2, and Atmospheric penetration rendering uses bands 12, 11, and 8a. Courtesy of Sentinel Hub Playground.

SERNAGEOMIN raised the Alert Level from Green to Yellow in early August 2019 due to the increase in activity that included incandescent ejecta and bombs reaching 200 m from the summit crater (BGVN 44:09). An increase in seismic tremor activity on 8 September was accompanied by vigorous Strombolian explosions reported by POVI. The following day, SERNAGEOMIN raised the Alert Level from Yellow to Orange. Poor weather prevented visual observations of the summit on 8 and 9 September, but high levels of incandescence were observed briefly on 10 September. Incandescent ejecta reached 200 m from the crater rim late on 10 September (figure 86). Activity increased the next day with ejecta recorded 400 m from the crater, and the explosions were felt 12 km from the summit.

Figure 86. A new pulse of activity at Villarrica reached its maximum on 10 (left) and 11 (right) September 2019. Incandescent ejecta reached 200 m from the crater rim on 10 September and up to 400 m the following day. Courtesy of POVI (Volcan Villarrica, Resumen grafico del comportamiento, Septiembre 2019 a enero 2020).

Explosions decreased in intensity by 13 September, but avalanches of incandescent material were visible on the E flank in the early morning hours (figure 87). Small black plumes later in the day were interpreted by POVI as the result of activity from landslides within the crater. Fine ash deposited on the N and NW flanks during 16-17 September was attributed to wind moving ash from within the crater, and not to new emissions from the crater (figure 88). SERNAGEOMIN lowered the Alert Level to Yellow on 16 September as tremor activity decreased significantly. Activity continued to decrease during the second half of September; incandescence was moderate with no avalanches observed, and intermittent emissions with small amounts of material were noted. Degassing of steam plumes rose up to 120 m above the crater.

Figure 87. By 13 September 2019, a decrease in activity at Villarrica was apparent. Incandescence (red arrow) was visible on the E flank of Villarrica early on 13 September (left). Fine ash, likely from small collapses of new material inside the vent, rose a short distance above the summit later in the day (right). Courtesy of POVI (Volcan Villarrica, Resumen grafico del comportamiento, Septiembre 2019 a Enero 2020).

Figure 88. Fine-grained material covered the summit of Villarrica on 17 September 2019. POVI interpreted this as a result of strong winds moving fine ash-sized particles from within the crater and depositing them on the N and NW flanks. Courtesy of POVI (Volcan Villarrica, Resumen grafico del comportamiento, Septiembre 2019 a enero 2020).

Low-altitude degassing was typical activity during October-December 2019; occasionally steam and gas plumes rose 300 m above the summit, but they were generally less than 200 m high. Incandescence was visible at night when weather conditions permitted. Occasional Strombolian explosions were observed in the webcam (figure 89). During January and February 2020, similar activity was reported with steam plumes observed to heights of 300-400 m above the summit, and incandescence on nights where the summit was visible (figure 90). A drone overflight on 19 January produced a clear view into the summit crater revealing a 5-m-wide lava pit about 120 m down inside the crater (figure 91).

Figure 89. Activity continued at a lower level at the summit of Villarrica from October-December 2019. The 30-m-wide vent at the bottom of the summit crater (120 m deep) of Villarrica (left) was emitting wisps of bluish gas on 30 October 2019. Sporadic Strombolian explosions ejected material around the crater rim on 12 December (right). Courtesy of POVI (Volcan Villarrica, Resumen grafico del comportamiento, Septiembre 2019 a enero 2020).

Figure 90. Small explosive events were recorded at Villarrica during January and February 2020, including these events on 4 (left) and 18 (right) January where ejecta reached about 50 m above the crater rim. Courtesy of POVI (Volcan Villarrica, Resumen grafico del comportamiento, Septiembre 2019 a Enero 2020).

Figure 91. An oblique view into the bottom of the summit crater of Villarrica on 19 January 2020 was captured by drone. The diameter of the lava pit was calculated at about 5 m and was about 120 m deep. Image copyright by Leighton M. Watson, used with permission; courtesy of POVI (Volcan Villarrica, Resumen grafico del comportamiento, Septiembre 2019 a Enero 2020).

Geologic Background. Glacier-clad Villarrica, one of Chile's most active volcanoes, rises above the lake and town of the same name. It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. A 6-km-wide caldera formed during the late Pleistocene. A 2-km-wide caldera that formed about 3500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesitic cone at the NW margin of the Pleistocene caldera. More than 30 scoria cones and fissure vents dot the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Historical eruptions, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

Information Contacts: Servicio Nacional de Geología y Minería (SERNAGEOMIN), Observatorio Volcanológico de Los Andes del Sur (OVDAS), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); Proyecto Observación Villarrica Internet (POVI) (URL: http://www.povi.cl/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Leighton M. Watson, Department of Earth Sciences at the University of Oregon, Eugene, OR 97403-1272, USA (URL: https://earthsciences.uoregon.edu/).

Semisopochnoi is a remote stratovolcano located in the western Aleutians dominated by an 8 km-wide caldera containing the small (100 m diameter) Fenner Lake and a three-cone cluster: a northern cone known as the North cone of Mount Cerberus, an eastern cone known as the East cone of Mount Cerberus, and a southern cone known as the South cone of Mount Cerberus. Previous volcanism has included small explosions, ash deposits, and gas-and-steam emissions. This report updates activity during September 2019 through March 2020 using information from the Alaska Volcano Observatory (AVO). A new eruptive period began on 7 December 2019 and continued until mid-March 2020 with activity primarily focused in the North cone of Mount Cerberus.

During September-November 2019, low levels of unrest were characterized by intermittent weeks of elevated seismicity and gas-and-steam plumes visible on 8 September, 7-8 October, and 24 November. On 6 October an SO₂ plume was visible in satellite imagery, according to AVO.

Seismicity increased on 5 December and was described as a strong tremor through 7 December. This tremor was associated with a small eruption on 7 December; intermittent explosions occurred and continued into the night. Increased seismicity was recorded throughout the rest of the month while AVO registered small explosions during 11-19 December. On 11-12 December, a gas-and-steam plume possibly containing some of ash extended 80 km (figure 2). Two more ash plumes were observed on 14 and 17 December, the latter of which extended 15 km SE. Sentinel-2 satellite images show gas-and-steam plumes rising from the North Cerberus crater intermittently at the end of 2019 and into early 2020 (figure 3).

Figure 2. Sentinel-2 satellite image showing a gray ash plume extending up to 17 km SE from the North Cerberus crater on 11 December 2019. Image taken by Hannah Dietterich; courtesy of AVO.

Figure 3. Sentinel-2 satellite images of gas-and-steam plumes at Semisopochnoi from late November 2019 through mid-March 2020. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

The month of January 2020 was characterized by low levels of unrest due to intermittent low seismicity. Small explosions were reported during 14-17 February and a gas-and-steam plume was visible on 26 February. Seismic unrest occurred between 18 February-7 March. Gas-and-steam plumes were visible on 1, 9, 14-17, 20, and 21 March (figure 4). During 15-17 March, small explosions occurred, according to AVO. Additionally, clear satellite images showed gas-and-steam emissions and minor ash deposits around North Cerberus’ crater rim. After 17 March the explosions subsided and ash emissions were no longer observed. However, intermittent gas-and-steam emissions continued and seismicity remained elevated through the end of the month.

Figure 4. Satellite image of Semisopochnoi showing degassing within the North Cerberus crater on 22 March 2020. Image taken by Matt Loewen; courtesy of AVO.

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

Ubinas, located 70 km from the city of Arequipa in Peru, has produced frequent eruptions since 1550 characterized by ash plumes, ballistic ejecta (blocks and bombs), some pyroclastic flows, and lahars. Activity is focused at the summit crater (figure 53). A new eruptive episode began on 24 June 2019, with an ash plume reaching 12 km altitude on 19 July. This report summarizes activity during September 2019 through February 2020 and is based on agency reports and satellite data.

Figure 53. A PlanetScope satellite image of Ubinas on 16 December 2019. Courtesy of PlanetLabs.

Prior to September 2019 the last explosion occurred on 22 July. At 2145 on 1 September moderate, continuous ash emission occurred reaching nearly 1 km above the crater. An explosion produced an ash plume at 1358 on the 3rd that reached up to 1.3 km above the summit; six minutes later ashfall and lapilli up to 1.5 cm in diameter was reported 6 km away, with ashfall reported up to 8 km away (figure 54 and 55). Three explosions produced ash plumes at 0456, 0551, and 0844 on 4 September, with the two later ash plumes reaching around 2 km above the crater. The ash plume dispersed to the south and ashfall was reported in Ubinas, Tonohaya, San Miguel, Anascapa, Huatahua, Huarina, and Matalaque, reaching a thickness of 1 mm in Ubinas.

Figure 54. An eruption at Ubinas produced an ash plume up to 1.3 km on at 1358 on 3 September 2019. Courtesy of INGEMMET.

Figure 55. Ash and lapilli fall up to 1.5 cm in diameter was reported 6 km away from Ubinas on 3 September 2019 (top) and an Ingemmet geologist collects ash samples from the last three explosions. Courtesy of INGEMMET.

During 8-9 September there were three explosions generating ash plumes to less than 2.5 km, with the largest occurring at 1358 and producing ashfall in the Moquegua region to the south. Following these events, gas and water vapor were continuously emitted up to 1 km above the crater. There was an increase in seismicity during the 10-11th and an explosion produced a 1.5 km high (above the crater) ash plume at 0726 on the 12th, which dispersed to the S and SE (figure 56). During 10-15 September there was continuous emission of gas (blue in color) and steam up to 1.5 km above the volcano. Gas emission, thermal anomalies, and seismicity continued during 16-29 September, but no further explosions were recorded.

Figure 56. An explosion at Ubinas on 12 September 2019 produced an ash plume to 1.5 km above the volcano. The ash dispersed to the S and SE. Courtesy of IGP.

Throughout October activity consisted of seismicity, elevated temperatures within the crater, and gas emissions reaching 800 to 1,500 m above the crater. No explosions were recorded. Drone footage released in early October (figure 57) shows the gas emissions and provided a view of the crater floor (figure 58). On the 15th IGP reported that the likelihood of an eruption had reduced.

Figure 57. IGP flew a fixed-wing drone over Ubinas as part of their monitoring efforts. This photograph shows gas emissions rising from the summit crater, published on 7 October 2019. Courtesy of IGP.

Figure 58. Drone image showing gas emissions and the summit crater of Ubinas. Image taken by IGP staff and released on 7 October 2019; courtesy of IGP.

Similar activity continued through early November with no reported explosions, and the thermal anomalies were no longer detected at the end of November (figure 59), although a faint thermal anomaly was visible in Sentinel-2 data in mid-December (figure 60). A rockfall occurred at 1138 on 13 November down the Volcanmayo gorge.

Figure 59. This MIROA Log Radiative Power plot shows increased thermal energy detected at Ubinas during August through November 2019. Courtesy of MIROVA.

Figure 60. Sentinel-2 thermal satellite image showing elevated temperatures in the Ubinas crater on 16 December 2019. Courtesy of Sentinel Hub Playground.

There were no explosions during January or February 2020, with seismicity and reduced gas emissions continuing. There was a small- to moderate-volume lahar generated at 1620 on 4 January down the SE flank. A second moderate- to high-volume lahar was generated at 1532 on 24 February, and three more lahars at 1325 and 1500 on 29 February, and at 1601 on 1 March, moved down the Volcanmayo gorge and the Sacohaya river channel. The last three lahars were of moderate to large volume.

Geologic Background. A small, 1.4-km-wide caldera cuts the top of Ubinas, Perú'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. 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 3,700 years ago extend 10 km from the volcano. Widespread Plinian pumice-fall deposits include one of Holocene age about 1,000 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: Observatorio Volcanologico del INGEMMET (Instituto Geológical Minero y Metalúrgico), Barrio Magisterial Nro. 2 B-16 Umacollo - Yanahuara Arequipa, Peru (URL: http://ovi.ingemmet.gob.pe); Instituto Geofisico del Peru (IGP), Calle Badajoz N° 169 Urb. Mayorazgo IV Etapa, Ate, Lima 15012, Perú (URL: https://www.gob.pe/igp); 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/); Planet Labs, Inc. (URL: https://www.planet.com/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Yasur has remained on Alert Level 2 (on a scale of 0-4) since 18 October 2016, indicating "Major Unrest; Danger Zone remains at 395 m around the eruptive vents." The summit crater contains several active vents that frequently produce Strombolian explosions and gas plumes (figure 60). This bulletin summarizes activity during June 2019 through February 2020 and is based on reports by the Vanuatu Meteorology and Geo-Hazards Department (VMGD), visitor photographs and videos, and satellite data.

Figure 60. The crater of Yasur contains several active vents that produce gas emissions and Strombolian activity. Photo taken during 25-27 October 2019 by Justin Noonan, used with permission.

A VMGD report on 27 June described ongoing Strombolian explosions with major unrest confined to the crater. The 25 July report noted the continuation of Strombolian activity with some strong explosions, and a warning that volcanic bombs may impact outside of the crater area (figure 61).

Figure 61. A volcanic bomb (a fluid chunk of lava greater than 64 mm in diameter) that was ejected from Yasur. The pattern on the surface shows the fluid nature of the lava before it cooled into a solid rock. Photo taken during 25-27 October 2019 by Justin Noonan, used with permission.

No VMGD report was available for August, but Strombolian activity continued with gas emissions and explosions, as documented by visitors (figure 62). The eruption continued through September and October with some strong explosions and multiple active vents visible in thermal satellite imagery (figure 63). Strombolian explosions ejecting fluid lava from rapidly expanding gas bubbles were recorded during October, and likely represented the typical activity during the surrounding months (figure 64). Along with vigorous degassing producing a persistent plume there was occasional ash content (figure 65). At some point during 20-29 October a small landslide occurred along the eastern inner wall of the crater, visible in satellite images and later confirmed to have produced ashfall at the summit (figure 66).

Figure 62. Different views of the Yasur vents on 7-8 August 2019 taken from a video. Strombolian activity and degassing were visible. Courtesy of Arnold Binas, used with permission.

Figure 63. Sentinel-2 thermal satellite images show variations in detected thermal energy emitting from the active Yasur vents on 18 September and 22 December 2019. False color (bands 12, 11, 4) satellite images courtesy of Sentinel Hub Playground.

Figure 64. Strombolian explosions at Yasur during 25-27 October 2019. Large gas bubbles rise to the top of the lava column and burst, ejecting volcanic bombs – fluid chunks of lava, out of the vent. Photos by Justin Noonan, used with permission.

Figure 65. Gas and ash emissions rise from the active vents at Yasur between 25-27 October 2019. Photos by Justin Noonan, used with permission.

Figure 66. Planet Scope satellite images of Yasur show a change in the crater morphology between 20 and 29 October 2019. Copyright of Planet Labs.

Continuous explosive activity continued in November-February with some stronger explosions recorded along with accompanying gas emissions. Gas plumes of sulfur dioxide were detected by satellite sensors on some days through this period (figure 67) and ash content was present at times (figure 68). Thermal anomalies continued to be detected by satellite sensors with varying intensity, and with a reduction in intensity in February, as seen in Sentinel-2 imagery and the MIROVA system (figures 69 and 70).

Figure 67. SO2 plumes detected at Yasur by Aura/OMI on 21 December 2019 and 31 January 2020, drifting W to NW, and on 14 and 23 February 2020, drifting W and south, and NWW to NW. Courtesy of Global Sulfur Dioxide Monitoring Page, NASA.

Figure 68. An ash plume erupts from Yasur on 20 February 2020 and drifts NW. Courtesy of Planet Labs.

Figure 69. Sentinel-2 thermal satellite images show variations in detected thermal energy in the active Yasur vents during January and February 2020. False color (bands 12, 11, 4) satellite images courtesy of Sentinel Hub Playground.

Figure 70. The MIROVA thermal detection system recorded persistent thermal energy emitted at Yasur with some variation from mid-May 2019 to May 2020. There was a reduction in detected energy after January. Courtesy of MIROVA.

Geologic Background. Yasur, the best-known and most frequently visited of the Vanuatu volcanoes, has been in more-or-less continuous Strombolian and Vulcanian activity since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island, this mostly unvegetated pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide, horseshoe-shaped caldera associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD), Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); 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/); Justin Noonan (URL: https://www.justinnoonan.com/, Instagram: https://www.instagram.com/justinnoonan_/); Doro Adventures (Twitter: https://twitter.com/DoroAdventures, URL: http://doroadventures.com/).

Cleveland is a stratovolcano located in the western portion of Chuginadak Island, a remote island part of the east central Aleutians. Common volcanism has included small lava flows, explosions, and ash clouds. Intermittent lava dome growth, small ash explosions, and thermal anomalies have characterized more recent activity (BGVN 44:02). For this reporting period during February 2019-January 2020, activity largely consisted of gas-and-steam emissions and intermittent thermal anomalies within the summit crater. The primary source of information comes from the Alaska Volcano Observatory (AVO) and various satellite data.

Low levels of unrest occurred intermittently throughout this reporting period with gas-and-steam emissions and thermal anomalies as the dominant type of activity (figures 30 and 31). An explosion on 9 January 2019 was followed by lava dome growth observed during 12-16 January. Suomi NPP/VIIRS sensor data showed two hotspots on 8 and 14 February 2019, though there was no evidence of lava within the summit crater at that time. According to satellite imagery from AVO, the lava dome was slowly subsiding during February into early March. Elevated surface temperatures were detected on 17 and 24 March in conjunction with degassing; another gas-and-steam plume was observed rising from the summit on 30 March. Thermal anomalies were again seen on 15 and 28 April using Suomi NPP/VIIRS sensor data. Intermittent gas-and-steam emissions continued as the number of detected thermal anomalies slightly increased during the next month, occurring on 1, 7, 15, 18, and 23 May. A gas-and-steam plume was observed on 9 May.

Figure 30. The MIROVA graph of thermal activity (log radiative power) at Cleveland during 4 February 2019 through January 2020 shows increased thermal anomalies between mid-April to late November 2019. Courtesy of MIROVA.

Figure 31. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) confirmed intermittent thermal signatures occurring in the summit crater during March 2019 through October 2019. Some gas-and-steam plumes were observed accompanying the thermal anomaly, as seen on 17 March 2019 and 8 May 2019. Courtesy of Sentinel Hub Playground.

There were 10 thermal anomalies observed in June, and 11 each in July and August. Typical mild degassing was visible when photographed on 9 August (figure 32). On 14 August, seismicity increased, which included a swarm of a dozen local earthquakes. The lava dome emplaced in January was clearly visible in satellite imagery (figure 33). The number of thermal anomalies decreased the next month, occurring on 10, 21, and 25 September. During this month, a gas-and-steam plume was observed in a webcam image on 6, 8, 20, and 25 September. On 3-6, 10, and 21 October elevated surface temperatures were recorded as well as small gas-and-steam plumes on 4, 7, 13, and 20-25 October.

Figure 32. Photograph of Cleveland showing mild degassing from the summit vent taken on 9 August 2019. Photo by Max Kaufman; courtesy of AVO/USGS.

Figure 33. Satellite image of Cleveland showing faint gas-and-steam emissions rising from the summit crater. High-resolution image taken on 17 August 2019 showing the lava dome from January 2019 inside the crater (dark ring). Image created by Hannah Dietterich; courtesy of AVO/USGS and DigitalGlobe.

Four thermal anomalies were detected on 3, 6, and 8-9 November. According to a VONA report from AVO on 8 November, satellite data suggested possible slow lava effusion in the summit crater; however, by the 15th no evidence of eruptive activity had been seen in any data sources. Another thermal anomaly was observed on 14 January 2020. Gas-and-steam emissions observed in webcam images continued intermittently.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows intermittent weak thermal anomalies within 5 km of the crater summit during mid-April through November 2019 with a larger cluster of activity in early June, late July and early October (figure 30). Thermal satellite imagery from Sentinel-2 also detected weak thermal anomalies within the summit crater throughout the reporting period, occasionally accompanied by gas-and-steam plumes (figure 31).

Geologic Background. The beautifully symmetrical Mount Cleveland stratovolcano is situated at the western end of the uninhabited Chuginadak Island. It lies SE across Carlisle Pass strait from Carlisle volcano and NE across Chuginadak Pass strait from Herbert volcano. Joined to the rest of Chuginadak Island by a low isthmus, Cleveland is the highest of the Islands of the Four Mountains group and is one of the most active of the Aleutian Islands. The native name, Chuginadak, refers to the Aleut goddess of fire, who was thought to reside on the volcano. Numerous large lava flows descend the steep-sided flanks. It is possible that some 18th-to-19th century eruptions attributed to Carlisle should be ascribed to Cleveland (Miller et al., 1998). In 1944 Cleveland produced the only known fatality from an Aleutian eruption. Recent eruptions have been characterized by short-lived explosive ash emissions, at times accompanied by lava fountaining and lava flows down the flanks.

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/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); NASA Worldview (URL: https://worldview.earthdata.nasa.gov/).

San Miguel, locally known as Chaparrastique, is a stratovolcano located in El Salvador. Recent activity has consisted of occasional small ash explosions and ash emissions. Infrequent gas-and-steam and ash emissions were observed during this reporting period of June 2018-March 2020. The primary source of information for this report comes from El Salvador's Servicio Nacional de Estudios Territoriales (SNET) and special reports from the Ministero de Medio Ambiente y Recursos Naturales (MARN) in addition to various satellite data.

Based on Sentinel-2 satellite imagery and analyses of infrared MODIS data, volcanism at San Miguel from June 2018 to mid-February was relatively low, consisting of occasional gas-and-steam emissions. During 2019, a weak thermal anomaly in the summit crater was registered in thermal satellite imagery (figure 27). This thermal anomaly persisted during a majority of the year but was not visible after September 2019; faint gas-and-steam emissions could sometimes be seen rising from the summit crater.

Figure 27. Sentinel-2 satellite imagery of a faint but consistent thermal anomaly at San Miguel during 2019. Images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Volcanism was prominent beginning on 13-20 February 2020 when SO₂ emissions exceeded 620 tons/day (typical low SO₂ values are less than 400 tons/day). During 20-21 February the amplitude of microearthquakes increased and minor emissions of gas-and-steam and SO₂ were visible within the crater (figure 28). According to SNET and special reports from MARN, on 22 February at 1055 an ash cloud was visible rising 400 m above the crater rim (figure 29), resulting in minor ashfall in Piedra Azul (5 km SW). That same day RSAM values peaked at 550 units as recorded by the VSM station on the upper N flank, which is above normal values of about 150. Seismicity increased the day after the eruptive activity. Minor gas-and-steam emissions continued to rise 400 m above the crater rim during 23-24 February; the RSAM values fell to 33-97 units. Activity in March was relatively low; some seismicity, including small magnitude earthquakes, occurred during the month in addition to SO₂ emissions ranging from 517 to 808 tons/day.

Figure 28. Minor gas-and-steam emissions rising from the crater at San Miguel on 21 February 2020. Courtesy of Ministero de Medio Ambiente y Recursos Naturales (MARN).

Figure 29. Gas-and-steam and ash emissions rising from the crater at San Miguel on 22 February 2020. Courtesy of Ministero de Medio Ambiente y Recursos Naturales (MARN).

Geologic Background. The symmetrical cone of San Miguel volcano, one of the most active in El Salvador, rises from near sea level to form one of the country's most prominent landmarks. The unvegetated summit rises above slopes draped with coffee plantations. A broad, deep crater complex that has been frequently modified by historical eruptions (recorded since the early 16th century) caps the truncated summit, also known locally as Chaparrastique. Radial fissures on the flanks of the basaltic-andesitic volcano have fed a series of historical lava flows, including several erupted during the 17th-19th centuries that reached beyond the base of the volcano on the N, NE, and SE sides. The SE-flank flows are the largest and form broad, sparsely vegetated lava fields crossed by highways and a railroad skirting the base of the volcano. The location of flank vents has migrated higher on the edifice during historical time, and the most recent activity has consisted of minor ash eruptions from the summit crater.

Information Contacts: Servicio Nacional de Estudios Territoriales (SNET), Ministero de Medio Ambiente y Recursos Naturales (MARN), Km. 5½ Carretera a Nueva San Salvador, Avenida las Mercedes, San Salvador, El Salvador (URL: http://www.snet.gob.sv/ver/vulcanologia); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Ambrym is an active volcanic island in the Vanuatu archipelago consisting of a 12 km-wide summit caldera. Benbow and Marum are two currently active craters within the caldera that have produced lava lakes, explosions, lava flows, ash, and gas emissions, in addition to fissure eruptions. More recently, a submarine fissure eruption in December 2018 produced lava fountains and lava flows, which resulted in the drainage of the active lava lakes in both the Benbow and Marum craters (BGVN 44:01). This report updates information from January 2019 through March 2020, including the submarine pumice eruption during December 2018 using information from the Vanuatu Meteorology and Geohazards Department (VMGD) and research by Shreve et al. (2019).

Activity on 14 December 2018 consisted of thermal anomalies located in the lava lake that disappeared over a 12-hour time period; a helicopter flight on 16 December confirmed the drainage of the summit lava lakes as well as a partial collapse of the Benbow and Marum craters (figure 49). During 14-15 December, a lava flow (figure 49), accompanied by lava fountaining, was observed originating from the SE flank of Marum, producing SO2 and ash emissions. A Mw 5.6 earthquake on 15 December at 2021 marked the beginning of a dike intrusion into the SE rift zone as well as a sharp increase in seismicity (Shreve et al., 2019). This intrusion extended more than 30 km from within the caldera to beyond the east coast, with a total volume of 419-532 x 106 m3 of magma. More than 2 m of coastal uplift was observed along the SE coast due to the asymmetry of the dike from December, resulting in onshore fractures.

Figure 49. Sentinel-2 thermal satellite images of Ambrym before the December 2018 eruption (left), and during the eruption (right). Before the eruption, the thermal signatures within both summit craters were strong and after the eruption, the thermal signatures were no longer detected. A lava flow was observed during the eruption on 15 December. Sentinel-2 atmospheric penetration (bands 12, 11, 8A) images courtesy of Sentinel Hub Playground.

Shreve et al. (2019) state that although the dike almost reached the surface, magma did not erupt from the onshore fractures; only minor gas emissions were detected until 17 December. An abrupt decrease in the seismic moment release on 17 December at 1600 marked the end of the dike propagation (figure 50). InSAR-derived models suggested an offshore eruption (Shreve et al., 2019). This was confirmed on 18-19 December when basaltic pumice, indicating a subaqueous eruption, was collected on the beach near Pamal and Ulei. Though the depth and exact location of the fissure has not been mapped, the nature of the basaltic pumice would suggest it was a relatively shallow offshore eruption, according to Shreve et al. (2019).

Figure 50. Geographical timeline summary of the December 2018 eruptive events at Ambrym. The lava lake level began to drop on 14 December, with fissure-fed lava flows during 14-15 December. After an earthquake on 15 December, a dike was detected, causing coastal uplift as it moved E. As the dike continued to propagate upwards, faulting was observed, though magma did not breach the surface. Eventually a submarine fissure eruption was confirmed offshore on 18-19 December. Image modified from Shreve et al. (2019).

In the weeks following the dike emplacement, there was more than 2 m of subsidence measured at both summit craters identified using ALOS-2 and Sentinel-1 InSAR data. After 22 December, no additional large-scale deformation was observed, though a localized discontinuity (less than 12 cm) measured across the fractures along the SE coast in addition to seismicity suggested a continuation of the distal submarine eruption into late 2019. Additional pumice was observed on 3 February 2019 near Pamal village, suggesting possible ongoing activity. These surveys also noted that no gas-and-steam emissions, lava flows, or volcanic gases were emitted from the recently active cracks and faults on the SE cost of Ambrym.

During February-October 2019, onshore activity at Ambrym declined to low levels of unrest, according to VMGD. The only activity within the summit caldera consisted of gas-and-steam emissions, with no evidence of the previous lava lakes (figure 51). Intermittent seismicity and gas-and-steam emissions continued to be observed at Ambrym and offshore of the SE coast. Mével et al. (2019) installed three Trillium Compact 120s posthole seismometers in the S and E part of Ambrym from 25 May to 5 June 2019. They found that there were multiple seismic events, including a Deep-Long Period event and mixed up/down first motions at two stations near the tip of the dike intrusion and offshore of Pamal at depths of 15-20 km below sea level. Based on a preliminary analysis of these data, Mével et al. (2019) interpreted the observations as indicative of ongoing volcanic seismicity in the region of the offshore dike intrusion and eruption.

Figure 51. Aerial photograph of Ambrym on 12 August 2019 showing gas-and-steam emissions rising from the summit caldera. Courtesy of VMGD.

Seismicity was no longer reported from 10 October 2019 through March 2020. Thermal anomalies were not detected in satellite data except for one in late April and one in early September 2019, according to MODIS thermal infrared data analyzed by the MIROVA system. The most recent report from VMGD was issued on 27 March 2020, which noted low-level unrest consisting of dominantly gas-and-steam emissions.

References:

Shreve T, Grandin R, Boichu M, Garaebiti E, Moussallam Y, Ballu V, Delgado F, Leclerc F, Vallée M, Henriot N, Cevuard S, Tari D, Lebellegard P, Pelletier B, 2019. From prodigious volcanic degassing to caldera subsidence and quiescence at Ambrym (Vanuatu): the influence of regional tectonics. Sci. Rep. 9, 18868. https://doi.org/10.1038/s41598-019-55141-7.

Mével H, Roman D, Brothelande E, Shimizu K, William R, Cevuard S, Garaebiti E, 2019. The CAVA (Carnegie Ambrym Volcano Analysis) Project - a Multidisciplinary Characterization of the Structure and Dynamics of Ambrym Volcano, Vanuatu. American Geophysical Union, Fall 2019 Meeting, Abstract and Poster V43C-0201.

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

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD), Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

Lava flows, pyroclastic flows, loud noises, and repeated forceful emissions were witnessed during June 2007-March 2008. Previously, there were brief periods of effusive activity and almost daily thermal anomalies during June 2006 through May 2007 (BGVN 32:04). Emissions during June 2007 consisted largely of steam of variable density.

On 12 June, there was a particularly forceful emission. Glow was observed on the night of 14 June. This kind of behavior continued into July. On 8 July observers saw glow and watched a single forceful release of pale gray ash.

On 14 July, Bagana generated a particularly forceful release that generated a pyroclastic flow. The release spewed out thick, dark-gray ash. The pyroclastic flow descended the S flank of the volcano stopping at the base near a small hot-spring-fed lake located at the head of the Torokina river. Since that event, rock falls from the edge of the active lava flow triggered thin ash clouds of light brown color from the S flank. This was accompanied by a loud roaring noise persisting into 15 July.

On 6 August, some emissions occasionally contained gray ash. The lava flow from the summit crater on the SE flank became active again and continued through 23 August. Thick white plumes escaped forcefully during 13-16 August. Ash clouds seen then were attributed to rock falls from collapse at the edges of the active lava flow. The Darwin VAAC reported that a diffuse plume rose to an altitude of 3.7 km on 23 August.

A particularly forceful emission occurred on 25 August and 12 September and the latter generated thin gray ash clouds directed over the SE flank.

Into October, the summit continued to release gentle emission of thin to thick white vapor. A weak to bright fluctuating glow was visible at night from 2-5 October and a continuous rumbling noise that lasted about an hour was heard on 5 October. On 6 October, there was a particularly forceful emission and the lava flow on the SE flank became active. Observers saw the lava flow emitting glow as it passed down the SE flank on 6-7, 10-12, and 17 October. Occasional thin pale gray ash clouds observed at the edges of the active lava flow were visible on 9-10, and 14-15 October. Based on satellite imagery, the Darwin VAAC reported that ash plumes drifted N then NW on 19 October.

White vapor escaped through November and into December. It was occasionally accompanied by plumes containing ash that were generated along the lava flow.

Two explosions sent forth ash plumes on 19 and 27 November. The SE-flank lavas descended almost continuously and lava fragments vented at the summit on 7 and 9 December. On 9 December an ash plume rose to an altitude of 2.8 km; another on 17 December rose to uncertain height; and one on 26-27 December rose to 3 km altitude and drifted W.

Activity in January through March was generally weak but persistent, with earthquakes absent. Satellite imagery and information from RVO led the Darwin VAAC to report a diffuse plume on 3 March. It rose to an altitude of less than 3 km and drifted SW. Later that day, an ash-and-steam plume drifted SW.

Throughout the reporting period, the MODVOLC satellite system typically detected multiple thermal anomalies monthly. The system uses MODIS (the Moderate Resolution Imaging Spectroradiometer) and a processing algorithm and staff at HIGP (see Information Contacts, below).

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

Information Contacts: Herman Patia, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea; 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/); Hawai'i Institute of Geophysics and Planetology (HIGP) Hot Spots System, University of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

Olga Girina of the Kamchatka Volcanic Eruptions Response Team (KVERT) reported no eruptive activity at Chikurachki volcano [activity that began 4 March 2007 (BGVN 32:05)] after about 18 April 2007. The following report was based primarily on information found on the KVERT website. Chikurachki is not monitored with seismic instruments, but KVERT has satellite monitoring and receives occasional reports of visual observations (figure 5).

Figure 5. Ash plume extending to the ESE from Chikurachki on 8 September 2007. Photo by L. Kotenko, supported by JSPS (Japan Society for the Promotion of Science); courtesy of KVERT Current Activity of Chikurachki website.

According to observations, no eruptive activity was noted on 12 and 14 August. However, visual information from Podgorny (20 km SSE) indicated that an eruption began on 18 August 2007 at 2200 UTC. Ashfall was noted in Podgorny at that time and on 19-20 August, and satellite data showed an ash plume extending about 120 km SE (figure 6). An ash plume extending about 100 km SE at an altitude of 5 km was observed by pilots on 20 August 20 at 0140 UTC. An ash plume extending about 160 km to the NNE at an altitude of 3 km and ashfall on Alaid volcano were noted by volcanologists on 21 August. Table 2 lists observations, when available, of the ash plume during this eruption.

Figure 6. Plume from Chikurachki taken 19 August 2007 by the Moderate Resolution Imaging Spectroradiometer (MODIS) flying on NASA's Aqua satellite. Besides Chikurachki, whose plume blows SE over the ocean, the image captures the summits of neighboring volcanos Atlasova Island and Fuss Peak above the cloud cover. Courtesy of NASA Earth Observatory.

Table 2. Ash plume observations for the eruption of Chikurachki beginning 18 August 2007. Clouds obscured the volcano on most days not noted. Courtesy of KVERT.

The eruption continued through at least 25 October 2007, and perhaps through 8 November. Clouds obscured the volcano on many days, making estimates of the continuity of this eruption and its ending date difficult. KVERT has reported no later plumes observed over Chikurachki to mid-April 2008. No thermal anomalies were measured by the MODIS satellites during 2007 or 2008 to 20 April.

Geologic Background. Chikurachki, the highest volcano on Paramushir Island in the northern Kuriles, is actually a relatively small cone constructed on a high Pleistocene volcanic edifice. Oxidized basaltic-to-andesitic scoria deposits covering the upper part of the young cone give it a distinctive red color. Frequent basaltic plinian eruptions have occurred during the Holocene. Lava flows from 1781-m-high Chikurachki reached the sea and form capes on the NW coast; several young lava flows also emerge from beneath the scoria blanket on the eastern flank. The Tatarinov group of six volcanic centers is located immediately to the south of Chikurachki, and the Lomonosov cinder cone group, the source of an early Holocene lava flow that reached the saddle between it and Fuss Peak to the west, lies at the southern end of the N-S-trending Chikurachki-Tatarinov complex. In contrast to the frequently active Chikurachki, the Tatarinov volcanoes are extensively modified by erosion and have a more complex structure. Tephrochronology gives evidence of only one eruption in historical time from Tatarinov, although its southern cone contains a sulfur-encrusted crater with fumaroles that were active along the margin of a crater lake until 1959.

Information Contacts: Olga Girina, Kamchatka Volcanic Eruptions Response Team (KVERT), a cooperative program of the Institute of Volcanic Geology and Geochemistry, Far East Division, Russian Academy of Sciences, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia, the Kamchatka Experimental and Methodical Seismological Department (KEMSD), GS RAS (Russia), and the Alaska Volcano Observatory (USA) (URL: http://www.kscnet.ru/ivs/kvert/updates.shtml); Alaska Volcano Observatory (AVO), a cooperative program of the U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), the Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and the Alaska Division of Geological and Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA; NASA Earth Observatory Natural Hazards (URL: http://earthobservatory.nasa.gov/NaturalHazards/); KVERT Current Activity of Chikurachki (URL: http://www.kscnet.ru/ivs/kvert/current/chkr/).

The Mt. Erebus Volcano Observatory (MEVO) website activity log gives information on each eruption of the volcano detected. Daily activity that usually includes several eruptions. Erebus eruption sizes are measured in the pressure unit of Pascals (Pa) from the infrasonic overpressure (at Station E1S.IS1). The eruption size index scale is divided into events classified as small (0-19 Pa), medium (20-39 Pa), large (40-59 Pa), and very large (>= 60 Pa).

Table 2 lists large and very large eruptions for the period December 2006 through 23 October 2007 (BGVN 31:12 gave a similar list for the year 2006 through November). The absence of recorded eruptions from 13 April 2007 to 29 August 2007 is notable. No eruptions were reported on the website during 23 October 2007 to 29 April 2008.

Table 2. Eruptions recorded at Erebus in the instrumentally derived categories "large" and "very large" during December 2006-23 October 2007. Courtesy of MEVO.

Thermal anomalies over Erebus, measured from the MODIS (Moderate Resolution Imaging Spectroradiometer) satellite images were analyzed by the Hawai'i Institute of Geophysics and Planetology (HIGP) MODVOLC algorithm. They commonly appeared throughout the 2007 due to the presence of a molten lava lake within the crater.

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

Information Contacts: Philip R. Kyle and Kyle Jones, Mt. Erebus Volcano Observatory (MEVO), New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA (URL: https://nmtearth.com/); Hawai'i Institute of Geophysics and Planetology (HIGP) MODIS Thermal Alerts, 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/).

As reported in (BGVN 31:07) Galeras displayed dome growth and elevated seismicity from November 2005 through mid-August 2006; ~ 10,000 residents evacuated but the crisis later abated. The key source of this report was the Instituto Colombiano de Geologia y Mineria (INGEOMINAS). This report follows the August 2006 events and covers the period through April 2008.

In September 2006, INGEOMINAS recorded continuing low-level minor earthquakes, M 1.4, corresponding to the movement of fluids at depths between 4 and 8 km and low SO₂ fluxes. A fly-over observed gas and steam emissions from the periphery of the active cone with diminished intensity through early November.

Beginning in late November and continuing through December 2006, an increase in the level of the volcanic activity occurred indicating the movement of solid material at focal depths to 9.6 km and at intensities to M 2.1. INGEOMINAS raised the Alert Level from 3 to 2 elevating the hazard status to "likely eruption in days or weeks" on 22 November 2006. The scale extends from 4 (lowest) to 1 ( highest hazard). The change was based on the increase in activity, behavior resembling characteristics that preceded earlier eruptions, i.e., increased earthquake activity associated with rock fractures within 2 km of the surface and weak gas emissions caused by the apparent capping of the lava dome.

On 2 March 2007, a tectonic earthquake was recorded ~ 2 km NNW of Galeras at M 3.5 and focal depth of 8.2 km. On 15 March, observations made with the support of the Colombian Air Force (FACE), showed continuing low rates of gas discharge continuing from secondary craters and fumaroles mainly located in the periphery of the main crater. On 20 March, because of decreased seismicity, low gas emissions, and no indication of changes below the surface of the dome, the Alert Level shifted towards less severe, from 2 to 3 (to "changes in the behavior of volcanic activity have been noted").

On 19 and 21 May 2007, two earthquakes registered, M 3.0 and M 2.1 respectively. These earthquakes were located SW of Galeras and felt by residents. The inclinometer to the SW of the active crater continued showing deformation indicating deeper volcanic activity.

Little volcanic activity occurred through September 2007. From October 2007 through January 2008, INGEOMINAS and the Washington Volcanic Ash Advisory Center reported an increase in gas-and steam plumes emitted from Galeras (table 8). During an overflight on 27 November, thermal images recorded by INGEOMINAS indicated an increase in temperatures at the point sources of emissions. The Alert Level remained at 3. Occasional gas and steam eruptions continued through January 2008.

Table 8. Summary of activity reported at Galeras from October 2007 through January 2008. Based on information from INGEOMINAS and the Washington Volcanic Ash Advisory Center.

On 11 January 2008, INGEOMINAS noted variations in seismicity associated with greater volumes of gas discharge. On 16-17 January, 5 tremors were recorded near the active cone. Early on 17 January, INGEOMINAS noted the similarity of these events to those preceding the eruptions of 1992, 1993, and 2004-2006.

Later, on the 17th, an explosive eruption was registered by the seismic network and prompted INGEOMINAS to raise the Alert Level from 3 ("changes in the behavior of volcanic activity have been noted") to 1 ("imminent eruption or in course"). The Washington VAAC reported that an ash plume rose to an altitude of 11 km and drifted W. According to a news article, small settlements to the N were ordered to evacuate; about 100 people moved to shelters.

About 2 km away from the main crater, military personnel saw blocks 1.5 m in diameter on a highway. Several impact craters of 17 January were spotted; the largest, ~ 15 m across and ~ 5 m deep (figure 111).

Figure 111. A composite of several photos showing a large impact crater formed by the Galeras eruption of 17 January 2008. The impact site was 1.5 km S of the main crater. Courtesy of INGEOMINAS.

On 19 January 2008, INGEOMINAS lowered the Alert Level to 2 ("likely eruption in days of weeks") because seismic events decreased in occurrence and energy and on 21 January, INGEOMINAS further lowered the Alert Level to 3 and reported that the initial ash plume from the eruption drifted SW, then W. Through February and into March seismic activity remained low. However, in mid-March, a a cluster of earthquakes (several events in a relatively short time interval), associated mainly with movement of magmatic fluids to the interior of the volcanic system were recorded. Volcanic gas and steam columns were routinely observed between 200 and 450 m from the top of Galeras, with variable directions of dispersion depending on the wind direction. Seismicity decreased in early April and SO2 emissions remained low.

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

Information Contacts: Diego Gomez Martinez, Observatorio Vulcanológico y Sismológico de Pasto (OVSP), INGEOMINAS, Carrera 31, 1807 Parque Infantil, PO Box 1795, Pasto, Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html; Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Associated Press (URL: http://www.ap.org/).

During late 2007 and continuing into 2008, it became clear the Karkar's vegetation had suffered and seismicity was significant (tens of earthquakes per day). Herman Patia of the Rabaul Volcano Observatory (RVO) reported that the Bagiai cone situated in the inner caldera of Karkar volcano continued to release thin to moderate white vapor while a RVO team was at the volcano from 27-31 December 2007. The white vapor plume was also visible from the mainland. Prior to the visit, communities on the W and SW had heard occasional roaring noises associated with the gas emission from the Bagiai cone. The last Bulletin (BGVN 25:11) discussed light ashfall ultimately attributed to Ulawun. In early November 2007, RVO had reported vegetation die-back and increased fumarolic activity at Bagiai cone on the floor of the inner caldera (figure 5). Latest images sent to RVO by Sir Peter Barter on 11 December 2007 indicated that vegetation on the SE flank had withered completely. According to RVO, the last eruption of Karkar was in 1979.

Figure 5. Vegetation die-back and increased fumarolic activity on Bagiai cone at Karkar; (top) photo taken early in 2007, (bottom) photo taken during the last week of October 2007. Courtesy of RVO; photos by Paul Goodyear.

During the team's December visit, they deployed three portable seismic recorders on the NW, SW, and E sides of the island (figure 6, open triangles). Preliminary results indicated a total of 30 high-frequency (HF) earthquakes recorded during the 3 days of deployment. These events were interpreted as indicative of rock-breaking due to magma movement under the volcano. The overall seismicity was low.

Figure 6. A map of the island of Karkar showing morphology. Open triangles indicate seismograph stations during 28-31 December 2007 (KSUG, KWAD, and KKEV). The filled triangles indicate seismograph stations during 24 January-3 February 2008 (KMAT, KARS, and KMID). The outlined oval-shaped region endorses the approximate area where the high-frequency earthquakes had epicenters. The regions decorated with square dots indicate channels, which provide possible pathways for mudflows and pyroclastic flows. Small dots villages, some of which lie within these channels. Courtesy of RVO.

Bagiai cone continued to release variable volumes of white vapor towards the end of January 2008. A second phase of seismic monitoring at Karkar was carried on from 24 January to 3 February 2008. (figure 6, filled triangles). The closest seismometer to the cone was placed ~ 3 km away Seismic activity was low, dominated by high-frequency earthquakes, but low-frequency earthquakes also occurred. About 15?20 earthquakes were recorded daily during the first 3 days of recording (24-28 January), the earthquakes occurring near Bagiai cone in the center of the inner caldera.

The two phases of seismic monitoring detected both high-frequency volcano-tectonic (VT) earthquakes and low-frequency earthquakes. VT earthquakes were taken to indicate magma intrusion underneath or near Karkar volcano and were detected during the December 2007 deployment by two of the three stations (KWAD and KKEV) on the E and SE side. Station KSUG did not record the HF earthquakes.

The seismic monitor installed about 3 km from Bagiai cone (KMAT), at a spot adjacent to the thermal activity, recorded LF earthquakes as well. LF earthquakes were presumed to be associated with movement of steam and gas and the hydrothermal activity at Bagiai cone.

To provide continuous seismic monitoring at Karkar, on 3 February 2008 a portable seismic recorder was installed 9 km N of the cone. RVO intends to download and analyze the data every 2 months.

For several weeks during late February into early March 2008, RVO scientists visited Karkar to monitor the increased seismic activity first monitored during December 2007. Once again, the group reported that thermal activity from within the cone had caused the vegetation to die and turn brown. On this visit, withered and dry vegetation could be observed on Bagiai's flanks. Seismicity was continuing, but at low levels. On this visit, three portable seismic recorders were deployed close to the summit area on the outer caldera, 3.5 km from Bagiai. They recorded 15-20 volcanic earthquakes per day.

There have been no thermal anomalies measured over Karkar by MODIS instruments since at least the beginning of 2007 through mid-April 2008.

Geologic Background. Karkar is a 19 x 25 km wide, forest-covered island that is truncated by two nested summit calderas. The 5.5-km-wide outer caldera was formed during one or more eruptions, the last of which occurred 9000 years ago. The eccentric 3.2-km-wide inner caldera was formed sometime between 1500 and 800 years ago. Parasitic cones are present on the N and S flanks of this basaltic-to-andesitic volcano; a linear array of small cones extends from the northern rim of the outer caldera nearly to the coast. Most historical eruptions, which date back to 1643, have originated from Bagiai cone, a pyroclastic cone constructed within the steep-walled, 300-m-deep inner caldera. The floor of the caldera is covered by young, mostly unvegetated andesitic lava flows.

Information Contacts: Herman Patia, Rabaul Volcanological Observatory (RVO), P.O. Box 3386, Kokopo, Papua New Guinea; MODVOLC 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/).

The extrusion of a substantial dome into the center of the active crater lake at Kelut (also spelled Kelud) started in early November 2007. The volcano and lake are among the most historically active and dangerous in Indonesia (Thouret and others, 1998). They were studied by members of the Volcanological Survey of Indonesia (VSI), Alain Bernard, and colleagues. During about 15 years prior to the eruption, the crater lake showed considerable hydrothermal influence, with temperatures several degrees above the ambient air temperature of 19°C, but with near-neutral pH. Prior to this eruption, the lake was ~ 34 m deep, ~ 350 m in diameter, and it held ~ 2.1 x 10⁶ m³ of water (Bernard and Mazot, 2004).

Lava was clearly seen emerging from the center of the lake on 4 November 2007. The activity was passive, even at the contact between the dome and lake. Neither water nor substantial ash were thrown forcefully out of the lake and onto the flanks. The dome rose rapidly above the lake, building a steep construct surrounded by a placid but dwindling lake. A well-defined depression crossed the dome's center, dividing its top surface in two. A few undated photos showed a mildly explosive phase. During 29-30 November the still-erupting dome was stable. As of early May 2008, tentative reports suggested that dome extrusion had ceased or paused. A lake still existed at that point.

Setting, historical lahars, and morphology. The volcano resides in a densely populated part of Java (1,800 people/km²) and could threaten over 3 million residents (Bernard, 2000). Bernard (2000) also noted that Kelut's approximately 30 historical eruptions have caused over 15,000 deaths since 1500 AD. Kelut's last eruption occurred in 1990 (BGVN 15:01). One of the most detailed VSI reports on Kelud's pre-eruptive behavior was issued 30 October 2007 (Surono, 2007).

Although lahars were absent during the 2007 eruption, lahars were associated with eruptions in 1919 and 1966; post-1996 lahars came in response to rainfall (figure 2). To control lahars and related problems, decades before engineers had driven a complex series of drainage tunnels through the edifice's walls, draining much of the lake.

Figure 2. Map of Kelut showing prominent drainages on the W side and key settlements such as Kediri, Tulungagung, and Blitar (respective populations, 252,000, 970,000 and 1,200,000), and three sets of lahars. Heavy (often straight) lines indicate some local political boundaries. The 2007 eruption did not trigger lahars. After Rodolfo (1999).

Lake chemistry. Active crater lakes such as Kelut's trap some fraction of the heat and fluids escaping the magmatic and hydrothermal system (Delmelle and Bernard, 1999), and their study has led to breakthroughs in eruption prediction. One example of this kind of study (figure 3) presents various heat and mass-balance factors in a model of Kelut's lake (Bernard and Mazot, 2004). Heat is derived from the enthalpy (E) of hydrothermal fluids (Ebrine + steam) and from solar and atmospheric radiation (Erad). Heat is lost by evaporation (Eevap), conduction (Econd), radiation (Erad), and by the overflow (Eover) of hot waters through the drainage tunnel.

Figure 3. A sketch of Kelut's summit crater made prior to the 2007 eruption, looking E. The 2007 eruption built a dome in the lake's center. The irregular high area on the far wall of the crater (labeled "dome") is called Gunung Kelut, and is but one of many domes at the complex. The arrows are explained in the text. The dashed 'drainage tunnel' through the edifice walls is schematic, the actual tunnels consist of a network built in successive stages. Diagram after Bernard and Mazot (2004).

Monitoring instrumentation is in place on and around the lake (figure 4). Fieldwork is also performed to measure the flux of CO₂ emitted at the lake surface (figure 5). Numerous CO₂-bearing gas bubbles rising to the surface were seen in July 2006. Bubbles were also widespread on bathymetric soundings (eg. detected at 50 and 200 kHz) in July 2007, and in some cases observers witnessed frequent discontinuous gas releases (puffing) from bottom fumaroles.

Figure 4. A pre-eruption photo showing Kelut's lake from a high point on the rim. Numbered sites are monitoring stations, as follows: 1) temperature and conductivity at 15 m depth and meteorological conditions (air temperature, relative humidity, and wind velocity), 2-4) lake level sensors, where the pressure difference between stations 3 and 4 functions as a N-S tilt meter), and 5) a radon sensor. Instrumentation also monitors the runoff volume in the drainage tunnel. A buoy (at 1) was one of three ultimately installed in the lake. A service road down the crater wall leads to the lake end of a drainage tunnel. Courtesy of A. Bernard.

Figure 5. (bottom left) A July 2006 photo at Kelut of the team taking a CO2 flux measurement at a sample site. The team consisted of (left to right) Loic Peiffer, Khirul Huda from VSI, and Alain Bernard. The team used a floating accumulation chamber connected by tubing to a dedicated spectrometer residing in the boat. (top left) A graph of 2007 spectrometer data from a sampling cycle with the accumulation chamber. After a lag time of ~ 30 seconds, the accumulation rate was stable at a slope of ~ 400 ppm/s. (right) Resulting map of lake surface showing CO2 flux per unit area (in the units of grams per square meter per day, g/(m2/d)). The map resulted from 230 spot measurements taken between 30 July and 2 August 2007. Courtesy of Alain Bernard.

The CO₂ flux from the lake's surface was measured by IR spectrophotometry using a Dr?ger Polytron instrument. Bernard's team modified a technique initially developed for monitoring the flux of gases in soil (Chiodini and others, 1996), applying this method by means of the floating accumulation chamber at multiple sites.

According to the VSI report, carbon dioxide (CO₂) concentrations measured during 30 July to 2 August 2007 ranged from below 500 g/m²/d to hotspots of 12,000 g/m²/d, especially in the E portion of the lake. The overall flux of CO₂ from the lake reached more than 500 tons/day on 11 September 2007, about ten times greater than measurements made in 2005 and 2006 (figure 6).

Figure 6. A plot for Kelut from 2001 through 2 August 2007 showing water temperature and total CO2 flux from the lake. The total CO2 flux was estimated by normalizing the data to the relevant lake area at Kelut, 103,600 m2). The latest CO2 field measurements were made during 30 July to 2 August 2007. The line shows lake temperature readings (taken at uncertain depth and location, but presumably more consistently measured than temperature data shown on table 2. Unfortunately, these plotted temperature data do not extend into late 2007 when table 2 suggests lake temperatures rose more than 50°C higher, to ~ 78°C).

Data on lake chemistry (table 2) was compiled by Surono (2007) and Bernard (2000). The water chemistry of the active crater lake showed both stable and variable parameters. Comparatively stable ones included pH and during various time periods (including 2007), some chemical species. Among the largest perturbations were a sudden, almost two-fold rise in SO₂ during September-October 2007; and a rapid increase in lake water temperature during November 2007. Soluble Cl stood over 1,000 ppm during 1993 and dropped sharply reaching a low of 67 ppm on 20 August 2007. It climbed after that, reaching 354 ppm in the last (11 November) measurement, a value taken about a week after the dome broke the lake surface.

Table 2. A compilation for Kelut's lake water showing temperature, pH, and chemical concentration data from VSI for 2007 (Surono, 2007) and Alain Bernard (2000) during 1993 to 2005. Some of the data presented here were rounded and the number of significant figures reduced. The 23 October 2007 Cl value was variously reported. Some of the original data were presumably collected at different locations and depths; and some of the original data included additional parameters such as total dissolved solids (see cited publications). Eruptions began on 3 November 2007, and the dome emerged above the lake surface on 4 November.

Monitoring, hazards status, and dome extrusion. Visual monitoring was carried out by means of a closed-circuit video monitor installed on Mount Lirang, as well as from photographs taken in or near the crater. During 15-28 September, gas emissions from the crater lake increased and spread over a zone within a radius of ~ 5 m.

According to Surono (2007), pre-eruption CO₂ fluxes from the lake were typically 50 metric tons/day. During August 2007 they rose to 333 tons/day; during late August to early September they reached 500 tons/day.

During 2006, the Darwin Volcanic Ash Advisory Center (VAAC) reported a pilot observation. An ash plume on 18 May 2006 allegedly reached an altitude of 5.5 km.

On 17 October 2007 Kelut was the subject of further VAAC reports, first noting the elevation of the hazard status to 4 (the highest level, indicating an eruption imminent). On 23 October there was a brief noting evidence from a satellite of a eruption (to ~ 6 km altitude) but ground observers suggested that it was a meteorological cloud. A VAAC report on 4 November noted "ash not identifiable on satellite imagery." On 8 November an advisory noted the continued absence of identifiable ash.

Seismicity rose suddenly on 10 September 2007 (figure 7). It peaked on 16 October at all four seismic stations on or adjacent the volcano, at 510 events. The next day, the number of earthquakes still stood quite high, 151.

Figure 7. Kelut seismicity, lake-water temperature, and Alert Levels registered during June to early November October 2007. After plots by Surono (2007) and Bernard.

Cross sections showing hypocenters for 10-11 and 26-29 September 2007 depicted them broadly centered below the edifice but distributed around 2.5 km depth; they were initially absent in a zone about 2-3 km below the summit . During mid-October the hypocenters became more closely packed along a narrow vertical band beneath the edifice. They then filled a zone 0.7-1.2 km beneath the summit, with a few other hypocenters centered ~ 2 km below the summit. During 24-29 October, many hypocenters clustered ~ 6 km below the summit, but others strung out on or about a vertical line intersecting near the summit. The shallowest events plotted were then ~ 1 km below the summit. Reports also noted tremor was common during 24 October through 4 November.

VSI issued a series of increases in Kelut's hazard status (a scale of 1-4, figure 7). On 11 September 2007, VSI raised the status from 1 to 2. This corresponded to the CO2 flux mentioned above, a sudden jump in seismicity on 10 September (figure 7), and changes in both lake temperature and color, which shifted from its usual green, becoming yellow in some areas and blue-white in others. On 29 September, the status went from 2 to 3 based on visual observations, increased seismicity, deformation measurements, and further changes of crater lake water chemistry and temperature.

VSI brought the status to 4 on 16 October (figure 7). Factors included the sudden rise in seismicity, and the summit's inflation during 13-16 October. Before the crisis of 16 October the lake water was whitish green; after the crisis, dominantly green. VSI to recommend that villagers within a 10-km radius evacuate. According to a United Nations report, local authorities evacuated ~ 117,000 people within this radius. The UN report cited Indonesian media as stating that an eruption could affect as many as ~ 290,000 people (figure 8).

Figure 8. A map of a portion of E Java that indicates the location of Kelut (sometimes written as "Kelud," as is the case here) and the major city Surabaya (~ 85 km NE; population, ~ 4 million). The map was issued after the alert status was raised to the highest level ("4"; at 1800 on 16 October) and indicates the number of people in two adjacent jurisdictions that could be affected by its eruption. Courtesy of Relief Web (United Nations); boundaries and names shown and the designations used on this map do not imply official endorsement or acceptance by the United Nations.

According to a news article, thousands returned to their homes on 17 October to tend to crops and animals, and to retrieve food. On 8 November the status fell to 3 and residents were allowed to return home. On 29 November the status fell from 3 to 2 following both decreased seismicity and a lack of deformation. At this stage, people were advised to remain at least 1.5 km from the lake.

During 24-31 October, a series of regional earthquakes occurred, dominated by shallow events and tremor. Seismicity intensified during 2-3 November, but then decreased on 4 November.

Dome emerges during 3-4 November 2007. On 3 November, VSI and news media mentioned plumes, and possibly some evidence of erupted solids entering the lake. Also, their buoy ceased functioning. On 4 November, white plumes rose to an altitude of 2.2 km and drifted N.

Plumes on the 4th came from a fresh black lava dome, protruding from the then turbid green lake. Monitoring cameras showed copious steam obscuring the dome. The exposed mass grew quickly. Although steaming continued, relative calm usually prevailed at both the dome and the lake. Although the dome steadily displaced the lake, the water did not undergo violent broad-scale boiling.

According to VSI, the temperature at the surface of the crater lake on 6 November had climbed to over 75°C. The newly exposed dome surface was 150-210°C. Plumes generally inhibited clear views.

On 8 November, VSI reported a decrease in seismicity, and deformation-monitoring suggested greater stability. An infrared camera (FLIR) captured images of the dome on 9 November as it emerged from the lake. The images revealed considerable radiant heat in the FLIR-sensitive wavelengths (figure 9).

Figure 9. On 9 November 2007, scientists looking at Kelut's new dome took these two photos, and at right, coinciding infrared (FLIR) images. The scale bars on the FLIR images indicate that the highest temperatures were on the order of 135°C. The hottest zones occurred both over a large area at the dome's top and along a band following the dome near the lake surface. Courtesy of VSI and taken from Bernard (2007).

According to a news article by Agence France Presse on 12 November, a volcanologist reported that the lava dome had reached 250 m in diameter and was 120 m above the lake surface.

November photos and videos. On 11 November, a plume rose to an altitude of 3.7 km and ashfall was reported in several areas. News accounts indicated that tremors continued and that Kelut was spewing ash and lava. More photos of the dome, particularly during 10-29 November, would be useful for understanding activity in this period.

An undated video provides views of a short-lived avalanche down from the new dome's upper walls. Based on the size of the dome then, the scene was probably captured in mid- to late November (it was posted on 7 December; Masdjawa, 2007). The avalanche initially contained on the order of 5-20 m³ of loose material, much of it incandescent in daylight. A large portion of this material bounced downslope into the steaming lake. When sufficient fragmental material entered the lake an intense phreatic eruption took place. The clouds rose vertically; they were initially jet black, but within tens of seconds became dominantly white steam, hiding the dome for ~ 1-2 minutes.

Daniel Brazilier visited during 25-26 November and saw mildly to moderately explosive activity; his photos appeared in Societe de Volcanologie Geneve reports (SVG, 2007). Many of his photos were taken during daylight from ~ 1.5 km away; they showed several explosions with billowing white-to-tan clouds. The foreground, the W crater wall, contained small amounts of tephra and some bombs. The billowing clouds appeared to contain minor ash; they vented from the dome upper area or side, and accompanied numerous steaming bombs, which from their arcing trails, seemed destined to land within the crater. Night photos disclosed large areas of incandescence on the W side.

Tom Pfeiffer took a series of remarkable photos on 29-30 November 2007, documenting a surprisingly large and clearly fast-growing dome. He posted over 60 photos on the Volcano Discovery website and elsewhere, and several of them appear here (figures 10, 11, and 12).

Figure 10. Kelut's dome seen in low-light conditions on 29 or 30 November 2007 in a view looking towards the E. Myriad incandescent fragments detached from the dome, leaving incandescent scars in the middle to upper dome area. The dome's summit area and much of its lower skirt are chiefly dark, except in the latter case for the trails of material bouncing and falling past. The much reduced lake was calm and wrapping around the dome's left (N) side. The segment of the crater rim towering above the new dome's right side is the older dome mentioned in figure 3. Copyrighted photo by Tom Pfeiffer (Volcano Discovery).

Figure 11. A NE view under dark conditions of Kelut's growing dome at a time on 29 or 30 November when dome incandescence was particularly high. In the foreground is the pathway leading to the lake. Comparatively few bombs littered the curbing along the pathway, but pelting from bombs had apparently damaged the steel hand-rail in a few places. Copyrighted photo by Tom Pfeiffer (Volcano Discovery).

Figure 12. Kelut's new lava dome had reduced the crater lake to a narrow band by 29-30 November 2007. This low-light photo looking NE captured the shrinking lake and its contact with the new dome. At right is a prominent avalanche chute choked with the incandescent trails of bouncing blocks. Upon entry into the lake some of the trails made a second bounce. Copyrighted photo by Tom Pfeiffer (Volcano Discovery).

Note that Pfeiffer's photos are night-time shots with long exposures and thus the impression of large glowing areas implies more activity than really occurred at any one time. The dome had clearly crowded out the then green or brownish lake, which in the field of view had been reduced to an arcuate sliver. The extent of the lake on the dome's W and SW sides was unclear from his perspective.

Particularly on figures 10 and 11, the dome was rife with abundant glowing zones and numerous red traces due to incandescent dome rocks bouncing downslope. Abundant were glowing avalanche trails, and large rockfall scars. The photos also suggest possible lava seeps and narrow lava flows, although Tom Pfeiffer attributed most of the incandescence to mobile and solidified material, rather than narrow zones occupied by fluid moving lava.

A few of the glowing traces in the photos terminate upon entering the crater lake (figure 12). After their first contact with the water, some of those descending traces also seemingly shattered and bounced, producing one or more secondary arcs (akin to a skipping stone).

Pfeiffer described the scene as "filled with the noises of cracking lava, falling debris, and chilled lava blocks that splashed into the lake." He went on to note the lack of "explosions, or major ash emissions attached to the activity. The lava dome was simply growing quietly and not doing anything else than what is visible on the photos." He was struck by the observation "that the lake was simply there and NOT boiling. A sign how well rock insulates. Also, the upper 10 meters of the dome, its very top, were rather inactive, like the top of a mushroom being lifted up. The most active zones were just underneath that upper crust . . .."

References. Bernard A., and Mazot A., 2004, Geochemical evolution of the young crater lake of Kelud volcano in Indonesia: Proceedings of the Eleventh International Symposium on Water-Rock Interaction, Saratoga Springs, New York, USA, v. 1, p. 87-90.

Bernard, A., 2000, Geochemistry of the crater lake of Kelut volcano, Indonesia: Essay labeled "in preparation" on the http://www.ulb.ac.be/ website.

Bourdier, J. L., Pratomo, I., Thouret, J.C., Boudon, G. and Vincent, P.M., 1997. Observations, stratigraphy and eruptive processes of the 1990 eruption of Kelut volcano, Indonesia: J. Volcanol. Geotherm. Res., v. 79, p. 181-203.

Delmelle, P., and Bernard, A., 1999, Volcanic lakes, in Encyclopedia of volcanoes, H. Sigurdsson (ed.): Academic Press, p. 877-895.

Masdjawa, 2007, Kelud-Kubah Lava: Kelud_03.mpg (23.2 Mb), 2 min 20 sec; http://masdjawa.multiply.com/video/item/4

Rodolfo, K. S., 1999, The hazard from lahars and Jökulhaups, in Encyclopedia of volcanoes, H. Sigurdsson (ed.): Academic Press, p. 973-995.

Surono, 2007, Pusat Vulkanologi Dan Mitigasi Bencana Geologi, Pos Pengamatan Gunungapi Kelut (Hasil evaluasi tingkat kegiatan G. Kelut): Departemen Energi Dan Sumber Daya Mineral, Republik Indonesia, Badan Geologi, Nomor, 112/GK/X/2007, 30 Oktober 2007.

Thouret, J. C., Abdurachman, K. E., and Bourdier, J. L., 1998, Origin, characteristics, and behavior of lahars following the 1990 eruption of Kelud volcano, eastern Java (Indonesia): Bull. Volcanol., v. 59, p. 460-480.

Geologic Background. The relatively inconspicuous Kelut stratovolcano contains a summit crater lake that has been the source of some of Indonesia's most deadly eruptions. A cluster of summit lava domes cut by numerous craters has given the summit a very irregular profile. Satellitic cones and lava domes are also located low on the E, W, and SSW flanks. Eruptive activity has in general migrated in a clockwise direction around the summit vent complex. More than 30 eruptions have been recorded from Gunung Kelut since 1000 CE. The ejection of water from the crater lake during the typically short but violent eruptions has created pyroclastic flows and lahars that have caused widespread fatalities and destruction. After more than 5000 people were killed during an eruption in 1919, an ambitious engineering project sought to drain the crater lake. This initial effort lowered the lake by more than 50 m, but the 1951 eruption deepened the crater by 70 m, leaving 50 million cubic meters of water after repair of the damaged drainage tunnels. After more than 200 deaths in the 1966 eruption, a new deeper tunnel was constructed, and the lake's volume before the 1990 eruption was only about 1 million cubic meters.

Information Contacts: Volcanological Survey of Indonesia, Center of Volcanology and Geological Hazard Mitigation, Saut Simatupang, 57, Bandung 40122, Indonesia (URL: http://vsi.esdm.go.id/); Alain Bernard, Free University of Brussels, CP 160/02, 50, avenue F, Roosevelt, 1050 Brussels, Belgium (URL: http://www.ulb.ac.be/sciences/cvl/); Relief Web, United Nations Office for the Coordination of Humanitarian Affairs, Resident Coordinator's Office, Jakarta, Indonesia (URL: https://reliefweb.int/, http://www.unocha.org/); Darwin Volcanic Ash Advisory Center, Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, Northern Territory 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Tom Pfeiffer, Volcano Discovery (URL: http://www.VolcanoDiscovery.com/); Daniel Brazilier, France.

On 28 March 2008, reporter Michael Field noted that an eruption of the submarine volcano Monowai was taking place. Olivier Hyvernaud was quoted in the article as saying that they recorded on the Polynesian Seismic Network (Réseau Sismique Polynésien, or RSP) a "big acoustic event" on 8 February. [He also noted that the volcano was in an eruptive phase, but it was not clear if it was a strong eruption.] The news article went on to say that, according to geologist Cornel de Ronde, the French Polynesian RSP currently receives submarine hydrophone signals from Monowai eruptions more easily than stations in New Zealand. The article concluded that this activity went unnoticed as its location is off the main shipping routes.

Ian Wright of the New Zealand National Institute of Water and Atmospheric Research (NIWA) informed us about new volcano discoveries along the S-central Kermadec arc and some recent mapping results from Monowai. In recent years, New Zealand scientists have mapped, using soundings made by multibeam acoustic arrays, most of the Kermadec arc, with the consequent discovery and naming of a number of 'new' arc volcanoes. Some of the more recent work for the 30°-35°S latitude sector was published in Wright and others (2006). A second manuscript detailing the 25°-30°S latitude sector will be completed soon for publication by Graham and others.

Wright and his colleagues mapped Monowai using the multibeam system in 1998 and again in 2004, identifying drastic changes in morphology during that 6-year period. They found edifice collapse and cone regrowth. They interpreted these changes in morphology in the context of T-wave data recorded by Hyvernaud and his colleague Dominique Reymond [Wright and others, 2008 (in press); BGVN 32:01].

As indicated on figures 20 and 21, the group subsequently re-mapped Monowai in mid-2007 for a third time, again finding drastic changes coinciding with a period of ongoing and high T-wave activity. They are currently preparing a manuscript detailing these latter changes (Chadwick and others, in preparation). According to Bill Chadwick, while the research ship was on site conducting the 2007 survey and attempting some remotely operated vehicle (ROV) dives, scientists heard booming sounds and saw slicks and bubbles on the surface.

Figure 20. Multibeam bathymetry and shaded terrain model of the Monowai volcanic complex, including its caldera and cone. Isobaths are shown at 50 m intervals. Courtesy of Wright and others, 2008 (in press).

Figure 21. Cumulative number of T-wave events centered at Monowai during the latter half of 2002 through 2007 from monitoring data at RSP (covering the times of the September 2004 and May 2007 bathymetric surveys, and the anomalous 24 May 2002 swarm, as reported in BGVN 27:05 and 32:01). Courtesy of Hyvernaud and Reymond, Laboratoire de Geophysique (LDG); from Chadwick and others (in preparation).

Bob Dziak of NOAA informed the Bulletin staff that Monowai T-phases are recorded on the NOAA East Pacific Rise hydrophone arrays, but analysis of data from those arrays await their retrieval of recording packages from ocean deployment sites. (In contrast, Hyvernaud of LDG in French Polynesia recovers data in real-time.) Dziak also mentioned that, from time to time, T-phase events from what is likely volcanic activity in the Izu-Bonin Mariana region are recorded by the NOAA real-time system in the North Pacific. He offered to provide a later Bulletin report.

A recent paper by de Rhonde and others (2008) noted that all the major submarine volcanic centers on the Kermadec intraoceanic arc NE of New Zealand (including Monowai) are hydrothermally active. The Monowai volcanic complex has two separate and extensive hydrothermal fields associated with the Monowai caldera and the Monowai cone, respectively.

References. Wright, I.C., Worthington, T.J., and Gamble, J.A., 2006, New multibeam mapping and geochemistry of the 30°-35°S sector, and overview, of southern Kermadec arc volcanism, Journal of Volcanology and Geothermal Research, v. 149, p. 263-296.

Wright, I. C., Chadwick, W., de Ronde, C. E. J., Reymond, D., Hyvernaud, O., Gennerich, H., Stoffers, P., Mackay, K., Dunkin, M., and Bannister, S., 2008 (in press), Collapse and reconstruction of Monowai submarine volcano, Kermadec arc, 1998-2004, Journal of Geophysical Research, doi:10.1029/2007JB005138.

de Ronde, C.E.J., Baker, E.T., Lupton, J.L., Sprovieri, M., Bruno, P.P., Faure, K., Leybourne, M.I., Walker, S.L., Italiano, F., Embley, R.W., Graham, I., Greene, R.R., Wright, I.C., and NZAPLUME III & Aeolian'07 shipboard parties, 2008, Contrasting examples of submarine hydrothermal venting along the Kermadec intraoceanic arc and the Aeolian island arc, Geophysical Research Abstracts, v. 10, EGU2008-A-05597, 2008 (SRef-ID: 1607-7962/gra/EGU2008-A-05597).

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

Information Contacts: Ian Wright, New Zealand National Institute of Water and Atmospheric Research (NIWA), Private Bag 14-901, Wellington, 6003, New Zealand; Cornel de Ronde, GNS Science, Lower Hutt, 5040 New Zealand; Olivier Hyvernaud and Dominique Reymond, Laboratoire de Géophysique, Commissariat a l'Energie Atomique (CEA/DASE/LDG), PO Box 640, Papeete, Tahiti, French Polynesia; GNS Science, Wairakei Research Center, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Michael Field, Fairfax Media, Auckland, New Zealand; William Chadwick and Robert Dziak, NOAA and Cooperative Institute for Marine Resources Studies at Oregon State University, 2115 SE OSU Drive, Newport, OR 97365.

An ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometry) satellite image became available, showing a Montagu Island plume blowing NNE on 17 December 2006 (figure 19). A persistent ash plume over Montagu was previously noted in October 2006 ASTER imagery (BGVN 31:11).

Figure 19. ASTER near-infrared image of Montagu Island volcano at 1115 UTC on 17 December 2006. Courtesy of ASTER Volcano Archive.

Thermal anomalies from Montagu were often detected by MODIS satellite instruments nearly weekly from at least 2006 until 20 September 2007. However, during that interval anomalies were absent for more than two months, from January 2007 through late March 2007. Anomalies were also absent from 21 September 2007 to 17 April 2008. The absence of anomalies could be due to lack of visibility, or the chilling of lava flows after the end of an eruptive phase.

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

Information Contacts: ASTER Volcano Archive (URL: http://ava.jpl.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/);.

This report describes ash plumes (figure 48) and explosions (table 9) located at Tavurvur, a cone located on the NE flank of Rabaul caldera. Tavurvur's summit sits at ~ 240 m elevation. The largest nearby settlement is Rabaul Town. Throughout the course of this report, audible sounds such as roaring, glowing of the cone, incandescent events, and hydrogen-sulfide (H₂S) odor were frequently reported. RVO interpreted high-frequency earthquakes as rocks breaking or explosion events, and low-frequency earthquakes driven by fluids, steam or gas (rarely liquid magma), their motions imparting a slower shaking or rocking to the ground.

Figure 48. MODIS satellite image of a Rabaul ash plume on 18 March 2008.The plume can be seen over 150 km. Courtesy of NASA Earth Observatory.

Table 9. Summary of events at Rabaul's Tavurvur cone during August 2007 to April 2008. Not all events are reported here. Further details of some of the events can be found in the text. Some data such as plume height or direction of plume were not measured. Areas effected by ashfall can generally be found in the text. Courtesy of the Darwin VAAC.

Low eruptive activity such as reported in this issue have been periodically occurring since the powerful explosion in 1994. Our last report (BGVN 32:06) reported the six explosions that occurred in June and July (2007) at Tavurvur cone that produced shockwaves that rattled windows of houses in Rabaul Town and surrounding areas. The explosions also showered the flanks with lava fragments and conveyed ashfall and sulfurous odors to the NW.

RVO stated that there was no indication of any build up that might lead to significant eruptive activity like in October 2006. Ground deformation remains to be in a deflated but stable state. Seismic activity remains at a moderate to high level dominated by low-frequency earthquakes.

Throughout the entire period covered by these observations and reports, authorities have been regularly advising the public not to venture close to the volcano due to the possibility of rocks being expelled during the occasional eruptions.

Late July 2007. Rabaul Volcanic Observatory (RVO) described this time as marked by minor eruptions. The activity consisted of emission of thin to thick, white, and bluish vapor, which rose to an altitude of ~ 0.9 km and drifted NNW. Roaring noises were occasionally heard and incandescence was intermittently visible at the crater rim.

Red glow was visible at night, associated with a small lava dome centrally located within Tavurvur's wide vent. A weak smell of sulphur was evident on the downwind side of the vapor plume on 25 July. Occasional low roaring noise continued to be heard and a weak to bright red glow was visible above the crater rim on 28 and 29 July. On 30 July, a white plume with little ash content rose to an altitude of 2.7 km and drifted SW.

Seismicity was low but it and deformation were consistent with a dynamic and restless caldera. The real-time GPS at the caldera's center of the showed that centimeter-scale movements often occurred over a few hours. Small inflation events sometimes preceded activity by 6-12 hours. Only 17 low-frequency earthquakes were recorded between 22 and 27 July. One high-frequency earthquake was recorded on 26 July which originated NE of the caldera. Ground deformation continued to show a slow inflation trend with movement N.

August 2007. August activity was characterized by Tarvurvur emitting almost continuous ash and vapor plumes. During 1-7 August 2007, ashfall was reported at Rabaul Town (~ 6.5 km NW of the vent) and surrounding areas. Seismicity was generally moderate during the earlier part of August but increased to higher levels between 22-29 August. Activity was usually low frequency earthquakes, with occasional high-frequence earthquakes between 25-29 August. Five weak explosions were recorded on 27 August.

Ground deformation was stable until the middle of August when minor uplifts were noted. On 22 August, a marked uplift began and then subsided with the resumption of ash emissions. The subsidence continued until 28 August when a minor uplift began but subsided on 30 August.

A total of 1,087 low frequency earthquakes were recorded during 28-31 August. Three weak explosions were recorded on 30 August, but no high-frequency earthquakes were recorded. Ash emission persisted before declining significantly on the night of 30 August. A total of 150 low-frequency earthquakes were recorded on 31 August. After a momentary eruptive interlude took place at the end of August, blending into early September

September 2007. On 2 September, fine ashfall continued on Rabaul Town. Seismicity continued at a moderate level, dominated by bands of irregular tremor and discrete low-frequency earthquakes. A total of 886 low-frequency earthquakes were recorded during 1-5 September; no high-frequency events were recorded. During 6-10 September there was little or no ash emitted. Emissions consisted of billowing white fume when atmospheric conditions were humid or cool. During hot dry periods, observers saw clear air above the cone, with a white plume appearing several hundred meters higher. On 8 September, odors of H₂S became noticeable downwind; this coincided with a blue tinge to the plume. Ground deformation measurements indicated an uplift. Emissions began again on 20 September, with ashfall in Rabaul Town and areas downwind, including Namanula Hill (3 km W). On 27 September, a large explosion was noted. During 30 September-2 October, incandescent fragments were ejected from the summit and rolled down the flanks.

October 2007. On 3 October ashfall was reported from areas downwind, including Rabaul Town. On 4 October ash plumes resulted in ashfall in Matupit Island (3.3 km SE), Malaguna. Incandescent fragments were ejected from the summit. On 5 October, vapor plumes with minor ash content were noted. During 8-23 October, occasional explosions produced ash plumes. Ashfall was reported at Namanula Hill and surrounding areas. Continuous weak glow was visible at night and incandescence at the summit was observed. The glow was bright on the night of 17 October. On 29-30 October ashfall was reported in Rabaul Town. Seismicity continued at moderate to moderately high level between the 17th and 20th. One high-frequency event was recorded on 21 October from NE of Rabaul.

November 2007. In late November, after five weeks of low-level activity, Tavurvur began to emit ash from a new vent on the NE crater rim. The new vent was formed as a result of the lava dome blocking the vent on the crater floor. The activity progressed and on 8-9 December emissions were thick white gray ash. The new dome has been the source of the continuous red glow visible at night.

December 2007. There was a slight increase in seismicity during December, but it was still low. The average daily number of low-frequency earthquakes was 20 during 1-3 December, before increasing to 55 during 4- 6 December, and 85 during 7- 8 December. The activity was accompanied by low-level sub-continuous signals. Two high-frequency earthquakes were recorded on 3 December which originated NE of the caldera. Ashfall continued downwind, including Rabaul Town. During 13-18 December, white plumes were observed and a strong smell of H₂S gas was reported.

January 2008. January 2008 continued the December activity. White ash and vapor plumes continued from the Tavurvur cone. The eruptive activity came from vents based on the inner eastern wall. One vigorous coneless fumarole on the upper outer eastern flank occasionally erupted ash. Unfortunately, NW winds carried ash towards the Provincial Airport (5.3 km NW) on a few occasions, causing closures.

During 11-12 January slight ashfall was reported about 20 km SE of Tokua. On 17 January ashfall at Tokua, prompted Air Niugini to cancel some flights. During 18-20 January, the ash plumes were released at 10-20 minute intervals. Slight ashfall was reported in areas on the E coast. Incandescence from the center of the crater was visible at night throughout most of January.

Deformation-monitoring instruments indicated that uplift started on 23 January and peaked during 25-26 January with 2 cm of inflation. On 26 January, ashfall was quite heavy but died down on the morning of 27 January. Seismicity remained moderately high, with small sub-continuous low-frequency signals dominating. In the preceeding 24 hrs there were 400 low-frequency events and 3 explosion type signals, most of them were not associated with the seen emissions. There were no high-frequency or hybrid events. There were small explosion type signals, even when ash was not emitted. Deformation monitoring showed a slight uplift superimposed on the gradual 6 month long subsidence. On 29 January two small, instrumentally recorded, high-frequency events occured within the caldera, one between Tavurvur and Rabalanakia and the other just off the E coast of Vulcan (the first here since the '94 eruption). Deformation monitoring showed that the center of the caldera underwent a rapid centimetre scale uplift and matching deflation on 31 January.

February 2008. There was little variance in the activity at Tarvurur which was essentially a continuation of the January activity. Because of light winds, the plumes reached 1 km above Tavurvur. Drift was predominantly E. During 1-3 February ashfall was reported in Kokopo (20 km SE). On 4 February, a strong smell of H₂S gas was reported from Rabaul Town (3-5 km NW). Incandescence from the center of the crater was visible almost every night.

Low-frequency seismicity was moderately high and increased slightly, with occasional low-frequency signals dominating. Some hybrid events were also recorded. Seismic activity did not always appear to be related to the observed events. Deformation monitoring showed that the center of the caldera remaining reasonable stable during the early part of the month, although the trend was towards inflation. On 5 February, deformation monitoring showed some small, but significant movements with horizontal strain greater than vertical. A slight deflation was noted.

Toward the middle of February, ashfall was reported everyday in areas downwind, including Matupit, Kokopo, and Rabaul Town, and surrounding areas. Incandescence at the summit was noted and incandescent material was propelled from a vent on the inner E wall of the crater. Seismic activity remained at moderate levels; but again, the activity did not always appear to be related to observed events. Deflation appeared to continue but only slightly. Occasional periods of high level seismic activity were dominated by low-frequency volcanic earthquakes. A total of over 1,570 events were recorded during 7-8 February. Ground deformation showed no significant movement although the trend after 9 February was towards inflation.

From 13-19 February, ashfall was reported in Barovon, Lalakua, Raluana, Kokopo, and surrounding villages. During 19-20 February, incandescence at the summit was accompanied by projections of lava fragments. Ground deformation as indicated by both the GPS and water-tube tiltmeter continued to indicate a trend towards inflation. On 25 February an explosion showered the flanks with lava fragments. On 26 February a large explosion occurred. The flanks were again showered with lava fragments. Ashfall was reported in Kokopo and surrounding areas.

March 2008. Tavurvur's activity during March was a continuation of the preceeding months. During 27 February-4 March ashfall was reported in areas downwind, including Matupit. A smell of H₂S gas was again reported in Rabaul Town. During 3-7 March, incandescence at the summit. A slight smell of H₂S was reported in areas to the S on 5 March. During 8-11 March, ash fall was reported in areas downwind, including Kokopo town (SE), and Rabaul Town (NW) on 11 and 13 March. Seismic activity often remained at a high level during March, but, the instrument's batteries died during 10-11 March. A total of over 980 events were recorded on 9 March. No high-frequency earthquakes were recorded. Deformation continued to indicate an inflationary trend after 8 March. On 13 March fine ash fell upon Rabaul Town. Ground deformation began towards an inflation trend after previous indications towards deflation. Unlike most plume eruptions, on 13 March sounds were not recorded. On 17 March moderate to heavy ash fall rained on Matupit island and surrounding areas.

At 1105 on 20 March a large explosion occurred showering the flanks with lava fragments. The shockwave rattled windows in Rabaul Town. At 1730 on 22 March 2008 an explosion occurred showering the flanks with lava fragments. During 22-23 March areas downwind had ashfall.

On 25 March 2008 ash clouds formed a broad fan from S at Barovon/Ialakua to Kokopo. The cloud drifted SE towards Tokua later that morning. During the morning on 26 March 2008 ash plumes caused Air Niugini flights into Tokua to be affected.

During 27 March into July 2007 overall deflation was 5 cm of subsidence, step-wise with small superimposed up lifts. RVO suggested that low-pressure intrusions were periodically rising in an open conduit causing the uplift before intersecting with the surface. The overall deflation implied that the deeper source was being depleted. The deformation measurements were made at Matupit. Constant expansion and degassing of magma in the recent weeks had apparently kept the conduit open. Pressure and debris have started to block the mouth of the vent by compaction and partial welding of molten material. This would lead to pressure build-up causing periodic explosions, in a plausible waning explosive phase.

April-May 2008. On 2 April ground deformation was stable with small and continued rapid fluctuations due to the repeating sealing and rupturing of the shallow conduit. Seismicity generally became moderate, but still generally dominated by low-frequency earthquakes. Activity was no longer preceded by notable explosions. The vent would be clear for a period of time. On 7 April a high-frequency event occurred NE of the caldera. On 9-10 April 9 mm of uplift occurred. On 11 April moderate ashfall was noted in Rabaul Town. Fine ashfall occurred in Matupit island. Seismic activity returned to a high level dominated by low-frequency earthquakes. On 11 April a total of 1,000 earthquakes were recorded. At 1100 on 22 April a modest explosion occurred. On 23 April 1-2 mm of non compacted flocculated pale ash was deposited in a sector from Malaguna E to S of Matupit. The cone was obscured to vision. On 28 April ground deformation was in a deflated but stable state. Ashfalls on 2 May left 3-4 cm in eastern Rabaul and 1-2 cm in western Rabaul.

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

Information Contacts: Steve Saunders and Herman Patia, Rabaul Volcanological Observatory (RVO), Department of Mining, Private Mail Bag, Port Moresby Post Office, National Capitol District, Papua New Guinea (URL: http://www.pngndc.gov.pg/); NASA Earth Observatory (URL: http://earthobservatory.nasa.gov/).

Our previous report on Sangay (BGVN 21:03) described occasional, but sometimes conspicuous, steam and/or ash plumes between January 2004 and January 2006. The current report continues coverage of plume emissions through December 2007.

Sangay has continued to erupt, sending ash plumes up to an altitude of about 11 km. A summary of plume activity is indicated in table 1. The information is from the Washington Volcanic Ash Advisory Center (VAAC), and is based on reports from the Guayaquil Meteorologic Watch Office, pilot reports, satellite imagery, and the Instituto Geofísico-Departamento de Geofísica (Escuela Politécnica Nacional). We did not receive any report of activity during the period February 2006 through September 2006, or during the first three months of 2008.

Table 1. Ash plume advisories about Sangay activity, October 2006 through December 2007. Courtesy of the Washington VAAC.

According to a report from the Instituto Geofísico, activity at Sangay increased at the end of 2006 through the beginning of 2007. They reported that a thermal anomaly was detected by satellite imagery during several days in December 2006. During that time, mountain guides near the volcano observed the fall of incandescent rocks down the volcano's flanks at night and a recent deposit of ash that was sufficiently deep to affect birds, rabbits, and other small animals. The report indicated that the Instituto Geofísico has not installed monitoring instrumentation near Sangay because of a significant logistics problem in maintaining them in this inhospitable area, and also because the area is uninhabited and thus poses no direct human risk. However, the report notes that because ash emissions from Sangay may pose problems for aircraft in the S, SE, and SW parts of the country, the Instituto maintains contact with the civil aviation authority.

Geologic Background. The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador's volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within horseshoe-shaped calderas of two previous edifices, which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been sculpted by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of a historical eruption was in 1628. More or less continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

Information Contacts: 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/); P. Ramón, Instituto Geofísico-Departamento de Geofísica (IG), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador.

This report updates activity through March 2008. Our last overview of Ulawun (BGVN 32:02) reported little activity of note other than frequent ash plumes from March 2006 to January 2007. Typical activity at Ulawun has consisted of gentle emission of thin-to-thick white vapor from the summit Based on satellite imagery and information from the Rabaul Volcano Observatory (RVO), the Darwin VAAC reported that diffuse plumes from Ulawun drifted N on 28 April 2007. On 1 May, an ash plume rose to an altitude of 4 km and drifted W.

[On 29 May 2007, RVO reported thick white vapor; there were no audible noises or night glow.] The two N valley vents remained quiet. Seismicity was at a low to moderate level dominated by low-frequency earthquakes. Through May, between 500 and 1,265 low frequency events were recorded daily with the most recorded on 28 and 29 May.

Similar conditions continued through the end of 2007 with only minor incidental variation. On 6 June, the elevated characteristics of the forceful emissions of 28-29 May were repeated. The daily total number of low-frequency earthquakes fluctuated between 400 and 1,042 events with the highest numbers recorded on 24 June (1,032) and 8 August (1,042). A high-frequency earthquake was recorded on 1 August. On 3 September forceful emissions were recorded sending the vapor plume ~ 1 km above the summit before being blown SE. On 25 December, based on satellite imagery observations, the Darwin VAAC reported that an ash-and-steam plume from Ulawun drifted W.

Low levels of activity continued from January through March 2008. Emissions consisted of thin to thick white vapor and with no audible noises and no glow visible at night. Seismicity continued at moderate level dominated by low frequency volcanic earthquakes. Variable amounts of white fume were emitted, sometimes forcefully. The two N valley vents continued to remain quiet.

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

Information Contacts: Herman Patia, Rabaul Volcano Observatory (RVO), P. O. Box 386, Rabaul, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Commonwealth Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); US Air Force Weather Agency (AFWA), Satellite Applications Branch, Offutt AFB, NE 68113-4039, USA; 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/); James Mori, Disaster Prevention Research Institute, Kyoto University, Uji, Kyoto 611-0011, Japan (URL: http://eqh.dpri.kyoto-u.ac.jp/~mori/).