Erta Ale is a shield volcano located in Ethiopia and contains multiple active pit craters in the summit and southeastern caldera. Volcanism has been characterized by lava flows and large lava flow fields since 2017. Surficial lava flow activity continued within the southeastern caldera during November 2019 until early April 2020; source information was primarily from various satellite data.

The number of days that thermal anomalies were detected using MODIS data in MODVOLC and NASA VIIRS satellite data was notably higher in November and December 2019 (figure 96); the number of thermal anomalies in the Sentinel-2 thermal imagery was substantially lower due to the presence of cloud cover. Across all satellite data, thermal anomalies were identified for 29 days in November, followed by 30 days in December. After December 2019, the number of days thermal anomalies were detected decreased; hotspots were detected for 17 days in January 2020 and 20 days in February. By March, these thermal anomalies became rare until activity ceased. Thermal anomalies were identified during 1-4 March, with weak anomalies seen again during 26 March-8 April 2020.

Figure 96. Graph comparing the number of thermal alerts using calendar dates using MODVOLC, NASA VIIRS, and Sentinel-2 satellite data for Erta Ale during November 2019-March 2020. Data courtesy of HIGP - MODVOLC Thermal Alerts System, NASA Worldview using the “Fire and Thermal Anomalies” layer, and Sentinel Hub Playground.

MIROVA (Middle Infrared Observation of Volcanic Activity) analysis of MODIS satellite data showed frequent strong thermal anomalies from 18 April through December 2019 (figure 97). Between early August 2019 and March 2020, these thermal signatures were detected at distances less than 5 km from the summit. In late December the thermal intensity dropped slightly before again increasing, while at the same time moving slightly closer to the summit. Thermal anomalies then became more intermittent and steadily decreased in power over the next two months.

Figure 97. Two time-series plots of thermal anomalies from Erta Ale from 18 April 2019 through 18 April 2020 as recorded by the MIROVA system. The top plot (A) shows that the thermal anomalies were consistently strong (measured in log radiative power) and occurred frequently until early January 2020 when both the power and frequency visibly declined. The lower plot (B) shows these anomalies as a function of distance from the summit, including a sudden decrease in distance (measured in kilometers) in early August 2019, reflecting a change in the location of the lava flow outbreak. A smaller distance change can be identified at the end of December 2019. Courtesy of MIROVA.

Unlike the obvious distal breakouts to the NE seen previously (BGVN 44:04 and 44:11), infrared satellite imagery during November-December 2019 showed only a small area with a thermal anomaly near the NE edge of the Southeast Caldera (figure 98). A thermal alert was seen at that location using the MODVOLC system on 28 December, but the next day it had been replaced by an anomaly about 1.5 km WSW near the N edge of the Southeast Caldera where the recent flank eruption episode had been centered between January 2017 and January 2018 (BGVN 43:04). The thermal anomaly that was detected in the summit caldera was no longer visible after 9 January 2020, based on Sentinel-2 imagery. The exact location of lava flows shifted within the same general area during January and February 2020 and was last detected by Sentinel-2 on 4 March. After about two weeks without detectable thermal activity, weak unlocated anomalies were seen in VIIRS data on 26 March and in MODIS data on the MIROVA system four times between 26 March and 8 April. No further anomalies were noted through the rest of April 2020.

Figure 98. Sentinel-2 thermal satellite imagery of Erta Ale volcanism between November 2019 and March 2020 showing small lava flow outbreaks (bright yellow-orange) just NE of the southeastern calderas. A thermal anomaly can be seen in the summit crater on 15 November and very faintly on 20 December 2019. Imagery on 19 January 2020 showed a small thermal anomaly near the N edge of the Southeast Caldera where the recent flank eruption episode had been centered between January 2017 and January 2018. The last weak thermal hotspot was detected on 4 March (bottom right). Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

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

Information Contacts: 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); NASA Worldview (URL: https://worldview.earthdata.nasa.gov/).

Rincón de la Vieja is a remote volcanic complex in Costa Rica containing an acid lake that has regularly generated weak phreatic explosions since 2011 (BGVN 44:08). The most recent eruptive period occurred during late March-early June 2019, primarily consisting of small phreatic explosions, minor deposits on the N crater rim, and gas-and-steam emissions. The report period of August 2019-March 2020 was characterized by similar activity, including small phreatic explosions, gas-and-steam plumes, ash and lake sediment ejecta, and volcanic tremors. The most significant activity during this time occurred on 30 January, where a phreatic explosion ejected ash and lake sediment above the crater rim, resulting in a pyroclastic flow which gradually turned into a lahar. Information for this reporting period of August 2019-March 2020 comes from the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA) using weekly bulletins.

According to OVSICORI-UNA, a small hydrothermal eruption was recorded on 1 August 2019. The seismicity was low with a few long period (LP) earthquakes around 1 August and intermittent background tremor. No explosions or emissions were reported through 11 September; seismicity remained low with an occasional LP earthquake and discontinuous tremor. The summit’s extension that has been recorded since the beginning of June stopped, and no significant deformation was observed in August.

Starting again in September 2019 and continuing intermittently through the reporting period, some deformation was observed at the base of the volcano as well as near the summit, according to OVSICORI-UNA. On 12 September an eruption occurred that was followed by volcanic tremors that continued through 15 September. In addition to these tremors, vigorous sustained gas-and-steam plumes were observed. The 16 September weekly bulletin did not describe any ejecta produced as a result of this event.

During 1-3 October small phreatic eruptions were accompanied by volcanic tremors that had decreased by 5 October. In November, volcanism and seismicity were relatively low and stable; few LP earthquakes were reported. This period of low activity remained through December. At the end of November, horizontal extension was observed at the summit, which continued through the first half of January.

Small phreatic eruptions were recorded on 2, 28, and 29 January 2020, with an increase in seismicity occurring on 27 January. On 30 January at 1213 a phreatic explosion produced a gas column that rose 1,500-2,000 m above the crater, with ash and lake sediment ejected up to 100 m above the crater. A news article posted by the Universidad de Costa Rica (UCR) noted that this explosion generated pyroclastic flows that traveled down the N flank for more than 2 km from the crater. As the pyroclastic flows moved through tributary channels, lahars were generated in the Pénjamo river, Zanjonuda gorge, and Azufrosa, traveling N for 4-10 km and passing through Buenos Aires de Upala (figure 29). Seismicity after this event decreased, though there were still some intermittent tremors.

Figure 29. Photo of a lahar generated from the 30 January 2020 eruption at Rincon de la Vieja. Photo taken by Mauricio Gutiérrez, courtesy of UCR.

On 17, 24, and 25 February and 11, 17, 19, 21, and 23 March, small phreatic eruptions were detected, according to OVSICORI-UNA. Geodetic measurements observed deformation consisting of horizontal extension and inflation near the summit in February-March. By the week of 30 March, the weekly bulletin reported 2-3 small eruptions accompanied by volcanic tremors occurred daily during most days of the week. None of these eruptions produced solid ejecta, pyroclastic flows, or lahars, according to the weekly OVSICORI-UNA bulletins during February-March 2020.

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

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/, https://www.facebook.com/OVSICORI/); Luis Enrique Brenes Portuguéz, University of Costa Rica, Ciudad Universitaria Rodrigo Facio Brenes, San José, San Pedro, Costa Rica (URL: https://www.ucr.ac.cr/noticias/2020/01/30/actividad-del-volcan-rincon-de-la-vieja-es-normal-segun-experto.html).

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/).

The seismic swarm along a branch of the Azores-Gibraltar Fracture Zone was ending in mid-November. No surface evidence of submarine volcanism has been reported.

On 21 November at 1556, a second swarm started with an [Ms 5.6] shock centered 25 km NW of Sao Miguel along the Sete Cidades Fault, a branch of the same fracture zone. The hypocenter was 53 km SE of Don Joao de Castro Bank [preliminary location by WWSSN at 37.97°N, 26.11°W, 10 km depth]. By the next day, the number of seismic events/hour had decreased from 24 to 4; several of the shocks were migrating along the main portion of the Sao Miguel Fault. The swarm caused 30 houses to collapse and damaged hundreds of other buildings. Modified Mercalli intensities were VII-VIII in the NW part of the island and V at the capital.

Geologic Background. Reports of floating pumice from an unknown source, hydroacoustic signals, or possible eruption plumes seen in satellite imagery.

Information Contacts: V. Forjaz, Univ of the Azores; NEIC; Lisbon International Service.

While flying 170 km E of the Kuril Islands on 27 October at 1907, the pilot of Japan Airlines flight 81 (Anchorage, Alaska to Tokyo) observed a spherical blue-white cloud slightly above the WNW horizon. The cloud looked to the pilot like a volcanic plume and was rapidly developing a mushroom head. Visibility was unlimited in moonlight. Airborne radar is generally not able to detect volcanic clouds, and there was no echo from this cloud on the aircraft's radar scope. Winds were blowing from the cloud toward the aircraft at ~55-75 km/hour, and the pilot diverted S to avoid it.

The air route nearest the Kuril Islands (R220) and the neighboring westbound route (R580) were closed to air traffic by Japanese authorities. A third parallel route (A590), normally eastbound, was opened in both directions (at different altitudes) to accommodate aircraft from the two closed routes. Although a reconaissance flight the next day detected what its pilot described as a possible ash cloud below 8.5 km altitude, the closed routes were reopened for their normal use by higher altitude traffic.

At the time of the sighting, the aircraft was at about 48.65 N, 157.45 E, 11 km altitude. The cloud was ~45 to the right of the flight path, prescribed at 238 for that section of the air route (R220). The resultant bearing of 283 to the cloud crosses the northern Kurils near Harimkotan Island, ~170 km from the aircraft. Several recently active volcanoes, including Harimkotan, Chrinokotan, Ekarma, Sinarka, and the Tao Rusyr caldera, are within a few degrees of the 283 bearing from the point of the sighting. However, the IV had no reports of any eruptions in the area at that time, and an October survey of the southern Kurils found only mild fumarolic activity. A strong cold front was passing through the area around the time of the 27 October observation, and might have produced volcanic-like cloud formations.

Geologic Background. Reports of floating pumice from an unknown source, hydroacoustic signals, or possible eruption plumes seen in satellite imagery.

Information Contacts: N. Krull, FAA; E. Miller, ALPA; Y. Tsukamoto, ALPA of Japan; W. Gould, NOAA/NESDIS; S. Fedotov and B. Ivanov, IV.

Explosive activity . . . continued with five explosions in November . . . . The explosions caused no damage. An explosion on 1 November at 0234 produced a large air shock and an incandescent column that was 500 m high for 10 seconds. Lightning was seen in the eruption cloud. The highest November ash cloud rose 1,000 m above the summit, accompanying an explosion at 1211 on the 10th. The month's ashfall at KLMO was only 12 g/m².

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

Information Contacts: JMA; AP; UPI.

Lidar stations in Germany, Japan, and Hawaii detected no apparent new stratospheric aerosol layers, and no recent large explosive eruptions have been reported. Substantially increased backscattering was measured between 17 and 22 km altitude at Mauna Loa, Hawaii on 1 November. Despite some instrument problems that night, the increased aerosols appeared real, but the profile did not have the characteristics of material from a new eruption.

Figure 63. Lidar data from various locations, showing altitudes of aerosol layers during September-November 1988. Note that some layers have multiple peaks. Backscattering ratios from Fukouka, Japan, are for the Nd-YAG wavelength of 1.06 µm; all others are for the ruby wavelength of 0.69 µm. Integrated values show total backscatter, expressed in steradians-1, integrated over 300-m intervals from 16-33 km at Mauna Loa and from the tropopause to 30 km at Hampton, Virginia. Altitudes of maximum backscattering ratios and coefficients are shown for each layer at Mauna Loa. Some upper and lower limits of layers at Mauna Loa were not clearly evident and are therefore not reported.

Geologic Background. The enormous aerosol cloud from the March-April 1982 eruption of Mexico's El Chichón persisted for years in the stratosphere, and led to the Atmospheric Effects section becoming a regular feature of the Bulletin. Descriptions of the initial dispersal of major eruption clouds remain with the individual eruption reports, but observations of long-term stratospheric aerosol loading will be found here.

Information Contacts: Thomas DeFoor, Mauna Loa Observatory, P.O. Box 275, Hilo, HI 96720 USA; Motowo Fujiwara, Physics Department, Fukuoka University, Jonan-ku, Fukuoka 814-01, Japan; Horst Jäger, Fraunhofer-Institut für Atmosphärische Umweltforschung, Kreuzeckbahnstrasse 19, D-8100 Garmisch-Partenkirchen, West Germany.

"Seismic activity continued at a steady low level until 7 November when a swarm of 1,500 small explosion-type earthquakes were recorded. Visual reports were obtained of red material sliding or rolling down the E slopes of the volcano on the 6th and pale brown dust/vapour rising from the same area on the 7th. Seismic activity then returned to a normal level with 15 rockfall-related tremor events/day, indicating continued slow steady extrusion of lava from the summit crater. Seismic telemetry to Rabaul stopped on the 14th. Records continued to be obtained at Panguna until the nearby Mt. Kupara repeater station, containing RVO telemetry equipment, was destroyed on 2 December."

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: I. Itikarai and P. Lowenstein, RVO.

Seismicity increased toward the end of November. A total of 188 events were recorded by the seismometer 1.8 km NNW of the summit, up sharply from the background level of ~20/month (figure 1).

Figure 1. Monthly number of recorded earthquakes at Bandai, 1965-88. Courtesy of JMA.

Geologic Background. One of Japan's most noted volcanoes, Bandaisan rises above the north shore of Lake Inawashiro. This complex is formed of several overlapping andesitic stratovolcanoes, the largest of which is Obandai. Kobandai volcano, which collapsed in 1888, was formed about 50,000 years ago. Obandai volcano was constructed within a horseshoe-shaped caldera that formed about 40,000 years when an older volcano collapsed, forming the Okinajima debris avalanche, which traveled to the SW and was accompanied by a plinian explosive eruption. The last magmatic eruption took place more than 25,000 years ago, but four major phreatic eruptions have occurred during the past 5000 years, two of them in historical time, in 806 and 1888. Seen from the south, Bandaisan presents a conical profile, but much of the north side of the volcano is missing as a result of the collapse of Ko-Bandai volcano during the 1888 eruption, in which a debris avalanche buried several villages and formed several large lakes.

Information Contacts: JMA; AP; UPI.

Fumarolic activity in the summit crater remained at the same level. Steaming ground was observed in many parts of the crater, but well-formed fumaroles were not evident. The intensity of steam release increases when atmospheric pressure drops and after precipitation. Tiatia's last reported activity ejected a 1-1.5-km-high white steam column in February 1982.

Geologic Background. Chachadake, also known as Tiatia, consists of a beautifully symmetrical cone that rises above the broad rim of an erosionally furrowed, 2.1 x 2.4 km wide caldera. The edifice occupies the NE tip of Kunashir Island and morphologically resembles Mount Vesuvius. The pristine-looking conical central cone, mostly formed by basaltic to basaltic-andesite strombolian eruptions, rises 400 m above the floor of the caldera and contains a 400 x 250 m wide crater with two explosion vents separated by a linear septum. Fresh lava flows cover much of the SW caldera floor and have overflowed the rim, extending to the foot of the older somma, which formed during the late Pleistocene or early Holocene. A lava flow from a flank cone on the northern caldera rim reached the Sea of Okhotsk. A major explosive eruption in 1973 followed an initial historical eruption in 1812.

Information Contacts: G. Steinberg, Yuzhno-Sakhalinsk.

Deformation and a brief seismic swarm preceded a new fissure eruption on 14 December. Lava production from the fissure eruption that began 31 August had stopped on 12 September. Strong degassing continued until early October. Between September and mid-December, the permanent telemetered EDM (5-minute period) recorded 5 cm expansion of the summit crater, associated with fissure extension measured by strainmeters. Radial tiltmeters detected no significant changes. Seismicity remained weak until 12 November, when 25 minutes of low-energy summit seismicity was recorded, without associated deformation. Since then, discrete shallow events had increased in the summit area.

On 14 December at 0830, a seismic crisis began that included both shallow and deeper events in the summit area. Deformation indicated northward magma migration between 0850 and 0910. The seismic crisis continued until 1220, when low-frequency tremor appeared on the summit seismic station (SFR). At 1306 [but see 13:12], an eruptive fissure opened in the N part of the Enclos Caldera, ~400 m E of the August 1985 crater. Three main NNE-trending, en-echelon fissures developed between 1,900 and 2,050 m elevation, and at 1400 a fissure opened just above them.

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

Information Contacts: H. Delorme, P. Nerbusson, D. Vandamme, J. Delmond, and P. Taochi, OVPDLF; P. Bachelery, Univ de la Réunion; J. Dubois, J-L. Cheminée, A. Hirn, J. LePine; P. Blum, and J. Zlotnicki, IPGP.

On 5 November at 1130, ~1/3 of the 400-450 x 60 m lava bench collapsed, and numerous smaller bench collapses were detected seismically throughout November. A large littoral cone that formed on 28 November produced 1-5-cm flakes of volcanic glass.

On 10 November, a series of surface outbreaks near the top of the fault scarp at ~350 m elevation fed lava that flowed into the Royal Gardens subdivision but caused no threat to remaining structures. By 14 November, the flow was barely moving. Two weeks later, an outbreak occurred at 180 m elevation, flowed E of the subdivision, and stagnated days later at ~100 m elevation. The Kupaianaha lava pond level remained stable at 25-30 m below the rim through November. During overflights on the 3rd and the 28th, low fountaining (~5-10 m high) was observed in Pu`u `O`o crater, covering as much as ½ of its floor with lava. Irregular tremor . . . near Pu`u `O`o had ended 4 November and typical low-level tremor resumed. Most upper East rift zone events were deeper than 5 km except along the rift axis where events were generally more shallow. Seismicity was steady beneath Kiluaea's S flank, but episodic swarms of intermediate-depth (5-13 km), long-period earthquakes were measured beneath the summit.

Geologic Background. Kilauea, which overlaps the E flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 km2, destroying nearly 200 houses and adding new coastline to the island.

Information Contacts: C. Heliker and R. Koyanagi, HVO.

"Activity returned to a low level in November. Weak-moderate amounts of white vapour with occasional grey [ash] were emitted from Crater 2. Weak rumbling noises occasionally were heard on the 4th. Ashfall was observed on the 11th. Two Vulcanian explosions, on the 18th and 27th, were accompanied by ash columns that rose a few hundred meters. Crater 3 was inactive throughout the month. Seismicity remained low and only 9 explosion earthquakes were recorded."

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

Information Contacts: I. Itikarai and P. Lowenstein, RVO.

Between 30 June at 2000 and early the next morning, a new cone (T8) had formed and emitted a large lava flow (F6) that reached the N and E crater wall (figure 10). On the afternoon of 26 July, a party visiting the crater noted lava in the E part of T4/T7, bubbling actively at some depth below the vent's edge. A new cone (T9) had formed a few meters from T5, and lava could be heard moving within the vent. The top of T8 had collapsed somewhat and no lava was visible inside. About five small flows, radiating from a source between T4/T7 and T8, were still warm and black and had probably formed within the last few hours. One flow had moved S and partly entered T1's overhang. Another flow had almost reached T2. No changes were observed on the crater walls or rim.

Figure 10. View from halfway up Ol Doinyo Lengai's E crater wall, looking SW in the early morning of 1 July 1988. The crater floor is 200-240 m across. Tracing of a slide taken by C. Nyamweru.

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

Information Contacts: C. Nyamweru, Kenyatta Univ.

. . . seismicity remained above background levels in early December, with ~3-4 shallow events recorded weekly by the temporary seismic net installed after the swarm began. Hypocenters were at ~5-10 km depth, almost directly below or slightly W of Mt. Liamuiga, and magnitudes were generally in the 1.5-2 range. The shocks continued to have impulsive P and S wave arrivals typical of both A-type volcanic events and tectonic earthquakes. No tremor has been recorded. Persons familiar with the volcano report that hot springs within the crater remain unchanged.

Geologic Background. Mount Liamuiga volcano, comprising the NW end of St. Kitts Island, contains a steep-walled, 1-km-wide summit crater, which contained a shallow lake until 1959. Two lava domes are located on the upper W flank, and intrusion of a 3rd dome, Brimstone Hill, on the lower SW flank uplifted a Pleistocene limestone block. Liamuiga, sometimes referred to as Mount Misery, is the youngest of three NW-migrating volcanic centers on St. Kitts. Its most recent major eruptions less than 2000 years ago produced pyroclastic flows and mudflows whose deposits underlie populated coastal areas. Reports of possible historical eruptions in 1692 and 1843 are considered uncertain. An earthquake swarm from late 1988 to early 1989 caused small landslides in the summit crater; another earthquake swarm took place in 1999-2000. Active fumaroles are found in the summit crater.

Information Contacts: J. Shepherd, UWI.

One of Long Valley caldera's more significant earthquake swarms of the last several years occurred 20-22 November (figure 4). Of the 393 recorded events (to M 2.0), most were located in the E moat of the caldera (near the E margin of the resurgent dome) with minor activity in the S moat (figure 5). The swarm trended N-S at depths of about 6 km. As the number of events/hour decreased, average magnitude increased. First order levelling surveys were completed across the epicentral area in 1986; about two weeks before the swarm; and the day after it began. The data suggested slight uplift of the area W of the epicentral zone relative to the E side, consistent with normal faulting, but the measured changes were within error limits (figure 6).

Figure 4. Number of events/hour measured at Long Valley caldera on station CNOC, 10 km from most epicenters (detection threshold about M 0). Courtesy of Stephen McNutt.

Figure 5. Epicenters of the 20-22 November Long Valley caldera earthquake swarm. Courtesy of John Estrem.

Figure 6. Preseismic (1986-88) and coseismic (1988-88) elevation changes across the epicentral area of the 20 November swarm at Long Valley caldera. Courtesy of John Estrem.

Further Reference. Langbein, J., 1989, Deformation of the Long Valley Caldera, Eastern California, from mid-1983 to mid-1988; Measurements Using a Two-Color Geodimeter; Journal of Geophysical Research, v. 94, p. 3833-3849.

Geologic Background. The large 17 x 32 km Long Valley caldera east of the central Sierra Nevada Range formed as a result of the voluminous Bishop Tuff eruption about 760,000 years ago. Resurgent doming in the central part of the caldera occurred shortly afterwards, followed by rhyolitic eruptions from the caldera moat and the eruption of rhyodacite from outer ring fracture vents, ending about 50,000 years ago. During early resurgent doming the caldera was filled with a large lake that left strandlines on the caldera walls and the resurgent dome island; the lake eventually drained through the Owens River Gorge. The caldera remains thermally active, with many hot springs and fumaroles, and has had significant deformation, seismicity, and other unrest in recent years. The late-Pleistocene to Holocene Inyo Craters cut the NW topographic rim of the caldera, and along with Mammoth Mountain on the SW topographic rim, are west of the structural caldera and are chemically and tectonically distinct from the Long Valley magmatic system.

Information Contacts: S. McNutt, California Division of Mines and Geology, Sacramento; D. Hill, John Estrem, and James Savage, USGS Menlo Park.

. . . . The number of shallow volcanic earthquakes began to increase sharply on 20 July. Based on seismic and visual data, VSI anticipated that an eruption would begin within two weeks, and the 15,000 residents of Makian Island were evacuated to Moti Island, ~6 km to the N.

On 28 July, 521 seismic events were recorded, and tremor began . . . at 2200. The eruption started the next morning at 1112 with a continuous thunderous explosion that was clearly heard on Moti Island. A dark ash cloud reached 8-10 km height. On 30 July at 1006, an explosion was followed by nuées ardentes that advanced E (along the Ng. Powate valley) and N (Ng. Para valley). Originating from ~1,200 m asl, the nuées ardentes descended to 250 m altitude, and some finally reached the sea. A series of smaller explosions began on 31 July and continued until 6 August, feeding ash columns that decreased from 6 to 1-2 km above the crater.

As of the first week in December, white fume was still rising weakly from the crater. Seismicity continued to decrease, with 17 tectonic and 14 volcanic earthquakes recorded 1-7 December.

Geologic Background. Makian volcano forms a 10-km-wide island near the southern end of a chain of volcanic islands off the west coast of Halmahera and has been the source of infrequent, but violent eruptions that have devastated villages on the island. The large 1.5-km-wide summit crater, containing a small lake on the NE side, gives the peak a flat-topped profile. Two prominent valleys extend to the coast from the summit crater on the north and east sides. Four parasitic cones are found on the western flanks. Eruption have been recorded since about 1550; major eruptions in 1646, 1760-61, 1861-62, 1890, and 1988 caused extensive damage and many fatalities.

Information Contacts: VSI.

"Activity continued at a low level during November with weak-moderate white vapour emissions from the two summit craters. Emissions from Southern Crater frequently contained small amounts of grey ash and blue vapour. On the 29th, red glow became sub-continuous and weak incandescent projections were observed. Rumbling noises from the same crater were heard throughout the month. Seismicity remained at a normal inter-eruptive level with a daily average of 1,120 low-frequency events. Tilt measurements indicated 3 µrad of inflation over the month."

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

Information Contacts: I. Itikarai and P. Lowenstein, RVO.

Faint crater glow continued to be observed during nights with good visibility in October and November. Moderate steam emission covered 30-50% of the crater and blue volcanic fumes sometimes moved slowly downslope.

In October and November, 77 high-frequency events, 59 low-frequency events, and 119 harmonic tremor episodes were recorded. Mudflows were detected (by seismographs and by a lahar mapping team) along the SE slopes on 12 and 23 October, and along the SE and SW slopes on 4, 6, 20, and 21 November. The 12 October lahar moved at 2.5 m/s down Basud gully between 2347 and 0141 the next morning. On the 23rd, three lahars with velocities of about 3.2 m/s were triggered by a typhoon. The Basud River was incised by 4 m (near the Lidong-Basud boundary), and a jeep caught by a flow surge along the river was partially buried by debris. Continuous undercutting caused 3-4 m of a cement road to collapse and a house was carried away by a flow. No casualties were reported.

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

Information Contacts: PHIVOLCS.

Small events recorded late November-early December were attributed to freezing phenomena as winter came to N California. On 13 December at 2035, an M 1.9 earthquake, ~0.25 km SW of Medicine Lake glass flow, was recorded. During the next 75 minutes, nine events (M less than 1.9) were detected, followed by seven events on 14 December from 0121 to 0129. Seismicity was shallow (below 1 km) and had a high-frequency character. The 3-component station (LMD) is not currently operating.

Geologic Background. Medicine Lake is a large Pleistocene-to-Holocene, basaltic-to-rhyolitic shield volcano east of the main axis of the Cascade Range. Volcanism, similar in style to that of Newberry volcano in Oregon, began less than one million years ago. A roughly 7 x 12 km caldera truncating the summit contains a lake that gives the volcano its name. A series of young eruptions lasting a few hundred years began about 10,500 years before present (BP) and produced 5 km3 of basaltic lava. Nine Holocene eruptions clustered during three eruptive episodes at about 5000, 3000, and 1000 years ago produced a chemically varied group of basaltic lava flows from flank vents and silicic obsidian flows from vents within the caldera and on the upper flanks. The last eruption produced the massive Glass Mountain obsidian flow on the E flank about 900 years BP. Lava Beds National Monument on the N flank of Medicine Lake shield volcano contains hundreds of lava-tube caves displaying a variety of spectacular lava-flow features, most of which are found in the voluminous Mammoth Crater lava flow, which extends in several lobes up to 24 km from the vent.

Information Contacts: S. Walter, USGS Menlo Park.

Strombolian eruptions accompanied by lava extrusion continued at Pacaya during 1988. The SW flank lava flow observed in February remained active for about 2 months. In March and April lava extrusion began from new vents about 200-400 m below the summit. Lava effusion stopped in May, but resumed 26 May from new vents on the SW flank and continued into June, feeding flows that traveled about 1 km down the W, WSW, SW, SSW, and S flanks. Counts of explosions derived by Otoniel Matías from INSIVUMEH seismic records (figure 3) indicate that explosions increased from a few hundred/day in early June to about 2,000/day in mid-June. Ash fell 2.5 km from the volcano on 11 June. Explosions dropped to a few hundred/day in July and lava effusion stopped from all but one vent. Activity remained low in August, although a SW flank lava flow was emitted on 23 August. A lava flow formed on the NW flank at about 2330 on 6 September, and was active until 18-19 September. When the seismograph resumed operation in mid-September, daily explosion counts ranged from about 1,500 to 2,300. On 20 September a new lava flow began on the S flank at about 2,100 m altitude. Activity increased late September to early October, when some seismic events were felt on Cerro Chino (on the NW somma rim) and rumblings were heard in the S part of Guatemala City. A new lava flow was emitted 4-5 October from a vent at 2,070 m on the SW flank. The daily number of explosions peaked at 3,300 on 5 October, and gradually decreased after 10 October to fewer than 1,000 by 29 October, when lava emission ceased.

Figure 3. Estimated number of explosions/day at Pacaya, June-October 1988. Explosion events were counted on a vertical section of each day's seismic records from station PCG (on Cerro Chino, 1.5 km NW of MacKenney Crater) then extrapolated to yield 24-hour values. Upward-pointing arrows indicate the appearance of a new lava flow, downward arrows the cessation of feeding for a previously active flow; 2-headed arrows indicate the same observations but for two flows. Courtesy of Otoniel Matías.

During fieldwork 12-26 November on the S side of Pacaya, geologists observed MacKenney Crater during another period of increased activity. On 20 November the active vent was seen from the summit of the 1775 cone. More or less continuous weak Strombolian explosions ejected bombs to a few tens of meters above the crater rim. These were punctuated several times a minute to every few minutes by detonations from stronger explosions that ejected incandescent bombs and blocks to 100-200 m height from a vent at the NW end of MacKenney Crater. Some incandescent blocks rolled 400 vertical meters down the flanks of the cone as far as the moat between MacKenney Crater and the N somma rim. Incandescent ejecta was sometimes visible in daylight from the somma rim in contrast to the less vigorous February activity, and daytime explosions could also be seen from Guatemala City, 25 km NNE.

An area of active fumaroles was located on the N flank about 100 m below the summit. The accumulation of near-vent ejecta in the absence of major explosions since February had considerably narrowed the crater's width and recently raised MacKenney cone to an altitude slightly above that of the 1775 cone, which had formed the highest point on Pacaya at 2552 m. A lava flow originated in early November from a vent high on the SW flank at about the elevation of the saddle between the two summit cones. Lava flowed in several channels to about 2,000 m altitude on the SW flank, and extrusion was continuing on 26 November.

Geologic Background. Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and was last active in the 19th century. During the past several decades, activity has consisted of frequent strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.

Information Contacts: Otoniel Matías, Jorge Girón, and Enrique Molina, INSIVUMEH; Jim Vallance, Michigan Tech; Lee Siebert, SI.

"Seismic activity continued to decrease in November with a total of 301 earthquakes. The daily number of events averaged <20 with the highest number (54 events) recorded on the l4th. Four locatable events were detected: on the E side (1) and N of (2) Greet Harbour, and on the W side of Matupit Island (1). Ground deformation rates remained low. Levelling on 3 November showed 12 mm of uplift at the S part of Matupit Island since 20 October. EDM data showed slight expansion (5 microstrain) at Greet Harbour's entrance."

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

Information Contacts: I. Itikarai and P. Lowenstein, RVO.

Energy released in November by high- and low-frequency earthquakes and volcanic tremor remained similar to October values. A tremor episode on 23 November was associated with fumarolic activity and a brief landslide in the canyon of the Río Azufrado, 2 km NE of the crater (figure 21).

Figure 21. Epicenters of high-frequency earthquakes, November 1988, and the position of the Palestina Fault. Courtesy of the Observatorio Vulcanológico de Colombia.

Although the tremor episode lasted only a few minutes, it produced one of the largest displacements of the energy release curve since 1986. A slight increase in seismicity followed for the next few hours. The month's main high-frequency activity was centered parallel to the regional Palestina Fault, occurring in two clusters. Depths were between 0.5 and 6 km. No significant deformation was measured during the month.

Geologic Background. Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.

Information Contacts: C. Carvajal, INGEOMINAS, Manizales.

INSIVUMEH geologist Otoniel Matías reports that the dacite lava flow that extended 3.5 km SSW of the active Caliente vent by February 1988 (13:02) had stagnated there since February, although extrusion was continuing at a reduced rate. Geologists noted continuing small avalanches from the upper portion of the flow on 23 November. The middle portion of the block lava flow (about 1.5 km NNW of Mirador La Florida) was steaming, but remained stagnant. However a new lobe had advanced along the W margin of the flow to about 1.3 km from Caliente vent (figure 6).

Figure 6. Map of Santiaguito Dome, showing the ages of its domes. The 1986-88 flow is emphasized by a shaded pattern; other recent lobes are stippled. Successive positions of the 1986-88 flow are dated, and the approximate November 1988 location of the new lobe is shown. Modified from Rose (1987).

Small to moderate vertical explosions from the Caliente vent have continued. The number of explosions, as determined from field observations and seismic records from stations 5 km NNW and 2.6 km S of Santiaguito, has been tabulated by Matías since June (figure 7). Daily explosion totals during June ranged from 5 to 22. Activity decreased steadily through most of July, but increased again August-October, reaching a peak of 28 explosions on 19 October. Larger explosions produced steam and ash columns that rose 1-2 km above Caliente vent; secondary explosions to 400-1,000 m height occurred at roughly similar rates. The number of small block-and-ash avalanches from the active lava flow ranged from about 100 to 250/day in June and dropped to around 50-150/day in July, paralleling the drop in explosion frequency. From August through October the daily number of avalanches ranged from about 100 to over 300.

Figure 7. Number of daily explosions (bottom) and an extrapolation of the number of daily avalanche events (top) recorded by seismic stations near Santiaguito, June-October 1988. Field observations of eruptive phenomena were correlated with records from a portable seismograph to identify their seismic signatures. Courtesy of Otoniel Matías.

The sediment load from Santiaguito has continued to impact downslope river drainages, but the effects of the 1988 rainy season were relatively mild compared to past years. The El Palmar area was observed in November to be essentially unchanged from February, as the Río Nimá II remained contained within perched levees above the town. However, downstream lahars destroyed the supports of an important foot suspension bridge across the Río Samalá below San Felipe, about 14 km SSW of Santiaguito (figure 8); reconstruction of this bridge was continuing in November. The Carretera Internacional del Pacífico (CA2) below Santa Cruz Muluá was closed briefly in late August and around 4-5 September as floods deposited sand and gravel over a 150-m section of the highway. The Río Samalá was again diverted by rainy season lahars into the Río Ixpatz drainage, innundating portions of the Finca San José La Granja (about 5 km S of the sharp bend in route CA2). This diversion of river courses into parallel drainages has occured each year since 1983. The annual construction of barriers to return the Samalá to its normal course had not been completed in November. The Samalá also partially diverted the Río Muluá to the east.

Figure 8. Sketch map of rivers and towns S of Santiaguito, modified from a February 1988 sketch by William Rose. Locations of drainages are approximate. Arrows mark the location of the diversion of the Río Samalá into the Río Ixpatz and the former confluence of Ríos Nimá I and II near El Palmar. Points 1 and 2 indicate the damaged bridge below San Felipe and the flooded segment of route CA2.

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: Otoniel Matías and Enrique Molina, INSIVUMEH; Jim Vallance, Michigan Tech; Lee Siebert, SI.

During an October visit to the crater, activity remained at previous levels. Fumaroles were concentrated in five groups with gas temperatures ranging from 98 to 108°C. Gas was released under pressure in four of the five groups, to 2-6 m height.

Geologic Background. The Sashiusudake (also known as Baransky) volcanic complex along the Pacific coast in the central part of Iturup Island consists of an eroded Pleistocene volcano that is capped by a Holocene stratovolcano. A young summit lava dome is cut by a NW-trending chain of small explosion craters. A group of flank cones farther to the NW with a similar NW-SE orientation is partially surrounded by lava flows from the central crater of the andesitic-dacitic volcano. Lava flows from descended 4-5 km SE to reach the Pacific Ocean along a broad front. The only historical eruption occurred in 1951, when local inhabitants reported weak explosive activity at the summit. Strong solfataric activity continues from the summit and several flank craters, and the SW flank geothermal field contains hot springs and geysers. A small hydrothermal explosion took place in 1992 at an exploratory well in the SW-flank geothermal field.

Information Contacts: G. Steinberg, Yuzhno-Sakhalinsk.

Geologists visited Stromboli in October and November. Surface temperatures associated with Strombolian and fumarolic activity were studied for comparison with remotely sensed data. Temperatures were recorded using a Minolta Cyclops 33 radiometer operating at [8-14 mm] wavelength.

Craters 1, 3, and 4 were estimated to be 45 m deep; the floor of Crater 2 was not seen. Crater 1 contained three active vents (figure 2). On 26 and 27 October, a circular pit ([vent 1-1]) 1 m in diameter contained lava that glowed bright orange in daylight. Infrequent incandescent scoria and gas eruptions from vent [1-1] closely followed activity in [vent 1-2], a rubbly surface ~3 m away. At 10-30-minute intervals, [1-2] was ruptured by violent emission of blue incandescent gases (visible only after dark) followed by glowing scoria ejection. Ejecta from [1-1] and [1-2] usually fell within the crater, but on one occasion fell several meters beyond the S rim. A 2-m-diameter glowing vent ([1-3]) almost continuously ejected spatter to 50 m height. The maximum brightness temperature for the lava surface in vent [1-3] was 835°C, although readings sometimes fell as low as 240°C (when taken through dense fumes that frequently accumulated within the crater).

Figure 2. Sketch of active craters at Stromboli, October-November 1988. Courtesy of C. Oppenheimer and D. Rothery.

On 28 October, vent [1-1] had increased in area four-fold but was no longer glowing visibly in daylight. Incandescent scoria, ejected at 5-30-minute intervals, usually fell inside the crater although medium-coarse ash often reached the crater rim. Tephra ejections were usually immediately preceded by brief, rapid, bluish-gray steam emission and a roaring sound. Vent [1-3] was faintly glowing in daylight. Separate activity at former site [1-2] was no longer evident.

When geologists returned 3-6 November, a large volume of dark scoria and agglutinate had accumulated within the crater. Two new incandescent cracks had developed near site [1-1] and sharp cracking noises, like pistol shots, were often heard. Activity was dominated by ~7 explosions/hour at site [1-1]. Two distinct eruption types (ejecting tephra well above the crater rim) were recognized: very brief, violent detonations expelling gases and comminuted scoria; and longer duration (5-10-second) ejections of incandescent, highly vesiculated bombs. Site [1-3] glowed brightly but erupted infrequently.

Crater 2 was inaccessible and could not be observed directly. The crater continuously emitted high volumes of thick white fume. An eruption on 28 October that ejected a brown ash plume may have originated from this crater. A very low inner wall separated craters 3 and 4, and it was difficult to determine the origin of some eruptions. Dirty-brown plumes, attributed to Crater 3, frequently reached a height of 200-300 m above the crater rim. Brief (3-8-second) powerful incandescent bomb ejections at 5-40-minute intervals deposited tephra onto the crater's outer flanks. Infrequent explosions, clearly from Crater 4, obliquely ejected incandescent scoria over the crater's E rim, accompanied by small mushrooming ash columns. On 5 November, two small glowing vents, a few meters apart, were observed on the crater floor.

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: C. Oppenheimer and D. Rothery, Open Univ.

Local seismicity was at a high level in November. A seismometer, 4.5 km NW of the three craters active in 1962, recorded 29 events on 15 November, 9 on the 19th, and 10 on the 26th. The month's total increased to 93 from [43] in October. Four shocks were felt, three on 15 November and one on the 27th. Epicenters were estimated to be around crater 62-2. On 22 November, personnel at the JMA Tokachidake Observatory saw a 1,200-m steam plume emerge from crater 62-2, the highest since a 1,400-m plume in June 1981.

Addendum. The press reported that Tokachi began to erupt on 19 December at 2148 [but see 13:12], ejecting incandescent tephra and a plume that rose about 2 km. Ash fell on two cities more than 100 km NE of the volcano. A lahar about 30 m wide flowed 2.5 km downslope. Children within 25 km of the volcano were kept home from school the next day and residents were warned by officials to be ready to evacuate. The eruption had apparently declined, but seismicity was continuing.

Geologic Background. Tokachidake volcano consists of a group of dominantly andesitic stratovolcanoes and lava domes arranged on a NE-SW line above a plateau of welded Pleistocene tuffs in central Hokkaido. Numerous explosion craters and cinder cones are located on the upper flanks of the small stratovolcanoes, with the youngest Holocene centers located at the NW end of the chain. Frequent historical eruptions, consisting mostly of mild-to-moderate phreatic explosions, have been recorded since the mid-19th century. Two larger eruptions occurred in 1926 and 1962. Partial cone collapse of the western flank during the 1926 eruption produced a disastrous debris avalanche and mudflow.

Information Contacts: JMA; AP; UPI.

Fumarolic activity, concentrated at the foot of the lava dome, continued at a constant level. The temperature of the hot lake in the same area had not changed, but varied within the lake from 34 to 84°C. The temperature of the stream that flowed from the lake remained at 30-34°.

Geologic Background. Tomariyama, also known as Golovnin, forms the southern end of Kunashir Island, across the Nemuro Strait from Hokkaido. Explosive activity has dominated in the formation of this andesitic-dacitic volcano; no lava flows are exposed. The gently sloping stratovolcano, is truncated by a 4-5 km wide caldera that formed during a series of late-Pleistocene eruptions beginning about 43,00 years ago. Several lava domes were subsequently emplaced on the caldera floor. Topographic highs outside the caldera rim define a series of lava domes extruded along a ring structure or an outer caldera. A 1 x 2.5 km caldera lake on the northern side of the inner caldera drains through a narrow breach in the western caldera wall. Solfataric activity occurs at the northern lake shore and at explosion craters (one of which contains a hot crater lake with reported temperatures from 36-100 degrees C) that cut the caldera-floor lava domes. The only known historical eruption was a minor explosion in 1848.

Information Contacts: G. Steinberg, Yuzhno-Sakhalinsk.

"Ulawun's summit crater was covered by clouds during most of November. When visible, weak-moderate white vapour emissions were observed. Vapour emission intensified during the last week of the month. November's recorded seismicity was mainly characterized by an average of 9 bands of low-amplitude, high-frequency harmonic tremor, each lasting 1-2 hours. The number and size of accompanying B-type events also increased with a maximum of 1,055 recorded on the 19th.

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

Information Contacts: I. Itikarai and P. Lowenstein, RVO.

Geologists visited Vulcano on 25 and 30 October and 1, 7, and 8 November to obtain spatial and temporal surface temperature distributions (figure 5). Fumaroles typically formed linear zones of acid steam discharge. Transects of a zone extending 40 m somewhat radially along the N rim of Gran Cratere were surveyed.

Figure 5. Apparent surface temperature profiles transverse to an elongated fumarolic zone on the N rim of Vulcano's Gran Cratere measured at 0930 (filled circles) and 1230 (open circles) on 8 November. Temperatures were recorded using a Minolta Cyclops 33 radiometer operating at [8-14 µm] wavelength. Each datum is the integrated temperature for the whole field of view of the radiometer, between 2.5 and 4.5 cm in diameter. The later survey shows warming of the downwind side of the zone by hot clouds of condensates blowing across the area. Courtesy of C. Oppenheimer and D. Rothery.

Gas temperatures (recorded by a thermocouple) were stable during the visits. The highest temperature measured was 396°C, although surface temperatures above 300°C were uncommon and highly localized (<0.01 m²) near vents. Because sublimates were unstable above about 150°C, there was a gray sublimate-free belt within 5-40 cm of the vents, flanked on either side first by white ammonium chloride, then yellow sulfur sublimates.

Further Reference. Oppenheimer, C., and Rothery, D., 1991, Infrared monitoring of volcanoes by satellite: J. of the Geological Society, London, v. 148, p. 563-569.

Geologic Background. The word volcano is derived from Vulcano stratovolcano in Italy's Aeolian Islands. Vulcano was constructed during six stages during the past 136,000 years. Two overlapping calderas, the 2.5-km-wide Caldera del Piano on the SE and the 4-km-wide Caldera della Fossa on the NW, were formed at about 100,000 and 24,000-15,000 years ago, respectively, and volcanism has migrated to the north over time. La Fossa cone, active throughout the Holocene and the location of most of the historical eruptions, occupies the 3-km-wide Caldera della Fossa at the NW end of the elongated 3 x 7 km island. The Vulcanello lava platform forms a low, roughly circular peninsula on the northern tip of Vulcano that was formed as an island beginning in 183 BCE and was connected to Vulcano in about 1550 CE. Vulcanello is capped by three pyroclastic cones and was active intermittently until the 16th century. The latest eruption from Vulcano consisted of explosive activity from the Fossa cone from 1898 to 1900.

Information Contacts: C. Oppenheimer and D. Rothery, Open Univ.

When geologists visited ... on 16 November, fine pink/red ash emerged from Hitchhiker vent, and moist acidic tephra fell near 1978 Crater. Since the last visit, on [14] October, up to 10 mm of ash had been deposited near its E rim. A new noisy fumarole (~1 m in diameter) discharged transparent blue vapor from the W edge of 1978 Crater's floor, near the location of the ephemeral vent documented 20 November 1987. Other fumaroles emitted gases at temperatures as high as 681°C. No incandescence was observed.

Geologic Background. The uninhabited Whakaari/White Island is the 2 x 2.4 km emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes. The SE side of the crater is open at sea level, with the recent activity centered about 1 km from the shore close to the rear crater wall. Volckner Rocks, sea stacks that are remnants of a lava dome, lie 5 km NW. Descriptions of volcanism since 1826 have included intermittent moderate phreatic, phreatomagmatic, and Strombolian eruptions; activity there also forms a prominent part of Maori legends. The formation of many new vents during the 19th and 20th centuries caused rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project. Explosive activity in December 2019 took place while tourists were present, resulting in many fatalities. The official government name Whakaari/White Island is a combination of the full Maori name of Te Puia o Whakaari ("The Dramatic Volcano") and White Island (referencing the constant steam plume) given by Captain James Cook in 1769.

Information Contacts: E.F. Lloyd, NZGS Rotorua.