Klyuchevskoy, located in northern Kamchatka, has had historical eruptions dating back 3,000 years characterized by major explosive and effusive eruptions from the flank craters. The current eruption began in April 2019 and has recently consisted of Strombolian activity, ash plumes, and an active lava flow descending the SE flank (BGVN 45:09). This report covers September-December 2020 and describes similar activity of Strombolian explosions, ash plumes, and active lava flows beginning in early October. Information primarily comes from weekly and daily reports from the Kamchatkan Volcanic Eruption Response Team (KVERT), the Tokyo Volcanic Ash Advisory (VAAC), and satellite data.

Activity from July through September was relatively low, with no thermal activity detected during August-September. On 2 October renewed Strombolian explosions began at 1003, ejecting ash 300-400 m above the summit and producing gas-and-steam plumes with some ash that drifted down the E flank (figure 48). That night, crater incandescence was visible. On 5 October KVERT reported that a lava flow began to effuse along the Apakhonchich chute at 0100. During 7-8 October activity intensified and was characterized by strong explosions, collapses of the sides of the drainage, strong thermal anomalies, and ash plumes that extended over 200 km SE from the crater; the lava flow remained active and continued to descend the SE flank. A Tokyo VAAC advisory issued on 7 October reported that an ash plume rose to 8.8 km altitude and drifted E and SE; during 8-9 October ash plumes rose to 5.5 km altitude and drifted as far as 270 km SE. A strong, bright, thermal anomaly was observed daily in satellite imagery, which represented the new lava flow. Strombolian explosions continued throughout the month, accompanied by gas-and-steam plumes containing some ash and an active lava flow advancing down the Apakhonchich chute on the SE flank (figure 49).

Figure 48. Photos of a gray ash plume (left) and the beginning of the lava flow (right), represented as summit crater incandescence at Klyuchevskoy on 2 October 2020 at 1030 and 2100, respectively. Photos by Y. Demyanchuk; courtesy of Volkstat.

Figure 49. Photo of Strombolian explosions at the summit of Klyuchevskoy accompanied by ash emissions and a lava flow advancing down the SE-flank Apakhonchich chute on 25 October 2020. Photo by Y. Demyanchuk (color corrected); courtesy of Volkstat.

Similar activity continued to be reported in November, consisting of Strombolian explosions, ash plumes, and a lava flow advancing down the SE flank. A bright thermal anomaly was observed in thermal satellite imagery each day during the month. During 16-19 November explosions recorded in satellite and video data showed ash plumes rising to 7.5 km altitude and drifting as far as 108 km to the NE, E, SE, and S (figure 50). On 19 November an ash cloud 65 x 70 km in size drifted 50 km SE, according to a KVERT VONA (Volcano Observatory Notice for Aviation). During 26-30 November video and satellite data showed that gas-and-steam plumes containing some ash rose to 7 km altitude and extended as far as 300 km NW and E, accompanied by persistent moderate explosive-effusive activity (figure 51).

Figure 50. Photo of the Strombolian and Vulcanian explosions at Klyuchevskoy on 18 November 2020 which produced a dense gray ash plume. Photo by Yu. Demyanchuk, IVS FEB RAS, KVERT

Figure 51. Photo of the summit of Klyuchevskoy (right foreground) showing incandescent Strombolian explosions, the lava flow descending the Apakhonchich chute on the SE flank, and a gray ash plume on 29 November 2020. Kamen volcano is the cone at back left. Photo by Y. Demyanchuk (color corrected); courtesy of Volkstat.

Moderate explosive-effusive activity continued through December; a strong daily thermal anomaly was visible in satellite images. During 2-3 December gas-and-steam plumes containing some ash rose to 7 km altitude and extended 300 km NW and E. Intermittent gas-and-ash plumes continued through the month. On 7 December KVERT reported that a new lava flow began to advance down the Kozyrevsky chute on the S flank, while the flow on the SE flank continued. Strombolian explosions in the crater ejected incandescent material up to 300 m above the crater on 8 December while hot material was deposited and traveled 350 m below the crater. A cinder cone was observed growing in the summit crater and measured 75 m tall.

Strombolian and Vulcanian activity continued during 11-25 December, accompanied by the lava flow on the S flank; according to Sentinel-2 thermal satellite images, the effusion on the SE flank had stopped around 13 December and had begun to cool. The lava flow in the Kozyrevsky chute spalled off incandescent material that continued to travel an additional 350 m. Gas-and-steam plumes that contained some ash rose to 6 km altitude and drifted up to 350 km generally E. On 24 December the Kamchatka Volcanological Station field team visited Klyuchevskoy to do work on the field stations. The scientists observed explosions that ejected incandescent material 300 m above the crater and the S-flank lava flow (figure 52). On 28 December KVERT reported that the moderate explosive-effusive eruption continued, but the intensity of the explosions had significantly decreased. The lava flow on the S flank continued to effuse, but its flow rate had already decreased.

Figure 52. Photos of a dense ash plume (left) and a color corrected photo of the lava flow advancing on the S flank (right) of Klyuchevskoy on 24 December 2020, accompanied by incandescent Strombolian explosions and a gray ash plume. Photos by Y. Demyanchuk; courtesy of Volkstat.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows frequent and strong thermal activity beginning in early October and continuing through December 2020, which is represented by the active lava flows reported in the summit crater (figure 53). According to the MODVOLC thermal algorithm, a total of 615 thermal alerts were detected at or near the summit crater from 1 October to 31 December; none were reported in September. Sentinel-2 thermal satellite imagery frequently showed the progression of the active lava flows as a strong thermal anomaly descending the SE flank during October through late November and the SW flank during December, sometimes even through weather clouds (figure 54). The thermal anomalies were commonly accompanied by a gas-and-steam plume that drifted mainly E and NE. A total of 164 VAAC advisories were issued from 2 October through 31 December.

Figure 53. Strong and frequent thermal anomalies were detected in early October at Klyuchevskoy and continued through December 2020, as recorded by the MIROVA graph (Log Radiative Power). Courtesy of MIROVA.

Figure 54. Sentinel-2 thermal satellite images showing the progression of two lava flows (bright yellow-orange) originating from the summit crater at Klyuchevskoy from 4 October through December 2020. Crater incandescence was visible on 4 October (top left), which marked the beginning of the lava flow. By 31 October (top right) the active flow had traveled down the Apakhonchich chute on the SE flank, accompanied by a gas-and-steam plume that drifted NE. On 10 November (bottom left) the lava flow continued down the SE flank; the darker black color represents parts of the lava flow that began to cool. The gas-and-steam plume drifted E from the summit. On 25 December (bottom right) a new lava flow was observed descending the SW flank, also accompanied by a strong gas-and-steam plume. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Geologic Background. Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Kamchatka Volcanological Station, Klyuchi, Kamchatka Krai, Russia (URL: http://volkstat.ru/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); 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).

Kadovar is located in the Bismark Sea offshore from the mainland of Papua New Guinea about 25 km NNE from the mouth of the Sepik River. Its first confirmed eruption began in early January 2018, characterized by ash plumes and a lava extrusion that resulted in the evacuation of around 600 residents from the N side of the island (BGVN 43:03). Activity has recently consisted of intermittent ash plumes, gas-and-steam plumes, and thermal anomalies (BGVN 45:07). Similar activity continued during this reporting period of July-December 2020 using information from the Rabaul Volcano Observatory (RVO), the Darwin Volcanic Ash Advisory Center (VAAC), and various satellite data.

RVO issued an information bulletin on 15 July reporting minor eruptive activity during 1-5 July with moderate light-gray ash emissions rising a few hundred meters above the Main Crater. On 5 July activity intensified; explosions recorded at 1652 and 1815 generated a dense dark gray ash plume that rose 1 km above the crater and drifted W. Activity subsided that day, though fluctuating summit crater incandescence was visible at night. Activity increased again during 8-10 July, characterized by explosions detected on 8 July at 2045, on 9 July at 1145 and 1400, and on 10 July at 0950 and 1125, each of which produced a dark gray ash plume that rose 1 km above the crater. According to Darwin VAAC advisories issued on 10, 16, and 30 July ash plumes were observed rising to 1.5-1.8 km altitude and drifting NW.

Gas-and-steam emissions and occasional ash plumes were observed in Sentinel-2 satellite imagery on clear weather days during August through December (figure 56). Ash plumes rose to 1.2 and 1.5 km altitude on 3 and 16 August, respectively, and drifted NW, according to Darwin VAAC advisories. On 26 August an ash plume rose to 2.1 km altitude and drifted WNW before dissipating within 1-2 hours. Similar activity was reported during September-November, according to several Darwin VAAC reports; ash plumes rose to 0.9-2.1 km altitude and drifted mainly NW. VAAC notices were issued on 12 and 22 September, 4, 7-8, and 18 October, and 18 November. A single MODVOLC alert was issued on 27 November.

Figure 56. Sentinel-2 satellite data showing a consistent gas-and-steam plume originating from the summit of Kadovar during August-December 2020 and drifting NW. On 21 September (top right) a gray plume was seen drifting several kilometers from the island to the NW. Images with “Natural color” (bands 4, 3, 2) rendering; courtesy of Sentinel Hub Playground.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows intermittent low-power anomalies during July through December 2020 (figure 57). Some of this thermal activity in the summit crater was observed in Sentinel-2 thermal satellite imagery, accompanied by gas-and-steam emissions that drifted primarily NW (figure 58).

Figure 57. Intermittent low-power thermal anomalies at Kadovar were detected in the MIROVA graph (Log Radiative Power) during July through December 2020. The island location is mislocated in the MIROVA system by about 5.5 km SE due to older mis-registered imagery; the anomalies are all on the island. Courtesy of MIROVA.

Figure 58. Sentinel-2 satellite data showing thermal anomalies at the summit of Kadovar on 23 July (top left), 7 August (top right), 1 September (bottom left), and 21 September (bottom right) 2020, occasionally accompanied by a gas-and-steam plume drifting dominantly NW. Two thermal anomalies were visible on the E rim of the summit crater on 23 July (top left) and 7 August (top right). Images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Geologic Background. The 2-km-wide island of Kadovar is the emergent summit of a Bismarck Sea stratovolcano of Holocene age. It is part of the Schouten Islands, and lies off the coast of New Guinea, about 25 km N of the mouth of the Sepik River. Prior to an eruption that began in 2018, a lava dome formed the high point of the andesitic volcano, filling an arcuate landslide scarp open to the south; submarine debris-avalanche deposits occur in that direction. Thick lava flows with columnar jointing forms low cliffs along the coast. The youthful island lacks fringing or offshore reefs. A period of heightened thermal phenomena took place in 1976. An eruption began in January 2018 that included lava effusion from vents at the summit and at the E coast.

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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).

Tinakula is located 100 km NE of the Solomon Trench at the N end of the Santa Cruz. The current eruption began in December 2018 and has recently been characterized by intermittent small thermal anomalies and gas-and-steam plumes (BGVN 45:07), which continued into the current reporting period of July-December 2020. Information primarily comes from various satellite data, as ground observations are rarely available.

Infrared MODIS satellite data processed by MIROVA (Middle InfraRed Observation of Volcanic Activity) showed a total of ten low-power thermal anomalies during July through December; one anomaly was detected in early July, two in late August, three in November, and four in December (figure 44). A single MODVOLC alert was issued on 16 December, which was visible in Sentinel-2 thermal satellite imagery on 17 December (figure 45). Though clouds often obscured the view of the summit crater, Sentinel-2 satellite imagery showed intermittent dense gas-and-steam plumes rising from the summit that drifted in different directions (figure 45).

Figure 44. Low-power thermal anomalies at Tinakula were detected intermittently during April-December 2020 by the MIROVA system (Log Radiative Power). Courtesy of MIROVA.

Figure 45. Sentinel-2 satellite imagery shows ongoing gas-and-steam plumes rising from Tinakula during July-December 2020. A small thermal anomaly (bright yellow-orange) is visible on 17 December (bottom right) using “Atmospheric penetration” (bands 12, 11, 8a) rendering. All other images using “Natural color” rendering (bands 4, 3, 2); courtesy of Sentinel Hub Playground.

Geologic Background. The small 3.5-km-wide island of Tinakula is the exposed summit of a massive stratovolcano at the NW end of the Santa Cruz islands. Similar to Stromboli, it has a breached summit crater that extends from the summit to below sea level. Landslides enlarged this scarp in 1965, creating an embayment on the NW coast. The satellitic cone of Mendana is located on the SE side. The dominantly andesitic volcano has frequently been observed in eruption since the era of Spanish exploration began in 1595. In about 1840, an explosive eruption apparently produced pyroclastic flows that swept all sides of the island, killing its inhabitants. Frequent historical eruptions have originated from a cone constructed within the large breached crater. These have left the upper flanks and the steep apron of lava flows and volcaniclastic debris within the breach unvegetated.

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).

Erebus, located on Ross Island, Antarctica, and overlooking the McMurdo research station, is the southernmost active volcano in the world. The stratovolcano, which frequently has active lava lakes in its 250-m wide summit crater, is primarily monitored by satellite.

Thermal activity during 2020 was at lower levels than in recent years. The total number of thermal pixels, as recorded by MODIS thermal emission instruments aboard NASA’s Aqua and Terra satellites, was 76 (table 6), similar to low totals recorded in 2000 and 2015.

Table 6. Number of monthly MODIS-MODVOLC thermal alert pixels recorded at Erebus during 2017-2020. See BGVN 42:06 for data from 2000 through 2016. The table was compiled using data provided by the Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System.

Sentinel-2 satellite images showed two lava lakes, with one diminishing in size during the year (figure 29). Occasionally a gas plume could be observed. The volcano was frequently covered by atmospheric clouds on days when the satellite passed over.

Figure 29. Infrared Sentinel-2 thermal images of the summit crater area of Erebus in 2020. Left: Image on 28 February 2020 showing two lava lakes in the summit crater. Right: Image on 4 October 2020 showing a single primary lake, with a much diminished second lake immediately SW. The main crater is 500 x 600 m wide. Both images are using the Atmospheric Penetration filter (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

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

Information Contacts: 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).

Sakurajima is the active volcano within the Aira Caldera in Kyushu, Japan. With several craters historically active, the current activity is concentrated in the Minamidake summit crater. Activity usually consists of small explosions producing ashfall and ballistic ejecta, with occasional pyroclastic flows and lahars. The current eruption has been ongoing since 25 March 2017, but activity has been frequent over the past few hundred years. This bulletin summarizes activity that occurred during July through December 2020 and is largely based on reports by the Japan Meteorological Agency (JMA) and satellite data. The Alert Level remains at 3 on a 5-level scale. There was no activity at the Showa crater in 2020.

The number of recorded explosive and ash eruptions for 2020 at the Minamidake crater were 221 and 432, respectively (228 and 393 the previous year). Activity declined in July and remained low through the end of December. There was ash reported on 79 days of the year, most frequently in January, and only 26 of those days during August-December (table 24 and figure 104). The largest ash plumes during this time reached 5 km at 0538 on 9 August, 3 km at 1959 on 17 December, and 3.5 km at 1614 on 29 December. The decline in events was reflected in thermal data, with a decline in energy detected during June through October (figure 105). Recorded SO₂ was generally high in the first half of the year then began to decrease from April to around 1,000 tons/day until around late May. Emissions increased after August and were extremely high in October. There were no notable changes in the geothermal areas around the craters.

Table 24. Number of monthly total eruptions, explosive eruptions, days of ashfall, and ashfall amounts from Sakurajima's Minamidake crater at Aira during 2020. Note that smaller events that did not reach the threshold of explosions or eruptions also occurred. Ashfall was measured at Kagoshima Local Meteorological Observatory; ash weights are rounded down to the nearest 0.5 g/m² and zero values indicate that less than this amount was recorded. Data courtesy of JMA.

Figure 104. The total calculated observed ash erupted from Aira's Sakurajima volcano. Top: Annual values from January 1980 to November 2020. Bottom: the monthly values during January 2009 through November 2020. Courtesy of JMA (January 2021 Sakurajima monthly report).

Figure 105. Thermal data detected at Aira's Sakurajima volcano during February through December 2020 by the MIROVA thermal detection system that uses MODIS satellite middle infrared data. There was a decline in activity during June-September, with energy emitted in November-December remaining lower than earlier in the year. Courtesy of MIROVA.

During July "very small" explosions were observed on the 1st, 2nd, and 8th, with the last explosion producing a plume up to 600 m above the crater. These events didn't generate enough of an ash plume to be counted as either a quiet or explosive eruption, leaving no eruptions reported during July. No incandescence was observed at the crater since 3 June. Field surveys on 2, 13, and 21 July detected 600 to 1,300 tons of SO₂ per day.

An explosion occurred at 0538 on 9 August, producing an ash plume to 5 km above the crater, dispersing NE (figure 106). This was the largest explosion observed through the Sakurajima surveillance camera since 8 November 2019. Ashfall was reported in Kagoshima City, Aira City, Kirishima City, Yusui Town, and parts of Miyazaki and Kumamoto Prefectures. Ashfall measured to be 300 g/m² in Shirahama on Sakurajima island (figure 106). No ballistic ejecta were observed due to clouds at the summit, but very small explosions were occasionally observed afterwards.

Figure 106. An explosion at Aira's Sakurajima volcano at 0538 on 9 August 2020 (top, taken from the Ushine surveillance camera in Kagoshima) produced ashfall in Shirahama on Sakurajima (bottom). The plume contains a white steam-rich portion on the left, and a darker relatively ash-rich portion on the right. Images courtesy of JMA (Sakurajima August 2020 monthly report).

A small lake or pond in the eastern Minamidake crater was first observed in PlanetScope satellite imagery on 1 August (through light cloud cover) and intermittently observed when the summit was clear through to the 22nd (figure 107). The summit is obscured by cloud cover in many images before this date. An observation flight on 14 August confirmed weak gas emission from the inner southern wall of the Showa crater, and a 200-m-high gas plume rose from the Minamidake crater, dispersing SE (figure 108). Thermal imaging showed elevated temperatures within the crater. SO₂ measurements were conducted during field surveys on the 3rd, 13th, 24th and 31st, with amounts similar to July at 600 to 1,400 tons per day.

Figure 107. A crater lake is visible in the eastern part of the Minamidake summit crater at Aira's Sakurajima volcano on 5, 18, and 22 August 2020. Four-band PlanetScope satellite images courtesy of Planet Labs.

Figure 108. Gas emissions from the Minamidake and Showa craters at Sakurajima in the Aira caldera on 14 August 2020. Photos taken from the from Kagoshima Prefecture disaster prevention helicopter at 1510-1513. Courtesy of JMA (Sakurajima August monthly report).

Activity continued at Minamidake crater throughout September with seven observed eruptions sending plumes up to 1.7 km above the crater, and additional smaller events (figure 109). An ash plume reached 1 km at 0810 on the 15th. Ashfall was reported on four days through the month with a total of 2 g/m² measured. Incandescence was observed in nighttime surveillance cameras from the 9-10th for the first time since 2 June, then continued through the month. There was an increase in detected SO₂, with measurements on the 11th and 25th ranging from 1,300 to 2,000 tons per day.

Figure 109. Examples of activity at Aira's Sakurajima volcano on 4, 10, and 14 September 2020. The images show an ash plume reaching 1.7 km above the crater (top left), a gas-and-steam plume (bottom left), and incandescence at night visible in a gas-and steam plume (right). Images courtesy of JMA (September 2020 Sakurajima monthly report).

During October two eruptions and occasional smaller events occurred at the Minamidake crater and there were six days where ashfall occurred at the Kagoshima Local Meteorology Observatory (including remobilized ash). An ash plume rose to 1.7 km above the crater at 1635 on the 3rd and 1 km on the 30th. Incandescence was observed at night through the month (figure 110). Gas surveys on the 20th, 21st, 23rd, and 26th recorded 2,200-6,600 tons of SO₂ per day, which are high to very high levels and a large increase compared to previous months. An observation flight on the 13th confirmed lava in the bottom of the Minamidake crater (figure 111). Gas emissions were rising to 300 m above the Minamidake crater, but no emissions were observed at the Showa crater (figure 112).

Figure 110. Gas emissions and incandescence seen above the Sakurajima Minamidake crater at Aira on 10 and 23 October 2020. Courtesy of JMA (Sakurajima October 2020 monthly report).

Figure 111. Lava was observed on the floor of the Minamidake summit crater at Aira's Sakurajima volcano on 13 October 2020, indicated by the yellow dashed line. Courtesy of JMA (Sakurajima October 2020 monthly report).

Figure 112. An observation flight on 13 October 2020 noted gas emissions up to 300 m above the Minamidake crater at Sakurajima, but no emissions from the Showa crater. Courtesy of JMA (Sakurajima October 2020 monthly report).

Eight ash eruptions and six explosive eruptions occurred during November as well as additional very small events. At 1551 on the 3rd an ash plume reached 1.8 km above the crater and an event at 1335 on the 10th produced large ballistic ejecta out to 600-900 m from the crater (figure 113). Ashfall was reported on 11 days this month (including remobilized ash). Incandescence was observed at night and elevated temperatures in the Minamidake crater were detected by satellites (figure 114). Detected SO₂ was lower this month, with amounts ranging between 1,300 and 2,200 on the 9th, 18th and 24th.

Figure 113. Ash plumes at Aira's Sakurajima volcano rise from the Minamidake crater in November 2020. Left: an ash plume rose to 1.8 km above the crater at 1551 on the 3rd and drifted SE. on 3 (left) and 10 (right) November 2020. Right: An explosion at 1335 on the 10th produced an ash plume to 1.6 km above the crater and ballistic ejecta out to 600-900 m, with one projectile indicated by the red arrow. Courtesy of JMA (Sakurajima November 2020 monthly report).

Figure 114. An ash plume drifts SE from the Minamidake crater at Aira's Sakurajima volcano on 8 November 2020. This thermal image also shows elevated temperatures in the crater. Sentinel-2 False color (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

During December there were 25 ash eruptions and 18 explosive eruptions recorded, with large ballistic ejecta reaching 1.3-1.7 km from the crater (figure 115). An explosion on the 2nd sent an ash plume up to 1 km above the crater and ballistic ejecta out to 1-1.3 km, and an event at 0404 on the 12th produced incandescent ballistic ejecta reached out to 1.3-1.7 km from the crater. At 1959 on 17 December an explosion generated an ash plume up to 3 km above the crater and ejecta out to 1.3-1.7 km. A photograph that day showed an ash plume with volcanic lightning and incandescent ejecta impacting around the crater (figure 116). On the 18th an ash plume reached 1.8 km and ejecta impacted out to 1-1.3 km. An event at 1614 on the 29th produced an ash plume reaching 3.5 km above the crater. Elevated temperatures within the Minamidake crater and plumes were observed intermittently in satellite data through the month (figure 117). This month there were four days where ashfall was recorded with a total of 14 g/m². Incandescence continued to be observed at night through the month. High levels of gas emission continued, with field surveys on 2nd, 7th, 16th and 21st recording values ranging from 1,500 to 2,900 tons per day at the Observatory located 11 km SW.

Figure 115. Explosions at Aira's Sakurajima volcano from the Minamidake summit crater in December 2020. Top: An explosion recorded at 0404 on the 12th produced incandescent ballistic ejecta out to 1.3-1.7 km from the crater, with an example indicated in the red circle. Bottom: An explosion at 1614 on the 29th produced an ash plume up to 3.5 km above the crater, and ballistic ejecta out to 1.3-1.7 km. Courtesy of JMA (top, from Sakurajima December 2020 monthly report) and Volcano Time Lapse (bottom).

Figure 116. An explosion from Sakurajima's Minamidake crater at Aira produced an ash plume with volcanic lightning on 17 December 2020. Photograph taken from Tarumizu city, courtesy of Kyodo/via Reuters.

Figure 117. Activity at Aira's Sakurajima volcano during December 2020. Top: Sentinel-2 thermal satellite image showing a diffuse gas-and-steam plume dispersing to the SE with elevated temperatures within the Minamidake summit crater on the 22nd. PlanetScope satellite image showing an ash plume dispersing between the N and E on the 26th. Sentinel-2 False color (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground. PlanetScope satellite image courtesy of Planet Labs.

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: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); Kyodo/via REUTERS, "Photos of the Week" (URL: https://www.reuters.com/news/picture/photos-of-the-week-idUSRTX8HYLR); Volcano Time-Lapse, YouTube (URL: https://www.youtube.com/watch?v=jTgd152oGVo).

Japan’s Nishinoshima volcano, located about 1,000 km S of Tokyo in the Ogasawara Arc, erupted above sea level in November 2013 after 40 years of dormancy. Activity lasted for two years followed by two brief eruptions in 2017 and 2018. The next eruption, from early December 2019 through August 2020, included ash plumes, incandescent ejecta, and lava flows; it produced a large pyroclastic cone with a wide summit crater and extensive lava flows that significantly enlarged the island. This report covers the end of the eruption and cooling during September 2020-January 2021. Information is provided primarily from Japan Meteorological Agency (JMA) monthly reports and the Japan Coast Guard (JCG), which makes regular observation overflights.

Ash emissions were last reported on 27 August 2020. The very high levels of thermal energy from numerous lava flows, ash, and incandescent tephra that peaked during early July decreased significantly during August and September. Continued cooling of the fresh lava and the summit crater lasted into early January 2021 (figure 107). Monthly overflights and observations by scientists confirmed areas of steam emissions at the summit and on the flanks and discolored water around the island, but no eruptive activity.

Figure 107. High levels of thermal activity at Nishinoshima during June and July 2020 resulted from extensive lava flows and explosions of incandescent tephra. Although the last ash emission was reported on 27 August 2020, cooling of new material lasted into early January 2021. The MIROVA log radiative power graph of thermal activity covers the year ending on 3 February 2021. Courtesy of MIROVA.

Thermal activity declined significantly at Nishinoshima during August 2020 (BGVN 45:09). Only two days had two MODVOLC alerts (11 and 30), and four other days (18, 20, 21, 29) had single alerts. During JCG overflights on 19 and 23 August there were no ash emissions or lava flows observed, although steam plumes rose over 2 km above the summit crater during both visits. The last ash emission was reported by the Tokyo VAAC on 27 August 2020. No eruptive activity was observed by JMA during an overflight on 5 September, but steam plumes were rising from the summit crater (figure 108). No significant changes were observed in the shape of the pyroclastic cone or the coastline. Yellowish brown discolored water appeared around the western half of the island, and high temperature was still measured on the inner wall of the crater. Faint traces of SO₂ plumes were present in satellite images in early September; the last plume identified was on 18 September. Six days with single MODVOLC alerts were recorded during 3-19 September, and the final thermal alert appeared on 1 October 2020.

Figure 108. No eruptive activity was observed during a JMA overflight of Nishinoshima on 5 September 2020, but steam rose from numerous places within the enlarged summit crater (inset). Courtesy of JMA and JCG (Monthly report of activity at Nishinoshima, September 2020).

Steam plumes and high temperatures were noted at the summit crater on 28 October, and brown discolored water was present around the S coast of the island (figure 109), but there were no other signs of volcanic activity. Observations from the sea conducted on 2 November 2020 by researchers aboard the Maritime Meteorological Observatory marine weather observation ship "Ryofu Maru" confirmed there was no ongoing eruptive activity. In addition to steam plumes at the summit, they also noted steam rising from multiple cracks on the cooling surface of the lava flow area on the N side of the pyroclastic cone (figure 110). Only steam plumes from inside the summit crater were observed during an overflight on 24 November.

Figure 109. On a JCG overflight above Nishinoshima on 28 October 2020 there were no signs of eruptive activity; steam plumes were present in the summit crater and brown discolored water was visible around the S coast of the island. Courtesy of JMA and JCG (Monthly report of activity at Nishinoshima, October 2020).

Figure 110. Observations of Nishinoshima by staff aboard the Maritime Meteorological Observatory ship "Ryofu Maru" on 2 November 2020 showed a steam plume rising from the lava flow area on the N side of the pyroclastic cone (arrow) and minor steam above the cone. Courtesy of JMA (Monthly report of activity at Nishinoshima, November 2020).

JMA reduced the warning area around the crater on 18 December 2020 from 2.5 to 1.5 km due to decreased activity. On 7 December a steam plume rose from the inner wall of the summit crater and thermal imaging indicated the area was still hot. Brown discolored water was observed on the SE and SW coasts. Researchers aboard a ship from the Earthquake Research Institute at the University of Tokyo and the Marine Research and Development Organization reported continued steam plumes in the summit crater, around the lava flows on the N flank, and along the S coast during 15-29 December (figure 111). Steam plumes and elevated temperatures were still measured inside the summit crater during an overflight by the Japan Coast Guard on 25 January 2021, and discolored water persisted on the SE and SW coasts; there was no evidence of eruptive activity.

Figure 111. Observations of Nishinoshima from the sea by researchers from the Earthquake Research Institute (University of Tokyo) and the Marine Research and Development Organization, which took place from 15-29 December 2020, showed fumarolic acitivity not only inside the summit crater, but also in the lava flow area on the N side of the pyroclastic cone (left, 20 December) and in places along the southern coast (right, 23 December). (Monthly report of activity at Nishinoshima, December 2020).

Geologic Background. The small island of Nishinoshima was enlarged when several new islands coalesced during an eruption in 1973-74. Another eruption that began offshore in 2013 completely covered the previous exposed surface and enlarged the island again. Water discoloration has been observed on several occasions since. The island is the summit of a massive submarine volcano that has prominent satellitic peaks to the S, W, and NE. The summit of the southern cone rises to within 214 m of the sea surface 9 km SSE.

Information Contacts: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Japan Coast Guard (JCG) Volcano Database, Hydrographic and Oceanographic Department, 3-1-1, Kasumigaseki, Chiyoda-ku, Tokyo 100-8932, Japan (URL: http://www.kaiho.mlit.go.jp/info/kouhou/h29/index.html); Volcano Research Center (VRC-ERI), Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan (URL: http://www.eri.u-tokyo.ac.jp/topics/ASAMA2004/index-e.html); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA 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/).

Nyiragongo is a stratovolcano in the DR Congo with a deep summit crater containing a lava lake and a small active cone. During June 2018-May 2020, the volcano exhibited strong thermal signals primarily due to the lava lake, along with incandescence, seismicity, and gas-and-steam plumes (BGVN 44:05, 44:12, 45:06). The volcano is monitored by the Observatoire Volcanologique de Goma (OVG). This report summarizes activity during June-November 2020, based on satellite data.

Infrared MODIS satellite data showed almost daily strong thermal activity during June-November 2020 from MIROVA (Middle InfraRed Observation of Volcanic Activity), consistent with a large lava lake. Numerous hotspots were also identified every month by MODVOLC. Although clouds frequently obscured the view from space, a clear Sentinel-2 image in early June showed a gas-and-steam plume as well as a strong thermal anomaly (figure 76).

Figure 76. Sentinel-2 satellite imagery of Nyiragongo on 1 June 2020. A gas-and-steam is visible in the natural color image (bands 4, 3, 2) rising from a pit in the center of the crater (left), while the false color image (bands 12, 11, 4) reveals a strong thermal signal from a lava lake (right). Courtesy of Sentinel Hub Playground.

During the first half of June 2020, OVG reported that SO₂ levels had decreased compared to levels in May (7,000 tons/day); during the second half of June the SO₂ flux began to increase again. High levels of sulfur dioxide were recorded almost every day in the region above or near the volcano by the TROPOspheric Monitoring Instrument (TROPOMI) aboard the Copernicus Sentinel-5 Precursor satellite (figure 77). According to OVG, SO₂ flux ranged from 819-5,819 tons/day during June. The number of days with a high SO₂ flux decreased somewhat in July and August, with high levels recorded during about half of the days. The volume of SO₂ emissions slightly increased in early July, based on data from the DOAS station in Rusayo, measuring 6,787 tons/day on 8 July (the highest value reported during this reporting period), and then declined to 509 tons/day by 20 July. The SO₂ flux continued to gradually decline, with high values of 5,153 tons/day in August and 4,468 tons/day in September. The number of days with high SO₂ decreased further in September and October but returned to about half of the days in November.

Figure 77. TROPOMI image of SO2 plume on 27 June 2020 in the Nyiragongo-Nyamulagira area. The plume drifted SSE. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

During 12-13 July a multidisciplinary team of OVG scientists visited the volcano to take measurements of the crater using a TCRM1102 Plus2 laser. They noted that the crater had expanded by 47.3 mm in the SW area, due to the rise in the lava lake level since early 2020. The OVG team took photos of the small cone in the lava lake that has been active since 2014, recently characterized by white gas-and-steam emissions (figure 78). OVG noted that the active lava lake had subsided roughly 20 m (figure78).

Figure 78. Photos (color corrected) of the crater at Nyiragongo showing the small active cone generating gas-and-steam emissions (left) and the active lava lake also characterized by white gas-and-steam emissions on 12 July 2020 (right). Courtesy of OVG (Rapport OVG Juillet 2020).

Geologic Background. One of Africa's most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. The steep slopes of a stratovolcano contrast to the low profile of its neighboring shield volcano, Nyamuragira. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

Information Contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; 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 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/).

Whakaari/White Island, located in the Bay of Plenty 50 km offshore of North Island, has been New Zealand’s most active volcano since 1976. Activity has been previously characterized by phreatic activity, explosions, and ash emissions (BGVN 42:05). The most recent eruption occurred on 9 December 2019, which consisted of an explosion that generated an ash plume and pyroclastic surge that affected the entire crater area, resulting in 21 fatalities and many injuries (BGVN 45:02). This report updates information from February through November 2020, which includes dominantly gas-and-steam emissions along with elevated surface temperatures, using reports from the New Zealand GeoNet Project, the Wellington Volcanic Ash Advisory Centre (VAAC), and satellite data.

Activity at Whakaari/White Island has declined and has been dominated by white gas-and-steam emissions during the reporting period; no explosive eruptive activity has been detected since 9 December 2019. During February through 22 June, the Volcanic Activity Level (VAL) remained at a 2 (moderate to heightened volcanic unrest) and the Aviation Color Code was Yellow. GeoNet reported that satellite data showed some subsidence along the W wall of the Main Crater and near the 1914 landslide scarp, though the rate had reduced compared to previous months. Thermal infrared data indicated that the fumarolic gases and five lobes of lava that were first observed in early January 2020 in the Main Crater were 550-570°C on 4 February and 660°C on 19 February. A small pond of water had begun to form in the vent area and exhibited small-scale gas-and-steam-driven water jetting, similar to the activity during September-December 2019. Gas data showed a steady decline in SO₂ and CO₂ levels, though overall they were still slightly elevated.

Similar activity was reported in March and April; the temperatures of the fumaroles and lava in the Main Crater were 746°C on 10 March, the highest recorded temperature to date. SO₂ and CO₂ gas emissions remained elevated, though had overall decreased since December 2019. Small-scale water jetting continued to be observed in the vent area. During April, public reports mentioned heightened gas-and-steam activity, but no eruptions were detected. A GeoNet report issued on 16 April stated that high temperatures were apparent in the vent area at night.

Whakaari remained at an elevated state of unrest during May, consisting of dominantly gas-and-steam emissions. Monitoring flights noted that SO₂ and CO₂ emissions had increased briefly during 20-27 May. On 20 May, the lava lobes remained hot, with temperatures around 500°C; a nighttime glow from the gas emissions surrounding the lava was visible in webcam images. Tremor levels remained low with occasional slightly elevated episodes, which included some shallow-source volcanic earthquakes. Satellite-based measurements recorded several centimeters of subsidence in the ground around the active vent area since December 2019. During a gas observation flight on 28 May there was a short-lived gas pulse, accompanied by an increase in SO₂ and CO₂ emissions, and minor inflation in the vent area (figure 96).

Figure 96. Photo of a strong gas-and-steam plume rising above Whakaari/White Island on 28 May 2020. Courtesy of GeoNet.

An observation flight made on 3 June reported a decline in gas flux compared to the measurements made on 28 May. Thermal infrared images taken during the flight showed that the lava lobes were still hot, at 450°C, and continued to generate incandescence that was visible at night in webcams. On 16 June the VAL was lowered to 1 (minor volcanic unrest) and on 22 June the Aviation Color Code had decreased to Green.

Minor volcanic unrest continued in July; the level of volcanic tremors has remained generally low, with the exception of two short bursts of moderate volcanic tremors in at the beginning of the month. Temperatures in the active vents remained high (540°C) and volcanic gases persisted at moderate rate, similar to those measured since May, according to an observation flight made during the week of 30 July. Subsidence continued to be observed in the active vent area, as well as along the main crater wall, S and W of the active vents. Recent rainfall has created small ponds of water on the crater floor, though they did not infiltrate the vent areas.

Gas-and-steam emissions persisted during August through October at relatively high rates (figures 97 and 98). A short episode of moderate volcanic tremor was detected in early August, but otherwise seismicity remained low. Updated temperatures of the active vent area were 440°C on 15 September, which had decreased 100°C since July. Rain continued to collect at the crater floor, forming a small lake; minor areas of gas-and-steam emissions can be seen in this lake. Ongoing subsidence was observed on the Main Crater wall and S and W of the 2019 active vents.

Figure 97. Photo of an observation flight over Whakaari/White Island on 8 September 2020 showing white gas-and-steam emissions from the vent area. Photo courtesy of Brad Scott, GeoNet.

Figure 98. Image of Whakaari/White Island from Whakatane in the North Island of New Zealand showing a white gas-and-steam plume on 26 October 2020. Courtesy of GeoNet.

Activity during November was primarily characterized by persistent, moderate-to-large gas-and-steam plumes that drifted downwind for several kilometers but did not reach the mainland. The SO₂ flux was 618 tons/day and the CO₂ flux was 2,390 tons/day. New observations on 11 November noted some occasional ash deposits on the webcams in conjunction with mainland reports of a darker than usual plume (figure 99). Satellite images provided by MetService, courtesy of the Japan Meteorological Agency, confirmed the ash emission, but later images showed little to no apparent ash; GNS confirmed that no eruptive activity had occurred. Initial analyses indicated that the ash originated from loose material around the vent was being entrained into the gas-and-steam plumes. Observations from an overflight on 12 November showed that there was no substantial change in the location and size of the active vents; rainfall continued to collect on the floor of the 1978/90 Crater, reforming the shallow lake. A small sequence of earthquakes was detected close to the volcano with several episodes of slightly increased volcanic tremors.

During 12-14 November the Wellington VAAC issued multiple advisories noting gas, steam, and ash plumes that rose to 1.5-1.8 km altitude and drifted E and SE, based on satellite data, reports from pilots, and reports from GeoNet. As a result, the VAL was increased to 2 and the Aviation Color Code was raised to Yellow. Scientists on another observation flight on 16 November reported that small amounts of ash continued to be present in gas-and-steam emissions, though laboratory analyses showed that this ash was resuspended material and not from new eruptive or magmatic activity. The SO₂ and CO₂ flux remained above background levels but were slightly lower than the previous week’s measurements: 710 tons/day and 1,937 tons/day. Seismicity was similar to the previous week, characterized by a sequence of small earthquakes, a larger than normal volcanic earthquake located near the volcano, and ongoing low-level volcanic tremors. During 16-17 November plumes with resuspended ash were observed rising to 460 m altitude, drifting E and NE, according to a VAAC advisory (figure 99). During 20-24 November gas-and-steam emissions that contained a minor amount of resuspended ash rose to 1.2 km altitude and drifted in multiple directions, based on webcam and satellite images and information from GeoNet.

Figure 99. Left: Photo of a gas observation flight over Whakaari/White Island on 11 November 2020 showing some dark particles in the gas-and-steam plumes, which were deposited on some webcams. Photo has been color corrected and straightened. Courtesy of GeoNet. Right: Photo showing gas, steam, and ash emissions rising above the 2019 Main Crater area on 16 November 2020. Courtesy of GNS Science (17 November 2020 report).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows a total of eleven low-power thermal anomalies during January to late March 2020; a single weak thermal anomaly was detected in early July (figure 100). The elevated surface temperatures during February-May 2020 were detected in Sentinel-2 thermal satellite images in the Main Crater area, occasionally accompanied by gas-and-steam emissions (figure 101). Persistent white gas-and-steam emissions rising above the Main Crater area were observed in satellite imagery on clear weather days and drifting in multiple directions (figure 102). The small lake that had formed due to rainfall was also visible to the E of the active vents.

Figure 100. Low-power, infrequent thermal activity at Whakaari/White Island was detected during January through late March 2020, as reflected in the MIROVA data (Log Radiative Power). A single thermal anomaly was shown in early July. Courtesy of MIROVA.

Figure 101. Sentinel-2 thermal satellite images in the Main Crater area of Whakaari/White Island show residual elevated temperatures from the December 2019 eruption, accompanied by gas-and-steam emissions and drifting in different directions during February-May 2020. Images using “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Figure 102. Sentinel-2 images showing persistent white gas-and-steam plumes rising from Main Crater area of Whakaari/White Island during March-November 2020 and drifting in multiple directions. A small pond of water (light blue-green) is visible in the vent area to the E of the plumes. On 11 November (bottom right), the color of the plume is gray and contains a small amount of ash. Images using “Natural color” rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

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: New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/); GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Wellington Volcanic Ash Advisory Centre (VAAC), Meteorological Service of New Zealand Ltd (MetService), PO Box 722, Wellington, New Zealand (URL: http://www.metservice.com/vaac/, http://www.ssd.noaa.gov/VAAC/OTH/NZ/messages.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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Brad Scott, GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: https://twitter.com/Eruptn).

Kerinci, located in Sumatra, Indonesia, has had numerous explosive eruptions since 1838, with more recent activity characterized by gas-and-steam and ash plumes. The current eruptive episode began in April 2018 and has recently consisted of intermittent brown ash emissions and white gas-and-steam emissions (BGVN 45:07); similar activity continued from June through November 2020. Information primarily comes from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, the Darwin Volcanic Ash Advisory Centre (VAAC), and satellite data.

Activity has been characterized by dominantly white and brown gas-and-steam emissions and occasional ash plumes, according to PVMBG. Near daily gas-and-steam emissions were observed rising 50-6,400 m above the crater throughout the reporting period: beginning in late July and continuing intermittently though November. Sentinel-2 satellite imagery showed frequent brown emissions rising above the summit crater at varying intensities and drifting in different directions from July to November (figure 21).

Figure 21. Sentinel-2 satellite imagery of brown emissions at Kerinci from July through November 2020 drifting in multiple directions. On 27 July (top left) the brown emissions drifted SW. On 31 August (top right) the brown emissions drifted W. On 2 September (bottom left) slightly weaker brown emissions drifting W. On 4 November (bottom right) weak brown emissions mostly remained within the crater, some of which drifted E. Images using “Natural Color” rendering (bands 4, 3, 2), courtesy of Sentinel Hub Playground.

During June through July the only activity reported by PVMBG consisted of white gas-and-steam emissions and brown emissions. On 4 June white gas-and-steam emissions rose to a maximum height of 6.4 km above the crater. White-and-brown emissions rose to a maximum height of 700 m above the crater on 2 June and 28 July.

Continuous white-and-brown gas-and-steam emissions were reported in August that rose 50-1,000 m above the crater. The number of ash plumes reported during this month increased compared to the previous months. In a Volcano Observatory Notice for Aviation (VONA) issued on 7 August at 1024, PVMBG reported an ash plume that rose 600 m above the crater and drifted E, SE, and NE. In addition, the Darwin VAAC released two notices that described continuous minor ash emissions rising to 4.3 km altitude and drifting E and NE. On 9 August an ash plume rose 600 m above the crater and drifted ENE at 1140. An ash plume was observed rising to a maximum of 1 km above the crater, drifting E, SE, and NE on 12 August at 1602, according to a PVMBG VONA and Darwin VAAC advisory. The following day, brown emissions rose to a maximum of 1 km above the crater and were accompanied by a 600-m-high ash plume that drifted ENE at 1225. Ground observers on 15 August reported an eruption column that rose to 4.6 km altitude; PVMBG described brown ash emissions up to 800 m above the crater drifting NW at 0731 (figure 22). During 20-21 August pilots reported an ash plume rising 150-770 m above the crater drifting NE and SW, respectively.

Figure 22. Webcam image of an ash plume rising above Kerinci on 15 August 2020. Courtesy of MAGMA Indonesia.

Activity in September had decreased slightly compared to the previous month, characterized by only white-and-brown gas-and-steam emissions that rose 50-300 m above the crater; solely brown emissions were observed on 30 September and rose 50-100 m above the crater. This low level of activity persisted into October, with white gas-and-steam emissions to 50-200 m above the crater and brown emissions rising 50-300 m above the crater. On 16 October PVMBG released a VONA at 0340 that reported an ash plume rising 687 m above the crater and drifting NE. On 17 October white, brown, and black ash plumes that rose 100-800 m above the crater drifted NE according to both PVMBG and a Darwin VAAC advisory (figure 23). During 18-19 October white, brown, and black ash emissions rose up to 400 m above the crater and drifted NE and E.

Figure 23. Webcam image of a brown ash emission from Kerinci on 17 October 2020. Courtesy of MAGMA Indonesia.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Suwanosejima, an andesitic stratovolcano in Japan's northern Ryukyu Islands, was intermittently active for much of the 20th century, producing ash plumes, Strombolian explosions, and ashfall. Continuous activity since October 2004 has included intermittent explosions which generate ash plumes that rise hundreds of meters above the summit to altitudes between 1 and 3 km. Incandescence is often observed at night and ejecta periodically reaches over a kilometer from the summit. Ashfall is usually noted several times each month in the nearby community on the SW flank of the island. Ongoing activity for the second half of 2020, which includes significantly increased activity in December, is covered in this report with information provided by the Japan Meteorological Agency (JMA), the Tokyo Volcanic Ash Advisory Center (VAAC), and several sources of satellite data.

A steady increase in activity was reported during July-December 2020. The number of explosions recorded increased each month from only six during July to 460 during December. The energy of the explosions increased as well; ejecta was reported 600 m from the crater during August, but a large bomb reached 1.3 km from the crater at the end of December. After an increased period of explosions late in December, JMA raised the Alert Level from 2 to 3 on a 5-level scale. The MIROVA graph of thermal activity indicated intermittent anomalies from July through December 2020, with a pulse of activity in the second half of December (figure 48).

Figure 48. MIROVA thermal activity for Suwanosejima for the period from 3 February through December 2020 shows pulses of activity in February and April, with intermittent anomalies until another period of frequent stronger activity in December. Courtesy of MIROVA.

Six explosions were recorded during July 2020, compared with only one during June. According to JMA, the tallest plume rose 2,000 m above the crater rim. Incandescent ejecta was occasionally observed at night. The Tokyo VAAC reported a number of ash plumes that rose to 1.2-2.7 km altitude and drifted NW and W during the second half of the month (figure 49). Activity increased during August 2020 when thirteen explosions were reported. The Tokyo VAAC reported a few ash plumes during 1-6 August that rose to 1.8-2.4 km altitude and drifted NW; a larger pulse of activity during 18-22 August produced plumes that rose to altitudes ranging from 1.8 to over 2.7 km. Ashfall was reported on 19 and 20 August in the village located 4 km SSW of the crater; incandescence was visible at the summit and ash plumes drifted SW in satellite imagery on 19 August (figure 50). A MODVOLC thermal alert was issued on 19 August. On 21 August a large bomb was ejected 600 m from the Otake crater in an explosion early in the day; later that afternoon, an ash plume rose to more than 2,000 m above the crater rim. During 19-22 August, SO₂ emissions were recorded each day by the TROPOMI instrument on the Sentinel-5P satellite (figure 51).

Figure 49. An ash emission at Suwanosejima rose to 2.7 km altitude and drifted NW on 27 July 2020. Courtesy of JMA (Volcanic activity commentary material on Suwanosejima, July 2020).

Figure 50. Ash drifted SW from the summit crater of Suwanosejima on 19 August 2020 and a bright thermal anomaly was present at the summit. Residents of the village 4 km SW reported ashfall that day and the next. Courtesy of Sentinel Hub Playground.

Figure 51. A period of increased activity at Suwanosejima during 19-22 August 2020 produced SO2 emissions that were measured by the TROPOMI instrument on the Sentinel-5P satellite. Nishinoshima, was also producing significant SO2 at the same time. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Thirteen explosions were recorded during September 2020, with the highest ash plumes reaching 2,000 m above the crater rim, and bombs falling 400 m from the crater. Ashfall was recorded on 20 September in the community located 4 km SSW. The Tokyo VAAC reported intermittent ash plumes during the month that rose to 1.2-2.1 km altitude and drifted in several directions. Incandescence was frequently observed at night (figure 52). Explosive activity increased during October with 22 explosions recorded. Ash plumes rose over 2,000 m above the crater rim, and bombs reached 700 m from the crater. Steam plumes rose 2,300 m above the crater rim. Ashfall and loud noises were confirmed several times between 2 and 14 October in the nearby village. A MODVOLC thermal alert was issued on 6 October. The Tokyo VAAC reported multiple ash plumes throughout the month; they usually rose to 1.5-2.1 km altitude and drifted in many directions. The plume on 28 October rose to over 2.7 km altitude and was stationary.

Figure 52. Incandescence at night and ash emissions were observed multiple times at Suwanosejima during September and October 2020 including on 21 and 26 September (top) and 29 October 2020. Courtesy of JMA (Volcanic activity commentary material on Suwanosejima, September and October 2020).

Frequent explosions occurred during November 2020, with a sharp increase in the number of explosions to 105 events compared with October. Ash plumes rose to 1,800 m above the crater rim and bombs were ejected 700 m. Occasional ashfall and loud noises were reported from the nearby community throughout the month. Scientists measured no specific changes to the surface temperature around the volcano during an overflight early on 5 November compared with the previous year. At 0818 on 5 November a small ash explosion at the summit crater was photographed by the crew during an observation flight (figure 53). On 12 and 13 November, incandescent ejecta fell 600 m from the crater and ash emissions rose 1,500 m above the crater rim (figure 54).

Figure 53. A minor explosion produced a small ash plume at Suwanosejima during an overflight by JMA on the morning of 5 November 2020. The thermal activity was concentrated at the base of the explosion (inset). Image taken from off the E coast. Courtesy of JMA (Volcanic activity commentary material on Suwanosejima, November 2020).

Figure 54. On 12 and 13 November 2020 incandescent ejecta from Suwanosejima reached 600 m from the crater (top) and ash emissions rose 1,500 m above the crater rim (bottom). Courtesy of JMA (Volcanic activity commentary material on Suwanosejima, November 2020).

During December 2020 there were 460 explosions reported, a significant increase from the previous months. Ash plumes reached 1,800 m above the summit. Three MODVOLC thermal alerts were issued on 25 December and two were issued the next day. The number of explosions increased substantially at the Otake crater between 21 and 29 December, and early on 28 December a large bomb was ejected to 1.3 km SE of the crater (figure 55). A second explosion a few hours later ejected another bomb 1.1 km SE. An overflight later that day confirmed the explosion, and ash emissions were still visible (figure 56), although cloudy weather prevented views of the crater. Ashfall was noted and loud sounds heard in the nearby village. A summary graph of observations throughout 2020 indicated that activity was high from January through May, quieter during June, and then increased again from July through the end of the year (figure 57).

Figure 55. Early on 28 December 2020 a large explosion at Suwanosejima sent a volcanic bomb 1.3 km SE from the summit (bright spot on left flank in large photo). Thermal imaging taken the same day showed the heat at the eruption site and multiple fragments of warm ejecta scattered around the crater area (inset). Courtesy of JMA (Volcanic activity commentary material on Suwanosejima, December 2020).

Figure 56. Ash emissions were still visible midday on 28 December 2020 at Suwanosejima during a helicopter overflight by the 10th Regional Coast Guard. Image taken from the SW flank of the volcano. Two large explosions earlier in the day had sent ejecta more than a kilometer from the crater. Courtesy of JMA (Volcanic activity commentary material on Suwanosejima, December 2020).

Figure 57. Activity summary for Suwanosejima for January-December 2020 when 764 explosions were recorded. Black bars represent the height of steam, gas, or ash plumes in meters above the crater rim, gray volcano icons represent explosions, usually accompanied by an ash plume, red icons represent large explosions with ash plumes, orange diamonds indicate incandescence observed in webcams. Courtesy of JMA (Suwanosejima volcanic activity annual report, 2020).

Geologic Background. The 8-km-long, spindle-shaped island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. The summit is truncated by a large breached crater extending to the sea on the east flank that was formed by edifice collapse. Suwanosejima, one of Japan's most frequently active volcanoes, was in a state of intermittent strombolian activity from Otake, the NE summit crater, that began in 1949 and lasted until 1996, after which periods of inactivity lengthened. The largest historical eruption took place in 1813-14, when thick scoria deposits blanketed residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed forming a large debris avalanche and creating the horseshoe-shaped Sakuchi caldera, which extends to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

Information Contacts: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.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/); 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 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/).

Karangetang (also known as Api Siau) is located on the island of Siau in the Sitaro Regency, North Sulawesi, Indonesia and consists of two active summit craters: a N crater (Kawah Dua) and a S crater (Kawah Utama, also referred to as the “Main Crater”). More than 50 eruptions have been observed since 1675. The current eruption began in November 2018 and has recently been characterized by frequent incandescent block avalanches, thermal anomalies in the crater, and gas-and-steam plumes (BGVN 45:06). This report covers activity from June through November 2020, which includes dominantly crater anomalies, few ash plumes, and gas-and-steam emissions. Information primarily comes from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, and various satellite data.

Activity decreased significantly after mid-January 2020 and has been characterized by dominantly gas-and-steam emissions and occasional ash plumes, according to PVMBG. Daily gas-and-steam emissions were observed rising 25-600 m above the Main Crater (S crater) during the reporting period and intermittent emissions rising 25-300 m above Kawah Dua (N crater).

The only activity reported by PVMBG in June, August, and October was daily gas-and-steam emissions above the Main Crater and Kawah Dua (figure 47). MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data shows intermittent low-power thermal anomalies during June through late July, which includes a slight increase in power during late July (figure 48). During 14-15 July strong rumbling from Kawah Dua was accompanied by white-gray emissions that rose 150-200 m above the crater. Crater incandescence was observed up to 10 m above the crater. According to webcam imagery from MAGMA Indonesia, intermittent incandescence was observed at night from both craters through 25 July. In a Volcano Observatory Notice for Aviation (VONA) issued on 5 September, PVMBG reported an ash plume that rose 800 m above the crater.

Figure 47. Webcam image of gas-and-steam plumes rising above the two summit craters at Karangetang on 16 June 2020. Courtesy of MAGMA Indonesia.

Figure 48. Intermittent low-power thermal anomalies at Karangetang were reported during June through July 2020 with a slight increase in power in late July, according to the MIROVA graph (Log Radiative Power). No thermal activity was detected during August to late October; in mid-November a short episode of increased activity occurred. Courtesy of MIROVA.

Thermal activity increased briefly during mid-November when hot material was reported extending 500-1,000 m NW of the Main Crater, accompanied by gas-and-steam emissions rising 200 m above the crater. Corresponding detection of MODIS thermal anomalies was seen in MIROVA graphs (see figure 48), and the MODVOLC system showed alerts on 13 and 15 November. On 16 November blue emissions were observed above the Main Crater drifting W. Sentinel-2 thermal images showed elevated temperatures in both summit craters throughout the reporting period, accompanied by gas-and-steam emissions and movement of hot material on the NW flank on 19 November (figure 49). White gas-and-steam emissions rose to a maximum height of 300 m above Kawah Dua on 22 November and 600 m above the Main Crater on 28 November.

Figure 49. Persistent thermal anomalies (bright yellow-orange) at Karangetang were detected in both summit craters using Sentinel-2 thermal satellite imagery during June through November 2020. Gas-and-steam emissions were also occasionally detected in both craters as seen on 17 June (top left) and 20 September (bottom left) 2020. On 19 November (bottom right) the Main Crater (S) showed a hot thermal signature extending NW. Images using “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); 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).

Colombia’s broad, glacier-capped Nevado del Ruiz has an eruption history documented back 8,600 years, including documented observations since 1570. Ruiz remained quiet for 20 years after the deadly September 1985-July 1991 eruption until a period of explosive activity from February 2012 into 2013. Renewed activity beginning in November 2014 included ash and gas-and-steam plumes, ashfall, and the appearance of a slowly growing lava dome inside the Arenas crater in August 2015. Additional information has caused a revision to earlier reporting that eruptive activity ended in May 2017 and began again that December (BGVN 44:12); activity appears to have continued throughout 2017 with intermittent ash emissions and thermal evidence of dome growth. Periods of increased thermal activity alternated with periods of increased explosive activity during 2018-2019 and into 2020; SO₂ emissions persisted at significant levels. The lava dome has continued to grow through 2020. This report covers ongoing activity from July-December 2020 using information from reports by the Servicio Geologico Colombiano (SGC) and the Observatorio Vulcanológico y Sismológico de Manizales, the Washington Volcanic Ash Advisory Center (VAAC) notices, and various sources of satellite data.

Gas and ash emissions continued throughout July-December 2020; they generally rose to 5.8-6.1 km altitude with the highest reported plume at 6.7 km altitude on 7 December. SGC interpreted repeated episodes of “drumbeat seismicity” as an indication of continued dome growth throughout the period. Satellite thermal anomalies also suggested that dome growth continued. The MIROVA graph of thermal activity suggests that the dome was quiet in July and early August, but small pulses of thermal energy were recorded every few weeks for the remainder of 2020 (figure 115). Plots of the cumulative number and magnitude of seismic events at Nevado del Ruiz between January 2010 and November 2020 show a stable trend with periodic sharp increases in activity or magnitude throughout that time. SGC has adjusted the warning levels over time according to changes in the slope of the curves (figure 116).

Figure 115. Thermal energy shown in the MIROVA graph of log radiative power at Nevado del Ruiz from 3 February 2020 through the end of the year indicates that higher levels of thermal energy lasted through April 2020; a quieter period from late May-early August was followed by low-level persistent anomalies through the end of the year. Courtesy of MIROVA.

Figure 116. Changes in seismic frequency and energy at Nevado del Ruiz have been monitored by SGC for many years. Left: the cumulative number of daily VT, LP-VLP, TR, and HB seismic events, recorded between 1 January 2010 and 30 November 2020. The arrows highlight the days with the highest number of seismic events; the number and type of event is shown under the date. Right: The cumulative VT and HB seismic energy recorded between 1 January 2010 and 30 November 2020. The arrows highlight the days with the highest energy; the local magnitude of the event is shown below the date. SGC has adjusted the warning levels over time (bar across the bottom of each graph) according to changes in the slope of the curves. Courtesy of SGC (INFORME TÉCNICO – OPERATIVO DE LA ACTIVIDAD VOLCÁNICA, SEGMENTO VOLCÁNICO NORTE DE COLOMBIA – NOVIEMBRE DE 2020).

Activity during July-December 2020. Seismic energy increased during July compared to June 2020 with events localized around the Arenas crater. The depth of the seismicity varied from 0.3-7.8 km. Some of these signals were associated with small emissions of gas and ash, which were confirmed through webcams and by reports from officials of the Los Nevados National Natural Park (NNNP). The Washington VAAC reported a possible ash emission on 8 July that rose to 6.1 km altitude and drifted NW. On 21 July a webcam image showed an ash emission that rose to the same altitude and drifted W; it was seen in satellite imagery possibly extending 35 km from the summit but was difficult to confirm due to weather clouds. Short- to moderate-duration (less than 40 minutes) episodes of drumbeat seismicity were recorded on 5, 13, 17, and 21 July. SCG interprets this type of seismic activity as related to the growth of the Arenas crater lava dome. Primarily WNW drifting plumes of steam and SO₂ were observed in the webcams daily. The gas was occasionally incandescent at night. The tallest plume of gas and ash reached 1,000 m above the crater rim on 30 July and was associated with a low-energy tremor pulse; it produced ashfall in parts of Manizales and nearby communities (figure 117).

Figure 117. Images captured by a traditional camera (top) and a thermal camera (bottom) at Nevado del Ruiz showed a small ash emission in the early morning of 30 July 2020. Ashfall was reported in Manizales. The cameras are located 3.7 km W of the Arenas crater. Courtesy of SGC (Emisión de ceniza Volcan Nevado del Ruiz Julio 30 de 2020).

Seismicity increased in August 2020 with respect to July. Some of the LP and TR (tremor) seismicity was associated with small emissions of gas and ash, confirmed by web cameras, park personnel, and the Washington VAAC. The Washington VAAC received a report from the Bogota MWO of an ash emission on 1 August that rose to 6.1 km altitude and drifted NW; it was not visible in satellite imagery. Various episodes of short duration drumbeat seismicity were recorded during the month. The tallest steam and gas plume reached 1,800 m above the rim on 31 August. Despite the fact that in August the meteorological conditions made it difficult to monitor the surface activity of the volcano, three ash emissions were confirmed by SGC.

Seismicity decreased during September 2020 with respect to August. Some of the LP and TR (tremor) seismicity was associated with small emissions of gas and ash, confirmed by web cameras, park personnel and the Washington VAAC. The Washington VAAC reported an ash emission on 16 September that rose to 6.1 km altitude and drifted NW. A minor ash emission on 20 September drifted W from the summit at 5.8 km altitude. A possible emission on 23 September drifted NW at 6.1 km altitude for a brief period before dissipating. Two emissions were reported drifting WNW of the summit on 26 September at 5.8 and 5.5 km altitude. Continuous volcanic tremors were registered throughout September, with the higher energy activity during the second half of the month. One episode of drumbeat seismicity on 15 September lasted for 38 minutes and consisted of 25 very low energy earthquakes. Steam and gas plumes reached 1,800 m above the crater rim during 17-28 September (figure 118). Five emissions of ash were confirmed by the webcams and park officials during the month, in spite of difficult meteorological conditions; three of them occurred between 15 and 20 September.

Figure 118. A dense plume of steam rose from Nevado del Ruiz in the morning of 17 September 2020. Courtesy of Gonzalo.

Seismicity increased during October with respect to September. A few of the LP and tremor seismic events were associated with small emissions of gas and ash, confirmed by web cameras, park personnel, and the Washington VAAC. The Washington VAAC issued advisories of possible ash emissions on 2, 6, 9, 11, 15, 17, 18, and 21 October. The plumes rose to 5.6-6.4 km altitude and drifted primarily W and NW. Steam plumes were visible most days of the month (figure 119). Only a few were visible in satellite data, but most were visible in the webcams. Several episodes of drumbeat seismicity were recorded on 13, 22-25, and 27 October, which were characterized by being of short duration and consisting of very low energy earthquakes. The tallest plume during the month rose about 2 km above the crater rim on 18 October. Ash emissions were recorded eight times during the month by SGC.

Figure 119. A steam plume mixed with possible ash drifted SE from Nevado del Ruiz on 7 October 2020. Courtesy of vlucho666.

During November 2020, the number of seismic events decreased relative to October, but the amount of energy released increased. Some of the seismicity was associated with small emissions of gas and ash, confirmed by webcams around the volcano. The Washington VAAC reported ash emissions on 22 and 30 November; the 22 November event was faintly visible in satellite images and was also associated with an LP seismic event. They rose to 5.8-6.1 km altitude and drifted W. Various episodes of drumbeat seismicity registered during November were short- to moderate-duration, very low energy, and consisted of seismicity associated with rock fracturing (VT). Multiple steam plumes were visible from communities tens of kilometers away (figure 120).

Figure 120. Multiple dense steam plumes were photographed from communities around Nevado del Ruiz during November 2020, including on 18 (top) and 20 (bottom) November. Top image courtesy of Jose Fdo Cuartas, bottom image courtesy of Efigas Oficial.

Seismic activity increased in December 2020 relative to November. It was characterized by continuous volcanic tremor, tremor pulses, long-period (LP) and very long-period (VLP) earthquakes. Some of these signals were associated with gas and ash emissions, one confirmed through the webcams. The Washington VAAC reported ash emissions on 5 and 7 December. The first rose to 5.8 km altitude and drifted NW. The second rose to 6.7 km altitude and drifted W. A single discrete cloud was observed 35 km W of the summit; it dissipated within six hours. Drumbeat seismic activity increased as well in December; the episode on 3 December was the most significant. Steam and gas emissions continued throughout the month; a plume of gas and ash reached 1,700 m above the summit on 20 December, and drifted NW.

Sentinel-2 satellite data showed at least one thermal anomaly inside the Arenas crater each month during August-December 2020, corroborating the seismic evidence that the dome continued to grow throughout the period (figure 121). Sulfur dioxide emissions were persistent, with many days every month recording DU values greater than two with the TROPOMI instrument on the Sentinel 5-P satellite (figure 122).

Figure 121. Thermal anomalies at Nevado del Ruiz were recorded at least once each month during August-December 2020 suggesting continued growth of the dome within the Arenas crater at the summit. Courtesy of Sentinel Hub Playground.

Figure 122. Sulfur dioxide emissions were persistent at Nevado del Ruiz during August-December 2020, with many days every month recording DU values greater than two with the TROPOMI instrument on the Sentinel 5-P satellite. Ecuador’s Sangay had even larger SO2 emissions throughout the period. Dates are at the top of each image. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Additional reports of activity during 2017. Activity appears to have continued during June-December 2017. Ash emissions were reported by the Bogota Meteorological Weather Office (MWO) on 13 May, and by SGC on 28 May. During June, some of the recorded seismic events were associated with minor emissions of ash; these were confirmed by webcams and by field reports from both the staff of SGC and the Los Nevados National Natural Park (PNNN). Ash emissions were confirmed in webcams by park officials on 3, 16, and 17 June. Gas emissions from the Arenas crater during July 2017 averaged 426 m above the crater rim, generally lower than during June. The emissions were mostly steam with small amounts of SO₂. Emissions were similar during August, with most steam and gas plumes drifting NW. No ash emissions were reported during July or August.

SGC reported steam and gas plumes during September that rose as high as 1,650 m above the crater rim and drifted NW. On 21 September the Washington VAAC received a report of an ash plume that rose to 6.4 km altitude and drifted NNW, although it was not visible in satellite imagery. Another ash emission rising to 6.7 km altitude was reported on 7 October; weather clouds prevented satellite observation. An episode of drumbeat seismicity was recorded on 9 October, the first since April 2017. While SGC did not explicitly mention ash emissions during October, several of the webcam images included in their report show plumes described as containing ash and gas (figure 123).

Figure 123. Plumes of steam, gas, and ash rose from Arenas crater at Nevado del Ruiz most days during October 2017. Photographs were captured by the webcams installed in the Azufrado Canyon and Cerro Gualí areas. Courtesy of SGC (INFORME DE ACTIVIDAD VOLCANICA SEGMENTO NORTE DE COLOMBIA, OCTUBRE DE 2017).

The Washington VAAC received a report from the Bogota MWO of an ash emission that rose to 6.1 km altitude and drifted NE on 8 November 2017. A faint plume was visible in satellite imagery extending 15 km NE from the summit. SGC reported that plumes rose as high as 2,150 m above the rim of Arenas crater during November. The plumes were mostly steam, with minor amounts of SO₂. A diffuse plume of ash was photographed in a webcam on 24 November. SGC did not report any ash emissions during December 2017, but the Washington VAAC reported “a thin veil of volcanic ash and gases” visible in satellite imagery and webcams on 18 December that dissipated within a few hours. In addition to the multiple reports of ash emissions between May and December 2017, Sentinel-2 thermal satellite imagery recorded at least one image each month during June-December showing a thermal anomaly at the summit consistent with the slowly growing dome first reported in August 2015 (figure 124).

Figure 124. Thermal anomalies from the growing dome inside Arenas crater at the summit of Nevado del Ruiz appeared at least once each month from June-December 2017. A strong anomaly was slightly obscured by clouds on 3 June (top left). On 2 August, a steam plume obscured most of the crater, but a small thermal anomaly is visible in its SE quadrant (top right). Strong anomalies on 30 November and 20 December (bottom) have a ring-like form suggestive of a growing dome. Atmospheric penetration rendering (bands 12, 11, 8A), courtesy of Sentinel Hub Playground.

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: MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Gonzalo (URL: https://twitter.com/chaloc22/status/1306581929651843076); Jose Fdo Cuartas (URL: https://twitter.com/JoseFCuartas/status/1329212975434096640); Vlucho666 (URL: https://twitter.com/vlucho666/status/1313791959954268161); Efigas Oficial (URL: https://twitter.com/efigas_oficial/status/1329780287920873472).

Three explosions . . . were recorded in August, bringing the 1987 total of explosions to 25. The month's highest ash plume reached 1,700 m and accompanied quiet ash emission on 22 August. Ash accumulated 51 g/m² during the month at [KLMO]. The eruptions did not cause any damage.

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.

At about 1000 on 28 August pilots Charles Kozler, Wayne Russell, and George Wooliver (Reeve Aleutian Airways) reported an eruption plume reaching 10.5 km altitude in the vicinity of Amukta, drifting WNW. The FAA issued a NOTAM warning pilots to stay 25 miles [40 km] from Amukta Island. Heavy weather clouds covered Amukta Island so its activity could not be directly observed. Mt. Cleveland, 100 km ENE, was apparently active that same morning and winds were blowing in the direction of Amukta (see Mt. Cleveland 12:08). The origin of the large cloud remains both uncertain and controversial at the time of this report.

On 4 September Wooliver observed a small dark ash plume rising at least 300 m above the summit of Amukta then drifting as much as 1 km NW. Only the NW flank was visible because of cloud cover. His observations were made from 9,750 m altitude from nearly 120 km N. Wooliver has flown in the Aleutian Islands since the 1950's and is experienced at observing eruptions.

Amukta's last known eruptive activity was on 12 July 1984 (BVE, no. 24). Harold Wilson (Peninsula Airways) notes that normal activity . . . is continuous minor steam emission from several small vents just inside the summit crater rim.

Geologic Background. The symmetrical Amukta stratovolcano lies in the central Aleutians SW of Chagulak Island and is the westernmost of the Islands of the Four Mountains group. Amukta was constructed at the northern side of an arcuate caldera-like feature that is open to the sea along the southern coast of the 8-km-wide Amukta Island. The 1066-m-high stratovolcano overlies a broad shield volcano and is topped by a 400-m-wide crater. A cinder cone is located near the NE coast. Amukta has had several eruptions in historical time from both summit and flank vents.

Information Contacts: T. Miller, USGS Anchorage; J. Reeder, ADGGS.

Strombolian activity persisted from Crater C with continuous emission of lava and gases, and sporadic ejection of pyroclastic material. The stronger June/July activity produced occasional nuées ardentes that extended ~500 m from the crater on ... 13 July at 1630 (burning 1/2 hectare of forest on the S flank) and 17 July at 1430. Ash emission also increased in June, with fine ash generally carried to ~4-5 km W and NW from the crater by the prevailing winds. Lava flows continued to descend the N and NE flanks. The incipient lava flow seen 23 May during a helicopter overflight continued to advance NW toward the Río Tabacón. At the end of July, its front was at ~1,000 m elevation, roughly 1 km from the summit.

Activity declined sharply in August. Only 21 explosion earthquakes were recorded compared to 248 in July, and tremor weakened considerably.

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

Information Contacts: J. Barquero, OVSICORI; R. Barquero and Guillermo Alvarado, ICE; G. Soto and L. Morales, Univ de Costa Rica.

The last two Bulletins reported lower stratospheric layers, perhaps from forest fires in China. Since June, however, no evidence of these layers has been detected by lidar at Hampton, VA or Mauna Loa, Hawaii (figure 46). August profiles at Hampton were smooth, without significant sublayering. Altitudes of peak backscattering at Mauna Loa dropped from 26-29 km in July to 22-25 km in August. There were no indications of recent aerosol injections.

Figure 46. Lidar data from Virginia and Hawaii, showing altitudes of aerosol layers during August 1987. Note that some layers have multiple peaks. Backscattering ratios 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.

Samples taken on 3 August near San Francisco (about 37.7°N, 122.5°W) by a NASA aircraft at about 12 km altitude did not show unusual concentrations of aerosols. Most particles were H₂SO4 spheres, with a few chlorides and nitrates. The size distribution was generally unimodal, with a mean geometric radius of 0.06 µm, but there was a small bulge at about 0.3 µm radius.

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: Mary Osborn, NASA Langley Research Center, Hampton, VA 23665 USA; Thomas DeFoor, Mauna Loa Observatory, P. O. Box 275, Hilo, HI 23665 USA; Rudolf Pueschel, Mail Stop 245-5, NASA Ames Research Center, Moffett Field, California 94035 USA.

A moderately thick white to brown plume was continuously released from the summit crater. Plume emission intensified 14-15 August when incandescent rockfalls down the N and W flanks and strong night glow from the summit were reported. On 29 August the summit crater was reported to be completely filled with a smoking lava dome that continued to feed the long-active lava flow on the N flank. Seismicity remained at a low level throughout the month, with 10-20 rockfall events/day.

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: C. McKee, P. de Saint-Ours, and P. Lowenstein, RVO.

On 8 September, eight earthquakes were recorded at the Banda Api observatory post, the first seismic activity there since the 17 June regional earthquake. No change in the activity of the volcano was noted.

Geologic Background. The small island volcano of Banda Api is the NE-most volcano in the Sunda-Banda arc and has a long period of historical observation because of its key location in the Portuguese and Dutch spice trade. The basaltic-to-rhyodacitic volcano is located in the SW corner of a 7-km-wide mostly submerged caldera that comprises the northernmost of a chain of volcanic islands in the Banda Sea. At least two episodes of caldera formation are thought to have occurred, with the arcuate islands of Lonthor and Neira considered to be remnants of the pre-caldera volcanoes. A conical peak rises to about 600 m at the center of the 3-km-wide Banda Api island. Historical eruptions have been recorded since 1586, mostly consisting of Strombolian eruptions from the summit crater, but larger explosive eruptions have occurred and occasional lava flows have reached the coast.

Information Contacts: VSI.

During at least five overflights between 6 and 10 August, H. Wilson (Peninsula Airways) observed incandescent lava and summit glow, but did not recognize any lava fountains or moving flows. High-pressure steam emission was occurring and steam drifted as far as 3 km from the summit. At about 1500 on 26 August, pilot T. Madsen (Aleutian Air) observed a 600-m-high ash and steam plume. Two days later, on 28 August at about 0930, Scott Kerr and Pete Galaktionoff heard a distant rumbling sound lasting ~15 seconds while camping on Kagamil Island (25 km NE of Mt. Cleveland, 120 km NE of Amukta). Overcast skies prevented observations. At 0944 that day the National Warning Center of the North American Air Defense Command (NORAD) issued a warning of a large eruption of Mt. Cleveland, after detecting a hot spot that morning at 52.78°N, 169.93°W through remote sensing. Steve Shivers (USGS Anchorage) recognized a WNW-trending plume on a NOAA 10 satellite image returned at 1030. The ~15-km plume was elongated WNW from a point ~15 km W of Mt. Cleveland. From more than 100 km away at about 1100, pilot Charles Nickerson (Reeve Aleutian Airways) reported that the plume, which appeared to be drifting WNW, reached 9-10.6 km altitude with about a 25 km upper radius, but the plume was by then apparently detached from its origin and the volcano that fed it is not certain. He estimated that the plume was just ENE of Amukta and W of Cleveland. Mt. Cleveland's summit appeared to be emitting a 300 m-high steam plume. At about 1200, Larry Conner (MarkAir) also observed the eruption plume from a point ~30 km S of Amukta, which was completely covered by clouds and not emitting a plume. At about 1400, pilot William Redmond (Peninsula Airways) observed unusual, thin, brown-tinted, cirrus layers beginning 65 km WNW of Mt. Cleveland at 2,400 m altitude and higher. The wind was blowing from the E.

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 it 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: J. Reeder, ADGGS.

Imagery from the NOAA 10 polar orbiting weather satellite showed a plume that extended S then W ~200 km from Una Una on 14 July at 0708. VSI could not confirm that an eruption had occurred.

Geologic Background. Colo volcano forms the isolated small island of Una Una in the middle of the Gulf of Tomini in northern Sulawesi. The broad, low volcano contains a 2-km-wide caldera with a small central cone. Only three eruptions have been recorded in historical time, but two of those caused widespread damage over much of the island. The last eruption, in 1983, produced pyroclastic flows that swept over most of the island shortly after all residents had been evacuated.

Information Contacts: W. Gould, NOAA/NESDIS; VSI.

Infrared imagery from the NOAA 10 polar orbiting weather satellite on 23 July at about 1300 GMT showed a plume that extended ~100 km SE from Deception Island. In early August, personnel on King George Island reported that seismic instruments at the Chinese "Great Wall" station, 110 km from Deception Island, had recently detected local seismicity, but gave no date or time. During an 11 August overflight, no volcanic activity was evident on Deception Island [see also 13:02].

Geologic Background. Ring-shaped Deception Island, one of Antarctica's most well known volcanoes, contains a 7-km-wide caldera flooded by the sea. Deception Island is located at the SW end of the Shetland Islands, NE of Graham Land Peninsula, and was constructed along the axis of the Bransfield Rift spreading center. A narrow passageway named Neptunes Bellows provides entrance to a natural harbor that was utilized as an Antarctic whaling station. Numerous vents located along ring fractures circling the low, 14-km-wide island have been active during historical time. Maars line the shores of 190-m-deep Port Foster, the caldera bay. Among the largest of these maars is 1-km-wide Whalers Bay, at the entrance to the harbor. Eruptions from Deception Island during the past 8700 years have been dated from ash layers in lake sediments on the Antarctic Peninsula and neighboring islands.

Information Contacts: W. Gould, NOAA; G. Gutheridge, National Science Foundation.

On 26 May, the pilot of a charter aircraft observed a heavy "boil" on the ocean surface over Esmeralda, feeding an elongate zone of discolored water. The pilot reported that he had not seen activity at Esmeralda in many years. On 4 June, L.G. Eldredge and the same pilot flew over Esmeralda, but saw no water movement or discoloration.

Geologic Background. Esmeralda Bank is a massive submarine volcano with three summit cones oriented along a N-S line. Their summits are from 43 to 140 m beneath the sea surface. The highest, middle peak contains a 3-km-wide caldera open to the west and several parasitic cones. Frequent sulfur boils and water discoloration have been observed, which have variously been attributed to eruptive events or solfataric activity.

Information Contacts: L. Eldredge, University of Guam.

Seismicity beneath the summit continued after the 2 June intrusion. Minor inflation was recorded through 6 June. The volcano then remained stable until a new intrusion developed below the E summit zone at 0411 on 9 June. Seismicity ceased at 0500 but no eruption occurred. Hypocenters were concentrated along a N-S axis, 1-1.5 km under Dolomieu.

On 10 June, 50 µrads of inflation in the upper summit zone were recorded. At 1510 that day an eruption began in the S part of the crater along a 50-m N-S fissure. Lava broke out the next day in the E part of the crater (figure 18). About 10⁶ m³ of aphyric basalt were extruded by 28 June. During this phase, two inflation pulses were recorded by the permanent tiltmeter network, on 18 and 22-26 June. After 28 June, moderate seismicity and slight deformation were recorded. Significant inflation was observed on 19 July from 0450 to 0630 during a new intrusion crisis, mainly in the NE part of Dolomieu. Seismicity shifted from N to S at about 0535. An eruption then occurred at two sites. The main eruption was 1 km S of the summit craters, close to Chateau-Fort (1948 eruption site), lasted ~32 hours, and produced slightly more than 10⁶ m³ of aphyric basalt. Poor weather conditions prevented clear observation of the less-active site 1.5 km NNE of the summit. Deformation changes have not been significant since the eruptions, but weak summit-area seismicity began 15 August and was continuing in the first week of September.

Figure 18. Map of the summit area of Piton de la Fournaise showing 1987 lava flows. Courtesy of P. Bachélery.

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 and B. Gillet, OVPDLF; P. Bachelery, Univ de la Réunion; J-L. Cheminee, A. Hirn, J. LePine, P. Blum, and J. Zlotnicki, IPGP.

Gas emission from the crater and nearby microearthquakes continued through July. Seismic station FG3 registered 50 microearthquakes with S-P <= 2.0 seconds. The tiltmeter, at the same site, did not show abnormal variation. A small fumarole was also active about 100 m below the crater on the E flank.

Geologic Background. Volcán Fuego, one of Central America's most active volcanoes, is also one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between Fuego and Acatenango to the north. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at the mostly andesitic Acatenango. Eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

Information Contacts: E. Sánchez, INSIVUMEH.

About nine small earthquakes of M < 2 occurred beneath the summit 20 August-1 September. Four were felt at intensities of I-III (JMA scale) by personnel at the summit meteorological observatory, but were not felt at the weather station 19 km ESE of the summit. Seismographs confirmed that the earthquakes originated just underneath the summit. JMA installed a portable seismograph at the summit on 25 August. The strongest earthquake, on 20 August at 0556, had a magnitude of 1.8 (table 1). No signs of wall collapse or landslides were observed by a field survey group around the summit that day. Earthquakes on 20 and 24 August were recorded by the Univ of Tokyo's Earthquake Research Institute seismographs within 20 km of the summit.

Table 1. Earthquakes at Mt. Fuji, 20 August-1 September 1987.

Small earthquakes are not rare at Fuji, but because the earthquakes occurred in the summit region during the height of the climbing season, there was some concern among government officials. However, the relatively sharp P-wave arrivals suggest that the earthquakes were tectonic in origin.

Geologic Background. The conical form of Fujisan, Japan's highest and most noted volcano, belies its complex origin. The modern postglacial stratovolcano is constructed above a group of overlapping volcanoes, remnants of which form irregularities on Fuji's profile. Growth of the Younger Fuji volcano began with a period of voluminous lava flows from 11,000 to 8000 years before present (BP), accounting for four-fifths of the volume of the Younger Fuji volcano. Minor explosive eruptions dominated activity from 8000 to 4500 BP, with another period of major lava flows occurring from 4500 to 3000 BP. Subsequently, intermittent major explosive eruptions occurred, with subordinate lava flows and small pyroclastic flows. Summit eruptions dominated from 3000 to 2000 BP, after which flank vents were active. The extensive basaltic lava flows from the summit and some of the more than 100 flank cones and vents blocked drainages against the Tertiary Misaka Mountains on the north side of the volcano, forming the Fuji Five Lakes, popular resort destinations. The last confirmed eruption of this dominantly basaltic volcano in 1707 was Fuji's largest during historical time. It deposited ash on Edo (Tokyo) and formed a large new crater on the east flank.

Information Contacts: Yoshiaki Ida and Harry Glicken, Earthquake Research Institute, Univ of Tokyo; JMA.

On 4 September 1987 at 1500, flight engineer George Wooliver (Reeve Aleutian Airways) observed a narrow flow-like feature that had descended the E flank, from the N crater rim at 1,500 m elevation to at least 1,100 m. A thick cloud cover obscured it below that level. Steam was rising as much as 100 m above the flow feature along its entire visible length. Steaming from the crater appeared more vigorous than usual.

Geologic Background. The 8 x 10 km Gareloi Island, the northernmost volcano of the Delarof Group at the western end of the Andreanof Islands, consists of a stratovolcano with two summits and a prominent SE-trending fissure. The fissure was formed during an eruption in 1929 and extends from the southern summit to the sea. Steep sea cliffs that are cut into rocks of an older, eroded center are found on the SW coast, and submarine deposits of three debris avalanches produced by edifice collapse are found offshore. Young lava flows cover the older volcano from the summit to the coast along three broad axes trending NW, ENE, and S. The 1929 eruption originated from 13 craters along a 4-km-long fissure. Phreatic explosions were followed by the ejection of glassy pumice, lapilli, scoria, and older blocks, as well as by the emission of four short, steep lava flows, one of which reached the SE coast.

Information Contacts: J. Reeder, ADGGS.

Fumarolic activity continued on the NW flank, with temperatures of 80°C. The crater lake that had formed in 1984 disappeared in June, probably by water drainage.

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

Information Contacts: J. Barquero, OVSICORI.

The low-level eruptive activity . . . continued through August. Lava advanced SE from the vent area through well-developed tubes over the steep slope of a major fault scarp ("pali") threatening only the E end of Royal Gardens Subdivision and covering a small portion of an unused access road. At ~150 m elevation, lava moved slightly W of earlier flows, and by the end of the month the flow front had advanced to ~25 m elevation, 1 km from the ocean. During the first week of September, lava overrode earlier flows that covered Hwy 130, and the most active part of the 200-m-wide flow, along its W margin, had moved to within 100 m of the Chain of Craters Road inside the national park (figure 52). A small lobe was approaching the ocean E of the park, but advance was only sporadic. The level of the lava pond over the vent continued to vary, with a few small, brief overflows onto the shield during the month. Most of the lava emptied from the neck at the SE end of the pond into the tube system.

Figure 52. Kilauea's recent lava flows near the S coast. The hachured area is a preliminary sketch of the August-September flows; outlines of other flows are based on airphoto data. Filled squares represent houses destroyed in September.

Harmonic tremor continued at a low level below the shield vent and Pu`u `O`o. Tremor occasionally varied at intervals of a few hours, but generally remained constant for periods of a few days. Bursts of 40-60-km-deep tremor SW of Kilauea became increasingly frequent during the last half of the month after three weeks of relative quiet. By mid-August, the number of seismic events beneath Pu`u `O`o (structural adjustments after the 26 June conduit collapse event) had declined considerably, from ~200 shallow microshocks/day in July to ~50/day in late August. There were no unusually significant earthquakes in August; eight had magnitudes of 2.5-4.2. Most occurred in persistent seismic source areas 5-10 km deep in the S flanks of Kilauea and Mauna Loa.

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.

The following . . . is a compilation of reports from visitors to the volcano since 1983. Names of sources are in parentheses after their information. [See Nyamweru, 1988, for a more detailed version.]

Photographs taken on a flight over the crater in early April 1983 showed a narrow tongue of black lava stretching from the base of the N wall over more than half of the ~180-m-wide crater floor (figure 1) (Croze and Fanshawe). Three months later, in July, a group visited the crater rim and observed that on the upper 10% of the outer slopes vegetation had died and a thin layer of white ash had fallen. Many fissures along the rim of the N crater were issuing clouds of sulfurous steam and sulfur crystals were forming in cracks in the ground. The N crater appeared shallower than it had before the eruption of early 1983. Very liquid, dark colored "mud" was ejected at intervals to heights of ~2-3 m, from two or three small vents at the N end of the crater, with a noise similar to ocean surf (Peterson).

Figure 1. Near-vertical aerial view of Ol Doinyo Lengai's N crater in early April 1983. Traced from photo by J. Fanshawe; courtesy of C. Nyamweru. Key: A: Upper segment of crater wall, sloping and crossed by shallow rills. Most parts are light gray to brown in color. B: Vertical to near-vertical lower segment of crater wall. C: Small ash cones; color ranges from black (fresh) to pale gray (weathered). D: Dark gray to black lava, rough surface (aa?). E: Dark gray to black lava, smooth surface often with flow structures (pahoehoe?) F: Talus slope. G: Crater floor with no sign of recent lava flows (within the last few weeks or months); mid-pale gray or almost white in color. J: Bank of pale gray ash (?). K: Outer flanks; mid-gray to brown surface of indurated pyroclasts. Variable vegetation. L: Crater rim. M: Saddle separating the larger, active, lower part of N crater from smaller, inactive, higher S corner.

During a May 1984 visit, two vents on the N side of the crater floor (figure 2) contained a black bubbling liquid that was occasionally thrown an estimated 6 m into the air (Trott). Three months later, on 2 August 1984, dark gray to black, ropy, mud-like crust had formed over the inside surface of the inner crater (surface G in figure 2). On the N side of the crater floor, a small cluster of cones, ~3 m high, ejected small blobs of mud-like lava. A continuous deep rumbling occurred from within the crater (Skelton). By February 1985, a lake that was very black, quite liquid, and boiling vigorously, covered ~1/4 of the crater floor (Borner). In October 1985, the lake was covered with a solid crust, but three cones, ~3 m high, had formed. The largest one, on the W side, had bubbling black "mud" inside, that was being thrown violently towards the cone's rim (Borner).

A group spent two hours on the crater floor on 27 December 1985. The crater floor was generally flat with a 10-m rock "spine" (probably made of lava) near the N end. A number of deep holes in the crater floor led into tunnels that emitted steam with considerable force. The fissures described by Peterson in 1983 also continued to emit steam and sulfurous fumes. Noise and tremor seemed to originate from below the crater at 5- to 30-minute intervals (Waldron). Lava samples from the crater floor were analyzed and found to be natrocarbonatite, consisting almost entirely of nyerereite and gregoryite. A thin section showed clear tabular nyerereite and cloudy rounded gregoryite phenocrysts in a finely crystalline groundmass that was primarily carbonate minerals (Hay). The texture and composition of this lava was very similar to those formed in [1960 and 1966].

Figure 2. Ol Doinyo Lengai's N crater seen from the rim in May 1984. North is to the right or the lower right corner. See figure 1 for key. Traced from photo by F. Trott; courtesy of C. Nyamweru.

On 1 May 1986 the same group found that the tunnels beneath the crater had all been filled by more recent flows and there were three small peaks (instead of one), each ~8 m high. Eruption of clots of "brownish dark cement" was occurring every few seconds from a small vent near the top of one of the peaks. Very fresh-looking, dark brown, ropy lava had spread out around the base of the peaks and extended several tens of meters from the base of the cone (Waldron).

In November 1986 there was a considerably larger area of dark fresh-looking lava visible on the N side of the crater than there had been in May. Several small vents were concentrated towards the N side of the crater and at least three were throwing out clots of lava. Black lava had flowed into the crater from a small cone on the crater rim that formed between July 1984 and July 1985. The crater appeared shallower than it had been in 1983; the vertical cliff that had formed the lower segment of the slope (area B in figure 2) into the crater had completely disappeared, and at the S end of the crater the slope above it was also much shorter than it was in 1983. Very roughly, some 10-20 m of vertical slope could have been lost due to infilling by the volcanic material erupted since 1983 (Peterson).

In February 1987 an aerial view of the crater (figure 3) confirmed the crater's shallow appearance. The crater floor also looked much paler than in November 1986, suggesting that the lava surface had undergone characteristic alteration and little new material had been erupted in the previous few weeks. On 30 June 1987, a couple of small vents on the N side were still active. The vent on the N rim had grown some since last seen in November 1986 (Peterson).

Figure 3. Ol Doinyo Lengai on 4 February 1987, traced by C. Nyamweru from photograph by Adrian Warren and Keith Scholey. Key: C1: Rim cone apparently formed between July 1984 and June 1985. D: Possible lava flow originating from a vent on the N wall of the crater. N1-N4: Steep sections of the wall of the inactive S corner of the N crater, green with vegetation. T1-T3: Small features similar to lava domes or blisters on the crater floor; they were partially collapsed with vents a few meters in diameter. (see figure 1 caption for key to other features).

Reference. Nyamweru, C., 1988, Activity of Ol Doinyo Lengai volcano, Tanzania, 1983-1987: Journal of African Earth Science, v. 7, p. 603-610.

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, Nairobi, Kenya.

During the November 1977 visit by Nairn and Bachri, the crater lake was 80 m in diameter and its temperature was 65.5°C (correcting the values reported in 12:07). Lake depth was estimated at 10 m by a guide, based on his earlier observation of the crater floor at a time when the lake was dry. The explosions from the lake were quite small.

Geologic Background. The elongated Mahawu volcano immediately east of Lokon-Empung volcano is the northernmost of a series of young volcanoes along a SSW-NNE line near the margin of the Quaternary Tondano caldera. Mahawu is capped by a 180-m-wide, 140-m-deep crater that sometimes contains a small crater lake, and has two pyroclastic cones on its N flank. Historical activity has been restricted to occasional small explosive eruptions recorded since 1789. In 1994 fumaroles, mudpots, and small geysers were observed along the shores of a greenish-colored crater lake.

Information Contacts: I. Nairn, NZGS Rotorua, New Zealand.

A low level of activity prevailed through August. Southern Crater released only a thin white plume. Main Crater released white vapor at low rates, and displayed steady night glow from 18 August. A moderately low level of seismicity continued with 1,400-1,500 sub-continuous, small-amplitude, low-frequency events/day. No significant tilt change was recorded during the month. Figures 2 and 3 show the distribution of the products of the 30 June eruption. Pyroclastic flow volume was estimated at 5-10 x 10⁶ m³. Estimated volume of airfall ash was 10⁶ m³.

Figure 2. Scoria distribution (hatched pattern) and thickness (cm), and ash distribution (stippled) and thickness (mm) from Manam's 30 June 1987 eruption. Ash fell after the scoria and overlies it. Courtesy of RVO.

Figure 3. Distribution of flow products of Manam's 30 June 1987 eruption. PF = pyroclastic flow, WS = welded scoria, 1 = lava flow. Courtesy of RVO.

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 basaltic-andesitic stratovolcano to its lower flanks. These 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 observed eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent 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: C. McKee, P. de Saint-Ours and P. Lowenstein, RVO.

Comparison of photographs taken during visits to the summit in May, July, and on 8 August, showed that the lava dome continued to increase in volume. Most of the growth seems to have occurred by addition of material to the top of the dome and in its NE sector. No perceptible new growth has occurred on the SW part of the dome. . . .

Geologic Background. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities.

Information Contacts: VSI.

New observations show that the July 1986 eruption vent was located 4.5 km S of the caldera's edge at the S foot of Kitazungurwa in Mashiga (figure 6) rather than . . . 3.5 km SW of the caldera's edge.

Figure 6. Map of the Nyamuragira/Nyiragongo area by N. Zana (1984), appended with vents and flows through 1988. The heavy dashed line indicates the approximate path of the 1989 flow.

Geologic Background. Africa's most active volcano, Nyamulagira (also known as Nyamuragira), is a massive high-potassium basaltic shield about 25 km N of Lake Kivu and 15 km NE of the steep-sided Nyiragongo volcano. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Documented eruptions have occurred within the summit caldera, as well as from the numerous flank fissures and cinder cones. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Recent lava flows extend down the flanks more than 30 km from the summit as far as Lake Kivu; extensive lava flows from this volcano have covered 1,500 km2 of the western branch of the East African Rift.

Information Contacts: B. Louant, GEOVAR, Kigali, Rwanda.

During the first 20 days of July, activity was weak, limited to sporadic explosions from MacKenney Crater. No lava flows had been observed since the strong 14 June explosive eruption. Activity increased on 23 July, to 5-10 explosions/15 minutes from MacKenney Crater as recorded by seismic instruments. About 26 July, a new lava flow was observed emerging from MacKenney Crater and advancing W. Two small vents were observed within MacKenney Crater, ejecting gas, dark gray ash and pyroclastics. Most fell back into the crater, but fresh bombs were found on the older summit cone about 100 m to the south.

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: E. Sánchez, INSIVUMEH.

L.G. Eldredge visited Pagan for a few hours on 4 June. The only visible activity was steam emission from the crater. Scoria from the 1981 eruption appeared to have become a slurry-like material during the past 3 years, flowing into the village where it had filled rooms at the infirmary and reached almost to the roof of the school.

The 6 September edition of the Guam Sunday News included a photograph that showed a moderately dense cloud rising perhaps 1 km from the summit of Pagan during what was described as an eruption in the morning of 4 September.

Geologic Background. Pagan Island, the largest and one of the most active of the Mariana Islands volcanoes, consists of two stratovolcanoes connected by a narrow isthmus. Both North and South Pagan stratovolcanoes were constructed within calderas, 7 and 4 km in diameter, respectively. North Pagan at the NE end of the island rises above the flat floor of the northern caldera, which may have formed less than 1,000 years ago. South Pagan is a stratovolcano with an elongated summit containing four distinct craters. Almost all of the recorded eruptions, which date back to the 17th century, have originated from North Pagan. The largest eruption during historical time took place in 1981 and prompted the evacuation of the sparsely populated island.

Information Contacts: L. Eldredge, Univ of Guam.

Eruptive activity was continuing in late August. At about 1130 on 29 August, pilot Chuck Nickerson (Reeve Aleutian Airways) observed a thick dark ash horizon at 1200-1800 m altitude extending 50 km SSW from Pavlof. The ash appeared to originate from a SE flank vent. Below that vent, white steam was rising along a 100 m, narrow, flow-like, feature or crack. At 1550 pilots Andy Livingston and James Fredenhagen (Reeve Aleutian Airways) observed from Sand Point (88 km E), a diffuse ash layer at 1200-1800 m altitude that extended at least 15 km SW. Ben and Lorie Kirker reported that no ash reached King Cove, about 40 km SW. On 30 August at 1400 Theresa Dubber (FAA) saw no ash being emitted during a clear view of the volcano from Cold Bay.

Geologic Background. The most active volcano of the Aleutian arc, Pavlof is a 2519-m-high Holocene stratovolcano that was constructed along a line of vents extending NE from the Emmons Lake caldera. Pavlof and its twin volcano to the NE, 2142-m-high Pavlof Sister, form a dramatic pair of symmetrical, glacier-covered stratovolcanoes that tower above Pavlof and Volcano bays. A third cone, Little Pavlof, is a smaller volcano on the SW flank of Pavlof volcano, near the rim of Emmons Lake caldera. Unlike Pavlof Sister, Pavlof has been frequently active in historical time, typically producing Strombolian to Vulcanian explosive eruptions from the summit vents and occasional lava flows. The active vents lie near the summit on the north and east sides. The largest historical eruption took place in 1911, at the end of a 5-year-long eruptive episode, when a fissure opened on the N flank, ejecting large blocks and issuing lava flows.

Information Contacts: J. Reeder, ADGGS.

Geyser-like phreatic eruptions, the first since September 1980, resumed in June. The crater lake had been relatively quiet and the eroded 1953-55 [dome] in the lake had been gradually cooling for the past several years. The eruptions, from the W part of the crater lake, ejected columns of water and sediments that typically rose to about 30 m height, then fell back into the lake, generating a wave surge. The eruptions were followed by vapor column emission. Sporadic activity continued in July and August. On 1 July, three phreatic eruptions were observed, with ejecta from the last, at 1130, reaching 75 m above the lake. Three more phreatic episodes were seen on 14 August (at 0845, 1120, and 1225), with the second only producing a small bubble. On 19 August, three explosions and another small bubble were observed (at 0958, 1133, 1210, and 1358). Witnesses of the second and third explosions reported that a mud and vapor column rose suddenly from the center of the lake without any apparent premonitory activity. The column ejection was accompanied by a loud noise that increased as the ejecta fell back, causing 1-m waves that eroded sediments at the shore.

During the first 8 months of 1987, fumarole temperatures averaged 540°C at the top of the 1953-55 [dome] and 800°C on its W flank. Temperatures had dropped from more than 800°C in late 1983 to around 300°C in mid-1985. Fumaroles were less vigorous than last year. Crater lake temperature varied, but increased from 58°C in January to 70°C in June; pH was 0-0.5. The lake level has continued to fall, exposing three terraces of gray, water-saturated sediment since January, and dropping about 2 m in the past 6 months. Concentric fractures have developed along the shore, particularly on the E and NE sides (striking N-S and NW-SE respectively). Landslides have occurred on the E wall of the crater and on the 1953-55 [dome].

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

Information Contacts: J. Barquero, OVSICORI; R. Barquero and Guillermo Alvarado, ICE; G. Soto and Luis D. Morales, Sección de Sismología, Vulcanología, y Exploración Geofísica, Escuela Centroamericana de Geología, Univ de Costa Rica, San José, Costa Rica.

Seismicity declined to its lowest level since the 1983-85 unrest; only 34 caldera earthquakes were recorded in August, compared to 80-150/month in the last seven months. There were periods of several consecutive days with no events and only three small events were recorded 13-20 August. The six located earthquakes were in the Greet Harbour and Karavia Bay areas (NE and E parts of the caldera).

Dry tilt readings on Vulcan Headland . . . showed a steady deflation of 20 µrad since May. In Greet Harbour, usually the most active area, tilt readings remained virtually unchanged although levelling revealed a slight subsidence of 10 mm at Matupit Island since the end of June. This slight deflationary trend was consistent with EDM results.

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: C. McKee, P. de Saint-Ours and P. Lowenstein, RVO.

Crater Lake temperature had increased from 11.5 to 24.5°C between visits by geologists on 3 July and 17 August. Convection of lake water was occurring at both the central and N vents on 17 August. Outflow had increased from 30 l/s to >200 l/s, and total heat flow from the lake had increased by a factor of 4 since the July visit, reaching ~180 MW.

No recent eruptions appear to have occurred and no significant deformation or seismicity has accompanied the lake heating. Lake temperature had been relatively stable after dropping rapidly between November and December 1986, but reached a low in July (figure 7).

Geologic Background. Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The dominantly andesitic 110 km3 volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 ring plain of volcaniclastic debris, including the Murimoto debris-avalanche deposit on the NW flank. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. A single historically active vent, Crater Lake (Te Wai a-moe), is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene. Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent, and tephra characteristics suggest that the crater lake may have formed as early as 3,000 years ago. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys.

Information Contacts: I. Nairn, NZGS Rotorua; P. Otway, NZGS Wairakei.

The eruption . . . continued in August, with ~25 explosions/day ejecting plumes to ~600 m above the crater rim. A seismometer 5 km from the summit recorded no earthquakes accompanying the explosions.

Geologic Background. Sangeang Api volcano, one of the most active in the Lesser Sunda Islands, forms a small 13-km-wide island off the NE coast of Sumbawa Island. Two large trachybasaltic-to-tranchyandesitic volcanic cones, Doro Api and Doro Mantoi, were constructed in the center and on the eastern rim, respectively, of an older, largely obscured caldera. Flank vents occur on the south side of Doro Mantoi and near the northern coast. Intermittent eruptions have been recorded since 1512, most of them during in the 20th century.

Information Contacts: VSI.

An incandescent block lava flow continued to emerge from Cono Caliente (the active crater on the E side of the dome), advancing down the S flank. By the end of July its front was between 1,200 and 1,300 m elevation in a canyon 80 m wide and 30 m deep, about 1.5 km from the Nimá II river. Numerous avalanches occurred from the flow front and along its channel. There were some reports of explosions from the flow front; fumaroles and a gaseous odor were noted there by geologists. Sporadic explosions from Cono Caliente ejected light-colored ash, and gas emission was continuous.

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: E. Sánchez, INSIVUMEH.

. . . Vulcanian activity continued through August. Field geologists observed several [glowing avalanches] that traveled down the SE flank . . . .

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: VSI.

Gas and ash plumes from the extrusive dome were sighted more frequently in 1987. Four or five plumes were seen each month March-June and 6 in July. Seismic activity also intensified and each explosion was accompanied by volcanic tremor. Vertical columnar ash plumes with a maximum height of 5 km were often accompanied by base surges that extended 300 m. Explosion products included ash and andesitic sand-sized tephra with rare blocks as large as 1 m.

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 km3 volcano is one of Kamchatka's largest and most active volcanic structures. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: G. Bogoyavlenskaya and V. Beloussov, IV.

Temperatures increased at two fumaroles during August: from 104 to 197°C at the N crater, and from 95 to 108°C at Sibangor Julu. White fume was almost continuously present, rising to ~100 m above the crater. In late August, seismic activity began to increase. By early September, near-surface earthquakes averaged ~7/day and deeper, tectonic earthquakes averaged ~40/day.

Geologic Background. Sorikmarapi is a forested stratovolcano with a 600-m-wide summit crater containing a lake and substantial sulfur deposits. A smaller parasitic crater (Danau Merah) on the upper SE flank also contains a crater lake; these two craters and a series of smaller explosion pits occur along a NW-SE line. Several solfatara fields are located on the E flank. Phreatic eruptions have occurred from summit and flank vents during the 19th and 20th centuries.

Information Contacts: VSI.

During July, the SBG seismic station registered 20 microearthquakes with S-P <= 2.0 seconds. There have been no recent reports about the state of the vent formed by the 8 May 1986 phreatic eruption.

Geologic Background. Tacaná is a 4064-m-high composite stratovolcano that straddles the México/Guatemala border at the NW end of the Central American volcanic belt. The volcano rises 1800 m above deeply dissected plutonic and metamorphic terrain. Three large calderas breached to the south, and the elongated summit region is dominated by a series of lava domes intruded along a NE-SW trend. Volcanism has migrated to the SW, and a small adventive lava dome is located in the crater of the youngest volcano, San Antonio, on the upper SW flank. Viscous lava flow complexes are found on the north and south flanks, and lobate lahar deposits fill many valleys. Radial drainages on the Guatemalan side are deflected by surrounding mountains into the Pacific coastal plain on the SW side of the volcano. Historical activity has been restricted to mild phreatic eruptions, but more powerful explosive activity, including the production of pyroclastic flows, has occurred as recently as about 1950 years ago.

Information Contacts: E. Sánchez, INSIVUMEH.

Fumarolic activity continued, with temperatures of 91°C in the W crater and 85° in the central crater, similar to those measured in mid-1985 (10:07).

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

Information Contacts: J. Barquero, OVSICORI.