Pacaya, located in Guatemala, is a highly active volcano that has previously produced continuous Strombolian explosions, multiple lava flows, and the formation of a small cone within the crater due to the constant deposition of ejected material (BGVN 45:02). This reporting period updates information from February through July 2020 consisting of similar activity that dominantly originates from the Mackenney crater. Information primarily comes from reports by the Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH) in Guatemala and various satellite data.

Strombolian explosions were recorded consistently throughout this reporting period. During February 2020, explosions ejected incandescent material 100 m above the Mackenney crater. At night and during the early morning the explosions were accompanied by incandescence from lava flows. Multiple lava flows were active during most of February, traveling primarily down the SW and NW flanks and reaching 500 m on 25 February. On 5 February the lava flow on the SW flank divided into three flows measuring 200, 150, and 100 m. White and occasionally blue gas-and-steam emissions rose up to 2.7 km altitude on 11 and 14 February and drifted in multiple directions. On 16 February Matthew Watson utilized UAVs (Unmanned Aerial Vehicle) to take detailed, close up photos of Pacaya and report that there were five active vents at the summit exhibiting lava flows from the summit, gas-and-steam emissions, and small Strombolian explosions (figure 122).

Figure 122. Drone image of active summit vents at Pacaya on 16 February 2020 with incandescence and white gas-and-steam emissions. Courtesy of Matthew Watson, University of Bristol, posted on 17 February 2020.

Activity remained consistent during March with Strombolian explosions ejecting material 100 m above the crater accompanied by occasional incandescence and white and occasionally blue gas-and-steam emissions drifting in multiple directions. Multiple lava flows were detected on the NW and W flanks reaching as far as 400 m on 9-10 March.

In April, frequent Strombolian explosions were accompanied by active lava flows moving dominantly down the SW flank and white gas-and-steam emissions. These repeated explosions ejected material up to 100 m above the crater and then deposited it within the Mackenney crater, forming a small cone. On 27 April seismicity increased at 2140 due to a lava flow moving SW as far as 400 m (figure 123); there were also six strong explosions and a fissure opened on the NW flank in front of the Los Llanos Village, allowing gas-and-steam to rise.

Figure 123. Infrared image of Pacaya on 28 April 2020, showing a lava flow approximately 500 m long and moving down the S flank on the day after seismicity increased and six strong explosions were detected. Courtesy of ISIVUMEH (Reporte Volcán de Pacaya July 2020).

During May, Strombolian explosions continued to eject incandescent material up to 100 m above the Mackenney crater, accompanied by active lava flows on 1-2, 17-18, 22, 25-26, and 29-30 May down the SE, SW, NW, and NE flanks up to 700 m on 30 May. White gas-and-steam emissions continued to be observed up to 100 m above the crater drifting in multiple directions. Between the end of May and mid-June, the plateau between the Mackenney cone and the Cerro Chiquito had become inundated with lava flows (figure 124).

Figure 124. Aerial views of the lava flows at Pacaya to the NW during a) 18 September 2019 and b) 16 June 2020 showing the lava flow advancement toward the Cerro Chiquito. Courtesy of INSIVUMEH (Reporte Volcán de Pacaya July 2020).

Lava flows extended 700 m on 8 June down multiple flanks. On 9 June, a lava flow traveled N and NW 500 m and originating from a vent on the N flank about 100 m below the Mackenney crater. Active lava flows continued to originate from this vent through at least 19 June while white gas-and-steam emissions were observed rising 300 m above the crater. At night and during the early mornings of 24 and 29 June Strombolian explosions were observed ejecting incandescent material up to 200 m above the crater (figure 125). These explosions continued to destroy and then rebuild the small cone within the Mackenney crater with fresh ejecta. Active lava flows on the SW flank were mostly 100-600 m long but had advanced to 2 km by 30 June.

On 10 July a 1.2 km lava flow divided in two which moved on the NE and N flanks. On 11 July, another 800 m lava flow divided in two, on the N and NE flanks (figure 126). On 14 and 19 July, INSIVUMEH registered constant seismic tremors and stated they were associated with the lava flows. No active lava flows were observed on 18-19 July, though some may have continued to advance on the SW, NW, N, and NE flanks. On 20 July, lava emerged from a vent at the NW base of the Mackenney cone near Cerro Chino, extending SE. Strombolian explosions ejected incandescent material up to 200 m above the crater on 22 July, accompanied by active incandescent lava flows on the SW, N, NW, NE, and W flanks. Three lava flows on the NW flank were observed on 22-24 July originating from the base of the Mackenney cone. Explosive activity during 22 July vibrated the windows and roofs of the houses in the villages of San Francisco de Sales, El Patrocinio, El Rodeo, and others located 4 km from the volcano. The lava flow activity had decreased by 25 July, but remnants of the lava flow on the NW flank persisted with weak incandescence observed at night, which was no longer observed by 26 July. Strombolian explosions continued to be detected through the rest of the month, accompanied by frequent white gas-and-steam emissions that extended up to 2 km from the volcano; no active lava flows were observed.

Figure 125. Photos of Pacaya on 11 July 2020 showing Strombolian explosions and lava flows moving down the N and NE flanks. Courtesy of William Chigna, CONRED, posted on 12 July 2020.

Figure 126. Infrared image of Pacaya on 20 July 2020 showing a hot lava flow accompanied by gas-and-steam emissions. Courtesy of INSIVUMEH (BEPAC 47 Julio 2020-22).

During February through July 2020, multiple lava flows and thermal anomalies within the Mackenney crater were detected in Sentinel-2 thermal satellite imagery (figure 127). These lava flows were observed moving down multiple flanks and were occasionally accompanied by white gas-and-steam emissions. Thermal anomalies were also recorded by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system during 10 August through July 2020 within 5 km of the crater summit (figure 128). There were a few breaks in thermal activity from early to mid-March, late April, early May, and early June; however, each of these gaps were followed by a pulse of strong and frequent thermal anomalies. According to the MODVOLC algorithm, 77 thermal alerts were recorded within the summit crater during February through July 2020.

Figure 127. Sentinel-2 thermal satellite images of Pacaya showing thermal activity (bright yellow-orange) primarily as lava flows originating from the summit crater during February to July 2020 frequently accompanied by white gas-and-steam emissions. All images with "Atmospheric penetration" (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Figure 128. The MIROVA thermal activity graph (Log Radiative Power) at Pacaya during 10 August to July 2020 shows strong, frequent thermal anomalies through late July with brief gaps in activity during early to mid-March, late April, early May, and early June. Courtesy of MIROVA.

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: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); 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); Matthew Watson, School of Earth Sciences at the University of Bristol (Twitter: @Matthew__Watson, https://twitter.com/Matthew__Watson); William Chigna, CONRED (URL: https://twitter.com/william_chigna).

Sangeang Api is a 13-km-wide island located off the NE coast of Sumbawa Island, part of Indonesia's Lesser Sunda Islands. Documentation of historical eruptions date back to 1512. The most recent eruptive episode began in July 2017 and included frequent Strombolian explosions, ash plumes, and block avalanches. The previous report (BGVN 45:02) described activity consisting of a new lava flow originating from the active Doro Api summit crater, short-lived explosions, and ash-and-gas emissions. This report updates information during February through July 2020 using information from the Darwin Volcanic Ash Advisory Center (VAAC) reports, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, or CVGHM) reports, and various satellite data.

Volcanism during this reporting period was relatively low compared to the previous reports (BGVN 44:05 and BGVN 45:02). A Darwin VAAC notice reported an ash plume rose 2.1 km altitude and drifted E on 10 May 2020. Another ash plume rose to a maximum of 3 km altitude drifting NE on 10 June, as seen in HIMAWARI-8 satellite imagery.

The MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data detected a total of 12 low power thermal anomalies within 5 km from the summit during February through May 2020 (figure 42). No thermal anomalies were recorded during June and July according to the MIROVA graph. Though the MODVOLC algorithm did not detect any thermal signatures between February to July, many small thermal hotspots within the summit crater could be seen in Sentinel-2 thermal satellite imagery (figure 43).

Figure 42. Thermal anomalies at Sangeang Api from 10 August 2019 through July 2020 recorded by the MIROVA system (Log Radiative Power) were infrequent and low power during February through May 2020. No thermal anomalies were detected during June and July. Courtesy of MIROVA.

Figure 43. Sentinel-2 thermal satellite imagery using “Atmospheric penetration” (bands 12, 11, 8A) rendering showed small thermal hotspots (orange-yellow) at the summit of Sangeang Api during February through June 2020. Courtesy of Sentinel Hub Playground.

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 historical eruptions have been recorded since 1512, most of them during in the 20th century.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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).

Stromboli is a stratovolcano located in the northeastern-most part of the Aeolian Islands composed of two active summit vents: the Northern (N) Crater and the Central-South (CS) Crater that are situated at the head of the Sciara del Fuoco, a large scarp that runs from the summit down the NW side of the volcano. The ongoing eruption began in 1934 and has been characterized by regular Strombolian explosions in both summit craters, ash plumes, and occasional lava flows (BGVN 45:08). This report updates activity from January to April 2020 with information primarily from daily and weekly reports by Italy's Istituto Nazionale di Geofisica e Vulcanologia (INGV) and various satellite data.

Activity was consistent during this reporting period. Explosion rates ranged from 1-20 per hour and were of variable intensity, producing material that rose from less than 80 to over 250 m above the vents (table 8). Strombolian explosions were often accompanied by gas-and-steam emissions, spattering, and lava flows which has resulted in fallout deposited on the Sciara del Fuoco and incandescent blocks rolling toward the coast up to a few hundred meters down the slopes of the volcano. According to INGV, the average SO2 emissions measured 300-650 tons/day.

Table 8. Summary of activity at Stromboli during January-April 2020. Low-intensity activity indicates ejecta rising less than 80 m, medium-intensity is ejecta rising less than 150 m, and high-intensity is ejecta rising over 200 m above the vent. Data courtesy of INGV.

During January 2020, explosive activity mainly originated from three vents in the N crater and at least three vents in the CS crater. Ejecta from numerous Strombolian explosions covered the slopes on the upper Sciara del Fuoco, some of which rolled hundreds of meters down toward the coast. Explosion rates varied from 2-12 per hour in the N crater and 9-14 per hour in the CS crater; ejected material rose 80-200 m above the craters. According to INGV, a small cone growing in the S1 crater produced some explosions that ejected coarse material mixed with fine ash. On 18 and 19 January a lava flow was observed, both of which originated in the N crater. In addition, two explosions were detected in the N crater that was associated with two landslide events.

Explosive activity in February primarily originated from 2-3 eruptive vents in the N crater and at least three vents in the CS crater (figure 177). The Strombolian explosions ejected material 80-250 m above the craters, some of which fell onto the upper part of the Sciara. Explosion rates varied from 3-12 per hour in the N crater and 2-14 per hour in the CS crater (figure 178). On 3 February a short-lived lava flow was reported in the N crater.

Figure 177. A drone image showed spattering accompanied by gas-and-steam emissions at Stromboli rising above the N crater on 15 February 2020. Courtesy of INGV (Rep. No. 08/2020, Stromboli, Bollettino Settimanale, 10/02/2020 - 16/02/2020, data emissione 18/02/2020).

Figure 178. a) Strombolian explosions during the week of 17-23 February 2020 in the N1 crater of Stromboli were seen from Pizzo Sopra La Fossa. b) Spattering at Stromboli accompanied by white gas-and-steam emissions was detected in the N1 and S2 craters during the week of 17-23 February 2020. c) Spattering at Stromboli accompanied by a dense ash plume was seen in the N1 and S2 craters during the week of 17-23 February 2020. All photos by F. Ciancitto, courtesy of INGV (Rep. No. 09/2020, Stromboli, Bollettino Settimanale, 17/02/2020 - 23/02/2020, data emissione 25/02/2020).

Ongoing explosive activity continued into March, originating from three eruptive vents in the N crater and at least three vents in the CS crater. Ejected lapilli and bombs rose 80-250 m above the craters resulting in fallout covering the slopes in the upper Sciara del Fuoco with blocks rolling down the slopes toward the coast and explosions varied from 4-13 per hour in the N crater and 1-16 per hour in the CS crater. Discontinuous spattering was observed during 9-19 March. On 19 March, intense spattering was observed in the N crater, which produced a lava flow that stretched along the upper part of the Sciara for a few hundred meters. Another lava flow was detected in the N crater on 28 March for about 4 hours into 29 March, which resulted in incandescent blocks breaking off the front of the flow and rolling down the slope of the volcano. On 30 March a lava flow originated from the N crater and remained active until the next day on 31 March. Landslides accompanied by incandescent blocks rolling down the Sciara del Fuoco were also observed.

Strombolian activity accompanied by gas-and-steam emissions continued into April, primarily produced in 3-4 eruptive vents in the N crater and 2-3 vents in the CS crater. Ejected material from these explosions rose 80-250 m above the craters, resulting in fallout products covering the slopes on the Sciara and blocks rolling down the slopes. Explosions varied from 4-15 per hour in the N crater and 1-10 per hour in the CS crater. On 1 April a thermal anomaly was detected in satellite imagery accompanied by gas-and-steam and ash emissions downstream of the Sciara del Fuoco. A lava flow was observed on 15 April in the N crater accompanied by gas-and-steam and ash emissions; at the front of the flow incandescent blocks detached and rolled down the Sciara (figure 179). This flow continued until 16 April, ending by 0956; a thermal anomaly persisted downslope from the lava flow. Spatter was ejected tens of meters from the vent. Another lava flow was detected on 19 April in the N crater, followed by detached blocks from the front of the flow rolling down the slopes. Spattering continued during 20-21 April.

Figure 179. A webcam image of an ash plume accompanied by blocks ejected from Stromboli on 15 April 2020 rolling down the Sciara del Fuoco. Courtesy of INGV via Facebook posted on 15 April 2020.

Moderate thermal activity occurred frequently during 16 October to April 2020 as recorded in the MIROVA Log Radiative Power graph using MODIS infrared satellite information (figure 180). The MODVOLC thermal alerts recorded a total of 14 thermal signatures over the course of nine different days between late February and mid-April. Many of these thermal signatures were captured as hotspots in Sentinel-2 thermal satellite imagery in both summit craters (figure 181).

Figure 180. Low to moderate thermal activity at Stromboli occurred frequently during 16 October-April 2020 as shown in the MIROVA graph (Log Radiative Power). Courtesy of MIROVA.

Figure 181. Thermal anomalies (bright yellow-orange) at Stromboli were observed in thermal satellite imagery from both of the summit vents throughout January-April 2020. Images with Atmospheric Penetration rendering (bands 12, 11, 8A); courtesy of Sentinel Hub Playground.

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

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/en/, Facebook: https://www.facebook.com/ingvvulcani/); 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).

Columbia’s broad, glacier-capped Nevado del Ruiz has an eruption history documented back 8,600 years, and historical observations since 1570. It’s profound notoriety stems from an eruption on 13 November 1985 that produced an ash plume and pyroclastic flows onto the glacier, triggering large lahars that washed down 11 valleys, inundating most severely the towns of Armero (46 km W) and Chinchiná (34 km E) where approximately 25,000 residents were killed. It remains the second deadliest volcanic eruption of the 20th century after Mt. Pelee killed 28,000 in 1902. Ruiz remained quiet for 20 years after the September 1985-July 1991 eruption until a new explosive event occurred in February 2012; a series of explosive events lasted into 2013. Renewed activity beginning in November 2014 included ash and gas-and-steam plumes, ashfall, and the appearance of a lava dome inside the Arenas crater in August 2015 which has regularly displayed thermal anomalies through 2019. This report covers ongoing activity from January-June 2020 using information primarily 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 at Nevado del Ruiz throughout January-June 2020; they generally rose to 5.8-6.1 km altitude with the highest reported plume at 7 km altitude during early March. SGC confirmed the presence of the growing lava dome inside Arenas crater during an overflight in January; infrared satellite imagery indicated a continued heat source from the dome through April. SGC interpreted repeated episodes of ‘drumbeat seismicity’ as an indication of continued dome growth throughout the period. Small- to moderate-density sulfur dioxide emissions were measured daily with satellite instruments. The MIROVA graph of thermal activity indicated a heat source consistent with a growing dome from January through April (figure 102).

Figure 102. The MIROVA graph of thermal activity at Nevado del Ruiz from 2 July 2019 through June 2020 indicated persistent thermal anomalies from mid-November 2019-April 2020. Courtesy of MIROVA.

Activity during January-March 2020. During January 2020 some of the frequent tremor seismic events were associated with gas and ash emissions, and several episodes of “drumbeat” seismicity were recorded; they have been related by SGC to the growth of the lava dome on the floor of the Arenas crater. An overflight on 10 January, with the support of the Columbian Air Force, confirmed the presence of the dome which was first proposed in August 2015 (BGVN 42:06) (figure 103). The Arenas crater had dimensions of 900 x 980 m elongate to the SW-NE and was about 300 m deep (figure 104). The dome inside the crater was estimated to be 173 m in diameter and 60 m high with an approximate volume of 1,500,000 m³ (figures 105 and 106). In addition to the dome, the scientists also noted ash deposits on the summit ice cap (figure 107). The Washington VAAC reported an ash plume on 19 January that rose to 5.5 km altitude and drifted SW, dissipating quickly. On 30 January they reported an ash plume visible in satellite imagery extending 15 km NW from the summit at 5.8 km altitude. A single MODVOLC alert was issued on 15 January and data from the VIIRS satellite instrument reported thermal anomalies inside the summit crater on 14 days of the month. Sulfur dioxide plumes with DU values greater than 2 were recorded by the TROPOMI satellite instrument daily during the month.

Figure 103. SGC confirmed the presence of a lava dome inside the Arenas crater at Nevado del Ruiz on 10 January 2020. The dome is shown in brown, and zones of fumarolic activity are labelled around the dome. Courtesy of SGC (El Nuevo Domo de Lava del Volcán Nevado del Ruiz y la Geomorfología Actual del Cráter Arenas 2020).

Figure 104. A view of the Arenas crater at the summit of Nevado del Ruiz on 10 January 2020 (left) is compared with a view from 2010 (right). They were both taken during overflights supported by the Colombian Air Force (FAC). Ash deposits on the ice fields are visible in both images. Fumarolic activity rises from the inner walls of the crater in January 2020. Courtesy of SGC (El Nuevo Domo de Lava del Volcán Nevado del Ruiz y la Geomorfología Actual del Cráter Arenas 2020).

Figure 105. The dome inside the Arenas crater at Nevado del Ruiz appeared dark against the crater rim and ash-covered ice field on 10 January 2020. Features observed include (A) the edge of the Arenas crater, (B) a secondary crater 150 m in diameter located to the west, (C) interior cornices, (D) the lava dome, (E) a depression in the center of the dome caused by possible subsidence and cooling of the lava, (F) a source of gas and ash emission with a diameter of approximately 15 m (secondary crater), and (G, H, and I) several sources of gas emission located around the crater. Courtesy of SGC (El Nuevo Domo de Lava del Volcán Nevado del Ruiz y la Geomorfología Actual del Cráter Arenas 2020).

Figure 106. Images of the summit of Nevado del Ruiz captured by the PlanetScope satellite system on 14 March 2018 (A) and 10 January 2020 (B) show the lava dome at the bottom of Arenas crater. Courtesy Planet Lab Inc. and SGC (El Nuevo Domo de Lava del Volcán Nevado del Ruiz y la Geomorfología Actual del Cráter Arenas 2020).

Figure 107. Ash covered the snow and ice field around the Arenas crater at the summit of Nevado del Ruiz on 10 January 2020. The lava dome is the dark area on the right. Courtesy of SGC (posted on Twitter @sgcol).

The Washington VAAC reported multiple ash plumes during February 2020. On 4 February an ash plume was observed in satellite imagery drifting 35 km W from the summit at 5.8 km altitude. The following day a plume rose to 6.1 km altitude and extended 37 km W from the summit before dissipating by the end of the day (figure 108). On 6 February an ash cloud was observed in satellite imagery centered 45 km W of the summit at 5.8 km altitude. Although it had dissipated by midday, a hotspot remained in shortwave imagery until the evening. Late in the day another plume rose to 6.7 km altitude and drifted W. Diffuse ash was seen in satellite imagery on 13 February fanning towards the W at 5.8 km altitude. On 18 February at 1720 UTC the Bogota Meteorological Weather Office (MWO) reported an ash emission drifting NW at 5.8 km altitude; a second plume was reported a few hours later at the same altitude. Intermittent emissions continued the next day at 5.8-6.1 km altitude that reached as far as 50 km NW before dissipating. A plume on 21 February rose to 6.7 km altitude and drifted W (figure 109). Occasional emissions on 25 February at the same altitude reached 25 km SW of the summit before dissipating. A discrete ash emission around 1550 UTC on 26 February rose to 6.1 km altitude and drifted W. Two similar plumes were reported the next day. On 28 and 29 February plumes rose to 5.8 km altitude and drifted W.

Figure 108. Emissions rose from the Arenas crater at Nevado del Ruiz on 5 February 2020. The Washington VAAC reported an ash plume that day that rose to 6.1 km altitude and drifted 37 km W before dissipating. Courtesy of Camilo Cupitre.

Figure 109. Emissions rose from the Arenas crater at Nevado del Ruiz around 0600 on 21 February 2020. The Washington VAAC reported ash emissions that day that rose to 6.7 km altitude and drifted W. Courtesy of Manuel MR.

SGC reported several episodes of drumbeat type seismicity on 2, 8, 9, and 27 February which they attributed to effusion related to the growing lava dome in the summit crater. Sentinel-2 satellite imagery showed ring-shaped thermal anomalies characteristic of dome growth within Arenas crater several times during January and February (figure 110). The VIIRS satellite instrument recorded thermal anomalies on twelve days during February.

Figure 110. Persistent thermal anomalies from Sentinel-2 satellite imagery during January and February 2020 suggested that the lava dome inside Nevado del Ruiz’s Arenas crater was still actively growing. Atmospheric penetration rendering (bands 12, 11, 8A) courtesy of Sentinel Hub Playground.

On 4, 14, and 19 March 2020 thermal anomalies were visible in Sentinel-2 satellite data from within the Arenas crater. Thermal anomalies were recorded by the VIIRS satellite instrument on eight days during the month. Several episodes of drumbeat seismicity were recorded during the first half of the month and on 30-31 March. Distinct SO₂ plumes with DU values greater than 2 were recorded by the TROPOMI satellite instrument daily throughout February and March (figure 111). The Washington VAAC reported an ash emission on 1 March that rose to 5.8 km altitude and drifted NW; it was centered 15 km from the summit when detected in satellite imagery. The next day a plume was seen in satellite imagery moving SW at 7.0 km altitude, extending nearly 40 km from the summit. Additional ash emissions were reported on 4, 14, 15, 21, 28, 29, and 31 March; the plumes rose to 5.8-6.7 km altitude and drifted generally W, some reaching 45 km from the summit before dissipating.

Figure 111. Distinct SO2 plumes with Dobson values (DU) greater than 2 were recorded by the TROPOMI satellite instrument daily during February and March 2020. Ecuador’s Sangay produced smaller but distinct plumes most of the time as well. Dates are shown at the top of each image. Courtesy of NASA’s Sulfur Dioxide Monitoring Page.

Activity during April-June 2020. The Washington VAAC reported an ash emission that rose to 6.7 km altitude and drifted W on 1 April 2020. On 2 April, emission plumes were visible from the community of Tena in the Cundinamarca municipality which is located 100 km ESE (figure 112). The unusually clear skies were attributed to the reduction in air pollution in nearby Bogota resulting from the COVID-19 Pandemic quarantine. On 4 April the Bogota MWO reported an emission drifting SW at 5.8 km altitude. An ash plume on 8 April rose to 6.7 km altitude and drifted W. On 25 April the last reported ash plume from the Washington VAAC for the period rose to 6.1 km altitude and was observed in satellite imagery moving W at 30 km from the summit; after that, only steam and gas emissions were observed.

Figure 112. On the evening of 2 April 2020, emission plumes from Nevado del Ruiz were visible from Santa Bárbara village in Tena, Cundinamarca municipality which is located 100 km ESE. The unusually clear skies were attributed to the reduction in air pollution in the nearby city of Bogota resulting from the COVID-19 Pandemic quarantine. Photo by Williama Garcia, courtesy of Semana Sostenible (3 April 2020).

Distinct SO₂ plumes with DU values greater than 2 were recorded by the TROPOMI satellite instrument daily throughout the month. On 13 April, a Sentinel-2 thermal image showed a hot spot inside the Arenas crater largely obscured by steam and clouds. Cloudy images through May and June prevented observation of additional thermal anomalies in satellite imagery, but the VIIRS thermal data indicated anomalies on 3, 4, and 26 April. SGC reported low-energy episodes of drumbeat seismicity on 4, 9, 10, 12, 15, 16, 20, and 23 April which they interpreted as related to growth of the lava dome inside the Arenas crater. The seismic events were located 1.5-2.0 km below the floor of the crater.

Small emissions of ash and gas were reported by SGC during May 2020 and the first half of June, with the primary drift direction being NW. Gas and steam plumes rose 560-1,400 m above the summit during May and June (figure 113). Drumbeat seismicity was reported a few times each month. Sulfur dioxide emissions continued daily; increased SO₂ activity was recorded during 10-13 June (figure 114).

Figure 113. Gas and steam plumes rose 560-1,400 m above the summit of Nevado del Ruiz during May and June 2020, including in the early morning of 11 June. Courtesy of Carlos-Enrique Ruiz.

Figure 114. Increased SO2 activity during 10-13 June 2020 at Nevado del Ruiz was recorded by the TROPOMI instrument on the Sentinel-5P satellite. Sangay also emitted SO2 on those days. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

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: El Servicio Geológico Colombiano (SGC), Diagonal 53 No. 34-53 - Bogotá D.C., Colombia (URL: https://www.sgc.gov.co/volcanes, https://twitter.com/sgcol); 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/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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/); NASA Worldview (URL: https://worldview.earthdata.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Camilo Cupitre (URL: https://twitter.com/Ccupitre/status/1225207439701704709); Manuel MR (URL: https://twitter.com/ElPlanetaManuel/status/1230837262088384512); Semana Sostenible (URL: https://sostenibilidad.semana.com/actualidad/articulo/fumarola-del-nevado-del-ruiz-fue-captada-desde-tena-cundinamarca/49597); Carlos-Enrique Ruiz (URL: https://twitter.com/Aleph43/status/1271800027841794049).

Japan's 24-km-wide Asosan caldera on the island of Kyushu has been active throughout the Holocene. Nakadake has been the most active of 17 central cones for 2,000 years; all historical activity is from Nakadake Crater 1. The largest ash plume in 20 years occurred on 8 October 2016. Asosan remained quiet until renewed activity from Crater 1 began in mid-April 2019; explosions with ash plumes continued through the first half of 2020 and are covered in this report. The Japan Meteorological Agency (JMA) provides monthly reports of activity; the Tokyo Volcanic Ash Advisory Center (VAAC) issues aviation alerts reporting on possible ash plumes, and Sentinel-2 satellite images provide data on ash emissions and thermal activity.

The Tokyo VAAC issued multiple daily reports of ash plumes from Nakadake Crater 1 from 1 January-14 June 2020. They were commonly at 1.8-2.1 km altitude, and often drifted E or S. JMA reported that ashfall continued downwind from the ash plumes until mid-June; seismic activity was relatively high during January and February and decreased steadily after that time. The measured SO₂ emissions ranged from 1,000-4,900 tons per day through mid-June and dropped to 500 tons per day during the second half of June. Intermittent thermal activity was recorded at the crater through mid-May.

Explosive activity during January-June 2020. Ash plumes rose up to 1.1 km above the crater rim at Nakadake Crater 1 during January 2020 (figure 70). Ashfall was confirmed downwind of an explosion on 7 January. During February, ash plumes rose up to 1.7 km above the crater, and ashfall was again reported downwind. The crater camera provided by the Aso Volcano Museum occasionally observed incandescence at the floor of the crater during both months. Incandescence was also occasionally observed with the Kusasenri webcam (3 km W) and was seen on 20 February from a webcam in Minamiaso village (8 km SW).

Figure 70. Ash plumes rose up to 1.1 km above the Nakadake Crater 1 at Asosan during January 2020 (left) and up to 1.7 km above the crater during February 2020 (right) as seen in these images from the Kusasenri webcam. Ashfall was reported downwind multiple times. Courtesy of JMA (Volcanic activity commentary material for Mt. Aso, January and February 2020).

During March 2020, ash plumes rose as high as 1.3 km. Ashfall was reported on 9 March in Ichinomiyamachi, Aso City (figure 71). In field surveys conducted on the 18th and 25th, there was no visible water inside the crater, and high-temperature grayish-white plumes were observed. The temperature at the base of the plume was measured at 300°C (figure 72).

Figure 71. Ashfall from Asosan appeared on 9 March 2020 in Ichinomiyamachi, Aso City around 10 km N. Courtesy of JMA (Volcanic activity commentary material for Mt. Aso, March 2020).

Figure 72. During a field survey of Nakadake Crater 1 at Asosan on 25 March 2020, JMA staff observed a gray ash plume rising from the crater floor (left). The maximum temperature of the ash plume was measured at about 300°C with an infrared thermal imaging device (right). Courtesy of JMA (Volcanic activity commentary material for Mt. Aso, March 2020).

Occasional incandescence was observed at the bottom of the crater during April and May 2020; ash plumes rose 1.1 km above the crater on most days in April and were slightly higher, rising to 1.8 km during May, although activity was more intermittent (figure 73). A brief increase in SO₂ activity was reported by JMA during field surveys on 7 and 8 May; satellite data captured small plumes of SO₂ on 1 and 6 May (figure 74). A brief increase in tremor amplitude was reported by JMA on 16 May.

Figure 73. Although activity at Asosan’s Nakadake Crater 1 was more intermittent during April and May 2020 than earlier in the year, ash plumes were still reported most days and incandescence was seen at the bottom of the crater multiple times until 15 May. Left image taken 11 May 2020 from the Kusachiri webcam; right image taken from the crater webcam on 10 May provided by the Aso Volcano Museum. Courtesy of JMA (Volcanic activity commentary material for Mt. Aso, May 2020).

Figure 74. The TROPOMI instrument on the Sentinel-5P satellite detected small but distinct SO2 plumes from Asosan on 1 and 6 May 2020. Additional small plumes are visible from Aira caldera’s Sakurajima volcano. Courtesy of NASA’s Global Sulfur Dioxide Monitoring Page.

The last report of ash emissions at Nakadake Crater 1 from the Tokyo VAAC was on 14 June 2020. JMA also reported that no eruption was observed after mid-June. On 8 June they reported an ash plume that rose 1.4 km above the crater. During a field survey on 16 June, only steam was observed at the crater; the plume rose about 100 m (figure 75). In addition, a small plume of steam rose from a fumarole on the S crater wall.

Figure 75. A steam plume rose about 100 m from the floor of Nakadake Crater 1 on 16 June 2020. A small steam plume was also observed by the S crater wall. Courtesy of JMA (Volcanic activity commentary material for Mt. Aso, June 2020).

Thermal activity during January-June 2020. Sentinel-2 satellite data indicated thermal anomalies present at Nakadake Crater 1 on 2 January, 6 and 21 February, 16 April, and 11 May (figure 76). In addition, thermal anomalies from agricultural fires appeared in satellite images on 11 February, 7 and 17 March (figure 77). The fires were around 5 km from the crater, thus they appear on the MIROVA thermal anomaly graph in black, but are likely unrelated to volcanic activity (figure 78). No thermal anomalies were recorded in satellite data from the Nakadake Crater 1 after 11 May, and none appeared in the MIROVA data as well.

Figure 76. Thermal anomalies appeared at Asosan’s Nakadake Crater 1 on 2 January, 6 and 21 February, 16 April and 11 May 2020. On 2 January a small ash plume drifted SSE from the crater (left). On 6 February a dense ash plume drifted S from the crater (center). Only a small steam plume was visible above the crater on 21 February (right). Images use Atmospheric penetration rendering (bands 12, 11, 8A), courtesy of Sentinel Hub Playground.

Figure 77. Thermal anomalies from agricultural fires located about 5 km from the crater appeared in satellite images on 11 February, and 7 and 17 March 2020. Although a dense ash plume drifted SSE from the crater on 11 February (left), no thermal anomalies appear at the crater on these dates. Images use Atmospheric penetration rendering (bands 12, 11, 8A), courtesy of Sentinel Hub Playground.

Figure 78. The MIROVA project plot of Log Radiative Power at Asosan from 29 June 2019 through June 2020 shows only a few small thermal alerts within 5 km of the summit crater during January-June 2020, and a spike in activity during February and March located around 5 km away. These data correlate well with the Sentinel-2 satellite data that show intermittent thermal anomalies at the summit throughout January-May and agricultural fires located several kilometers from the crater during February and March. Courtesy of MIROVA.

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

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

Sakurajima rises from Kagoshima Bay, which fills the Aira Caldera near the southern tip of Japan's Kyushu Island. Frequent explosive and occasional effusive activity has been ongoing for centuries. The Minamidake summit cone has been the location of persistent activity since 1955; the adjacent Showa crater on its E flank has also been intermittently active since 2006. Numerous explosions and ash-bearing emissions have been occurring each month at either Minamidake or Showa crater since the latest eruptive episode began in late March 2017. This report covers ongoing activity at Minamidake from January through June 2020; the Japan Meteorological Agency (JMA) provides regular reports on activity, and the Tokyo VAAC (Volcanic Ash Advisory Center) issues tens of reports each month about the frequent ash plumes.

Activity continued during January-June 2020 at Minamidake crater with tens of explosions each month. The Tokyo VAAC issued multiple daily reports of ash emissions during January and February. Less activity occurred during the first half of March but picked up again with multiple daily reports from mid-March through mid-April. Emissions were more intermittent but continued through early June, when activity decreased significantly. JMA reported explosions with ash plumes rising 2.5-4.2 km above the summit, and ejecta traveling generally up to 1,700 m from the crater, although a big explosion in early June send a large block of tephra 3 km from the crater (table 23). Thermal anomalies were visible in satellite imagery on a few days most months and were persistent in the MIROVA thermal anomaly data from November 2019 through early June 2020 (figure 94). Incandescence was often visible at night in the webcams through early June; the Showa crater remained quiet throughout the period.

Table 23. Monthly summary of eruptive events recorded at Sakurajima's Minamidake crater within the Aira Caldera, January through June 2020. The number of events that were explosive in nature are in parentheses. No events were recorded at the Showa crater during this time. Ashfall is measured at the Kagoshima Local Meteorological Observatory (KLMO), 10 km W of Showa crater. Data courtesy of JMA (January to June 2020 monthly reports).

Figure 94. Persistent thermal anomalies were recorded in the MIROVA thermal energy data for the period from 2 July 2019 through June 2020. Thermal activity increased in October 2019 and remained steady through May 2020, decreasing abruptly at the beginning of June. Courtesy of MIROVA.

Explosions continued at Minamidake crater during January 2020 with 65 ash plumes reported. The highest ash plume rose 2.5 km above the crater on 30 January, and incandescent ejecta reached up to 1,700 m from the Minamidake crater on 22 and 29 January (figure 95). Slight inflation of the volcano since September 2019 continued to be measured with inclinometers and extensometers on Sakurajima Island. Field surveys conducted on 15, 20, and 31 January measured the amount of sulfur dioxide gas released as very high at 3,400-4,700 tons per day, as compared with 1,000-3,000 tons in December 2019.

Figure 95. An explosion at the Minamidake summit crater of Aira’s Sakurajima volcano on 29 January 2020 produced an ash plume that rose 2.5 km above the crater rim and drifted SE (left). On 22 January incandescent ejecta reached 1,700 m from the summit during explosive events. Courtesy of JMA (Sakurajima Volcanic Activity Commentary, January 2020).

About the same number of explosions produced ash plumes during February 2020 (67) as in January (65) (figure 96). On 10 February a large block was ejected 1,800 m from the crater, the first to reach that far since 5 February 2016. The tallest plume, on 26 February rose 2.6 km above the crater. Sentinel-2 satellite imagery indicated two distinct thermal anomalies within the Minamidake crater on both 1 and 6 February (figure 97). Activity diminished during March 2020 with only 10 explosions out of 26 eruptive events. On 21 March a large bomb reached 1,700 m from the crater. The tallest ash plume rose 3 km above the crater on 17 March. Scientists noted during an overflight on 16 March that a small steam plume was rising from the inner wall on the south side of the Showa crater; a larger steam plume rose to 300 m above the Minamidake crater and drifted S (figure 98). Sulfur dioxide emissions were similar in February (1,900 to 3,100 tons) and March (1,300 to 3,400 tons per day).

Figure 96. An ash plume rose from the Minamidake crater at the summit of Aira’s Sakurajima volcano on 6 February 2020 at 1752 local time, as seen looking S from the Kitadake crater. Courtesy of JMA (Sakurajima Volcanic Activity Commentary, February 2020).

Figure 97. Sentinel-2 satellite imagery revealed two distinct thermal anomalies within the Minamidake crater at Aira’s Sakurajima volcano on 1 and 6 February 2020. Images use Atmospheric penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub playground.

Figure 98. During an overflight of Aira’s Sakurajima volcano on 16 March 2020, JMA captured this view to the SW of the Kitadake crater on the right, the steam-covered Minamidake crater in the center, and the smaller Showa crater on the left adjacent to Minamidake. Courtesy of JMA and the Maritime Self-Defense Force 1st Air Group P-1 (Sakurajima Volcanic Activity Commentary, March 2020).

During April 2020, ejecta again reached as far as 1,700 m from the crater; 14 explosions were identified from the 51 reported eruptive events, an increase from March. The tallest plume, on 4 April, rose 3.8 km above the crater (figure 99). The same number of eruptive events occurred during May 2020, but 24 were explosive in nature. A large plume on 9 May rose to 4.2 km above the rim of Minamidake crater, the tallest of the period (figure 100). On 20 May, incandescent ejecta reached 1,300 m from the summit. Sulfur dioxide emissions during April (1,700-2,100 tons per day) and May (1,200-2,700 tons per day) were slightly lower than previous months.

Figure 99. A large ash plume at Aira’s Sakurajima volcano rose from Minamidake crater at 1621 on 4 April 2020. The plume rose to 3.8 km above the crater and drifted SE. Courtesy of JMA (Sakurajima Volcanic Activity Commentary, April 2020).

Figure 100. Activity continued at Aira’s Sakurajima volcano during May 2020. A large plume rose to 4.2 km above the summit and drifted N in the early morning of 9 May (left). The Kaigata webcam located at the Osumi River National Highway Office captured abundant incandescent ejecta reaching 1,300 m from the crater during the evening of 20 May. Courtesy of JMA (Sakurajima Volcanic Activity Commentary, May 2020).

A major explosion on 4 June 2020 produced 137 Pa of air vibration at the Seto 2 observation point on Sakurajima Island. It was the first time that air vibrations exceeding 100 Pa have been observed at the Seto 2 station since the 21 May 2015 explosion at the Showa crater. The ash plume associated with the explosion rose 1.5 km above the crater rim. During an 8 June field survey conducted in Higashisakurajima-cho, Kagoshima City, a large impact crater believed to be associated with this explosion was located near the coast 3 km SSW from Minamidake. The crater formed by the ejected block was about 6 m in diameter and 2 m deep (figure 101); fragments found nearby were 10-20 cm in diameter (figure 102). A nearby roof was also damaged by the blocks. Smaller bombs were found in Kurokami-cho, Kagoshima City, around 4- 5 km E of Minamidake on 5 June; the largest fragment was 5 cm in diameter. Multiple ash plumes rose to 3 km or more above the summit during the first ten days of June; explosions on 4 and 5 June reached 3.7 km above the crater (figure 103). Larger than normal inflation and deflation before and after the explosions was recorded during early June in the inclinometers and extensometers located on the island. Incandescence at the summit was observed at night through the first half of June. The Tokyo VAAC issued multiple daily ash advisories during 1-10 June after which activity declined abruptly. Two brief explosions on 23 June and one on 28 June were the only two additional ash explosions reported in June.

Figure 101. A large crater measuring 6 m wide and 2 m deep was discovered 3 km from the Minamidake crater in Higashisakurajima, part of Kagoshima City, on 8 June 2020. It was believed to be from the impact of a large block ejected during the 4 June explosion at Aira’s Sakurajima volcano. Photo courtesy of Kagoshima City and JMA (Sakurajima Volcanic Activity Commentary, June 2020).

Figure 102. Fragments 10-30 cm in diameter from a large bomb that traveled 3 km from Minamidake crater on Sakurajima were found a few days after the 4 June 2020 explosion at Aira. Courtesy of JMA, photo courtesy of Kagoshima City (Sakurajima Volcanic Activity Commentary, June 2020).

Figure 103. An ash plume rose 3.7 km above the Minamidake crater at Aira’s Sakurajima volcano on 5 June 2020 and was recorded in Sentinel-2 satellite imagery. Image uses Atmospheric penetration rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub playground.

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); 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).

Nevados de Chillán is a complex of late-Pleistocene to Holocene stratovolcanoes in the Chilean Central Andes. An eruption started with a phreatic explosion and ash emission on 8 January 2016 from a new crater (Nicanor) on the E flank of the Nuevo crater, itself on the NW flank of the large Volcán Viejo stratovolcano. Strombolian explosions and ash emissions continued throughout 2016 and 2017; a lava dome within the Nicanor crater was confirmed in early January 2018. Explosions and pyroclastic flows continued during 2018 and 2019, with several lava flows appearing in late 2019. This report covers continuing activity from January-June 2020 when ongoing explosive events produced ash plumes, pyroclastic flows, and the growth of new dome inside the crater. Information for this report is provided primarily by Chile's Servicio Nacional de Geología y Minería (SERNAGEOMIN)-Observatorio Volcanológico de Los Andes del Sur (OVDAS), and by the Buenos Aires Volcanic Ash Advisory Center (VAAC).

Explosions with ash plumes rising up to three kilometers above the summit area were intermittent from late January through early June 2020. Some of the larger explosions produced pyroclastic flows that traveled down multiple flanks. Thermal anomalies within the Nicanor crater were recorded in satellite data several times each month from February through June. A reduction in overall activity led SERNAGEOMIN to lower the Alert Level from Orange to Yellow (on a 4-level, Green-Yellow-Orange-Red scale) during the first week of March, although tens of explosions with ash plumes were still recorded during March and April. Explosive activity diminished in early June and SERNAGEOMIN reported the growth of a new dome inside the Nicanor crater. By the end of June, a new flow had extended about 100 m down the N flank. Thermal activity recorded by the MIROVA project showed a drop in thermal energy in mid-December 2019 after the lava flows of September-November stopped advancing. A decrease in activity in January and February 2020 was followed by an increase in thermal and explosive activity in March and April. Renewed thermal activity from the growth of a new dome inside the Nicanor crater was recorded beginning in mid-June (figure 52).

Figure 52. MIROVA thermal anomaly data for Nevados de Chillan from 8 September 2019 through June 2020 showed a drop in thermal activity in mid-December 2019 after the lava flows of September-November stopped advancing. A decrease in activity in January and February 2020 was followed by an increase in explosive activity in March and April. Renewed thermal activity from the growth of a new dome inside the Nicanor crater was recorded beginning in mid-June. Courtesy of MIROVA.

Weak gas emissions were reported daily during January 2020 until a series of explosions began on the 21st. The first explosion rose 100 m above the active crater; the following day, the highest explosion rose 1.6 km above the crater. The Buenos Aires VAAC reported pulse emissions visible in satellite imagery on 21 and 24 January that rose to 3.9-4.3 km altitude and drifted SE and NE, respectively. Intermittent explosions continued through 26 January. Incandescent ejecta was observed during the night of 28-29 January. The VAAC reported an isolated emission on 29 January that rose to 5.2 km altitude and drifted E. A larger explosion on 30 January produced an ash plume that SERNAGEOMIN reported at 3.4 km above the crater (figure 53). It produced pyroclastic flows that traveled down ravines on the NNE and SE flanks. The Washington VAAC reported on behalf of the Buenos Aires VAAC that an emission was observed in satellite imagery on 30 January that rose to 4.9 km altitude and was moving rapidly E, reaching 15 km from the summit at midday. The altitude of the ash plume was revised two hours later to 7.3 km, drifting NNE and rapidly dissipating. Satellite images identified two areas of thermal anomalies within the Nicanor crater that day. One was the same emission center (CE4) identified in November 2019, and the second was a new emission center (CE5) located 60 m NW.

Figure 53. A significant explosion and ash plume from the Nicanor crater at Nevados de Chillan on 30 January 2020 produced an ash plume reported at 7.3 km altitude. The left image was taken within one minute of the initial explosion. Images posted by Twitter accounts #EmergenciasÑuble (left) and T13 (right); original photographers unknown.

When the weather permitted, low-altitude mostly white degassing was seen during February 2020, often with traces of fine-grained particulate material. Incandescence at the crater was observed overnight during 4-5 February. The Buenos Aires VAAC reported an emission on 14 February visible in the webcam. The next day, an emission was visible in satellite imagery at 3.9 km altitude that drifted E. Episodes of pulsating white and gray plumes were first observed by SERNAGEOMIN beginning on 18 February and continued through 25 February (figure 54). The Buenos Aires VAAC reported pulses of ash emissions moving SE on 18 February at 4.3 km altitude. Ash drifted E the next day at 3.9 km altitude and a faint plume was briefly observed on 20 February drifting N at 3.7 km altitude before dissipating. Sporadic pulses of ash moved SE from the volcano on 22 February at 4.3 km altitude, briefly observed in satellite imagery before dissipating. Thermal anomalies were visible from the Nicanor crater in Sentinel-2 satellite imagery on 23 and 28 February.

Figure 54. An ash emission at Nevados de Chillan on 18 February 2020 was captured in Sentinel-2 satellite imagery drifting SE (left). Thermal anomalies within the Nicanor crater were measured on 23 (right) and 28 February. Images use Atmospheric penetration rendering (bands 12, 11, 8a); courtesy of Sentinel Hub Playground.

Only low-altitude degassing of mostly steam was reported for the first half of March 2020. When SERNAGEOMIN lowered the Alert Level from Orange to Yellow on 5 March, they reduced the affected area from 5 km NE and 3 km SW of the crater to a radius of 2 km around the active crater. Thermal anomalies were recorded at the Nicanor crater in Sentinel-2 imagery on 4, 9, 11, 16, and 19 March (figure 55). A new series of explosions began on 19 March; 44 events were recorded during the second half of the month (figure 56). Webcams captured multiple explosions with dense ash plumes; on 25 and 30 March the plumes rose more than 2 km above the crater. Fine-grained ashfall occurred in Las Trancas (10 km SW) on 25 March. Pyroclastic flows on 25 and 30 March traveled 300 m NE, SE, and SW from the crater. Incandescence was observed at night multiple times after 20 March. The Buenos Aires VAAC reported several discrete pulses of ash that rose to 4.3 km altitude and drifted SE on 20 and 21 March, SW on 25 March, and SE on 29 and 30 March. Another ash emission rose to 5.5 km altitude later on 30 March and drifted SE.

Figure 55. Sentinel-2 Satellite imagery of Nevados de Chillan during March 2020 showed thermal anomalies on five different dates at the Nicanor crater, including on 9, 11, and 16 March. A second thermal anomaly of unknown origin was also visible on 11 March about 2 km SW of the crater (center). Images use Atmospheric penetration rendering (bands 12, 11, 8a); courtesy of Sentinel Hub Playground.

Figure 56. Forty-four explosive events were recorded at Nevados de Chillan during the second half of March 2020 including on 19 March. Courtesy of SERNAGEOMIN webcams and chillanonlinenoticia.

In their semi-monthly reports for April 2020, SERNAGEOMIN reported 94 explosive events during the first half of the month and 49 during the second half; many produced dense ash plumes. The Buenos Aires VAAC reported frequent intermittent ash emissions during 1-13 April reaching altitudes of 3.7-4.3 km (figure 57). They reported the plume on 8 April visible in satellite imagery at 7.3 km altitude drifting SE. An emission on 13 April was also visible in satellite imagery at 6.1 km altitude drifting NE.

Figure 57. Sentinel-2 satellite imagery captured a strong thermal anomaly and an ash plume drifting SE from Nevados de Chillan on 10 April 2020. Image uses Atmospheric penetration rendering (bands 12, 11, 8a); courtesy of Sentinel Hub Playground.

During the second half of April 2020, SERNAGEOMIN reported that only one plume exceeded 2 km in height; on 21 April, it rose to 2.4 km above the crater (figure 58). The Buenos Aires VAAC reported isolated pulses of ash on 18, 26, 28, and 30 April. During the second half of April SERNAGEOMIN also reported that a pyroclastic flow traveled about 1,200 m from the crater rim down the SE flank. The ash from the pyroclastic flow drifted SE and S as far as 3.5 km. Satellite images showed continued activity from multiple emission centers around the crater. Pronounced scarps were noted on the internal walls of the crater, attributed to the deepening of the crater from explosive activity.

Figure 58. Tens of explosions were reported at Nevados de Chillan during the second half of April 2020 that produced dense ash plumes. The plume on 21 April rose 2.4 km above the Nicanor crater. Photo by Josefa Carrasco Acuña from San Fabián de Alico; posted by Noticias Valpo Express.

Intermittent explosive activity continued during May 2020. The plumes contained abundant particulate material and were accompanied by periodic pyroclastic flows and incandescent ejecta around the active crater, especially visible at night. The Buenos Aires VAAC reported several sporadic weak ash emissions during the first week of May that rose to 3.7-5.2 km altitude and drifted NE. SERNAGEOMIN reported that only one explosion produced an ash emission that rose more than two km above the crater during the first two weeks of the month; on 6 May it rose to 2.5 km above the crater and drifted NE. They also observed pyroclastic flows on the E and SE flanks that day. Additional pyroclastic flows traveled 450 m down the S flank during the first half of the month, and similar deposits were observed to the N and NE. Satellite observations showed various emission points along the NW-trending lineament at the summit and multiple erosion scarps. Major erosion was noted at the NE rim of the crater along with an increase in degassing around the rim.

During the second half of May 2020 most of the ash plumes rose less than 2 km above the crater; a plume from one explosion on 22 May rose 2.2 km above the crater; the Buenos Aires VAAC reported the plume at 5.5 km altitude drifting NW (figure 59). Continuing pyroclastic emissions deposited material as far as 1.5 km from the crater rim on the NNW flank. There were also multiple pyroclastic deposits up to 500 m from the crater directed N and NE during the period. SERNAGEOMIN reported an increase in steam degassing between Nuevo-Nicanor and Nicanor-Arrau craters.

Figure 59. Explosions produced dense ash plumes and pyroclastic flows at Nevados de Chillan multiple times during May 2020 including on 22 May. Courtesy of SERNAGEOMIN.

Webcam images during the first two weeks of June 2020 indicated multiple incandescent explosions. On 3 and 4 June plumes from explosions reached heights of over 1.25 km above the crater; the Buenos Aires VAAC reported them drifting NW at 3.9 km altitude. Incandescent ejecta on 6 June rose 760 m above the vent and drifted NE. In addition, pyroclastic flows were distributed on the N, NW, E and SE flanks. Significant daytime and nighttime incandescence was reported on 6, 9, and 10 June (figure 60). The VAAC reported emission pulses on 6 and 9 June drifting E and SE at 4.3 km altitude.

Figure 60. Multiple ash plumes with incandescence were reported at Nevados de Chillan during the first ten days of June 2020 including on 6 June, after which explosive activity decreased significantly. Courtesy of SERNAGEOMIIN and Sismo Alerta Mexicana.

SERNAGEOMIN reported that beginning on the afternoon of 9 June 2020 a tremor-type seismic signal was first recorded, associated with continuous emission of gas and dark gray ash that drifted SE (figure 61). A little over an hour later another tremor signal began that lasted for about four hours, followed by smaller discrete explosions. A hybrid-type earthquake in the early morning of 10 June was followed by a series of explosions that ejected gas and particulate matter from the active crater. The vent where the emissions occurred was located within the Nicanor crater close to the Arrau crater; it had been degassing since 30 May.

Figure 61. A tremor-type seismic signal was first recorded on the afternoon of 9 June 2020 at Nevados de Chillan. It was associated with the continuous emission of gas and dark gray ash that drifted SE, and incandescent ejecta visible after dark. View is to the S, courtesy of SERNAGEOMIN webcam, posted by Volcanology Chile.

After the explosions on the afternoon of 9 June, a number of other nearby vents became active. In particular, the vent located between the Nuevo and Nicanor craters began emitting material for the first time during this eruptive cycle. The explosion also generated pyroclastic flows that traveled less than 50 m in multiple directions away from the vent. Abundant incandescent material was reported during the explosion early on 10 June. Deformation measurements showed inflation over the previous 12 days.

SERNAGEOMIN identified a surface feature in satellite imagery on 11 June 2020 that they interpreted as a new effusive lava dome. It was elliptical with dimensions of about 85 x 120 m. In addition to a thermal anomaly attributed to the dome, they noted three other thermal anomalies between the Nuevo, Arrau, and Nicanor craters. They reported that within four days the base of the active crater was filled with effusive material. Seismometers recorded tremor activity after 11 June that was interpreted as associated with lava effusion. Incandescent emissions were visible at night around the active crater. Sentinel-2 satellite imagery recorded a bright thermal anomaly inside the Nicanor crater on 14 June (figure 62).

Figure 62. A bright thermal anomaly was recorded inside the Nicanor crater at Nevados de Chillan on 14 June 2020. SERNAGEOMIN scientists attributed it to the growth of a new lava dome within the crater. Image uses Atmospheric penetration rendering (bands 12, 11, 8a); courtesy of Sentinel Hub Playground.

A special report from SERNAGEOMIN on 24 June 2020 noted that vertical inflation had increased during the previous few weeks. After 20 June the inflation rate reached 2.49 cm/month, which was considered high. The accumulated inflation measured since July 2019 was 22.5 cm. Satellite imagery continued to show the growth of the dome, and SERNAGEOMIN scientists estimated that it reached the E edge of the Nicanor crater on 23 June. Based on these images, they estimated an eruptive rate of 0.1-0.3 m³/s, about two orders of magnitude faster than the Gil-Cruz dome that emerged between December 2018 and early 2019.

Webcams revealed continued low-level explosive activity and incandescence visible both during the day and at night. By the end of June, webcams recorded a lava flow that extended 94 m down the N flank from the Nicanor crater and continued to advance. Small explosions with abundant pyroclastic debris produced recurring incandescence at night. Satellite infrared imagery indicated thermal radiance from effusive material that covered an area of 37,000 m², largely filling the crater. DEM analysis suggested that the size of the crater had tripled in volume since December 2019 due largely to erosion from explosive activity since May 2020. Sentinel-2 satellite imagery showed a bright thermal anomaly inside the crater on 27 June.

Geologic Background. The compound volcano of Nevados de Chillán is one of the most active of the Central Andes. Three late-Pleistocene to Holocene stratovolcanoes were constructed along a NNW-SSE line within three nested Pleistocene calderas, which produced ignimbrite sheets extending more than 100 km into the Central Depression of Chile. The largest stratovolcano, dominantly andesitic, Cerro Blanco (Volcán Nevado), is located at the NW end of the group. Volcán Viejo (Volcán Chillán), which was the main active vent during the 17th-19th centuries, occupies the SE end. The new Volcán Nuevo lava-dome complex formed between 1906 and 1945 between the two volcanoes and grew to exceed Volcán Viejo in elevation. The Volcán Arrau dome complex was constructed SE of Volcán Nuevo between 1973 and 1986 and eventually exceeded its height.

Information Contacts: Servicio Nacional de Geología y Minería (SERNAGEOMIN), Observatorio Volcanológico de Los Andes del Sur (OVDAS), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/, https://twitter.com/Sernageomin); 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/); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); #EmergenciasÑuble (URL: https://twitter.com/urgenciasnuble/status/1222943399185207296); T13, Channel 13 Press Department (URL: https://twitter.com/T13/status/1222951071443771394); Chillanonlinenoticia (URL: https://twitter.com/ChillanOnline/status/1240754211932995595); Noticias Valpo Express (URL: https://twitter.com/NoticiasValpoEx/status/1252715033131388928); Sismo Alerta Mexicana (URL: https://twitter.com/Sismoalertamex/status/1269351579095691265); Volcanology Chile (URL: https://twitter.com/volcanologiachl/status/1270548008191643651).

Kerinci is a stratovolcano located in Sumatra, Indonesia that has been characterized by explosive eruptions with ash plumes and gas-and-steam emissions. The most recent eruptive episode began in April 2018 which has included intermittent explosions and ash plumes. The previous report (BGVN 44:12) described more recent activity consisting of intermittent gas-and-steam and ash plumes which occurred during June through early November 2019. This volcanism continued through May 2020, though little to no activity was reported during December 2019. The primary source of information for this report comes from Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC).

Activity during December 2019 consisted of white gas-and-steam emissions rising 100-500 m above the summit. White and brown emissions continued intermittently through May 2020, rising to a maximum altitude of 1 km above the summit on 14 April. During 3-6 and 8-9 January 2020, the Darwin VAAC and PVMBG issued notices reporting brown volcanic ash rising 150-600 m above the summit drifting S and ESE (figure 19). PVMBG published a VONA notice on 24 January at 0828 reporting ash rising 400 m above the summit. Brown emissions continued intermittently throughout the reporting period. On 1 February, volcanic ash was observed rising 300-960 m above the summit and drifting NE; PVMBG reported continuing brown emissions during 1-3 February. During 16-17 February, two VONA notices reported that brown ash plumes rose 150-400 m above the summit and drifted SW accompanied by consistent white gas-and-steam emissions (figure 20).

Figure 19. Brown ash plume rose 500-600 m above Kerinci on 4 January 2020. Courtesy of MAGMA Indonesia via Øystein Lund Andersen.

Figure 20. White gas-and-steam emissions rose 400 m above Kerinci on 19 February 2020. Courtesy of MAGMA Indonesia via Øystein Lund Andersen.

During 1-16 and 25-26 March 2020 brown ash emissions were frequently observed rising 100-500 m above the summit drifting in multiple directions. During 6-8 and 10-15, April brown ash emissions were reported 50-1,000 m above the summit. The most recent Darwin VAAC and VONA notices were published on 14 April, reporting volcanic ash rising 400 and 600 m above the summit, respectively; however, PVMBG reported brown emissions rising up to 1,000 m. By 25-27 April brown ash emissions rose 50-300 m above the summit. Intermittent white gas-and-steam emissions continued through May. The last brown emissions seen in May were reported on the 7th rising 50-100 m above the summit.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: http://www.oysteinlundandersen.com, images at https://twitter.com/OysteinLAnderse/status/1213658331564269569/photo/1 and https://twitter.com/OysteinLAnderse/status/1230419965209018369/photo/1).

Tinakula is a remote stratovolcano located 100 km NE of the Solomon Trench at the N end of the Santa Cruz. In 1971, an eruption with lava flows and ash explosions caused the small population to evacuate the island. Volcanism has previously been characterized by an ash explosion in October 2017 and the most recent eruptive period that began in December 2018 with renewed thermal activity. Activity since then has consisted of intermittent thermal activity and dense gas-and-steam plumes (BGVN 45:01), which continues into the current reporting period. This report updates information from January-June 2020 using primary source information from various satellite data, as ground observations are rarely available.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed weak, intermittent, but ongoing thermal activity during January-June 2020 (figure 41). A small cluster of slightly stronger thermal signatures was detected in late February to early March, which is correlated to MODVOLC thermal alert data; four thermal hotspots were recorded on 20, 27, and 29 February and 1 March. However, observations using Sentinel-2 satellite imagery were often obscured by clouds. In addition to the weak thermal signatures, dense gas-and-steam plumes were observed in Sentinel-2 satellite imagery rising from the summit during this reporting period (figure 42).

Figure 41. Weak thermal anomalies at Tinakula from 26 June 2019 through June 2020 as recorded by the MIROVA system (Log Radiative Power) were intermittent and clustered more strongly in late February to early March.

Figure 42. Sentinel-2 satellite imagery shows ongoing gas-and-steam plumes rising from Tinakula during January through May 2020. Images with atmospheric penetration (bands 12, 11, 8a) rendering; courtesy of Sentinel Hub Playground.

Three distinct thermal anomalies were observed in Sentinel-2 thermal satellite imagery on 22 January, 11 April, and 6 May 2020, accompanied by some gas-and-steam emissions (figure 43). The hotspot on 22 January was slightly weaker than the other two days, and was seen on the W flank, compared to the other two that were observed in the summit crater. According to MODVOLC thermal alerts, a hotspot was recorded on 6 May, which corresponded to a Sentinel-2 thermal satellite image with a notable anomaly in the summit crater (figure 43). On 10 June no thermal anomaly was seen in Sentinel-2 satellite imagery due to the presence of clouds; however, what appeared to be a dense gas-and-steam plume was extending W from the summit.

Figure 43. Sentinel-2 thermal satellite images showing a weak thermal activity (bright yellow-orange) on 22 January 2020 on the W flank of Tinakula (top) and slightly stronger thermal hotspots on 11 April (middle) and 6 May (bottom) in at the summit, which are accompanied by gas-and-steam emissions. Images with atmospheric penetration (bands 12, 11, 8a) rendering; 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).

Ibu is an active stratovolcano located along the NW coast of Halmahera Island in Indonesia. Volcanism has recently been characterized by frequent ash explosions, ash plumes, and small lava flows within the crater throughout 2019 (BGVN 45:01). Activity continues, consisting of frequent white-and-gray emissions, ash explosions, ash plumes, and lava flows. This report updates activity through June 2020, using data from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Darwin Volcanic Ash Advisory Centre (VAAC), and various satellites.

Volcanism during the entire reporting period dominantly consisted of white-and-gray emissions that rose 200-800 m above the summit drifting in multiple directions. The ash plume with the maximum altitude of 13.7 km altitude occurred on 16 May 2020. Sentinel-2 thermal satellite imagery detected multiple smaller hotspots within the crater throughout the reporting period.

Continuous ash emissions were reported on 6 February rising to 2.1 km altitude drifting E, accompanied by a hotspot visible in infrared satellite imagery. On 16 February, a ground observer reported an eruption that produced an ash plume rising 800 m above the summit drifting W, according to a Darwin VAAC notice. Ash plumes continued through the month, drifting in multiple directions and rising up to 2.1 km altitude. During 8-10 March, video footage captured multiple Strombolian explosions that ejected incandescent material and produced ash plumes from the summit (figures 21 and 22). Occasionally volcanic lightning was observed within the ash column, as recorded in video footage by Martin Rietze. This event was also documented by a Darwin VAAC notice, which stated that multiple ash emissions rose 2.1 km altitude drifting SE. PVMBG published a VONA notice on 10 March at 1044 reporting ash plumes rising 400 m above the summit. PVMBG and Darwin VAAC notices described intermittent eruptions on 26, 28, and 29 March, all of which produced ash plumes rising 300-800 m above the summit.

Figure 21. Strombolian explosions recorded at the crater summit of Ibu during 8-10 March 2020 ejected incandescent ejecta and a dense ash plume. Video footage copyright by Martin Rietze, used with permission.

Figure 22. Strombolian explosions recorded at the crater summit of Ibu during 8-10 March 2020 ejected incandescent ejecta and ash. Frequent volcanic lightning was also observed. Video footage copyright by Martin Rietze, used with permission.

A majority of days in April included white-and-gray emissions rising up to 800 m above the summit. A ground observer reported an eruption on 9 April, according to a Darwin VAAC report, and a hotspot was observed in HIMAWARI-8 satellite imagery. Minor eruptions were reported intermittently during mid-April and early to mid-May. On 12 May at 1052 a VONA from PVMBG reported an ash plume 800-1,100 m above the summit. A large short-lived eruption on 16 May produced an ash plume that rose to a maximum of 13.7 km altitude and drifted S, according to the Darwin VAAC report. By June, volcanism consisted predominantly of white-and-gray emissions rising 800 m above the summit, with an ash eruption on 15 June. This eruptive event resulted in an ash plume that rose 1.8 km altitude drifting WNW and was accompanied by a hotspot detected in HIMAWARI-8 satellite imagery, according to a Darwin VAAC notice.

The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected frequent hotspots during July 2019 through June 2020 (figure 23). In comparison, the MODVOLC thermal alerts recorded a total of 24 thermal signatures over the course of 19 different days between January and June. Many thermal signatures were captured as small thermal hotspots in Sentinel-2 thermal satellite imagery within the crater (figure 24).

Figure 23. Thermal anomalies recorded at Ibu from 2 July 2019 through June 2020 as recorded by the MIROVA system (Log Radiative Power) were frequent and consistent in power. Courtesy of MIROVA.

Figure 24. Sentinel-2 thermal satellite imagery (bands 12, 11, 8A) showed occasional thermal hotspots (bright orange) in the Ibu summit crater during January through June 2020. Courtesy of Sentinel Hub Playground.

Geologic Background. The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, contained several small crater lakes through much of historical time. The outer crater, 1.2 km wide, is breached on the north side, creating a steep-walled valley. A large parasitic cone is located ENE of the summit. A smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. Only a few eruptions have been recorded in historical time, the first a small explosive eruption from the summit crater in 1911. An eruption producing a lava dome that eventually covered much of the floor of the inner summit crater began in December 1998.

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/); 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); Martin Rietze, Taubenstr. 1, D-82223 Eichenau, Germany (URL: https://mrietze.com/, https://www.youtube.com/channel/UC5LzAA_nyNWEUfpcUFOCpJw/videos, video at https://www.youtube.com/watch?v=qMkfT1e4HQQ).

Suwanosejima is an active stratovolcano located in the northern Ryukyu Islands. Volcanism has previously been characterized by Strombolian explosions, ash plumes, and summit incandescence (BGVN 45:01), which continues to occur intermittently. A majority of this activity originates from vents within the large Otake summit crater. This report updates information during January through June 2020 using monthly reports from the Japan Meteorological Agency (JMA), the Tokyo Volcanic Ash Advisory Center (VAAC), and various satellite data.

During 3-10 January 2020, 13 explosions were detected from the Otake crater rising to 1.4 km altitude; material was ejected as far as 600 m away and ashfall was reported in areas 4 km SSW, according to JMA. Occasional small eruptive events continued during 12-17 January, which resulted in ash plumes that rose 1 km above the crater rim and ashfall was again reported 4 km SSW. Crater incandescence was visible nightly during 17-24 January, while white plumes rose as high as 700 m above the crater rim.

Nightly incandescence during 7-29 February, and 1-6 March, was accompanied by intermittent explosions that produced ash plumes rising up to 1.2 km above the crater rim (figure 44); activity during early February resulted in ashfall 4 km SSW. On 19 February an eruption produced a gray-white ash plume that rose 1.6 km above the crater (figure 45), resulting in ashfall in Toshima village (4 km SSW), according to JMA. Explosive events during 23-24 February ejected blocks onto the flanks. Two explosions were recorded during 1-6 March, which sent ash plumes as high as 900-1,000 m above the crater rim and ejected large blocks 300 m from the crater.

Figure 44. Surveillance camera images of summit incandescence at Suwanosejima on 29 January (top left), 21 (middle left) and 23 (top right) February, and 25 March (bottom left and right) 2020. Courtesy of JMA (Monthly bulletin reports 511, January, February, and March 2020).

Figure 45. Surveillance camera images of which and white-and-gray gas-and-steam emissions rising from Suwanosejima on 5 January (top), 19 February (middle), and 24 March 2020 (bottom). Courtesy of JMA (Monthly bulletin reports 511, January, February, and March 2020).

Nightly incandescence continued to be visible during 13-31 March, 1-10 and 17-24 April, 1-8, 15-31 May, 1-5 and 12-30 June 2020; activity during the latter part of March was relatively low and consisted of few explosive events. In contrast, incandescence was frequently accompanied by explosions in April and May. On 28 April at 0432 an eruption produced an ash plume that rose 1.6 km above the crater rim and drifted SE and E, and ejected blocks as far as 800 m from the crater. The MODVOLC thermal alerts algorithm also detected four thermal signatures during this eruption within the summit crater. An explosion at 1214 on 29 April caused glass in windows to vibrate up to 4 km SSW away while ash emissions continued to be observed following the explosion the previous day, according to the Tokyo VAAC.

During 1-8 May explosions occurred twice a day, producing ash plumes that rose as high as 1 km above the crater rim and ejecting material 400 m from the crater. An explosion on 29 May at 0210 produced an off-white plume that rose as high as 500 m above the crater rim and ejected large blocks up to 200 m above the rim. On 5 June an explosion produced gray-white plumes rising 1 km above the crater. Small eruptive events continued in late June, producing ash plumes that rose as high as 900 m above the crater rim.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed relatively stronger thermal anomalies in late February and late April 2020 with an additional six weaker thermal anomalies detected in early January (2), early February (1), mid-April (2), and mid-May (1) (figure 46). Sentinel-2 thermal satellite imagery in late January through mid-April showed two distinct thermal hotspots within the summit crater (figure 47).

Figure 46. Prominent thermal anomalies at Suwanosejima during July-June 2020 as recorded by the MIROVA system (Log Radiative Power) occurred in late February and late April. Courtesy of MIROVA.

Figure 47. Sentinel-2 thermal satellite images showing small thermal anomalies (bright yellow-orange) from two locations within the Otake summit crater at Suwanosejima. Images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

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); 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).

Bagana lies in a nearly inaccessible mountainous tropical rainforest area of Bougainville Island in Papua New Guinea and is primarily monitored by satellite imagery of ash plumes and thermal anomalies. After a state of elevated activity that lasted through December 2018 (BGVN 43:05, 44:06, 44:12), the volcano entered a quieter period that persisted through at least May 2020. This report focuses on activity between December 2019 and May 2020.

Atmospheric clouds often obscured satellite views of the volcano during the reporting period. When the volcano could be observed, light-colored gas plumes were often observed (figure 43). Based on satellite and wind model data, the Darwin Volcanic Ash Advisory Centre (VAAC) reported that during 29 February-2 March ash plumes rose to an altitude of 1.8-2.1 km and drifted SW and N. On 1 May an ash plume rose to an altitude of 3 km and drifted NW and W. According to both Darwin VAAC volcanic ash advisories, the Aviation Color Code was Orange (second highest of four hazard levels).

Figure 43. Sentinel-2 image of Bagana, showing a gas plume drifting SE on 13 March 2020, during a period when the Darwin VAAC had not reported any ash explosions (Natural Color rendering, bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

During the reporting period, the MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system recorded only intermittent thermal anomalies, all of which were of low radiative power. Sulfur dioxide emissions detected by satellite-based instruments over this reporting period were at low levels.

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: Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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/).

Sakurajima rises from Kagoshima Bay, which fills the Aira Caldera near the southern tip of Japan's Kyushu Island. Frequent explosive and occasional effusive activity has been ongoing for centuries. The Minamidake summit cone has been the location of persistent activity since 1955; the Showa crater on its E flank has been the most active site since 2006. Tens of explosions and ash-bearing emissions have been occurring monthly for the last several years and were continuous through October 2015. After a three-month break, activity resumed in February 2016 and lasted through August 2016. No further activity was reported through December 2016. The Japan Meteorological Agency (JMA) provided regular reports on activity, and the Tokyo VAAC (Volcanic Ash Advisory Center) issued hundreds of reports about ash plumes during 2015-2016.

The number of explosive events at the Showa crater of Sakurajima increased from January-May 2015. During the period, ash emissions commonly rose 3,000 m above the crater rim, and a few exceeded 4,000 m; tephra was often ejected 1.3 km and as far as 1.8 km from the crater. Incandescence was observed every week; multiple MODVOLC thermal alerts were reported monthly from January-June 2015. The Tokyo VAAC issued 845 reports between 1 January and 14 October 2015. The number of monthly explosions decreased sharply during June-August. Tiltmeter and strainmeter data indicated continuing inflation through mid-August when the inflation rate increased significantly for a brief period. This was followed by deflation for the remainder of 2015. Pyroclastic flows were reported in March, April, and June. Minor emissions occurred at Minamidake crater in May, June, and August. Activity increased at both craters during September, with the first substantial explosion at Minamidake in almost a year. An emission from Showa on 2 November 2015 was noted in a JMA weekly report, but its composition was not described; the last confirmed ash emission of the year was on 14 October 2015.

After three months of quiet, a substantial explosion at Showa in early February 2016 marked the beginning of a new eruptive episode that continued through the end of July, after which explosive activity ceased at Showa for the remainder of the year (figure 49). Minor emissions were reported at Minamidake through August 2016. Pyroclastic flows occurred in April and June from explosions at the Showa crater. Inflation was measured again beginning in April 2016 and continued through December 2016.

Figure 49. Explosions from the Showa crater at Sakurajima, January 2013-December 2016. Data do not include activity at Minamidake crater, or passive (non-explosive) ash or steam emissions from Showa. After many years of multiple monthly explosions, activity decreased in September 2015. A smaller burst of activity occurred from February to July 2016. Data compiled from JMA reports.

Activity during January-May 2015. JMA reported 61 explosions from the Showa crater during January 2015, twice the number recorded in December 2014 (figure 50). Explosions on 4 and 30 January sent ejecta as far as 1.8 km from the crater. The maximum plume height reported by JMA was 4,000 m above the crater rim on 23 January. Lapilli up to 2 cm in diameter from recent explosions were found in Kurokami (3.5 km E) and Arimura (3 km S) during JMA field visits on 16 and 30 January.

Figure 50. An ash emission at Sakurajima on 20 January 2015 was captured by a webcam in Kagoshima (10 km W). Courtesy of Volcano Discovery.

The number of explosions increased to 88 during February 2015, with events on 21 and 22 February sending tephra 1.8 km from the crater. Plumes rose as much as 3,500 m above the rim during the month. During a field survey on 4 March scientists observed ash deposits with fragments up to 2 cm in diameter, in an area 3 km S of Showa Crater. JMA reported that the largest number of explosions they have recorded in a month, 178, occurred at the crater in March. Numerous plumes rose 3,300 m above the crater. A small pyroclastic flow on 17 March traveled 600 m SE.

Seismicity below the island increased briefly between 31 March and 2 April 2015. An explosion on 17 April sent tephra 1.8 km from the crater rim. Two pyroclastic flows were reported on 18 and 28 April 2015; Showa crater had 112 explosions throughout the month. The pyroclastic flow on 28 April travelled 500 m down the SE flank. The highest ash plume rose 4,000 m on 24 April. JMA calculated that about 1.2 million tons of ash fell during April, the largest monthly amount recorded since 2006.

Several of the 169 explosions at the Showa crater during May 2015 produced ejecta that was deposited up to 1.8 km from the crater. Many explosions had plume heights exceeding 3,000 m. A small emission, rising 200 m, was observed from the Minamidaki crater on 12 May and was the first in several months. JMA scientists observed 2-cm-diameter tephra in the vicinity of Kurojin-cho, Kagoshima-shi on 14 May, likely from an explosion the previous day; significant ashfall covered the ground as well. The highest ash plume of the month rose 4,300 m above the Showa crater on 21 May 2015 (figures 51 and 52).

Figure 51. An ash plume rose 4,300 m above Sakurajima on 21 May 2015, shown in this webcam image from Kagoshima. Courtesy of Volcano Discovery.

Figure 52. A dense plume of ash drifted S and E from Sakurajima on 21 May 2015. This natural-color satellite image was taken by the Operational Land Imager on Landsat 8. Courtesy of NASA Earth Observatory.

Activity during June-December 2015. Five of the 64 explosions recorded during June produced ejecta that landed up to 1.3 km from the Showa Crater (figure 53). A 3,300-m-high ash plume on 1 June was the highest for the month. After three explosions on 4 June, a small pyroclastic flow traveled 400 m down the E flank. A second small event on 22 June at Minamidake produced a gray plume that rose 200 m.

Figure 53. Ash rose from Showa Crater at Sakurajima on 9 June 2015. Image taken by a drone managed by Naoto Yoshitome and Krishima Aerial Photography. Courtesy of Naoto Yoshitome, Twitter.

Activity decreased significantly beginning in July 2015, with 14 explosions reported from the Showa Crater, and declined further during August with only 5 explosions. A small explosion from the Minamidake crater on 16 July sent emissions likely containing ash (described as "non-white") to 200 m. A rapid increase in seismicity directly beneath Minamidake began on 15 August and lasted about 48 hours; along with tiltmeter and strainmeter observations of rapid inflation (figure 54), this led JMA to briefly raise the Alert Level from 3 (Do not approach the volcano) to 4 (Prepare to evacuate) an a scale of 1-5. They lowered it back to 3 on 1 September 2015. Only small explosions with tephra ejected up to 800 m were recorded during the rest of the August. Minor emissions occurred at Minamidake Crater on 30 August.

Figure 54. An interference image of Sakurajima using PALSAR-2 high-resolution mode (3 m resolution) data comparing displacement between 4 January and 16 August 2015. The data showed a displacement toward the satellite (inflation) of about 16 cm maximum (within the white square), on the E side of the Minamidake summit crater. The synthetic aperture radar (PALSAR - 2) equipped with Daichi 2 (Land Observing Satellite No. 2 "Daichi 2" (ALOS- 2)) can measure the displacement of the ground surface (how much the ground moved) by taking the difference between two sets of observation data. Such an analysis method is called interference SAR analysis (or interferometry, InSAR). The color changes represent the differences in the two observations, a pattern of green to red to blue indicates movement of the surface towards the satellite (inflation); a pattern of green to blue to red indicates movement away from the satellite (deflation). Courtesy of JAXA (http://www.eorc.jaxa.jp/ALOS-2/img_up/jpal2_sakurajima_20150816-17.htm).

Incandescence at the Showa Crater was observed several times during September 2015; 46 explosive events were reported. The first significant explosions at the Minamidake summit crater since 7 November 2014 occurred on 13 and 28 September. The 28 September plume rose to 2,700 m above the crater rim. Tiltmeter data indicated no additional inflation since the rapid ground deformation of 15-16 August. The last explosive event of 2015 reported by JMA at the Showa crater was on 17 September and at the Minamidaki crater on 29 September.

The Tokyo VAAC reported an ash emission on 14 October 2015 that rose to 1.8 km and drifted SW. This was the last VAAC report until 5 February 2016. No explosions were recorded at the Showa crater in October, but minor ash emissions were reported on 14, 15, 21, 22, and 30 October. No activity was observed at Minamidake. Data from continuous GNSS (Global Navigation Satellite System) observations suggested that deflation began after the 15 August rapid inflation event.

A minor emission was reported by JMA from the Showa crater on 2 November 2015, the last emission reported for the year. After not having explosive activity since late September, JMA lowered the Alert Level to 2 (Do not approach the crater) on 25 November, reducing the exclusion area to 1 km around the two craters. Only steam plumes rising 50-200 m above the Showa crater and 50-600 m above the Minamidake crater were observed during December 2015.

Aerial observation on 2 December 2015 revealed 100-m-high steam plumes around the floor of the Showa crater. Thermal observations showed high heat flow around the edges and at the center of the crater floor, unchanged since the previous observation in August 2015; 200-m-high steam plumes around the Minamidake crater prevented observation of the crater floor.

Activity during 2016. No explosive activity was observed at Showa or Minamidake craters from October 2015 to 5 February 2016. JMA raised the Alert Level back to 3 after a substantial explosion on 5 February sent incandescent tephra up to 1.8 km from the Showa crater; lightning was observed in the ash cloud (figure 55). The Tokyo VAAC reported that an ash plume visible in satellite imagery was at 3 km altitude drifting SE. Multiple explosions continued from the Showa crater for the rest of February with ash plumes rising to 2.2 km above the crater, and tephra was frequently ejected 1.3 km from the crater. Four MODVOLC thermal alerts in February were the only alerts for 2016. At the Minamidake summit crater, minor emissions occurred on 8, 9, and 20 February with plumes rising 800 m above the crater rim.

Figure 55. Incandescent tephra explodes from Showa crater at Sakurajima on 5 February 2016 after three months of inactivity. Photo by Kyoto News/AP. Courtesy of the Washington Post.

Eight explosions at the Showa crater were reported by JMA, and six at the Minamidake summit crater during March 2016. Ash plumes at Minamidake on 4, 8, and 11 March rose 1,600-1,900 m above the crater rim; on 25 and 26 March they rose 2,000 m. Minor emissions were also noted on 14 and 15 March. Three explosions from the Showa Crater on 26 March sent ash plumes 2,700 m high (figure 56); tephra as large as 8 mm in diameter was found in areas 4 km E.

Figure 56. Multiple explosions on 26 March 2016 at Sakurajima sent tephra as large as 8 mm in diameter as far as 4 km from Minamidake crater. Image taken from a drone managed by Naoto Yoshidome. Courtesy of Naoto Yoshidome, Twitter.

Activity increased during April 2016 with 51 emission events that included 15 explosions at Showa, and JMA reported inflation again after several months of stability. Reports of falling tephra, 2 cm in diameter, came from a town 3 km S after explosions were witnessed during 1-3 April. On 1 April, an explosion at Minamidake summit crater produced an ash plume which rose 800 m above its crater rim; another on 3 April rose 1,700 m. Minor emissions also occurred at Minamidake on 5, 6, and 9 April. Explosions on 6 and 8 April at Showa sent ash plumes 3,500-3,700 m high and tephra 1.3 km. During the 8 April explosion at Showa, a small pyroclastic flow traveled 400 m down the E flank, the first since June 2015. A 2,200-m-high ash plume rose from Showa crater on 17 April. Minor emissions that rose 800 m were detected at Minamidake on 20 and 28 April. Two explosions occurred on 27 April at Showa, followed by additional explosions on 28, 29, and 30 April; the events generated ash plumes that rose 3,000 m. Pyroclastic flows were generated during the events of 28 and 30 April; they each flowed about 500 m, SE and E, respectively.

A large explosion at the Showa crater on 1 May sent an ash plume to 4,100 m above the crater rim (figure 57). It was the first time since 21 May 2015 that a plume rose higher than 4,000 m. At the Minamidake summit crater, ash emissions on 1 and 13 May rose 3,500 and 3,700 m, respectively, the first plumes at Minamidake over 3,000 m since October 2009. An explosion on 8 May at Showa sent an ash plume over 3,300 m above the crater rim, and tephra reached 1,300 m from the crater. Numerous ash emissions continued throughout the month, some with plumes rising to 3,500 m. The Tokyo VAAC issued 26 reports between 13 and 22 May. Activity diminished toward the end of the month, but minor inflation continued.

Figure 57. An explosive eruption at Sakurajima's Showa Crater on 1 May 2016 sent an ash plume 4,100 m above the crater that drifted SE. It was the highest plume in the last year. Taken with the "Cattle Root" webcam, courtesy of JMA (May 2016 Monthly Sakurajima report).

Multiple ash emissions in early June 2016 produced plumes as high as 2,000 m above the Showa crater rim. An explosion on 3 June produced a pyroclastic flow that traveled 400 m SE, and tephra that was ejected 800 m from the crater. An emission at the Minamidake crater on 3 June rose 1,500m high. No further explosive activity was reported for June; only a minor emission from the Showa crater on 29 June. During the month, the Tokyo VAAC issued only six reports (during 2-3 June).

Two explosive events were recorded at Showa crater in July 2016. An explosion occurred on 2 July that produced a 1,200-m-high ash plume and sent large blocks 800 m from the crater. A substantial explosion on 26 July at Showa sent blocks 800 m from the crater, and produced an ash plume that rose 5,000 m. A minor amount of ashfall on the W and SW flanks of Sakurajima was observed, and ashfall was confirmed in a wide area from Kagoshima City (10 km W) to Hioki City (25 km NW). The Tokyo VAAC reported an ash plume drifting SW at 6.1 km altitude that day.

Minor emissions were observed at the Minamidake crater intermittently throughout August 2016, but no emissions or explosions were reported from Showa. The Tokyo VAAC reported a low-level ash plume on 22 August at 1.2 km altitude drifting 50 km SW (figure 58). This was the last VAAC report for 2016. Although there were no emissions or explosive activity reported from either crater during September-December 2016, inflation of the volcano continued, and thus the Alert Level remained at 3.

Figure 58. An ash emission rose from Sakurajima's Minamidake crater on the morning of 22 August 2016. This was the last reported ash emission of 2016. Taken from the Tarumizu City MBC (Minaminihon Broadcasting Co., Ltd.) webcam no. 14, located about 14 km E. Courtesy of Minaminihon Broadcasting Co., Ltd. (http://www.mbc.co.jp/web-cam/).

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), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); 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/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); Japan Aerospace Exploration Agency (JAXA) (URL: http://global.jaxa.jp/); Associated Press (URL: http://www.ap.org/); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/ ); Naoto Yoshidome, Twitter (URL: https://twitter.com); Minaminihon Broadcasting Co., Ltd (MBC). (http://www.mbc.co.jp/web-cam/).

Ambae (formerly called Aoba) is a large basaltic shield volcano in the New Hebrides arc that has generated periodic phreatic and pyroclastic explosions originating in the summit crater lakes Manaro Lakua and Voui during the last 25 years; the central edifice with the active summit craters is also commonly referred to as Lombenben, Manaro Voui, or simply the Manaro volcano. From late November 2005 to mid-February 2006 explosions from Lake Voui resulted in the formation of a pyroclastic cone in the lake. By late November 2006 the side of the cone was breached, and its central crater filled with lake water (figure 30, BGVN 31:12). The Vanuatu Meteorology and Geo-Hazards Department (VMGD) reported intermittent increases in degassing activity between 2006 and August 2017, and minor ash emissions during June-July 2011 and August 2016. An explosive eruption from a new pyroclastic cone in the lake began in mid-September 2017 and lasted through mid-November. This report summarizes activity between 2010 and the new eruption in September 2017 and provides details for the eruption through December 2017, with information provided primarily by the Vanuatu Geohazards Observatory of VMGD, the Wellington Volcanic Ash Advisory Center (VAAC), and satellite data from several sources.

Local ashfall around the pyroclastic cone in Lake Voui during June-July 2011 and August 2016 were the only eruptive events between February 2006 and September 2017, although intermittent SO₂ emissions were noted throughout the period. Renewed explosive activity was reported beginning on 6 September 2017. Lava was first observed on 22 September emerging from a vent at the summit of the pyroclastic cone. Ash plumes and fountaining lava persisted for a few weeks as the pyroclastic cone increased in size. Activity became more intermittent by mid-October, but explosions still produced ash plumes; the highest was reported at 9.1 km altitude. Pulses of thermal activity suggesting lava flows continued through early November. The last ash emission of the year was reported on 23 November 2017, after which only steam and gas were noted.

Activity during 2010-August 2017. After several years of quiet since early 2006, substantial gas plumes were observed beginning in December 2009 and the Volcanic Alert Level was raised to 1 (on a 0-5 scale). Plumes of gas emissions were observed during 6-11 April 2010, and steam emissions were photographed during 3-4 June 2010 (figure 32).

Figure 32. Steam plumes rose from the crater of the pyroclastic cone in Lake Voui at Ambae on 4 June 2010. Courtesy of Vanuatu Meteorology and Geo-Hazards Department (VMGD) (Vanuatu Volcanic Activity Bulletin No. 1-Ambae activity, Monday, July 11th, 2011).

Sulfur dioxide emissions were often elevated, and plumes were identified multiple times with satellite instruments during 2011 (figure 33). Local ashfall around the crater of the pyroclastic cone in Lake Voui was reported after explosions and seismicity on 4 June 2011; additional explosions occurred on 10 July 2011. Compared to January 2010, the cone was significantly eroded when photographed on 12 July 2011.

Figure 33. SO2 plumes from Ambae and Ambrym volcanoes during 2011. SO2 plumes drifted W from both Ambae (N) and Ambrym (S) on 19 April 2011 (left). The SO2 plume from Ambae is small but also distinct from the much larger plume from Ambrym on 30 October 2011 (right). It is often difficult to distinguish between the two sources of the SO2. Courtesy of NASA Goddard Space Flight Center.

While no ash emissions or explosions were reported during 2012 from Ambae, SO₂ plumes were recorded by satellite instruments every month except June and August (figure 34). Villagers in Ambanga reported a "phase of minor activity" beginning in December 2012. Increased SO₂ plumes were recorded in satellite data during December as well (figure 35). Nearby Ambrym often produces large SO₂ plumes which obscure SO₂ emissions from Ambae.

Figure 34. SO2 plumes were recorded every month of 2012 except June and August. Plumes emerging from Ambae are often difficult to distinguish from larger plumes released from Ambrym, located 100 km S. Data from the OMI instrument on the Aura satellite on both 9 January and 5 April (top images) showed SO2 emissions from three volcanos in the New Hebrides arc; from N to S, Gaua, Ambae, and Ambrym. Plumes from both Ambae and Ambrym drifted SE on 21 September (lower left), and smaller plumes drifted W from both Ambrym and Ambae on 3 November (lower right). Courtesy of NASA Goddard Space Flight Center.

Figure 35. Increased gas emissions from Ambae were reported by nearby residents in Ambanga during December 2012. More frequent SO2 emissions were also recorded by the OMI satellite instrument including on 1 (top left), 12 (top right), 17 (bottom left), and 21 (bottom right) December 2012. Courtesy of NASA, Goddard Space Flight Center.

Site observations during 30 January-2 February 2013 confirmed continuing degassing at Lake Voui, and remnants of the old pyroclastic cone still visible in the lake. The Aura satellite instrument detected SO₂ emissions a number of times throughout 2013-2016 (figure 36), and VMGD noted continuing unrest multiple times during 2015.

Figure 36. Selected SO2 emissions during 2013-2016 at Ambae. SO2 emissions drifted W from both Ambae (N) and Ambrym (S) on 13 February 2013 (top left). A rare image of an SO2 plume from Ambae with no plume from Ambrym was recorded on 5 May 2014 (top right). SO2 emissions were also distinct from each volcano on 10 November 2015 (bottom left) and 28 December 2016 (bottom right). Courtesy of NASA Goddard Space Flight Center.

VMGD reported that during 18-19 August 2016 a steam plume was accompanied by a small ash emission in the caldera area. The Vanuatu Volcanic Alert Level (VVAL) was raised from 1 to 2 on 21 August 2016 and remained there for just over a year. Changing conditions were first reported by VMGD on 30 August 2017.

Activity during September-December 2017. The Alert Level was raised to 3 on 6 September 2017, indicating that a minor eruption was occurring. A week later VMGD reminded residents of the 3 km danger zone around the lake and added a 1 km exclusion zone within that area (figure 37). Explosive activity began building a new pyroclastic cone in Lake Voui, and ash plumes generated local ashfall on the island.

Figure 37. "Safety Map" showing hazard zones in the summit area of Ambae, consisting of a Danger Zone A (red oval line) around the summit caldera and a 1-km-radius Exclusion Zone around Manaro Voui. Courtesy of VMGD (Vanuatu Volcano Alert Bulletin No 10-Ambae Activity, Friday September 15th 2017).

On 22 September 2017, lava was observed at the surface by VMGD staff, there was a MODVOLC thermal alert, and a volcanic ash advisory was issued by the Wellington VAAC. The VAAC report estimated the ash plume observed in satellite data to be at an altitude of 3 km drifting E. On 23 September the VMGD stated that activity had continued to increase, prompting them to raise the VVAL to 4, indicating that a moderate eruption was taking place. They warned that ejecta and gas would affect an area within 6.5 km of Lake Voui, and many communities were at risk from various types of volcanic activity (figure 38). A dense plume of dark ash was photographed on 23 September by airplane travelers going to Ambae (figure 39).

Figure 38. Volcanic hazard map for Ambae. On 23 September 2017, VMGD raised the alert level to 4 and warned that ejecta and gas would likely affect an area within 6.5 km of Lake Voui (pink zone). Villages located in the gray and orange areas of the map could see ashfall and other hazards such as lahars and pyroclastic flows. The lighter area outlined with a dashed border indicates where villages would be more susceptible to ashfall and acid rain based on the general wind direction. Courtesy of VMGD (Vanuatu Volcano Alert Bulletin No. 11 - Ambae Activity, Saturday, September 23rd, 2017).

Figure 39. Ash emission photographed on 23 September 2017 from an airplane going to Ambae. Courtesy of Batik Bong Shem, Facebook.

Eruptive activity increased over the next few days. Larger explosions generated ash plumes that caused local ashfall. A photo taken on 24 September showed incandescent ejections and an ash plume rising from the pyroclastic cone (figure 40). The Wellington VAAC reported intermittent emissions that day at 2.4 km altitude drifting N, and again on 26 September at 2.1 km altitude drifting W. The New Zealand Defense Force conducted an overflight on 25 September 2017 and witnessed incandescence at the summit and lava flowing into the lake (figures 41, 42, and 43).

Figure 40. An eruption from the pyroclastic cone in Lake Voui at Ambae on 24 September 2017. Courtesy of Yumi Toktok Stret News, Facebook.

Figure 41. The New Zealand Defence Force (NZDF) aerial survey on 25 September 2017 showed large columns of gas, ash, and volcanic rocks emerging from Lake Voui on Ambae. Courtesy of NZDF.

Figure 42. Lava flows into Lake Voui at Ambae, causing steam plumes. Incandescence is visible at the cone's summit through the clouds. The photo was likely taken on 25 or 26 September 2017. Posted by Geoff Reid NZ on Facebook on 2 October 2017.

Figure 43. Incandescent lava from the crater of the Lake Voui cone was photographed at Ambae on 25 September 2017. Image courtesy of Reuters, reported by BBC.

A 27 September a news article from ABC.net stated that about 8,000 residents had been evacuated from the northern and southern parts of the island to eastern and western areas. An overflight by the New Zealand Defence Force showed ongoing activity. Multiple MODVOLC thermal alerts were issued nearly every day from 22 September through 7 October.

Photographs and thermal infrared images taken by VMGD during observation flights on 30 September and 1 October 2017 showed explosions of tephra, and lava flowing from small vents into the lake (figures 44-48). The number of vents on the cone varied from 2 to 4 during the observation flights.

Figure 44. Aerial view of the pyroclastic cone that formed in Lake Voui during September in the Ambae summit caldera. The active lava-producing vents are near the center of the island. The blue steaming zone is a lava flow. The white steaming to the right is lava entering the lake. Photo taken on 30 September 2017. Courtesy of VMGB, posted on Facebook 2 October 2017.

Figure 45. The pyroclastic cone in Lake Voui at the summit of Ambae had active steam, ash, and gas emissions, in addition to lava flowing into the lake, on 1 October 2017. Courtesy of VMGD.

Figure 46. Aerial view of the cone that formed in Lake Voui during September 2017 in the summit caldera of Ambae. The Manaro Lakua lake can be seen in the background. The active vents are near the center of the island. The white steaming zone at the far end of the island was caused by lava flows entering the lake. Photo taken on 1 October 2017. Courtesy of VMGB, posted on Facebook 2 October 2017.

Figure 47. Infrared aerial view of the volcanic cone that has formed in Lake Voui during September 2017 near the summit of Ambae Island. The active lava producing vents are the hottest areas near the center of the island (inwhite). The white streak in the foreground is a lava flow. The red areas in the foreground are areas where lava recently entered the lake. The caldera rim at the summit of Ambae is visible in the background. Photo taken on 1 October 2017. Courtesy of VMGB, posted on Facebook, 2 October 2017.

Figure 48. Closeup view of a lava flow from the cone entering into Lake Voui at Ambae on 1 October 2017. Courtesy of VMGB, posted on Facebook 2 October 2017.

On 6 October 2017, the VMGD noted that there was no evidence of the eruption escalating; the Alert Level was lowered to 3 and residents and tourists were reminded to stay outside of the Red Zone, defined as a 3 km radius around the active cone. The Wellington VAAC reported ash emissions on 9 October visible in satellite imagery spreading N of the island as high as 3.7 km altitude. They reported low-level (2.4-4.6 km) ash plumes daily through 15 October. A short-lived eruption on 13 October produced an ash plume clearly visible in satellite imagery that rose to 9.1 km altitude.

Webcam observations and seismic analysis reported on 13 October by VMGD indicated ongoing minor explosive activity and ash emission from vents on the cone in Lake Voui over the previous several days (figure 49). Lava had apparently ceased flowing to the lake. The local population from Ambae and neighboring islands could still hear some of the explosions, see volcanic ash and gas plumes, and see incandescence at night. Multiple MODVOLC thermal alerts were issued on 15 and 16 October, and again during 19-23 October. Wellington VAAC reports during 22-23 October indicated intermittent low-level ash plumes at 2.4-3.7 km altitude moving E.

Figure 49. An ash plume rises over Ambae island on 12 October 2017 in this photo taken from Santo - Pekoa Airport 65 km W on Espiritu Santo Island. Photo by Steve Clegg, courtesy of VMGD (posted on their Facebook page).

A new surge of activity created multiple MODVOLC thermal alerts between 27 October and 1 November 2017. The Wellington VAAC reported an ash plume on 29 October at 6.1 km altitude drifting SE. The activity ceased, and the plume dissipated by the end of the day. VMGD reported on 31 October that seismic activity was ongoing, and explosions could be seen in webcam photos; incandescence and explosions were also heard and seen from neighboring islands at night.

Webcam photos from 5 and 6 November showed that ash emissions and incandescent explosions continued (figures 50 and 51). The Wellington VAAC reported an ash emission rising to 4.3 km altitude and drifting W on 5 November. By the next day the altitude of the ash plume had dropped to 2.1 km. This was followed late on 6 November by an ash emission reported at 3.9 km altitude extending 25 km W and SW of the volcano, which continued through the next day. Another emission on 8 November drifted W at 3 km altitude for several hours before dissipating. Fourteen MODVOLC thermal alerts were issued on 5 November, and two more the next day. A final alert on 9 November was the last for 2017.

Figure 50. Webcam images of Ambae indicate that ash emissions and incandescent explosions were continuing on 5 November 2017. Image taken from the Saratamata webcam located 22 km NE on the NE tip of Ambae Island. Courtesy of VMGD, posted on Facebook 5 November 2017.

Figure 51. Steam and ash emissions were visible from the Saratamata webcam (22 km NE) in the early morning of 6 November 2017. Courtesy of VMGD, posted on Facebook 5 November 2017 (UTC).

VGO reported on 8 November 2017 that the eruption had been continuing, and photos taken during the first week of the month confirmed that the pyroclastic cone in Lake Voui continued to grow in height and size, with frequent explosions and ash plumes. The Wellington VAAC reported a ground observation of an ongoing minor eruption on 21 November that produced an ash plume that rose to 1.8 km altitude. By the following day, the plume appeared to be mostly steam. A new eruption the next day (23 November) produced a plume estimated at 3.7 km altitude moving W. An ash emission later that day was estimated at 3 km altitude drifting N based on satellite imagery. It had dissipated by the following day, and there were no further VAAC reports issued during 2017.

By 7 December 2017, activity had decreased significantly, and emissions consisted of only steam and gas plumes; VMGD lowered the Alert Level from 3 to 2, and reduced the restricted area to within 2 km of the active vent in Lake Voui, noting that the eruption had ceased. The MIROVA plot of Log Radiative Power at Ambae (Aoba) correlates well with visual and thermal observations of activity between 23 September and early November 2017 (figure 52). Significant quantities of SO₂ were released at Ambae during October-December 2017 (figure 53). SO₂ emissions continued into December after the ash emissions ceased.

Figure 52. The MIROVA plot of Log Radiative Power at Ambae (Aoba) for the year ending on 29 December 2017 correlates well with visual and thermal observations of activity between 23 September and early November 2017. Courtesy of MIROVA.

Figure 53. Significant quantities of SO2 were released from Ambae during October-December 2017. Variable wind directions seem to create complex patterns of SO2 plumes. Emissions on 23 and 28 October (top), 8, 13, and 17 November (middle row and bottom left) all show plumes that appear to be mostly sourced from Ambae, but some component of source from Ambrym is also likely. By 31 December 2017 (bottom right) SO2 emissions at Ambae were still significant even though no ash emissions had been reported for over a month. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. The island of Ambae, also known as Aoba, is a massive 2,500 km3 basaltic shield that is the most voluminous volcano of the New Hebrides archipelago. A pronounced NE-SW-trending rift zone dotted with scoria cones gives the 16 x 38 km island an elongated form. A broad pyroclastic cone containing three crater lakes (Manaro Ngoru, Voui, and Manaro Lakua) is located at the summit within the youngest of at least two nested calderas, the largest of which is 6 km in diameter. That large central edifice is also called Manaro Voui or Lombenben volcano. Post-caldera explosive eruptions formed the summit craters about 360 years ago. A tuff cone was constructed within Lake Voui (or Vui) about 60 years later. The latest known flank eruption, about 300 years ago, destroyed the population of the Nduindui area near the western coast.

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department, Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); 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/); 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); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); New Zealand Defence Force (URL: http://www.nzdf.mil.nz/); BBC News (URL: http://www.bbc.com/news); ABC News (http://abcnews.go.com/); Batik Bong Shem, Facebook (URL: https://www.facebook.com/batick.shem); Yumi Toktok Stret News, Facebook URL: https://www.facebook.com/ytsnews.today/); Geoff Reid NZ, Facebook (URL: https://www.facebook.com/GeoffReidNZ/).

Occasional weak eruptions and low-level ash emissions are typical of activity at Ambrym. The most recent ash emission was on 3 April 2017 (BGVN 42:05). The current report summarizes activity from late April through December 2017.

On 30 August 2017, the Vanuatu Meteorology and Geo-Hazards Department (VMGD) reported that "drastic changes" at Ambrym prompted an increase in the Alert Level from 2 to 3 (on a scale of 0-5). Areas deemed hazardous were near and around the active vents (Benbow, Maben-Mbwelesu, Niri-Mbwelesu and Mbwelesu), and in downwind areas prone to ashfall. According to a news report (Radio New Zealand), a representative of VMGD indicated that the Alert Level change was based on increased seismicity detected since the beginning of August, but which became more notable on 25 August.

According to VMGD, aerial observations on 24 and 30 September, and 1 and 6 October, combined with analysis of seismic data, confirmed that minor eruptive activity within the caldera was characterized by hot volcanic gas and steam emissions. Areas deemed hazardous were within a 2-km radius from Benbow Crater and a 3-km radius from Marum Crater.

A news report (The Vanuatu Independent) quoted an official from VMGD as stating that on 8 November 2017 at 0500, the Niri-Mbwelesu eruptive vent emitted a minor ash plume. On 7 December 2017, VGO lowered the Alert Level to 2, noting that activity had stabilized by the end of November and was characterized by gas-and-steam emissions. Seismicity had also declined. The report reminded the public to stay outside of the Permanent Danger Zone, defined as a 1-km radius from Benbow Crater and a 2.7-km radius from Marum Crater.

During the reporting period, thermal anomalies based on MODIS satellite instruments and analyzed using the MODVOLC algorithm, continued to be numerous every month, possibly reflecting lava lakes in Benbow and Marum craters. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system also detected numerous hotspots every month within 5 km of the volcano.

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

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department, Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); Radio New Zealand (URL: https://www.radionz.co.nz); The Vanuatu Independent (URL: https://vanuatuindependent.com/); 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/); Middle InfraRed Observation of Volcanic Activity (MIROVA), Mirova (collaborative project between the Universities of Turin and Florence, Italy)(URL: http://www.mirovaweb.it).

Eruptions at Fernandina Island in the Galapagos often occur from vents located around the caldera rim along boundary faults and fissures, and occasionally from side vents on the flank. The last eruption in 2009 generated fountaining basaltic lava along several fissure vents. Lava flowed down the SW flank and entered the sea for a few weeks during April 2009. A new eruption began on 4 September 2017 after eight years of no surface activity, and lasted for about one week. Information about this new eruption was provided by Ecuador's Institudo Geofisica, Escuela Politécnica Nacional (IG-EPN), the Dirección del Parque Nacional Galápagos (DPNG), the Washington Volcanic Ash Advisory Center (VAAC), and several sources of satellite data.

A brief fissure vent eruption began on 4 September 2017 at Fernandina, located at the SW rim of the caldera. Small amounts of ash were noted in the plume that rose 2.5 km, but most of the emission was steam and SO₂. Vegetation fires were ignited on the SW flank, but lava did not reach the ocean. There was no sign of volcanic activity within the summit crater. A significant area with thermal anomalies was seen in infrared satellite data through 7 September.

Eruption of early September 2017. After eight years of little activity, Fernandina (La Cumbre) began a new eruptive phase on 4 September 2017, at approximately 1225 (Galápagos time) (figure 22). Inflation between March 2015 and September 2017 was 17 cm centered on the caldera; 5 cm of that inflation occurred in the last two months before the eruption (figure 23).

Figure 22. Fernandina began a new eruption on 4 September 2017. The initial plume was mostly steam, but contained significant SO2 and possibly minor ash. Photo by DPNG personnel, courtesy of IG-EPN (INFORME ESPECIAL VOLCÁN FERNANDINA N°1 – 2017, Lunes, 04 Septiembre 2017 16:49).

Figure 23. Interferogram image of Fernandina between 19 March 2015 and 4 September 2017 shows about 17 cm of inflation in the caldera. Each concentric band of colors within the caldera represents several centimeters of inflation. Created by Yu Zhou and Mike Stock, courtesy of IG-EPN (INFORME ESPECIAL DEL VOLCÁN FERNANDINA N°2 – 2017, Miércoles, 06 Septiembre 2017 17:16).

Seismic activity began with hybrid-type earthquakes (fractures with fluid movements) followed by Long Period (LP) earthquakes (fluid movements). The seismic network of the Geophysical Institute installed in the Galapagos began to detect activity at the volcano around 0955 on 4 September 2017. The beginning of the eruption was associated with a volcanic tremor that began at 1225. At 1428, an eruptive column was visible in satellite imagery, interpreted at an approximate height of 4,000 m above the crater, drifting WNW (figure 24).

Figure 24. This false-color satellite image of Fernandina on 4 September 2017 showed the eruption column drifting NW estimated at 4,000 m altitude. Source: http://goes.higp.hawaii.edu/cgi-bin/imageview?sitename=galapagos. Courtesy of IG-EPN (INFORME ESPECIAL VOLCÁN FERNANDINA N°1 – 2017, Lunes, 04 Septiembre 2017 16:49).

The Washington VAAC reported that satellite imagery indicated a lava eruption which produced a plume of steam and gas that rose to 2,400 m above sea level and extended about 60 km W of the summit. While initially no ash was reported in the plume, a few hours later a new VAAC report suggested that minor ash was possibly present, although it was most likely primarily SO₂. Satellite data reported by the NASA Goddard Space Flight Center showed SO₂ emissions on 4-6 and 8 September (figure 25).

Figure 25. SO2 emissions from Fernandina were identified with the OMI instrument on the Aura satellite and the OMPS instrument on Japan's Suomi satellite during 4-8 September 2017. Upper left: A small SO2 emission emerges very close in time to the first reported observation of the eruption on 4 September. Upper right: The low-resolution OMPS image clearly shows a large plume drifting W about 24 hours later. Lower left and right: SO2 is present NW of the Galapagos over the eastern Pacific on 6 and 8 September. Courtesy of NASA Goddard Space Flight Center.

Thermal alerts indicative of fresh lava flows from the rim of the summit crater were first reported by MODVOLC on 4 September 2017 (UTC), and abundant through 7 September (figure 26). No thermal anomalies were recorded in MODVOLC data on 8 September. An additional group of alert pixels was recorded on 9 September, but it's not clear if they were caused by fresh lava flows or burning fires; a few more intermittent pixels were recorded through 20 September. The MIROVA system also captured a significant spike in heatflow at Fernandina during the same period (figure 27). Some of the anomalies measured by both systems were likely the result of the fires caused by the lava flows as well as the flows themselves.

Figure 26. Map showing the location of new lava flows at Fernandina during 4-7 September 2017 using MODVOLC thermal alerts. Fires may have caused some of the alert pixels. Courtesy of HIGP MODVOLC Thermal Alerts System.

Figure 27. MIROVA thermal anomalies show a spike in activity at Fernandina during the period of the September 2017 eruption in this graph of log radiative power for the year ending on 16 October 2017. The initial spike that was located more than 5 km from the summit confirms the lava flows were located on the crater rim and flank and not in the summit crater. Some anomalies may also be due to the fires caused by the lava flows. Courtesy of MIROVA.

Incandescence was first observed during the night of 4 September (figure 28). Lava flows apparently originated from a circumferential fissure near the fissure of the 2005 eruption on the SSW rim of the caldera. The lava flowed down the S and SW flanks but did not reach the sea. Active lava flows were observed during the night of 5 September (figure 29). The intensity of the eruption decreased significantly after about 48 hours.

Figure 28. Incandescence at Fernandina on 4 September 2017. Photo by Alex Medina, courtesy of IG-EPN (INFORME ESPECIAL DEL VOLCÁN FERNANDINA N°2 – 2017, Miércoles, 06 Septiembre 2017 17:16).

Figure 29. A lava flow is visible on the SW flank of Fernandina on 5 September 2017. Photo by Alex Medina, courtesy of IG-EPN (INFORME ESPECIAL DEL VOLCÁN FERNANDINA N°2 – 2017, Miércoles, 06 Septiembre 2017 17:16).

A technical team from the Directorate of the Galapagos National Park (DPNG) made an aerial inspection using the seaplane Sea Wolf on 7 September 2017. They observed a radial fissure in the same area where the 2005 eruption occurred, and several lava flows. No recent volcanic activity or any landslides were seen inside the caldera. The lava flows had ceased movement, but there were isolated fires burning patches of vegetation surrounded by older lava flows (figures 30 and 31). The lava had traveled from the summit crater at about 1,200 m down to 500 m elevation. While lava was not observed flowing into the sea, coastal monitoring by the park rangers showed water vapor on the SW coast, so it was possible that lava had reached the ocean through subsurface lava tubes.

Figure 30. Lava flows burn vegetation on Fernandina during the eruption of September 2017. Observers on a 7 September 2017 flyover by DPNG reported that the active flows had ceased, but vegetation was burning at four different sites. Courtesy of Directorate of the Galapagos National Park (DPNG) (11/09/2017– Sobrevuelo al volcán La Cumbre, en Galápagos).

Figure 31. Vegetation on Fernandina burns on 7 September 2017 after lava flows erupted beginning on 4 September 2017. There was no evidence of flowing lava during the overflight. Courtesy of the Galapagos Conservancy.

Geologic Background. Fernandina, the most active of Galápagos volcanoes and the one closest to the Galápagos mantle plume, is a basaltic shield volcano with a deep 5 x 6.5 km summit caldera. The volcano displays the classic "overturned soup bowl" profile of Galápagos shield volcanoes. Its caldera is elongated in a NW-SE direction and formed during several episodes of collapse. Circumferential fissures surround the caldera and were instrumental in growth of the volcano. Reporting has been poor in this uninhabited western end of the archipelago, and even a 1981 eruption was not witnessed at the time. In 1968 the caldera floor dropped 350 m following a major explosive eruption. Subsequent eruptions, mostly from vents located on or near the caldera boundary faults, have produced lava flows inside the caldera as well as those in 1995 that reached the coast from a SW-flank vent. Collapse of a nearly 1 km3 section of the east caldera wall during an eruption in 1988 produced a debris-avalanche deposit that covered much of the caldera floor and absorbed the caldera lake.

Information Contacts: Instituto Geofísico (IG-EPN), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec ); Dirección del Parque Nacional Galápagos (DPNG), Isla Santa Cruz, Galápagos, Ecuador (URL: http://www.galapagos.gob.ec/); 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/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: http://so2.gsfc.nasa.gov/index.html ); Galapagos Conservancy, (URL:https://www.galapagos.org).

Guatemala's Volcán de Fuego was continuously active throughout 2017, and has been erupting vigorously since 2002; historical observations of eruptions date back to 1531. These eruptions have resulted in major ashfalls, pyroclastic flows, lava flows, and damaging lahars. Reports of activity are provided by the Instituto Nacional de Sismologia, Vulcanología, Meteorología e Hidrologia (INSIVUMEH), and aviation alerts of ash plumes are issued by the Washington Volcanic Ash Advisory Center (VAAC). Satellite data from NASA, NOAA, and other sources provide valuable information about heat flow and gas emissions.

Activity remained high at Fuego throughout July-December 2017. Background levels of activity included frequent explosions (4-6 per hour) with incandescent material rising 150 m above the summit and sending blocks 200 m down the flanks. Block avalanches commonly traveled down the major ravines for hundreds of meters. Ash plumes regularly rose 500-1,000 m above the summit (4.3-4.8 km altitude); ashfall affected communities SW of the summit within 15 km every week. During the multiple short-lived (48-hour or less) eruptive episodes, the hourly explosion rates increased significantly (6-12 per hour), and incandescent material often rose 300 m above the summit; one or more lava flows would also travel more than a kilometer down major ravines. Higher ash plumes (often rising to 5-6 km altitude) during the eruptive episodes sent ash plumes drifting hundreds of kilometers in various directions causing ashfall in cities tens of kilometers away in various directions. Pyroclastic flows often accompanied the eruptive episodes. Seven episodes were reported by INSIVUMEH during July-December 2017 (table 17); they are clearly discernible as periods of higher heat flow in the MIROVA thermal anomaly data (figure 73) as well.

Table 17. Eruptive episodes at Fuego during July-December 2017. Information provided primarily by INSIVUMEH. Some ash plume information is from the Washington VAAC.

Figure 73. MIROVA thermal anomaly data for Fuego for 2017 shows the continuing activity that included intermittent pulses of high-heat-flow from twelve defined eruptive episodes shown by red arrows. Courtesy of MIROVA. Eruptive episodes defined by INSIVUMEH.

Activity during July 2017. Activity increased at Fuego during July 2017, compared with the previous month. INSIVUMEH reported that explosions per hour increased during 6-7 July from 4-7 to 7-10; a lava flow also traveled 1.5 km down Las Lajas ravine. Incandescent material was ejected 100-200 m above the crater rim and caused avalanches of material that traveled down the Ceniza (SSW), Taniluyá (SW), Santa Teresa (SW), and Trinidad (S) drainages (figure 74). Ash plumes during 7-9 July caused ashfall in Santa Sofía (12 km SW), Morelia (9 km SW), Panimaché I and II (8 km SW), El Porvenir (8 km ENE), Sangre de Cristo (8 km WSW), and possibly San Pedro Yepocapa (8 km N).

Figure 74. Incandescent material was ejected over a hundred meters above the summit of Fuego and blocks of material traveled hundreds of meters down the flank on 9 July 2017. Courtesy of INSIVUMEH and OVFGO (Reporte Semanal de Monitoreo: Volcán Fuego (1402-09), Semana del 08 al 14de julio 2017).

The Washington VAAC reported dense ash emissions seen in satellite data on 10 July extending WNW 60 km from the summit at 4.6 km altitude. They noted that ashfall was reported 10 km SW from the summit the following morning. The 6th eruptive episode of the year occurred on 11-12 July 2017. Explosions generated ash plumes that rose as high as 1.3 km above the crater and drifted 35 km W, and shock waves rattled nearby structures. Ash fell in areas to the SW. Two lava flows were fed by lava fountains 150-250 m high; one flow traveled 2.3 km down the Las Lajas drainage and another traveled 1.7 km down the Santa Teresa (SW) drainage. The increased activity levels lasted for about 31 hours, with tens of explosions. Weak-to-moderate explosions continued afterwards, generating ash plumes that rose 850 m and drifted 6 km W.

Multiple explosions continued generating ash plumes and block avalanches during 13-14 July. On 16 July, a 30-m-wide, 2-m-deep, hot lahar descended tributaries of the Pantaleón (W) drainage, carrying blocks more than 2 m in diameter, branches, and tree trunks. The lahars again overtook the road between communities on the SW flank, isolating the village of Sangre de Cristo (8 km WSW) and the Palo Verde estate. The Washington VAAC estimated that the ash plumes released early on 16 July rose to 5.2 km altitude, and drifted SE from the summit. By afternoon they had risen to 5.8 km and were drifting SW, extending about 75 km. Explosions during 17-18 July produced dense ash plumes that drifted 15 km W and NW causing ashfall in Panimache, Morelia, and Santa Sofía. Satellite imagery on 19 July showed an ash plume extending 65 km WNW of the summit in a narrow band at 4.3 km altitude. Similar plumes were reported daily between 19-23 July at 4.3-4.9 km altitude drifting generally W up to about 50 km before dissipating (figure 75).

Figure 75. Ash emissions were reported almost daily from Fuego during July 2017. A small pulse of ash on 20 July was captured on the Panimaché I webcam (10 km SW) in this view looking NE in the early morning. Courtesy of OVFGO-INSIVUMEH (Reporte Semanal de Monitoreo: Volcán Fuego (1402-09), Semana del 15 al 21 de julio 2017).

Activity during August 2017. MODVOLC thermal alerts that were issued on 28 and 30 July confirmed the continuing incandescent summit activity which produced block avalanches down the major drainages. Multiple daily alerts were also issued during 15 days of August. Coordinadora Nacional Para la Reduccion de Desastres (CONRED) reported increased activity on 4 August that included 300-m-high ejections of incandescent material and a lava flow that traveled 600 m down the Ceniza ravine. During 7-8 August two lava fountains rose 150 m high, prompting INSIVUMEH to announce the seventh effusive episode at Fuego in 2017. The fountains fed lava flows, 1.5 km and 700 m long, in the Ceniza and the Santa Teresa ravines (figure 76). Explosions (occurring at a rate of 6-8 per hour) produced ash plumes that drifted 20 km W, causing ashfall in Panimache, Morelia, Santa Sofía, El Porvenir, and Yepocapa. The Washington VAAC also noted increasing ash emissions on 7 August. Weather clouds prevented observations from satellite images on 7 and 8 August, but the VAAC reported a "" strong hotspot in infrared imagery on 8 August. Although the lava flow in the Ceniza drainage remained active, explosive activity decreased to an average of three explosions per hour the following week, with ash emissions rising to 4.4-4.6 km and drifting 10 or more km W and SW, bringing ashfall to communities on the W and SW flank.

Figure 76. A lava flow at Fuego during eruptive episode 7 descends the SE flank on 7 August 2017. Courtesy of OVFGO-INSIVUMEH (Reporte Semanal de Monitoreo:, Volcán Fuego (1402-09), Semana del 5 al 11 de agosto 2017).

Activity intensified again during 19-20 August, when constant explosions generated ash plumes that rose 2.3 km above the crater and drifted more than 50 km W and SW. INSIVUMEH reported that the eighth effusive episode at Fuego in 2017 began on 20 August and lasted for about 48 hours. Two lava fountains, each 300 m high, fed lava flows that traveled 1.4 km SSW down the Ceniza ravine and 1.2 km W down the Seca (Santa Teresa) ravine (figure 77). Incandescent block avalanches occurred throughout the crater. Pyroclastic flows (figure 78) were concentrated in the Santa Teresa ravine, possibly filling the drainage with deposits (similar to activity from 5 May) and increasing the chances for lahars. A bright hotspot was visible in satellite imagery from 19-21 August. Seismicity remained elevated through 21 August. During 21 August, the Washington VAAC reported the ash plume near 5.5 km altitude extending 75 km WNW. A remnant cloud of ash was detected in satellite imagery over 200 km WNW of the summit in extreme SE Mexico late on 21 August.

Figure 77. Incandescent explosions and block avalanches descend the SE flank of Fuego during eruptive episode 8, 19-21 August 2017 in this view from the Panimaché I webcam. Courtesy of OVGFO-INSIVUMEH (Reporte Semanal de Monitoreo: Volcán de Fuego (1402-09), Semana del 19 al 25 de agosto 2017).

Figure 78. A pyroclastic flow descends the Santa Teresa ravine at Fuego during eruptive episode 8 on 21 August 2017 in this view from the Panimaché I webcam. Courtesy of OVGFO-INSIVUMEH (Reporte Semanal de Monitoreo: Volcán de Fuego (1402-09), Semana del 19 al 25 de agosto 2017).

INSIVUMEH reported that on 25 August multiple lahars descended the Pantaleón, Cenizas, El Jute, and Las Lajas drainages on Fuego's W, SSW, and SE flanks. The lahar in the Pantaleón river (fed by the Santa Teresa and El Mineral rivers) was 35 m wide, 2.5-3 m deep, and carried trees and blocks more than 2-3 m in diameter. The Cenizas lahar was about 25 m wide, 3 m deep, and carried blocks up to 2 m in diameter. The lahars in El Jute and Las Lajas drainages were 20 m wide, 1.5 m deep, and carried tree debris and blocks up to 2 m in diameter.

Explosions during 26-29 August generated ash plumes that rose as high as 950 m above the crater and drifted 7-12 km SW, W, and NW. The Washington VAAC reported near continuous emissions of ash on 28 August moving WSW and extending about 100 km at 4.6 km altitude, rising to 5.8 km altitude the following day. Incandescent material was ejected 100-200 m above the crater rim and caused avalanches of material around the crater area. Explosions were audible within a 20-km radius, and shock waves vibrated local structures. Ash fell in areas downwind including Panimache I and II, Morelia, Finca Palo verde, Sangre de Cristo, and El Porvenir. On 29 August, lahars 10 m wide and 1.5 m deep again descended the Santa Teresa and El Mineral drainages, carrying tree debris and blocks up to 2 m in diameter.

Activity during September 2017. Lahars were reported in the Santa Teresa and El Mineral drainages intermittently during September. Ash emissions continued to cause ashfall in communities within 10 km W and SW throughout the month. Continuous ejection of incandescent blocks rose 200-300 m above the crater and sent material 300 m down the flanks. The Washington VAAC reported a continuous plume of ash detected in satellite imagery and in the webcam extending about 95 km WSW on 8 September at 4.6 km altitude. INISVUMEH reported that the increase in activity during 8 September fed a lava flow that traveled 800 m down Barranca Seca.

The ninth eruptive episode of 2017 began late on 12 September and lasted about 35 hours (figure 79). Pyroclastic flows descended the Seca (Santa Teresa) ravine on the W flank, along with a lava flow that traveled 1.3 km during the episode. Ashfall was reported in Morelia, Palo Verde Estate, Sangre de Cristo, El Porvenir, Santa Sofía, and Panimaché I and II. The Washington VAAC reported that an ash plume extended about 65 km N from the summit on 13 September at 4.6 km altitude. After several days of weather clouds obscuring the satellite images, they reported a plume drifting W on 17 September extending 95 km from the summit. A hotspot intermittently appeared during 13-17 September.

Figure 79. Incandescent lava rises 200-300 m above the summit of Fuego, and a lava flow traveled down the Santa Theresa ravine on the W flank during eruptive episode 9 on 12 September 2017. View from Panimaché I webcam. Courtesy of OVFGO-INSIVUMEH (Reporte Semanal de Monitoreo: Volcán de Fuego (1402-09), Semana del 09 al 15 de septiembre 2017.

The Washington VAAC reported weak puffs of ash drifting N and quickly dissipating on 25 September, and another ash plume extending 15 km W on 28 September at 4.6 km. Hotspots were also observed both days in satellite images. INSIVUMEH reported eruptive episode 10 during 27-28 September, lasting about 40 hours. The ash plume generated during the episode drifted in multiple directions simultaneously (figure 80) and resulted in ashfall more than 30 km from the crater, primarily N and NE, in La Soledad (7 km N), Pastores (20 km NNE), San Miguel Dueñas (10 km NE) and Antigua Guatemala (20 km NE). The incandescent material reached 300 meters above the crater and fed two lava flows, the first went 300 m down the Seca Canyon, and the second traveled 500 m down Las Lajas Canyon.

Figure 80. The ash plumes drift in multiple directions (W, NW, SW and S) from the summit of Fuego on 28 September 2017 during eruptive episode 10. Image taken in San Pedro Yepocapa, 8 km NW. Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo: Volcán de Fuego (1402-09), Semana del 23 al 29 de septiembre 2017).

Seven lahars were recorded during September in the main ravines of Fuego, on days 3, 4, 5, 6, 8, 27, and 29, as a result of the unusually large amount of rainfall during the month (1,059 mm) (figure 81). The larger ones at the beginning of the month contained blocks up to 3 m in diameter, and many were warm enough to generate steam with strong odors of SO₂. Several roads were damaged.

Figure 81. High rainfall (1,059 mm) during September 2017 generated large lahars in the Seca, Mineral, Taniluya, Ceniza, Trinidad, Las Lahas, El Jute, and Honda ravines at Fuego, shown in purple. Many dirt roads (shown in red) were damaged. Courtesy of INSIVUMEH (VOLCÁN DE FUEGO, INFORME MENSUAL, Septiembre 2017).

Activity during October 2017. Overall activity was quieter during October 2017. Background levels of activity included incandescent material rising up to 250 m above the summit and falling a similar distance down the flanks, and ash plumes rising to 4.4-5.0 km altitude and drifting more than 25 km W, NW, and E. Eight to twelve explosions per hour were not uncommon, although 4-6 per hour were more typical. A few of the block avalanches traveled 2 km down the flanks. The communities that experienced persistent ashfall were all located 10-20 km SW, and included Morelia, Palo Verde Farm, Sangre de Cristo, El Porvenir, Santa Sofía, and Panimaché I and II. Due to the wind conditions and increased activity during the first week of October, ashfall was also reported farther away in Guatemala City (40 km NE), Antigua Guatemala, Villa Nueva (30 km ENE) and San Miguel Petapa (35 km ENE). INSIVUMEH reported three increases in explosive activity during the month on 2, 3, and 5 October, but they did not develop into eruptive episodes.

Four lahars were reported on 1, 2, and 4 October in the Seca and Mineral drainages. They carried blocks of volcanic rocks and debris as large as 3 m in diameter and were 6-12 m wide and 1-2 m deep. The Washington VAAC reported a series of explosions on 4 October, after which ash emissions were seen in multispectral imagery at 5.2 km altitude drifting SW that reached as far as 75 km. They reported occasional puffs of ash on 15 October extending up to 95 km W of the summit. By 17 October, imagery showed continuous emissions with an ash plume extending 95 km SSW from the summit before dissipating. A possible ash plume was reported by the Washington VAAC on 31 October extending 45 km W from the summit at 4.3 km altitude.

Activity during November 2017. There were numerous periods of intermittent ash emissions during November. Continuous emissions often drifted 65-100 km or more SW or W at altitudes around 4.6-5.2 km during periods of activity. INSIVUMEH reported that during 2-3 November tremor at Fuego increased. Explosions during the first week averaged 5-8 per hour and ash plumes rose as high as 1.3 km above the crater. Incandescent material was ejected 300 m above the crater, causing avalanches that were confined to the crater. The 11th eruptive episode in 2017 began on 5 November and lasted for two days. Lava flowed 1-1.2 km W down the Seca drainage and 800 m SSW down the Ceniza drainage. Avalanches of material from the ends of the lava flows descended the flanks and reached vegetated areas.

Ashfall was reported in areas downwind in the communities 8-12 km SW including Morelia, Santa Sofia, Palo Verde Farm, and Panimaché I and II throughout the month. Shockwaves from explosions often rattled windows and roofs around the volcano. Avalanche blocks were reported in the Cenizas, Trinidad, Taniluyá and Seca canyons. Multiple VAAC reports were issued on 25 days of November, and multiple daily MODVOLC thermal alerts were issued on 20 days of the month. On 10 November the emissions extended about 275 km WSW from the summit. A lahar during the third week descended the Seca and el Mineral drainages.

Activity during December 2017. Explosions averaged 4-8 per hour during most of December sending incandescent material 200-250 m above the crater. INSIVUMEH reported that the 12th eruptive episode at Fuego in 2017 began on 10 December and, based on seismicity, lasted for about 36 hours. Ash plumes from moderate-to-strong explosions rose as high as 1.2 km above the crater rim and drifted 20 km S and SW. Lava flowed as far as 1.5 km W down the Seca (Santa Teresa), SW down the Taniluyá, and SSW down the Ceniza ravines. Ash fell many times in the communities of La Rochela, San Andrés Osuna, Morelia, and Panimaché I and II. On 12 December there was an average of 10 explosions per hour, generating avalanches in the Ceniza and Taniluyá drainages and ashfall in nearby areas. Ashfall was also reported in San Miguel Dueñas, Alotenango, and Ciudad Vieja (13.5 km NE) on 14 December.

Multiple MODVOLC thermal alerts appeared on 20 days during December, and the Washington VAAC issued 91 reports of continuous or intermittent ash plume activity. During eruptive episode 12 on 11 December, they reported an intense hot spot seen at the crater in satellite imagery despite meteoric cloud cover. For most of the second half of December, either continuous or intermittent ash emissions drifted 100-150 km WNW from the summit before dissipating. The Washington VAAC reported an ash emission on 20 December drifting WNW at 5.8 km altitude that extended over 300 km from the summit. A remnant of the plume was observed almost 450 km away late on 20 December before dissipating. Plumes were repeatedly observed over 200 km from the summit during 20-25 December.

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: Coordinadora Nacional para la Reducción de Desastres (CONRED), Av. Hincapié 21-72, Zona 13, Guatemala City, Guatemala (URL: http://conred.gob.gt/www/index.php ); Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/ ); 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/).

An eruption at Sheveluch has been ongoing since 1999, and volcanic activity was previously described through August 2017 (BGVN 42:08). Ongoing activity consists of pyroclastic flows, explosions, and lava dome growth with a viscous lava flow in the N. Strong fumarole activity, ash explosions, hot avalanches and incandescence from the dome accompany this process. Explosions and ash flows were reported by Kamchatka Volcanic Eruption Response Team (KVERT) during the August 2017 through January 2018 period.

During this report period the Aviation Color Code (ACC) remained at Orange (the second highest level on a four-color scale), except for 10 January 2018 when it was briefly elevated to Red (highest level) and lowered back to Orange later the same day. Satellite infrared data also showed increased activity on this day. Ash plume altitudes ranged from a low of 5 km to a high of 11 km on 10 January 2018. The farthest lateral extent of the ash plume was reported at 990 km to the NE on 8 November 2017.

On 4 and 8 August 2017 large ash clouds reached altitudes of 6.5 km and approximately 10 km, respectively. Ashfall was reported in Klyuchi Village (50 km SW) on 8 August and drifted about 180 km E, NW, and NE during 12 and 15-16 August. On 7 September ash plumes rose to 8-10 km altitude and drifted NE, SE, and S; another ash plume was photographed on 8 September (figure 47). On 15-22 September ash plumes rose to 9-10 km altitude and drifted about 400 km NW, E, and SE. Explosions on 10 October generated ash plumes to 10 km altitude and drifted about 250 km N (figure 48). Plumes comprised of re-suspended ash drifted about 350 km SE on 12 October and about 230 km SE on 13 October.

Figure 47. Photo of an ash cloud from Sheveluch generated by an explosion on 8 September 2017. Photo by G. Teplitsky; courtesy of the Institute of Volcanology and Seismology FEB RAS, KVERT.

Figure 48. Explosions from Sheveluch sent ash up to 10 km altitude on 10 October 2017. Photo from a webcam, courtesy of the Institute of Volcanology and Seismology FEB RAS, KVERT.

Explosions on 2 and 8 November generated ash plumes that rose to an altitude of 8 km and drifted approximately 990 km NE. Weather prevented observations on the other days from 4-10, 12-17, and 19-24 November. A strong explosive event on 5 December generated ash plumes that rose to altitudes of 10.5 km and 5 km and drifted NE and E, respectively. Explosions on 26 December generated an ash plume that rose to an altitude of 8 km and drifted about 300 km NE.

On 10 January 2018 satellite images captured an ash cloud with a dimension of 192 x 132 km drifting 230 km NE from explosions rising to altitudes of 10-11 km. In response, KVERT raised the ACC to Red. Later that same day, satellite images showed the ash cloud expanded to 350 x 180 km in dimension and had drifted 400 km E; the ACC was lowered back to Orange. The 10 January explosions began at 1035 with resulting ash that drifted about 900 km E during 10-11 January.

Thermal anomalies. As reported by KVERT, satellite imagery continue to detect the existence of a thermal anomaly over Sheveluch. The anomaly was reported on 10-30 days every month from August 2017 through January 2018. Detections of the thermal anomaly were lower in certain months because cloudy conditions obscured satellite imagery. The MIROVA system detected numerous hotspots every month during August 2017-January 2018, most of which were about 5 km or less from the summit with mainly low to a few high power signatures in August, September 2017 and January 2018. Thermal anomalies based on MODIS satellite instruments analyzed using the MODVOLC algorithm were detected in 11-12 August 2017 and 10 January 2018 corresponding to the explosive eruptions on those days.

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

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far East Division, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

Confirmed historical eruptions at Italy's Stromboli volcano go back 2,000 years as this island volcano in the Tyrrhenian Sea has been a natural beacon for eons with its near-constant fountains of lava. Eruptive activity at the summit consistently occurs from multiple vents at both a north crater area (N Area) and a southern crater group (S or CS Area) on the Terrazza Craterica at the head of the Sciara del Fuoco, a large scarp that runs from the summit down the NW side of the island (figures 102 and 103). Thermal and visual cameras placed on the nearby Pizzo Sopra La Fossa monitor activity at the Terrazza Craterica. Eruptive activity continued at low to moderate levels during 2015 and 2016, with intermittent periods of frequent explosions from both crater areas that sent ash, lapilli, and bombs across the Terrazza Craterica and onto the head of the Sciara del Fuoco (BGVN 42:07).

Figure 102. A view of Stromboli looking SW with the Sciara del Fuoco on the NW flank on the right. Image taken during 10-12 June 2017. Copyrighted photo by Martin Rietze, used with permission.

Figure 103. A view to the NW of the Terrazza Craterica from the summit of Stromboli shows the CS Area (left) and N Area (right) vents during 10-12 June 2017. Copyrighted photo by Martin Rietze, used with permission.

This report covers activity from January-October 2017. Activity similar to 2016 continued through March 2017 when an increase began in explosion rates. The increase peaked during June and then declined through August, returning to background levels in September (figures 104). Thermal energy increased beginning in early May and lasted through mid-August (figure 105). Multiple MODVOLC thermal alerts were issued for Stromboli between 4 May and 25 August 2017. Weekly reports of activity were provided by the Instituto Nazionale de Geofisica e Vulcanologia (INGV), Sezione de Catania, which monitors the gas geochemistry, deformation, and seismology, as well as the surficial activity.

Figure 104. Increased rates of explosive activity at Stromboli were recorded between early April and late August 2017, peaking during mid-June. Rates declined to background levels by early September. The green line represents the number of daily explosions from the S Area, the red line is the number of daily explosions from the N Area, and the blue line is the cumulative of the two areas. Graph includes activity from 28 March-30 October 2017. Courtesy of INGV (Rep. 44/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 31/10/2017).

Figure 105. After a lengthy period of low to intermittent thermal activity during 2015 and 2016, a distinct increase in thermal energy was recorded in satellite thermal imagery and is shown in the MIROVA system data for the year ending on 25 August 2017. Courtesy of MIROVA.

Activity during January 2017 consisted of low to moderate intensity explosions from the southern crater area (S Area), and low intensity explosions at the northern crater area (N Area). Two vents in the S Area generated explosive activity. Modest explosions with ash and lapilli occurred regularly from the southernmost vent, and rare explosions were observed from the northernmost vent (figure 106). At the northern crater area (N Area) the southern vent was active, generating ash and lapilli that was ejected a few tens of meters from the vent. There were no explosions from the northern vent in the N Area.

Figure 106. Typical activity at Stromboli's Terrazza Craterica during January 2017 photographed from visible cameras on the Pizzo sopra la Fossa. Left: Explosions at the S Area on 23 January 2017 included moderate activity at the southern vent (yellow arrow) and low activity at the northern vent (white arrow). Right: The southern vent (green arrow) of the N Area showed moderate explosive activity on 17 January 2017. Courtesy of INGV (Rep. 04/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 24/01/2017).

There were no notable changes in activity until the second week of February 2017 when explosive activity returned to the northern vent of the N Area. During the third week of February, a gradual increase in the rate and intensity of the explosions at both areas was observed which lasted throughout the rest of the month (figure 107). Coarse pyroclastic material was ejected onto the Terrazza Craterica and occasionally onto the Sciara del Fuoco. The stronger explosions generated modest plumes of dilute ash that quickly dissipated.

Figure 107. Explosive activity at Stromboli during the third week of February 2017: A) The colored arrows indicate the active vents in the S and N Areas as seen by the visible camera of the Pizzo. B) Explosion at the northern vent (blue arrow) of the N area (visible camera). C) Explosion at the southern vent (yellow arrow) of the S area (visible camera). D-F) explosions from the N and S Areas taken by the 400 level Thermal camera. Courtesy of INGV (Rep. 08/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 21/02/2017).

During the first week of March 2017, the most active vents were the southernmost vent of the S Area and the northernmost vent of the N Area. The strongest explosions from the northern vent of the N Area produced dilute ash emissions and pyroclastic ejecta that landed on the upper part of the Sciara del Fuoco. By the third week of March, and through the end of the month, most of the activity had shifted to the vents in the N Area and diminished in the S Area. On 28 March, Etna Observatory personnel restored operations at both the infrared and visible cameras on the Pizzo sopra la Fossa which allowed for more detailed observations of the activity at the summit (figure 108).

Figure 108. The Terrazza Craterica at Stromboli seen from the thermal camera on the Pizzo sopra la Fossa on 31 March 2017, showing active vents in the two crater areas (AREA N, AREA CS). The abbreviations and arrows indicate the names and locations of the active vents. Courtesy of INGV (Rep. 14/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del, vulcano Stromboli del 04/04/2017).

Throughout April 2017, the N1 vent produced low (less than 80 m high) to medium (80-150 m) intensity explosions containing ash, lapilli, and bombs. The N2 vent showed sporadic low intensity explosive activity with occasional ash emissions until 20 April when more coarse (lapilli and bombs) material was ejected. Vent C showed continuous degassing throughout the month, and low intensity explosions began there during the third week of April, causing intense spattering on 29 April. The S1 vent showed sporadic and weak explosive activity of low intensity with the ejection of coarse material until the third week when activity ceased. Vent S2 showed explosive activity of medium-low intensity (less than 120 m high) of coarse material sometimes mixed with ash. Explosion rates were around 2-10 events per hour during the first half of the month, rising to 10-15 per hour for the second half of April.

In the N Area, the N1 and N2 vents continued with a similar level of activity throughout May 2017 (figure 109). Explosions of low to medium intensity sent coarse ejecta of lapilli and bombs up to 150 m high at N1 and 120 m high at N2. The rate of explosions in the N Area ranged from 4-12 per hour.

Figure 109. The Terrazza Craterica at Stromboli seen from the thermal camera located on the Pizzo sopra la Fossa on 18 May 2017, showing active vents in the two crater areas (AREA N, AREA CS). The abbreviations and arrows indicate the names and locations of the active vents. The vents in the N Area exhibited similar levels of activity throughout the month. Courtesy of INGV (Rep. 21/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 23/05/2017).

In the S Area, activity was more variable during May, and the rate of explosions ranged from 2-10 per hour. Vent C also continued with intense degassing and low-intensity explosions and spattering. On 13 May, two emission points were observed at vent C, one a few meters S of the other. Vent S1 showed no activity until late in the second week of May when low to moderate intensity explosions rose up to 150 m with coarse ejecta. During 14-15 May, a second vent opened a few meters north of S1, and simultaneous explosions from both S1 vents sent jets of gas and incandescent material into the air. Activity decreased to low intensity explosions (less than 80 m high) with ejecta during the third week, but then increased significantly during the last week of the month. Ejecta reached 200 m high from the S1 vents (figure 110). The southern S1 vent built a surrounding hornito and produced high and narrow jets of incandescent material, while the northern emission point produced more modest jets of gas and material. Vent S2 was quiet for most of May, producing only low-intensity explosions of coarse material sometimes mixed with ash for a few days near the beginning of the month.

Figure 110. The Terrazza Craterica at Stromboli seen from the thermal camera on the Pizzo sopra la Fossa on 29 May 2017, showing active vents in the two crater areas (AREA N, AREA CS). The abbreviations and arrows indicate the names and locations of the active vents. The S1 vent in the CS Area produced high intensity jets of incandescent material that rose 200 m during the last week of the month. Courtesy of INGV (Rep. 22/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 30/05/2017).

An increase in activity during June 2017 was apparent at both the N and S Areas (figure 111). Video taken by drone and from the summit during 10-12 June shows periodic explosions with ash, lapilli, and bombs ejected around the Terrazza Craterica (See Information Contacts for link). Vent N1 was characterized by low to medium-high intensity explosive activity that ejected lapilli and bombs to 200 m and was sometimes accompanied by ash that drifted S over the island. N2 also showed variable activity which ranged from low to high intensity (ejecta rising over 200 m high) during the first week, and low to medium-high (ejecta rose to 150 m) for the rest of the month (figure 112). Numerous bombs and lapilli were deposited both inside and outside the crater rim. Intense spattering was reported at N2 on 11, 12, 18, 19, and 26 June. The explosion rate in the N Area was 9-18 per hour.

Figure 111. Thermal activity increased during June 2017 at Stromboli. Simultaneous explosions from both the S (left) and N (right) Areas during 10-12 June 2017 were photographed from the summit. Copyrighted photo by Martin Rietze, used with permission.

Figure 112. Increased thermal activity was apparent in the N Area of the Terrazza Craterica at Stromboli as seen from the thermal camera located on the Pizzo sopra la Fossa on 5 June 2017. Courtesy of INGV (Rep. 23/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 06/06/2017).

In the CS Area, sporadic low-intensity explosions (less than 80 m high) characterized vent C, with modest spattering reported on 11, 12, 13, 26, 30 June 2017. Activity at S1 continued from two vents simultaneously with low to medium intensity explosive activity (figure 113 and 114). The vent at S2 reactivated briefly on 3 June after about a month of quiet with weak spattering activity but was not active again during the month. The CS Area was characterized by an explosion frequency of 1-10 per hour.

Figure 113. Explosions of incandescent ejecta from the CS Area at Stromboli during 10-12 June 2017. Copyrighted photo by Martin Rietze, used with permission.

Figure 114. Increased activity at the CS Area of Stromboli on 26 June 2017 was recorded by the thermal camera located on the Pizzo sopra la Fossa. Activity at S1 continued from two vents simultaneously with low to medium intensity explosive activity for most of the month. Courtesy of INGV (Rep. 26/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 27/06/2017).

During July 2017, thermal activity at the vents remained moderate to high; explosions at the N1 vent sent lapilli and bombs, sometimes mixed with ash, to 200 m above the vent. At vent N2, lapilli and bombs were ejected outside the crater rim, sometimes rolling down the Sciara del Fuoco to the ocean. The hourly frequency of explosions ranged from 5-18. At S1, both vents exploded simultaneously with lapilli, bombs and occasional ash rising to 150 m numerous times.

Beginning in the afternoon of 26 July, an explosive sequence at the CS Area lasting about 90 seconds was recorded with the thermal and visible image cameras on the Pizzo sopra la Fossa (figure 115). It began with explosions from vents C and S1, followed by a second explosion at S2. More explosions from C and S1 sent debris to the SE and were followed by fountaining to about 50 m from the vents for about a minute. INGV personnel witnessed 10-cm-diameter bombs on the SW side of the Pizzo at about 850 m elevation during a 30 July site visit.

Figure 115. The explosive sequence of 26 July 2017 at Stromboli was recorded by the thermal and visible cameras located on the Pizzo sopra la Fossa. Details of the 90-second-long event are described in the text. Courtesy of INGV (Rep. 31/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 01/08/2017).

A return to background activity during August consisted of explosions of varying intensity from low (less than 80 m) to medium-low (ejecta sometimes reached 120 m in height) at both the N and CS Area vents. Explosion frequency ranged from 2-11 per hour, decreasing significantly by the end of the month. Activity continued to diminish during September. Periodic spattering from vent C occurred. Only one vent was active in the CS Area during the month. A brief increase in intensity at vent N1 during 8-9 September sent ejecta over 150 m high. By the end of September, few explosions reached over 80 m in height. A brief episode of intense spattering at vent C on 24 September sent bombs and lapilli to 40 m above the vent. Explosion frequency averaged only 2-6 per hour by the end of September.

Continuous spattering, occasionally intense, from vent C continued during October. The vents in the N Area produced low to moderate intensity explosions, and one vent in the CS Area produced low intensity explosions. A strong explosive sequence in the CS Area lasted for about five minutes on 23 October 2017 (figure 116). The first explosion of the sequence came from vent C and lasted 30 seconds. It destroyed the hornito formed around the vent. About a minute later, two explosions occurred at the S1 vent, reaching about 120 m in height and dispersing to the SE. Another explosion at vent C about 3 minutes later sent ejecta 100 m high. The event ended with a series of small ash emissions that rose a few tens of meters. Low intensity activity continued from both areas through the end of October, with low explosion rates of around 2-6 per hour.

Figure 116. An explosive sequence from the CS Area at Stromboli on 23 October 2017 lasted about five minutes. Ejecta from vents C and S1 rose 100-150 m above the vents and dispersed SE. Courtesy of INGV (Rep. 43/2017, Bollettino settimanale sul monitoraggio vulcanico, geochimico, delle deformazioni del suolo e sismico del vulcano Stromboli del 24/10/2017).

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

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy, (URL: http://www.ct.ingv.it/en/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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/); Martin Rietze, Taubenstr. 1, D-82223 Eichenau, Germany (URL: https://mrietze.com/, https://www.youtube.com/channel/UC5LzAA_nyNWEUfpcUFOCpJw/videos, http://mrietze.com/web16/Stromb_Vesuv17.htm).

Remote Tinakula lies 100 km NE of the Solomon Trench at the N end of the Santa Cruz Islands, part of the country of the Solomon Islands, which generally lie 400 km to the W. It has been uninhabited since an eruption with lava flows and ash explosions in 1971 when the small population was evacuated (CSLP 87-71). The nearest inhabitants live on Te Motu (Trevanion) Island (about 30 km S), Nupani (40 km N), and the Reef Islands (60 km E); they occasionally report explosion noises from Tinakula. Ashfall from larger explosions has historically reached these islands. The last reported evidence of activity came from MODVOLC thermal alerts between August 2010 and October 2012, and observations of incandescent lava blocks rolling into the sea in May 2012. A new eruptive episode with a large ash explosion and substantial SO₂ plume during 21-26 October 2017 is reported below, along with newly available historical newspaper accounts of earlier eruptions.

Reports of ash plumes are issued by the Wellington Volcanic Ash Advisory Center (VAAC); the National Disaster Management Office (NDMO) of the Solomon Islands Government also issues situation reports when significant activity is reported. Satellite data from infrared, visual, and SO₂ monitoring instruments are an important source of information for this remote volcano. News reports from local (and social) media are often the only sources of information for the smaller events. Recently identified 19th- and 20th-century newspaper accounts of eruptive activity witnessed by sailors passing nearby is a valuable new resource for previously unreported events.

Eruption of 21-26 October 2017. Reports of a substantial explosion with an ash plume from Tinakula appeared on social media and in the local press during 22-26 October 2017. Staff from the Lata Met Service Office approached the island by boat on 23 October to make direct observations (figures 17-19). A video clip from the Himawari8 Satellite showing the ash plume explosion was posted by Stephan Armbruster on Twitter on 22 October. The Solomon Islands NDMO issued a situation report on 26 October showing ashfall covering vegetation on the island. According to the NDMO, ashfall was concentrated on the island, although a small amount of ash drifted SE and was reported to briefly contaminate drinking water in several communities in the nearby Reef Islands (60 km ENE) . Ashfall was also reported on Fenualoa Island (50 km ENE) (Radio New Zealand). The eruption was categorized by NMDO as a VEI 3. A team of geologists from NDMO brought seismic monitoring equipment to Tinakula in early November, and measured a high frequency volcanic tremor on 5 November 2017.

Figure 17. View from the SE of the eruption at Tinakula on 23 October 2017 during a site visit by staff from the Lata Office of the Solomon Islands Meteorological Service. Photo by Okano Gamara.

Figure 18. Ash and steam emissions rose from Tinakula on 23 October 2017 during a site visit by staff from the Lata Office of the Solomon Islands Meteorological Service. Photo by Okano Gamara.

Figure 19. Ash emission from Tinakula on 23 October 2017 during a site visit by staff from the Lata Office of the Solomon Islands Meteorological Service. Photo by Okano Gamara.

The Wellington VAAC first reported an ash plume visible in satellite imagery shortly after midnight (UTC) on 21 October 2017. The plume was estimated to be at 4.6 km altitude and drifting N. About 90 minutes later they reported a second eruption with a much higher plume drifting SE at 10.7 km altitude using IR imagery cloud top temperatures to estimate the altitude. They reported ongoing ash emissions visible in satellite imagery drifting SE at 6.1 km altitude throughout the morning, dropping to 3 km altitude by the end of the day. The following day, 22 October, intermittent ash emissions were reported at 3.7 km altitude moving E. By that afternoon, they had dropped to 2.4 km, and had lowered to 1.8 km by late on 23 October. Ongoing low-level ash emission (2.1 km altitude) continued through 25 October; by early on 26 October, there was no further evidence of ongoing activity.

No MODVOLC thermal alerts were associated with this event, but there was a brief MIROVA signal from the MODIS infrared data during 20-23 October 2017 (figure 20). A major SO₂ plume was released from Tinakula on 21 October, and a smaller one was recorded on 28 October as well (figure 21).

Figure 20. Moderate thermal signals were recorded from Tinakula on 20 and 23 October 2017 (top graph) by the MIROVA system that captures MODIS infrared satellite data. Another signal reported during the first week of March 2017 (bottom graph) could also have been an eruptive event, but no other corroborating evidence is available. Courtesy of MIROVA.

Figure 21. Major SO2 plumes from Tinakula and the Vanatu volcanoes of Ambae and Ambrym were released during October 2017. A substantial SO2 plume drifted in several directions from Tinakula on 21 October 2017 (left). Much smaller plumes are also visible from Ambae and Ambrym which are located farther south. On 28 October (right), a smaller SO2 plume was drifting SE from Tinakula while much larger plumes were apparent from Ambae and Ambrym. Data gathered by the OMI instrument on the Aura Satellite. Courtesy of NASA Goddard Space Flight Center.

Summary of activity during 1971-2012. After the 1971 eruption, intermittent ash emissions, lava bombs, and pyroclastic flows were reported by geologists and sailors passing nearby in 1984, 1985, 1989-1990, 1995, and 1999. Infrared MODIS thermal data was first reported as MODVOLC thermal alerts beginning in 2000 and has provided satellite-based confirmation of thermal activity since then. Months with thermal activity included February 2000-May 2001, February 2006-November 2007, September-November 2008, August 2009, and January 2010-October 2012 (figure 22). No additional thermal alerts were issued through 2017. Since 2004, SO₂ data has been gathered by satellite instruments and processed by NASA Goddard Space Flight Center; in February and April 2006 small SO₂ plumes were recorded (figure 23).

Figure 22. Months with MODVOLC thermal alerts from MODIS infrared data for Tinakula, during January 2000-December 2017. The orange boxes indicate months where at least one MODVOLC thermal alert was issued; the number of alerts is indicated inside the square. Months highlighted in green represent contiguous periods of time of three months or greater with no recorded MODVOLC thermal alerts. Pale orange squares indicate months with no MODVOLC thermal alerts issued, but within a three-month buffer of an earlier thermal alert. Data courtesy of MODVOLC.

Figure 23. SO2 emission data captured by the OMI instrument on the Aura satellite indicated small plumes from Tinakula (top center of images) on 12 and 14 February 2006 (top) and 21 and 23 April 2006 (bottom). Small plumes were also visible from Ambrym on 12 February, and from Ambae and Ambrym on 14 February and 21 and 23 April 2006. Courtesy of NASA Goddard Space Flight Center.

Eruption reports during 1868-1932. Reports of eruptions at Tinakula between 1868 and 1932 have recently been found in 19th and 20th century newspaper accounts from Australia and New Zealand (table 6). The accounts describe incandescence, water discoloration of the sea, explosions, ash plumes, and lava flows extending from the summit to the ocean.

Table 6. Newly discovered historical newspaper accounts of volcanic activity from ships passing near Tinakula between 1868 and 1932. This is not a full eruptive history for the time period. Online links provided in the References section. Courtesy of Steve Hutcheon.

References. The Age (Melbourne, Victoria) 10 November 1868, page 2b (URL: http://nla.gov.au/nla.news-article177002744).

The Empire (Sydney, NSW) 27 October 1869, page 2a, (URL: http://nla.gov.au/nla.news-article60895166).

The Sydney Morning Herald (NSW) 19 Februay 1872, page 6a (URL: http://nla.gov.au/nla.news-article13252748).

The Daily Telegraph (Sydney, NSW) 1887 20 July, page 4f (URL: http://nla.gov.au/nla.news-article239817295).

The Daily Telegraph (Sydney, NSW) 1 September 1910, page 7a (URL: http://nla.gov.au/nla.news-article237993807; http://nla.gov.au/nla.news-article15183461 ).

The New Zealand Herald (Auckland, NZ) 27 June 1932, page 6a (URL: https://paperspast.natlib.govt.nz/newspapers/NZH19320627.2.19 ).

The Auckland Star (NZ) 10 September 1932, page 1h (Supplement) (URL: https://paperspast.natlib.govt.nz/newspapers/AS19320910.2.180.6 ).

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: National Disaster Management Office (NDMO), Solomon Islands Government, Prince Philip Highway, Ranadi, Solomon Islands (URL: http://www.ndmo.gov.sb); 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); 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 Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: http://so2.gsfc.nasa.gov/index.html ); Radio New Zealand (URL: http://www.radionz.co.nz/international/pacific-news/342267/solomons-pm-calls-for-calm-in-communities-close-to-volcano); Solomon Islands Broadcasting Corporation, SIBC Voice of the Nation, Honiara, Solomon Islands (URL: http://www.sibconline.com.sb/no-its-not-snow-in-the-solomons-its-ash-from-the-tinakula-volcano/); Andy Prata, AIRES Atmospheric Industrial Research and Environmental Solutions, Melbourne, Australia (URL: https://www.aires.space/, https://twitter.com/andyprata/status/922177129944625157); Gamara Okzman Bencarson, Facebook.

Episodic eruptive activity at Ecuador's Tungurahua has persisted since November 2011. Periods of activity over several weeks that included ash plumes, Strombolian activity, pyroclastic flows, and lava flows were often followed by quiescence for a similar time span. This type of activity continued throughout 2015 (BGVN 42:08, 42:12); Strombolian activity, significant ash emissions, and SO₂ plumes in mid-November 2015 marked the last significant activity for that year. The next episode began in late February 2016 and is discussed below with information provided by the Observatorio del Volcán Tungurahua (OVT) of the Instituto Geofísico (IG-EPN) of Ecuador, aviation alerts from the Washington Volcanic Ash Advisory Center (VAAC), and other sources of satellite data.

The latest eruptive episode at Tungurahua lasted from 26 February-16 March 2016. Multiple explosions with ash plumes that rose 3-8 km were frequent. Incandescent blocks were ejected up to 1,500 m down most flanks. Pyroclastic flows affected many of the ravines, although no communities reported damage. Significant SO₂ emissions were recorded by satellite data between 27 February-8 March. An inflationary trend was recorded from early March through late September 2016, after which a period of deflation began. Tungurahua had occasional seismic swarms after the eruption, but no reported surface activity for the remainder of 2016 and 2017.

IG reported an ash emission on 5 January 2016 that rose 2 km above the crater and drifted NE, causing minor ashfall in the Pondoa and Bilbao sectors. Otherwise, no volcanic activity was reported until a new episode began on 26 February 2016 with a seismic swarm followed by a series of explosions and ash plumes that rose 3-8 km above the crater (figures 96 and 97). Incandescent blocks were ejected up to a kilometer down the NW, W, and SW flanks (figure 98). Pyroclastic flows were also generated that descended through the gorges of Juive, La Hacienda, Mandur and Cusúa, reaching distances of 500-1,500 m (figure 99).

Figure 96. An ash emission at Tungurahua observed from OVT on 26 February 2016. Courtesy of IG-EPN, (Explosion en el Volcan Tunguraha, No. 20 [1], Informe especial Tungurahia No. 1).

Figure 97. Ejecta traveled 1,000 m from the crater, an ash plume rose 2 km, and pyroclastic flows traveled down several drainages on the NW flank at Tungurahua on 26 February 2016 in this thermal image taken from the Mandur camera. Courtesy of OVT, IG-EPN (INFORME No. 836, SÍNTESIS SEMANAL DEL ESTADO DEL VOLCÁN TUNGURAHUA, Semana: Del 23 de febrero al 01 de marzo de 2016).

Figure 98. Incandescent blocks descended 1,000 m down the NW, W, and SW flanks of Tungurahua on 26 February 2016, and explosions were audible at OVT. Photo by F. Vásconez, courtesy of OVT, IG-EPN (INFORME No. 836, SÍNTESIS SEMANAL DEL ESTADO DEL VOLCÁN TUNGURAHUA, Semana: Del 23 de febrero al 01 de marzo de 2016).

Figure 99. Pyroclastic flows descended the Mandur, La Hacienda and other ravines on the W flank of Tungurahua on 26 February 2016 as far as 1 km. Photo by F. Vásconez, courtesy of OVT, IG-EPN (INFORME No. 836, SÍNTESIS SEMANAL DEL ESTADO DEL VOLCÁN TUNGURAHUA, Semana: Del 23 de febrero al 01 de marzo de 2016).

Continuous emissions with low to moderate ash content drifted W and SW on 27 February. The communities most affected by ashfall were Choglontus, Cotaló, El Manzano, Palitahua, Bilbao, Pillate, Juive, Ambato, Tisaleo, Riobamba, and Quero. The ash was mostly fine-grained, except in the area near Pillate and Choglontus, where the grain size reached up to 3 mm and consisted of reddish, black, gray, and beige fragments (figure 100). On the morning of 1 March 2015, several pyroclastic flows were observed descending through the Juive, Mandur, Achupashal, La Hacienda, and Romero ravines; they traveled 1.5-1.7 km (figure 101).

Figure 100. Coarse-grained ash fragments from Tungurahua collected in Ambato on 26 February 2016. Photo by Marco Montesdeoca (ECU911 Ambato), Courtesy of OVT, IG-EPN (Explosion en el Volcan Tunguraha, No. 2, Informe especial Tungurahia No. 2, 26 de febrero del 2016 (16h45)).

Figure 101. A pyroclastic flow descended 1.5 km down the Hacienda Ravine on 1 March 2016 at Tungurahua and was captured by the Mandur thermal camera. Courtesy of OVT, IG-EPN (INFORME No. 836, SÍNTESIS SEMANAL DEL ESTADO DEL VOLCÁN TUNGURAHUA, Semana: Del 23 de febrero al 01 de marzo de 2016).

Ash emissions were constant throughout the first week in March (figures 102 and 103). During 1-5 March they drifted NW, SW and E, with ashfall reported in the towns of Pillate, Manzano, Choglontus, Palictahua and El Altar (figure 104). Incandescent blocks descended most of the flanks (figure 105). Beginning on 6 March, plumes drifted SW and S, with variable ash content. Pyroclastic flows along the W and NW flanks descended the Cusua, Juive, Mandur, Ashupashal, Romero, and Rhea drainages (figure 106), the farthest traveled went 2.2 km down the Ashupashal on 7 March. In addition to ash and other explosive debris, daily sulfur dioxide emissions were identified from 27 February-8 March 2016 by the OMI instrument on the Aura satellite (figure 107).

Figure 102. Constant ash emissions rose at least 1 km above the summit of Tungurahua during the first week of March 2016. Photo take on 3 March 2016 by P. Espin. Courtesy of OVT, IG-EPN (INFORME No. 837, SÍNTESIS SEMANAL DEL ESTADO DEL VOLCÁN TUNGURAHUA, Semana: Del 01 al 08 de marzo de 2016).

Figure 103. A dark ash plume formed a mushroom cloud over Tungurahua on 5 March 2016; it rose 2 km above the summit and drifted SW. Photo by E. Telenchana , courtesy of OVT, IG-EPN (INFORME No. 837, SÍNTESIS SEMANAL DEL ESTADO DEL VOLCÁN TUNGURAHUA, Semana: Del 01 al 08 de marzo de 2016).

Figure 104. Ashfall in Choglontus on 6 March 2016 from Tungurahua. Photo by P. Espín, courtesy of OVT, IG-EPN (INFORME No. 837, SÍNTESIS SEMANAL DEL ESTADO DEL VOLCÁN TUNGURAHUA, Semana: Del 01 al 08 de marzo de 2016).

Figure 105. Strombolian explosions send incandescent blocks down the flanks of Tungurahua on 6 March 2016. Photo by E. Gaunt, courtesy of OVT, IG-EPN (INFORME No. 837, SÍNTESIS SEMANAL DEL ESTADO DEL VOLCÁN TUNGURAHUA, Semana: Del 01 al 08 de marzo de 2016).

Figure 106. Visual (upper) and thermal (lower) images of Tungurahua taken from Cotalo showing a pyroclastic flow extending down the Achupashal drainage on 6 March 2016. Photo by E. Gaunt, thermal image by M. Almeida, courtesy of OVT, IG-EPN (INFORME No. 837, SÍNTESIS SEMANAL DEL ESTADO DEL VOLCÁN TUNGURAHUA, Semana: Del 01 al 08 de marzo de 2016).

Figure 107. Substantial SO2 emissions from Tungurahua were measured daily during 27 February-8 March 2016 by the OMI instrument on the Aura satellite. The plumes drifted 300 km or more W on 27 February, 1, 3, and 5 March. Columbia's Nevado del Riuz (upper plume in images) also produced SO2 emissions during this same period. Courtesy of NASA Goddard Space Flight Center.

Beginning on 28 February, a strong inflationary trend (almost 3 cm) was observed in the GPS data at the Mazón (SW flank) station. Three inclinometers on the NW flank also indicated inflation during 28 February-4 March.

Episodic explosions on 8 March 2016 produced plumes with high ash contents that rose 6 km. Small pyroclastic flows descended the NW flank in the Mandur, Rea, Achupashal, and La Hacienda ravines. Sporadic emissions continued for most of the second week of March, with varying ash contents, reaching between 1.5 and 4 km above the crater and drifting to the SSW. Reports of ashfall were received in the sectors of Choglontús, Manzano, Pillate, El Altar, and Palitahua, and minor ashfall in Juive and Cusúa. Several ash plumes (figure 108) and a small pyroclastic flow were observed on 13 March 2016. The Manzano lookout reported loud noises on 14 March, and ashfall in the afternoon, but weather obscured views of emissions. Rainy weather on 16 March also obscured views, but Manzano, Chacauco, Cusúa, and Juive lookouts reported ashfall and explosions. There were no further reports from the observatory of ash emissions, ashfall, or explosions; only minor steam plumes were observed on clear days after 16 March 2016.

Figure 108. An ash emission at Tungurahua on 13 March 2016 was the last photographed for the eruption. Photo by M. Córdova from OVT, courtesy of IG-EPN (INFORME No. 838, SÍNTESIS SEMANAL DEL ESTADO DEL VOLCÁN TUNGURAHUA, Semana: Del 08 al 15 de marzo de 2016).

The Washington VAAC reported possible ash emissions on 31 March 2016, but information from OVT indicated no surface activity. Intense rain on 28 March generated a small lahar that descended through the La Pampa ravine. Significant rainfall on 2 April caused lahars to affect Vazcun, Juive, Pondoa, Bilbao, Achupashal, Chontapamba and Malpayacu drainages. Seismicity continued to decrease throughout April 2016. A small swarm of Long Period seismic events (LP's) occurred between 1 and 20 May that were associated with fluid movements. The Washington VAAC reported ash emissions on 3, 8, and 13 May, but OVT reported no surface activity during the entire month (figure 109).

Figure 109. Clear skies on 31 May 2016 at Tungurahua revealed a snow-covered summit with no evidence of emissions. Photo by M. Córdova, courtesy of OVT, IG-EPN (INFORME No. 849, SÍNTESIS SEMANAL DEL ESTADO DEL VOLCÁN TUNGURAHUA, Semana: Del 24 al 31 de mayo del 2016).

In a Special Report released on 2 June 2016, IG-EPN noted a clear inflationary trend in data collected from two stations at Tungurahua since the end of the eruption in mid-March. The Retu inclinometer, located N of the crater, showed inflation on the radial axis of about 600 μrad (microradians), and about 200 μrad on the tangential axis. The same axis at the Mandur inclinometer (on the NW flank) had a smaller but distinct (~30 μrad) inflationary signal (figure 110).

Figure 110. The pattern of deformation registered at the Retu (Refugio Tungurahua) and Mndr (Mandur) inclinometers from 14 February-30 May 2016 at Tungurahua. The gray area corresponds to the eruption of 26 February -16 March. An inflationary trend is apparent on both axes at the Retu instrument and on the tangential axis of the Mndr site. Courtesy of IG-EPN (Informe Especial Volcán Tungurahua - N°6, 2 de Junio de 2016).

A Washington VAAC report on 1 June 2016 noted that the Guayaquil Meteorological Weather Office (MWO) reported an ash plume at Tungurahua, but OVT confirmed no surface activity. A very small lahar was recorded in the La Pampa ravine on 2 June. Although there were rains of varying intensity many days during June, they did not generate significant lahars, except one of medium size that occurred on 21 June in the Achupashal ravine. The Washington VAAC noted a report from the Guayaquil MWO of an ash emission on 5 July, but it was not detected in satellite imagery, and the OVT reported no surface activity. There was no surface activity reported by OVT from July to mid-September (figure 111), and internal seismicity remained very low. Occasional rainy periods generated muddy water in the ravines, but no significant lahars were reported.

Figure 111. The summit of Tungurahua showed no sign of surface activity on 1 August 2016. Photo by Bernard J., courtesy of OVT, IG-EPN (INFORME No. 858, SÍNTESIS SEMANAL DEL ESTADO DEL VOLCÁN TUNGURAHUA, Semana: Del 26 de julio al 02 de agosto de 2016).

A significant increase in the number of LP seismic events began on 12 September 2016, and a small seismic swarm was recorded on 18 September (figure 112). Small fumaroles were visible at the edges of the crater on 15 and 16 September (figure 113). At this same time, the inflationary trend that had been ongoing since the eruption earlier in the year switched to deflation as measured at the Retu inclinometer.

Figure 112. The number of different types of seismic events and explosions recorded at Tungurahua between 1 January and 18 September 2016. The largest spike between 26 February and 16 March corresponds to the eruption of that period. Other episodes of seismicity were recorded during May and mid-September, but did not result in ash emissions or explosions. Courtesy of IG-EPN (Informe Especial Volcán Tungurahua - N°7, 18 de Septiembre de 2016).

Figure 113. Closeup images of the summit of Tungurahua on 15 (top) and 16 (bottom) September 2016 reveal minor fumarolic activity. Top: Steam rises from two snow free areas on 15 September (INFORME No. 865, SÍNTESIS SEMANAL DEL ESTADO DEL VOLCÁN TUNGURAHUA, Semana: Del 13 al 20 de septiembre de 2016). Bottom: Fumarolic activity was also apparent in this telephoto image taken from OVT on 16 September. Photo by P. Ramón (Informe Especial Volcán Tungurahua - N°7, 18 de Septiembre de 2016). Courtesy of OVT, IG-EPN.

Another increase in LP seismicity and tremors occurred on 24 September, but there were no reports of surface activity other than minor steam fumaroles. Seismicity remained elevated through early October; a one-hour tremor event was reported on 1 October. Seismicity decreased gradually over the following two weeks. Low-energy steam and gas emissions from fumaroles located on the S and SW flanks were observed during a flyover on 7 October 2016. This corresponded to the warmest areas revealed in the thermal image of the summit (figure 114). with a TMA (maximum apparent temperature) of 47.9°C and 36.5°C.

Figure 114. A thermal image of the summit of Tungurahua taken during a flyover on 7 October 2016 showed two areas on the crater rim with slightly elevated temperatures where fumarolic activity was occasionally observed. Image by P. Ramón, courtesy of OVT, IG-EPN (INFORME No. 868, SÍNTESIS SEMANAL DEL ESTADO DEL VOLCÁN TUNGURAHUA, Semana: Del 4 al 11 de octubre de 2016).

Re-suspended ash from high winds in mid-November 2016 caused several VAAC notices to be issued, but no new emissions were reported by OVT through the end of 2016.

Tungurahua remained quiet throughout 2017. A 90-minute seismic swarm on 8 January 2017 and a minor increase in seismicity in the second half of March were the only seismic events above background levels. There were no emissions except for occasional minor fumarolic activity around the crater rim. Periods of heavy rainfall occasionally produced muddy water in the ravines; the only lahars were reported during 5-6 January, late April and 15 November.

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

Information Contacts: Instituto Geofísico (IG), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec ); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html).

Regular monitoring reports about Yasur from the Vanuatu Meteorology and Geo-Hazards Department (VMGD) indicated that the centuries-long eruptive activity continued from mid-June 2017 through January 2018. VMGD volcano bulletins on 21 July, 30 August, 29 September, 31 October, and 8 December 2017, and 30 January 2018, stated that major unrest was continuing, and the Alert Level remained at 2 (on a scale of 0-4). Based on seismic data, explosions continued to be intense. Visitors were reminded of the closed 395-m-radius Permanent Exclusion Zone (figure 47) and that volcanic ash and gas could impact other areas near the volcano due to trade winds.

Figure 47. Oblique aerial photograph of Yasur with an overlay of designated hazard zones that may be closed depending on the level of eruptive activity. Courtesy of Vanuatu Meteorology and Geo-Hazards Department.

During the reporting period thermal anomalies based on MODIS satellite instruments analyzed using the MODVOLC algorithm were numerous every month. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system also detected numerous hotspots every month (figure 48).

Figure 48. Thermal anomalies detected in MODIS data by the MIROVA system (log radiative power) at Yasur for the year ending 23 February 2018. Courtesy of MIROVA.

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

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department, Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); Radio New Zealand (URL: https://www.radionz.co.nz); 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/).