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).

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/).

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).

The steeply sloped 1.4-km-diameter Kadovar Island is located in the Bismark Sea offshore from the mainland of Papua New Guinea about 25 km NNE from the mouth of the Sepik River. Its first confirmed observed eruption began in early January 2018, with ash plumes and lava extrusion resulting in the evacuation of around 600 residents from the N side of the island (BGVN 43:03). A dome appeared at the base of the E flank during March-May 2018 (Planka et al., 2019); by November activity had migrated to a new dome growing near the summit on the E flank. Pulsating steam plumes, thermal anomalies, and periodic ash emissions continued throughout 2019 (BGVN 44:05, 45:01), and from January-June 2020, the period covered in this report. Information was provided by the Rabaul Volcano Observatory (RVO), the Darwin Volcanic Ash Advisory Center (VAAC), satellite sources, and photographs from visitors.

Activity during January-June 2020. Intermittent ash plumes, pulsating gas and steam plumes, and thermal anomalies continued at Kadovar during January-June 2020. MIROVA thermal data suggested persistent low-level anomalies throughout the period (figure 45). Sentinel-2 satellite data confirmed thermal anomalies at the summit on 5 and 25 January 2020, and an ash emission on 20 January (figure 46). Persistent pulsating steam plumes were visible whenever the skies were clear enough to see the volcano.

Figure 45. Persistent low-level thermal activity at Kadovar was recorded in the MIROVA graph of radiative power from 2 July 2019 through June 2020. The island location is mislocated in the MIROVA system by about 5.5 km SE due to older mis-registered imagery; the anomalies are all on the island. Courtesy of MIROVA.

Figure 46. Sentinel-2 satellite data confirmed thermal anomalies at the summit of Kadovar on 5 (left) and 25 January 2020, and an ash emission and steam plume that drifted SE on 20 January (center). Pulsating steam-and-gas emissions left a trail in the atmosphere drifting SE for several kilometers on 25 January (right). Left image uses Atmospheric penetration rendering (bands 12, 11, 8a), center and right images use Natural color rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

On 2 February 2020 the Darwin VAAC reported a minor eruption plume that rose to 1.5 km altitude and drifted ESE for a few hours. Another plume was clearly discernible in satellite imagery on 5 February at 2.1 km altitude moving SE. RVO issued an information bulletin on 7 February reporting that, since the beginning of January, the eruption had continued with frequent Vulcanian explosions from the Main Vent with a recurrence interval of hours to days. Rocks and ash were ejected 300-400 m above the vent. Rumbling could be heard from Blupblup (Rubrub) island, 15 km E, and residents there also observed incandescence at night. On clear days the plume was sometimes visible from Wewak, on the mainland 100 km W. Additional vents produced variable amounts of steam. The Darwin VAAC reported continuous volcanic ash rising to 1.5 km on 22 February that extended ESE until it was obscured by a meteoric cloud; it dissipated early the next day. A small double ash plume and two strong thermal anomalies at the summit were visible in satellite imagery on 24 February (figure 47).

Figure 47. Ash emissions and thermal anomalies continued at Kadovar during February 2020. Two small plumes of ash or dense steam rose from the summit on 24 February 2020, seen in this Natural color rendering (bands 4, 3, 2) on the left. The same image rendered in Atmospheric penetration (bands 12, 11, 8a) on the right shows two thermal anomalies in the same locations as the ash plumes. Courtesy of Sentinel Hub Playground.

The Darwin VAAC reported continuous ash emissions beginning on 13 March 2020 that rose to 1.5 km altitude and drifted SE. The plume was visible intermittently in satellite imagery for about 36 hours before dissipating. During April, pulsating steam plumes rose from two vents at the summit, and thermal anomalies appeared at both vents in satellite data (figure 48). Small but distinct SO₂ anomalies were visible in satellite data on 15 and 16 April (figure 49).

Figure 48. Steam plumes and thermal anomalies continued at Kadovar during April 2020. Top: A thermal anomaly at the summit accompanied pulsating steam plumes that drifted several kilometers SE before dissipating on 4 April 2020. Bottom left: Two gas-and-steam plumes drifted E from the summit on 9 April. Bottom right: Two adjacent thermal anomalies were present near the summit on 19 April. Top and bottom right images use Atmospheric penetration rendering (bands 12, 11, 8a), bottom left image uses Natural color rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

Figure 49. Small but distinct SO2 anomalies were detected at Kadovar on 15 and 16 April 2020 with the TROPOMI instrument on the Sentinel-5P satellite. Nearby Manam often produces larger SO2 plumes that obscure evidence of activity at Kadovar. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Two summit vents remained active throughout May and June 2020, producing pulsating steam plumes that were visible for tens of kilometers and thermal anomalies visible in satellite data (figure 50). A strong thermal anomaly was visible beneath meteoric clouds on 8 June.

Figure 50. During May and June 2020 thermal and plume activity continued at Kadovar. Top: Gas-and-steam plumes drifted NW from two sources at the summit of Kadovar on 19 May 2020. Bottom left: Two thermal anomalies marked the E rim of the summit crater on 28 June 2020. Bottom right: A zoomed out view of the same 28 June image shows pulsating steam plumes drifting 10 km NW from Kadovar. Top image is Natural color rendering (bands 4, 3, 2). Bottom images are Atmospheric penetration rendering (bands 12, 11, 8a) of Sentinel-2 images. Courtesy of Sentinel Hub Playground.

Visitor observations on 21 October 2019. Claudio Jung visited Kadovar on 21 October 2019. Shortly before arriving on the island an ash plume rose tens of meters above the summit and drifted W (figure 51). From the NW side of the summit crater rim, Jung saw the actively growing dome on the side of a larger dome, and steam and gas issuing from the growing dome (figure 52). The crater rim was covered with dead vegetation, ash, and large bombs from recent explosions (figure 53). The summit dome had minor fumarolic activity around the summit area and dead vegetation halfway up the flank (figure 54) while the fresh blocky lava of the actively growing dome on the E side of the summit produced significant steam and gas emissions. The growing dome produced periodic pulses of dense steam during his visit (figure 55).

Figure 51. Views looking S show the shoreline dome at the base of the E flank of Kadovar that was active during March-May 2018 (left), and an ash plume drifting W from the summit dome located on the E side of the summit crater (right) on 21 October 2019. Copyrighted photos courtesy of Claudio Jung, used with permission.

Figure 52. A panorama looking SE from the crater rim of Kadovar on 21 October 2019 shows the actively growing dome on the far left with a narrow plume of steam and gas being emitted. A large dome fills the summit crater; the crater rim is visible on the right. Copyrighted photo courtesy of Claudio Jung, used with permission.

Figure 53. The crater rim of Kadovar on 21 October 2019 was covered with dead vegetation, ash, and large bombs from recent explosions. Person is sitting on a large bomb; weak fumarolic activity is visible along the rim. Copyrighted photo courtesy of Claudio Jung, used with permission.

Figure 54. The summit dome of Kadovar on 21 October 2019 had minor fumarolic activity around most of its summit and dead vegetation half-way up the flank (left). The dead tree stumps suggest that vegetation covered the lower half of the dome prior to the eruption that began in January 2018. The fresh blocky lava of the actively growing dome on the E side of the summit dome produced significant steam and gas emissions (right). Copyrighted photos courtesy of Claudio Jung, used with permission.

Figure 55. Dense steam from the growing dome on the E side of the summit drifted W from Kadovar on 21 October 2019. Copyrighted photo courtesy of Claudio Jung, used with permission.

Reference: Planka S, Walter T R, Martinis S, Cescab S, 2019, Growth and collapse of a littoral lava dome during the 2018/19 eruption of Kadovar Volcano, Papua New Guinea, analyzed by multi-sensor satellite imagery, Journal of Volcanology and Geothermal Research, v. 388, 15 December 2019, 106704, https://doi.org/10.1016/j.jvolgeores.2019.106704.

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

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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/); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Claudio Jung (URL: https://www.instagram.com/jung.claudio/).

Frequent activity at Ecuador's Sangay has included pyroclastic flows, lava flows, ash plumes, and lahars reported since 1628. Its remoteness on the east side of the Andean crest make ground observations difficult; remote cameras and satellites provide important information on activity. The current eruption began in March 2019 and continued through December 2019 with activity focused on the Cráter Central and the Ñuñurco (southeast) vent; they produced explosions with ash plumes, lava flows, and pyroclastic flows and block avalanches. In addition, volcanic debris was remobilized in the Volcan river causing significant damming downstream. This report covers ongoing similar activity from January through June 2020. Information is provided by Ecuador's Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), and a number of sources of remote data including the Washington Volcanic Ash Advisory Center (VAAC), the Italian MIROVA Volcano HotSpot Detection System, and Sentinel-2 satellite imagery. Visitors also provided excellent ground and drone-based images and information.

Throughout January-June 2020, multiple daily reports from the Washington Volcanic Ash Advisory Center (VAAC) indicated ash plumes rising from the summit, generally 500-1,100 m. Each month one or more plumes rose over 2,000 m. The plumes usually drifted SW or W, and ashfall was reported in communities 25-90 km away several times during January-March and again in June. In addition to explosions with ash plumes, pyroclastic flows and incandescent blocks frequently descended a large, deep ravine on the SE flank. Ash from the pyroclastic flows rose a few hundred meters and drifted away from the volcano. Incandescence was visible on clear nights at the summit and in the ravine. The MIROVA log radiative power graph showed continued moderate and high levels of thermal energy throughout the period (figure 57). Sangay also had small but persistent daily SO₂ signatures during January-June 2020 with larger pulses one or more days each month (figure 58). IG-EPN published data in June 2020 about the overall activity since May 2019, indicating increases throughout the period in seismic event frequency, SO₂ emissions, ash plume frequency, and thermal energy (figure 59).

Figure 57. This graph of log radiative power at Sangay for 18 Aug 2018 through June 2020 shows the moderate levels of thermal energy through the end of the previous eruption in late 2018 and the beginning of the current one in early 2019. Data is from Sentinel-2, courtesy of MIROVA.

Figure 58. Small but persistent daily SO2 signatures were typical of Sangay during January-June 2020. A few times each month the plume was the same or larger than the plume from Columbia’s Nevado del Ruiz, located over 800 km NE. Image dates are shown in the header over each image. Courtesy of NASA’s Global Sulfur Dioxide Monitoring Page.

Figure 59. A multi-parameter graph of activity at Sangay from May 2019 to 12 June 2020 showed increases in many types of activity. a) seismic activity (number of events per day) detected at the PUYO station (source: IG-EPN). b) SO2 emissions (tons per day) detected by the Sentinel-5P satellite sensor (TROPOMI: red squares; source: MOUNTS) and by the IG-EPN (DOAS: green bars). c) height of the ash plumes (meters above crater) detected by the GOES-16 satellite sensor (source: Washington VAAC). d) thermal emission power (megawatt) detected by the MODIS satellite sensor (source: MODVOLC) and estimate of the accumulated lava volume (million M3, thin lines represent the error range). Courtesy of IG-EPN (Informe Especial del Volcán Sangay - 2020 - N°3, “Actualización de la actividad eruptiva”, Quito, 12 de junio del 2020).

Activity during January-March 2020. IG-EPN and the Washington VAAC reported multiple daily ash emissions throughout January 2020. Gas and ash emissions generally rose 500-1,500 m above the summit, most often drifting W or SW. Ashfall was reported on 8 January in the communities of Sevilla (90 km SSW), Pumallacta and Achupallas (60 km SW) and Cebadas (35 km WNW). On 16 January ash fell in the Chimborazo province in the communities of Atillo, Ichobamba, and Palmira (45 km W). Ash on 28 January drifted NW, with minor ashfall reported in Púngala (25 km NW) and other nearby communities. The town of Alao (20 km NW) reported on 30 January that all of the vegetation in the region was covered with fine white ash; Cebadas and Palmira also noted minor ashfall (figure 60).

Figure 60. Daily ash plumes and repeated ashfall were reported from Sangay during January 2020. Top left: 1 January 2020 (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-2, JUEVES, 2 ENERO 2020). Top right: 20 January 2020 (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-21, MARTES, 21 ENERO 2020). Bottom left: 26 January-1 February 2020 expedition (Martes, 18 Febrero 2020 12:21, EXPEDICIÓN AL VOLCÁN SANGAY). Bottom right: 30 January 2020, minor ashfall was reported in the Province of Chimborazo (#IGAlInstante Informativo VOLCÁN SANGAY No. 006, JUEVES, 30 ENERO 2020). Courtesy of IG-EPN.

A major ravine on the SE flank has been the site of ongoing block avalanches and pyroclastic flows since the latest eruption began in March 2019. The pyroclastic flows down the ravine appeared incandescent at night; during the day they created ash clouds that drifted SW. Satellite imagery recorded incandescence and dense ash from pyroclastic flows in the ravine on 7 January (figure 61). They were also reported by IG on the 9th, 13th, 26th, and 28th. Incandescent blocks were reported in the ravine several times during the month. The webcam captured images on 31 January of large incandescent blocks descending the entire length of the ravine to the base of the mountain (figure 62). Large amounts of ash and debris were remobilized as lahars during heavy rains on the 25th and 28th.

Figure 61. Sentinel-2 satellite imagery of Sangay from 7 January 2020 clearly showed a dense ash plume drifting W and ash and incandescent material from pyroclastic flows descending the SE-flank ravine. Left image uses natural color (bands 4, 3, 2) rendering and right images uses atmospheric penetration (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Figure 62. Pyroclastic flows at Sangay produced large trails of ash down the SE ravine many times during January 2020 that rose and drifted SW. Top left: 9 January (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-9, JUEVES, 9 ENERO 2020). Top right: 13 January (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-14, MARTES, 14 ENERO 2020). On clear nights, incandescent blocks of lava and pyroclastic flows were visible in the ravine. Bottom left: 16 January (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-17, VIERNES, 17 ENERO 2020). Bottom right: 31 January (#IGAlInstante Informativo VOLCÁN SANGAY No. 007, VIERNES, 31 ENERO 2020). Courtesy of IG-EPN.

Observations by visitors to the volcano during 9-17 January 2020 included pyroclastic flows, ash emissions, and incandescent debris descending the SE flank ravine during the brief periods when skies were not completely overcast (figure 63 and 64). More often there was ash-filled rain and explosions heard as far as 16 km from the volcano, along with the sounds of lahars generated from the frequent rainfall mobilizing debris from the pyroclastic flows. The confluence of the Rio Upano and Rio Volcan is 23 km SE of the summit and debris from the lahars has created a natural dam on the Rio Upano that periodically backs up water and inundates the adjacent forest (figure 65). A different expedition to Sangay during 26 January-1 February 2020 by IG personnel to repair and maintain the remote monitoring station and collect samples was successful, after which the station was once again transmitting data to IG-EPN in Quito (figure 66).

Figure 63. Hikers near Sangay during 9-17 January 2020 witnessed pyroclastic flows and incandescent explosions and debris descending the SE ravine. Left: The view from 40 km SE near Macas showed ash rising from pyroclastic flows in the SE ravine. Right: Even though the summit was shrouded with a cap cloud, incandescence from the summit crater and from pyroclastic flows on the SE flank were visible on clear nights. Courtesy of Arnold Binas, used with permission.

Figure 64. The steep ravine on the SE flank of Sangay was hundreds of meters deep in January 2020 when these drone images were taken by members of a hiking trip during 9-17 January 2020 (left). Pyroclastic flows descended the ravine often (right), coating the sides of the ravine with fine, white ash and sending ash billowing up from the surface of the flow which resulted in ashfall in adjacent communities several times. Courtesy of Arnold Binas, used with permission.

Figure 65. Debris from pyroclastic flows that descended the SE Ravine at Sangay was carried down the Volcan River (left) during frequent rains and caused repeated damming at the confluence with the Rio Upano (right), located 23 km SE of the summit. These images show the conditions along the riverbeds during 9-17 January 2020. Courtesy of Arnold Binas, used with permission.

Figure 66. An expedition by scientists from IG-EPN to one of the remote monitoring stations at Sangay during 26 January-1 February 2020 was successful in restoring communication to Quito. The remote location and constant volcanic activity makes access and maintenance a challenge. Courtesy of IG-EPN (Martes, 18 Febrero 2020 12:21, EXPEDICIÓN AL VOLCÁN SANGAY).

During February 2020, multiple daily VAAC reports of ash emissions continued (figure 67). Plumes generally rose 500-1,100 m above the summit and drifted W, although on 26 February emissions were reported to 1,770 m. Ashfall was reported in Macas (40 km SE) on 1 February, and in the communities of Pistishi (65 km SW), Chunchi (70 km SW), Pumallacta (60 k. SW), Alausí (60 km SW), Guamote (40 km WNW) and adjacent areas of the Chimborazo province on 5 February. The Ecuadorian Red Cross reported ash from Sangay in the provinces of Cañar and Azuay (60-100 km SW) on 25 February. Cebadas and Guamote reported moderate ashfall the following day. The communities of Cacha (50 km NW) and Punín (45 km NW) reported trace amounts of ashfall on 29 February. Incandescent blocks were seen on the SE flank multiples times throughout the month. A pyroclastic flow was recorded on the SE flank early on 6 February; additional pyroclastic flows were observed later that day on the SW flank. On 23 February a seismic station on the flank recorded a high-frequency signal typical of lahars.

Figure 67. Steam and ash could be seen drifting SW from the summit of Sangay on 11 February 2020 even though the summit was hidden by a large cap cloud. Ash was also visible in the ravine on the SE flank. Courtesy of Sentinel Hub Playground, natural color (bands 4, 3, 2) rendering.

A significant ash emission on 1 March 2020 was reported about 2 km above the summit, drifting SW. Multiple ash emissions continued daily during the month, generally rising 570-1,170 m high. An emission on 12 March also rose 2 km above the summit. Trace ashfall was reported in Cebadas (35 km WNW) on 12 March. The community of Huamboya, located 40 km ENE of Sangay in the province of Morona-Santiago reported ashfall on 17 March. On 19 and 21 March ashfall was seen on the surface of cars in Macas to the SE. (figure 68). Ash was also reported on the 21st in de Santa María De Tunants (Sinaí) located E of Sangay. Ash fell again in Macas on 23 March and was also reported in General Proaño (40 km SE). The wind changed direction the next day and caused ashfall on 24 March to the SW in Cuenca and Azogues (100 km SW).

Figure 68. Ashfall from Sangay was reported on cars in Huamboya on 17 March 2020 (left) and in Macas on 19 March (right). Courtesy IG-EPN, (#IGAlInstante Informativo VOLCÁN SANGAY No. 024, MARTES, 17 MARZO 2020 and #IGAlInstante Informativo VOLCÁN SANGAY No. 025, JUEVES, 19 MARZO 2020).

Incandescence from the dome at the crater and on the SE flank was noted by IG on 3, 4, and 13 March. Remobilized ash from a pyroclastic flow was reported drifting SW on 13 March. The incandescent path of the flow was still visible that evening. Numerous lahars were recorded seismically during the month, including on days 5, 6, 8, 11, 15, 30 and 31. Images from the Rio Upano on 11 March confirmed an increase from the normal flow rate (figure 69) inferred to be from volcanic debris. Morona-Santiago province officials reported on 14 March that a new dam had formed at the confluence of the Upano and Volcano rivers that decreased the flow downstream; by 16 March it had given way and flow had returned to normal levels.

Figure 69. Images from the Rio Upano on 11 March 2020 (left) confirmed an increase from the normal flow rate related to lahars from Sangay descending the Rio Volcan. By 16 March (right), the flow rate had returned to normal, although the large blocks in the river were evidence of substantial activity in the past. Courtesy of IG (#IGAlInstante Informativo VOLCÁN SANGAY No. 018, MIÉRCOLES, 11 MARZO 2020 and #IGAlInstante Informativo VOLCÁN SANGAY No. 023, LUNES, 16 MARZO 2020).

Activity during April-June 2020. Lahar activity continued during April 2020; they were reported seven times on 2, 5, 7, 11, 12, 19, and 30 April. A significant reduction in the flow of the Upano River at the entrance bridge to the city of Macas was reported 9 April, likely due to a new dam on the river upstream from where the Volcan river joins it caused by lahars related to ash emissions and pyroclastic flows (figure 70). The flow rate returned to normal the following day. Ash emissions were reported most days of the month, commonly rising 500-1,100 m above the summit and drifting W. Incandescent blocks or flows were visible on the SE flank on 4, 10, 12, 15-16, and 20-23 April (figure 71).

Figure 70. A significant reduction in the flow of the Upano River at the entrance bridge to the city of Macas was reported on 9 April 2020, likely due to a new dam upstream from lahars related to ash emissions and pyroclastic flows from Sangay. Courtesy of IG-EPN (#IGAlInstante Informativo VOLCÁN SANGAY No. 032, JUEVES, 9 ABRIL 2020).

Figure 71. Incandescent blocks rolled down the SE ravine at Sangay multiple times during April 2020, including on 4 April (left). Pyroclastic flows left two continuous incandescent trails in the ravine on 23 April (right). Courtesy of IG-EPN (INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-95, SÁBADO, 4 ABRIL 2020 and INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-114, JUEVES, 23 ABRIL 2020).

Activity during May 2020 included multiple daily ash emissions that drifted W and numerous lahars from plentiful rain carrying ash and debris downstream. Although there were only a few visible observations of ash plumes due to clouds, the Washington VAAC reported plumes visible in satellite imagery throughout the month. Plumes rose 570-1,170 m above the summit most days; the highest reported rose to 2,000 m above the summit on 14 May. Two lahars occurred in the early morning on 1 May and one the next day. A lahar signal lasted for three hours on 4 May. Two lahar signals were recorded on the 7th, and three on the 9th. Lahars were also recorded on 16-17, 20-22, 26-27, and 30 May. Incandescence on the SE flank was only noted three times, but it was cloudy nearly every day.

An increase in thermal and overall eruptive activity was reported during June 2020. On 1 and 2 June the webcam captured lava flows and remobilization of the deposits on the SE flank in the early morning and late at night. Incandescence was visible multiple days each week. Lahars were reported on 4 and 5 June. The frequent daily ash emissions during June generally rose to 570-1,200 m above the summit and drifted usually SW or W. The number of explosions and ash emissions increased during the evening of 7 June. IG interpreted the seismic signals from the explosions as an indication of the rise of a new pulse of magma (figure 72). The infrasound sensor log from 8 June also recorded longer duration tremor signals that were interpreted as resulting from the descent of pyroclastic flows in the SE ravine.

Figure 72. Seismic and infrasound signals indicated increased explosive and pyroclastic flow activity at Sangay on 7-8 June 2020. Left: SAGA station (seismic component) of 7 and 8 June. The signals correspond to explosions without VT or tremor signals, suggesting the rise of a new magma pulse. Right: SAGA station infrasound sensor log from 8 June. The sharp explosion signals are followed a few minutes later (examples highlighted in red) by emergent signals of longer duration, possibly associated with the descent of pyroclastic material in the SE flank ravine. Courtesy if IG-EPN (Informe Especial del Volcán Sangay - 2020 - N°3, “Actualización de la actividad eruptiva”, Quito, 12 de junio del 2020).

On the evening of 8 June ashfall was reported in the parish of Cebadas and in the Alausí Canton to the W and SW of Sangay. There were several reports of gas and ash emissions to 1,770 m above the summit the next morning on 9 June, followed by reports of ashfall in the provinces of Guayas, Santa Elena, Los Ríos, Morona Santiago, and Chimborazo. Ashfall continued in the afternoon and was reported in Alausí, Chunchi, Guamote, and Chillanes. That night, which was clear, the webcam captured images of pyroclastic flows down the SE-flank ravine; IG attributed the increase in activity to the collapse of one or more lava fronts. On the evening of 10 June additional ashfall was reported in the towns of Alausí, Chunchi, and Guamote (figure 73); satellite imagery indicated an ash plume drifting W and incandescence from pyroclastic flows in the SE-flank ravine the same day (figure 74).

Figure 73. Ashfall from Sangay was reported in Alausí (top left), Chunchi (top right) and Guamote (bottom) on 10 June 2020. Courtesy of IG-EPN (#IGAlInstante Informativo VOLCÁN SANGAY No. 049, MIÉRCOLES, 10 JUNIO 2020).

Figure 74. Incandescent pyroclastic flows (left) and ash plumes that drifted W (right) were recorded on 10 June 2020 at Sangay in Sentinel-2 satellite imagery. Courtesy of Sentinel Hub Playground.

Ashfall continued on 11 June and was reported in Guayaquil, Guamote, Chunchi, Riobamba, Guaranda, Chimbo, Echandía, and Chillanes. The highest ash plume of the report period rose to 2,800 m above the summit that day and drifted SW. That evening the SNGRE (Servicio Nacional de Gestion de Riesgos y Emergencias) reported ash fall in the Alausí canton. IG noted the increase in intensity of activity and reported that the ash plume of 11 June drifted more than 600 km W (figure 75). Ash emissions on 12 and 13 June drifted SW and NW and resulted in ashfall in the provinces of Chimborazo, Cotopaxi, Tungurahua, and Bolívar. On 14 June, the accumulation of ash interfered with the transmission of information from the seismic station. Lahars were reported each day during 15-17 and 19-21 June. Trace amounts of ashfall were reported in Macas to the SE on 25 June.

Figure 75. The ash plume at Sangay reported on 11 June 2020 rose 2.8 km above the summit and drifted W according to the Washington VAAC and IG (left). Explosions and high levels of incandescence on the SE flank were captured by the Don Bosco webcam (right). Courtesy of IG-EPN (#IGAlInstante Informativo VOLCÁN SANGAY No. 055, JUEVES, 11 JUNIO 2020 and INFORME DIARIO DEL ESTADO DEL VOLCÁN SANGAY No. 2020-164, VIERNES, 12 JUNIO 2020).

During an overflight of Sangay on 24 June IG personnel observed that activity was characterized by small explosions from the summit vent and pyroclastic flows down the SE-flank ravine. The explosions produced small gas plumes with a high ash content that did not rise more than 500 m above the summit and drifted W (figure 76). The pyroclastic flows were restricted to the ravine on the SE flank, although the ash from the flows rose rapidly and reached about 200 m above the surface of the ravine and also drifted W (figure 77).

Figure 76. A dense ash plume rose 500 m from the summit of Sangay on 24 June 2020 and drifted W during an overflight by IG-EPN personnel. The aerial photograph is taken from the SE; snow-covered Chimborazo is visible behind and to the right of Sangay. Photo by M Almeida, courtesy of IG EPN (Jueves, 02 Julio 2020 10:29, INFORME DEL SOBREVUELO AL VOLCÁN SANGAY EL 24 DE JUNIO DE 2020).

Figure 77. Pyroclastic flows descended the SE flank ravine at Sangay during an overflight by IG-EPN personnel on 24 June 2020. Ash from the pyroclastic flow rose 200 m and drifted W, and infrared imagery identified the thermal signature of the pyroclastic flow in the ravine. Photo by M Almeida, IR Image by S Vallejo, courtesy of IG EPN (Jueves, 25 Junio 2020 12:24, SOBREVUELO AL VOLCÁN SANGAY).

Infrared imagery taken during the overflight on 24 June identified three significant thermal anomalies in the large ravine on the SE flank (figure 78). Analysis by IG scientists suggested that the upper anomaly 1 (125°C) was associated with explosive activity that was observed during the flight. Anomaly 2 (147°C), a short distance below Anomaly 1, was possibly related to effusive activity of a small flow, and Anomaly 3 (165°C) near the base of the ravine that was associated with pyroclastic flow deposits. The extent of the changes at the summit of Sangay and along the SE flank since the beginning of the eruption that started in March 2019 were clearly visible when images from May 2019 were compared with images from the 24 June 2020 overflight (figure 79). The upper part of the ravine was nearly 400 m wide by the end of June.

Figure 78. A thermal image of the SE flank of Sangay taken on 24 June 2020 indicated three thermal anomalies. Anomaly 1 was associated with explosive activity, Anomaly 2 was associated with effusive activity, and Anomaly 3 was related to pyroclastic-flow deposits. Image prepared by S Vallejo Vargas, courtesy of IG EPN (Jueves, 02 Julio 2020 10:29, INFORME DEL SOBREVUELO AL VOLCÁN SANGAY EL 24 DE JUNIO DE 2020).

Figure 79. Aerial and thermal photographs of the southern flank of the Sangay volcano on 17 May 2019 (left: visible image) and 24 June 2020 (middle: visible image, right: visible-thermal overlay) show the morphological changes on the SE flank, associated with the formation of a deep ravine and the modification of the summit. Photos and thermal image by M Almeida, courtesy of IG EPN (Jueves, 02 Julio 2020 10:29, INFORME DEL SOBREVUELO AL VOLCÁN SANGAY EL 24 DE JUNIO DE 2020).

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

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Arnold Binas (URL: https://www.doroadventures.com).

The Karangetang andesitic-basaltic stratovolcano (also referred to as Api Siau) at the northern end of the island of Siau, north of Sulawesi, Indonesia, has had more than 50 observed eruptions since 1675. Frequent explosive activity is accompanied by pyroclastic flows and lahars, and lava-dome growth has created two active summit craters (Main to the S and Second Crater to the N). Rock avalanches, observed incandescence, and satellite thermal anomalies at the summit confirmed continuing volcanic activity since the latest eruption started in November 2018 (BGVN 44:05). This report covers activity from December 2019 through May 2020. Activity is monitored by Indonesia's Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), and ash plumes are monitored by the Darwin VAAC (Volcanic Ash Advisory Center). Information is also available from MODIS thermal anomaly satellite data through both the University of Hawaii's MODVOLC system and the Italian MIROVA project.

Increased activity that included daily incandescent avalanche blocks traveling down the W and NW flanks lasted from mid-July 2019 (BGVN 44:12) through mid-January 2020 according to multiple sources. The MIROVA data showed increased number and intensity of thermal anomalies during this period, with a sharp drop during the second half of January (figure 40). The MODVOLC thermal alert data reported 29 alerts in December and ten alerts in January, ending on 14 January, with no further alerts through May 2020. During December and the first half of January incandescent blocks traveled 1,000-1,500 m down multiple drainages on the W and NW flanks (figure 41). After this, thermal anomalies were still present at the summit craters, but no additional activity down the flanks was identified in remote satellite data or direct daily observations from PVMBG.

Figure 40. An episode of increased activity at Karangetang from mid-July 2019 through mid-January 2020 included incandescent avalanche blocks traveling down multiple flanks of the volcano. This was reflected in increased thermal activity seen during that interval in the MIROVA graph covering 5 June 2019 through May 2020. Courtesy of MIROVA.

Figure 41. An episode of increased activity at Karangetang from mid-July 2019 through mid-January 2020 included incandescent avalanche blocks traveling up to 1,500 m down drainages on the W and NW flanks of the volcano. Top left: large thermal anomalies trend NW from Main Crater on 5 December 2019; about 500 m N a thermal anomaly glows from Second Crater. Top center: on 15 December plumes of steam and gas drifted W and SW from both summit craters as seen in Natural Color rendering (bands 4,3,2). Top right: the same image as at top center with Atmospheric penetration rendering (bands 12, 11, 8a) shows hot zones extending WNW from Main Crater and a thermal anomaly at Second Crater. Bottom left: thermal activity seen on 14 January 2020 extended about 800 m WNW from Main Crater along with an anomaly at Second Crater and a hot spot about 1 km W. Bottom center: by 19 January the anomaly from Second Crater appeared slightly stronger than at Main Crater, and only small anomalies appeared on the NW flank. Bottom right: an image from 14 March shows only thermal anomalies at the two summit craters. Courtesy of Sentinel Hub Playground.

A single VAAC report in early April noted a short-lived ash plume that drifted SW. Intermittent low-level activity continued through May 2020. Small SO₂ plumes appeared in satellite data multiple times in December 2019 and January 2020; they decreased in size and frequency after that but were still intermittently recorded into May 2020 (figure 42).

Figure 42. Small plumes of sulfur dioxide were measured at Karangetang with the TROPOMI instrument on the Sentinel-5P satellite multiple times during December 2019 (top row). They were less frequent but still appeared during January-May 2020 (bottom row). Larger plumes were also detected from Dukono, located 300 km ESE at the N end of North Maluku. Courtesy of Global Sulfur Dioxide Monitoring Page.

PVMBG reported in their daily summaries that steam plumes rose 50-150 m above the Main Crater and 25-50 m above Second Crater on most days in December. The incandescent avalanche activity that began in mid-July 2019 also continued throughout December 2019 and January 2020 (figure 43). Incandescent blocks from the Main Crater descended river drainages (Kali) on the W and NW flanks throughout December. They were reported nearly every day in the Nanitu, Sense, and Pangi drainages, traveling 1,000-1,500 m. Incandescence from both craters was visible 10-25 m above the crater rim most nights.

Figure 43. Incandescent block avalanches descended the NW flank of Karangetang as far as 1,500 m frequently during December 2019 and January 2020. Left image taken 13 December 2019, right image taken 6 January 2020 by PVMBG webcam. Courtesy of PVMBG, Oystein Anderson, and Bobyson Lamanepa.

A few blocks were noted traveling 800 m down Kali Beha Barat on 1 December. Incandescence above the Main crater reached 50-75 m during 4-6 December. During 4-7 December incandescent blocks appeared in Kali Sesepe, traveling 1,000-1,500 m down from the summit. They were also reported in Kali Batang and Beha Barat during 4-14 December, usually moving 800-1,000 m downslope. Between 5 and 14 December, gray and white plumes from Second Crater reached 300 m multiple times. During 12-15 December steam plumes rose 300-500 m above the Main crater. Activity decreased during 18-26 December but increased again during the last few days of the month. On 28 December, incandescent blocks were reported 1,500 m down Kali Pangi and Nanitu, and 1,750 m down Kali Sense.

Incandescent blocks were reported in Kali Sesepi during 4-6 January and in Kali Batang and Beha Barat during 4-8 and 12-15 January (figure 44); they often traveled 800-1,200 m downslope. Activity tapered off in those drainages and incandescent blocks were last reported in Kali Beha Barat on 15 January traveling 800 m from the summit. Incandescent blocks were also reported traveling usually 1,000-1,500 m down the Nanitu, Sense, and Pangi drainages during 4-19 January. Blocks continued to occasionally descend up to 1,000 m down Kali Nanitu through 24 January. Pulses of activity occurred at the summit of Second Crater a few times in January. Steam plumes rose 25-50 m during 8-9 January and again during 16-31 January, with plumes rising 300-400 m on 20, 29, and 31 January. Incandescence was noted 10-25 m above the summit of Second Crater during 27-30 January.

Figure 44. Incandescent material descends the Beha Barat, Sense, Nanitu, and Pangi drainages on the NW flank of Karangetang in early January 2020. Courtesy of Bobyson Lamanepa; posted on Twitter on 6 January 2020.

Activity diminished significantly after mid-January 2020. Steam plumes at the Main Crater rose 50-100 m on the few days where the summit was not obscured by fog during February. Faint incandescence occurred at the Main Crater on 7 February, and steam plumes rising 25-50 m from Second Crater that day were the only events reported there in February. During March, steam plumes persisted from the Main Crater, with heights of over 100 m during short periods from 8-16 March and 25-30 March. Weak incandescence was reported from the Main Crater only once, on 25 March. Very little activity occurred at Second Crater during March, with only steam plumes reported rising 25-300 m from the 22nd to the 28th (figure 45).

Figure 45. Steam plumes at Karangetang rose over 100 m above both summit craters multiple times during March, including on 26 March 2020. Courtesy of PVMBG and Oystein Anderson.

The Darwin VAAC reported a continuous ash emission on 4 April 2020 that rose to 2.1 km altitude and drifted SW for a few hours before dissipating. Incandescence visible 25 m above both craters on 13 April was the only April activity reported by PVMBG other than steam plumes from the Main Crater that rose 50-500 m on most days. Steam plumes of 50-100 m were reported from Second Crater during 11-13 April. Activity remained sporadic throughout May 2020. Steam plumes from the Main Crater rose 50-300 m each day. Satellite imagery identified steam plumes and incandescence from both summit craters on 3 May (figure 46). Faint incandescence was observed at the Main Crater on 12 and 27 May. Steam plumes rose 25-50 m from Second Crater on a few days; a 200-m-high plume was reported on 27 May. Bluish emissions were observed on the S and SW flanks on 28 May.

Figure 46. Dense steam plumes and thermal anomalies were present at both summit craters of Karangetang on 3 May 2020. Sentinel 2 satellite image with Natural Color (bands 4, 3, 2) (left) and Atmospheric Penetration rendering (bands 12, 11, 8a) (right); courtesy of Sentinel Hub Playground.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); 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/); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: http://www.oysteinlundandersen.com); Bobyson Lamanepa, Yogyakarta, Indonesia, (URL: https://twitter.com/BobyLamanepa/status/1214165637028728832).

Shishaldin is located near the center of Unimak Island in Alaska, with the current eruption phase beginning in July 2019 and characterized by ash plumes, lava flows, lava fountaining, pyroclastic flows, and lahars. More recently, in late 2019 and into January 2020, activity consisted of multiple lava flows, pyroclastic flows, lahars, and ashfall events (BGVN 45:02). This report summarizes activity from February through May 2020, including gas-and-steam emissions, brief thermal activity in mid-March, and a possible new cone within the summit crater. The primary source of information comes from the Alaska Volcano Observatory (AVO) reports and various satellite data.

Volcanism during February 2020 was relatively low, consisting of weakly to moderately elevated surface temperatures during 1-4 February and occasional small gas-and-steam plumes (figure 37). By 6 February both seismicity and surface temperatures had decreased. Seismicity and surface temperatures increased slightly again on 8 March and remained elevated through the rest of the reporting period. Intermittent gas-and-steam emissions were also visible from mid-March (figure 38) through May. Minor ash deposits visible on the upper SE flank may have been due to ash resuspension or a small collapse event at the summit, according to AVO.

Figure 37. Photo of a gas-and-steam plume rising from the summit crater at Shishaldin on 22 February 2020. Photo courtesy of Ben David Jacob via AVO.

Figure 38. A Worldview-2 panchromatic satellite image on 11 March 2020 showing a gas-and-steam plume rising from the summit of Shishaldin and minor ash deposits on the SE flank (left). Aerial photo showing minor gas-and-steam emissions rising from the summit crater on 11 March (right). Some erosion of the snow and ice on the upper flanks is a result of the lava flows from the activity in late 2019 and early 2020. Photo courtesy of Matt Loewen (left) and Ed Fischer (right) via AVO.

On 14 March, lava and a possible new cone were visible in the summit crater using satellite imagery, accompanied by small explosion signals. Strong thermal signatures due to the lava were also seen in Sentinel-2 satellite data and continued strongly through the month (figure 39). The lava reported by AVO in the summit crater was also reflected in satellite-based MODIS thermal anomalies recorded by the MIROVA system (figure 40). Seismic and infrasound data identified small explosions signals within the summit crater during 14-19 March.

Figure 39. Sentinel-2 thermal satellite images (bands 12, 11, 8A) show a bright hotspot (yellow-orange) at the summit crater of Shishaldin during mid-March 2020 that decreases in intensity by late March. Courtesy of Sentinel Hub Playground.

Figure 40. MIROVA thermal data showing a brief increase in thermal anomalies during late March 2020 and on two days in late April between periods of little to no activity. Courtesy of MIROVA.

AVO released a Volcano Observatory Notice for Aviation (VONA) stating that seismicity had decreased by 16 April and that satellite data no longer showed lava or additional changes in the crater since the start of April. Sentinel-2 thermal satellite imagery continued to show a weak hotspot in the crater summit through May (figure 41), which was also detected by the MIROVA system on two days. A daily report on 6 May reported a visible ash deposit extending a short distance SE from the summit, which had likely been present since 29 April. AVO noted that the timing of the deposit corresponds to an increase in the summit crater diameter and depth, further supporting a possible small collapse. Small gas-and-steam emissions continued intermittently and were accompanied by weak tremors and occasional low-frequency earthquakes through May (figure 42). Minor amounts of sulfur dioxide were detected in the gas-and-steam emissions during 20 and 29 April, and 2, 16, and 28 May.

Figure 41. Sentinel-2 thermal satellite images (bands 12, 11, 8A) show occasional gas-and-steam emissions rising from Shishaldin on 26 February (top left) and 24 April 2020 (bottom left) and a weak hotspot (yellow-orange) persisting at the summit crater during April and early May 2020. Courtesy of Sentinel Hub Playground.

Figure 42. A Worldview-1 panchromatic satellite image showing gas-and-steam emissions rising from the summit of Shishaldin on 1 May 2020 (local time) (left). Aerial photo of the N flank of Shishaldin with minor gas-and-steam emissions rising from the summit on 8 May (right). Photo courtesy of Matt Loewen (left) and Levi Musselwhite (right) via AVO.

Geologic Background. The beautifully symmetrical Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The glacier-covered volcano is the westernmost of three large stratovolcanoes along an E-W line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." A steam plume often rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the W and NE sides at 1,500-1,800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of Strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.gov/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Masaya, which is about 20 km NW of the Nicaragua’s capital of Managua, is one of the most active volcanoes in that country and has a caldera that contains a number of craters (BGVN 43:11). The Santiago crater is the one most currently active and it contains a small lava lake that emits weak gas plumes (figure 85). This report summarizes activity during February through May 2020 and is based on Instituto Nicaragüense de Estudios Territoriales (INETER) monthly reports and satellite data. During the reporting period, the volcano was relatively calm, with only weak gas plumes.

Figure 85. Satellite images of Masaya from Sentinel-2 on 18 April 2020, showing and a small gas plume drifting SW (top, natural color bands 4, 3, 2) and the lava lake (bottom, false color bands 12, 11, 4). Courtesy of Sentinel Hub Playground.

According to INETER, thermal images of the lava lake and temperature data in the fumaroles were taken using an Omega infrared gun and a forward-looking infrared (FLIR) SC620 thermal camera. The temperatures above the lava lake have decreased since November 2019, when the temperature was 287°C, dropping to 96°C when measured on 14 May 2020. INETER attributed this decrease to subsidence in the level of the lava lake by 5 m which obstructed part of the lake and concentrated the gas emissions in the weak plume. Convection continued in the lava lake, which in May had decreased to a diameter of 3 m. Many landslides had occurred in the E, NE, and S walls of the crater rim due to rock fracturing caused by the high heat and acidity of the emissions.

During the reporting period, the MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system recorded numerous thermal anomalies from the lava lake based on MODIS data (figure 86). Infrared satellite images from Sentinel-2 regularly showed a strong signature from the lava lake through 18 May, after which the volcano was covered by clouds.

Figure 86. Thermal anomalies at Masaya during February through May 2020. The larger anomalies with black lines are more distant and not related to the volcano. Courtesy of MIROVA.

Measurements of sulfur dioxide (SO2) made by INETER in the section of the Ticuantepe - La Concepción highway (just W of the volcano) with a mobile DOAS system varied between a low of just over 1,000 metric tons/day in mid-November 2019 to a high of almost 2,500 tons/day in late May. Temperatures of fumaroles in the Cerro El Comalito area, just ENE of Santiago crater, ranged from 58 to 76°C during February-May 2020, with most values in the 69-72°C range.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras caldera and is itself a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The Nindirí and Masaya cones, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6,500 years ago. Historical lava flows cover much of the caldera floor and there is a lake at the far eastern end. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals have caused health hazards and crop damage.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); 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).

Krakatau, located in the Sunda Strait between Indonesia’s Java and Sumatra Islands, experienced a major caldera collapse around 535 CE, forming a 7-km-wide caldera ringed by three islands. On 22 December 2018, a large explosion and flank collapse destroyed most of the 338-m-high island of Anak Krakatau (Child of Krakatau) and generated a deadly tsunami (BGVN 44:03). The near-sea level crater lake inside the remnant of Anak Krakatau was the site of numerous small steam and tephra explosions. A larger explosion in December 2019 produced the beginnings of a new cone above the surface of crater lake (BGVN 45:02). Recently, volcanism has been characterized by occasional Strombolian explosions, dense ash plumes, and crater incandescence. This report covers activity from February through May 2020 using information provided by the Indonesian Center for Volcanology and Geological Hazard Mitigation, also known as Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), the Darwin Volcanic Ash Advisory Center (VAAC), and various satellite data.

Activity during February 2020 consisted of dominantly white gas-and-steam emissions rising 300 m above the crater, according to PVMBG. According to the Darwin VAAC, a ground observer reported an eruption on 7 and 8 February, but no volcanic ash was observed. During 10-11 February, a short-lived eruption was detected by seismograms which produced an ash plume up to 1 km above the crater drifting E. MAGMA Indonesia reported two eruptions on 18 March, both of which rose to 300 m above the crater. White gas-and-steam emissions were observed for the rest of the month and early April.

On 10 April PVMBG reported two eruptions, at 2158 and 2235, both of which produced dark ash plumes rising 2 km above the crater followed by Strombolian explosions ejecting incandescent material that landed on the crater floor (figures 108 and 109). The Darwin VAAC issued a notice at 0145 on 11 April reporting an ash plume to 14.3 km altitude drifting WNW, however this was noted with low confidence due to the possible mixing of clouds. During the same day, an intense thermal hotspot was detected in the HIMAWARI thermal satellite imagery and the NASA Global Sulfur Dioxide page showed a strong SO₂ plume at 11.3 km altitude drifting W (figure 110). The CCTV Lava93 webcam showed new lava flows and lava fountaining from the 10-11 April eruptions. This activity was evident in the MIROVA (Middle InfraRed Observation of Volcanic Activity) graph of MODIS thermal anomaly data (figure 111).

Figure 108. Webcam (Lava93) images of Krakatau on 10 April 2020 showing Strombolian explosions, strong incandescence, and ash plumes rising from the crater. Courtesy of PVMBG and MAGMA Indonesia.

Figure 109. Webcam image of incandescent Strombolian explosions at Krakatau on 10 April 2020. Courtesy of PVMBG and MAGMA Indonesia.

Figure 110. Strong sulfur dioxide emissions rising from Krakatau and drifting W were detected using the TROPOMI instrument on the Sentinel-5P satellite on 11 April 2020 (top row). Smaller volumes of SO2 were visible in Sentinel-5P/TROPOMI maps on 13 (bottom left) and 19 April (bottom right). Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Figure 111. Thermal activity at Anak Krakatau from 29 June-May 2020 shown on a MIROVA Log Radiative Power graph. The power and frequency of the thermal anomalies sharply increased in mid-April. After the larger eruptive event in mid-April the thermal anomalies declined slightly in strength but continued to be detected intermittently through May. Courtesy of MIROVA.

Strombolian activity rising up to 500 m continued into 12 April and was accompanied by SO₂ emissions that rose 3 km altitude, drifting NW according to a VAAC notice. PVMBG reported an eruption on 13 April at 2054 that resulted in incandescence as high as 25 m above the crater. Volcanic ash, accompanied by white gas-and-steam emissions, continued intermittently through 18 April, many of which were observed by the CCTV webcam. After 18 April only gas-and-steam plumes were reported, rising up to 100 m above the crater; Sentinel-2 satellite imagery showed faint thermal anomalies in the crater (figure 112). SO₂ emissions continued intermittently throughout April, though at lower volumes and altitudes compared to the 11th. MODIS satellite data seen in MIROVA showed intermittent thermal anomalies through May.

Figure 112. Sentinel-2 thermal satellite images showing the cool crater lake on 20 March (top left) followed by minor heating of the crater during April and May 2020. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering; courtesy of Sentinel Hub Playground.

Geologic Background. The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Remote Heard Island in the southern Indian Ocean is home to the snow-covered Big Ben stratovolcano, which has had confirmed intermittent activity since 1910. The nearest continental landmass, Antarctica, lies over 1,000 km S. Visual confirmation of lava flows on Heard are rare; thermal anomalies and hotspots detected by satellite-based instruments provide the most reliable information about eruptive activity. Thermal alerts reappeared in September 2012 after a four-year hiatus (BGVN 38:01), and have been intermittent since that time. Information comes from instruments on the European Space Agency's (ESA) Sentinel-2 satellite and MODVOLC and MIROVA thermal anomaly data from other satellite instruments. This report reviews evidence for eruptive activity from November 2017 through September 2018.

Satellite observations indicated intermittent hot spots at the summit through 12 December 2017. A few observations in January and February 2018 suggested steam plumes at the summit, but no significant thermal activity. An infrared pixel indicative of renewed thermal activity appeared again on 7 March, and similar observations were made at least twice each month in April and May. Activity increased significantly during June and remained elevated through September 2018 with multiple days of hotspot observations in satellite data each of those months, including images that indicated lava flowing in different directions from Mawson Peak. MODVOLC and MIROVA data also indicated increased thermal activity during June-September 2018.

Activity during October-December 2017. MIROVA thermal anomalies recorded during October 2017 indicated ongoing thermal activity at Heard (figure 32). This was confirmed by Sentinel-2 satellite imagery that revealed hotpots at the summit on ten different days in October (3, 6, 8, 13, 16, 21, 23, 26, 28, and 31), and included images suggesting lava flows descending from the summit in different directions on different days (figure 33).

Figure 32. MODVOLC thermal alerts indicated significant thermal activity at Heard during October 2017 that tapered off during November. Intermittent signals appeared in December 2017, March, and April 2018, and a strong signal returned in June 2018 that continued through September. Courtesy of MIROVA.

Figure 33. Sentinel-2 images of Heard Island's Big Ben volcano during October 2017 showed strong evidence of active effusive activity. a) 3 October 2017: at least three hot spots were visible through cloud cover at the summit and W of Mawson Peak, suggesting active lava flows. b) 6 October 2017: a small hot spot is visible at the peak with a small steam plume, and a larger hotspot to the NW suggested a still active lava flow. c) 16 October 2017: a small hotspot at the summit and larger hotspots W of the summit were indicative of ongoing flow activity. d) 23 October 2017: a steam plume drifted SE from a small summit hotspot and a larger hotspot to the W suggested a lava lake or active flow. Sentinel-2 images with Atmospheric Penetration view (bands 12, 11, and 8A), courtesy of Sentinel Hub Playground.

The MODVOLC thermal alert data showed no further alerts for the year after 22 October 2017, and the MIROVA system anomalies tapered off in mid-November 2017. The Sentinel-2 satellite imagery, however, continued to record intermittent hotspots at and around Mawson Peak, the summit of Big Ben volcano, into December 2017 (figure 34). Hotspots were visible during six days in November (7, 15, 20, 25, 27, and 30) and three days during December (5, 7, and 12).

Figure 34. Sentinel-2 images of Heard Island's Big Ben volcano showed reduced but ongoing thermal activity during November and December 2017. a) 7 November 2017: a steam plume drifts NE from a hotspot at Mawson Peak. b and c) 15 November and 12 December 2017: a small hotspot is distinct at the summit. d) 20 December 2017: a steam plume drifts east from the peak, but no clear hotspot is visible. Sentinel-2 images with Atmospheric Penetration view (bands 12, 11, and 8A), courtesy of ESA Sentinel Hub Playground.

Activity during January-May 2018. The satellite images during January and February 2018 were indicative of steam plumes at the summit, but distinct thermal signals reappeared on 7 and 12 March 2018 (figure 35). In spite of extensive cloud cover, the Sentinel-2 imagery also captured thermal signals twice each month in April (4 and 14) and May (9 and 14) (figure 36).

Figure 35. Sentinel-2 images of Heard Island's Big Ben volcano showed only steam plumes at the summit during January and February, but hotspots reappeared in March 2018. a) 4 January 2018: a steam plume drifts SE from the summit under clear skies. b) 8 February 2018: a steam plume drifts SE from the summit adjacent to a large cloud on the N side of the volcano. c) 7 March 2018: the first hotspot in about three months is visible at the summit. d) 12 March 2018: a distinct hotspot is visible at Mawson Peak. Sentinel-2 images with Atmospheric Penetration view (bands 12, 11, and 8A), courtesy of ESA Sentinel Hub Playground.

Figure 36. Sentinel-2 images of Heard Island's Big Ben volcano showed intermittent low-level thermal activity during April and May 2018. a) 4 April 2018: a small hotspot is visible at the summit through a hazy atmosphere. b) 9 May 2018: a distinct hotspot glows from the summit beneath cloud cover. Sentinel-2 images with Atmospheric Penetration view(bands 12, 11, and 8A), courtesy of ESA Sentinel Hub Playground.

Activity during June-September 2018. Thermal signals increased significantly in the satellite data during June 2018. The sizes of the thermal anomalies were bigger, and they were visible at least nine days of the month (3, 5, 8, 10, 15, 18, 23, 25, and 30). Five substantial thermal signals appeared during July (3, 10, 15, 18, and 28); images on 23 June and 3 July distinctly show a lava flow trending NE from the summit (figure 37). MODVOLC thermal alerts appeared in June 2018 on three days (2, 26, and 27) and on four days during July (7, 8, 9, 10) indicating increased activity during this time. The MIROVA thermal signals also showed a substantial increase in early June that peaked in mid-July and remained steady through September 2018 (figure 32).

Figure 37. Sentinel-2 images of Heard Island's Big Ben volcano showed significantly increased thermal activity during June and July 2018. a) 8 June 2018: a substantial hotspot is visible through the cloud cover at the summit of Big Ben. b) 10 June 2018: the darker red hotspot at Mawson Peak was significantly larger than it was earlier in the year. c) 23 June 2018: the first multi-point hotspot since 31 October shows a distinct glow trending NE from the summit. d) 3 July 2018: a trail of hotspots defines a lava flow curving NNE from Mawson Peak. e) 18 July 2018: a second significant hotpot is visible a few hundred meters NE of the summit hotspot indicating a still active flow. f) 28 July 2018: the summit hotspot continued to glow brightly at the end of July, but no second hotspot was visible. Sentinel-2 images with Atmospheric Penetration view (bands 12, 11, and 8A), courtesy of ESA Sentinel Hub Playground.

Six images in August (2, 7, 9, 22, 27, 29) showed evidence of active lava at the summit, and suggested flows both NE and SE from the summit that were long enough to cause multiple hotspots (figure 38). During September and early October 2018 the satellite images continued to show multiple hotspots that indicated flow activity tens of meters SE from the summit multiple days of each month (figure 39).

Figure 38. Sentinel-2 images of Heard Island's Big Ben volcano showed lava flow activity in two different directions from the summit during August 2018. a) 2 August 2018: lava flows NE from Mawson Peak while a steam plume drifts E from the summit. b) 9 August 2018: a second hotspot NE of the summit hotspot indicates continued flow activity in the same area observed on 2 August. c and d) 27 and 29 August 2018: a different secondary hotspot appeared SSE from the summit indicating a distinct flow event from the one recorded earlier in August. Sentinel-2 images with Atmospheric Penetration view (bands 12, 11, and 8A), courtesy of ESA Sentinel Hub Playground.

Figure 39. Sentinel-2 images of Heard Island's Big Ben volcano in September and October 2018 showed hotspots indicating active flows SE of the summit on multiple days. a) 3 September 2018: a small hotspot at the summit and a larger hotspot SE of the summit indicated continued flow activity. b) 3 October 2018: a small steam plume drifted east from a small hotspot at the summit and a larger pair of hotspots to the SE indicated continued effusive activity. Sentinel-2 images with Atmospheric Penetration view (bands 12, 11, and 8A), courtesy of ESA Sentinel Hub Playground.

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

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

The first confirmed eruption of Kadovar began on 5 January 2018 with dense ash plumes and steam and a lava flow. The eruption continued through February and then slowed during March (BGVN 43:04). This report describes notices of ash plumes from the Darwin Volcanic Ash Advisory Centre (VAAC) and satellite images during April through 1 October 2018.

According to the Darwin VAAC a pilot observed an ash plume rising to an altitude of 1.2 km on 10 June. The ash plume was not identified in satellite data. Another ash plume identified by a pilot and in satellite images rose to an altitude of 1.8 km on 20 June and drifted W. An ash plume was visible in satellite images on 28 September drifting SE at an altitude of 2.1 km. On 1 October an ash plume rose to 2.7 km and drifted W.

Infrared satellite data from Sentinel-2 showed hot spots in the summit crater and at the Coastal Vent along the W shoreline on 10, 15, and 25 April 2018; plumes of brown discolored water were streaming from the western side of the island (figure 18). Similar activity was frequently seen during clear weather in the following months. A steam plume was also often rising from the crater. The Coastal Vent cone was still hot on 8 August, but no infrared anomaly was seen in imagery from 28 August through September.

Figure 18. Sentinel-2 natural color satellite image of Kadovar on 10 April 2018. The island is about 1.5 km in diameter. Steam can be seen rising from the summit and the Coastal Vent just off the western shore; both locations show thermal anomalies in infrared imagery. Discolored water plumes extend NE from the island. Courtesy of Sentinel Hub Playground.

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

Information Contacts: 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).

The most recent eruptive period at Karymsky, on the Kamchatka Peninsula of Russia, began on 28 April 2018, with thermal anomalies, gas-and-steam emissions, and ash plumes observed through July 2018. The current report discusses activity through September 2018 (table 11). This report was compiled using information from the Kamchatka Volcanic Eruptions Response Team (KVERT).

KVERT reported ongoing thermal anomalies and intermittent ash plumes over Karymsky during August and September 2018 (table 11). Ash plumes drifted 50 km SE on 7 August, and 40 km S on 25 August. Stronger activity during 10-11 September consisted of continuous dense ash emissions along with explosions that sent plumes 5-6 km high which drifted 860 km NE. Incandescence photographed the next night was attributed to fumarolic activity (figure 41). Ash plumes were identified drifting 365 km E on 22-23 September. The last thermal anomaly was identified in satellite images on 28 September, and an ash plume was last visible on 30 September.

Table 11. Ash plumes and thermal anomalies at Karymsky, 1 August-30 September 2018. Clouds often obscured the volcano. Data compiled from KVERT reports.

Figure 41. Incandescence, attributed to fumarolic activity, was visible above the crater of Karymsky on 12 September 2018. Photo by D. Melnikov; courtesy of Institute of Volcanology and Seismology (IVS FEB RAS, KVERT).

Figure 42. Sentinel-2 satellite imagery of Karymsky on 30 September 2018 showing a diffuse plume and thermal anomaly in the crater. Top: Natural color view (bands 4, 3, 2). Bottom: Short-wave Infrared view (bands 12, 8A, 4). Courtesy of Sentinel Hub Playground.

Thermal anomalies, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, were last observed on 31 July 2018. The MIROVA (Middle InfraRed Observation of Volcanic Activity) system detected one hotspot in early August (moderate power), and two hotspots in late September (low power).

Geologic Background. Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); 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://hotspot.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Gas-and-steam emissions were previously reported at Ketoi (figure 1) in January, July, and August 2013 (BGVN 40:09). Intense fumarolic activity originating from the same area, the N slope of Pallas Peak, was reported in 1981, 1987, and 1989. Based on a report from the Sakhalin Volcanic Eruption Response Team (SVERT) using Himawari-8 imagery, the Tokyo VAAC reported an ash plume on 21 September 2018 which drifted to the NE; however, evidence of the plume could not be confirmed by the VAAC from satellite imagery. The original VONA (Volcano Observatory Notice for Aviation) issued by SVERT noted a volcanic cloud without a specific mention of ash, but also remarked that thermal anomalies had been observed on 17 and 20 September.

Figure 1. Natural color Sentinel-2 satellite image of Ketoi on 18 September 2018. A large freshwater lake can be seen SW of the Pallas Peak andesitic cone, which also hosts a crater lake. Lava flows originating from the younger cone extend primarily N to SW, and a white fumarolic area is immediately NE of the crater. The island is approximately 10 km in diameter. Courtesy of Sentinel Hub Playground.

Geologic Background. The circular, 10-km-wide Ketoi island, which rises across the 19-km-wide Diana Strait from Simushir Island, hosts of one of the most complex volcanic structures of the Kuril Islands. The rim of a 5-km-wide Pleistocene caldera is exposed only on the NE side. A younger 1172-m-high stratovolcano forming the NW part of the island is cut by a horst-and-graben structure containing two solfatara fields. A 1.5-km-wide freshwater lake fills an explosion crater in the center of the island. Pallas Peak, a large andesitic cone in the NE part of the caldera, is truncated by a 550-m-wide crater containing a brilliantly colored turquoise crater lake. Lava flows from Pallas Peak overtop the caldera rim and descend nearly 5 km to the SE coast. The first historical eruption of Pallas Peak, during 1843-46, was its largest.

Information Contacts: Sakhalin Volcanic Eruption Response Team (SVERT), Institute of Marine Geology and Geophysics, Far Eastern Branch, Russian Academy of Science, Nauki st., 1B, Yuzhno-Sakhalinsk, Russia, 693022 (URL: http://www.imgg.ru/en/, http://www.imgg.ru/ru/svert/reports); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Kilauea's East Rift Zone (ERZ) has been intermittently active for at least two thousand years. Open lava lakes at the summit caldera, and a lava lake and flows from the East Rift Zone, have been almost continuously active since the current eruption began in 1983. A marked increase in seismicity and ground deformation at Pu'u 'O'o Cone on the upper East Rift Zone during the afternoon of 30 April 2018 and the subsequent collapse of its crater floor marked the beginning of the largest lower East Rift Zone eruptive episode in at least 200 years. The daily events of this episode underscored the nature of the interconnected components of the volcanic system. The lava lake level at Halema'uma'u began dropping on 1 May 2018, and fissures first opened on the lower East Rift Zone two days later. The eruptive events of May 2018 (figure 332), the first month of this episode, are described in this report with information provided primarily from the US Geological Survey's (USGS) Hawaii Volcano Observatory (HVO) in the form of daily reports, volcanic activity notices, and abundant photo, map, and video data.

Figure 332. A timeline of events at Kilauea for 1-28 May 2018. Blue shaded region includes seismic events greater than M 4.0 and activity at Halema'uma'u crater at the summit. Green shaded area lists activity on the lower East Rift Zone.

Summary of events. During 1-11 May, seismicity propagated eastward from Pu'u 'O'o, indicating the intrusion of magma into the middle and lower East Rift Zone (LERZ). The first surface cracks appeared in the LERZ on 2 May, and the first eruptive fissure opened the next afternoon. Fissures were several hundred meters long and formed a NE-SW trending line near the axis of the LERZ that reached about 4 km in length by 8 May. Three large (greater than M 5) earthquakes shook the island on 4 May. New fissures opened daily, with activity consisting of spattering and lava flows; the largest effusion was a flow from fissure 8 that traveled N for a little over 1 km. By 9 May, 15 fissures had opened in the vicinity of the Leilani Estates subdivision; the residents had been evacuated and numerous structures were destroyed by the flows, spatter, and fissures. Active spattering paused on 10 and 11 May, although strong degassing continued, and many cracks within the fissure zone continued to widen.

The lava lake level in the Overlook vent at Halema'uma'u crater at the summit began to drop slowly on 1 May; the rate of deflationary tilt increased by late the next afternoon. The lake level had dropped about 128 m below the vent rim by 5 May, and satellite data indicated a 10 cm subsidence of the Halema'uma'u crater floor during that time. Rockfalls from the crater walls produced ash plumes above Halema'uma'u, resulting in light ashfall in the summit area. By 8 May the lake level was 295 m below the floor of Halema'uma'u crater. Larger rockfalls caused by the dropping lake level generated larger explosions and ash plumes on 9 May.

New fissures began opening again on 12 May in an area about 1.5 km NE of the previous activity on the LERZ, and over the following 11 days flow activity increased substantially, creating multiple flow channels. The fissure 17 flow reached 2.5 km in length on 15 May. A fast-moving flow from fissure 20 headed 4 km SE on 18 May, traveling over 300 m per hour. The two lobes of the flow reached the SE Puna coast overnight on 19-20 May and were joined by another adjacent flow to the west two days later. Fissures 16-23, all located in the NE half of the fissure zone, were active during 12-23 May.

Steam and ash emissions were persistent at Halema'uma'u crater during 12-23 May; they varied in intensity with abrupt increases associated with large rockfalls into the vent, and ashfall reported more than 50 km from the summit. Strong earthquakes at the summit continued in response to the deflation, causing frequent ground shaking and damage to roads and buildings. A large explosion on 17 May generated the highest ash plume for the period; it reached 9.1 km altitude and drifted NE. Intermittent explosive eruptions continued at the summit, and robust plumes of gas, ash, and steam periodically emerged from the Overlook vent.

Beginning on 24 May, activity on the LERZ shifted back towards the SW part of the fissure zone, again impacting the residents of the Leilani Estates subdivision with reactivation of fissures and new flows. While flows continued to reach the ocean on the SE coast, the volume of lava gradually decreased until the supply of lava ceased by 28 May. During 24-26 May fissures 7 and 21 were feeding a perched lava pond and flows that moved E and N within the subdivision. Overnight on 26-27 May activity increased substantially at fissure 7 with a 30-m-tall spatter rampart, and fountains that reached 70 m high feeding a flow moving N. Large cracks opened into fissure 24 adjacent to the reactivated fissure 8; fast-moving flows traveled W then N through the subdivision. By 28 May the eruptive activity was focused on vigorous fountaining at fissure 8, which supplied a voluminous flow that headed rapidly NE.

Intermittent explosions continued from the summit Overlook vent during 24-28 May as a result of the ongoing subsidence at Halema'uma'u. Ash clouds generally rose to about 3.1 km altitude and drifted SW. Earthquakes in the summit region continued as the summit area subsided and adjusted to the withdrawal of magma.

Activity during 1-11 May 2018. An intrusion of magma began overnight on 30 April-1 May into the lower East Rift Zone (LERZ), extending from the vicinity of Pu'u 'O'o eastward at least as far as Highway 130 (15 km E of Pu'u 'O'o). The intrusion began after the collapse of the Pu'u 'O'o crater floor on the afternoon of 30 April; about 250 located earthquakes were reported through the afternoon of 1 May, with the locations migrating eastward during the day. The seismicity consisted primarily of small-magnitude (less than M 3) earthquakes at depths of less than 10 km. During a helicopter overflight to Pu'u 'O'o on 1 May, HVO geologists observed a new fissure and crack extending about 1 km uprift (west) from the W flank of the Pu'u 'O'o cone (figures 333 and 334). A small amount of lava had erupted from the crack, apparently during the collapse of the Pu'u 'O'o crater floor. They also noted a few small, sluggish breakouts of the 61g lava flow, likely from lava still moving through the lava-tube system.

Figure 333. HVO geologists observed a fracture on the W flank of Pu'u 'O'o at Kilauea during an overflight on the afternoon of 1 May 2018. The 61g flow field as of 13 April 2018 is shown in pink. The crack that formed on the west side of Pu'u 'O'o on 30 April 2018, during or immediately after the crater floor collapse, is shown as a solid red line. Older Pu'u 'O'o lava flows (1983–2016) are shown in gray. The yellow line is the trace of the active lava tubes. The blue lines over the Pu'u 'O'o flow field are steepest-descent paths calculated from a 2013 digital elevation model (DEM), while the blue lines on the rest of the map are steepest-descent paths calculated from a 1983 DEM. Courtesy of HVO.

Figure 334. A new fissure appeared on the W flank of Pu'u 'O'o at Kilauea on 1 May 2018. Top: In this view to the NE, the fissure was visible as a line of white steam extending roughly 1.5 km W of Pu'u 'O'o Crater. Photo taken 3 May 2018. Bottom: A telephoto view of a small lava flow (lighter in color) and spatter (blue-gray) that were erupted from a section of the crack on the west flank of Pu'u 'O'o. Photo taken during overflight on 1 May 2018, courtesy of HVO.

Overnight on 1-2 May, earthquakes continued at a high rate in the area from Highway 130 eastward towards Kapoho (32 km NE of Pu'u 'O'o). Many events were felt by residents and there were reports of nearly constant ground vibration in some areas; seismicity generally migrated eastward (figure 335). During the morning of 2 May a GPS station located about 1.5 km SW of Nanawale Estates (24 km NE of Pu'u 'O'o ) began moving toward the north by several centimeters, indicating the approaching magma intrusion. A tiltmeter at Pu'u 'O'o recorded steady, deflationary tilt throughout the day, with several sharp inflation offsets. Some of these offsets corresponded to short-lived ashy plumes rising from the crater. New small ground cracks less than a few centimeters wide developed across some roads in and adjacent to Leilani Estates (23 km NE of Pu'u 'O'o).

Figure 335. Starting on the afternoon of 30 April 2018, magma beneath Kilauea's Pu'u 'O'o Cone drained and triggered the collapse of the crater floor. Within hours, earthquakes began migrating east of Pu'u 'O'o, signaling an intrusion of magma along the middle and lower East Rift Zone (ERZ). As of about noon on 2 May there were many reports of earthquakes felt by residents in nearby subdivisions. The orange oval marks the approximate area within which most of the earthquakes were located based on automatic earthquake locations and analysis by seismologists. A GPS device located in Nanawale Estates began moving towards the N on 2 May, and new, small ground cracks were reported in the Leilani Estates area. Courtesy of HVO.

The summit lake level showed very little change immediately after the collapse of the Pu'u 'O'o crater floor, but tiltmeters at the summit began recording deflationary tilt in the early morning of 1 May. The lava lake level had dropped about 20 m by the afternoon of 2 May when the rate of deflationary tilt increased. By the evening of 3 May, it had dropped an additional 37 m.

At 1030 HST on 3 May 2018 ground shaking from a M 5.0 earthquake south of Pu'u 'O'o caused rockfalls and possibly additional collapse into the Pu'u 'O'o crater (figure 336). A short-lived plume of ash produced by this event rose and dissipated as it drifted SW (figure 337).

Figure 336. Clear weather on 3 May 2018 allowed good airborne observations of the collapse crater in Pu'u 'O'o. This view to the E shows the deep collapse crater that formed on 30 April when magma beneath Pu'u 'O'o drained. For scale, the crater is about 250 m wide. Courtesy of HVO.

Figure 337. At 1030 HST on 3 May 2018 ground shaking from a preliminary M 5.0 earthquake south of Pu'u 'O'o caused rockfalls and possibly additional collapse into the Pu'u 'O'o crater on Kilauea's East Rift Zone. A short-lived plume of ash produced by this event rose and dissipated as it drifted SW. USGS photo by Kevan Kamibayashi, courtesy of HVO.

New ground cracks were reported in Leilani Estates late in the afternoon of 3 May. Hot white vapor and blue fumes emanated from an area of cracking in the eastern part of the subdivision. Spatter began erupting from the cracks shortly before 1700 local time. The Hawaii County Civil Defense coordinated the evacuation of the subdivision. Lava spatter and gas bursts erupted from the fissure for about two hours; lava spread less than 10 m (figure 338).

Figure 338. An eruption from fissure 1 began in the Leilani Estates subdivision at the lower East Rift Zone of Kilauea during the afternoon of 3 May 2018. Hot white vapor and blue fumes emanated from an area of cracking in the eastern part of the subdivision. Spatter began erupting shortly before 1700 HST; lava was confirmed at the surface in the eastern end of the subdivision. According to the Hawai'i County Civil Defense update at 1740 all residents in Leilani Estates and Lanipuna Gardens subdivsions were required to evacuate. View is to the NE on 3 May, courtesy of HVO.

By the morning of 4 May 2018 three fissures had opened in the eastern portion of Leilani Estates; activity consisted primarily of vigorous lava spattering and development of short lava flows (figure 339). Additional eruptive fissures or vents opened during the day, each several hundred meters long (figure 340). Spatter and lava accumulated primarily within a few tens of meters of the vents. Fissure 6 opened on the eastern edge of the subdivision by the afternoon. Between 1130 and 1500 three large earthquakes (M 5.4, M 6.9, and M 5.3) shook the island along with numerous lower-magnitude events. The M 6.9 event at 1232 HST (the largest on the island in 43 years) produced a robust ash plume at Pu'u 'O'o (figure 341), and numerous rockfall events were triggered at both Pu'u 'O'o and Halema'uma'u craters.

Figure 339. Fissure 3 was actively erupting at Leilani and Kaupili Streets in the Leilani Estates subdivision of the lower East Rift Zone at Kilauea at 0807 HST on 4 May 2018. Lava on the road was approximately 2 m thick. Courtesy of HVO.

Figure 340. Fissure 5 in the lower foreground was actively erupting at 1207 HST on 4 May 2018 in the Leilani Estates subdivision at Kilauea. View is to the SW. Behind fissure 5 are fissures 1, 4, and 3 from front to back. Courtesy of HVO.

Figure 341. At 1246 HST on 4 May 2018 a column of reddish-brown ash rose from Pu'u 'O'o crater at Kilauea after a M 6.9 south flank earthquake shook the island. View is to the S with the steaming fissure on the SW flank of the cone visible behind to the right of the ash plume. Courtesy of HVO.

Fissures 7, 8, and 9 opened in the Leilani Estates subdivision on 5 May. Fissure 7 was only active until mid-afternoon (figure 342). Fissure 8 activity included fountaining and occasional bursts of spatter to 100 m as well as building a spatter cone (figure 343); the flow from fissure 9 migrated W. New ground cracks were reported on Highway 130 along the W edge of the subdivision.

Figure 342. Fissure 7 began erupting around dawn on 5 May 2018 at Kilauea and was active for several hours. At the peak of its activity, large bubble bursts occurred at one spot (lower left) in the fissure while spattering was present in other locations. A short lava flow was erupted from the fissure around 0800, moving NE and crossing Hookupu Street (left). View is to the S, emissions in upper right are from fissure 2. Image taken on 5 May 2018, courtesy of HVO.

Figure 343. Fissure 8 erupted in the evening on 5 May 2018 at Kilauea, located near fissures 2 and 7; it began with small amounts of lava spattering at about 2044 HST. By 2100, lava fountains as high as about 70 m (when this photo was taken) were erupting from the fissure. Courtesy of HVO.

Tiltmeters at the summit continued to record a deflationary trend. Satellite InSAR data showed that between 23 April and 5 May 2018 the summit caldera floor subsided about 10 cm. Corresponding to this deflation, the lava lake in the Overlook vent had dropped about 128 m below the crater rim during that same period. Rockfalls from the crater walls into the retreating lake produced ashy plumes above Halema'uma'u crater, resulting in light ashfall in the summit area. During 4 and 5 May about 152 M 2 and M 3 earthquakes occurred at depths less than 5 km beneath the summit area. These earthquakes were related to the ongoing subsidence of the summit area and south flank of the volcano.

Fissure 8 erupted lava fountains until about 1600 on 6 May. By early that afternoon, ten fissures had opened in the Leilani Estates subdivision, but not all were continuing to erupt (figure 344). A lava flow from fissure 8 advanced northward, reaching 1.1 km in length by early evening (figure 345). Deflation continued at the summit with the lava lake dropping at a rate of about 2 m per hour throughout the day, and by evening it had dropped a total of 220 m since 30 April (figure 346).

Figure 344. Between 3 and 6 May 2018 ten fissures opened in the Leilani Estates area of the lower East Rift Zone at Kilauea. This thermal map shows the ''a'a flow from fissure 8 spreading northward (top) during an overflight of the area on the afternoon of 6 May. The dark area is the extent of the thermal map. Temperature in the thermal image is displayed as gray-scale values, with the brightest pixels indicating the hottest areas (whitish areas show the active lava flow). The gray linear features are the other fissures (numbered in red). The thermal map was constructed by stitching overlapping oblique thermal images collected by a handheld thermal camera during a helicopter overflight of the flow field. The base is a copyrighted color satellite image (used with permission) provided by Digital Globe. Courtesy of HVO.

Figure 345. A lava flow from fissure 8 flowed N on Makamae Street in Leilani Estates at Kilauea at 0932 HST on 6 May 2018. Courtesy of HVO.

Figure 346. The Kilauea summit lava lake began dropping on 1 May 2018, and by the evening of 6 May when this image was taken it was roughly 220 m below the crater rim. This very wide-angle camera view captured the entire north portion of the Overlook crater. Courtesy of HVO.

Two new fissures broke ground in the morning on 7 May. The first (fissure 11) opened in a forested area SW of Leilani Estates and was active for only 3 hours. The second (fissure 12) opened around noon between fissures 10 and 11. By 1515 both new fissures were inactive but the west end of fissure 10 was steaming heavily. Cracks on Highway 130 widened from 7 to 8 cm over the course of the day and additional cracks were found just W of the highway on trend with the previous fissures (figure 347).

Figure 347. Cracks several centimeters wide had opened along Highway 130 by 0930 HST on 7 May 2018. The highway runs N-S along the W edge of the Leilani Estates subdivision on Kilauea's East Rift Zone, about 15 km E of Pu'u 'O'o. Orange paint was used to outline the cracks. Courtesy of HVO.

By the evening of 8 May 2018, the overall fissure zone was about 4 km long (figure 348), stretching SW-NE across most of the now-evacuated Leilani Estates subdivision; 14 distinct fissures had been mapped, and a lava flow starting from fissure 8 had traveled about 1 km NE from its source. Officials noted that 35 structures had been destroyed. Loud jetting and booming noises were heard from fissure 13 that evening. Rockfalls into the Overlook vent at the summit were intermittently producing small ash plumes that rose several hundred meters above the summit and traveled downwind as the lava lake continued to fall. Based on model data collected in the afternoon, the lake level was about 295 m below the floor of Halema'uma'u Crater by the end of the day on 8 May.

Figure 348. The 4-km-long fissure zone that began erupting on 3 May 2018 at Kilauea's lower East Rift zone had crossed most of the Leilani Estates subdivision by 1900 on 8 May with 14 distinct fissures within the zone. An ''a'a flow from fissure 8 had traveled about 1 km NE since it emerged on the evening of 5 May. Inset shows numbered locations of each fissure in red. The purple areas are lava flows erupted in 1840, 1955, 1960, and 2014-2015. Courtesy of HVO.

At 0832 HST on 9 May 2018, a large rockfall from the steep crater walls into the summit lava lake triggered an explosion that generated an ash column above Halema'uma'u crater; the ash was blown SSW (figure 349). During the day on 9 May fissure 15 broke ground at the NE edge of the LERZ fissure area and generated a pahoehoe flow about 20 m long. Severe ground cracks associated with fissure 14 were steaming vigorously in the morning (figure 350). During an overflight around 1500 in the afternoon HVO geologists also noticed an area of steaming uprift (west) of Highway 130 at the SW edge of the fissure area. Rates of motion increased late in the morning at a GPS station located 1.5 km SE of Nanawale Estates (about 2 km N of Leilani Estates). The direction of motion was consistent with renewed movement of magma in the downrift direction (to the NE).

Figure 349. An ash plume rose from Halema'uma'u crater at the summit of Kilauea around 0830 on 9 May 2018. HVO's interpretation was that the explosion was triggered by a rockfall from the steep walls of the Overlook vent. The photograph was taken at 0829 HST from the Jaggar Museum overlook. Geologists examining the ash deposits on the rim of Halema'uma'u crater found fresh lava fragments ejected from the lava lake. Courtesy of HVO.

Figure 350. Severe ground cracks associated with fissure 14 in Leilani Estates at Kilauea were steaming vigorously at 0953 on 9 May 2018. Courtesy of HVO.

Strong degassing continued from existing fissures on 10 and 11 May; although active spatter and lava had paused, several cracks within the fissure zone continued to widen (figure 351). A 3D model constructed of thermal images of Pu'u 'O'o crater taken on 11 May indicated that the deepest part of the crater was 350 m below the rim (figure 352). Hawai'i Volcanoes National Park closed to the public on 11 May due to heightened (daily) earthquake activity at the summit, and concerns about a potentially larger summit explosion.

Figure 351. Ground cracks continued to widen near Leilani Estates subdivision at Kilauea on 10 May 2018 even though active spatter and lava flows had paused. At 1354 a geologist inspected a crack that widened considerably during the previous day on Old Kalapana Road. In other areas, new cracks appeared along sections of Highway 130, some with visible escaping fumes. Courtesy of HVO.

Figure 352. A clear view into Pu'u 'O'o crater of Kilauea was possible on 11 May 2018. The upper part of the crater had a flared geometry, which narrowed to a deep circular shaft. The deepest part of the crater was about 350 m below the crater rim according to a 3D model constructed from thermal images. The crater is about 250 m wide, and N is to the left. Courtesy of HVO.

Activity during 12-23 May 2018. Minor spattering resumed from a new fissure (16) that opened about 0645 on 12 May around 1.5 km NE of fissure 15, at the NE end of the existing vent system (figure 353). It produced a lava flow that traveled about 230 m before stalling in the early afternoon. A steady, vigorous plume of steam and variable amounts of ash rose from the Overlook vent and drifted SW. Over the course of the day, rockfalls from the steep enclosing crater walls at the summit crater periodically generated small ash clouds mixed with water vapor. These ash clouds rose only about a hundred meters above the ground, a few generating very localized ashfall downwind.

Figure 353. Fissure 16 opened in the morning on 12 May 2018 at around 0830 HST; it was located about 1.3 km NE of fissure 15, visible at the top left. The fissure is also located 500 m NE of the Puna Geothermal Venture (PGV) site (green piping, top right). View is uprift to the SW. Photograph courtesy of Hawai`i County Fire Department and HVO.

A plume of steam and volcanic gas, occasionally mixed with ash, rose from the Overlook vent within Halema'uma'u for much of the day on 13 May 2018. That morning, a new outbreak was reported about 0.5 km NE of fissure 16. Aerial observations of this new fissure (17) indicated it was at least several hundred meters long and produced spatter rising tens of meters into the air. By late in the day, activity was dominated by lava fountaining, explosions of spatter bombs, and several advancing lava flow lobes moving generally NE at the downrift (NE) end of the new fissure system. As of about 1900 on 13 May, one lobe was 2 m thick and advancing roughly parallel to Highway 132 (figure 354). A smaller fissure 18, a few hundred meters S of 17, was weakly active late in the day. A new fissure (19) was spotted early on 14 May producing a sluggish lava flow. By 1430 on 14 May, fissure 17 was producing a lava flow extending about 1.7 km from the fissure (figure 355).

Figure 354. Fissures 15-19 opened along the fissure zone NE of Leilani Estates between 9 and 14 May 2018 on Kilauea's East Rift Zone. As of the early morning on 14 May, lava from fissure 17 had traveled about 1.2 km, roughly ESE parallel to the rift zone, and was turning slightly S; at 0830 HST, the flow was about 0.9 km S of Highway 132. Fissure 18, which became active late on 13 May, and fissure 19, which opened early on 14 May, were both weakly active. Updated at 1430 on 14 May, this map shows the location of the front of the fissure 17 flow at that time. The flow is following a path of steepest descent (blue line), immediately south of the 1955 ''a'a flow boundary. Shaded purple areas indicate lava flows erupted in 1840, 1955, 1960, and 2014-2015. Courtesy of HVO.

Figure 355. A thermal map of the NE end of the fissure system on the lower East Rift Zone of Kilauea as of 1430 on 14 May 2018 shows the active fissure 17 flow extending about 1.7 km from the fissure. The black and white area is the extent of the thermal map. Temperature in the thermal image is displayed as gray-scale values, with the brightest pixels indicating the hottest areas. The thermal map was constructed by stitching many overlapping oblique thermal images collected by a handheld thermal camera during a helicopter overflight of the flow field. The base is a copyrighted color satellite image (used with permission) provided by Digital Globe. Courtesy of HVO.

Activity on the LERZ on 15 May 2018 was concentrated at fissure 17 with intermittent spattering at fissure 18; the fissure 17 flow continued to slowly advance ESE reaching a length of nearly 2.5 km in the early morning (figures 356 and 357). A new fissure (20) opened up SW of fissure 18 and produced two small pads of lava. During the morning, ash emissions from the Overlook vent inside Halema'uma'u varied greatly in intensity with abrupt increases likely associated with large rockfalls deep into the vent (figure 358). Ashfall was reported as far away as Discovery Harbor (55 km SW), Pahala (30 km SW), at locations along Highway 11 from Pahala to Volcano, and in the Ka'u Desert section of Hawaii Volcanoes National Park near the summit. NWS radar and pilot reports indicated the top of the ash cloud ranged from 3.0 to 3.7 km altitude.

Figure 356. The 2.5-km-long fissure 17 lava flow on Kilauea's lower East Rift Zone at 0844 on 15 May 2018 was an active ''a'a flow moving ESE from fissure 17, which was visible as low lava fountains in the middle of the photo. Highway 132 appears on the right side of the photograph; the view is toward the W. Photograph courtesy of the Hawai`i County Fire Department and HVO.

Figure 357. Highly viscous (sticky) lava oozed from the edge of the ''a'a flow spreading slowly ESE from fissure 17 at Kilauea's lower East Rift Zone on 15 May 2018. Courtesy of HVO.

Figure 358. Activity at Halema'uma'u crater at Kilauea increased in the morning of 15 May 2018 to include the nearly continuous emission of ash with intermittent stronger pulses that formed occasional higher plumes 1-2 km above the summit. At about 0900 HST the plume was drifting SW with the tradewinds toward the Ka`u Desert. The dark area to the right of the ash column rising from the Overlook vent is ash falling from the cloud. Courtesy of HVO.

On the morning of 16 May dense ballistic blocks up to 60 cm across were found in the parking lot a few hundred meters from Halema'uma'u crater, reflecting the most energetic explosions to date. Strong earthquakes within the summit continued in response to ongoing deflation and lava column drop. By the afternoon of 16 May the floor of the larger Kilauea Caldera had dropped 90 cm from the ongoing deflation, stressing faults around the caldera and causing multiple earthquakes. Employees at the Hawaiian Volcano Observatory, Hawai`i Volcanoes National Park, and nearby residents reported frequent ground shaking and damage to roads and buildings. The decision was made to evacuate HVO's office building on Uekahuna Bluff overlooking Halema'uma'u Crater. Low-level eruption of lava continued from multiple points along the NE end of the active fissure system on the lower East Rift Zone, but spattering generally decreased in vigor throughout the day.

At about 0415 on 17 May an explosion from the Overlook vent produced a volcanic cloud that reached 9.1 km altitude and drifted NE. Traces of ash fell with rain on the Volcano Golf Course, in Volcano Village, and in other areas immediately around the summit (figure 359). Subsequent continued emissions reached 3.7 km altitude; vog or volcanic air pollution produced by volcanic gas was reported in Pahala. After the explosion, seismic levels increased gradually throughout the day.

Figure 359. At 0745 on 17 May 2018 the view of Halema'uma'u crater at Kilauea from the visitor viewing area in front of the Jaggar Muesum at Hawai'i Volcanoes National Park included a light coating of ash on the Park's interpretative sign caused by ashfall after significant explosive events the previous day. Note the contrast of the mostly-steam plume rising from the Overlook vent in the background with the eruption column that emerged during explosive activity in May 1924 (shown in the middle photograph on the sign). Courtesy of HVO.

At the LERZ, fissures 18, 19, and 20 reactivated during the afternoon of 17 May, and a new fissure opened (21) between fissures 7 and 3 (figure 360). Ground cracks continued to open and widen around Leilani Estates, several with both horizontal and vertical offsets (figures 361 and 362). An area 50-90 m wide, parallel to and N of the line of fissures between Highway 130 and Lanipuna Gardens, dropped slightly, forming a depression that pahoehoe flows from fissures 20 and 21 began filling. Fissure 22 opened just downrift of fissure 19.

Figure 360. Fissure 21 opened between fissures 3 and 7 on 17 May 2018 on the lower East Rift Zone at Kilauea. Around 1500 an aerial view of the fissure showed fountaining and a lava flow expanding outward from the fissure. View is toward the west. Courtesy of HVO.

Figure 361. SW-trending en-echelon ground cracks dissected and offset NW-trending Pohoiki Road around 0700 on 17 May 2018 as seen during an overflight by HVO of the eruptive fissure area at Kilauea's East Rift Zone. Cracks continued to open and widen, many with both horizontal and vertical offsets. These cracks were caused by the underlying intrusion of magma into the lower East Rift Zone. Courtesy of HVO.

Figure 362. HVO geologists examined widening cracks on Nohea Street in Leilani Estates at Kilauea's lower East Rift Zone on 17 May 2018. These cracks had expanded significantly during the previous day. Courtesy of HVO.

Spattering continued on 18 May 2018 from fissures 15, 17, 18, 20, 21, and new fissure 22. Pahoehoe lava flows were also erupted from fissures 17, 18, and 20 (figure 363). During the afternoon, fissure 17 was actively spattering fragments as high as 100 m, and the flow was active but had not covered new ground (figure 364). A flow from fissure 18 had traveled approximately 1 km SE. The graben area N of the fissures was still being filled by pahoehoe flows from fissures 20 and 21; fissure 15 produced a flow that crossed Pohoiki Road. Later in the afternoon a fast-moving pahoehoe flow emerged from fissure 20 and traveled SE, moving over 300 m per hour. By late that evening, the flow had three main lobes; the easternmost was E of Pohoiki Road moving about 200 m per hour while the westernmost was near Malamaki Road and moving about 40 m per hour. At the summit, for much of the day, a steady steam plume rose from the Overlook vent. Several minor emissions of ash were observed in web cameras; no significant explosions and no earthquakes greater than M 3.5 had occurred in the previous 24 hours. At 2358 local time, however, a short-lived explosion from Halema'uma'u created an ash cloud that reached up to 3.1 km altitude and was carried SW by the wind.

Figure 363. By the early afternoon of 18 May 2018, fissures 21, 4, 15, 22, 20, 18, and 17 (SW to NE) were all erupting with either pahoehoe flows, fountaining, or spatter on Kilauea's lower East Rift Zone. Shaded purple areas indicate lava flows erupted in 1840, 1955, 1960, and 2014-2015. Courtesy of HVO.

Figure 364. The line of fountains on fissure 17 coalesced into a large fountain sending lava fragments 50 m into the air in the morning on 18 May 2018 at the lower East Rift Zone of Kilauea; small bits of spatter reached 100 m high. Courtesy of HVO.

The rate of lava eruption increased overnight on 18-19 May; fountaining continued at fissure 17, and fissures 16 and 20 merged into a continuous line of spatter and fountaining. Two flows from this consolidated fissure complex were wide, very active, and advancing southward at rates up to 300 m per hour (figures 365 and 366). Flows from fissures 17 and 18 were also still active but advancing slowly, and fissure 18 had stalled by the end of the day. By mid-afternoon on 19 May the two fast-moving flows had joined about a kilometer from the coast and continued to flow southward (figure 367). The GPS instrument located on the NE side of Leilani Estates was no longer moving. While earthquake activity continued, it had not moved farther downrift in the previous few days.

Figure 365. Channelized lava flows originating from a merged, elongated fountaining source between fissures 16 and 20 in Kilauea's lower East Rift Zone split into two flows that both traveled rapidly S as seen at 0737 on 19 May 2018. This view to the SW also showed the steaming line of fissures on the lower East Rift Zone that continued SW of the fountaining source. Courtesy of HVO.

Figure 366. 'A'a lava flows emerged from the elongated fissure 16-20 at Kilauea to form several channels. The flow direction is from upper center to the lower left of image. Incandescence from the second flow is visible in the upper left. Image taken around 0818 on 19 May 2018 during a helicopter overflight of Kilauea's lower East Rift zone by HVO geoscientists. Courtesy of HVO.

Figure 367. Around 1215 on 19 May 2018 the two primary lava-flow fronts originating from the fissure 20-22 area on Kilauea's lower East Rift Zone were about to merge as they flowed SE. The flow front position based on a later update at 1840 is shown by the red circle. The black and white area is the extent of the thermal map. Temperature in the thermal image is displayed as gray-scale values, with the brightest pixels indicating the hottest areas. The thermal map was constructed by stitching many overlapping oblique thermal images collected by a handheld thermal camera during a helicopter overflight of the flow field. The base is a copyrighted color satellite image (used with permission) provided by Digital Globe. Courtesy of HVO.

The two flows from the fissure 20 complex entered the ocean at two points along the SE Puna coast overnight on 19-20 May (figure 368). Soon after, a crack opened under the E lava channel diverting some of the lava into underground voids (figure 369) and reducing the amount of lava flowing into the ocean. Spattering continued from fissures 6 and 17 during the day on 20 May. Fissure 23 first appeared at 1100 on 20 May, at the NE corner of the Leilani Estates subdivision near fissures 4 and 14, about 2 km SW of fissure 20; it was only active during 19-20 May. Volcanic gas emissions tripled as a result of the voluminous eruptions from the fissure 20 complex; satellite instruments measured a major increase in SO₂ emissions on 19 May (figure 370). Intermittent explosive eruptions continued at the summit, and plumes of gas and steam periodically emerged from the Overlook vent and drifted SW.

Figure 368. The fissure 20 complex flows from Kilauea's lower East Rift Zone reached the ocean overnight during 19-20 May 2018, as seen in this image from an HVO overflight in the early morning on 20 May. Dense white plumes of "laze" (short for "lava haze") formed as lava entered the ocean. Laze is formed as lava boils seawater. The process leads to a series of chemical reactions that result in the formation of a billowing white cloud composed of a mixture of condensed seawater steam, hydrochloric acid gas, and tiny shards of volcanic glass. This mixture has the stinging and corrosive properties of dilute battery acid and is hazardous to breathe. Because laze can be blown downwind, its corrosive effects can extend far beyond the actual ocean entry area. Courtesy of HVO.

Figure 369. Lava from the eastern channel of the fissure 20 complex flowed into a crack in the ground that opened on the morning of 20 May 2018. The resulting decrease in lava volume caused the easternmost channel of lava and the eastern ocean entry to be less vigorous than the western entry point. Courtesy of HVO.

Figure 370. SO2 emissions increased substantially at Kilauea when the rate of lava emission increased significantly on 19 May 2018 on the lower East Rift Zone. The OMI instrument on the Aura satellite measured 8.2 Dobson Units (DU) of atmospheric SO2 on 3 May, the day fissure 1 opened, and 18.11 DU on 19 May when the flow rates increased at the fissure 20 complex. Courtesy of NASA Goddard Space Flight Center.

The most vigorous eruptive activity during 21-23 May in the lower East Rift Zone, was concentrated in the middle portion of the system of fissures, primarily between fissure 20 on the NE and fissure 23 on the SW (figure 371). Fountaining 50 m high from fissure 22 was feeding the channelized flow reaching the coast (figure 372). Fissure 6 reactivated with spattering and a short flow on 21 May. Fissure 17, at the NE end of the fissure system was only weakly active. On 22 May lava fountains continued from fissures 6 and 22, with fissures 19 and 5 also active; a new area of fountaining also appeared near fissure 23. Fountaining from fissures 5 and 23 fed flows in the eastern part of Leilani Estates and blue methane was observed burning in road cracks overnight on 22-23 May (figure 373). Observers noted that the height of the perched lava pond forming on the NW side of fissures 5 and 6 had reached 11 m above the ground level.

Figure 371. By 20 May 2018, two lava flows from fissures 20 and 22 in the lower East Rift Zone at Kilauea had coalesced and reached the ocean. Activity at the fissure 17 flow had diminished significantly. The most vigorous eruptive activity during 21-23 May 2018 was concentrated in the middle portion of the system of fissures, primarily between fissure 20 on the NE and fissure 23 on the SW. Courtesy of HVO.

Figure 372. HVO geologists reported fountaining from fissure 22 as 50 m high on 21 May 2018 at Kilauea's lower East Rift Zone. Courtesy of HVO.

Figure 373. Blue flames of methane emerged from ground and road cracks on 22 May 2018. This early morning photo was taken on Kahukai Street in the Leilani Estates subdivision at Kilauea looking SE, with an active lava flow from fissure 13 behind the blue flames. Photo by L. DeSmither, courtesy of HVO.

By 23 May, fountains from fissures 5, 6 (figure 374), 13, and 19 were feeding a flow advancing to the S, roughly parallel to the western flow from fissure 22 (figure 375); it reached the ocean late in the afternoon, creating multiple entry points that produced occasional small explosions. Small ash emissions from the Overlook vent occurred frequently during 21-23 May (figure 376). Fissure 8 reactivated briefly in the morning of 23 May and erupted two small pahoehoe flows over the initial `a`a flow.

Figure 374. Fissure 6 in the lower East Rift Zone at Kilauea built a lava berm across Pohoiki Road as seen on 23 May 2018. Flows from fissure 6 and adjacent fissures formed a flow parallel to an earlier flow that traveled SE reaching the coast that afternoon. Courtesy of HVO.

Figure 375. Multiple channels of lava flowed SE from the fissure zone at Kilauea's lower East Rift Zone to the sea on 23 May 2018. Overflows from the channels spread out over existing, older flows; note the large agriculture buildings as indicators of the scale of the flows. The visible haze is sulfur dioxide gas from the fissures. Photo taken by J. Ozbolt, Hilo Civil Air Patrol, courtesy of HVO.

Figure 376. A pulse of ash rose from Halema'uma'u on 23 May 2018 as part of semi-continuous emissions at Kilauea's summit. Ash could be seen falling from the plume as it was blown downwind around 1528 HST on 23 May. USGS photo by I. Johanson, courtesy of HVO.

Activity during 24-28 May 2018. Overnight on 23-24 May field crews observed that fissure areas 2, 7, 8, 3, 14, and 21 had reactivated and were spattering (figure 377). Fissure 22 continued to erupt lava flowing SE to the coast (figure 378). Fissures 7 and 21 were feeding a perched lava pond and pahoehoe flow that advanced eastward later that afternoon. An explosion from the summit Overlook vent just after 1800 on 24 May produced an ash cloud that rose to 3.1 km altitude and had more ash than most recent explosions (figure 379). The National Weather Service Nexrad radar tracked the cloud for 15-20 minutes; moderate trade winds were blowing to the SW.

Figure 377. Reactivation of fissures 2, 7, 8, 3, 14, and 21 was noted on 24 May 2018 at the lower East Rift Zone at Kilauea. Fissures 7 and 21 were feeding a perched lava pond and pahoehoe flow. Several ocean entries were also active from the channelized flow down the SE flank sourced from the region of fissures 6-20. Courtesy of HVO.

Figure 378. During HVO's overflight in the morning of 24 May 2018, the fissure 22 fountain was not as high as several days earlier, but was still erupting significant lava that was flowing to the SE Puna coast at Kilauea. USGS photo by M. Patrick, courtesy of HVO.

Figure 379. An explosion was detected from the summit Overlook Crater at Kilauea just after 1800 on 24 May 2018 that produced an ash cloud that rose to 3.1 km altitude, carrying more ash than most recent explosions. This view to the SW is from the caldera rim near Volcano House where USGS scientists were stationed to track the ongoing summit explosions. Courtesy of HVO.

By 25 May, the two flows from fissure 22 and fissures 6 and 13 were still reaching the ocean with two entry points (figure 380); fissures 7 and 21 were feeding a flow that continued to slowly advance NE, covering several streets in Leilani Estates (figure 381). By the next day, the flow front of fissure 21 had become an 'a'a flow and was continuing to move NE (figure 382), reaching the PGV (Puna Geothermal Venture) property by late afternoon on 26 May. Fissure 7 was feeding a flow that had turned S toward the coast, and at dusk the lava was cascading into the Pawaii crater, adjacent to the western margin of the fissure 6 flow that fed one of the ocean entries. On the W side of fissure 7 a perched pahoehoe flow broke out around 0400 on 26 May, feeding short flows to the W. Multiple small eruptions continued to occur at the summit, most ejecting ash to under 3.1 km altitude. One of the largest occurred about 1617 on 25 May sending ash as high as 3.7 km altitude.

Figure 380. Fissures 6 (left) and 13 (right) at midday on 25 May 2018 on Kilauea's lower East Rift Zone, with lava flows merging into one channel that flows SE into the ocean. Note plume in distance at the ocean entries (top left). Courtesy of HVO.

Figure 381. Reactivated fissures 7 and 21 within the Leilani Estates subdivision at Kilauea were feeding new flows moving NE towards the Puna Geothermal Venture (PGV) property during 25 and 26 May 2018. Courtesy of HVO.

Figure 382. An 'a'a flow, erupted from fissure 21 at Kilauea was approximately 3-4 m high at the flow front and slowly advancing to the NE in the Leilani Estates subdivision around 1030 HST on 26 May 2018. Courtesy of HVO.

Overnight during 26-27 May fissure 17 was the source of multiple booming gas emissions. Fissure 7 activity increased overnight, producing a large spatter rampart over 30 m tall from fountains reaching 50-70 m high (figure 383). The fountains fed two perched channels, the N channel, 8-15 m thick, fed a lava flow that advanced toward pad E of the PGV property; the S channel was a flow advanced SE. Large cracks were observed overnight near fissure 9 which developed into fissure 24. Fissure 8 had three vents active overnight on 26-27 May that were spattering and flaming; they had doubled in size over the previous 24 hours.

Figure 383. Pahoehoe lava advanced rapidly W from fissure 7 on Leilani Avenue in Kilauea's lower East Rift Zone on 27 May 2018. Activity had increased overnight, with lava fountains reaching 50 to 60 m high. Courtesy of HVO.

The fissure 21 'a'a flow continued to advance NE onto PGV property but at a slower pace on 27 May. By the end of the day, fissures 7 and 8 were the most active, fountaining and feeding lava flows that advanced NE onto PGV property. At about 1900 HST a fast-moving lava flow broke from this area and advanced rapidly to the N and W through the eastern portion of Leilani Estates, causing additional evacuations. Activity had noticeably diminished from fissures 22 and 13, and the supply of lava to the channel flowing to the sea had ceased by the next day, 28 May. Ash continued to erupt intermittently from the Overlook vent at the summit. Observations from the ground and by UAV during the previous week documented retreat of the Overlook vent wall due to collapse of the steep enclosing walls and rim. Trade winds carried the ash clouds primarily SW.

Fissure 8 fed a fast-moving flow early on 28 May that moved N along the margin of the existing fissure 7 flow before turning E and crossing out of Leilani Estates (figure 384). Flow activity from fissure 8 diminished abruptly midday and a few other fissures reactivated briefly with fissure 7/21 having the tallest fountains. Vigorous fountaining resumed at fissure 8 late in the afternoon, spawning a flow that traveled an estimated 20 m per hour to the NE over the flow of the previous day; fountains were 50-60 m tall (figure 385). During the evening, fissures 16, 18, 22, 13, and 20 were also active, with flows moving S from fissures 16/18. Pele's hair from vigorous fountaining of fissure 8 was being transported downwind, and there were reports of some strands falling in Pahoa. Residents were warned to minimize exposure to Pele's hair, which could cause skin and eye irritation similar to exposure to volcanic ash. Ash continued to erupt intermittently from the vent within Halema'uma'u crater. A magnitude 4.1 earthquake occurred at 1739 HST on the Koa'e fault zone south of the caldera. Earthquakes in the summit region continued as the area subsided and adjusted to the withdrawal of magma.

Figure 384. A fast-moving flow from fissure 8 moved N and then E out of Leilani Estates on 28 May 2018 marking a new phase in the 2018 Kilauea eruption. Courtesy of HVO.

Figure 385. Fissure 8 on Kilauea's lower East Rift Zone reactivated after a brief pause on the afternoon of 28 May 2018 with lava fountains that reached heights of 60 m and fed a lava flow that advanced rapidly to the NE. Courtesy of HVO.

By 26 May 2018, flows on the lower East Rift Zone had destroyed at least 82 structures including 41 homes since the beginning of May. Twelve more were destroyed on 27 and 28 May as flows continued to move across the region, according to USA Today. By 29 May, activity on the lower East Rift Zone was focused on the vigorous eruption of lava from fissure 8 advancing rapidly downslope towards the NE and Highway 132.

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

Information Contacts: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawai'i National Park, HI 96718, USA (URL: http://hvo.wr.usgs.gov/); 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/); USA Today (URL: https://www.kiiitv.com/article/news/nation-now/hawaii-lava-flow-destroys-12-more-homes-as-Kilauea -volcano-continues-exploding/465-afd62fc3-91d2-4764-9eb9-c3dee473033d).

Krakatau volcano in the Sunda Strait between Java and Sumatra, Indonesia experienced a major caldera collapse, likely in 535 CE, that formed a 7-km-wide caldera ringed by three islands (see inset figure 23, BGVN 36:08). Remnants of this volcano coalesced to create the pre-1883 Krakatau Island which collapsed during the 1883 eruption. The post-collapse cone of Anak Krakatau (Child of Krakatau), constructed within the 1883 caldera has been the site of frequent eruptions since 1927. The most recent event was a brief episode of Strombolian activity, ash plumes, and a lava flow during the second half of February 2017. Activity resumed in late June 2018 and continued through early October, the period covered in this report. Information is provided primarily by the Indonesian Center for Volcanology and Geological Hazard Mitigation, referred to as Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG). Aviation reports are provided by the Darwin Volcanic Ash Advisory Center (VAAC), and photographs came from several social media sources and professional photographers.

After the brief event during February 2017, Anak Krakatau remained quiet for about 15 months. PVMBG kept the Alert Level at II, noting no significant changes until mid-June 2018. Increased seismicity on 18 June was followed by explosions with ash plumes beginning on 21 June. Intermittent ash emissions were accompanied by Strombolian activity with large blocks of incandescent ejecta that traveled down the flanks to the ocean throughout July. Explosions were reported as short bursts of seismic activity, repeating multiple times in a day, and producing dense black ash plumes that rose a few hundred meters from the summit. Similar activity continued throughout August, with the addition of a lava flow visible on the S flank that reached the ocean during 4-5 August. Generally increased activity in September resulted in the highest ash plumes of the period, up to 4.9 km altitude on 8 September; high-intensity explosions were heard tens of kilometers away during 9-10 September. PVMBG reported significantly increased numbers of daily explosions during the second half of the month. The thermal signature recorded in satellite data also increased during September, and a large SO2 plume was recorded in satellite data on 23 September.

Activity during June-July 2018. PVMBG noted an increase in seismic activity beginning on 18 June 2018. Foggy conditions hampered visual observations during 19-20 June, but on 21 June gray plumes were observed rising 100-200 m above the summit (figure 41). Two ash plumes were reported on 25 June; the first rose to about 1 km altitude and drifted N, and the second rose to 600 m altitude and drifted S (figure 42).

Figure 41. Anak Krakatau began a new eruptive episode on 21 June 2018 with an ash plume that rose 200 m above the summit. Photo by undisclosed source, courtesy of Øystein Lund Andersen‏.

Figure 42. The first of two ash plumes rose to about 1 km altitude and drifted N from Anak Krakatau on 25 June 2018; the first events after about 18 months of no activity were reported on 21 June. Courtesy of PVMBG (Eruption Information on Mt. Anak Krakatau, June 25, 2018).

Incandescence was observed at the summit during 1-2 July 2018, and two ash emissions were reported in VONA's (Volcano Observatory Notice for Aviation) on 3 July. PVMBG reported that during 4-5 July there were four additional ash-producing events, each lasting between 30 and 41 seconds. The last three of these events produced ash plumes that rose 300-500 m above the crater rim and drifted N and NW. The Darwin VAAC reported essentially continuous ash emissions during 3-9 July drifting generally W and SW at about 1.2 km altitude (figure 43). They were intermittently visible in satellite imagery when not obscured by meteoric clouds.

Figure 43. A dense gray ash plume rose several hundred meters above Anak Krakatau on 7 July 2018 (local time) while large volcanic bombs traveled down the flanks. Photo by Sam Hidayat, courtesy of Øystein Lund Andersen‏.

Ash plumes were again observed by the Darwin VAAC in satellite imagery beginning on 13 July 2018 at 1.2 km altitude drifting NW. They were essentially continuous until they gradually decreased and dissipated early on 17 July, rising to 1.2-1.5 km altitude and drifting W, clearly visible in satellite imagery several times during the period. Satellite imagery revealed hotspots several times during July; they ranged from small pixels at the summit (9 July) to clear flow activity down the SE flank on multiple days (12, 19, and 24 July) (figure 44). In the VONA's reported by PVMBG during 15-17 July, they noted intermittent explosions that lasted around 30-90 seconds each. PVMBG reported a black ash plume 500 m above the summit drifting N during the afternoon of 16 July. The Darwin VAAC continued to report ash emission to 1.2-1.5 km altitude during 18-19 July, moving in several different directions; Strombolian activity sent incandescent ejecta in all directions on 19 July (figure 45). During 25-26 July the Darwin VAAC noted continuous minor ash emissions drifting SW at 1.2 km altitude, and a hotspot visible in infrared imagery.

Figure 44. Sentinel-2 satellite imagery clearly documented the repeated thermal activity at Anak Krakatau throughout July 2018. a) 9 July 2018: a small hotspot was visible at the summit and an ash plume drifted NW. b) 12 July 2018: a much larger hotspot showed a distinct flow down the SE flank. c) 19 July 2018: even under partly cloudy skies, incandescent ejecta is visible on the S flank. d) 24 July 2018: incandescent lava had almost reached the SE coast. Sentinel-2 images with Atmospheric Penetration view (bands 12, 11, and 8A), courtesy of Sentinel Hub Playground.

Figure 45. Strombolian activity sent incandescent ejecta down all the flanks and into the sea at Anak Krakatau on 19 July 2018, as seen from the island of Rakata (5 km SE). Courtesy of Reuters / Stringer.

Activity during August-early October 2018. A series of at least nine explosions took place on 2 August 2018 between 1333 and 1757 local time. They ranged from 13 to 64 seconds long, and produced ash plumes that drifted N. The Darwin VAAC reported minor ash observed in imagery at around 2 km altitude for much of the day. In a special report, PVMBG noted a black ash plume 500 m above sea level drifting N at 1757 local time. Continued explosive activity was reported by local observers during the early nighttime hours of 3 August (figure 46).

Figure 46. A dark ash plume rose 100-200 m from Anak Krakatau during the early morning hours of 3 August 2018, and incandescent ejecta rolled down the flanks. Tens of explosions were heard in Serang (80 km E) and Lampung (80 km N). Courtesy of Sutopo Purwo Nugroho.

The Darwin VAAC reported continuous ash emissions rising to 1.8 km altitude and drifting E on 5 August, clearly visible in satellite imagery, along with a strong hotspot. The ash plume drifted SE then S the next day before dissipating. PVMBG reported incandescence visible during the nights of 5-15 August. Photographer Øystein Lund Andersen visited Krakatau during 4-6 August 2018 and recorded Strombolian activity, lava bomb ejecta, and a lava flow entering the ocean (figures 47-50).

Figure 47. Strombolian explosions sent incandescent ejecta skyward, and blocks of debris down the flanks of Anak Krakatau on 5 August 2018 as captured in this drone photograph. Copyrighted photo by Øystein Lund Andersen‏, used with permission.

Figure 48. Large volcanic bombs flew out from the summit vent of Anak Krakatau while a dark gray plume of ash rose a few hundred meters on 5 August 2018 in this drone photograph. Copyrighted photo by Øystein Lund Andersen‏, used with permission.

Figure 49. A blocky lava flow traveled down the S flank of Anak Krakatau on 5 August 2018 in this closeup image taken by a drone. Copyrighted photo by Øystein Lund Andersen‏, used with permission.

Figure 50. Views of Anak Krakatau from the SE showed Strombolian activity and incandescent lava (upper photo) and steam from the lava flowing into the ocean and dark ash emissions from the summit (lower photo) on 5 August 2018. Copyrighted photo by Øystein Lund Andersen‏, used with permission.

Emissions were reported intermittently drifting W on 11, 14, and 16 August at 1.2-1.5 km altitude. Video of explosions on 12 August with large bombs and dark ash plumes were captured by photographer James Reynolds (Earth Uncut TV). PVMBG reported black ash plumes drifting N at 500 m above the summit on 17 and 18 August after explosions that lasted 1-2 minutes each. The Darwin VAAC also reported ash plumes rising to 1.2 km altitude on 17-18 drifting NE. VONA's were issued during 22-23 August reporting at least three explosions that lasted 30-40 seconds and produced ash plumes that drifted N and NE. The Darwin VAAC reported the plume on 22 August as originating from a vent below the summit. PVMBG noted that a dark plume on 23 August drifted NE at about 700 m above the summit. During 27-30 August, the Darwin VAAC reported ash plumes intermittently visible in satellite imagery extending SW at 1.2-1.5 km altitude.

Ash plumes drifting N and NW were visible in satellite imagery during 3-4 September at 1.2-1.5 km altitude. The Darwin VAAC reported an ash plume moving NW and W at 4.9 km altitude on 8 September, the highest plume noted for the report period. The following day, the plume height had dropped to 1.5 km altitude, and was clearly observed drifting W in satellite imagery. A hotspot was reported on 12 September. During the night of 9-10 September PVMBG reported bursts of incandescent material rising 100-200 m above the peak, with explosions that rattled windows at the Anak Krakatau PGA Post, located 42 km from the volcano. Ash plumes continued to be observed through 13 September. The Darwin VAAC reported continuous ash emissions to 1.8 km altitude drifting W and NW on 16-17 September (figure 51). The ash plume was no longer visible on 18 September, but a hotspot remained discernable in satellite data through 20 September.

Figure 51. On 16 September 2018 a dark ash plume rose several hundred meters above Anak Krakatau as incandescent lava flowing down the SE flank to the sea created steam plumes. Courtesy of Thibaud Plaquet.

PVMBG reported incandescence at the summit and gray and black ash plumes on 20 September that rose 500 m above the summit. A low-level ash emission was reported drifting S on 21 September and confirmed in the webcam. Four VONA's were issued that day, reporting explosions at 0221, 0827, 2241, and 2248, lasting from 72-115 seconds each. PVMBG subsequently reported observing 44 explosions with black ash plumes rising 100-600 m above the summit, and incandescence at night on 21 September. Ash emissions continued on 22 September at 1.5 km altitude, with a secondary explosion rising to 2.4 km altitude drifting W. The plume height was based on and infrared temperature measurement of 12 degrees C. Later in the day, an additional plume was observed in satellite imagery at 3.7 km altitude drifting N. PVMBG reported observations of 56 explosions, with 200-300 m high (above the summit) black ash plumes and incandescence at night on 22 September. Observations from nearby Rakata Island on 22 September indicated that tephra from incandescent explosions of the previous night mostly fell on the flanks, but some reached the sea. A lava flow on the SSE flank had also reached the ocean (figure 52).

Figure 52. Activity at Krakatau during 22-23 September 2018 included substantial Strombolian explosions, a dark ash plume, lava flows, and large volcanic bombs traveling nearly to the ocean. Photo courtesy of Malmo Travel.

By 23 September 2018, a single plume was observed at 2.1 km altitude drifting WNW. A glow at the summit was visible in the webcam that day, and a hotspot was seen in satellite imagery the next day as observations of an ash plume drifting W at 2.1 km continued. A significant SO2 plume was captured in satellite data on 23 September (figure 53).

Figure 53. A significant SO2 plume dispersed NW of Krakatau (lower right corner) on 23 September 2018 after a surge in activity was observed the previous two days. Courtesy of NASA Goddard Space Flight Center.

On 24 September, PVMBG reported black ash plumes rising 1,000 m above the summit, incandescence at the summit, and lava flowing 300 m down the S flank observed in the webcam during the night. An ash plume was observed by the Darwin VAAC drifting WSW and then W on 25-26 September at 2.1 km altitude, lowering slightly to 1.8 km the following day, and to 1.2 km on 28 September. Continuous ash emissions were observed through 29 September. A new emission was reported on 30 September drifting SW at 1.8 km altitude. Ash emissions were observed daily by the Darwin VAAC from the 1st to at least 5 October at 2.1 km altitude drifting W. A large hotspot near the summit was noted on 3 October. The thermal activity at Anak Krakatau from late June into early October 2018, as recorded in infrared satellite data by the MIROVA project, confirmed the visual observations of increased activity that included Strombolian explosions, lava flows, ash plumes, and incandescent ejecta witnessed by ground observers during the period (figure 54).

Figure 54. The MIROVA project graph of thermal activity at Krakatau from 12 February through early October 2018 showed the increasing thermal signature that appeared in late June at the onset of renewed explosive activity, the first since February 2017. Courtesy of MIROVA.

Geologic Background. The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Sutopo Purwo Nugroho, BNPB (Twitter: @Sutopo_PN, URL: https://twitter.com/Sutopo_PN); Øystein Lund Andersen (Twitter: @OysteinLAnderse, https://twitter.com/OysteinLAnderse, URL: http://www.oysteinlundandersen.com); Reuters Latam (Twitter: @ReutersLatam, URL: http://www.reuters.com/); James Reynolds, Earth Uncut TV (Twitter: @EarthUncutTV, URL: https://www.earthuncut.tv/, Video: https://www.youtube.com/watch?v=UD3SLWtuPZs); Thibaud Plaquet (Instagram: tibomvm, URL: https://www.instagram.com/tibomvm/); Malmo Travel (Instagram: malmo.travel, URL: https://www.instagram.com/malmo.travel/).

Ol Doinyo Lengai is the only volcano on Earth currently erupting carbonatite lavas. Activity is based in the crater offset to the N about 100 m below the summit, where hornitos (small cones) and pit craters produce lava flows and spattering. After displaying effusive activity in the north crater since at least 1983, it became filled and lava began overflowing in 1998. The eruption transitioned to significant explosive activity in September 2007 through March 2008 that cleared out and recreated the crater (figure 175). Since then, intermittent effusive carbonatite eruptions have continued. This report summarizes observed activity from August 2014 through August 2018, including observations by visitors and satellite data (figure 176).

Figure 175. The northern summit crater of Ol Doinyo Lengai on 29-30 November 2017. The crater is ~100-125 m deep and ~175-190 m in diameter at the vertical crater wall, and 260-300 m wide at the crater rim. Top: orthorectified photography showing the light-colored crater floor with dark spots indicating the locations of recently active vents. Bottom: Shaded relief of the crater. Courtesy of M. Kervyn and Antoine Dille at Vrije Universiteit Brussel.

Figure 176. Selected satellite imagery showing typical activity at Ol Doinyo Lengai during 2017-18. These Sentinel-2 thermal (left) and true color (right) satellite images show the active areas indicated by elevated thermal activity (bright orange) and darker gray-black areas on the crater floor. The dark fresh lavas rapidly cool to a light brown-white color. Courtesy of Sentinel Hub Playground.

Lava fountaining was seen by geologists on 5 July 2014 (BGVN 39:07). A tourist report on Trip Advisor for an unknown date in July 2014 described potential fumarolic activity, while another report that month did not note any activity. No clear reports are known describing activity between August 2014 and May 2015. On 20 June 2015 an Earth Sciences group from the University of Glasgow and University of Dodoma, including volcanologist David Brown, visited the crater (figure 177). They observed minor eruptive activity consisting of gentle spattering at one of the mounds. Evidence of this activity continuing through August is seen in Landsat satellite images (figure 178).

Figure 177. The active Ol Doinyo Lengai crater on 20 June 2015 showing the cone along the western wall (top) and the northern wall (bottom). Photos courtesy of David Brown, University of Glasgow.

Figure 178. Landsat-8 satellite images show color variations on the Ol Doinyo Lengai active crater floor. Darker areas may indicate activity and changing morphology during July through August 2015. Landsat-8 true-color pansharpened images courtesy of Sentinel Hub Playground.

Only one Sentinel-2 thermal image (out of 22 cloud-free images) contained elevated temperatures during 2016. The image showed activity in the northern part of the crater. Landsat-8 true color images show color variations on the crater floor in October 2016 indicating activity at that time (figure 179).

Figure 179. Landsat-8 images showing color variations on the Ol Doinyo Lengai active crater floor indicating activity in October 2016. Landsat-8 true-color pansharpened images courtesy of Sentinel Hub Playground.

On 29-30 November 2017, a French-Belgium team including M. Kervyn conducted a summit morphology study. Accounts from previous visitors in September-October 2017 reported significant activity in the large half-cone with regular emission of spatter from the summit vent. They observed significant fumarolic activity and the remnants of rockfalls in the crater. Several secondary vents were visible on the side of the large half-cone along the western wall, but no activity was witnessed at this time (figure 180). Active spattering was occurring from a lava pool within a vent in the north-central part of the crater where spattering up to 10 m above the vent continued for several hours (figure 181). A circular cavity in the north-central part of the crater contained a lava pool that had partially crusted over. Darker surfaces suggested recent activity from several vents in the crater.

Figure 180. The ~50-m-high half-cone that formed by a vent along the western wall of the Ol Doinyo Lengai north crater as seen on 29-30 November 2017. Several secondary vents were observed at the foot of the cone. In the lower right of the image, several pit structures are visible along the northern part of the crater. Photo courtesy of M. Kervyn, Vrije Universiteit Brussel.

Figure 181. Sporadic activity from an active vent in the northern-central part of the Ol Doinyo Lengai active crater was observed for two hours on 30 November 2017. Explosions were regularly heard emanating from the laval pool and jets of spatter were observed reaching up to 10 m above the crater and depositing on the wall and edges of the pit crater. Courtesy of M. Kervyn, Vrije Universiteit Brussel.

Sentinel-2 thermal satellite images acquired during 2017 show intermittent activity in the crater (figure 182). Out of 21 cloud-free images, 13 contained elevated thermal signatures between April through December. The locations of the activity move around the crater, indicating that the center of activity was variable through time. Lava pond activity was also noted in early December 2017 by Gian Schachenmann, documented with photos taken during an overflight and posted at Volcano Discovery.

Figure 182. Sentinel-2 thermal satellite images showing areas of high temperatures (bright orange to red) in the summit crater of Ol Doinyo Lengai through 2017. The hotpots show where current or very recent activity has occurred at the time of the satellite image acquisition. The active area moves around the crater throughout the year. False color (Urban) images (bands 14, 11, 4) courtesy of Sentinel Hub Playground.

On 1-2 July 2018, K. A. Laxton and F. Boschetty from University College London visited the summit, accompanied by local guides Papakinye Lemolo Ngayeni, Amadeus Mtui, and Ignas Mtui. Vigorous fumarolic activity was observed near the summit, with sulfur deposits and acrid-smelling gases. A small lava flow was observed that had cooled and turned from black to white by later that day. A pool of lava was observed inside a small hornito in the southern area of the crater floor (figure 183). A small cluster of hornitos were developing in the southern area of the crater and one produced a lava flow on 2 July (figure 184).

Figure 183. View of the crater floor at Ol Doinyo Lengai on 1 July 2018. Small inactive carbonatite flows that emanated from the collapse scar and flank vent on the NW hornito. An active hornito with a lava pool is visible in the center-bottom of the image and a semi-collapsed hornito is visible in the bottom-right. Courtesy of K. A. Laxton, University College London.

Figure 184. A view inside the active Ol Doinyo Lengai crater on 2 July 2018. New natrocarbonate flows are visible in the S and SE of the crater floor and one degassing vent is visible and one active vent is visible in the lower part of the image. A second lava flow from a vent just out of this view below the rim produced a lava flow that covered one third of the crater floor. Annotated image courtesy of K. A. Laxton, University College London.

A video taken by Patrick Marcel in August 2018 showed a recent lava flow that had occurred from a vent at the base of the crater wall and an active flow over-spilling from an active lava pond (figure 185). Throughout 2018, there were 18 out of 24 Sentinel-2 thermal cloud-free images which contained areas of elevated thermal activity. Like 2017, the 2018 activity was located in different areas around the crater (figure 186).

Figure 185. Scenes captured from a video taken in August 2018 show activity on the Ol Doinyo Lengai crater floor. A recent faded flow along the crater floor edge can be seen in the upper images and the active black lava lake with an active lava flow is seen in all images. Courtesy of Patrick Marcel.

Figure 186. Sentinel-2 thermal satellite images showing areas of high temperatures (bright orange to red) in the summit crater of Ol Doinyo Lengai through 2018. The hotpots show where current or very recent activity has occurred at the time of the image acquisition. Similar to activity in 2017, the active area moves around the crater throughout the year. False color (Urban) images (bands 14, 11, 4) courtesy of Sentinel Hub Playground.

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

Information Contacts: Matthieu Kervyn, Vrije Universiteit Brussel, Department of Geography, Pleinlaan 2, 1050 Brussels, Belgium (URL: http://we.vub.ac.be/en/matthieu-kervyn-de-meerendre); Kate Laxton and Felix Boschetty, University College London, Gower Street, London, WC1E 6BT, United Kingdom (URL: https://www.ucl.ac.uk/earth-sciences/people/research-students/kate-laxton); Patrick Marcel (URL: https://www.youtube.com/watch?v=ZqxuYOEFNLk); David Brown, School of Geographical and Earth Sciences, University of Glasgow, University Avenue, Glasgow G12 8QQ, United Kingdom (URL: https://www.gla.ac.uk/schools/ges/staff/davidbrown/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Gian Schachenmann, Volcano Discovery (URL: https://www.volcanodiscovery.com/nl/photos/ol-doinyo-lengai/dec2017/crater.html); Trip Advisor (URL: https://www.tripadvisor.com with initial search term 'Ol Doinyo Lengai').

Mayon is a frequently active volcano in the Philippines that produces ash plumes, lava flows, pyroclastic flows, and lahars. In early 2018, eruptive activity included lava fountaining that reached 700 m above the summit, and lava flows that traveled down the flanks and collapsed to produce pyroclastic flows (figure 39). Lava fountaining and lava flows decreased then ceased towards late March. Lava effusion was last detected on 18 March 2018, and the last pyroclastic flow for this eruptive episode occurred on 27 March 2018 (see BVGN 43:04). The hazard status for was lowered from alert level 4 to 3 (on a scale of 0 to 5) on 6 March 2018 due to decreased seismicity and degassing; the level was lowered again to 2 on 29 March. This report summarizes the activity during April through September 2018 and is based on daily bulletins issued by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) and satellite data.

Figure 39. Sentinel-2 thermal satellite images showing the lava flow activity at Mayon during January through March 2018. Three lava flow lobes flowed down the Mi-isi, Bonga-Buyuan, and Basud channels, and are shown in bright orange/red in these images. These are false color images created using bands 12, 11, 4, courtesy of Sentinel Hub Playground.

The hazard status remained on Alert level 2 (increasing unrest) throughout the reporting period. Activity was minimal with low seismicity (zero to four per day) and a total of 19 rockfall events throughout the entire period. White to light-brown plumes that reached a maximum of 1 km above the crater were observed almost every day from April through September (figure 40). Two short-lived light brown plumes were noted on 27 and 28 August and both reached 200 m above the crater.

Figure 40. An emission of white steam-and-gas at Mayon and a dilute brown plume that reached 200 m above the crater was seen on 24 May 2018. Courtesy of PHIVOLCS.

On the days that sulfur dioxide was measured, the amount ranged from 436 to 2,800 tons per day (figure 41). Mayon remains inflated relative to 2010 baselines but the edifice has experienced deflation since 20 February, a period of inflation from 2-14 April, and slight inflation of the mid-slopes beginning 5 May, which then became more pronounced beginning 25 June. No other notable inflation or deflation was described throughout the reporting period.

Figure 41. Measurements of sulfur dioxide output at Mayon during 1 April-30 September 2018. Data courtesy of PHIVOLCS.

Incandescence at the summit was observed almost every night (when weather permitted) from April through to the end of September 2018, and this elevated crater temperature is also seen in satellite thermal imagery (figure 42). Thermal satellite data showed a slight increase in output during April through to June, although not as high as the earlier 2018 activity, with a decline in thermal output starting in July (figure 43).

Figure 42. Sentinel-2 thermal satellite image showing an elevated thermal signature in the crater of Mayon and a steam-and-gas plume on 15 May 2018. Similar indications of activity in the crater were frequently imaged on cloud-free days from April through September. This is a false color image created using bands 12, 11, 4, courtesy of Sentinel Hub Playground.

Figure 43. Log radiative power MIROVA plot of MODIS thermal data for the year ending 11 October 2018 at Mayon. An elevated period of activity reflecting the lava flows in January through March is notable, followed by a second period of lower intensity activity during May into June, then a prolonged period of reduced activity through to the end of the reporting period; the August anomaly was not at the volcano. Courtesy of MIROVA.

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

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); 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).

Historical observations of eruptive activity on ice-covered Mount Michael stratovolcano on Saunders Island in the South Sandwich Islands were not recorded until the early 19th century at this remote site in the southernmost Atlantic Ocean. With the advent of satellite observation technology, indications of more frequent eruptive activity have become apparent. The last confirmed eruption evidenced by MODVOLC thermal alerts was during August-October 2015 (BGVN 41:02). Limited thermal anomaly data and satellite imagery since then have indicated intermittent activity through September 2018. Information for this report comes from MODVOLC and MIROVA thermal anomaly data and Sentinel-2, Landsat, and NASA Terra satellite imagery.

Evidence for thermal activity at Mount Michael tapered off in MIROVA data from October 2015 through January 2016. MODVOLC thermal alerts reappeared on 28 September 2016 and recurred intermittently through 6 January 2017. Low-level MIROVA thermal signals appeared in June and September-November 2017. During January-September 2018, evidence for some type of thermal or eruptive activity was recorded from either MODVOLC, MIROVA, or satellite imagery each month except for May and June.

Although MODVOLC thermal alerts at Mount Michael ended on 8 October 2015, the MIROVA radiative power data showed intermittent pulses of decreasing energy into early January 2016 (figure 10, BGVN 41:02). At a high-latitude, frequently cloud-covered site such as Saunders Island, this could be indicative of continued eruptive activity. A white plume in low resolution NASA's Terra satellite data was spotted drifting away from Saunders in April 2016, but no thermal activity was reported. The only high-confidence data available from April 2016 through May 2017 is from the MODVOLC thermal alert system, which recorded two thermal alerts on 28 September 2016, one the next day, one on 30 October, and eight alerts on four days in November. Activity continued into January 2017 with one alert on 17 December 2016, and six alerts on 2 and 6 January 2017 (figure 11).

Figure 11. Seventeen MODVOLC thermal alerts between 28 September 2016 and 6 January 2017 were the best evidence available for eruptive activity on Saunders Island from April 2016 through May 2017. Courtesy of MODVOLC.

A low-level log radiative power MIROVA signal appeared in early June 2017; two more signals appeared in September 2017, one in early October and one in late November (figure 12). Additional signals plotted as more than 5 km from the source may or may not reflect activity from the volcano. Steam plumes were visible in NASA Terra satellite images drifting away from the island in August, October, and December 2017, but no thermal signatures were captured.

Figure 12. The MIROVA log radiative power graph for Mount Michael on Saunders Island from 25 May-30 December 2017 showed intermittent heat sources that indicated possible eruptive activity each month except July and December. Location uncertainty makes the distinction between greater and less than 5 km summit distance unclear.

More sources of evidence for activity became available in 2018 with the addition of the Sentinel-2 satellite data during the months of February-April and September. Multiple thermal signals appeared from MIROVA in January 2018 (figure 13), and the first Sentinel-2 satellite image showed a distinct hotspot at the summit on 10 February (figure 14).

Figure 13. MIROVA thermal data for January-September 2018 indicated intermittent thermal anomaly signals in January, March, April, and July-September (top). A Sentinel-2 image with a hotspot was captured on 23 September, the same day as the MIROVA thermal signal (bottom). Courtesy of MIROVA.

Figure 14. A Sentinel-2 image of Saunders Island on 10 February 2018 revealed a distinct hotspot and small steam plume rising from the summit crater of Mount Michael. Sentinel-2 image with Atmospheric Penetration view (bands 12, 11, and 8A), courtesy of Sentinel Hub Playground.

A MODVOLC thermal alert appeared on 26 March 2019 followed by a significant hotspot signal in Sentinel-2 imagery on 29 March (figure 15). The hotspot was still present along with a substantial steam plume on 3 April 2018. Sentinel-2 imagery on 11 April revealed a large steam plume and cloud cover, but no hotspot.

Figure 15. Hotspots in Sentinel-2 imagery on 29 March and 3 April 2018 indicated eruptive activity at Mount Michael on Saunders Island. Sentinel-2 image with Atmospheric Penetration view (bands 12, 11, and 8A), courtesy of Sentinel Hub Playground.

MIROVA thermal signals appeared in mid-July and mid-August 2018 (figure 13) but little satellite imagery was available to confirm any thermal activity. The next clear signal of eruptive activity was evident in a Sentinel-2 image as a hotspot at the summit on 23 September. A small MIROVA signal was recorded the same day (figure 13, bottom). A few days later, on 28 September 2018, a Landsat 8 image showed a clear streak of dark-gray ash trending NW from the summit of Mount Michael (figure 16).

Figure 16. Satellite imagery confirmed eruptive activity at Mount Michael on Saunders Island in late September 2018. Top: a hotpot in a Sentinel-2 image on 23 September coincided with a MIROVA thermal signal (see figure 13); Bottom: A Landsat 8 image on 28 September has a distinct dark gray streak trending NW from the summit indicating a fresh ash deposit. The lighter gray area SW of the summit is likely a shadow. Sentinel-2 image with Atmospheric Penetration view, (bands 12, 11, and 8A), Landsat 8 image with pansharpened image processing, both courtesy of Sentinel Hub Playground.

Geologic Background. Saunders Island is a volcanic structure consisting of a large central edifice intersected by two seamount chains, as shown by bathymetric mapping (Leat et al., 2013). The young constructional Mount Michael stratovolcano dominates the glacier-covered island, while two submarine plateaus, Harpers Bank and Saunders Bank, extend north. The symmetrical Michael has a 500-m-wide summit crater and a remnant of a somma rim to the SE. Tephra layers visible in ice cliffs surrounding the island are evidence of recent eruptions. Ash clouds were reported from the summit crater in 1819, and an effusive eruption was inferred to have occurred from a N-flank fissure around the end of the 19th century and beginning of the 20th century. A low ice-free lava platform, Blackstone Plain, is located on the north coast, surrounding a group of former sea stacks. A cluster of parasitic cones on the SE flank, the Ashen Hills, appear to have been modified since 1820 (LeMasurier and Thomson, 1990). Analysis of satellite imagery available since 1989 (Gray et al., 2019; MODVOLC) suggests frequent eruptive activity (when weatehr conditions allow), volcanic clouds, steam plumes, and thermal anomalies indicative of a persistent, or at least frequently active, lava lake in the summit crater. Due to this observational bias, there has been a presumption when defining eruptive periods that activity has been ongoing unless there is no evidence for at least 10 months.

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

Historical eruptions at Chile's Villarrica, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. An intermittently active lava lake at the summit has been the source of explosive activity, incandescence, and thermal anomalies for several decades. A large explosion on 3 March 2015 included a 9-km-altitude ash plume; significant thermal anomalies from intermittent Strombolian activity at the lava lake and small ash emissions have continued since that time. Sporadic but reduced activity during November 2017-August 2018 is covered in this report, with information provided primarily by the Southern Andes Volcano Observatory (Observatorio Volcanológico de Los Andes del Sur, OVDAS), part of Chile's National Service of Geology and Mining (Servicio Nacional de Geología y Minería, SERNAGEOMIN), and Projecto Observación Villarrica Internet (POVI), part of the Fundacion Volcanes de Chile, a research group that studies volcanoes across Chile.

Seismicity increased during the second half of November 2017, along with observations of increased incandescence at night from occasional explosions inside the summit crater. Satellite instruments measured a brief surge of thermal activity from late November through early December. The next episode of increased activity occurred in the second half of February 2018 with minor satellite thermal data and webcam views of incandescence. A slow but sustained increase in energy was recorded during March 2018; sporadic incandescence was reported a few times each month between March and May, but observations indicated that the lava lake level was over 100 m below the crater rim. Satellite and webcam observations of incandescence increased in frequency and intensity during June; sporadic ash emissions were noted during mid- and late July. Continuous incandescence was observed in webcams during August 2018; satellite thermal data identified an abrupt rise in thermal energy in late July that remained at a low level into early September 2018.

Activity during November 2017-January 2018. OVDAS reported that during November 2017, the webcams near the summit showed evidence of low-intensity, predominantly white degassing to low altitudes (100 m above the summit). Nighttime incandescence associated with occasional explosions inside the crater were typical. They also noted that long-period (LP) seismicity increased in both energy amplitude and frequency during the last few days of the month. A gradual increase in RSAM values began on 15 November with a continuous tremor signal. A magnitude 4.1 event occurred on 24 November located 2.6 km ESE of the summit at a depth of 1.8 km. A single MODVOLC thermal alert was reported on 28 November. According to POVI the lava lake on the crater floor subsided 8 m between 10 and 20 November (figure 54); during the second half of the month they documented 50-m-high lava fountains, spatter on the crater rim, incandescent jets, and fresh ashfall on the snow cover around the crater rim (figures 55 and 56).

Figure 54. The SW part of the crater floor at Villarrica subsided about 8 m between 10 and 20 November 2017. Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

Figure 55. During the second half of November 2017, POVI documented 50 m high lava fountains, spatter on the crater rim, incandescent jets, and fresh ashfall on the snow cover around the crater rim at Villarrica. Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

Figure 56. A sample of reticulite or basaltic pumice collected on 28 November 2017 from the summit of Villarrica. It is a highly vesiculated scoria, with greater than 98% porosity. Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

On 5 December 2017, SERNAGEOMIN raised the Alert Level at Villarrica from Green to Yellow (on a 4-level scale), noting a progressive increase in seismic and thermal energy since 15 November. They increased the restricted radius from 500 to 1,000 m from the summit crater. SERNAGEOMIN reported low-intensity degassing during the first half of December 2017, mostly white, and rising not more than 650 m above the crater. Incandescence was visible on clear nights, with occasional explosions that remained below the crater rim. They reported that increased surficial activity was visible during the first few days of December, followed by a decrease in activity (figure 57). POVI images at the end of December (figure 58) showed that the lake level had dropped more than 45 m between 5 and 27 December 2017. Seismicity also decreased throughout the month, reaching its lowest level of the year at the end of December.

Figure 57. POVI reported that on 9 December 2017 at Villarrica the level of the lake at the bottom of the crater was stable at about 70 m below the rim, and five days had passed with no observations of lava ejecta in the webcams. Images by Víctor Marfull, courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

Figure 58. The lava lake at Villarrica subsided more than 45 m between 5 and 27 December 2017 when this image was taken. Seismic activity also decreased significantly throughout December, reaching its lowest level of the year. Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

On 6 January 2018 SERNAGEOMIN lowered the Alert Level to Green, noting a reduced thermal signal, low-level white degassing rising less than 300 m above the crater, and only occasional nighttime incandescence associated with explosions below the crater rim during the second half of December. POVI noted that the drop in seismicity at the end of December corresponded to the end of a 17-month-long period of increased seismicity (figure 59).

Figure 59. The drop in seismicity at the end of December 2017 suggested the end to a 17-month-long period of increased seismicity that began in July 2016 after a similar decrease in activity at the end of June 2016. Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

Activity during February-August 2018. Activity remained low at Villarrica during January 2018. Steam plumes rose less than 550 m above the crater and no thermal activity was apparent. After about six weeks of low activity, Sentinel-2 images indicated an increase in thermal activity between 5 and 18 February 2018 (figure 60). The Villarrica webcam also recorded incandescence at the summit for the first time in two months on 25 February 2018.

Figure 60. After about six weeks of low activity at Villarrica, Sentinel-2 images indicated an increase in thermal activity between 5 and 18 February 2018. Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

While SERNAGEOMIN reported only white degassing to less than 50 m above the summit in March 2018, POVI noted that seismic instruments recorded a slow but sustained increase in released energy. The lava lake was not visible and remained more than 110 m below the crater rim; a small spatter event was detected by a webcam on 7 March 2018 (figure 61). Sporadic incandescence, including on 13 and 20 March, was captured with a webcam located in Pucón, about 16 km N of the summit.

Figure 61. The surface of the lava lake at the summit of Villarrica remained more than 110 m below the crater rim on 6 March 2018. A small spatter of lava was detected by one of the POVI cameras on 7 March 2018, but little other activity was recorded. A slow but sustained increase in seismic energy was evident in the seismic amplitude data (inset). Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

A research effort in mid-March 2018 by Liu et al. (2019) to capture gas emissions close to the vent using Unmanned Aerial Systems (UAS) demonstrated good agreement between gas ratios obtained from simultaneous UAS- and ground-based multi-GAS acquisitions. The UAS measurements, however, taken from the young, less diluted gas plume revealed additional short-term patterns that reflected active degassing through discrete, audible gas exhalations (figures 62 and 63).

Figure 62. A research expedition to Villarrica on 20 and 21 March 2018 demonstrated the effectiveness of Unmanned Aerial Systems (UAS) in measuring gas emissions close to an active vent. a) This view to the SE shows Lanin and Quetrapillan volcanoes in the distance behind the summit of Villarrica. (b, c) The lava level was extremely low in the conduit during the measurement campaign, with the lake surface only visible as several pixels in aerial imagery. (d) Unmanned Aerial Systems (UAS) were launched from a sheltered plateau on the N rim of the crater, with the multi-GAS station visible on the eastern rim. (e, top right) Location map of the region, showing the position of UV camera. The green shaded region delimits the extent of the national park. Inset: Aerial map of the summit region shown in (d); the summit crater is ~200 m in diameter. (e, bottom left) Two instrumented multi-rotor vehicles were used in the campaign, the Vulcan octocopter with multi-GAS (left) and DJI Phantom 3 Pro with Aeris gas sensor (right). (f) Vulcan UAS in flight on 20 March 2018. UAV = Unmanned Aerial Vehicle. Taken from Figure 1 of Liu et al. (2019).

Figure 63. A comparison between contemporaneous proximal UAV and crater rim SO2 measurements at Villarrica. (a) The same-scaled axis highlights the magnitude of plume dilution between the proximal measurements from the UAV made directly above the conduit and those made at the crater rim only 100 m downwind. (b) When the time series are displayed on individually scaled axes it is apparent that even considering the temporal offset imposed by the downwind travel time, the periodic component of the proximal UAV trace is indistinguishable in the crater rim data. Taken from Figure 6 of Liu et al. (2019).

A minor collapse of the crater wall caused a small plume of ash that rose a short distance above the summit on 29 March 2018. POVI's time-lapse webcams located in Pucón captured the event. Overnight on 1-2 April, sporadic incandescence was observed in the webcams and in Sentinel-2 satellite imagery. SERNAGEOMIN reported a single MIROVA alert signal on 13 April and an abrupt fall of the seismic signal on 27 April. The POVI webcam captured the brightest incandescence since mid-December 2017 on 3 May 2018. SERNAGEOMIN reported incandescence at the summit again on 23 May, and two thermal alerts on 22 and 25 May 2018.

While gas emissions remained less than 150 m above the summit during June 2018, observations of incandescence at night increased and were reported on 14, 18, 24, and 28 June, and were accompanied by satellite thermal signals on 14 and 24 June. Sporadic ash emissions that reached 400 m above the summit were reported by SERNAGEOMIN during July. The POVI webcam in Pucón captured an ash emission on 16 July 2018 that left ash and pyroclastic debris around the crater rim (figures 64 and 65). A second emission was recorded on 18 July;the Sentinel-2 satellite recorded the largest summit thermal signature since 10 December 2017 the same day.

Figure 64. A steam and ash emission at Villarrica on 16 July 2018 was captured by the POVI webcam. Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

Figure 65. Ash and pyroclastic debris were deposited around the inside rim of the crater at Villarrica on 16 July 2018. Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

Activity continued to increase during July 2018; POVI photographed significant incandescence at the summit on 19 July and again on 25, 29, and 30 July after a period of cloudy weather. ESA's Sentinel-2 camera measured the largest heat area on the summit since August 2015 on 30 July (figure 66). As a result, the interior of the crater lost much of its snow cover and ice (figure 67). Ash and lapilli were visible in satellite imagery on the eastern edges of the crater.

Figure 66. On July 30 2018 ESA's Copernicus program satellite, Sentinel-2, measured the largest heat area on the summit of Villarrica since August 2015. Due to the heat, the interior of the crater had lost much of its snow cover and ice. Ash and lapilli stand out on the eastern edges of the crater. Left: terrestrial images (objective 120 mm, 0.0001 lux), center: Sentinel-2, filters bands 8, 4 and 3; Right: Sentinel-2, filters bands 12, 11 and 4. Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

Figure 67. Sequential images of the Sentinel-2 satellite (ESA), with filters of bands 8, 4, and 3, illustrate the evolution of the heat surface emitted by the lava pit, and the decrease in snow and ice within and around the crater rim between 8 July and 2 August 2018. Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

SERNAGEOMIN reported continuous incandescence at the summit during August nights when the weather was clear. POVI noted on 31 August 2018 that the lake level had not changed during the month and was about 75 m below the inner W rim of the crater. The lake level remained unchanged during the first 10 days of September 2018 as well (figure 68).

Figure 68. The lava lake level at the bottom of the summit crater of Villarrica was unchanged during the first 10 days of September 2018. Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

The thermal signature in the MIROVA graph for the period from October 2017 through August 2018 showed two clear increases in thermal energy between late November and mid-December 2017, and again from mid-June through August 2018 (figure 69). These corresponded well with MODVOLC thermal alert data which recorded one alert on 28 November 2017, 10 alerts during 2-11 December 2017, and five alerts between 30 July and 2 August 2018.

Figure 69. MIROVA thermal anomaly graph of log radiative power at Villarrica from 28 September 2017 through August 2018 shows two clear increases in activity, one in mid-November through mid-December 2017 and a second longer-lived phase that began in June 2018, peaked in late July-early August, and remained steady throughout the month of August. Courtesy of MIROVA.

Reference: Liu, E. J., Wood, K., Mason, E., Edmonds, M., Aiuppa, A., Giudice, G., Bitetto, M., Francofonte, V., Burrow, S., Richardson, T., Watson, M., Pering, T.D., Wilkes, T.C., McGonigle, A.J.S., Velasquez, G., Melgarejo, C., and Bucarey, C., 2019. Dynamics of outgassing and plume transport revealed by proximal unmanned aerial system (UAS) measurements at Volcán Villarrica, Chile. Geochemistry, Geophysics, Geosystems, 20. https://doi.org/10.1029/2018GC007692

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

Information Contacts: Servicio Nacional de Geología y Minería (SERNAGEOMIN), Observatorio Volcanológico de Los Andes del Sur (OVDAS), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); Proyecto Observación Villarrica Internet (POVI) (URL: http://www.povi.cl/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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/).