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).

Our last report on Cumbal volcano (BGVN 19:07) highlighted fumarolic activity from the NE craters, and monitoring efforts by scientists collaborating with the Servicio Geológico Colombiano (SGC). The SGC (formerly known as Instituto Colombiano de Geología y Minería, “INGEOMINAS”) monitors the volcano from Pasto, ~72 km NE of Cumbal (figure 3). In this report we describe field observations during 2005-2012, significant new monitoring instruments installed during 2008-2012, and episodes of seismic unrest. Earthquake swarms during 2011 and 2012 accompanied increased fumarolic activity.

Figure 3. This 2008 map of the Cumbal region indicates locations of telemetered monitoring instruments (see legend), major towns (black labels), and nearby volcanoes (yellow text; red text for Cumbal). Yellow text is also used for the radio repeater at “Cruz de Amarillo” ~65 km ENE of Cumbal volcano. More instruments were added to the system later. Courtesy of SGC.

SGC maintained Alert Level Green (Level IV, the lowest status on a 4-step system; figure 4) with two exceptions. Reduced monitoring during May-July 2010 caused the status to be unassigned during that time. Elevated seismicity and emissions noted in June 2012 raised the status from Green (Level IV) to Yellow (Level III) signifying detected “changes in behavior of the volcanic system.”

Figure 4. This pictogram describes the volcano Alert Levels used for communicating hazards in Colombia (translated from original in Spanish). This is a four-step system similar to the USGS volcanic activity alert-notification system (Gardner and Guffanti, 2006), except that each step is numbered in addition to having a color code: Green (Level IV), Yellow (Level III), Orange (Level II), and Red (Level I). All SGC observatories (based in Pasto, Popayán, and Manizales) apply this qualitative system. Courtesy of SGC.

Local hazard map. SGC published a hazard map in 1988 for the region surrounding Cumbal (figure 5). The three asymmetrical hazard zones, high (red), medium (orange), and low (yellow), are at risk for ashfall and pyroclastic flows.

Figure 5. This hazard map for Cumbal volcano was developed in 1988 by Ricardo Méndez and María Luisa Monsalve of INGEOMINAS (now the Servicio Geológico Colombiano). Three major zones delineate high, medium, and low risk. Note that ashfall could occur in any of the three zones. Courtesy of SGC.

Areas at highest risk, in the red zone, could be affected by lava and pyroclastic flows, especially within the narrow valleys of Chiquito, Blanco, and Río Grande. Ashfall, ballistics, mudflows, and gas emissions could also occur as far away as ~8 km from the summit. Areas at medium risk, the orange zone, could also be affected by pyroclastic flows, ashfall, and mudflows over an area extending up to 14 km SE from the summit, encompassing the town of Cumbal. Areas at lowest risk, yellow zone, is located primarily downwind of the volcano where pyroclastic flows and ashfall could occur; this zone extends beyond the view of the map.

Monitoring efforts. Aerial investigations conducted since 2005 revealed persistent plumes rising from Cumbal’s NE craters, El Verde and La Plazuela (figure 6; see also figure 2 in BGVN 19:07 for an annotated sketch map of the summit craters). In their online Technical Bulletins, SGC emphasized the frequency of plumes from this region that were documented since at least 1988.

Figure 6. Cumbal is an elongate volcano with multiple peaks. In 2005 and 2007, clear conditions provided views of plumes rising from Cumbal’s summit craters, El Verde and La Plazuela. (top) On 29 January 2007, white plumes rose from the fumaroles El Verde and Rastrojo; the look direction is N. (bottom) On 29 December 2005, discrete plumes were visible from the fumaroles El Verde (1), El Tábano (2), and La Desfondada (3); the look direction is NNW. Some snow had collected along the ridges and a small pond of water was visible within La Plazuela crater that day. Courtesy of SGC.

To help understand Cumbal’s state, SGC installed seismic and electronic tilt equipment in late 2008 (figure 3). The La Mesa (2.5 km ESE) and Limones (2 km SE) stations had electronic tilt and short-period seismic instrumentation (figure 7). During installation on 24 September 2008, technicians observed steam plumes rising from the fumarolic areas El Verde and La Plazuela (figure 8).

Figure 7. This satellite image-based map includes upgrades in Cumbal’s monitoring network as of 2012. Courtesy of SGC.

Figure 8. Clear conditions revealed the pale, fumarolic summit area of Cumbal during the mornings of two days in September 2008. (top) Two white plumes seen at 0704 on 24 September 2008; the smaller plume (center) rose from La Plazuela crater while the larger plume (to the right) rose from El Verde. Emissions from these sites have been noted since the late 1980s. This photograph was taken from a location ~6.5 km SE from the summit. (bottom) From the center of town, near the Cumbal Nariño Temple, the view NW toward Cumbal’s summit and fumarolic sites was clear on 25 September 2008. Courtesy of SGC.

In June 2009, SGC installed a broadband seismometer at Limones station, upgrading from the short-period sensor. Unfortunately, monitoring capabilities were significantly reduced when, in December 2009, vandals stole station instrumentation at this site.

Data from the remaining station, La Mesa, was only acquired intermittently during January-June 2010 owing to radio repeater problems. From May to July, the Alert Level status went unassigned, but upon repair of the system, later returned back to Green (Level IV).

In August 2010 a short-period seismic station (CUMZ) came online (figure 7). This station was maintained by the National Seismological Network of Colombia (RSNC). The electronic tiltmeter at La Mesa was offline during August-November 2010 due to electronic malfunctions.

In November and December 2011, SGC collaborated with the Colombia Air Force (FAC) to conduct overflights of the volcanic complex. In addition to aerial photos and observations, a thermal camera was used to determine the hotspot distribution and measure temperatures for those sites (figure 9).

Figure 9. This thermal image was taken during an overflight of Cumbal’s summit on 27 November 2011. The look direction was approximately S with El Verde (43.6°C) and the highest part of La Plazuela’s rim (34.5°C) showing the highest temperatures. Steam plumes rising from the craters partly obscured the view. Courtesy of FAC and SGC.

Monitoring capabilities were expanded when SGC installed an infrasound sensor at the La Mesa monitoring site in March 2012 and a webcamera was installed in the town of Cumbal (~11 km SE) in May (figure 10). During March-December 2012, white plumes were frequently observed rising from Cumbal’s fumarolic sites.

Figure 10. An image taken by the new Cumbal webcamera on 23 May 2012. The black arrow points to the source of the strongest plumes, El Verde crater. Courtesy of SGC.

The Limones short-period seismometer was back online in October 2012. Additionally, two new stations, Nieve and Punta Vieja (figure 7), were added to the network in December; these stations had broadband seismic and electronic tilt equipment.

Summit fumarole monitoring. During 2010-2012, SGC conducted field campaigns to monitor Cumbal’s summit fumarolic sites. Three fumaroles (Desfondada, El Verde, and El Rastrojo) were visited during this time period with repeat observations and measurements. Lab analyses were conducted at the Manizales Volcanological and Seismological Observatory.

The Desfondada fumarole, located near the W rim of La Plazuela crater (see the sketch map in figure 2 in BGVN 19:07), was visited only once for sampling with the Giggenbach bottle method in August 2010; this site had a relatively high temperature, 278.4°C. The other sites were visited frequently and also sampled to determine gas species and condensates (table 1).

Table 1. Maximum temperatures measured from Cumbal's fumaroles during 2010-2012 at Desfondada, El Rastrojo, and El Verde. Site locations appear in figure 2 of BGVN 19:07, while the location of El Rastrojo is closest to the S-most crater of the complex, Mundo Nuevo. Courtesy of SGC.

The earliest measured temperature from El Verde (in August 2010) yielded the highest value of the three fumaroles (313°C). Compared with temperatures measured in 1994 (378°C, BGVN 19:07), El Verde’s values were slightly lower; however, the three available temperatures from 2010 and 2012 were within the measured range determined by SGC field campaigns conducted during previous years (BGVN 19:07).

The El Rastrojo site was located ~1.6 km SW of the summit (figure 11); this fumarolic area, on the outer edge of Mundo Nuevo crater regularly emitted plumes and had temperatures in the range 104-178.9°C.

Figure 11. On 27 November 2011, white plumes were visible rising from fumarolic features along the ridge of Cumbal volcano. (top) This oblique view of Cumbal is centered on Mundo Nuevo crater, the SW crater of the ~2 km-long volcanic complex. The area highlighted in red shows the location of El Rastrojo, an active fumarolic site that frequently emitted white plumes and was monitored by SGC. White plumes also emerge from La Plazuela and El Verde craters in the middle-ground (near the right edge of the image). (bottom) In this zoomed image (clipped from the top image), a short column of white vapor rises from El Rastrojo fumarole. This area is a scree slope where several large boulders are discolored by yellow sulfur deposits. Courtesy of SGC.

Hot spring investigations. Inferred magmatic compositions were detected from hot springs during 1988-1996 (Lewiki and others, 2000). Field investigators sampled from sites located within the central crater and from sites along the SE flank, up to 10 km from the summit and towards the town of Cumbal (figure 12). However, they concluded that “from 1995 to 1996, geochemical data show increasing hydrothermal signatures, suggesting a decline in magmatic volatile input.”

Figure 12. This sketch map of Cumbal and the surrounding area highlights the locations of hot springs. During 2010-2012, SGC monitored four of these sites: El Salado (“S”), Cuetial (“C”), El Zapatero (“Z”), and Hueco Grande (also known as Quebrada el Corral, “QC”). Note that the generalized name “Cumbal Crater” is assigned to the area of La Plazuela and El Verde craters. Modified from Lewiki and others (2000).

During 2010, SGC monitored four hot springs for temperature and chemical changes. Results from sampling during May, August, and November 2010 determined chemical classifications for the springs El Salado, Cuetial, El Zapatero, and Hueco Grande (figure 13).

Figure 13. Based on geochemical results from investigations in May (triangles), August (squares), and November 2010 (circles), SGC scientists classified four of Cumbal’s hot springs. Within this ternary diagram, the datapoints were generally well within the “Periferal Water” (Aguas Periféricas, significant HCO3) class. Datapoints from Hueco Grande, approached the “Volcanic Water” (translated from Spanish “Aguas Calentadas por Vapor,” significant SO4) class than the others. No datapoints were within the “Mature Water” (Aguas Maduras, significant Cl) class. Courtesy of SGC.

Sampling and analysis of the four hot springs continued during 2011-2012. SGC maintained a growing database of characteristics from these springs and released the results in online bulletins. In particular pH, temperature, conductivity, and concentrations of carbonates were repeatedly measured. During this time period, pH values measured from the hot springs were in the range of 5.9-7.3; temperatures were 26.4-34.4°C (the highest values were from Cuetial spring); conductivity values (Oxidation-Reduction Potential, “ORP”) ranged from 7.7-42.2 mV (highest values were from Cuetial and the lowest was from Hueco Grande springs); bicarbonate (HCO₃) concentrations were 271.7-1,008.0 mg/L (the highest value was obtained from El Zapatero spring).

Cumbal seismicity. When the seismic stations Limones and La Mesa came online in late 2008, SGC began characterizing Cumbal’s seismicity based on the following interpretive scheme:

• Hybrid (HYB): Seismicity associated with signals characterizing fracturing and fluid movement.

• Long period (LPS): Seismicity associated with unsteady fluid movement (magma or hydrothermal fluids, for example).

• Tremor (TRE): Seismicity associated with fluid movement in which the source behaves in a sustained manner.

• Tornillo (TOR): Seismicity associated with fluid movement in which subterranean structures are linked with special conditions in such a manner that makes the cavities resonate. In their January 2009 online bulletin, SGC acknowledged that tornillo earthquakes have been an important indicator of eruptive activity at Galeras volcano, but the occurrence of the same signature at Cumbal volcano required additional analysis before associating specific unrest with this seismicity.

• Volcano-tectonic (VT): Earthquakes associated with brittle failure events caused by magma movement.

• Unclassified volcanic (VOL): Earthquakes from the region of Cumbal that do not correspond with the other classes; SGC stated that these events will be analyzed in more detail after more baseline data is collected. This category was also applied to seismic analyses of Doña Juana, a volcano that was instrumented around the same time (see report on Doña Juana in BGVN 38:01).

Seismicity in 2009. During 2009, as SGC began to establish baseline data for Cumbal’s seismicity, a wide range of earthquake classes was detected (figure 14). LPS and VT events dominated the records and TRE, HYB, and TOR earthquakes were also detected (in order of decreasing occurrence). TOR earthquakes occurred more frequently during August to early December. Due to vandalism, the 2009 record ended on 13 December 2009.

Figure 14. The daily seismicity detected from Cumbal during 2009 in three plots that display January-August, August-November, and 1-13 December. Five different classes of earthquakes were tallied daily (VT, HYB, TRE, LPS, and TOR). Data gaps are attributed to station outages and time periods requiring re-processing; gray regions signify the reporting period in which the plots appear. Courtesy of SGC.

Seismicity in 2010. From January to July 2010, La Mesa station detected earthquakes intermittently and the Limones seismic station remained offline. When the network connection was re-established for La Mesa in late July, LPS earthquakes again dominated the records through the end of December (figure 15).

Figure 15. Daily seismicity from Cumbal during 1 September-31 December 2010 was dominated by LPS events. Six different classes of earthquakes were tallied daily (VT, LP, TRE, HYB, TOR, and VOL); the gray region highlights the month when the plot was released online. Courtesy of SGC.

Seismicity in 2011. LPS, VT, and HYB events dominated seismicity at Cumbal for most of 2011; more VOL events occurred than HYB, but this category was described as temporary until more analysis is possible (table 2 and figure 16). Data quality enabled some events to be located and some swarms were apparently driving a several-fold increase in monthly counts. Until November 2011, TOR events were occurring ~5 times per month and TRE were occurring ~13 times per month. In November, seismicity increased significantly and SGC reported that several earthquake swarms had occurred; in particular, one event occurred on 18 November. A swarm of LPS earthquakes also occurred during 20-21 and on 31 December. Epicenters could not be calculated from the data and there were no reports of felt earthquakes.

Table 2. Monthly seismicity at Cumbal was tabulated by the occurrence of events: VT, LPS, TRE, HYB, TOR, VOL, and the overall total. Courtesy of SGC.

Figure 16. Cumbal earthquakes tallied by month based on event class during 2011-2012. Elevated seismicity persisted during November 2011-January 2012, particularly VT, LPS, and TRE. The “TOTAL” class is the sum of VT, LPS, TRE, HYB, TOR, and VOL earthquakes for each month (see table 2 for values). Courtesy of SGC.

Seismicity in 2012. SGC reported that seismic swarms continued to occur in January 2012. The swarm that began at 2200 on 31 December 2011 continued until 1 January 2012 and a total of 211 LPS events were detected. Two more swarms occurred later that month, amounting to a total of 274 earthquakes. Seismicity declined during February-April but swarms reappeared: in May, one; in July, five; in August, two; in September, six; in October, six; in November, seven.

Due to elevated seismicity, persistent swarms, and observations of increased emissions from El Verde and La Plazuela, SGC announced on 10 July that the Alert Level was raised to Yellow (Level III). This status was maintained through December 2012. In their online July 2012 Activity Report, SGC noted that residents in the area had also reported notable gas emissions, seismicity, and possible noises associated with earthquakes.

Epicenters of Cumbal’s VT earthquakes were calculated during July-December 2012 and located on regional maps (table 3). Earthquake locations tended to be dispersed throughout the region, although some clustering was notable between 2 and 6 km of the summit region and at depths less than 12 km (as measured from the summit elevation) (figure 17).

Table 3. VT earthquakes from Cumbal during July-December 2012 tended to be low-magnitude events at shallow depths. This table compiles announcements from weekly activity reports; the date listed corresponds to the release date of the information. During the listed weeks, VT events were often clustered; SGC made special note of events that were clustered between La Plazuelas and Mundo Nuevo (“Cent.”) and events that were dispersed (“Disp.”). Depths were measured as km below the summit. Magnitudes were not available (“na”) during the week of 18 December. Courtesy of SGC.

Figure 17. A total of 97 volcano-tectonic earthquakes were located during December 2012 within the region of Cumbal volcano. Five seismic stations (dark red squares) were online near the volcano: LIMC (Limones), MEVZ (La Mesa), NIEV (Nieve), VIEZ (Punta Vieja), and CUMZ (the RSNC Cumbal station). Earlier in the month, VTs were primarily dispersed in the region while later in the month, they were more clustered around the edifice and N (table 3). Courtesy of SGC.

In September, October, and November 2012, during field investigations at various locations around Cumbal’s flanks, SGC scientists also noted increased emissions from the summit fumaroles. In particular, white plumes were strong from El Verde and El Rastrojo fumaroles.

Geodetic monitoring during 2009-2010. Electronic tilt data available during 2009 showed oscillations within the expected range of the instruments. During 2010, while instrumentation was reduced and electronic problems persisted, tilt records continued to show minor variations. In July, a decreasing trend was observed from the tangential component of La Mesa tiltmeter (figure 18). Unfortunately, the instrument was offline from August through November. When monitoring resumed in December, no deformation trends were noted.

Figure 18. The two components of the La Mesa electronic tiltmeter recorded stable conditions from Cumbal’s SW flank (in the Mundo Nuevo region) during 1 January-31 July 2010. The four plots, from top to bottom, contain radial tilt component (in µrad), tangential tilt component (in µrad), temperature (°C), and voltage (V) data. Note that minor variations in temperature and daily variations in the voltage correspond to the recharging cycle controlled by the solar panels and consequent voltage drain at night. The gray shaded section represents the reporting period when the data was published online. Courtesy of SGC.

Geodetic monitoring during 2011-2012. In their April 2011 Technical Bulletin, SGC highlighted the onset of a decreasing trend in La Mesa’s tangential data; the trend began on 30 April and continued to 30 June for a total decrease of ~25 µrad (figure 19); this trend ended in July. A period of increasing tilt began on 29 September and ended on 30 November 2011 (total increase was ~35 µrad). The signal from La Mesa station (effecting electronic tilt as well as seismic records) was intermittent in August. From December 2011 through December 2012, fluctuations persisted in the tilt data; however, stable conditions were characteristic of 2012 deformation.

Figure 19. Tilt record of Cumbal during 2011 (tangential component on top plot, radial on bottom). In their Technical Bulletins, SGC highlighted several trends that became apparent in the tangential data from La Mesa station; a decreasing event began at the end of April reaching a total decrease of ~25 µrad by late June. The station detected an increase in tilt of equal magnitude in late September and ending by late November. Courtesy of SGC.

References. Gardner, C.A., and Guffanti, M.C., 2006, U.S. Geological Survey’s Alert Notification System for Volcanic Activity, U.S. Geological Survey, Fact Sheet 2006-3139, Version 1.0.

Lewiki, J.L., Fischer, T., and Williams, S.N., 2000, Chemical and isotopic compositions of fluids at Cumbal Volcano, Colombia: evidence for magmatic contribution, Bulletin of Volcanology, 62: 347-361.

Geologic Background. Many youthful lava flows extend from the glacier-capped Cumbal volcano, the southernmost historically active volcano of Colombia. The volcano is elongated in a NE-SW direction and is composed primarily of andesitic-dacitic lava flows. Two fumarolically active craters occupy the summit ridge: the main crater on the NE side and Mundo Nuevo crater on the SW. A young lava dome occupies the 250-m-wide summit crater, and eruptions from the upper E flank produced a 6-km-long lava field. The oldest crater lies NNE of the summit crater, suggesting SW-ward migration of activity. Explosive eruptions in 1877 and 1926 are the only known historical activity. Thermal springs are located on the SE flanks.

Information Contacts: Servicio Geológico Colombiano (SGC), Observatorio Vulcanológico y Sismológico de Pasto, Pasto, Colombia (URL: http://www.SGC.gov.co/Pasto.aspx).

Our previous report on Izu-Tobu (BGVN 23:04) summarized the elevated seismicity that began on 20 April 1998 in the eastern Izu Peninsula and started declining around 10 May. The activity included crustal deformation, indicating inflation likely linked to shallow magmatic activity. Izu-Tobu is located 100 km SW of Tokyo and just inland from the coast on the Izu peninsula.

Recent reports from the Japan Meteorological Agency (JMA) noted the Tohoku megathrust of March 2011, centered 400 km to the NE of Izu-Tobu, and that Izu-Tobu lacked any signs of correlated behavior as a result of that M 9.0 earthquake event and the numerous aftershocks.

Izu-Tobu had been quiet since March 2011 until 17 July when seismicity increased and small earthquakes with epicenters around Ito city (8.5 km N) were detected. Earthquakes on 18 July were M 2.5 and M 2.8 (interim values). A maximum seismic intensity of 1 on the JMA scale was observed in Ito-city and Higashi-Izu town (15 km SSW). Seismicity declined to the usual background level the following day. Ground deformation was observed around seismically active areas.

Seismicity along an area from Arai (8 km N) through offshore Shiofuki-zaki (2 km E of Ito-city), increased during 18-23 August 2011, then declined after 24 August. No earthquakes were observed until 22 September when the number of earthquakes temporarily increased at a shallower area around Usami; this activity was interpreted as not being directly related to magma intrusion.

Prior to the 22 September 2011 seismic activity, the volumetric strainmeter at Higashi-Izu town (15 km SSW) showed continuous contraction; the tiltmeter at Ito-city showed an apparent change on 18 September. The trend slowed as seismicity decreased; no change was observed after 23 September. GPS measurements did not exhibit remarkable changes and low-frequency earthquakes and tremor were not observed. The Alert Level at Izu-Tobu remained at 1.

Geologic Background. The Izu-Tobu volcano group (Higashi-Izu volcano group) is scattered over a broad, plateau-like area of more than 400 km2 on the E side of the Izu Peninsula. Construction of several stratovolcanoes continued throughout much of the Pleistocene and overlapped with growth of smaller monogenetic volcanoes beginning about 300,000 years ago. About 70 subaerial monogenetic volcanoes formed during the last 140,000 years, and chemically similar submarine cones are located offshore. These volcanoes are located on a basement of late-Tertiary volcanic rocks and related sediments and on the flanks of three Quaternary stratovolcanoes: Amagi, Tenshi, and Usami. Some eruptive vents are controlled by fissure systems trending NW-SE or NE-SW. Thirteen eruptive episodes have been documented during the past 32,000 years. Kawagodaira maar produced pyroclastic flows during the largest Holocene eruption about 3000 years ago. The latest eruption occurred in 1989, when a small submarine crater was formed NE of Ito City.

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

This report discusses eruptive highlights at Kilauea during 2009, with occasional reference to earlier and later events. Within the E rift zone, Pu`u `O`o crater was relatively quiet during 2009, while lava flows escaping from the Thanksgiving Eve Breakout (TEB) tube system continued to feed emissions along the SE coast. Along the E portion of the TEB system, the Waikupanaha ocean entry remained active for up to 363 days during 2009 before ceasing altogether on 4 January 2010. Along the W branches and ocean entries of the TEB tube system, lava emissions halted in July 2009.

At Kilauea's summit, lava returned to the active vent within Halema`uma`u crater in January 2009, ending a pause in lava emissions there that began in December 2008. The active vent's shape was explored using Lidar, and in mid-2009 the lava lake's surface sat ~200 m below the floor of Halema`uma`u crater. The active vent underwent numerous cycles of lava rise, surface cooling, and collapse. Unless otherwise noted, all information in this report is from USGS Hawaiian Volcano Observatory (HVO) reports.

Pu`u `O`o crater quiescence. During the first four months of 2009, heavy fuming at Pu`u `O`o prevented visual observation of areas within the crater. HVO reported gas-rushing noises, but nothing unusual in available views from Forward Looking Infrared Radiometer (FLIR) thermal imaging. FLIR instruments detect infrared radiation, and produce calibrated thermal videos and still images.

On 15 May, favorable wind directions provided clear views of the crater floor. Observers reported patches of less broken, ponded surfaces near locations previously observed as spattering vents, as well as a V-shaped trough that ran SW-NE traversing the length of the crater (figure 197). They also observed an incandescent, fuming vent emitting puffing sounds in the NE part of the crater (also heard during a later visit in June), and an unseen vent distinguished by sounds on the W end of the crater floor (figure 197). Until October, further observation was limited to FLIR imagery, showing a few small, hot vents on the crater floor.

Figure 197. Map of Pu`u `O`o crater (dark gray) and vicinity showing active vents during 2009 (red dots) and the V-shaped trough (dashed line) that was observed on 15 May 2009. The webcam (POcam) location on the crater's rim is indicated by the yellow triangle. Other mapped units correspond to previous flow fields emplaced in 1983-1986 (light gray), 1992-2007 (tan and orange), and 2008 (pink, top right); during 1986-1992, lava flows were emplaced outside of the mapped area. A small lithic debris field observed on the NE rim on 2 December 2009 is also indicated. Courtesy of USGS-HVO.

Crater glow at Pu`u `O`o was observed via webcam on most nights during the last three months of 2009. Ground observation on 2 December revealed a small (estimated3) surficial deposit of lithic lapilli and small blocks on the NE rim from a small explosion estimated to have occurred as early as 23 September (figure 197). The lithic debris was most likely sourced from one of the nearby vents on the NE crater wall.

During 2009 (and possibly since August 2007), a series of collapses removed a significant portion of the N crater rim. HVO reported that the series of collapses removed some of the highest points of the summit of the Pu`u `O`o rim, thus lowering the local elevation by a few meters.

Flow field and coastal plain breakouts and changes. Lava flows emplaced during 2009 covered an area of 6.5 km², most of which covered previous lava flows; only 0.8 km² of vegetated land (chiefly forested kipukas within the flow field) was overrun by lava (2009 flow field changes are shown in figure 198).

Figure 198. Map of the changes to Pu`u `O`o's 21 July 2007 eruption flow field during 2009. The pre-existing (July 2007-2008) extent of the flow field is shown in pink, and the 2009 flow field additions are shown in red. Note that the portions of 2009 lava flows that overran the 2008 flow field extent are not represented, only changes to the extent of the July 2007-2008 flow field in 2009. The TEB tube system is shown in yellow with points where lava escaped to the surface, breakout points, indicated ('B/O points'). Ocean entries are indicated and labeled along the coast. Pool 1 (green) indicates the location of a lava lake roof collapse (discussed in text). Flow fields active during 1983-86 are shown in light gray, 1986-92 shown in light yellow, and 1992-2007 shown in orange. Courtesy of USGS-HVO.

The TEB vent and rootless shields (a pile of lava flows built over a known lava tube rather than over a conduit feeding magma; explained in BGVN 27:03) showed little change in early 2009, with small (most <300 m long) breakout-fed lava flows occurring occasionally during February and March on the fault scarp and cliffs (pali) in the Royal Gardens subdivision (figure 198) and the upper flow field. In early March, a breakout-fed lava flow reached the ocean, establishing the Kupapa`u ocean entry, which was active for a few months (discussed below) and consisted of several points where lava entered the sea (entry points). The long-lived Waikupanaha ocean entry (active since 5 March 2008) frequently produced littoral explosions and underwent delta collapses.

Other short-lived ocean entries occurred during this time, stemming from coastal plain breakouts from the W branch of the TEB tube system. These breakouts often slowed or stopped in harmony with deflation-inflation (DI) events at the summit. DI events, measured by tiltmeters at Kilauea's summit, are thought to result from changes in magma supply to a storage reservoir less than 1 km deep and just E of Halema`uma`u crater. These fluctuations often propagate through the magmatic system, and are usually measured by another tiltmeter at Pu`u `O`o crater a few hours later. Typically occurring over weekly timescales during 2009 (up to a few days of deflation, followed by up to a few days of inflation; figure 199), DI events often correlate to pulses and/or pauses in lava emission at E rift zone vents.

Figure 199. Radial deformation recorded by tiltmeters at Kilauea's summit (blue) and Pu`u `O`o crater (pink) during 2009. The sawtooth patterns delineate what have come to be called deflation-inflation (DI) events, which typically occurred over weekly timescales during 2009. The timing and behavior of DI events often coincided with vent collapses at Kilauea's summit and decreases or pauses in lava effusion along the E rift zone. Courtesy of USGS-HVO.

On 8 March 2009, the pool 1 lava lake roof (labeled in figure 198, feeding a perched lava channel - a lava channel with walls built up from previous overflows - from the 21 July 2007 fissure eruption, BGVN 34:03) collapsed. Subsequent cooling and further collapses during 11-19 March caused the channel to seal. No further active lava was observed in pool 1.

By 29 April, surface lava flows leading to the Kupapa`u ocean entry were no longer visible. This observation was taken to indicate that a tube branch leading to the Kupapa`u entry had been established. Later, during May-June, the multiple entries at Kupapa`u coalesced into one entry point. This entry was weaker and less persistant than the Waikupanaha entry and never formed a significant delta. Lava flows at the Kupapa`u entry pulsated in a manner closely correlated to DI events, unlike flows at the Waikupanaha entry, and the Kupapa`u ocean entry ceased by 21 July.

The onset of a strong DI event correlated with a breakout on June 1 from the Waikupanaha branch of the TEB tube system. Although beginning slowly, it remained active through mid-August. As is common, the flows slowed during deflation stages of DI events, and advanced further during inflation stages.

The Waikupanaha entry underwent common delta collapses throughout the year. The vigor of lava effusion at the entry, however, made up for the area lost to collapses, and the size of the delta continued to increase. The only known pause in lava entering the sea at Waikupanaha during 2009 occurred during a DI event, when the entry stopped for two days during 28-29 September.

On 31 October, surface lava flows reached the ocean ~700 m W of Waikupanaha, and established the W Waikupanaha entry. The new entry point was fed by an inferred secondary lava tube crossing over the main Waikupanaha tube branch (see the dashed portion of the yellow line labeled 'E Tube Branch', figure 198). Following the termination of the W Waikupanaha entry on 17 December, HVO concluded that its feeder tube had eroded down into the main Waikupanaha tube, thus tapping off its supply. Breakouts and surface flows during the end of the year continued to be affected by DI events.

Second longest ocean entry ceases. A large and prolonged DI event at Kilauea's summit in December correlated with a brief pause in lava effusion at the E rift zone. As a result, by 4 January 2010, lava ceased entering the ocean at Waikupanaha after 22 months of near-continuous lava entry. This was the second longest ocean entry in the history of the eruption, being about half a month shorter than the 2005-2007 E Lae`apuki entry.

Lava lake returns to Kilauea's summit. A lull in activity at Halema`uma`u crater began in mid-December 2008; on 14 January 2009, rockfall sounds returned to the summit, attributed to rising lava digesting talus slopes along the steep walled vent. Four days later, gas-rushing sounds, increased temperature, and collapses of the vent rim (figure 200) occurred, dusting nearby areas with ash and further marking the summit's re-awakening.

Figure 200. Time lapse photographs of a collapse of a portion of the Halema`uma`u vent rim, Kilauea, taken one minute apart (at 1528 and 1529) on 18 January 2009. The black line in the left frame indicates the area of collapse, which is absent in the right frame. Courtesy of USGS-HVO.

Vent glow, temperature increases, gas-rushing noises, and production of vitric ash continued during early 2009, indicating fresh lava had ascended to a shallow level in the vent. These eruption related processes fluctuated in a manner that suggested that they were moderated by in-falling crater walls burying the vent bottom.

Onset of a DI event on 3 February correlated with the retreat of the lava within the vent, removing support for the rubble clogging the vent cavity and collapsing the rubble into the cavity. This disturbance was accompanied by an ash plume that was sustained for 8 minutes. FLIR images captured the following day disclosed a lava lake situated deep within the vent (the rubble clogging the vent cavity was gone). HVO noted upwelling on the lake's E side, draining and filling events (figure 201) and spattering from the lake. Similar fluctuations at Halema`uma`u occurred in concert with DI events through late April.

Figure 201. Observational and geophysical data highlight filling (pink) and draining (gray) cycles at Kilauea's summit vent within Halema`uma`u crater. (a) Filling and draining cycles over 3 hours on 6 February 2009 were observed with FLIR, and compared with seismicity (Realtime Seismic Amplitude Measurement - RSAM - , top) and infrasound (sound at lower than audible frequencies, bottom). RSAM provides rapid analysis of ground-motion amplitudes across multiple stations; measurements are unitless and usually reported as 'RSAM units'. (b) Filling and draining cycles over ~1 hour on 7 February 2009 were observed via acoustic noises and compared with tilt (top), seismicity (middle, reported in instrument counts, here representing the seismometer response to the vertical component of ground motion velocity), and infrasound (bottom). Courtesy of USGS-HVO.

On 28-29 April 2009, a series of collapses at the vent within Halema`uma`u dislodged rubble and tephra covering the lava surface within the vent. As a result, for the next two months, particle emissions became > 50% juvenile (figure 202). Tephra emissions (juvenile, or glassy, and lithic components) have been measured nearly daily at Halema`uma`u since April 2008 by collecting passively emitted tephra (i.e. derived from non-explosive activity) in an array of buckets deployed around the vent. The resulting assessments led to the compilation of isomass maps and calculations of the total mass emitted (Swanson and others, 2009). By 6 May, bubbling and churning at the lava lake surface was visible with the naked eye.

Figure 202. Calculated monthly ejected mass of tephra from Kilauea's summit during April 2008-January 2010. The histogram excludes any explosive eruptions during that period. Collected tephra were assigned to one of two components: juvenile (glass, shown in black) and lithic (lava, shown in gray). Note that more than half of the mass ejected during May-June 2009 was juvenile, following a series of collapses on 28-29 April. See text or Swanson and others (2009) for a description of the daily tephra emission measurement technique. Courtesy of USGS-HVO.

A strong DI event in early June (reflected in the E rift zone by breakouts on the pali on 1 June, see above) marked the peak of lava activity within Halema`uma`u crater during 2009. The vent's lava lake showed strong upwelling in the NE, at times forming a dome-shaped fountain. The surface of the lava lake was circulating rapidly enough to prevent any significant crust from forming. The lava lake's circulation and activity slowed near the end of June and its surface appeared almost completely crusted over. A tripod mounted Lidar (T-Lidar) survey of the vent during 10-12 June indicated that the lava surface was ~207 m below the floor of Halema`uma`u crater (figure 203).

Figure 203. 2-D projection of 3-D reconstruction of the Halema`uma`u crater vent as measured by a T-Lidar survey on 10-12 June 2009. The reconstruction (gray) is shown on a black background. The T-Lidar was shot from the Halema`uma`u crater rim, adjacent to the active vent. The plane projected here trends approximately NNE-SSW. The lava surface (indicated in purple at the bottom) was measured to be ~207 m below the floor of Halema`uma`u crater (indicated in green). Various other dimensions of the vent's geometry are shown. Image by Todd Ericksen, University of Hawaii-Manoa; courtesy of USGS-HVO.

On 30 June, a series of significant collapses of the vent wall again clogged the vent with rubble. For the following several days, lava appeared through the rubble and established a ponded surface. The lava retreated during a DI event on 4 July, and the vent became very quiet until mid-August. On the night of 9 August, the vent emitted a faint glow. Areas of degassing appeared within days, but the vent floor lacked visible molten material.

On 13 September, lava reappeared briefly, but a DI event a few days later coincided with another vent-wall collapse, again covering the lava surface. The vent floor collapsed further on 26 September, and two days later, lava had re-entered the vent and webcam videos confirmed the filling and draining behavior of the lava surface. This collapse coincided with a strong hybrid earthquake with large very-long-period waveforms. Hybrid earthquakes at Kilauea typically begin as high-frequency earthquakes (similar to local earthquakes or rockfalls), then transition to long- and sometimes very-long-period oscillations. During 2009, hybrid earthquakes (i.e. the 26 September event) and ongoing very-long-period tremor at Kilauea's summit suggested a source location beneath the summit, and within ~500 m above or below sea level.

The lava level within the vent fluctuated until the lava surface froze and sealed shut. It collapsed again on 18 November, revealing a fresh and mobile lava surface. Similar fluctuations and crusting of the lava surface continued through the end of 2009, when the lava level again dropped out of view deep below the Halema`uma`u crater floor.

2009 deformation trends. Satellite based radar interferometry determined that broad-scale deformation at Kilauea during 2009 was marked by subsidence of the summit and E rift zone (figure 204; see the report on Mauna Loa, BGVN 37:05, for an explanation of the technique). This pattern was interpreted as deflation of the magma system, with displacement of the S flank towards the sea. Deflation also occurred in the E rift zone, but ceased by September. 64 DI events were recorded during 2009, a record number of short-lived DI events since they have been monitored. The largest and longest DI events tended to coincide with decreases or pauses in lava effusion in the E rift zone, and vent collapses at the summit (discussed above, figure 199).

Figure 204. Subsidence and deflation of Kilauea and the E rift zone during 2009, as seen in an ENVISAT interferrogram spanning 12 January 2009 to 3 February 2010. Approximately 8 cm of subsidence occurred at Kilauea's summit (Halema`uma`u crater, which is labeled), and ~6 cm of subsidence occurred in the E rift zone near Pu`u `O`o crater. Colored stripes indicate offsets as shown in the scale, top right (see Mauna Loa report in BGVN 37:05 for an explanation of the technique). The image was acquired with an incidence angle of 18° with the ground, looking W to E. Courtesy of USGS-HVO.

Hexahydrite spherules discovered at Kilauea's summit.While collecting Pele's hair on 30 March, HVO scientists discovered and collected small (less than 3 mm diameter), extremely fragile, white spherules that were stuck into wads of Pele's hair (figure 205).

Figure 205. Hexahydrite (MgSO4·6H2O) spherules discovered and collected from just S of Kilauea's summit vent in 2009. Photomicrographs (a, b) with scales show surface and textural details of the spherules. An in-situ photograph (c, key for scale) shows the spherules as they were found, within wads of Pele's hair. From Hon and Orr (2011).

X-ray diffraction revealed that the spherules were nearly pure magnesium-sulfate hexahydrite (MgSO₄·6H₂O). Hon and Orr (2011) proposed that the spherules form from the percolation of rainwater through vesicular vent rocks, enriching the water in soluble sulfates. Magnesium sulfate resists precipitation owing to its higher solubility, and most other hydrothermal minerals would precipitate from the enriched fluid sooner. Hon and Orr (2011) suggested that boiling of the residual magnesium sulfate enriched fluids formed a foam of magnesium sulfate-coated bubbles, which formed the spherules when the bubbles were subsequently entrained into the eruptive plume.

Petrologic trends, shallow magma mixing. Through long-term petrologic monitoring and analysis of Kilauea's summit and E rift zone lavas, HVO scientists noted that the weight percent MgO (an indicator of the temperature of tapped magmas) of E rift zone lavas indicated well-buffered, shallow magma conditions that were maintained by "near-continuous recharge and eruption." Similarly, textural and compositional evidence highlighted pre-eruptive magma mixing between a shallow, cooler, degassed component and a gaseous, hotter, recharge magma component. Combined, the two components are erupted as a hybrid lava at the E rift zone.

Interestingly, since 2001, increased magma supply (interpreted from cross-summit extension distance) has correlated with an increase in the shallower, degassed magma component in the E rift zone lavas (interpreted from MgO weight percent; figure 206). HVO reported that this inverse relationship (higher magma supply coincident with cooler erupted lavas) is explained by more efficient flushing of the shallow edifice during times of increased magma supply.

Figure 206. MgO weight percent (green points and blue trend, left axis) plotted versus Kilauea's cross-summit extension distance (red, right axis) during 2000-2009 shows an inverse relationship between magma supply (i.e. variations in cross-summit extension) and the temperature of erupted lavas (i.e. variation in MgO weight percent). Courtesy of USGS-HVO.

Summit gas emissions exceed health standards. Based on Flyspec measurements, the total SO₂ emissions from Kilauea in 2009 (~0.72 x 10⁶ tons) were 35% less than in 2008 (the highest annual SO₂ emissions since measurements began in 1979, correlating to the opening of a new vent in Halema`uma`u crater; BGVN 35:01). Of the total 2009 emissions, ~60% and ~40% were attributed to the E rift and the summit, respectively (figure 207). Although 2009 emissions were down from the previous year, a record number of Ambient Air Quality exceedences occurred at the summit during 2009 (figure 208).

Figure 207. Daily average SO2 emissions from Kilauea's summit (green) and from the E rift (pink) during 1992-2009. The total daily average emissions are shown in blue. 2008 marked an increase in emissions from the summit (and the highest annual SO2 emissions since measurements began in 1979) correlating with the opening of a new vent in Halema`uma`u crater (BGVN 35:01). In 2009, although total emissions were down 35% from 2008, summit emissions remained elevated. Courtesy of USGS-HVO.

Figure 208. Histograms show the number of days per year that the Ambient Air Quality standard was exeeded, as monitored at the HVO building (left) and at the Kilauea Visitor Center (right) since 2001. Since air quality monitoring began, the standard was exceeded most often in 2009. Courtesy of USGS-HVO.

Vog health concerns. A recent clinic study by Longo and others (2010) highlighted the health effects of increased volcanic air pollution (volcanic smog, or 'vog') exposure at Kilauea, and identified population subgroups who are more susceptible to the effects of vog. They found that periods of increased vog emission and exposure coincide with increases in medical visits for "cough, headache, acute pharyngitis, and acute airway problems." Among previously identified population subgroups with increased susceptibility to health problems from exposure to vog, Longo and others (2010) found a specific correlation with Pacific Islander children living in exposed rural communities. The native children showed higher rates of acute respiratory effects both in times of low- and high-vog emissions. Longo and others (2010) suggested that this unique population showed the highest vulnerability due to physiological and genetic contributions, as well as the built environment and a lack of prevention efforts for vog exposure.

References. Hon, K., and Orr, T., 2011, Hydrothermal hexahydrite spherules erupted during the 2008-2010 summit eruption of Kilauea Volcano, Hawai`i, Bulletin of Volcanology, 73(9), pgs. 1369-1375.

Longo, B.M., Yang, W., Green, J.B., Crosby, F.L., and Crosby, V.L., 2010, Acute health effects associated with exposure to volcanic air pollution (vog) from increased activity at Kilauea in 2008, Journal of Toxicology and Environmental Health, Part A, 73(20), pgs. 1370-1381.

Swanson, D., Wooten, K., and Orr, T.R., 2009, Mass flux of tephra sampled frequently during the ongoing Halema'uma'u eruption [abs.], Eos, Transactions, American Geophysical Union, v. 90, no. 52 (fall meeting supplement), abstract no. V52B-01.

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: Michael Poland, Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawai'i National Park, HI 96718, USA (URL: https://volcanoes.usgs.gov/observatories/hvo/).

On 7 February 1996, hydrophone data and water level changes suggested that a small hydrothermal ejection may have occurred at Kusatsu-Shirane (also known as Kusatsu-Shiranesan) at Yugama crater's pond (BGVN 21:02). Several months later, on 8 July, numerous small earthquakes were detected by the Kusatsu-Shirane Volcano Observatory (BGVN 21:07). The volcano is about 150 km NW of Tokyo (figures 6 and 7; also refer to the sketch map in figure 1, SEAN 07:10). This report summarizes seismicity between May 2011 and February 2013 based on available reports from the Japan Meteorological Agency (JMA).

Figure 6. A sketch map showing the location of Kusatsu-Shirane (Kusatsu-Shiranesan) in Honsho, Japan. Courtesy of JMA.

Figure 7. An aerial photo of Kusatsu-Shirane, as viewed from the S. The photo, taken on 29 May 2008, shows the overlapping pyroclastic cones and two of the three crater lakes. Courtesy of Flickr user rangaku1976.

On 27 May 2011, tremor was detected at Kusatsu-Shirane; no further information was provided. During 5-7 June 2011, an elevated number of microearthquakes with low amplitude occurred around Yugama crater (the main crater). No volcanic tremor or significant deformation was detected during this time. Thereafter, activity gradually diminished to background levels.

Field surveys during 27-29 June and 12-13 July 2011 revealed that elevated thermal anomalies persisted inside Yugama crater's N flank, the N fumarole area, and the slope located N to NE of Mizunuma crater. Ground temperatures around fumaroles remained high.

On 18 July 2011, a short period of tremor (duration 2.5 min) was detected. No change in fumarole activity was observed.

On 10 August 2011, an aerial survey was conducted in cooperation with Gunma prefecture. The survey found that the distribution of thermal anomalies and fumaroles in Yugama crater and the N fumarole area had not changed.

During 16-18 August, an elevated number of microearthquakes with low amplitude occurred near and to the S of Yugama crater. Significant deformation was not detected. Seismicity remained at background levels during the other days in August. High temperatures persisted on the N flank inside the main crater.

A field survey on 8 March 2012 found that the high temperatures on the N slope of Mizugama crater and the N fumarole area were the same as those found during a previous survey conducted during 27-29 June 2011. Very weak steam plumes at the N fumarole area of Yugama were sometimes observed by a camera at Okuyamada, though bad weather and mechanical trouble prevented their observation for long periods. The ground temperature in the fumarole area NE of Yugama crater remained elevated since its rapid rise in May 2009, despite occasional fluctuations.

According to JMA, the occurrence of small amplitude volcanic earthquakes occasionally increased during March 2012. The hypocenters were located just beneath the S part of Yugama crater. No tremor or significant crustal change was noted in GPS data.

During 1-2 April 2012, seismicity increased slightly, then subsided. No tremor, change in fumarole activity, or crustal change was observed, and no further reports have been issued on activity at Kusatsu-Shirane as of February 2013.

Geologic Background. The Kusatsu-Shiranesan complex, located immediately north of Asama volcano, consists of a series of overlapping pyroclastic cones and three crater lakes. The andesitic-to-dacitic volcano was formed in three eruptive stages beginning in the early to mid-Pleistocene. The Pleistocene Oshi pyroclastic flow produced extensive welded tuffs and non-welded pumice that covers much of the E, S, and SW flanks. The latest eruptive stage began about 14,000 years ago. Historical eruptions have consisted of phreatic explosions from the acidic crater lakes or their margins. Fumaroles and hot springs that dot the flanks have strongly acidified many rivers draining from the volcano. The crater was the site of active sulfur mining for many years during the 19th and 20th centuries.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/); rangaku1976, Flickr (URL: http://www.flickr.com/photos/rangaku1976/).

Sabancaya volcano, located 72 km NW of Arequipa city, is one of the most active volcanoes of the Central Andes (figure 10). Our last report of Sabancaya described ashfall during July 2003 (BGVN 29:01). This report describes an increase in anomalous seismic and fumarolic activity, beginning in late 2012 and continuing through the end of March 2013. The restlessness spurred increased monitoring of the volcano.

Figure 10. A map illustrating hazards at the Ampato-Sabancaya volcanic complex (high danger, red; moderate danger, orange; and low danger, yellow). Types of volcanic hazards include pyroclastic flows (including debris flows), mudflows, lava flows, and avalanches. The overall thickness of ash deposits from eruptions during 1990-1998 is indicated by 1 and 0.1 cm isopachs. Major roads and highways are shown as thick, dark red lines; thin lighter red lines are elevation contours. The map shown is featured on a poster with more details. From Mariño and others (2013).

Between 1988 and 1997, activity at Sabancaya was intermittent and characterized by low to moderate Vulcanian eruptions (VEI 2) and mainly modest eruption columns (less than 5 km above the summit) with local ashfall (e.g., SEAN 13:06; BGVN 19:03). After this eruptive episode, between 1998 and 2012, minor and intermittent fumarolic emissions rose from the active crater. During the last months of 2012, a slight increase of fumarolic activity was observed during a field campaign by Peru's Instituto Geológico Minero y Metalúrgico (INGEMMET) volcanologists and their counterparts from the Laboratoire Magmas et Volcans (Clermont-Ferrand, France).

The Instituto Geofisico del Peru (IGP) reported that inhabitants from Sallalli hamlet, ~ 11 km S of Sabancaya, observed an increase in fumarolic emissions beginning 5 December 2012. Meteorological conditions prevented IGP scientists from visiting the area during the rainy season.

In mid-February 2013, local residents reported an increase in fumarolic activity, which was confirmed by INGEMMET scientists that visited the volcano on 15 and 22-23 February (figure 11). Scientists also reported a strong sulfur odor within an 8-km radius, and felt several strong earthquakes probably associated with the volcano's unrest.

Figure 11. Photograph taken of a gas plume above the active vent of Sabancaya, as seen from the SE flank on 17 February 2013. Courtesy of Pablo Samaniego, IRD.

IGP reported that within a span of 95 minutes on 22 February 2013, three earthquakes, of M 4.6, 5.2, and 5.0 respectively, were registered at Sabancaya (figure 12). This activity prompted IGP to install a network of close proximity seismic stations. Earthquakes continued through the following day (23 February) and caused damage at Maca village, 20 km NE of the crater.

Figure 12. The principal earthquakes (red dots) registered at Sabancaya on 22 February 2013. Of these, three earthquakes of M 4.6, 5.2, and 5.0 occurred within a span of 95 minutes. Courtesy of IGP.

During 22-23 February, a seismic station installed by INGEMMET registered more than 500 small volcano tectonic (VT) seismic events at Sabancaya. On 23 February IGP separately reported 560 events at the Cajamarcana seismic station (CAJ on figure 13b) on the SE flank. According to a Reuters article from 27 February, 80 homes were damaged by the seismicity during 22-23 February, leading to some evacuations. During that seismicity, a plume rose ~100 m above Sabancaya. After 24 February, VT, long period (LP), and hybrid seismicity continued (figure 13).

Figure 13. (a) Plot of daily earthquakes at Sabancaya, showing the number of volcano tectonic, long period, and hybrid events that occurred during 24 February-27 March 2013. (b) The locations of earthquake epicenters on 27 March 2013 (red dots) and the seismic stations that were monitoring the volcano as of that date (yellow triangles). Courtesy of IGP.

Reference. Mariño J., Samaniego P., Rivera M., Bellot N., Manrique N., Macedo L., Delgado R., 2013, Mapa de peligros del Complejo Volcánico Ampato-Sabancaya, Esc. 1:50.000. Edit. INGEMMET-IRD.

Geologic Background. Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning "tongue of fire" in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of historical eruptions date back to 1750.

Information Contacts: Instituto Geológico Minero y Metalúrgico (INGEMMET), Av. Dolores (Urb. Las Begonias B-3), J.L. Bustamante y Rivero, Arequipa, Perú (URL: http://www.ingemmet.gob.pe); Pablo Samaniego Eguiguren, Laboratoire Magmas et Volcans, Université Blaise Pascal, Le Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD), Casilla 18-1209, Calle Teruel 357 - Miraflores, Lima 18 - PERU (URL: https://lmv.univ-bpclermont.fr/en/); Reuters, report by Lima Newsroom; Orlando Macedo, PhD, Chief of Volcanology Research Department, Instituto Geofisico del Peru, (IGP), Arequipa Volcano Observatory, Urb. La Marina B-19, Cayma, Arequipa, Peru.

Matthew Patrick (USGS-HVO) notified Bulletin editors that in late 2012 images from thermal sensing satellites showed a 'new' active vent on Mount Michael on Saunders Island in the South Sandwich Islands (see location map, figure 1 in BGVN 28:02). This prompted scrutiny of the same vent in earlier images. Patrick noted that, although the vent was first identified in the 2012 images, it also appeared as activity in satellite images starting in 2006. The South Sandwich Islands are generally devoid of vegetation and habitants, and are largely ice-bound. Thus, satellite thermal alerts are strong evidence of volcanism.

Patrick shared with us the following information from a paper by Patrick and Smellie (2013) about the vent, labeled as Old Crater (SE and outside of main crater, see figure 2 in BGVN 28:02). ASTER [Advance Spaceborne Thermal Emission and Reflection Radiometer] imagery provided "new information on the small subordinate crater, marked as 'Old Crater' by Holdgate and Baker (1979), presumably because it was inactive at the time of their observations." An ASTER image on 28 October 2006 showed an apparent SWIR [short-wave infrared] anomaly at Old Crater. The crater itself appeared to be snow-free and was approximately 150 m in diameter. An ASTER image from 5 January 2008, showed a steam plume coming from this vent, which appeared to be about 190 m wide, as well as a TIR [thermal infrared] anomaly. A very high resolution image from November 2009 available on Google Earth showed a small steam plume emanating from the crater, which is about 190 m wide (figure 8). An ASTER image from 17 November 2010, showed apparently recent eruptive activity in Old Crater, evidenced by tephra fallout emanating from the crater and a small TIR anomaly (at the time there was also a TIR anomaly in the main crater). According to Patrick and Smellie, the plume, tephra fall, SWIR anomalies, and crater enlargement (from 150 to 190 m) indicated that this vent had reactivated by late 2006.

Figure 8. Annotated Google Earth imagery of Michael volcano (Saunders Island) acquired on 19 November 2009. (a) Saunders Island is mostly glacier covered, and steam plumes rose from the summit area. The scale bar indicates a distance of ~2.4 km. (b) A close up of the summit area that clearly shows steam plumes emanating from both the summit crater as well as the snow-filled 'Old Crater' (as termed by Holdgate and Baker, 1979). The scale bar indicates a distance of ~0.5 km. Courtesy of Google Earth.

MODVOLC satellite thermal alerts measured from the volcano since our last Bulletin report (BGVN 33:04, activity through May 2008) and to 4 April 2013 are shown in Table 3. A solitary alert appeared 25 October 2008, followed by a four year period of apparent inactivity. Then, another solitary alert was measured in late June 2012, followed by alerts for two days in October 2012 and two days in November 2012. Patrick noted that occasional and sporadic alerts are very typical for Michael.

Table 3. Satellite thermal alerts measured by MODVOLC over Michael from 2008-February 2013. Pixel sizes generally range from 1-1.5 km². Note that previous satellite thermal alerts for Michael were listed in BGVN 31:10 (October 2005-November 2006) and 33:04 (August 2000-May 2008). Courtesy of MODVOLC.

References. Patrick, M.R., and Smellie, J.L., 2013, A spaceborne inventory of volcanic activity in Antarctica and southern oceans, 2000-2010, Antarctic Science, v. 25, no. 4, p. 475-500.

Holdgate, M.W., and Baker, P.E., 1979. The South Sandwich Islands: I. General description, British Antarctic Survey Scientific Reports, No. 91, pp. 1-76.

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: Matthew Patrick, Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawai'i National Park, HI 96718, USA (URL: https://volcanoes.usgs.gov/observatories/hvo/); MODVOLC, Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

Degassing that followed the May 2011 explosive eruption of Telica (figure 29; see also BGVN 36:11) continued through 2012 and into 2013. The following information summarizes observations by the Nicaraguan Institute of Territorial Studies (INETER) for 2012 and through March 2013.

Figure 29. A location map of Telica, Nicaragua, in Central America. Telica (red triangle) is located ~105 km NW of the capitol, Managua. It last erupted in May 2011 (BGVN 36:11), but no major damage was reported. Gases emitted by Telica normally affect communities in the nearby provinces of Leon and Chinandega. Small black triangles in the figure depict other known Holocene volcanos in the region. Courtesy of USGS.

INETER issues a monthly bulletin, Boletín mensual Sismos y Volcanes de Nicaragua (Newsletter, Earthquakes and Volcanoes in Nicaragua), reporting on monitoring of Nicaraguan volcanoes including San Cristóbal, Telica, Cerro Negro, Momotombo, Masaya, and Concepcion (figure 30). In the Boletín, INETER presents monitoring data for Telica crater and adjacent fumarol temperatures, seismic activity, and sulfur dioxide (SO₂) fluxes. In addition, visual observations are made during periodic field trips. Generally, the time difference between the arrival of P (primary) and S (secondary) waves from local earthquakes ranges from 0.5 to 2 sec, suggesting a source depth of 4 to 10 km.

Figure 30. An oblique view of a schematic map of Nicaragua with high vertical exaggeration highlights the locations of Nicaraguan volcanoes. Courtesy of INETER.

As an example of normal ongoing activity at Telica, INETER reported that during 10-11 September 2012, 'jet' sounds were heard from the volcano, and two incandescent fumaroles were observed, along with gas-and-steam plumes rising 100-200 m above the crater. On 11 September two small explosions occurred in the crater. During 12-14 and 17 September gas plumes rose 30-150 m and incandescence from the crater was observed. Gas measurements on 14 and 17 September showed normal levels of SO₂ flux.

2012 Sulfur dioxide flux. Average daily SO₂ flux measurements made using the Mini-DOAS (differential optical absorption spectroscopy) mobile technique in 2012 were 303 metric tons per day in April, 627 metric tons per day in June, 377 metric tons per day in August, and 130 metric tons per day in October.

2012 Seismic Events. INETER has developed some novel ways for grouping seismic events at Telica. The types of seismic events monitored at Telica and activity during 2012 are shown in tables 5 and 6, respectively.

Table 5. Types of seismic activity monitored at Telica volcano, with characteristics as recorded and interpreted during 2012. Courtesy of Virginia Tenorio, INETER.

Table 6. Total volcano-seismic events and numbers of various types of events (see table 5 for descriptions) that were reported at Telica during 2012; percentages indicate the contribution of each type of event to the total recorded number of events during that month. Courtesy of INETER.

2012 Temperature measurements. Figure 31 shows INETER staff members measuring crater and fumarole vent temperatures at Telica; temperatures are measured approximately once per month (figure 32). Temperatures measured during 2012 at the 4 fumaroles (figure 33), vents located E and outside of Telica crater, ranged between 52° and 79°C.

Figure 31. INETER staff measuring temparatures at the Telica crater using a thermal imaging camera (left) and one of the fumarole vents using an IR thermometer (right). Courtesy of INETER.

Figure 32. (a) Maximum monthly temperatures for Telica crater during January 2011-February 2012, and (b) average monthly temperatures during 2012. Courtesy of INETER.

Figure 33. A W looking Google Earth view of Telica showing the approximate location of the fumarole vents E of Telica crater (lower arrow) and the location of temperature measurements in the crater (upper arrow). Courtesy of INETER.

2013 activity. The Costa Rica News reported on 24 March 2013 that Virginia Tenorio of INETER announced that Telica was experiencing increased micro-earthquakes. According to the INETER report, dozens of micro-earthquakes had occurred per day since 17 March. The increase continued to at least 24 March; 20 earthquakes occurred on 22 March, but only one reached as high as M 2.1. Tenorio was reported to state that, although earthquakes were located within the volcano's structure, an imminent eruption was not indicated. She further stated that while some changes may occur in the magmatic system and in the expulsion of gases, conditions were stable. Local observers reported elevated vapor and gas emissions associated with the spike in seismicity and incandescence in a fissure at the bottom of the active crater. Since 21 March 2013, the member institutions of the National System for Prevention, Mitigation and Attention to Disasters (SINAPRED), have been ordered to monitor Telica's activity and keep it under close observation.

Geologic Background. Telica, one of Nicaragua's most active volcanoes, has erupted frequently since the beginning of the Spanish era. This volcano group consists of several interlocking cones and vents with a general NW alignment. Sixteenth-century eruptions were reported at symmetrical Santa Clara volcano at the SW end of the group. However, its eroded and breached crater has been covered by forests throughout historical time, and these eruptions may have originated from Telica, whose upper slopes in contrast are unvegetated. The steep-sided cone of Telica is truncated by a 700-m-wide double crater; the southern crater, the source of recent eruptions, is 120 m deep. El Liston, immediately E, has several nested craters. The fumaroles and boiling mudpots of Hervideros de San Jacinto, SE of Telica, form a prominent geothermal area frequented by tourists, and geothermal exploration has occurred nearby.

Information Contacts: Virginia Tenorio, Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni); Costa Rica News, San Jose, Costa Rica (URL: http://thecostaricanews.com); Sistema Nacional para la Prevención, Mitigación y Atención de Desastres (SINAPRED), Managua, Nicaragua (URL: http://www.sinapred.gob.ni/); MODVOLC, Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

As noted by our previous report (BGVN 37:06), on 12 January 2012 Turrialba emitted ash for a few hours due to the opening of a vent, named 2012 Vent, on the SW inside slope of Central Crater. Since then, 2012 Vent has been an active contributor to the regular plume generation at the volcano. Our previous report noted activity through May 2012. This report primarily highlights activity through December 2012, based on online documents from the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA) showing a diminution in activity during 2012 compared to 2010 and 2011.

Seismicity. According to OVSICORI-UNA, the seismic activity at Turrialba in 2012 was characterized primarily by shallow and volcano-tectonic events concentrated in the upper part of the edifice, and minor seismicity in nearby faults. In general, seismicity was lower in 2012 than in 2011, and notably lower than that in 2010. Seismic activity climbed slightly during September-October 2012 (from about 20/day, peaking at 150/day on 13 October, and then declining back to normal values after 1 November; figure 30). OVSICORI-UNA noted that seismic activity in 2012 was caused by water and heat interactions causing gas pressure.

Figure 30. The number of seismic events registered per day at Turrialba during 2012. Courtesy of OVSICORI-UNA.

Deformation. OVSICORI-UNA reported that during 2012 the distances between the Electronic Distance Measurement (EDM) station "Pilar" and several nearby reflectors contracted from 2 to 7 cm/year, with the highest value at the N reflector and lowest at the ENE and NE reflectors (see figure 31 for EDM station locations).

Figure 31. The location of geodetic monitoring stations at Turriabla during 2012. Red circles are reflectors of the EDM network, and measurements were made from the Pilar station (red square). Blue circles are permanent GPS stations (CAPI and GIBE). Courtesy of OVSICORI-UNA.

Emissions. According to OVSICORI-UNA, the opening of the 2012 vent was not associated with new magmatic activity. Vent temperatures measured with a thermocouple were similar during 2010-2012, suggesting to OVSICORI-UNA a sustained and common magmatic source. Measured vent temperatures also correlated with CO₂ and H₂S gas emissions (figure 32).

Figure 32. (Background image) Thermal image of Turrialba's W wall in Cráter Central (Central Crater) on 27 October 2012. Two vents are indicated, Boca 2012 (2012 Vent) and Cráter Oeste (West Crater). (Plots) For the measurement locations indicated by arrows, plots compare CO2 flux measurements (black) to both H2S flux measurements (blue) and thermal measurements acquired at 10-cm depth (red). Courtesy of OVSICORI-UNA; thermal photo taken by G. Avard.

OVSICORI-UNA noted that gas emissions during 2012 had decreased considerably compared to those during 2010 and 2011. OVSICORI-UNA suggested that this decrease might be due to various factors, including a decline in rainfall that resulted in less water vapor, the primary component of the emissions. In a report discussing activity during January-February 2013, OVSICORI-UNA noted that the emissions from 2012 Vent had decreased, even though nighttime incandescence could be observed. Emissions drifted primarily NW during 2012.

Figures 33 and 34 summarize SO₂ measurements from both miniature Differential Optical Absorption Spectrometer (mini-DOAS, fluxes) and OMI satellite data (masses). SO₂ fluxes were lower than those in 2010-2011 when fluxes often reached above 1,000 tons/day (and in one case, nearly 4,000 tons/day; figure 34).

Figure 33. (Left) Daily SO2 flux (metric tons/day) at Turrialba measured by a mini-DOAS station at La Central school, ~2.2 km SW of West Crater, between 1 May 2012 and 1 January 2013. (Right) SO2 mass (uncorrected for any noise) emitted by Turrialba as recorded by NASA's Ozone Monitoring Instrument (OMI) aboard the AURA satellite during 2012. The SO2 mass corresponds to the total mass detected by the OMI sensor in the Central America area at 1800-1900 UTC. According to OVSICORI, both mini-DOAS and OMI measurements were consistent and of the same magnitude. The red-shaded area in the satellite data represents the time period corresponding to that of the mini DOAS data. Courtesy of OVSICORI-UNA and NASA-OMI.

Figure 34. SO2 mass emitted by Turrialba as recorded by NASA's OMI instrument aboard the AURA satellite between 1 October 2008 and 6 November 2012. These represent masses in the atmospheric column that are thought to have roughly 1 day residence times. Courtesy of NASA-OMI.

As in previous years, rain and fog absorbed volcanic gases in 2011 and 2012, producing acid rain with consequent damage and destruction to vegetation, especially in downwind areas in the sector sweeping clockwise from SW to N from the vents (figure 35).

Figure 35. Annotated photo of Turrialba taken on 26 August 2012. The vegetation on the top and on the flanks of the edifice (zone 1) showed severe effects such as necrosis. The pasture vegetation (zone 2), used for milk production, turned yellowish (chlorosis). Interestingly, part of the native vegetation such as the tall trees (Quercus species) showed a stronger resistance to environmental acidification. Courtesy of OVSICORI-UNA; photo taken by G. Avard.

OVSICORI-UNA observed that hydrothermal activity modified the mineralogy and decreased the cohesion of the rocks in contact with the fluids, which alter and reduce the stability of the slopes of the volcanic edifice, triggering gravitational collapses, rockfalls, and strong erosion during the main rain events. These phenomena were especially observed after storms on 15 August and in November 2012, when coarse and fine material was transported from the walls to the bottom of Central Crater, deepening the W and NW gullies.

In an M.S. thesis, Rivera (2011) compared SO₂ concentrations in Turriabla's volcanic plume using a ground-based mini-DOAS and three new data analysis techniques using NASA's OMI instrument. The three new techniques were the MODIS smoke estimation, OMI SO₂ lifetime, and OMI SO₂ transect techniques. All four techniques involve UV sensor analysis. She found that the OMI SO₂ lifetime technique provided qualitative agreement between the ground-based and satellite-based data, while the OMI transect technique provided occasional quantitative agreements with the mini-DOAS measurements. The MODIS smoke estimation technique was inaccurate in estimating SO₂ emission rates.

Reference. Rivera, A.M., 2011, Comparisons between OMI SO₂ data and ground-based SO₂ measurements at Turrialba volcano, M.S. Thesis, Michigan Technological University.

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

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/).