The Aira caldera is located in the northern half of Kagoshima Bay in Kyushu, Japan and contains the active post-caldera Sakurajima volcano. Though several craters have been historically active, current activity is focused in the Minamidake summit crater, which has recently been erupting since March 2017. Activity is characterized by intermittent explosions, ash plumes and resulting ashfall, ballistic ejecta, and crater incandescence (BGVN 46:01). This report updates similar activity from January through June 2021 and uses information primarily from the Japan Meteorological Agency (JMA) and various satellite data.

During the reporting period, the number of eruptions had decreased significantly compared to previous months; at the Minamidake crater there were about 127 ash eruptions, 83 of which were explosive (compared to 432 and 221, respectively during the previous year). No eruptions were reported in the Showa crater through June. Ash was reported most frequently during March and April for 14 and 22 days, respectively (table 25). The tallest ash plume reached 4 km above the crater on 27 March, while the most amount of ashfall was 42 g/m² during April. A decline in eruptive events after April was reflected both in JMA reports and thermal data (figure 118). Sentinel-2 infrared and natural color satellite imagery captured both thermal anomalies in the summit craters as well as significant ash plumes that resulted from the explosive eruptions (figure 119). Recorded sulfur dioxide emissions were relatively high during the beginning of the year and began to decrease to 1,300 tons/day in May.

Table 25. Number of monthly explosive eruptions, total eruptions, days of ashfall, ashfall amounts, and sulfur dioxide emissions from Sakurajima’s Minamidake crater at Aira during January-June 2021. Note that smaller events that did not reach the threshold of explosions or eruptions also occurred. Ashfall was measured at Kagoshima Local Meteorological Observatory. Data courtesy of JMA.

Figure 118. Clusters of low-intensity thermal anomalies were detected at Aira’s Sakurajima volcano during January-June 2021 based on the MIROVA graph (Log Radiative Power). The number of relatively higher thermal anomalies seemed to decrease after April. Courtesy of MIROVA.

Figure 119. Sentinel-2 infrared satellite images showing white gas-and-steam plumes rising from Aira’s Sakurajima volcano on 31 January (top left) 2021 accompanied by a thermal anomaly in the summit crater and two thermal anomalies in the summit crater on 21 April (bottom right). On 5 February (top right) and 27 March (bottom left) natural color satellite images showed distinct ash plumes drifting NE and NW, respectively, due to explosive eruptions. Images using “Atmospheric penetration” (bands 12, 11, 8A) rendering on 31 January and 21 April, and “Natural Color” (bands 4, 3, 2) rendering on 5 February and 27 March. Courtesy of Sentinel Hub Playground.

During January a total of 21 ash eruptions were detected, 18 of which were explosive. The number of volcanic earthquakes notably increased from 55 in December 2020 to 117, accompanied by white gas-and-steam emissions that rose 200 m above the crater and nighttime crater incandescence, as captured by a high-sensitivity surveillance camera. An explosion at 1642 on 4 January produced an ash plume that rose 1.8 km above the Minamidake crater. On 31 January an explosion at 0720 generated an ash plume that rose 2.3 km above the crater and ejected bombs 1.3-1.7 km high. JMA reported that sulfur dioxide emissions had been high since September 2020, and during January reported 1,500-5,000 tons/day, with the highest value recorded on 6 January. During seven days in the month, 3 g/m² of ash fell, according to the Kagoshima Local Meteorological Observatory in Higashikorimoto (11 km WSW). Overall, about 100,000 tons of ash had fallen during the month.

Similar eruptive events continued in February, with 22 ash eruptions, 11 of which were explosive and ejected volcanic bombs 1-1.3 km from the Minamidake crater. The number of volcanic earthquakes increased to 292. During seven days of the month, ashfall was reported, accumulating to 11 g/m²; observation data showed that about 90,000 tons of ash had fallen during the month. SO₂ emissions were between 1,100-4,300 tons/day, the higher of which was measured on 16 February. On 28 February an explosion at 2247 ejected bombs up to 1.3 km from the summit, produced an ash plume that rose 2.3 km above the crater, and was accompanied by crater incandescence.

Activity increased slightly during March and April, with 31 and 42 ash eruptions, respectively. The number of volcanic earthquakes decreased slightly from 195 in March to 148 in April. Explosions ejected incandescent material as far as 1.7 km from the Minamidake crater, accompanied by nighttime crater incandescence. An explosion on 5 March generated an ash plume that rose 2.7 km above the crater and ejected material as far as 1.1 km from the summit. On 27 March an eruption at 0236 produced an ash plume that rose 2.5-4 km above the crater and drifted NW, resulting in a large amount of ashfall in Kagoshima City (10 km W) (figure 120). Bombs were ejected up to 1.3 km from the crater. On 29 March at 1557 an ash plume rose 2.2 km above the crater and drifted SE, an accompanying pyroclastic flow was observed down the SE flank and ashfall was reported in Kagoshima City and the Kagoshima Prefecture. An explosion on 30 March at 0433 generated an ash plume 2.7 km above the crater and drifted E, ejecting material as far as 900 m from the crater and resulting in ashfall in Kagoshima City. Ashfall was reported on 14 days in March (21 g/m²) and 22 days in April (42 g/m²). A single thermal alert was detected by the MODVOLC system on 4 April; an explosion the following morning at 0641 on 5 April produced an ash plume 3 km above the crater. On 25 April an explosion at 0109 ejected material 1-1.3 km from the crater and an ash plume 2.3 km high. The explosion generated what was initially described as a pyroclastic flow that descended 1.8 km down the SW side of the crater; later field inspections did not observe pyroclastic flow deposits or damaged vegetation, and concluded that the plume was generated by winds. About 110,000-120,000 tons of ash was measured during the two months, and sulfur dioxide emissions remained consistent at 1,800-2,900 tons/day, according to JMA.

Figure 120. Webcam images of Aira’s Sakurajima volcano showing dense gray ash plumes on 27 March (top left) rising 3.2 km above the crater, on 6 May (bottom left) rising 2.5 km above the crater, and on 28 April (right) 2021 incandescent material was visible on the flanks of the volcano accompanied by a small ash plume. Images courtesy of JMA (Sakurajima March, April, and May 2021 monthly reports).

During May and June, the number of eruptive events declined; 11 eruptions were detected during May, six of which were explosive and ejected material 800-1,100 m from the crater. On 6 May an explosion produced an ash plume that rose 2.5 km above the crater (figure 120). In June small, intermittent eruptions were detected, though none were explosive. Resulting ash plumes rose 1-2.5 km above the crater and were accompanied by nighttime crater incandescence, based on imagery from a high-sensitivity surveillance camera. The number of volcanic earthquakes continued to decrease each month from 91 to 18, respectively. During May ashfall was reported for four days, accumulating to 16 g/m²; about 50,000 tons of ash was measured. Less than 0.5 g/m² was reported over the course of a day in June. SO₂ emissions also gradually decreased from May at 1,300 tons/day to 600-2,700 tons/day in June.

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

Information Contacts: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Volcán de Fuego, located in Guatemala, has been vigorously erupting since 2002, with historical eruptions dating back to 1531. Major eruptions have been characterized by ashfalls, pyroclastic flows, lava flows, and lahars. More recently, activity has consisted of ash plumes, ashfall, incandescent block avalanches, and lava flows (BGVN 46:04). Similar activity continued during this reporting period of April through July 2021, dominated by daily explosions, ash plumes, ashfall, and incandescent block avalanches. Information primarily comes from daily reported by the Instituto Nacional de Sismologia, Vulcanología, Meteorología e Hidrologia (INSIVUMEH), Washington Volcanic Ash Advisory Center (VAAC), and various satellite data.

Summary of activity during April-July 2021. Hourly explosions were reported at Fuego during April-July 2021 that vibrated roofs and windows in nearby communities. These explosions generated gray ash plumes that rose 4.3-4.9 and generally drifted W and SW, the highest of which occurred on 25 April. The Washington VAAC issued 422 daily ash advisories during the reporting period. Ashfall was common throughout this period in several nearby communities, dominantly Panimaché I and II (8 km SW), Morelia (9 km SW), Santa Sofía (12 km SW), El Porvenir (8 km ENE), Sangre de Cristo (8 km WSW), Yepocapa (8 km NW). Occasional white gas-and-steam plumes accompanied the explosive activity, rising as high as 4.5 km altitude. Incandescent block avalanches accompanied the explosions, descending several flanks, such as the Seca (W), Ceniza (SSW), Trinidad (S), and Taniluyá (SW) drainages and reaching as far as vegetated areas. Incandescent ejecta was observed as high as 450 m above the crater during most nights and early mornings. According to the MIROVA graph (Log Radiative Power), thermal activity was consistently strong and frequent during April through July (figure 148). The MODVOLC algorithm detected 39 thermal alerts during six days in April, nine days in May, five days in June, and six days in July. Sentinel-2 infrared satellite imagery showed strong thermal anomalies in the summit crater, which represents the incandescent block avalanches that descended the S and SW flanks as a result of persistent explosions (figure 149). Many of these avalanches were accompanied by gray ash plumes. Weak sulfur dioxide emissions were infrequently observed in Sentinel-5P TROPOMI satellite imagery on 24 April and 24 May, which drifted S and W, respectively (figure 150).

Table 23. Eruptive activity was consistently high at Fuego throughout April-July 2021 with multiple explosions every hour, ash plumes, block avalanches, and near-daily ashfall in nearby communities. Courtesy of INSIVUMEH daily reports.

Figure 148. Consistently strong thermal anomalies continued at Fuego during April through July 2021. Courtesy of MIROVA.

Figure 149. Sentinel-2 infrared satellite imagery showing strong thermal anomalies at the summit of Fuego, frequently accompanied by gray ash plumes drifting primarily W. Incandescent block avalanches are visible descending the flanks on 9 April (top left), 14 May (top right), 18 June (bottom left), and 3 July (bottom right) 2021, dominantly on the S and SW flanks. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Figure 150. Weak sulfur dioxide emissions observed from Fuego drifted S on 24 April 2021 (left) and W on 24 May 2021 (right), based on the Sentinel-5P satellite using TROPOMI data. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Frequent daily explosions continued during April. Two to fourteen explosion per hour were detected, which generated ash plumes that rose to 4.3-4.9 km altitude and drifted usually up to 15 km, and occasionally as far as 20 km in different directions. Ashfall was commonly reported in multiple communities, including Panimaché I and II, Morelia, Santa Sofía, El Porvenir, Sangre de Cristo, Yepocapa. Due to heavy rains on 16 April, lahars were observed in the Ceniza, Seca, and Mineral drainages. Additional ash was reported in La Rochela on the 20th, Palo Verde on the 23rd and 25th, Yucales (12 km SW) on the 26th, and Asuncion on the 29th. The explosions ejected material as high as 400 m above the crater and caused constant incandescent block avalanches to descend several flank drainages, including Seca, Taniluyá, Ceniza, Trinidad, Santa Teresa, Las Lajas (SE), and Honda.

Explosive activity during May was similar to previous months, with 3-17 explosions per hour that rattled windows and roofs in nearby communities. Gas-and-ash plumes rose to 4.2-4.8 km altitude and drifted as far as 15 km S, SW, N, NE, W, and NW. Near-daily reports of resulting ashfall affected mainly Panimaché I and II, Morelia, El Porvenir, Santa Sofía, Sangre de Cristo, Yepocapa, and Yucales. Ashfall was also observed in Palo Verde (5 May), La Soledad (11 km N) (20 May), San José calderas (20 May), Acatenango (20 May), and San Pedro (21 May). Block avalanches caused by frequent explosions descended the Seca, Ceniza, Taniluyá, Trinidad, Las Lajas, Honda, and Santa Teresa drainages, sometimes reaching vegetated areas, and incandescent material was ejected 100-450 m above the crater.

Loud explosions continued throughout June, with 3-15 explosions per hour that produced ash plumes that rose to 4.3-4.8 km altitude and drifted 10-20 km in different directions. Ash was observed primarily in Panimaché I and II, Morelia, Santa Sofía, Yucales, Sangre de Cristo, Yepocapa, and El Porvenir. Other communities receiving ashfall included Palo Verde, Ceilán, La Rochela, La Soledad, El Campamento, and El Zapote. Incandescent ejecta rose 100-400 m above the crater. Constant block avalanches were reported in the Ceniza, Taniluyá, Trinidad, Santa Teresa, Seca, Las Lajas, and Honda drainages, sometimes reaching vegetated areas. On 15 and 24 June, INSIVUMEH reported that lahars descended the Las Lajas and El Jute drainages on the SE flank, due to heavy rainfall; tree branches and blocks are large as 1.5 km in diameter were carried down the flanks.

During July, daily explosions persisted at a rate of 3-15 per hour, which produced gas-and-ash plumes that rose to 4.3-4.8 km altitude (figure 151). These plumes drifted 8-30 km primarily W and SW, resulting in ashfall in several nearby communities, including Sangre de Cristo, Panimaché I and II, El Porvenir, Morelia, Santa Sofía, Yucales, and Yepocapa. Other communities less affected included Palo Alto (13 July), Palo Verde (19 and 24 July), La Rochela (25 July), Ceilán (25 July), and La Conchita (29 July). During the night and early morning, crater incandescence was visible, accompanied by ejecta that rose 100-400 m above the crater. Explosions also generated constant block avalanches that descended drainages along the flanks, including Ceniza, Taniluyá, Trinidad, Santa Teresa, Las Lajas, Honda, and Seca, frequently reaching vegetation.

Figure 151. Photo of an ash plume rising from the summit of Fuego on 9 July 2021 while blocks descend multiple drainages and resuspending ash on the flanks. Photo by Jose Jose Leonardo Quexel Hernandez en julio 9, 2021, 08:43 am hora local. Courtesy of INSIVUMEH.

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

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/ ); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA 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).

Volcán El Reventador is located 100 km E of the main axis of active volcanoes in Ecuador and has had historical eruptions dating back to the 16th century, characterized by explosive events and lava flows. The most recent eruption began in 2008 and has recently consisted of ash emissions, incandescent block avalanches, a new lava dome, and lava flows (BGVN 46:02). This report updates information from February through July 2021 and is characterized by daily explosions, ash plumes, incandescent block avalanches, lava flows, and occasional pyroclastic flows and lahars, based on daily reports from Ecuador's Instituto Geofisico (IG-EPN), the Washington Volcano Ash Advisory Center (VAAC), and infrared satellite data.

During February to July 2021, IG-EPN reported daily explosions, gas-and-steam and ash plumes, and frequent crater incandescence, often accompanied by incandescent block avalanches and lava flows. The highest average number of explosions per day was 73 in March, followed by 65 in February (table 13). During May-June the average number of daily explosions had declined to 34 and 33, respectively. Ash plumes rose to a maximum height of 2.3 km above the crater on 11 June. At night and early morning, frequent crater incandescence was visible, occasionally accompanied by lava flows generally on the eastern flanks and incandescent block avalanches traveling as far as 900 m from the summit. Seismicity, which was noted throughout the reporting period, was characterized by harmonic tremor events, signals indicating emissions, few volcano-tectonic earthquakes, and dominantly long-period (LP) earthquakes.

Table 13. Monthly summary of explosions and plume heights recorded at Reventador from February through July 2021. Data courtesy of IG-EPN (February to July 2021 daily reports).

Activity at the summit was consistent during February and March 2021. There were 25-121 daily explosive events during these two months, generating gas-and-steam and ash plumes to 400-1,500 m above the crater that drifted in multiple directions (figure 142). At night, crater incandescence and incandescent block avalanches were visible on all flanks, though primarily on the NE and S flanks traveling 500-800 m below the crater (figure 143), though it was not uncommon for weather to prevent clear views of the summit. Two lava flows were reported moving down the N and NE flanks.

Figure 142. Webcam (Rebeca) images of two gray ash plumes rising from Reventador on 9 February (left) and 30 March (right) 2021. The NE flank is visible on the right side of the volcano, highlighted by recent block avalanches and active lava flows (light brown) in the February image. On 30 March white gas-and-steam emissions can be seen on the NE flank. Courtesy of IG-EPN (INFORME DIARIO DEL VOLCAN REVENTADOR No. 2021-040, 09 de febrero de 2021 and No. 2021-090, 31 de marzo de 2021).

Figure 143. Webcam (Rebeca) infrared image of Reventador’s NE flank showing the active incandescent block avalanches (bright yellow-orange) on 13 March 2021. Courtesy of IG-EPN (INFORME DIARIO DEL VOLCAN REVENTADOR No. 2021-072, 13 de marzo de 2021).

During April and May, explosions remained frequent, with 4-105 per day; ash plumes rose 400-1,400 m above the crater (figure 144) and drifted in different directions, though cloudy weather often prevented clear observations. Nighttime crater incandescence was reported during clear weather, accompanied by gas-and-steam emissions and incandescent blocks of material rolling down all flanks as far as 800 m, though the NE and S flanks were dominantly affected. On 21 April an infrared webcam recorded low temperatures of the lava flow on the NE flank, which IG-EPN indicated was no longer active. Small pyroclastic flows descending the SW flank for 600-700 m were noted on 23 and 26-27 April, but none reached the base of the cone. During 4-6 May a pyroclastic flow was reported 400 m down the SW flank, (figure 145). According to an infrared webcam, a lava flow on the NE flank became active again on 10 May; by 22 May, two flows were reported descending the NE and SE flanks (figure 144). Some blocks of material from the front of the lava flow traveled 800 m below the summit. IG-EPN reported that some inflation was noted on the N summit on 13 May, which continued into the following month. On 17 May around 1600 lahars were detected in the upper part of the Reventador River on the N drainages due to heavy rain. By 25 May the number of lahars had decreased and as a result, the seismic stations recorded consistent seismic signals starting around 0741 and continuing throughout the day.

Figure 144. Webcam (Rebeca) images showing an ash plume rising above Reventador on 20 April 2021 (left) accompanied by white gas-and-steam emissions and block avalanches rolling down the NE flank. An infrared image (right) shows the two active lava flows (bright yellow) descending the NE and SE flanks on 29 May 2021. Courtesy of IG-EPN (INFORME DIARIO DEL VOLCAN REVENTADOR No. 2021-110, 20 de abril de 2021 and No. 2021-150, 29 de mayo de 2021).

Figure 145. Webcam (Copete) image of a dense gray ash plume rising from Reventador, accompanied by a pyroclastic flow descending the SW flank at 0706 on 6 May 2021. Courtesy of IG-EPN (INFORME DIARIO DEL VOLCAN REVENTADOR No. 2021-126, 06 de mayo de 2021).

Persistent explosions and ash plumes were reported during June and July, with 3-87 daily events that rose 300-2,300 m above the crater (figure 146). The plumes drifted primarily W, N, NW, NE, and SW. At night and during the early morning, incandescence was observed on the upper part of the flanks while the two lava flows continued to descend the NE and S flanks (figure 146). Incandescent blocks of material rolled down the NE, S, and SE flanks as far as 800 m below the summit. On 7 June during 1200 and 1300 a lahar was reported on the SE flank.

Figure 146. Webcam (Copete) images showing dense ash plumes rising from Reventador on 1 June (left) and 2 July (right) 2021. The ash plume from 1 June is accompanied by a lava flow on the SE flank. Courtesy of IG-EPN (INFORME DIARIO DEL VOLCAN REVENTADOR No. 2021-153, 01 de junio de 2021 and No. 2021-184, 02 de julio de 2021).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed intermittent thermal anomalies of moderate-to-high intensity during February through July 2021 (figure 147), which reflected the active lava flows and incandescent block avalanches occurring throughout that time. In comparison, the MODVOLC thermal algorithm identified nine thermal alerts between February and July on 9 and 14 February, 20 March, 12 May, 10 and 22 June, and 28 July. Some incandescent avalanches were visible in Sentinel-2 infrared satellite imagery, though clouds often obscured the view of the summit (figure 148). These avalanches were observed descending the NE flanks.

Figure 147. Intermittent thermal activity was detected at Reventador at moderate to high levels during February through July 2021, based on the MIROVA graph (Log Radiative Power). Courtesy of MIROVA.

Figure 148. Sentinel-2 infrared satellite images of Reventador on 15 February 2021 (left) and 10 June (right) showed strong incandescent block avalanches descending the NE flanks, even through frequently dense cloud cover. Images with “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Geologic Background. Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well east of the principal volcanic axis. The forested, dominantly andesitic Volcán El Reventador stratovolcano rises to 3562 m above the jungles of the western Amazon basin. A 4-km-wide caldera widely breached to the east was formed by edifice collapse and is partially filled by a young, unvegetated stratovolcano that rises about 1300 m above the caldera floor to a height comparable to the caldera rim. It has been the source of numerous lava flows as well as explosive eruptions that were visible from Quito in historical time. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the caldera. The largest historical eruption took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Frequent historical eruptions have been reported from Mexico's Popocatépetl dating back to the 14th century. Activity increased in the mid-1990s after about 50 years of quiescence, and the current eruption, ongoing since January 2005, has included numerous episodes of lava-dome growth and destruction within the 500-m-wide summit caldera. Multiple emissions of steam and gas occur daily, rising generally 1-2 km above the summit at about 5,400 m elevation; many contain small amounts of ash. Larger, more explosive events with ash plumes and incandescent ejecta landing on the flanks and causing ashfall in nearby communities are periodically reported. Activity through January 2021 was characterized by tens to hundreds of daily low-intensity emissions that included gas-and-steam and small amounts of ash, and occasional minor and moderate explosions that sent ash plumes more than 1 km above the crater (BGVN 46:02). This report covers decreased activity from February-July 2021 using information from México's Centro Nacional de Prevención de Desastres (CENAPRED), the Washington Volcanic Ash Advisory Center (VAAC), and various satellite data.

Popocatépetl had ongoing water vapor, gas, and ash emissions throughout February-July 2021, but fewer explosions than during the period of the previous report. Ash emissions generally rose to 5.8-7.1 km altitude and drifted in many different directions. Ashfall was reported only a few times in some communities during March, May, and July. Thermal anomalies were recorded in satellite images inside the summit crater multiple times each month. The MIROVA thermal anomaly data indicated steady low-levels of thermal activity during February-April and decreased thermal activity after that through July (figure 176). CENAPRED reported the number of low-intensity emissions or ‘exhalations’ and the number of minutes of tremor in their daily reports (figure 177). Tremor activity reached 1,000 minutes per day each month from February to May but then dropped off significantly. The daily number of exhalations was relatively consistent throughout ranging from tens to hundreds per day.

Figure 176. The MIROVA graph of thermal anomalies at Popocatepetl from 14 September 2020 through July 2021 shows steady, low-level, activity through April, followed by fewer anomalies through July. Courtesy of MIROVA.

Figure 177. CENAPRED reported the number of daily ‘exhalations’ (in blue, left scale), and the number of minutes of tremor (in gold, right scale) at Popocatepetl each day during February-July 2021. The number of daily exhalations fluctuated throughout the period, but the minutes of tremor remained high through early May and then decreased. Data from CENAPRED daily reports.

Water vapor, gas, and small quantities of ash were present in the tens of daily exhalations during February 2021. There was a wide range in the number of minutes of tremor each day from a low of 33 to a high of 1,101. On many days during the month, 1-3 explosions were recorded; CENAPRED reported an explosion on 7 February that sent an ash plume 2,000 m above the summit crater. Incandescence was observed on about half the nights of the month. A swarm of 24 volcano-tectonic (VT) earthquakes was reported overnight during 10-11 February with magnitudes in the 1.0-2.6 range. Thermal anomalies appeared inside the inner crater at the summit in Sentinel-2 satellite images on 5, 10, 15, 20, and 25 February. The images on 5 and 25 February also captured ash plumes (figure 178). Small but distinct SO₂ emissions were also present in satellite imagery each day.

Figure 178. Thermal anomalies and ash emissions were both recorded in Sentinel-2 satellite images from Popocatepetl on 5 and 25 February 2021. Thermal anomalies were additionally recorded on 10, 15, and 20 February. Images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Multiple daily VAAC reports from the Washington VAAC noted emissions drifting tens of kilometers in multiple directions at altitudes of 5.8-6.4 km throughout the month. On 1 February 2021 the Washington VAAC reported an ash emission at 5.8 km altitude drifting 20 km S (figure 179); on 3 February continuous diffuse ash emissions at the same altitude drifted 45 km SW of summit. On 6 February the emissions were drifting E at 6.1 km and the next day emissions at that altitude were fanning out NE and NW of the summit. On 13 February emissions were observed in both the webcam and satellite imagery extending 35 km E at 5.8 km altitude. A remnant ash cloud at 6.1 km altitude was located 175 km W of the summit on 23 February while a new emission was located 35 km NW at 6.4 km altitude. On 28 February a concentrated ash plume extended 45 km NNW of the summit while a diffuse plume extended 120 km NNW at 5.8 km altitude.

Figure 179. Ash emissions and incandescence at the summit occurred often at Popocatepetl during February 2021 including on 1 (left) and 20 (right) February. Courtesy of CENAPRED daily reports.

During March 2021 the number of daily exhalations ranged widely from 11 to 133 and consisted of gas, water vapor, and small quantities of ash. The number of minutes of tremor ranged from a few tens to almost 1,000. Minor explosions and VT events occurred intermittently throughout the month. During an overflight on 6 March CENAPRED reported the dimensions of the internal crater as 360-390 m wide and 150-180 m deep, and it was covered with tephra (figure 180). There was no sign of a growing dome within the crater. Trace amounts of ashfall were reported on 13 March in the municipalities of Amecameca and Tlalmanalco, and again overnight 14-15 March in Amecameca. Incandescence was reported at night during 20-23 and 29-31 March. Minor explosions on 27 and 28 March produced plumes with low amounts of ash that rose 800-1,000 m and drifted N and NW. Very small but distinct SO₂ plumes were measured in satellite data each day; thermal anomalies inside the summit crater were observed in Sentinel-2 images on 2, 12, 17, 22, and 27 March (figure 181). Multiple daily VAAC reports continued, but were more intermittent during the last third of the month. On 4 March an existing ash plume was moving SW at 6.1 km altitude 45 km from the summit when a new emission occurred that rose to 7 km altitude and extended 30 km WNW. The plume reported on 13 March was typical of many during the month, drifting NW as far as 150 km from the summit at 6.4 km altitude; they were frequently observed in both satellite data and with the webcam.

Figure 180. The summit crater at Popocatepetl was 360-390 m wide, 150-180 m deep and covered with tephra on 5 March 2021 when viewed during an overflight by government officials. Courtesy of CENAPRED daily report.

Figure 181. Thermal anomalies inside the summit crater of Popocatepetl were different shapes and intensities in Sentinel-2 images on 12 and 27 March 2021 shown here, and also on 2, 17, and 22 March. Images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Daily exhalations ranging from 13-148 per day continued during April 2021. The emissions were primarily gas and water vapor, although intermittent events with small quantities of ash were frequent. Daily tremors ranged from 34-955 minutes in length. Incandescence was visible at the summit during 1-6 and 17-19 April. A moderate explosion overnight on 3-4 April produced incandescent ejecta that traveled up to 1 km down the slopes of the volcano and produced an ash plume that rose 1,200 m and drifted SE. The Washington VAAC reported the ash plume at 7.3 km altitude drifting 30 km E from the summit. Daily VAAC reports were issued for ash plumes that rose to 5.8-7 km altitude and were often visible up to 50 km from the summit. A very bright thermal anomaly appeared inside the summit crater in Sentinel-2 satellite imagery on 1 April, and a very faint one was present on 21 April. A few small to moderate plumes of SO₂ were detected with satellite instruments during April, but most days the anomalies were small (figure 182).

Figure 182. Moderate size SO2 plumes were measured at Popocatepetl intermittently throughout April 2021 including on 2 and 29 April. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Gas and small quantities of ash were typical of the 25-136 daily emissions throughout May 2021. Tens to hundreds of minutes of tremors were also reported each day. Thermal anomalies at the center of the summit crater were distinct in Sentinel-2 satellite images on 6, 26, and 31 May. Moderate SO₂ plumes were common during the first half of May but diminished during the second half. Significantly fewer ash emissions were reported by the Washington VAAC than during the previous few months. Ash plumes during 1-4 May rose to 5.8-6.4 km altitude and drifted NE up to 65 km from the summit. The ash plumes reported during 7-9 May rose to 5.8 km and drifted mostly E. Additional plumes during 14-15, 18, 20-22, 28-29 May and 31 May-1 June rose to 5.8-6.1 km and drifted for a few hours in multiple directions before dissipating (figure 183). Trace amounts of ash fell in Tetela del Volcán during the afternoon of 28 May.

Figure 183. Ash plumes at Popocatepetl were recorded in webcams on 2, 12, 15, and 29 May 2021. Courtesy of CENAPRED daily reports.

Ash emissions were only reported twice during June and four times during July 2021 by the Washington VAAC. They rose to 6.1 km on 11-12 June and 5.8 km on 17 June, drifting NW both times. Similar emissions also occurred during 7, 11-12, 16-18, and 22 July. Exhalations continued to be reported daily at the same rate as May, but there were fewer minutes of tremor both months, and no tremors occurred on nine days of June and ten days of July. Small thermal anomalies appeared in Sentinel satellite images in the same location as earlier images at the center of the summit crater on 10 June, and 10 and 25 July. Small but distinct SO₂ plumes were recorded throughout both months, with only a few days of larger emissions measured by the satellite instruments. CENAPRED reported incandescent ejecta visible a short distance from the crater on the morning of 17 July and an explosion on 21 July that produced an ash plume that rose 800 m and drifted W. An explosion on 22 July produced incandescent ejecta and an ash plume that rose 900 m above the summit and also drifted W (figure 184). Ashfall was reported in the communities of Tlalnepantla, Totolapan, and Huitzilac in the state of Morelos. Another explosion on 24 July sent incandescent fragments down the N flank and an ash plume to 800 m high that drifted NW.

Figure 184. Ash plumes and incandescent ejecta were less frequent at Popocatepetl during July 2021 than during previous months, but were still recorded a number of times, including on 12 and 29 July. Courtesy of CENAPRED daily reports.

Geologic Background. Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Information Contacts: Centro Nacional de Prevención de Desastres (CENAPRED), Av. Delfín Madrigal No.665. Coyoacan, México D.F. 04360, México (URL: http://www.cenapred.unam.mx/, Daily Report Archive https://www.gob.mx/cenapred/archivo/articulos); 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/).

The dacitic Santiaguito lava-dome complex of Guatemala's Santa María volcano has been actively erupting since 1922. It formed within a large crater on the SW flank which was created during the VEI 6 1902 eruption. Ash explosions, pyroclastic, and lava flows have emerged from Caliente, the youngest of the four vents in the complex, for more than 40 years. The Caliente vent is at about 2.5 km elevation, and the summit of Santa Maria is around 3.7 km elevation. A lava dome that appeared within the summit crater of Caliente in October 2016 has continued to grow, producing frequent block avalanches down the flanks. Daily explosions with ash plumes and block avalanches continued during February-July 2021, the period covered in this report, with information primarily from Guatemala's INSIVUMEH (Instituto Nacional de Sismologia, Vulcanologia, Meterologia e Hidrologia).

Blocky lava extrusion from the active dome inside the summit crater of Caliente persisted throughout February-July 2021. This resulted in ongoing block avalanches and ash that descended primarily the W and SW flanks of Caliente, and occasionally the S and SE flanks. Material frequently reached the base and resulted in fine-grained ashfall and suspended ash around the perimeter. Near-constant degassing of water vapor and magmatic gases occasionally contained small amounts of ash; plumes rose to 3.0-3.2 km altitude (up to 700 m above the summit of Caliente) and drifted in multiple directions. Sounds similar to a turbine engine from the constant degassing were reported on most days. Explosions with gas and ash occurred almost daily; the plumes rose to 3.0-3.6 km altitude, and a few drifted up to 10-15 km, producing ashfall in nearby communities before dissipating. Thermal activity remained constant through May, dropped off in June, and returned to typical levels in July 2021 (figure 122).

Figure 122. Steady levels of thermal activity persisted at Santa Maria from December 2020 through May 2021 as seen in the graph of Log Radiative Power produced by the MIROVA project from 22 September 2020 through July 2021. Activity declined in June and returned to typical levels in July 2021. Courtesy of MIROVA.

Ashfall was reported in El Faro (7 km SSW), Aldea Las Marias (10 km S), and El Viejo Palmar (10 km S) on 5 February 2021. The next day a small pyroclastic flow was reported early in the morning on the W flank. The Washington VAAC reported an ash emission that rose to 4.6 km altitude on 7 February. It was seen moving WSW and extending approximately 15 km from the summit before dissipating later in the day. This was the only VAAC report issued for the reporting period. In a special bulletin that day INSIVUMEH noted pyroclastic flows on the SW flank that reached the head of the Rio San Isidro drainage (figure 123). They also reported ash moving SW reaching Finca Montebello, Loma Linda (7 km SW), and San Marcos Palajunoj (8 km SW). On 10 February ashfall was reported in Palajunoj. A thermal anomaly seen in Sentinel-2 satellite imagery extended down the W flank on 16 February (figure 124), likely from either incandescent blocks or a pyroclastic flow. A strong sulfur odor was noted in the area around Las Marias on 20 February. Weak pyroclastic flows affected the E and W flanks of the Caliente on 22 February; ash plumes drifted 2.5 km SW on 26 February.

Figure 123. Explosions produced ash plumes and pyroclastic flows at the Caliente vent of Santa Maria on 7 February 2021. Courtesy of INSIVUMEH (Special Bulletin BESAN-007-2021, 7 February 2021).

Figure 124. A linear thermal anomaly was apparent on the W flank of the Caliente dome at Santa Maria on 16 February 2021. It was likely due to either incandescent blocks or a pyroclastic flow. Image uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

The loud noises from constant degassing were heard in El Palmar on 4 March 2021; ash plumes that day drifted up to 2 km SW. Thermal anomalies appeared in satellite data inside the summit crater of Caliente on 8 and 23 March. Explosions with ash on 9 March rose to 3.0 km altitude and drifted S and SW (figure 125). On 22 March ashfall was reported in Aldea Las Maria, Calaguache, and other nearby communities. Ashfall was reported on 25 and 27 March in Aldeas San Marcos and Loma Linda Palajunoj.

Figure 125. An explosion at the Caliente dome of Santa Maria’s Santiaguito complex on 9 March 2021 rose to 3 km altitude and drifted S and SW Photograph by Lluis Lopez, taken from El Palmar, Quetzaltenango, courtesy of Stereo100Noticias.

Ash plume heights were slightly higher during April 2021, reaching 3.5 or 3.6 km altitude on most days, especially during the second half of the month. Resuspended ash from debris descending the flanks of Caliente dome produced ashfall in Viejo Palmar on 2 April. Sentinel-2 satellite imagery showed a thermal anomaly inside the summit crater that day as well. On 6 April ash plumes drifted 2.5 km SW before dissipating. On 13 and 16 April ashfall was reported in Aldeas San Marcos, Loma Linda Palajunoj, and other nearby communities. INSIVUMEH released a Special Bulletin on 18 April about a lahar that descended Rio San Isidro, carrying branches, tree trunks, volcanic ash, and blocks 1-2 m in diameter.

Ashfall was reported on 1, 6, 11, 16, 21, 26, and 31 May 2021 in Aldeas San Marcos, Loma Linda Palajunoj and other nearby communities from frequent ash plumes that rose to 3.4-3.6 km altitude and drifted SW (figure 126). Increased rainfall resulted in lahars reported on 15, 16, 24, and 30 May. The lahars on 15 and 16 May descended the Rio Cabello de Angel drainage. Branches, trunks, and volcanic blocks 1-3 m in diameter caused vibrations as they passed the seismic stations on 15 May; the next day the flow was a 25-m-wide and 1 m high pasty slurry of sulfur-smelling material full of ash and blocks from 30 cm to 1 m in diameter. The lahar on 24 May descended Rio Tambor and Rio San Isidro with tree trunks, branches, volcanic ash, and blocks 1-2 m in diameter. On 30 May heavy precipitation produced a lahar in Rio San Isidro that occurred near the Finca Filadelfia as a pasty mixture of water, blocks up to 1 m in diameter, and fine sediment, along with branches and tree trunks. A thermal anomaly was present in satellite imagery inside the summit crater on 27 May.

Figure 126. Weak explosions of ash on 31 May 2021 rose to 2.8 km altitude, drifted 5 km SW, and fine-grained ash fell in San Marcos and Loma Linda. Courtesy of CONRED .

The ash explosions reported on 5 June 2021 rose to 2.8 km altitude and drifted 7 km SW resulting in ashfall in Aldeas San Marcos and Loma Linda Palajunoj. Ashfall was reported in the mountainous areas of Monte Claro on 8 June from plumes that reached 3.6 km altitude and drifted W and SW. On 12 and 13 June lahars descended the Rio Nima 1 (figure 127). Rio Cabello de Angel and Nima 1 were the sites of lahars on 15 June where fine-grained material and blocks 30 cm to 1 m in diameter moved down the drainages in a 1-m-deep and 20-m-wide slurry. On 15 June ashfall was reported in Calaguache and Santa Maria de Jesus (5 km SE), and on 20 and 25 June it was again reported in Loma Linda and San Marcos Palajunoj. Another lahar descended Rio Cabello de Angel and Nima 1 on 29 June after rainfall on the upper parts of the volcano. Thermal anomalies were present in Sentinel-2 satellite images inside the summit crater of Caliente on 11 and 26 June.

Figure 127. On 12 June 2021 a lahar of mud and debris descended the Nimá 1 river channel near Finca El Faro. Photo by Edgar Cabrera from COLRED at Finca El Faro, El Palmar, Quetzaltenango. Courtesy of Rony Veliz.

During July 2021 incandescence around the summit crater of Caliente was reported more frequently than during the previous months. The constant block avalanches continued from the extruding lava primarily on the W, SW, and S flanks with some blocks reaching the base and producing ash plumes. On 5, 10, 15, 20, and 30 July ash plumes from explosions drifted 8-12 km W and SW and caused ashfall in Loma Linda and San Marcos (figure 128). The extrusion of blocky lava from the crater was reported as a 600-700 m long flow on the W flank on 10, 15, and 25 July. A lahar on 14 July in the El Tambor ravine was a pasty mixture of water, blocks up to 3 m in diameter, and fine sediments that produced seismic vibrations. Sulfur odors occurred in Las Marias on 20 and 25 July. Thermal anomalies at the summit were recorded in satellite images on 6, 16, and 31 July.

Figure 128. Norma Cardona of COLRED San Marcos Palajunoj El Palmar Quetzaltenango, reported that on 5 July 2021 the Caliente dome of Santiaguito was weakly degassing with minor ash drifting W. Ashfall was reported in communities to the SW that day. Courtesy of Frídel Mejicanos.

Geologic Background. Symmetrical, forest-covered Santa María volcano is part of a chain of large stratovolcanoes that rise above the Pacific coastal plain of Guatemala. The sharp-topped, conical profile is cut on the SW flank by a 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank, and was formed during a catastrophic eruption in 1902. The renowned Plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic-andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four vents, with activity progressing W towards the most recent, Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); 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); 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); CONRED, Coordinadora Nacional para la reduccion de desastres (URL: https://conred.gob.gt/, https://twitter.com/ConredGuatemala/status/1399369155544076295 ); Stereo100Noticias (URL: https://twitter.com/stereo100xela/status/1369295245272363014); Rony Veliz (URL: https://twitter.com/ronyveliz692/status/1403836189841494019); Frídel Mejicanos (URL: https://twitter.com/FridelMejicanos/status/1412189491289264129).

A brief period of ash emissions in January 2012 was the first documented activity in over 50 years (BGVN 36:12) at Lewotolok (also known as Lewotolo), on the island of Lembata (Lomblen) in the Lesser Sunda Islands of Indonesia. Between then and November 2020, intermittent thermal activity was identified using MODVOLC and Sentinel-2 infrared data (BGVN 41:09, 46:02) and a single episode of increased seismicity was noted by PVMBG in October 2017. The only emissions reported were white steam and gas plumes rising up to 500 m above the summit crater. Increased seismicity at the end of November 2020 was accompanied by explosions with ash plumes and incandescent ejecta (BGVN 46:02) that resulted in ashfall and evacuations from surrounding communities. Explosions with ash emissions rising up to 1,500 m and incandescent ejecta rising 600 m above the crater were reported through the end of January 2021. This report covers similar explosive activity that continued from February-July 2021 with information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, and satellite data.

Multiple daily explosions were reported throughout February-July 2021 except for a brief pause during late April and early May (figure 13). Multi-day periods of incandescent ejecta rising hundreds of meters above the summit and extending a similar distance from the crater continued in February and increased to near-daily during June and July; multiple episodes of ejecta fell 1 km from the crater rim. Dense gray and black ash plumes were infrequent in January and February but increased to multiple times a day in mid-March, rising 1,000-1,500 m above the summit; the highest plume of the period reached over 3 km above the summit on 13 June. Daily explosive activity with ash plumes and incandescent ejecta continued through the end of July. Thermal anomalies in MIROVA data indicated pulses of higher activity during March-early April and late June-July (figure 14). Satellite imagery provided thermal and visual evidence of fresh lava flow activity inside the summit crater on multiple occasions.

Figure 13. The number of daily explosions at Lewotolok during 1 February-31 July 2021 ranged from 0-41. Data compiled from PVMBG daily reports.

Figure 14. Periods of increased thermal activity at Lewotolok were recorded by the MIROVA project during December-2020-early January 2021, March-early April 2021, and late June-July 2021. Courtesy of MIROVA.

Activity during February-April 2021. PVMBG reported daily white and gray emissions that rose 200-700 m above the summit, and occasionally higher, during February 2021. Explosions occurred virtually every day with a maximum of 21 reported on 3 February, but 5-10 per day were typical. During 5-9 February loud noises accompanied bursts of incandescent ejecta that rose 300 m above the summit and extended 300-500 m SE (figure 15). MAGMA Indonesia reported an eruption on 10 February that produced an ash plume that rose 700 m and drifted E (figure 16). Thermal anomalies appeared in satellite images on 7, 12, 17, and 22 February.

Figure 15. A strong thermal anomaly recorded at the summit of Lewotolok on 7 February 2021 was likely due to the incandescent ejecta reported by PVMBG that rose 300 m high and sent material 500 m SE. Sentinel-2 satellite imagery uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Figure 16. An ash plume rose 700 m above the summit of Lewotolok and drifted E on 10 February 2021. Courtesy of MAGMA Indonesia and PVMBG.

The abrupt increase in the number of daily explosions at the beginning of March 2021 was accompanied by loud rumbling noises and observations of incandescent ejecta. During 2-5 March incandescent ejecta rose 200-800 m above the summit towards the SE. On 9 March the ejecta was reported 1,300 m E and SE of the summit. From 11-15 March the incandescent ejecta rose 500 m above the crater rim and was ejected as far as 1,000 m E and SE. The Darwin VAAC reported ash plumes on 13 and 14 March that drifted SW at 1.2 km altitude. MAGMA Indonesia reported two explosions, one on 14 March that rose 1,300 m above the summit and drifted S (figure 17) and one on 15 March that rose 1,000 m and drifted E. During 19-31 March there were 4-20 explosions each day that produced audible booms and rumbling; incandescent ejecta rose as high as 500 m and was thrown the same distance E and SE. Thermal anomalies at the center of the summit crater were apparent in Sentinel-2 satellite imagery on 4 and 19 March.

Figure 17. An explosion at Lewotolok on 14 March 2021 produced an ash plume that rose 1,300 m above the summit and drifted S. Courtesy of MAGMA Indonesia and PVMBG.

Cloudy weather obscured views of the summit for several days in early April 2021, but during 5-17 April multiple daily explosions produced incandescent ejecta often reaching 500 m high, loud noises, and dense gray and black ash plumes (figure 18). Sentinel-2 imagery indicated thermal anomalies inside the summit crater likely caused by fresh lava flows on 8 April. The thermal anomalies and visual imagery from 13 April revealed a new dark area, still hot around the edges, that also likely represented fresh lava (figure 19). Ejecta reached 300-500 m E and SE of the summit during 8-12 April; on 16 April PVMBG reported incandescent ejecta 1,000 m above the summit. MAGMA Indonesia noted one to five eruptions each day during 12-18 April; dense white, gray, and black ash plumes rose 500-1,500 m above the summit and drifted W or SW most days. The Darwin VAAC reported ash emissions on 15 and 16 April which rose 400-700 m above the summit and drifted WNW, and a plume that rose to 3,000 m altitude (1,500 m above the summit) on 18 April and drifted W (figure 20). Additional explosions were reported on 20-21 and 24-25 April, producing gray and black ash plumes that rose 600-1,000 m above the summit. By 28 April only steam emissions were observed, and no thermal anomalies were present around the fresh dark flow visible inside the summit crater.

Figure 18. Incandescent ejecta rose several hundred meters above the summit of Lewotolok on 13 April 2021. Courtesy of MAGMA Indonesia and PVMBG.

Figure 19. A comparison of visual and thermal imagery of Lewotolok from 4 March (left), 8 (middle) and 13 April 2021 (right) shows the appearance of fresh dark lava (natural color images, top) and thermal anomalies (Atmospheric penetration images, bottom) in the 8 and 13 April images that were not present in the 4 March images. Two plumes of steam and ash rose from the summit crater of Lewotolok on 8 April 2021 (top center) and corresponded with two thermal anomalies inside the crater (bottom center). The NW -trending linear anomaly was likely caused by a fresh lava flow. Small anomalies around the dark area on 13 April (bottom right) suggested cooling lava. Natural color images use bands 4, 3, and 2; Atmospheric penetration rendering uses bands 12, 11, and 8a. Courtesy of Sentinel Hub Playground.

Figure 20. A dense gray and black ash plume rose 1,500 m above the summit of Lewotolok and drifted S and SW on 18 April 2021.

Activity during May-July 2021. A single explosion reported by PVMBG and Magma Indonesia on 2 May caused a VONA and a VAAC report to be issued. The ash plume rose 500-600 m above the summit and drifted W. Lewotolok was quiet with white and gray emissions, and no explosions reported, until 14 May when incandescent ejecta and ash emissions resumed for the rest of the month. Strombolian activity accompanied by loud noises sent incandescent ejecta 300 m high and 400-700 m SE from the summit; satellite imagery from 18 May showed a small thermal anomaly inside the summit crater. The ash plumes from the multiple explosions were dense and gray, and rose 400-800 m high. The Darwin VAAC reported multiple ash emissions during 21-25 and 28-29 May that were clearly seen in satellite imagery extending SE, S, or SW at 2,100 m altitude; the plume on 28 May (figure 21) rose 1,000 m above the summit to about 2,400 m altitude and drifted SW.

Figure 21. An ash plume at Lewotolok on 28 May 2021 rose 1,000 m above the summit and drifted SW. Courtesy of PVMBG and MAGMA Indonesia.

Multiple explosions with either ash plumes or Strombolian activity were reported daily throughout June 2021. During 1-9 June incandescent ejecta fell at least 300 m in all directions from the summit with loud noises reported (figure 22). On 5 June the 300-m-high ejecta reached 1,000 m NW and 200 m SE. During 8-16 June eruptions with ash plumes were reported by MAGMA Indonesia; both VONA’s and VAAC reports were issued each day. The white and gray ash emissions generally rose 500-800 m above the summit. On 10, 14, and 21 June the plumes were reported 2,000 m above the summit drifting W and NW. An explosion on 13 June produced an ash plume to 3 km above the summit, the highest of the period, that was observed drifting W in satellite imagery at 4.9 km altitude. Rumbling reported during 16-20 June accompanied incandescent ejecta sent 300-500 m in all directions from the crater. On 2, 7, 12, and 27 June thermal anomalies appeared in Sentinel-2 imagery inside the summit crater; the strong anomaly on 27 June suggested new flow activity (figure 23).

Figure 22. Incandescent ejecta rose several hundred meters above the summit of Lewotolok on 8 June 2021 and many other days during the month. Courtesy of PVMBG and MAGMA Indonesia.

Figure 23. Thermal anomalies appeared inside the summit crater at Lewotolok on multiple days during June 2021 including 12 (left) and 27 June (right). The strong anomaly on 27 June suggested new flow activity with a weaker anomaly just off the N end of the larger one. Images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Heightened levels of activity continued throughout July 2021. Thermal and visual evidence of fresh lava flows inside the summit crater appeared in satellite images on 2 July (figure 24). Additional thermal anomalies were recorded on 12, 22, and 27 July. Bursts of incandescent ejecta frequently caused loud noises. Vegetation caught fire around the summit from incandescent material on 3 and 28 July (figure 25). The tephra was usually reported 300-500 m from the crater but was sent 1,000 m SW on 3 July, and 1,000 m SE on 12, 18, 28, and 30 July. Five or more explosions were reported daily by PVMBG during 1-20 July, with a maximum of 28 reported on 9 July. The dense gray or gray-and-black ash emissions consistently rose 800-1,000 m above the summit, usually drifting W or NW (figure 26). The tallest plume on 7 July was reported by MAGMA Indonesia at 1,100 m above the summit, drifting E.

Figure 24. Evidence of fresh lava flow activity at Lewotolok appeared in Sentinel-2 satellite imagery on 2 July 2021. A thin line of dark material seen in natural color rendering (left, bands 4,3,2) is the area of strongest thermal anomaly seen in the Atmospheric penetration rendering image (right, bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Figure 25. Vegetation near the summit of Lewotolok caught fire from incandescent ejecta on 28 July 2021. Courtesy of PVMBG and MAGMA Indonesia.

Figure 26. Gray ash and steam plumes rose 800 m from a pyroclastic cone-like feature inside the summit of Lewotolok on 14 July 2021. Courtesy of PVMBG and MAGMA Indonesia.

Geologic Background. The Lewotolok (or Lewotolo) stratovolcano occupies the eastern end of an elongated peninsula extending north into the Flores Sea, connected to Lembata (formerly Lomblen) Island by a narrow isthmus. It is symmetrical when viewed from the north and east. A small cone with a 130-m-wide crater constructed at the SE side of a larger crater forms the volcano's high point. Many lava flows have reached the coastline. Eruptions recorded since 1660 have consisted of explosive activity from the summit crater.

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.esdm.go.id/v1); 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).

Indonesia’s Sinabung volcano in north Sumatra had its first confirmed Holocene eruption during August and September 2010. It remained quiet until September 2013 when a new eruptive phase began that continued through mid-2018. Dome growth and destruction resulted in block avalanches, multiple explosions with ash plumes, and deadly pyroclastic flows during the period. After a pause in activity from September 2018 through April 2019, explosions resumed during May and June 2019. Rock avalanches, frequent, dense, ash-bearing explosions, and periodic pyroclastic flows continued through February 2021. This report covers ongoing similar activity from March through June 2021 with information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, and the Darwin Volcanic Ash Advisory Centre (VAAC). Additional information comes from satellite instruments and the Indonesian National Disaster Management Agency (BNPB).

Hundreds of block avalanches and tens of ash-bearing explosions were reported each month during March to mid-May 2021. Ash plumes rose 500-2,000 m above the summit (3,000-4,500 m altitude) on most days; occasional larger events produced much higher plumes. Two major sets of explosions, on 2 March and 13-14 May, each produced ash plumes that rose to 12.2 km altitude, more than 10 pyroclastic flows, and significant SO₂ plumes measured by satellite instruments. Reports of activity during the period came from the Sinabung Observation Post (in Surbakhti, 10 km SE of the volcano) and from geoscientists monitoring seismic instruments and webcams from remote locations; the combined information provides a more complete picture of activity at the volcano (table 10). Thermal activity was recorded by the MIROVA project and indicated a spike in radiative power that began in late February and lasted through May 2021, attributable to increased explosive activity (figure 93). Two notable sequences of explosions on 2 March and 13-14 May produced significant plumes of SO₂ that were measured by the TROPOMI instrument on the Sentinel-5P satellite (figure 94). None of the other explosions during the period produced significant SO₂ anomalies. Only two days of explosions, 3 and 6 June, occurred after 19 May through the end of June.

Table 10. A summary of information and sources reporting activity at Sinabung during March-June 2021 includes the distance block avalanches traveled, the number of eruptions, pyroclastic flows, and lahars reported by the observatory, the seismic eruptions recorded by MAGMA Indonesia, and the VONA’s issued. All heights and distances shown are in meters. Information provided by PVMBG unless otherwise noted. Courtesy of PVMBG and MAGMA Indonesia.

Figure 93. An increase in thermal activity at Sinabung during late February-May 2021 corresponded to an increase in explosive activity during the period as shown in the MIROVA graph of Log Radiative Power for 24 Aug 2020 through June 2021. Courtesy of MIROVA.

Figure 94. High level explosions at Sinabung on 2 March and 13 May 2021 produced significant plumes of SO2 that drifted NW from the volcano and were measured by the TROPOMI Instrument on the Sentinel-5P satellite. The ash plumes were reported at 12.2 km altitude. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Activity during March-June 2021. Significant explosive activity continued at Sinabung during March 2021. In a special press release on 2 March, PVMBG reported a series of pyroclastic flows that began at 0642 local time and traveled 2,000-5,000 m ESE from the summit accompanied by a column of ash that rose 4,000-5,000 m above the body of the pyroclastic flow (figure 95). MAGMA Indonesia reported three explosions that rose to about 1,000 m above the summit and drifted E and SW. The Darwin VAAC first reported that the ash emissions from the eruption rose to 7.6 km altitude (5.1 km above the summit) and drifted W; they were clearly discernable in satellite imagery. About an hour later they updated the altitude of the plume to 12.2 km based on analysis of HIMAWRI-8 imagery. In the following hours the plume was observed drifting W at 12.2 km altitude and SW at 7.6 km before dissipating. According to BNPB ashfall was noted in 17 villages in the Tiganderket District, eight villages in the Kutabuluh District, and 15 villages in the Tigabinaga District.

Figure 95. This explosion at 0836 local time was one of three at Sinabung on 2 March 2021 that produced 15 pyroclastic flows and ash plumes that rose to 12.2 km altitude according to the Darwin VAAC. The pyroclastic flows descended up to 3.7 km down the SE and E flanks. Photo by PVMBG - Sinabung PGA Post. Courtesy of PVMBG (Press Release Volcanic Activity of Mount Sinabung – North Sumatra March 2, 2021).

On most days in March steam plumes were observed rising 50-500 m above the summit; they reached 1,000 m high on 7 March. Block avalanches were reported descending the E and SE flanks 500-1,500 m on 12 days of the month. The Sinabung Observation Post reported 49 explosion earthquakes and gray ash emissions. There were 1-2 explosions on most days; six were observed on 11 March (figure 96) that all rose only 500-1,000 m above the summit and drifted W and SW with no ashfall reported. MAGMA Indonesia reported an explosion on 15 March that rose 2,000 m above the summit; the Darwin VAAC could not confirm it in satellite imagery due to meteoric clouds. For the second half of March, 1-4 explosions were reported daily; dense gray ash rose 500-1,000 m above the summit and drifted SW, W, NW, and NE.

Figure 96. Six explosions with ash emissions from Sinabung were reported on 11 March 2021. The plumes rose 500-1,000 m above the summit and drifted S and SW. Courtesy of MAGMA Indonesia.

MAGMA Indonesia reported 42 eruptions throughout March with dense gray ash emissions that rose 500-2,000 m above the summit and drifted SW, W, or NW. The Darwin VAAC issued 53 ash advisories. VONAs were issued 22 times; two on 2 and 11 March were for pyroclastic flows, the others were for ash plumes from explosions. There were 20 pyroclastic flows reported by PVMBG during the month; 15 of them occurred on 2 March when they traveled 1,000-3,700 m down the E and SE flanks and 2,300 m down the S flank (figure 97). One pyroclastic flow was reported on 1 March, and two others were reported on 3 and again on 11 March that traveled 2,000-3,000 m ESE from the summit. Three seismic signals indicative of lahars were recorded on 12, 16, and 18 March.

Figure 97. A strong thermal anomaly at Sinabung was recorded in Sentinel-2 satellite imagery on 2 March 2021. Its location near the summit on the ESE flank suggests it was related to one of the 15 pyroclastic flows observed that day. Image uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

The frequency of explosive activity increased significantly during April 2021. Block avalanches were reported on 15 days, traveling 500-1,500 m down the S and SE flanks. PVMBG reported 123 eruptions with gray ash plumes rising 500-1,000 m above the summit. VONA’s were issued for 30 events. MAGMA Indonesia reported 74 explosions with dense gray ash emissions rising 500-2,000 m above the summit. There were 1-10 explosions nearly every day; only two days had no explosions reported. Eight explosions were reported on 2 April with heights of 500-1,000 m above the summit. On 4 April PVMBG reported an ash emission to 3.7 km altitude, but the Darwin VAAC revised that estimate to 5.5 km based on satellite infrared temperature data (figure 98). During 7-8 April the VAAC reported ash emissions at 4.3 km altitude. MAGMA Indonesia reported eight explosions on 17 April with plume heights ranging from 500 to 1,500 m above the summit, drifting S and W. On 19 April emissions were reported by the Darwin VAAC drifting SE at 4.6 km altitude; they reached 4.3 km on 24 April. For the remainder of the month six or more explosions occurred most days, with altitudes of 3.0-3.9 km. Seven pyroclastic flows were reported during April. On 1 April, one traveled 1,500 m down the SE flank. One was reported on 8 April, two on 13 April, and one each on 19, 21, and 29 April. The pyroclastic flow on 21 April traveled 2,000 m down the flank. Signals indicating lahars were recorded on 12, 16, 24, 29, and 30 April.

Figure 98. PVMBG reported 123 explosions with ash at Sinabung during April 2021, including four on 4 April (top left), five on 16 April (top right), nine on 20 April (bottom left), and six on 28 April (bottom right). Courtesy of MAGMA Indonesia and PVMBG.

Substantially fewer explosions were reported during May 2021 than April, although the ash plumes were higher for several events. The Sinabung Observation Post reported 37 explosions that produced gray ash plumes rising 500-3,000 m above the summit; 1-6 explosions occurred daily through 14 May; a single explosion on 19 May was the last one recorded for the month. The ten VONA’s also recorded plume heights 700-3,000 m. MAGMA Indonesia reported 26 seismic events with dense gray emissions ranging from 500-3,500 m high. During 6-10 May ash emissions were reported 2,000 m or higher above the summit each day; six explosions were reported by PVMBG and MAGMA Indonesia on 8 May. The Darwin VAAC noted that ash plumes on 6 May rose to 4.6 km altitude. The next day the emissions rose to 5.2-5.5 km altitude and were discernable late in the day drifting NNW in RGB satellite imagery. On 8 May the ash plumes were reported at 4.3-5.2 km altitude drifting E; on 10 May two discrete events rose to 4.9 and 3.7 km and drifted S, both noted in satellite imagery (figure 99). Four explosions were reported on 11 May. Sentinel-2 satellite imagery recorded incandescent material in the large SE flank ravine that day (figure 100).

Figure 99. Three explosions at Sinabung on 10 May 2021, including this one at 0750 local time produced ash emissions that rose up to 2,500 m above the summit (4.9 km altitude) and drifted S. Courtesy of MAGMA Indonesia and PVMBG.

Figure 100. Four explosions were reported at Sinabung on 11 May 2021; a thermal anomaly extended hundreds of meters down the SE flank ravine in this Sentinel-2 satellite image. Image uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

During 13-14 May six explosions and 15 pyroclastic flows were reported by PVMBG with ash plumes 700-1,000 m above the summit, and pyroclastic flows descending the SE and E flanks 2,500-4,000 m. A larger eruption with ash to 12.2 km that drifted NW, clearly identifiable in satellite imagery, was reported by the Darwin VAAC on 13 May. A second explosion three hours later produced a plume that was identifiable in RGB satellite imagery at 9.8 km altitude moving WNW. Eruptions were ongoing on 14 May, with plumes rising to 9.1-10.7 km altitude and drifting NW (figure 101). A significant SO₂ plume was measured by satellite instruments that day. A single large explosion early on 19 May (local time) produced an ash plume to 3,500 m above the summit (5.9 km altitude). The Jakarta Meteorological Office reported the eruption to the Darwin VAAC but it was not visible in satellite imagery due to meteoric clouds. This was the last explosion reported for May. Five lahars were recorded during the month; one each day on 12, 15, and 16 May, and two on 13 May.

Figure 101. This photo was posted to Twitter on 15 May 2021 with the caption “..areas affected by the eruption of Mount Sinabung” and likely represents ashfall from the large explosions of 13-14 May 2021. Courtesy of amoy rest buying.

Very little activity was reported from Sinabung during June 2021. Steam emissions rose 50-300 m above the summit on most days, occasionally rising to 500 m. Block avalanches were reported only on 11 and 12 June. PVMBG reported two seismic eruption events, on 3 and 5 June, but they were not observed. A single pyroclastic flow occurred on 6 June, the only day a single VONA was issued. MAGMA Indonesia reported two eruption events on 4 June and one on 6 June; none were observed due to poor weather conditions. The Darwin VAAC reported a significant eruption on 6 June that sent an ash plume to 9.1 km altitude that drifted W. Initially it was not visible, but later appeared on RGB satellite imagery moving N and W. A few hours after the eruption the plume was drifting N at 4.3 km altitude, W at 7.3 km, and WSW at 9.1 km. It dissipated the following morning, and was the last explosion reported for June. Lahars were recorded on 3, 15, and 25 June.

Geologic Background. Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical andesitic-to-dacitic edifice is at the southern end of the four overlapping summit craters. The youngest deposit is a SE-flank pyroclastic flow 14C dated by Hendrasto et al. (2012) at 740-880 CE. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.

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.esdm.go.id/v1); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); 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/); 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/); amoy rest buying (URL: https://twitter.com/jjaemshine/status/1393531437949743111).

Tofua is a remote volcano in the central part of the Tonga Islands group that contains a 5-km-wide caldera; three post-caldera cones were constructed at the N end of a caldera lake. The easternmost cone has three craters that have produced young basaltic-andesite lava flows, some of which traveled into the caldera lake. The largest and northernmost of the cones, Lofia, has a steep-sided crater that is 70 m wide and 120 m deep and has been the source of historical eruptions dating back to the 18th century. Recent activity has been characterized by intermittent thermal anomalies in the Lofia crater (BGVN 45:08), which continues through this reporting period of August 2020 through July 2021. Information primarily comes from satellite data.

Summary of activity during August 2020-July 2021. No ash advisories were issued during the reporting period; however, intermittent hotspots were detected by Sentinel-2 thermal satellite imagery and Suomi NPP/VIIRS sensor data throughout the reporting period (figure 12). Anomalies from the MODVOLC system clustered during February 2021 through April and June. There was a notable increase in activity during mid-February through July, compared to the previous months, which included distinct sulfur dioxide plumes (figure 13) and consecutive days with thermal anomalies, according to NASA VIIRs satellite data.

Figure 12. Timeline summary of observed activity at Tofua from August 2020 through July 2021. For Sentinel-2, MODVOLC, and VIIRs data, the dates indicated represent detected thermal anomalies. For the SO2 data, the dates indicated represent detected sulfur dioxide plumes. White areas indicate no activity was observed, which may also be due to cloud cover. Each cell represents one calendar day. Data courtesy of Sentinel Hub Playground, HIGP, NASA Worldview using the “Fire and Thermal Anomalies” layer, and NASA Global Sulfur Dioxide Monitoring Page.

Figure 13. Weak but distinct sulfur dioxide emissions were detected from Tofua on 17 (top left), 18 (top right), 19 (bottom left), and 25 (bottom right) February 2021, each of which drifted W, based on data from the TROPOMI instrument on the Sentinel-5P satellite. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Sentinel-2 infrared satellite imagery and NASA Worldview detected intermittent thermal anomalies during August 2020 through July 2021 dominantly in the Lofia crater (figure 14); rare fires were noted along the NW coast of the island. Beginning in mid-February, the activity notably increased with a stronger thermal anomaly. This increase was accompanied by white gas-and-steam emissions, which included distinct sulfur dioxide plumes.

Figure 14. Sentinel-2 infrared satellite imagery showed a persistent thermal anomaly in the Lofia crater at Tofua during September 2020 through May 2021; the intensity of the anomaly notably increased during February through May and was occasionally accompanied by white gas-and-steam emissions. Images with "Atmospheric penetration" (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Geologic Background. The low, forested Tofua Island in the central part of the Tonga Islands group is the emergent summit of a large stratovolcano that was seen in eruption by Captain Cook in 1774. The summit contains a 5-km-wide caldera whose walls drop steeply about 500 m. Three post-caldera cones were constructed at the northern end of a cold fresh-water caldera lake, whose surface lies only 30 m above sea level. The easternmost cone has three craters and produced young basaltic-andesite lava flows, some of which traveled into the caldera lake. The largest and northernmost of the cones, Lofia, has a steep-sided crater that is 70 m wide and 120 m deep and has been the source of historical eruptions, first reported in the 18th century. The fumarolically active crater of Lofia has a flat floor formed by a ponded lava flow.

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/); 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/); NASA Worldview (URL: https://worldview.earthdata.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Mount Pelée is a stratovolcano that forms the north end of the French island of Martinique, along the Lesser Antilles subduction zone. There have been at least four eruptions over the past 250 years: phreatic eruptions in 1792 and 1851, and more recently, magmatic eruptions that built lava domes during 1902-1905 and 1929-1932. Fumaroles at the summit in the area of those lava domes were active until 1970, but not since then. There are thermal springs on the upper and lower flanks of the volcano, most notably at the Rivière Chaude, Rivière Claire, Rivière Picodo and Rivière Mitan, as well as a few hydrothermal submarine springs on the Caribbean Sea coast to the southwest (figure 1). Information for this report was provided by the Volcanological and Seismological Observatory of Martinique (OVSM), Institut de Physique du Globe de Paris (IPGP), with contributions from F.R. Fontaine (IPGP, OVSM), J-C. Komorowski (IPGP), J. Corbeau (IPGP, OVSM), A. Burtin (IPGP), F. Jadelus (IPGP, OVSM), D. Melezan (IPGP, OVSM), C. Vidal (IPGP, OVSM), B. Zimmermann (IPGP, OVSM), J.M. Lavenaire (IPGP, OVSM), J.-G. Gabriel (IPGP, OVSM), J.-M. Saurel (IPGP), A. Lemarchand (IPGP), R. Grandin (IPGP), J.-B. de Chabalier (IPGP), F. Beauducel (IPGP), S. Moune (IPGP, OVSG), E. Chilun-Eusebe (IPGP, OVSG), V. Robert, R. Moretti (IPGP, OVSG), G. Boudon (IPGP), G. Carazzo (IPGP), A. Michaud-Dubuy (IPGP), and S. Tait (OMP).

Figure 1. Map of Mount Pelée showing the monitoring networks in Martinique. Courtesy of OVSM – IPGP.

Seismicity since 1980 and the installation of monitoring networks (figures 1 and 2) has typically been low. A few volcano-tectonic (VT) earthquakes were observed between 1 January 2015 and 1 April 2019, with a mean of two and a standard deviation of six earthquakes per month. Increased volcanic seismicity was recorded starting in April 2019 located 4-5 km below the summit (figure 3). A stronger increase was recorded between 2-15 December 2020 with 316 VT earthquakes during this period.

Figure 2. The seismic network of the OVSM - IPGP used for monitoring Mount Pelée. Broad-band three component seismic stations are in blue, short-period one component seismometers are in black, and temporary seismic nodes are in red. Courtesy of IPGP.

Figure 3. Graphs showing the daily number of volcano-tectonic (VT) earthquakes (top) recorded and the cumulated number of VT earthquakes (bottom) from 1 January 2019 to 14 January 2021 at Mount Pelée. The VT earthquakes were derived from the manual catalog of OVSM – IPGP. Courtesy of IPGP.

In addition to the shallow VT events, a few deep VT earthquakes (~15 km below sea level) were recorded below the volcano in April-May 2019 (5) and November 2019 (1); this type of seismicity was not observed between January 2014 and March 2019. New tremor-type signals were recorded on 8 and 9 November 2020 (figure 4). Eight long-period (LP) earthquakes were detected in December 2020 during the stronger increase in volcanic seismic activity. Seismic activity typically occurred in swarms lasting up to a few days and has fluctuated since 4 December 2020, but remained significantly higher than base level (table 1 and figure 5). Despite the ongoing unrest, the seismic energy released has remained low and no volcanic earthquakes have been felt.

Figure 4. Spectrograms (a and b) of volcanic tremor at Mount Pelée recorded by a seismic station (MLM) of the OVSM - IPGP from 8-9 November 2020. (c) Cumulated number of long-period events detected within the volcanic tremor signal. Courtesy of IPGP.

Table 1. Monthly numbers of volcanic earthquakes recorded at Mount Pelée by the OVSM – IPGP during December 2020-June 2021. Courtesy of IPGP.

Figure 5. Map of Mount Pelée with N-S (right) and E-W (bottom) cross-sections showing the position and depth of hypocenters of the seismic events in April 2021. Only earthquakes that could be located are shown. Courtesy of IPGP.

Due to the increased seismicity, OVSM - IPGP raised the Volcanic Alert Level (VAL) to Yellow (the second level on a four-color scale) on 4 December 2020. A zone of damaged, browned, and dead vegetation was observed at the end of December 2020 on the southwest flank between the upper Rivière Claire and the Rivière Chaude, above their confluence. A field expedition on 8 February 2021 by OVSM - IPGP investigators, with the support of the Emergency and Fire Department (STIS) and the civil protection helicopter, confirmed that the vegetation damage was associated with elevated levels of diffuse passive soil degassing of carbon dioxide from the ground. There were no visible fumaroles. This area is less than 200 m from the Rivière Claire where the presence of hydrogen sulfide has been reported in scientific literature for several years, in the vicinity of thermal springs.

Ground fractures in the center of the most deteriorated vegetation zone were 20-60 cm wide, 2-3 m deep, and several tens of meters long. Although some fractures had formed in the past, the clearest ones linked to the damaged vegetation may have formed recently. No fumarolic, water vapor, or gas emissions were visible and there was no thermal anomaly associated with these fractures. There was no evidence of significant fluid movements at depth recorded by the deformation network, or any changes in temperature or pH of the water at the regularly monitored sites. These observations are interpreted as reflecting increased activity of the hydrothermal system.

Geologic Background. Renowned Montagne Pelée forms the northern end of the island of Martinique. Three major edifice failures since the late Pleistocene, the last about 9,000 years ago, have left large open calderas breached to the SW inside which the modern volcano has been constructed. More than 20 major eruptions have occurred here during the past 5,000 years. Extensive pyroclastic-flow deposits, incised by steep-walled ravines, mantle the slopes of the volcano. The l'Etang Sec summit crater is filled by two lava domes emplaced during the 1902 and 1929 eruptions. Recorded eruptions date back to the 18th century; only two modest phreatic or phreatomagmatic eruptions took place prior to 1902. The catastrophic 1902 eruption, which destroyed the city of St. Pierre, became the type-example of Pelean eruptions and marked the onset of modern volcanological studies of the behavior of pyroclastic flows.

Information Contacts: Université de Paris, Institut de Physique du Globe de Paris (IPGP), CNRS, F-75005 Paris, France (URL: http://www.ipgp.fr/); Observatoire Volcanologique et Sismologique de la Martinique (OVSM), Institut de Physique du Globe de Paris, 97250, Fonds Saint Denis, France (URL: http://www.ipgp.fr/fr/ovsm/actualites-communiques-publics-de-lovsm, https://doi.org/10.18715/MARTINIQUE.OVSM, real-time location of seismic events are available at ws.ipgp.fr/fdsnws/event/1/ and https://renass.unistra.fr/fr/zones/les-antilles/); Observatoire Volcanologique et Sismologique de la Guadeloupe (OVSG), Institut de Physique du Globe de Paris, 97113, Gourbeyre, France (URL: https://www.ipgp.fr/fr/ovsg/observatoire-volcanologique-sismologique-de-guadeloupe); Observatoire Midi-Pyrénées (OMP), 31400 Toulouse, France (URL: https://www.omp.eu/).

Piton de la Fournaise, a massive basaltic shield volcano, is located on the SE part of the French island of Réunion in the western Indian Ocean. Its most recent eruption period occurred during 7-8 December 2020 and was characterized by lava fountains and short lava flows (BGVN 46:01). This report covers January through May 2021 and describes a new eruption with lava fountaining and flows that began in early April, using information from the Observatoire Volcanologique du Piton de la Fournaise (OVPF) and satellite data.

Activity during January through March 2021 was relatively low and primarily characterized by a strong seismicity starting on 13 March. Rockfalls were frequently reported in the Dolomieu crater due to the seismic events. During January 2021 a total of 7 volcano-tectonic earthquakes were detected below the summit crater, accompanied by 182 rockfalls in the crater. The number of volcano-tectonic earthquakes during February was 6, with 165 rockfalls. During 13-31 March about 522 volcano tectonic earthquakes of a magnitude up to 2.6 were detected under the E part of the Dolomieu crater. Small sulfur dioxide emissions accompanied this seismicity. On 24 March 81 earthquakes were recorded beneath the summit area, including one that reached an Mw of 2.6. The increase in seismicity resulted in 286 rockfall collapses along the edges of the Dolomieu crater. The daily number of volcano-tectonic earthquakes on 26 March was 95, which then decreased to 55 and 8 during the following days (27 and 28 March, respectively) (figure 206). On 31 March at 0009 an earthquake with a magnitude of 2.3 was reported and felt by nearby residents 1 km E of La Plaine des Cafres. Following this event, the number of volcano-tectonic events increased to 29.

Figure 206. Histogram showing the daily number of volcano-tectonic earthquakes at Piton de la Fournaise during 13-31 March 2021. The number of daily earthquakes steadily increased from 13 through 26 March, after which it declined. Courtesy of OVPF-IPGP (Bulletin mensuel Mars 2021).

During April a total of 1,575 volcano-tectonic earthquakes were detected below the summit craters, accompanied by 366 rockfall events in the Dolomieu crater, along the edges of the Enclos Fouqué caldera, the Piton de Crac, and the Rivière de l’Est. A notable seismic swarm was detected during 1447-1745 on 9 April consisting of 700 volcano-tectonic earthquakes beneath the Dolomieu crater and the S flank. At 1457 OVPF reported that the swarm was accompanied by rapid deformation, which indicated that magma was moving toward the surface. The seismicity indicated that a fissure had opened at 1900 on the S flank in the Enclos Fouqué caldera but could not be visually confirmed due to weather conditions. As a result, the Volcano Alert Level was raised to 2-2. An overflight at 0840 on 10 April showed an NNW-oriented fissure (700 m S of Château Fort), active lava fountains originating from two vents that rose no higher than 30 m, and a slow-moving `a`a lava flow that traveled SE and then curved E for 1.6 km to 1.8 km elevation (figure 207).

Figure 207. Photo of active lava fountains and white gas-and-steam emissions emerging from a fissure at Piton de la Fournaise taken at 0840 on 10 April 2021. Courtesy of OVPF-IPGP (Communiqué du 10/04/2021 - 10h00).

By the morning of 11 April two cones were forming around the two active vents; the more northern of those was larger while the S one contained two vents (figure 208). Strong thermal anomalies on the S and SE flanks were visible on clear weather days during late April through mid-May 2021, based on Sentinel-2 infrared satellite imagery (figure 209), which were represented by the lava fountain activity that occurred during the eruptive period. Intermittent lava fountains rose 20-60 m high, and a single lava flow was observed at a rate of 8 m³/s, which increased to 10-30 m³/s, according to satellite data via the HOTVOLC platform (figures 210 and 211) at an elevation of 1.7 km. By 1900 on 11 April the lava flow was 3.2 km long. A gradual drop in the number of earthquakes was reported after the start of the eruption; on 11 April 89 shallow earthquakes were detected, which further decreased to 5 per day during 26-30 April.

Figure 208. Overflight photo showing the three active vents at Piton de la Fournaise: a large northern vent (top right) and two smaller vents (bottom left) farther S, each of which generate lava fountains and white gas-and-steam emissions at 0930 on 16 April 2021. Courtesy of OVPF-IPGP (Communiqué du 16/04/2021 - 16h00).

Figure 209. Sentinel-2 infrared satellite image of the thermal activity (bright yellow-orange) on the S and SE flanks of Piton de la Fournaise on 26 April (top left), 1 May (top right), 11 May (bottom left), and 16 May (bottom right) 2021, representing both the active lava fountains and flows. The larger thermal anomaly represents the N main vent, while the two weaker anomalies represent the smaller S vents. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Figure 210. Satellite map of the evolution of the lava flows at Piton de la Fournaise during 10 April (black color within red and yellow zone), 11 April (yellow color), and 20 April (red color) 2021. Flows traveled SE before advancing dominantly E. The white line represents the fissure that opened on 9 April. The flow originated on the SE flank and migrated SE. Courtesy of OVPF-IPGP (Communiqué du 21/04/2021 - 16h00).

Figure 211. Photo of the activity at Piton de la Fournaise on 11 April 2021 showing lava fountains rising 30-60 m high from two vents, accompanied by an active lava flow. Courtesy of OVPF-IPGP (Communiqué du 11/04/2021 - 15h30).

The sulfur dioxide emissions gradually increased from 400-859 tons/day during 9-12 April to an average of 4,054 tons/day on 13 April. The resulting plumes reached altitudes of 2.5-3.5 km altitude, according to NOVAC data. Distinct sulfur dioxide plumes were also detected by the Sentinel-5P/TROPOMI instrument each day during 10-13 April and drifted generally SW, which accompanied the new eruptive activity that began on 9 April (figure 212). Lava fountains continued at the two vents during 12-13 April, rising 20-60 m high while the flow continued to advance; by 13 April it was 3.6 km long and reached an elevation of 1.5 km. The lava flow rate increased to a maximum of 59 m³/s by 13 April, which later dropped to 12.5 m³/s on 14 April and 1.2-8.3 m³/s during 16-23 April. The approximate volume of lava erupted was 5 million cubic meters. In addition, the SO₂ emissions dropped to 2,100 tons/day on 14 April and further to 1,100 tons/day on 15 April.

Figure 212. Distinct sulfur dioxide emissions rising above Piton de la Fournaise during 10-13 April 2021, accompanying the start of the new eruptive activity. The plume on 10 April (top left) drifted SW, on 11 April (top right) the plume remained above the island, on 12 April (bottom left) the plume drifted W, and on 13 April (bottom right) 2021 it drifted SW. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

During an overflight on 16 April, scientists observed that the most distal part of the lava flow had stopped advancing while other parts were moving at rates of 1.2-8.3 m³/s. The larger northernmost cone was 28 m high; the smaller cone fed lava flows that traveled through tubes that occasionally broke the surface. The overall flow field was 3.5 km long and 750 m wide (figure 210). During the latter half of April and into early May, weather conditions frequently prevented visual observations of the activity, though the fountains and flows continued. The flow rates during 16-23 April were 1.2-8.3 m³/s, based on the gas emission rates. Lava flows continued to travel E through tubes, sometimes setting fire to local vegetation.

During May activity decreased slightly compared to the previous month; the intensity of the volcano-tectonic earthquakes declined and on clear weather days (figure 213), the lava fountains were still visible in the smaller vents but were weaker, occasionally ejecting material just above the crater rim. A total of 261 rockfalls were detected in the Dolomieu crater and along the Enclos Fouqué caldera, the Piton de Crac, and the Rivière de l’Est. Photo analysis of the larger N cone showed that its base width was 226 m and had a height of 35 m. The lava flow had resumed its advancement E by 2 May at a rate of 7 m³/s after a pause in activity during 29 April to 1 May, extending to 180 m long to an elevation of 1.5 km (figure 214). Some local vegetation caught fire due to the flow. During 3-4 May a small active lava lake was reported in the N vent, lava fountains ejected material 5-6 m high, while stronger and denser gas-and-steam plumes rose above the two smaller S vents. On the morning of 12 May OVPF-IPGP reported that the lava lake in the N main cone had disappeared, and by 13 May the lava flows that were traveling through tubes had migrated E to an elevation of 920 m. OVPF-IPGP reported that on 24 May around 0200 the eruption ended, based on the cessation of volcanic tremors; the number of volcano-tectonic earthquakes had declined to two shallow volcano-tectonic earthquakes per day and the total volume of lava effusions was about 13 million cubic meters. Inclement weather again prevented visual confirmation, however.

Figure 213. Graph showing the intensity of the volcano-tectonic earthquakes detected at Piton de la Fournaise (in RSAM units) from 9 April through 19 May 2021. There is a significant spike in RSAM units at the start of the eruption, which continued to increase overall through at least 24 April; a gradual decrease is observed from late April through May. Courtesy of OVPF-IPGP (Communiqué du 19/05/2021 14h00).

Figure 214. Photo of the front of the cooling lava flow at Piton de la Fournaise at 0915 on 3 May 2021 taken from the SAG helicopter overflight. The darker lava is the active flow that is slowly advancing downslope while the lighter lava is older and cooled. To the left is a white gas-and-steam plume indicating burning vegetation; a white gas-and-steam plume is also visible in the background (to the right). Courtesy of OVPF-IPGP (Communiqué du 03/05/2021 – 15h00).

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

Information Contacts: Observatoire Volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, 14 route nationale 3, 27 ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Kerinci is located in Sumatra, Indonesia, and has had numerous moderate explosive eruptions since 1838. Its most recent eruption began in April 2018 and has been characterized by intermittent gas-and-steam and ash plumes through November 2020 (BGVN 45:12). This report covers and similar, but relatively low activity during December 2020 through June 2021 based on information from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), the Darwin Volcanic Ash Advisory Centre (VAAC), and satellite imagery.

Volcanic earthquakes and intermittent white-to-brown gas-and-steam plumes rose 50-800 m above the summit during December 2020 through June 2021 (figure 24); the volcano was often obscured by clouds. Brown ash plumes filling much of the crater could be observed in satellite imagery on 21 and 26 December 2020 and 5 and 8 January 2021. During 21-22 March, PVMBG and the Darwin VAAC reported an ash plume that rose 600 m above the summit and drifted SW. Small plumes of steam and possibly ash were present in a clear satellite view of the crater on 8 April. On 31 May at 0614 an ash plume rose 700 m above the summit and drifted NW, based on ground reports. An ash plume on 6 June rose to 4 km altitude and extended WNW according to HIMAWARI-8 satellite imagery. Another ash plume was reported at 1730 on 13 June that rose 700 m above the summit and drifted W.

Figure 24. Sentinel-2 satellite imagery of brown, white, and gray emissions at Kerinci during 21 December (top left) 2020, 5 January (top right), 8 April (bottom left), and 17 June (bottom right) 2021. The brown emissions mostly remained within the crater area. The gray emissions drifted NE. Images using “Natural Color” rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Tinakula, located 100 km NE of the Solomon Trench at the N end of the Santa Cruz Islands, is a small 3.5-km-wide island with a breached summit crater that extends to below sea level. Its most recent eruption period began in December 2018 and has recently been characterized by intermittent gas-and-steam plumes and weak thermal anomalies (BGVN 46:01). Evidence of similar activity continued during this reporting period of January through June 2021 based on various satellite data; ground observations are rarely available.

Infrared MODIS satellite data processed by MIROVA (Middle InfraRed Observation of Volcanic Activity) showed fifteen low-power thermal anomalies during January through June 2021: one in early January, two in late February, four during March, five during mid- to late April, two during early May, and one in early June (figure 46). Some of these anomalies were also observed in Sentinel-2 infrared satellite imagery, occasionally accompanied by white gas-and-steam plumes drifting SW and E (figure 47).

Figure 46. Low-power thermal anomalies at Tinakula were detected fifteen times during January through June 2021, based on the MIROVA system (Log Radiative Power). Courtesy of MIROVA.

Figure 47. Sentinel-2 satellite imagery shows ongoing white gas-and-steam plumes rising from Tinakula during January through May 2021. Plumes drifted SW on 1 January (top left), 17 March (bottom left), and 11 May (bottom right) 2021 and E on 19 February (top right). A persistent thermal anomaly (bright yellow-orange) is visible in the summit crater on 15 February, 17 March, and 11 May using “Atmospheric penetration” (bands 12, 11, 8a) rendering. Image on the top left uses “Natural color” rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

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

Information Contacts: MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

The Aira caldera is located in the northern half of Kagoshima Bay in Kyushu, Japan and contains the active post-caldera Sakurajima volcano. Though several craters have been historically active, current activity is focused in the Minamidake summit crater, which has recently been erupting since March 2017. Activity is characterized by intermittent explosions, ash plumes and resulting ashfall, ballistic ejecta, and crater incandescence (BGVN 46:01). This report updates similar activity from January through June 2021 and uses information primarily from the Japan Meteorological Agency (JMA) and various satellite data.

During the reporting period, the number of eruptions had decreased significantly compared to previous months; at the Minamidake crater there were about 127 ash eruptions, 83 of which were explosive (compared to 432 and 221, respectively during the previous year). No eruptions were reported in the Showa crater through June. Ash was reported most frequently during March and April for 14 and 22 days, respectively (table 25). The tallest ash plume reached 4 km above the crater on 27 March, while the most amount of ashfall was 42 g/m² during April. A decline in eruptive events after April was reflected both in JMA reports and thermal data (figure 118). Sentinel-2 infrared and natural color satellite imagery captured both thermal anomalies in the summit craters as well as significant ash plumes that resulted from the explosive eruptions (figure 119). Recorded sulfur dioxide emissions were relatively high during the beginning of the year and began to decrease to 1,300 tons/day in May.

Table 25. Number of monthly explosive eruptions, total eruptions, days of ashfall, ashfall amounts, and sulfur dioxide emissions from Sakurajima’s Minamidake crater at Aira during January-June 2021. Note that smaller events that did not reach the threshold of explosions or eruptions also occurred. Ashfall was measured at Kagoshima Local Meteorological Observatory. Data courtesy of JMA.

Figure 118. Clusters of low-intensity thermal anomalies were detected at Aira’s Sakurajima volcano during January-June 2021 based on the MIROVA graph (Log Radiative Power). The number of relatively higher thermal anomalies seemed to decrease after April. Courtesy of MIROVA.

Figure 119. Sentinel-2 infrared satellite images showing white gas-and-steam plumes rising from Aira’s Sakurajima volcano on 31 January (top left) 2021 accompanied by a thermal anomaly in the summit crater and two thermal anomalies in the summit crater on 21 April (bottom right). On 5 February (top right) and 27 March (bottom left) natural color satellite images showed distinct ash plumes drifting NE and NW, respectively, due to explosive eruptions. Images using “Atmospheric penetration” (bands 12, 11, 8A) rendering on 31 January and 21 April, and “Natural Color” (bands 4, 3, 2) rendering on 5 February and 27 March. Courtesy of Sentinel Hub Playground.

During January a total of 21 ash eruptions were detected, 18 of which were explosive. The number of volcanic earthquakes notably increased from 55 in December 2020 to 117, accompanied by white gas-and-steam emissions that rose 200 m above the crater and nighttime crater incandescence, as captured by a high-sensitivity surveillance camera. An explosion at 1642 on 4 January produced an ash plume that rose 1.8 km above the Minamidake crater. On 31 January an explosion at 0720 generated an ash plume that rose 2.3 km above the crater and ejected bombs 1.3-1.7 km high. JMA reported that sulfur dioxide emissions had been high since September 2020, and during January reported 1,500-5,000 tons/day, with the highest value recorded on 6 January. During seven days in the month, 3 g/m² of ash fell, according to the Kagoshima Local Meteorological Observatory in Higashikorimoto (11 km WSW). Overall, about 100,000 tons of ash had fallen during the month.

Similar eruptive events continued in February, with 22 ash eruptions, 11 of which were explosive and ejected volcanic bombs 1-1.3 km from the Minamidake crater. The number of volcanic earthquakes increased to 292. During seven days of the month, ashfall was reported, accumulating to 11 g/m²; observation data showed that about 90,000 tons of ash had fallen during the month. SO₂ emissions were between 1,100-4,300 tons/day, the higher of which was measured on 16 February. On 28 February an explosion at 2247 ejected bombs up to 1.3 km from the summit, produced an ash plume that rose 2.3 km above the crater, and was accompanied by crater incandescence.

Activity increased slightly during March and April, with 31 and 42 ash eruptions, respectively. The number of volcanic earthquakes decreased slightly from 195 in March to 148 in April. Explosions ejected incandescent material as far as 1.7 km from the Minamidake crater, accompanied by nighttime crater incandescence. An explosion on 5 March generated an ash plume that rose 2.7 km above the crater and ejected material as far as 1.1 km from the summit. On 27 March an eruption at 0236 produced an ash plume that rose 2.5-4 km above the crater and drifted NW, resulting in a large amount of ashfall in Kagoshima City (10 km W) (figure 120). Bombs were ejected up to 1.3 km from the crater. On 29 March at 1557 an ash plume rose 2.2 km above the crater and drifted SE, an accompanying pyroclastic flow was observed down the SE flank and ashfall was reported in Kagoshima City and the Kagoshima Prefecture. An explosion on 30 March at 0433 generated an ash plume 2.7 km above the crater and drifted E, ejecting material as far as 900 m from the crater and resulting in ashfall in Kagoshima City. Ashfall was reported on 14 days in March (21 g/m²) and 22 days in April (42 g/m²). A single thermal alert was detected by the MODVOLC system on 4 April; an explosion the following morning at 0641 on 5 April produced an ash plume 3 km above the crater. On 25 April an explosion at 0109 ejected material 1-1.3 km from the crater and an ash plume 2.3 km high. The explosion generated what was initially described as a pyroclastic flow that descended 1.8 km down the SW side of the crater; later field inspections did not observe pyroclastic flow deposits or damaged vegetation, and concluded that the plume was generated by winds. About 110,000-120,000 tons of ash was measured during the two months, and sulfur dioxide emissions remained consistent at 1,800-2,900 tons/day, according to JMA.

Figure 120. Webcam images of Aira’s Sakurajima volcano showing dense gray ash plumes on 27 March (top left) rising 3.2 km above the crater, on 6 May (bottom left) rising 2.5 km above the crater, and on 28 April (right) 2021 incandescent material was visible on the flanks of the volcano accompanied by a small ash plume. Images courtesy of JMA (Sakurajima March, April, and May 2021 monthly reports).

During May and June, the number of eruptive events declined; 11 eruptions were detected during May, six of which were explosive and ejected material 800-1,100 m from the crater. On 6 May an explosion produced an ash plume that rose 2.5 km above the crater (figure 120). In June small, intermittent eruptions were detected, though none were explosive. Resulting ash plumes rose 1-2.5 km above the crater and were accompanied by nighttime crater incandescence, based on imagery from a high-sensitivity surveillance camera. The number of volcanic earthquakes continued to decrease each month from 91 to 18, respectively. During May ashfall was reported for four days, accumulating to 16 g/m²; about 50,000 tons of ash was measured. Less than 0.5 g/m² was reported over the course of a day in June. SO₂ emissions also gradually decreased from May at 1,300 tons/day to 600-2,700 tons/day in June.

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

Information Contacts: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Volcán de Fuego, located in Guatemala, has been vigorously erupting since 2002, with historical eruptions dating back to 1531. Major eruptions have been characterized by ashfalls, pyroclastic flows, lava flows, and lahars. More recently, activity has consisted of ash plumes, ashfall, incandescent block avalanches, and lava flows (BGVN 46:04). Similar activity continued during this reporting period of April through July 2021, dominated by daily explosions, ash plumes, ashfall, and incandescent block avalanches. Information primarily comes from daily reported by the Instituto Nacional de Sismologia, Vulcanología, Meteorología e Hidrologia (INSIVUMEH), Washington Volcanic Ash Advisory Center (VAAC), and various satellite data.

Summary of activity during April-July 2021. Hourly explosions were reported at Fuego during April-July 2021 that vibrated roofs and windows in nearby communities. These explosions generated gray ash plumes that rose 4.3-4.9 and generally drifted W and SW, the highest of which occurred on 25 April. The Washington VAAC issued 422 daily ash advisories during the reporting period. Ashfall was common throughout this period in several nearby communities, dominantly Panimaché I and II (8 km SW), Morelia (9 km SW), Santa Sofía (12 km SW), El Porvenir (8 km ENE), Sangre de Cristo (8 km WSW), Yepocapa (8 km NW). Occasional white gas-and-steam plumes accompanied the explosive activity, rising as high as 4.5 km altitude. Incandescent block avalanches accompanied the explosions, descending several flanks, such as the Seca (W), Ceniza (SSW), Trinidad (S), and Taniluyá (SW) drainages and reaching as far as vegetated areas. Incandescent ejecta was observed as high as 450 m above the crater during most nights and early mornings. According to the MIROVA graph (Log Radiative Power), thermal activity was consistently strong and frequent during April through July (figure 148). The MODVOLC algorithm detected 39 thermal alerts during six days in April, nine days in May, five days in June, and six days in July. Sentinel-2 infrared satellite imagery showed strong thermal anomalies in the summit crater, which represents the incandescent block avalanches that descended the S and SW flanks as a result of persistent explosions (figure 149). Many of these avalanches were accompanied by gray ash plumes. Weak sulfur dioxide emissions were infrequently observed in Sentinel-5P TROPOMI satellite imagery on 24 April and 24 May, which drifted S and W, respectively (figure 150).

Table 23. Eruptive activity was consistently high at Fuego throughout April-July 2021 with multiple explosions every hour, ash plumes, block avalanches, and near-daily ashfall in nearby communities. Courtesy of INSIVUMEH daily reports.

Figure 148. Consistently strong thermal anomalies continued at Fuego during April through July 2021. Courtesy of MIROVA.

Figure 149. Sentinel-2 infrared satellite imagery showing strong thermal anomalies at the summit of Fuego, frequently accompanied by gray ash plumes drifting primarily W. Incandescent block avalanches are visible descending the flanks on 9 April (top left), 14 May (top right), 18 June (bottom left), and 3 July (bottom right) 2021, dominantly on the S and SW flanks. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Figure 150. Weak sulfur dioxide emissions observed from Fuego drifted S on 24 April 2021 (left) and W on 24 May 2021 (right), based on the Sentinel-5P satellite using TROPOMI data. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Frequent daily explosions continued during April. Two to fourteen explosion per hour were detected, which generated ash plumes that rose to 4.3-4.9 km altitude and drifted usually up to 15 km, and occasionally as far as 20 km in different directions. Ashfall was commonly reported in multiple communities, including Panimaché I and II, Morelia, Santa Sofía, El Porvenir, Sangre de Cristo, Yepocapa. Due to heavy rains on 16 April, lahars were observed in the Ceniza, Seca, and Mineral drainages. Additional ash was reported in La Rochela on the 20th, Palo Verde on the 23rd and 25th, Yucales (12 km SW) on the 26th, and Asuncion on the 29th. The explosions ejected material as high as 400 m above the crater and caused constant incandescent block avalanches to descend several flank drainages, including Seca, Taniluyá, Ceniza, Trinidad, Santa Teresa, Las Lajas (SE), and Honda.

Explosive activity during May was similar to previous months, with 3-17 explosions per hour that rattled windows and roofs in nearby communities. Gas-and-ash plumes rose to 4.2-4.8 km altitude and drifted as far as 15 km S, SW, N, NE, W, and NW. Near-daily reports of resulting ashfall affected mainly Panimaché I and II, Morelia, El Porvenir, Santa Sofía, Sangre de Cristo, Yepocapa, and Yucales. Ashfall was also observed in Palo Verde (5 May), La Soledad (11 km N) (20 May), San José calderas (20 May), Acatenango (20 May), and San Pedro (21 May). Block avalanches caused by frequent explosions descended the Seca, Ceniza, Taniluyá, Trinidad, Las Lajas, Honda, and Santa Teresa drainages, sometimes reaching vegetated areas, and incandescent material was ejected 100-450 m above the crater.

Loud explosions continued throughout June, with 3-15 explosions per hour that produced ash plumes that rose to 4.3-4.8 km altitude and drifted 10-20 km in different directions. Ash was observed primarily in Panimaché I and II, Morelia, Santa Sofía, Yucales, Sangre de Cristo, Yepocapa, and El Porvenir. Other communities receiving ashfall included Palo Verde, Ceilán, La Rochela, La Soledad, El Campamento, and El Zapote. Incandescent ejecta rose 100-400 m above the crater. Constant block avalanches were reported in the Ceniza, Taniluyá, Trinidad, Santa Teresa, Seca, Las Lajas, and Honda drainages, sometimes reaching vegetated areas. On 15 and 24 June, INSIVUMEH reported that lahars descended the Las Lajas and El Jute drainages on the SE flank, due to heavy rainfall; tree branches and blocks are large as 1.5 km in diameter were carried down the flanks.

During July, daily explosions persisted at a rate of 3-15 per hour, which produced gas-and-ash plumes that rose to 4.3-4.8 km altitude (figure 151). These plumes drifted 8-30 km primarily W and SW, resulting in ashfall in several nearby communities, including Sangre de Cristo, Panimaché I and II, El Porvenir, Morelia, Santa Sofía, Yucales, and Yepocapa. Other communities less affected included Palo Alto (13 July), Palo Verde (19 and 24 July), La Rochela (25 July), Ceilán (25 July), and La Conchita (29 July). During the night and early morning, crater incandescence was visible, accompanied by ejecta that rose 100-400 m above the crater. Explosions also generated constant block avalanches that descended drainages along the flanks, including Ceniza, Taniluyá, Trinidad, Santa Teresa, Las Lajas, Honda, and Seca, frequently reaching vegetation.

Figure 151. Photo of an ash plume rising from the summit of Fuego on 9 July 2021 while blocks descend multiple drainages and resuspending ash on the flanks. Photo by Jose Jose Leonardo Quexel Hernandez en julio 9, 2021, 08:43 am hora local. Courtesy of INSIVUMEH.

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

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/ ); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); NASA 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).

A brief period of ash emissions in January 2012 was the first documented activity in over 50 years (BGVN 36:12) at Lewotolok (also known as Lewotolo), on the island of Lembata (Lomblen) in the Lesser Sunda Islands of Indonesia. Between then and November 2020, intermittent thermal activity was identified using MODVOLC and Sentinel-2 infrared data (BGVN 41:09, 46:02) and a single episode of increased seismicity was noted by PVMBG in October 2017. The only emissions reported were white steam and gas plumes rising up to 500 m above the summit crater. Increased seismicity at the end of November 2020 was accompanied by explosions with ash plumes and incandescent ejecta (BGVN 46:02) that resulted in ashfall and evacuations from surrounding communities. Explosions with ash emissions rising up to 1,500 m and incandescent ejecta rising 600 m above the crater were reported through the end of January 2021. This report covers similar explosive activity that continued from February-July 2021 with information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, and satellite data.

Multiple daily explosions were reported throughout February-July 2021 except for a brief pause during late April and early May (figure 13). Multi-day periods of incandescent ejecta rising hundreds of meters above the summit and extending a similar distance from the crater continued in February and increased to near-daily during June and July; multiple episodes of ejecta fell 1 km from the crater rim. Dense gray and black ash plumes were infrequent in January and February but increased to multiple times a day in mid-March, rising 1,000-1,500 m above the summit; the highest plume of the period reached over 3 km above the summit on 13 June. Daily explosive activity with ash plumes and incandescent ejecta continued through the end of July. Thermal anomalies in MIROVA data indicated pulses of higher activity during March-early April and late June-July (figure 14). Satellite imagery provided thermal and visual evidence of fresh lava flow activity inside the summit crater on multiple occasions.

Figure 13. The number of daily explosions at Lewotolok during 1 February-31 July 2021 ranged from 0-41. Data compiled from PVMBG daily reports.

Figure 14. Periods of increased thermal activity at Lewotolok were recorded by the MIROVA project during December-2020-early January 2021, March-early April 2021, and late June-July 2021. Courtesy of MIROVA.

Activity during February-April 2021. PVMBG reported daily white and gray emissions that rose 200-700 m above the summit, and occasionally higher, during February 2021. Explosions occurred virtually every day with a maximum of 21 reported on 3 February, but 5-10 per day were typical. During 5-9 February loud noises accompanied bursts of incandescent ejecta that rose 300 m above the summit and extended 300-500 m SE (figure 15). MAGMA Indonesia reported an eruption on 10 February that produced an ash plume that rose 700 m and drifted E (figure 16). Thermal anomalies appeared in satellite images on 7, 12, 17, and 22 February.

Figure 15. A strong thermal anomaly recorded at the summit of Lewotolok on 7 February 2021 was likely due to the incandescent ejecta reported by PVMBG that rose 300 m high and sent material 500 m SE. Sentinel-2 satellite imagery uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Figure 16. An ash plume rose 700 m above the summit of Lewotolok and drifted E on 10 February 2021. Courtesy of MAGMA Indonesia and PVMBG.

The abrupt increase in the number of daily explosions at the beginning of March 2021 was accompanied by loud rumbling noises and observations of incandescent ejecta. During 2-5 March incandescent ejecta rose 200-800 m above the summit towards the SE. On 9 March the ejecta was reported 1,300 m E and SE of the summit. From 11-15 March the incandescent ejecta rose 500 m above the crater rim and was ejected as far as 1,000 m E and SE. The Darwin VAAC reported ash plumes on 13 and 14 March that drifted SW at 1.2 km altitude. MAGMA Indonesia reported two explosions, one on 14 March that rose 1,300 m above the summit and drifted S (figure 17) and one on 15 March that rose 1,000 m and drifted E. During 19-31 March there were 4-20 explosions each day that produced audible booms and rumbling; incandescent ejecta rose as high as 500 m and was thrown the same distance E and SE. Thermal anomalies at the center of the summit crater were apparent in Sentinel-2 satellite imagery on 4 and 19 March.

Figure 17. An explosion at Lewotolok on 14 March 2021 produced an ash plume that rose 1,300 m above the summit and drifted S. Courtesy of MAGMA Indonesia and PVMBG.

Cloudy weather obscured views of the summit for several days in early April 2021, but during 5-17 April multiple daily explosions produced incandescent ejecta often reaching 500 m high, loud noises, and dense gray and black ash plumes (figure 18). Sentinel-2 imagery indicated thermal anomalies inside the summit crater likely caused by fresh lava flows on 8 April. The thermal anomalies and visual imagery from 13 April revealed a new dark area, still hot around the edges, that also likely represented fresh lava (figure 19). Ejecta reached 300-500 m E and SE of the summit during 8-12 April; on 16 April PVMBG reported incandescent ejecta 1,000 m above the summit. MAGMA Indonesia noted one to five eruptions each day during 12-18 April; dense white, gray, and black ash plumes rose 500-1,500 m above the summit and drifted W or SW most days. The Darwin VAAC reported ash emissions on 15 and 16 April which rose 400-700 m above the summit and drifted WNW, and a plume that rose to 3,000 m altitude (1,500 m above the summit) on 18 April and drifted W (figure 20). Additional explosions were reported on 20-21 and 24-25 April, producing gray and black ash plumes that rose 600-1,000 m above the summit. By 28 April only steam emissions were observed, and no thermal anomalies were present around the fresh dark flow visible inside the summit crater.

Figure 18. Incandescent ejecta rose several hundred meters above the summit of Lewotolok on 13 April 2021. Courtesy of MAGMA Indonesia and PVMBG.

Figure 19. A comparison of visual and thermal imagery of Lewotolok from 4 March (left), 8 (middle) and 13 April 2021 (right) shows the appearance of fresh dark lava (natural color images, top) and thermal anomalies (Atmospheric penetration images, bottom) in the 8 and 13 April images that were not present in the 4 March images. Two plumes of steam and ash rose from the summit crater of Lewotolok on 8 April 2021 (top center) and corresponded with two thermal anomalies inside the crater (bottom center). The NW -trending linear anomaly was likely caused by a fresh lava flow. Small anomalies around the dark area on 13 April (bottom right) suggested cooling lava. Natural color images use bands 4, 3, and 2; Atmospheric penetration rendering uses bands 12, 11, and 8a. Courtesy of Sentinel Hub Playground.

Figure 20. A dense gray and black ash plume rose 1,500 m above the summit of Lewotolok and drifted S and SW on 18 April 2021.

Activity during May-July 2021. A single explosion reported by PVMBG and Magma Indonesia on 2 May caused a VONA and a VAAC report to be issued. The ash plume rose 500-600 m above the summit and drifted W. Lewotolok was quiet with white and gray emissions, and no explosions reported, until 14 May when incandescent ejecta and ash emissions resumed for the rest of the month. Strombolian activity accompanied by loud noises sent incandescent ejecta 300 m high and 400-700 m SE from the summit; satellite imagery from 18 May showed a small thermal anomaly inside the summit crater. The ash plumes from the multiple explosions were dense and gray, and rose 400-800 m high. The Darwin VAAC reported multiple ash emissions during 21-25 and 28-29 May that were clearly seen in satellite imagery extending SE, S, or SW at 2,100 m altitude; the plume on 28 May (figure 21) rose 1,000 m above the summit to about 2,400 m altitude and drifted SW.

Figure 21. An ash plume at Lewotolok on 28 May 2021 rose 1,000 m above the summit and drifted SW. Courtesy of PVMBG and MAGMA Indonesia.

Multiple explosions with either ash plumes or Strombolian activity were reported daily throughout June 2021. During 1-9 June incandescent ejecta fell at least 300 m in all directions from the summit with loud noises reported (figure 22). On 5 June the 300-m-high ejecta reached 1,000 m NW and 200 m SE. During 8-16 June eruptions with ash plumes were reported by MAGMA Indonesia; both VONA’s and VAAC reports were issued each day. The white and gray ash emissions generally rose 500-800 m above the summit. On 10, 14, and 21 June the plumes were reported 2,000 m above the summit drifting W and NW. An explosion on 13 June produced an ash plume to 3 km above the summit, the highest of the period, that was observed drifting W in satellite imagery at 4.9 km altitude. Rumbling reported during 16-20 June accompanied incandescent ejecta sent 300-500 m in all directions from the crater. On 2, 7, 12, and 27 June thermal anomalies appeared in Sentinel-2 imagery inside the summit crater; the strong anomaly on 27 June suggested new flow activity (figure 23).

Figure 22. Incandescent ejecta rose several hundred meters above the summit of Lewotolok on 8 June 2021 and many other days during the month. Courtesy of PVMBG and MAGMA Indonesia.

Figure 23. Thermal anomalies appeared inside the summit crater at Lewotolok on multiple days during June 2021 including 12 (left) and 27 June (right). The strong anomaly on 27 June suggested new flow activity with a weaker anomaly just off the N end of the larger one. Images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Heightened levels of activity continued throughout July 2021. Thermal and visual evidence of fresh lava flows inside the summit crater appeared in satellite images on 2 July (figure 24). Additional thermal anomalies were recorded on 12, 22, and 27 July. Bursts of incandescent ejecta frequently caused loud noises. Vegetation caught fire around the summit from incandescent material on 3 and 28 July (figure 25). The tephra was usually reported 300-500 m from the crater but was sent 1,000 m SW on 3 July, and 1,000 m SE on 12, 18, 28, and 30 July. Five or more explosions were reported daily by PVMBG during 1-20 July, with a maximum of 28 reported on 9 July. The dense gray or gray-and-black ash emissions consistently rose 800-1,000 m above the summit, usually drifting W or NW (figure 26). The tallest plume on 7 July was reported by MAGMA Indonesia at 1,100 m above the summit, drifting E.

Figure 24. Evidence of fresh lava flow activity at Lewotolok appeared in Sentinel-2 satellite imagery on 2 July 2021. A thin line of dark material seen in natural color rendering (left, bands 4,3,2) is the area of strongest thermal anomaly seen in the Atmospheric penetration rendering image (right, bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Figure 25. Vegetation near the summit of Lewotolok caught fire from incandescent ejecta on 28 July 2021. Courtesy of PVMBG and MAGMA Indonesia.

Figure 26. Gray ash and steam plumes rose 800 m from a pyroclastic cone-like feature inside the summit of Lewotolok on 14 July 2021. Courtesy of PVMBG and MAGMA Indonesia.

Geologic Background. The Lewotolok (or Lewotolo) stratovolcano occupies the eastern end of an elongated peninsula extending north into the Flores Sea, connected to Lembata (formerly Lomblen) Island by a narrow isthmus. It is symmetrical when viewed from the north and east. A small cone with a 130-m-wide crater constructed at the SE side of a larger crater forms the volcano's high point. Many lava flows have reached the coastline. Eruptions recorded since 1660 have consisted of explosive activity from the summit crater.

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.esdm.go.id/v1); 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).

Frequent historical eruptions have been reported from Mexico's Popocatépetl dating back to the 14th century. Activity increased in the mid-1990s after about 50 years of quiescence, and the current eruption, ongoing since January 2005, has included numerous episodes of lava-dome growth and destruction within the 500-m-wide summit caldera. Multiple emissions of steam and gas occur daily, rising generally 1-2 km above the summit at about 5,400 m elevation; many contain small amounts of ash. Larger, more explosive events with ash plumes and incandescent ejecta landing on the flanks and causing ashfall in nearby communities are periodically reported. Activity through January 2021 was characterized by tens to hundreds of daily low-intensity emissions that included gas-and-steam and small amounts of ash, and occasional minor and moderate explosions that sent ash plumes more than 1 km above the crater (BGVN 46:02). This report covers decreased activity from February-July 2021 using information from México's Centro Nacional de Prevención de Desastres (CENAPRED), the Washington Volcanic Ash Advisory Center (VAAC), and various satellite data.

Popocatépetl had ongoing water vapor, gas, and ash emissions throughout February-July 2021, but fewer explosions than during the period of the previous report. Ash emissions generally rose to 5.8-7.1 km altitude and drifted in many different directions. Ashfall was reported only a few times in some communities during March, May, and July. Thermal anomalies were recorded in satellite images inside the summit crater multiple times each month. The MIROVA thermal anomaly data indicated steady low-levels of thermal activity during February-April and decreased thermal activity after that through July (figure 176). CENAPRED reported the number of low-intensity emissions or ‘exhalations’ and the number of minutes of tremor in their daily reports (figure 177). Tremor activity reached 1,000 minutes per day each month from February to May but then dropped off significantly. The daily number of exhalations was relatively consistent throughout ranging from tens to hundreds per day.

Figure 176. The MIROVA graph of thermal anomalies at Popocatepetl from 14 September 2020 through July 2021 shows steady, low-level, activity through April, followed by fewer anomalies through July. Courtesy of MIROVA.

Figure 177. CENAPRED reported the number of daily ‘exhalations’ (in blue, left scale), and the number of minutes of tremor (in gold, right scale) at Popocatepetl each day during February-July 2021. The number of daily exhalations fluctuated throughout the period, but the minutes of tremor remained high through early May and then decreased. Data from CENAPRED daily reports.

Water vapor, gas, and small quantities of ash were present in the tens of daily exhalations during February 2021. There was a wide range in the number of minutes of tremor each day from a low of 33 to a high of 1,101. On many days during the month, 1-3 explosions were recorded; CENAPRED reported an explosion on 7 February that sent an ash plume 2,000 m above the summit crater. Incandescence was observed on about half the nights of the month. A swarm of 24 volcano-tectonic (VT) earthquakes was reported overnight during 10-11 February with magnitudes in the 1.0-2.6 range. Thermal anomalies appeared inside the inner crater at the summit in Sentinel-2 satellite images on 5, 10, 15, 20, and 25 February. The images on 5 and 25 February also captured ash plumes (figure 178). Small but distinct SO₂ emissions were also present in satellite imagery each day.

Figure 178. Thermal anomalies and ash emissions were both recorded in Sentinel-2 satellite images from Popocatepetl on 5 and 25 February 2021. Thermal anomalies were additionally recorded on 10, 15, and 20 February. Images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Multiple daily VAAC reports from the Washington VAAC noted emissions drifting tens of kilometers in multiple directions at altitudes of 5.8-6.4 km throughout the month. On 1 February 2021 the Washington VAAC reported an ash emission at 5.8 km altitude drifting 20 km S (figure 179); on 3 February continuous diffuse ash emissions at the same altitude drifted 45 km SW of summit. On 6 February the emissions were drifting E at 6.1 km and the next day emissions at that altitude were fanning out NE and NW of the summit. On 13 February emissions were observed in both the webcam and satellite imagery extending 35 km E at 5.8 km altitude. A remnant ash cloud at 6.1 km altitude was located 175 km W of the summit on 23 February while a new emission was located 35 km NW at 6.4 km altitude. On 28 February a concentrated ash plume extended 45 km NNW of the summit while a diffuse plume extended 120 km NNW at 5.8 km altitude.

Figure 179. Ash emissions and incandescence at the summit occurred often at Popocatepetl during February 2021 including on 1 (left) and 20 (right) February. Courtesy of CENAPRED daily reports.

During March 2021 the number of daily exhalations ranged widely from 11 to 133 and consisted of gas, water vapor, and small quantities of ash. The number of minutes of tremor ranged from a few tens to almost 1,000. Minor explosions and VT events occurred intermittently throughout the month. During an overflight on 6 March CENAPRED reported the dimensions of the internal crater as 360-390 m wide and 150-180 m deep, and it was covered with tephra (figure 180). There was no sign of a growing dome within the crater. Trace amounts of ashfall were reported on 13 March in the municipalities of Amecameca and Tlalmanalco, and again overnight 14-15 March in Amecameca. Incandescence was reported at night during 20-23 and 29-31 March. Minor explosions on 27 and 28 March produced plumes with low amounts of ash that rose 800-1,000 m and drifted N and NW. Very small but distinct SO₂ plumes were measured in satellite data each day; thermal anomalies inside the summit crater were observed in Sentinel-2 images on 2, 12, 17, 22, and 27 March (figure 181). Multiple daily VAAC reports continued, but were more intermittent during the last third of the month. On 4 March an existing ash plume was moving SW at 6.1 km altitude 45 km from the summit when a new emission occurred that rose to 7 km altitude and extended 30 km WNW. The plume reported on 13 March was typical of many during the month, drifting NW as far as 150 km from the summit at 6.4 km altitude; they were frequently observed in both satellite data and with the webcam.

Figure 180. The summit crater at Popocatepetl was 360-390 m wide, 150-180 m deep and covered with tephra on 5 March 2021 when viewed during an overflight by government officials. Courtesy of CENAPRED daily report.

Figure 181. Thermal anomalies inside the summit crater of Popocatepetl were different shapes and intensities in Sentinel-2 images on 12 and 27 March 2021 shown here, and also on 2, 17, and 22 March. Images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Daily exhalations ranging from 13-148 per day continued during April 2021. The emissions were primarily gas and water vapor, although intermittent events with small quantities of ash were frequent. Daily tremors ranged from 34-955 minutes in length. Incandescence was visible at the summit during 1-6 and 17-19 April. A moderate explosion overnight on 3-4 April produced incandescent ejecta that traveled up to 1 km down the slopes of the volcano and produced an ash plume that rose 1,200 m and drifted SE. The Washington VAAC reported the ash plume at 7.3 km altitude drifting 30 km E from the summit. Daily VAAC reports were issued for ash plumes that rose to 5.8-7 km altitude and were often visible up to 50 km from the summit. A very bright thermal anomaly appeared inside the summit crater in Sentinel-2 satellite imagery on 1 April, and a very faint one was present on 21 April. A few small to moderate plumes of SO₂ were detected with satellite instruments during April, but most days the anomalies were small (figure 182).

Figure 182. Moderate size SO2 plumes were measured at Popocatepetl intermittently throughout April 2021 including on 2 and 29 April. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Gas and small quantities of ash were typical of the 25-136 daily emissions throughout May 2021. Tens to hundreds of minutes of tremors were also reported each day. Thermal anomalies at the center of the summit crater were distinct in Sentinel-2 satellite images on 6, 26, and 31 May. Moderate SO₂ plumes were common during the first half of May but diminished during the second half. Significantly fewer ash emissions were reported by the Washington VAAC than during the previous few months. Ash plumes during 1-4 May rose to 5.8-6.4 km altitude and drifted NE up to 65 km from the summit. The ash plumes reported during 7-9 May rose to 5.8 km and drifted mostly E. Additional plumes during 14-15, 18, 20-22, 28-29 May and 31 May-1 June rose to 5.8-6.1 km and drifted for a few hours in multiple directions before dissipating (figure 183). Trace amounts of ash fell in Tetela del Volcán during the afternoon of 28 May.

Figure 183. Ash plumes at Popocatepetl were recorded in webcams on 2, 12, 15, and 29 May 2021. Courtesy of CENAPRED daily reports.

Ash emissions were only reported twice during June and four times during July 2021 by the Washington VAAC. They rose to 6.1 km on 11-12 June and 5.8 km on 17 June, drifting NW both times. Similar emissions also occurred during 7, 11-12, 16-18, and 22 July. Exhalations continued to be reported daily at the same rate as May, but there were fewer minutes of tremor both months, and no tremors occurred on nine days of June and ten days of July. Small thermal anomalies appeared in Sentinel satellite images in the same location as earlier images at the center of the summit crater on 10 June, and 10 and 25 July. Small but distinct SO₂ plumes were recorded throughout both months, with only a few days of larger emissions measured by the satellite instruments. CENAPRED reported incandescent ejecta visible a short distance from the crater on the morning of 17 July and an explosion on 21 July that produced an ash plume that rose 800 m and drifted W. An explosion on 22 July produced incandescent ejecta and an ash plume that rose 900 m above the summit and also drifted W (figure 184). Ashfall was reported in the communities of Tlalnepantla, Totolapan, and Huitzilac in the state of Morelos. Another explosion on 24 July sent incandescent fragments down the N flank and an ash plume to 800 m high that drifted NW.

Figure 184. Ash plumes and incandescent ejecta were less frequent at Popocatepetl during July 2021 than during previous months, but were still recorded a number of times, including on 12 and 29 July. Courtesy of CENAPRED daily reports.

Geologic Background. Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Information Contacts: Centro Nacional de Prevención de Desastres (CENAPRED), Av. Delfín Madrigal No.665. Coyoacan, México D.F. 04360, México (URL: http://www.cenapred.unam.mx/, Daily Report Archive https://www.gob.mx/cenapred/archivo/articulos); 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/).

Volcán El Reventador is located 100 km E of the main axis of active volcanoes in Ecuador and has had historical eruptions dating back to the 16th century, characterized by explosive events and lava flows. The most recent eruption began in 2008 and has recently consisted of ash emissions, incandescent block avalanches, a new lava dome, and lava flows (BGVN 46:02). This report updates information from February through July 2021 and is characterized by daily explosions, ash plumes, incandescent block avalanches, lava flows, and occasional pyroclastic flows and lahars, based on daily reports from Ecuador's Instituto Geofisico (IG-EPN), the Washington Volcano Ash Advisory Center (VAAC), and infrared satellite data.

During February to July 2021, IG-EPN reported daily explosions, gas-and-steam and ash plumes, and frequent crater incandescence, often accompanied by incandescent block avalanches and lava flows. The highest average number of explosions per day was 73 in March, followed by 65 in February (table 13). During May-June the average number of daily explosions had declined to 34 and 33, respectively. Ash plumes rose to a maximum height of 2.3 km above the crater on 11 June. At night and early morning, frequent crater incandescence was visible, occasionally accompanied by lava flows generally on the eastern flanks and incandescent block avalanches traveling as far as 900 m from the summit. Seismicity, which was noted throughout the reporting period, was characterized by harmonic tremor events, signals indicating emissions, few volcano-tectonic earthquakes, and dominantly long-period (LP) earthquakes.

Table 13. Monthly summary of explosions and plume heights recorded at Reventador from February through July 2021. Data courtesy of IG-EPN (February to July 2021 daily reports).

Activity at the summit was consistent during February and March 2021. There were 25-121 daily explosive events during these two months, generating gas-and-steam and ash plumes to 400-1,500 m above the crater that drifted in multiple directions (figure 142). At night, crater incandescence and incandescent block avalanches were visible on all flanks, though primarily on the NE and S flanks traveling 500-800 m below the crater (figure 143), though it was not uncommon for weather to prevent clear views of the summit. Two lava flows were reported moving down the N and NE flanks.

Figure 142. Webcam (Rebeca) images of two gray ash plumes rising from Reventador on 9 February (left) and 30 March (right) 2021. The NE flank is visible on the right side of the volcano, highlighted by recent block avalanches and active lava flows (light brown) in the February image. On 30 March white gas-and-steam emissions can be seen on the NE flank. Courtesy of IG-EPN (INFORME DIARIO DEL VOLCAN REVENTADOR No. 2021-040, 09 de febrero de 2021 and No. 2021-090, 31 de marzo de 2021).

Figure 143. Webcam (Rebeca) infrared image of Reventador’s NE flank showing the active incandescent block avalanches (bright yellow-orange) on 13 March 2021. Courtesy of IG-EPN (INFORME DIARIO DEL VOLCAN REVENTADOR No. 2021-072, 13 de marzo de 2021).

During April and May, explosions remained frequent, with 4-105 per day; ash plumes rose 400-1,400 m above the crater (figure 144) and drifted in different directions, though cloudy weather often prevented clear observations. Nighttime crater incandescence was reported during clear weather, accompanied by gas-and-steam emissions and incandescent blocks of material rolling down all flanks as far as 800 m, though the NE and S flanks were dominantly affected. On 21 April an infrared webcam recorded low temperatures of the lava flow on the NE flank, which IG-EPN indicated was no longer active. Small pyroclastic flows descending the SW flank for 600-700 m were noted on 23 and 26-27 April, but none reached the base of the cone. During 4-6 May a pyroclastic flow was reported 400 m down the SW flank, (figure 145). According to an infrared webcam, a lava flow on the NE flank became active again on 10 May; by 22 May, two flows were reported descending the NE and SE flanks (figure 144). Some blocks of material from the front of the lava flow traveled 800 m below the summit. IG-EPN reported that some inflation was noted on the N summit on 13 May, which continued into the following month. On 17 May around 1600 lahars were detected in the upper part of the Reventador River on the N drainages due to heavy rain. By 25 May the number of lahars had decreased and as a result, the seismic stations recorded consistent seismic signals starting around 0741 and continuing throughout the day.

Figure 144. Webcam (Rebeca) images showing an ash plume rising above Reventador on 20 April 2021 (left) accompanied by white gas-and-steam emissions and block avalanches rolling down the NE flank. An infrared image (right) shows the two active lava flows (bright yellow) descending the NE and SE flanks on 29 May 2021. Courtesy of IG-EPN (INFORME DIARIO DEL VOLCAN REVENTADOR No. 2021-110, 20 de abril de 2021 and No. 2021-150, 29 de mayo de 2021).

Figure 145. Webcam (Copete) image of a dense gray ash plume rising from Reventador, accompanied by a pyroclastic flow descending the SW flank at 0706 on 6 May 2021. Courtesy of IG-EPN (INFORME DIARIO DEL VOLCAN REVENTADOR No. 2021-126, 06 de mayo de 2021).

Persistent explosions and ash plumes were reported during June and July, with 3-87 daily events that rose 300-2,300 m above the crater (figure 146). The plumes drifted primarily W, N, NW, NE, and SW. At night and during the early morning, incandescence was observed on the upper part of the flanks while the two lava flows continued to descend the NE and S flanks (figure 146). Incandescent blocks of material rolled down the NE, S, and SE flanks as far as 800 m below the summit. On 7 June during 1200 and 1300 a lahar was reported on the SE flank.

Figure 146. Webcam (Copete) images showing dense ash plumes rising from Reventador on 1 June (left) and 2 July (right) 2021. The ash plume from 1 June is accompanied by a lava flow on the SE flank. Courtesy of IG-EPN (INFORME DIARIO DEL VOLCAN REVENTADOR No. 2021-153, 01 de junio de 2021 and No. 2021-184, 02 de julio de 2021).

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed intermittent thermal anomalies of moderate-to-high intensity during February through July 2021 (figure 147), which reflected the active lava flows and incandescent block avalanches occurring throughout that time. In comparison, the MODVOLC thermal algorithm identified nine thermal alerts between February and July on 9 and 14 February, 20 March, 12 May, 10 and 22 June, and 28 July. Some incandescent avalanches were visible in Sentinel-2 infrared satellite imagery, though clouds often obscured the view of the summit (figure 148). These avalanches were observed descending the NE flanks.

Figure 147. Intermittent thermal activity was detected at Reventador at moderate to high levels during February through July 2021, based on the MIROVA graph (Log Radiative Power). Courtesy of MIROVA.

Figure 148. Sentinel-2 infrared satellite images of Reventador on 15 February 2021 (left) and 10 June (right) showed strong incandescent block avalanches descending the NE flanks, even through frequently dense cloud cover. Images with “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Geologic Background. Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well east of the principal volcanic axis. The forested, dominantly andesitic Volcán El Reventador stratovolcano rises to 3562 m above the jungles of the western Amazon basin. A 4-km-wide caldera widely breached to the east was formed by edifice collapse and is partially filled by a young, unvegetated stratovolcano that rises about 1300 m above the caldera floor to a height comparable to the caldera rim. It has been the source of numerous lava flows as well as explosive eruptions that were visible from Quito in historical time. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the caldera. The largest historical eruption took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

The dacitic Santiaguito lava-dome complex of Guatemala's Santa María volcano has been actively erupting since 1922. It formed within a large crater on the SW flank which was created during the VEI 6 1902 eruption. Ash explosions, pyroclastic, and lava flows have emerged from Caliente, the youngest of the four vents in the complex, for more than 40 years. The Caliente vent is at about 2.5 km elevation, and the summit of Santa Maria is around 3.7 km elevation. A lava dome that appeared within the summit crater of Caliente in October 2016 has continued to grow, producing frequent block avalanches down the flanks. Daily explosions with ash plumes and block avalanches continued during February-July 2021, the period covered in this report, with information primarily from Guatemala's INSIVUMEH (Instituto Nacional de Sismologia, Vulcanologia, Meterologia e Hidrologia).

Blocky lava extrusion from the active dome inside the summit crater of Caliente persisted throughout February-July 2021. This resulted in ongoing block avalanches and ash that descended primarily the W and SW flanks of Caliente, and occasionally the S and SE flanks. Material frequently reached the base and resulted in fine-grained ashfall and suspended ash around the perimeter. Near-constant degassing of water vapor and magmatic gases occasionally contained small amounts of ash; plumes rose to 3.0-3.2 km altitude (up to 700 m above the summit of Caliente) and drifted in multiple directions. Sounds similar to a turbine engine from the constant degassing were reported on most days. Explosions with gas and ash occurred almost daily; the plumes rose to 3.0-3.6 km altitude, and a few drifted up to 10-15 km, producing ashfall in nearby communities before dissipating. Thermal activity remained constant through May, dropped off in June, and returned to typical levels in July 2021 (figure 122).

Figure 122. Steady levels of thermal activity persisted at Santa Maria from December 2020 through May 2021 as seen in the graph of Log Radiative Power produced by the MIROVA project from 22 September 2020 through July 2021. Activity declined in June and returned to typical levels in July 2021. Courtesy of MIROVA.

Ashfall was reported in El Faro (7 km SSW), Aldea Las Marias (10 km S), and El Viejo Palmar (10 km S) on 5 February 2021. The next day a small pyroclastic flow was reported early in the morning on the W flank. The Washington VAAC reported an ash emission that rose to 4.6 km altitude on 7 February. It was seen moving WSW and extending approximately 15 km from the summit before dissipating later in the day. This was the only VAAC report issued for the reporting period. In a special bulletin that day INSIVUMEH noted pyroclastic flows on the SW flank that reached the head of the Rio San Isidro drainage (figure 123). They also reported ash moving SW reaching Finca Montebello, Loma Linda (7 km SW), and San Marcos Palajunoj (8 km SW). On 10 February ashfall was reported in Palajunoj. A thermal anomaly seen in Sentinel-2 satellite imagery extended down the W flank on 16 February (figure 124), likely from either incandescent blocks or a pyroclastic flow. A strong sulfur odor was noted in the area around Las Marias on 20 February. Weak pyroclastic flows affected the E and W flanks of the Caliente on 22 February; ash plumes drifted 2.5 km SW on 26 February.

Figure 123. Explosions produced ash plumes and pyroclastic flows at the Caliente vent of Santa Maria on 7 February 2021. Courtesy of INSIVUMEH (Special Bulletin BESAN-007-2021, 7 February 2021).

Figure 124. A linear thermal anomaly was apparent on the W flank of the Caliente dome at Santa Maria on 16 February 2021. It was likely due to either incandescent blocks or a pyroclastic flow. Image uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

The loud noises from constant degassing were heard in El Palmar on 4 March 2021; ash plumes that day drifted up to 2 km SW. Thermal anomalies appeared in satellite data inside the summit crater of Caliente on 8 and 23 March. Explosions with ash on 9 March rose to 3.0 km altitude and drifted S and SW (figure 125). On 22 March ashfall was reported in Aldea Las Maria, Calaguache, and other nearby communities. Ashfall was reported on 25 and 27 March in Aldeas San Marcos and Loma Linda Palajunoj.

Figure 125. An explosion at the Caliente dome of Santa Maria’s Santiaguito complex on 9 March 2021 rose to 3 km altitude and drifted S and SW Photograph by Lluis Lopez, taken from El Palmar, Quetzaltenango, courtesy of Stereo100Noticias.

Ash plume heights were slightly higher during April 2021, reaching 3.5 or 3.6 km altitude on most days, especially during the second half of the month. Resuspended ash from debris descending the flanks of Caliente dome produced ashfall in Viejo Palmar on 2 April. Sentinel-2 satellite imagery showed a thermal anomaly inside the summit crater that day as well. On 6 April ash plumes drifted 2.5 km SW before dissipating. On 13 and 16 April ashfall was reported in Aldeas San Marcos, Loma Linda Palajunoj, and other nearby communities. INSIVUMEH released a Special Bulletin on 18 April about a lahar that descended Rio San Isidro, carrying branches, tree trunks, volcanic ash, and blocks 1-2 m in diameter.

Ashfall was reported on 1, 6, 11, 16, 21, 26, and 31 May 2021 in Aldeas San Marcos, Loma Linda Palajunoj and other nearby communities from frequent ash plumes that rose to 3.4-3.6 km altitude and drifted SW (figure 126). Increased rainfall resulted in lahars reported on 15, 16, 24, and 30 May. The lahars on 15 and 16 May descended the Rio Cabello de Angel drainage. Branches, trunks, and volcanic blocks 1-3 m in diameter caused vibrations as they passed the seismic stations on 15 May; the next day the flow was a 25-m-wide and 1 m high pasty slurry of sulfur-smelling material full of ash and blocks from 30 cm to 1 m in diameter. The lahar on 24 May descended Rio Tambor and Rio San Isidro with tree trunks, branches, volcanic ash, and blocks 1-2 m in diameter. On 30 May heavy precipitation produced a lahar in Rio San Isidro that occurred near the Finca Filadelfia as a pasty mixture of water, blocks up to 1 m in diameter, and fine sediment, along with branches and tree trunks. A thermal anomaly was present in satellite imagery inside the summit crater on 27 May.

Figure 126. Weak explosions of ash on 31 May 2021 rose to 2.8 km altitude, drifted 5 km SW, and fine-grained ash fell in San Marcos and Loma Linda. Courtesy of CONRED .

The ash explosions reported on 5 June 2021 rose to 2.8 km altitude and drifted 7 km SW resulting in ashfall in Aldeas San Marcos and Loma Linda Palajunoj. Ashfall was reported in the mountainous areas of Monte Claro on 8 June from plumes that reached 3.6 km altitude and drifted W and SW. On 12 and 13 June lahars descended the Rio Nima 1 (figure 127). Rio Cabello de Angel and Nima 1 were the sites of lahars on 15 June where fine-grained material and blocks 30 cm to 1 m in diameter moved down the drainages in a 1-m-deep and 20-m-wide slurry. On 15 June ashfall was reported in Calaguache and Santa Maria de Jesus (5 km SE), and on 20 and 25 June it was again reported in Loma Linda and San Marcos Palajunoj. Another lahar descended Rio Cabello de Angel and Nima 1 on 29 June after rainfall on the upper parts of the volcano. Thermal anomalies were present in Sentinel-2 satellite images inside the summit crater of Caliente on 11 and 26 June.

Figure 127. On 12 June 2021 a lahar of mud and debris descended the Nimá 1 river channel near Finca El Faro. Photo by Edgar Cabrera from COLRED at Finca El Faro, El Palmar, Quetzaltenango. Courtesy of Rony Veliz.

During July 2021 incandescence around the summit crater of Caliente was reported more frequently than during the previous months. The constant block avalanches continued from the extruding lava primarily on the W, SW, and S flanks with some blocks reaching the base and producing ash plumes. On 5, 10, 15, 20, and 30 July ash plumes from explosions drifted 8-12 km W and SW and caused ashfall in Loma Linda and San Marcos (figure 128). The extrusion of blocky lava from the crater was reported as a 600-700 m long flow on the W flank on 10, 15, and 25 July. A lahar on 14 July in the El Tambor ravine was a pasty mixture of water, blocks up to 3 m in diameter, and fine sediments that produced seismic vibrations. Sulfur odors occurred in Las Marias on 20 and 25 July. Thermal anomalies at the summit were recorded in satellite images on 6, 16, and 31 July.

Figure 128. Norma Cardona of COLRED San Marcos Palajunoj El Palmar Quetzaltenango, reported that on 5 July 2021 the Caliente dome of Santiaguito was weakly degassing with minor ash drifting W. Ashfall was reported in communities to the SW that day. Courtesy of Frídel Mejicanos.

Geologic Background. Symmetrical, forest-covered Santa María volcano is part of a chain of large stratovolcanoes that rise above the Pacific coastal plain of Guatemala. The sharp-topped, conical profile is cut on the SW flank by a 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank, and was formed during a catastrophic eruption in 1902. The renowned Plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic-andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four vents, with activity progressing W towards the most recent, Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); 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); 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); CONRED, Coordinadora Nacional para la reduccion de desastres (URL: https://conred.gob.gt/, https://twitter.com/ConredGuatemala/status/1399369155544076295 ); Stereo100Noticias (URL: https://twitter.com/stereo100xela/status/1369295245272363014); Rony Veliz (URL: https://twitter.com/ronyveliz692/status/1403836189841494019); Frídel Mejicanos (URL: https://twitter.com/FridelMejicanos/status/1412189491289264129).

Indonesia’s Sinabung volcano in north Sumatra had its first confirmed Holocene eruption during August and September 2010. It remained quiet until September 2013 when a new eruptive phase began that continued through mid-2018. Dome growth and destruction resulted in block avalanches, multiple explosions with ash plumes, and deadly pyroclastic flows during the period. After a pause in activity from September 2018 through April 2019, explosions resumed during May and June 2019. Rock avalanches, frequent, dense, ash-bearing explosions, and periodic pyroclastic flows continued through February 2021. This report covers ongoing similar activity from March through June 2021 with information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, and the Darwin Volcanic Ash Advisory Centre (VAAC). Additional information comes from satellite instruments and the Indonesian National Disaster Management Agency (BNPB).

Hundreds of block avalanches and tens of ash-bearing explosions were reported each month during March to mid-May 2021. Ash plumes rose 500-2,000 m above the summit (3,000-4,500 m altitude) on most days; occasional larger events produced much higher plumes. Two major sets of explosions, on 2 March and 13-14 May, each produced ash plumes that rose to 12.2 km altitude, more than 10 pyroclastic flows, and significant SO₂ plumes measured by satellite instruments. Reports of activity during the period came from the Sinabung Observation Post (in Surbakhti, 10 km SE of the volcano) and from geoscientists monitoring seismic instruments and webcams from remote locations; the combined information provides a more complete picture of activity at the volcano (table 10). Thermal activity was recorded by the MIROVA project and indicated a spike in radiative power that began in late February and lasted through May 2021, attributable to increased explosive activity (figure 93). Two notable sequences of explosions on 2 March and 13-14 May produced significant plumes of SO₂ that were measured by the TROPOMI instrument on the Sentinel-5P satellite (figure 94). None of the other explosions during the period produced significant SO₂ anomalies. Only two days of explosions, 3 and 6 June, occurred after 19 May through the end of June.

Table 10. A summary of information and sources reporting activity at Sinabung during March-June 2021 includes the distance block avalanches traveled, the number of eruptions, pyroclastic flows, and lahars reported by the observatory, the seismic eruptions recorded by MAGMA Indonesia, and the VONA’s issued. All heights and distances shown are in meters. Information provided by PVMBG unless otherwise noted. Courtesy of PVMBG and MAGMA Indonesia.

Figure 93. An increase in thermal activity at Sinabung during late February-May 2021 corresponded to an increase in explosive activity during the period as shown in the MIROVA graph of Log Radiative Power for 24 Aug 2020 through June 2021. Courtesy of MIROVA.

Figure 94. High level explosions at Sinabung on 2 March and 13 May 2021 produced significant plumes of SO2 that drifted NW from the volcano and were measured by the TROPOMI Instrument on the Sentinel-5P satellite. The ash plumes were reported at 12.2 km altitude. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Activity during March-June 2021. Significant explosive activity continued at Sinabung during March 2021. In a special press release on 2 March, PVMBG reported a series of pyroclastic flows that began at 0642 local time and traveled 2,000-5,000 m ESE from the summit accompanied by a column of ash that rose 4,000-5,000 m above the body of the pyroclastic flow (figure 95). MAGMA Indonesia reported three explosions that rose to about 1,000 m above the summit and drifted E and SW. The Darwin VAAC first reported that the ash emissions from the eruption rose to 7.6 km altitude (5.1 km above the summit) and drifted W; they were clearly discernable in satellite imagery. About an hour later they updated the altitude of the plume to 12.2 km based on analysis of HIMAWRI-8 imagery. In the following hours the plume was observed drifting W at 12.2 km altitude and SW at 7.6 km before dissipating. According to BNPB ashfall was noted in 17 villages in the Tiganderket District, eight villages in the Kutabuluh District, and 15 villages in the Tigabinaga District.

Figure 95. This explosion at 0836 local time was one of three at Sinabung on 2 March 2021 that produced 15 pyroclastic flows and ash plumes that rose to 12.2 km altitude according to the Darwin VAAC. The pyroclastic flows descended up to 3.7 km down the SE and E flanks. Photo by PVMBG - Sinabung PGA Post. Courtesy of PVMBG (Press Release Volcanic Activity of Mount Sinabung – North Sumatra March 2, 2021).

On most days in March steam plumes were observed rising 50-500 m above the summit; they reached 1,000 m high on 7 March. Block avalanches were reported descending the E and SE flanks 500-1,500 m on 12 days of the month. The Sinabung Observation Post reported 49 explosion earthquakes and gray ash emissions. There were 1-2 explosions on most days; six were observed on 11 March (figure 96) that all rose only 500-1,000 m above the summit and drifted W and SW with no ashfall reported. MAGMA Indonesia reported an explosion on 15 March that rose 2,000 m above the summit; the Darwin VAAC could not confirm it in satellite imagery due to meteoric clouds. For the second half of March, 1-4 explosions were reported daily; dense gray ash rose 500-1,000 m above the summit and drifted SW, W, NW, and NE.

Figure 96. Six explosions with ash emissions from Sinabung were reported on 11 March 2021. The plumes rose 500-1,000 m above the summit and drifted S and SW. Courtesy of MAGMA Indonesia.

MAGMA Indonesia reported 42 eruptions throughout March with dense gray ash emissions that rose 500-2,000 m above the summit and drifted SW, W, or NW. The Darwin VAAC issued 53 ash advisories. VONAs were issued 22 times; two on 2 and 11 March were for pyroclastic flows, the others were for ash plumes from explosions. There were 20 pyroclastic flows reported by PVMBG during the month; 15 of them occurred on 2 March when they traveled 1,000-3,700 m down the E and SE flanks and 2,300 m down the S flank (figure 97). One pyroclastic flow was reported on 1 March, and two others were reported on 3 and again on 11 March that traveled 2,000-3,000 m ESE from the summit. Three seismic signals indicative of lahars were recorded on 12, 16, and 18 March.

Figure 97. A strong thermal anomaly at Sinabung was recorded in Sentinel-2 satellite imagery on 2 March 2021. Its location near the summit on the ESE flank suggests it was related to one of the 15 pyroclastic flows observed that day. Image uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

The frequency of explosive activity increased significantly during April 2021. Block avalanches were reported on 15 days, traveling 500-1,500 m down the S and SE flanks. PVMBG reported 123 eruptions with gray ash plumes rising 500-1,000 m above the summit. VONA’s were issued for 30 events. MAGMA Indonesia reported 74 explosions with dense gray ash emissions rising 500-2,000 m above the summit. There were 1-10 explosions nearly every day; only two days had no explosions reported. Eight explosions were reported on 2 April with heights of 500-1,000 m above the summit. On 4 April PVMBG reported an ash emission to 3.7 km altitude, but the Darwin VAAC revised that estimate to 5.5 km based on satellite infrared temperature data (figure 98). During 7-8 April the VAAC reported ash emissions at 4.3 km altitude. MAGMA Indonesia reported eight explosions on 17 April with plume heights ranging from 500 to 1,500 m above the summit, drifting S and W. On 19 April emissions were reported by the Darwin VAAC drifting SE at 4.6 km altitude; they reached 4.3 km on 24 April. For the remainder of the month six or more explosions occurred most days, with altitudes of 3.0-3.9 km. Seven pyroclastic flows were reported during April. On 1 April, one traveled 1,500 m down the SE flank. One was reported on 8 April, two on 13 April, and one each on 19, 21, and 29 April. The pyroclastic flow on 21 April traveled 2,000 m down the flank. Signals indicating lahars were recorded on 12, 16, 24, 29, and 30 April.

Figure 98. PVMBG reported 123 explosions with ash at Sinabung during April 2021, including four on 4 April (top left), five on 16 April (top right), nine on 20 April (bottom left), and six on 28 April (bottom right). Courtesy of MAGMA Indonesia and PVMBG.

Substantially fewer explosions were reported during May 2021 than April, although the ash plumes were higher for several events. The Sinabung Observation Post reported 37 explosions that produced gray ash plumes rising 500-3,000 m above the summit; 1-6 explosions occurred daily through 14 May; a single explosion on 19 May was the last one recorded for the month. The ten VONA’s also recorded plume heights 700-3,000 m. MAGMA Indonesia reported 26 seismic events with dense gray emissions ranging from 500-3,500 m high. During 6-10 May ash emissions were reported 2,000 m or higher above the summit each day; six explosions were reported by PVMBG and MAGMA Indonesia on 8 May. The Darwin VAAC noted that ash plumes on 6 May rose to 4.6 km altitude. The next day the emissions rose to 5.2-5.5 km altitude and were discernable late in the day drifting NNW in RGB satellite imagery. On 8 May the ash plumes were reported at 4.3-5.2 km altitude drifting E; on 10 May two discrete events rose to 4.9 and 3.7 km and drifted S, both noted in satellite imagery (figure 99). Four explosions were reported on 11 May. Sentinel-2 satellite imagery recorded incandescent material in the large SE flank ravine that day (figure 100).

Figure 99. Three explosions at Sinabung on 10 May 2021, including this one at 0750 local time produced ash emissions that rose up to 2,500 m above the summit (4.9 km altitude) and drifted S. Courtesy of MAGMA Indonesia and PVMBG.

Figure 100. Four explosions were reported at Sinabung on 11 May 2021; a thermal anomaly extended hundreds of meters down the SE flank ravine in this Sentinel-2 satellite image. Image uses Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

During 13-14 May six explosions and 15 pyroclastic flows were reported by PVMBG with ash plumes 700-1,000 m above the summit, and pyroclastic flows descending the SE and E flanks 2,500-4,000 m. A larger eruption with ash to 12.2 km that drifted NW, clearly identifiable in satellite imagery, was reported by the Darwin VAAC on 13 May. A second explosion three hours later produced a plume that was identifiable in RGB satellite imagery at 9.8 km altitude moving WNW. Eruptions were ongoing on 14 May, with plumes rising to 9.1-10.7 km altitude and drifting NW (figure 101). A significant SO₂ plume was measured by satellite instruments that day. A single large explosion early on 19 May (local time) produced an ash plume to 3,500 m above the summit (5.9 km altitude). The Jakarta Meteorological Office reported the eruption to the Darwin VAAC but it was not visible in satellite imagery due to meteoric clouds. This was the last explosion reported for May. Five lahars were recorded during the month; one each day on 12, 15, and 16 May, and two on 13 May.

Figure 101. This photo was posted to Twitter on 15 May 2021 with the caption “..areas affected by the eruption of Mount Sinabung” and likely represents ashfall from the large explosions of 13-14 May 2021. Courtesy of amoy rest buying.

Very little activity was reported from Sinabung during June 2021. Steam emissions rose 50-300 m above the summit on most days, occasionally rising to 500 m. Block avalanches were reported only on 11 and 12 June. PVMBG reported two seismic eruption events, on 3 and 5 June, but they were not observed. A single pyroclastic flow occurred on 6 June, the only day a single VONA was issued. MAGMA Indonesia reported two eruption events on 4 June and one on 6 June; none were observed due to poor weather conditions. The Darwin VAAC reported a significant eruption on 6 June that sent an ash plume to 9.1 km altitude that drifted W. Initially it was not visible, but later appeared on RGB satellite imagery moving N and W. A few hours after the eruption the plume was drifting N at 4.3 km altitude, W at 7.3 km, and WSW at 9.1 km. It dissipated the following morning, and was the last explosion reported for June. Lahars were recorded on 3, 15, and 25 June.

Geologic Background. Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical andesitic-to-dacitic edifice is at the southern end of the four overlapping summit craters. The youngest deposit is a SE-flank pyroclastic flow 14C dated by Hendrasto et al. (2012) at 740-880 CE. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.

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.esdm.go.id/v1); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); 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/); 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/); amoy rest buying (URL: https://twitter.com/jjaemshine/status/1393531437949743111).

Tofua is a remote volcano in the central part of the Tonga Islands group that contains a 5-km-wide caldera; three post-caldera cones were constructed at the N end of a caldera lake. The easternmost cone has three craters that have produced young basaltic-andesite lava flows, some of which traveled into the caldera lake. The largest and northernmost of the cones, Lofia, has a steep-sided crater that is 70 m wide and 120 m deep and has been the source of historical eruptions dating back to the 18th century. Recent activity has been characterized by intermittent thermal anomalies in the Lofia crater (BGVN 45:08), which continues through this reporting period of August 2020 through July 2021. Information primarily comes from satellite data.

Summary of activity during August 2020-July 2021. No ash advisories were issued during the reporting period; however, intermittent hotspots were detected by Sentinel-2 thermal satellite imagery and Suomi NPP/VIIRS sensor data throughout the reporting period (figure 12). Anomalies from the MODVOLC system clustered during February 2021 through April and June. There was a notable increase in activity during mid-February through July, compared to the previous months, which included distinct sulfur dioxide plumes (figure 13) and consecutive days with thermal anomalies, according to NASA VIIRs satellite data.

Figure 12. Timeline summary of observed activity at Tofua from August 2020 through July 2021. For Sentinel-2, MODVOLC, and VIIRs data, the dates indicated represent detected thermal anomalies. For the SO2 data, the dates indicated represent detected sulfur dioxide plumes. White areas indicate no activity was observed, which may also be due to cloud cover. Each cell represents one calendar day. Data courtesy of Sentinel Hub Playground, HIGP, NASA Worldview using the “Fire and Thermal Anomalies” layer, and NASA Global Sulfur Dioxide Monitoring Page.

Figure 13. Weak but distinct sulfur dioxide emissions were detected from Tofua on 17 (top left), 18 (top right), 19 (bottom left), and 25 (bottom right) February 2021, each of which drifted W, based on data from the TROPOMI instrument on the Sentinel-5P satellite. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Sentinel-2 infrared satellite imagery and NASA Worldview detected intermittent thermal anomalies during August 2020 through July 2021 dominantly in the Lofia crater (figure 14); rare fires were noted along the NW coast of the island. Beginning in mid-February, the activity notably increased with a stronger thermal anomaly. This increase was accompanied by white gas-and-steam emissions, which included distinct sulfur dioxide plumes.

Figure 14. Sentinel-2 infrared satellite imagery showed a persistent thermal anomaly in the Lofia crater at Tofua during September 2020 through May 2021; the intensity of the anomaly notably increased during February through May and was occasionally accompanied by white gas-and-steam emissions. Images with "Atmospheric penetration" (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Geologic Background. The low, forested Tofua Island in the central part of the Tonga Islands group is the emergent summit of a large stratovolcano that was seen in eruption by Captain Cook in 1774. The summit contains a 5-km-wide caldera whose walls drop steeply about 500 m. Three post-caldera cones were constructed at the northern end of a cold fresh-water caldera lake, whose surface lies only 30 m above sea level. The easternmost cone has three craters and produced young basaltic-andesite lava flows, some of which traveled into the caldera lake. The largest and northernmost of the cones, Lofia, has a steep-sided crater that is 70 m wide and 120 m deep and has been the source of historical eruptions, first reported in the 18th century. The fumarolically active crater of Lofia has a flat floor formed by a ponded lava flow.

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/); 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/); NASA Worldview (URL: https://worldview.earthdata.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).