Tofua is located in the central part of the Tonga Islands group and 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 recorded eruptions dating back to the 18th century. The current eruption period began in October 2015 and recent activity has consisted of mostly intermittent thermal anomalies in the Lofia crater and sulfur dioxide emissions (BGVN 46:08). This reporting period covers persistent thermal anomalies in the Lofia crater during August 2021 through July 2022. Information primarily comes from satellite data.

Summary of activity during August 2021-July 2022. Intermittent hotspots were detected by Sentinel-2 infrared satellite imagery, the MODVOLC infrared satellite data using NASA’s MODIS instrument, and Suomi NPP/VIIRS sensor data (figure 15). Sentinel-2 imagery showed a bright thermal anomaly in the Lofia crater 2-5 times each month during the reporting period (figure 16). A total of 14 thermal alerts were detected by the MODVOLC system 1-3 times every month of the reporting period. Many of these hotspots were also reflected in the Sentinel-2 and Suomi NPP/VIIRS data. There was a total of 114 days of hotspots during the reporting period that ranged from 3-14 each month in Suomi NPP/VIIRS data.

Figure 15. Timeline summary of thermal activity at Tofua detected using satellite data from August 2021 through July 2022. The dates indicated represent detected thermal anomalies for Sentinel-2, MODVOLC, and VIIRS data. 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 - MODVOLC Thermal Alerts System, and NASA Worldview using the “Fire and Thermal Anomalies” layer.

Figure 16. Sentinel-2 infrared satellite imagery showed a persistent bright thermal anomaly (bright yellow-orange) in the Lofia crater at Tofua during August 2021 through July 2022. Images were taken on 15 August 2021 (top left), 24 September 2021 (top middle), 17 January 2022 (top right), 12 April 2022 (bottom left), 12 May 2022 (bottom middle), and 16 July 2022 (bottom right). 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 Worldview (URL: https://worldview.earthdata.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Etna is located on the island of Sicily, Italy, and has had documented records of eruptions dating back to 1500 BCE. Activity frequently originates from multiple cones at the summit, where several craters have formed and evolved. The currently active craters consist of Northeast Crater (NEC), Voragine (VOR), and Bocca Nuova (BN) that were formerly the “Central” crater, and the Southeast Crater (SEC). The original Southeast crater formed in 1978, and a second eruptive site that opened on its SE flank in 2011 was named the New Southeast Crater (NSEC). Another eruptive site between the SEC and NSEC was referred to as the "cono della sella" (saddle cone) and developed during early 2017. The current eruption period began in September 2013 and has consisted of Strombolian explosions, ash plumes, lava fountaining, pyroclastic flows, and lava flows associated primarily with the Southeast crater (SEC). This report covers continuing activity during February through June 2022, based on weekly and special reports by the Osservatorio Etneo (OE), part of the Catania Branch of Italy's Istituo Nazionale di Geofisica e Vulcanologica (INGV) and satellite data.

Summary of activity during February-June 2022. Most of the strong eruptive activity during February-June 2022 occurred in the Southeast Crater (SEC), which included Strombolian explosions, ash plumes, lava fountains, and lava flows. Persistent fumarolic activity at Bocca Nuova (BN), Voragine (VOR), and Northeast Crater (NEC) were accompanied by occasional diffuse ash emissions (table 12). Lava flows were reported by INGV during 10-11 and 21 February, 12, 20, and 29 May, and 6 and 11 June, moving SW, N, and NE. Lava fountaining occurred on 10 and 21 February. Pyroclastic flows were detected on 10 February, 12 May, and 20-21 May. Intermittent ash plumes rose to 3.5-12 km altitude throughout the reporting period, accompanied by Strombolian explosions. INGV reported that the eruption ended during the night of 15-16 June following effusive activity in the Valle del Bove.

A total of 201 MODVOLC thermal alerts were detected during the reporting period: 32 during February, 114 during May, and 71 during June. During these months specifically, INGV reported strong Strombolian explosions, lava fountains, and lava flows, which contributed to the stronger thermal activity detected in satellite data. These notable numbers also correlate to spikes detected in thermal activity in the MIROVA graph (figure 369). The lava flows that originated from SEC were also visible in Sentinel-2 infrared satellite imagery during February, May, and June, moving down the SW and NE flanks (figure 370). Accompanying this strong thermal activity were occasional sulfur dioxide plumes, as shown on 11 February and 24 May and recorded by the TROPOMI instrument on the Sentinel-5P satellite, where the emissions reached more than 2 Dobson Units (DU) and drifted generally N and NE (figure 371).

Table 12. Summary of activity at the four primary crater areas at the summit of Etna during February-June 2022. Information is from INGV weekly reports.

Figure 369. Thermal activity at Etna varied in intensity during January through June 2022, according to this MIROVA (Log Radiative Power) graph. Two brief increases in power occurred during February. Beginning in mid-May, both the frequency and power of the detected thermal anomalies markedly increased, which corresponded to observations of lava flows. The power of these anomalies gradually declined by mid-June. Courtesy of MIROVA.

Figure 370. Multiple Sentinel-2 infrared satellite images showed lava effusion originating from Etna’s SEC on 11 February 2022 (top left), 21 February 2022 (top middle), 14 May 2022 (top right), 17 May 2022 (bottom left), 6 June 2022 (bottom middle), and 13 June 2022 (bottom right). The lava flow on 11 February descended the SW flank. On 21 February Strombolian explosions and lava fountaining activity occurred, represented by the strong thermal anomaly (bright yellow-orange) at SEC. The lava flow on 14 May traveled to the N and NE into the Valle del Leone and was still visible on 17 May, joined by additional new flows near the summit crater. A continuous flow on 6 June was visible moving E from a new effusive vent and began to cool by 13 June. Images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Figure 371. Sulfur dioxide plumes were emitted from Etna following strong explosive and effusive events at SEC on 11 February 2022 (left) and 24 May 2022 (right). The plumes drifted N and NE, respectively. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Activity during February 2022. Discontinuous Strombolian activity and mild ash emissions occurred at SEC during February, while degassing was reported at BN, NEC, and VOR. During the early morning of 2 February, the Strombolian explosions had stopped. On 10 February modest explosive activity resumed in SEC, as detected by video surveillance cameras. The activity was initially confined to the crater and generated discontinuous and mild ash emissions that drifted SW. As a result, there was a collapse detected on the S flank of SEC, which often showed a thermal anomaly in infrared cameras. That same day, at 1520, a new lava flow was visible from SEC that traveled WSW. The front of the flow reached an elevation of 2.9 km by 1956. At 2140 INGV reported a lava fountain at SEC, accompanied by an ash plume 8-10 km high that drifted W. Around 2140, 2219, and 2226, three pyroclastic flows breached the S flank of SEC, two of which traveled a few hundred meters toward the Valle Bove while the last one went S. As a result, some small collapses of material produced small ash emissions. This activity continued to be observed through the next day. By 11 February, the fountaining activity has stopped, but the lava flow from SEC continued, the front of which had advanced to 2.7 km elevation. On 11 February at 1107 the lava flow from SEC had stopped, though weak and discontinuous explosions persisted, emitted weak ash emissions that drifted to the NW. These explosions also resuspended and redeposited pyroclastic material in areas to the NW, particularly in Maletto and up to the Tyrrhenian coast of Sicily, in S Agata di Militello and Capo d'Orlando. A thermal anomaly was detected at the SE base of SEC the same day. On 15 and 18 February modest ash emissions occurred at NEC, which was deposited in the summit area.

Two small ash emissions from SEC were detected on 20 February (figure 372). INGV reported that on 21 February weak Strombolian activity persisted at SEC, accompanied by lava fountaining; an ash plume rose to 10 km altitude and drifted SE (figure 373). A lava overflow was detected around 1210 from SEC that descended toward the SW (figure 374). An ash plume was also visible, rising to 11 km altitude. By 1340 the lava fountaining stopped at SEC, but explosions continued, producing an ash plume that rose to 12 km altitude that drifted SSE. Some ashfall was reported in Viagrande, Trecastagni, and Zafferana. The lava flow continued to be fed weakly, the front of which is located at an elevation of 2.9 km and expanded to the E. Explosive activity in SEC stopped by 1350 on 21 February. INGV personnel in the field reported ashfall from the lava fountain activity in Viagrande, Milo, and Acicastello, and was mainly dispersed between Petrulli and Zafferana. After the fountaining a small pit crater formed and began showing signs of weak degassing. Additionally, surveillance cameras and INGV personnel reported another lava flow moving along the eastern slope of SEC, the front of which was at an estimated elevation of 2.9 km.

Figure 372. Ash emissions were visible in satellite images rising above Etna’s Southeast Crater on 20 February 2022 taken at 1006 UTC (left) and 1650 UTC (right). Images taken with a high-resolution camera from Etna’s eastern slope (left) and the south slope (right). Courtesy of INGV (Report 08/2022, ETNA, Bollettino Settimanale, 14/02/2022 - 20/02/2022).

Figure 373. Strombolian activity at Etna’s SEC was observed by the La Montagnola (south) thermal camera on 21 February 2022 (top left), which generated strong ash plumes, as seen from the webcam image later in the day on 21 February 2022 (top right). Lava fountaining activity and a lava flow was recorded by the La Montagnola and Nicolosi (south) thermal cameras (bottom left). Two lava flows on the S and E slopes of SEC were seen in the Nicolosi thermal camera images (bottom right). The inset image on the bottom right was taken by the Mt. Cagliato (east) thermal camera showing the lava flow on the E slope. Courtesy of INGV (Report 08/2022, ETNA, Bollettino Settimanale, 14/02/2022 - 20/02/2022).

Figure 374. Map of the summit area of Etna showing the location and direction of the lava flow (light orange color) that began on 21 February 2022. The locations of each of the active craters are labeled as NEC (Northeast Crater), VOR (Voragine), BN (Bocca Nuova), and SEC (Southeast Crater). The red dots represent active craters, the yellow dots represent craters with degassing activity, and the green dots represent the location of GPS points taken by INGV personnel. The map was created using Sentinel-2 and PlanetScope data on 23 and 24 February, respectively, and the GPS track was acquired by INGV personnel on 24 February 2022. Courtesy of INGV (Report 08/2022, ETNA, Bollettino Settimanale, 14/02/2022 - 20/02/2022).

Weak Strombolian explosions were detected in SEC again during 22-25 February; during the morning of 23 February the lava flow moving along the lower E slope had started to cool. Several collapses were observed on the S flank of SEC and on the upper E slope following the lava fountaining, which caused fewer and more dilute ash puffs. On 24 February at 1338 surveillance cameras showed ash emissions rising above NEC that drifted SSE, followed by other less intense ash pulses.

Activity during March-April 2022. Activity during March and April was relatively low and consisted of gas-and-steam emissions from the summit craters, sporadic ash emissions from NEC, and modest collapses of material from the inner walls of SEC. Thermal activity in the summit area was low after the lava fountaining on 21 February. On 3 March a thermal anomaly was observed on the S inner wall of SEC associated with an ash cloud that rapidly dispersed into the atmosphere. According to INGV, the anomaly was likely caused by hot material that had accumulated during activity on 21 February. During the morning of 18 March a small ash emission was visible from the base of the S slope of SEC (figure 375).

Figure 375. Webcam images observed by the La Montagnola (south) camera showing the small ash emission emitted from the base of Etna’s SEC as indicated by the yellow arrow. BN is also visible in the background. Courtesy of INGV (Report 12/2022, ETNA, Bollettino Settimanale, 14/03/2022 - 22/03/2022).

An overflight on 8 April described intense gas-and-steam pulses from two vents in the center of BN. No activity was detected in VOR. Some small fumarolic activity and weak gas-and-steam emissions were observed in SEC and NEC. During the early morning hours of 27 April, very faint reddish ash emissions were observed in webcam images. Some degassing was also visible at SEC, mainly from fumaroles along the N crater rim and near the collapsed area from 10 February. On 21 April at 1006 a small landslide occurred on the S flank of the cone, accompanied by a thermal anomaly that was visible from the Montagnola camera. Another landslide event occurred at the same place on 22 April at 2214.

Activity during May 2022. Strombolian activity continued in SEC during May, occasionally accompanied by ash emissions. Some effusive activity was also reported in the Valle del Bove. On 9 May a mild ash emission was observed at SEC; similar and more frequent events occurred on the 11th. Thermal cameras showed an active vent on the upper N side of the cone. On 12 May at 1900 ash emissions intensified and rose to 3.5 km altitude from SEC to the SW from one or more vents along the N side of the crater. Small pyroclastic flows were reported on the N flank of SEC and reached the N base of the crater on 12 May. Additionally, a small lava flow effused from an eruptive vent and traveled N and NE into the snowy Valle del Leone, where lava blocks that rolled onto the snow caused gas-and-steam plumes. The SEC was also affected by discontinuous and variable Strombolian explosions, where the most intense phases ejected ash into the atmosphere, some of which dispersed to the SW during 14-15 May.

By 17 May the lava flow developed toward the ENE in the Valle del Leone, the front of which reached an elevation of 2.3-2.4 km. On 18 May the lava flow had begun to cool while new flows developed from the vent and followed the older flow (figure 376). On 20 May at 1730 a second effusive vent open on the N side of SEC at an elevation of 3.2 km. A small lava flow effused from this new vent that traveled NE (figure 377). During 20-21 May a pyroclastic flow originated from SEC and traveled NNE for 700 m. There was a gradual increase in explosive activity at SEC on 22 May at 1940, which produced ash emissions that rose to 5 km altitude and extended to the S. Weak ashfall was reported on the SE flank as far as Catania. At the same time, the lava emissions continued with varying intensity at the effusive vents formed on 12 and 20 May. On 29 May a third effusive vent opened in the upper part of the Valle del Bove and Strombolian activity at SEC stopped. Field observations showed that in the upper part of the W wall of the Valle del Bove there were two points of lava effusion along an eruptive fissure-oriented ENE. In the following days, low-rate effusion was reported, with flows reaching an elevation of 2.1 km. A series of fractures on the E side of SEC were noted at 3-3.2 km elevation; slope instability generated avalanches of material.

Figure 376. Thermal images taken of Etna’s SEC on 18 May 2022 showing the active and cooling lava flows. Strombolian explosions continued at the summit crater. The brighter active flow is in the foreground (towards bottom right in each image), while the flow in the background has started to cool. Courtesy of INGV (Report 21/2022, ETNA, Bollettino Settimanale, 16/05/2022 - 22/05/2022).

Figure 377. Map of the summit area of Etna showing the location and direction of the lava flows (red and light green) that began on 20 May 2022 (light green) and 22 May 2022 (red). Both lava flows traveled to the N and NE. The locations of each of the active craters are labeled as NEC (Northeast Crater), VOR (Voragine), BN (Bocca Nuova), and SEC (Southeast Crater). The red dots represent active craters and the yellow dots represent craters with degassing activity. The topographic base was taken from Pleiades images from 22 August 2020, while the topography of craters was obtained from photogrammetric processing of photos taken on a helicopter flyover on 8 April 2022. Courtesy of INGV (Report 21/2022, ETNA, Bollettino Settimanale, 16/05/2022 - 22/05/2022).

Activity during June 2022. Strombolian at SEC occasionally accompanied by ash emissions continued during June. Variable and pulsating effusive activity also persisted in the upper part of the Valle del Bove. Over time, the variability in effusion rate was reflected in the development of a branched lava field with overlapping flows. The flow fronts reached a maximum height of about 1.9 km altitude on 5 June and retreated to 2.4 km altitude on 6 June (figure 378).

Figure 378. An updated map of Etna’s SEC showing the lava flow field on 6 June 2022. The red color represents an active lava flow on 6 June, orange color represents an active lava flow on 5 June, and yellow represents a cooling lava flow. Each of the flows traveled to the ENE. The locations of each of the active craters are labeled as NEC (Northeast Crater), VOR (Voragine), BN (Bocca Nuova), and SEC (Southeast Crater). The blue hatched line represents places of collapse. The topographic base was taken from Pleiades images from 22 August 2020, while the topography of craters was obtained from photogrammetric processing of photos from a helicopter flyover on 8 April 2022. Courtesy of INGV (Report 23/2022, ETNA, Bollettino Settimanale, 30/05/2022 - 05/06/2022).

Ongoing ash emissions reported on 1 June drifted SSE. Variable Strombolian activity continued and was accompanied by a lava flow on 2 June (figure 379). Particularly intense explosions during 1-3 June produced continuous ash emissions that dispersed SSE (figure 380). An ash plume on 3 June rose to 4-5 km altitude and drifted SSW. During the late afternoon on 7 June a new fracture opened at the base of the N wall of the Valle del Bove. Field observations reported a slightly active lava flow on 8 June that was mostly cooling and reached a maximum length of 170 m. On 11 June another new effusive vent at an elevation of 1.9 km fed another slightly active lava flow that expanded for a few tens of meters. A field inspection on 12 June showed a total of three active effusive vents; the most advanced lava flow front reached 1.8 km elevation (figure 381). During 13-14 June a single vent located at 1.9 km elevation produced a well-fed lava flow that had advanced to 1.8 km elevation on 14 June; by the night of 15 June the flow had stopped. Drone imagery from 14 June showed that small lava tunnels had developed, and two small vents located at 1.87 km and 1.95 km elevation had formed.

Figure 379. Photo of the effusive vent at Etna’s SEC and the resulting lava flow traveling over a pre-existing lava field on 2 June 2022. Courtesy of INGV (Report 23/2022, ETNA, Bollettino Settimanale, 30/05/2022 - 05/06/2022).

Figure 380. Photos of explosive Strombolian activity at Etna’s SEC on 3 June 2022 taken during a field inspection (a) and through webcam images (b and c). Ash plumes rose as high as 5 km altitude and drifted generally S. Courtesy of INGV (Report 23/2022, ETNA, Bollettino Settimanale, 30/05/2022 - 05/06/2022).

Figure 381. A series of a thermal image and photos showing the effusive activity at Etna during 7-11 June 2022. A thermal image (top left) showing the effusive vent that opened on 7 June 2022. An annotated drone image from 8 June 2022 (top right) showing locations of cooled lava flows (outlined in yellow) and the active lava flow (red arrow). The effusive vent occurred at an elevation of 2 km (middle left) and the lava flow front stood at an elevation of 1.9 km (middle right). Various fractures were observed during a field inspection on 9 June 2022 (bottom left), and a new eruptive vent that opened on 11 June produced another lava flow (bottom right). Courtesy of INGV (Report 24/2022, ETNA, Bollettino Settimanale, 06/06/2022 - 12/06/2022).

According to INGV, effusive activity in the Valle del Bove had stopped during the night of 15-16 June and no further eruptive activity was observed. Degassing at the summit craters continued except at VOR. Gas-and-steam emissions and some small fumaroles were observed rising from the inner walls of NEC.

Geologic Background. Mount Etna, towering above Catania on the island of Sicily, has one of the world's longest documented records of volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Information Contacts: Sezione di Catania - Osservatorio Etneo, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/it/ ); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard MD 20771, USA (URL: https://so2.gsfc.nasa.gov/).

Bulusan lies at the SE end of the Bicol volcanic arc in the Philippines. It is flanked by several other large intra-caldera lava domes and cones and its summit contains a 300-m-wide, 50-m-deep crater. Three small craters are located on the SE flank. Moderate explosive eruptions have been recorded since the mid-19th century. The previous eruption period, during June 2017, consisted of weak phreatic explosions and produced minor ashfall in nearby villages (BGVN 42:08). This reporting period covers a new eruption period during June 2022, characterized by similar phreatic explosions, based on information from the Philippine Institute of Volcanology and Seismology (PHIVOLCS).

Summary of activity during January 2020-May 2022. Activity since the last eruption in June 2017 mainly consisted of occasional volcanic earthquakes and weak gas-and-steam emissions, sulfur dioxide emissions were below detectable levels since 2018, and the frequency of volcanic earthquakes had been at baseline levels of 0-2 earthquakes/day since May 2019. During 3-7 July 2020 a total of 72 volcanic earthquakes were detected, which included 43 low-frequency events. Diffuse white gas-and-steam plumes rose from the lower SE vent. Ground deformation data from continuous GPS measurements indicated short-term inflation of the edifice since late February 2020. On 6 July the Volcano Alert Level (VAL) was raised to 1, but activity remained relatively low, and on 26 October the VAL was lowered to 0 (normal conditions). Diffuse white gas-and-steam plumes continued to rise from the summit vents.

Unrest increased again during 7-10 May 2021, according to PHIVOLCS. There was a total of 186 volcanic earthquakes detected during 7-11 May. Inflation that was first recorded on the upper flanks on 6 March had continued. Sulfur dioxide emissions peaked at 48 tons/day on 20 May 2021, which was still within baseline levels. The VAL was raised to 1 on 11 May. During 12 June a total of 95 weak volcanic earthquakes were detected, in addition to diffuse white gas-and-steam plumes rising from the SW vent. Seismicity declined to the baseline level of 2-3 volcanic earthquakes per day during 1 July-17 August 2021, during which a total of 109 weak events were recorded. Short-term inflation had been detected since July 2020.

Activity during June 2022. During 4-5 June, PHIVOLCS reported 77 volcanic earthquakes. Ground deformation data from continuous GPS monitoring indicated short-term inflation, and electronic tilt data recorded an inflation event on the SE lower slopes beginning in April 2022. A phreatic eruption occurred at 1037 on 5 June 2022 and lasted approximately 17 minutes, based on seismic and infrasound monitoring by the Bulusan Volcano Network (BVN). Though cloud cover obscured most visual observations, a gray ash plume seen from Juban (Sorsogon Province) rose at least 1 km high and drifted W. Ashfall was reported to the NW in Puting Sapa, Añog, Guruyan, Catanusan, Buraburan, Bacolod, and Sangkayon in Juban, and Bolos in Irosin, Sorsogon Province. Residents of Añog, Guruyan, and Catanusan also reported rumbling sounds and a sulfur odor. As a result, the VAL was raised to 1. After this event, gas-and-steam emissions rose from the main crater, as well as the NW summit vent. A total of 27 weak volcanic earthquakes were recorded until 1600 by the BVN.

Increased seismicity began at 0500 on 9 June, which included a total of 45 volcanic earthquakes, including two low-frequency events. Most of these events were low magnitude and shallow. Another phreatic explosion was detected by the BVN at 0337 on 12 June, which lasted 18 minutes, based on seismic records. The eruption plume was not visible in webcams, but residents of Inlagadian (Casiguran municipality) briefly saw incandescence at the base of a plume. An explosion was felt by residents within 5 km, including in the barangays of Añog (Juban) and Inlagadian. Rumbling was heard in Sitio Bagong Barrio, and in the barangays of Santa Lourdes (Barcelona), Inlagadian and San Juan (Casiguran), Bentuco (Gubat), and Añog, Calateo, and Puting Sapa (Juban). Sporadic ash emissions were detected starting at 0430; ash emissions were visible rising from six vents: Blackbird Crater (the main crater), three explosion pits in the summit crater, and two vents on the NW and N sides of the summit. Gas-and-steam and ash plumes rose 400-750 m above the summit and drifted several kilometers NW. Ashfall was reported in areas as far as 50 km NW in Sorsogon City and Palanas, Pilar, Sorsogon Province, across Sorsogon Bay, and as far as Anislag (Daraga, Albay). Minor ashfall was detected in several barangays in the municipalities of Casiguran, Juban, and Magallanes. Sulfur dioxide emissions averaged 1,900 tons/day during 5-12 June. According to a Rappler news article, more than 11,000 people (at least 2,800 families) in Juban evacuated, and flights in and out of the Bicol International Airport were cancelled.

Unrest persisted through the rest of June. Gas-and-steam emissions rose 100-500 m above the summit and drifted NW, WSW, SW, and W. Daily sulfur dioxide emissions were 559-1,255 tons/day. Seismicity increased on 20 June; during 0500-1145 a total of 65 volcanic earthquakes were detected, including one low-frequency volcanic earthquake, though most were weak shallow events. During 24-29 June the BVN detected a total of 213 volcanic earthquakes, the strongest of which was an Mw 3.5 that occurred at 2327 on 24 June. Residents of Irosin and Bulusan in the Sorsogon Province felt the earthquake. A small-volume lahar began approximately at 1904 on 26 June during a thunderstorm, based on seismic and infrasound data. The event lasted 54 minutes and the Bulusan Volcano Observatory (BVO) confirmed thin, channel-confined lahar deposits along the Calang Creek on the SW flank, in the Cogon barangay.

Seismicity decreased to background levels during the third week of July. During 25 July-6 August sulfur dioxide emissions were 230 tons/day. On 21 August PHIVOLCS lowered the Alert Level to 0, reporting that unrest continued to decline to background levels.

Geologic Background. Luzon's southernmost volcano, Bulusan, was constructed along the rim of the 11-km-diameter dacitic-to-rhyolitic Irosin caldera, which was formed about 36,000 years ago. It lies at the SE end of the Bicol volcanic arc occupying the peninsula of the same name that forms the elongated SE tip of Luzon. A broad, flat moat is located below the topographically prominent SW rim of Irosin caldera; the NE rim is buried by the andesitic complex. Bulusan is flanked by several other large intracaldera lava domes and cones, including the prominent Mount Jormajan lava dome on the SW flank and Sharp Peak to the NE. The summit is unvegetated and contains a 300-m-wide, 50-m-deep crater. Three small craters are located on the SE flank. Many moderate explosive eruptions have been recorded since the mid-19th century.

Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/); Rappler, Unit B, 3/F, North Wing Estancia Offices, Capitol Commons, Ortigas Center, Pasig City 1605, Bulusan Volcano erupts again, ash spreads to more areas, (URL: https://www.rappler.com/nation/phivolcs-bulusan-volcano-phreatic-eruption-advisory-june-12-2022-420am/).

The Aira caldera in the northern half of Kagoshima Bay contains the active post-caldera Sakurajima volcano near the southern tip of Japan’s Kyushu Island. Eruptions date back to the 8th century, which have deposited ash on Kagoshima, 8 km from the summit. The Minamidake summit cone and crater has had persistent activity since 1955; the Showa crater on the E flank has also been intermittently active since 2006. More recent activity has consisted of minor ash emissions, low thermal activity, and ashfall events (BGVN 47:01). The current eruption period began in late March 2017, characterized by some explosions and ash emissions in the Minamidake crater. This report updates information from January through June 2022 using monthly activity from the Japan Meteorological Agency (JMA), the Tokyo Volcanic Ash Advisory Center (VAAC), and various satellite data.

Low levels of activity from the Minamidake crater during this reporting period dominantly consisted of volcano-tectonic earthquakes, eruption plumes, and nighttime incandescence, with the addition of some explosions, ashfall, and sulfur dioxide emissions (table 27). Reports of activity in the Showa crater mainly described occasional white gas-and-steam emissions. Thermal activity remained at low levels throughout the period (figure 127), though summit crater incandescence was frequently reported at night during clear weather. Some thermal anomalies at the Minamidake crater were visible in Sentinel-2 infrared satellite imagery (figure 128).

Table 27. Number of monthly explosive events, days of ashfall, area of ash covered, and sulfur dioxide emissions from Sakurajima’s Minamidake crater at Aira during January-June 2022. Note that smaller ash events are not listed. Ashfall days were measured at Kagoshima Local Meteorological Observatory, and ashfall amounts represent material covering all the Kagoshima Prefecture. Data courtesy of JMA monthly reports.

Figure 127. Thermal activity at Sakurajima in the Aira caldera remained relatively low during January through June 2022, according to this MIROVA graph (Log Radiative Power). Three anomalies were detected during January, three during late February, three during early March, four during April, and one during early June. Courtesy of MIROVA.

Figure 128. Sentinel-2 infrared satellite imagery showed weak thermal anomalies in the Minamidake crater at Aira’s Sakurajima volcano on 1 January 2022 (top left), 25 February 2022 (top right), 16 April 2022 (bottom left), and 30 June 2022 (bottom right). The brighter anomaly in the 1 January image is from vent A, while the fainter anomaly is vent B; both vents A and B are part of the Minamidake crater. The anomalies notably decreased in strength during 25 February and 16 April. On 30 June a stronger anomaly was visible in vent B, but clouds covered visibility in vent A. Images use “Atmospheric penetration” rendering (bands 12, 11, and 8a). Courtesy of Sentinel Hub Playground.

There were 103 volcanic earthquakes reported during January, a decrease from December 2021 (136). Additionally, a field survey reported that 400-1,000 tons/day (t/d) of sulfur dioxide emissions were emitted during the month, compared to December (600-1,200 t/d). Eruption plumes rose 1-2 km above the crater and drifted E and SE following eruption events detected on 1, 7, and 18 January. Nighttime crater incandescence was also visible on these days, based on surveillance cameras. On 7 and 18 January large volcanic blocks were ejected 600-900 m and 1-1.3 km from the Minamidake crater. Two eruptions were detected at the Minamidake crater on 28 January, one of which was described as an explosion; at 1319 a plume rose as high as 3.4 km above the crater and material traveled 1.3-1.7 km from the Minamidake summit crater (figure 129); crater incandescence accompanied this event. That same day, a field survey reported that ashfall was observed in Arimura Town (753 g/m²) and Kurokami-cho, according to JMA (figure 129).

Figure 129. Webcam image of the explosion at the Minamidake summit crater of Aira’s Sakurajima at 1319 on 28 January 2022 (left). The resulting plume rose 3.4 km above the crater rim. Ashfall from the event was observed on 28 January in Arimura Town; about 753 g/m2 was recorded (right). Courtesy of JMA monthly report (Sakurajima volcanic activity explanatory material, January 2022).

Activity during February was relatively low and consisted of 22 volcanic earthquakes and eruption events at 1620 on 13 February and 1540 on 15 February. A field survey reported that 700-1,700 t/d of sulfur dioxide emissions were measured during this month. The event on 13 February the eruption plume rose 1 km above the crater and drifted SE and on 15 February the plume rose 1.3 km above the crater and drifted E. Similar low activity during March and April was characterized by 36 and 37 volcanic earthquakes, respectively, and intermittent crater incandescence, based on surveillance camera data. Sulfur dioxide emissions were 800-1,300 t/d during March and 500-1,300 t/d during April. An eruption event on 17 March produced a small plume that rose 600 m above the crater rim, and one on 20 April sent a plume 900 m above the crater (figure 130).

Figure 130. Webcam image of the eruption event at Sakurajima’s Minamidake crater at 1243 on 20 April 2022. The eruption plume rose 900 m above the crater rim. Courtesy of JMA monthly report (Sakurajima volcanic activity explanatory material, April 2020).

During May, the number of volcanic earthquakes detected increased to 154 and the sulfur dioxide emissions ranged from 500 to 1,700 t/d. An eruption at 1453 on 3 May generated a plume that rose 1 km above the crater. On 15 May an eruption event at 1141 produced a plume that rose 1.2 km above the crater. Another eruption event on 17 May occurred at 0900 and produced plumes that rose 1.5 km above the crater (figure 131). Nighttime crater incandescence also accompanied this event, based on high-sensitivity surveillance cameras. Volcanic tremors were detected during 17-19 May and JMA reported that there was a notable increase in the number of tremors on 19 May. Intermittent incandescence was visible at the Minamidake crater throughout the rest of the month. Activity during June remained consistent, with frequent nighttime incandescence and 57 volcanic earthquakes. Daily sulfur dioxide emissions were 800-1,200 t/d during June. Eruption events reported by JMA on 27, 28, and 29 June generated eruption plumes that rose 1.2-1.6 km above the crater and drifted NE. An explosion on 27 June at 1221 produced an eruption plume that rose 1.6 km above the crater and ejected volcanic blocks 600-900 m from the Minamidake crater.

Figure 131. Webcam image of the eruption event at Sakurajima’s Minamidake crater at 0900 on 17 May 2022. The eruption plume rose 1.5 km above the crater rim. Courtesy of JMA monthly report (Sakurajima volcanic activity explanatory material, May 2022).

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

Information Contacts: Japan Meteorological Agency (JMA), 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Sheveluch, in the northeastern region of the Kamchatka peninsula, Russia, has produced at least 60 eruptions during the Holocene, with eruptions known from tephrochronology dating back 10,000 years. Frequent collapses of dome complexes have produced debris avalanches; the resulting deposits cover much of the caldera floor. A major south-flank collapse during a 1964 Plinian explosion produced a scarp within which a “Young Sheveluch” dome began to form in 1980. Repeated episodes of dome formation and destruction since then have produced major and minor ash plumes, pyroclastic flows, block-and-ash flows, and two “whaleback domes” of spine-like extrusions in 1993 and 2020 (BGVN 45:11). The current eruption period began in August 1999 and has more recently consisted of ongoing explosions, frequent ash emissions, incandescent block avalanches, and lava dome growth (BGVN 47:02). This report describes similar activity of intermittent explosions, ash plumes, continued lava dome growth, strong fumarolic activity, and block avalanches during January through June 2022 using information from the Kamchatka Volcanic Eruptions Response Team (KVERT), the Kamchatka Volcano Station (part of the Kamchatka Branch of the Geophysical Survey, Russian Academy of Science (KB GS RAS) and various satellite data.

Activity during this reporting period was relatively low. The growth of the lava dome inside the 1964 flank collapse scarp continued through June 2022 and on clear weather days, a small thermal anomaly was visible in satellite data (figure 85). Strong fumarolic activity with gas-and-steam emissions often accompanied this dome growth from multiple vents. Frequent low-level thermal activity persisted, though there was a gradual decline in power during January through April that remained low through June, as is shown in the MIROVA Log Radiative Power graph (figure 86).

Figure 85. Sentinel-2 satellite imagery of Sheveluch showed weak thermal anomalies over the lava dome on 22 January 2022 (left) and 11 February 2022 (right) on clear weather days. White gas-and-steam emissions often accompanied this thermal activity from multiple vents, which can be seen in both images. Images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Figure 86. Frequent low-level thermal anomalies were detected at Sheveluch during January through June 2022, according to this MIROVA (Log Radiative Power) graph. There is a gradual decline in the power of the thermal anomalies that occurred during January through April. Courtesy of MIROVA.

The incandescent lava dome continued to grow during January 2022, in addition to observations of strong fumarolic activity and block avalanches. A thermal anomaly was visible over the dome daily. Satellite data showed a strong gas-and-steam plume containing some amount of ash on 7 January that rose to 4-4.5 km altitude and drifted as far as 24 km W. Explosions during 9-11 January generated gas-and-ash plumes to 3.5-5.5 km altitude and drifted 20-140 km WNW, 175 km W, and 80 km SW, respectively. Continued explosions were detected on 13 and 15-16 January, which produced ash plumes that rose to 5-6.5 km altitude and drifted 10-31 km NNW, W, and WSW.

Low activity persisted during February and March with strong fumaroles, block avalanches, and incandescence from the growing lava dome. A thermal anomaly was frequently visible over the lava dome on clear weather days. An ash cloud detected in satellite imagery on 15 March rose to 4.5 km altitude and drifted 50 km WNW. During April, lava dome growth continued, accompanied by strong fumarolic activity, block avalanches, and frequent thermal anomalies. Satellite data by KVERT on 9 April showed that explosions sent ash plumes to 12 km altitude and extended more than 2,000 km NE. Continued explosions during 14-17 April produced ash plumes that rose to 4-6.5 km altitude and drifted generally 4-45 km SW and SE.

During May and June, activity was relatively low and consisted of lava dome growth, strong fumarolic activity (figure 87), block avalanches, and incandescence. Thermal anomalies continued to be frequently detected in satellite data on clear weather days. According to video data, explosions on 10 June generated an ash plume that rose to 6.5 km altitude and extended 130 km SSE and E over the volcano. On 20 June at 0847 video data from KVERT showed an ash plume rose to 7 km altitude that extended 10 km E (figure 88). The next day on 21 June explosions produced an ash plume that rose to 5 km altitude and drifted 70 km SW.

Figure 87. Photo of strong fumarolic activity at Sheveluch on 5 May 2022. Photo has been color corrected. Photo by Yu Demyanchuk, courtesy of IVS FEB RAS, KVERT.

Figure 88. A dense ash plume rose to 7 km altitude from Sheveluch on 20 June 2022 and drifted E. Photo has been color corrected. Photo by Yu Demyanchuk, courtesy of IVS FEB RAS, KVERT.

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1,300 km3 andesitic volcano is one of Kamchatka's largest and most active volcanic structures, with at least 60 large eruptions during the Holocene. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes occur on its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large open caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

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

Karangetang (also known as Api Siau), located on the island of Siau in the Sitaro Regency, consists of two active summit craters: Kawah Dua (the N crater) and Kawah Utama (the S crater, also referred to as the “Main Crater”). Twentieth century eruptions have included frequent explosive activity, sometimes accompanied by pyroclastic flows and lahars. The most recent eruption period began in November 2018 and has more recently consisted of weak thermal anomalies, intermittent ash plumes, and gas-and-steam emissions (BGVN 47:01). Similar activity occurred during this report of January through June 2022, with continued white-to-gray gas-and-steam emissions and thermal anomalies, described in reports from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, and satellite data.

Activity was relatively low during this reporting period. Bluish white gas-and-steam emissions drifted S on 2 January and intermittent white-and-gray plumes typically rose 25-250 m above the summit through June (figure 55). On 15 and 16 January gas-and-steam emissions rose as high as 500 m. Intermittent N summit crater incandescence was reported by PVMBG during early January 2022, which was sometimes detected in satellite data. MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data detected very low power thermal anomalies during late January (3), late April (1), and early May (1). Sentinel-2 infrared thermal satellite imagery showed small thermal anomalies in both the N and S summit craters on 8 January, 27 February, 9 March, 18 and 28 April, 3 May, and 2, 17, 22, and 27 June, accompanied by gas-and-steam emissions that drifted in different directions (figure 56).

Figure 55. Webcam images of Karangetang showing white-to-gray plumes rising above both summit craters on 9 January 2022 (top left), 21 April 2022 (top right), 8 June 2022 (bottom left), and 29 June 2022 (bottom right). Courtesy of MAGMA Indonesia.

Figure 56. Small thermal anomalies (bright yellow-orange) at Karangetang were detected in the N and S summit craters on 8 January 2022 (top left), 27 February 2022 (top right), 3 May 2022 (bottom left), and 27 June 2022 (bottom right). Thermal anomalies from both craters were accompanied by gas-and-steam plumes that drifted in different directions. Images using “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

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

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

Semeru, located in East Java, Indonesia, contains the active Jonggring-Seloko vent at the Mahameru summit. Hundreds of eruptive events occurred during the 19th and 20th centuries, including nearly continuous activity since 1967. Eruptions have been characterized by Vulcanian and Strombolian explosions, lava flows, pyroclastic flows, lava domes, and lahars. The current eruption has been ongoing since April 2014 and has more recently consisted of explosions, ash plumes, lava flows, pyroclastic flows, lahars, and dome collapse. An eruption and dome collapse occurred near the summit on 4 December 2021, which produced a notable ash plume and pyroclastic flows, the latter of which generated major lahars (BGVN 47:01). As a result, several communities were partially buried, causing fatalities and significant damage. This report covers intermittent pyroclastic flows, incandescent avalanches, and ash eruptions during January through June 2022 using daily and VONA reports from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), the Darwin Volcanic Ash Advisory Centre (VAAC), and various satellite data.

Activity during January 2022 consisted of continuous nighttime crater incandescence, gray-white ash emissions, and occasional pyroclastic flows and avalanches. Gray-white ash emissions were reported rising 50-1,000 m above the summit and drifted in different directions. Near daily white gas-and-steam emissions rose as high as 1 km above the summit crater. Pyroclastic flows occurred on 1, 5, 6, 7, 8, 9, and 17 January and primarily descended the Kobokan (SE) and Lengkong drainages, traveling 700-5,000 m. Incandescent avalanches traveled 700 m and 500 m down the Kobokan drainage during 6-7 and 11-12 January, respectively. A collapse from the end of the active lava flow in the Kobokan drainage generated a pyroclastic flow and an ash plume that rose 1.5 km high and drifted N at 1020 on 16 January.

During February, activity was relatively low and consisted of gray-white ash emissions rising 50-700 m above the summit and drifting in multiple directions, and occasional nighttime crater incandescence. White gas-and-steam emissions rose as high as 1.2 km above the crater rim. The active lava flow on the SE flank measured 3.5 km long. According to PVMBG, pyroclastic flows were reported on 2 February. Avalanches were detected during 7-8 February and descended 100-200 m toward the Kobokan drainage. A series of eruptions were detected at 0554 and 0709 on 17 February, 0558 on 18 February, 0551 on 19 February, and 0701 on 20 February that generated ash plumes 500-700 m high and drifted N, W, and SW. Eruptions were also recorded at 0605 on 24 February, 0538, 0557, and 0755 on 25 February, 0535 on 27 February, and 0555 on 29 February that produced ash plumes 700 m high.

During March, gray-white ash emissions rose 200-1,800 m above the summit and drifted mainly N, W, and SW. On 2 March two incandescent lava avalanches were reported moving 200-300 m down the Kobokan drainage, accompanied by white-gray emissions that rose 500 m high and drifted SW. On 3 March an ash plume was detected rising 4.2 km above the summit, based on ground observers, and later that day, at 2004, a pyroclastic flow originated from the end of a lava flow and descended as far as 4.5 km down the Kobokan drainage on the SE flank. Intermittent ash plumes continued to be reported in VONA notices, rising 400-1,000 m high and drifting in various directions. Pyroclastic flows were detected on 1, 4, and 13 March, though weather often obscured the travel distance and direction. Nighttime crater incandescence was visible on 5 March. Avalanches were reported during 12-13 and 22 March, though they were not visually confirmed. On 22 March a pyroclastic flow originated from the end of a lava flow and descended the Kobokan drainage, producing an ash plume that rose 1.5 km above the summit and drifted SE.

Eruptive events during April consisted of near daily ash plumes that rose 200-1,000 m above the summit and drifted in different directions; white gas-and-steam emissions rose 200-300 m high. Cloudy weather sometimes prevented visual observations of the activity. On 1 April avalanches were reported. A strong thermal anomaly was detected in infrared satellite imagery on 3 April, according to a Darwin VAAC notice. Ash plumes during May rose 200-700 m high and drifting mainly N, S, and SW and white gas-and-steam emissions rose 100-700 m above the summit. On 1 May at 0630 a pyroclastic flow that originated from the end of the lava flow on the SE flank was detected, producing ash plumes that rose as high as 500 m above the summit (figure 73). Similar activity continued to be recorded during June; ash plumes rose 200-700 m above the summit and drifted generally N, W, and SW. White gas-and-steam emissions rose 100-600 m high and drifted in different directions.

Figure 73. Webcam image of a pyroclastic flow descending the SE flank of Semeru at 0636 on 1 May 2022. The accompanying ash plume rose 500 m high. Courtesy of MAGMA Indonesia.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed intermittent thermal anomalies of varying power during January through June (figure 74). Beginning in May, the frequency of these anomalies increased. Based on data from the MODVOLC thermal algorithm, a total of 56 thermal hotspots were detected: five in January, five in February, three in March, two in April, 29 in May, and 12 in June. Thermal anomalies were visible on clear weather days in the summit crater, occasionally extending toward the SE flank; on 25 April two thermal anomalies were visible: one in the summit crater and the second farther down the SE flank (figure 73). The increase in thermal activity was a result of a persistent lava flow that descended the SE flank during mid-May through June, based on infrared satellite images from Sentinel-2 (figure 74). By 19 June the flow no longer seemed to advance.

Figure 74. Intermittent thermal activity was recorded in the MIROVA graph (Log Radiative Power) during January through June 2022, with gradual power fluctuations. Beginning in May, the frequency and power of the anomalies gradually increased. This increased frequency could be due to more than one anomaly occurring at the summit crater, as well as on the nearby flanks. Courtesy of MIROVA.

Figure 75. A continuous bright thermal anomaly (bright yellow-orange) was visible on clear weather days at the summit crater of Semeru on 25 January 2022 (top left), 24 February 2022 (top right), 16 March 2022 (bottom left), and 25 April 2022 (bottom right). Each of these anomalies also appeared to extend toward the SE flank from the summit crater. On 25 April two anomalies were detected: one in the summit crater and the second father down the SE flank. Images use “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Figure 76. Sentinel-2 infrared satellite imagery showing a strong lava flow originating from the summit crater of Semeru and descending the SE flank on 15 May 2022 (top left), 4 June 2022 (top right), 19 June 2022 (bottom left), and 29 June 2022 (bottom right). By 19 June the flow no longer seemed to advance down the SE flank, and by 29 June the anomaly in the summit crater visible decreased in size compared to the previous days. Images use “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Geologic Background. Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.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/); 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); National Public Radio (NPR) (URL: https://www.npr.org/2021/12/05/1061611299/indonesia-volcano-eruption-java-mount-semeru).

Stromboli is a SE Tyrrhenian Sea stratovolcano in Italy that has exhibited nearly constant lava fountains for the past 2,000 years; recorded eruptions date back to 300 BCE. Eruptive activity occurs at the summit from multiple vents, which include a north crater area (N area) and a central-southern crater (CS area) on a terrace known as the ‘terrazza craterica’ at the head of the Sciara del Fuoco, a large scarp that runs from the summit down the NW side of the volcano-island. Activity typically consists of Strombolian explosions, incandescent ejecta, lava flows, and pyroclastic flows. Thermal and visual monitoring cameras are located on the nearby Pizzo Sopra La Fossa, above the terrazza craterica, and at multiple flank locations. This report covers activity during January through June 2022 using Italy's Istituto Nazionale di Geofisica e Vulcanologia (INGV) and various satellite data.

Stromboli continued to exhibit a range of explosive activity during January through June 2022 with a gradual decrease in the number of hourly explosions at the summit crater during April through June (figure 234, table 14). Thermal activity for this period remained relatively low, with a short spike in activity toward the end of May, based on the MIROVA graph of radiative power (figure 235). Sentinel-2 infrared satellite imagery showed minor thermal intensity fluctuations at the active summit vents (figure 236).

Figure 234. The range of activity continued at Stromboli during January through June 2022, showed a general decline in the number of hourly explosions at the summit crater during April through June. The average number of hourly explosions (left axis) during January-June are broken out by area and as a total with blue for the CS area, red for the N area, and black for the combined total. The data are smoothed as daily (thin lines) and weekly (thick lines) averages. The black squares along the top represent days with no observation from poor visibility (Visib. Scarsa). The right axis indicates the qualitative descriptors of the activity levels from low (basso) to highest (altissimo) with the green highlighted band indicating the most common level of activity. Courtesy of INGV (Report 27/2022, Stromboli, Bollettino Settimanale, 27/06/2022 - 03/07/2022).

Table 14. Summary of type, frequency, and intensity of explosive activity at Stromboli by month from January-June 2022; information from webcam observations. Courtesy of INGV weekly reports.

Figure 235. Thermal activity at Stromboli was relatively low during January through June 2022, though there was a notable spike of three strong anomalies toward the end of May, as shown in this MIROVA graph (Log Radiative Power). Courtesy of MIROVA.

Figure 236. Minor variations in the size, shape, and intensity of thermal anomalies at the two major crater areas (N and CS) from the active vents of Stromboli on 22 January 2022 (top left), 21 February 2022 (top middle), 28 March 2022 (top right), 12 April 2022 (bottom left), 12 May 2022 (bottom middle), and 26 June 2022 (bottom right), as shown in Sentinel-2 infrared satellite images. Some gas-and-steam emissions were also visible accompanying the thermal activity. Images use “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Activity during January-February 2022. Variable low to medium explosive activity occurred in the N crater area during January, ejecting coarse lapilli and bombs mixed with ash as high as 130 m above the crater. Spattering was localized to the N2 crater in the upper part of the Sciara del Fuoco and continued during 1-2 January. Lower frequency explosions in the CS area, mostly from the S2 crater, ejected mainly fine to some coarse products 100-120 m above the terrazza craterica. Gas-and-steam emissions dominated the S1 crater; explosions rarely occurred at this crater. Based on webcam images, there was an increase in explosive spattering in the N2 crater on 16 January and as a result, a continuous accumulation of pyroclastic material in the upper part of the Sciara del Fuoco. Around 1930 a small lava flow was observed in the upper part of the Sciara del Fuoco, the front of which consisted of large, incandescent blocks that rolled down the flanks (figure 237); by 2326 the blocks had stopped rolling along the scarp.

Figure 237. Webcam images showing spattering activity in the N summit crater area of Stromboli from the N2 crater on 16 January 2022 (infrared image shown on the right). Incandescent material accompanied this activity, descending the flanks toward the coastline. Courtesy of INGV (Report 03/2022, Stromboli, Bollettino Settimanale, 10/01/2022 - 16/01/2022).

Strombolian explosions that varied from low-to-high intensity were observed with spattering in the N crater area during February. The explosions ejected fine ash mixed with coarse lapilli and bombs 80-150 m high. The CS area did not show significant explosive activity. During 2-4 and 9-12 February discontinuous spattering activity was notably stronger. On 11 February incandescent gases rose from the S1 crater, accompanied by coarse material; at the same time, two vents in the S2 crater generated low-to-medium explosions that ejected coarse and fine material higher than 80 m high.

Activity during March-April 2022. Similar explosive Strombolian events continued during March with spattering in the N crater area. Explosions in the N crater area varied in intensity, with fine to coarse material ejected 80-150 m high. Short, intense spattering activity occurred on 3 March. The CS area did not show significant explosive activity; low intensity explosions that ejected products less than 80 m high from two emission points in the S2 crater. Intense degassing was observed from the N2 crater, which included gas-and-steam rings (figure 238). During 10-12, 16-17, 25, 27, and 30 March low-to-medium explosive activity originated from the N2 crater that contained four emission points, ejecting coarse material less than 120 m high; spattering activity was intense for short intervals.

Figure 238. Photos from Pizzo at Stromboli during early March 2022 showing strong gas-and-steam emissions (left) and degassing rings (right) rising from the N2 crater. Courtesy of INGV (Report 10/2022, Stromboli, Bollettino Settimanale, 28/02/2022 - 06/03/2022).

During April the N1 crater generated explosions of various intensity that ejected material 80-150 m high. During 8-9, 12, and 16 April four emission points in the N2 crater showed low-to-medium explosive activity, accompanied by spattering, that ejected material less than 120 m high. There was not significant explosive activity in the CS area, but low-to-medium explosions ejected products at least 80 m high. A vent near the CS produced episodic but prolonged and dense ash emissions associated with Strombolian activity in the southernmost vent. In the N1 crater, an asymmetrical hornito was open toward the Sciara del Fuoco and contained a vent that produced continuous spattering and discontinuous explosions that ejected coarse material.

Activity during May-June 2022. Activity persisted through May, with low intensity Strombolian explosions in the N and CS area. According to INGV, the S2 crater, which consisted of two emissions points, showed explosions varying from low to high, where some coarse products reached 250 m high. Two field inspections were made on 5 and 7 May. On 5 May mild explosions characterized the S1 and N1 craters, ejecting fine to coarse material from the vents. The N2 crater dominantly showed gas-and-steam emissions. On 7 May cloud cover mostly obscured views of the summit, but INGV reported that activity was less frequent and intense.

On 13 May at 1643 a sequence of six main explosions was detected in the CS area that began from a southern vent in the S2 crater that rapidly evolved to the S1 crater (figure 239). This explosion lasted about 8 seconds, ejecting material 300 m above the crater, and falling to the E and SE, as well as in Pizzo. The resulting ash cloud drifted S. A second explosion at 1643 occurred at the S1 crater, but was of a lower intensity than the initial one, and lasted about 10 seconds. The explosions during 1643-1644 were also detected from the S1 crater, though the intensity was lower, and deposited material on Pizzo and Sciara del Fuoco. Finer material was dispersed to the SE. After this explosive sequence, INGV reported that activity stopped through at least the 15th.

Figure 239. Infrared webcam images showing the explosive sequence that occurred at Stromboli during 1643-1647 (local time) on 13 May 2022. Material was ejected 190 m high according to webcam data. Courtesy of INGV (Report 20/2022, Stromboli, Bollettino Settimanale, 09/05/2022 - 15/05/2022).

A small collapse detected on 20 May caused a landslide along the Sciara del Fuoco. A thermal camera mounted on a drone detected a major thermal anomaly was detected in the N1 crater; activity in the N1 crater has been characterized by explosions and reddish-brown ash emissions. In the CS area, anomalies were also recorded. On 25 May two strong explosions were reported by INGV in the CS area (figure 240): the first of which occurred at 1611 from the N vent in the S2 crater, ejecting material 250 m high and falling in the main crater area; the second event ended at 1612 and occurred in the CS area, ejecting coarse material 80 m high. The resulting ash cloud drifted S.

Figure 240. Infrared webcam images showing two explosions at Stromboli during 1611-1612 (local time) on 25 May 2022. Material was ejected as high as 250 m according to webcam data. Courtesy of INGV (Report 22/2022, Stromboli, Bollettino Settimanale, 23/05/2022 - 29/05/2022).

During June, surveillance cameras showed that explosive activity at the N1 crater consisted of low-to-high intensity explosions where material was ejected 80-180 m high. Three emission points in the N2 crater showed gas-and-steam emissions accompanied by occasional weak spattering activity. The S2 crater showed low intensity explosions that ejected fine material 80-150 m high. The most active crater was N1, which contained two main vents, the first of which faced Pizzo and produced ash emissions on 29 and 30 June and the second, that overlooked the Sciara, emitted ash mixed with coarse incandescent materials on 29 June (figure 241). Crater N2 and S2 showed continuous diffuse degassing. The vents in the CS area did not show significant explosive behavior, though two emission points from the S2 crater were characterized by low intensity explosions.

Figure 241. Photos of the summit crater of Stromboli, labeling each of the active craters (S1, S2, N1, and N2) (top). Ash emissions were visible rising from the N1 crater on the Pizzo side on 29 and 30 June 2022 (bottom). Courtesy of INGV (Report 27/2022, Stromboli, Bollettino Settimanale, 27/06/2022 - 03/07/2022).

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

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy, (URL: http://www.ct.ingv.it/en/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Ulawun rises above the N coast of New Britain, Papua New Guinea, and is part of the Bismarck arc. Documented eruptions date back to the 18th century and mildly explosive eruptions occurred during the 20th century through 1967. The most recent eruption began in July 2021 and ended on 29 November 2021, which was primarily characterized by ash eruptions, seismicity, small thermal anomalies, and sulfur dioxide emissions (BGVN 46:12). This report covers a new eruption on 2 June 2022 using information from the Rabaul Volcano Observatory (RVO), the Darwin Volcanic Ash Advisory Centre (VAAC), and satellite data.

Activity during December 2021 and May 2022 was relatively low and consisted mostly of intermittent sulfur dioxide emissions, based on data from the TROPOMI instrument on the Sentinel-5P satellite (figure 30). According to a report from RVO, a short, single day eruption was detected at 0820 on 2 June 2022. Dense ash plumes were visible rising about 3 km above the summit and drifting NW for 10-15 minutes, causing light ashfall in downwind areas to the SE, including Ulamona Mission and on Lolobau Island. A sulfur dioxide plume drifting to the NW was detected by the TROPOMI instrument aboard the Sentinel-5P satellite; maximum column abundance more than 2 Dobson Units (DU) was detected in the plume. On 3 June diffuse white gas-and-steam plumes were visible rising above the summit. Seismicity increased during this event, dominated by continuous volcanic tremors, and consisted of RSAM units between 400 and 500. After the eruption, the units dropped back to lower levels of less than 100 and by the end of June, they had risen to 200.

Figure 30. Sentinel-5P/TROPOMI data showing intermittent sulfur dioxide plumes above originating from Ulawun on 7 March 2022 (top left), 12 March 2022 (top right), 30 May 2022 (bottom left), and 2 June 2022 (bottom right) that generally drifted W and NW. Each of these plumes exceeded 2 Dobson Units (DU). Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Geologic Background. The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

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

Nyiragongo, part of the Virunga Volcanic Province (VVP), is located in the Democratic Republic of the Congo along the western branch of the East African Rift system. It contains a 1.2 km-wide summit crater with a lava lake that has been active since at least 1971. Lava flows have been a hazard in the past for the nearby city of Goma (15 km S). During May 2021 a notable flank fissure eruption consisted of intense seismicity, lava lake drainage, lava flows reaching Goma, and ash plumes (BGVN 46:06). The current eruption has been ongoing since 2002 and has recently been characterized by active lava on the crater floor and some spatter, as evidenced by strong thermal anomalies and occasional photos (BGVN 46:12). This report updates information from December 2021 through June 2022 and describes lava effusions along the crater floor during January and March 2022, lava fountaining, and persistent gas-and-steam emissions. The volcano is monitored by the Observatoire Volcanologique de Goma (OVG) and various satellite instruments.

Activity was relatively low during December 2021; according to a news article, notable long-period (LP) earthquakes were detected during 30 November through 5 December and residents of Goma observed crater incandescence on 4 December. OVG reported gas-and-steam plumes and visible incandescence from the crater during 3-5 January 2022. In addition, lava fountaining and collapses at active vents on the crater floor were observed. A growing lava lake was reported, which was also reflected in a 12 January 2022 infrared satellite image of lava effusions covering much of the crater floor. During 13-18 March lava effusion from vents along the crater floor was detected in satellite images. Significant gas-and-steam emissions were visible drifting SW on 13 March.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed a gradual increase in thermal activity during late November through mid-December 2021 (figure 92). Thermal activity remained relatively high through mid-January 2022 and was followed by a gradual decrease in both power and frequency, which was relatively low during late January through February. Activity gradually increased again in both power and frequency during early March; relatively lower peaks of anomalies were also noted in late April and mid-June. The MODVOLC thermal algorithm detected a total of 97 anomalies in the summit crater, a majority of which were detected during January. Sentinel-2 infrared satellite images intermittently showed a consistent thermal anomaly in the summit crater, with a notably strong anomaly on 12 January and 13 March, representing lava effusions covering much of the crater floor (figure 93). These stronger anomalies were also represented in the MIROVA graph as the stronger peaks during January and March.

Figure 92. Thermal anomalies at Nyiragongo from 13 October 2021 through June 2022 as recorded by the MIROVA system (Log Radiative Power) spiked in activity during late November to mid-December. Thermal activity remained relatively high through mid-January, followed by a gradual decrease in power. During late January through February, thermal anomalies were low in power and less frequent. Then, during early March, there was a gradual increase in both power and frequency. Lower-power peaks of thermal anomalies also occurred in late April and mid-June. Courtesy of MIROVA.

Figure 93. Sentinel-2 infrared satellite imagery showed intermittent thermal anomalies during January through May 2022 when not obscured by clouds. On 12 January 2022 (top left) and 13 March 2022 (bottom left) showed lava effusions covering the crater floor. Gas-and-steam emissions also accompanied the stronger anomalies. Smaller thermal anomalies were also observed on 6 February 2022 (top right) and 27 May 2022 (bottom right), with possible smaller lava effusions to the E and NE, respectively from the point of origin. Images using “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

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

Information Contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Isabelle Kasoki, Les Volcans News, (URL: https://lesvolcansnews.net/2021/12/07/surveillance-du-nyiragongo-lovg-note-une-baisse-considerable-du-nombre-de-seismes-tectoniques-dans-le-lac-kivu/).

Nevados de Chillán, located in the Chilean Central Andes, has had multiple recorded eruptions dating back to the seventeenth century. The most recent eruption began in January 2016 with a phreatic explosion and ash emission from the new Nicanor crater on the E flank of Nuevo crater. More recently, lava flows and domes, along with multiple daily reports of ash emissions and block-and-ash flows, have been reported (BGVN 46:12). Two new lava domes were described in September and October 2021, followed by a surge of lava flow activity in November. This report covers activity from December 2021 through May 2022 and describes seismic and thermal activity, gas-and-ash plumes, and pyroclastic flows. Information comes primarily from Chile's Servicio Nacional de Geología y Minería (SERNAGEOMIN)-Observatorio Volcanológico de Los Andes del Sur (OVDAS), the Buenos Aires Volcanic Ash Advisory Center (VAAC), and satellite data.

According to an analysis of digital elevation models, about 1.5 million cubic meters of effusive material was emitted during 17 September-2 December 2021. During December 2021-May 2022 there was continuing eruptive activity in the Nicanor crater, which consisted dominantly of seismic events, sulfur dioxide emissions, and thermal anomalies (table 2). By 13 December the L7 and L8 flows were no longer advancing, based on Sentinel-2 L2A imagery. Gas-and-ash plumes rose generally 1-2.2 km above the crater, generated by the several hundreds of explosions detected each month. Intermittent pyroclastic flows accompanied these eruptive events, traveling as far as 580 m down multiple flanks. Incandescent ejecta rose several hundred meter above the crater rim during many of the explosions, with some material falling back on the proximal flanks. A new dome (Dome 4) was first detected in early March.

Table 2. Summary of seismic events, maximum sulfur dioxide values, and number of thermal anomalies at Nevados de Chillán during December 2021-May 2022. Data from SERNAGEOMIN bi-weekly reports.

During mid-November 2021 there were multiple surges along the L7 and L8 flows; lava from the L7 flow reached 477 m to the N and 465 m down the L7b channel to the NE and 198 m in the L8 channel (BGVN 46:12). Thermal activity gradually decreased in energy from mid-November through early December 2021, due to the cessation of the L7 and L8 lava flows (figure 95). After December, the thermal anomalies became intermittent and relatively low in power compared to November. Four anomalies were detected by the MODVOLC thermal system during this time, on 1 December 2021, 14 January, and 28 January 2022. Sentinel-2 infrared satellite imagery showed a persistent thermal anomaly in the active Nicanor crater, sometimes accompanied by a gas-and-ash plume that drifted NE and E (figure 96).

Figure 95. During mid-November 2021, there was a surge of multiple new lava flow pulses from Nevados de Chillán that was reflected in this MIROVA graph (Log Radiative Power). Following this spike in thermal activity, there was a gradual decrease in thermal energy that continued through early December 2021. Thermal activity became less frequent through May 2022. Courtesy of MIROVA.

Figure 96. Sentinel-2 infrared satellite imagery of Nevados de Chillán showing a persistent thermal anomaly in the Nicanor crater on 24 December 2021 (top left), 7 February 2022 (top right), 1 March 2022 (bottom left), and 10 May 2022 (bottom right). Incandescent material was visible descending the NE flank on 7 February. A gas-and-ash plume drifted NE and E on 1 March and 10 May, respectively. Images use “Atmospheric penetration” rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Activity during December 2021 consisted of frequent seismic events and daily explosive events that originated from the Nicanor crater. Surveillance cameras showed that explosions often ejected gas-and-ash plumes 300 m high; the highest was 1.6 km on 4 December. Strong nighttime incandescence was visible on 7 and 11 December, accompanied by material that was ejected less than 600 m away. Based on high-resolution SkySat satellite images, the L7 lava flow advanced 560 m with a speed of 0.5 m/hour along the central lobe and 596 m with a speed of 1.6 m/hour along the secondary lobe. According to analysis of Sentinel-2 L2A images, the L7 and L8 flows no longer advanced after 13 December. On 24-25 December a gas-and-ash plume rose 1.8 km above the crater. Some new effusive material was reported in the Nicanor crater, based on thermal camera images and Sentinel-2 L2A images during 16-31 December. The average sulfur dioxide values, recorded by Differential Absorption Optical Spectroscopy (DOAS) equipment, were 236 ± 51 t/d during 1-15 December and 196 ± 42 t/d during 16-31 December.

Seismicity increased in January 2022 and intermittent incandescence was observed throughout the month. Around 1944 on 6 January an explosion generated a pyroclastic flow which traveled less than 400 m NE from the crater rim, according to SERNAGEOMIN. A gas-and-ash plume from the event rose 2.2 km above the crater (figure 97), accompanied by nighttime incandescence visible less than 250 m high. A small cone was growing in the active crater due to the constant accumulation of pyroclasts. A gas-and-ash plume rose 1.6 km high on 19 January. Explosions generated pyroclastic flows on 19, 25, and 26 January that traveled less than 500 m down the NE, N, and NW flanks. During 25-26 January incandescent material was ejected 500 m toward the N flank. The average sulfur dioxide value was 269 ± 67 t/d during 1-15 January and 285 ± 60 t/d during 16-31 January.

Figure 97. Webcam image of the gas-and-ash plume that rose 2.2 km above Nevados de Chillán on 6 January 2022 as a result of an explosion. Courtesy of SERNAGEOMIN (Reporte Especial de Actividad Volcanica (REAV) Region De Nuble, Complejo Volcanico Nevados de Chillan, 6 de enero de 2022, 2145 Hora local (Chile continental)).

Similar explosive activity and seismicity persisted in February with intermittent nighttime incandescence. Pyroclastic flows due to continued explosions were detected on 5, 7, 9, 12, 13, and 19-20 February which descended the NE and E flanks as far as 580 from the crater rim. An explosion on 13 February generated a gas-and-ash plume that rose 1.9 km above the crater and produced a pyroclastic flow. Gas-and-ash plumes rose 1.6 km high on 16 February, 1.2 km high on 19 February, and 1.7 km high on 20 February. Material was ejected less than 500 m from the crater, accompanied by gas-and-steam emissions during 25-28 February. The event on 20 February also ejected incandescent material radially less than 500 m from the crater onto the N and W flanks. The average sulfur dioxide value was 137 ± 29 t/d during 1-15 February and 221 ± 70 t/d during 16-28 February.

On 1 March new effusive material was observed in the Nicanor crater using Planet satellite images, which was also reflected as a thermal anomaly in Sentinel-2 L2A images. Explosions continued, generating gas-and-ash plumes as high as 1.6 km above the crater. Plumes on 10, 11, 13, and 15 March rose 1 km, 1.2 km, 1 km, and 1.6 km high, respectively. Some explosions generated pyroclastic flows down the SE and E flanks as far as 460 m from the crater rim. Intermittent incandescence of varying power persisted in the active crater. On 13 March incandescence rose as high as 230 m. According to a SkySat satellite image from 15 March the effusive mass in the active crater (now called “Dome 4”) was 57 m long, 33 m wide, growing to the NE and SE, and covered an area of 1.7 m² (figure 98). On 25 March a pyroclastic flow descended the NW flank of the active crater as far as 500 m. Incandescent material was ejected 500 m to the NE and N on 23, 25, and 31 March. The average sulfur dioxide value was 454 ± 24 t/d during 1-15 March and 537 ± 140 t/d during 16-31 March. The increase in sulfur dioxide rates was due to a new effusion in the Nicanor crater, according to SERNAGEOMIN.

Figure 98. SkySat image showing the Nicanor crater at Nevados de Chillán. New effusive material (labeled “Cuerpo Efusivo”) was observed on 15 March 2022. Courtesy of SERNAGEOMIN (Reporte Especial de Actividad Volcánica (REAV), Región De Ñuble, Complejo Volcánico Nevados de Chillán, 17 de marzo de 2022, 19:30 Hora local (Chile continental)).

The new lava effusion was still visible in the Nicanor crater during April. Gas-and-ash plumes rose as high as 1.6 km on 15 April. As a result, a pyroclastic flow descended 500 m down the N and NE slope. Crater incandescence remained at low to moderate levels. The average sulfur dioxide value was 595 ± 80 t/d during 1-15 April and 551 ± 68 t/d during 16-30 April.

Explosions persisted during May, producing gas-and-ash plumes as high as 900 m on 16 May, which generated pyroclastic flows down the SE, NE, and W flanks as far as 400 m from the crater rim. Low to moderate incandescence was also visible up to 200 m high. Based on a SkySat image, numerous fissures and emission centers were noted in a E-W trend in the S and SW part of the growing lava dome, characterized by passive degassing. On 20 and 21 May gas-and-ash plumes rose 920 m high and generated proximal pyroclastic flows down the E flank as far as 400 m from the crater rim; material was ejected 350 m down the W slope, which included ashfall deposits. Incandescence was visible up to 200 m high on 31 May. The average sulfur dioxide value decreased compared to the previous month to 466 ± 54 t/d during 1-15 May and 363 ± 58 t/d during 16-31 May.

Geologic Background. The compound volcano of Nevados de Chillán is one of the most active of the Central Andes. Three late-Pleistocene to Holocene stratovolcanoes were constructed along a NNW-SSE line within three nested Pleistocene calderas, which produced ignimbrite sheets extending more than 100 km into the Central Depression of Chile. The dominantly andesitic Cerro Blanco (Volcán Nevado) stratovolcano is located at the NW end of the massif. Volcán Viejo (Volcán Chillán), which was the main active vent during the 17th-19th centuries, occupies the SE end. The Volcán Nuevo lava-dome complex formed during 1906-1945 on the NW flank of Viejo. The Volcán Arrau dome complex was then constructed on the SE side of Volcán Nuevo between 1973 and 1986, and eventually exceeded its height. Smaller domes or cones are present in the 5-km valley between the two major edifices.

Information Contacts: Servicio Nacional de Geología y Minería (SERNAGEOMIN), Observatorio Volcanológico de Los Andes del Sur (OVDAS), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/, https://twitter.com/Sernageomin); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); 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 Dempo stratovolcano in SE Sumatra, Indonesia, has had many small explosive eruptions reported since 1817. The active Marapi crater (750 x 1,100 m) in the summit area contains a 400-m-wide crater lake (figure 7). Recent activity has consisted of single-day phreatic explosions in September 2006, January 2009, and November 2017. Indonesian’s Center of Volcanology and Geological Hazard Mitigation (CVGHM), also known as Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), is the monitoring agency.

Figure 7. Satellite image of Dempo on 30 May 2022, showing the 400-m-wide crater lake within the Marapi summit crater. Sentinel-2 image with natural color rendering (bands 4, 3, 2). Courtesy of Sentinel Hub Playground.

PVMBG reported phreatic explosion similar to those of recent years at 0154 on 31 May 2022. This event lasted 239 seconds and produced ashfall in areas within 5 km, including Pagar Alam Utara district (E) and North Dempo District; ash deposits were as thick as 1 mm. The Alert Level remained at 2 (on a scale of 1-4), and the public were reminded to stay 1 km away from the crater and as far as 2 km on the N flank.

Geologic Background. Dempo is a stratovolcano that rises above the Pasumah Plain of SE Sumatra. The andesitic complex has two main peaks, Gunung Dempo and Gunung Marapi, constructed near the SE rim of a 3-km-wide amphitheater open to the north. The high point of the older Gunung Dempo crater rim is slightly lower, and lies at the SE end of the summit complex. The taller Marapi cone was constructed within the older crater. Remnants of seven craters are found at or near the summit, with volcanism migrating WNW over time. The active 750 x 1,100 m active crater cuts the NW side of the Marapi cone and contains a 400-m-wide lake at the far NW end. Eruptions recorded since 1817 have been small-to-moderate explosions that produced local ashfall.

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

Ol Doinyo Lengai is located near the southern end of the East African Rift in Tanzania. It is known for its unique low-temperature carbonatitic lava. Activity primarily occurs in the crater offset to the north about 100 m below the summit where hornitos (small cones) and pit craters produce lava flows and spattering. Eruptions have been recorded since the late 19th century and the current eruption period began in April 2017. Recent activity has mostly consisted of small lava flows in the summit crater (BGVN 46:11). This report covers similar effusive activity during November 2021 through July 2022 using information primarily from satellite data.

Activity remained relatively low during this reporting period; satellite views were occasionally blocked by weather clouds. The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system based on the analysis of MODIS data showed a total of 12 thermal anomalies: one in late November 2021, two in January 2022, one in early March, two in early May, four in late June, and two in July (figure 217). Thermal anomalies were intermittently visible in Sentinel-2 infrared satellite images on clear weather days dominantly in the center of the summit crater, possibly representing ongoing lava effusions from the central hornito (figure 218). On 9 November there were two small anomalies in the summit crater; one was located to the W side of the crater and smaller in size and the second was located offset to the E. Two larger anomalies were visible in the crater on 24 December offset to the SW and NE (figure 218).

Figure 217. Thermal activity during November 2021-July 2022 at Ol Doinyo Lengai was relatively low in power, based on MODIS satellite data shown on this MIROVA graph (Log Radiative Power). A single anomaly was detected in late November; two during January 2022; one during early March; two during early May; four during late June; and two during July. Courtesy of MIROVA.

Figure 218. Sentinel-2 infrared imagery of Ol Doinyo Lengai from 24 December 2021 through 22 June 2022 showed thermal anomalies (bright yellow-orange) in the summit crater on clear weather days. On 24 December 2021 (top left) there were strong two anomalies offset slightly to the NE and SW side of the summit crater. On 8 January 2022 (top middle) two anomalies were visible: one in the center of the summit crater and the second close to the N side of the crater. On 17 February 2022 (top right) and 14 March 20220 (bottom left) a single anomaly was visible in the center of the crater. On 18 May three small anomalies occurred in the center of the crater and on the W and E side of the crater. On 22 June 2022 (bottom left) a stronger anomaly was visible in the center of the crater and also expanded toward the N side. Images use “Atmospheric penetration” rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

On 8 January 2022 two anomalies occurred that have decreased in size compared to the ones in late December. One of these hotspots remained in the center of the crater while the second one was located to the N side of the crater. During 8 January through 13 May only a single central anomaly was visible in infrared satellite imagery. On 18 May two anomalies appeared again, one of which remained in the center while the second on drifted more to the E of the crater. The size of the anomaly increased on 12 June, filling up much of the center of the summit crater. This larger size remained visible through the end of July, according to satellite data. During late July, the intensity of the thermal anomalies increased slightly and were larger in size, as reflected in Sentinel-2 infrared satellite imagery (figure 219). This increase is also reflected in the stronger thermal anomaly detected in late July in the MIROVA graph. A single thermal alert was detected by the MODVOLC system on 22 July.

Figure 219. Sentinel-2 infrared imagery of Ol Doinyo Lengai during July 2022 showed slightly stronger and consistent thermal anomalies (bright yellow-orange) in the center of the summit crater on clear weather day compared to the previous months. Images use “Atmospheric penetration” rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

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

Information Contacts: 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).

Manam is located 13 km off the N coast of mainland Papua New Guinea and has had eruptions recorded since 1616. It consists of two active summit craters, Main and South, which occasionally produce Strombolian activity, lava flows, pyroclastic flows, and ash plumes. The current eruption period has been ongoing since 2014. More recent activity included a strong explosion in October 2021, intermittent ash plumes, sulfur dioxide plumes, and thermal anomalies (BGVN 46:11). This report updates activity characterized by Strombolian explosions, strong ash plumes, and thermal activity during November 2021 through July 2022 using information primarily from the Rabaul Volcano Observatory (RVO), the Darwin Volcanic Ash Advisory Center (VAAC), and various satellite data.

Activity was relatively low during November through mid-December 2021 and consisted of intermittent ash plumes and sulfur dioxide plumes (figure 87). Intermittent sulfur dioxide plumes were detected using the TROPOMI instrument on the Sentinel-5P satellite, some of which exceeded at least two Dobson Units (DU) and drifted in different directions. Ash plumes on 3 and 8 November rose to 1.8 km altitude and drifted NW and W, according to HIMAWARI-8 satellite data and weather models from the Darwin VAAC. Ash plumes rose to 6 km altitude and drifted SW on 15 and 16 December, but had dissipated by mid-morning on the 16th. A thermal anomaly was also visible during 14-16 December. Minor ash emissions continued during 16 December, rising to 2.4 km altitude and drifting S, according to an RVO ground report. During 17-18 December ground observers saw a continuous ash plume rise to 3.4 km altitude and drift SE; a hotspot remained visible in satellite imagery. A discrete ash emission rose to 1.5 km altitude and drifted NE at 1600 on 21 December; later that day, discrete ash emissions rose to 3.4 km altitude and drifted SE, and the hotspot remained. Ash plumes may have risen to 10.7 km altitude and drifted S and SW during 0137-0300 on 22 December, though weather clouds and heavy rain obscured satellite views and the plumes were unconfirmed by ground observers. At 1200 later that day, an ash plume rose to 4.9 km altitude and drifted E.

Figure 87. Small but distinct sulfur dioxide plumes rising from Manam were detected using data from the TROPOMI instrument on the Sentinel-5P satellite on 2 November 2021 (top left), 26 January 2022 (top right), 10 February 2022 (middle left), 10 March 2022 (middle right), 18 April 2022 (bottom left), and 14 May 2022 (bottom right). Plumes generally drifted in different directions, and the ones shown here exceeded 2 Dobson Units (DU). On 18 April 2022 a strong sulfur dioxide plume was captured above Manam and had a mass of about 6.8 kilotons. Courtesy of the NASA Global Sulfur Dioxide Monitoring Page.

Stronger activity resumed in March 2022. RVO reported that a small pyroclastic flow was visually observed and recorded in webcam images at 0911 on 8 March. RSAM values increased markedly at 1900, which was reflected in the heightened activity. Minor ash emissions were also observed throughout the day and drifted NW. Intense Strombolian explosions in the South crater observed during 1910-2030 produced loud roaring and rumbling sounds heard on the mainland (22 km SW). Bright summit incandescence and ash emissions were also reported. The Darwin VAAC estimated that on 8 March a high ash plume rose to 15.2 km altitude and drifted W based on RGB satellite imagery. The plume detached from the summit around 2050; lower ash emissions rose to 3 km altitude and continued to extend to the W, though it had dissipated by 0050 on 9 March. The Volcano Alert Level (VAL) was raised to a 3. The next day, staff conducted a field visit and reported no roof collapses or casualties in areas to the NW; vegetation including food crops were covered with ash. After the intense eruption phase at the South crater, white gas-and-steam emissions were visible drifting W. Ash plumes rose to 2.4-3 km altitude and drifted W, SW, and NW during 14-17 March, according to the Darwin VAAC. A thermal anomaly was also detected in RGB satellite imagery on 16 March.

A strong ash plume was also detected in April. On 18 April a high-level ash plume rose to 13.7 km altitude and drifted E and N, according to RVO, RGB and satellite imagery, and weather models. Another ash plume was detected at 2000 that same day and rose to 4.9 km altitude and drifted NE; ash dissipated by 0830 on 19 April. On 30 April a continuous ash emission rose to 2.4 km altitude and drifted E. During May, intermittent ash plumes persisted. RVO reported ash emissions rose to 1.8-2.7 km altitude and drifted SE, ESE, NW, and WNW during 1-7 May, based on satellite imagery and ground reporters. Continuous ash plumes during 13-19 May rose to 2.4-3.7 km altitude and extended SW, W, NE, and NW. Similar ash plumes persisted during 25-29 May and rose to 2.1-2.4 km altitude and drifted in different directions; on 28 May a hotspot was also visible in RGB satellite imagery. An eruptive event at 0657 on 27 May was observed by RVO and webcam images, which produced an ash plume that rose to 2.4 km altitude.

Intermittent ash plumes continued during early June and mid-July. During 1-3 and 5 June ash plumes rose to 2.4-3 km altitude and drifted SW, W, and NW based on ground observations, satellite imagery, and reports from RVO. On 14 July ash plumes rose to 2.1 km altitude and drifted NW, according to satellite and RVO webcam images.

Multiple distinct thermal pulses were recorded during October 2021 through July 2022, as recorded by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system (figure 88). Pulses occurred during October, early December, early January, March, mid-April through May, and July. The pulses in January and March were slightly stronger than the others. A total of 56 thermal anomalies were detected by the MODVOLC thermal alerts system, which occurred near the summit craters on 28 and 30 November 2021, 3, 5, and 21 December 2021, 3, 10, 12, 15, and 16 January 2022, 18 February 2022, 8, 18, and 20 March 2022, 23, 25, and 28 May 2022, and 1, 13, 19, and 23 July 2022. Much of this thermal activity was also captured in Sentinel-2 infrared satellite images on clear weather days, dominantly in the South summit crater, but also occasionally in both the Main and South craters (figure 89). Two thermal anomalies were visible on each of these days: 10 November 2021, 23 February 2022, and 14 April 2022.

Figure 88. Distinct pulses of thermal activity at Manam were recorded during October 2021 through July 2022, as shown in this MIROVA graph (Log Radiative Power). Courtesy of MIROVA.

Figure 89. Sentinel-2 infrared satellite images show a persistent thermal anomaly (bright yellow-orange) dominantly at the South summit crater on 10 November 2021 (top left), 10 December 2021 (top middle), 23 February 2022 (top right), 14 April 2022 (bottom left), 24 May 2022 (bottom middle), and 18 July 2022 (bottom right). The Main summit crater also showed a thermal hotspot on 10 November 2021, 23 February 2022, and 14 April 2022. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Geologic Background. The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical basaltic-andesitic stratovolcano to its lower flanks. These valleys channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island's shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most observed eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Information Contacts: Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); 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).

Tofua is located in the central part of the Tonga Islands group and 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 recorded eruptions dating back to the 18th century. The current eruption period began in October 2015 and recent activity has consisted of mostly intermittent thermal anomalies in the Lofia crater and sulfur dioxide emissions (BGVN 46:08). This reporting period covers persistent thermal anomalies in the Lofia crater during August 2021 through July 2022. Information primarily comes from satellite data.

Summary of activity during August 2021-July 2022. Intermittent hotspots were detected by Sentinel-2 infrared satellite imagery, the MODVOLC infrared satellite data using NASA’s MODIS instrument, and Suomi NPP/VIIRS sensor data (figure 15). Sentinel-2 imagery showed a bright thermal anomaly in the Lofia crater 2-5 times each month during the reporting period (figure 16). A total of 14 thermal alerts were detected by the MODVOLC system 1-3 times every month of the reporting period. Many of these hotspots were also reflected in the Sentinel-2 and Suomi NPP/VIIRS data. There was a total of 114 days of hotspots during the reporting period that ranged from 3-14 each month in Suomi NPP/VIIRS data.

Figure 15. Timeline summary of thermal activity at Tofua detected using satellite data from August 2021 through July 2022. The dates indicated represent detected thermal anomalies for Sentinel-2, MODVOLC, and VIIRS data. 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 - MODVOLC Thermal Alerts System, and NASA Worldview using the “Fire and Thermal Anomalies” layer.

Figure 16. Sentinel-2 infrared satellite imagery showed a persistent bright thermal anomaly (bright yellow-orange) in the Lofia crater at Tofua during August 2021 through July 2022. Images were taken on 15 August 2021 (top left), 24 September 2021 (top middle), 17 January 2022 (top right), 12 April 2022 (bottom left), 12 May 2022 (bottom middle), and 16 July 2022 (bottom right). 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 Worldview (URL: https://worldview.earthdata.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).