Sarychev Peak forms the surface of Matua Island in the Kurile Islands with reported activity dating back to around 1765. Recent activity that started in May 2019 included ash and gas emission and elevated temperatures within the summit crater detected by satellite sensors, with the last reported activity being an ash plume reaching 2.7 km altitude on 10 August and thermal anomalies present until 7 October 2019 (BGVN 44:11). This bulletin summarizes activity during November 2019-April 2021 using reports by the Sakhalin Volcanic Eruption Response Team (SVERT) and the Kamchatka Volcanic Eruptions Response Team (KVERT), along with satellite data.

No cloud-free satellite images were found of the summit in November 2019, but Sentinel-2 satellite images showed weak gas-and-steam emissions on 2 and 20 December. Cloud-free Sentinel-2 images showed gas-and-steam emission through January 2020, and a thermal anomaly was detected in the crater on the 29th (figure 30). No clear satellite images of the summit area were found, but there is evidence of gas emission in February. Evidence of a new eruption is seen in satellite imagery of thin linear ash deposits across the snow on 1, 19, and 30 March 2020, all extending SE from the crater (figure 31). The crater was obscured by gas emissions on the 19th and a clear view of the crater floor showed no thermal anomaly on the 31st.

Figure 30. These thermal satellite images show the Sarychev Peak summit area in December 2019 and January 2020. The images from 2 December 2019, 6 January, and 19 January 2020 show gas emissions (solid arrows). The 29 January image shows a small area with an elevated temperature on the crater floor (dashed arrow). Sentinel-2 thermal satellite images with false color (urban) (bands 12, 11, 4) rendering. Courtesy of Sentinel Hub Playground.

Figure 31. Three ashfall deposits are visible SW of the Sarychev Peak summit through March 2020. Based on satellite images, the deposit at the top was emplaced during an event that occurred during 28 February (ash-free image) and 1 March, the middle during 17 (ash-free image) and 19, and the bottom during 26 (ash-free image) and 29 March. Gas-and-steam emissions are obscuring the view into the crater. All images are at the same scale. Sentinel-2 satellite image with natural (bands 4, 3, 2) rendering. Courtesy of Planet Labs.

The MIROVA system began detecting elevated temperatures in early April 2020, which corresponded to the Sentinel-2 thermal sensor detecting high temperatures on the crater floor (figures 32 and 33). Satellite images also showed continued gas emissions, some days obscuring the view of the crater floor.

Figure 32. This plot shows thermal energy detected at Sarychev Peak by the MIROVA system during March 2020-March 2021. there was an increase in energy detected in April 2020, which was intermittent through to October. After a few months the system detected thermal energy again in mid-January through to early February with a higher output. Courtesy of MIROVA.

Figure 33. Satellite images showing the Sarychev Peak summit crater on 4, 5, 18, and 20 April 2020. The first (top left) PlanetScope image shows the snow-covered summit area with a darker snow-free area on the crater floor. The other three images are Sentinel-2 thermal satellite images with the yellow to red colors indicating high temperatures on the crater floor. There is gas and steam in the crater on the 18th. The high temperature areas correlate to the darker snow-free area in NW part of the crater in the first image; blue colors in the thermal images are snow. Sentinel-2 thermal satellite images have false color (urban) (bands 12, 11, 4) rendering. Courtesy of Planet Labs and Sentinel Hub Playground.

The thermal anomaly on the crater floor continued through May and June, with cloud-free images showing the same area of elevated temperature as the previous months. By 20 May 2019 data from Sentinel-1 Synthetic Aperture Radar (SAR) showed morphological change in the crater associated with the area of high temperature, and this change continued through June. The TROPOspheric Monitoring Instrument (TROPOMI) detected sulfur dioxide (SO₂) content within the plume on 27 May (figure 34). Gas-and-steam emission also continued in June, with more substantial plumes visible on 22 and 27 June (figure 35). TROPOMI again detected SO₂ on 24 and 25 June; the plume on 24 June was also visible in Sentinel-2 imagery (figure 36).

Figure 34. This image shows a weak gas plume from Sarychev Peak dispersing to the SE on 27 May 2020, as well as other volcanoes in Kamchatka. TROPOspheric Monitoring Instrument (TROPOMI) data showing sulfur dioxide (SO2) in Dobson Units (DU). Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Figure 35. These Planet Scope satellite scenes show gas-and-steam plumes emanating from the Sarychev Peak summit crater and dispersing SSW (left) and NW (right) on 22 and 27 June 2020, respectively. Courtesy of Planet Labs.

Figure 36. Weak gas emission at Sarychev Peak detected by satellite sensors on 25 and 26 June 2020. The top image and the bottom-left images were acquired on the 25th and show the plume being redirected by a meteorological vortex northward before curving to the W and N. Top: Sentinel-2 satellite image with natural color (bands 4, 3, 2) rendering. Courtesy of Planet Labs. Bottom: TROPOspheric Monitoring Instrument (TROPOMI) data showing sulfur dioxide (SO2) in Dobson Units (DU). Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Throughout July satellite data show thermal emission and gas-and-steam emission, mostly within plumes dispersing from the summit crater in different directions and sometimes restricted to within the crater (figure 37). On 18 July a PlanetScope image showed lava extrusion in the crater, at the location of the elevated temperature. Sentinel-2 thermal satellite images showed weak thermal energy detected in the same location during August, and degassing continued (figure 38). By 12 August the deformation on the crater floor was clear in SAR data (figure 39), matching the PlanetScope and Sentinel-2 data. From 21 August through to 12 October there was a reduction in thermal energy detected in Sentinel-2 TIR data, with many days not having clear views of the crater floor. Plume emission continued throughout this time. There were no images showing elevated temperatures during November and December when clouds frequently covered the crater area, and there were also no anomalies detected by the MIROVA system.

Figure 37. The PlanetScope natural color (top) and Sentinel-2 thermal (bottom) satellite images indicate lava in the crater during July 2020. Gas emission is also visible in the images. Sentinel-2 thermal satellite images have false color (urban) (bands 12, 11, 4) rendering. Courtesy of Planet Labs and Sentinel Hub Playground.

Figure 38. PlanetScope and Sentinel-2 satellite images acquired during August 2020 show lava in the crater and gas-and-steam plumes being dispersed in different directions by winds. Sentinel-2 satellite image with natural color (bands 4, 3, 2) rendering. Courtesy of Planet Labs and Sentinel Hub Playground.

Figure 39. These satellite images show the morphological change in the Sarychev Peak summit crater between 10 November 2019 and 12 August 2020. The three gray-scale images use Sentinel-1 Synthetic Aperture Radar (SAR) data acquired on 10 November 2019, 20 May, and 12 August 2020. The color image in the lower left is a Sentinel-2 thermal image acquired on 22 June 2020. The SAR images show morphological changes in the crater in the same location as the elevated temperatures in the thermal images, indicating lava extrusion. Sentinel-1 SAR images are VV, decibel gamma0, and orthorectified. Sentinel-2 thermal satellite images have false color (urban) (bands 12, 11, 4) rendering. Courtesy of Sentinel Hub Playground.

On 11 January 2021 KVERT released a Volcano Observatory Notice for Aviation (VONA) with an elevation of the Aviation Color Code from Green to Yellow. The temperature within the crater had increased above background levels by 79.8°?, indicating that renewed lava extrusion had begun in the crater on the 10th. A gas-and-steam plume extended 36 km NE on the 12th. On 15 January KVERT reported that moderate activity continued, including a gas-and-steam plume that extended 40 km NE. SAR data through January shows the lava volume increasing before flowing over the NW rim and down a preexisting channel on the flank (figure 40). KVERT reported that a lava flow on the northern flank had reached 400 m by the 20th. Lava extrusion with associated moderate gas and steam emission continued throughout the month.

Figure 40. These SAR images of Sarychev Peak during 3 January to 20 February 2021 show lava extrusion filling the summit crater and descending a channel on the NW flank. Note that the 6 January image has a different look angle to the other images, and this alters how the surface appears. Sentinel-1 SAR images are VV, decibel gamma0, and orthorectified. Courtesy of Sentinel Hub Playground.

A 3 February satellite image of the NW flank showed that the lava flow front had reached approximately 1.9 km from the crater rim where it had overflowed (figure 41). The Aviation Color Code was lowered to Green on the 18th with KVERT reporting that the eruption had ended, though thermal anomalies and gas-and-steam emission continued.

Figure 41. Satellite image scenes show the lava flow at Sarychev Peak on 3 and 14 February 2021. Top: PlanetScope image from 3 February showing the lobate lava flow front approximately 1.9 km from the NW crater rim. Bottom: Sentinel-2 satellite scenes from 14 February (thermal infrared to the left and natural color to the right) showing the summit crater area with lava extrusion and the lava flow overtopping the NW rim. Sentinel-2 satellite images have natural color (bands 4, 3, 2) rendering, and thermal false color (urban) (bands 12, 11, 4) rendering. Courtesy of Planet Labs and Sentinel Hub Playground.

Satellite images of the lava flow acquired during March and April show the narrow lava lobe with pressure ridges and levees (figure 42). A comparison between a September 2019 satellite image and a clear 29 April 2021 image shows the change to the crater after the lava emplacement. The last Sentinel-2 image acquired within this period showing elevated temperatures within the crater was on 19 March and there was no more thermal energy detected by the MIROVA system by early February.

Figure 42. The PlanetScope satellite images across the top of this figure show the lava flow on the NW flank of Sarychev Peak during March-April 2021. The different degrees of snow cover show different surface morphological aspects like pressure ridges and levees. The bottom images show the crater on 7 September 2019 for comparison (left) and the lava within the summit crater on 29 April 2021 (right). Fumaroles are also visible around the crater walls in the 2019 image. The top images and bottom right image are PlanetScope satellite images and the lower left image is by CNES/Airbus through Google Earth. Courtesy of Planet Labs and U.S. Dept. of State Geographer Data via Google Earth, ©2019 Google.

Geological Summary. Sarychev Peak, one of the most active volcanoes of the Kuril Islands, occupies the NW end of Matua Island in the central Kuriles. The andesitic central cone was constructed within a 3-3.5-km-wide caldera, whose rim is exposed only on the SW side. A dramatic 250-m-wide, very steep-walled crater with a jagged rim caps the volcano. The substantially higher SE rim forms the 1496 m high point of the island. Fresh-looking lava flows, prior to activity in 2009, had descended in all directions, often forming capes along the coast. Much of the lower-angle outer flanks of the volcano are overlain by pyroclastic-flow deposits. Eruptions have been recorded since the 1760s and include both quiet lava effusion and violent explosions. Large eruptions in 1946 and 2009 produced pyroclastic flows that reached the sea.

Information Contacts: Sakhalin Volcanic Eruption Response Team (SVERT), Institute of Marine Geology and Geophysics, Far Eastern Branch, Russian Academy of Science, Nauki st., 1B, Yuzhno-Sakhalinsk, Russia, 693022 (URL: http://www.imgg.ru/en/, http://www.imgg.ru/ru/svert/reports); 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/); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); Google Earth (URL: https://www.google.com/earth/).