Saunders Island consists of a large central volcanic edifice intersected by two seamount chains in the remote South Sandwich Volcanic Arc in the South Atlantic. The young Mount Michael stratovolcano dominates the glacier-covered island, while two submarine plateaus, Harpers Bank and Saunders Bank, extend north. The symmetrical Michael has a 500-m-wide summit crater. Ash clouds were reported from the summit crater in 1819, and an effusive eruption was inferred to have occurred from a N-flank fissure around the end of the 19th century and beginning of the 20th. The current eruption period began in November 2014 and more recently has been characterized by intermittent thermal anomalies and gas-and-steam emissions (BGVN 47:03). Visits are infrequent because of the remote location, and views are often obscured by cloudy weather. This report covers activity from February 2022 through January 2023 primarily using satellite data.

Activity at the Mount Michael summit crater consisted of intermittent thermal activity during the reporting period. MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed a total of 15 low-power thermal anomalies detected near the summit crater (figure 46). One anomaly was recorded in late May, four in early June, two in late July, two in late September, one in early October, two in late November, one in mid-December 2022, and two in January 2023. Some of this thermal activity was also visible in Sentinel-2 infrared satellite imagery at the summit crater (figure 47). A strong gas-and-steam plume drifted NE on 6 February, based on a satellite image. On 24 September and 16 November two hotspots of similar size and intensity were detected at the summit crater. Weak sulfur dioxide emissions were recorded on 6, 11, 26, and 27 February, 2 and 3 March, 5, 6, and 8 October, 16 and 25 November, and 9 December as detected by the TROPOMI instrument on the Sentinel-5P satellite that drifted in different directions (figure 48).

Figure 46. A total of 15 thermal anomalies were detected near the Mount Michael summit crater at Saunders during 17 April 2022 through January 2023. One anomaly occurred during late May, four during early June, two during late July, two during late September, one during early October, two during late November, one in mid-December 2022, and two during January 2023. Courtesy of MIROVA.

Figure 47. Sentinel-2 infrared satellite images showed an intermittent thermal anomaly (bright yellow-orange) within the Mount Michael summit crater at Saunders on 6 February 2022 (top left), 3 August 2022 (top right), 24 September 2022 (bottom left), and 16 November 2022 (bottom right). Strong gas-and-steam plumes were visible on 6 February. Two visible hotspots of similar size and brightness were visible in the images taken on 24 September and 16 November. Images use “Atmospheric penetration” rendering (bands 12, 11, 8a) rendering. Courtesy of Sentinel Hub Playground.

Figure 48. Small sulfur dioxide plumes rising from Saunders were detected by the TROPOMI instrument on the Sentinel-5P satellite on 6 February 2022 (left) and 8 October 2022 (right) that drifted NW and SE, respectively. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

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

Information Contacts: MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard MD 20771, USA (URL: https://so2.gsfc.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).