Heard is a remote island located in the southern Indian Ocean and consists of two volcanic structures: Big Ben and the smaller Mt. Dixon. The active Mawson Peak is located within a 5-6 km wide caldera breached to the SW side of Big Ben. Intermittent eruptions have occurred since 1910 and the most recent eruption began in September 2012 and has mainly been characterized by consistent thermal activity and lava flows (BGVN 47:02). Similar events are covered in this report during February 2022 through January 2023 primarily using various satellite data.

MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed that intermittent low-to-moderate thermal activity occurred during July 2022 through January 2023 (figure 51). Periods of increased thermal activity were recorded during late July through early August, late September through early October, mid-November, and early-to-mid-December. MODIS satellite instruments using the MODVOLC thermal algorithm also detected a total of 34 strong thermal hotspots on 15 March, 1 and 6 April, 29 May, 14, 20, 22, and 23 June, 10 and 12 August, 23 September, 11, 13, 15, and 26 November, 2, 6, and 8 December, and 11, 13, and 23 January 2023. On clear weather days, Sentinel-2 infrared satellite imagery also captured thermal activity at and near the summit of Mawson Peak (figure 52). A persistent thermal anomaly sometimes accompanied by gas-and-steam emissions was captured to the NW of Mawson Peak at a second vent on 4 and 17 February, 3 August, 15, 25 September, 15 October and at Mawson Peak on 4 June.

Figure 51. Intermittent low-to-moderate thermal activity was recorded at Heard during July 2022 through January 2023, according to this MIROVA graph (Log Radiative Power). Periods of more frequent thermal anomalies occurred during late July through early August, late September through early October, mid-November, and early December. Courtesy of MIROVA.

Figure 52. Sentinel-2 infrared satellite imagery of Heard Island’s Big Ben showed persistent thermal anomalies at the Mawson Peak summit crater and occasionally at a secondary vent to the NW of Mawson Peak on 4 February 2022 (top left), 2 June 2022 (top right), 11 August 2022 (bottom left) and 25 September 2022 (bottom right). Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Stronger thermal anomalies indicative of active lava flows originated from the second NW flank vent and moved W and SW were captured in Sentinel-2 infrared satellite imagery 39 times on 11 and 31 March, 13 April, 3, 10, 13, 15, 18, 20, 25, and 30 May, 2, 12, 14, 17, 22, and 24 June, 2, 9, 17, and 24 July, 1, 6, 11, 13, and 31 August, 20 September, 2, 22, and 25 October, 9, 14, 16, 21, 24, and 26 November, 4 and 21 December, and 23 January; a hotspot was also detected over Mawson Peak, sometimes accompanied by gas-and-steam emissions (figure 53).

Figure 53. Sentinel-2 infrared satellite imagery of Heard Island’s Big Ben showed lava flow activity (bright yellow-orange) from the NW flank vent moving to the SW and W on 11 March 2022 (top left), 13 April 2022 (top right), 30 May 2022 (middle left), 14 June 2022 (middle right), 16 November 2022 (bottom left), and 21 December 2022 (bottom right). A secondary hotspot was detected above Mawson Peak on 11 March, 13 April, 30 May, and 14 June. Sentinel-2 satellite images with “Atmospheric penetration” (bands 12, 11, 8A) rendering. Courtesy of Sentinel Hub Playground.

Geological Summary. Heard Island on the Kerguelen Plateau in the southern Indian Ocean consists primarily of the emergent portion of two volcanic structures. The large glacier-covered composite basaltic-to-trachytic cone of Big Ben comprises most of the island, and the smaller Mt. Dixon lies at the NW tip of the island across a narrow isthmus. Little is known about the structure of Big Ben because of its extensive ice cover. The active Mawson Peak forms the island's high point and lies within a 5-6 km wide caldera breached to the SW side of Big Ben. Small satellitic scoria cones are mostly located on the northern coast. Several subglacial eruptions have been reported at this isolated volcano, but observations are infrequent and additional activity may have occurred.

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).