The Dempo stratovolcano in SE Sumatra, Indonesia, has had many small explosions reported since 1817. The active crater contains a 400-m-wide lake was the source of phreatic explosions in 2006, 2009, 2017, and most recently in May 2022. This report covers activity from June 2022 to December 2023, based on daily and special reports of the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), and satellite data. Throughout the reporting period, 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.

PVMBG reported that at 2115 on 25 July 2023, an explosion produced a white-and-gray ash plume that rose at least 2 km above the summit and drifted S and SW. Additional ash explosions were recorded at 1547 and 2215 on 26 July, the latter rising 2 km above the summit crater and drifting S and SW, based on ground observations. Another explosion was reported by PVMBG at 2105 on 21 August, but no ash emissions were observed. Webcam images posted in daily MAGMA Indonesia reports showed possible patches of discolored water or material floating on the surface of the crater lake during 27-29 August (figure 8).

Figure 8. Webcam image of Dempo’s crater lake on 29 August 2023, showing material floating on surface. Courtesy of MAGMA Indonesia.

Most Sentinel-2 satellite views of Dempo during the reporting period were obscured by weather clouds. When observations were possible, the crater lake surface typically looked milky gray, indicating high levels of particulate matter. However, during several days in March and April 2023 the lake took on a blue appearance.

Geological Summary. 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/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1); Copernicus Browser (URL: https://dataspace.copernicus.eu/browser).