Sirung, located at the S end of Pantar Island, is truncated by a 2-km-wide caldera with a floor that often contains one or more small lakes. Fourteen eruptions have been documented since 1852, often with phreatic activity, including its most recent one that occurred during 7-8 July 2015; activity was characterized by a small, short-lived ash eruption (BGVN 41:02). This report updates information through September 2021 and includes a short eruption during July 2021, based on information from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation) and the Darwin Volcanic Ash Advisory Center (VAAC).

No significant activity has been reported since an ash plume on 7 and 8 July 2015. Low seismicity was recorded during April through June 2021; a minor increase in tremor amplitude lasted 10 hours on 21 July, though there were no volcanic earthquakes indicative of magma movement. However, the Volcano Alert Level was raised to 2 (on a scale of 1-4) later that day. Following this increase in seismicity, a phreatic eruption was recorded at 1644 through 1800 on 21 July, which produced a white-and-gray ash plume that rose 2 km above the summit and drifted N (figure 1). Weak, intermittent, white gas-and-steam emissions continued to rise up to 500 m above the summit through August, according to PVMBG; some gas-and-steam emissions were noted during September.

Figure 1. Webcam image of the phreatic eruption at Sirung on 21 July 2021 that consisted of a white-and-gray ash plume. Courtesy of PVMBG.

Geological Summary. Sirung volcano is located at the NE end of a 14-km-long line of volcanic centers that form a peninsula at the southern end of Pantar Island. The volcano is truncated by a 2-km-wide caldera whose floor often contains one or more small lakes. Much of the volcano is constructed of basaltic lava flows, and the Gunung Sirung lava dome forms the high point on the caldera's western rim. A number of phreatic eruptions have occurred from vents within the caldera during the 20th century. Forested Gunung Topaki, the high point of the volcanic chain, lies at the SW end and contains a symmetrical summit crater.

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/).