The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that eruptive activity at Marapi (on Sumatra) was ongoing during 23-29 October. At 0139 on 23 October a dense gray ash plume rose 800 m above the summit and drifted NW. On 26 October a dense gray ash plume rose 800 m above the summit and drifted NE at 1305, and at 1710 that same day a loud booming sound was accompanied by a dense gray ash plume that rose 1 km and drifted NW. Dense gray ash plumes from eruptive events at 0700, 0736, 0956, and 1601 on 27 October rose 800-2,000 m above the summit and drifted NW and NE. According to a 28 October news article an Early Warning System (EWS) to detect lahars on the flanks became operational after final testing by BNPB. The EWS was comprised of sensor devices to detect river water levels in drainages, surveillance cameras (CCTV), and siren towers to notify the public to evacuate, spread across 23 installation locations. The locations were selected based on the results of a field mapping survey and evaluation of lahars that occurred in mid-May. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to stay 3 km away from the active crater.

Geological Summary. Gunung Marapi, not to be confused with the better-known Merapi volcano on Java, is Sumatra's most active volcano. This massive complex stratovolcano rises 2,000 m above the Bukittinggi Plain in the Padang Highlands. A broad summit contains multiple partially overlapping summit craters constructed within the small 1.4-km-wide Bancah caldera. The summit craters are located along an ENE-WSW line, with volcanism migrating to the west. More than 50 eruptions, typically consisting of small-to-moderate explosive activity, have been recorded since the end of the 18th century; no lava flows outside the summit craters have been reported in historical time.

Sources: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM), Antara News, Antara News