BNPB reported increased activity at Sinabung on 24 August. Observers at the PVMBG Sinabung observation post noted a marked increase in seismicity, and counted 19 pyroclastic flows and 137 avalanches from the early morning until the late afternoon. Foggy conditions obscured visual observations of the activity through most of the day, although incandescent lava as far as 500 m SSE and 1 km ESE was noted in the morning, and a pyroclastic flow was seen traveling 3.5 km ESE at 1546. The lava dome had grown to a volume of 2.6 million cubic meters. There continued to be 2,592 families (9,319 people) displaced to nine shelters. Activity remained very high on 25 August; pyroclastic flows continuously descended the flanks, traveling as far as 2.5 km E and SE, and 84 avalanches occurred during the first part of the day. Based on satellite images and model data, the Darwin VAAC reported that on 26 August ash plumes rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted NW and NNE. On 29 August ash plumes reported by ground-based observers rose to an altitude of 4.6 km (15,000 ft) a.s.l. and drifted ENE. The next day an ash plume rose to an altitude of 5.2 km (17,000 ft) a.s.l. and drifted NW. The Alert Level remained at 4 (on a scale of 1-4), with an exclusion zone of 7 km from the volcano on the SSE sector, and 6 km in the ESE sector, and 4 km in the NNE sector.

Geological Summary. Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical andesitic-to-dacitic edifice is at the southern end of the four overlapping summit craters. The youngest deposit is a SE-flank pyroclastic flow 14C dated by Hendrasto et al. (2012) at 740-880 CE. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.

Sources: Badan Nacional Penanggulangan Bencana (BNPB), Darwin Volcanic Ash Advisory Centre (VAAC)