PVMBG reported that during 2-9 September foggy weather sometimes prevented visual observations of Sinabung and the growing lava dome in the summit crater. Lava flows on the flanks were incandescent as far as 2 km ESE to SSE. The daily number of pyroclastic flows usually ranged from one to seven, although 11 were observed on 4 September; none were detected on 8 September. The pyroclastic flows traveled as far as 3.5 km E to SE and generated ash plumes that rose as high as 2.5 km. Seismicity consisted of avalanche signals, low-frequency and hybrid events, tremor, tectonic events, and volcanic earthquakes. The Alert Level remained at 4 (on a scale of 1-4), indicating that people within 7 km of the volcano on the SSE sector, and within 6 km in the ESE sector, should evacuate. BNPB reported that on 15 September pyroclastic flows traveled as far as 4 km ESE. Ash plumes rose as high as 3 km and drifted E, causing thick ashfall deposits in Berastagi, Kabanjahe, and surrounding areas. The number of displaced people totaled 2,572.

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.

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)