PVMBG reported that during 31 July-10 August foggy weather sometimes prevented visual observations of Sinabung and the growing lava dome in the summit crater. White plumes rose as high as 500 m above the crater, and lava flows on the flanks were incandescent as far as 2 km S to SE. The occurrence of pyroclastic flows per day ranged from one to seven, although none were noted on 8 August. The pyroclastic flows traveled as far as 4 km E to SE and generated ash plumes that rose as high as 3 km. Seismicity consisted of avalanche signals, low-frequency and hybrid events, tremor, tectonic events, and volcanic earthquakes; RSAM values increased due to an increase of avalanche signals. Based on information from PVMBG, the Darwin VAAC reported that on 13 August a pyroclastic flow generated an ash plume that rose 1 km above the crater. A thermal anomaly was visible in satellite images. 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.

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: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM), Darwin Volcanic Ash Advisory Centre (VAAC)