PVMBG reported that RSAM values from Sinabung were low and stable during 12-20 September. Earthquake signals indicating lava-dome instability were recorded and had increased from 96 to 110 events/day since the 5-11 September period. Seismicity also continued to signify growth of the main lava flow on the flanks; incandescent lava was visible at the top, middle, and front of the lava flow. The length of the lava flow was 2.9 km on 6 September. White and sometimes bluish plumes rose as high as 1 km above the lava dome. Pyroclastic flows traveled 2.5 km SE on 15 September and 2 km S on 18 September. The Alert Level remained at 3 (on a scale of 1-4).

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)