PVMBG described activity at Sinabung during 3-10 January based on observations from a post in the Ndokum Siroga village, 8.5 km away. Each day ash plumes rose as high as 5 km, pyroclastic flows traveled 0.5-4.5 km E, SE, and S, and incandescent material was observed as far as 2 km SE and E. Roaring was periodically heard and burned trees on the S flank were noted on 4 January. Seismicity remained high, with constant tremor, hybrid earthquakes indicating a growing lava dome, and volcanic earthquakes. The number of low-frequency earthquakes dropped dramatically, however. The Alert Level remained at 4 (on a scale of 1-4). Visitors and tourists were prohibited from approaching the crater within a radius of 7 km on the SE flank and 5 km elsewhere. Badan Nacional Penanggulangan Bencana (BNPB) reported that the number of hybrid earthquakes decreased on 11 January and volcanic earthquakes increased. Ash plumes rose 1-5 km and drifted W, and pyroclastic flows traveled 1-4.5 km SE and 1 km E. Several villages in the Namanteran district reported ashfall. The 11 January report noted that the number of displaced people reached 25,516 (7,898 families) in 38 evacuation centers.

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), Badan Nacional Penanggulangan Bencana (BNPB)