PVMBG reported that foggy weather often prevented visual observations of Sinabung during 25 May-2 June, except for a few clearer periods on some days. White plumes rose 200-700 m above the crater, and lava flows on the flanks were incandescent as far as 2 km S and SE. Pyroclastic flows traveled 2-3 km down the S and SE flanks during 26-28 May. An ash plume from a pyroclastic flow on 28 May rose into the fog. Two pyroclastic flows occurred on 2 June but fog prevented visual observations. 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. Deformation data showed a trend of inflation. The Alert Level was raised to 4 (on a scale of 1-4), indicating that people within 7 km of the volcano on the S to E flanks should evacuate. On 3 June BNPB reported that the lava dome volume had increased to more than 3 million cubic meters and was unstable.

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)