During 3-9 September lava flowed 0.5-1.8 km towards the Kahetang and Keting rivers. Lava avalanches that originated from the edges of the flows traveled up to 1 km. On 9 September at 0001 a pyroclastic flow traveled as far as 750 m from the main crater to the Batang River (West Siau). During the week seismicity was dominated by small explosion, avalanche, and multiphase earthquakes. Discontinuous volcanic tremor was also detected. The volcano remained at Alert Level 3 (on a scale of 1-4).

Geological Summary. Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi. The stratovolcano contains five summit craters along a N-S line. It is one of Indonesia's most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented (Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts have produced pyroclastic flows.

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