The VSI reported that volcanic activity during 21-27 November was similar to the previous week. A thin ash plume was observed rising ~600 m above the summit from the main crater and Crater II. Booming sounds were frequently heard from the volcano's summit, and a "red flame" was observed some nights rising ~100 m above the summit. Seismic activity was high and dominated by discontinuous tremor. In total, 21 small explosions were recorded. The Alert Level remained at 2 (ranging from 1 to 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)