During 15-21 October volcanic activity at Karangetang continued to decrease, as it did the previous week, and the Alert Level was reduced from 3 to 2 (on a scale of 1-4). The number of volcanic earthquakes decreased compared to the previous week and no avalanche, tremor, or explosion earthquakes were recorded. Multiphase earthquakes, associated with lava dome growth, were detected. White plumes rose 400 m above main crater, and 50-100 m above Crater II. A "red reflection" was observed reaching up to 25 m above the crater.

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)