During 17-23 September lava flows and lava avalanches rarely occurred at Karangetang. Small white-colored emissions rose ~500 m above the main crater and 50-200 m above Crater II. A 10- to 100-m-high "red reflection" was visible above the volcano. Seismic activity decreased in comparison to the previous week and was dominated by multiphase and avalanche earthquakes. During 24-30 September seismic activity continued to decrease and few lava avalanches were observed emanating from main crater. Plumes rose 400 m above the summit of the main crater and 50-100 m above Crater II. A 25-m-high "red reflection" was observed. The Alert Level remained at 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)