Based on analyses of satellite imagery and wind data, the Darwin VAAC reported that on 20 October ash plumes from Karangetang rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted 75 km NW.

Source: Darwin Volcanic Ash Advisory Centre (VAAC)

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.