CVGHM reported that on 28 November seismicity from Karangetang increased and indicated rockfalls. White plumes rose from summit craters I and II to approximate altitudes of 1.8-2.2 km (5,900-7,200 ft) a.s.l. On 29 November white and brownish plumes rose to an altitude of 1.8 km (5,900 ft) a.s.l. Incandescent rockslides from the main crater traveled 250 m S towards the Bahembang River, 250 m W towards the Beha Timur River, and 500-1,000 m S towards the Keting River. Thunderous noises were reported. On 30 November, fog prevented visual observations; the seismic network recorded 160 rockfalls. On 1 December, incandescent rockslides traveled 250 m S towards the Bahembang River, 750 m W towards the Beha Timur River, and 500-1,500 m S towards the Keting River. On 2 December, the Alert Level was raised to 3 (on a scale of 1-4) due to the continuation of elevated seismicity, run-out distances of incandescent rockslides, and height of incandescent material ejected from the summit.

Based on analysis of satellite imagery and information from CVGHM, the Darwin VAAC reported that on 2 December an ash plume from Karangetang rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted W.

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.

Sources: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM), Darwin Volcanic Ash Advisory Centre (VAAC)