PVMBG reported that activity at Karangetang had intensified in May, leading to a change in the Alert Level status. During 1-17 May white gas-and-steam plumes were sometimes dense and rose as high as 250 m above the summit, slightly higher than the 200 m maximum height noted in April. Incandescence at North Crater was visible at night 10-25 m above the lava dome. Incandescence also emanated from Main Crater though the glow was less intense, reaching about 10 m above the dome. Sounds of falling rocks at Main Crater were heard on 15 May, the seismic network recorded 32 rockfall events in the crater on 17 May, and rock avalanches on 18 May traveled as far as 1.5 km down the SW and S flanks accompanied by rumbling sounds. On 19 May the Alert Level was raised to 3 (on a scale of 1-4) and the public was warned to stay 2.5 km away from the craters on the S and SW flanks and 1.5 km away on the other flanks. A webcam image from 2025 on 19 May showed incandescent material traveling down the flanks. On 21 May white gas-and-steam plumes rose 400 m above the summit.

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)