Report on Karangetang (Indonesia) — 16 March-22 March 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 16 March-22 March 2011
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2011. Report on Karangetang (Indonesia). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 16 March-22 March 2011. Smithsonian Institution and US Geological Survey.
2.781°N, 125.407°E; summit elev. 1797 m
All times are local (unless otherwise noted)
CVGHM reported that on 11 March the Alert Level for Karangetang was raised from 2 to 3 (on a scale of 1-4) due to increased seismicity. During 12-16 March when the weather was clear, bluish gas plumes rose 50-150 m above the main crater. On 17 March lava flows traveled as far as 2 km from the main crater, accompanied by roaring and booming noises.
On 18 March lava flows traveled 1.5 km and collapses from the lava flow fronts generated avalanches that moved another 500 m. Avalanches from the crater traveled 3.8 km down the flanks. Multiple pyroclastic flows about 1.5 km long destroyed a bridge, damaged a house, and trapped 31 people between the flow paths who were later evacuated. Later that day pyroclastic flows traveled 4 km, reaching the shore. The Alert Level was raised to 4. On 20 March lava flows traveled 1.8 km and avalanches from the lava flow fronts again went 500 m. Incandescent material rolled 1.5 km down the flanks and pyroclastic flows traveled 2.3 km from the crater. According to news articles, 600-1,200 people were evacuated from villages on the W flank.
Geologic Background. 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 island. 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 in the historical record (Catalog of Active Volcanoes of the World: 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.