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Report on Karangetang (Indonesia) — September 1984


Scientific Event Alert Network Bulletin, vol. 9, no. 9 (September 1984)
Managing Editor: Lindsay McClelland.

Karangetang (Indonesia) Seismicity and minor tephra emission since January; ash column and nuées ardentes in September

Please cite this report as:

Global Volcanism Program, 1984. Report on Karangetang (Indonesia) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 9:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198409-267020



2.781°N, 125.407°E; summit elev. 1797 m

All times are local (unless otherwise noted)

An explosive eruption on 5 September was preceded by seismicity and nine months of minor tephra ejection. Rumblings were heard on 4 January, followed by an explosion that ejected ash. From February through April, rumbling preceded episodes of ash emission. On 31 May at 0724, an ash column rose to 1.5 km above the summit. During the night of 7-8 June, glowing lava fragments were ejected from the main crater. On 20 July, ash emission was accompanied by rumbling. The number of local seismic events increased through the first half of 1984 (table 1). Volcanic tremors were recorded 24 August, although no surface activity was seen. Ash emission occurred 3 September at 0447, producing an eruption column that rose 600 m. Glowing lava fragments were occasionally ejected. Rumbling accompanied the activity.

Table 1. Number of local earthquakes/month recorded at Karangetang. Courtesy of VSI.

Date Tectonic Earthquakes Volcanic Earthquakes
Jan 1984 62 18
May 1984 82 57
Jun 1984 200 139
Jul 1984 456 85

On 5 September at 0905, an ash column rose 4 km from the main crater. Nuées ardentes flowed 2 km S and 1 km W, with estimated volumes of 1.5 and 0.5 x 106 m3. One week later, ash emission was continuing and weak rumbling was heard. Ten volcanic and five tectonic earthquakes were recorded daily through 16 September. About 4,500 people were temporarily evacuated from the S and W sides of the danger zone but were allowed to work in their fields during the day. No casualties were reported.

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.

Information Contacts: A. Sudradjat, VSI.