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Report on Karangetang (Indonesia) — August 2002

Bulletin of the Global Volcanism Network, vol. 27, no. 8 (August 2002)
Managing Editor: Richard Wunderman.

Karangetang (Indonesia) Shallow volcanic and small explosion earthquakes through early September

Please cite this report as:

Global Volcanism Program, 2002. Report on Karangetang (Indonesia). In: Wunderman, R. (ed.), Bulletin of the Global Volcanism Network, 27:8. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200208-267020.

Volcano Profile |  Complete Bulletin


Karangetang

Indonesia

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

All times are local (unless otherwise noted)


During 17 June-8 September 2002, seismicity at Karangetang was dominated by shallow volcanic (B-type) and small explosion earthquakes (table 5). The volcano's two currently active craters, the main crater and crater II lie to the S and N, respectively. The main crater nearly always issued white, medium-thick ash plumes that reached up to 500 m above the rim. The Alert Level remained at 2 throughout the report period.

Table 5. Earthquakes recorded at Karangetang during 17 June through 8 September 2002. "Plume details" compile visual observations from an observatory post at Salili, a village on the upper S flank. The plume from the main crater was nearly always described as "white, medium-thick" unless noted otherwise (as on 7-8 September). The plume from crater II was typically described as a "white ash plume" (exceptions noted). As noted in the text, the Alert Level remained at 2 throughout this period. Courtesy VSI.

Date Deep volcanic (A-type) Shallow volcanic (B-type) Multiphase Small explosion/emission Tectonic Plume Details (heights are above the summit)
17 Jun-23 Jun 2002 25 121 5 14 73 Plume emitted from main crater reached 350 m; plume from crater II rose 50 m; red reflection reached 25 m.
24 Jun-30 Jun 2002 17 166 0 10 97 Plume emitted from main crater reached 200 m; plume from crater II rose 50 m; red reflection reached 25 m.
01 Jul-07 Jul 2002 8 106 1 3 80 Ash plume from main crater reached 100 m, light plume also observed, but not clearly. Ash plume from crater II rose 25 m.
08 Jul-14 Jul 2002 64 144 0 4 78 Medium-thick ash plume from main crater reached 100 m; light plume also observed reaching 10 m. Thin ash plume from crater II rose 50 m. One explosion event.
15 Jul-21 Jul 2002 8 45 5 24 77 Medium-thick ash plume from main crater reached 500 m; light plume also observed reaching 10 m. Thin ash plume from crater II rose 250 m. One explosion event.
22 Jul-28 Jul 2002 75 122 4 20 89 Ash plume from main crater reached 350 m; light plume also observed reaching 10 m. Thin ash plume from crater II rose 250 m. Two explosion events.
29 Jul-04 Aug 2002 4 31 2 13 77 Ash plume from main crater reached 400 m; light plume also observed reaching 25 m. Thin ash plume from crater II rose 200 m.
05 Aug-11 Aug 2002 11 54 0 9 95 Ash plume from main crater reached 400 m; light plume also observed reaching 25 m. Thin ash plume from crater II rose 200 m.
12 Aug-18 Aug 2002 12 27 22 46 77 Ash plume from main crater reached 150 m; light plume also observed reaching 25 m. Thin ash plume from crater II rose 50 m.
19 Aug-25 Aug 2002 64 106 129 216 36 Ash plume from main crater reached 150 m; light plume also observed reaching 25 m. Thin ash plume from crater II rose 50 m.
26 Aug-01 Sep 2002 28 70 128 436 31 Ash plume from main crater reached 150-200 m; thin-medium ash plume from crater II rose 25 m.
02 Sep-08 Sep 2002 7 28 2 586 30 Ash plume from main crater reached 300-400 m; thundering sounds during 7-8 September were accompanied by a gray ash plume from main crater. Thin ash plume from crater II rose 25 m.

The Volcanological Survey of Indonesia (VSI) reported several explosions. On 8 July at 1806 a loud explosion from the main crater produced a white-gray ash plume that rose 1.0 km. Ash from the explosion spread NNW, while incandescence on the W flank burned vegetation. On 15 July at 1355 another loud explosion from the main crater produced white-gray ash that rose 1.5 km and spread N. A lava avalanche that accompanied the explosion entered the valley of the Kahetang river as far as 1.5 km. Multiphase earthquakes were recorded 5 times on 20 July. On 26 July at 0042 a very loud explosion heralded a lava avalanche to the W and partly to the E. The next day, at 1403, another explosion produced a lava avalanche in the same direction. The height of the ash from the explosion could not be determined because thick fog covered the edifice. Several felt tectonic earthquakes took place on 24 July, at 1014, 1839, and 1840 (intensity III on the modified Mercalli scale). Afterwards, there was a significant increase in seismic activity, mostly in deep- and shallow-volcanic earthquakes. Deep volcanic earthquakes increased from two on 23 July prior to the felt earthquakes to 58 on 24 July, while shallow volcanic earthquakes increased from 8 to 69. On 26 and 27 July, two avalanche earthquakes were recorded.

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.

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).