Report on Karangetang (Indonesia) — September 2003

Bulletin of the Global Volcanism Network, vol. 28, no. 9 (September 2003)
Managing Editor: Edward Venzke.

Karangetang (Indonesia) Ash explosions and lava avalanches in July; overall activity level declines

Please cite this report as:

Global Volcanism Program, 2003. Report on Karangetang (Indonesia). In: Venzke, E (ed.), Bulletin of the Global Volcanism Network, 28:9. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.BGVN200309-267020.

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Karangetang

Indonesia

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

All times are local (unless otherwise noted)


Ash explosions have been frequent at Karangetang during 2003 (BGVN 28:05 and 28:07). A red glow at night and lava avalanches were reported during 9-15 June (BGVN 28:07). Although detailed observations were not provided by the Volcanological Survey of Indonesia (VSI) for the next two weeks, the hazard status remained at Alert Level 2 (on a scale of 1-4).

VSI weekly reports from 30 June through 3 August indicated that white gas plumes from the S crater typically rose 350-500 m above the crater rim, night glow often extended 25 m above the crater, and white gas plumes from the N crater rose as high as 350 m. Seismic data showed that lava avalanches and shallow volcanic earthquakes in early July were significantly reduced compared to the first half of June (table 8).

Table 8. Seismicity at Karangetang during 2 June-28 September 2003. VSI did not issue reports for Karangetang during weeks not included in the table; a dash indicates no data reported. Courtesy of VSI.

[Skip text table]
    Date (2003)     Deep  Shallow  Explosion  Multiphase  Emission  Avalanches  Tectonic
                    Vol     Vol

    02 Jun-08 Jun    11     348       --          233        46         110        26
    09 Jun-15 Jun    32     438        1          228        21         447        20

    30 Jun-06 Jul    15      93       --          446        11          32        11
    07 Jul-13 Jul    15      93       --          534        22          35         7
    14 Jul-20 Jul    21     174       31          672        38          45        22
    21 Jul-27 Jul    17     112        9           94       131          66        25
    28 Jul-03 Aug    10       8       --          312       174          94        10

    01 Sep-07 Sep     8      44        1           80       341           1        20
    08 Sep-14 Sep     5      14        0           50       266           5        23
    15 Sep-21 Sep     6      90        0            3        16           0        74
    22 Sep-28 Sep     9      60        0           75       130           0        37

During 18-20 July there were ash-producing explosions and lava avalanches. On 21-22 July an ash explosion produced a 150-m-high ash column and a glowing lava avalanche flowed 350 m toward the Beha river. During the week of 28 July-3 August another glowing lava avalanche flowed 1,500 m toward the Beha river and 350 m toward the Batang river. On 29 July volcanic tremor was recorded with a maximum amplitude of 0.5-2 mm.

Karangetang was not included in August reports, but the report for 1-28 September noted white gas emissions from the S crater rising 150-350 m and red glow at night reaching 25 m over the crater, with the N crater exhibiting white gas emissions to 50-150 m above the crater. There were no lava avalanches during this period. The Alert Level remained at 2.

Geologic Background. Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, north 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 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 has also produced pyroclastic flows.

Information Contacts: Dali Ahmad, Hetty Triastuty, and Nia Haerani, Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (Email: dali@vsi.esdm.go.id, URL: http://www.vsi.esdm.go.id/).