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Report on Merapi (Indonesia) — December 1997

Bulletin of the Global Volcanism Network, vol. 22, no. 12 (December 1997)
Managing Editor: Richard Wunderman.

Merapi (Indonesia) Intermediate hazard status posted during September 1997

Please cite this report as:

Global Volcanism Program, 1997. Report on Merapi (Indonesia). In: Wunderman, R. (ed.), Bulletin of the Global Volcanism Network, 22:12. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199712-263250.

Volcano Profile |  Complete Bulletin


Merapi

Indonesia

7.54°S, 110.446°E; summit elev. 2910 m

All times are local (unless otherwise noted)


The following summary from the Merapi Volcano Observatory (MVO) describes the situation in September 1997. The alert status was "Waspada Merapi," the second of four progressive stages of alert, for all of September.

Visual accounts of activity were made from five observation posts surrounding Merapi, usually in the morning. A thin, white plume rising under low pressure was seen consistently. The plume rose 400 m above the summit in the first part of the month but attained heights of up to 1,000 m later in September. Low- and moderate- energy rockfalls containing glowing material occurred on the SW flanks, in the Sat, Krasak, Bebeng, Boyong, and Senowo river valleys, running to a maximum of 2.5 km from the summit. A persistent red glow was observed at the dome. No pyroclastic flows were reported in September.

Seismicity decreased in frequency in early September compared to August (table 8). Shallow earthquakes, such as multi-phase and rockfall types were most common. Data from tiltmeters indicated inflation in most areas in the first week of September. No significant changes were seen later in the month. Photographic evidence suggested no major change in the dome volume.

Table 8. Earthquake activity at Merapi during 11 August-21 September 1997. Courtesy MVO.

Dates Low-frequency Multiphase Rockfall Tectonic
11-17 Aug 1997 4 132 289 26
18-24 Aug 1997 1 136 330 3
25-31 Aug 1997 1 112 295 4
01-07 Sep 1997 -- 102 262 4
15-21 Sep 1997 -- 67 298 2

On 9 January 1998 the Associated Press reported a warning of potentially dangerous eruptive activity at Merapi. The warning followed observation of a significant amount of fresh lava at the summit. Local experts warned nearby residents to prepare for quick evacuation to avoid the effects of nuées ardentes and of the danger of debris slides following heavy rain.

Geologic Background. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequently growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent eruptive activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities during historical time.

Information Contacts: Mas Atje Purbawinata, Director, Merapi Volcano Observatory, Jalan Cendana 15, Yogyakarta 55166, Indonesia (URL: http://www.vsi.esdm.go.id/).