Report on Dempo (Indonesia) — August 1999
Bulletin of the Global Volcanism Network, vol. 24, no. 8 (August 1999)
Managing Editor: Richard Wunderman.
Dempo (Indonesia) Earthquakes 18-19 September increase alert status
Please cite this report as:
Global Volcanism Program, 1999. Report on Dempo (Indonesia) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 24:8. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199908-261230.
4.016°S, 103.121°E; summit elev. 3142 m
All times are local (unless otherwise noted)
At 1810 on 18 September an earthquake was felt in an area around Dempo. The Volcanological Survey of Indonesia (VSI) reported its Modified Mercalli (MM) Intensity as MM IV. The following day three more earthquakes were felt: the first event took place at 0900 (MM II), the next at 1155 (MM I), and the last at 1800 (MM I). Recorded seismicity during these days indicated 30 events/day with amplitudes of 20-30 mm and arrival time differences (S-P) of 2-3 seconds on average. Volcanologists took this to mean that the earthquakes were local tectonic events. No visible signs of changed activity were apparent at the crater. The VSI took the precaution of increasing the condition of alert to Level II.
Geologic Background. Dempo is a prominent stratovolcano that rises above the Pasumah Plain of SE Sumatra. The andesitic volcanic complex has two main peaks, Gunung Dempo and Gunung Marapi, constructed near the SE rim of a 3 x 5 km caldera breached to the north. The Dempo peak is slightly lower, and lies at the SE end of the summit complex. The taller Marapi cone was constructed within a crater cutting the older Gunung Dempo edifice. Remnants of seven craters are found at or near the summit, with volcanism migrating WNW over time. The large, 800 x 1100 m wide historically active crater cuts the NW side of the Marapi cone and contains a 400-m-wide lake located at the far NW end of the crater complex. Historical eruptions have been restricted to small-to-moderate explosive activity that produced ashfall near the volcano.
Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).