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.

Geological Summary. Dempo is a stratovolcano that rises above the Pasumah Plain of SE Sumatra. The andesitic complex has two main peaks, Gunung Dempo and Gunung Marapi, constructed near the SE rim of a 3-km-wide amphitheater open to the north. The high point of the older Gunung Dempo crater rim is slightly lower, and lies at the SE end of the summit complex. The taller Marapi cone was constructed within the older crater. Remnants of seven craters are found at or near the summit, with volcanism migrating WNW over time. The active 750 x 1,100 m active crater cuts the NW side of the Marapi cone and contains a 400-m-wide lake at the far NW end. Eruptions recorded since 1817 have been small-to-moderate explosions that produced local ashfall.

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