At 1830 on 8 September Marapi ejected a thick blackish-gray cauliflower-shaped cloud to 1500 m above the crater, accompanied by glow and a roaring noise. Andesitic ash and lapilli fell on a 30 km² area. This explosion was preceded by a number of smaller ones that produced 300-500-m-high clouds. Fumarolic emissions, rising as much as 700 m and containing some ash, were continuing as of 18 September. No seismicity was felt in villages around the volcano. The activity originated from the lateral extension of a small, pre-existing, summit area crater (figure 1), ~300 m E of the central crater. When visited on 13 September the active crater was an elongate feature 95 m long, 50 m wide, and ~50 m deep.

Figure 1. Sketch map showing Marapi's summit area and the 1978 eruption crater. Courtesy of VSI.

Geological Summary. Gunung Marapi, not to be confused with the better-known Merapi volcano on Java, is Sumatra's most active volcano. This massive complex stratovolcano rises 2,000 m above the Bukittinggi Plain in the Padang Highlands. A broad summit contains multiple partially overlapping summit craters constructed within the small 1.4-km-wide Bancah caldera. The summit craters are located along an ENE-WSW line, with volcanism migrating to the west. More than 50 eruptions, typically consisting of small-to-moderate explosive activity, have been recorded since the end of the 18th century; no lava flows outside the summit craters have been reported in historical time.

Information Contacts: F. Suparban Mitrohartono, VSI.