An eruption at 0016 on 12 August 1994 sent an ash column to ~6 km altitude, a height of 3,200 m above the summit. Another explosion at 0046 ejected ash 280 m high. From the observatory ~7 km from the crater, observers noted incandescent projections as high as 300 m above the crater rim, accompanied by explosion sounds and vibrations. Ashfall in and around the city of Bukittinggi . . . ranged from 0.5 to 1 mm thick. Shallow volcanic earthquakes were recorded after the explosions, but gradually decreased.

Eruptions during the first half of 1993 (VSI, 1993a) produced lapilli and ash that were deposited in a radius of 1.5-3 km from the active crater. A dark gray column rose as high as 1,200 m above the summit . . . , but was usually in the 400-500 m range. Explosion earthquakes from January to July 1993 fluctuated between 1 and 77 events/day. The frequency of explosions increased in July 1993, but then decreased from August through December (VSI, 1993b). These explosions during Jul-Dec 1993 deposited lapilli and ash within a 750-m-radius of the active crater. Incandescent material fell within a few tens of meters of the crater rim. Average plume height in the second half of 1993 was 400-800 m, reaching a maximum of 3,200 m above the summit. Throughout 1993, deep volcanic earthquakes (A-type) were detected at a rate of 6-41/month. Between 42 and 338 shallow (B-type) events were recorded each month.

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: VSI.