VSI reported that the Marapi eruption at 0814 on 16 April produced a cauliflower-shaped black ash plume that rose 2 km above the summit. Ash, lapilli, and volcanic bombs were ejected during the eruption and fell within the crater. In addition, ash fell in many villages on the S and SW flanks of the volcano. Within 1-4 km from the summit the thickness of the ash deposits was between 2 and 3 cm. Until 18 April approximately 150 smaller explosions continuously occurred. The 16 April eruption was preceded by shallow volcanic earthquakes that began on 7 April and by continuous volcanic tremor recorded on 9 April. Small eruptions occurred at 1283 and 1600 on 13 April. VSI had increased the Alert Level at Marapi from 1 to 2 following the minor activity that began on 13 April.

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.

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)