Report on Marapi (Indonesia) — 27 July-2 August 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 27 July-2 August 2011
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2011. Report on Marapi (Indonesia). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 27 July-2 August 2011. Smithsonian Institution and US Geological Survey.
0.381°S, 100.473°E; summit elev. 2891 m
All times are local (unless otherwise noted)
CVGHM reported increased seismicity from Marapi during 21 June-3 August. Observers noted that during June and July white plumes rose 15-75 m above the summit craters. On 1 August white plumes rose 15 m above the main crater; fog prevented observations the next day. On 3 August dense gray plumes rose 300-1,000 m above the crater on eight occasions. That same day CVGHM raised the Alert Level to 2 (on a scale of 1-4). Visitors and residents were prohibited from going within a 3-km radius of the summit.
Geologic Background. 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 2000 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.