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Report on Krakatau (Indonesia) — 29 April-5 May 2009


Krakatau

Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 29 April-5 May 2009
Managing Editor: Sally Sennert.

Please cite this report as:

Global Volcanism Program, 2009. Report on Krakatau (Indonesia) (Sennert, S, ed.). Weekly Volcanic Activity Report, 29 April-5 May 2009. Smithsonian Institution and US Geological Survey.

Weekly Report (29 April-5 May 2009)

Krakatau

Indonesia

6.1009°S, 105.4233°E; summit elev. 285 m

All times are local (unless otherwise noted)


CVGHM reported that the number of eruptions from Anak Krakatau increased significantly at the end of March and continued through 5 May. Seismic data were not collected during 26 April-29 April due to instrument malfunctions. Direct observations of the crater on 24, 25, and 29 April revealed that the eruption originated from a crater on the W slope of Anak Krakatau. Ash plumes generally drifted E and caused ashfall within a 5 km radius of the crater. Clear weather on 5 May allowed for visual observations; "smoke" rose 500 m above the crater. On 6 May, the Alert Level was raised to 3 (on a scale of 1-4).

Geological Summary. The renowned Krakatau (frequently mis-named as Krakatoa) volcano lies in the Sunda Strait between Java and Sumatra. Collapse of an older edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of that volcano are preserved in Verlaten and Lang Islands; subsequently the Rakata, Danan, and Perbuwatan cones were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption caused more than 36,000 fatalities, most as a result of tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former Danan and Perbuwatan cones. Anak Krakatau has been the site of frequent eruptions since 1927.

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