Report on Krakatau (Indonesia) — 29 April-5 May 2009
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 29 April-5 May 2009
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2009. Report on Krakatau (Indonesia). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 29 April-5 May 2009. Smithsonian Institution and US Geological Survey.
6.102°S, 105.423°E; summit elev. 813 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).
Geologic Background. The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes 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, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating 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 cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.