Report on Krakatau (Indonesia) — 29 August-4 September 2012
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 29 August-4 September 2012
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2012. Report on Krakatau (Indonesia). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 29 August-4 September 2012. 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 during 1 June-1 September observations of Anak Krakatau were often prevented by fog; occasionally diffuse white plumes were observed rising from the crater in June. Seismicity increased significantly in August. On 2 September seismicity again increased, and at 1830 a Strombolian eruption ejected lava 200-300 m above the crater. The Alert Level remained at 2 (on a scale of 1-4). Residents and visitors were warned not to approach the volcano within 1 km of the crater.
Based on analyses of satellite imagery, the Darwin VAAC reported that on 3 September ash plumes rose to altitudes of 2.4-4.3 km (8,000-14,000 ft) a.s.l. and drifted 35-95 km N.
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.