Report on Krakatau (Indonesia) — 20 June-26 June 2018
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 20 June-26 June 2018
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2018. Report on Krakatau (Indonesia). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 20 June-26 June 2018. Smithsonian Institution and US Geological Survey.
6.102°S, 105.423°E; summit elev. 813 m
All times are local (unless otherwise noted)
PVMBG and BNPB reported that an eruption at Anak Krakatau began on 18 June, along with increased seismicity, and reminded residents that the Alert Level remained at 2 (on a scale of 1-4); visitors were warned not to approach the volcano within 1 km of the crater. Foggy conditions hampered visual observations during 19-20 June, but on 21 June gray plumes were observed rising 100-200 m above the summit. An event at 0714 on 25 June produced a dense ash plume that rose about 1 km and drifted 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 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 volcanoes, and left only a remnant of Rakata volcano. 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.