Report on Krakatau (Indonesia) — 1 January-7 January 1920
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 1 January-7 January 1920
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 1920. Report on Krakatau (Indonesia). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 1 January-7 January 1920. Smithsonian Institution and US Geological Survey.
6.102°S, 105.423°E; summit elev. 155 m
All times are local (unless otherwise noted)
The partial collapse of the cone and resulting destructive tsunami, Surtseyan activity, and ash plumes with lightning in December 2018 is not covered in the WVAR, as I was under strict orders to not work as part of a government-wide shut down. It was frustrating to follow the unfolding story on my own and not collect the large amounts of reports and observations being shared widely; information from significant events like this can be buried and repeatedly overprinted by more information. Sometimes it is better to wait until it all sorts itself out and authorities have the chance to breath, curate the data, and write a more accurate account of events. Either way, the estimated removed volume above sea level was 150-180 million m3. The summit of the pre-collapse cone was 338 m, while the highest point post-collapse was reduced to 110 m. While the event was fascinating, scary videos of the tsunami emerged, and are reminders that volcanoes can change many lives in an instant.
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.