Report on Krakatau (Indonesia) — May 2000
Bulletin of the Global Volcanism Network, vol. 25, no. 5 (May 2000)
Managing Editor: Richard Wunderman.
Krakatau (Indonesia) Elevated May-June seismicity associated with small ash plumes
Please cite this report as:
Global Volcanism Program, 2000. Report on Krakatau (Indonesia) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 25:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200005-262000.
6.102°S, 105.423°E; summit elev. 155 m
All times are local (unless otherwise noted)
This report covers the period of 29 May-26 June 2000. Krakatau volcano was last reported on in BGVN 24:08 (August 1999) and had remained at a stable level of activity up until 0600 on 29 May, a time when seismometers began registering ~150 earthquakes attributed to the beginning of an eruption. Cloud cover made visual inspection impossible on 29 May but inspection on 30 May revealed a dark gray ash plume rising 500 m into the air. Further seismic data from 30 May registered an increase in the number of both deep and shallow volcanic earthquakes; eruption and emission earthquakes increased to ~330 events daily before dropping back down to ~200 events on 31 May. During 3-5 June seismicity remained elevated. A white plume reached ~20 m on 3 June, a very dark plume rose to ~50-500 m on 4 June, and a gray plume ascended to ~50-300 m on June 5. Bad weather inhibited visual observation throughout the rest of the reporting period.
Three booming explosions on 17 June coincided with a decrease in the number of volcanic earthquakes, as well as a marked increase in small explosion earthquakes. Seismic data for the week of 20-26 June contained several large and small explosion earthquakes; a thick gray ash plume was emitted on 25 June, rising to ~250 m. Krakatau remained at alert level 2 (on a scale of 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.
Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).