Report on Krakatau (Indonesia) — November 1996
Bulletin of the Global Volcanism Network, vol. 21, no. 11 (November 1996)
Managing Editor: Richard Wunderman.
Krakatau (Indonesia) July and August lava flows; September and October ash explosions
Please cite this report as:
Global Volcanism Program, 1996. Report on Krakatau (Indonesia) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 21:11. Smithsonian Institution.
6.102°S, 105.423°E; summit elev. 155 m
All times are local (unless otherwise noted)
Although a pilot report described a 3.7 km tall eruption column from Anak Krakatau on 29 September (BGVN 21:09), ash columns during that same month more typically reached only 800 m above the summit. During the bulk of September explosions took place at 5-minute to two-hour intervals; bombs up to 20 cm in diameter reached the N and NE coastlines, areas lying ~1-1.5 km from the vent. Lava flows during July-August reached the island's W coast and added to its size. Two vents emitted lava and Strombolian eruptions in the N part of the main crater.
During October, ash explosions occurred every minute, followed by rumbling sounds and lava fountains as high as 600 m above the crater. The main crater produced all the activity during October with the other two craters remaining quiet. There were no lava flows released to the surface during October. However, weak red glow was occasionally observed at night (from the Pasuaran observatory).
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: Wimpy S. Tjetjep, Volcanological Survey of Indonesia, Jalan Diponegoro No. 57, Bandung 40122, Indonesia.