Activity began to increase at the end of March. Detonations from explosions were heard 50 km away and window glass trembled on the W coast of Java. Incandescent material rose 200 m above the vent, which approximately coincided with the 1975 eruption center. About 65 explosion events were recorded on 13 April, and 290 on 16 April. The strongest activity occurred during a 5-hour period on 19 April, when 200 explosions were recorded. There were 335 explosions on 20 April, but activity was declining the next day. Rough seas prevented a landing on the island.

Geological Summary. The renowned Krakatau (frequently mis-named as Krakatoa) volcano lies in the Sunda Strait between Java and Sumatra. Collapse of an older edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of that volcano are preserved in Verlaten and Lang Islands; subsequently the Rakata, Danan, and Perbuwatan cones 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 caused more than 36,000 fatalities, most as a result of 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 Danan and Perbuwatan cones. Anak Krakatau has been the site of frequent eruptions since 1927.

Information Contacts: A. Sudradjat, L. Pardyanto, and Suparto S., VSI.