PVMBG reported that a total of six explosions at Anak Krakatau were recorded on 18 March, with dense white plumes rising as high as 500 m from the summit. During 18-24 March no other plumes were noted although weather conditions often prevented visual observations. Events were recorded at 0301 and 0305 on 24 March, though ash plumes were not visible. The Alert Level remained at 3 (on a scale of 1-4), and residents were warned to remain outside of the 5-km radius hazard zone from the crater. [Correction: the Alert Level was lowered to 2 on 25 March, and the hazard zone was adjusted to a 2-km radius.]

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.

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)