PVMBG reported that at 2158 and 2235 on 10 April an eruptive event at Anak Krakatau generated dense white, gray, and black ash plumes that rose as high as 2 km above the summit and drifted S and E. The events were followed by Strombolian activity that ejected incandescent material onto the crater floor and summit areas; video revealed lightning visible in the ash cloud. The Darwin VAAC issued a notice at 0145 on 11 April stating that an eruption plume had risen to 14.3 km (47,000 ft) a.s.l., but noted low confidence in the altitude due to the possible mixing of the eruption plume with meteorological storm clouds. An intense thermal anomaly was visible. An hour later the VAAC reported an on-going sulfur-rich plume rising to 11.3 km (37,000 ft) a.s.l. and drifting W; the previous plume remained visible and continued to drift NW. Later that day ash plumes rose to 3 km (10,000 ft) a.s.l. and drifted N. During 12-13 April plumes comprised mostly of sulfur dioxide and steam rose to 3 km (10,000 ft) a.s.l.; the plumes did not have a strong ash signal. The Alert Level remained at 2 (on a scale of 1-4), and the public was warned to remain outside of the 2-km-radius hazard zone from the crater.

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)