PVMBG issued four Volcano Observatory Notices for Aviation (VONAs) on 26 November describing ash plumes from Krakatau rising as high as 1 km above the summit and drifting NW and NE. Webcam images showed incandescent material being ejected above the vent. There were 12 VONAs issued on 27 November; white-and-gray ash plumes that were sometimes dense rose as high as 1.5 km and drifted NE and NW. Webcam images continued to show incandescence at the vent and material being ejected from the vent. At least nine VONAs on 28 November described ash plumes rising as high as 2 km and drifting NE, N, and NW. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay at least 5 km away 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)