PVMBG reported that the eruption at Anak Krakatau had intensified. Dense white, gray, and black ash plumes rose as high as 1 km above the summit and drifted SW during 17-19 April. Strombolian activity was first observed on 17 April; that same day that sulfur dioxide emissions increased to 181.1 tons per days from 28.4-68.4 tons per day recorded during 14-15 April. A dense gray-black ash plume rose around 800 m above the summit at 0621 on 21 April and drifted E. At 0049, 0145, 0237, and 1730 on 22 April dense gray-to-black ash plumes rose 500-1,500 m above the summit and drifted SW. Incandescent material was occasionally ejected above the vent. Sulfur dioxide emissions notably increased to 9,219 tons per day on 23 April. That same day, at around 1219, lava flowed into the sea and produced a white steam plume at the entry point. Ash plumes were taller on 23 April, rising to 3 km above the summit at 0608, 1200, and 2020, with SSW, S, and SE drifts. The plumes continued to be characterized as dense, and white, gray, and black in color. On 24 April PVMBG raised the Alert Level to 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)