CVGHM reported that seismicity from Slamet increased during 19-23 April. Diffuse white plumes rose about 50 m above the crater on 20 April. During 21-23 April, white and white-to-brownish plumes rose 50-800 m above the crater. On 23 April, the Alert Level was raised to 3 (on a scale of 1-4); people were advised not to climb the summit. According to a news article, a CVGHM volcanologist stated that lava was ejected 600 m high and ash bursts up to 112 times within a 6-hour period were detected.

Geological Summary. Slamet is one of Java's most active volcanoes. It has a cluster of about three dozen cinder cones on its lower SE-NE flanks and a single cinder cone on the W flank. It is composed of two overlapping edifices, an older basaltic-andesite to andesitic volcano on the west and a younger basaltic to basaltic-andesite one on the east. Gunung Malang II cinder cone on the upper E flank on the younger edifice fed a lava flow that extends 6 km E. Four craters occur at the summit of Gunung Slamet, with activity migrating to the SW over time. Eruptions recorded since the 18th century have originated from a 150-m-deep, 450-m-wide, steep-walled crater at the western part of the summit and have consisted of explosive eruptions generally lasting a few days to a few weeks.

Sources: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM), Jakarta Globe