PVMBG reported that during 1-12 August 100 thick gray ash plumes rose 300-800 m above the summit drifting N, E, and W, seismicity increased, and ejected material was deposited on the flanks 1.5 km from the crater on the W and SW at Slamet. Incandescence and rumbling/roaring noises were reported. The Alert Level was raised to 3 (on a scale of 1-4) on 12 August. Residents and tourists were warned not approach the crater within a radius of 4 km.

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.

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