PVMBG reported explosive activity from Slamet during 4-12 September. During the past week, activity peaked with incandescent explosions; rumbling sounds were heard by scientists at the Slamet observation post. On 11 September the largest ash plume was observed (200-1,500 m above the summit) and incandescent plumes reached 400 m above the summit. Seismicity was dominated by emissions and explosion signals. Deformation data indicated that relatively little pressure was accumulating due to magma movement. PVMBG maintained the Alert Level 3 (on a scale of 1-4).

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)