PVMBG reported that during 13-16 September white plumes rose 50-200 m above Slamet's crater. An explosion on 17 September produced a dense blackish-gray ash plume that rose as high as 1.2 km and drifted S and SW. Incandescent material was ejected 200-500 m high and booming noises were reported. Ash fell in areas as far as 20 km S. Although white plumes mostly rose from the crater the next day, an explosion generated an ash plume that rose 500 m and drifted W. During 19-20 September white plumes rose 100 m. The Alert Level remained at 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)