PVMBG reported continuing inflation and increased seismicity at Slamet in a 19 October press release. An increase in the amplitude of a continuous tremor signal was recorded by the seismic network on 1 October and a period of harmonic tremor that lasted one hour and 18 minutes was recorded on 18 October. Tiltmeter and Electronic Distance Measurement data from the Cilik station located at an elevation of 1,500 m showed inflation while another station (Buncis) showed deflation; the Jurangmangu station located at a lower elevation than Cilik showed no significant deformation pattern. Inflation was recorded in tilt data at the Bambangan station (at 2,000 m elevation) during 11-18 October. Gas emissions rose 50-300 m above the summit. The Alert Level was raised to 2 (on a scale of 1-4) due to increasing activity and the public was warned to stay outside a 2 km radius.

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)