On 26 May, CVGHM reported that since 21 April seismicity from Slamet continued to increase or remain elevated; the peak of activity was on 17 May. White-to-brown "eruption smoke" rose about 800 m above the crater and inflation was detected. Ashfall was detected in areas 5-9 km away. The temperature of water in several locations on the flanks increased. During 12 and 21-23 May, lava fountains rose 100-400 m above the crater rim. White-to-gray "smoke" rose 150 m above the crater and ejected incandescent material onto the W flank. On 22 May, ashfall was reported in Sawangan village, 5 km W. On 23 May, an ash plume rose 1 km above the crater and ash fell on the N flank. Ash accumulated to1 mm near the observation post. The next day, an ash plume rose 700 m above the crater. The Alert Level remained at 3 (on a scale of 1-4).

Geological Summary. Slamet, Java's second highest volcano at 3428 m and one of its most active, has a cluster of about three dozen cinder cones on its lower SE-NE flanks and a single cinder cone on the western 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. Historical 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)