PVMBG reported that the eruption at Semeru continued during 26 April-3 May. Almost daily ash plumes were visible rising 300-700 m above the summit that drifted W, SW, and E. Ash plumes were recorded at 0523 and 0557 on 28 April, 0502 and 0649 on 29 April, 0621 on 30 April, 0704 on 2 May, and 0922 on 3 May. A pyroclastic flow from the end of the lava flow descended the SE flank at 0630 on 1 May and produced ash plumes that rose as high as 500 m above the summit. The Alert Level remained at 3 (on a scale of 1-4). The public was warned to stay at least 500 m away from Kobokan drainages within 17 km of the summit, along with other drainages originating on Semeru, including the Bang, Kembar, and Sat, due to lahar, avalanche, and pyroclastic flow hazards.

Geological Summary. Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano.

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