PVMBG reported that the eruption at Semeru continued during 23-29 November. Daily explosions at the summit produced ash plumes that varied in color and density, which generally rose 500-700 m above the summit and drifted in various directions. A dense gray ash plume at 0002 on 23 November rose 700 m and drifted SE and S, at 0507 and 0540 on 24 November white-to-gray and dense gray ash plumes, respectively, rose 500 m and drifted N, at 0702 on 25 November a dense gray ash plume rose 500 m and drifted NE, at 0444 on 26 November an ash plume rose 700 m and drifted S, at 0552 on 27 November a white-to-gray ash plume rose 500 m and drifted S, at 0556 on 28 November a dense gray ash plume rose 500 m and drifted N, that same day at 0611 a dense gray ash plume rose possibly higher than 1 km, and at 0509 on 29 November a white-and-gray ash plume rose 600 m and drifted N. The Alert Level remained at 3 (on a scale of 1-4). The public was warned to stay at least 5 km away from the summit, and 500 m 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)