PVMBG reported that the eruption at Semeru continued during 21-27 June. White-and-gray or white-to-brown ash plumes of variable densities generally rose as high as 1 km above the summit and drifted in multiple directions; emissions were not visible on 25 June, a partly cloudy day. A webcam image showed incandescent material at the summit and on the flanks at 0145 on 23 June. According to Info Semeru (a local news source) a pyroclastic flow traveled 5 km down the SE flanks at 1910 on 26 June. PVMBG reported that at the same time a gray-to-brown ash plume rose 1.5 km above the summit and drifted NE and E, and a webcam image showed incandescent material descending the flank. The Alert Level remained at 3 (third highest on a scale of 1-4). The public was warned to stay at least 5 km away from the summit in all directions, 13 km from the summit to the SE, 500 m from the banks of the Kobokan drainage as far as 17 km from the summit, and to avoid other drainages 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.

Sources: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM), Info Semeru