Report on Semeru (Indonesia) — 30 August-5 September 2023
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 30 August-5 September 2023
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2023. Report on Semeru (Indonesia) (Sennert, S, ed.). Weekly Volcanic Activity Report, 30 August-5 September 2023. Smithsonian Institution and US Geological Survey.
8.108°S, 112.922°E; summit elev. 3657 m
All times are local (unless otherwise noted)
PVMBG reported that eruptive activity continued at Semeru during 30 August-5 September. At 0843 and 0916 on 30 August dense gray-to-white ash plumes rose 500-800 m above the summit and drifted NW and SW, respectively. White gas-and-steam emissions rose as high as 100 m above the summit and drifted in variable directions during 1-3 September; weather clouds sometimes hindered views. 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.