Report on Semeru (Indonesia) — 5 July-11 July 2023
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 5 July-11 July 2023
Managing Editor: Sally Sennert. Written by JoAnna G. Marlow.
Please cite this report as:
Global Volcanism Program, 2023. Report on Semeru (Indonesia) (Marlow, J G, and Sennert, S, eds.). Weekly Volcanic Activity Report, 5 July-11 July 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 5-11 July, though weather conditions prevented summit observations on most days. On 10 July a dense white plumes rose as high as 600 m above the summit and drifted N, NW, W, and SW. However, emergency management agencies Badan Nasional Penanggulangan Bencana (BNPB) and Badan Penanggulangan Bencana Daerah (BPBD) reported that on 7 July continuous heavy rainfall caused flooding and lahars that affected the following locations in the Lumajang Regency: Kloposawit Village and Tumpeng Village in the Candipuro Subdistrict, Sumerwuluh Village, Pronojiwo Village, Jugosari Village, and Sidomulyo Village in the Pronojiwo Subdistrict, and Nguter Village in the Pasirian Subdistrict. Starting at 0010, lahars descended Semeru’s flanks and damaged 13 bridges, 12 homes, over 80 hectares of crops, and affected livestock. As of 2035 on 10 July, a total of 1,294 people had evacuated to 18 shelter locations. 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), Badan Nacional Penanggulangan Bencana (BNPB), Badan Penanggulangan Bencana Daerah Provinsi Jawa Timur (East Java BPBD)