Report on Semeru (Indonesia) — 2 December-8 December 2020
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 2 December-8 December 2020
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2020. Report on Semeru (Indonesia) (Sennert, S, ed.). Weekly Volcanic Activity Report, 2 December-8 December 2020. 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 the eruption at Semeru continued during 1-8 December. Rock avalanches were recorded by the seismic network almost daily and were visible most days, traveling 200-1,500 m down the Kobokan drainage. Eruptive events and rockfalls generated pyroclastic flows that traveled as far as 2.5 km down the Kobokan drainage on the SE flank during 1-3 and 5-6 December. BNPB noted that deposits from the 1 December pyroclastic flow were as thick as 15 m. According to the Darwin VAAC, ash plumes rose to altitudes of 4-6.1 km (13,000-20,000 ft) a.s.l., or 300-2,400 m above the summit, and drifted E and NE during 2 and 5-6 December. PVMBG noted that incandescent material was ejected 50-100 m above the summit during 5-8 December. The Alert Level remained at 2 (on a scale of 1-4), with a general exclusion zone of 1 km and extensions to 4 km in the SSE sector.
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.