Volcanic hazards at Mount Semeru,East Java (Indonesia), with emphasis on lahars |
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| Authors: | Jean-Claude Thouret Franck Lavigne Hiroshi Suwa Bambang Sukatja Surono |
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| Institution: | (1) Département de géologie, Laboratoire Magmas et Volcans UMR 6524 CNRS, OPGC et IRD, université Blaise Pascal, 5 rue Kessler, 63038 Clermont-Ferrand cedex, France;(2) Laboratoire de Géographie physique, UMR 8591 CNRS et université Paris 1—Sorbonne, 1 place Aristide Briand, 92190 Meudon, France;(3) Disaster Prevention Research Institute, Kyoto University, Gokasho Uji Kyoto, 611-0011, Japan;(4) Balai Sabo, Sopalan, Maguwoharjo, Depok, Sleman, Yogyakarta, Java, Indonesia;(5) Directorate of Volcanology and Geological Hazard Mitigation, 55 Jalan Diponegoro, Bandung, Java, Indonesia |
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| Abstract: | Mt. Semeru, the highest mountain in Java (3,676 m), is one of the few persistently active composite volcanoes on Earth, with
a plain supporting about 1 million people. We present the geology of the edifice, review its historical eruptive activity,
and assess hazards posed by the current activity, highlighting the lahar threat. The composite andesite cone of Semeru results
from the growth of two edifices: the Mahameru ‘old’ Semeru and the Seloko ‘young’ Semeru. On the SE flank of the summit cone,
a N130-trending scar, branched on the active Jonggring-Seloko vent, is the current pathway for rockslides and pyroclastic
flows produced by dome growth. The eruptive activity, recorded since 1818, shows three styles: (1) The persistent vulcanian
and phreatomagmatic regime consists of short-lived eruption columns several times a day; (2) increase in activity every 5
to 7 years produces several kilometer-high eruption columns, ballistic bombs and thick tephra fall around the vent, and ash
fall 40 km downwind. Dome extrusion in the vent and subsequent collapses produce block-and-ash flows that travel toward the
SE as far as 11 km from the summit; and (3) flank lava flows erupted on the lower SE and E flanks in 1895 and in 1941–1942.
Pyroclastic flows recur every 5 years on average while large-scale lahars exceeding 5 million m3 each have occurred at least five times since 1884. Lumajang, a city home to 85,000 people located 35 km E of the summit,
was devastated by lahars in 1909. In 2000, the catchment of the Curah Lengkong River on the ESE flank shows an annual sediment
yield of 2.7 × 105 m3 km−2 and a denudation rate of 4 105 t km−2 yr−1, comparable with values reported at other active composite cones in wet environment. Unlike catchments affected by high magnitude
eruptions, sediment yield at Mt. Semeru, however, does not decline drastically within the first post-eruption years. This
is due to the daily supply of pyroclastic debris shed over the summit cone, which is remobilised by runoff during the rainy
season. Three hazard-prone areas are delineated at Mt. Semeru: (1) a triangle-shaped area open toward the SE has been frequently
swept by dome-collapse avalanches and pyroclastic flows; (2) the S and SE valleys convey tens of rain-triggered lahars each
year within a distance of 20 km toward the ring plain; (3) valleys 25 km S, SE, and the ring plain 35 km E toward Lumajang
can be affected by debris avalanches and debris flows if the steep-sided summit cone fails. |
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| Keywords: | Volcanic hazards Mount Semeru Java (Indonesia) Composite cone Eruptive activity Lahar Sediment yield |
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