Report on Semeru (Indonesia) — May 1999
Bulletin of the Global Volcanism Network, vol. 24, no. 5 (May 1999)
Managing Editor: Richard Wunderman.
Semeru (Indonesia) Mass wasting in March; ash eruptions continue; 9-km-high ash cloud in May
Please cite this report as:
Global Volcanism Program, 1999. Report on Semeru (Indonesia) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 24:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199905-263300.
8.108°S, 112.922°E; summit elev. 3657 m
All times are local (unless otherwise noted)
Due to increased seismicity, officials raised the status to "Caution" during the week of 23-29 March. Earlier, during the week of 9-15 March a white-gray ash plume attained heights of 400-500 m and the number of events involving debris flows rose from 6 to 42 (with a maximum run-out of 2 km). In addition, weekly volcanic B-type events increased from 1 to 35, tectonic events went from 9 to 27, and explosions increased from 280 to 385. From 23 to 29 March there were 224 earthquakes related to emissions. In addition there was one volcanic A-type, one volcanic B-type, and 14 events associated with moving debris.
On 19 April the Darwin Volcanic Ash Advisory Center (VAAC) issued an advisory to aviators, citing reported eruption ash clouds at 9 km. There was no evidence of the ash cloud from satellite imagery.
Seismic events decreased during 27 April-3 May, but a white-gray ash plume continued to reach up to 600 m. There was a marked increase in seismic events from 4-17 May. From 18-24 May the ash plume varied from white-gray to white-brown and extended to between 400 and 600 m above the summit. Eruptions dominated the seismic record, with a decrease in volcanic events. During the week pilots reported occasional ash clouds drifting NW. On 24 May the plume height reached ~6 km, drifting NW.
Geologic Background. 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.
Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).