Report on Merapi (Indonesia) — October 1986
Scientific Event Alert Network Bulletin, vol. 11, no. 10 (October 1986)
Managing Editor: Lindsay McClelland.
Merapi (Indonesia) Rockfall seismicity suggests increased lava dome growth
Please cite this report as:
Global Volcanism Program, 1986. Report on Merapi (Indonesia) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 11:10. Smithsonian Institution.
7.54°S, 110.446°E; summit elev. 2910 m
All times are local (unless otherwise noted)
Between 13 and 17 October, seismographs recorded numerous local rockfall events at rates that reached 300-400/day on the 15th and 16th, suggesting possible increased growth of the lava dome. No A- or B-type shocks were detected. Seismicity declined to background after 17 October. Geologists climbed the volcano 15 October. Heavy steaming was occurring from the lava dome, but rates of SO2 emission had declined slightly to 70 t/d, from typical rates of 100-200 t/d. Temperatures at Woro and Gendol fumaroles remained at ~600 and 800°C.
Geological Summary. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2,000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequent growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities.
Information Contacts: I. Bahar, MVO; T. Casadevall, VSI.