Report on Merapi (Indonesia) — April 1991
Bulletin of the Global Volcanism Network, vol. 16, no. 4 (April 1991)
Managing Editor: Lindsay McClelland.
Merapi (Indonesia) High-temperature fumaroles; no changes evident to summit dome
Please cite this report as:
Global Volcanism Program, 1991. Report on Merapi (Indonesia). In: McClelland, L. (ed.), Bulletin of the Global Volcanism Network, 16:4. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199104-263250.
7.54°S, 110.446°E; summit elev. 2910 m
All times are local (unless otherwise noted)
No changes were visible at the summit dome, whose volume remained at ~6.8 x 106 m3. Diffuse to dense gas plumes rose to 450 m above the summit. Temperatures of 832 and 543°C were measured at the dome's Gendol and Woro solfataras, respectively. The temperature measured through cracks in the 1956 lava was 86°C on 20 April. There was no significant change in seismicity, although the weekly number of volcanic earthquakes briefly rose to 17 during the second week in April from the long-term average of 1-4. One multiphase event and 3-10 tectonic earthquakes were recorded/week.
Geologic Background. 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 2000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequently growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent eruptive 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 during historical time.
Information Contacts: W. Modjo, VSI.