Report on Merapi (Indonesia) — 11 April-17 April 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 11 April-17 April 2001
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2001. Report on Merapi (Indonesia). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 11 April-17 April 2001. Smithsonian Institution and US Geological Survey.
7.54°S, 110.446°E; summit elev. 2910 m
All times are local (unless otherwise noted)
Visual and instrumental monitoring by VSI personnel during 2-9 April revealed that volcanic activity continued at Merapi. Lava avalanches continued to enter upstream areas of the Sat, Senowo, Lamat, and Bebeng rivers, with a maximum runout distance of 2.5 km in the Sat River. An observer reported that ten pyroclastic flows traveled down the Sat, Senowo, and Bebeng rivers, reaching as far as 2.3 km in the Sat River. Fumaroles emitted steam and gas up to 950 m above the volcano's summit. Both the number and amplitude of earthquakes was high, but less than previously recorded. Seismic activity was dominated by avalanche earthquakes. The volcano remained at Alert Level 2 (on a scale of 1-4).
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.