Report on Merapi (Indonesia) — 30 June-6 July 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
30 June-6 July 2021
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2021. Report on Merapi (Indonesia). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 30 June-6 July 2021. Smithsonian Institution and US Geological Survey.
7.54°S, 110.446°E; summit elev. 2910 m
All times are local (unless otherwise noted)
BPPTKG reported that the lava dome just below Merapi’s SW rim and the lava dome in the summit crater both remained active during 25 June-1 July. The SW rim lava-dome volume was an estimated 1.68 million cubic meters by 1 July, with a growth rate of 11,800 cubic meters per day, and continued to shed material down the flank. The summit lava dome was 0.5 m shorter than the previous week, corresponding to the increasing numbers of incandescent avalanches and pyroclastic flows as more material was shed to the SE. A total of 10 pyroclastic flows traveled a maximum of 2 km down the SW flank and 29 traveled as far as 3 km SE. As many as 100 incandescent avalanches traveled a maximum of 2 km down the SW flank and 26 traveled as far as 1.2 km down the SE flank. Ashfall was reported in several areas to the SE on 25 June. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 5 km away from the summit.
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.