Report on Merapi (Indonesia) — 11 August-17 August 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
11 August-17 August 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, 11 August-17 August 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 both the lava dome just below Merapi’s SW rim and the lava dome in the summit crater remained active during 5-12 August. The domes grew and shed material down the flanks, resulting in relatively stable dome volumes. A total of 28 pyroclastic flows descended the SW flank as far as 3 km; as many as 252 lava avalanches traveled a maximum of 2 km SW and one traveled 500 m SE. BNPB noted that ashfall was reported in 19 villages on 10 August and several on 12 August, in the districts of Dukun, Sawangan, Grabag, Pakis, Tegalrejo, Secang, Srumbung, Salam, Muntilan, and Mungkid. Winds played a role in the extensive distribution of ashfall. 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.