Report on Merapi (Indonesia) — 21 April-27 April 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
21 April-27 April 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, 21 April-27 April 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 continued to extrude lava during 16-22 April. The SW rim lava-dome volume was an estimated 1,069,600 cubic meters on 21 April, with a growth rate of about 11,900 cubic meters per day; the dome continued to shed material down the flank. A total of nine pyroclastic flows traveled a maximum of 1.8 km down the SW flank. Incandescent avalanches, recorded 144 times, traveled as far as 1.6 km down the SW flank and twice down the SE flank as far as 400 m. The volume of the summit lava dome was 1,794,000 cubic meters on 22 April. 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.