Report on Merapi (Indonesia) — 23 June-29 June 2021
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 23 June-29 June 2021
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2021. Report on Merapi (Indonesia) (Sennert, S, ed.). Weekly Volcanic Activity Report, 23 June-29 June 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 grow during 18-24 June. The SW rim lava-dome volume was an estimated 1.59 million cubic meters by 24 June, with a growth rate of 11,400 cubic meters per day, and continued to shed material down the flank. A total of 17 pyroclastic flows traveled a maximum of 2.5 km down the SW flank and five traveled 1.4 km SE. Incandescent avalanches, recorded 206 times, traveled as far as 2 km down the SW flank and 600 m SE. The summit lava dome grew taller by 0.5 m. Beginning at 0443 on 25 June a series of three pyroclastic flows traveled 3 km down the SE flank and produced ash plumes that rose 1 km above the summit and drifted SE. Several towns to the SE reported 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.