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Report on Merapi (Indonesia) — 21 July-27 July 2021


Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 21 July-27 July 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, 21 July-27 July 2021. Smithsonian Institution and US Geological Survey.

Weekly Report (21 July-27 July 2021)



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 16-22 July. The SW rim lava-dome volume was an estimated 1.88 million cubic meters and material continued to collapse down the flank. The volume of the summit lava dome was 2.808 million cubic meters. Lava avalanches traveled a maximum of 1.2 km SE (62 times), 1.8 km SW (101 times), 1.5 km W (two times), and 1.5 km NW (one time). Avalanches of material that descended the W flank originated from lava emplaced in 1992 and 1998, and material that descended the NW flank is from 1948 lava. According to the Darwin VAAC ash plumes rose to 3 km (10,000 ft) a.s.l. on 24 July and drifted WSW. 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.

Sources: Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG), Darwin Volcanic Ash Advisory Centre (VAAC)