Report on Merapi (Indonesia) — 8 September-14 September 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
8 September-14 September 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, 8 September-14 September 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 of Merapi’s two lava domes, situated just below the SW rim and in the summit crater, continued to grow during 3-9 September. The SW dome grew 5 m taller and had an estimated volume of 1.55 million cubic meters and the summit lava dome grew 1 m wider and had an estimated volume of 2.85 million cubic meters. One pyroclastic flow traveled 2 km down the SW flank and as many as 129 lava avalanches traveled a maximum of 2 km SW. According to the Darwin VAAC ash plumes rose 3 km (10,000 ft) a.s.l. and drifted E on 9 September, based on satellite and webcam views. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-5 km away from the summit based on location.
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.