Report on Merapi (Indonesia) — 6 January-12 January 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 6 January-12 January 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, 6 January-12 January 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 a new lava dome, first observed on 4 January, continued to emerge just below Merapi’s SW rim during 5-12 January. Incandescent avalanches were observed 19 times during 4-7 January with material traveling as far as 800 m down the Krasak River drainage on the SW flank. At 0802 on 7 January a block-and-ash flow traveled down the upper part of the Krasak; the total distance was not observable due to weather clouds, though the seismic data suggested it was small and was not more than 1 km in length. The event also produced a 200-m-high ash plume. Similar events were recorded that same day at 1250, 1315, and 1402. Deformation continued; electronic Distance Measurement (EDM) data continued to measure a distance shortening between points in the NW at a rate of 15 cm per day. On 7 January BNPB noted that 1,342 residents were housed in evacuation centers. The Alert Level remained at 3 (on a scale of 1-4), and the public were warned to stay 5 km away from the summit.
Geologic Background. 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.