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 12-18 March. The 2021 lava-dome volume was an estimated 840,000 cubic meters on 18 March, with a growth rate of about 12,900 cubic meters per day, and continued to shed material down the flank. A total of three pyroclastic flows traveled a maximum of 1 km down the SW flank. Incandescent avalanches, recorded 211 times, traveled as far as 1.2 km down the SW flank. The summit lava dome had grown to 65 m tall and had an estimated volume of 950,000 cubic meters with a growth rate of 12,800 cubic meters per day. 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.

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.

Source: Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG)