BPPTKG reported that the 2021 lava dome just below Merapi’s SW rim and the new lava dome in the summit crater both continued to grow during 12-18 February. The 2021 lava dome volume was an estimated 397,500 cubic meters on 17 February, with a growth rate of about 25,200 cubic meters per day; it was 258 m long, 133 m wide, and 30 m high. The summit lava dome was an estimated 426,000 cubic meters, with a growth rate of about 10,000 cubic meters per day; it was 160 m long, 120 m wide, and 50 m high. Seismicity was less intense than the previous week. Electronic Distance Measurement (EDM) data showed no notable deformation. PVMBG noted that foggy conditions often prevented visual observations during 18-23 February, though sometimes white emissions were observed rising up to 400 m above the summit. 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.

Sources: Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG), Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)