BPPTKG reported that the 2021 lava dome continued to grow just below Merapi’s SW rim during 5-11 February. The lava-dome volume was an estimated 295,000 cubic meters on 11 February, with a growth rate of about 48,900 cubic meters per day. Incandescent avalanches of material were occasionally visible; they traveled 700 m SW in the upper parts of the Krasak and Boyong drainages during 9-10 February. Weather conditions prevented visual observations of the lava dome in the summit crater. Seismicity was higher than the previous week. Electronic Distance Measurement (EDM) data showed no notable deformation. 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)