BPPTKG reported that during 20-26 November white emissions from Merapi rose as high as 750 m above the summit. Avalanches of material traveled down the flanks, as far as 1 km in the Lamat drainage (W flank) at 0648 on 22 November. A comparison of photos taken on 19 and 26 November showed morphology changes in the summit area from a collapse of part of the 1954 dome. Seismicity was higher than the previous week. Electronic Distance Measurement (EDM) data continued to measure a distance shortening between points in the NW at a rate of 11 cm per day. During overflights on 26 and 27 November BNPB and BPPTKG observers noted many new avalanche deposits on the NW, W, and SW flanks. As of 27 November, there were 2,318 people spread across 15 evacuation shelters, according to BNPB. The Alert Level remained at 3 (on a scale of 1-4).

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), Badan Nacional Penanggulangan Bencana (BNPB)