CVGHM reported that avalanches on Merapi's flanks were detected by the seismic network during 25-30 November. Although fog often prevented observations, white and brown plumes rising 100 m above the crater drifted SW on 25 November, and brownish plumes rose 300 m above the crater on 27 November. During 27-30 November, white plumes rose 100-800 m above the crater and drifted W, SW, N, and E. Incandescence from the crater was observed through cameras installed at the Merapi museum. According to news articles, a lahar in the Code River that runs through Yogyakarta, 30 km SSW, flooded streets and damaged bridges, and caused about 1,000 residents to evacuate. The Alert Level remained at 4, the highest level, 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: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM), BNO News