BPPTKG reported that during 25-31 December rock avalanches traveled as far as 1.5 km down Merapi’s NW flank in the Senowo drainage. A comparison of photos taken on 24 and 30 December showed minor morphological changes in the summit area. Seismic activity was more intense than the previous week. Electronic Distance Measurement (EDM) data continued to measure a distance shortening between points in the NW at a rate of 14 cm per day. Incandescence from the crater was visible at night on 31 December, possibly signifying the emergence of lava. At 1952 on 4 January avalanches on the SW flank were recorded by webcams and heard at the Merapi Babadan observation post, and were coincident with the appearance of another incandescent area. That same day BNPB noted that 1,115 residents remained in evacuation centers. Descending incandescent material was visible on the upper SW flank during 1847-1911 on 5 January. 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)