BPPTKG reported no significant morphological changes at Merapi’s lava domes, located just below the SW rim and in the summit crater, during 10-16 December. The estimated dome volumes were almost 1.63 million cubic meters for the SW dome and just over 3 million cubic meters for the summit dome. The intensity of the seismic signals remained at high levels. As many as 116 lava avalanches traveled a maximum of 2 km SW down the Bebeng drainage, and three pyroclastic flows traveled a maximum of 2.2 km SW. At 1643 on 18 December a pyroclastic flow advanced 2 km SW and produced an ash plume that rose 400 m. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-5 km away from the summit based on location.

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)