BPPTKG reported that the eruption at Merapi (on Java) continued during 23-29 August. Earthquakes were less intense compared to the previous week. The SW lava dome produced lava avalanches that descended the S and SW flanks; 327 traveled as far as 2 km SW down the upper part of the Sat/Putih drainage and two traveled as far as 1.3 km S down the Boyong drainage. Eight pyroclastic flows descended the Bebeng drainage as far as 1.5 km. Morphological changes to the SW lava dome were due to continuing effusion and collapses of material. The hottest temperature was around 243 degrees Celsius on 25 August, similar to the previous measurement. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-7 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)