BPPTKG reported that the eruption at Merapi (on Java) continued during 19-25 January. Seismicity remained at high levels. The SW lava dome produced a total of 47 lava avalanches that traveled as far as 1.5 km SW down the upper part of the Bebeng drainage. A total of 19 pyroclastic flows descended the Bebeng drainage as far as 3 km. The pyroclastic flows removed material from the upper parts of the Bebeng and Krasak drainages. According to news articles, minor ashfall was reported in Jelok Village (40 km S) at around 0845 on 21 January. An eruptive event with pyroclastic flows at 1355 that same day produced an ash plume that rose 1 km above the summit and caused ashfall in areas within 17 km SE, E, and NE, though some of the villages were located at greater distances. Minor amounts of ash fell in areas downwind, including Kemalang (15 km SE), Klaten (32 km SE), Selo Districts, Musuk, Boyolali (17 km E), Cepogo (4 km NE), Musuk (11 km ESE), Tamansari, Boyolali Kota, Teras (22 km E), Mojosongo (45 km E), and Sambi (28 ENE) at around 1430. The ash was washed away quickly due to rain. BPPTKG noted that morphological changes to the SW lava dome identified in webcam images were due to continuing collapses of material. 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.

Sources: Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG), Antara News, Antara News