BPPTKG reported that the eruption at Merapi (on Java) continued during 14-20 July and seismicity remained at elevated levels. The SW lava dome produced a total of 281 lava avalanches that descended multiple flanks; one avalanche traveled 1 km down the Sat/Putih drainage, two traveled as far as 500 m down the Senowo drainage, eight traveled a maximum distance of 2 km down the SW flank upstream from the Boyong drainage, and 270 traveled as far as 1.8 km down the Bebeng. Morphological changes to the SW lava dome were due to continuing collapses of material. The Darwin VAAC reported that multiple minor ash plumes were identified in satellite images on 19 July rising to 3.7 km (12,000 ft) a.s.l. and drifting S and SW. The emissions were more diffuse towards the end of the day and at 2350 on 19 July and 0600 on 20 July were only visible in webcam images. 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)