Based on pilot reports, the Darwin VAAC reported that eruption plumes from Merapi on 2 and 3 August reached altitudes of ~6.1 km (~20,000 ft) a.s.l. and drifted W. According to CVGHM, during 2-4 August rockfalls traveled 1 km SE toward the Gendol river and gas plumes reached a maximum of 400 m above the summit (10,900 ft a.s.l.). On 3 August, the Alert Level was lowered to 2 (on a scale of 1-4).

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: Darwin Volcanic Ash Advisory Centre (VAAC), Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)