PVMBG reported that an eruption at Merapi at 1631 on 14 October generated an ash plume that rose 3 km above the summit and caused ashfall in areas as far as 25 km SW. A pyroclastic flow traveled 2 km down the Gendol drainage on the SW flank. The event changed the shape of the dome by removing a NE-SW trending section that was 100 m long, 30 m wide, and 20 m deep. Lava continued to extrude during 14-20 October, generating at least two block-and-ash flows that traveled 1 km down the Gendol drainage. Foggy conditions sometimes prevented visual observations. White emissions rose as high as 500 m above the summit. The Alert Level remained at 2 (on a scale of 1-4), and residents were warned to stay outside of the 3-km exclusion zone.

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: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)