During 17-30 September incandescent lava avalanches traveled SW primarily down the Lamat, Senowo, and Bebeng rivers to a maximum run-out distance of 2.5 km. During 17-23 September 51 lava avalanches were observed. Temperatures at Gendol Crater increased from 590-595 ºC the previous week to 602-617 ºC during 17-23 September and to 598-618 ºC during 24-30 September. Avalanche earthquakes, which dominated the seismicity, increased in comparison to the previous week.

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)