CVGHM reported that from the end of September to 20 October the rate of inflation at Merapi was 0.6 cm per day. On 21 October the rate increased to 10.5 cm per day, and incidents of incandescence from the lava dome increased. CVGHM raised the Alert Level to 3 (on a scale of 1-4). The rate of inflation increased sharply on 24 October to a rate of 42 cm per day. The next day, CVGHM raised the Alert Level to 4, and recommended immediate evacuation for several communities (news reports estimated 11,000-19,000 people) within a 10-km radius.

An eruption began at about 1700 on 26 October that was characterized by explosions along with pyroclastic flows that traveled WSW and SE. CVGHM reported that multiple pyroclastic flows occurred until 1854, when the pyroclastic flow activity started to subside. Most of the pyroclastic flows lasted 2 to 9 minutes, except for two that lasted 33 minutes each. Booming noises were heard, and incandescence from the crater was seen from the Selo observation post to the N. An ash plume was also observed rising 1.5 km above the crater.

According to news articles, officials noted that about 15,000 people had not yet evacuated, even though several minor eruptions had already occurred prior to 26 October. Reports on 27 October noted that about 25 people died and several were injured.

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: Jakarta Globe, BBC News, Associated Press, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM), Associated Press