According to CVGHM, volcanic activity began to increase at Merapi on 11 April, and on 12 April at 1500 they raised the Alert level from 2 to 3 (on a scale of 1-4). They reported that an eruption could occur at any time and no one was permitted within 8 km of the summit. According to news reports, authorities informed people living in villages near the volcano to be prepared for possible evacuations.

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