PVMBG reported that an explosive eruption occurred at 0740 on 11 May. The eruption began with a small roar and vibrations that were felt at the observation post for 10 minutes. The eruption plume rose to 5.5 km (18,000 ft) above the peak. There was no seismic precursor and no seismic activity continued after the event. PVMBG did not change the alert level from Green/Normal; they interpreted the event as a minor eruption triggered by the accumulation of volcanic gases unlikely to be followed by further eruptions.

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