The Alert Level at Merapi remained at 4, the highest level, during 24-30 May. On 24-25 May, lava flows were observed moving SW towards the Krasak River and SE towards the Gendol River. According to news reports, on 27 May an M 6.3 earthquake that killed about 5,400 resulted in a three-fold increase in activity at Merapi. According to CVGHM, an M 5.9 earthquake coincided with pyroclastic flows of unknown origin that extended 3.8 km SW toward the Krasak River. During 28-30 May, multiple pyroclastic flows reached a maximum of 3 km SE toward the Gendol River and 4 km SW toward the Krasak and Boyong Rivers. Gas plumes reached a height above the volcano of 500 m (11,300 ft a.s.l.) on 25 May, 1,200 m (13,600 ft a.s.l.) on 26 May, 100 m (10,000 ft a.s.l.) on 29 May, and 900 m (12,600 ft a.s.l.) on 30 May.

Residents remained evacuated from villages within a 7 km radius from the volcano's summit and within 300 m of the banks of Krasak/Bebeng, Bedog, and Boyong Rivers to the SW, and Gendol River to the SE.

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), The Canadian Press