The Alert Level at Merapi remained at 4, the highest level, during 17-22 May.
Incandescence and sulfur-dioxide plumes were observed. Pyroclastic flows to the
SW and SE reached 4 km on 19 May and 3 km on 20 May. On 22 May, the lava dome
volume was estimated at ~ 2.3 million cubic meters. The Darwin VAAC reported
that low-level emissions continued during 18-19 and 23 May. CVGHM recommended
that residents who live in valleys on the NNW flanks near Sat, Lamat, Senowo,
Trising, and Apu Rivers and on the SE flank near Woro River be allowed to return
to their homes. Residents remained evacuated from villages within a 7 km radius
from the volcano's summit and within 300 m of the banks of the Krasak/Bebeng,
Bedog, and Boyong Rivers to the SW, and the Gendol River to the SE. 
        
According to news reports, an eruption producing a cloud of hot gas and ash was
witnessed on 17 May. Witnesses said the size of the plume was smaller than
ash-and-gas plumes on 15 May. On 18 May, a representative for Merapi from the
Center for Volcanological Research and Technology Development (part of CVGHM),
reported new ashfall. 

Geologic 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 N of the major city of Yogyakarta. The steep-sided modern Merapi
edifice, its upper part unvegetated due to frequent eruptive activity, was
constructed to the SW of an arcuate scarp cutting the eroded older Batulawang
volcano. Pyroclastic flows and lahars accompanying growth and collapse of the
steep-sided active summit lava dome have devastated cultivated and inhabited
lands on the volcano's western-to-southern flanks and caused many fatalities
during historical time. The volcano is the object of extensive monitoring
efforts by the Merapi Volcano Observatory of the Volcanological Survey of Indonesia.

Sources: Center of Volcanology and Geological Hazard Mitigation (CVGHM)
http://www.vsi.esdm.go.id/portal/html/index.php, 
Darwin Volcanic Ash Advisory Center 
http://www.bom.gov.au/products/IDD41290.shtml, 
Associated Press
http://www.cnn.com/2006/WORLD/asiapcf/05/17/indonesia.volcano/index.html, 
AFP http://news.yahoo.com/s/afp/20060518/wl_asia_afp/indonesiavolcano_060518151037, 
Reuters http://news.yahoo.com/s/nm/20060517/sc_nm/indonesia_merapi_dc