Report on Merapi (Indonesia) — 10 May-16 May 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 10 May-16 May 2006
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2006. Report on Merapi (Indonesia). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 10 May-16 May 2006. Smithsonian Institution and US Geological Survey.
7.54°S, 110.446°E; summit elev. 2910 m
All times are local (unless otherwise noted)
CVGHM reported that on 11 May, gas plumes rose to ~600 m above Merapi (or 11,600 ft a.s.l.). Avalanches of incandescent material extended 200 m SE towards the Gendol River, and 1.5 km SW towards the Krasak River. Several small incandescent avalanches of volcanic material were visible from observatory posts. The new lava dome at the volcano's summit had grown to fill the gap between the 2001 lava flows and the 1997 lava flows on the W side of the summit. The lava dome reached a height above that of the 1997 lava flows. Seismicity was dominated by multi-phase earthquakes and signals associated with avalanches. On 13 May at 0940, the Alert Level was raised from 3 to 4, the highest level.
The Darwin VAAC reported that on 11 May an ash plume was visible on satellite imagery below 3.7 km (12,000 ft) a.s.l. An ash plume at an unknown height was visible on satellite imagery on 15 May.
According to news reports, after the Alert Level was raised to 4 on 13 May, about 4,500 people living near the volcano were evacuated. Intense activity occurred on 15 May, with pyroclastic flows traveling as far as 4 km to the W. By 16 May a total of about 22,000 people were evacuated; according to figures posted at the district disaster task force center about 16,870 people were evacuated from three districts in Central Java Province, and more than 5,600 others were evacuated from the Slemen district, a part of Yogyakarta Province. Activity decreased on 16 May. On 17 May pyroclastic flows traveled as far as 3 km. Local volcanologists reported that the lava dome continued to grow, but at a slower rate than during previous days.
Geologic Background. 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 2000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequently growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent eruptive 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 during historical time.