Report on Merapi (Indonesia) — 3 November-9 November 2010
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 3 November-9 November 2010
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2010. Report on Merapi (Indonesia). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 3 November-9 November 2010. 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 during 3-8 November the eruption from Merapi continued at a high level, characterized by incandescent avalanches from the lava dome, pyroclastic flows, ash plumes, and occasional explosions. Visual observations were often difficult due to inclement weather and gas-and-ash plumes from the eruption. On 7 November, a news article stated that since the eruption began on 26 October approximately156 people have died and more that 200,000 people have been displaced.
On 3 November observers stationed at multiple posts reported ash plumes from pyroclastic flows. One pyroclastic flow traveled 10 km, prompting CVGHM to extend the hazard zone to a 15-km-radius and recommend evacuations from several more communities. Another pyroclastic flow traveled 9 km SE later that day. The Darwin VAAC reported that an ash plume rose to an altitude of 18.3 km (60,000 ft) a.s.l. and drifted 110 km W. Ground observers noted a significant eruption, but could not confirm the plume altitude. On 4 November an ash-and-gas plume rose to an altitude of 11 km (36,100 ft) a.s.l., and pyroclastic flows descended the NW, NNW, and N flanks as far as 3 km. Based on analyses of satellite imagery, the Darwin VAAC reported that ash plumes rose to altitudes of 10.7-11.9 km (35,000-39,000 ft) a.s.l. and drifted W. On 5 November, rumbling sounds were heard in areas 30 km away. Pyroclastic flows continued to descend the flanks. Ash fell in Yogyakarta, 30 km SSW, and "sand"-sized tephra fell within 15 km. CVGHM recommended evacuations from several more towns within a 20-km radius.
Activity remained very intense on 6 November. Pyroclastic flows descended the flanks; one traveled 4 km W. Incandescent avalanches traveled 2 km down multiple drainages to the SSE, S, and SSW. Ash plumes rose to an altitude of 7 km (23,000 ft) a.s.l. Flashes from the lava dome were reported from observations posts and incandescent material was ejected above the crater. A subsequent pyroclastic flow sent an ash plume to an altitude of 6 km (19,700 ft) a.s.l. that drifted W, N, and E. Throughout the day, ashfall was heavy on Merapi's flanks, and was observed in surrounding areas including Selo (6 km NNW) and Magelang (26 km WNW). In Muntilan (18 km WSW) tephra and ash depths reached 4 cm. On 5 and 6 November, the Darwin VAAC reported that ash plumes observed in satellite imagery rose to an altitude of 16.8 km (55,000 ft) a.s.l. News articles stated that three airlines cancelled flights to Jakarta due to the ash-induced aviation hazard.
On 7 November, the number of seismic signals indicating pyroclastic flows increased from the previous day. An explosion was heard and ash plumes rose 6 km and drifted W. Lightning was seen from Yogyakarta and ash fell within 10 km. Pyroclastic flows traveled 5 km and lava avalanches moved 600 m S and SW. High-altitude ash plumes drifted SW. According to the Darwin VAAC, during 7-8 November satellite imagery revealed ash plumes drifting 165-220 km W and SW at an altitude of 7.6 km (25,000 ft) a.s.l. On 8 November an SO2 cloud was seen over the Indian Ocean at altitudes of 12.2-15.2 km (40,000-50,000 ft) a.s.l. The airport in Yogyakarta closed. CVGHM reported that incandescent avalanches were sometimes seen through a closed-circuit television system. Ash plumes rose to an altitude of 4.5 km (14,800 ft) a.s.l. and drifted NE.
On 9 November CVGHM noted a reduction in intensity of activity from Merapi; one pyroclastic flow occurred in a 6-hour period. Rumbling sounds were accompanied by an ash plume that rose to an altitude of 4.5 km (14,800 ft) a.s.l. and lava-dome incandescence. Ashfall was reported in Selo and lava avalanches traveled 800 m SSE.
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.