Report on Merapi (Indonesia) — 7 February-13 February 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 7 February-13 February 2001
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2001. Report on Merapi (Indonesia). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 7 February-13 February 2001. Smithsonian Institution and US Geological Survey.
7.54°S, 110.446°E; summit elev. 2910 m
All times are local (unless otherwise noted)
Intense and dangerous volcanic activity continued at Merapi with hot lava avalanches, near-continuous pyroclastic flows, and an eruption on 10 February that deposited ash on many cities out to 60 km E of the volcano. During 30 January to 5 February, continuous hot lava avalanches and pyroclastic flows traveled down the SW flank of the volcano along the Sat, Senowo, and Bebeng rivers to a maximum runout distance of ~4.5 km. Lava avalanches also traveled down the Lamat River, a drainage that avalanches had not previously traveled down during the current period of volcanic activity. Approximately 25 pyroclastic flows occurred daily. Ash associated with the pyroclastic flows fell around Merapi. During 0430 to 0630 on 3 February heavy rain mixed with ash and produced minor lahars. On 6 February the dome was reported as being 1 million cubic meters in volume and growing at 45 cubic meters per day.
Pyroclastic-flow activity began at 2100 on 9 February and lasted up to 1 hour. At 0200 on 10 February, a medium-sized pyroclastic flow lasted for ~30 minutes. At 0330 the same day "lava dome 1998," which was under the new lava dome ("lava dome 2001"), partially collapsed. The collapse triggered a large and continuous pyroclastic flow that lasted as long as 2.5 hours. The pyroclastic flow traveled up to 7 km SW of the summit towards the Sat River, and 4.5 WSW to the Lamat River. The resultant ash cloud rose up to 5-8 km above the summit, spread ~60 km towards the E, and deposited ash on the towns of Klaten, Solo, Sukoharjo, and Boyolali. The greatest ash thickness was ~1 cm, reported within a 5 km radius around the volcano. At 0530 the Alert Level at the volcano was raised from 3 to 4, the highest level. News articles reported that ~12,000 residents near the volcano were evacuated on 10 February, though many people returned to their property the next day despite the evacuation order. By 11 February, lava dome 2001 was estimated to be 1.4 million cubic meters in volume and unstable, especially after the 10 February collapse of "lava dome 1998."
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.