The VSI reported that activity continued to increase during 23 January-1 February. At 0000 on 27 January an eruption produced continuous pyroclastic flows and molten lava avalanches that lasted as long as 2 hours. The eruption also produced a thick ash plume that rose 2 km above the volcano's summit and was accompanied by a strong sulfurous smell. On 28 January, "lava dome 2001" partially collapsed, resulting in pyroclastic flows and molten lava avalanches that occurred at 2-5 minute intervals. The avalanche and pyroclastic-flow material traveled down the Sat and Bebeng rivers to the SW, and Senowo River to the W. The maximum runout distance of 4.5 km occurred in the Sat River. Ash fell in 5 districts within a 15-20 km radius around the volcano; Dukun, Srumbung, Salam, Ngluwar, and Muntilan. On 31 January, pyroclastic flows continuously entered the Sat River, and to a lesser extent the Senowo and Bebeng rivers. The maximum runout distance was ~3.5 km. Again, ash fell on the towns within a ~15 km radius around the volcano. Visual observations and photographic analysis revealed that the dome became higher and larger than it was during the previous report period, and that there was a new active point at the summit that may have been a fumarole or a hot spot. The volcano remained at Alert Level 3 (on a scale of 1-4).

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: Agence France-Presse (AFP), Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM), Associated Press