The VSI reported that during 16-22 January visual and instrumental monitoring revealed a continued increase of volcanic activity at Merapi. Activity consisted of several pyroclastic flows, small ash eruptions, glowing lava flows, lava avalanches, and an increase in seismicity, especially in avalanche and multi-phase earthquakes. More than 20 pyroclastic flows per day traveled continuously to the Sat (upstream of River Putih), Senowo, and Bebeng rivers. The number of glowing lava avalanches also increased since last reported, with more than 150 events per day observed. The avalanches traveled down to the Sat, Senowo, and Bebeng rivers extending as far as 3,500 m. The new lava dome, "lava dome 2001," grew at the volcano's summit over the preexisting "lava dome 1998." The Darwin VAAC reported that an ash cloud that was not visible on satellite imagery reached 500 m above the summit on 19 January. The VSI reported that during the report period ash fell in the towns of Babadan, Ngepos, and Kaliurang. An average of 95 tons/day of SO2 was measured. 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: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM), Darwin Volcanic Ash Advisory Centre (VAAC), Associated Press