BPPTKG reported that the “2021 lava dome” continued to emerge just below Merapi’s SW rim during 8-14 January, producing a total of 128 incandescent lava avalanches that traveled as far as 900 m down the Krasak River drainage on the SW flank. A comparison of photos taken on 7 and 14 January showed that the morphological changes in the summit area were attributed to the emergence of new lava domes. The 2021 dome volume was an estimated 46,766 cubic meters on 14 January, with a growth rate of about 8,500 cubic meters per day. Deformation continued, though at a lower rate; Electronic Distance Measurement (EDM) data showed a distance shortening between points in the NW at a rate of 6 cm per day. Seismic activity significantly decreased compared to the previous week.

At around 0400 on 16 January a pyroclastic flow descended 1.5 km down the Krasak drainage and produced an ash plume that rose 500 m. A pyroclastic flow was visible in webcam images around 1700 on 16 January, though somewhat obscured due to weather clouds, and traveled an estimated 1 km. From 1800 on 16 January to 0600 on 17 January there were a total of 56 incandescent lava avalanches that went a maximum distance of 1.5 km SW. During the first six hours of 18 January six incandescent avalanches descended 600 m SW. At 0543 a pyroclastic flow traveled about 1 km down the Krasak drainage and produced an ash plume that rose 50 m above the summit and drifted SE. The Alert Level remained at 3 (on a scale of 1-4), and the public were warned to stay 5 km away from the summit.

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.

Source: Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG)