Report on Merapi (Indonesia) — 8 March-14 March 2023
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
8 March-14 March 2023
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2023. Report on Merapi (Indonesia). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 8 March-14 March 2023. Smithsonian Institution and US Geological Survey.
7.54°S, 110.446°E; summit elev. 2910 m
All times are local (unless otherwise noted)
BPPTKG reported that the eruption at Merapi (on Java) continued during 3-9 March and seismicity remained at high levels. The SW lava dome produced 19 lava avalanches that traveled as far as 1.7 km down the SW flank (upstream in the Bebeng, Boyong, and Sat/Putih drainages). No significant morphological changes to the central and SW lava domes were evident in webcam images.
Activity increased on 11 March with collapses of the SW lava dome. During 1212-1500 a series of 21 lava avalanches from the SW lava dome produced pyroclastic flows that traveled less than 4 km down the Bebeng and Krasak drainages. Ash plumes rose from the dome and in dense “curtains” from along the pyroclastic-flow deposits on the SW flank. The ash plumes rose as high as 3 km above the summit during 1212-1306 and drifted W and NW, causing ashfall in several areas downwind, especially in Magelang.
Avalanches and pyroclastic flows from additional collapses continued to be recorded on 12 March. A total of 15 avalanches descended the SW flank as far as 2.5 km and 21 pyroclastic flows traveled a maximum distance of 2 km SW. White-and-gray ash plumes of variable densities rose as high as 2.5 km above the summit and drifted N, NW, W, and E based on Darwin VAAC notices and PVGHM VONAs. A drone was deployed to inspect the SW dome and flank, the deposits, and the summit dome; the end of the pyroclastic-flow deposits in the Bebeng drainage was 3.7 km from the center of the summit crater. By early on 13 March a total of 60 pyroclastic flows had been mainly channeled down the Bebeng.
On 13 March there was a total of 36 lava avalanches; two pyroclastic flows went as far as 1.5 km down the SW flank. The Darwin VAAC reported that at 0100, 0630, and 0900 ash plumes rose as high as 4.3 km (14,000 ft) a.s.l., or 1.4 km above the summit, and drifted NW. A VONA issued on 14 March described a gray-and-brown ash plume that rose 2.5 km above the summit and drifted E and SE. The Alert Level remained at 3 (on a scale of 1-4), and the public was warned to stay 3-7 km away from the summit based on location.
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: Balai Penyelidikan dan Pengembangan Teknologi Kebencanaan Geologi (BPPTKG), Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM), Darwin Volcanic Ash Advisory Centre (VAAC)