Report on Asosan (Japan) — 23 February-1 March 2022
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 23 February-1 March 2022
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2022. Report on Asosan (Japan) (Sennert, S, ed.). Weekly Volcanic Activity Report, 23 February-1 March 2022. Smithsonian Institution and US Geological Survey.
32.884°N, 131.104°E; summit elev. 1592 m
All times are local (unless otherwise noted)
JMA reported that the amplitude of volcanic tremor signals at Asosan increased at around 0500 on 24 February and then increased again around 0900. About 45 minutes later JMA raised the Alert Level to 3 (on a scale of 1-5) and warned the public to stay at least 2 km away from the crater. Tremor amplitude decreased at around 1540 on 27 February. White plumes continued to rise 700-800 m above the crater rim during 24-28 February.
Geological Summary. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.