JMA reported that the amplitude of volcanic tremor signals at Asosan had decreased at around 1540 on 27 February and remained low. White plumes rose 600-800 m above the crater during 7-14 March. During field surveys conducted on 8 and 10 March sulfur dioxide gas emissions were 1,300 and 900 tons per day, respectively; these values were higher than those measured before the October 2021 eruption. No other changes were observed. JMA lowered the Alert Level to 2 (on a scale of 1-5) on 14 March and warned the public to stay at least 1 km away from the crater.

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.

Source: Japan Meteorological Agency (JMA)