Intermittent mud ejections from the lake in Crater 1 continued through mid-January. Mud ejections that rose 100 m on 2 January were accompanied by tremor, seven seismic events felt at the AWS, and a white plume rising to 2 km above the crater rim. At other times during January a white plume rose continuously to ~400 m above the crater rim from the water-covered crater floor, ~150 m below the rim. Large-amplitude tremor associated with the mud ejections was often registered, and one other event was felt on 4 January.

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.

Information Contacts: JMA.