Asama Volcano
1: Introduction / Geology and petrography of Asama Volcano and environs
2: Quaternary volcanic rocks
3: Pumice flow deposits / Pumice fall accompanied with pumice flow / Pumice and volcanic ash deposits of eastern foot area / Maekake crater
4: Activity of 1108 and Oiwake Pyroclastic Flow / Course of activity
5: Kamayama, the central cone, and recent activities
6: References
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5: Kamayama, the central cone, and recent activities
After the large eruption of 1783, Maekakeyama has been rather quiet except for repeated small eruptions. However, Kamayama, the central cone formed within the Maekakeyama outer crater, has grown by 70 m and became higher than Maekakeyama. The bottom of the Kamayama crater moves up and down with the amplitude of over 300 m. Between 1912 and 1913, the crater was shallowest to become almost zero depth, but from 1950s it became about 300 m deep. In 1989, the depth is about 180 m.
Recent activity is restricted within the Kamayama crater. The activity is explosive Vulcano-type. The duration of explosion is less than several minutes and rock blocks up to 400,000 ton are ejected with the initial velocity of up to 200 m/s. The blocks include bread crust bombs and compact multi-faced blocks. Those fly along ballistic curves ( however, smaller materials tend to fly along irregular curves because of air resistance ). Fine-grained materials such as lapilli and ash are brought up to the considerable heights and blown by westerly wind, and tend to land in eastern foot areas. Those Vulcano-type eruptions of recent years are only one thousandth in scale than those in 1108 or 1783. Most of energy brought to the surface is thermal energy carried by high temperature ejecta and the amount of energy is proportional to the amount of materials ejected.