On the Volcanic Products and History of Kaimon-dake Volcano

Abstract

The volumes and geologic ages of the lavas and ejecta of the Kaimon-dake volcano were studied from the standpoint of volano-ecology. The Kaimon-dake proper is a double volcano composed of stratovolcano and lava dome. According to the archaeological identification, the ¹⁴C age determination, and the study on the thickness of the weathering products (soils), it is concluded that the first eruption of the Kaimon-dake occurred ca. 4000 years ago and the last one ca. 1000 years ago. The thermal energy transported with the solid materials is 10²²～10²⁵ erg in a single eruptive cycle and ca. 1×10²⁶ erg in total through ca. 3000 years. Some notable facts are summarized as follows : 1) Volcanic products were rich in lithic ashes in the early stage, while rich in scoria lapilli in the later. 2) Outflows of lavas with scoria falls took place at least in four stages. 3) Eruptions occurred more frequently in the later stage than in the earlier stage. 4) Lava dome was built up and then gas explosion took place finally. These facts seem to show the possible ascending of the Kaimon-dake magma reservoir through growth.