BackgroundHachimantai was built from from widely scattered vents during the Pleistocene and is capped with andesitic lavas from vents in the center of the complex.
The Hachimantai volcanic group comprises the Chausudake-Maemoriyama, Ofukadake-Magarizakiyama and the Hachimantai-Morobidake group, which itself consists of several vents and volcanic edifices: 2 major andesitic cones of Hachimantai and Chausu-dake, and 2 major basaltic cones, Fukenoyu and Morobi-dake, as well as several minor dacitic, andesitic, and basaltic cones including Komono-morem, Mokko-dake, Ebisumori, Daikokumori, Yanomune-dake, Appi-dake.
Hachimantai is similar to the Iwate volcanic field in vent alignment and rock type, including high magnesium andesites, likely produced by 2-stage magma mixing. Both contain sub-parallel W-E trending volcanic chains at a spacing of about 12 km. In both volcanic chains, andesite cones are situated at the western end, and basalt to basaltic andesite magmas are erupted in the middle and eastern chains.
Volcanic activity at Hachimantai occurred in at least 3 major periods:
1) 0,7-1 million years ago (mainly andesites),
2) 300-400,000 years ago (basalt, high-magnesian andesite, andesite and dacite magmas).
3) 100-200,000 years ago (basalt magmas).
- Smithsonian / GVP volcano information
- Quaternary Volcanoes of Japan. Geol Surv Japan, AIST
- Ohba et al (2007) "High-Magnesian Andesite Produced by Two-Stage Magma Mixing: a Case Study from Hachimantai, Northern Honshu, Japan", J. Petrology, v. 48(3), pp 627-645
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