The Quaternary Research (Daiyonki-Kenkyu)
Online ISSN : 1881-8129
Print ISSN : 0418-2642
ISSN-L : 0418-2642
Tephrochronology and Eruptive Activity on Hakone Volcano in the Past 50ka
Makoto Kobayashi
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1999 Volume 38 Issue 4 Pages 327-343

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Abstract

In this study, we identified 22 pumice fall and pyroclastic flow deposits derived from Hakone Volcano, 18 tephras from Fuji Volcano, and 4 widespread tephras as key beds in and around Hakone caldera, and established their stratigraphy. On the basis of this stratigraphy, we constructed the history of eruptive activity and formation of Hakone central cones.
Eruptive activity during the Hakone-Central-Cone Stage began at the formation of pre-Kamiyama in Hakone young caldera, which was associated with pyroclastic flow related to Hakone-Tokyo Pumice. In this stage, first, pre-Kamiyama erupted Hk-SP (ca. 46ka), Hk-CC 1 (ca. 43ka), and Hk-CC 4 (ca. 40ka). The mode of eruption of pre-Kamiyama gradually changed after the eruption of Hk-CC 5 a, b (ca. 39ka), and pre-Kamiyama finally collapsed at the time of the Hk-CC 6 or 7 (ca. 38, 37ka) eruptions. The eruption mode after the collapse was characterized by the occurrence of repeated block and ash flows associated with the effusion of a large quantity of viscous lava and the production of lava domes. Repeated effusions of lava rapidly built the central cones. The average eruptive rate of Hakone volcano during the last 110k years is estimated to be 7.6×1011kg/ky. When examined in detail, however, it is clear that the eruptive rate decreases gradually.

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