大雪山御鉢平湖成層の電気探査と花粉分析

概要

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The Ohachidaira is a small caldera 2km across in Daisetsu Volcano, central Hokkaido, which was formed by a series of pyroclastic eruptions about 30, 000 years ago.Electroconductivity measurements and pollen analysis of the lake deposit in the caldera has been conducted to obtain information about thickness, facies changes, vegetation, and climatic condition during the deposition.a) The fine-grained lake deposit is more than 60m thick below the bottom of the caldera; its total thickness is more than 80 to 90m if the deposit exposed at the terrace-shaped cliff inside the caldera is included.b) The deposit exposed at the terrace-shaped cliff and buried in the caldera bottom is subdivided into 4 pollen zones (OH-I, OH-II, OH-III, and OH-IV) in ascending order.Each zone is characterized by high pollen percentages as follows:OH-I: BetulaOH-II: Betula and AlnusOH-III: Picea Betula and Pinus.OH-IV: Picea and ButalaBased on the present vegetation and the pollen transportation mechanism in the alpine region of Daisetsu Volcano, the climatic condition of 4 pollen zones is estimated to be cold; the OH-II zone in particular is very cold.
日本第四紀学会の論文