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Vol. 126 (2017) No. 1 小特集:富士山の地下水 p. 33-42




 Mt. Fuji, at 3,776m, is a stratovolcano located on the Pacific coast of central Japan. It started to form at ca. 100,000 yr. B.P. and continued eruptions ejected huge quantities of basaltic lavas and volcanic ashes. Its activities are divided into two stages: before and after ca. 11,000 yr. B.P. The old stage, or the Ko-Fuji stage, is characterized by frequent volcanic mudflows and ashes, and the new stage, or the Shin-Fuji stage, is characterized by continuous effusions of enormous basaltic lava flows at its initial phase. Basaltic lava flows ejected at the initial phase of the Shin-Fuji stage flew extended to cover most of the foot of the volcano. There are many springs at the foot of Mt. Fuji. Among these, large springs such as the Kakidagawa and Wakuike are located at the termini of the lava flows of the Shin-Fuji stage. Groundwater recharged at the upper parts of Mt. Fuji flows down the flanks under confined conditions through clincker zones formed above and below the massive central cores of basaltic lava flows. At the termini of the lava flows, confined groundwater gushes out of the clinker zones under pressure, forming many large springs. Hydrologic studies indicate that the total recharge to these confined aquifers in Mt. Fuji is ca. 4,700,000 m3/day.

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