The origin and the time of formation of an isolated pond in Tateyama Midagahara, Toyama, Japan


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  • 立山弥陀ヶ原における孤立した池塘の地下地形と成立時期

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The ground surface and underground structure of the pond, which exists independently in Tateyama Oiwake, were investigated, the heights that seemed to be clay layers were lined up from the north to the east of the pond just below the embankment surrounding the pond on the surface. However, there were few such topography from the south to the southwest of the pond. From the geological formations and dating of the soil core in and around the pond, it is estimated that the formation of the pond started before 14027calBP -13754calBP and 13625calBP -13615calBP, and then the surroundings are often transported during the cold season. It is estimated that dust (yellow sand, etc.) piled up and peat formation began about 8000 years after the end of the cold season, and it became the current topography. The water depth around 7300 years ago when the Akahoya volcanic ash from this pond came in was estimated to be about 30 cm, which was deeper than the current 10 cm. In addition, there is a place where the part estimated to be the bottom of the pond at that time is now a dike, and it is possible that its shape changed during the formation process.



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