北アルプス北部における高山湖沼の成因と分布に対する地すべりの影響

概要

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Little is known about the biotic and abiotic characteristics of alpine ponds and lakes even though they are prominent and important features of alpine landscape. This study examines the influence of gravitational landforms on the origins and spatial distribution of alpine ponds in a landslide-prone area in central Japan. Ninety-four ponds were detected by aerial-photo interpretation in an area above 2000 m a.s.l. (7838 ha) in a northern area of the Northern Japanese Alps. Of these, 60 ponds occurred inside or at the outer boundaries of gravitationally displaced masses, and 27 ponds occurred in linear depressions that were formed outside masses displaced by gravitational force; the remainder of the ponds were formed by volcanic activities. A logistic regression analysis was performed to determine whether environmental variables explain the presence of ponds in linear depressions. The results indicate that presence of ponds is related to the depth of a depression, snow-cover duration, and bedrock geology. Deeper depressions have ponds more frequently, and ponds tend to be found in depressions on snowy slopes underlain with ultramafic rocks. The concentration of alpine ponds in snowy, ultramafic rock areas suggests ponds are mainly fed by snow melt, and that soil material from weathered ultramafic rocks supports the water storage of ponds.