足尾山地北部古峰ヶ原高原の露岩に働く凍結・融解サイクル

概要

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This paper presents data on rock surface temperature observed on a tor (Point 1) and a big boulder (Point 2) in Kobugahara, an upland plateau composed of granodiorite and located below the forest limit in central Japan. The tor at Point 1 is situated at the upper end of a block deposition feature. The observation surface at the Point 1 dips 86° toword N50° E. The big boulder at Point 2 seems to have been detached from another tor. The observation surface at Point 2 dips 88° toword N24°E. The vegetation density at Point 2 is lower than that around Point 1. Rock surface temperatures were recorded every 30 minutes thoughout the period between November 30, 2002 and November 22, 2003 with thermister probes connected to miniture data loggers. The number of daily freeze-thaw cycles (FTC) and the number of effective freeze-thaw cycles (EFTC) were 33 and 6 at Point 1, and 30 and 2 at Point 2, respectively. Moreover, a seasonal freeze-thaw cycle was found at each point. Since water is supplied by snow, rain and fog to the two observation points, the occurrence of the freeze-thaw cycles suggest that both microgelivation and macrogelivation are operative on the rock surface. Diurnal range of rock surface temperature at Point 2 is larger than that at Point 1, probably reflecting on difference in the block size, vegetation density and location of observed blocks.
日本地形学連合の論文
2005-01-25