Mode and rate of soil creep by soil horizons; monitoring device and its application to forest-covered hillslopes in a humid temperate climate
Matsubayashi Takeshi; Tamura Toshikazu
Chigaku Zasshi = Journal of Geography 114(5): 751-766
The rate, mode and time of soil creep were observed by depths using the combination of a strain probe method and a white-sand marker method. The latter method has an advantage to know the total dislocation by depths while the former indicates the time of movement at each depth. Application of the combined method associated with temporal measurement of soil moisture to valley-head slopes covered by natural forest in Sendai, northeastern Japan, in humid temperate climate which was not expected to induce effective freeze-thaw action, revealed the following characteristics of soil creep. The rate of soil creep, which differs considerably from place to place, ranges from almost zero to several centimeters per year, which contains rates several times higher than previously reported ones. The dislocation often occurs synchronously at different positions in the slope in every season. The movement in B and BC horizons, which show almost the same dislocation within the same horizon and abrupt change of displacement at the boundaries of soil horizons, indicates a slide-type movement characterized by micro-slip planes at the boundaries of soil horizons. In contrast, the flow-type movement, in which dislocation is accumulating upward, is dominant in A horizon. This shows the significance of soil horizons in the occurrence of soil creep and suggests the importance of soil creep in soil-horizon differentiation on hillslopes.