HR: 14:15h
AN: H43A-02    [Abstracts]
TI: Field Observation and Numerical Simulation on Sediment Yield Due to Freeze and Thaw Action
AU: * Tsutsumi, D
EM: tsutsumi@sabom.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Higashinokuchi, Shimomisu, Yoko-oji, Fushimi Ward, Kyoto, Kyoto, 6128235, Japan
AU: Fujita, M
EM: fujita@sabom.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Higashinokuchi, Shimomisu, Yoko-oji, Fushimi Ward, Kyoto, Kyoto, 6128235, Japan
AU: Sawada, T
EM: t.sawada@neo.okuhida-dsl.com
AF: Disaster Prevention Research Institute, Kyoto University, 436-13 Nakao, Okuhidaonsengo, Takayama, Gifu, Takayama, 5061422, Japan
AB: Because most parts of the Japanese islands are located within temperate to subarctic climatic zones, freeze and thaw action during winter can be observed frequently in most mountainous areas. The freeze-thaw action usually causes bedrock weathering and produces sediment. Erosion induced by freeze-thaw action appears to be a major source of sediment from mountainous areas to streams. However, these processes are little understood. In this research, a detailed field observation was conducted to elucidate mechanisms of freeze-thaw action and the sediment yield on a bare slope in southern Shiga Prefecture, Japan. The bedrock of the observed bare slope consists of granite and is highly weathered. Two small plots (plots 1 and 2) were established by partitioning these areas with plastic borders. For each plot, surface and subsurface temperatures at depths of 0, 10, 25 and 50 cm, as well as air temperature were continuously measured every 10 min during the observation period from December 2004 to April 2005. The sediment produced from weathered bedrock was collected and weighed once in a week from the plot 1. In plot 2, the sediment was not disturbed and remained on the bedrock until the end of observation period. From the observation results, it was shown that the freeze-thaw action occurred repeatedly, and the freezing front where the bedrock temperature is 0 degree C, reached a depth of 10 cm. Sediment was actively produced when freeze-thaw action was observed; when freeze-thaw action stopped in April 2005, sediment yield decreased markedly. Sediment yields from plots 1 and 2 were 108 and 44 kg/m2/year, respectively. This difference indicates that the sediment cover on the bedrock surface mitigated the effect of freeze-thaw action on sediment yield from the bedrock. These observed results were simulated by a simplified thermal conductivity analysis. Comparison between the observed and simulated results suggests that multiple episodes of freeze-thaw activity are necessary for the bedrock to be converted into sediment.
DE: 1815 Erosion
DE: 1859 Rocks: physical properties
DE: 1863 Snow and ice (0736, 0738, 0776, 1827)
SC: Hydrology [H]
MN: 2007 Joint Assembly