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A freeze-thaw experiment was conducted to investigate the destruction mode of weathered bedrock in different lithologies. The experiment was conducted on bedrock samples of weathered granite (WGr), weathered granite porphyry (WGp), weathered shale (WS), weathered sandstone (WSa) and weathered rhyolite (WR). Because of freeze and thaw action, porosity of the bedrock samples increased and weight of the samples decreased. When porosity of WGr, WGp and WS increased greater than 0.43, 0.1 and 0.27, respectively, small pieces were detached from the main sample bodies. In contrast, freezing and thawing caused only slight increases in the porosity of WSa and WR and production of fine sediment from the surface. Depth of the sediment productions of WSa and WR due to one freeze-thaw cycle was equivalent to less than 1.0 and 0.2 mm, respectively. Hence, these rocks are exposed to only slight damage, which are at the ground surface. The experimental results were also used for developing a simple destruction model.

In previous sediment-runoff models, the sediment production rates of mountain slopes, and the sediment supply rates to streams typically have been developed using empirical methods. A process-based model for sediment production and supply is, however, required for more exact simulations of sediment runoff. In this study, we develop a method to calculate the sediment production rate due to both freeze-thaw action and the sediment supply rate (i.e. erosion rate of talus). These numerical models were then connected to an existing sediment transport model. The integrated model presented here was applied to a small mountainous watershed. We found that the calculated sediment production rate was within the range of values typically observed for this region. Additionally, the estimated annual sediment discharge using the model agreed with observational results. Lastly, we found that the model can be used to qualitatively characterize typical features of the actual sediment routine in mountainous watersheds.

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Rock breakdown by freeze and thaw action occurs at bare slopes in mountainous area in Japan. The quantitative estimation of the amount of sediment produced is indispensable because the sediment closely relates to sediment disaster. In relation to this, it is required to obtain the temperature and moisture profile. In this study, a concurrent numerical simulation of underground heat and water transfer was conducted and the characteristic of water flow during freezing was discussed. In the analysis, a physical model of the pore structure change due to freeze−thaw was used. If the pore structure change occurred, which did not accompany the increase of porosity, considerably small amount of water was supplied to the freezing layer. However, if the increase of porosity was considered, upward water flux occurred which was large enough to increase volumetric water content. Moreover, it was revealed that the water flux positively correlates with freezing speed and with the amount of temperature fall.