Notch Formation Due to Freeze-Thaw Action in the North-facing Valley Cliff of the Asama Volcano Region, Japan

There are notches at the base of vertical cliffs located at the foot of Asama Volcano, Japan. In the north-facing cliff, frost weathering is frequently observed on the notch surface in winter. Mean air temperature is below freezing point in winter. There are many fine days in winter, but the sunshine cannot hit the northfacing cliff due to its orientation. These conditions gradually cool the notch zone and make a frozen layer which grows parallel to the notch surface. The maximum frost penetration depth is estimated to be 20 to 30 cm in one winter season. Exfoliation occurs in spring due to thawing at the boundary between frozen and unfrozen layer. It may be inferred that the repetition of freeze-thaw cycles for several years gradually decrease the strength of the cliff materials and resulting fatigue failure induces the exfoliation.