Soil moisture variability in relation to diurnal frost heaving on Japanese high mountain slopes

Frost heave, ground temperature and moisture were concurrently monitored on two alpine slopes with thin debris mantles. Electrical sensors connected to data loggers permitted automated monitoring of the three variables. Diurnal frost heave of up to 3 cm frequently took place during spring and autumn. Soil moisture contents are regarded as the primary control on the amount of frost heave, while the intensity of freezing is secondary. Heave was usually greatest just after a major rainstorm that produced high moisture contents in the near-surface soil, and decreased with soil desiccation. Rainstorms often interrupted the desiccation process and reactivated frost heaving. Despite reaching a depth of 1 m or more, seasonal frost penetration caused only small amounts to heave, because the lower part of the seasonally frozen layer was not frost-susceptible. These observations imply that the thin debris mantle and periodic precipitation during periods of freeze-thaw combine to result in the predominance of shallow frost creep, which is typical of soil movements in Japanese high mountains.