Continuous Recording of Frost Heave and Creep on a Japanese Alpine Slope

Abstract

Frost heave, creep, and ground temperatures were continuously monitored during the winter of 1990/91 in an alpine, seasonal frost environment of the Akaishi Range, Japan. The ground at the two measurement sites consists of a debris layer ca. 60 cm thick overlying shale bedrock. The upper 20 to 40 cm of the debris layer is fine-textured and frost susceptible. Surface heave and slope deformation were monitored with strain-gauge type sensors which, together with temperature sensors, were installed at different depths and were connected to data loggers that stored the readings at 1- or 3-h intervals. Though seasonal freezing penetrated deeper than 1 m during the winter, it caused only small heave (2 cm) at both sites. Thin debris layers would have allowed the frost table to penetrate to the bedrock before a large heave was generated. Short-term frost heave cycles took place frequently in autumn and spring (30 to 40 events per year), resulting in surface heave of up to 3 cm when the frost table penetrated deeper than 5 cm. Most of the short-term cycles accompanied downslope displacement of soils shallower than 6 cm, whereas occasional deep frost (>10 cm) caused deeper movements. These results indicate that short-term frost heave cycles lead to large frost creep on alpine fine debris slopes in Japan, despite their activity being confined to the upper 15 cm of soil.