Thermal regime of sporadic permafrost in a block slope on Mt. Nishi-Nupukaushinupuri, Hokkaido Island, Northern Japan

In this study, we discuss the predominant factors that determine the ground temperature regime of an active layer in a block slope. The distribution of the bottom temperature of snow cover (BTS) measurements, warm funnels at the top of the slope, and ground temperature changes on the block slope indicate continuous air circulation during the winter. In the spring, snowmelt water flows to the valley bottom and refreezes, adding superimposed ice onto the perennial ice that fills the voids between coarse blocks. At the study site, the ground temperatures showed a simultaneous, abrupt increase at all depths in the active layer. These results strongly suggest that air circulation in winter, as well as the ice formation processes in the spring, control the thermal regime of the active layer of the block slope with mean annual air temperature (MAAT) above 0 °C.