Thermal anomaly in a cold scree slope (Creux du Van, Switzerland).

Abstract

Permafrost occurs on the scree slope of Creux du Van even if the mean annual air temperature is +5.5°C. A permanent frozen body is present only in the lower half and sunniest part of the slope. The main process leading to the strong thermal anomaly of the ground occurs during the cold winter periods. At that time, a direct relationship between the air temperature measured in a channel at the bottom of the talus slope and the air temperature outside indicates that air is aspirated into the ground allowing the overcooling of the interior of the scree. The talus slope acts like a chimney where natural advection occurs in winter due to air density contrast between cold and dense outside air and warm and light inside air. In summer, the chimney ef- fect is reverse and the permanent expiration of cold air prevents the vegetation from growing normally.