To find the mechanism of avalanches, the ground temperatures down to the depth S. Mwere measured by a self-registering electric resistance thermometer at a slope near Itayastation along Ou-line from January to March in 1948. Under snow the temperature of the ground surface rewained 0°C all through this interrol and those below the surface decreased steadily. Theoretical explanations are given and the thermal effect of a rod, to which the thermo-elements of the thermometer are fastened is discussed theoretically.