Cold scree slope, sagging
Elevation: 1790-1900m - Massif: Grand-Combin - Commune: Bagnes (VS)
Ice was discovered during construction works of the road that leads to the alp of Moay. Several ground temperature sensors were installed in October 2004. They have shown that the ice discovered during the construction works was located in the lower part of a heavily fractured slope (sagging zone) subject to an internal ventilation mechanism, which is called chimney effect. The internal air flow direction is reversible. In this place, the air flow is directed downwards as long as outside air temperature remains above about + 3°C and upwards in the reverse case. As a result, the lower sections of the fractured zone stay permanently cold (measured mean annual ground temperature between 0 and -2 °C) and provide conditions for the existence of permafrost. On the contrary, some 100 meters higher up, in the upper section of the ventilated zone, ground temperatures remain relatively high throughout the year. The ground does not freeze and even some melt windows, which are permanently snow free, may be observed in places all the winter along were the heat evacuation due to the air circulation is the most intensive.
Measurements and observations
Geophysics (electrical resistivity, refraction seismic)
Thermal (ground surface temperature : GST, BTS)
Daily sub-surface temperature in the lower (bru-04) and upper (bru-05) sections of the ventilated terrain.
Mean annual sub-surface temperature in the lower (bru-03, bru-04) and upper (bru-05) sections of the ventilated terrain.
Morard, S., (2011). Effets de la circulation d'air par effet de cheminée dans l'évolution du régime thermique des éboulis froids de basse et moyenne altitude. PhD thesis, Fac. Sciences, Univ. Fribourg, GeoFocus 29. (pdf)
Morard S., Delaloye R., Lambiel C., (2010). Pluriannual thermal behavior of low elevation cold talus slopes (western Switzerland). Geographica Helvetica, 65/2, 124-134. (pdf)
Morard S., Delaloye R., Dorthe, J. (2008). Seasonal thermal regime of a mid-latitude ventilated debris accumulation.Proceedings of the Ninth International Conference on Permafrost, July 2008, Fairbanks, Alaska, 1233-1238. (pdf)