Thermally induced temporal strain variations in rock walls observed at subzero temperatures

It has been predicted theoretically that frost weathering may take place in rock material at subfreezing temperatures. These predictions have been confirmed in laboratory experiments. The importance of such frost weathering mechanisms in natural environments have, however, remained an unsettled question. We present and discuss in situ measurements of temperature and strain conducted within permafrost rock walls at 3600 m asl, in the Jungfraujoch-Aletsch region (Valais, Switzerland). From the spatio-temporal variations of the temperature field, the rate of freezing and thawing is estimated. We find both freeze and thaw processes in the rock walls at negative temperatures. In fact, both freezing and melting of ice as well as concomitant temporal changes in strain regime are observed in regions were the bedrock is subjected to permafrost conditions. The annual variations in rock temperatures correlate with the rock deformations. Extensions are observed during cooling and contractions during warming periods. Furthermore, the spatial variation in strain is affected, to some degree, by the presence of a mechanically active joint system.