Flowing, rolling, bouncing, sliding: Synopsis of basic mechanisms

Summary

According to the combined effects of various parameters the displacement of large masses by gravitation may assume different forms, each characterized by certain basic mechanisms. The present state of knowledge does not allow an exhaustive description of the conditions under which flowing, rolling, bouncing or sliding may be expected. This is one of the reasons for the obvious lack of accuracy in predicting the range threatened by an impending event. Catastrophes like those of Longarone and Yungay show the importance of sufficiently wellfounded mathematical models.

Such models have to be based on the fact that from all possible mechanisms the one with the smallest energy consumption has normally the best chance of being automatically selected.

In the course of the last decade, however, certain improvements have been obtained for the case of large landslides. In particular it could be shown that voluminous masses of rock are displaced in first instance by gliding and that self-lubrication effects are at least very probable. These effects are fundamentally different for primitive rock and carbonate, but in both cases they are due to frictional heat. The lubricant is fused material for primitive rock and a cushion of carbonic acid for carbonate. The results are backed both by field evidence and experimental simulation. In particular, an explanation is given for the hitherto enigmatic size effect (economy improving in function of volume).