“Structural grain” in landscapes and its relationship to large-scale slope deformations

Abstract

High relief is often endowed with a «structural grain» of topographic highs and lows obtained by selective erosion of tectonic and structural lineaments. Rock-mass fracture patterns exert a major influence on slope stability both at the surface and at various depths beneath it. This paper discusses some of the endogenous causes of deep-seated gravitational deformations and relates them to morphostructure and lithological weaknesses produced by tectonics. Using examples from peninsular Italy, it examines the structural and tectonic setting of deep (and associated shallow) slope movements on an anticline, at a mountain front, and on the rim of an overthrust syncline. All of the movements occur in sedimentary material of varied coherence and resistance to erosion. Lastly, a simple conceptual model is proposed to relate deep-seated gravitational deformations to shallow slope movements. It is concluded that morphotectonic conditions must often be studied before deep-seated slope movements can be understood, but the subtle interplay of forces between deep and shallow mass movements leads to an equifinality that complicates the explanation of both phenomena and obscures their relationship with crustal stresses.