Rock Jointing and Abrasion forms on Roches Moutonnées , SW Finland

Abstract

The influence of bedrock structures, especially joints, on the formation of roches moutonnées and different glacial abrasion forms on roches moutonnées were studied in the southwest archipelago of Finland.The size and form of roches moutonnées are closely connected with the frequency and state of joints in the bedrock. The fewer and smaller the joints are, the larger are the roches moutonnées that can be formed. Vertical joints in the direction of the ice movement form the weakest zones and determine the width of the roches moutonnées . Joints dipping against glacial movement determine the dip of the eroded rock surface. Horizontal joints provide a suitable base for large and gently-dipping roches moutonnées , which are normally lower than others with less frequent horizontal joints. Striae, friction cracks, facets, fracture lines, and plucked surfaces, and their positions on the surfaces of roches moutonnées , were observed. On the basis of these observations, a stereographic model of the distribution of different abrasion features on the surfaces of roches moutonnées was produced.