rotational slip

The semi-circular motion of a mass of rock and/or soil as it moves downslope along a concave face. Evidence for rotational slip in cirques comes from the dirt bands observed in cirque ice, which become progressively steeper from the back wall, but then flatten towards the cirque mouth. The basic mechanism for rotational slip would seem to be the imbalance between accumulation at the head of the glacier and ablation at the snout, which steepens the gradient of the glacier.