Geomorphology and structure : a new genetic model for some glacial cirques in the Western Orobic Alps (Southern Alps, Italy)

A geological, geomorphologic and structural detailed mapping (1:5000) has been carried out in twelve glacial cirques of the Western Orobic Alps (Southern Alps, Italy), in order to compare the influence of geological structures (e.g. bedding, foliations, folds, faults) and glacial action on the present-day morphologies. The intersection relationships between structures observed on the field have been integrated with meso-structural data through stereographic projections and kinematic evaluations to identify and order six deformation phases: three pre-Alpine and three Alpine, represented both by ductile and brittle structures. On the basis of the structural reconstruction the observed morphologies have been interpreted. This analysis has made possible to identify the close relationship between cirque structures and morphologies. Besides, qualitative evaluations concerning the actual glacier action in the area have been made. Therefore a possible genesis for these cirques can be suggested. At the beginning the hollows would have been produced by tectonic processes acting during the Alpine orogenesis. Then they would have been deepened by water erosion and gravity. Afterwards cirque glaciers would have grown up within these hollows. The action of the glaciers is likely to have simply been limited to the transport of the debris generated before. After the last glacial period the only active process would have been gravity.