I fenomeni franosi nel quadro geologico e geomorfologico della Conca di Cortina d'Ampezzo (Dolomiti, Italia)

Abstract

The paper shows the results of geological and geomorphological investigations recently carried out in the area of Cortina d'Ampezzo (Dolomites, Northern Italy). The study is part of European research projects aiming at the recognition and characterisation of mass movements. The stratigraphical and structural conditions of the study area greatly influenced slope evolution after the retreat of glaciers, favouring the development of large gravitational processes. The geological structure of the area is, in fact, characterised on the one hand by a repeated succession of pelitic rocks and dolomites and on the other hand by the wide presence of pelitic terms (even if largely covered by superficial deposits) in the lower part of the basin. Landslide deposits, which form most of the outcropping Quaternary deposits, have been grouped into "landslide units", in order to make easier the understanding of the complex slope evolution occurred since the Late-glacial period. A "landslide unit" has been defined in this paper as the association of landslide accumulations strictly connected in space and time: it can consist of a single main landslide and successive reactivations or of a superimposition of accumulations caused by repeated activations of a main scarp. The characteristics and distinctive aspects of landslide units are given. Several landslides have been radiocarbon dated. Age and borehole data contributed substantially to the reconstruction of the geomorphological evolution of the area. In particular, they have shown a number of landslides distributed in two main periods. The first ranges between 10,000 and 8,000 years B.P. when, after the retreat of the glaciers, rock walls no longer sustained by the ice masses became prone to landsliding, giving rise to several large-scale mass movements. These consist of rock slides and rock avalanches of considerable size detached from the steep rock walls surrounding Cortina d'Ampezzo. These events have left clear morphological evidence in the landscape, because of their magnitude and the characteristics of the rock masses involved (dolomites). The second period ranges between 5,000 and 4,000 years B.P. when smaller and slower landslides took place generally affecting the pelitic rocks of the lower part of the slopes. The concentration of landslides in this period is likely to be connected to the wetter climatic phase which occurred during the Upper Atlantic which made the slopes more prone to landsliding. At present the area of Cortina d'Ampezzo is still affected by active landslides which, owing to their potential risk for human activities, are monitored by means of automatic surveying systems.