L’evoluzione recente dei ghiacciai delle Alpi Marittime

The recent evolution of glaciers in the Maritime Alps

Abstract

There are six small glaciers and seven glaceriets in the Maritime Alps. They are among the southernmost in Europe and are the residue of more important pleistocene and holocene structures. They were the object of careful observation until the 1930's, but were then little studied. By means of a thorough bibliographical investigation and field studies in operation for several years the evolution of the glaciers during this last century has been reconstructed. Curves of frontal oscillation have been produced with an approximation imposed by the fact the data is not continuous with time. Therefore a general picture of glacier behavior has been produced on the basis of the common trends of the various curves. This has revealed that an important regressive phase influenced the glaciers in 1940, to the extent that several became exticnt whereas others were reduced to simple glaceriets. The glacial structures have shown different tendencies as regards withdrawal. The Clapier and Eastern Gelàs have shown the maximum reduction, up to 90% of their surfaces area in about a century, whereas the Peirabròc displays the minimum reduction of about 50%. Their behavior has been associated both with the morphological conditions of their environment and climatic conditions. As far as the Clapier is concerned it was discovered that the form of the relative cirque has been determinant in the conservation of the ice mass. This is in the sense that the reduction is less the nearer to 2 is the parametric value of the ratio between length and width of the cirque. Furthermore, proximity of the basin to the main mountain ridge is particularly significative, that is the area of maximum precipitation. The frontal oscillations of the glaciers were therefore related with climatic conditions, in particular with the of summer temperature and precipitation means, their regime and typology. It was seen that the temperature factor affects the trend of the oscillation curves only when there are variations of a certain extent in a short period of time. The extent of precipitation is influential when there is accumulation of a succession of years of abundant or scarce rainfall. A clear relationship shows between precipitation regime and behavior of the ice fronts, in the sense that a consecutive series of years with maximum summer precipitation between 1935 and 1942 was the start of the phase of real regression of the main glaciers. There was also an attempt to assess response times of these smaller glacial structures to climatic stimuli, times which in the current phase have been practically annulled. On the basis of the information collected a model of present glacier behavior was produced. This model foresees a marked inertia of the residual glacial masses, a zeroing of response times and a tendency toward a slow and continual reduction of volume. The extent of this phenomenon leads to the hypothesis that the current phase is a prelude to the complete extinction of the ice masses.