Fifty Years of Glacial Variations and Climate Evolution on the Mont Blanc Massif

Abstract

On the Italian side of Mont Blanc in 1975 still four valley glaciers (Miage, Lex Blanche, Brenva and Prè-de-Bard glaciers) flowed downvalley reaching the bottom of Veny and Ferret valleys. Nowadays, Miage only can still be considered a valley glacier, while Lex Blanche and Brenva became cirque glaciers. Prè-de-Bard glacier shows a narrow tongue. The morphological variations of the glaciers of the southern side of Mont Blanc are not limited to the detachment of the valley tongue from the upper part, but also concern the separation of different ice flows in the high-altitude basins. Glaciers morphology is altered, thus resulting in the formation of new small glaciers totally independent from the original basins of which they were part of in the past. Starting from these considerations, morphological transformations of the Lex Blanche, Miage, Brenva and Frebouzie glaciers are discussed in this paper. An analysis of the climatic evolution is also carried out, on the basis of data collected by the Gran S. Bernardo weather station. The temperature increase, that intensified after 1986, also caused a rise of about 250 m in the climatic limit of snowline, thus causing the loss, for the Mont Blanc glaciers, of about 50% of their accumulation area, as shown by the aerophotogrammetry of 1975.