Le variazioni glaciali e climatiche durante l’ultimo secolo nei gruppi del Monte Bianco e del Monte Rosa

Glacial and climatic fluctuations during the last century in the Mont Blanc and Monte Rosa groups

Abstract

Although Mont Blanc and Monte Rosa rise at almost the same latitude, Mont Blanc rises where the Alpine chain bends, more or less leaving its southern direction and taking on a parallel trend, while Monte Rosa rises 80 km to the East, in the heart of the Pennine Alps. An examination of glacier fluctuations over the last 170 years shows that inversion phases are not contemporaneous in the two massifs. In Mont Blanc they always begin some years beforehand, and appear only 20 years later in Monte Rosa. The causes of this phenomenon must be sought in the altimetric fluctuations of the snow line on the two massifs and in the factors which determine it. This reveals a clear difference between the climate of Mont Blanc and Monte Rosa, mainly due to their different geographical positions: Mont Blanc lies directly in the path of the West wind from the Atlantic, rich in water vapor and with a relatively constant temperature. Instead, Monte Rosa is influenced by North and North-east winds of continental origin which bring both less precipitation and greater ranges in temperature. Consequently, although westerly winds bring climatic conditions favoring glacier formation on Mont Blanc, the same thing happens later on Monte Rosa, owing to the circulation of local winds which may contrast with general atmospheric circulation. An examination of the climatic parameters of meteorological stations working after 1936 in the Mont Blanc and Monte Rosa areas shows that glacier advance is preceded by an increase in precipitation and a fall in the 0°C July level, not more than 5 years from the beginning of snout advance. The delay in glacier fluctuations on Monte Rosa corresponds to a delay in the establishment of the climatic conditions responsible for the fluctuations themselves. In particular, it may be seen that the climatic phases leading to present expansion began on Mont Blanc during the 5-years period 1951-1955, while it took place on Monte Rosa only during the 5-year period 1971-75. This fact explains why the Monte Rosa glaciers remained in a regressive state until the middle of the 1970s, while those on Mont Blanc had already begun their expansion phase from 1954 onwards.