Variations of Italian glaciers between 1980 and 1999 inferred by the data supplied by the Italian Glaciological Committee

Abstract

The study synthesises the analysis of those data relevant to the variation registered in the Italian glaciers during glaciological surveys carried out by the Italian Glaciological Committee between 1980 and 1999. The last twenty years of the 20th century were characterized by a phase of general retreat of the glaciers, that followed an advancement phase that took place in the 70s and in the early 80s. The data matrix, which is largely incomplete, includes 335 glaciers. The percentages of advancing, stationary and retreating glaciers have been reckoned on the entire sample and on the single geographic sectors, mountain groups and glaciers having comparable aspects and size. Cumulative and yearly values of the front variations and of the terminus elevation changes have been quantified for those glaciers with at least 10 data out of 20. The percentage of advancing glaciers decreased from 66% in 1980 to 4% in 1999, while that of the retreating ones increased from 12% to 89%. These values changed quickly during the first decade, and then stabilized during the following one. The decrease in the number of advancing glaciers took place first in the Eastern Alps (Trentino-Alto Adige, Veneto and Friuli-Venezia Giulia: Triveneto Regions) and later in the Central (Lombardy) and Western (Piedmont-Aosta Valley) sectors. A similar trend has been also observed in the bigger glaciers and in those having a northern or southern exposure, while the smaller glaciers and those facing east and west have shown more irregular variations. The average annual variation per glacier was of – 4.8 m/year, for an average total variation per glacier of –95.4 m, during the twenty years considered. However, marked differences have been observed over the two decades, with stronger variations during the period between 1990 and 1999. The retreat phase was more marked in the Central sector (Lombardy), where the average total retreat of the fronts was of nearly 150 m. Modest variations (–44 m) occurred instead in the Western sector (Piedmont-Aosta Valley). The small glaciers had little annual average variations compared to the bigger ones, but greater, in proportion. The magnitude of the retreat was greater for those having an eastern and western exposure compared to the others. The minimum altitude of the glacier fronts raised 18 m on average. Marked variations (+38 m) were recorded in the Central (Lombardy) sector, while those in the Eastern sector were smaller (+12 m) and thosein the Western one marginal (+3 m).