Indagine glaciologica sulla Vedretta Alta e sulla Vedretta Occidentale di Ries (Alto Adige)

Glaciological investigation on the Vedretta Alta and Vedretta Occidentale di Ries (Alto Adige/South Tyrol)

Abstract

Two glaciers in the Alto Adige (South Tyrol) were studied, mainly from the glaciological point of view, from 1977 to 1979. They were the Vedretta Alta (Martello Valley) and the Vedretta Occidentale di Ries (Riva Valley) on the eastern and western sides respectively of the province of Bolzano. The two glaciers display fairly similar sizes and geographical features, allowing useful comparison of the research results. The fundamental core of the research was a two-year mass balance calculation. The balance was obtained by direct measurements taken on the surfaces of the two glaciers. The mass balance of the Vedretta Occidentale di Ries (2.5720 km²; 1979 survey) for hydrological year 1977-78 was positive, with a net accumulation of 1.6070 million m³ of water equivalent. In the following year (1978-79) records showed a practically nil balance, since gross ablation equalized gross accumulation. For the year 1977-78, the mass balance of the Vedretta Alta (1.7460 km²; 1978 survey) was positive and equal to a mass increase of 0.71 million m³ of water equivalent. In the following year (1978-79), mass balance was calculated on the basis of altitude variations over the entire surface during the whole year period. The parameters of this balance were net accumulation and net ablation only. The result for the year 1978-79 was a slightly negative mass balance, with a total loss of 0.3350 million m³ of water equivalent. Calculation of the balance of the Vedretta Alta for the ten-year span 1968-79 was also attempted, on the basis of a comparison between two different topographic surveys. The result showed an appreciable increase in the glacier mass: 11.6810 million m³ of water equivalent, corresponding to an average water depth of 6 690 mm. The profile of the surface variation was particularly interesting, revealing greater thickening in the ablation tongue, compared to the rest of the glacier. The behavior of the northern snout of the Vedretta Alta, observed during the two-year investigation period, displayed definite progression. Instead, the Vedretta Occidentale di Ries showed a tendency towards stability after a long period of considerable retreat.