Variazioni di livello e volumetriche sulla Vedretta del Caresèr (Gruppo Ortles-Cevedale) tra il 1980 ed il 1990

Ice level and volume variations of the Careser Glacier (Ortles-Cevedale Group) between 1980 and 1990

Abstract

A new aerial survey was carried out in 1990 on the Caresèr Glacier, allowing comparison with the previous survey of 1980 and determination of the variations in ice level and volume during last ten years. This research was similar to the comparison made between the 1967 and 1980 surveys, with improved data processing methods and further verification of surface measurements regarding the annual mass balance of the glacier itself. Digital models of the glacier surface, obtained by analytical photrogrammetry for the 1980 situation and directly by restitution for 1990, provided two matrixes of altitude variations. The algebraic sum of the nodal values of a 50-m square grid produced a third matrix giving altitude variations between 1980 and 1990. The latter matrix was then used to calculate increases (net accumulation) and losses (net ablation), expressed as ice thicknesses and volumes for the entire surface. The same matrix was further exploited to provide a computerized thematice map with isolines representing level variations and completed by longitudinal and cross profiles of the glacier. Level variations between 1980 and 1990 turned out to be negative at all altitudes and a mean value of – 11,24 m, corresponding to a volume of – 54,2565 X 106 m3 was found. Comparisons with glaciological measurements on mass balance, in terms of water equivalent, were more than satisfactory: compared with a mean variation of – 10,17 m Weq obtained using photogrammetry, the mean balance for the ten year period was – 10,80 m Weq, the difference between the two methods being less than 6%. The above results agree with a phase of strong reduction of the glacier, partly at the expense of the accumulation area, where mass loss between 1980 and 1990 was 35% that verified for the entire glacial basin; in the same period the overall surface area was reduced by more than 20%.