Le variazioni frontali ed areali recenti del Ghiacciaio Grande di Verra (Monte Rosa, Alpi)

Snout and area recent variations of Grande di Verra Glacier (Monte Rosa, Alps)

Abstract

A study has been carried out about the snout and area recent (XX century) variations of Grande di Verra Glacier on Monte Rosa (Italian Alps) by using terminus variation data and historical maps. From 1914 to 2001 the front showed a retreat of 816 m, but the gaps in the data series make this result not too much accurate. By means of statistical analysis (correlations between the data of Verra Glacier and Lys Glacier) the gaps have been filled, even if the correlation coefficient resulted insufficiently accurate. It is anyway interesting to emphasize two short phases of snout advance between 1914 and 1921 (78 m) and between 1975 and 1985 (16 m). The GIS elaboration of the historical maps permitted calculating an area reduction of 31% from the Little Ice Age to nowadays. This reduction was rather irregular during the whole period: in fact, it resulted very strong from 1934 to 1956 (m² 21,103 mean yearly reduction), lower between 1975 and 1991 (m² 7.3·10²), while this process intensified between 1991 and 2002 (m² 24.5·10²). Moreover, some geomorphological evidences (moraines) of the last advance phase have been found near the actual glacier terminus. By elaborating the data of the monthly weather station of Lago Gabiet, an increase in precipitation between 1976 and 1979 of 244 mm (+44% with respect to the average 1928-1994) has been calculated; otherwise, a precipitation reduction of 16% between 1952 and 1964 has been detected. As regards the temperature variations, between 1973 and 1984 the summer temperature reduced by 1°C. The advance glacier phase of the second half of the XX century has been attributed to those climate variations.