The glacier retreat in Valle d’Aosta (Western Italian Alps) from the Little Ice Age to the second half of the 20th Century: linear, areal, volumetric and Equilibrium Line Altitude changes

Abstract

This research has taken into account the areal reduction and the changes of the Equilibrium Line Altitude of 143 glaciers located in Valle d’Aosta (Western Alps, Italy), from the maximum expansion phase of the Little Ice Age (LIA), which in the study area culminated in around 1820, to 1975, date of the aerial photographs used for the elaboration of the regional topographic maps. Investigations were carried out by means of field survey, photo-interpretation, analysis of maps and historical documents and use of Geographical Information Systems. Furthermore, the data concerning the frontal, areal and volumetric retreat of the glaciers at the heads of Valpelline and Valtournenche (Valle d’Aosta), during the same time interval, are discussed. The areal retreat of the 143 glaciers during the past 150 years has been around 41.5%; the glaciated surface has in fact decreased from 270.6 km² during the LIA to 158.4 km² in 1975. The mean Equilibrium Line Altitude (ELA) was equal to 2845±165 m during the LIA whereas the present one is 3015±197 m. The ELA has attained its lowest mean value in the glaciers of the Monte Bianco group (2702±117 m in the LIA and 2896±198 m in 1975), whereas the highest is found in the glaciers of Dent d’Herens – Mt. Cervino – Mt. Rosa mountain range (2903±170 m in the LIA and 3099±225 m in 1975). The mean ELA rise in Valle d’Aosta is equal to 139±106 m and to 129±96 m, if glaciers, which have undergone a frontal retreat without splitting up into several smaller glaciers, are only considered. The highest values of mean ELA rise correspond to the glaciers exposed to the south. As a first approximation, the mean annual value of temperature increase, deduced from the ELA rise, is 0.8 °C. As regards the upper Valpelline and upper Valtournenche glaciers, the values of frontal retreat are extremely variable in the glaciers investigated: from a minimum value of 400 m in the Solatset Glacier up to 3600 m in the Tsa de Tsan Glacier in Valpelline. The areal retreat has been 42.34%. Indeed, the upper Valpelline and upper Valtournenche glaciers have decreased from an overall extension of 34.91 km² in the LIA to 20.13 km² at present. During the same period the volumetric reduction has been 0.35 km³ of ice. This value, calculated in 17 glaciers, has been extrapolated to the whole range of the 143 glaciers studied, for which a total value of volume reduction of 2.66 km³ of ice was obtained.