Volume decrease of Rutor Glacier (Western Italian Alps) since Little Ice Age: a quantitative approach combining GPR, GPS and cartography

The results of a dGPS assisted Ground Penetrating Radar survey made on Rutor Glacier (Aosta Valley, Italy) are discussed in this paper. The aim of the survey was to quantify the ice thickness and estimate the total glacier volume. The upper part of the basin was surveyed in 1996; in July 2006 this survey was completed in the lower part too. After the interpretation of the radar signals a model of the ice-bedrock interface was produced. The glacier volume in different periods between Little Ice Age (LIA) and present days was estimated by difference between the bedrock model and three surface models previously generated. This allowed not only to analyse the ice volume melt in a time interval but also the percentage it represents on the whole glacier volume. The dGPS data were used both to georeference the radar tracks and to measure the ablation rate, by comparing them with former surface data. Furthermore, the dGPS tracks are intended to be the first step of a periodic series of measures for a geodetic mass balance evaluation. By comparing glacier surface reconstructions obtained with different techniques and bedrock data, an ice volume loss of about 500 Millions of m3 from LIA to 1975 was calculated, which represents a volume reduction of about 60%. From 1975 to present days another 50% of the remaining volume got lost. This resulted in a volume reduction rate of –0,5%yr–1 from the Little Ice Age maximum to 1975, a value of –1,1%yr–1 between 1975 and 1991 and a volume reduction rate of –2,1%yr–1 up to 2006