Recent (1975-2003) changes in the Miage debris-covered glacier tongue (Mont Blanc, Italy) from analysis of aerial photos and maps

Abstract

The present study aims at identifying any changes in volume and thickness of the Miage Glacier tongue (Mont Blanc Massif, Italy) during the period 1975-2003. The Miage glacier developed the largest part of its debris cover over the last century, now found mostly between the glacier terminus (about 1850 m a.s.l.) and the upper ablation tongue (c. 2400 m a.s.l.) on a surface area of c. 4 km². The period examined (1975-2003) addresses climate conditions which were glacier-favourable (around the 1980s), as well as glacier-unfavourable (since the early to mid-1990s), thus contributing to an understanding of the behaviour of debris covered glaciers under a changing climate. The analysis was based on the comparison between digital elevation models (DEMs), derived from historical records, specifically maps (1975; scale 1:10,000) and photogrammetric surveys (1991 and 2003, scale 1:15,000). The results show a general glacier volume loss (–16.640 x 106 m³) from 1975 to 2003; nevertheless if we focus on the two time sub-windows (i.e.: 1975-1991 and 1991-2003) opposite trends are found: in the period 1975-1991 the volume variation of the Miage Glacier was about +19.25x106 m³, in the period 1991-2003, on the other hand, a volume decrease of about –36.2x106 m³ occurred. Analysis shows that volume changes were strongly influenced by the supraglacial debris coverage which on Miage glacier tongue modulates the magnitude and rates of buried ice ablation.