Volumetric variations of glacier de Sarennes, French Alps, during the last two centuries

The Glacier de Sarennes is located in the heart of the French Alps and has been observed closely since 1906 and regularly measured since 1948 (snow accumulation, ablation and mass balance). Several publications have stemmed from this research, such as the 1906 glaciological map, the 1958 one and the 1981 and 1991 photogrammetric analysis. In 1992, a field radar campaign determined the ice thickness and allowed the construction of the bedrock map with reasonable accuracy. The "little ice age" stage was reconstructed with the bed-rock tracks, in 1995. Above-mentioned documents were digitized and the computer programm Arc-Info permitted the calculation of the successive volume stages occupied by the glacier between 1850 and 1991. Cross sections and slope profiles illustrate the evolution of the thickness of the Glacier de Sarennes during the last hundred and fifty years. All of these results, consistent with the variation of the mass balance observed or restitued, show the main conclusion : compared with today's stage, the glacier was about 4 times more voluminous (loss of 3/4 of its ice volume) ninety years ago and 5 times bigger one and a half century ago in circa 1850. / Cet article présente le Glacier de Sarennes (France) dont le bilan de masse est mesuré depuis 1948. Chaque été, les paramètres glaciologiques caractéristiques sont mesurés à cinq stations représentatives du glacier, permettant de suivre l'accumulation hivernale, l'ablation estivale, le bilan de masse et le régime. L'ensemble de ces résultats est annuellement comparé avec ceux des années antérieures et avec les données météorologiques de la station de Grenoble. Grâce aux traces laissées par le glacier au siècle dernier, à la cartographie du Bedrock, aux cartes glaciologiques de 1906, 1958, 1981 et 1991 ainsi qu'aux diverses restitutions photogrammétriques, il a été possible de reconstituer en trois dimensions les phases du glacier