| Résumé: |
Glacier advance and recession are considered as one of the key indicators of climate change by the Intergovernmental Panel on Climate Change (Houghton et al., 1996). Understanding the relationship between climatic variations and glacial responses is crucial. The main objective of this study is to use remote sensing methods to establish the advance and recession history of an unmonitored Alpine valley glacier, the Haut Glacier d’Arolla, in Switzerland, at three different time scales: decadal, seasonal and daily. At the decadal scale, the purpose is to apply archival digital photogrammetry to this glacier with no established advance/retreat history and to use the data generated to explore the linkages between glacier recession and climate forcing. The key question is whether or not archival photogrammetric methods can be used to reconstruct glacial history. At the seasonal and daily scales, the purpose is to show how repeat measurement of a glacier surface using the new generation of laser scanners can be used to study glacier surface ablation and other elements of glacial hydrodynamics. The key question is over what timescale can meaningful results be obtained using an ultra long range LiDAR RIEGL VZ-6000 scanner specifically designed for measurement of snow and ice cover surfaces.
Results from the use of Digital Elevation Models (DEMs) to perform surface and volume changes with high precision show continual recession of the glacier since 1967, associated with long-term climatic amelioration but only a weak response to shorter-term climatic deterioration within this trend. Glacier surface velocity estimates obtained using surface particle tracking showed that, unlike for most Swiss glaciers, ice mass flux from the accumulation zone was too low to compensate for the effects of glacier thinning and subsequent snout recession. At the seasonal and daily scales, the LiDAR was confirmed to be exceptionally powerful as a potential tool for ablation studies. It was shown that spatial variation in seasonal melt was controlled by both aspect and differential debris cover. The daily scale showed the effect of ogive-related debris cover on melt patterns and also revealed possible hydraulic jacking of the glacier snout associated with short term water pressure rises. This latter demonstration brings out how LiDAR may revolutionise cryosphere studies and points to a series of new and important research questions. |
Mémoire [4.1 Mo]