Data issues in a moving environment: remote and in situ tools to monitor glacier dynamics and their hydrological consequences in the Austre Lovènbreen basin
Résumé
The precise quantification of glacier movements over time is one of the goals of glaciology. Understanding how and where ice is appearing, melting, and what happens once it’s gone are at the core of the Hydro - Se nsor - FlOWS program (IPY #16, IPEV 304, ANR 0310) that just ended and will be one of the aspects of the new Cryo - Sensors program. Obtaining a precise digital elevation model (DEM) of a glacier surface is not straightforward. When using old datasets, caution should be applied to the interpretation made of the results as the variability tends to increase. Recent monitoring techniques (DGPS, airborne Lidar) do provide a higher level of accuracy but still require a good knowledge of technology and its drawbacks, as well as field - specific issues (i.e. snow cover). Mass balance computations have been applied to Austre Lovénbreen using such techniques. When compared to ablation stakes measurements, results show striking differences, especially in accumulation areas. In areas where stakes do record accumulation, DEM differences account for ablation only. And the ablation measured using DEM seems greater than the vertical velocity of the glacier. Could it be possible that these two techniques do record processes occurr ing at the same time but at different scales? While stakes are measuring surface ice evolution only, DEM calculations are documenting the general trend of the glacier. It is possible that new ice is appearing in the upper cirques of the glacier while at th e scale of the basin, the glacier is in a global retreat trend. We are currently attempting to instrument the glacier in order to confirm our hypothesis and to quantify its extent. In an effort to precisely compute the volume of ice constituting today's gl acier, the surface DEM had to be complemented with a model of the bedrock on which the glacier is flowing. Ground Penetrating Radar (GPR) was used to get precise elevation values of the ice - rock interface. The difference between surface and bedrock DEM all owed us to evaluate the ice volume of the glacier. Bedrock DEM also gave us a unique view of underlying geomorphology and of its potential consequences on hydrology. The question of slopes and the dynamics of newly deglaciated areas will be approached in t he upcoming program. Slopes do account for 35% of the glacier basin area. Permafrost in the slopes and at the slopes/glacier interface are points of great interest and are not easy to monitor. Terrestrial Laser Scanning (TLS) techniques will be used to get a better understanding of processes occurring on the slopes (rockfall, rockslides, creeping). TLS will also provide data on snow accumulation on the slopes and therefore bring an insight on the importance of this term in the hydrological budget.