Snow zonation on Hielo Patagónico Sur, Southern Patagonia, derived from Landsat 5 TM data

• Hielo Patagónico Sur (HPS), an icefield in Southern Patagonia, is the largest temperate ice mass in the southern hemisphere. Despite continued research efforts during the last decade many glaciological variables, especially mass balance, are still poorly known. This is partly because access to the icefield is difficult due to remoteness and persistent harsh weather conditions. Therefore, remote sensing appears to be a more suitable tool for the acquisition of data. In this work we present a remote sensing study of snow zonation on HPS using Landsat 5 Thematic Mapper data acquired on 12March 2001. By using image processing and classification techniques, proved to be useful in other glaciated regions, we map for the first time the extent and occurrence of major snow zones on the whole HPS. We separate between two classes of ice and three classes of snow. Ice facies are classified as bare or debris (i.e. dirt) covered ice, covering 2454 km2 and 777 km2 respectively, or 18.4% and 5.8% of the icefield on the day of image acquisition. Snow types are classifiedaccording to spectral differences in the images, following the glacier facies concept. Two of the three snow cover types are interpreted to represent differences in snow grain size within a fairly homogeneous snowpack whereas the third one is interpreted to represent the slush zone. A first order altitudinal control on the distribution of these snow facies is evident. In addition, our results show that snow accumulation on HPS is markedly controlled by the interaction of strong west–northwest snow-bearing winds and the roughmountainous terrain. In order of decreasing altitude we find that the two snow facies and the slush facies occupy 3819 km2, 3292km2 and2295 km2 respectively, or 28.6%, 24.6%and 17.2%of the icefield, on the day of image acquisition. Estimates of equilibrium line altitude using our results yield values of 800–900 m above sea level for the western side and 1500–1600 m above sea level for the eastern side, with an accumulation area ratio of 0.74.

Nyckelord

Patagonia

icefield

remote sensing

snow

classification

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