Spatio-temporal measurements and analysis of snow depth in a rock face

Snow in rock faces plays a key role in the alpine environment for permafrost distribution, snow water storage or run off in spring. However, a detailed assessment of snow depths in steep rock walls has never been attempted. To understand snow distribution in rock walls a high-resolution terrestrial laser scanner (TLS), including a digital camera, was used to obtain snow depth (HS) data with a resolution of one metre. The mean HS, the snow covered area and their evolution in the rock face were compared to a neighbouring smoother catchment and a flat field station at similar elevation. Further we analyzed the patterns of HS distribution in the rock face after different periods and investigated the main factors contributing to them. In a first step we could show that with TLS reliable information on surface data of a steep rocky surface can be obtained. In comparison to the flatter sites in the vicinity, mean HS in the rock face was lower during the entire winter, but trends of snow depth changes were similar. We observed repeating accumulation and ablation patterns in the rock face, while maximum snow depth loss always occurred at those places with maximum snow depth gain. Further analysis of the main factors contributing to the snow depth distribution in the rock face revealed terrain-wind-interaction processes to be dominant. Processes related to slope angle seem to play a role, but no linear function of slope angle and snow depth was found. Further analyses should involve measurements in rock faces with other characteristics and higher temporal resolutions to be able to distinguish individual processes better. Additionally the relation of spatial and temporal distribution of snow depth to terrain-wind interactions should be tested.