Snow in a Very Steep Rock Face: Accumulation and Redistribution During and After a Snowfall Event

Christian G Sommer,Rebecca Mott,Michael Lehning

doi:10.3389/feart.2015.00073

Christian G Sommer, Rebecca Mott + Show 1 more

Open Access

https://doi.org/10.3389/feart.2015.00073

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Abstract

Terrestrial laser scanning was used to measure snow thickness changes (perpendicular to the surface) in a rock face. The aim was to investigate the accumulation and redistribution of snow in extremely steep terrain (>60°). The north-east face of the Chlein Schiahorn in the region of Davos in eastern Switzerland was scanned before and several times after a snowfall event. A summer scan without snow was acquired to calculate the total snow thickness. An improved postprocessing procedure is introduced. The data quality could be increased by using snow thickness instead of snow depth (measured vertically) and by consistently applying Multi Station Adjustment to improve the registration. More snow was deposited in the flatter, smoother areas of the rock face. The spatial variability of the snow thickness change was high. The spatial patterns of the total snow thickness were similar to those of the snow thickness change. The correlation coefficient between them was 0.86. The fresh snow was partly redistributed from extremely steep to flatter terrain, presumably mostly through avalanching. The redistribution started during the snowfall and ended several days later. Snow was able to accumulate permanently at every slope angle. The amount of snow in extremely steep terrain was limited but not negligible. Areas steeper than 60° received 15% of the snowfall and contained 10% of the total amount of snow.

Highlights

Snow in rock faces influences the occurrence of permafrost and affects the stability of steep slopes and rockfall danger (Gruber et al, 2004; Luetschg et al, 2008; Haberkorn et al, 2015)
The subareas were compared in terms of winter slope angle, snow thickness change during the snowfall event ( DS) between 21 and 25 March and snow thickness (DS) on 25 March (Figure 4)
The two ranges overlap for the most part but the slope angles are significantly higher in the “steep/rough” areas than in the “snowfields.” DS and DS were highest in the “slope toe,” lowest in the “steep/rough” areas and reached intermediate values in the “snowfields” (Figures 4B,C)

Summary

Introduction

Snow in rock faces influences the occurrence of permafrost and affects the stability of steep slopes and rockfall danger (Gruber et al, 2004; Luetschg et al, 2008; Haberkorn et al, 2015). Snow in very steep slopes is important for avalanche danger forecasting because snow avalanches often form in steep terrain interspersed with rock (Schweizer et al, 2003) and it contributes to runoff in spring (Anderton et al, 2002; Lehning et al, 2006). Blöschl and Kirnbauer (1992) observed that snow covered area (SCA) decreased with increasing slope angle and that terrain steeper than 60◦ was usually snow-free due to gravitational effects (avalanching) and wind. Many studies suggest that the amount of snow is inversely proportional to the slope angle and that no snow accumulates (permanently) above a certain critical angle. Blöschl and Kirnbauer (1992) observed that snow covered area (SCA) decreased with increasing slope angle and that terrain steeper than 60◦ was usually snow-free due to gravitational effects (avalanching) and wind. Winstral et al (2002) and Gruber Schmid and Sardemann (2003) assumed that slopes steeper than

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