Combining sediment analysis and seismic refraction to describe the structure, thickness and distribution of periglacial slope deposits at Niwot Ridge, rocky mountains Front Range, Colorado, USA

In alpine and subalpine areas periglacial slope deposits (PSD) are a widespread component of the critical zone (CZ, upper subsurface) that controls and influences many processes of the biogeosphere. Measuring the thickness, layering, distribution and material properties of periglacial slope deposits that underlie ecological sensitive alpine areas poses major challenges for the analytical approach. Extensive pits and trenches may impact current hydrologic and biogeospheric processes or distort them for future research. The application of geophysical methods offers a possible solution. Application of shallow seismic refraction (SSR) to several hundred meters of 2D-sections and field studies show that alpine slopes in the vicinity of Niwot Ridge, Colorado Front Range (3450-3800 m a.s.l.) are underlain by layers of fine to coarse, blocky deposits of periglacial origin. In general, depth to bedrock ranges from 4 to 10 m and reaches maximum depths of over 15 m. Depth is not simply related to local slope. The structure of PSD shows both similarities and differences compared to the German PSD-scheme. The structure, distribution and thickness of lower heads at Niwot are equivalent to those of European studies. The upper head at Niwot Ridge is similar in composition to the ones described in European studies but shows differences in topographic distribution as it is restricted to lee positions at the American study area.