Snow stratigraphy over a uniform depositional surface: spatial variability and measurement tools

Instrumentation and methods for measuring snow properties are compared in an investigation of millimeter- to meter-scale stratigraphy in a snowpack not influenced by topography, vegetation, or a warm and variable ground surface. Field measurements were conducted within a 20×20×2 m plot at Pika Glacier, Alaska. The snow was characterized by more than 600 point measurements of density, stratigraphic mapping in 19 snow-pits, and by pulse-radar imaging along 20 cross-plot profiles. Density was measured manually and was calculated from electric permittivity, which was determined with a hand-held probe and by radar velocity analysis. Stratigraphic mapping in snow-pit walls with manual measurements of density identified comparatively few layers, suggesting a relatively homogeneous snowpack. Both the permittivity probe and the radar imaging, however, identified a larger number of layers based on vertical density contrasts. Image analysis of a back-illuminated column of snow revealed the highest level of stratigraphic complexity, identifying layers mm in thickness that extended up to 10 cm laterally. Despite minor variations in snow properties at the mm scale, major features in the vertical density profiles were laterally continuous over tens of meters. These results provide evidence for spatial homogeneity of densification processes leading to decimeter scale layering in a situation where the snowpack is not influenced by local terrain factors. In addition, these observations demonstrate that the complexity of snow stratigraphy is highly dependent upon choice of scale and measurement tool.