Snow bedforms: A review, new data, and a formation model

Abstract

Snow bedforms, like sand bedforms, consist of various shapes that form under the action of wind on mobile particles. Throughout a year, they can cover up to 11% of the Earth surface, concentrated toward the poles. These forms impact the local surface energy balance and the distribution of precipitation. Only a few studies have concentrated on their genesis. Their size ranges from 2 cm (ripple marks) to 2.5 m tall (whaleback dunes). We counted a total of seven forms that are widely recognized. Among them sastrugi, an erosional shape, is the most widespread. From laser scans, we compared scaling of snow versus sand barchan morphology. We found that both have proportionally the same footprint, but snow barchans are flatter. The key difference is that snow can sinter, immobilizing the bedform and creating an erodible material. Using a model, we investigated the effect of sintering on snow dune dynamics. We found that sintering limits their size because it progressively hardens the snow and requires an ever-increasing wind speed to maintain snow transport. From the literature and results from this model, we have reclassified snow bedforms based on two parameters: wind speed and snow surface conditions. The new data show that snow dune behavior mirrors that of sand dunes, with merging, calving, and collision. However, isolated snow barchans are rare, with most of the snow surfaces encountered in the field consisting of several superimposed bedforms formed sequentially during multiple weather events. Spatially variable snow properties and geometry can explain qualitatively these widespread compound snow surfaces.

Wind-packing of snow in Antarctica

“…The dune is about 25 m long, 11 m wide and 15-20 cm high. With these dimensions, the dune is rather large in the horizontal and average in the vertical compared to values reported in the literature Filhol and Sturm (2015). It is clear from Fig.…”

“…2B) of the dune. Zastrugi Filhol and Sturm (2015) are erosional surface features meaning that the dune has already been partly eroded again. The dune is about 25 m long, 11 m wide and 15-20 cm high.…”

Changes in snow distribution and surface topography following a snowstorm on Antarctic sea ice

“…At the same time, ridges and ice blocks serve as aerodynamic obstacles that modify wind transport over the surface and enhance deposition of drifting and blowing snow. Resultant dunes and drifts may extend for tens of meters across the ice floe, causing high spatial variability in snow depth over short spatial scales [Massom et al, 2001;Filhol and Sturm, 2015]. Snow transport processes modify the surface topography and hence affect the geometric roughness of sea ice, resulting in changes in the aerodynamic roughness of the surface [Sturm et al, 1998;Andreas and Claffey, 1995].…”

“…Similarities between snow and sand bedforms have long been recognized [Cornish, 1914], but received considerably less attention. The variety of snow dunes and bedforms observed, and mechanisms for genesis, have recently been reviewed by Filhol and Sturm [2015]. On sea ice depositional forms typically take the form of crescent-shaped barchans or whaleback dunes [e.g., Sturm and Massom, 2009].…”

Brief communication: Two well-marked cases of aerodynamic adjustment of sastrugi

“…For a given erosion threshold, the quantity of windborne snow increases with friction velocity according to a power law (Mann et al, 2000). As sastrugi mainly form through snow erosion/deposition processes (Filhol and Sturm, 2015), it is likely that under the strong wind (shear) conditions in Adélie Land, rougher snow surfaces develop, which have a greater aerodynamic adjustment ability than at the less windy Ice Station Weddell.…”