The evolution of snow bedforms in the Colorado Front Range and the processes that shape them

When wind blows over dry snow, the snow surface self-organizes into bedforms such as dunes, ripples, snow waves, and sastrugi. These bedforms govern the interaction between wind, heat, and the snowpack, but thus far they have attracted few scientific studies. We present the first time-lapse documentation of snow bedform movement and evolution, as part of a series of detailed observations of snow bedform movement in the Colorado Front Range. We show examples of the movement of snow ripples, snow waves, barchan dunes, snow steps, and sastrugi. We also introduce a previously undocumented bedform: the stealth dune. These observations show that (1) snow dunes accelerate minute-by-minute in response to gusts, (2) sastrugi and snow steps present steep edges to the wind and migrate downwind as those edges erode, (3) snow waves and dunes deposit layers of cohesive snow in their wake, and (4) bedforms evolve along complex cyclic trajectories. These observations provide the basis for new conceptual models of bedform evolution, based on the relative fluxes of snowfall, aeolian transport, erosion, and snow sintering across and into the surface. We find that many snow bedforms are generated by complex interactions between these processes. The prototypical example is the snow wave, in which deposition, sintering, and erosion occur in transverse stripes across the snowscape.