Remarkable Snow Structure Observed   

Snow has a habit of continually amazing observant winter travelers, and adding dust to the dynamic nature of snowpack surface processes in the San Juan Mountains, known for their continental, radiation snow climate, only amplifies the magic.  In late April, 2008, we observed the short-lived, multi-dimensional snow surface structure seen here, instigated largely by dust in the snow.  Notice that there are two distinct surface patterns, one representing ‘runnel ridging’ and caused by free water percolation along the fall line of the slope, and the other, a closely-spaced fin structure, running across the axis of the runneling.  These features are similar to, but perhaps also different from, the initial development of ‘penitentes’ in the snow surface, as are routinely observed in some snow climates, and these patterns were eventually entirely lost to diurnal melt-freeze cycles and evolved into a smooth ‘corn snow’ surface.

This closer view of the fin structure shows that there was an additional vertical pattern present within the fins, perhaps representing ice layers formed by diurnal wetting fronts.  Close inspection of the crystals within these fins revealed very fresh, ‘crisp’, and advanced faceted features growing directly off of thawing polycrystals, but with no common orientation – they seemed to be responding to extremely local and large vapor pressure gradients within the structure of the fins and adjoining ‘gaps’ between fins, irrespective of up or down.  In one extraordinarily spectacular ‘void’, pristine examples of capped column crystals were observed, apparently formed when the conditions in that pore space within the melt-freeze dominated snow structure mimicked cloud conditions that would produce a capped column precipitation particle.  Wow!