Geomorphometry of a Sorted Patterned Ground Field: Fluvial Processes and Cryoplanation Terrace Development

Abstract:

Large staircase-like erosional landforms known as cryoplanation terraces (CTs) are comprised of series of gently sloping treads bounded by steep ascending risers (scarps). These landforms are pervasive in unglaciated periglacial regions. The nivation hypothesis of CT formation holds that the stepped profiles are created by weathering and transportation processes associated with late-lying snow patches. Opponents of the nivation hypothesis point to the absence of rampart-like sediment accumulations on inner CT treads, a deduced result of sediment transport over the scarp face from the superjacent tread.

Periglacial sorted stripes, frequently encountered on CT treads, have recently been linked to the hydrologic connectivity of periglacial hillslopes, acting as preferential flow conduits for water and sediment moving through the interstitial spaces of clasts comprising the coarse portions of sorted stripes. Although fluvial activity within sorted stripes has been documented previously, no studies have considered these features in the context of CT development.

The research reported here addresses the absence-of-ramparts problem through geomorphometric analysis of a well-developed sorted-stripe field occupying a CT tread at an active periglacial site. Using a Digital Elevation Model (DEM), drainage channel identification via the D8 flow algorithm, and morphometric parameters, we demonstrate that the sorted stripe field has many characteristics of a drainage network. Results from the analysis, combined with field data, demonstrate the strong hydrologic connectivity of the sorted stripes. Morphometric parameters calculated from a stream detection raster were used to provide insight into a system of features that operates to evacuate water and sediment from late-lying snowpatches near CT scarp backwalls and over tread margins, thereby clarifying some of the problematic aspects of the nivation hypothesis and contributing to an improved understanding of CT formation.