Morphological Development of Dunes in a Subarctic Environment, Central Kobuk Valley, Northwestern Alaska

Abstract

Widespread eolian sand deposits occur in the central Kobuk Valley in northwestern Alaska. Major dune development in this valley was synchronous with the onset of the last glacial advance about 24 000 years B.R and reflects an abundant supply of sandy sediments derived from glacial erosion and fluvial redeposition.The morphology of the dune fields is described by airphoto interpretation supplemented by field observations. The largest active dune field (the Great Kobuk Sand Dunes) is characterized by large transverse and barchanoid dune ridges, and flat interdune areas, representing a dry eolian environment with abundant sand supply. However, in the eastern part of the study area complex, elongated, parabolic dunes as well as eolian sand sheets represent a moist eolian phase in a mainly vegetated area. These dunes are largely stabilized and very uniformly orientated WNW-ESE. Dune forms indicate that both present-day and former wind directions are parallel to the valley axis. Due to the opposite bimodal wind regime parabolic dune heads have developed in two opposite directions, giving rise to the rare phenomenon of hairpin' dunes converging at both ends of the blowouts. These forms are called ‘canoe-shaped blowout dunes’. It is concluded that specific dune forms characteristic for periglacial and/or permafrost conditions are unknown.