Probable Origin of Laterally Coalesced Nabkas and Adjacent Bare Lanes at Dugway Proving Ground, Utah, USA

Abstract

ABSTRACT Unvegetated soil surface patterns 1 to 3 m wide, between 10 to over 1,000 m long, slightly curved to strongly sinuous, and usually parallel, were found to cover about 400 km2 in and near Dugway Proving Ground, western Utah, USA. In the only previously published reference to these features, they were called “desert ripples” and described as “small transverse clay dunes with intervening caliche troughs.” Contemporary world-wide literature reviews of banded vegetation and desert geomorphology indicates that “nabka” is the preferred label for the mounded features. The adjacent bare lanes are apparently unique. That previous article asserted that the combined features were caused by wind erosion. We proposed eight possible mechanisms for the creation and maintenance of these laterally coalesced nabkas and adjacent bare lanes and then investigated the physical, chemical, and biological character of them at small (cm to meters) and large (km) spatial scales. Significantly higher surface soil salinity was found in the lanes compared to either the adjacent mounds or internabka areas. The lanes are not usually concave and do not consistently run down slope or converge. They also are not underlain by petrocalcic layers. The associated mounds are not composed of clay, but are dominated by silt and not consistently on the down slope side. These pieces of evidence discount a sheet flood origin or being created by wave action of retreating ancient Lake Bonneville. Most of the evidence points to post-lake wind erosion as the force building and maintaining the mound-lane pattern. The mounds are thin deposits of silt over clay-dominated exposed lake bed. Variation in the morphology of these features can be explained by interaction with differing species and sizes of shrubs that grow in particular locations. Shrubs probably facilitate mound formation by enhancing wind turbulence. If shrubs become dense enough, individual shrub-centered mounds laterally coalesce, and sinuously linear lanes develop and become self-maintaining if the shrubs are not destroyed.