Late Quaternary Soil Development Enhances Aeolian Landform Stability, Moenkopi Plateau, Southern Colorado Plateau, USA

Amy Ellwein,Shannon Mahan,Joseph McAuliffe,Leslie McFadden

doi:10.3390/geosciences8050146

Abstract

The Moenkopi dune field in northeastern Arizona covers roughly 1250 km2, but most of the field is inactive. Dune deposits on the Moenkopi Plateau (MP) have remained inactive throughout the Holocene despite periods of elevated aridity or historical reductions of vegetation cover by livestock grazing. We argue that this inactivity is not because of any diminishment of driving forces in the aeolian system (e.g., insufficient winds), but rather because of increased cohesion due to soil development that enhances resistance to wind erosion. Abundant aeolian sediments were supplied to the Black Mesa region by the Little Colorado River and its tributaries during the late Pleistocene (MIS 2 and 3), which enabled the development of climbing dunes and transport of sand over the Adeii Eechii Cliffs and onto the MP. These deposits (Qe1) stabilized during the Pleistocene/Holocene climatic transition (~12–7.5 ka) because of reduced sediment supply and high dust flux which resulted in rapid soil formation. Erosion of climbing dunes/sand ramps from the Adeii Eechii Cliffs eliminated delivery of large quantities of new sand to the MP during the mid to late Holocene. Soil development within the Qe1 mantle increased sediment cohesion and prevented widespread aeolian reactivation during the Holocene, despite the occurrence of conditions (wind speed, climate, etc.) under which dune reactivation would be expected. Drylands comprise roughly 40% of the land cover of earth and climate models predict their expansion. Pedogenic stability is not commonly considered in climate-based models used to predict aeolian activity. To improve predictions of future dune activity in drylands, the degree of soil development in aeolian deposits should be considered when evaluating sediment availability in aeolian systems.

Highlights

Aeolian deposits are ubiquitous on the southern Colorado Plateau [1,2,3] and strongly influence landscape evolution (e.g., [3,4,5])
These sand sheets locally contain a wide variety of active aeolian landforms, such as barchan and parabolic dunes, small climbing and falling dunes, and complex dune forms that exhibit characteristics of more than one aeolian landform
The other mapped aeolian unit in this landscape position, bedrock-adjacent dunes, exhibits very little spectral contrast between bedrock and aeolian landforms; aeolian landforms are clearly identifiable in the 1 m digital orthophoto quadrangles (DOQs) mosaic

Summary

Introduction

Aeolian deposits are ubiquitous on the southern Colorado Plateau [1,2,3] and strongly influence landscape evolution (e.g., [3,4,5]). Decreased effective moisture produced either through increased temperature and/or reduced precipitation is predicted to destabilize vegetative cover on currently stable dunes and cause reactivation of the many North American dune fields, such as those in the Great Plains (e.g., [7,8,9,10,11]) and even high-latitude dunes on Geosciences 2018, 8, 146; doi:10.3390/geosciences8050146 www.mdpi.com/journal/geosciences. Geosciences 2018, 8, 146 vegetative cover on currently stable dunes and cause reactivation of the many North American dune fields, such as those in the Great Plains e.g., [8,9,10,11,12] and even high-latitude dunes on the Canadian prairies[12,13]. American dune fields, such as those in the Great Plains e.g., [8,9,10,11,12] and even high-latitude dunes on the Canadian prairies[12,13]. [13,14].But

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