LATE QUATERNARY SOIL DEVELOPMENT ENHANCES EOLIAN LANDFORM STABILITY, MOENKOPI PLATEAU, SOUTHERN COLORADO PLATEAU, USA

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, such as the mid Holocene climatic optimum, or historical reductions of vegetation cover by livestock grazing. We argue that this inactivity is not due any diminishment of driving forces in the eolian system (e.g. insufficient winds), but rather because of increased cohesion due to advanced soil development that enhances resistance to wind erosion.

Abundant eolian 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 because of 1) reduced sediment supply and 2) high dust flux which resulted in rapid soil formation (Reheis et al., 2005; Ellwein et al., 2015). 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 horizon development within the Qe1 mantle increased sediment cohesion and prevented widespread eolian reactivation during the Holocene, despite the occurrence of conditions (wind speed, climate, etc.) under which dune reactivation would be expected.

Drylands comprise >40% of the land cover of earth and climate models predict their expansion. Pedogenic stability is not explicitly considered in climate-based models used to predict eolian activity. To improve predictions of future dune activity in drylands, the degree of soil development in eolian deposits should be considered when evaluating sediment availability in eolian systems.