Contemporary Soil Wedge Formation in Western South Dakota
1971
White, E. M.
Subsoil wedges, ranging from narrow, dark-colored infusions of surface soil between prisms to V-shaped clay or light-colored sandy wedges more than 1 meter across, occur in some semiarid soils of western South Dakota. Light-colored wedges usually form in gravelly subsoils. A proposed explanation of how the wedges form is: (i) surface material falls downward into narrow subsoil desiccation cracks, (ii) in subsequent cycles of rewetting the dry soil, water drains more rapidly into the wedge than into the enclosing soils so the wedge swells first and closes the desiccation cracks in the adjacent dry soil, (iii) the wedge widens more at the top to form a V-shape because the moisture content changes frequently near the soil surface, and (iv) growth ceases when individual sand grains in the wedge are bridged by clay to form stable peds or the V-shape becomes sufficiently wide so water flows down along the inclined wedge boundary and wets and swells the enclosing soil as rapidly as the center of the wedge.
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