Evolution of Loess Tablelands in the Central Great Plains: Relief Generation by Loess Accumulation and the Importance of Closed Depressions

Abstract Loess tablelands, plateau‐like landforms built of wind‐blown dust, store large volumes of sediment on its path from bedrock sources to sedimentary basins. Long‐term storage of organic carbon also occurs in buried soils beneath loess tableland summits. The evolution of loess tablelands can be conceptualized as a process of relief generation through loess accumulation, raising tableland summits above local base level, followed by stream dissection driven by the increased local relief. We investigated how these landforms of highly erodible material have persisted over 10,000–100,000 years timescales in the central Great Plains, USA, using stratigraphic data, field measurements of soil strength, geospatial analysis, and numerical modeling. Where subsurface data are adequate, it appears that loess tablelands developed on pre‐existing bedrock tablelands. The presence of many closed depressions on tableland summits is the key factor limiting the rate of tableland dissection, rather than an erosion‐resistant cap as in bedrock tablelands. These depressions capture most runoff on tableland summits, limiting the drainage area of channels eroding the steep tableland margins. Numerical modeling of loess tableland evolution with the Landlab toolkit produces tablelands similar to those of our study area; tableland summits with many closed depressions persisted substantially longer than those without depressions. Modeling also indicates that depression‐breaching by gullies is an important process in tableland dissection, and there is clear evidence of this process in tablelands of our study area.