Slope Movements Related to Expansive Soils on the Blackland Prairie, North Central Texas

When the subject of slope movement is discussed, geomorphologists rarely consider regions such as the Blackland prairie as problem areas. This is unfortunate because, owing to a combination of wet-dry climatic cycles and the presence of highly expansive montmorillonite clay soils, movements even on very gentle slopes are responsible for considerable damage and destruction to property. Slope movements related to expansive soils are generally of two types: (a) those from soil creep and (b) rotational slides. Soil creep is due to the shrinking and swelling of the clay soils with seasonal moisture changes. Rotational slides are noticeable particularly along oversteepened road cuts, although they also occur on natural slopes. Two aspects of the clay soils help contribute to the formation of rotational slides: (a) the formation of large desiccation cracks provides easy access of surface waters to the soil, where they are adsorbed and help overload slope; and (b) the desiccation cracks often form what eventually becomes the head of the rotational slip surface.