CONTROLS ON GULLY CUT AND FILL CYCLES IN THE LOESS CANYONS OF NORTHWESTERN KANSAS

In northern Cheyenne County, Kansas, gullies are carving canyons over 100m deep and expanding into the wheat-producing loess plateau. The northern fringe of the county, known regionally as the Breaks, exhibits striking examples of Holocene erosion where the canyons drain north into the Republican River of Nebraska. To the south of the Breaks though, canyons draining southeast into the South Fork Republican River show less severe topography that may indicate a younger stage of gully development. The goals of this research are to document the rate and magnitude of landscape change in the loess canyons of the Breaks and South Fork regions through time and to provide an analysis of the dominant forces driving the cycles of gully advance and healing. The three canyons in the South Fork region chosen for study - Hells, Arnold Harvey, and Heinzelman - are similar in size and orientation but differ in bedrock geology. Based on current literature, synchronous evolution should indicate the dominance of external factors such as climatic cycles or base-level changes, while dissimilar evolution may result from variations in bedrock geology and hydrology. The model of landscape change developed in the three canyons of the South Fork region is being compared to Hay and Carol Canyons in the Breaks in order to expand the applicability of the model into the central Great Plains. Land surveying along the main canyon axes and at key cross-valley segments reveal gully knickpoints and valley gradients as well as serve to identify terrace surfaces from previous valley fills. Multi-parameter stratigraphic investigation of sediment packages within the canyons yield much of the data to be used for reconstructing the chronology of cut and fill events. Within the historical period, aerial photography and local testimony augment stratigraphic data. Investigations in the region indicate evidence of middle- and late Holocene, as well as historic, episodic gully expansion.