HISTORIC PATTERNS OF DUNE INSTABILITY IN THE CIMARRON NATIONAL GRASSLANDS, SOUTHWESTERN KANSAS

Dramatic historic landscape change has occurred in the Cimarron River valley of southwestern Kansas as a result of both climatic variability and land-use change. The Dust Bowl of the 1930s, for example, produced widespread instability in the sand dunes, expressed as blowouts, dune migration and dune reformulation. Cimarron National Grasslands serves as an ideal study area due to data availability and to the minimization of human impact in the post 1930’s era, while adjacent privately managed areas serve as a comparative database. To document the temporal and spatial patterns of change, a GIS database was constructed to consist of historic GLO survey records (1887), rectified black and white aerial photography from 1939, 1942, 1953, 1960, and 1986, and digital orthophoto quarter quads from 1991 and 2002. Further, anecdotal ground-based, repeat photography provides qualitative site-specific impressions of change. During database development, dune forms were classified and directional components recorded, and, for each time window, areas of dune instability were classified, digitized, and spatially characterized. Further, changes in the nature of the Cimarron River channel and alluvial bottoms were documented, as was the zone of interaction between the active channel and adjacent dune fields. Most common sand forms are parabolic dunes, some of which appear to date to the Last Glacial Maximum, linear dunes of yet unknown age, and compound and complex dunes. The dramatic increase in instability during the Dust Bowl and subsequent stabilization to the present are quantified, as are less pronounced patterns in dune instability. Since the early 1900s, the Cimarron River channel has been reduced to a mere vestige of the presettlement expression due primarily to groundwater mining for irrigation and to upstream reservoir construction. Prehistoric context is provided by radiocarbon ages on alluvial soils beneath the dune field: terrace treads apparently have been mantled by sand from before 10ka to 5 ka.