Figure 9. Enhanced Landsat Thematic Mapper (TM) principal components image developed by georegistering and processing data acquired on 12 August and 15 October 1985. Dark parabolic landforms adjacent to the South Platte River in northeastern Colorado are currently stabilized dunes found to have been mobile at least four times during the Holocene. The origin(s) of these unprecedented drought events are poorly understood (image from Overpeck, 1996, and courtesy of R. Yuhas and A. Goetz, Center for the Study of Earth from Space, University of Colorado at Boulder).