How do rivers escape from mountain ranges?
The necessary and sufficient conditions for antecedent streams (i.e., those with routes that pre-date deformation and uplift) to maintain their courses over growing structures are increasingly better understood. However, many streams that exit from large orogens cross large structures but are not so easily classified as antecedent (e.g., the Colorado River on the Colorado Plateau). Furthermore, there is also abundant evidence that many fluvial systems that drain externally from mountain ranges formerly drained internally. This switch in behavior changes the ability of rivers to unload the lithosphere and thus affect its deformation, as well as may substantially change the stratigraphic architecture of internal and foreland basins. With Peter Sak (Dickinson College) and Eric Leonard (Colorado College), I am investigating the history of the Arkansas River in central Colorado in order to try to determine whether the integration of the upper Arkansas River Valley with the lower Arkansas River was driven by headward capture or if its former course (to the Rio Grande) was closed by faulting and it found its current course (onto the Great Plains) by filling and spilling out of its upper basin [Sak et al., 2006, GSA meeting]. How the evolution of the river relates to regional tectonics and climate change remains unknown.