Landscape instability in an experimental drainage basin

Do drainage basins develop static river networks when subject to steady for cing? While current landscape evolution models differ in formulation and im plementation, they have the common characteristic that when run for long ti mes at constant forcing, they evolve to a static steady-state configuration in which erosion everywhere balances uplift rate. This results in temporal ly stationary ridge and valley networks. We have constructed a physical mod el of a drainage basin in which we can impose constant rainfall and uplift conditions. The model landscapes never become static, and they are not sens itive to initial surface conditions. Ridges migrate laterally, change lengt h, and undergo topographic inversion (streams occupy former ridge locations ). Lateral stream migration can also produce strath terraces. This occurs w ithout any change in external forcing, so the terraces must be considered a utocyclic. The experimental drainage basin also exhibits autocyclic (intern ally generated) oscillations in erosion rate over a variety of time scales, despite constant forcing. The experimental landforms are clearly not perfe ct analogs of natural erosional networks, but the results raise the possibi lity that natural systems may be more dynamic than the current models would suggest, and that features like strath terraces that are generally interpr eted in terms of external forcing may arise autocyclically as well.