We used 10-Be to infer when, how fast and why the Susquehanna River incised through bedrock along the U.S. Atlantic seaboard, one of the world’s most prominent and ancient passive margins. Although the rate at which large rivers incise rock is a fundamental control on the development of landscapes, only a few studies have directly measured how quickly such incision occurs either in tectonically active environments or along passive margins.
Exposure ages of bedrock terraces along the lower Susquehanna River indicate that even passive margin rivers are capable of incising quickly through rock for short periods of time. Beginning ~36 ka and ending ~14 ka, coincident with the Late Wisconsinan glacial period, incision rates increased dramatically resulting in nearly 10 meters of channel bed lowering. It appears that changing climatic conditions during the late Pleistocene promoted an increase in the frequency and magnitude of flood events capable of exceeding thresholds for rock detachment and bedrock erosion, thus enabling a short-lived episode of rapid incision into rock.
Results from this study offer compelling evidence that episodes of river incision into bedrock are tied to glacial cycles and changes in global climate. These findings provide valuable insights into the nature of bedrock channel incision across a wide range of settings around the globe. Because such incision transmits the effects of changing climate and tectonics through fluvial networks to hillslopes, comprehending when, where and why rivers incise has important implications for the evolution of landscapes.
- Reusser, L., Bierman, P., Pavich, M., Zen, E., Larsen, J., and Finkel, R., 2004, Rapid Late Pleistocene Incision of Atlantic Passive-Margin River Gorges: Science Magazine, v. 305, p. 499-502
- Reusser, L., Bierman, P., Pavich, M., Butler, E., Larsen, J., and Finkel, R., 2003, Late Pleistocene Bedrock Channel Incision of the Lower Susquehanna River: Holtwood Gorge, PA in Mettitts, D., Walter, R., and de Wet, A.: Channeling Through Time: Landscape Evolution, Land Use Change, and Stream Restoration in the Lower Susquehanna Basin, SE Friends of the Pleistocene Guidebook, p. 41-45.
- Reusser, L., Bierman, P., Pavich, M., Larsen, J., and Finkel, R., (accepted), An Episode of Rapid Bedrock Channel Incision During the Last Glacial Cycle, Measured with 10-Be, American Journal of Science.