River valleys come in many different shapes and sizes, from the narrow gorges of Utah’s canyon country to the broad coastal plains of Texas. These valleys form as rivers erode Earth’s surface, and their shapes alone result from the interplay of local geology and global forces. Geologists have long sought to use valley shapes alone to reconstruct past changes in climate and tectonics on Earth and on other planets, but Limaye and Lamb provide new evidence that the importance of local geology should not be overlooked.
The researchers used a simple numerical model to explore the influence of river erosion on valley shape in the absence of major climate or tectonic shifts. They considered the pace at which a river erodes through sediment and bedrock laterally and vertically and the initial distribution of both materials in the vicinity of the channel. They found that as rivers erode bedrock and deposit sediment, these bank materials help steer future patterns of channel migration, producing a wide range of valley morphologies.
The new results reveal that many types of river valleys—even deeply entrenched channels—can form under steady erosion rates and do not require rapid pulses of river downcutting due to uplift or sea level changes, as previously thought. The authors also found that when an abrupt geologic event does trigger rapid downcutting, it may not always leave a lasting imprint on valley morphology because subsequent erosion can wipe out the evidence.
All of these conclusions suggest that the intrinsic patterns of river migration, which can be influenced by the surrounding bank materials, should be considered when interpreting climate and tectonic histories from river valleys. (Journal of Geophysical Research: Earth’s Surface, doi:10.1002/2013JF002997, 2014)
—Julia Rosen, Freelance Writer
Citation: Rosen, J. (2015), Bank materials strongly influence river valley evolution, Eos, 96, doi:10.1029/2015EO023943. Published on 13 February 2015.