QGG MARIE MORISAWA AWARD: SEARCHING FOR UPLIFT ALONG THE SHOSHONE RIVER TRANSECT ACROSS THE LEADING EDGE OF THE YELLOWSTONE HOTSPOT

The Yellowstone hotspot has been deforming the western U.S. lithosphere for millions of years, driving uplift at its leading edge, but there are few measurements from the geomorphic record to verify geodynamic models. As the North American lithosphere approached its current position over the hotspot, shifts in late-Cenozoic climate are also thought to have increased river erosion throughout the Rocky Mountain region. Despite J.H. Mackin’s seminal 1937 work recording tilted Shoshone River terraces, the roles that uplift and Quaternary climate each play in landscape evolution around the Yellowstone hotspot have yet to be resolved due to a lack of geochronology in regional studies. The purpose of this research is to correlate and luminescence-date Shoshone River terraces in longitudinal profile and explore landscape steepness to test for patterns that reflect either uplift on the leading edge of the hotspot or Quaternary climate as a primary driver of erosion. Hypothetically, channel steepness should be anomalously high in the Shoshone headwaters due to tilting. Terrain analysis indicates there are few knickpoints, and that regions of high normalized channel steepness (k_sn) in the upper drainages primarily corresponds to bedrock variability. Reach-averaged k_sn and chi values along the mainstem Shoshone are nearly constant along the entire river, with one steeper section formed by the Rattlesnake Canyon knickzone which we interpret to be caused by bedrock. Terrace mapping, surveying, and luminescence results will fill knowledge gaps, identify spatial and temporal river erosion patterns, and provide quantitative constraints on Yellowstone hotspot uplift.