Evaluating Uplift at the Leading Edge of the Yellowstone Hotspot - A Study of the Shoshone River Drainage

The stationary mantle plume (or hotspot) underlying the Yellowstone region has caused parts of the surrounding landscape to rise as the continental plate migrates over it. However, scientists do not fully agree on the spatial pattern of this uplift and few measurements of the landscape have been made to provide estimates of uplift rates. To better understand uplift patterns and rates, this study examines the Shoshone River, which flows across the predicted zone of highest uplift at the northeastern, leading edge of the hotspot. Digital-terrain analysis is used to measure channel steepness and field and imagery approaches are used to study the position of river terraces – planar landforms underlain by river deposits indicating the river and valley-bottom position in the past. Numerical dating of the terrace deposits enables calculation of how fast the river has cut down into the landscape over the last 350 thousand years, and this incision is assumed to reflect the pattern of uplift. Incision rates in the study area appear to be increasing over the past ~350,000 years, and the zone of fastest uplift does not coincide with the high terrain near Yellowstone; instead it occurs at the western edge of the Bighorn Basin where the continental plate is just starting to move over the hotspot. This study provides the first ages of these terraces and clear evidence that the fastest uplift associated with the Yellowstone hotspot is happening farther east than some workers previously thought.