POSITION OF WATERSHED DIVIDES FROM FILTERED TOPOGRAPHY AS AN INDICATOR OF GEODYNAMIC PROCESS: USING THE SNAKE RIVER AND GREATER YELLOWSTONE AREA AS A CASE STUDY

The spatial position of present-day and synthesized regional-scale drainage basin divides is an underutilized geomorphic metric that can be used to identify various overlapping geodynamic processes responsible for landscape evolution. In considering the stability or mobility of regional-scale drainage basin divides, two end-member scenarios may be envisioned. The first is where the divide remains spatially fixed over long periods of time during which an overthickened orogenic crustal root is passively consumed via erosional unloading and its isostatic response. The second is where divides actively migrate in response to dynamic mantle support of topography. Knowing that active drainage divide migration can be a key feature in distinguishing between passive and active geodynamic settings, we investigate drainage divide migration potential in the greater Yellowstone region (GYR), a geodynamically active area where the processes influencing the present-day topography are fairly well defined. The GYR is an opportune location for this investigation because contrasting models have been proposed to explain the parabolic shape of elevated topography and active seismicity that outline the imprint of hypothesized hotspot activity. Drainage divides synthesized from topography filtered at 50, 100, and 150 km wavelengths within the GYR show that the locations of the actual and synthetic Snake River drainage divides are controlled by both dynamic and flexural mechanisms in the eastern GYR, but by flexural mechanisms only in the western GYR. The location of the actual divide deviates from its predicted position in the filtered topography where tectonic controls, such as active faults (e.g., Centennial and Teton faults), have uplifted large footwall blocks. Our results are consistent with the notion of a northeastward-propagating GYR topographic and seismic parabola, and suggest that adjacent Basin and Range extension follows from, rather than precedes, GYR dynamic topography. Furthermore, our analysis suggests that eastward migration of the Snake River drainage divide lags behind the continued northeastward propagation of high-standing topography associated with the Yellowstone geophysical anomaly by 1–2 m.y.