Morphology And Potential Retreat Processes Of East Fork Falls, Roan Plateau, Colorado
Thul, David 1 ; Berlin, Maureen 2 ; Anderson, Robert S. 3
1 Geological Sciences, Univ. of Colorado at Boulder
2 Geological Sciences, Univ. of Colorado at Boulder
3 INSTAAR and Geological Sciences, Univ. of Colorado at Boulder
Colorado's Roan Plateau provides a natural laboratory for the study of bedrock river incision due to its predominantly horizontal stratigraphy and numerous waterfalls up to 50 m in height. The morphology of these waterfalls can provide an important constraint on processes of waterfall retreat. Using a laser range finder we documented the morphology of East Fork Falls by surveying stratigraphic markers along the waterfall face, cliff tops, and points around the plunge pool. East Fork Falls has areas of undercutting where the face is recessed 2-20 m beyond the waterfall lip. The north and south faces have markedly different morphology; the north face is overhanging and blocky while the south face is smooth and nearly vertical. Also, the plan form of the waterfall alcove is roughly parabolic with a slight northeast skew. At the time of surveying, the waterfall jet did not access the plunge pool and instead impacted a mottled surface on the waterfall face 5 m upstream of the pool. We calculated that an upstream horizontal velocity of 2.6 m/s was required for the jet to access the plunge pool. As this high velocity is typically not met by the upstream flow conditions, plunge pool erosion may not be the dominant waterfall retreat process here