Bedrock structural influences on river morphology

Bedrock rivers largely set the pace for landscape evolution in unglaciated terrain and yet little is known about what controls their morphologies. I examine the role that geologic structure plays in the alignment and morphology of bedrock canyons at different scales. At the watershed scale, I examine the striking alignment of the Fraser River with the Fraser River Fault zone and its largely unmapped secondary fault structures. I explore how large sediment inputs affect bedrock canyons alignment and their morphological characteristics. At the reach scale, I investigate how geological structure influences bedrock canyon width. I find that width constrictions coincide with dominant sub-horizontal joint sets whereas widenings coincide with dominant sub-vertical joint sets. I consider this in the context of sequential constrictions and widenings and propose a conceptual model where sub-vertical jointing makes canyon walls more susceptible to failure due to river undercutting than horizontal jointing.