Drivers of inner gorge incision in the Fraser Canyon (British Columbia, Canada)

<p>Bedrock inner gorges, or narrow and deeply-incised canyons set within broader valleys, are common features in post-glacial landscapes and may reflect the interaction of glacial-fluvial processes. Though widespread, the origins of bedrock inner gorges are enigmatic and have been variably attributed to subglacial meltwater during deglaciation, outburst floods, and subaerial fluvial incision as a response to base level change. It is also unclear if their morphology reflects erosion from a single deglacial period or evolution over multiple glacial-interglacial cycles.</p><p>Given widespread inner gorges, quartz-bearing rocks, and a history of multiple glaciations, the Fraser Canyon &#8211; a 375-km stretch of the Fraser River in British Columbia (Canada) characterized by alternating bedrock and non-bedrock reaches &#8211; is an ideal area to explore the drivers of inner gorge incision. Using topographic analyses to characterize the morphology of these bedrock gorges, we assess incision rates required to form the canyons since deglaciation (~14 &#8211; 11.7 ka). Using the morphology (e.g., slope) of glacio-fluvial terraces and channel long profile analyses (e.g., <em>k_sn</em>), we evaluate whether inner gorges likely formed through 1) interaction of glacial and fluvial erosion during glaciation, 2) one or more catastrophic outburst floods, or 3) steady subaerial fluvial erosion due to isostatic uplift/base level fall since deglaciation. We conclude by exploring the relative efficacy of these erosional processes and implications for the longevity of fluvial and glacial landscapes.</p>