CascadiaCanyons_Turnaround2

Submarine canyons are ubiquitous along continental margins, and often thought of as key conduits for the transfer of terrestrial sediment, nutrients and organic material to the deep sea. During sea level highstands, most of this shelf to deep-sea transport occurs on an episodic basis, driven by seabed resuspension in and around the canyon head, associated with large storms, floods, earthquakes and other energetic events that are thought to induce gravity-driven, downslope sediment flows. However, the processes that control canyon flushing and sediment infilling remain poorly understood. To date, most of the direct monitoring of these processes has been focused on large submarine canyon and fjord systems that are highly active during the current sea level highstand. This proposed effort is a collaborative, interdisciplinary effort with the goal of understanding the origin of modern deep-water stratigraphy associated with submarine canyon dynamics. The observational component will deploy two instrumented arrays in canyons of differing morphology (Astoria Canyon and Quinault Canyon) to develop a spatially distributed minute-scale record of water and particulate transport processes over a complete annual cycle. This data would yield the timing and magnitude of canyon transport processes, and help constrain the sedimentary response to oceanographic disturbances. A seasonal seabed surface core survey in the region will examine annual depositional cycles, and allow for the direct testing of seafloor remobilization thresholds along canyon thalwegs. All of these data will then be used as model inputs, providing the constraints for locally-parameterized hydrodynamic modeling of sediment gravity-flow triggering and runout distances.