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Esther J. Sumner, University of Southampton, UK
Charles K. Paull, Monterey Bay Aquarium Research Institute, US
Canyon filling and flushing along the California Margin

This study presents the results of a ten-year coring and mapping campaign that collected 110 precisely located cores from 21 submarine canyons along the northern California Margin, enabling a holistic analysis of the gamut of processes operating within submarine canyons. (I) Canyons with their heads on the shelf, or at the shelf break, contain fine-grained sediments of both hemipelagic origin and those deposited from relatively dilute turbidity currents. These are the types of turbidity currents that have been successfully monitored by anchoring moorings in submarine canyons. (II) Canyons, with their heads close to the shoreline, intersect littoral cells and contain chaotic deposits of sand, gravel and boulders in their axes, thus providing evidence of extremely high-energy, high-concentration flows. The only measurements yet made of these high-concentration axial flows are the displacement of heavy instruments e.g. 60 kg instrument frames and moorings with 1000 kg anchors. (III) Finally, one of the studied canyons contained a series of giant scours in its axis that were up to 790 m long, 670 m wide and 50 m deep that cut down to bedrock and were draped by a veneer of 20th century flow deposits. These scours are inferred to represent a flow of sufficient size and energy to rip pre-exiting deposits out of the canyon axis and flush them out onto the submarine fan. These flows have never been observed but are probably responsible for both carving submarine canyons and providing sediment to construct submarine fans.

Special Session 1: Sediment Transport monitoring in submarine canyons
Oral Presentation
Canyons flows California