HR: 1330h
AN: OS52A-0893    [PDF]
TI: Form of Submarine Erosion From Confluences in mid-Atlantic USA Continental Slope Canyons
AU: * Mitchell, N C
EM: neil@ocean.cf.ac.uk
AF: Cardiff University, School of Earth, Ocean and Planetary Sciences PO Box 914, Cardiff, CF10 3YE United Kingdom
AB: In models for fluvial incision, channel bed erosion rates (E) depend on rainfall catchment area A and channel gradient S: E$\sim$A$^{m}$S$^{n}$. Canyons of the continental slope were incised by turbidity currents, debris flows and other sedimentary mass movements. If such flows are initiated by failure of over-steepened hemipelagic deposits in canyon walls, the frequency of flows experienced by the channel could depend on canyon upstream area, leading to erosion rate also depending on area. Considering that channel gradient additionally affects erosion-relevant flow properties, there may be analogous erosional relationships to those of subaerial geomorphology. To address this possibility, a database of hemipelagic catchment area and channel gradient was created for dendritic canyons in the upper continental slope. At a river confluence, the long-term erosion rates of the two branches are equal so that their contrast in areas and gradients can reveal the ratio of exponents m/n (Seidl and Dietrich, 1992). Such data for these submarine canyons show significant scatter, but they suggest on average E$\sim$A$^{m}$S$^{n}$ with m/n=0.2-0.3. Interestingly, gradient and area are related by a power-law relationship (S$\sim$A$^{-0.3}$) that is consistent with the erosion law if the landscape is in a steady state. This relationship is similar to that found for debris flow erosion in subaerial colluvial channels. Furthermore, gradient-area graphs are similar whether the canyons head at the shelf break or away from it, so there is little evidence to suggest that shelf spillover has contributed greatly to canyon incision here. Seidl, M., and Dietrich, W. E., 1992, The problem of channel erosion into bedrock: Catena Suppl., v. 23, p. 101-124.
DE: 3022 Marine sediments--processes and transport
DE: 3045 Seafloor morphology and bottom photography
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting