Morphological Modelling of Continental Slopes

Mitchell, Neil¹ (1) The University of Manchester, Manchester, United Kingdom

The processes affecting continental slopes are different from those affecting landscapes above sea level, but geomorphological properties of the two environments can be remarkably similar. This prompts a search for models of erosion, transport and deposition processes that can explain this similar geometry.

Slope-confined canyons are typically upwards-concave a property also of many bedrock-eroding rivers. When channel gradients are plotted against contributing area, as though canyon topography were to form a rainfall catchment, canyon "concavity indices" are similar to those of rivers. The frequency of flows experienced by the channel should increase down-slope reflecting the up-stream area of unstable deposits, so concavity could arise from channels adjusting gradients to compensate and achieve balanced erosion.

Knickpoints in tectonically active slopes both migrate upstream and smooth out. In rivers, these tendencies are described as detachment-limited and transport-limited erosion, respectively, so submarine erosion involves a similar diversity of mechanisms.

The diffusion equation is often used in modelling of margin stratigraphy to represent downslope redistribution of sediments. Although the model is generally weakly justified because sedimentary processes do not always follow its assumptions, interfluves in Atlantic upper slopes are commonly smoothly parabolic, a feature of steady state diffusion with constant erosion along channels. The gravity effect on saltating sand may produce a transport flux that depends on local gradient and thus diffusion. Such a model is developed and applied to show that the rounded uppermost slope rollover can be explained by gravity-affected saltation in the presence of bottom currents that decline with depth.