Morphometrics of submarine channels: variation between channel types and around bends

Submarine channels are common sediment pathways along the sea floor globally. Single-thread submarine channels in the modern can be classified depending on the environmental setting as: submarine-fan, slope, axial, isolated deep ocean, confined slope, and non-margin ocean channels, yet all have been considered morphologically similar. Bend migration for aggradational single-thread submarine channels is dominantly controlled by bend expansion with very limited downstream migration. However, paradoxically, laboratory experiments and numerical simulations predict that submarine channels exhibit a downstream bend migration similar to rivers. In rivers, the importance of bend morphology, especially channel width, on bend migration is known. Here, the morphometrics of submarine channels in different environmental settings, and the morphology around submarine channel bends, are investigated. A detailed analysis of 177 bends from 11 submarine channels, composed of 3 channel types, has been undertaken. For each bend, 13 cross-sections were measured, and width analysed at different heights from the channel bed to the channel banks. Additional cross-sections from a range of channel types have been extracted from the literature, and integrated with the new data to assess the morphometric variation with channel type. The main outcomes of this study are: 1) Submarine channels types are distinguishable based on their morphometry with for example submarine-fan, slope, and non-margin ocean channels having a similar aspect ratio to rivers, and axial and isolated deep-ocean channels having a greater aspect ratio than rivers, 2) Contradictions of bend migration between laboratory experiments or numerical simulations, and observations, can be explained by width variation around bends, 3) Width variation around bends is variable between channel types with submarine-fan channels having a wider width at bend apices, whereas isolated deep-ocean channels exhibit a constant channel width around bends. 4) Width variation around bends may be controlled by allogenic controls such as flow magnitude and bank resistance.