What controls submarine channel development and the morphology of deltas entering deep‐water fjords?

Abstract

River deltas and associated turbidity current systems produce some of the largest and most rapid sediment accumulations on our planet. These systems bury globally significant volumes of organic carbon and determine the runout distance of potentially hazardous sediment flows and the shape of their deposits. Here we seek to understand the main factors that determine the morphology of turbidity current systems linked to deltas in fjords, and why some locations have well developed submarine channels while others do not. Deltas and associated turbidity current systems are analysed initially in five fjord systems from British Columbia in Canada, and then more widely. This provides the basis for a general classification of delta and turbidity current system types, where rivers enter relatively deep (>200 m) water. Fjord‐delta area is found to be strongly bimodal. Avalanching of coarse‐grained bedload delivered by steep mountainous rivers produces small Gilbert‐type fan deltas, whose steep gradient (11°–25°) approaches the sediment's angle of repose. Bigger fjord‐head deltas are associated with much larger and finer‐grained rivers. These deltas have much lower gradients (1.5°–10°) that decrease offshore in a near exponential fashion. The lengths of turbidity current channels are highly variable, even in settings fed by rivers with similar discharges. This may be due to resetting of channel systems by delta‐top channel avulsions or major offshore landslides, as well as the amount and rate of sediment supplied to the delta front by rivers. © 2018 John Wiley & Sons, Ltd.

Retreat Pattern of Glaciers Controls the Occurrence of Turbidity Currents on High‐Latitude Fjord Deltas (Eastern Baffin Island)

“…Recently, Pope et al () showed that a stable ice front was necessary for the formation of turbidity current channels at marine‐terminating glaciers and that large watersheds increased the likelihood of turbidity currents. Gales et al () have also shown shown that the watershed area and river discharge control the type of deltas created, that is, small Gilbert‐type deltas or deltas with long‐running channels. Our results show no significant differences between small and large watersheds on the occurrence of turbidity currents.…”

Dispersion, Accumulation, and the Ultimate Fate of Microplastics in Deep-Marine Environments: A Review and Future Directions

“…In thick turbidites of the same system, erosion by repeated turbidity currents tended to leave only the lowermost and coarsest fraction of individual beds in the channel axis, hence any other fines are reworked (Hage et al, 2018). On an even larger scale, intrachannel erosion by upstream-migrating knickpoints has been shown to result in poor preservation potential of deposits in the channel axis, while terraces and levees were sites of enhanced deposit preservation (Gales et al, 2018). In summary, channel axes are considered to be important conveyors of and temporary storage sites for microplastics, but it is levees and terraces that are the most likely hotspots for their long-term accumulation.…”

The evolution of submarine slope-channel systems: Timing of incision, bypass, and aggradation in Late Cretaceous Nanaimo Group channel-system strata, British Columbia, Canada

“…The findings of this study corroborate observations from modern deepwater sediment-routing systems. Repeat bathymetric surveys and direct monitoring provide evidence for multiphase sediment-transport processes in many active unfilled canyons and slope-channel systems (Conway et al, 2012;Gales et al, 2019;Vendettuoli et al, 2019). For example, local deposition of sediment by regular turbidity currents is commonly observed in slope channels but these deposits are eventually flushed downslope during less-frequent, larger-magnitude flow events (Jobe et al, 2018;Paull et al, 2018;Stacey et al, 2019).…”