Turbidity current

Turbidity currents are a kind of sediment gravity flow. Suspended particles increase the density of water relative to the clearer water around it, so gravity drives the mixture down a slope. An earthquake, slope failure, sediment collapse or other disturbance can initiate a flow. As it descends it may erode the bed and entrain additional sediment, changing its density and behaviour. The term is often used broadly for sediment-laden underwater flows, although real events vary in concentration and structure.

A current can move through submarine canyons and channels and transport sediment from continental margins toward deep-sea basins. It can reshape the seabed by scouring and moving sediment, and when it slows, particles settle. Coarser grains generally settle before finer ones, so deposits may form graded layers. Repeated deposits, known as turbidites, preserve evidence of past flows and are used to interpret sedimentary environments. Depending on setting, turbidity currents can also redistribute organic carbon and build or modify submarine features.

Direct measurement is difficult because energetic flows can damage or displace instruments. Researchers combine moored current meters, acoustic measurements, seabed mapping before and after events, sediment cores and other sensors to reconstruct their speed, extent and effects. During the Coordinated Canyon Experiment in Monterey Canyon, instruments at multiple sites recorded 15 flows; the largest travelled more than 50 kilometres. Observations showed that dense, water-saturated sediment at the base of some events moved across and remoulded the seabed, alongside sediment-laden water above it. This is evidence from a particular canyon and should not be assumed to describe every flow.

Turbidity currents can pose a hazard to seafloor cables, pipelines and other infrastructure because they may travel long distances and carry sediment capable of striking, burying or displacing equipment. A well-known early example occurred in 1929, when an earthquake-triggered flow damaged transatlantic cables. The currents are also important geological agents: they transfer sediment from shallow to deep water and create deposits that help scientists reconstruct past events. Their impacts depend on local slope, sediment supply, channel shape and the flow itself.