Turbidity current
A turbidity current or density current is a current of of rapidly moving, sediment-laden water moving down a slope through air, water, or another fluid. The current moves because it has a higher density and turbidity than the than the fluid through which it flows. The term "turbidity current" is most commonly used to describe underwater currents in lakes and oceans, which are usually triggered by earthquakes or slumping. In such cases, high-speed sediment-laden water flows down the slope under the clearer water, causing a great deal of erosion and subsequent sedimentation. Turbidity currents are characteristic of areas where there is seismic instability and an underwater slope, especially submarine trench slopes of convergent plate margins and continental slopes and submarine canyons of passive margins. For a video showing a turbidity current in motion, see this link. As the slope of the flow increases, the speed of the current increases. As the speed of the flow increases, turbulence increases, and the current draws up more sediment. The increase in sediment increases the density of the current, and thus its speed, even further. For a video illustration of this process, see this link.
Examples of turbidity currents Grand Banks earthquake of 1929, off the coast of Newfoundland. Minutes later, transatlantic telephone cables began breaking sequentially, farther and farther downslope, away from the epicenter. Twelve cables were snapped in a total of 28 places. Exact times and locations were recorded for each break. Investigators suggested that a 60-mile-per-hour (100 km/h) submarine landslide or turbidity current of water saturated sediments swept 400 miles (600 km) down the continental slope from the earthquake’s epicenter, snapping the cables as it passed. Avalanches
References
Bruce C. Heezen and Maurice Ewing, “Turbidity Currents and Submarine Slumps, and the 1929 Grand Banks Earthquake,” American Journal of Science, Vol. 250, December 1952, pp. 849–873.
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