Influence of Coriolis forces on turbidity currents and sediment deposition
Using laboratory analogue experiments I show how the Earth’s rotation can influence the deposition patterns of large-scale turbidity currents. While it has been previously recognized that the EarthÕs rotation can influence the trajectories of turbidity currents (Middleton 1993; Huppert 1998; Kneller & Buckee, 2000) the experiments discussed in this paper represent the first systematic laboratory study of the Coriolis forces acting upon turbidity currents. The scale at which Coriolis forces become important is best expressed using the Rossby number, defined as Ro = U/fL, where U is a depth averaged velocity, L the length scale and the Coriolis frequency, f, is defined by f = 2Ω sin θ, where Ω is the Earth’s rotation rate and θ is the latitude. Coriolis forces will dominate a current when Ro < 1 (Nof 1996). For example a large turbidity current with a velocity of U = 10m s−1 at a latitude of 45° North where f = 1 × 10− 4 s −1, has Ro < 1 for length scales greater than 100 km.
In this paper I discuss two effects of the Coriolis forces upon large-scale turbidity currents. The first series of experiments document how an increase in the Coriolis parameter resulted in a decrease in the rate of turbulent entrainment of overlying sea-water into a density current. The second set of experiments look at the maximum radius of deposition of a turbidity current on a flat plane, and we find that the resulting radius is inversely proportional to the Coriolis parameter. This result implies that there may be a latitudinal dependence upon the radius of turbidite deposition on the flat oceanic abyssal plane. I compare the scaling developed from these idealized laboratory models to field observations of the 300–500 km spatial extent of the turbidites arising during the 1929 Grand Banks earthquake. By making estimates of the velocity we find that this turbidity current had Ro ∼ 1, so that Coriolis forces may have limited the spatial extent of the resulting turbidite.
KeywordsFroude Number Coriolis Force Gravity Current Turbidity Current Coriolis Parameter
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- Etling, D., Gelhardt, F., Schrader, U., Brennecke, F., Kuhn, G., Chabert d’Hieres, G. & Didelle, H. (2000) Experiments with density currents on a sloping bottom in a rotating fluid. Dyn. Atmos. Oceans. 31:139–164Google Scholar
- Hallworth, M.A., Huppert, H.E. & Ungarsish, M. (2001) Axisymmetric gravity currents in a rotating system: experimental and numerical investigations. J. Fluid Mech. 447:1–29Google Scholar
- Huppert, H.E. (1998) Quantitative modelling of granular suspension flows. Proc. Royal Soc. 356:2471–2496Google Scholar
- Jacobs, P. & Ivey, G.N. (1998) The influence of rotation on shelf convection. J. Fluid Mech. 369:23–48Google Scholar
- Wells, M.G. & Wettlaufer, J.S. (2006) The long-term circulation driven by density currents in a two-layer stratified basin. J. Fluid. Mech. (accepted)Google Scholar