Basal Pressure in Turbidity Currents: Experimental Data on Causes for Substrate Deformation

Eggenhuisen, Joris¹, William McCaffrey¹ (1) University of Leeds, Leeds, United Kingdom

After a turbidity current has passed and waned, the turbidite bed is still located at the sediment water interface where it is subject to a range of processes that may alter its appearance. A particular set of processes involves the impact of subsequent turbidity currents on the recently deposited substrate.

An experimental program has been devised to look into the common denominator of substrate deformation by gravity flows: the stresses exerted by such flows on the topography they flow over.

The development of a pressure sensitive laboratory setup allows for quantitative analysis of base-of-flow pressure and stresses exerted on the substrate. A first set of experiments regards the dynamic pressure variations under gravity currents over flat, featureless surfaces. The reason for looking into this subject lies in the possibility that these pressure variations are responsible for liquefaction occurrences at the base of flows. This could take place either: 1) In the non-depositing phase, where liquefaction may cause failure or slurryfication of the pre-event substrate. Or: 2) During aggradation of the bed, where it may cause periodic remobilisation of compacting substrate. This type of flow induced reorganisation of grains may play an important role in creating the post-event grain packing in turbidite beds. A second set of experiments determines stress fields exerted by flows on substrate with topography. The generic results of these experiments give information about what eroding interaction to expect around irregularities in the substrate. One application of these results is the expected preferred geometry of scour zones where connectivity is enhanced through removal of fine grained deposits that would normally present a barrier between subsequent turbidite beds.