Experimental Gravity Currents: Correlation of Flow Structure and Pressure Field

Joris T. Eggenhuisen and Bill McCaffrey
School of Earth and Environment, University of Leeds, Leeds, United Kingdom

Fluid flow is closely associated with differential pressure fields, yet observations of pressure in sedimentologically relevant settings are rare. Here we present results from experiments in which fluid pressures where measured at the base of passing experimental gravity currents. Synchronous measurement of the velocity fields of the flows enables correlation of the observed pressures with the internal structure of the flows. The following characteristics of the flows are explored in greater depth and their implications for real world sedimentological processes are discussed.

Firstly, a field of elevated pressure extends in the ambient fluid in front of the head of the flow. This elevated pressure field extends forwards in the order of 3-4 times the flow thickness. Any topography or obstruction present in this field will interact with the front of the flow and influence the structure of the head before it has reached the location of the obstruction.

Secondly, during the passage of the main body of the flow, its substrate experiences an overpressure related to the concentration profile of the column of the flow at the measurement location. First order fluctuations relate to the passage of large-scale billows in the flow.

Thirdly, creation of high-intensity turbulence in the near wall regions of the flow by small scale topographic irregularities can be correlated to dynamic pressure variations exerted on the wall of the flow. These results are significant because turbulence related pressure variations have been linked with liquefaction and soft sediment deformation processes in recent studies. The experimental data presented here supports the plausibility of such autogenic liquefaction(i.e. not triggered by allogenic controls like seismic shaking or storm waves), taking place.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas