Transformation of debris flows into turbidity currents: mechanisms inferred from laboratory experiments

Three sets of lock exchange experiments were run to look at the generation of turbidity currents from debris flows. The flows ranged from reasonably dilute (4% volumetric concentration) to dense (40% volumetric concentration) with cohesive, non-cohesive and mixed cohesive/non-cohesive sediment. Concentration was measured at one height using an Ultrasonic High Concentration Meter. Velocity was measured using Ultrasonic Doppler Velocimetry Profiling at 10 different heights in each run. The resulting flows range from plug flows to well mixed flows. Comparison of the concentration profiles, velocity time–height plots and vertical profiles of downstream velocity and root mean square velocity showed several different transformation mechanisms. Depending on the concentration and composition of the flow, transformation took place through one or more of the following processes: erosion of material from the dense mass, breaking apart of the dense underflow, breaking of internal waves and turbulent mixing. The extent of transformation depends on the viscosity and density of the flow. Initially very dense and viscous flows experience minor transformation only at the surface, resulting in a dilute turbidity current. Flows that are initially not so dense and viscous are churned up entirely, undergoing the different transformation processes. For these flows, transformation processes work throughout the entire flow, not just at the surface. Transformation of the less-dense flows is efficient with all or most material ending up in the resulting turbidity current.

[1]  J. Peakall,et al.  Combined measurements of velocity and concentration in experimental turbidity currents , 2005 .

[2]  P. Kuenen,et al.  Turbidity Currents as a Cause of Graded Bedding , 1950, The Journal of Geology.

[3]  Kelin X. Whipple,et al.  Hydroplaning of subaqueous debris flows , 1995 .

[4]  J. Imberger,et al.  Entrainment and turbulence in saline underflow in Lake Ogawara , 2001 .

[5]  J. Stix.  Flow Evolution of Experimental Gravity Currents: Implications for Pyroclastic Flows at Volcanoes , 2001, The Journal of Geology.

[6]  N R Morgenstern,et al.  Submarine slumping and the initiation of turbidity currents , 1967 .

[7]  T. H. Andel,et al.  Ponded Sediments of the Mid-Atlantic Ridge between 22° and 23° North Latitude , 1969 .

[8]  W. Nemec,et al.  Large floating clasts in turbidites: a mechanism for their emplacement , 1988 .

[9]  P. Kuenen.  Estimated size of the Grand Banks [Newfoundland] turbidity current , 1952 .

[10]  H. Schwarz.  Subaqueous Slope Failures: Experiments and Modern Occurrences , 1982 .

[11]  M. Hampton,et al.  The Role of Subaqueous Debris Flow in Generating Turbidity Currents , 1972 .

[12]  Jeffrey G. Marr,et al.  Experiments on subaqueous sandy gravity flows: The role of clay and water content in flow dynamics and depositional structures , 2001 .

[13]  M. Felix,et al.  Flow structure of turbidity currents , 2002 .

[14]  C. Ravenne,et al.  Apport des expériences en canal à l'interprétation sédimentologique des dépôts de cônes détritiques sous-marins . . . , 1983 .

[15]  Jeffrey G. Marr,et al.  Constraining the efficiency of turbidity current generation from submarine debris flows and slides using laboratory experiments , 2003 .

[16]  W. Knaap,et al.  SOME EXPERIMENTS ON THE GENESIS OF TURBIDITY CURRENTS , 1968 .

[17]  Donald R. F. Harleman,et al.  Steady-state characteristics of subsurface flow , 1952 .

[18]  J. E. Sanders.  Primary Sedimentary Structures Formed by Turbidity Currents and Related Resedimentation Mechanisms , 1960 .

[19]  D. Waltham.  Flow Transformations in Particulate Gravity Currents , 2004 .

[20]  F. Weirich.  The generation of turbidity currents by subaerial debris flows, California , 1989 .

[21]  J. R. Allen.  Mixing at Turbidity Current Heads, and Its Geological Implications , 1971 .

[22]  Z. Sylvester,et al.  Textural trends in turbidites and slurry beds from the Oligocene flysch of the East Carpathians, Romania , 2004 .

[23]  P. Komar.  Hydraulic Jumps in Turbidity Currents , 1971 .