Experimental Investigations from the Role of Jets in Submarine Channel Initiation

Joel C. Rowland¹, George Hilley¹, Andrea Fildani², and Timothy McHargue^2
1Geological and Environmental Sciences, Stanford University, Stanford, CA
²Chevron Energy Technology Co, Chevron, San Ramon, CA

In fluvial systems the role of sediment-laden jets in the formation and progradation of river channels into basins has long been recognized. Recent physical experiments highlight that levee formation and channel initiation by jets arises from the development of distinct shear zones along the margins of the discharging jet. These shear zones create a sharp lateral transition in bed shear stresses and sediment re-entrainment between the high velocity core and margins of the jet. Shear-driven lateral diffusion of sediment from the erosion-dominated core to the depositional margins allows for levee development and channel initiation. In turbidity currents, excess density leads to lateral flow collapse which should work against the persistence of jet-like conditions at transitions from channelized to unchannelized regions of the sea floor. Scaling analysis suggests that the transition from a momentum dominated jet to a density dominated plume should occur around a densimetric Froude number of one. Studies of surface plumes, however, show that this transition is not binary; buoyant outflows commonly have jet-like cores surrounded by spreading plumes. Through a series of experiments on submerged jets with increasing excess density we seek to determine if jet-like outflow is a necessary condition for channel initiation in submarine systems. If so, our experiments will further determine whether a critical Froude number can characterize the transition from flows capable of developing leveed channels to flows marked by more radial spreading and distributed sedimentation. The quantification of the presence and longitudinal persistence of jet-like conditions in unconfined turbidity currents offers the potential to provide additional insights into the controls on sedimentation patterns and depositional mechanics in submarine fan settings.

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