HR: 17:15h
AN: H44D-06    [Abstracts]
TI: Channel Levees Built by Turbidity Currents in the Laboratory
AU: * Mohrig, D
EM: mohrig@mit.edu
AF: Dept. of Earth, Atmospheric and Planetary Sciences, MIT, 77 Mass Ave., Building 54-814, Cambridge, MA 02139 United States
AU: Straub, K M
EM: kmstraub@mit.edu
AF: Dept. of Earth, Atmospheric and Planetary Sciences, MIT, 77 Mass Ave., Building 54-814, Cambridge, MA 02139 United States
AU: Buttles, J
EM: buttles@erl.mit.edu
AF: Dept. of Earth, Atmospheric and Planetary Sciences, MIT, 77 Mass Ave., Building 54-814, Cambridge, MA 02139 United States
AU: Pirmez, C
EM: Carlos.Pirmez@shell.com
AF: Shell International Exploration and Production, Inc., P.O. Box 481, Houston, TX 77001 United States
AB: A laboratory experiment resolves, at a reduced scale, many of the interactions between turbidity currents and bottom topography that lead to construction of channel-bounding levees. Analysis of the experimental data focuses on establishing the connections between levee thickness, levee taper and composition (grain size). These levee characteristics are in turn related to the following physical properties of the depositing currents: 1) current thickness relative to the local depth of the channel; and 2) vertical profiles of suspended-sediment concentration and grain size within the interiors of currents. Change in local depth confined more or less current within the channel and determined the fraction of current present at and above the levee-crest elevation where it could act as a sediment source for bank construction. A relatively thick, steep and coarse-grained levee was constructed at locations along the channel where the currents were significantly thicker than the channel was deep and a relatively thin, weakly tapered and fine-grained levee formed where the channel was deeper. Levee deposition rate varied as a function of both the absolute concentration and size of the particles suspended in the depositing current at the elevation of the local levee crest. Likewise, the laterally varying deposition rates that produced the levee taper were controlled by the vertical gradients in suspended-sediment concentration and grain size for only that fraction of the current moving out onto the bank of the channel. Trends reported here were measured in a straight channel and not affected by any cross-channel variation associated with channel bends. Variability in levee form and composition induced by irregularity in channel plan-form complicates the connection between properties of the depositing flows and the levees they construct, increasing the number of measurements necessary to resolve any systematic change in levee properties through space or time. The experimental results are intended to compliment recent quantitative studies of natural submarine levees in order to improve the accuracy with which processes associated with the levee construction can be estimated from the morphology and composition of the levees themselves.
DE: 1824 Geomorphology: general (1625)
DE: 1861 Sedimentation (4863)
DE: 1862 Sediment transport (4558)
DE: 4863 Sedimentation (1861)
SC: Hydrology [H]
MN: Fall Meeting 2005