HR: 17:00h
AN: H44D-05    [Abstracts]
TI: Does Sinuosity Influence Channel Length: A Study of Mixing in Turbidity Currents Induced by Channel Bends
AU: * Straub, K M
EM: kmstraub@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA 02139 United States
AU: Mohrig, D
EM: mohrig@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA 02139 United States
AU: Buttles, J
EM: buttles@erl.mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, MIT, 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: We present results from two laboratory experiments that aim to resolve the following question: why are all submarine channels of substantial length (>100 km) moderately to highly sinuous? Our results document the importance of channel bends in vertically mixing the suspended sediment within the interiors of turbidity currents. The two experiments also illustrate how current velocities, deposition rates, and deposit composition (grain size) vary in a straight vs. moderately sinuous (1.32) channel. The reduced scale channels for both experiments had the same initial cross sectional shape, which did not vary with distance from the source or with curvature. Ten turbidity currents were released into both channels, each having constant input values for height, fluid discharge, and excess density of 0.1 m, 2.67 x 10-3 m3/sec, and 3.8 % respectively. Sediment suspended in each current consisted of silica with particle diameters between 5-120 μm and a median diameter of 30 microns. Vertical sediment-concentration profiles were collected at the centerline of each channel at the same distance from the current source. These profiles show that currents moving through the straight channel become more stably stratified than currents moving through the sinuous channel. This resulted in higher near bed concentrations and therefore higher deposition rates for currents in the straight channel at equivalent distances from the current source. Associated vertical profiles of particle size also reveal that coarser sediment is suspended higher up into the interiors of currents moving through the sinuous channel. These observations indicate large-scale vertical mixing associated with the currents interacting with channel bends. This mixing helps to maintain relatively high suspended-sediment concentrations in current interiors, maintaining an excess density structure necessary to drive the currents down slope. We hypothesize that a wholesale vertical mixing of currents induced by channel bends is a necessary condition for the construction of turbidity current channels in excess of 100 km in length.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1861 Sedimentation (4863)
DE: 1862 Sediment transport (4558)
DE: 3002 Continental shelf and slope processes (4219)
DE: 3022 Marine sediments: processes and transport
SC: Hydrology [H]
MN: Fall Meeting 2005