HR: 1330h
AN: OS22A-1151    [PDF]
TI: Submarine Landslides, Isostasy, and Drastic Reorganizations of Depositional Environments on the Shelf and the Slope
AU: * Dykstra, M
EM: dykstram@umail.ucsb.edu
AF: Dept. of Geological Sciences, University of California Bldg. 526, Santa Barbara, CA 93106-9630 United States
AU: Kneller, B
EM: ben@crustal.ucsb.edu
AF: Institute for Crustal Studies, 1140 Girvetz Hall University of California, Santa Barbara, CA 93106-1100 United States
AB: We present analytical evidence that large-scale submarine landslides will result in isostatic readjustment of the crust and lithosphere. Some of the possible results of this readjustment include: (1) increased seismic activity, (2) relative sea-level fall and a consequent basinward shift in facies, (3) development of sequence boundaries due to subaerial exposure of a shallow continental shelf, (4) deflection of drainage patterns and sediment pathways on land, on the shelf, and on the slope, and (5) oversteepening of the headwall region due to domal uplift of the evacuated slide scar. We demonstrate that isostatic readjustment can be increased by almost a factor of two due to the feedback effect of overlying seawater. Many of these factors are also positive feedbacks toward future mass-failure events. Considering that gas hydrates may be destabilized by mass-failure, isostatic readjustment associated with submarine landsliding may be a strong positive feedback toward climate change. Isostatic readjustment of the crust and lithosphere takes the form of uplift in the area of the evacuated slide scarp, and subsidence in the area of the mass-transport deposit (MTD). Two-dimensional mathematical modeling indicates that for a slide scarp or MTD with dimensions of 100 km wide, 100 km long, and 100 m thick, the magnitude of the primary isostatic readjustment will vary from about 21-48m, depending on the effective elastic thickness (Te) of the lithosphere (a lower Te leads to a greater isostatic response). Additionally, changes in the depth of the overlying water column act as a feedback to both the uplift and/or the subsidence. The magnitude of this factor is nearly as great as the primary isostatic response, bringing the total isostatic adjustment to approximately 39-88 m. The wavelength of the isostatic response (area affected) also depends on the Te of the lithosphere. Calculations show this to vary from 28 km for lithosphere of very low Te (2 km) to greater than 250 km for lithosphere with high Te ($>$38 km). Therefore, the isostatic response of the lithosphere and crust to submarine landslides is of sufficient amplitude and wavelength to significantly alter large areas of continental shelves, and is almost certainly an important but previously unrecognized mechanism for drastic reorganizations of depositional environments.
DE: 1208 Crustal movements--intraplate (8110)
DE: 3022 Marine sediments--processes and transport
DE: 4203 Analytical modeling
DE: 4219 Continental shelf processes
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting