Transcript for Drift Ice as a Geologic Agent, segment 08 of 11


{{{Sediment Entrainment & Ice Rafting}}}

Ice also captures and then transports sedimentary particles of all sizes. Once entrained and brought with the ice to the sea surface, the load can be carried great distances until melting. This transport requires no additional energy, normally required for suspension and resuspension.

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One mechanism of sediment entrainment is associated with ice compression and the formation of pressure ridges. This ten-meter high pile of ice rubble is grounded in Lake Erie at nearly twenty meters water depth, forming an obstacle for the thirty centimeter thick sheet of ice drifting at a rate of one-half knot with a wake in the lea. Windward, the advancing sheet is subducted below the growing pile of rubble. The noise records the breaking of ice.

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Ice mixed with bottom sediment is extruded from the center of the growing pile, showing that the subducted sheet scoops sediment from the bed and raises it to the surface. The entrainment mechanism is suggested in this hypothetical cross section where sediments occur in pockets and lenses as matrix throughout the pile.

With progressive summer melting, originally discreet layers and pockets of these rubble pile many kilometers from shore are concentrated into surface layers. After sediment-charged ice piles consolidate into massive flows, long-range drifting can occur. On Alaska's Arctic shelf, sediment-laden pressure ridges form principally in the twenty to thirty meter depth range where drifting pack ice shears along the smooth, fast ice adjoining land.

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