Proceedings of the U.S. Geological Survey (USGS) Sediment Workshop, February 4-7, 1997

MARINE AND LACUSTRINE SEDIMENTARY PROCESSES INVOLVING NON-GLACIAL ICE

Studies of how glacial and permafrost ice shape the landscape are well reported. Here we focus on the roles of lacustrine and sea-ice in their respective environments. There are three primary methods by which ice impacts sediment erosion, transportation and deposition;

1. its influence on hydraulic processes,
   
2. its physical interaction with the bed, and
   
3. its thermal and physical growth and decay.

Waves, currents and river flow are deflected, reflected and intensified in the vicinity of ice masses which enhances sediment erosion and transport. Effects are especially pronounced where ice is in close proximity to the sediment bed causing intensified hydraulic erosion. Where ice develops primarily along the shoreline as in the Great Lakes the wave and current energy is displaced from acting at the shoreline sediments to the sediment bed along the outer boundary of the ice. Spring-time river flood overflow on sea ice in the Arctic drains as jets through cracks and holes in the ice canopy scouring the bed up to several meters.

The movement of ice in contact with the bed physically disrupts or gouges the sediment bed mixing and bulldozing material. Sea, lake, and fluvial ice are pressured and rearranged by winds, waves and currents forming irregular masses with many downward protrusions or keels that can interact with the bottom in sufficiently shallow water. These keels are moved through the sediment bed to depths of up to 10 meters. The energy available to the gouging tools are considerable, as the ice masses can integrate water column currents, as well as surface winds and waves, and energy imparted by motion of the surrounding ice sheet. Ice gouging creates a distinctive morphology that has been identified in the sedimentary record but a distinctive facies has not yet been reported.

Thermal and physical growth and decay of ice erodes, transports and deposits sediments. Ice crystallizes and grows at the water's surface, in the water column and on the bed. Surface ice growth has little effect on sediments except when ice masses are physically commingled with sediments in fluvial or wave turbulence. Ice growth, in a turbulent water column (which allows super-cooling) results in the formation of frazil ice crystals. With growth, increased buoyancy and decreased turbulence, individual crystals and flocs rise to the surface, scavenging the water of particulate matter. Ice growth at the bed (as adhered frazil or anchor ice) is the most significant (and least understood) sedimentologic interaction by ice. Frazil and anchor ice growth in fluvial and coastal settings incorporates sediment at the bed until ice growth has generated sufficient buoyancy to break free and roll along the bottom or become a surface ice feature. Anchor ice formation is a common occurrence, observed on 15 out of 30 days during the winter in Lake Michigan. Anchor ice can incorporate upwards of 100 g/l and still have buoyancy to transport sediment. Sediments thus rafted are not dependent on ongoing turbulence to remain in suspension and material can be rafted great distances at low energies. The highest concentrations and quantities of sediment in the ice canopy are associated with anchor and frazil ice in studies of the Great Lakes and in the Arctic Ocean.

Opportunities for research to enhance and improve our knowledge of ice processes would be most productive and useful if focused on a better understanding of anchor and frazil ice processes. Transport of pollutants in the Great Lakes and from Arctic sources of the former Soviet Union are linked to an understanding of how sediments are bound into the ice canopy and transported to distant depocenters. Other opportunities would focus on the more definitive studies of the role of ice in interactions with the bed in fluvial, nearshore lacustrine, and marine environments where all three processes, hydraulic, physical, and freeze-thaw, are especially active.

SELECTED REFERENCES

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Barnes, P.W., Kempema, E.W., Reimnitz, Erk, and McCormick, Michael, 1994, The influence of ice on Lake Michigan Coastal Erosion: Journal of Great Lakes Research, v. 20, p. 179-195.

Kempema, E.W., and Reimnitz, Erk, 1991, Nearshore sediment transport by slush/brash ice in southern Lake Michigan, in N.C. Kraus , K.J. Gingerich, and D.L. Kriebel (eds.), Coastal Sediments '91: American Society of Civil Engineers, NY, p. 212-219.

Héquette, Arnaud, M. Desrosiers, and P.W. Barnes, Ice scouring and onshore sediment transport on the inner shelf of the Canadian Beaufort Sea: Marine Geology, 1995.

Rearic, D.M., E. Reimnitz, and P.W. Barnes, Bulldozing and resuspension of shallow-shelf sediment by ice keels: Implications for Arctic sediment transport: Marine Geology, 91, 133-1, 1990.

Reimnitz, Erk, and P.W. Barnes, Sea ice as a geologic agent on the Beaufort Sea shelf of Alaska: In, The Coast and Shelf of the Beaufort Sea, edited by J.C. Reed, and J.E.Sater, Arctic Institute of North America, Arlington, VA, 301-351, 1974.

Reimnitz, E., Hayden, E., McCormick, M., and Barnes, P.W., Preliminary observations on coastal sediment loss through ice rafting in Lake Michigan, Journal of Coastal Research, v. 7, p. 653-664,1991.

Reimnitz, Erk, Barnes, P.W., and Weber, W.S., Particulate matter in pack ice of the Beaufort Gyre: Journal of Glaciology, v. 39, no. 131, p. 186-198, 1993.

Vorren, T.O., M. Hald, M. Edvardsen, and O. Lind-Hansen, Glaciogenic sediments and sedimentary environments on continental shelves: general principles with a case study from the Norwegian shelf. In, Glacial Deposits of Northwest Europe: edited by J. Ehlers, Balkema, Rotterdam, 61-73, 1983.

Woodworth-Lynas, C.M.T., A. Simms, and C.M. Rendell, Iceberg grounding and scouring on the Labrador Continental Shelf, Cold Regions Science and Technology, 10, 163-186, 1985.