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Z. Geomorph. N. F., Vol. 25(1981), 1-16
ICE EFFECT ON EROSION AND
SEDIMENTATION ON THE ONTARIO SHORES OF JAMES BAY, CANADA
I. PETER MARTINI
University of Guelph,
Ontario, Canada
¡¡
 James Bay is a cold,
brackish, inland sea covered for approximately six months of the year by sea
ice. Although occasional storm surges occur, it is normally a low energy,
shallow (offshore slope 0.5-1.0 m/km), tidal coast. During break-up and at times
in summer when pack ice is piled against the shore by wind, the coast is criss-crossed
by gouges, and accumulates ice rafted materials. Many of these features remain
visible at river mouths, and or near promotories where rates of deposition are
low. They disappear during summer from tidal flats, where scattered boulders and
patches of unsorted gravel and coarse sand testify to previous ice action.
Several types of beam ridges are common along this coast, and they are scoured
by ice, and receive considerable amount of ice rafted material. This material is
reworked by storm waves, and the legacy of ice action is seldom recognizable,
except for rare basal cut and fills.
The freezing of ice
blocks to the ground is another significant sea ice process. When the blocks are
lifted during spring tides they remove clumps of vegetation and sediments from
lower marshes. This, plus semi-circular depositional features formed around
melting ice blocks, generates a pattern of highs and lows whim is rapidly
stabilized by vegetation on this fast emerging coast, and is preserved as a
slightly modified form in the patterns of pools of upper marshes and fens.
An indirect effect of sea ice is the mange it creates in
longshore and tidal currents, creating ice-walled channels and bays. Parts of
the sand flats are eroded by canalized tidal currents, and the infauna
population destroyed. A drastic geomorphologic effect is the annual blocking of
the shallow Akimiski Strait to the north. For several weeks it becomes an
ice-walled bay open to the south and experiencing large tides and tidal
currents. Its northwestern coast acquires unique characteristics sum as steep
narrow tidal flats, and marshes with long 'U' shaped channels flushed by high
tides.
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