Figure 8. Horizontal movement of ice against rocks in early winter.
Figure 9. Spring breakup on the St. Marys River. Note the large floating ice
masses in the foreground.
Damage due to horizontal forces can occur natu-
vately owned structures are often contained within
rally during the unstable early ice period (Fig. 8)
a band of shore-fast ice that can provide effective
or during ice cover breakup events (Fig. 9). Ships
protection (Hodek et al. 1986). Rather, they may
do not typically transfer forces to a structure
break up or dislodge ice, allowing it to be moved
through the ice, unless they come very close to
by natural water currents, waves or winds against
shore, since any forces imparted to the ice cover
a structure. Since the St. Clair River is typically
are rapidly distributed through the ice, render-
ice-free over much of its length, ship passage
ing point loads quite small. Further, small pri-
through the natural ice arch on Lake Huron has
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