Geology Reference
In-Depth Information
(C)
Figure 10.2.
River freeze-up processes. (A) Growth of ice cover at freeze-up and its associated
water-level changes. (B) Formation of a river icing in a shallow section of a multiple-channel system.
(C) Photograph showing river-icing mound formed in winter 1978-79 on the fl ood plain of Big River,
Central Banks Island, Arctic Canada. The mound is 2.2 m high. The photograph, taken in April
1979, is courtesy of D. Nasagaloak (Sachs Harbour Hunters and Trappers Association). Diagrams
A and B are modifi ed from Gerard (1990).
of the braid bars. The icing mound shown in Figure 10.2C is one of several that occur
annually in approximately the same location on the braided channel of the Big River in
central Banks Island, Canada. These river-icing mounds are a type of seasonal-frost
mound discussed earlier in Chapter 6 (see Figure 6.11).
Break-up usually occurs rapidly, often with considerable fl ooding. The problem is
accentuated in rivers that have headwaters in the south where snow and ice melt begins
earlier. Ice jams frequently occur, as described above for the Mackenzie River. On smaller
rivers, where ice may have frozen to the bed, break-up sometimes involves avulsion, fl ow
is diverted around ice obstructions, and local bank erosion may occur.
