Geology Reference
In-Depth Information
Standard frequency and magnitude concepts can be used in the study of cold-climate
coasts. Periods of maximum wave generation are likely to occur during those storm events
which coincide with the existence of maximum ice-free fetch. For example, in the Western
at Sachs Harbour during the period 1971-1977, no storms acted over a fetch greater than
100 km and the long-term probability of such an event was less then 0.1%. Of the 47 storm
events with ice-free fetch in the same period, less than 40% had predicted signifi cant wave
heights greater than 2.0 m (Harry et al., 1983). Storm surges and storm-generated sedi-
ment transport in the Beaufort Sea area are also described (Forbes, 1989; Hequette and
Hill, 1993). These, and other such studies, demonstrate not only that sea ice is an impor-
tant restraint upon wave generation and coastal erosion, but also that traditional methods
of coastal analysis are useful, even in ice-infested waters.
There are problems inherent in isolating and defi ning the geomorphic effectiveness of
single, major events. For example, beach borrow associated with construction activity may
increase the effectiveness of a storm event, while coastal engineering structures will
reduce such events (Hume and Schalk, 1964; Walker, 1991).
As the direct result of the limited wave action experienced by many Arctic beaches,
beach processes and the transport and redistribution of material are thought to operate
at slow rates. In general, beaches are poorly developed and narrow, often composed pri-
marily of coarse sand and cobbles. Beach sediments are poorly sorted and possess low
roundness values compared to other beach environments (Table 10.9). However, there is
abundant evidence that considerable long-shore transport of material may take place
because many coastlines show dynamic growth of complex depositional features such as
spits and offshore bars (Hequette and Ruz, 1991; Ruz et al., 1992). In the Western Arctic,
two of the largest are those at Point Barrow, Alaska, and Cape Kellett, southwest Banks
Island. The latter extends for a total distance in excess of 12 km. In the vicinity of Sachs
Harbour, M. J. Clark et al. (1984) concluded that annual sediment gain over a 29-year
period was
57 000 m
3
and that a 1.6 km long spit at the mouth of the harbor could have
grown in a period estimated at between 70 and 230 years (Figure 10.12). Along the north-
ern coast of Alaska, Hume and Schalk (1967) report approximately 10 000 m
3
of annual
net sediment transport is typical.
∼
Table 10.9.
Some roundness values for beach materials in various periglacial and non-periglacial
environments.
Locality
Beach Environment
Rock Type
Cailleux roundness values
Periglacial:
Devon Island, NWT, Canada
Sheltered
Limestone
25-267
Hall Beach, NWT, Canada
Sheltered
Limestone
216
Jacobshaven, west Greenland
Sheltered
Quartz
90-105
Kuggsa Dessa, west Greenland
Exposed
Quartz
135-160
Godthaab, west Greenland
Exposed
Quartz
270-388
Non-periglacial:
Western Mediterranean
Enclosed sea
Limestone
355
(various sites)
Lake Ontario, Canada
Enclosed sea
Gneiss
388
Finistère, northwest France
Exposed
Quartz
250-270
400-460
Source: McCann and Owens (1969).
