Landforms of British Columbia 1976 - Department of Geography

CHAPTER III.-SPECIAL ASPECTS OF THE
BRITISH COLUMBIA LANDSCAPE
British Columbia spans a thousand-mile length of the Canadian Cordillera and
of the vast cordilleran mountain chain that extends along the western side of North
America. Its position is not unique, and yet certain features of the landscape give the
Province a special flavour and set it apart topographically from the rest of the Cor-
dillera. These features are five in number. No other large segment of the Cordillera
has been so completely covered during the Pleistocene with glacial ice, as a conse-
quence of which the landscape in all parts of the Province shows the effects of glacial
erosion and deposition. The pre-glacial topography, the product of erosion by the
various river systems, shows deviations from normal river patterns that are the result
of stream piracy on a major scale. The fiord coastline is taken very much for granted
by the local inhabitants, yet it is comparable in dimension and grandeur to the world-
famous coasts of Norway, Patagonia, New Zealand, and elsewhere. To these special
features of landscape-namely, glaciation, drainage, and coastline-may be added
Tertiary volcanic activity and lineaments. Of these, none is in any way unique or
restricted to this region, but they nevertheless combine to give distinction and charac-
ter to British Columbia landscapes. In the following pages these five features are
treated separately to unify and give meaning to the scattered references made to them
in Chapter II.
GLACIATION IN BRITISH COLUMBIA
There is abundant evidence that the earth’s climate has been continuously
changing in an extremely complex way. Warm periods have been succeeded by cold,
and more than once in the geologic past conditions have been sufhciently severe to
produce a glacial period. The latest of these refrigerated periods began with the
Pleistocene epoch, about one million years ago. The Pleistocene is the time interval
on the geological calendar when glaciation was widespread, not only in British
Columbia, but over large areas in the northern and southern hemispheres. Even in
regions that were not glaciated there was sufhcient change in the Pleistocene climate
to one that was cool and moist so that the plants, animals, and physical history were
affected.
A background knowledge of glaciation is important in the consideration of land-
forms in British Columbia because the Province was intensely glaciated during the
Pleistocene. Almost the entire Province was covered by ice which, at.its maximum
extent, covered all but some of the highest mountain peaks and parts of the northern
and southern Rocky Mountains. The topography everywhere shows the effects of
glacial erosion and deposition. In this Province, as in eastern North America,
Europe, and other parts of the northern hemisphere, the glacial history was probably
complex, but the visible effects of glaciation are almost entirely those of the last,
Wisconsin stage.
Glaciation in British Columbia resulted in the eventual accumulation of enough
ice to form an ice-sheet of continental dimensions. The growth, culmination, and
decline of this Cordilleran ice-sheet was in response to world-wide factors of climatic
control. Climatic cycles during the Pleistocene produced cyclic advances and reces-
sions of glaciers and resulted, in some parts of the world, in four glacial stages of ice
advance separated by three interglacial stages of ice recession and partial deglacia-
tion.
Glaciation in British Columbia differed from much of the rest of Canada in that
the ice-sheet occupied an initially mountainous terrain. In mountain regions the
cycle of glaciation is considered to begin with the formation of small cirque glaciers
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