| Summary: | The objective of this study is to reconstruct the history of
glaciation from the start of Fraser (Late Wisconsinan)
Glaciation to the end of deglaciation, for three areas in the
Cascade Mountains. The Cascade Mountains are located between
the Coast Mountains and the Interior Plateau in southwestern
British Columbia. The Coast Mountains were glaciated by
mountain glaciation followed by frontal retreat, whereas the
Interior Plateau underwent ice sheet glaciation followed by
downwasting and stagnation. The Cascades were supposed to have
undergone a style of glaciation transitional between these
two.
Terrain mapping on air photographs followed by field checking
was used to locate surficial materials and landforms
indicative of glaciation style and pattern. All three study
areas were glaciated by mixed mountain and ice sheet
glaciation. At the start of Fraser Glaciation, alpine and
valley glaciers formed around higher summits as occurred in
the Coast Mountains. At the glacial maximum the entire area
was covered by the Cordilleran Ice Sheet. Deglaciation was
largely by continuous downvalley retreat of active glaciers,
contrasting with downwasting and stagnation in the Interior
Plateau, and frontal retreat in the Coast Mountains. The
scarcity of fresh moraines in the cirques suggests that,
unlike in the Coast Mountains, most cirque glaciers were not
active at the end of glaciation. Only the highest north facing
cirques remained above the local snowline throughout
deglaciation and, as a result, glaciers in these valleys
remained active and retreated up valley.
The pattern of glaciation in the Cascade Mountains was similar
to that of other areas which underwent mixed mountain and ice
sheet glaciation, such as the Presidential Range in New
Hampshire, the Green Mountains in Vermont, mountain ranges in
west central Maine and the Insular Mountains on Vancouver
Island. However, deglaciation in al l areas was complex and
depended strongly on local conditions. For this reason local
patterns cannot be predicted easily on the basis of glaciation
style.
The value of an understanding of glaciation style to improve
the accuracy of terrain mapping was also investigated. It was
found that the model developed for the Cascade Mountains was
of some use in predicting the presence of fine-textured
material in valley bottoms and for the prediction of
glaciofluvial material overlying till . However fine-textured
sediments were not found in al l valleys which were predicted
to contain them. The model appears to be most useful as an
indicator of where to concentrate field checking in order to
locate fine-textured sediments.
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