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Case Study 4

The Cascades

Connecting Canada and the United States

Malcolm Cooper Geophysical aspects and

Introduction history of activity
The Cascades form part of the Pacific Rim
The Cascades are a 700+km long group of volcanic zone and result from the Pacific Plate and
volcanoes as well as non-volcanic origin mountains its smaller companion the Juan de Fuca Plate
that stretch along the west coast of North America, being subducted under the North American Plate
from Northern California, USA into British (Hill, 2004, pp4–7). This 960km long area lies
Columbia, Canada (Hill, 2004; Dzurisin et al, between 96 and 240km offshore, but produces its
2008; Figure CS4.1). At its southern end the range tectonic effects in the Cascade range. These effects
is about 50 to 80km wide and 1370 to 1520m are eruptions and earthquakes, all of which are
high. At its northern end at Lytton Mountain extreme events. Most of the major peaks are
(2049m) in Canada, near the confluence of the stratovolcanoes made up of layers of lava and other
Fraser and Thompson Rivers, the range is only volcanic debris, and many are quite young (e.g. Mt
16km wide. The tallest volcanoes of the Cascades St Helens), although some such as Mt Rainier are
are known as the High Cascades and include the thought to be considerably older. However, almost
4392m high Mt Rainier. Overall the North all the major volcanoes shown in Figure CS4.1
Cascades and south-western Canadian Cascades have erupted in the past 4000 years, with 7 being
are extremely rugged, with many of the lesser active within the past 250 years (Dzurisin et al,
peaks steep and glaciated, but the majority of the 2008). All are presently classed as active and can be
volcanoes lie in Washington, Oregon and northern expected to erupt in the future.
California. This history of activity is also reflected in local
In addition to their latent and active volcanism myth and legend, as is common with geothermal
the Cascades are a watershed range that has played areas (Cooper-Erfurt and Cooper, 2009). Indigenous
a key role in human settlement in the Pacific peoples have inhabited the area for thousands of
Northwest of the USA and Canada. Heavy rainfall years and developed their own beliefs concerning
and forest environments produced rivers and lakes the origin and nature of the Cascades (Cashman
as well as good agricultural land and timber for and Cronin, 2008). According to some of these
industry. As a consequence the mountains support tales the mountains Baker, Jefferson and Shasta
numerous population centres and are heavily used were used as refuges from a great flood. Other
for recreation.
stories, such as the Bridge of the Gods tale, had

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