Understanding the Geology of Canyons
Key Topics
An Introduction to Mountain Canyons
Often overlooked in a landscape of towering peaks, are the rare,
yet fascinating mountain canyons. Why are they rare? After all, rivers have been
carving canyons for as long as there have been rivers. Although true, we must
also remember that rivers have only recently begun to re-sculpt the mountain
landscape. When glaciers co-opted the former river beds, they widened and
smoothed out most of our canyons, leaving wide u-shaped valleys. With the
retreat of the ice, the rivers had to begin anew.
Research suggests that some canyons may have either existed
beneath a few large glaciers, or that they may have been subterranean caves
exposed by the erosion of their roof by glacial ice. Of particular interest in
this theory is Maligne Canyon in Jasper National Park. This canyon is
intricately connected with a vast cave system.
The rare nature of our mountain canyons is reflected in their
prominence as a focal point for hiking trails, roadside stops, interpretive
sites, and even winter guided crampon creeps. Looking into hiking guides
you’ll find trails leading to locations like Johnston Canyon, Sundance Canyon,
Mistaya Canyon, and even Turbine Canyon. Each exhibits a unique character that
makes is a worthy hiking destination. In other cases, the canyons are located
adjacent to major highways. Marble Canyon, North Saskatchewan Canyon, Sunwapta
Falls Canyon and Athabasca Falls Canyons are typical examples. Most are signed
and designed to attract roadside visitors. Another roadside canyon, Maligne
Canyon, has inspired not only interpretive trails, but an entire gift shop and
restaurant.
How Are They Formed?
The formation of canyons can be related to the natural tendency
of rivers to reach a base line elevation. This is generally defined as the point
at which the river reaches the elevation of the large body of water into which
it will drain. Essentially, the larger the difference in height between the
river and its inlet into a large lake, the more energy the river will expend in
the process of erosion. Much of this energy will be expended towards increasing
the efficiency of the drainage system, and facilitating a speedy drop in
elevation.
In the case of Maligne Canyon, the river suddenly found itself
elevated in a hanging valley as the Athabasca Glacier carved a much deeper
valley than its smaller tributary. To facilitate drainage to a now distant
valley bottom, the river expended incredible amounts of energy to deepen the
channel into the narrow, deep canyon visible today.
Other rivers, like the river flowing down Johnston Canyon, were
forced to find new channels when their ancestral streambeds were blocked. A
landslide dammed Johnston Canyon’s original channel. In other cases, glacial
debris may have the same affect.
How Old Are They?
Most of our canyons are very recent additions to the landscape.
In most cases, the creation of canyons coincides with the departure of glaciers
from their valleys. As the ice began to melt, it not only released ancestral
river beds from their icy prison, but it also released immense amounts of water.
So much water was released that the rivers were provided with an incredible
erosional potential. This extra water supply allowed them to rapidly alter their
channels, and the down-cutting may have begun almost instantly. As the glaciers
largely, eventually the initial deluge subsided, and the rate of erosion slowed
accordingly, but didn’t stop. Most of our canyons continue to deepen even
today. While you stand at the top of Maligne or Marble Canyon, the valley floor
is slowly being etched and scoured. The rate may have slowed, but the process is
unrelenting.
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All Material © Ward Cameron 2005