

What Lies Beneath Devon presentation at Pioneer 73

Submitted by Devon Nature Club --

What Lies Beneath Devon presentation at Pioneer 73

Dr. Alberto Reyes, Geology Professor at the University of Alberta, and Greg Hartman professional geologist from the Alberta Geological Survey gave a talk Thursday evening about the geological materials that make up the geology beneath Devon, the processes that affect these materials and how they affect our lives, local ecology and future.

Dr. Reyes spoke about the big picture. The Canadian Prairies are flat because of multiple ice ages that had melts and frozen periods. During the melts water from the glaciers became rivers that wandered in different paths across the prairies carrying silt, fine clay, sand and an ancient volcanic ash called Bentonite, which were deposited smoothing the prairie area. These prairie soils are fragile and wind erosion carried soil into low areas, resulting in a flat surface that has become our prairies. Exceptions are composed of ancient volcanic rock more resistant to erosion that forms the more stable Canadian Shield area of northeast Alberta and the Cypess Hills in southeast Alberta that were left behind when an uplift formed the Rockies.

The Bentonite common in the Devon-Edmonton area is like a sponge and swells four times its size with water. It is white in color and can be seen along the west bank at the south end of Lions Park, called the “Hoodoo Hill”. The moisture-laden Bentonite makes the soil in these areas unstable and easily eroded. It is extremely slippery when wet. The slumps and seeps in Voyager and Lions parks as well as Battery and Washout ravines come from the saturated Bentonite slowly leaking moisture. Because Bentonite holds moisture, the rain can permeate the layers of soil above but cannot permeate the saturated Bentonite which results in the upper layers sliding or sloughing off.

The underlying bedrock is weak as it is not solid rock but a composite aggregate unlike the solid Canadian Shield.

The landslide on Whitemud Road in Edmonton a few years back was caused by building houses too near the top of the river bank. The crown was disturbed, undoing the stable forces that evolved over time to hold the bank in place. The result was houses sliding down the bank.

This shows that it is important not to disturb the crown of the bank.

Dr. Reyes and Mr. Hartman reassured Devon residents that our area is reasonably able but it is

important to keep development or any activity that can causes disturbance to the crown of the bank well away from the river and ravine banks.


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