On the 29th of April, 1903, 40 million cubic yards of rock slid down from the face of Turtle Mountain and buried the town of Frank, Alberta. This catastrophic episode of deposition created a pile of debris that locally raised the lowland floor into a series of irregular hills and valleys.

Roll the cursor over the buttons from left to right to study the effects of differential deposition due to landslides.

A stream flows along the side of a valley, next to a steep bluff.

As time passes, the stream cuts down and steepens the valley walls on each side.

With the passage of more time, the valley wall on the right gradually erodes and becomes less steep. The valley wall on the left, however, makes no such adjustment.

Now the valley wall on the left is becoming seriously oversteepened. The valley wall on the right maintains its gentler angle and stability by continuing gradually to erode.

A curving fracture develops within the material that makes up the valley wall on the left.

The material detached by the fracture crashes down, raising the elevation of the valley floor, displacing the stream, and creating a series of minor hills and valleys.

Despite the landslide, the valley wall on the left remains too steep. Another fracture develops.

Once again there is a landslide. Debris that is a mixture of sharp-edged fragments of all sizes (unsorted) buries the valley floor ever more deeply, and even rides part way up the right hand valley slope before it comes to rest.

The valley wall on the left is still overly steep, and another fracture forms.

Once again a landslide occurs, and debris is deposited irregularly over the valley floor and much of the way up the opposite slope.

When the dust clears, it may be seen that the valley floor has become the site of a hummocky landscape, characterized by a series of irregular hills and valleys. The left valley wall now has significantly reduced its steepness and is finally stable.

David J. Leveson