The Shrinking Mountains

Have you ever taken a look out the window and thought to yourself: "It's funny, but I could swear Mount Rundle looked bigger yesterday"? You haven't? Well, neither have most people. The mountains are getting smaller but they are shrinking according to a timescale that we as humans find very difficult to comprehend.

When the front ranges were formed around 85 million years ago, they were quite a bit larger then they are today--almost twice the size--but slowly they are being worn down and washed back into the seas from which they originally rose. There are a variety of forces working to renovate the surrounding mountains, each of which helps to chip away at a bit of the old block.

Water is perhaps the greatest agent of erosion as it flows down the mountain as runoff streams. Picking up materials as it flows, these materials in turn act as abrasives to wear away at the rock. Johnston Canyon in Banff is a good example. For hundreds of millions of years the waters flowed along a certain route in this area until the glaciers left behind debris that dammed that original route. The canyon we see today has formed as a result of the river finding a new route down the valley and quite rapidly carving a new channel. This canyon has formed since the retreat of the glaciers and can show the extent of change that can occur in 10,000 years.

Another of the primary forces working to wear the mountains down is the regular process of freezing and thawing that takes place over the course of the year. Water is a very special liquid in that it expands when it freezes. This can act as a very powerful wedge when it flows into small cracks and subsequently freezes. When you look at the large scree or loose rock slopes that can be found at the base of most cliffs in the area, you're looking at the results of millions of years of freezing and thawing.

Much of the scree that makes up these slopes was actually formed near the end of the last ice age. During this period, the areas adjacent to the receding glaciers were under climatic conditions similar to permafrost areas. This type of climate is known as periglacial or near glacial and resulted in much more frost wedging than we see today. So for a short time geologically, the mountains were being worn down at a more rapid rate than they are today.

There are still other processes acting against the mountains. Chemical erosion of the limestone can actually dissolve the rock and wash it away. In this process, water and carbon dioxide in the atmosphere react to form a weak carbonic acid which easily dissolves the limestone.

Plants are also slowly wearing the mountains down. Some, like the orange lichens that you see coating many of the local rocks, can actually slowly dissolve the rock and help in the creation of soil. Others, force roots down the smallest of cracks and cause results similar to frost wedging.

The mountains are slowly shrinking as we sit under their shadow. The processes work at a very slow pace, but work unrelentingly. As you hike, take the time to look around you and notice some of the processes that sculpt our mountains.