There are many features about the Canadain Rockies that engender a sense of wonder when you first look at them. The number of mountains in the range is one feature. Stand in the towns of Jasper, Banff or Canmore and there are mountains in every direction, the towns seeming to sit in a bowl or caldera, surrounded on all sides by jagged mountain peaks. The jagged prominences are another feature that catches the eye and which provides a clue as to their geology. The last thing you might think of as you look as them is that the rock of which they are made started off beneath a shallow sea. It is kind of mind boggling!
A major distinction between the American and the Canadian Rockies is the type of rocks that they are made from. The American Rockies are primarily made of metamorphic and igneous rock such as gneiss and granite. Metamorphic rocks is made when heat, pressure or fluids act on existing rock, subjecting them to extreme conditions. During these compressive events the original rocks are re-crystallised into other forms and shapes. Gneiss, for example, is granite or sandstone subjected to high temperatures and pressure.
The Canadian Rockies on the other hand are primarily made up of layered sedimentary rock such as limestone and shale. Limestone is often made up of the skeletons of minute marine animals that sink in their millions to the bottom of shallows seas where they form layers. Shale originates as mud that is rich in clay minerals and under pressure creates a thinly bedded, fine grained sedimentary rock. How do you go from rocks created in shallow seas and mudbanks to the Southern Canadian Rockies?
During the Paleozoic time period (from about 540 million years ago to 250 million years ago) western North America lay beneath a shallow sea, creating the conditions for the laying down of the limestone and shale rock forms. During a period of mountain building activity known as the Laramide orogeny (exact dates for this period are debateable but begining 70 / 80 million yrs ago, ending 35 / 55 millions years ago), plate tectonic activity that included the Kula Plate being subducted beneath the Continental Plate, resulted in the creation of the mountains.
Subsequent glacial activity helped shape and form the landscape we see today in the Canadian Rockies. This includes the large U-shaped valleys scraped out by the glaciers and the mounds of moraine glacial drift deposits that litter the valley floors. In addition to the changes worked by the glaciers, the mountains are being constantly eroded by the effects of water, wind, snow and ice. As the mountains are eroded even older rock is revealed below. The Southern Canadian Rockies still have a number of glaciers on or near the peaks from which many rivers and creeks flow, part of the continual recycling of water in the region that results in a wetter and cooler climate than in their counterparts in the USA.
Subsequent glacial activity helped shape and form the landscape we see today in the Canadian Rockies. This includes the large U-shaped valleys scraped out by the glaciers and the mounds of moraine glacial drift deposits that litter the valley floors. In addition to the changes worked by the glaciers, the mountains are being constantly eroded by the effects of water, wind, snow and ice. As the mountains are eroded even older rock is revealed below. The Southern Canadian Rockies still have a number of glaciers on or near the peaks from which many rivers and creeks flow, part of the continual recycling of water in the region that results in a wetter and cooler climate than in their counterparts in the USA.