Alberta & BC Rockies How the Rockies Were Made
The story of the Rockies goes back about 120 million years ago, when their peaks started poking out of ancient marshland.
In the days of dinosaurs, southern Alberta was a very flat and low-lying marshland. For a period of 50 to 100 million years, dinosaurs lived here, feeding on marsh or lowland vegetation, and some meat-eating dinosaurs feeding on the vegetarian dinosaurs. After the dinosaurs died, their bones were gradually covered and they became part of the rocks. The vegetation that was buried at the same time rotted and with great temperatures and pressures over time became the oil and gas that now fuels AlbertaĖs petro-chemical industry. Over millions of years the layers became hardened and compressed into visible layers of rocks.
The southern Alberta region is world famous because of the discoveries of Joseph Tyrell, a geologist with the Canadian Pacific Railway, who in 1884 discovered dinosaur bones in the badlands 100 km east of the Canadian Rockies. In the badlands, the dinosaur bones were exposed by erosion. In the mountains, the dinosaur bones are exposed through lifting. It was not until the 1950's that the continental drift theory of continents was proven after the ocean floors were mapped using sonar (which was invented to find submarines in the Second World War). This proves that the mountains were created by tectonic plates of land being pushed against each other, and being forced to tremendous elevation. This explains the unusual rock lines in the mountains, some rising from the valley floor to the sky, and others folding up and down like ocean waves.
After the mountains were formed by upthrusting sheets of rock, they were subject to erosion not only by the usual forces of wind and rain, but also (because of their elevation) glaciers on their slopes and (during the ice ages) extensive glaciers in their valleys.
The Ranges of the Rocky Mountains
The Rocky Mountains are actually only 120 miles deep, from east to west. Many people figure that they go all the way to the Pacific Ocean, but thatĖs not true. The Rockies actually consist of four sets of ranges that extend from Alberta's foothills to the Rocky Mountain Trench that includes the Columbia Valley. Each of these ranges is separated by parallel valleys.
The Front Ranges
are those east of the Bow, North Saskatchewan, and Athabasca Rivers (and also east of the Bow Valley Parkway and Icefields Parkways). The eastern slopes of this range was worn down by multiple glacial periods and rise over 1, 000 or 2, 000 metres above the 1, 000 metre elevation of the foothills. A stunning example of this is the Endless Chain Ridge, which goes on for over 20 miles on the eastern side of Highway 93, rising over a mile above the highway. These ranges are relatively dry, since they are in a "rain shadow" after moisture-laden clouds have dumped most of their water on more westerly (and often higher) mountains.
The Eastern Main Ranges
are those that form the Continental Divide, and contain the 20 tallest peaks in the Canadian Rockies, including Mount Robson (3, 954 metres, 12, 972 feet). Water on one slope falls toward the Pacific Ocean 600 km away, and water on the other slope flows to the Arctic Ocean 1, 500 km away (in the northern Rockies) or the Hudson's Bay 1, 700 km away (in the southern Rockies). Because of the elevation and the massive amounts of snowfall, this range contains some of the largest glaciers including the Columbia Icefield.
The Western Main Range
includes the mountains west of the Kootenay River. Rivers cutting through this range are much steeper than those in the eastern ranges of the Rockies, because they travel a much shorter distance to the ocean. The valley bottoms are also at a much lower elevation and therefore receive more rainfall.
The Western Range
occupies the area between Golden and Radium Hot Springs in British Columbia. These mountains, the oldest in the Rockies, are made of weak shale, and are more eroded and rounded than the ones to the east. There is also evidence that these mountains escaped much of the glaciation of the past few ice ages. The mountain valleys are more V-shaped than those in the eastern Rockies.
Rocky Mountain Trench
forms the western boundary of the Rockies, by creating a broad valley that extends in a north-westerly direction for hundreds of miles. The Columbia River was a broad glacial trough, beginning near Radium Hot Springs. The weather here is warm and dry: there are 100 more frost-free days a year here than in Banff. Just to the west of the Columbia River are the Buggaboo, Selkirk and Purcell ranges that are so popular with heli-skiers. Because of their proximity, these are often thought to be part of the "Rockies".
Here are some geological terms you'll need when visiting the mountain parks.
- Arch-shaped folds in rocks. The top of the arch is stretched and is fairly susceptible to erosion.
- Castellated mountain
- Found in the Eastern Main Ranges where resistant limestone or dolomite formations are separated by weaker layer of shale, creating a layer-cake appearance (example: Castle Mountain).
- A break or fissure in a glacier, as it bends to conform to the shape of the underlying bedrock.
- Dogtooth mountain
- When sheets of rock were thrust nearly vertical during mountain building, and some of the layers were eroded away more than others. Usually found in the Front and Western Main ranges.
- A permanent build-up of ice and snow caused by snowfalls greater than the annual summertime melting (note: Canada has over 29, 000 glaciers). Glaciers are often found at high elevations and move slowly down the mountain due to the weight of new snow and ice above.
- Horn mountain
- A peak eroded by several glaciers on several sides at once. This is evidenced by sharp ridges pointing up the slope of the mountain (examples: Mt Assiniboine, Mt Chephren).
- Gravel and rock left behind as a glacier retreats. Also the accumulation found at the sides (a "lateral moraine") and the ends of the glaciers (a "terminal moraine").
- Overthrust mountain
- Flat slope on one side, and heavily eroded on the other (examples: Endless Chain, and Mount Rundle)
- Sawtooth mountain
- These mountain feature a series of parallel ridges marking peaks of strong layers, separated by eroded weaker layers (examples: Sawback Range, Mt Ishbel).
- Sedimentary rock
- Formed by layers of erosion sediment settling in ancient oceans or seas.
- U-shaped folds in rocks. The bottom is compressed and therefore fairly erosion-resistant
- Rocks in a continental plate lifted skyward by collision with another plate.