The Earth's major mountain systems lie along the margins of crustal plates where concentrated tectonic forces have caused uplift, deformation and igneous activity (see GEOLOGICAL PROCESSES; PLATE TECTONICS). Individual mountain ranges may be formed by volcanic eruptions or, more commonly, by differential EROSION of an uplifted terrane. When rapid uplift is accompanied by slow erosion, a plateau results. If erosion keeps pace with uplift, streams and GLACIERS erode away less competent rock, leaving more resistant rock standing as mountain ranges between the valleys.
The long, narrow ranges of the ROCKY MOUNTAIN system of western Canada reflect the structure of resistant beds of folded and faulted sedimentary strata; the broader ranges and massifs of the Coast Range of BC were etched by water and glacier ice from an uplifted, granitic terrane of more uniform resistance to erosion. The relief and ruggedness of a mountain range depend on its age. The precipitous, very young ranges of the St Elias Mountains in the southwestern Yukon, where rapid uplift is still proceeding, include the highest individual peaks in Canada.
Uplift of the somewhat less rugged Rocky Mountains began to decline after an episode of deformation about 70 million years ago. The subdued topography of the ancient Appalachian Mountains is the result of erosion during the 150 million years since the last major uplift and deformation in eastern Canada. Submarine mountain ranges, which rise from the ocean floor along mid-ocean ridges, such as the mid-Atlantic Ridge and East Pacific Rise, are of volcanic origin. On the moon and on planets that have little atmosphere, such as Mercury and Mars, circular or crescent-shaped mountain ranges around impact craters have survived for hundreds of millions of years without being destroyed by erosion.
Author J.G. SOUTHER
Links to Other Sites
Life of a Rock Star
This site tells the story of an extraordinary group of scientists who tramped, paddled and rolled across Canada in the nineteenth century to study the geology of Canada's varied terrain.
An extensive information source about the geological history, human settlement patterns, earth and water resources, and natural hazards found in locations across the country. Click on the red symbols on the interactive map of Canada to explore aerial landscapes, maps, photos, colourful online posters, and more. A Geoscape Canada website from Natural Resources Canada.
The Alpine Club of Canada - Vancouver Section
See online copies of the "Avalanche Echoes" newsletter. Great photographs and updates of club activites on local mountains.