A delta is a deposit of sediment at the mouth of a river that accumulates as the river flows into a standing body of water such as a lake or ocean. Because sediment tends to be rich in nutrients, deltas become fertile wetlands inhabited by diverse wildlife. Among the largest deltas in Canada are those of the Mackenzie and Saskatchewan rivers, as well as the Peace-Athabasca Delta (where the Peace, Athabasca and Birch rivers meet). Certain deltas offer advantageous access to natural resources and maritime transportation, but development projects are often controversial due to the ecological importance of these environments.
A glacier is a large mass of ice, formed at least in part on land, that shows evidence of present or past movement. It is formed by the compaction and recrystallization of snow into ice crystals and commonly also contains air, water and rock debris. With approximately 200,000 km2 of glacier coverage in the Arctic and the West, Canada is home to a significant percentage of the world’s glaciers. By 2100, however, scientists predict that those in Alberta and British Columbia will have lost 70 per cent of their 2005 volume due to climate change.
Tundra, which comes from a Sami word meaning “barren land,” refers to a treeless arctic region characterized by permafrost. Canada’s tundra is known for its freezing temperatures, lack of trees, low-growing vegetation and abundant rock outcrops. The southern boundary of tundra in Canada extends from the Mackenzie River delta to the southern reaches of Hudson Bay and northeast to the Labrador Peninsula. The term “alpine tundra” is often used to describe any area above the treeline in mountainous areas. But “alpine tundra” and “arctic tundra” are not interchangeable. (While the two regions share some similarities, the differences are significant.)
The Rocky Mountain Trench is a long and deep valley extending approximately 1,500 km from the Bitterroot Valley in northwest Montana through British Columbia to the Liard Plain just south of the Yukon Territory. Its predominantly flat floor is 3–20 km wide and ranges in elevation between 600 m and 1,000 m above sea level. With walls made of sedimentary, volcanic and igneous rock, the Trench is sometimes referred to as the “Valley of a Thousand Peaks” because of the towering mountain ranges on either side: the Rocky Mountains to the east and the Columbia, Omineca and Cassiar mountains to the west. Humans have relied on the rich resources provided by this distinctive landscape from pre-colonial times to the present.
A continental divide is a ridge or natural boundary of elevated terrain that separates the drainage basins of a continent. Each drainage basin contributes its water to river systems, which in turn flow into distinct larger bodies of water, such as oceans. The main continental divide in Canada follows the ridge of the Rocky Mountains.
The Canadian Shield refers to the exposed portion of the continental crust underlying the majority of North America. The crust, also known as the North American Craton, extends from northern Mexico to Greenland and consists of hard rocks at least 1 billion years old. With the exception of the Canadian Shield, the rocks of the North American Craton are buried deep within the continent and covered by soil and other material. At 5 million km2, the Shield makes up roughly 50 per cent of Canada’s land mass. Shaped like a horseshoe — or the shields carried during hand-to-hand combat — the Canadian Shield extends from Labrador in the east to include nearly all of Québec, much of Ontario and Manitoba, the northern portion of Saskatchewan, the northeast corner of Alberta, much of the Northwest Territories and Nunavut and into the Arctic Archipelago. (It also reaches into parts of the United States, in New York, Wisconsin and Minnesota.) While at times a barrier to settlement, the Shield has also yielded great resources, including minerals, coniferous forests and the capacity for hydroelectric developments.2