Canadian Shield

Canadian Shield or Laurentian Plateau, vast horseshoe-shaped geological region that covers central and eastern Canada and small parts of the northern United States. The shield extends in a great semi-circle around Hudson Bay, ranging from the Arctic coast north of Great Bear Lake in the Northwest Territories to northern Quebec and Labrador. It covers about 4.8 million sq km (1.9 million sq mi) and occupies almost one-half of Canada's total area, including portions of six provinces (Newfoundland and Labrador, Quebec, Ontario, Manitoba, Saskatchewan, and Alberta) and two territories (Northwest Territories and Nunavut). In the United States it includes the Superior Upland of northern Minnesota, northern Wisconsin, northern Michigan, and the Adirondack Mountains of north-eastern New York.

The oldest part of the North American crustal plate, its rocks contain fossils of some of the earliest forms of life, such as algae and bacteria from more than 2 billion years ago. During the most recent of the Ice Ages, beginning about 2.5 million years ago, continental ice sheets covered the region, stripping away soil, depositing glacial drift, and creating many lake basins and riverbeds. Present-day elevations in the shield are mostly between 300 and 600 m (984 and 1,969 ft) above sea level, except in limited areas, such as the Quebec-Labrador Peninsula, where they rise to about 1,070 m (3,510 ft). Where the shield has been tilted upwards, elevations are greatest—Mount Thule on Baffin Island reaches a height of 1,711 m (5,614 ft), while the highest point in the Torngat Mountains of Labrador is 1,652 m (5,420 ft).

The climate is arctic in the northern shield, where the average January temperature is about -32° C (-25° F). The growing season lasts less than 40 days a year, and lakes are free of ice for only about three months each year. North-west of Hudson Bay are vast regions of permanently frozen subsoil. The more temperate southern shield has forests of pine and northern hardwoods. Tundra, carpeted with sedges, grasses, lichens, and dwarf shrubs, lies north of the forests. Muskegs (sphagnum bogs), swamps, and lakes are found throughout the shield area. Black bears, brown fox, and beavers occupy the subarctic zone, while polar bears and arctic fox live in the arctic zone. Caribou migrate to the arctic in the summer to feed on the lush tundra plants and migrate southwards in the winter to the boreal forest.

The northern Canadian Shield is sparsely populated, mainly by Inuit and other indigenous people. The southern shield has many urban areas, which have developed principally as centres for exploiting natural resources. The southern parts of the shield in Canada are important for mining, hydroelectricity, and harvesting pulpwood. Minerals found there include iron, nickel, copper, zinc, uranium, gold, silver, platinum, and molybdenum. Many of the mines are located south of James Bay. Commercial diamond mining began in the Northwest Territories in the 1990s. The shield was a major obstacle in the political development of Canada—an impasse that was not overcome until the Canadian Pacific Railway forced its route through the rock and muskeg north of Lake Superior, connecting the settled East of the country with the developing prairie region.