Canadian Shield

Canadian Shield, vast horseshoe-shaped physiographic region that covers central and eastern Canada and small parts of the northern United States. The shield extends in a great semicircle around Hudson Bay, reaching from the Arctic coast north of Great Bear Lake in the Northwest Territories to northern Québec and Labrador. The Canadian Shield is the largest physiographic region in Canada. It was formed as part of the earth’s crust some 3 billion years ago, and the hard, crystalline rocks of the shield are among the oldest in the world. In the late 19th century, the rockiness of the shield represented a major obstacle to the construction of the Canadian Pacific Railway, Canada’s first transcontinental railway.

The Canadian Shield occupies an area of 4.6 million sq km (1.8 million sq mi) in Canada, or nearly half the area of Canada. The region includes portions of six provinces (Newfoundland and Labrador, Québec, Ontario, Manitoba, Saskatchewan, and Alberta) and two territories (Northwest Territories and Nunavut). The shield also extends into the northern areas of Minnesota, Wisconsin, Michigan, and New York in the United States.

Except for mountainous areas in Labrador and Baffin Island, the Canadian Shield forms a rough, rolling upland. Most of this upland ranges in elevation from 300 to 500 meters (1,000 to 1,600 ft). In Labrador and Baffin Island, the shield has been tilted upwards, and elevations reach upwards of 1,500 m (5,000 ft). 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 Canadian Shield is the ancient geological core of Canada. It was formed some 3 billion years ago when the earth cooled sufficiently to create a crust of solid rock. During the most recent Ice Age, which lasted until about 10,000 years ago, continental ice sheets covered the region, stripping away soil, depositing glacial drift, and creating many glacial lakes.

Within the wide area covered by the shield in Canada, climates range from the subarctic to the arctic. Subarctic climates have cold winters but summers warm enough to permit some tree growth. Arctic climates have year-round low temperatures, which prevent trees from growing. In the subarctic region, a boreal forest, consisting of black and white spruce, birch, and, along its southern edge, aspen, covers the shield. In the arctic areas, the natural vegetation changes to the low-lying grasses, heaths, and mosses of the tundra. 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 southward in the winter to the boreal forest.

The Canadian Shield has three major natural resources: forests, minerals, and water. The commercial forests are found in the provinces of Québec, Ontario, Manitoba, and Saskatchewan. The main minerals are copper, iron, lead, nickel, gold, silver, uranium, and zinc. In the 1990s commercial diamond mines began operating in the Northwest Territories. The extensive rivers and lakes of the region make it an important source of hydroelectric power. The Canadian Shield contains very little agricultural land.

The region is sparsely populated. The major population centers are mining towns and small industrial cities. The largest metropolitan regions are Sudbury, Ontario, with a population in 2006 of 162,000, and Chicoutimi, Québec (162,300).