Great Lakes and St. Lawrence Lowlands

Great Lakes and St. Lawrence Lowlands, Canadian physiographic region located in southern Ontario and southern Québec. Although the Great Lakes and St. Lawrence Lowlands region makes up less than 2 percent of Canada’s territory, it contains the most densely populated area of Canada, with the nation’s two largest cities, Toronto, Ontario, and Montréal, Québec. It also has the most productive agricultural lands and houses most of Canada’s manufacturing firms.

The area of the Great Lakes and St. Lawrence Lowlands is about 180,000 sq km (70,000 sq mi), making it the smallest of the major physiographic regions of Canada. The region lies south of the Canadian Shield and extends west along the St. Lawrence River and lakes Erie and Ontario from Québec City to Windsor, Ontario. These lowlands form the southernmost area of Canada, extending as far south as latitude 42° north.

Across the flat to rolling topography of the region, elevations vary from 100 to 400 m (300 to 1,300 ft). One of the few relief features in these lowlands is the Niagara Escarpment, a ridge that extends from Rochester, New York, across southern Ontario to the Manitoulin Islands in Georgian Bay. The highest points in the region are found in Québec’s Monteregian Hills, the highest of which is Mont Brome (533 m/1,749 ft). Mount Royal (234 m/768 ft), located in the heart of Montréal, is the best known of the Monteregian Hills.

The sedimentary rocks that lie under the surface of the Great Lakes and St. Lawrence Lowlands were formed some 500 million years ago, in the early Paleozoic Era. At that time, a shallow sea existed along the southern edge of the Canadian Shield. Over time the water and the sediments at the bottom of the sea pushed down on sediments beneath them. This pressure gradually turned the lower sediments into sedimentary rocks such as limestone.

Some 12,000 years ago, glacial lakes occupied the Great Lakes lowland while the waters of the Atlantic Ocean spread over the St. Lawrence lowland. When these waters receded, they left behind deposits from which the rich soils of this region developed.

The climate of the Great Lakes and St. Lawrence Lowlands is classified as a middle latitude continental climate. Summers are hot and humid while winters are short but cold. The natural vegetation consists of broadleaf and mixed hardwood forests. Little of the original vegetation remains, as farmland and industrial plants have transformed the landscape. The major natural resource found in this region is its highly productive soil. Waterpower from Niagara Falls and the St. Lawrence River is another important resource.

Some 16 million Canadians, over half of the country’s population, live in the Great Lakes and St. Lawrence Lowlands. The region holds most of Canada’s major population centers, including the two largest metropolitan regions, Toronto (5,304,100 in 2005) and Montréal (3,635,700). Other important metropolitan areas are Ottawa, Ontario (1,148,800), Québec City (717,600), Hamilton, Ontario (714,900) and London, Ontario (464,300).