Laurentian Upland


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Laurentian Upland

 

a mountainous area in northeastern North America, in Canada and partly in the United States. In the southeast it is bordered by the Appalachians, in the south by the Central Plains, in the southwest by the Great Plains, in the west by the Mackenzie Lowland, and in the north by the Hudson Bay lowland. In the north and northeast it extends to the Arctic and Atlantic oceans. It has an area of about 5 million sq km.

The Laurentian Upland has a gently rolling surface, with elevations of 200–400 m predominating. The eastern part (the Labrador Peninsula) is more uplifted, and along the coastline there is mountainous terrain (the Torngat Mountains, 1,621 m). Another elevated sector (up to 1,100 m) is located north of the St. Lawrence River. The upland is composed of Archean and Proterozoic gneisses, crystalline schists, granites, and diorites. The Laurentian Upland is rich in iron and copper ores, nickel, gold, uranium, and other minerals. During the Pleistocene the Laurentian Upland was entirely covered by an ice sheet up to 3,000 m thick. Glacial forms are seen in hilly morainic plains, drumlin zones, and esker ridges. Vast areas of bedrock show traces of glacial action (roches moutonnées, for example). Glaciation was accompanied by oceanic transgressions that engulfed mainly the marginal parts of the upland. The formation of the numerous lakes that filled the basins plowed by the glacier was associated with the transgressions. Vast outwash plains are found in the south.

The Laurentian Upland is located in the temperate and subarctic climate zone. The winter is long, with abundant snowfall in the east. The summer is short and cool owing to the influence of ice-covered Hudson Bay and the cold Labrador Current. Permafrost is widespread everywhere. There is a dense but weakly developed river network. The most important rivers are the Churchill, Koksoak, Nelson, Back, and Coppermine. There are many lakes, the largest being Reindeer, Dubawnt, and Nipigon. The rivers are fast-flowing, with many rapids. Most of them are channels connecting various lakes. Turbulent spring high water is typical of the rivers, which are frozen over for six to seven months. From north to south the order of zones is tundra, forest-tundra, and taiga. The tundra, which occupies one-third of the upland, typically has moss-lichen, sedge, and brush (dwarf birch, Ledum, and other plants) associations on tundra-gley and marshy soils. South of the tundra there are forest-tundras and sparse northern taiga forests consisting primarily of black spruce and balsam fir (in the east), white spruce (in the west), and balsam poplar (along the river valleys). Larch is distributed throughout the area. The southern part of the Laurentian Upland is covered with dense coniferous forests of the taiga type growing on podzolic soils. The composition of the forests is most varied in the east, where white pine, Banks pine, red pine, and Canadian hemlock predominate, mixed with various species of maple, birch, and aspen.

Among the animals found in the tundra are the caribou, arctic fox, lemming, and arctic wolf; birds include the ptarmigan and snowy owl. In the taiga, moose, Rangifer caribou, black bear, marten, skunk, beaver, mink, and muskrat are common.

REFERENCES

Eardley, A. Strukturnaia geologiia Severnoi Ameriki. Moscow, 1951. (Translated from English.)
Vitvitskii, G. N. Klimaty Severnoi Ameriki Moscow, 1953.
Ignat’ev, G. M. Severnaia Amerika: Fizicheskaia geografiia. Moscow, 1965.
Atwood, W. W. The Physiographic Provinces of North America. Boston [1940].