North America: position, relief, climate and waters

Because North America is long from north to south, its climate is varied. There are six climate zones: arctic, subarctic, temperate, subtropical, tropical and subequatorial. In the north arctic air dominates and it is cold nearly all year; the temperate zone is very varied by its width: maritime near the ocean and continental inland. The Cordillera blocks moist air from the west and makes the plains drier. Cold arctic air from the north enters freely southwards across the open plains. Big rivers flow to the Atlantic, Pacific and Arctic basins; the Great Basin’s waters do not reach the ocean (an inland drainage basin). The largest river system is the Mississippi: the Missouri flows into it, and the Missouri itself is longer than the Mississippi; together they exceed 6 000 km. The Great Lakes — Superior, Michigan, Huron, Erie and Ontario — lie in basins carved by glaciers; Lake Superior is one of the world’s largest freshwater lakes (about 82 000 km²). Between Erie and Ontario lies Niagara Falls (about 50 m high), with a hydropower plant. The Colorado River cut the Grand Canyon, and the Mackenzie River, which flows to the Arctic Ocean, links northern lakes (Great Bear, Great Slave). Greenland and Alaska glaciers hold a huge store of ice.