Northwest Territories GeographyNorthwest Territories is a massive slice of land; one dominated by the Mackenzie Mountains, Mackenzie River and two of the planet's largest lakes. Part of its land is above the Arctic Circle, including Banks Island, nearly half of Victoria Island, and a few additional islands to the north of Melville Sound. Speaking of land, much of it to the north of Great Bear Lake is tundra, a vast area of stark landscape that is frozen for most of the year. The Canadian Shield, covering the eastern half of Northwest Territories, is a base of granite covered by a shallow layer of soil. This flat to rolling landscape is covered by dozens of rivers and lakes. The Mackenzie Mountains, forming part of the Yukon-Northwest Territories border, are an extension of North America's Rocky Mountains. They include the highest mountain within Northwest Territories, Mount Nirvana at 2,773 m (9,098 ft). Located along the South Nahanni River in the Mackenzie Mountains, Nahanni National Park contains deep canyons, huge waterfalls, and a very unique limestone cave system. The Mackenzie River is the longest river in Canada and dissects the Northwest Territories. It flows generally northwest into Mackenzie Bay and the Beaufort Sea. It's (1,200 miles) (1,800 km) in length. Frozen solid from October through April, the river is navigable for only five months of the year. Great Bear Lake is the largest lake entirely within Canada; the third largest in North America, and the seventh largest in the world. The lake has a surface area of 31,153 sq km (12,028 sq miles) with a maximum depth of 446 m (1,463 ft). Great Slave Lake is the second-largest lake in the Northwest Territories of Canada behind Great Bear Lake. It's the deepest lake in North America at 614 m (2,015 ft), and the ninth-largest lake in the world.