Continental divide

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This article is about continental divides in general. For the Atlantic/Pacific divide, see Continental Divide. For the movie, see Continental Divide (movie)

A continental divide is a line of elevated terrain which forms a border between two watersheds such that water falling on one side of the line eventually travels to one ocean or body of water, and water on the other side travels to another, generally on the opposite side of the continent. Because the exact border between bodies of water is usually not clearly defined, the continental divide is not always definite for any continent (The International Hydrographic Organization's publication Limits of Oceans and Seas defines exact boundaries of oceans, but it is not universally recognized). Moreover, some rivers empty into deserts or inland seas, and thus do not end up in the oceans.

[edit] Examples

Image:NorthAmericaDivides.gif

North America has four continental divides:
- The Great Divide, also called the Continental Divide separates the watersheds of the Pacific Ocean from those of the Atlantic or Arctic Oceans. It runs from the Seward Peninsula in Alaska, through western Canada along the crest of the Rocky Mountains to New Mexico. From there, it follows the crest of Mexico's Sierra Madre Oriental and extends to the tip of South America. It is crossed by the Panama Canal
- The Northern Divide, or Laurentian Divide, separates the watershed of the Atlantic Ocean from that of the Arctic Ocean
- The St. Lawrence Seaway Divide separates the Great Lakes watershed from the rest of the Atlantic Ocean watershed. Two canals cross the divide: The Chicago Sanitary and Ship Canal crosses the Chicago Portage and connects Lake Michigan to the Mississippi River watershed. The Erie Canal connects Lake Erie to the Hudson River watershed.
- The Eastern Continental Divide separates the watershed of the Gulf of Mexico from the Atlantic Ocean. It runs from northern Pennsylvania down the Appalachian Mountains to the tip of Florida, dividing the Atlantic from the Gulf of Mexico. The city of Atlanta sits atop this divide.
In South America, the Continental Divide lies along the Andes, but the divide does not run along the highest peaks of the mountain system.
Australia has less distinct ocean boundaries and fewer prominent mountain ranges, making it hard to define a single divide. Much of the interior of the continent drains into the endorheic Lake Eyre Basin.
It is similarly difficult to distinguish the continental divides of Europe and Asia, because of the large number of distinct bodies of water into which their rainfall drains (for example, the Mediterranean Sea and its various lobes, the Atlantic Ocean, the North Sea, the Baltic Sea, the Arctic Ocean and the Black Sea with Europe).
The most significant continental divide in Africa is that between the watersheds of the Nile and the Congo, passing through the area of the African Great Lakes. Between the Congo and the Sahara, a vast area drains into the endorheic Lake Chad, so puncturing the Atlantic-Mediterranean divide. The Mediterranean-Indian Ocean divide is punctured in West Africa by the endorheic lake systems of the Great Rift Valley; in the south of the continent the divide between the Atlantic and Indian Oceans snakes between the watersheds of the Congo, Zambezi, Limpopo and Orange Rivers, with the Okavango terminating in the Kalahari Desert.
As the interior of the continent receives very little precipitation, and that in the form of snow, and also as it is entirely surrounded by the Southern Ocean, Antarctica is not generally considered to have a continental divide. The Transantarctic Mountains divide the ice streams draining West Antarctica into the Ronne Ice Shelf, toward the Pacific and into the Ross Ice Shelf, from those draining East Antarctica toward the Atlantic and Indian Oceans.