Continental divide

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A continental divide is a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea, or else is endorheic, not connected to the open sea. Every continent on earth except Antarctica which has no free-flowing water has at least one continental drainage divide; islands, even small ones like Killiniq Island on the Labrador Sea in Canada, may also host part of a continental divide or have their own island-spanning divide.

The endpoints of a continental divide may be coastlines of gulfs, seas or oceans, the boundary of an endorheic basin, or another continental divide. One case, the Great Basin Divide, is a closed loop around an endoreic basin. The endpoints where a continental divide meets the coast are not always definite since the exact border between adjacent bodies of water is usually not clearly defined. The International Hydrographic Organization's publication Limits of Oceans and Seas defines exact boundaries of oceans, but it is not universally recognized. Where a continental divide meets an endorheic basin, such as the Great Divide Basin of Wyoming, the continental divide splits and encircles the basin. Where two divides intersect, they form a triple divide, where three watersheds meet.

Whether a divide is considered a continental divide distinguished from other secondary drainage divides may depend on whether the associated gulfs, seas, or oceans are considered separate. For example, the Gulf of Mexico is considered separate from the Atlantic Ocean, so the Eastern Continental Divide separates their respective watersheds. But the Sea of Cortez is usually not considered separate from the Pacific Ocean, so the divide between the Colorado River watershed which drains to the Sea of Cortez, and Columbia River Watershed which drains to the Pacific Ocean, is not considered to be a continental divide.

Together, continental divides demarcate a set of drainage basins or watersheds, each of which drains to a specific ocean, sea or gulf, such as the North American Atlantic seaboard watershed which is demarcated by the Eastern Continental Divide and Great Lakes-St. Lawrence Divide.

Divides by continent

A 'continent' for the purpose of water divides may not correspond to a geopolitical or geophysical continent.

Major continental divides, showing drainage into the major oceans and seas of the world. Grey areas are endorheic basins that do not drain to the ocean.

Africa

In Africa, the most significant continental divide is the Congo-Nile Divide 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, puncturing the AtlanticMediterranean divide. The Mediterranean–Indian Ocean divide is punctured in East Africa by the endorheic lake systems of the East African Rift; 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.

Antarctica

Arabian Peninsula

Arabian Peninsula

Australia

  • In Australia the Great Dividing Range largely separates those rivers flowing to the eastern seaboard and the Pacific Ocean from those flowing westward to the Murray–Darling Basin and to the Southern Ocean. However, Australia has fewer distinct ocean boundaries and fewer prominent mountain ranges, which makes it hard to clearly and precisely define any one divide. Much of the interior of the continent drains into the endorheic Lake Eyre Basin.

British Isles

Eurasia

Eurasia has various divides, depending on the definition of "ocean" (for example, the Mediterranean Sea and its various lobes, the Atlantic Ocean, the Arctic Ocean, the Baltic Sea, the Black Sea, and the North Sea). Examples include:

Greenland

New Zealand

North America

If the Gulf of California or Sea of Cortez is considered to be separate from the Pacific Ocean, there is a divide which separates the Pacific Ocean basin from the basin which drains into that gulf/sea, i.e the Colorado River basin:

  • The Colorado River divide (not an official name) separates the Colorado River basin which drains to the Gulf of California from the Pacific Ocean basin. It runs between the Continental Divide and Great Basin Divide in Wyoming. It intersects the divides at the respective triple points Three Waters Mountain (Colorado, Colombia, Mississippi) @43° 23' 13\'\' N, 109° 46' 58\'\' W, and Commissary Ridge Triple Divide (Colorado, Columbia, Great Basin) @42° 35' 18\'\' N, 110° 44' 9\'\' W. The divide is very short, running only about 90 miles.

South America

See also

References

  1. ^ In Europe and internationally, divides are called 'watersheds'.
  2. ^ Latin for "unknown limits"
  3. ^ Foster, John E.; Eccles, W.J. (1985). "Fur Trade". The Canadian Encyclopedia. The Historica Foundation of Canada. Retrieved 2007-12-30.
  4. ^ Gonzalez, Mark (2007). "Continental Divides in North Dakota and North America" (PDF). NDGS Newsletter. North Dakota Geographical Society. Archived from the original (PDF) on 2013-01-17. Retrieved 2009-03-29.

External links

  • nationalatlas.gov
  • "Continental Divides in North Dakota and North America by Mark A. Gonzalez. Excellent article on America's other continental divides" (PDF). (123 KiB)
  • Map of drainage basins in Canada
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