Continental Divide

Continental Divide

Continental Divide, the "backbone" of a continent. In North America, from N Alaska to New Mexico, it moves along the crest of the Rocky Mts., which separates westward-flowing streams from eastward-flowing waters. In SW New Mexico the divide crosses an area of low relief; it becomes more distinct in N Mexico, where it follows the Sierra Madre Occidental. In the United States it has been called the Great Divide, a name also occasionally used to designate the whole Rocky Mt. system, especially the southern section, where the high, rugged ranges presented an almost impenetrable barrier to westbound explorers and settlers. Glacier, Yellowstone, and Rocky Mountain national parks lie on the Continental Divide, and the Continental Divide National Scenic Trail runs along it (see National Parks and Monuments, table).

Most notable watershed of the North American continent. The mountains comprising it extend generally north-south, thus dividing the continent's principal drainage into waters flowing eastward (e.g., into Hudson Bay in Canada or the Mississippi River in the U.S.) and waters flowing westward (into the Pacific Ocean). Most of the divide runs along the crest of the Rocky Mountains, through British Columbia in Canada and through the states of Montana, Wyoming, Colorado, and New Mexico in the U.S. Its central point is Colorado, where it has many peaks above 13,000 ft (3,962 m). It continues southward into Mexico, roughly paralleling the Sierra Madre, and into Central America.

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For continental divides in general, see Continental Divide.

Continental Divide or Great Divide is the name given to the North American portion of the mountainous ridge which separates the watersheds that drain into the Pacific Ocean from, 1) those river systems which drain into the Atlantic Ocean (including those which drain via the Gulf of Mexico), and 2) along the northernmost reaches of the Divide, those river systems which drain into the Arctic Ocean. A secondary, non-mountainous divide further separates other river systems that drain into the Arctic Ocean (including those which drain via Hudson Bay, James Bay, and Ungava Bay) from those which drain into the Atlantic Ocean (including those which drain via the Great Lakes and Saint Lawrence Seaway).

Geography

The divide begins at Cape Prince of Wales in Alaska. It runs northeast-/eastward across the north of the state into the Yukon Territory, Canada, where it turns south and travels through British Columbia (forming part of the B.C.-Alberta boundary), in Canada; then through Montana (forming part of the Montana-Idaho boundary), Wyoming, Colorado, and New Mexico, in the United States; then along the crest of the Sierra Madre Occidental through the Mexican states of Chihuahua, Durango, Zacatecas, Aguascalientes, Jalisco, Guanajuato, Querétaro, México, the Federal District, Morelos, Puebla, Oaxaca, and Chiapas; thence through southern Guatemala, southwestern Honduras, western Nicaragua, and western/southwestern Costa Rica, and southern Panama.

The physical divide continues (though the name "Great Divide" does not) into South America, where it follows the peaks of the Andes Mountains, traversing western Colombia, central Ecuador, western and southwestern Peru, and eastern Chile (essentially conforming to the Chile-Bolivia and Chile-Argentina boundaries), southward to the southern end of Patagonia and Tierra del Fuego.

In North America, Triple Divide Peak in Glacier National Park, in Montana, is the point at which two of the principal continental divides in North America converge, the Great Divide and the Northern Divide. From this point, waters flow to the Pacific, the Atlantic and the Arctic Oceans. Another triple divide or triple point occurs in Canada on a prominent peak directly on the border between Alberta and British Columbia, called Snow Dome because the Columbia Icefield completely covers the summit. Water flows off this mountain into the Pacific, via the Columbia River system; the Arctic via the Athabasca River and MacKenzie River systems; and Hudson Bay via the North Saskatchewan River system. Because Canadians consider Hudson Bay to be an extension of the Atlantic Ocean, they consider Snow Dome to be the hydrological apex of North America.

In fact, there are such triple divide points wherever two continental divides meet. North America can be considered to have five major drainage systems: into the Pacific, Atlantic and Arctic Oceans, plus Hudson Bay and the Gulf of Mexico. Within this system there are four continental divides and three triple points, the two mentioned previously and a third near Hibbing, Minnesota where the Northern Divide intersects the Eastern Continental Divide. Since there is no true consensus on what a continental divide is, there is no real agreement on where the triple points are. However, the main Continental Divide described in this article is a far more distinctive geological feature than the others and its two main triple points are much more prominent.

The Continental Divide Trail follows the divide through the U.S. from the Mexican border to the Canadian border. A less-developed Canadian extension called the Great Divide Trail continues on through five National Parks of Canada and six provincial parks to end at Kakwa Lake in northeastern British Columbia.

Exceptions

Many endorheic regions in North America complicate the simple view of east or west, "ocean-bound" water flow.

The Great Basin of the Western US, The Valley of Mexico and Bolson de Mapimi in Mexico, the Tularosa Basin in New Mexico and Texas, and the Salton Trough are examples of internally draining areas. In these cases, water often drains to low basins, where sedimentation and evaporation form salt lakes, playas, salt flats, and alkali flats.

On the Llano Estacado in Texas and New Mexico, many thousands of seasonal playa lakes form during wet months, an average of one per square mile. This region is very flat, and water mostly evaporates before draining.

Zuni Salt Lake is one example of a larger, seasonal maar which does not drain to an ocean. There are a number of seasonal lakes of this sort in North America. In areas of karst topography (such as northern Florida), isolated drainages can also occur.

The Great Divide Basin in Wyoming has no natural outlet except as groundwater, and hence it lies between the Atlantic and Pacific watersheds, being part of neither. Water from the North Two Ocean Creek in Wyoming flows into both oceans.

Additionally, although Panama's isthmus provides clear division between Atlantic and Pacific, the boundaries between the Atlantic and Arctic Oceans in Baffin Bay are not well defined, rendering the easternmost portion of this divide arbitrary.

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