Continental Divide

views updated May 17 2018

Continental divide

A continental divide is a topographic feature separating streams that flow towards opposite sides of a continent. It is a continental scale version of the topographic divides that separate drainage basins of all scales.

In the conterminous United States and Canada, the continental divide follows an irregular course from the Basin and Range and Colorado Plateau physiographic provinces of New Mexico north through the Rocky Mountains, the Yellowstone region, and the Canadian Rockies. Water in streams to the west of the continental divide flows toward the Pacific Ocean, whereas that to the east of the continental divide flows toward the Atlantic Ocean. In Alaska, however, the continental divide marks the boundary between rivers flowing north and west to the Arctic Ocean and those flowing south and west into the Bering Sea.

Continental divides are often associated with mountainous terrain. Elevations along the continental divide through the conterminous United States, however, range from approximately 1400 meters above sea level in the Basin and Range topography of southern New Mexico to more than 4000 meters above sea level in the Rocky Mountains of Colorado and Wyoming.

A common, but inaccurate, notion is that precipitation falling on different sides of the divide necessarily travels to different oceans . Some precipitation that falls as snow, however, may be sublimated. Snowmelt or water that falls as rain may either evaporate or be transpired by vegetation after percolating into the soil . In either of those cases, the water may not travel to any ocean until it falls again as precipitation. In the extreme case of internally drained basins common to arid

regions such as the American Southwest, virtually all water flows towards the center of the basins and is removed through evaporation , transpiration, and infiltration. Water that infiltrates deep enough to recharge underlying aquifers may ultimately be discharged on the opposite side of the continental divide because, although groundwater divides do exist, they do not necessarily correspond exactly to topographic divides. Humans can also play a role, most notably by constructing diversion tunnels through which water is carried from one side of the continental divide to the other as part of water supply projects. Therefore, it is best to restrict the usage of the term continental divide to a topographic divide that separates streams flowing towards opposite sides of the continent than to include speculations about the ultimate fate of individual drops of water.

See also Drainage basins and drainage patterns; Freshwater; Hydrologic cycle; Landscape evolution; Precipitation; Runoff

Continental Divide

views updated Jun 08 2018

Continental Divide ★★ 1981 (PG)

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Continental Divide

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