TheContinental Divide of the Americas (also known as theGreat Divide, theWestern Divide or simply theContinental Divide;Spanish:Divisoria continental de las Américas, Gran Divisoria) is the principal, and largelymountainous,hydrological divide of theAmericas. The Continental Divide extends from theBering Strait to theStrait of Magellan, and separates thewatersheds that drain into thePacific Ocean from those river systems that drain into theAtlantic andArctic Ocean, including those that drain into theGulf of Mexico, theCaribbean Sea, andHudson Bay.
Although there are many other hydrological divides in the Americas, the Continental Divide is by far the most prominent of these because it tends to follow a line of high peaks along the main ranges of theRocky Mountains andAndes, at a generally much higher elevation than the other hydrological divisions.
Beginning at the westernmost point of theAmericas,Cape Prince of Wales, just south of the Arctic Circle, the Continental Divide's geographic path runs throughArctic Alaska, where it reaches its more northerly point close to the U.S.-Canada border near the Beaufort Sea. The Divide zig-zags southwardly overYukon, and forms part of the boundary between Yukon and theNorthwest Territories in theMackenzie Mountains. It then proceeds through theNorthern British Columbia Interior via theCassiar Mountains,Omineca Mountains and northernNechako Plateau toSummit Lake, north of the city ofPrince George and just south of the community ofMcLeod Lake. From there the Divide traverses theMcGregor Plateau to the spine of the Rockies, following the crest of theCanadian Rockies southeast to the120th meridian west, from there forming the boundary between southern British Columbia and southernAlberta.
The Divide crosses into theUnited States in northwesternMontana, at the boundary betweenWaterton Lakes National Park andGlacier National Park. In Canada, it forms the western boundary of Waterton Lakes National Park, and in the US bisects Glacier National Park. Further south, the Divide forms the backbone of theRocky Mountain Front (Front Range) in theBob Marshall Wilderness, heads south towardsHelena andButte, then west past the namesake community ofDivide, Montana, through the Anaconda-Pintler Wilderness to theBitterroot Range, where it forms the eastern third of the state boundary betweenIdaho and Montana. The Divide crosses intoWyoming withinYellowstone National Park and continues southeast around theGreat Divide Basin, through theSierra Madre Range intoColorado where it reaches its highest point in North America at the summit ofGrays Peak at 4,352 metres (14,278 ft).[citation needed] It crosses US Hwy 160 in southwestern Colorado atWolf Creek Pass, where a line symbolizes the division. The Divide then proceeds south into westernNew Mexico, passing along the western boundary of the endorheic Plains of San Agustin. Although the Divide represents the height of land between watersheds, it does not always follow the highest ranges/peaks within each state or province.
InMexico, it passes throughChihuahua,Durango,Zacatecas,Aguascalientes,Jalisco,Guanajuato,Querétaro,México, theFederal District,Morelos,Puebla,Oaxaca, andChiapas. In Central America, it continues through southernGuatemala, southwesternHonduras, westernNicaragua, western/southwesternCosta Rica, and southernPanama. The divide reaches its lowest natural point in Central America at theIsthmus of Rivas at 47 metres (154 ft) in Nicaragua. In Panama, theCanal cuts through it at 26 metres (85 ft).
The Divide continues intoSouth America, where it follows the peaks of theAndes Mountains, traversing westernColombia, centralEcuador, western and southwesternPeru, and easternChile (essentially conforming to the Chile-Bolivia and Chile-Argentina boundaries), southward to Cabo San Diego at the southern end ofPatagonia andTierra del Fuego. The Divide passes through the Punta Cancanan Pass in Peru at 4,700 metres (15,420 ft).[1]
TheArctic Divide or Northern Divide in northern and western Canada separates the Arctic Ocean watershed from theHudson Bay watershed. Another, mainly non-mountainous, divide, theLaurentian Divide (also sometimes called the Northern Divide), further separates theHudson Bay-Arctic Ocean drainage region from the Atlantic watershed region. Secondary divides separate the watersheds that flow into theGreat Lakes andSaint Lawrence River (ultimately into the Atlantic) from watersheds that flow to the Gulf of Mexico (also part of the Atlantic Ocean) via theMissouri-Mississippi-Ohio river system.Another secondary divide follows the Appalachian chain, which separates those streams and rivers that flow directly into the Atlantic Ocean from those that exit via the Ohio and Mississippi Rivers.
Triple Divide Peak inGlacier National Park, Montana, is the point where two of the principal continental divides in North America converge, the primary Continental Divide and the Northern or Laurentian Divide. From this point, waters flow to the Pacific Ocean, the Atlantic Ocean via the Gulf of Mexico, and theArctic Ocean viaHudson Bay. Most geographers, geologists, meteorologists, and oceanographers consider this point the hydrological apex of North America, as Hudson Bay is generally considered part of the Arctic Ocean. For example, theInternational Hydrographic Organization (in its current unapproved working edition only[2] ofLimits of Oceans and Seas) defines the Hudson Bay, with its outlet extending from 62.5 to 66.5 degrees north (just a few miles south of theArctic Circle) as being part of the Arctic Ocean, specifically "Arctic Ocean Subdivision 9.11."
This hydrological apex of North America status of Triple Divide Peak is the main reason behind the designation ofWaterton-Glacier International Peace Park as the "Crown of the Continent" of North America.[3] The summit of the peak is the world's only oceanic triple divide point.[4] DiscountingAntarctica and its ice sheets, only one other continent (Asia) borders three oceans, but the inward-drainingEndorheic basin area ofCentral Asia from westernChina to theAral andCaspian Seas is so vast that any Arctic andIndian Ocean tributaries are never within proximity of each other.[4] Thus, North America's status of having a single location draining into three oceans is unique in the world.
Sources differ, however, on whether Hudson Bay, entirely south of theArctic Circle, is part of the Atlantic or Arctic Ocean.[5] Hudson Bay's water budget connects to the Atlantic more than to the Arctic Ocean.[6] The channels to the north of Hudson Bay are largely cut off byBaffin Island from the Arctic, so much of the water that enters it mixes with the Atlantic to the east viaHudson Strait rather than north into the Arctic. The result is that most of the ice flowing down theSaskatchewan Glacier eventually ends up as water in the Atlantic Ocean.[7][8]
If Hudson Bay is considered part of the Atlantic, then thetriple point is at an unimportant-looking, permanently snow and ice covered hump on the border betweenAlberta andBritish Columbia, on the southern slope ofSnow Dome at 3,456 metres (11,300 ft). The exact location of this potential triple point is somewhat indeterminate because the Columbia Icefield and the snow on top of it shifts from year to year. The snow that falls on it (about 10 metres (33 ft) per year) does not actually flow downhill as water, but creeps downhill in the form of glacial ice. That ice flows down theAthabasca Glacier to the Arctic Ocean via theAthabasca andMackenzie rivers. Ice flowing west goes to the Pacific Ocean via Bryce Creek and theBush andColumbia Rivers. Ice flowing down the Saskatchewan Glacier goes via theNorth Saskatchewan,Saskatchewan, andNelson rivers intoHudson Bay.[9]
While Triple Divide Peak (or, alternatively, Snow Dome) is the world's only oceanic triple divide, there are secondary triple divide points wherever any two continental divides meet. North America has five major drainage systems: into the Pacific, Atlantic and Arctic oceans, plus Hudson Bay and the Gulf of Mexico. Other sources such as theInternational Hydrographic Organization add a sixth: Canada'sNorthwest Passage basin. Using just the five, there are four secondary continental divides and three secondary triple points, the two mentioned previously and a third nearHibbing, Minnesota, where theNorthern Divide intersects theSaint Lawrence Seaway divide.[10] Since there is no true consensus on what a continental divide is, there is no real agreement on where the secondary triple points are located.[11] 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.
TheContinental Divide National Scenic Trail (CDT) follows the Divide through the U.S. from theMexico–US border to theCanada–US border. The trail itself is a corridor of pathways; that is, dedicated footpaths or back roads, either on or near the Continental Divide. A less-developed Canadian extension called theGreat Divide Trail continues through fivenational parks and sixprovincial parks, ending at Kakwa Lake in east-central British Columbia.[12]
Manyendorheic regions in North and South America complicate the simple view of east or west, "ocean-bound" water flow. Several endorheic basins straddle or adjoin the Continental Divide, notably theGreat Divide Basin in Wyoming, thePlains of San Agustin and theAnimas Valley in New Mexico, theGuzmán Basin in New Mexico and Chihuahua, Mexico, and both theBolsón de Mapimí and theLlanos el Salado in Mexico. Such basins can be, and routinely are, assigned to one side of the Divide or the other by their lowest perimeter pass; in other words, an assignment is made by determining how the drainage would occur if the basin were to be progressively filled with water until it overflowed.
Large-scale maps, such as those on this page, often show double divide lines when endorheic basins are involved. However, the detailedUSGS topographic maps of the United States generally show only the main Divide as determined by the overflow rule. Among other things, this eliminates the need to trace out the boundary for a basin that is very shallow and has a nebulous rim, such as theSan Luis Closed Basin in Colorado and the basin of thelost streams of Idaho.
Another rare exception occurs when a stream near a divide splits and flows in both directions, or a lake straddling the divide overflows in both directions. Examples of these are, respectively,North Two Ocean Creek andIsa Lake, both located on the Continental Divide in Wyoming. ThePanama Canal has this same feature, but is man-made. Both theChagres and Gatun rivers flow intoGatun Lake, which empties to both oceans.
Several small lakes along the Divide in theRocky Mountains between Alberta and British Columbia flow into both provinces and thus into both the Arctic and Pacific Oceans. An example is the "Committee's Punch Bowl", a small lake located in theAthabasca Pass.[a]
TheAlpine Club of Canada'sAbbot Pass Hut sat directly astride the Divide inAbbot Pass on the boundary betweenBanff National Park andYoho National Park, and thus precipitation falling on the eastern half of the roof flowed viaLake Louise into Hudson Bay, while rain falling on the western half flowed viaLake O'Hara into the Pacific Ocean.
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