||Continental Divides in North Dakota and North America
Divides and Drainage Basins
Northern, or Laurentian, Divide
St. Lawrence Seaway Divide
Facts and Features of Continental Divides
Fourth Dimension of Continental Divides
and Suggested Readings
||To the uninitiated
eye, the countryside between Valley City and Jamestown is seemingly
among the most unremarkable stretches of Interstate 94 (I-94), not
just in North Dakota, but along its entire route from Chicago to Seattle.
Granted, the terrain here is pretty flat with gentle undulations amounting
to less relief than one finds on the waves of the open ocean. And
yes, some travelers battle with insomnia in this stretch where the
view cannot seem plainer (nor more planar), although the Red River
Valley is arguably plainer and indisputably more planar. And just
when the landscape cannot seem any more unremarkable, a highway sign
proclaims in oxymoronic fashion (Fig. 1):Continental Divide Elevation
1490 feet. To many travelers of I-94, the sign appears to be
a mistake, or perhaps a self-deprecating joke dreamt up by the North
Dakota Tourism Office to make light of one of the flattest landscapes
in the world.
Fig. 1 - View of the continental divide from I-94 in eastern North
Photo credit:Mark A. Gonzalez
In reality, the sign is no mistake and no joke. I suspect that
the perception of error is due, in part, to the misconceptions contained
in countless textbooks and maps from reputable map makers, who propagate
a myth that there is only one continental divide in the United States
and North America. Too many geography textbooks and maps show only
one continental divide—the one along the crest of the Rocky
Mountains. Indeed, most sources even refer to it as The Continental
Divide, treating it as a singular and unique feature, furthermore
as a formal place name complete with capital letters.
This leads to some basic questions: What are continental divides,
and where are they located on the North American continent? My objectives
here are to discuss various concepts incorporated into different
definitions of continental divide; to discuss the continental divide
that runs in part through North Dakota; and to describe the other
continental divides of the North American continent. I will also
discuss some of the more interesting features of continental divides,
such as triple points, closed basins, and the dynamic nature of
||Drainage Divides and Drainage Basins
Fig. 2. Schematic diagram showing a drainage
divide, the boundary of a drainage basin.
What is a continental divide? To address this question, we must back
up and first define the terms "drainage basin" and "drainage
divide." A drainage basin is the area drained by a river or
lake. All the surface runoff within a drainage basin will drain eventually
into a specific river or lake (Fig. 2).
A drainage divide is the boundary of a drainage basin; it is the
boundary that physically separates the drainage of one drainage
basin from that of another (Fig. 2). Precipitation on one side of
a divide will drain into one basin, whereas precipitation on the
other side will drain into another basin. [Note: This simplified
view of a drainage divide works well for nearly all surface waters,
but does not address those situations where groundwater can flow
in the subsurface from an area beneath one drainage basin into another
drainage basin, a complex situation that in itself would constitute
||The term "continental
divide" refers to a particular type of drainage divide. Unfortunately,
various references provide different definitions for continental divide.
Consequently, there is no clear consensus, and some notable disagreements,
on what constitutes a continental divide. In examining a variety of
definitions, some concepts are repeatedly used (or misused). Some
of the major concepts include: direction of stream flow, flow to different
oceans and/or different seas, flow to different sides of a continent,
and presence of high or mountainous ground. Let's examine the
value or utility of each of these criteria.
Many definitions contain the idea that a continental divide separates
waters that flow in opposite directions. This stipulation seems
obvious, but is actually quite unnecessary and potentially ambiguous.
For example, situations can be found where streams flow generally
parallel to each other, yet are on opposite sides of a continental
divide; and in converse, numerous cases can be identified where
streams, which do flow in opposite directions, are not separated
by a continental divide. Therefore, the phrase "opposite directions"
is ambiguous and serves no constructive purpose in defining a continental
divide. A more meaningful stipulation is that a continental divide
separates major streams that ultimately flow in divergent paths
and will never flow into each other before entering an ocean or
Many definitions either explicitly state, or implicitly imply,
that continental divides separate waters that flow to different
oceans. By this rather restrictive definition, it is obvious that
the North American continent must have more than one continental
divide, because three oceans surround the continent. Therefore,
there must be a continental divide between the drainages of the
Pacific and Atlantic oceans, between the drainages of the Pacific
and Arctic oceans, and between the drainages of the Arctic and Atlantic
oceans. This point alone is sufficient to forever abolish the formalized
place name, The Continental Divide, from all geography textbooks
and references. Clearly, no single, unique divide qualifies for
this singular place name on the North American continent.
Other definitions substitute the restrictive idea of different
oceans with a less restrictive idea of different seas and/or coastlines
on different sides of a continent, which in the case of North America
seems appropriate. For example, both the Gulf of St. Lawrence and
the Gulf of Mexico are seas that are connected to the same ocean,
the Atlantic Ocean. But in examining the major drainages of the
North American continent, it is evident that precipitation falling
in or near the Great Lakes will flow either north and east through
the St. Lawrence Seaway, or west and south through the Mississippi
River basin. More on this divide below.
Several dictionaries contain within their definition of continental
divide the requirement that the continental divides follow "an
extensive stretch of high ground" or "an extensive ridge
of mountains" (e.g., The American Heritage Dictionary of the
English Language, 2000; Wordsmyth Educational Dictionary, 2002).
This requirement is unnecessary, misleading, and completely inappropriate.
Many places along the best-known continental divide of North America,
which roughly coincides along much of its trace with the crest of
the Rocky Mountains, are not mountainous. Some stretches of the
divide are gently sloping or planar. In fact, many of the early
western trappers, traders, and explorers crossed this continental
divide at South Pass in southwestern Wyoming without noticing that
they had indeed crossed from the Gulf of Mexico to the Pacific Ocean
drainage systems. The climb over South Pass is so gradual that it
was the point on the Oregon Trail where emigrants with heavily laden
Conestoga wagons crossed the continental divide. Reaches of this
continental divide in New Mexico and western Alaska are relatively
flat too. Any stipulation for high ground or mountainous terrain
is best stricken from all definitions of continental divide.
Some definitions require that waters flow great distances from
the continental divide. Yet in at least three places along the so-called
Great Divide of the western parts of North and South America, the
continental divide is separating waters that drain a few miles or
less into coastlines that are a few tens of miles, or less, apart!
At the very northern terminus of the Great Divide at the Cape Prince
of Wales at the tip of Seward Peninsula, the demarcation between
the Chukchi Sea of the Arctic Ocean and the Bering Sea of the Pacific
Ocean is an arbitrary line on a beach. Similarly, at the southern
terminus of the Great Divide in Tierra del Fuego, the demarcation
between the Atlantic and Pacific oceans is an arbitrary line on
a beach. And at the Isthmus of Panama, the coastlines of the Atlantic
and Pacific oceans are within a few tens of miles apart.
Whereas general dictionaries of the English language commonly fail
to provide an acceptable definition of continental divide, those
specialized dictionaries with strong emphasis on the natural sciences
commonly provide simpler and more appropriate definitions of continental
divide. For example, Bates and Jackson (1980) define continental
divide as "a drainage divide that separates streams flowing
toward opposite sides of a continent, often into different oceans…"
Similarly, the North American Lake Management Society (2002) defines
continental divide as "a drainage divide separating the rivers
which flow toward opposite sides of a continent." Neither
definition specifies how many sides there are to a continent. These
definitions have no requirement for the existence of high ground,
extensive ridges, or mountainous terrain. Nor does either necessarily
require that the streams drain into different oceans!
In view of the various definitions used, my prerogative is to identify
continental divides using two simple, general criteria. One, a continental
divide separates major streams that ultimately flow in divergent
paths and will not join each other before they enter an ocean or
sea. Two, a continental divide separates surface waters that ultimately
flow to different oceans, different seas, or different coastlines
on different sides of a continent. From these criteria, the North
American continent has at least four distinct continental divides
that separate drainages of the Pacific Ocean, Arctic Ocean, Hudson
Bay, Gulf of St. Lawrence, Gulf of Mexico, and Atlantic Seaboard
(Fig. 3). Three of these divides have pre-existing formal names:
the Great Divide, the Northern Divide, and the Eastern Divide. The
fourth divide is herein referred to as the St. Lawrence Seaway Divide.
These divides are described below.
Fig. 3. Continental divides of North America
include the so-called Great Divide, the Northern Divide, the
Eastern Divide, and the St. Lawrence Seaway Divide.
||The Great Divide
||In the conterminous
United States, the crest of the Rocky Mountains divides waters into
generally eastward-flowing streams, bound for the Gulf of Mexico,
and generally westward-flowing streams, bound for the Pacific Ocean
or Sea of Cortez (a.k.a. Gulf of California; Fig. 3). In Canada, the
crest of the Rocky Mountains divides waters that flow into the Hudson
Bay, Beaufort Sea, or the Arctic Ocean, from waters that flow to the
Pacific Ocean (Fig. 3).
Many refer to this as The Continental Divide. But this term is
totally unacceptable because it implies that there is a single continental
divide that is unique to North America. Others, me included, prefer
the name, Great Divide, which is more fitting and suitable. The
Great Divide is distinguished by high elevations along much (though
not all) of its course. Also, it is a divide of great length, running
from Tierra del Fuego near the southern tip of South America, through
the Isthmus of Panama to the coastal plains of Seward Peninsula
in northwestern Alaska. It is a continental divide of not only North
America, but also of Central and South America.
Scenery is not in short supply along the Great Divide, which is
adorned with splendors, such as the Hanging Garden, China Wall,
the Dinwoody Glacier and its satellite glaciers high in the Wind
River Range, the mountain majesties of the Collegiate Range, and
the volcanic fabrications of El Malpais in New Mexico. One of my
favorite spots along the Great Divide is the Highline Trail near
Logan Pass in Glacier National Park. Highline Trail traverses a
long ridge, known as Garden Wall, a photogenic alpine meadow with
statuesque glacial-carved cliffs of jagged sedimentary rocks resting
in the shadows of the Great Divide. Many nature calendars include
a photograph of the Garden Wall when the Bear Grass and alpine varieties
of lupines are in full bloom. It is certainly among the most beautiful
patches anywhere on Earth. Near Dinwoody Glacier is Grasshopper
Glacier, named because a horde of grasshoppers was trapped and fossilized
in the glacial ice!
Place names along the Great Divide speak to the typical climate
at great elevations: Never Summer Mountains, Snowdrift Lake, Snowbank
Lake, Ice Lake, Glacier Peak. Other features bear the names of alpine
denizens, such as Ptarmigan Lake (lots of these along the divide),
Ouzel Lake, Junco Lake, Pipit Lake, Bighorn Lake, and Grizzly Peak.
Others conjure images of powerful alpine storms, battering the towering
crags of the divide, such as Thunder Peak, Nimbus Peak, Ice Mountain,
Blizzard Hill, Thunderbolt Mountain, Storm Mountain.
||The Northern, or Laurentian, Divide
||An examination of
the major drainage basins, or watersheds, of the North American
continent shows that the headwaters of several major drainage
basins bear no relation to the Great Divide. For example, the
headwaters of the Mississippi River system, the Ohio River system,
the Nelson/Red-River-of-the-North system, and Great Lakes system
(or St. Lawrence Seaway) originate deep in the interior of the
North American continent and far from the Rocky Mountains and
the Great Divide. Nevertheless, these basins drain into different
oceans or seas on different sides of the continent.
The drainage divide, which separates drainages to the Hudson Bay and
Arctic Ocean from all other drainages in North America, is known as
the Northern Divide. In northern Minnesota, the Northern Divide is
commonly known as the Laurentian Divide. The Northern Divide shares
the same path as the Great Divide from Seward Peninsula to Triple
Divide Peak, Montana. From Triple Divide Peak, the Northern Divide
trends to the east through Montana, Alberta, Saskatchewan, North Dakota,
South Dakota, and Minnesota. The Laurentian Divide in Minnesota follows
an especially prominent ridge that runs for 120 miles from just east
of Grand Rapids to Hoyt Lake. The Chippewa or Ojebwe Indians referred
to this stretch of the Laurentian Divide as the sleeping giant, or
Mesabi. The Mesabi Range is well known for the high-grade iron ore
that was mined for decades. From northern Minnesota, the Northern
Divide continues north and east across parts of Ontario and Quebec.
It eventually demarcates the boundary between Quebec and Newfoundland
and Labrador. It terminates at the coastline marking the boundary
between the Labrador Sea and Hudson Bay.
North Dakotans will readily recognize the approximate trace of
the Northern Divide across the state by examining the state's
major drainages. Streams in the west, southwest, and south-central
parts of North Dakota, such as the James, Cannonball, Cedar, Heart,
Knife, and Little Missouri rivers, flow to the Missouri River, which
in turn joins the Mississippi River and eventually flows to the
Gulf of Mexico. In contrast, streams of the northwest, north, and
eastern parts of the state, such as the Souris River, the Red River
of the North, and all their tributaries, including the Sheyenne,
Goose, Maple, Pembina, Tongue, and Turtle rivers, flow to Hudson
Bay (Fig. 4). In the southern part of the state, the continental
divide runs between the James and the Sheyenne valleys from the
border with South Dakota northward toward Harvey. South of Harvey,
the divide angles westward and roughly follows a crest in the Missouri
Coteau that is slightly west and south of the Missouri Escarpment.
Fig. 4. Map of the interior of North America
illustrating the continental divides and major drainage basins of
The Northern Divide is not just of geographic and hydrologic importance,
but it has political significance too. When the Louisiana Purchase
was added to the United States in 1803, the Northern Divide served
as the boundary between the territory of the United States and Great
Britain (Canada). The present-day boundary between the United States
and Canada was not established until 1818, when the Treaty of Ghent
set the international boundary at 49º N latitude.
The Northern Divide still has important political ramifications,
because water in North Dakota drains into Canada. For example, Manitoba
is citing international water laws, treaties, and compacts in its
concerns over the Northwest Water Pipeline, which diverts water
from the Missouri River to Minot, the proposed Garrison Diversion,
which would divert Missouri River water to all of eastern North
Dakota, and the planned Devils Lake outlet, which would transfer
water from a closed basin to the Sheyenne/Red River system.
||The Eastern Divide
||Many people have argued
that the crest of the Appalachian Mountains is also a continental
divide, commonly referred to as the Eastern Divide. The Eastern Divide
does separate eastward flowing streams, which cross the Piedmont and
Coastal Plain and empty into the Atlantic Ocean, from westward flowing
streams, which join the Mississippi River and eventually empty into
the Gulf of Mexico (Fig. 3). Clearly the crest of the Appalachian
Mountains divides streams that flow toward different and distant coastlines
of the continent. Some critics do not recognize the Eastern Divide
as a continental divide, arguing that the Gulf of Mexico is part of
the Atlantic Ocean. These individuals recognize only waters flowing
into different oceans as being separated by continental divides. The
definition adopted here for discussion purposes states only that waters
flow to different coastlines on different sides of a continent, which
may be in the same, or different, oceans.
||The St. Lawrence Seaway Divide
||Again, some people
will raise the same objection used against an Eastern Divide to
argue against a divide between the Atlantic Ocean and the Gulf
of St. Lawrence as well as the divide between the Gulf of Mexico
and the Gulf of St. Lawrence. However, other definitions, which
merely require that continental divides separate divergent waters
destined for different sides of a continent, apply here.
For example, let's take the case of Oak Park, a suburb on the
west side of Chicago, Illinois. [Note: The following material is drawn
exclusively from the work of William Dring (2002). I encourage interested
readers to read his outstanding article on the Oak Park Continental
Divide for more information.] The St. Lawrence Seaway Divide runs,
in part, through Oak Park along a slightly elevated ridge—an
old beach ridge of Lake Michigan. The crest of this ridge is 17 feet
higher than the mean elevation of Lake Michigan. On the east side
of the ridge, water drains toward Lake Michigan through the St. Lawrence
Seaway to the Gulf of St. Lawrence (Fig. 3). Water on the west side
will travel to the Des Plaines River then to the Illinois River before
passing to the Mississippi River and Gulf of Mexico (Fig. 3). Oak
Park provides a clear example of where precipitation that falls inches
apart on the ground will take radically divergent paths through different
river systems, none of which will ever merge before they empty into
the sea. When they do empty into the sea, these waters are on distant
coastlines on different sides of a continent.
The continental divide through Oak Park and the greater Chicago
area was significant in early exploration of the continent's
interior. French voyageurs, who traveled primarily by canoe along
the waterways of the interior, were interested in finding passage
between the St. Lawrence River and Great Lakes and the Mississippi
River drainage. Such a passage would permit water navigation from
Montreal to New Orleans. In 1673, French explorers, Louis Joliet
and Father Jacques Marquette, were the first Europeans to use the
Chicago Portage, thanks to some navigational tips from native Indians
(Dring, 2002). Joliet noted in his reports that a canal of half
a league (one and one-half miles) across the Chicago Portage would
allow easy navigation from Lake Erie to the Gulf of Mexico (Dring,
This divide and the Chicago Portage have witnessed another remarkable
chapter in history too. The low-lying areas on the east side of
the divide became the outlets for the sanitary drains of the Chicago
metropolitan area. With pumps, the dirty water could be diverted
into the Illinois and Michigan Canal, which had been excavated
in 1848. This approach to waste disposal was the classic (paraphrased
in a Chicago accent), "Dilution is da solution to da pollution."
However, Chicago's population grew from about 100 in 1830
to 50,000 by 1850 and 1.6 million by 1900 (Dring, 2002). The volume
of waste greatly exceeded the capacity of the Illinois and Michigan
Canal, and Chicago was besieged with cholera outbreaks, the worst
occurring in 1854 and 1885. A new canal, the Sanitary Canal,
was authorized in 1889, and by 1900 the Sanitary Canal diverted
water from Lake Michigan across the continental divide and to the
Des Plaines River. Of course, the Sanitary Canal also sent the
effluent of Chicago across the continental divide and down the
Des Plaines River too—out
of sight, out of mind. In effect, the Sanitary Canal reversed the
flow direction of the Chicago River. It used engineering to change
the location of the "natural" continental divide and
replace it with a man-made divide.
||Assorted Facts and Features of Continental Divides
A triple point, or triple divide, is the place where two continental
divides intersect and water drains into three different watersheds.
Five widely-recognized triple divides exist in the United States,
including: Triple Divide Peak, Montana, The Hill of Three Waters,
Minnesota, Three Waters Mountain, Wyoming, an unnamed hilltop near
Gold, Pennsylvania, and the unofficially named Headwaters Hill, Colorado.
Triple Divide Peak in Glacier National Park, Montana, marks the
intersection of the Great Divide and Northern Divide. Water is diverted
from Triple Divide Peak into the Pacific-bound Columbia basin, the
Gulf of Mexico-bound Missouri basin, and the Hudson Bay-bound Saskatchewan
and Nelson drainages.
Another triple point exists in northern Minnesota near Hibbing.
Here the Northern Divide intersects the St. Lawrence Seaway Divide.
From this point, water flows in three directions, north to Hudson
Bay, south to the Gulf of Mexico, and east to the Gulf of St. Lawrence.
The Chippewa Indians referred to the location as "The Hill
of Three Waters" or "The Top of the World" and
frequently held their council meetings there for tribes living within
about a 100-mile radius. The site is not publicly accessible due
to mining operations. Its official platting is Section 26, Township
58, Range 21. (Hibbing Chamber of Commerce, 2001).
Another triple point exists atop an unnamed peak near Gold, Pennsylvania,
where waters separate into the Mississippi, Great Lakes, and Susquehanna
drainages. Hopefully, someone will champion a fitting name for so
distinguished a peak.
Two other peaks have been suggested as triple points: Headwater
Hill in south-central Colorado, and Three Waters Mountain in western
Wyoming. Three Waters Mountain in Wyoming is the source of the Columbia,
Colorado, and Missouri-Mississippi river systems. Technically, both
the Columbia and Colorado rivers flow into the Pacific Ocean, although
the Colorado River empties into the Sea of Cortez before its waters
co-mingle with those of the Pacific Ocean. From Headwater Hill,
water diverges into the Colorado River, the Rio Grande drainage,
and the Arkansas-Mississippi drainage. However, both the Rio Grande
and Arkansas drain into the Gulf of Mexico, making the case for
triple-point status of Headwater Hill somewhat less certain than
the other four triple points. By the definition I have adopted herein,
the Sea of Cortez and the mouth of the Columbia River would be distinct
coastlines, and the Three Water Mountain would qualify as a triple
point. In contrast, the mouths of the Rio Grande and Mississippi
River share the same coastline—the Gulf of Mexico. Therefore,
the status of Headwater Hill as a triple divide is more dubious
than that of the other four triple-points.
To various extents, some geography texts have pointed out that not
all of North America has drainage to an ocean. For example, the
Great Basin, which sprawls across much of Nevada, and parts of Wyoming,
California, Utah, Idaho, and Oregon is internally drained (Fig.
3). Internal drainage means that no river carries water out of the
basin. Also, the Great Divide actually bifurcates in Wyoming creating
another closed basin (Fig. 3). Another sizeable, closed basin exists
in the Lake Estancia basin of central New Mexico. And extensive
parts of southern Saskatchewan and Alberta are closed basins.
No geography text that I have found shows that the Devils Lake
basin and parts of the Missouri Coteau province in North Dakota
are closed basins. Because these basins have no external drainage,
they are not technically part of any watershed that drains to the
ocean. They are in effect rimmed by a continental divide. As discussed
below, these basins are only temporarily closed as water may spill
into an externally draining river if the water level rises high
||The Fourth Dimension of Continental Divides
||Lost thus far in this
treatise on continental divides is the fourth dimension, time.
The entire discussion has examined only the continental divides
as observed today. However, the number and position of continental
divides is strongly affected by climatic and tectonic forces,
which can raise mountain ranges and alter drainage patterns. Let's
explore how climatic forces have affected the continental divides
and drainage in North Dakota.
In the 1930s, North Dakota suffered a major drought. Lake levels fell
in the region. The water level in Devils Lake fell to 1401 feet above
mean sea level. In 1993, a wet interval began in northeastern North
Dakota and the lake rose to 1448 feet above mean sea level by 2001
(it has since dropped slightly). If the lake should rise to an elevation
of 1459 feet, as it has in the geologic past (Murphy et al., 1997),
water will spill by natural processes out of the lake basin and into
the Sheyenne River, which eventually flows to Hudson Bay. The rise
and fall of Devils Lake in response to natural climatic fluctuations
illustrates a case where closed basins can become integrated into
through-flowing, ocean-bound drainages.
Another example of climate-induced changes in continental drainages
is preserved in the history of glacial Lake Agassiz, once the largest
(in surface area) freshwater lake in North America. Toward the end
of the last Ice Age, continental glaciers covered much of North
America, particularly the Canadian Shield and northern tier of states
in the United States. North-flowing drainages, such as the Red River
of the North and Nelson River, were blocked by the continental glaciers.
Water ponded to form an enormous inland lake, glacial Lake Agassiz.
Water rose in glacial Lake Agassiz until it spilled over into one
of three outlets: a northwestern, eastern, and southern outlet.
The northwest outlet shunted Lake Agassiz water to glacial Lake
McConnell (located in the Northwest Territory of Canada), which
in turn spilled over and drained to the Arctic Ocean. The eastern
outlet delivered water to the Great Lakes and the St. Lawrence Seaway.
The southern outlet delivered water through Lake Traverse and Big
Stone Lake on the South Dakota/Minnesota border and into the Minnesota
River, which joins the Mississippi River at Minneapolis, Minnesota.
Each of these three outlets drained water from glacial Lake Agassiz
at different times, depending upon which paths were obstructed by
glacial advances, the degree of isostatic rebound related to crustal
adjustments from glacial and water loading on the earth's
crust, and the depth of water in Lake Agassiz. These multiple drainage
routes to the Arctic Ocean, Hudson Bay, Gulf of St. Lawrence, and
Gulf of Mexico illustrate how dynamic continental divides can be
in response to climatic forces and isostatic adjustments in the
crust following deglacial unloading. [Note: A recent article by
T.G. Fisher (2003) provides a scientific review of the history of
drainage changes in glacial Lake Agassiz. His work includes numerous
other citations on the topic.]
In recent decades, humans have altered natural drainage divides
by pumping and transferring water from one basin to others, sometimes
across continental divides. The example of the Chicago Sanitary
Canal has already been mentioned. In Colorado, water has been diverted
from the West Slope of the state across the Great Divide to quench
the growing thirst of the highly populated Front Range.
||The notion that there
is a single, unique continental divide in North America is untenable.
This notion is based on a poor understanding of the geography of North
America and on the unfortunate propagation of misinformation in introductory
geography texts. The continental divide, which is commonly referred
to as "The Continental Divide," is perhaps more appropriately
called the Great Divide, reflecting the great elevations along much
of its trace and its great length from Seward Peninsula, Alaska, to
Tierra del Fuego near the southern tip of South America.
Other continental divides include the Northern Divide, the Eastern
Divide, and the St. Lawrence Seaway Divide. The Northern Divide
runs from the Labrador Sea in northern Quebec through the continent's
deep interior including Minnesota and the Dakotas, to Triple Divide
Peak in Glacier National Park, Montana, where it joins and parallels
the Great Divide to the Bering Sea and Chukchi Sea off the coast
of Alaska. The Eastern Divide separates waters draining to the Gulf
of Mexico and Gulf of St. Lawrence from those draining across the
Atlantic Piedmont to the Atlantic Ocean. The St. Lawrence Seaway
Divide separates the waters of the Great Lakes basins and St. Lawrence
River from those of Hudson Bay, Gulf of Mexico, and Atlantic Seaboard.
Furthermore, it is a myth that continental divides must coincide
with mountainous areas. Even some reaches of the Great Divide are
devoid of mountains. The Northern Divide is relatively flat through
much of the prairie states and provinces, as is the St. Lawrence
Seaway Divide through much of Illinois and Indiana. The Eastern
Divide has little relief in all of Florida.
Finally, the position of a continental divide is not static; rather,
it is dynamic and changes in response to tectonic forces, isostatic
adjustments in the earth's crust, climatic forces that can
alter drainage patterns or block outlets through the growth and
decay of continental glaciers, and human forces, such as the case
of the Sanitary Canal and its effect on St. Lawrence Divide through
the Chicago metropolitan area.
A more liberal and enlightened definition of a continental divide
is one that examines the major drainages of an entire continent.
It defines a continental divide as a drainage divide that separates
waters flowing to different oceans, seas, or coastlines on different
sides of a continent. The most restrictive reading of this definition
would argue that there are at least three continental divides on
the North American Continent—one separating drainages of the
Pacific and Atlantic oceans, another separating drainages of the
Pacific and Arctic Oceans, and a third separating drainages of the
Arctic and Atlantic oceans. A more liberal interpretation of the
definition provided herein would also recognize that water originating
in the heartland of North America, but taking radically divergent
paths through the Great Lakes/St. Lawrence Seaway versus the Gulf
of Mexico, would also constitute a continental-scale drainage divide,
even though waters of the Gulf of St. Lawrence and Gulf of Mexico
eventually commingle with water of the Atlantic Ocean.
At some point, individuals will have to settle for themselves which
seas and coastlines are distinctly different enough to constitute
different sides of a continent. For example, are the Sea of Cortez
and the Colorado River basin distinct (and separated by a continental
divide) from the Columbia River system that empties into the Pacific
Ocean at the Washington-Oregon border? Is the Mackenzie River, which
enters the Arctic Ocean northwest of the Canadian Archipelago, distinct
and separated by a continental divide from the Nelson River, which
flows into the Hudson Bay at Churchill, Manitoba? Does the drainage
divide circumscribing the closed drainage of the Great Basin constitute
another continental divide, one separating ocean-bound from continent-bound
The next time you travel the undulating topography of the Missouri
Coteau and feel the urge to stifle a yawn, pay attention to the
streams you encounter. From the top of countless, nameless hills
and the crests of undulating ridges in the dead-ice moraines of
the Missouri Coteau, one can look at waters headed in opposite directions.
Some waters will travel north into the icy realm of Hudson Bay.
Whereas others will flow south to the subtropical shores of the
Gulf of Mexico.
||References and Suggested Readings
Dictionary of the English Language, Fourth Edition, 2002, Houghton
Mifflin Company, New York.
Bates, R.L., and Jackson, J.A., 1980. Glossary of Geology, Second
Edition, American Geological Institute, Falls Church, Virginia.
Earth: An Introduction to Geologic Change, by S. Judson and S.M. Richardson
(Englewood Cliffs, NJ, Prentice Hall, 1995).
T.N., 1976. Continental Divide—Article #23
Dring, W., 2002. Oak
Park Continental Divide.
Fisher, T.G., 2003. Chronology of glacial Lake Agassiz meltwater routed
to the Gulf of Mexico: Quaternary Research 59:271-276.
Murphy, E.C., Fritz, A.M.K., and Fleming, R.F., 1997. The Jerusalem
and Tolna Outlets in the Devils Lake Basin, North Dakota: North Dakota
Geological Survey Report of Investigation No. 100, 36 p.
American Lake Management Society, 2002.
Sutherland, W.O.S., 1999. Buena Vista, Minnesota.
||Adapted from Gonzalez,
Mark A., Summer 2003, Continental
Divides in North Dakota and North America: North Dakota Geological
Survey Newsletter, v. 30, no. 1.