Today, triple divides. The University of Houston's College of Engineering
presents this series about the machines that make our civilization
run, and the people whose ingenuity created them.
A recent trip to the Canadian Rockies has left me thinking
about continental divides. One such divide runs from Panama, up through Mexico,
along the American and Canadian Rockies, and finally curves across northern Alaska.
All rain and snowfall west of that divide eventually finds the Pacific Ocean. Things
are more complex on the inland side. Water in Mexico and the US generally runs into
the Gulf of Mexico.
But another continental divide runs across southern Canada from Labrador to the Canadian
Rockies. North of it, water runs off into the Arctic Ocean. From Minnesota eastward,
water on the south side finds its way into the Great Lakes, the St. Lawrence Seaway,
and the Atlantic. Between Minnesota and the Rocky Mountains, water runs south into
the Gulf of Mexico.
And the United States has two more continental divides. One runs up from the tip of
Florida, along the Appalachians to central Pennsylvania. One side drains into the Gulf,
the other into the Atlantic. The other American divide skims across our northeastern
border from Minnesota to New England. Its water drains north into the St. Lawrence and
south into either the Gulf or the Atlantic.
Look at all this on a map, and we see three places where continental divides intersect
-- points where a raindrop has to decide which of three oceans it might go to. One of
these points lies near the Pennsylvania-New York border. Another is near Hibbing,
Minnesota. Neither of these triple divides is very well defined. You'll find no markers
But the third intersection lies in tourist country where geography is far more dramatic
and identifiable. The northern divide meets the Rocky Mountain divide at aptly-named
Triple Divide Mountain in Montana's Glacier Park.
The plot thickens when Canada claims a fourth triple divide. The place is the Snow Dome,
just above a glacier in the Canadian Rockies. Its water drains into the Columbia River
and the Pacific and into the MacKenzie River and the Arctic Ocean. But it also finds a
third river system that empties into Hudson's Bay. And Hudson's Bay can be considered
part of either the Arctic or Atlantic Oceans.
While we're talking about such flukes, here's another one: In the middle of the western
US watershed lies the Great Basin, a dry region including western Utah, most of Nevada,
and parts of three other states. It's our largest endorheic basin. That's a region
water cannot leave. What little rain or snow falls upon it simply evaporates away
without ever reaching an ocean.
All this complex water movement became very real to me two weeks ago. That's when I
dipped a cup into the glacier melt leaving Snow Dome. I drank some of that crystal
pure water and watched the rest flow away. This particular rivulet parted from snowflakes
that'd fallen very nearby it to begin its own long journey to faraway Hudson's Bay.
The melt of Athabaska Glacier beginning its journey to Hudson's Bay
I'm John Lienhard at the University of Houston,
where we're interested in the way inventive minds
See the Wikipedia article on
Continental Divide of North America.
The map (above) of North American divides is courtesy of Wikimedia Commons. Photos by J. Lienhard.