The Continental Divide

[md2000]

@Xema

An interesting point (kinda obvious when you think about it) is that drainage divides not at the highest points along a mountain ridge or chain, but at the lowest: the passes.

A really interesting case is Isa Lake (which is more like a pond than a lake) in Yellowstone Park. It straddles the Continental Divide (in Craig Pass) and thus has 2 outlets, one of which carries water to the Atlantic, the other to the Pacific. To add to the curiosity, it’s the water that departs to the west that ends up in the Atlantic; the water that starts off headed east is destined for the Pacific.

Usually, a phenomenon like this does not last. Over time (geology has plenty of time) on outlet will erode more than the other, and it’s a positive feedback phenomenon. The higher outlet will remain high and dry as more and more current erodes the other outlet lower and lower. Not there are not a lot of large lakes in the Rockies; the runoff is seasonal, so heavy flows, carrying abrasive debris from the mountains, tend to wear away the outlets. You end up with canyons and deep valleys instead, and that debris becomes floodplains on the coast. (and what does not get carried away fills the lakes with silt pretty fast too.)

[igor_frankensteen]

I think the most informative thing to recognize, is that The Continental Divide, is a post-reality, conceptual title that humans gave to an IMAGINARY line that they drew on a map, based on surveying where most larger creeks and rivers flow to.

It gets confusing if you accidentally think that the continent was DESIGNED by someone or something, who decided to draw a line down it somewhere, and to channel the water this way and that. Or if you worry that getting the exact location of a “continental divide” wrong, will cause significant problems.

[DSYoungEsq]

The best part of the Continental Divide is that there is a place in Wyoming where it splits into two branches that surround an endorheic basin. If you drive through that area on Interstate 80, you can be forgiven for being quite underwhelmed by the “divide”.

[Chronos]

And if we’re talking about getting it wrong, the border between Montana and Idaho was originally supposed to follow the continental divide. And in fact, it starts off by doing so. But the surveyors made a wrong turn, and didn’t notice it until hundreds of miles later when a stream crossed their path (which should never happen on the real divide). At which point they basically said “screw it”, and just drew a line straight north from there.

[Colibri]

@Ludovic

If we’re counting that, then all the Great Lakes and their streams except Erie and Ontario would partly drain into the Gulf due to the reversal of the Chicago River.

Another place where there is an artificial two-ocean drainage is the Panama Canal. Most of the water for the Canal comes from the Chagres River, which naturally flows into the Atlantic/Caribbean. Some of the water from the Chagres now flows into the Pacific through the Canal.

[hajario]

@Chronos

And if we’re talking about getting it wrong, the border between Montana and Idaho was originally supposed to follow the continental divide. And in fact, it starts off by doing so. But the surveyors made a wrong turn, and didn’t notice it until hundreds of miles later when a stream crossed their path (which should never happen on the real divide). At which point they basically said “screw it”, and just drew a line straight north from there.

The Myth Behind the Montana-Idaho Border