Real world geology: Greyhawk

[Menexenus]

Quasqueton's poll/thread about real world geology reminded me of a question that has been smo(u)ldering in the back of my mind for many years now. I didn't want to hijack his thread, but I do want to get an answer to my question at long last.

Has anyone other than me found it strange that in the Greyhawk setting there are 2 separate rivers that empty from the Nyr Dyv lake into the Woolly Bay? The two rivers in question are the Selintan (which passes by the City of Greyhawk) and the Nesser (running through the Celadon Forest, forming the border between the Duchy of Urnst and Nyrond). Here's the question: Isn't this situation (2 entirely separate rivers running from the same lake to the ocean) geologically impossible? Can someone with some real geological knowledge answer this question for me?

Assuming that it is impossible (or virtually so), how should it be explained in the Greyhawk setting? Should it just be chalked up to some hand-wavy magical effect? I'm curious if anyone is aware of any quasi-official explanation for this geological oddity.

Please help me put this long-burning question to rest once and for all! Thanks.

 

[Whizbang Dustyboots]

The only possible explanation is that more water is being added into the lake than is being taken out. Whether that's rain that for some reason only dumps into the lake (I can't think of a natural reason why this would be so) or underground rivers, I can't say.

And yes, it's bugged me since I was a kid.

 

[Grunk]

Dunno for sure, but I always assumed that the Nyr Dyv (or Lake of Endless Depth) was connected to the Elemental Plane of Water which would explain the more-water-coming-in-then-going-out angle.

 

[the Jester]

The Nyr Dyv, or Lake of Unknown Depths, probably has some kind of underground source- whether the Sunless Sea, underground rivers, a portal to the elemental plane of water, or whatever.

 

[Quasqueton]

I guess I'm just exceptionally ignorant and accepting when it comes to geology. That has never, would never, and even if I learn it is geologically impossible in the real world, will never bother me in the slightest.

Quasqueton

 

[MerricB]

Has anyone other than me found it strange that in the Greyhawk setting there are 2 separate rivers that empty from the Nyr Dyv lake into the Woolly Bay? The two rivers in question are the Selintan (which passes by the City of Greyhawk) and the Nesser (running through the Celadon Forest, forming the border between the Duchy of Urnst and Nyrond). Here's the question: Isn't this situation (2 entirely separate rivers running from the same lake to the ocean) geologically impossible? Can someone with some real geological knowledge answer this question for me?

It's not impossible.

In fact, if you've ever seen an island in the middle of a river, you've already seen the same thing on a smaller scale.

It is just very unlikely in nature. (Still, see Nile Delta).

Take a bath. Turn the tap on so there's water flowing into it, then wait until it's full. Remove the plug. Water flows out. Punch a second hole in it. Water will flow out of *both* holes. If one hole is higher than the other, then when the water falls below that level it will only flow out of one hole.

Assuming the level of the lake remains relatively constant, then the water flow in will equal the water flow out. So, you get one very wide and rapid river coming in, and then two "slower" rivers coming out. If they're of basically the same heights, there's no problem.

Cheers!

 

[MerricB]

Doing a little more research,

Wollastone Lake (http://en.wikipedia.org/wiki/Wollaston_Lake) drains naturally in two locations - to different locations, mind, but it shows that it's possible to have more than one outflow from a lake.

Cheers!

 

[JustKim]

I'm a little puzzled why you would think it's impossible. It is neither all that unusual in the real world nor physically improbable, unless you're talking about a lake with dry tributaries and two draining rivers. Rivers branch apart all the time and a lake is essentially a river that's become backed up by a hole in the ground.

 

[helium3]

Generally (there can of course be exceptions) rivers only branch from a single bed to multiple beds in places where there is little to no slope. So, river deltas and the tigris and euphrates valleys come to mind.

The long term problem with the Nyr Dyv thing is that over time one river path is going to erode faster than the other, which means that eventually one path will be favored over another and the other will cease to drain the lake.

But whatever. It's Greyhawk. Realism is optional.

 

[Slife]

Obviously the lake's outlets were created through magical blasting of the adamantine-rich bedrock, which leads to a drastically reduced rate of erosion