Lake going over a cliff
I was wondering if there's any way at all to justify a lake going over a cliff and creating a waterfall that spans and entire coastal cliff. Maybe 10-20 miles long or so. The lake would be very shallow throughout. Probably about 2-8 feet deep.
The source for this lake would be a mountain range that has very frequent a large storms, and the entire portion of the landmass that the lake would be on would be at a downward slant towards the cliffs, so all the water would drain into that area, but I'm not sure that would be enough considering how much friggin' water would be flowing over that 20 mile long waterfall.
Another option would be for the lake to be farther inland and have a river that run out of it over the cliffs. When the lake floods, it would burst the boundaries of the river coming out of it and flood over the cliffs, creating that massive waterfall afore mentioned. This seems more realistic, but not as awesome.
I've attached a pic of roughly what I'm thinking. I don't mind if it's highly, highly improbably, but impossible is probably a deal-breaker. I really love this feature of my world, so I want to find a way to make it work.
The lake should also be crystal clear, which I think would be hard due to the flowing of the water.
Maybe I should move the lake somewhere else on the map and just have a big river/waterfall(s) running off those cliffs. I'm not sure. Just interested in y'all's opinions.
I'll call it impossible. Erosion would quickly wear down the edges, if you start out with a ragged edge like this you'll probably end up with a number of canyons until the water flow settles into one that happens to be the deepest. Also, you'll need to have as much water flowing into your lake as flows out of your lake. You can actually work that out mathematically if you really want to. iirc such massive "floods" did happen in earth's past, but they were very temporary and always left a heavily eroded canyon-y terrain behind.
If the volume of those rivers varies a lot seasonally, it's maybe possible that you could have a main channel during the dry season and then a wider flooding surface going over the cliff in the wet season. I don't think it'd be possible to have it like that all the time, though, and it would just be a wide river, not a lake.
Thanks guys. Not what I wanted to hear, but what I suspected. I'll rework things.
Actually, before you rework the idea...
Of course my thoughts turn to a fantasy setting, and may not suit your needs.....but here goes....
In the real world, and unless there are major engineering works at play, I have to agree with bartmoss. Erosion would kill this idea. However....in fanasy setting where there be MAGIC, of a geological scale, I can see this as a battle between two elemental gods/kings....The water one opening the flood gates to the plane of water in an effort to destroy this plain, and the earth one doing its best to shore up the land and suppress the water. Call it a war between the two who's beginnings is lost in time......Some where in the middle of this lake is the gateway, and possibly an answer to the riddle...
Just some thoughts that may or may not help you make up your mind
Trying to think of something like this and the only thought I get is Niagra Falls, specifically Horseshoe Falls. They are about 2,600 feet (790 m) wide. You can read about them Here but it says "the Niagara River draining Lake Erie into Lake Ontario, is the collective name for the Horseshoe Falls and the adjacent American Falls along with the comparatively small Bridal Veil Falls, which combined form the highest flow rate of any waterfall in the world."
Obviously that's nowhere near 10-20 miles wide but if it's fantasy and you want to go big well, you just need to make up some reason.
Even a magical world needs to follow player/reader expectations, and that means you will generally want to stick to the laws of nature as we know them. If you add weird physics, you need to deal with the consequences. For example, take Korash's idea. Of course it would work. But you'll need to explain it. Why are they fighting? Earth and water are not tarditionally opposed to oneanother. What happens in places where there's no water to keep the earth in check? Does the Earth push up without opposition, resulting in huge mountains? What about erosion? The huge amounts of water would carry a lot of earth downriver, where it would create a gigantic delta/marsh/whatever. And then there's the question - if water and earth fight here, what about the other elements?
Of course you can just handwave all of that away, but that's cheating.
Instead, I'd think about the effect I want to achieve. What purpose does my 20mile-wide waterfall serve? Is it just scenery? Do I need it for a climactic scene in a book? Etc. Then try to come up with something else that works. Limiting oneself isn't always a bad thing, it can result in some great work. (Compare old star wars, which had to work under physical and, at first, budget limitations, to the new star wars, where they had all the technology and all the money they could hope for...)
i'm not so big on bounding imagination with 'reality', since it's fantasy anyway. to flesh it in if you want, of course massive scale for a flooded/shallow river more than a lake helps.. there could also be high mineral content in the water.
i have seen in certain undisclosed locations :D waterfalls and rivers form 'walled pools', almost exactly like a series of hot tubs squished together with 2-3' smooth walls built around them.. let's see if i can find a pic.. i expect one could conceive of a similar thing happening to a wide waterfall, forming a retaining lip.
ahh, a painting, even more anonymous..
Ah - Travertine Dams. Cool formations. The problem with a 'normal' waterfall for your purposes is that erosion would tend to turn a broad fall into a few narrow ones. Travertine dams are formed due to *deposition* of a dissolved mineral - typically calcium carbonate. So wherever water is flowing gets built up instead of worn down. Large gaps where there's too much water flowing to get much deposition are naturally the places where debris tends to go, and whatever gets stuck (logs, leaves, whatever) will slow the flow, improve the deposition, and 'heal' the rift. Google for images of them. You'll see a number of Earthly examples that are not twenty miles wide, but do span hundreds and hundreds of yards. If you don't need *continual* flow across the *whole* width of your 20-mile waterfall, this could be the situation you need. Travertine dams have the nice characteristic that they bow outward, instead of the inward-curving collapse characteristics of most waterfall rims.
To get at least occasional periods of spectacular wide-rim flow, just postulate flooding -- enough of a storm upstream, and the volume of flow goes way up, turning a trickle into a band of falling water.
Iguazu Falls spans 1.7 miles, but that's not continuous. Victoria Falls is "only" 5600 ft wide, but that's a continuous sheet of water... at least in wet season. In dry season it dwindles to a series of smaller cascades separated by rock outcrops. Niagara has a bigger mean annual flow (85,000 cu ft/ sec) but both Iguazu and Victoria have peaked at over 400,000 cu ft/ sec for short periods. Comparison : average flow of the Amazon and Mississippi are about 7.4 million, and 590 thousand cu ft/ sec. Peak for those is more like 10.6 million and 3 million cu ft/ sec, respectively.
Thus a carefully placed waterfall :-) on even an earthly large river could have a flow rate of a hundred to a few hundred times that of Earth's largest waterfalls. So in theory, you could easily get enough water to "look like Niagara" across a twenty-mile span. All you have to do ( ALL :-) ) is devise a hard enough, level enough lip to not wear away in a year or a century, OR devise a way to get a WHALE of a lot of calcium dissolved. For B, how about if your river gathers its water way upstream in rainy mountains, and then flows across a former seabed - like the salt flats in the US southwest. Rivers like the Nile do that - long stretches are in arid surroundings. Say you once had an inland sea, with evaporation jacking up the mineral content of the water. The area shifts to be more arid, and the sea dries up. There's your salt flats. And what can be more level than a former seabed filled over eons with minerals? Nothing the least bit implausible there. Now, do a little creative faulting, and create you a crack across said salt flat. Not just a slim crack - make it like the Great Rift Valley. Heck - imagine that such rifting is what drained the inland sea in the first place -- say, a low-ish part of the former rim-of-watershed is breached - now it's no longer an endorheic basin. Now gather you a whole bunch of rainfall - make it a climate shift and the arid valley is no longer arid, or make it periodic incursions of rain into an otherwise dry zone - take your pick, based on your storyline needs and your wild whims :-).
Boom. Waterfall of whatever width you desire; choose travertine process for keep-the-edge-built-up, or posit a nice layer of basalt as the rim for long-term resistance to erosion. Dial the rainfall up or down for duration of full flow vs trickle. Since you're drawing up the whole landscape, pick a larger or smaller drainage basin to collect rain, and slide it north-south to get the desired wet or dry climate. Want some spectacular differences in normal vs. flood, and all you have to do is place this near a coast that's subject to hurricanes -- several times a year you can have immense flow, and the rest of the time some stable amount.
Such a formation might be short-lived, in geological terms. So what? Cities, highways, and nations are all short-lived in geological terms....
If we're doing rationalization exercises here, don't get me started on the effects of a high concentration of industrious beavers....