The Premise

Planet K is a lot like Earth in terms of size, atmosphere and land to water ratio, though the continent shapes and sizes may vary. There is one other major difference: the planet's oceans have boundaries. Real, waterfall-like boundaries.

These boundaries are formed due to super wide and super deep chasms in the ocean floor. The chasms are so wide and so deep that the water literally flows down these chasms, creating gigantic waterfalls along the boundaries of the oceans.

The planet is therefore divided into 7-8 giant territories comprising of land surrounded by oceans, and the chasms form natural borders for the oceans i.e. the oceans are separated by giant waterfalls due to the chasms.

The Question

  1. Can this kind of a planet be scientifically (and not magically) explained?

  2. If so, how?

  3. The oceans do not run dry. So, if all the water disappears down the chasms, is there a scientifically plausible way to explain how they don't run dry?

  • $\begingroup$ What do you mean, it borders the ocean? Do you mean that all land is actually on cliffs above the water, and rivers turn into waterfalls? Or do you mean there are giant chasms in the middle of the oceans within the oceans rushing into them? $\endgroup$ Feb 28, 2016 at 2:44
  • $\begingroup$ @XandarTheZenon - It's the second of the alternatives identified by you. I think the second and third paragraphs should be adequately clear but I've added an edit for further clarity. Hope it reads better now. $\endgroup$ Feb 28, 2016 at 14:33
  • $\begingroup$ Much better! I wrote you an answer $\endgroup$ Feb 28, 2016 at 14:55
  • $\begingroup$ As others have pointed out, the issue seems to be that the water going into these chasms need to get out and refill the oceans, otherwise it'd just fill up. $\endgroup$ Sep 21, 2018 at 7:15
  • $\begingroup$ where does the water fall and how does it get back in the oceans? Think about equlibriums and such $\endgroup$
    – Fl.pf.
    Sep 21, 2018 at 9:30

6 Answers 6



At least, not naturally.

Water will follow the simple path of gravity. It will all flow into the trenches until it reaches some kind of equilibrium. So you'll either have really deep trench seas, or you'll have shallow seas that have deep water trenches in them. Which would still border your oceans, just not like you intended. Also, there is another problem. If there are large trenches, then that means the tectonic plates will be moving away from each other. So they would also be moving towards other plates to create mountains. So keep that in mind.


If you have a society with very powerful futuristic technology, maybe they made the seas do this. Maybe aliens have installed gigantic underwater pumps and pipes that take water from the ditch and dump it next to land masses. Or in the middle of an ocean.

  • $\begingroup$ Could the hole somehow be deep enough to hit the mantle and then evaporate? This might prevent the equilibrium from forming. $\endgroup$ Feb 29, 2016 at 19:49
  • $\begingroup$ @Sam It would be like a giant open volcano, eventually the water would cause some of the molten rock to solidify and form a cap. I'm reasonably sure, but I'm not a geologist. $\endgroup$ Feb 29, 2016 at 20:15
  • 1
    $\begingroup$ Trenches are where ocean plates are being destroyed, so the tectonic plates are moving toward each other at that point. $\endgroup$
    – Oldcat
    Feb 29, 2016 at 22:08
  • $\begingroup$ @Oldcat Interesting, I didn't know that. But it works either way. $\endgroup$ Mar 1, 2016 at 1:56
  • $\begingroup$ @Bellerophon no the water would cool it to the point it no longer boiled the water in no time. That is what the mid oceanic spreading center is afterall. $\endgroup$
    – John
    Jun 29, 2019 at 14:45

As Xandir said, such a situation could not happen naturally. Water is a very lazy substance. It always flows to the lowest point to which gravity pulls it, and stays there, unless acted upon by another force. That force might be artificial, like a pump, or natural, like the sun evaporating it. If you have deep trenches in your world, they would simply just fill up with water, and you'd have a shallow sea with an abrupt trench in it. Such a thing could plausible if created artificially, though. If there was some massive pump emptying the trenches and pumping the water back to the surface in some way. But then there would have to be some purpose for it. A society wouldn't go through the trouble of doing what you described, unless there was some purpose for it.


(Consider Xandar's second case) It could be a terraforming project. The ocean basins are too deep compared to the amount of water present, so they add pumps to move (desalinated) water to the highlands to cause a water cycle over land.

Now this tech might not look like plumbing parts to us. The mechanisms arranged would harness planetary-scale forces, and would become geography. Just not naturally occurring.


idk how the canyons could have come about in the first place (geology is not a strong suit of mine) but the first thing that comes to mind in regards to the oceans being replenished is that the heat from the planets core would evaporate the water at the same rate it flows in. To compensate for the massive amounts of energy this would require, the planet would have to either start at a higher temperature or regain heat at the same speed. the first option would probably make the planet uninhabitable, but the second option could be achieved by having the planet have a much higher concentration of radioactive elements in its crust, the decay of which would heat up the surrounding stone and balance out the water. Of course, having massive open holes to the mantle coupled with giant pillars of steam to transfer heat would drastically raise the average surface temp of the planet, both through convection and the greenhouse effect. If you wanted to make the planet habitable, you could place it farther from the star it orbits than earth is, which would than raise the problem of getting enough light to sustain life (also compounded by cloud cover). maybe something w/ geothermal heat again, like life around deep-sea ocean vents? a few other ideas: first, the continual evaporation and condensation process would result in oceans with little to no salt content, or indeed any impurities in the water at all. secondly, i (may) have thought of a way to explain large tectonic fractures as well as increased radioisotopes: the planet originated as a small, rocky planetoid, but at some point near the end of its life (after cooling almost completely), the planet was hit by a radioactive asteroid. the resulting increase in heat causes the planet to expand, cracking the surface; it also explains some problems with solar heat by letting you say the star is also very old and produces little light. sorry for any style or formatting problems, this is my first post here!

  • $\begingroup$ I think this could actually work, so long as the situation doesn't have to last for long. Maybe just a few centuries? That may allow for an earth-like atmosphere and temperature before too much steam supersaturates the atmosphere and raises the temp past human tolerance, or the core cools enough for the water to fill the trenches. $\endgroup$
    – Jason K
    Jan 26, 2017 at 20:41
  • $\begingroup$ doesn't work, those vents only stay hot because only a very small amount a water is able to reach the hot portions. the parts exposed to the open water are too cold to create evaporation because the water cools it too quickly. . $\endgroup$
    – John
    Jun 29, 2019 at 14:51

The Earth's oceans are pulled towards the moon. In some parts of the Earth, the changes in tide can vary as much as 50 feet. Some other configuration of planet and moon could create more extreme tides, which would create opportunities for waterfalls to occur regularly.

If the surface of the planet were shaped like a gear, wrapped around the whole planet, the gravitational pull from a moon could cause the water to constantly spill over the "teeth" creating regular waterfalls continuously across the planet.

                                                            ( moon )
                               -------> pull of gravity
----------------\~~~~~~~~~~~~~~~~~ .  .
                 \----------------\  .
  • 2
    $\begingroup$ So why don’t the teeth quickly erode? $\endgroup$
    – JDługosz
    Jan 26, 2017 at 4:15
  • $\begingroup$ @JDlugosz conviently volcanic teeth? And um handwavium... Lots of it $\endgroup$
    – apaul
    Jan 26, 2017 at 4:29
  • $\begingroup$ As JDługosz pointed out, erosion is a thing. So your teeth should probably be made of some super-strong unobtainium rock. Maybe your planet was modified by highly advanced aliens in the distant past, for unknown reasons? Or some unlikely but possible tectonic process could be creating them. $\endgroup$
    – Draconis
    Jan 26, 2017 at 4:29
  • $\begingroup$ I recall a story in which the ocean flopped from one basin to another due to extreme tides, much to the surprise of the colonists. $\endgroup$
    – JDługosz
    Jan 26, 2017 at 6:14
  • $\begingroup$ @apaul34208 handwavium? so that ignores points 1 and 2 of the OP’s question. $\endgroup$
    – JDługosz
    Jan 26, 2017 at 6:16

It kind of could happen with a few caveats. A warm planet would help, because warm air holds more water and the only mechanism for creating waterfalls is evaporation and weather systems. Water doesn't rise, unless it evaporates, then it rises. All the rain in the world is evaporated, risen water.

So you'd need a warm planet with a strong weather system, perhaps a lower gravity planet, half way between Earth and Mars with lower surface gravity, and a more massive atmosphere, which would balance out with the lower gravity to a similar atmospheric pressure. More volume in the atmosphere would assist in more stored atmospheric water vapor.

Lower gravity would allow higher stable plateaus and cliffs and rain would fall slower and rivers flow with less force, causing less erosion. None of these factors in and of themselves is essential, but each helps.

Lower gravity also leads to lower lapse rate, which means the atmosphere loses heat as air rises more slowly. Clouds could rise higher and there could be more of them. More atmosphere, warm air, so more water vapor and more rain to feed the waterfalls.

The 2nd problem is the shape or drop off, from the continent into the ocean. Granite/continental plates is lighter than Basalt rock that makes up most of the crust. Continents essentially float on the Earth's crust like corks in water.

enter image description here

Source of image

Oceanside cliffs do exist, but they're relatively rare, only a small percentage of total coastline. And oceanside waterfalls are even more rare, if they exist at all. That's the real problem, how to create abundant oceanside waterfalls. Rivers tend to flow somewhat steadily into oceans. They rarely fall from above.

But lets say we have a warm planet with abundant granite and high plateau land masses, mostly a couple/few miles above sea level. The weather on the land masses is warm/temperate, so there's enough water vapor and rain. The weather at sea level is balmy/hot, leading to high evaporation rates, formation of clouds which rise, create rain and disappear. Because much of the rain happens at lower elevation, much of the erosion happens there too, leaving high plateau land masses.

The waterfalls would mostly be cloud fed, not river fed. There will never be enough rivers to make entire coastlines of waterfalls. Rivers tend to combine as they flow down hill, they don't spread out, though there can be some spreading right on the coast.

So, basically this, at least, the left part of the diagram, but instead of a mountain, it's a plateau.

enter image description here

So if you stood at the edge of the cliff overlooking the ocean, you'd see clouds below you. You probably wouldn't see the ocean at all and you might (just maybe) hear the flow of water down the cliff below you, but it wouldn't be a traditional waterfall from the land above. It would look more like a continent wide waterfall flowing down the Oceanside cliffs from below.

Its worth noting that we've never seen a planet in another solar-system. So we don't really know what to expect, but many things are possible. Lower or higher gravity, certainly. Thicker or thinner atmospheres, hotter, colder, more water, less water more extreme seasons, due to higher axial tilt, higher winds. There's an enormous range of what might exist on other planets.

An entire coastline of waterfalls is problematic because rivers tend to cause grooves and combine as they flow downhill, so river based waterfalls should be local, not spread out. Glacial melt waterfalls might be more spread out, and maybe you could have a weather system where a glacier forms every winter and melts every summer, but glacial melt waterfalls would be periodic, like a flood, not permanent.

So, as others have said, not really possible, but some adjustments, you can sort of have that.


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