In a different evolutionary timeline, humans evolved, some become an aquatic race, some become a land dweller, and some capable of living both on land and underwater.

Due to the limited amount of land available (maybe a 90% water/10% land ratio), only the most powerful and wealthiest could live on land.

However, someone found a way to harness the power of something to raise and lower the water level of the planet, causing there to be much more land and thus an easier opportunity to live on land. Changing the water level so drastically had catastrophic consequences and mass casualties since at this point the wealthy race adapted to live solely on land, some only in the water, and a vast minority that stayed amphibious. This something is only available every several millennia.

My main question is simply: How a sea-dweller submerge the entire planet and make sure it cannot be undone? Consider this is when the something is available.

I already have a few ideas but I do not want to simply describe a comet or something else that's overdone because I want this to be a little more original.

Any ideas?

  • $\begingroup$ I want to say I've heard of some effect that threatens to raise sea level many meters with horrible consequences. Maybe a lowering helped people switch continents thousands of years ago too. $\endgroup$ – user25818 Mar 24 '17 at 21:44
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    $\begingroup$ Interesting question but as it stands it is really broad. Any number of things could cause this...or be a magical excuse. Try setting some criteria for the event to narrow things down. $\endgroup$ – James Mar 25 '17 at 1:35
  • $\begingroup$ I hope this explains it a little bit. The world is composed of a race on land that is completely ignorant of a hidden race underwater. Since the world's sea level had been changed a few times before and countless fatalities resulted, the leaders of both races at the time thought it best to separate the two as a preventative measure. It is now current times and a sea dweller wants to completely submerge the planet and make sure it cannot be undone. It would need to be something that has to be caused by an individual and not a natural occurrence. Hope this helps and thanks so much. $\endgroup$ – Askance_tortoise14 Mar 25 '17 at 6:36
  • $\begingroup$ "exponentially" does not mean what you probably think it does. $\endgroup$ – Mołot Mar 25 '17 at 11:34

Increasing Water:

Breaking ICE from the poles, creating ice flows. Ice seperated from the poles melts faster, releasing more water. Only possible during periods of high Solar Activity that coincides with x years.

Decreasing Water:

Starting an ice age. How to do this depends on your planet, but if you have the power to effect it to your proposed scale, this should be possible.


Make floating islands out of some sort of fast growing algae. The algae spreads quickly, rapidly clotting up the ocean. The algae can only spread or grow due to radiation x released during the x millennial solar cycle. Or is spurred on by some exotic material x caused by the cyclical asteroid shower. This shower happens every year, but only actually hits your planet when the planets align. Which only happens every x years.


I'm assuming the reason of the change of water level is caused by this 'someone' and not occur naturally without interference of certain individual. I also assume that the event allow for increasing and decreasing sea level, whatever the individual choose.

Here are few ideas for magical reasons:

1. Conjunction of celestial bodies

Waterbending is greatly strengthened and enhanced during the night, due to its lunar affinity. During a full moon in particular, waterbending is greatly enhanced, to the point where a single waterbender can overpower multiple opponents with relative ease. Source

The planet has several moons, and every 100 years when the moons are in alignment, the waterbending species can perform a water-bending ritual to increase or decrease the water level semi-permanently by freezing or melting polar caps. This must be done in group of many powerful waterbenders.

2. Portal to Water Dimension

Every millenium there is a conjunction with a water dimension, and allow someone to forcefully open the portal to get more water from it. However, when the timing is off, the portal open to the 'dry' part, causing water to pour out from the planet to the other dimension instead, effectively decreasing the sea level.

Here are few ideas of natural reasons:

1. A 100-year Long Eclipse

Every millenium, there is a sun eclipse that lasts 100-year. This cause a century of ice age, which will be reversed back to normal after the eclipse ends.

2. Volcanic Activity

The land is actually a dormant volcano, and erupt every 1000 years. The magma creates more land, but later the eruption is controlled by the nobles to prevent more land to keep the gap between land-nobles and sea-commoners.


There are many rare natural occurrences that you could use, volcanoes erupting, fire rainbows, alignment of certain planets with each other etc. You would just have to find one that would make sense for your current state of water to landmass ratio.

other non-natural totally made up occurrences could be:

a certain species of fish/mammal or any other aquatic creature only procreate every couple of thousand years, or migrate to the surface, into the water or across each landscape

A plant or mineral or element take thousands of years to grow accumulate or come the stable state it needs to be in order to be harnessed.

It could also be something more spiritual or magical. A visit from a god, alien or powerful being?

Of course you could make up any excuse as to why these things happen that fit with your story.

Hope this helps!


A celestial body of some sort seems like a good choice here. Halley's Comet, for example, comes close enough to the Earth to be seen with the naked eye every 75 years. It is in fact notable because it appears so frequently. A comet that came so close to earth everyone couple hundred thousand years or would not be absurd. Comets are also mostly water, so if you are partial to dropping stuff out of space for your cataclysm, one could have been literally slammed into the planet with the effect of a sea level rise.

I would expect such an impact to have other bad effects for life on the planet, but since it was drawn it in with magic in this scenario, I don't think it's unreasonable that the same magic was used to mitigate the effect.

Conversely, for lowering the water level, siphon the oceans into a passing comet. This is a little less sciency, but again, magic.

  • $\begingroup$ Highly related, a conjunction of two celestial bodies could also serve as a good choice. $\endgroup$ – Cort Ammon Mar 24 '17 at 23:20
  • $\begingroup$ @CortAmmon For clarification, a conjunction of what sort of celestial bodies? And how would this affect sea levels? $\endgroup$ – a4android Mar 25 '17 at 11:36
  • $\begingroup$ @a4android Pick your favorite. The power of a conjunction is that, by their nature, they happen less often than other events, so they qualify as the "occasional" event. As for your second question, the answer is magic =) $\endgroup$ – Cort Ammon Mar 25 '17 at 16:01
  • $\begingroup$ @CortAmmon Magic, eh! Foolish me. I was assuming an astronomical event. So you were thinking of a 'if the stars are right' type of event instead of the physically realistic. $\endgroup$ – a4android Mar 26 '17 at 0:41
  • $\begingroup$ @a4android Well, I suppose if you define an asteroid crashing to Earth as one qualifying definition of a conjunction, physics could play a part too! =) $\endgroup$ – Cort Ammon Mar 26 '17 at 2:01

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