In the novel I'm writing, there is an island that sinks below sea level and rises up again at a later date. How is it possible to do this, while both keeping the surface of the island dry when it rises above the sea, and also to keep it connected to the mines beneath?

The island must sink and rise via a man-made method. The island raising and falling must be mechanical, with pistons or some kind of mechanical elevation or something, since it's activated by someone. It cannot be natural.

(Note: Quantum forcefield technology exists in the universe of my novel, which is essentially a barrier that prevents matter from passing through it, but it cannot lift or push anything since it has no force behind it. )

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    $\begingroup$ How quickly does this need to happen? Because it's happened on Earth, but not over night. $\endgroup$ – Frostfyre Mar 9 '17 at 13:28
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    $\begingroup$ There exist islands that rise and sink daily, in areas subject to strong tides. There are others that do so annually- mainly within rivers- as winter droughts give way to spring run-off and rains. And then there is Hawaii, where to the west end islands are eroding away, and on the east end the volcano is poised to add a new one any day now. Oh, and I almost forgot Krakatoa and Anak Krakatoa- daddy blew itself up in 1883, but then the son emerged in 1927. $\endgroup$ – cobaltduck Mar 9 '17 at 13:28
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    $\begingroup$ Does it need to be Natural/Geological or can it be done by the inhabitants of the island, given the use of a quantum force field. $\endgroup$ – Enigma Maitreya Mar 9 '17 at 13:40
  • $\begingroup$ What exactly is "quantum forcefield technology" and what can and can't it do in your universe? $\endgroup$ – Philipp Mar 9 '17 at 14:16
  • $\begingroup$ The island raising and falling must be mechanical, with pistons or some kind of mechanical elevation or something, since it's activated by someone. Quantum forcefield technology is esentially just a barrier that prevents matter from passing through it, but it cannot lift or push anything since it has no force behind it. $\endgroup$ – CitadelCore Mar 9 '17 at 14:22

Your Force fields could potentially be projected underground and used to disrupt or alter the flow of magma in the Earth's mantle to create a cool spot which would sink causing an artificial subduction zone or caldera to form around your island lowering the entire section of the Earth's crust containing your island below the ocean. The process could then be reversed (possibly just by turning off the force field) allowing the magma flows to change and raise the island back up. This would be more likely to succeed if your island is of volcanic origin already and not part of a large continental plate.

Normally these processes are not very fast (on the order of inches per year), but aided by force fields they could potentially be accelerated; although much of the action depends on thermal changes in the rock (i.e. heating and cooling) which likely would still be pretty slow.

This is definitely a mad scientist level project, normal subduction zones are known for associated volcanic and earthquake activity, artificially accelerating or causing this will likely cause significant earthquakes and volcanic eruptions effecting a very large area around the island (likely all adjacent plate boundaries would be disrupted).

  • $\begingroup$ That sounds like just what I need. One problem though: how far down could this potentially go? There are mines far below the island that need to be connected to it. $\endgroup$ – CitadelCore Mar 9 '17 at 15:35
  • $\begingroup$ I was thinking this but perhaps more along the lines of Cities in Flight. Create a sphere including the mines. Now the island is a detached island. One could then raise and lower or move it. I didn't get the sense the OP was looking for that kind of answer though. Good answer though :) $\endgroup$ – Enigma Maitreya Mar 9 '17 at 15:43
  • $\begingroup$ I'm talking about using force fields below the Earth's crust into the mantle where the rock is liquefied magma, your mines won't be this deep. $\endgroup$ – Josh King Mar 9 '17 at 15:49
  • $\begingroup$ I imagine you would do this with an existing, non-active, volcanic mountain (Oahu, Mauritius, etc) , so you could be sure to know what you were making sink, plus most of the volcanic activity would then be on the ocean floor. On the flip side, I don't know how you are going to get the island back up without an active volcano in the middle of it...mad scientist problems. $\endgroup$ – kingledion Mar 9 '17 at 15:52

So having a man made island that can sink and float isn't hard by having buyancy chambers like a submarine, and having force fields to keep the water at bay could keep it dry and habitable even when submerged.

But then the whole "island" would just be a big ship/sub. Being connected to the mines below the city wouldn't be easily done unless they were connected with flexible tubing or you went up and down in bathyspheres.

Alternately the whole island could be connected to the sea floor with something like hydraulics, so that it could be raised and lowered at will, and the stairways and passages to get down to the mines on the sea floor would just expand when the island is raised and contract when the island lowers.

Making it water tight would be very hard, so the force fields to keep the water out of the structure would be very helpful.

Another thought is that the island could be natural, like a giant pillar of stone, and be raised and lowered by pressure in geothermal vents. enter image description here

The pressure could be vented to lower the island, and bottled up to raise the island. It wouldn't really be connected to the mines that way though, but you could have an airlock/force field to go from the base of the tower to the mines.

  • $\begingroup$ Interesting answer! I might be able to use the forcefields to hold back the water in places - allowing safe passage to the mines. $\endgroup$ – CitadelCore Mar 9 '17 at 15:49

The upwards-directed force of water on an object is equivalent to the weight of the water it replaces, in other words the volume of the object.

So all you need is a big, airtight, vacuum filled box, which can change size. Which can be easily accomplished by a hydraulic arm on the inside. And better make it a lot of medium sized boxes, for balancing.
A flexible tube at the bottom can be used as a connection to everything below.

If you want a more static version, which does not float around, you can just use a very big hydraulic arm (protected from the water in a telescopic pipe) and an elevator (on a second hydraulic arm or hanging from a rope) in a second telescopic pipe.

  • $\begingroup$ replace your vacuum with air, and you have almost the same effect with a lot less engineering issues. $\endgroup$ – Burki Mar 9 '17 at 15:31


Simply build the island upon containers that have the ability to act has weights or floats. In other words, containers utilise valves which can either let water in, or out.

When water is let in, the island sinks. When dispensed and replaced with some type of (light) gas, such as helium, the island floats.

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    $\begingroup$ It doesn't even have to be a light gas. It could just be air. This is how submarines work, ballast tanks that can be flooded to let the sub sink, or pumped out and filled with air to rise back up to the surface. $\endgroup$ – AndyD273 Mar 9 '17 at 15:21
  • $\begingroup$ Yeah, or just air. Even a vacuum would work (under certain conditions). But helium would actually make the island rise faster than air. Good for if it's super deep and in need for a quick accent. $\endgroup$ – Luka Mar 9 '17 at 15:57
  • $\begingroup$ And hydrogen a lot better still... $\endgroup$ – R.. Mar 9 '17 at 20:35

Does it have to be in the open ocean? If it can be in an inland sea (such as the Mediterranean or Black Sea) or large lake, it might be easier to change the water level of the sea. You could divert rivers running into the sea or block waterways leading out of it to have pretty fine and rapid control the water level.


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