The structural integrity of islands without the surrounding water

If the oceans were to disappear in a flash would some large islands collapse or crumble under their own weight? I’m thinking of places like the Big Island of Hawaii which is taller from base to summit than Mt. Everest or supposed “pedestal islands” (Cuba?) that have dry land masses equal to or more than their footprint on the ocean floor.

For that matter, would most fixed offshore oil platforms remain standing if the water under them were completely removed?

Is that true about Cuba? The only relevant hit on the first page of a google search on “pedestal island cuba” is this thread.

This is a very good question. But islands are generally not made out of stuff that floats.

Surely it would depend on the steepness of the coastline/seabed? I’d imagine you’d have some pretty epic landslides in places.

New Zealand’s main islands would be relatively okay as they have their own ‘continental’ shelves.

Stuff that floats, no. But they are made out of material that’s buoyant. The buoyancy won’t completely balance out the weight of the rock, but it will decrease the net effective weight.

I couldn’t find anything on that either, that’s why I used the question mark. I just remember talk during the Cold War about the theoretical possibility of sinking Cuba with a submersible nuke. Probably no more feasible than it sounds but I thought that tale might have been inspired by the island’s actual ocean floor footprint.

Based on this map, Cuba has a much larger underwater footprint than what you see above water. The same is also true for Hawaii; remember also that the vertical scale is greatly exaggerated on these maps, so they are more like pancakes than rock piles in cross section. I also don’t think the presence of an ocean has much to do with the stability of islands since rock is much heavier than water. Plus, the oceans have tides and currents, and being much denser than air, exerts much greater forces.

The water lapping at the sides of islands has a strong erosive effect, much more than anything mere air can provide. I am going to say that (excluding oddities like “floating islands,” that are not really islands at all) any island would last longer if the water were taken away.

Back in the 50’s and early 60’s there was quite a lot of Popular Science type thinking that we could do anything with nukes. Make a sea level Panama Canal, rip the land off a seam of coal,extinguish a fire in the Van Allen radiation belts,whatever. So sinking an island wouldn’t seem that farfetched.

That doesn’t make it possible, though.

I think landslides will create a shallower slope on the sides of the islands. The top should be affected the most. At the bottom the rock is pretty well compressed by the weight of the island already. Seismic activity (and there will be a lot of it if the weight of the oceans is gone) will do the most damage. Weather, not so much. There will be a lot less weather with almost all the water on the planet gone.

This. Here is a relevant XKCD, note the inset that shows Mauna Kea and the Marianas Trench with true horizontal scale. While Hawaii looks like a precipitous mountain jutting up from the sea floor on most maps/globes it’s actually more like a wide, gently sloping hill. Most islands will have similar, if not flatter profiles.

I do not see how they could. They are attached to the earth the same way the continents are. Sea levels rise and fall, and islands join the mainland, or go back to being islands - but they do not collapse. Example includes the Channel Islands in CA. It’s not like the water is causing them to buoy to the surface in any way at all.

As stated, the erosive effects of shorelines would be suspended. I imagine sand islands like the Outer Banks would be re-inforced and more stable if the sea were to go away.

A warning for people. I got a virus alert when I clicked on that link.

But without the surrounding water, it would no longer be an island, so technically the island would cease to exist :cool:

A glance at that xkcd link will show that the slope gets a lot steeper, right at the waterline. This suggests that the buoyancy increases the stable angle of repose, and that if the water went away, it’d be carved down to the above-water slope everywhere.

You weren’t the only one.

Quite the contrary, it shows that water erosion is carving into the “side” of the island much faster than air (wind rain etc.) erosion is. Buoyancy has nothing (well, virtually nothing) to do with it. (In the case of Hawaii, the slope profile probably also has something to do with lava solidifying as it reaches the water.)

If, after you took the water away, the slope evened out to the shallower slope of what was originally land, you would not be carving down, but carving up (which is clearly nonsense).

If such water was to such disappear in a instant I would expect the now exposed land to pretty much explode as ground water that was held back by sea water pressure now gushes out. Massive erosion as this ground water started the process of creating streams and even rivers full of mud and rock and landslides.

Now if you removed all the water including ground water in a instant you may get sink holes you may get minor slides as there is some buoyancy involved but I think it would be less dramatic in a geological level.

Moderator Note: I have broken the links.

The stench from all the rotting sea creatures would be unreal.