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Comment by GalenErso | Hacker News Reader

As someone with zero training in earth sciences, I gotta think: when those happen under the sea, the water must rush into the gap, right? The interior of the Earth must be full of water.

https://www.newscientist.com/article/2204528-the-oceans-are-...

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That's a strange conclusion. Gaps in the crust under the surface of the sea will if they open up deep enough cause sea water to come in contact with magma which will rapidly solidify and if it is less deep it will simply fill up the gap, the interior of the earth is a ball of molten iron covered with a layer of molten rock and given the density difference there is absolutely no way that water would displace any of that.

As a mere mammal, it's hard to comprehend the scale of things like the earth. The crust on the ocean floor is "only" about six to twelve kilometers thick. This is only one one-thousandths to two one-thousandths of the earth's radius. It might as well be a drop of sweat entering a crack on your chapped lips by comparison. Some would get into the lithosphere, but that's still quite near the surface, again, next to everything else.

Once you get past the crust, and then the various layers of the mantle, to the liquidy bits, well ... the density is so high that water would be completely forced to float to the top even if you could get the water down there. Plus it would be exposed to high temperatures and might well be steam (depending on local pressures).

It's actually not liquid (at least that's the theory). It's more like butter. The magma that you see at the surface is due to the rocks melting since there is a decreases in pressure and there are other minerals in the rock i.e. water. Don't quote me on that... that's what I remember from my Geology class from 10+ years ago.

The earth is best thought of as a ball of rock with an iron core that is slightly damp.

In a sense, yes. At fault zones underwater, the seawater does 'mix' with magma and volcanic rock, changing the form of the magma and rock. Rock is more dense than water, even when rock is liquid, so the center of the earth won't fill with liquid water.

https://en.wikipedia.org/wiki/Geothermal_gradient:

“As a general rule, the crust temperature rises with depth due to the heat flow from the much hotter mantle; away from tectonic plate boundaries, temperature rises in about 25–30 °C/km (72–87 °F/mi) of depth near the surface in most of the world.”

⇒ Even under pressure, I think most water would boil before it could reach the core. Certainly if there’s magma a steam explosion is likely.

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