Underwater, there are insane implosions at 25K feet below sea level. At that same depth on land, we have caves.
Why doesn’t the earth compress things like water does? Does gravity do different things to different materials?
In: Planetary Science
Pressure out in the ocean or atmosphere has to do with how much stuff is above you weighing down on you. Imagine instead of water you’re in a giant ball pit. At the top of the ball put you’d feel normal, but if you sunk to the bottom of the ball pit with thousands of feet worth of plastic balls on top of you, you’d be crushed by the weight of all those plastic balls. It’s the same thing going on with water molecules in the ocean. It also happens with air molecules on land, but we don’t usually notice it because we are used to the pressure at ground level.
Rock is solid.
Water is liquid.
Solids keep shape, liquids don’t.
That said, holes in rock “implode” too. That’s what, for example, a mine shaft collapse is. All the pressure of the rock above and around causes it to cave in (aha) on itself, just like a pocket of air underwater.
It just takes a lot more time.
the same reason you can build a sandwish tower but you cant build a tower with your cereal and milk.
Because one is liquid and the other is solid.
Also, caves are not even remotely as deep as the oceans. Not even close. Most of the underground caves that are below sea level are, unsurprisingly, filled with water.
Earth does compress things, but rock has a tensile strength and an elastic modulus value that needs to be overcome before it starts breaking down and fill cavitys. So down to a certain depth (pressure) it will be rigid and caves can exist if small enough, but further down we will find none.
And even further down, the earth itself is liquid due to the pressure. Rock, metal, everything becoems a liquid further down from the immense pressure.
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