Okay, so…
If I had a super-duper, magic machine, and I drilled through the Earth’s crust into the mantle, would I create a volcano? Is the mantle always under pressure, or only when pushed into/over by the crust plates?
And, if so, could some crazy alien race kill us all one day by systematically drilling holes in the crust? What would happen then (besides everyone being killed)?
Why, yes, I did recently take a road trip, why do you ask… 
There’s nothing magical in center of the Earth. Just matter and gravity. There is pressure gradient - just like, for example, in oceans. If you put tube reaching from ocean bottom to the surface you wouldn’t create magical fountain - water would just rise until pressure gradients would equalize. If you put unobtainium drill right into center of Earth, magma would rise until it reached surface, or probably even not that far, since heat loose accompanying decompression probably would cause it to become solid.
ETA - of course, I use term “magma” just as a shorthand. As far as we know, center of Earth is made of iron. Maybe even crystalline iron.
This issue was discussed at length in the documentary Fantastic Four: Rise of the Silver Surfer. As I recall the holes did not boil over with bubbling magma so I am assuming puppygod’s assumption of the magma not reaching the top is spot on.
Is it not safe to assume since volcanoes do not seem endless founts of magma that a pipe to below the earth’s crust does not equal emptying out the center of the earth?
As can be seen in this photo from Tom Swift and his Atomic Earth Blaster, liquid iron will indeed come jetting up from the core.
In real life, I expect the hole would quickly close behind any magic-digging machine. If you also had a magic casing to keep the hole open, I expect that core material would rise part way to the Earth’s surface before solidifying. If you heated the casing to the temperature of core material, so as to keep things liquid, you might get an intermittent geyser, as material around the core settles in and triggers pressure waves up the bore hole.
How about if we bring a small black hole into geosynchronous orbit above the borehole? The tidal effects alone would be interesting…
Effectively, the Earth is already full of holes. The structural strength of the materials that make up the Earth are negligible compared to all of the gravity-related forces, so if magma would gush up out of a hole, it would also break up the crust and gush through that, too.
I should warn you. If you drill to the center of the earth, you’ll have to make another stupid center-of-the-earth movie. It’s a package deal. Sorry.
It says in the Book Of Holes, “They knew not their holes from an ass on the ground.”
I don’t agree with the answers so far, so someone correct me. I agree that the earth already has holes that are NOT never-ending fountains, that this whole subject is impossible, etc, but…
As you go deeper within the earth, everything is under a tremendous amount of pressure. If you drilled into it and the hole didn’t fill in, wouldn’t all that pressure squeeze stuff up through the hole?
A volcano, the closest thing we really have for an example, doesn’t go anywhere near as deep as we are talking here. A volcano is just a hole in the crust created when a bubble of magma makes it’s way up through convection. A volcano would be somewhat like watching a bubble make it’s way up a glass of water. Once it gets to the top, it bursts.
What we are talking about would be more like sticking a straw into a juice box, but our juice box is being squeezed really really hard.
Uh… right?
I think the scale of what we are talking about so overwhelms human minds that it perfectly demonstrates not only what human can do but also what we can ever hope to comprehend. The Russians dug the deepest hole in the world called the Kola Superdeep Borehole and made it down as far as 7.6 miles deep before the project had to be abandoned because of heat and numerous technical issues. There is no reason to believe humans can drill much deeper than that. The Earth’s crust is thinner in the deep ocean but the technical challenge of drilling through that is even more difficult.
All drilling much deeper than that would become instantly clogged by molten elements and would not make it to the surface at all. The equipment itself would either fail or simply melt. If the aliens wanted to destroy us with their own super-bulldozers, the time it would take to make a single molten pool of lava would make it easy for rednecks to just kill their union heavy equipment operators with shotguns. None of that would hurt the neighboring trailer parks.
It simply cannot be done. Colonizing Mars with gorgeous models would be much easier. I hate to break it to all the kids that want to dig to China but they would die before they made it even 1% of the way there.
You failed to notice that the OP proposed using a “super-duper, magic machine.” I saw one in the Acme store recently, and I do believe it could get the job done.
Lasers. Aliens use lasers.
-FrL-
I don’t think so. The Earth isn’t being squeezed–it’s producing it’s own pressure. Because of this, I’m pretty sure the liquid inside would flow up to the surface, but only right to the surface and not catastrophically above the surface.
I’m not sure though.
-FrL-
I’m not sure either. I see what you’re saying but I don’t think the pressure would drop near the surface because it would be contained inside the drill hole, which we can assume acts like a pipe. We would basically be tapping something that is pressurized, not unlike an oil well shooting oil up in the air. I think all that would be necessary is for there to be enough pressure at the bottom of the hole to overcome the weight of whatever is in the ‘pipe.’
What is inspiring me here is thinking about an artesian well, which is basically a pipe stuck into a water table that is under pressure, and that pressure can cause water to shoot up into the air. What should be inspiring me is the geology books on my shelf though.
Let’s start over with some basic geology. I was making assumptions in my earlier posts, but I think we need to address the basics first.
The mantle is not made of magma, it is actually just rock that is more dense than the crust. The heat and pressure are so great in the mantle that the rocks there behave like slow moving fluids and the crust actually floats on top of the mantle because the rocks in the crust are less dense, but the mantle is still solid rock.
To create a volcano, you’d have to drill into a pocket of magma. Magma is formed near the upper mantle/lower crust, then it rises to the surface because it is less dense than rocks in the mantle or crust. It’s kinda like a river. It starts out with a few drops here and there, a little trickle here and there, and combining into blobs as it rises to the surface. It’s rise to the surface takes a long time. I don’t have a figure right now but I’m pretty sure it’s years, maybe even three digits.
Magma doesn’t explode out of volcanoes because of pressure from below, it explodes due to the gases in the lava. When the magma makes it’s way to the surface, it may come up fast or slow. If it comes up slow, it may have time for gases in the magma to escape. If it comes up fast, the gases will stay dissolved in the magma and will cause a more violent explosion when it hits the surface.
Soooo… what I’m getting at is that we can forget everything about exploding volcanoes because that is not related to pressure. Magma rises slowly due to buoyancy and the effects once it gets near the surface depend on the type of magma and how it comes to the surface.
We are basically left with the question of finding and tapping a pocket of fluid (magma), and getting it to the surface.
Ok, let’s assume we know where to find magma and are able to dig into it. My wild guess is that if you drilled into a pocket of magma near the mantle, I suspect it would be under pressure and come shooting out like an oil well, because all the rocks around it will be creating more pressure on the liquid magma than the weight of all the magma in the borehole. We won’t drain the earth that way, but we may drain a large portion of the pocket of magma. This wild guess goes for anything else we may encounter that has less pressure than the rocks at that depth, such as oil, water, gases etc. I might even argue that the rock would slowly ooze it’s way up the hole, but that’s getting too wild even for this thread.
It’s always under pressure because there are miles of rock above it, pushing down. It’s like swimming deep in water, all the water above exerts pressure on all the water below.
The Kola Borehole was already mentioned, and I mentioned that rocks behave like slow moving fluids at certain depths. One of the problems they encountered with the Kola Borehole was that the darn thing kept filling itself back up with solid rock. The rock flowed back into the hole when they pulled the drill out.
So, no, the earth is effectively self-sealing. That, of course means that everything I just talked about is impossible, but we have the Acme Super-Duper Magic Machine, and aliens do not shop at Acme.
Hmmm, ever read your post 20 minutes later and wonder why you didn’t proofread it when you typed it?
In my first post, when I said I didn’t agree with others, I was looking at this as a question of whether we could create an artificial volcano due to the pressure in the mantle pushing the magma up. I agree that the digging is impossible, draining the core is impossible, etc, my first two posts should be looked at as “if we could dig impossibly deep, will the pressure make stuff come out of the hole?” I think so, given different properties of magma and rock.
And this sentence should be deleted from my last post: “I might even argue that the rock would slowly ooze it’s way up the hole, but that’s getting too wild even for this thread.” I meant that it may start to rise up our hole but would quit behaving like a fluid before it got very far, then I realized that once it’s in the ‘pipe’, it’s not under enough pressure to make it act like a fluid so it would never even start it’s ascent.
So it behaves like a hole in the sand at the beach - you can dig down to water, but the water/sand mixture keeps spilling back in, making it impossible for your plastic beach shovel to do the job…
Hmmm…
We’ll need some alien lasers, then… 
The liquid’ll flow up until the pressure it exerts against the core (psi) matches the pressure exerted on the rest of the core by the crust and mantle.
Liquid iron has a density of about 7g/cc, while the Earth as a whole runs about 5.5g/cc.*
Pressure equilibrium at the core would thus require a column of iron only 5.5/7 = 78.6% of the way to the surface. That’s about 1300 km down
*The mantle and crust have a density somewhat lower than this, but I’m not finding any decent numbers tonight.
I think a lot would depend on just how your world-drilling worked. For example, if you drilled a hole to the center lined with indestructible adamant- ( looks at incoming Marvel lawyers ), ah, I mean unobtanium, and opened the bottom, I’d expect some impressive effects from the suddenly depressurized core material rushing to fill the void. If the bore is air filled you’d get an impressive blast from the displaced air even if nothing else reached the surface. If you keep drilling the hole open to clear out the solidified material I expect you could duct a lot of hot material much higher than it usually gets; that might have volcanic effects even if it doesn’t reach the surface and just superheats the rock around the bore; the outside of the bore itself could also help magma or gases escape from the mantle perhaps. And there could be interesting effects from opening the hole in the ocean bottom, especially if you keep drilling through any material that solidifies.
My question is sort of the reverse; and it is intended to be quite serious…
One has a block of carbon; It passes through the upper crust of the Earth …
IT becomes a diamond … It keeps sinking …
I know that magma will not melt a diamond … I do know that the Earths Core probably has the temperature to melt it.
My question is thus: Is there any evidence that a block of carbon COULD go from surface to Core and back to the surface again?