This may be a slightly unusual question. I know it wouldn't be possible, but what would the short and long term effects be, if a large (say, 1 mile diameter) round hole appeared, and went straight through the center of the earth, through the crusts on both sides. Would it be different if they opened on land, rather than ocean?
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2$\begingroup$ Most of the interior is not molten. The mantle is mostly solid. An elasto-plastic solid, but a solid nonetheless. $\endgroup$– David HammenSep 10, 2014 at 17:58
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2$\begingroup$ This is a "what do the laws of physics say would happen if the laws of physics are wrong" kind of question. There is no answer to such questions. $\endgroup$– David HammenSep 10, 2014 at 17:59
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3$\begingroup$ David, "no answer" is the easy answer. I think these kinds of questions are actually fun and make you think outside the box. Check out the xkcd link I gave in the answer to see what answers you can get for "stupid" questions. This question should not be closed, in my opinion. $\endgroup$– GimelistSep 10, 2014 at 18:07
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2$\begingroup$ @farrenthorpe - That's a widespread misconception. I myself had it until educated otherwise. The mantle (84% of the Earth's volume) is solid. The extreme pressure deep inside the Earth pretty much precludes melting. The mantle is not a sea of magma. Magma mostly forms near the surface (70 km or less), and it needs hydrated rock. That's why volcanos primarily occur on the ring of fire. Subduction carries rock, sediment, and water down to the top of the upper mantle. The presence of water reduces the solidus (the temperature above which melting starts) by a considerable margin. $\endgroup$– David HammenSep 12, 2014 at 20:16
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2$\begingroup$ @farrenthorpe - Magma is a near-surface phenomenon, maybe down to somewhere in the transition zone (~400 to ~600 km deep). Magma is generally not fully molten. Rock consists of multiple minerals; it doesn't all melt at one temperature. Instead you need to think in terms of the solidus and liquidus temperatures. Rock is solid below the solidus, liquid above the liquidus, and partially melted in between. Magmas lie in that partial melt regime. The lower mantle lies between the bottom of the transition zone (~600 km deep) and the core/mantle boundary (~2900 km deep), and it is quite solid. $\endgroup$– David HammenSep 12, 2014 at 23:08
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2 Answers
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The best place to ask this question is going to be at xkcd: http://what-if.xkcd.com/ but I will give it a shot.
I'm not a geophysicist, but I'll try to give you a reasonable enough answer. As you said, making such a hole is not possible.
However, let's try to think what if some magical force made a hole 1 km wide and then suddenly released it. This is what the Earth is made of:
(taken from here: http://www.nature.com/nature/journal/v479/n7374/fig_tab/479480a_F1.html)
The easiest part to explain will be to see what happens in the core. Both the inner and outer core are basically made out of impure iron. The liquid iron will just flow into itself and close the hole rather quickly (think about a similar hole in water). The solid iron is also ductile as there high pressures and temperatures, so it will also flow and close the hole. Think chocolate close to the melting temperature. It's still solid, but it moves. Probably some of the liquid iron will manage to flow into the hole of the solid iron, but it will then solidify because it will have to endure higher pressures.
Now, what happens at the mantle? The lower mantle is also ductile and it will also flow under the pressure. You have to remember the the walls of the hole are under huge pressures - 24 to 136 GPa according to the figure. Some things may "fall inside", but remember that it has to fall over hundreds of kilometers while the hole is only 1 km wide.
The upper mantle is where it becomes interesting. This is just thinking out loud though. The upper mantle is where magmas are being formed, and one of the reasons magma is formed is decompression. Usually this happens because of mid ocean spreading or mantle plumes, but removing one side of let's say a cube of rock is also going to decompress it somewhat. This may cause generation of magma. No worries though - I don't see any reason why it should rise to the surface. If anything at all, it's going to fall down through the hole (but not much, see above). Also, decompression may cause release of volatiles or gas, the most common being CO2 and H2O I guess, also H2S or SO2 depends exactly what is down there. Also, the movement of rocks in an area of the Earth that's not ductile anymore but rather brittle (lithosphere) is sure to cause some earthquakes. Are there earthquakes going to be dangerous for anyone? I don't know.
What would this hole look like if you peeked down? My guess that it will be filled with water. If this hole starts at the ocean, then the ocean will just flow inside and fill it. It is possible that some mega waves or tsunamis will accompany it. It will pour down until it either meets the closed rock, or just evaporates. Remember - it's pretty hot down there. It will evaporate and rise, then cool and starts raining down again and you will have a nice convective cell in the upper few kilometers of this hole.
In contrast, if this was not in the ocean but rather on land, groundwater will fill it in. I guess most of the earth has groundwater (maybe except the large deserts, but even there some water exists) that will just flow inside and create a similar convective cell.
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$\begingroup$ The inner core is solid because of pressure. Wouldn't a release like that cause it to depressurize, and quickly fill the hole, even out of the crust? $\endgroup$ Sep 10, 2014 at 18:01
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1$\begingroup$ Not really. Your hole is negligible in comparison with the entire code. It will just flow in to fill the hole. Think holding some kind of cylinder in a swimming pool, and then quickly pulling it out. The pressure is because of all of the water in all of the pool. The pool couldn't care less of your cylinder. It just flows in to fill in the hole. $\endgroup$– GimelistSep 10, 2014 at 18:06
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$\begingroup$ But the earth is under high pressure, unlike a pool. I was comparing it more with something like a high-pressure water tank. Put a very small (negligible) hole through it, and the pressure will try to dissipate. $\endgroup$ Sep 10, 2014 at 18:08
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$\begingroup$ A high pressure water tank is "high pressure" because it has a sharp boundary with the low pressure atmosphere. In the earth, there are no sharp pressure boundaries. But let's say it does dissipate. Where does it go to? Upwards? It will get blocked by the liquid iron that flows much faster. Under no circumstances any of the solid or liquid material from that depth is going to reach the surface of the Earth. $\endgroup$– GimelistSep 10, 2014 at 18:19
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i think that we simply do not have enough data on earth what would happen. and if such a task were even possible. as depicted by the movie The Core, there could be a crystallized structure between the core and the surface thats even impossible to dig through by conventional means. it would sound logical, given that there simply is that much pressure going on to make crystals, that an entire part of earth is made out of crystal. plus the constant shift of the earth's plates would also mean that the tunnel dug behind you would be closed off immediatly.
right now, the diagram shown above is still pure guess work. same as how the sun works, how black holes are working. we know how a bird flies and how to make electricity because we can experience it. but we havnt experienced going to the center of the earth, so we dont know yet how it works.
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$\begingroup$ Plates move on the order of a few centimeters per year... so it's not like that specifically would cause any closure of significance. $\endgroup$ Nov 18, 2018 at 1:50
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$\begingroup$ While I'm a big fan of encouraging humility and caution when predictions are based upon secondary observations... I'd think it's also fair to say that observations allow a lot of things to be ruled out, and over time a fairly confident theory and robust theory has developed. There certainly can be more room for unexpected changes, but I'd suggest that throwing out theory/evidences and just suggesting "who knows", everything is equal, and anything's possible is just as naive $\endgroup$ Nov 18, 2018 at 1:58
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$\begingroup$ I am not a geologist, either, just took one course... but I'd think if you went ahead and asked a new question of "Is the concept of a solid crystal geologic layer as proposed in the movie The Core possible?", it would be pretty interesting, and we might get some input on what evidence does/doesn't show on it. How earthquake waves travel certainly must give some good information, much like how if you were behind a locked door, secondary observations like listening for echo when knocking on the door, and what is emanating could tell you a fair bit about what is on the other side. $\endgroup$ Nov 18, 2018 at 1:59
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$\begingroup$ But if you're interested in hearing the input of those who spend a lot of time studying it, I'd definitely ask! Hoping they'll keep it to "we believe" on many aspects rather than many scientists who jump to "it is" (a very important distinction to get right in meteorology). Welcome to the site, and thanks for the contribution, hope you'll find some useful input and information around here :D $\endgroup$ Nov 18, 2018 at 2:05
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$\begingroup$ Actually, we have a pretty good idea of what the earth is like from inside. Yes, there are uncertainties and some (educated) guesswork but we have some very solid constraints on what can or cannot be in the core, and on the way to the core. $\endgroup$– GimelistNov 18, 2018 at 11:10