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An in-development game(Starbound) recently released a demo of their water physics. At about 39 seconds into the video, a volume of water in a container is released when the cap on the container is destroyed.

Then the water expands to about 10 times its initial volume in 3 seconds or so.

What would actually happen here? I imagine that compressing water to 1/10th its volume at STP would take an obscene amount of pressure, but I'm not sure about what would actually happen with this rapid decompression.

Would the water freeze from the drop in temperature as it expanded? How fast would the decompression actually take? Is the entire question moot because the pressures involved are too high?

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In the game, I believe the small box opened at around 39s is connected to a constant pressure water supply. This would be a bit like knocking the top off a fire hydrant, it may look like the water in the fire hydrant is expanding tremendously, but it's just more water that's flowing in from somewhere else. – Rick Feb 3 '15 at 17:13

There's a lot of info about water phase and density here.

Compressing water to a tenth of it's STP density would give a molar volume of 1.8 cm$^3$. The highest density mentioned in the article is 8 cm$^3$mol$^{-1}$ for ice VIII at about a terapascal, so a density of 1.8 cm$^3$mol$^{-1}$ while technically possible seems unlikely from a pratical point of view.

If water were compressed to anything like this density it would form ice of some form. On release of the pressure the ice would expand to it's normal density at approximately the speed of sound (in the ice) and probably shatter into bits in the process. The ice would them melt relatively slowly and without any further spectacle.

Later: it occurs to me that there would be so much elastic energy stored in the compressed ice that the expansion would actually be more like an explosion. The compressed ice would blow itself to bits along with anything else in the vicinity. Incidentally the density of matter in white dwarf stars is allegedly around $10^6$ g/cm$^3$, so compressing ice by a factor of ten is certainly possible.

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