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Reading questions of How much TNT needed to blow up Mount Everest and the Moon - and especially the comments below it, I have to ask it:

Can we blow up the sea?

Detonating atomic bomb undersea may look cool but for any sea-level attacks it is not proving anything extra. And It does not "blow up the sea"

So, what is the best way to tactically remove big body of water?

  • It has to happen fast (in matter of hours, one day is maximum)
  • It should be accompanied by some nice effect (boom!)

And, how much would it cost?

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    $\begingroup$ you can't really do this without wiping out all life on earth... $\endgroup$ – James Jan 20 '15 at 14:45
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    $\begingroup$ Can I ask..defined 'sea'? Is this an ocean reference? Black sea? Any size on this? By blow up...does a hole in the earth that it drains to works? I might have a science fictiony hydrolysis answer that probably sounds good in theory but wouldn't work. $\endgroup$ – Twelfth Jan 20 '15 at 17:45
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    $\begingroup$ Lets take the sea definition like this: If it has "sea" in name, then it is sea ;) To be more specific, as European, I would like to get rid of Mediterranean sea $\endgroup$ – Pavel Janicek Jan 21 '15 at 9:34
  • $\begingroup$ Remove it? Detonating a bomb on the ground "just" kicks up a lot of dirt... which just falls back to Earth again. Thus, where do you propose removing the water to? $\endgroup$ – RonJohn Oct 11 '18 at 18:38
  • $\begingroup$ Obligatory XKCD $\endgroup$ – Joe Bloggs Oct 11 '18 at 19:01
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tl;dr: Not without killing everything.

Let's do some maths and actually figure this out.

The specific heat capacity of water is $4.186 \text{ kJkg}^{-1}$. That means it takes 4186 joules of energy to heat 1 kilogram of water up by one degree.

The average temperature of the surface of the sea is 17oC. It gets a lot colder as you go deeper, so the average temperature overall is more like 0.

The seas contain a volume of 1.3 billion cubic kilometres of water. 1 litre of water = 1 kg. 1 litre of water also = 1 dm3, so there are 1000 litres in a cubic metre and thus a cubic metre of water weighs a ton. (This is assuming freshwater to keep the numbers reasonably nice - salt water is heavier.) Then, there are $1000^3 = 1,000,000,000$ cubic metres in one cubic kilometre. That means 1.3 billion billion or 1.3 quadrillion cubic metres of water and the same number of tons, which in turn is $1.3\times 10^{21} \text{ kg}$ or 1.3 quintillion kilograms.

Now let's heat all that up by one degree.

$$ (1.3 \times 10^{21} \text{ kg}) \times 4186 \text{ Jkg}^{-1} = 5.4418 \times 10^{24} \text{ J}$$

Multiply by 100 so we can heat the water to boiling:

$$ = 5.4418 \times 10^{26} \text{ J}$$

Finally, you need around 6x the energy to actually boil it:

$$ = 3.2651 \times 10^{27} \text{ J}$$

Now while that's not quite on the order of blowing up the Earth, that's a hell of a lot of energy. You're in the perfect region for an asteroid impact. We can work out how big and fast it needs to be:

$$ \text{KE} = \frac{1}{2} mv^{2} $$ $$ 2\text{KE} = mv^{2} $$ $$ 6.5301 \times 10^{27} = mv^2 $$

We can play around with mass and velocity. Let's say this asteroid is a perfect 10km cube with 5000kg/m3 density, thus giving it a weight of $5 \times 10^{12} \text{ kg}$. That means its velocity has to be:

$$ v = \sqrt{\frac{6.5301 \times 10^{27}}{5 \times 10^{12}}} $$ $$ v = 36138898.71 \text{ ms}^{-1} $$

or around $0.12c$. That speed isn't insignificant, and while an impact from an asteroid of this size and speed wouldn't destroy Earth, it would most likely make a massive crater, not vaporise the oceans because the energy isn't distributed easily, and kill all life on Earth.

And that's before we start on the water cycle dropping all that steam straight back where it came from.

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    $\begingroup$ Error: You heated the water to boiling, you didn't boil it. you need roughly 6x the energy you are supplying. Even more overkill. $\endgroup$ – Loren Pechtel Jan 20 '15 at 19:29
  • $\begingroup$ @LorenPechtel Ah. Thanks, I'll add that $\endgroup$ – ArtOfCode Jan 20 '15 at 19:44
  • $\begingroup$ Yeah, you need energy to do the state transition from liquid->gas as well as energy to actually reach the boiling temperature. $\endgroup$ – Tim B Jan 20 '15 at 20:44
  • $\begingroup$ @TimB It's already in there :) Forgot about it $\endgroup$ – ArtOfCode Jan 20 '15 at 21:44
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    $\begingroup$ According to this impact simulator, throwing your .12c asteroid at the Earth will completely melt the Earth, making the concept of "crater" a bit meaningless. Note that much of the ocean will be ejected rather than boiled. $\endgroup$ – Mark Jan 21 '15 at 0:38

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