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I want to achieve the following. Jet + secret base underwater + blow up water with bomb to gain entry to tunnel at bottom of the sea, see image:

enter image description here

Say that the depth is 1000m, then Based on calculation in this Quora-answer:

(4.2*10^3 J/kgC^-1) (1 kg) (90C) =
338000 J required to evaporate 1 kg water from 10 degree temperature

Since the water is ~10 degrees

enter image description here

The amount of water is the volume of a sphere with radius 500m:

$\frac{4}{3}\pi 500^3 = 5.24*10^8m^3$

Which is lets say about 5*10^11 kg (1L of water == 1 kg)

Giving about 170000 TJ, The energy of the detonation can be handwaved to some degree and it is not immensely* more than our current nuclear bombs at 100TJ.

How long does the plane have before the water collapses? Will mach 1 be enough to reach the entry point?

(Vaporising the water is just something i assumed I'd have to do. I'd consider any smart physics phenomenon that can be taken advantage of to extend the duration of the wake as on topic)

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    $\begingroup$ Is this supposed to be the NORMAL way people get in and out of this base, or is this a one-off? $\endgroup$ – Morris The Cat Apr 4 at 13:35
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    $\begingroup$ We often ask people if they're sure they want to require hard science in answers, but here I wonder if you really want reality-check. Might you prefer science-based (requires answers based on hard science but citations are optional) or hard-science (requires serious citations, etc)? If so, consider using one of these instead of reality-check $\endgroup$ – Cyn Apr 4 at 14:16
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    $\begingroup$ Supercavitation seems to be a much easier way to solve your problem. $\endgroup$ – Eth Apr 4 at 14:42
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    $\begingroup$ Oh no, no. Water won't boil just because it has reached 100 degrees centigrade. You have calculated the heat needed to warm up water from 10 to 100 degrees centigrade; now please add the latent heat of vaporization, which in the case of water is a whopping 2.3 MJ/kg. $\endgroup$ – AlexP Apr 4 at 16:17
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    $\begingroup$ (and video) $\endgroup$ – Starfish Prime Apr 4 at 20:37
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You're not going to evaporate the water, you're you're going to displace it. That actually makes it both easier, and no more possible.

The thing with displacing the water is that the easiest direction to displace it in is upwards. In any other direction there's something fundamentally in the way.

Operation Wigwam is the closest I can find to what you're looking for, a nuclear explosion at 610m (2000ft), the deepest nuclear test ever and still the only test below 300m.

This is what your pilot will be flying into if you try this:

wigwam surface surge

That's the surface effect of a 32kt warhead at 610m.

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  • $\begingroup$ Hmm that get's me in the direction of thinking up some scifFi way of increasing the pressure on the surface... Though I guess that does not take it closer to the realms of viability $\endgroup$ – Adam Apr 4 at 13:58
  • $\begingroup$ I note that the bubble formed in that test appeared to be ~115m across, and apparently collapsed in under 3 seconds. That should give you some idea of the constraints that the OP is up against. $\endgroup$ – Starfish Prime Apr 5 at 10:08
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Good news: creating a bubble that size seems emminently possible using current-day technology.

Bad news: promptly vapourising and displacing that much water, and the secondary effects of whatever means you use to do so, will result in an Extremely Hostile environment for aircraft.

You're trying to move something like 540 million tonnes of seawater out of a 1km deep volume faster than the entire ocean can flow back in. Canute got nothing on you.

Working out how quickly that cavity will collapse is hard, and alas this answer will be incomplete because I can't actually calculate it for you. Instead, lets look at the amount of energy required to excavate the cavity, and the effects it will have on the local environment.

How much energy? Well, for similar reasons, I can't give you anything other than very broad approximations, but it looks like you'll need 30-100 megatonnes TNT equivalent to form a big enough hole. I've got these numbers from a presentation on asteroid impacts in water. The authors didn't consider your specific scenario for some reason, but you'll see (on page 37) a brief mention of a 100m asteroid striking deep water, 66MT equivalent blast, 1.2km deep transient crater. That's a good ballpark figure. (The Operation Wigwam test that Separatrix references uses a ~30kt warhead to develop a ~100m bubble. A 1000m bubble has 1000 times the volume, and 30MT is about a thousand times more powerful a bomb, so it seems about right)

Now, quite a lot of that blast energy will go into vapourising seawater. The expansion of that steam will help push the surrounding water out of the way. Beacuse you want your cavity to reach the surface, a good deal of that steam will escape upwards. This is important, because you have just generated a (approximately) a cubic kilometre of steam which is going to rise up rapidly and mix turbulently with the atmosphere. This will result in hurricane force winds, which in the vicinity of the cavity will be boiling, wet, hurricane force winds (if you look at the asteroid impact presentation, it suggests hurricane force winds withing 22km, and temperatures >100C with 5km, which again, are good ballpark figures). Oh, and also radioactive. Mustn't forget that. This is not an aircraft friendly environment. You probably won't get a nuclear fireball forming, but from the point of view of your aircraft it won't really matter. Sure, these conditions won't persist, but they'll last at least as long as the cavity does, so you'll have to deal with them if you want to fly through the hole.

Finally, when the cavity collapses, you'll get all sorts of really interesting hydrodynamic effects. You'll get a jet of water formed that could reach a few kilometres into the sky. The formation of this jet will cause an intense pressure wave at the bottom of the cavity. Between this and the nuclear blast you've used to create the cavity in the first place, the chance of anything immediately underneath the cavity surviving are extremely slim. I hope that door and the thing it protects are very robust. Incidentally, can you rely on the door opening fast enough to fly in, and close fast enough such that everything doesn't get smooshed?

So, how quickly will the cavity collapse? It doesn't matter. Nothing will survive its flight into it.

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  • $\begingroup$ I see you came to much the same conclusion, that hostile environment above is more significant than the size of the hole created. $\endgroup$ – Separatrix Apr 5 at 10:17
  • $\begingroup$ @Separatrix it is certainly a much easier question to answer. I'm still wondering how hard it would be to run a quick'n'dirty fluid simulation of the cavity though... $\endgroup$ – Starfish Prime Apr 5 at 10:21
  • $\begingroup$ Just FYI: you are Canute in this scenario. He knew he could not stem the flood. $\endgroup$ – bukwyrm Apr 5 at 14:29
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    $\begingroup$ @bukwyrm I'm aware of the real story there, but I'm also well aware of how deeply the false version of the story is embedded in the popular consciousness and trying to hold back the tide of public opinion is clearly futile, as the famous story of king canute will attest... $\endgroup$ – Starfish Prime Apr 5 at 15:51

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