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According to TheTimes.co.uk, "Russian ‘nuclear tsunami’ will wipe out Britain, Kremlin-backed media threatens"

In his Sunday evening primetime show, the Channel One anchor Dmitry Kiselyov said a strike by Russia’s Poseidon nuclear underwater drone could turn Britain into a wasteland by drowning the country in a 500-metre tidal wave of radioactive seawater.

Is there reasonable modelling, or other evidence, that shows Poseidon nuclear underwater drone could create a 500-meter tidal wave?

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    Something to note, a 500m (1640 feet) tidal wave might not do as much damage as they claim. pbs.org/wgbh/nova/tsunami/once-nf.html ( Lituya Bay, Alaska, July 9, 1958) was higher and only damaged a few square miles) What is important to remember is the high of the land above sea level. Not to mention that any massive tidal wave will likely hit areas besides Britain that will retaliate.
    – Joe W
    May 2 at 18:00
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    @JoeW: yeah, but that bay is surrounded by tall(er) mountains.
    – Fizz
    May 2 at 18:26
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    All that being said, Russia has had the ability to wipe out any country with nuclear weapons for a very long time now. So what's really new, other than the backward way of turning blast into casualties?
    – DevSolar
    May 3 at 6:18
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    @DevSolar I think a key part of this claim/threat is that the supposed nuclear drone could not be intercepted. This differs from missile systems for which there are defences that may or may not prove effective. Perhaps the point is to ensure countries don't think their anti-missile shield will stop them being wiped out.
    – Eric Nolan
    May 3 at 10:42
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    I’m voting to close this question as theoretical in nature. Probably better suited for Physics.SE or EarthSciences.SE.
    – DevSolar
    May 3 at 12:17

5 Answers 5

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No multi-megaton nuclear warhead ever has been exploded underwater, so the best we can hope for in the way of sources is "what is the research on this".


Wikipedia: Underwater explosion -- Deep underwater explosion:

An example of a deep underwater explosion is the Wahoo test, which was carried out in 1958 as part of Operation Hardtack I. A 9 kt Mk-7 was detonated at a depth of 500 ft (150 m) in deep water. There was little evidence of a fireball. The spray dome rose to a height of 900 ft (270 m). Gas from the bubble broke through the spray dome to form jets which shot out in all directions and reached heights of up to 1,700 ft (520 m). The base surge at its maximum size was 2.5 mi (4.0 km) in diameter and 1,000 ft (300 m) high.[6]

During the Cold War, underwater explosions were thought to operate under the same principles as tsunamis, potentially increasing dramatically in height as they move over shallow water, and flooding the land beyond the shoreline.[7] Later research and analysis suggested that water waves generated by explosions were different from those generated by tsunamis and landslides. Méhauté et al. conclude in their 1996 overview Water Waves Generated by Underwater Explosion that the surface waves from even a very large offshore undersea explosion would expend most of their energy on the continental shelf, resulting in coastal flooding no worse than that from a bad storm.[2]

The Operation Wigwam test in 1955 occurred at a depth of 2,000 ft (610 m), the deepest detonation of any nuclear device.

Source [7]: Glasstone, Samuel; Dolan, Philip (1977). "Shock effects of surface and subsurface bursts". The effects of nuclear weapons, (third ed.). Washington: U.S. Department of Defense; Energy Research and Development Administration.

Source [2]: Le Méhauté, Bernard; Wang, Shen (1995). Water waves generated by underwater explosion. World Scientific Publishing. ISBN 981-02-2083-9.

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    "No multi-megaton nuclear warhead ever has been exploded underwater" - didn't Batman do that a few years back?
    – hanshenrik
    May 4 at 13:02
  • @hanshenrik: A very nice example of Poe's law...
    – DevSolar
    May 4 at 13:07
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Well, nobody has tested really, really big nuclear bombs underwater. But we do have some underwater tests we can look at.

In 1946, the US tested a 21 kt bomb underwater in Operation Crossroads. You can watch the unclassified detonation. Another source describes the detonation as follows:

When Helen of Bikini exploded, it created a giant, underwater bubble of hot gas. In seconds, the bubble hit the seafloor, where it blasted a crater 30 feet deep and at least 1,800 feet wide. At the same time, the surface of lagoon erupted into a giant column of water, two million tons of it, which shot more than 5,000 feet into the air, over an area a half-mile wide. In the seconds after the blast hit the surface, a cloud of radioactive condensation unfurled across the lagoon, hiding the column of water shooting upwards. At the top, a mushroom cloud of gas bloomed against the sky.

Several other tests have been conducted, including deep water detonations in Operation Hardtack.

What's notable is that there's not really a big tsunami - most of the water just got vaporized, it didn't get displaced. This is different from an earthquake, which does not vaporize water at all. It seems likely (although not certain without more exact details about the Russian device and comparable testing) that the main risk would be radioactive contamination, which is apparently quite extensive from underwater detonations.

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    Also worth noting is that when a big ball of seawater gets vaporized it leaves a void in its place. Any nearby water will tend to rush back into that void, which will fight against the tidal wave effect you're trying to create.
    – bta
    May 3 at 15:55
  • I wonder if a bigger bomb like an hydrogen bomb could create the tsunami. That said, this video is very informative and Russias aproach to truth has been... misleading
    – borjab
    May 3 at 19:58
  • @bta Following that logic, there will be a humongous splash in the middle as the huge streams of water filling the void from all sides crash together, then the excess water that was pushed up to form the splash will flow back outward in all directions, creating the tidal wave effect. May 3 at 22:32
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    Reports say the blast generated a 94-foot-high wave, though the waves were only 15 feet high when they reached Bikini 3.5 miles away: atomicheritage.org/history/operation-crossroads. Wave heights were initially estimated by nailing tin cans to palm trees at various heights and then checking them for water in the aftermath. May 3 at 23:22
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    It's hilarious that we have the technical capability to create and detonate a nuclear bomb, but to measure the height of water we nailed tin cans to a tree. May 4 at 13:53
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There's a big problem here:

Let's suppose the bomb can actually produce a 500m wave near the point of detonation--what happens? The circumference of a circle is linear to it's radius--double the distance and you double the total area and thus halve the height.

Thus, while it can wreck a coastal city it's not going to sweep across a whole country unless you're talking something like Singapore or Hong Kong.

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    When you provide an answer you need to provide something to back up your claims
    – Joe W
    May 3 at 1:07
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    @JoeW Provide what, the formula for the circumference of a circle? I'm simply showing the claim doesn't hold together, not directly rebutting it. May 3 at 1:59
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    The circumference of a circle is proportional to its radius, but the energy of a wave scales like the square of its amplitude. So when you double the distance you halve the energy, which reduces the height by a factor of square root of 2.
    – Dan Romik
    May 3 at 4:17
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    Aside from this issue, I think this answer gives a good heuristic way of thinking about the claim in the question and concluding that it is not very plausible. On the other hand, your model is too simplistic to be completely convincing IMO.
    – Dan Romik
    May 3 at 4:20
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    @MichaelKay, common sense and pure logic are frequently wrong. For example, it's not clear how effective nuclear blasts are at turning energy into water movement (I think the answer is "not very").
    – Mark
    May 5 at 3:31
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Most tsunamis are created by seabed displacement of large areas. Let's say a tectonic plate snaps and part of it is raised higher, the other part goes below. So a very large amount of water changes its elevation and naturally tries to return to the original state by flowing from raised areas or flowing into lowered areas. This volume of moving water cannot stop on a dime and the created wave keeps flowing very large distances. To reproduce this scenario a nuclear explosion must happen deep under the surface of the sea bed. I doubt it is practical to drill deep enough for the nuclear device in a war situation. Most people think that the scenario threatened by Russia is more like throwing a rock in the water and creating the wave. It is very difficult to answer whether it is a threat to UK. For example if this happen in a shallow place there could be no enough water to create large tsunami. This would be more like underwater volcanoes, which we know do not create tsunamis.

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  • please inlcude links to the different facts you allude to in you answer -
    – bukwyrm
    May 17 at 12:36
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This isn't an answer, but gives some visual context of the depth of the sea floor around Britain

At the red dot it is 5000 meters deep:

enter image description here

Tsunamis can grow a lot when they hit shallow water around land (which in Britain's case ranges from a few hundred meeters to just ~10 meters deep), but it's not clear if that would happen here, since it might be more of an underwater cliff than an underwater ramp.

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  • Would it? A true tsunami (one caused by an earthquake or a subsea landslide) might, but it's unclear if an underwater explosion will even produce a tsunami.
    – Mark
    May 5 at 3:25
  • @Mark thinking about it more, I know if the sea floor acts like a ramp, it will increase the size, but in this case it could be more like a cliff (so it might actually stop a lot of the wave?).The seafloor is a very interesting aspect, but I don't really know how to interpret it. Hopefully someone else does.
    – stevec
    May 5 at 3:26
  • @Mark I reworded. Hopefully there are some physicists here who know more about it.
    – stevec
    May 5 at 3:29
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    More than 300 kilometres from Ireland and more than 400 km from Britain. Otherwise shallow waters that could not contain an underwater explosion most of it would end in a vertical vapour jet. You had a good idea to post that picture, but the interpretation can be a little bit different.
    – FluidCode
    May 5 at 10:42
  • @FluidCode the choice of the deeper waters was intentional, since I think we want to know if the tidal wave is possible (not just whether it's likely). I agree with your implication (that it would in practice be used as close to mainland as possible) but I think in order to thoroughly answer the question, the idea of a detonation in deeper waters should not be ruled out, as tidal waves have been known to travel thousands of km.
    – stevec
    May 5 at 12:16

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