With limited knowledge (the What If link posted earlier), would a tsunami created by a nuke be more damaging than a direct nuke itself? You'd lose the explosive and heat damage for the most part, and at least in my head the water would contain and dampen a lot of the explosion (although on the other hand water isn't nearly as compressible as air)
The scale of energy released is the problem. Tohoku earthquake (which caused the Fukushima tsunami) released ~600 million Little Boy's worth of energy. Yeah, modern bombs are bigger- you'd only need a few hundred thousand Tsar Bombas to get that much energy- but still we're talking an absolutely gargantuan amount of energy.
This is why no one looked at the idea until Putin needed something to threaten America with after GWB did a really stupid thing and pulled out of the ABM Treaty. And I don't believe that the official Russian sources claim it can make a tsunami, I think that's mostly propaganda.
Well, they can't exactly test that particular system without causing massive ecosystem damage. As for your first comment - you are commenting from a politically motivated position, not a technical one. Said another way, you are making the warfare 101, chapter 1, paragraph 1 mistake.
The 2011 Tohoku earthquake that created the devastating tsunami was an energy release of something like 600 million Hiroshima bombs. Nuclear weapons are just the wrong order of magnitude to make a tsunami, this isn't about politics, it's about scale.
What every nation, Russia included, talks about and shows off has very little in common with what they can actually do.
In Russia's case we mere civilians can just directly observe the difference a lot of the time, enough for me to be comfortable projecting the same assumption where only real military analysis could actually tell for sure. The claim that this weapon could cause a tsunami is within the set of things even civilians can disprove.
This option is not available to us civilians for more competent cases such as China or Iran.
