Some warships staged near the explosions were vaporized. Others were tossed like toys in a bathtub and sank, while a few sustained cracked hulls and crippled engines. Notably, the explosions roughly doubled the height of waves to nearby islands, flooding inland areas.
"A well-placed nuclear weapon of yield in the range 20 MT to 50 MT near a sea coast could certainly couple enough energy to equal the 2011 tsunami, and perhaps much more," Rex Richardson, a physicist who researches nuclear weapons, told Business Insider in March, referring to the Tohoku earthquake and tsunami that killed more than 15,000 people in Japan.
"Taking advantage of the rising-sea-floor amplification effect, tsunami waves reaching 100 meters in height" — about 330 feet — "are possible," he said.
Richardson and other experts have also pointed out that a near-shore blast from this type of weapon could suck up tons of ocean sediment, irradiate it, and rain it upon nearby areas — generating catastrophic radioactive fallout.
"Los Angeles or San Diego would be particularly vulnerable to fallout due to the prevailing onshore winds," Richardson said, adding that he lives in San Diego.
The problem with blowing up nukes underwater
Greg Spriggs, a nuclear-weapons physicist at Lawrence Livermore National Laboratory, said a 50-megaton weapon "could possibly induce a tsunami" and hit a shoreline with the energy equivalent to a 650-kiloton blast.
But he also suggested that it "would be a stupid waste of a perfectly good nuclear weapon."
That's because Spriggs believes it's unlikely that even the most powerful nuclear bombs could unleash a significant tsunami after detonating underwater, especially miles from shore.
"The energy in a large nuclear weapon is but a drop in the bucket compared to the energy of a [naturally] occurring tsunami," Spriggs told Business Insider last year. "So any tsunami created by a nuclear weapon couldn't be very large."
For example, the 2011 tsunami in Japan released about 9.3 million megatons of TNT energy. That's hundreds of millions of times as much as the bomb dropped on Hiroshima in 1945 and roughly 163,000 times as much as the Soviet Union's test of Tsar Bomba on October 30, 1961.
Plus, Spriggs said, the energy of a blast wouldn't all be directed toward shore — it would radiate outward in all directions, so most of it "would be wasted going back out to sea."
A detonation several miles from a coastline would deposit only about 1% of its energy as waves hitting the shore. That scenario may be more likely than an attack closer to shore, assuming US systems could detect an incoming Poseidon torpedo.