No Superpower has ever detonated a multi-megaton warhead in deep water.
Crossroads Baker scared people so bad they abandoned 20kt deep water shot till I think Wigwam.
A 25MT device detonated just inside the Continental shelf could possibly create such an event.
Yep.
Sequence of blast events:
The Baker shot produced so many unusual phenomena that a conference was held two months later to standardize nomenclature and define new terms for use in descriptions and analysis.[92] The underwater fireball took the form of a rapidly expanding hot gas bubble that pushed against the water, generating a supersonic hydraulic shock wave which crushed the hulls of nearby ships as it spread out. Eventually it slowed to the speed of sound in water, which is one mile per second (1600 m/s), five times faster than that of sound in air.[93] On the surface, the shock wave was visible as the leading edge of a rapidly expanding ring of dark water, called the "slick" for its resemblance to an oil slick.[94] Close behind the slick was a visually more dramatic, but less destructive whitening of the water surface called the "crack".[95]
When the gas bubble's diameter equaled the water depth, 180 feet (55 m), it hit the sea floor and the sea surface simultaneously. At the bottom, it started digging a shallow crater, ultimately 30 feet (9 m) deep and 2,000 feet (610 m) wide.[96] At the top, it pushed the water above it into a "spray dome," which burst through the surface like a geyser. Elapsed time since detonation was four milliseconds.[97]
During the first full second, the expanding bubble removed all the water within a 500-foot (152 m) radius and lifted two million tons[98] of spray and seabed sand into the air. As the bubble rose at 2,500 feet per second (762 m/s),[99] it stretched the spray dome into a hollow cylinder or chimney of spray called the "column," 6,000 feet (1,829 m) tall and 2,000 feet (610 m) wide, with walls 300 feet (91 m) thick.[100]
As soon as the bubble reached the air, it started a supersonic atmospheric shock wave which, like the crack, was more visually dramatic than destructive. Brief low pressure behind the shock wave caused instant fog which shrouded the developing column in a "Wilson cloud", also called a "condensation cloud", obscuring it from view for two seconds. The Wilson cloud started out hemispherical, expanded into a disk which lifted from the water revealing the fully developed spray column, then expanded into a doughnut and vanished. The Able shot also produced a Wilson cloud, but heat from the fireball dried it out more quickly.[100]
By the time the Wilson cloud vanished, the top of the column had become a "cauliflower," and all the spray in the column and its cauliflower was moving down, back into the lagoon. Although cloudlike in shape, the cauliflower was more like the top of a geyser where water stops moving up and starts to fall. There was no mushroom cloud; nothing rose into the stratosphere.[101]
Russia has tested air-burst bombs far larger than Baker.
The Tsar Bomb test of 1961 was over 50 MT, and could have been scaled to 100MT.
Weighing 30 tons, it was too big to be transported by air. An unmanned sub, operating as a long range torpedo, could carry a really, really, really big bomb.