"would a nuclear bomb going off underwater create a tsunami?"
Possibly a small one. It would vaporize a large volume of water around the blast, leading to a vast surge in pressure, and as we all know, water isn't compressible. So you'd have a large pressure wave expanding away from the blast, followed by a trough when the vaporized region cooled, forming a partial vacuum and the area collapsed. It would be like a small version of a megathrust fault.
Fortunately however, the amount of energy even our larger H-bombs can release that way is miniscule compared to what a real megathrust fault would release, so the wave would probably not be much more than a slightly rougher surf for the nearest coastlines.
Possibly a small one. It would vaporize a large volume of water around the blast, leading to a vast surge in pressure, and as we all know, water isn't compressible. So you'd have a large pressure wave expanding away from the blast, followed by a trough when the vaporized region cooled, forming a partial vacuum and the area collapsed. It would be like a small version of a megathrust fault.
Fortunately however, the amount of energy even our larger H-bombs can release that way is miniscule compared to what a real megathrust fault would release, so the wave would probably not be much more than a slightly rougher surf for the nearest coastlines.