In the first Austin Powers movie, Dr. Evil steals a 50 kiloton nuclear weapon, straps it to a drill and is going to fire it into the mantle to trigger volcanic eruptions world wide.
My instinct is that, compared to a lot of nuclear weapons in the megaton range, 50 kilotons is not really a lot, and using it to try to move rock (even molten rock) is not going to accomplish his goal. Would it even cause a measurable change in the pressure that far down?
That’s a different kind of thing. Yes, they would have buried the bombs, but not that deep. Just deep enough to form a nice, deep and just slightly radioactive crater.
It would have been interesting to behold. There were plans to actually bomb a new Panama channel, several miles wide and without any locks. This would have resulted in a steady stream of water from the Pacific side to the Atlantic side, with basically unpredictable results.