Sounds like you are talking about the Bermuda Triangle!
I was not taliking about the Bermuda triangle as such but it may have got its reputation partly based on such incidents. There are volcanos beneath the sea. Many start that way and grow till they reach the surface. They will generate huge bubbles of gas occasionally that could well be the size of the Albert Hall. When such a bubble surfaces beneath a ship it will drop the height of the Albert Hall. Not a lot of time to send out a distress signal.
Assuming you witnessed such an event without concrete evidence to support your observation you would be laughed at. In these days of digital cameras and mobile phone cameras maybe the evidence will enable people to risk ridicule. Also after a disappearance satellite photogaphs can now be examined.
Then again it might never happen or ever have happened. BrianG