So the hypothesis loosley repeated, best I can goes like this; The massive pressure spray surging forth has a sandblasting effect from the debris that has also been freed. This erossive force is eating at the core of the pipes 2" thick steel walls alarmingly fast. Once the pipe is eaten through, it's the ocean floor being eroded faster by factor 10 or something. Then the pocket, once exhausted, collapses. There then is a massive influx of water into said cavity, some miles deep, super-heating the water to explosive levels causing the worst tsunami in imagination. THE global killer.
I'm not one for the big FEAR talk and such. This however seems logical and plausible. I pray to all that is holy this is wrong. But, maybe it's time. (sigh) Smoke em if you got em.