Was driving in my 98 blazer 4x4 when I heard a loud thump I was looking around and seen that the gas tank is now in the shape of a n I pulled the gas cap and had trouble from all the vacuum behind it please help with what could of caused it I do know I have a check engine like on for a code p0452 other than that I have no idea what would cause that

 

That is wild. I never heard of that, Im guessing it has to be an issue with evap. The truck is not getting rid of the excess vapors in the tank. When the vapors condense, it would cause negative pressure. Thus imploding the tank. you mention a p0452 pressure switch error. Maybe the switch is faulty or the wiring to the switch?