It's the battery that is bulging, it puts pressure on the screen an breaks the glue. Lithium Ion batteries do that for some reasons. Due to how much time I work outdoors I wouldn't be surprised if a combination of hot and cold cycles combined with humidity are hard on my phones. I have an appointment at the Apple Store near by to see if it is savable with a new battery. The screen might not go back in right now that it has been warped.
