Why does water in the water bottle freeze once I unscrew the top?

Question

I had a water bottle in the freezer but it didn't look frozen. I took it out and it wasn't until I unscrewed the cap that entire thing started freezing until it was one big slushy.

Answer 1

sometimes water can be super heated & not boil, supersaturated & not crystallized out excess solute, and even be super cooled & not crystallize,.... until it is seeded or shocked ( as it apparent was by the agitation of opening.

there was a time, when the air at yellowstone national park would get super cooled, higher than 100% humidity during the winter time until it found something to form snow upon.