"Sudden" Phase change of water to ice Last winter, I had a store-bought bottle of water I took snow camping. The closed bottle of water sat in the snow overnight. The next morning the water was still liquid, when I opened the bottle, I heard the hiss from the release of pressure on the bottle and, it "flashed" to a slushy ice almost instantly. At the time I figured it was an issue with the air pressure in the bottle (we were camping in the mountains) and a neat example of nucleation. Fast forward to this winter, I had two store-bought water bottles sitting in the car over night (this time, at home in the valley). The outside temperature was in the high teens to low 20's. Both of the bottles were closed, but of these two bottles, one was partially full and the other was completely full, and had not been opened yet. Both bottles of water were still liquid and laying on the car seat next to me. When I opened the partially full bottle, it flashed to ice just like the bottle last year. I was amused but not surprised. I was curious about the second bottle, I picked it up and, without opening it, it too flashed to a slushy ice right there in my hand, no opening or change in pressure involved. This did surprise me and gave me cause to question my assumption of the affect of pressure (or sudden change thereof) on the phase change from liquid to solid. Is this a simple matter of two different causes (delta P and agitation) of nucleation? Does the pressure in the bottle have any impact on nucleation? If so, would it matter if the bottle were under vacuum or pressurized? That is, is it just the change in pressure that initiates the nucleation? Would someone please elaborate on the physics involved with my experiences such that I could explain things further to my young son? Thanks.