Eli5: Why does water expand while freezing, and what would happen if it was frozen in pressurized enviroment/container that cannot expand?

Question

Eli5: Why does water expand while freezing, and what would happen if it was frozen in pressurized enviroment/container that cannot expand?

In: Physics

Answer 1

Fill a steel pipe with water and cap it and submerge it in liquid nitrogen, [you get a boom](https://www.youtube.com/watch?v=t5mdZD00POs#t=4m15s).