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

The water forms a crystal structure when it freezes. There is more room between the water molecules in the crystal structure. If the environment is pressurized enough, you can prevent it from freezing, you would need a very strong container though, because water freezing can crack through concrete and steel like it wasn’t even there.  

There are a bunch of different types of ice, based on the temperature and pressure attained. 
[https://en.wikipedia.org/wiki/Phases_of_ice#/media/File:Phase_diagram_of_water.svg](https://en.wikipedia.org/wiki/Phases_of_ice#/media/File:Phase_diagram_of_water.svg) 

Edit: typo