What causes Nitroglycerin to detonate while thawing?

[workinprogres]

While reading about Nitroglycerin a number of time I've read that it used to be frozen for transport but upon thawing it would detonate. What causes this to happen? It it expansion of the liquid as it heats up creating pressure? I have absolutely no intention or would ever consider making/buying/freezing nitroglycerin, I'm just curious.

 

[chemisttree]

If it cracks while thawing, the shock sensitive material can detonate. Take an ice cube out of the freezer and hold it in your hand. Did it crack?

boom!

 

[workinprogres]

Wow I'm retarded *facepalm* Thanks you!