Coldsnap + Unleash interaction ?

I'm wondering about placing the Unleash support gem into the Coldsnap skill (Sorcerer). Does reoccurring Coldsnap twice for 50% of the original damage effectively mean that the total damage is being doubled? (original 100% + 50% + 50%). It seemed odd because the other support gem for Coldsnap (Hourglass) only gives 40% more damage, for the price of a +10 second cooldown.

EDIT: I just checked the DMG numbers in a boss fight, Unleash actually does (approximately) double the damage of the Coldsnap explosion, even when used on a single freezed enemy.