This stamp was released on July 26th, 2010, as one of the original stamps.
Trivia
This is not a member stamp, but it is very difficult for a Non-Member to earn this stamp, since they can't open the igloo. They have to be in a server with at least 30 friends, and have them all go to their igloo. This makes it nearly impossible for Non-Members to obtain it, even if it is organized.