For those intereseted http://www.mountainz.co.nz have a good in depth article on snow anchors prepared by Don Bogie (DOC Canterbury, NZMSC Snow and Avalanche Committee
NZ LandSAR Technical Rescue sub-committee)

It is worthy of a read.

http://www.mountainz.co.nz/content/article/general/snowanchors.pdf

Cheers,
Shane