Snow can be the most difficult medium to retreat from, requiring combined and unconventional tactics. Generally snow can be simply down climbed, providing good solid buckets steps. Unfortunately you can find yourself committed above an overhanging bergshrund or serac with nothing solid except for the snow beneath your feet. Snow anchors are generally the most suspect and great care should be taken whenever forced in using any of the techniques below. All snow anchors, no matter how good they look, should be treated with extreme caution, with shock loading and load being kept to its minimum.
The classic snow anchor and one worth practicing before you find you need to use it in anger so that you fully understand its holding power. The snow bollard should be treated as a suspect anchor, with shock and load being kept to the minimum. The anchor can be backed up by having a person below it sitting in a bucket seat and ready to hold the ropes if they start to pull through. Once the leader is down it can be assumed that the bollard is up to the job.
If forced to abseil off very bad snow then one option is to fill a large stuff sack with snow and use this as the anchor, burying it as deep as possible like you would a t-axe belay. The drawback with this anchor is that you’re leaving a mess behind, although this may not be such a big deal if it will eventually find itself into the begshrund anyway.