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Much of the discussion is based on potential rescue loads of 20 kN, but the concepts are also applicable to climbers using snow anchors for pro, belay anchors, and rappels. Overall I would rate it a Climbing Nerd Level 2.
Consider these points:
- Strength of the snow (powder snow vs. consolidated and moist snow-- can you make a snowball?)
- Connection point to the anchor (top hole, middle hole)
- Upright or horizontal (deadman) placement (angle of placement important for uprights)
- Carabiner clip vs. girth-hitched sling
- Picket material (aluminum vs. steel)
Meaty tidbits of knowledge:
- Deeper horizontal (deadman) placements have a higher strength than shallower, because they create a larger "failure cone"
- For multiple placements, like in an equalized anchor, separate by a distance at least twice the depth of the deepest anchor
- If belaying from a snow anchor, keep at least 1.5 meters (4 to 5 feet) between the anchor and the belayer to avoid pulling up on the anchor
- In strong snow, tilt the picket back no more than 10 degrees from perpendicular to the snow surface to maximize the cone
- Beware of placements where the direction of pull is upward (running belays over a lip, belay anchors)
Recommendations:
- For snow that can be compacted (you can make a snowball), use an upright placement with a midclip or a horizontal placement (deadman) with a midclip
- For snow that is too hard to dig a trench, use an upright placement with top clip tilted back 10 degrees
- For very cold or very wet snow that cannot be compacted into strong snow (less typical in the Cascades), use a picket placed as a fluke or a horizontal placement (deadman)
Cool stuff, no?
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