Anchors are needed in snow for the same reasons they are needed on rock. The equipment is different but the purposes are the same: to anchor belays and rappcls. But rock anchors are usually easy to inspect and predictable in performance. Snow anchors are not. They vary widely in strength depending on snow conditions and placement, and their strength changes during the day with changes in the snow. This uncertainty makes it even more imperative than on rock to check and recheck any belay or rappel anchor. Snow anchors can also require a lot of time to put in place. They include deadman anchors (such as snow flukes), pickets, and bollards.
A deadman anchor is any object you bury in the snow as a point of attachment for the rope. The most common is the snow fluke, a specially shaped aluminum plate with a metal cable attached (fig. 12-3la). Snow flukes are available in various sizes, their holding ability generally increasing with size. For maximum strength and reliability, a buried fluke should be angled back about 45 degrees from the direction of pull (fig. 12-3lb). Dig a slot in the snow to permit the cable to be pulled in as direct a line as possible.
In theory, the fluke serves as a dynamic anchor, burrowing deeper into the snow when it takes a load, such as the weight of a climber on rappel. In practice, it may behave in more complicated ways, even coming out if it is tipped too far forward or back, or if the load is to the side rather than straight out. If the plate or the cable travels down into the snow and hits a harder layer, the fluke could be deflected and pull out. Flukes are available with bent faces, flanged sides, or fixed cables—features intended to make them maintain the correct orientation and to make them self-correct if deflected.
Flukes are most reliable—but also more diffi-
cult to place—in the hard homogeneous snow of summer. They are generally used in a softer but dense pack, snow that is moist and heavy. They are least reliable under typical winter conditions, with snow layers of varying density where they may deflect off harder layers. Neither do they do well in dry, unconsolidated snow.
Ice axes, ice tools, and snow pickets can serve as deadman anchors (fig. 12-32). Bury the implement horizontally in the snow, with a runner attached at the midpoint. Cut a slot in the snow to let the runner lie in the direction of pull, and then clip into the runner.
A picket is a stake driven into the snow as an anchor (fig. 12-33). Aluminum pickets are available in lengths from 18 to 36 inches and are found in different styles, including round or oval tubes and angled or T-section stakes.
Pickets work well in snow too firm for flukes but too soft for ice screws. As with flukes, angle
them back about 45 degrees from the direction of pull. Attach a carabiner or runner to the picket at the snowline—not higher on the picket, or a pull may lever it out. You can drive a picket into the snow with a rock or the side of an ice axe, but a North Wall hammer or other ice hammer works best and reduces the chance of equipment damage. An ice axe or ice tool can serve as a makeshift picket.
A bollard is a mound of snow that serves as an anchor when rope or webbing is positioned around it (fig. 12-34). Snow bollards provide highly reliable anchors for belaying or rappelling in soft snow and are possibly the most reliable in all snow conditions. There's a significant trade-off here, however. It takes a long time to build one.
Create the mound by making a trench around an oval area of snow. In hard snow, chop out the trench; in soft snow, just stamp it out. The bollard should end up as an oval-shaped island of snow. The softer the snow, the broader and deeper the bollard must be: up to 10 feet wide and 1V2 feet deep.
Try to use webbing around the bollard instead of rope because it's less likely to saw into the mound. For the same reason, avoid pulling on the rope or webbing after placing it. For more security, pad the rope or webbing with packs and clothing and whatever, especially in soft snow. For safety, inspect the bollard after each use to see it hasn't been damaged. You can also back up the bollard with a picket or fluke (which the last person on a rappel removes before rappelling).
Fig. 12-34. Snow bollard
Multiple anchors are the best insurance because of the inherent weakness and unpredictability of snow anchors. As with questionable anchors in rock, multiple anchors are safest. Two anchors can be chained sequentially so that the first takes the hit, but has a backup to absorb any remaining force. Or they can be connected in a way that will permit them to share any load (fig. 12-35). (More details and illustrations on joining multiple anchors are in Chapters 7, 8, and 10.) In general, place multiple snow anchors one behind the other to reduce the angle of pull and the potential load on the surviving anchor if the other one fails. Keep the anchors several feet apart so they don't end up sharing any localized weakness in the snow.
Continue reading here: Belaying On Snow
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