Vertical caving terminology and methods > Ice and snow
A flat or large object which can be buried in snow, and used as an anchor. It functions by pulling against a wide area of snow, and is surprisingly effective, with a very small surface area. This might be useful to descend a snow cone into a cave entrance using a rope, where there is nothing else to use as an anchor. It would not be useful further into a cave, since it can be used with snow, but not ice. Almost any large object can be used this way, as long as a rope can be attached to it. This includes an ice axe, rock, log or a sheet of fabric. However, dedicated devices are usually a mostly flat plate with several holes to reduce the weight, or a long stake made from angled aluminium. To bury the object, a hole might be dug using the adze (snow shovel) of an ice axe, and a notch for the rope might be dug using the sharp point of an ice axe. The strength of these anchors is hugely variable, and depends on snow conditions and how well they are configured, but in general they are much weaker than other types of anchor. A dedicated device might be able to hold between 130 and 1600 kg of weight, while other buried items might hold between 100 and 1500 kg. The most common strength when correctly configured is between 600 and 800 kg, but in some cases, the strength can be exceeded by bouncing around on a rope. The deadman itself will also have strength limits imposed by its construction. Manufacturers may be reluctant to give actual specifications, since the resulting strength is dependent on snow conditions, and how well it is used. If the deadman uses a 4 mm attachment wire, the wire itself can hold a maximum of about 1000 kg, but by bending it through holes in the deadman, the strength can be reduced by a large amount, sometimes as much as half. However, using aluminium for the body of the deadman might allow the aluminium to deform instead, reducing the bends, and allowing a slightly higher strength. Therefore, some common dedicated devices with wires might have a maximum strength of about 500-700 kg in ideal conditions. DMM have stated (personal communication) that with the aluminium plate held firmly in a metal fixture instead of snow, their branded Deadman typically fails at over 700 kg (stated as 7 kN), with the wire typically cutting though the aluminium plate at that load. Snow anchors of all kinds are best treated as a last resort only, with plenty of research into the best arrangements, orientation and burying techniques for different conditions.
<< Ice screw | Rope access and arboriculture >>
This page is not intended to be viewed this way, please load the entire article. This version exists only to make it easier for search engines to understand the contents.