Standard ice anchors often involve only two pieces of protection, instead of the three pieces that we typically use in rock climbing, because in strong, reliable ice, two ice screws are plenty strong enough. Plus, placing two screws takes way less time and helps you move faster in this super-cold environment. Because of this standard, ice enthusiasts need to be very specific about the structure of the anchor, particularly the angle of the ice screws in the ice as well as the orientation of the two pieces in relation to each other. Building the anchor in this specific configuration doesn’t take any extra time, but it will maximize the strength of this minimalist anchor.
First and Foremost
Once you’ve found where you want to build your belay, visually inspect the ice to make sure it’s as solid as possible. The ice should be clear or slightly blue; if it is solid white, then the ice is rotten. Obviously, cracks and running water (even water running behind thin ice) are bad. Avoid building your anchor on bulges where the ice bends outward and is less supported; instead, aim for depressions and concavities where the ice bends inward, which typically will be more solid because of the strength and support from surrounding ice.
First, the ice screws need to be at least 12” apart, with 18” to 24” being ideal, especially if the ice is suspect. If the ice fractures, the greater distance will reduce the chance that both screws will be affected by the same crack. When placing these screws, offset them from each other vertically, so one sits at least 12” to 18” higher (fig. 1). They can even be stacked perfectly in line as long as one is above the other. This does two major things. It reduces the vector forces put on the ice screws. To put it simply, the lower the angle between the two screws, the less force is applied to each and the closer you’ll get to each screw taking about the same amount of load. The second reason for offsetting screws vertically is that water ice tends to fracture horizontally as opposed to vertically. So if the ice does crack, having both your screws in one horizontal plane could be bad news. Equalize these pieces with a sling or cordelette, just like with rock anchors.
Ice Screw Angle
Contrary to what you might think, the best angle for the screws is slightly upward, meaning the hanger is slightly lower than the teeth in the ice. This counterintuitive method is better because the holding power comes from the threads themselves and not from a “snow picket” effect, meaning you don’t get any mechanical advantage having the shaft of the screw levered against the ice (Fig. 2). That levering action is actually bad for the screw’s overall holding power because when an ice screw fails, it’s because the ice near the surface right below the hanger has failed. When the ice at the surface gives way, the shaft becomes exposed and only adds more torque, which will cause the ice to deteriorate further. Eventually with enough force, total failure occurs. Place ice screws at a 5° to 10° upward angle. More than 10° is too much because it will lever the screw as well. Pointing the screw slightly upward keeps the screw more in line with the load, minimizes the torque, and lets the threads do their job.
As an AMGA-certified alpine and rock guide, Ian Nicholson lives in Seattle with his wife, Rebecca, and he loves climbing in the North Cascades so much that he authored the guidebook to it (SuperTopo: Washington Pass Climbing).