Climbing Anchors by the Numbers

Climbing Anchors by the Numbers

October 1, 2019 fmg-adminAlpine & Ice Climbing Guides' Tech Tips Rock Climbing

“Are three pieces necessary in all climbing anchors ? I only have two. What about that bomber bolt? Shouldn’t it be redundant?” 

Chances are you have come across a situation in your experiences building climbing anchors where some of these questions have come up. I know I have had a lot of questions on my instagram feed about when is it okay to have two pieces in an anchor. The answer as usual is, “It depends!” So let’s analyze some of the variables involved and see if we can come up with some guidelines for creating anchors that are sufficiently strong. 

One consideration is how the anchor is going to take force. For instance, are we belaying someone up third class or super slabby terrain where most of the weight of a fall would be on the climber’s feet? Or is it higher angle with no friction created by rope running over terrain resulting in the entire amount of force being applied directly to the belay.

Force/Use of Anchor

Intended use can also determine the amount of force on a climbing anchor. If the anchor is for multi-pitch climbing and will be the attachment for the team before a lead piece of protection is placed, then it could potentially take a factor two fall, which generates the greatest amount of force you can apply to an anchor. (Do remember if you are standing on a ledge or if the leader can hit terrain during the fall, then the fall will not produce as much force.)

How many people will be using the climbing anchor at the same time? One person: you get to the belay and may be clipped in but are standing on the ledge with no force being applied to the anchor, and only in the event of a fall would the anchor see any weight. Two people: you are hanging on the anchor and your partner can take a fall that would factor two the anchor. Three people: you are hanging on the anchor and belaying two seconds who could potentially fall and weight the anchor. In all these instances we want the anchor to be sufficiently strong, however the forces are vastly different. 

Three people using a climbing anchor in steep terrain.
Three people, multi-pitch anchor in steep terrain

Size/Strength of Piece

The size of the piece of protection in climbing anchors matters not only because bigger pieces are usually stronger, but also because they have a larger acceptable expansion range, making it easier to place them correctly.  Also, as pieces get larger they typically have more material which translates to more strength. A good guideline is to look for at least 10kn pieces when thinking about strength and creating an anchor that is suficiently strong. And as I discussed in a prior blog here, over-camming is better than under-camming!

A climbing anchor made of two large cams
Size matters!

Quality of rock

Rock quality is a significant factor. The rock does not just have to be solid but also has to be able to hold the force the gear is putting on it. Sandstone, for instance, cannot take as much compression as granite, so a single piece in granite might be sufficient while you would want pieces to share an equivalent load in sandstone. 

It also goes without saying that we want to make sure on a macro scale that the weakness we are placing the protection in is a “crack in the earth” and not just a loose flake. On a micro scale we want to see if there are any incipient cracks or fissures that could mean the rock could become dislodged or break. 

A three-piece climbing anchor in a block of rock.

Need/Experience/Exposure to Risk

Need, experience, and risk tolerance all relate to each other so much that it is impossible to separate them. Let’s look at need first. Do I need to move fast? Do I have more gear? Do I need to save gear for the next pitch? These factors all might influence why I am choosing more or less gear in the anchor. 

Next is experience. With more experience placing gear, falling on gear, and understanding the true forces climbing anchors can take, we might choose to build an anchor that can only hold slightly more than the anticipated loads. With less experience we might rely on more pieces and redundancy to catch any of our mistakes. I even use more gear when I start to climb in new areas and I am still figuring out the terrain just incase I would overlook something. 

Risk acceptance changes with each person and for me even on different days. For instance I am sure some people are okay with free soloing, while others are not. There are risks in getting off the couch, but we all choose to do it because the benefit is greater. So you just have to choose based on your knowledge and the exposure to risk you are willing to accept. If that means carrying a few extra pieces and throwing one in a particular belay, do it. If you are going for the speed ascent on a climb, you might want to consider carrying less, but that choice comes at a price.

Karsten Delap, AMGA Certified Rock and Alpine Guide

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