Experts only: Your buddy has toproped his gnarly new headpoint 317 times—blindfolded, barefoot, and singing the national anthem. Despite all the rehearsals, now and then his foot still pops on that desperate last move. But the season is winding down, and the air is crisp—today’s the day. He brushes the 30-foot mini-monster one last time and calls his mom for an awkward “I love you.”
The first and only pro is a solid nut your friend wedges in at 10 feet. After floating the start, his eyes grow wide. He flubs the last move, and then he’s flying, screaming like a banshee. Reacting instantly, you sprint backward. In less than two seconds, it’s over.
“Whoa,” he says, held safely a couple feet off the ground. “Thanks.” Your friend fell from 30 feet with his only piece at 10 feet, but you kept him off the deck. How is this possible?
Your sprint away from the cliff rapidly took in slack as your partner fell, and to make your action most effective, you used a ground-runner. In this specialty belay set-up, the rope passes through a directional placed at the base of the route. This gear must be absolutely bomber for outward and upward force. A sling and locking carabiner complete the set-up. There are three major advantages of a ground-runner belay compared to a “normal” run-from-the-cliff belay:
The belayer pulls in much more slack. Without a ground runner, a belayer running backward pulls the rope into a diagonal, recovering much less rope than the ground distance he travels. If the belayer covers 14 feet, simple geometry shows that he only reels in 7.2 feet of slack—and the climber decks in the scenario above. Using a ground runner, the belayer runs about 13 feet (since he catches the climber sooner) and pulls in 13 feet of slack. With rope stretch, the climber stops just before hitting the ground.
A ground runner keeps the rope out of the climber's way. Because the ground-level piece holds the rope close to the wall, the falling climber is in less danger of hitting the cord and suffering rope burns or other injuries.
The ground runner ensures the first piece of pro will be loaded downward. This is especially important when the first piece of pro is also the last. Normally, if the belayer backs away from the cliff, the first piece is partially loaded in the direction of the belayer—out from the rock—when a fall is caught. This outward force can easily pop a nut. With the rope through a ground runner, the force is directed downward.
Any run-from-the-cliff belay is a hazardous, highly specialized technique. The force from catching a fall this way will be violent. This technique is most helpful for a climb with a runout close to the ground, or when protecting the climber from a ledge fall higher on a route; it is less useful for catching very long falls, since, as the falling climber accelerates, the belayer’s slower movement will yield diminishing returns. Rope stretch will add distance to any fall, so figure accordingly, especially with falls higher on a route. If you choose to risk this kind of belay, wear a helmet, pick a path beforehand, and be aware of the considerable danger to the belayer.
Adam Scheer is a graduate student in physics at the University of Colorado at Boulder. He explores this topic in greater detail at climbinghouse.com/featured.