Rosita proceeds to show Sasha how to tie a butterfly knot. The problem? She doesn't explain the knot's application, or how it will help them survive the zombie apocalypse.
The alpine butterfly is known by a number of names: the butterfly knot, the lineman's loop, the alpine middleman's knot, or the lineman's rider. The construction of the knot allows it to be weighted in multiple directions, the same way an in-line knot might be weighted in a single direction. Additionally, it is a relatively easy knot to untie after loading.
The most common view of the Butterfly Knot.
An alternate view.
There are three common climbing applications for the knot:
Isolation of a Damaged Section of Rope
If you have a core-shot in a rope and need to continue to use it in order to finish your climb or get down, a butterfly knot is often the best way to isolate the damaged section of the rope. The in-line feature of the knot, and the ease of untying, both make this the best option in such a scenario.
Mid-Point Tie-In on a Glacier
Due to the knot's ability to be "in-line" regardless of the load direction, this is a commonly used knot for climber's clipped into the middle of a rope on a glacier. Personally, I don't think it matters that much. The loads in a crevasse fall are small enough that an overhand or a figure-eight-on-a-bight are adequate.
Stopper Knot on a Glacier
The best use of the butterfly is as a stopper knot between climbers on a glacier. Essentially, a climber falls through a bridge, and the rope slices into the lip of the crevasse. The knot wedges, and the climber stops falling, even -- in some cases -- without the other climber dropping into self-arrest.
Due to the fact that the butterfly knot has bulk on both sides of the rope, it is the most likely of the knot options to get stuck in the lip of a crevasse and stop you from falling to the bottom. We have tested this at AAI several times with several different types of knots, and the butterfly ranks as the most likely to stick. Indeed, during a guide training, I once had a guide drop into a hidden crevasse for real, and the knot stopped her instantly.
There are two considerations to this application. First, there should be two to four knots between climbers on a rope team. And second, the team should expect to use a drop-loop style crevasse rescue system if someone falls in, as neither a direct haul, nor a self-rescue with prussic-hitches will easily work.
Tying the Alpine Butterfly
Here is a quick tutorial on the most common way to tie the knot, "the hand wrap method."
The following video shows some other tying options:
Rosita was right to show Sasha the butterfly knot in The Walking Dead. Because if there's one place where you could probably escape the zombie apocalypse, it's on a glacier on a high alpine peak...
--Jason D. Martin
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