Or, “just say no to the MMO”
Short version: In my opinion, the munter mule overhand knot (from here on referred to as the MMO) is not a required component in a crevasse rescue system. Including it in a beginner crevasse rescue class adds further unnecessary complexity to an already very complicated situation. It’s fine when taught to intermediate or advanced climbers, and it certainly has a place in more advanced rescue scenarios, but it’s probably best not to teach it to new folks.
Long version: You’re considering taking a class in crevasse rescue from your local mountaineering club. You read the class curriculum online, and see that requires that you tie an MMO knot at the anchor to make a “releasable system”.
In addition, the generally always awesome and hilarious cartoon book, “Glacier Mountaineering: An Illustrated Guide to Glacier Travel and Crevasse Rescue”, says to use one also.
Conversely, the following reputable sources do NOT suggest using an MMO for crevasse rescue:
book: “The Freedom of the Hills”
book: “The Mountain Guide Manual” a reference book for, you guessed it, professional guides
The American Alpine Institute (AAI, see their crevasse rescue sequence here.)
YouTube instructional videos presented by professional mountain guides
The Munter mule overhand with a cordelette
(carabiner through the overhand knot for extra credit, I think I tied it right . . . =^)
So, what’s the dealio, you may be wondering. Do I really need an MMO for crevasse rescue, or not?
To help answer this, ask yourself a few questions.
Is the MMO a seldom used, specialized rescue knot, that’s tricky for most people, especially beginners, to tie correctly? Answer, yes.
Is it likely that you’re going to forget how to tie a seldom used, specialized rescue knot, that you never use in your day-to-day climbing, years from in a rescue scenario that’s already stressful and complicated? Answer, yes.
Is it possible to rig a successful mechanical advantage crevasse rescue system without using this knot? Answer, yes.
Are the vast majority of crevasse rescues performed by raising only, without ever needing to lower at all? Answer, yes.
Is it possible to lower a victim safely (if for some reason you need to) without having an MMO in the system? Answer, yes.
I’ve watched several crevasse rescue videos on YouTube, and none of the guides in the video tie an MMO at the anchor. Why is this? Answer - probably because of the answers to the previous five questions.
(If you go through the excellent crevasse rescue videos made by AMGA (American Mountain Guide Association) certified guides that you’ll find on the video portion of this website, nowhere do you see this knot.)
Side note: The MMO, as it’s usually taught, requires a cordelette. Which is probably okay if you have three or more people on your rope team, but if you’re a two person team, you probably already used your cordlette to build the 2 piece anchor. And I’m guessing you probably don’t want to carry a second one just for this knot.
Let’s get back to the stated purpose of having an MMO, which is to have a “releasable system”. Why is this needed?
Typical answer - if the person in the crevasse needs to be lowered, the releasable system lets you do so. Reality - if you want to lower them, all you need to is pull about 1 inch up on the whole raising system, loosen the holding prusik, then lower. You can easily do this without the complications of an MMO.
(There is one additional highly unlikely rescue scenario, and that is if the hauling team on top gets over enthusiastic, does not monitor the victim during the pull, and somehow manages the epic screwup of pulling the victim into the lip of the crevasse. In this case, theoretically, you may not even be able to get 1 inch of pull out of the raising system to initiate the lower. Well, there is a way to do it. It involves getting out your knife and carefully cutting that prusik knot, thus removing it from the system and getting your victim out of the problem that you caused. In this case, yes it could be argued that a MMO would be a superior solution, but it’s so unlikely to ever happen that in my mind it’s not worth planning for.)
Takeaway: the MMO component of a crevasse rescue system is entirely optional, and in a beginner level class, it adds needless complexity and a difficult to remember component to an already stressful and challenging situation.
Most everyone starting to learn crevasse rescue has their heads completely full with the mandatory things that need to happen. Most of them don’t have any room for anything optional or overly complicated, or in this case both.
Once you have the basic crevasse rescue skills down, or certainly if you’re on a professional mountain rescue team, then you can start adding in more advanced components such as two person rescue and releasable systems. But for beginners, teach the basics, make sure they understand it inside and out, and keep it simple.
That's probably why “Freedom of the Hills and “The Mountain Guide Manual” do not teach it.