It surprises me how few mountain climbers understand or know a safe and simple method to abseil down a climb leaving minimal gear. Usually if you plan to abseil down a climb either placing your own abseil points or by using old ones already in place you will need a few basic things.
In addition to your standard rack of climbing gear pack some extra 6mm cord. (usually around 10m), a knife, two screamers (expanding quick draws), short prussic, belay device, daisy/safety chain, and your ropes.
When descending a long route it could be possible to use your entire climbing rack building the abseil stations if you place more than one piece at each anchor. You can loose unnecessary amounts of rack if you miss good quality rock spikes / bollards etc. This could leave you stuck in the middle of the mountain with no means of continuing your descent. Therefore it is typical when abseiling in the mountains to leave single piece abseil stations. However, single piece abseil stations increase the risk of anchor failure. There is also the risk on long complicated descents that fatigue will play a factor in poor decision making. Therefore having a standard procedure for how you descend will help reduce the risk of anchor failure. Having a set process that you follow for every abseil ensures that when you are super tired on a long and stressful descent the chances of you taking short cuts or making a life ending mistake are reduced.
1 - Picking a good descent line
Try to avoid loose rock or lines that sit directly below objective hazards like cornices. If you must abseil down over bad rock where their is risk of knocking something onto people below you, or cutting your ropes, try to pick abseil stations that are sheltered from rock fall caused by your partner coming down or rock fall when you pull your ropes. If your line is subject to ice or snow fall, consider waiting until night to ensure cold temperatures reducing the risk of being hit by falling ice, or melting snow releasing rock fall etc.
2 - Setting the first abseil
The next set of rules apply for fixed abseil stations or for abseil stations you create yourself. Build a solid anchor (not the piece of protection you plan to abseil from), then place your single piece abseil point. Ideally look for rock spikes or bollards you can sling to save your rack. If your on ice look for a solid well formed piece of ice to make a v-thread. Connect your primary anchor to your abseil point via a screamer. Ensure that the primary anchor connection to the abseil point has some slack. i.e. it takes none of the weight. While still connected to the primary anchor attach yourself to the single piece abseil point. Bounce test this piece. Ensure your bounce test uses as much force as you can apply. Jump up and down and also give your anchor an outwards pull ensuring it can take force from multiple directions.
3 - Preparing the single piece abseil point for use
Now you have bounce tested your abseil point you can be fairly sure that it will hold the weight of a descending climber. There is no need to leave a carabiner on this piece. If you are using a rock spike or bollard slung with prussic or sling just thread the rope through. If you are leaving a wire take a small piece of prussic cord and make a loop running through the wire for the rope to run through (this saves you potentially damaging your rope by having it running directly onto the wire) it also makes the rope pull easier. If it is a cam just put the rope directly through the sling on the cam. Once the rope has been threaded clip the screamer which is attached to the primary anchor into your single piece abseil point. Ensure that it is not tight i.e. not taking any of the weight from the abseil but not so loose that the shock loading if the abseil point failed will cause the primary anchor to fail.
4 - Deciding if the ropes need to be thrown or coiled
If you are abseiling a steep clean face, ice wall, overhang etc it might be possible to simply throw your ropes. To avoid any tangles throw them with the free end of the rope first, one rope at a time. Before throwing the ropes ensure you have tied a knot in the free end of each rope. If you have high wind, or are abseiling down a slab / broken ground with the risk of rock fall that could cut your ropes then the safest thing to do is to coil your ropes into several small bundles, tie them to your harness and throw them progressively as you make your descent. I like to make my loops of rope around 15m long. You throw the first 15m leaving three other coils clipped to each side of my harness. As you descend throw the remaining coils one by one as they are needed. This stops my rope getting tangles, dislodging loose rock, or getting blown away when its really windy. The risk of high wind abseils is that your rope can be blown away and get caught on something in a position you can not climb over to.
5 - Attaching yourself to your abseil line
Always use a prussic when abseiling in the mountains. The prussic is there to ensure if you are knocked out or hit by rock fall you don't simply drop down your ropes. It is also useful to have a prussic so you can have your hands free to sort out any tangles in the rope, climb sideways to check out the abseil line etc. I prefer to have my abseil device away from my harness on my safety chain with the prussic connected to my harness and sitting under the abseil device. However each to his own when it comes to how you like to rig yourself for abseil.
6 - Set your roles Set the roles for abseiling just like in climbing
There is a leader and a follower and both have a separate function to play. The leader (the first person to go down the abseil) must take the climbing rack) ensure they have the best head torch if abseiling at night. You can make the leader the person who was following for the last block of climbing. But however you decide to appoint the leader do it in advance of the descent so everyone knows their role before the time comes. The leader will go first taking all the gear and will rig the next abseil. The follower will remove the back up anchor and abseil off the single piece anchor.
7 - The abseil
When abseiling an ice line ensure you kick off any ice daggers that are on your abseil line. This makes sure that your rope will not dislodge them so they fall on you from above. If you are abseiling a line with loose rock push or kick off any bits that might fall on you. Ensure your ropes are out of the way so they can not fall onto your ropes and cut them. The leader abseils first and somewhere around 45 - 50m down starts to look for a new abseil point. Think of the basics: will my rope pull easily from here, are you protected at this stance from things falling from above, will my new abseil point allow me to easily continue my descent, is there good protection to build my new anchor from. Before starting off on your abseil the last step is to clip your safety chain to the rope you intend to pull. Always re affirm this with your partner, i.e. pulling blue. It is easy to forget which rope to pull on a long descent.
8 - Building the next abseil station
First the leader places the single piece of protection that will be used for the next abseil. They then clip into this piece of protection with their safety/daisy chain. While they remain on the main abseil line they then bounce test the new anchor with all the force they can ensuring both downwards and outwards bounce tests. Once they are satisfied that it is a good piece they then build a back up for the single piece abseil line. Once the back up is in place and clipped (with a little slack) to the single abseil point they then come off the abseil line remaining clipped into the new abseil point. Ensure that you are clipped in such a way that you are both clipped to the single piece abseil point and also attached to the back up for the abseil anchor. Before calling ropes free, take your second screamer and connect it to the single piece abseil anchor. You then knot the ends of the abseil line and connect them to the screamer. This ensures if the top anchor fails while your partner is abseiling that there is a chance the new anchor will hold their fall. This is important for two reasons. One being it could save your partners life and two that it might save your own as if your partner falls with the ropes leaving your stuck high up on a mountain you might have no way of getting back down. You use the screamer (expanding quick draw) in this situation to reduce any force onto your anchor if the single piece abseil point above fails. Once all this is done call off rope. Your partner then follows first removing the back up to the anchor and abseils off the single piece left behind.
9 - Pulling the ropes
Leading the abseils is hard work, especially when your tired. Therefore to share the workload the second person should do the work of pulling the ropes. Sometimes both of you will need to help with this job but it is a nice way give the leader a break and to distribute the workload when the second or final person to abseil does the rope pulling. Before you pull the ropes ensure all knots are out from the ends, and the end you are pulling is threaded through the anchor ready for the next abseil. If necessary clip the rope to one of your harnesses to ensure it does not get dropped. After the rope is pulled and begins to fall be aware of falling ice or rocks that get dislodged as the rope comes down. Keep in close to the wall with your head down.
10 - Other tips
Auto locking carabiners are great for both your ATC and your daisy/safety chain when your alpine climbing. On long routes when your very tired it is great not to have to think if your carabiner is done up or not. When you knot the ends of your rope for throwing only tie one knot. If you tie two separate knots there is more chance they will get stuck in a crack when pulling your ropes. Mark the half way point on all your ropes. Even if your using two ropes for descent often you will cut one and having the half way point on your other rope marked will help save time finding the middle when you swap to single rope abseils