By Olly Allen, Mounatin Tracks guide.

As skiers or alpinists you may be crossing glaciated terrain which has visible or hidden crevasses. Crevasses are more prevalent where the glacier crosses a convexity and steepens or on the inside and outside of bends. The later in the day you are, the warmer the snow bridges and thus greater likelihood of the snow bridge collapsing, so get out early!

In addition to the usual kit mountaineering kit you'll have to be wearing a harness and carrying on it an ice screw, two prussik loops (or mechanical equivalent) two snap link karabiners, four screw gate karabiners and a two long slings. In addition to this the party will need carry a minimum 30m of 8mm rope (this depends on the number in the group and climbing objective). An ice axe and crampons is essential to stop you skidding around on an icy glacier and building a belay!

The first thing to remember if someone falls into a crevasse is stay calm and make sure the rest of the group is safe. Your priority is to regroup and try and communicate with the person down in the crevasse. Bear in mind if they've fallen in a long way ice is a good insulator so communication may not be possible unless you have line of sight. For this reason someone will have to build a safe belay using skis, an ice screw or the combined weights of the rest of the group tied on the end of the rope. Someone will need to attach themselves to the rope with a prussic loop and look into the crevasse. The easiest way to pull someone out is to then to get the group to walk backwards tied to the rope. Take care as the edges of crevasses can be overhung and the rope will cut into the lip of the overhang trapping or crushing the rescue victim. This can be avoided with slow extraction in addition to padding the edge of the crevasse with ski sticks or rucksacks. If you haven't got sufficient numbers to do this the victim could prussik out. This is an essential skill well worth practising. It involves using prussik knots to ascend the hanging rope. Prussiks can be made using a metre of 6mm cord tied in a loop. One is attached to stand in and the other from your harness to sit on. Sliding them up the rope independently allows ascent, this can be speeded up using mechanical rope jamming devices such as a Ropeman or Tibloc. If all else fails you'll have to pull the victim out using a pulley system. There are a few systems with different amounts of mechanical advantage depending on how much manpower you have for pulling and whether the faller was tied on before he fell or not (climbers tend to be, skiers don't). The most common is a 3:1 Z pulley. Remember that with this system 3 metres of rope must be pulled to lift the victim 1 metre. This process can be made more efficient by using self locking or free wheel pulleys and mechanical jammers in the system. I could try to describe how to build this pulley system but you would be much better served by being trained properly and practising.

Crevasse rescue is a complicated business and needs to be practised as it is very easy for the inexperienced to make the situation worse. If in doubt shout for help, get on your mobile phone, hire a guide or attend a course teaching these skills.

Despite this warning if you have sufficient rope between each member in the party , two people 20m, three people 15m and so on then you should be alright. The more people in the party the safer it is but as a rule of thumb there should be no less than 8m between each person in large groups so you may need a long rope! Critically there should be no slack anywhere in the system so never carry hand coils and keep the rope taught. Make sure you tie coils off correctly and if you're really worried tie overhand knots in the rope 3m from each end and one in the middle should be enough.

Key to photo

• 1 Harness
• 2 4 x Screw gate Carabiners
• 3 Ice Axe
• 4 Rope (minimum 30m / 8mm)
• 5 Quickdraw made from short sling
• 6 2 x Long slings with Carabiners
• 7 1 short (18cm) one long (22cm) ice screws
• 8 Prussik Loops (6mm cord 1meter long tied in a loop)
• 9 Pulley Karabiner
• 10 Mechanical Jammer (Ropeman)
• 11 Crampons

Olly Allenis a fully qualified UIAGM guide, member of the BMG (British Mountain Guides) and one of the directors of Mountain Tracks Guiding Company.He has 20 years of climbing, skiing and mountaineering experience in every region of the world. Occasionally, when we can get hold of him, he writes useful information and product reviews/recommendations for us at Facewest.By working with Olly and other experienced mountain professionals we hope to keep the product range at Facewest bang up to date.