High on a fragile snow bank in the mountains is not the place for tomfoolery. Yet at first glance the daily routine of the Cairngorm branch of the Scottish Avalanche Information Service seem somewhat imprudent. In a driving blizzard with 60mph gusts and piercing sub-zero temperatures, Wes Sterritt is taking running jumps on to steep banks of fresh snow and ice. If he is unlucky and loses his balance, he could fall more than 50ft down to where the rest of our small party is huddling in a corrie at the base of the slope.

If we are all unlucky he will bring more than a tonne of snow and ice crashing down with him, entombing us with concrete strength. But Wes is a highly-trained avalanche expert who knows his moutains.

He jumps. His legs sink in up to his knees but the vast white slab stays firm. Not satisfied, he begins to beat the snow with his ski-pole. A long crack stretches out laterally a few feet below him. It is enough to give him and his fellow avalanche analyst, Tom Rupar, their first piece of evidence that this is, as expected, a high-risk day. The mountains were buffeted by heavy snow storms during the night which dumped another few inches on the two metres already clinging to the rock beneath.

"We thought this would be a bad day," bellows Tom above the howl of the wind. "We predicted about a category four, which is high risk. The worst is a category five when you can't really rely on any snow being stable.

"On a day like this at this time of year the risks are quite high. Anything could happen, that's why we've given you one of these," shouts Tom, tapping the right side of my thick over-jacket, beneath which an electronic avalanche transmitter/receiver is strapped.

The device would enable fellow climbers to find me buried in an avalanche with relative ease. If you locate someone within the first 20 minutes of being buried in an avalanche they have a 95 per cent chance of getting out alive, after which their life expectancy drops dramatically. After two hours, chances of survival are down to just 5 per cent.

Such risks are an everyday occurrence for Wes and Tom who, through the winter, are employed to compile and broadcast daily avalanche warnings. As well as the basic tests of strength above, they examine the snow in close scientific detail, measuring temperatures, size and composition of crystals and the angle of slope. They also work for the Mountain Rescue team on a voluntary basis. They have been buried more times than they can remember.

"It's not a conventional way to earn a living, but it's a good one, especially if you love the countryside and the mountains," says Wes, whose gymnastics on the snow-bank have left his eyelashes frozen like thick white mascara. "People think avalanches only happen in places like the Alps. They can't believe they happen in Scotland. But last year we had more deaths by avalanches here than in Canada. What we're doing is trying to make people realise that these are serious risks.

"Some mountaineers think we're here to tell them what to do, but we're not. We don't have the power to close the hills. We're just giving people as much information as possible with which they can make their own choices."

A dozen people perished in avalanches during the 1994-1995 winter on Scottish mountains, the highest fatality rate for 10 years. There has been a general rise in incidents during the nine years the Avalanche Service has been going, simply because more and more people are mountaineering.

The service, which has sister branches in Lochaber and Glen Coe, is administered by the Scottish Sports Council, and it works hand in hand with the Cairngorm Mountain Rescue team.

Much is changing in the field of avalanche rescue in the Highlands. At present a major review is under way at the Scottish Office to assess the way forward for organisations such as these and how they are to be funded.

Technology is also progressing. Wes has recently been involved in trials of the Pipe Hawk, a new sonar device for finding buried bodies. The machine has already proved its worth in a range of underground detections, varying from the gruesome hunt for bodies in the Fred West murder case to mapping out the gas main under Buckingham Palace. Could it revolutionise mountain rescue?

"I doubt if it will be useful for saving lives," says Wes, "but it could speed up the recovery of dead bodies significantly. It is still very bulky at the moment, so there's no way you could get it up here fast enough, but you never know, it could be standard equipment on rescue helicopters in a few years."

The radio by my side crackles into life and Peter Finlayson, a teacher and the fourth member of our avalanche party, answers. The rest of the Cairngorm Mountain Rescue team are on an exercise in the next valley and want us to link up with them before the weather gets worse.

To do that we must traverse the high frozen ridge of Fiacaill a Choire Chais on the side of Cairngorm mountain. We leave Wes and Tom, who have sliced out a block of snow and are measuring its temperatures and crystal textures.

A break in the cloud has revealed a stunning mountain backdrop, brilliant white in the sunlight. We haul ourselves out of the corrie, our ski-poles and boot edges chipping at the frozen surface.

Peter moves with tremendous speed across the ice. As an experienced member of the rescue team, he is used to the pace. At the ridge we lose the sun. The wind gets stronger, slapping our hoods against our faces. We scramble over the ridge and slither down on to a sheltered snow field from where we can just make out the purple jackets of the team in the valley below.

By the time we reach them I am exhausted, stumbling, gasping for breath. I've covered less than three miles an hour with a light pack and carrying no rescue equipment - a fraction of the strain the team are usually under. Willie Anderson hands me a cup of coffee and grins at me through a beard of icicles. We slump into a snowhole and I ask him what makes someone want to volunteer to take these risks.

"I suppose the answer I should give you is that I'm dedicated to the mountains and the people who walk them and I want to do something to help, which is true, but what happened was that I got pissed in the pub one night and was talked into joining by him," says Willie, pointing to John Allen, team leader and local pharmacist.

Such mountain banter is cheering - just the sort of thing to warm you when you've been plucked from probable death on a cliff face. They are full of tales of past rescues: the man from London who slid 60ft off a snow field and down a crevasse, the face of a 10-year-old girl who died minutes before they found her, and the rescue the previous night (the busiest of the year to date) when 11 climbers were missing in five separate incidents.

Sometimes John and all 37 other members of his team can be out on the hills for up to 18 hours in temperatures that can dip as low as -20C, but they are not bitter, even when they are sure an emergency could have been avoided by, say, a check of the Avalanche Service's well-publicised daily report.

"You can't feel like that about this job," says John, squinting up at a line of four climbers attempting the treacherous Goat Track snow gully.

"All these people on the mountains are here to enjoy themselves and sometimes that means taking risks. You've just got to get on with your job and get your people down. It's not up to us to make judgements. Do you like pasta?"

And with that he radioed his wife in nearby Kingussie with instructions that he was bringing a tired, cold Englishman off the mountain and home for tea.

Everything you need to know about the Cairngorms

In the 1994/95 winter, 12 people were killed by avalanches and 70 brought off the mountains (of which 21 were injured)

The Scottish Mountain Safety Rescue Study examined all mountain rescue incidents in Scotland between 1964 and 1993 and found that more than 73 per cent of those involved had not considered themselves at risk

Only 0.01 per cent of people visiting the Scottish hills are likely to be involved in an accident

The avalanche season in the Cairngorms lasts from mid-December to mid- April

All members of Scottish mountain rescue teams are unpaid volunteers. The Cairngorm Mountain Rescue Team costs pounds 20,000 to run each year

The Scottish Avalanche Hotline is 01463 713191 or can be accessed on the Internet on htpp://www.dcs.gla.ac.uk/other/ avalanche/

If you would like to make a donation to the Cairngorm Mountain Rescue Team, send it to: The Cairngorm Mountain Rescue Association, Achantoul, Aviemore, Inverness-shire, PH22 1ZW