Skiing to disaster?

High above Courchevel, in the Trois Vallées in France, lies my favourite ski run, Creux. I have skied it almost every year for the past eight years, in brilliant sunshine, heavy snowfall, fog and bitter wind, and every time it brings me deep, unfettered pleasure. Vast, wide and long, starting on a vertiginously angled plateau and ending, via a series of shadowy bowls, in a long, meandering boulevard between dark fir trees, Creux has almost everything: elevation, pitch, length, a variety of terrain, and breathtaking views.

In the evenings, from the dining-room of our hotel in Courchevel 1850, my husband and I like to watch the winking lights of the piste-bashers. These vast, wide machines (which look, with their caterpillar runners, like a cross between army tanks and combine harvesters) make their way up the mountain to restore the pistes for the following day's skiers and snowboarders.

But often we have wondered, when watching the machines' steady progress up the blackened mountainside: how many of them are actually out there? How much do they cost and how much fuel do they use? And how long does it take, for example, to groom our beloved run, Creux? The meticulous care of the slopes for which the Trois Vallées ski area is rightly renowned consumes a substantial part of the price of your ski pass. But what are the costs (both financial and environmental) to the local area, and to the Alps as a whole? What price the pleasure of our annual sporting luxury?

After several years of speculating, we decided to find out. So we went to the Société des Trois Vallées main office, and managed to speak to the person in charge, Gilles Bianchi, the chef de damage (damage comes from the verb dammer, meaning to tamp down). Could we, we wondered, perhaps accompany a driver on a route up the mountain at night? We were fascinated by the process and the mechanics of slope-grooming. "Pas de problème," said Bianchi.

So at five the following afternoon, we met at the office and were introduced to Jean, an experienced driver who is in charge of coordinating much of each night's work. It was Jean who would take us up the mountain and explain to us what he did, bringing us down again at nine, when he took a break for supper.

The machine into which we climbed is known to the British as a piste-basher; in French it is a chenillette. Jean's chenillette had two squashy seats, with suspension. One for him, obviously, and one, it turned out, for my husband, as he's bigger than I am; I was the only one of us small enough to perch on the dashboard. Not comfortable.

Jean's window was open, ostensibly to let in fresh air, but the chenillette's chimney was not far from it, and all that came in was potent diesel fumes. It was also incredibly noisy, like being stuck right in the midst of busy road-works. We had to shout above the grind and clamour of the engine.

At the front of each chenillette is an array of heavy-duty attachments. The most frequently used is the wide scoop, which works like a giant shovel, gathering loose snow from the piste edge and pushing it back on to the slopes in enormous mounds. The process is called remonter la neige, which translates as pushing the snow back uphill. You don't think about why until Jean points out that when skiers ski, they bring all the snow downhill with them, or push it to the sides of the piste.

In tandem with the scoop, Jean skilfully operated two fin-like attachments at either end of it - a bit like flippers on a pinball machine - that angle the snow precisely, depending upon where it is most needed. Once the snow has been relocated, the chenillette is driven over it, tamping it down beneath its aluminium caterpillar tracks, while at the back of the machine giant combs are dragged through the newly ploughed snow, smoothing it out into wide, gently rippled tracks - absolutely perfect for skiing on. All the operators of the chenillettes are highly trained technicians, and most of them are experienced skiers and mountaineers: they know exactly how the snow should be.

Nothing, it seems, is too sheer or too awkwardly angled for the chenillettes. The machines are so designed that even on the steepest slopes it is almost impossible for them to slip or flip. There has been, to date, not a single accident in the Trois Vallées involving a chenillette. I was still concerned, however. There is a run in the Courchevel valley called M, which is so steep I couldn't imagine any vehicle, however brilliantly designed, being able to tackle it safely.

"Surely you can't drive up and down M all that easily," I said to Jean.

"Non," Jean agreed, adding, with typically Gallic nonchalance, "c'est difficile," and he explained that there are, dotted around the valleys upon the most precipitous slopes, 220 anchorage points to which the machines can be attached.

The Trois Vallées is the largest ski area in Europe, and its slopes are thought to be among the most well-maintained and beautifully groomed in the world. Courchevel is just one part of the Trois Vallées, and it incorporates its lower neighbour, La Tania. The other two valleys are that of Meribel and Val Thorens. In the Courchevel-La Tania area there are 140km of runs, amounting to 528 hectares of piste. In this area, all night, every night, 21 chenillettes are driven by 41 drivers, working separate shifts either between 5.30pm-1am, or 2am-9.30am. Each machine costs around €250,000 (about £145,000), and uses 25-30 litres of diesel per hour, during which time it can thoroughly groom two hectares of slope.

The numbers are staggering. Each hour of preparation in the Courchevel area (during which time 42 hectares will be groomed) uses £3.5m worth of machinery and consumes 577 litres of fuel - enough to drive a Land Rover from the UK to East Africa.

These statistics may alarm you but they are only a small part of the picture. The ski lifts, bubble and cable cars use huge quantities of electricity every minute in order to haul skiers, snowboarders, and our equipment, up the mountains, although, to be fair, some of this electricity is hydrogenerated. But in the Courchevel area of the Trois Vallées there are also 562 snow cannons, responsible for the creation of 142 hectares of artificial pistes and the refreshment of patchy or icy runs. Where do they get their water from? Not from fast-flowing rivers, but from lakes and streams, a practice which is fast having a negative impact on the balance of local plant and animal life. In some places it may even be desiccating the permafrost, making deep snow less stable and avalanches more likely.

Reaching the resort also takes its toll; most British skiers fly to their destination, whether in the Alps or the Rocky Mountains.

So, will we be skiing this season? After all, I turn off my low-voltage lights, recycle my rubbish, cycle everywhere I can, and buy organic food. I support Water Aid and Friends of the Earth. And I now know that it takes two chenillettes eight hours each to prepare Creux every night.

How unfettered the pleasure of that beautiful run now, I wonder? Well, I am afraid that, despite our better judgement, we will be skiing this season. Our eldest daughter, who is five, will be having her first lessons. The question is: will there be a healthy and sustainable Alpine environment for her to admire, wonder at, and ski in, when she's our age? I sincerely hope so. But if there isn't, will we not be partly to blame?

Mary Loudon's new book, 'Relative Stranger: A Life After Death' is published by Canongate on 2 March, price £16.99

TRAVELLER'S GUIDE

GETTING THERE

Geneva is the most convenient hub for the Trois Vallées. It is served by easyJet (0905 821 0905; www.easyJet.com), Bmibaby (0870 264 2229; www.bmibaby.com), British Airways (0870 850 9850; www.ba.com), flyglobespan (0870 556 1522; www.flyglobespan.com), Swiss (0845 601 0956; www.swiss.com), Jet2 (0871 226 1737; www.jet2.com) and FlyBe (0871 700 0123; www.flybe.com). A more environmentally friendly option is the train (08701 244646; www.rail europe.co.uk/snowtrains), which serves the Trois Vallées from London Waterloo, Ashford or Folkestone via the Eurotunnel to Calais or the Eurostar to Paris.

MORE INFORMATION

Les Trois Vallées (00 33 4 79 08 20 00; www.les3vallees.com).

Courchevel 1850 (00 33 4 79 08 00 29; www.courchevel.com).

La Tania (00 33 4 79 08 40 40; www.latania.com).

Meribel (00 33 4 79 08 60 01; www.meribel.net).

Val Thorens (00 33 4 79 00 08 08; www.valthorens.com).

Société des Trois Vallées ( www.s3v.com).