An avalanche that carried two Whitehorse residents down the clay cliffs this week buried one of them up to his chest.

The man was six feet, two inches tall, a local avalanche expert points out.

Kirstie Simpson said in an interview today that Tuesday evening's slide at the end of Main Street had the potential to cause injury or worse, as it does every year when conditions are right.

It was some 30 years ago when a child died months after he was dug out from an avalanche at the end of Black Street, having never recovered from the coma he lapsed, Simpson recalled.

'It is a place that kids should not be playing,' she said of the area at the end of Main Street and other avalanche zones along the clay cliffs.

'They are basically playing in avalanche terrain, and at this time of year, there are concerns up there, and there is a snow load.'

Of particular concern, she noted, are the areas along the bluffs that are unprotected by trees at the top and are instead open to snow loads being transported by winds blowing across the wide expanse of the airport.

On average, she said, there are 45 centimetres of snow in the Whitehorse area at this time of year. The depth of the snow where Tuesday's avalanche occurred was five times that, or 2 1/2 metres on the leeward side of the clay cliffs, Simpson pointed out.

She said the high snow load, together with three extreme fluctuations in weather since November, has left the snowpack unstable and ripe for avalanches.

The clay cliffs present avalanche danger and always have, she said.

She checks them every day or two through the winter as a matter of routine to get a feel for the stability of the snowpack along there and likely in the surrounding mountains.

Chances are high, Kirstie said, that if there is instability along the clay cliffs right now, there is instability in the mountains on the avalanche-prone slopes.

A qualified avalanche instructor who provides training courses, Simpson said the two key principles to know about avalanches are:

ï they occur on a slope angle of between 30 and 45 degrees, with their favourite angle being 38 degrees. Tuesday's avalanche at the end of Main Street occurred on a 38-degree slope, Simpson pointed out.

If you are on a slope of 25 degrees, she said, you're OK, unless there is a slope with avalanche potential above you.

ï the danger of avalanche is also found where there is significant wind loading of snow, she said.

Snow, said Simpson, is like water; you can never say it is safe, but you can say when the danger or the risk increases.

And with what she describes as three extreme weather fluctuations since November, the risk or danger are there, she said.

Simpson said at one point there was a 50-degree shift in temperature in a matter of a couple of days over Christmas.

Whenever that occurs, it's accompanied by furious winds, she pointed out.

The ingredients for Tuesday evening's avalanche included a metre-thick slab of wind-blown snow sitting on a weak crust of ice formed by the record-breaking warmth recorded Dec. 23, a day before the winds pushed the mercury downward at the speed of sound.

A good portion of the build-up of snow on top of the unstable crust likely occurred in the those short couple of days when the wind was wild, she said.

The clay cliffs, however, are by no means the only local threat.

Over the years, Simpson said, there have been a number of avalanche incidents in the city, such as the man who was buried by an avalanche at a quarry near Lobird about a decade ago. He was dug out alive, though unconscious.

There were probably five avalanche incidents in the White Pass last winter that she has heard of, involving people who were partially buried skiers, snowboarders and snowmobilers.

Simpson said there'll be some avalanche awareness activities next Friday, Saturday and Sunday, as part of Avalanche Awareness Day across the country.