Avalanche season: Stay informed of the risks

Published: Thursday, Dec. 13, 2007 12:11 a.m. MST
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Avalanche warnings are typically high after big snowstorms. Right now, they may be a little higher than otherwise expected, thanks, in part, to those early October storms.

The avalanche warnings on high-elevation, northern-facing slopes over the weekend were high. Warnings could well remain higher than usual for the next couple of weeks, and possibly longer, because of the early snow.

Typically, snow surfaces stabilize within a few days following a storm.

The October snow, however, followed by warm temperatures, created a weak base, which is the catalyst for a life-threatening avalanche.

"We do have a weak underlying snow structure that will plague us for at least a couple more weeks or longer, depending on what the weather pattern ends up doing to it. What we have now at higher elevations is an overloading on the weaker snow," said Brett Kobernik, avalanche forecaster for the Utah Avalanche Center.

"A lot of people at this time are starved for snow. Now, with the big snowfalls, people want to get out and enjoy the winter, but they need to be tuned into rising avalanche dangers."

The most dangerous time is immediately following storms. A new snowload sitting on an older base is a perfect recipe for an avalanche.

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As the upper level compresses and fuses with the lower level, the threat of an avalanche is reduced. It's either that or the snow slides, and with it goes the avalanche threat.

Because of current conditions, forecasters will be spending more time checking snow conditions at higher elevations, "paying very close attention to the weaker level."

The greatest protection people have against being caught in an avalanche is learning all they can about avalanches.

There are five levels of avalanche danger — low, moderate, considerable, high and extreme. The danger last Friday rose from considerable to high. The extreme rating, said Kobernik, is seldom called for.

When avalanche danger is high, only those with excellent route-finding and avalanche skills should even attempt to go into the backcountry. Those who are unsure of their backcountry skills should stay on fairly level ground until the threat passes.

Skiers, snowshoers and snowmobilers should know that there are two types of avalanches — loose-snow and slab. Slab avalanches are the greatest threat to backcountry adventurers.

They form on slopes as a result of wind, falling snow and changing temperatures.

When high winds pick up snow from the windward slopes and deposit it on the leeward side, the snowpack, in most cases, forms a dense layer, or slab, that will not successfully bond with the old snow layer.

As conditions stand now in some areas of Utah, new snowfall supported on a weaker layer creates this slab condition. And rapidly changing temperatures, causing a freeze-thaw effect, can create a slab that can break loose.

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Mike Terry, Deseret Morning News

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