January 19, 2012

IDPR Urges Caution As Avalanche Danger Increases




Avalanche danger has been moderate to considerable in many Idaho locations with the little snowpack that currently exists. The Idaho Department of Parks and Recreation (IDPR) urges snowmobilers and backcountry skiers to use caution as they head out to play. Incoming precipitation will likely increase the instability that currently exists by adding additional stress to a faceted snow base.

“Anyone heading outdoors to recreate in the fresh snow needs to take special precaution,” Rich Gummersall, Outdoor Education Coordinator for IDPR, said. “What exists out there currently is a base layer with no bonding properties with an ice layer sitting on top due to warming and rain showers. The incoming precipitation will add additional weight, which will increase the stress on the snow pack. The fresh snow will be deceiving and the perfect composition for avalanches.”

IDPR encourages you to know the capabilities of yourself and your equipment and familiarize yourself with terrain, snow and weather conditions. They also encourage people to carry and know how to use proper rescue gear, take an avalanche awareness course and visit avalanche.org for current forecasts.

The Idaho Department of Parks and Recreation (IDPR) offers free snowmobile-centered avalanche awareness courses throughout the state. Avalanche awareness training provides snowmobile riders with the information needed to make informed decisions.

Visit www.parksandrecreation.idaho.gov for additional information on IDPR sponsored avalanche classes and to locate a course taking place near you.

Avalanche Information

To avoid being caught in avalanche terrain, you could avoid it all together or roll the dice and hope for the best. However, you can also learn about avalanches, which helps minimize your risk.

Most large avalanche paths are obvious: an open slope, bowl or gully above timberline that leads to a swath through the trees. However, small avalanche paths in the trees can be just as dangerous. Slope angle is the most important factor, so you should carry a slope meter. You also need to observe snow deposition patterns and the effects of anchors such as rocks or trees that might prevent avalanches on some slopes. Finally, bent or damaged trees are good clues that show where avalanches have run in the past.

You can receive avalanche training from the Idaho Department of Parks and Recreation. There are also several avalanche centers where you can be trained: Sawtooth Avalanche Center, Payette Avalanche Center and Panhandle Avalanche Center.

Avalanches are caused by a steep slope, unstable snow and a trigger. An avalanche occurs when the stress (from gravity) trying to pull the snow downhill exceeds the strength (from bonds between snow grains) of the snow cover. The trigger for an avalanche can be human, animal or weather. As recreationists, we need to ready, willing and able to make safe travel decisions.

Avalanches only happen when the slope is steep enough. Generally slab avalanches can occur between 25 and 60 degrees, but most slab avalanches occur with starting zones between 30 and 45 degrees. Above 60 or below 25 degrees, the stresses on the pack from gravity typically are not enough to cause the snow to slide. The same is true above snow sluffs.

Avalanches only happen when snow conditions are unstable. When the snow cover is very unstable, nature often broadcasts clear danger signs. Fresh avalanches are the best clue. Snow that cracks, collapses or makes hollow sounds is also unstable. Weak layers that are found by digging snow pits are signs of unstable snow. Snow that has become wet from thaw or rain can also be dangerous. Even if you find no signs of unstable snow, you should always travel using the techniques listed above to minimize risk.

In order to travel safely, you try and stay updated with recent snowpack stability information. Since conditions in the backcountry can change daily, even hourly, it is important that you also make your own assessment for any given slope. Avalanche centers can provide you with information about previous snow and wind events, buried weak layers and general concerns. So, be sure to visit www.avalanche.org.

In addition, every snowmobiler and backcountry recreationist should carry a pack with three days emergency supplies, a probe, shovel and an avalanche transceiver (beacon). Most importantly, they should be comfortable using their rescue gear.

You can reliably avoid avalanches by recognizing and avoiding avalanche terrain. Travel at the valley floor away from large avalanche run outs, along ridge tops above avalanche paths, in dense timber or on slopes of 25 degrees or less that do not have steeper slopes above them. Avoid cornices on ridge tops.

You cannot entirely eliminate risk if you travel in avalanche terrain, but you can minimize risk by using good technique, such as: climb, descend or cross avalanche areas one at a time; cross a slope at the very top or bottom if possible; climb or descend the edge of a slope rather than the center; carry and know how to use avalanche rescue gear and turn back or alter your route if you detect signs of unstable snow.

Over the last five years, there have been 13 avalanche incidents in Idaho, 11 of which were snowmobilers. Nationally, over the last five years there have been 83 snowmobile and 39 skier fatalities. 85 percent of avalanche victims will survive if recovered within 15 minutes and 25 percent of avalanche victims die of trauma incurred during the slide.

Surviving avalanches can depend on luck; therefore, it is always better to avoid them in the first place. Only 1 of 3 victims buried without a beacon survives. If you are caught, first try to escape to the side or grab a tree or rock. Swim with the avalanche to try to stay on top and avoid trees. When the avalanche slows down, reach the surface or make an air pocket.

The avalanche danger increases with major snowstorms and periods of thaw. About 2,300 avalanches are reported to the Avalanche Center in an average winter. More than 80 percent of these fall during or just after large snowstorms. The most avalanche-prone months are, in order, February, March and January. Avalanches caused by thaw occur most often in April.

Almost all avalanches occur on slopes between 35 and 45 degrees. Slopes less than 30 degrees seldom produce avalanches and slopes steeper than about 50 degrees sluff, so they often do not build up into slabs. It’s the intermediate slope steepness that produces most of the avalanches. The bad news is that the kind of slopes we like to ski, snowboard or snowmobile usually produces most of the avalanches. A black diamond slope at a ski resort is usually around 35 degrees—prime steepness for producing avalanches.

Visit www.parksandrecreation.idaho.gov for additional information.








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