May 25, 2003 

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Forecasting Danger
April 25, 2003

avalanche
image: ABC News
Earlier this year, fourteen people died in the Revelstoke area of British Columbia in two avalanches that took place two weeks apart. In the United States, an average of 20 die each year, and that number has been increasing.

As shown on PBS’s NOVA, an avalanche happens when a slab, or new layer of snow, weighs down so heavily on a weak layer of snow that the weak layer collapses, causing part of the new slab to break off and slide down the mountain. Avalanches are most common on steeper slopes, such as those over 30 degrees, and can travel faster than 100 mph. Not all avalanches are dangerous; it is the slab avalanches, the big masses of snow that move along the ground, that are the biggest threat.

Most avalanches are triggered by the victims themselves, or someone in the victim’s party. “Avalanches don’t happen by accident, they happen for particular reasons,” Jill Fredston, co-director of the Alaska Mountain Safety Center, Inc., told PBS’s NOVA. “It’s the interaction of terrain and snowpack and weather that make it possible to have an avalanche. But there’s no avalanche hazard until you introduce people. It's the human factor. And really, it does come down to attitude. We're going to accept a different level of risk if we want to just go out snowboarding for the day and come back and live for another day. We're going to have a different level of acceptable risk if we want to climb this mountain no matter what. And if you have a ‘ski to die,’ or ‘snowboard to die,’ or ‘I'm going to live here no matter what’ [attitude], probably sooner or later, you will die in an avalanche.”

micropenetrometer
image: Doug Chabot, US Forest Service
Karl Birkeland, an avalanche scientist with the U.S. Forest Service's National Avalanche Center in Bozeman, Montana, says that the average number of deaths in the U.S. from avalanches is increasing. “It looks like we are up to 27 in the U.S. this year, and we are probably not done yet. Our average in the 1990s has been inching toward about 30. We have seen a general increase in the number of fatalities this past decade over previous decades due to increased recreational pressure in the backcountry, especially by snowmobilers on newer sleds able to access more dangerous avalanche terrain.”

But new technology may be leading to better avalanche forecasting, and fewer deaths on the slopes. Birkeland is the co-principal investigator for a two-year study funded by the National Science Foundation to measure how snowpack changes through time. Birkeland and his team use a snow micropenetrometer called the SnowMicroPen, a motorized probe with a small sensor at the tip that can measure how much resistance it takes to get through the varying layers of snow in a snowpack, revealing the strength of each snow layer on the microscopic level. The device makes about 250 measurements per millimeter, and stores the detailed data on a computer.

The information the avalanche scientists are gathering from the probe about snow stability will improve their ability to forecast avalanches in the future, which will lead to safer snow-filled vacations. “We hope to give people the tools to make better decisions in the back country which will hopefully save lives,” says Birkeland.

The SnowMicroPen was co-developed by the U.S. Army Engineer Research and Development Center Cold Regions Research and Engineering Laboratory and the Swiss Federal Institute for Snow and Avalanche Research.



by Karen Lurie


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