The Physics of Snow Is Helping Scientists Predict Catastrophic Avalanches

The slightest temperature change can turn a slow-moving avalanche into a deadly disaster, research shows.

Avalanches are dangerous.  In the United States alone, between two and three dozen people die each year due to avalanche events — most of them being recreational accidents.  The winter season, particularly December to April, is when most avalanches tend to happen. However, avalanche fatalities have been recorded every month of the year.

In order to avoid such tragedies, scientists are studying the fundamental physics of avalanches.  More specifically, they are researching what causes snow particles to clump together and how they interact as they move downhill.

An avalanche is composed of three main parts: starting zone, track and runout zone.  The starting zone is the most unstable part of a slope, which is often where the first amount of snow starts to move downhill.  However, given the right conditions, snow can fracture at any point.

The avalanche track is the path it follows as it travels downhill.  One of the primary indicators that an avalanche has occurred is swaths of missing trees or smaller trees surrounded by larger ones, and a pile of snow and debris at the bottom of the slope — the region defined as the runout zone.

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In the Swiss valley, scientists built the world’s most advanced avalanche research center where they trigger avalanches and monitor them with cameras, radar systems, pressure meters, and other high-tech instruments.  

Although there are several factors that affect the probability of an avalanche, including weather, slope, wind direction, snowpack etc., the researchers were most surprised at how a slight temperature shift profoundly changed the shape of an avalanche.  For example, a small drop in temperature could turn a slower-moving “wet” avalanche to a faster and more deadly “dry” one, which can have the force of up to 100 onrushing cars.

“Avalanches can have different flow forms, which is why they can do lots of different things,” said Perry Bartelt, an avalanche engineer at the WSL Institute for Snow and Avalanche Research SLF in Davos Dorf, Switzerland.  “That makes a big difference when you’re talking about how to protect yourself.”

This data is also being used in models to predict avalanche danger.  Recent computer simulations have shown that incorporating new types of particle motions — including snow particles acting like gas molecules in the atmosphere — improved the predictions of how far and how fast an avalanche will go.