Winter is back and people are flocking to the mountains for fun in the snow. But avalanches are a constant threat during the winter, so before you start exploring the back country outside the boundaries of your favorite ski resort, make sure you know how to stay safe.

According to Bruce Tremper, director of the U.S. Forest Service's Utah Avalanche Center, Utah averages about 100 unintentional, human-caused avalanches a year. About 20 people get caught in those avalanches each year, resulting in an average of four fatalities.

However, the overwhelming majority of these avalanches are avoidable, Tremper said. Contrary to the conventional wisdom, avalanches are not caused by noise. The trigger in almost all human-caused avalanches is the weight of a person on an unstable snowpack.

Avalanche conditions are caused by snow packs forming on weak layers of snow beneath them. When enough weight is applied, Tremper said, the snowpack fractures and shatters like a pane of glass.

"It's extremely weak snow that's kind of like a pile of potato chips or something like that. And then all the snow that we got last weekend is kind of like putting a brick on top of a pile of potato chips," Tremper said.

The first step to avoiding avalanches is knowing how to identify avalanche terrain. Tremper said avalanches generally occur on slopes of 35-45 degrees, in areas where there are no trees or large rocks to anchor the snowpack.

This type of terrain can be safely traversed about 95 percent of the time, Tremper said. The key is knowing how to spot the dangers the other 5 percent.

Tremper said there are five things people should check for to assess avalanche dangers: recent avalanches on similar slopes; avalanche-inducing weather such as recent snow storms or strong winds, which can deposit snow 10 times more rapidly than a storm; visible collapsing or cracking in a snowpack; thawing snow caused by winter rain or warming spring temperatures; and advisories by organizations such as the Utah Avalanche Center.

Avalanches generally occur in back country areas, a lesson learned by one snowboarder on Thursday who was partially buried in snow after leaving the boundaries of the Brighton Ski Resort. Ski resorts manually trigger avalanches within their boundaries to eliminate the threat, but anything outside the boundaries can be questionable, Tremper said. Oftentimes, there are few obvious signs of avalanche dangers in these areas, but there will usually still be visible fracture lines from previous avalanches.

"These avalanches kind of sit there, waiting for a trigger to come. ... That's what happened at Brighton," Tremper said. "A lot of folks get in trouble because visually it doesn't look any different. It just looks like nice powder."

Tremper said most avalanche accidents can be avoided by taking three essential steps. The first is to always carry rescue gear such as beacons, shovels and probes any time you go into the back country. Secondly, if you must cross avalanche-prone terrain, do it one at a time. That way, the risk to the group is minimized, and if there is an avalanche and someone needs rescuing, there are others there to help. If a person is buried in snow, it takes only 15 minutes to die by asphyxiation, so rescuers must work quickly.

Tremper's third tip is, once again, to always check avalanche advisories. These can be found at www.utahavalanchecenter.org, or on the organization's toll-free phone line at 888-999-4019.

The avalanche threat in Utah County is relatively low right now because the area hasn't seen much snowfall, according to Utah Department of Transportation spokesman Geoff Dupaix. Every winter, UDOT, the Utah Highway Patrol and the ski patrol at Sundance Ski Resort undertake avalanche control work on U.S. Highway 189 in Provo Canyon, but such measures have not been necessary yet.

But the need for avalanche control is imminent. On Wednesday, UDOT conducted a "dress rehearsal," Dupaix said, coordinating road closings and testing target coordinates where the department fires its howitzers to trigger avalanches before they get triggered by something else and bury a critical highway.

"The conditions aren't to the point where avalanche control work was needed," Dupaix said.

• Jeremy Duda can be reached at 344-2561 or jduda@heraldextra.com.