Avalanche beta from the Breckenridge Ski Patrol

Local snow safety experts discuss avalanche control and backcountry safety

As the CAIC likes to emphasize regarding early season avalanche hazard, if there's enough snow to even think about skiing, there's enough snow to avalanche. During early season avalanche control work in closed terrain on Breckenridge's Horseshoe Bowl, early season hazard in the Continental snowpack is easily illustrated. The first shot in 'Lulu' produced no results. The previous night's snowfall measured only 4 inches. Is that enough snow to produce hazard? What if, during and after, moderate winds blew?

By Matt Krane

As part of its community outreach and continuing education, the Breckenridge Ski Patrol’s snow safety department presented the first of five lectures on avalanche safety, snow science, and snow sense last Thursday in the Forest Room at The Village conference center.

In a survey, more than a few attendees raised their hands as first-year residents of the county, with more identifying themselves as second-year veterans.

Breckenridge Ski Patrol snow safety supervisor Will Barrett said — not unsympathetically — “Boy. You folks who got here for last winter are in for a surprise. That was not a normal winter.”

What we experienced last winter was an anomaly; extensive snowfall over almost 7 months that originated in the warmer, more moist Pacific Northwest region, according to avalanche technician Andy Lapkass.

This translated into basically a Maritime snowpack (think Cascades, Sierra) which is much more stable than the avalanche-prone Continental snowpack of the Central Rockies.

Our snowpack tends to be colder, drier, less consolidated, and very prone to the formation of faceted grains — unstable crystals that cannot hold the weight of successive snowfalls and windslabs reliably. To underscore this, Lapkass quoted historical data: From 1950-2007, there were 221 avalanche fatalities in Colorado, with 36 in Summit County. Alaska was second, with 122 deaths.

Faceted grains provide ideal failure layers and possess weak shear strength. In a continental snowpack, these grains appear as basal facets (depth hoar) as well as near-surface facets (surface hoar). With cold temperatures and more extreme temperature gradients within the snowpack, these “persistent weak layers” make avalanches hard to predict. Add to that the constant wind events we experience in the Ten Mile Range, and you have have large, high-consequence hard slab avalanches during active cycles, NOT just after a storm cycle, as in the Maritime or Intermountain (Utah) regions.

A second shot, not more than 100 feet to the north. The 4 inches that fell the night before with moderate winds turned into 15-20" of moderate hard slab which fractures easily more 100 feet wide into 'Humbug'. Note the patroller on rocky shelf above the smoke and, at lower left center, how the very bottom of the slab begins to break up. This early season slide ran close to 500 vertical feet, yet it ran on an older snow layer, possible from October, and did not go to ground.
The third shot produces a slightly larger slide in 'Humbug' and 'Tower 18 Gully'. Note at upper left how this deeper fracture involves multiple layers of snow, exposing the ground layer. Even this hard slab breaks up into 'dust' and becomes airborne on its way to the runout zone.
All of these factors are multiplied in the backcountry, where there is obviously not the benefit of avalanche control work and in most cases, skier/rider compaction.
Within the ski area boundaries, snow study, snow science, avalanche prediction and control work are ongoing to provide a safe experience on the steep upper reaches of the mountain.

Breckenridge includes 1,000 acres of avalanche terrain, most of which must be managed throughout the winter. Early season hazards, such as on the north side of Peak 9 and the south side of Peak 10, are mitigated by skier compaction. Upper terrain Such as Peak 7 and Snow White will often see explosives after just a wind event.

Lapkass explained that backcountry travel requires as extensive an analysis: he urges the use of the “Avalanche Triad” among other things to identify hazard.

Think of it as an equilateral triangle with these three categories at it’s points: terrain, weather, trigger. Our goal always, he insists, is to NOT be the trigger. To analyze terrain, identify and consider slope aspect (north, south,east and west); angle (30-45 degrees is most active)’ elevation contour (convex-concave); anchors, and trigger points.

Weather means not only snowfall, but wind trends during storms, and temperatures from the onset to finish. High winds can load a slope ten times faster than the snowfall rate alone.

So, if snow falls at a rate of 1 to 2 inches an hour for a number of hours, think of the snow load up high. Most transport happens within the first few hours after a storm, but snow plumes can be seen on the wind in the Ten Mile for more than a day after. If any one of these points raises a flag, find something else to do that day.

Possibly the best snow stability evaluation one can make can be done without digging pits or running computer profiles. Look around you. Is there evidence of a recent natural avalanche cycle?

What is nature telling you about the slope you want to ski? Aside from fresh slides on adjacent or similar terrain, is there any cracking or whoomphing beneath your skis (or split-board)? Have cornices grown? Then ask yourself, could I trigger this?

Lapkass urged everyone to develop their own process for snowpack stability evaluation. Keep a book, using field notes to record threshold values and trends.

Resources like field books and checklists are available from organizations like the American Institute for Avalanche Research and Education. Contact them for course schedules, field book, and visit the organization’s Facebook page.

Barrett added some perspective on inbounds vs. backcountry terrain. Within the ski area, he explained, the ski patrol accepts and mitigates risk for you, adding that it appears as though we will be in early season conditions for a while.

If you wonder why you hear blasting when there has not been snowfall in some time, the ski patrol is constantly assessing the ever-changing snowpack, wind loads, trying to keep the snow we have, while mitigating hazard.

“We are really trying to stabilize and save the snow we have right now,” Barrett said. “We are massaging the snow, manipulating our persistent weak layers, breaking up the slab.”

A catch phrase you may begin to hear more and more is shear plane disruption. Disrupting weak layers and slabs with explosives, boot-packing, ski cutting (typewritering), and compaction is commonplace at Breckenridge during early season.

The Tenmile Range viewed from Baldy in May 2011 with a near-record snowpack.

Last winter, stable and plentiful as it was, the Breckenridge Patrol used more than 6,000 pounds of explosives — imagine what a normal winter might require.

With this first lecture (free pizza and cash bar), a rapt audience received a great deal of practical knowledge as well as a very understandable introduction to snow science. Even more information will be disseminated at the next gathering on December 22 (same time and place), and on the third Thursday of each month thereafter.


One thought on “Avalanche beta from the Breckenridge Ski Patrol

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s