Juneau Area Avalanche Advisory
2006-03-09
Eaglecrest - Showboat - Troy Areas
by Bill Glude, SAAC Observer
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We are traveling out of town to teach courses most of the time until the 21st, but we managed to squeeze in a brief field check today between the heliguides course in Haines and travel tomorrow to teach two courses in Southcentral Alaska.

The new snow that fell over the last few days is as expected, highly unstable due to the underlying sugary faceted grains and icy melt-freeze crusts. But we saw no natural releases yet, even on the Juneau urban and Thane Road paths. The forecast NE winds are likely to trigger a natural cycle in the next few days though, and this snowpack will be extremely sensitive to additional snow or rain.

Until the winds, new snow, rain, or thaw arrive, the danger is that spring sunshine and the first good powder snow in some time will lure people out into a snowpack that is very easily human-triggerable. The weak layers are persistent types that do not settle out and bond rapidly. These faceted layers often remain weak for three to six weeks.

It is a particularly dangerous situation because many people perceive this as a low-snow winter and think of avalanches as a problem only when there is lots of snow. In fact, thin snowpacks develop grains that are much weaker when loaded than thick ones do.

Take extra care to stay off steep slopes of any size and avoid terrain traps and runouts of slopes above. If the wind kicks up or there is new snow, thaw, or rain, you should stay home, go skating, or ride inbounds at Eaglecrest.

Though snow volumes in the starting zones of the larger mainland paths are still small, the fast icy bed surface and snow to sea level make it possible that runouts may reach developed areas if we have enough new or wind transported snow, new snow, or thaw.

Take care, we will not be here to advise you or to rescue you for a couple weeks. You're on your own, if you go into the backcountry choose the lowest risk terrain you can find and treat every steep slope and roll as though it will slide.

Field Notes
Photos
Though we saw no natural releases even on the Juneau urban and Thane Road paths, explosive and ski cutting work by the ski patrol produced some sizable slabs like this one on Steep Chutes today. We also heard of at least two skier-triggered slabs over the last two days, one of which reportedly caught and carried a person who escaped unhurt.
Telemarker Marc Scholten enjoys the good powder at Eaglecrest today. The combination of highly unstable and easily triggerable snow with good surface conditions and sunny weather makes this a very likely time for human-triggered avalanches in the backcountry. The instability is persistent and will not just settle out in a few days like many weaknesses in the snowpack in this region often do. It is likely to remain triggerable for some time, and new snow, wind transported snow, or thaw will probably produce a cycle of natural releases.
Mt Troy shows rippled snow textures where the SE storm winds loaded the slopes from right to left. Windloaded areas like these are very likely to release if ridden now.
An explosive charge placed by the Eaglecrest Ski Patrol goes off high on Lindh's chute in the East Bowl.
As the smoke clears, the crown face of the slab the charge released can be seen below the patroller on the right, extending all the way across the top of the chute. Debris extends beyond the lower left edge of the photo.
The top few centimeters on sunny aspects were wetting in the afternoon and crusting lightly later as clouds moved in. Meltwater dripping off the trees wetted the snow in this photo.
Slab tests on the new snow produced very sensitive #1 results (SLAB 1). The slab ripped out rapidly into snow beyond the undermined area. This indicates that the slab propagates fracture well.
Slope tests on small steep rolls produced mini-slabs like this one.
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