Monthly Archives: November 2011

Sunday, November 27, 2011

A few inches of new snow this week has made a small improvement to the skiing quality. On the wind slabs dust on supportable crust conditions exist and in some places a little deeper, but you still feel wind board underneath. In very isolated and protected patches, mostly North, you can find powder skiing. The new snow has also covered up thin rocky areas that were previously scoured hiding rocks and turf.

BOTTOM LINE:

Natural and human triggered avalanches are unlikely.

Assessment expires in 24 hours.

TREND:

Increasing with new snow and wind expected Tuesday through Wednesday.

DISCUSSION:

No new natural avalanches have been observed in at least 5 days to a week. If you have seen any action please email, jedworkman@hatcherpassavalanchecenter.org. The last cycle was brought on by wind deposition and the snowpack has adjusted to it. Some small avalanches were released during this cycle in the range of R1D1. Recently some cracking has been observed underfoot around your boots, but whumphing and shooting cracks are rare. While we can never say that it would be impossible to trigger an avalanche, we can assess the likelihood.

Wind slabs are in high variety these days. You can find 2 cm breakable to 5 cm supportable near the surface or you can find 30cm wind slabs buried mid-pack. In some starting zones and bowls near ridgelines you can find even thicker slabs. A simple pole test indicates slab presence. You should inspect further for bonding and most important right now, how consistently thick and wide is this slab over the terrain you want to enter?

All of these slabs are sitting on weak structures. In most cases the weak underlying structure is a very thick layer which has very little energy. This means triggering a slab could occur, but that it will be limited to a small size and may not even run. Some of the slabs nearer to the surface are thinner and sit on thin weak layers that could propagate further producing wider avalanches, but again the likelihood is small. The spatial variation is high and the energy is low which are in your favor.

What to watch out for:

1. A small slab that could carry you over a cliff. Avoid double exposure or more, ie: don’t cross a slab over a cliff.

2. Uniform, large slabs, in steep terrain. Inspect their bond to the underlying layers for strength, structure and energy through stability tests and hasty tests. Recognize that more expansive, thicker slabs pose greater consequence if triggered. Right now the hazard is lower, but with the addition of a new snow load this can change quickly. Watch the weather for Tues-Wed snowstorms.

 

Daniel, Upper Eldo, Nov 27 2011

-Jed Workman