| Posted: 8:03 a.m., Sunday, February 25, 2007 |
Huntington Ravine has LOW avalanche danger. Natural avalanches are very unlikely and human triggered avalanches are unlikely except in isolated pockets. Normal caution is advised.
Yesterday was a great day for us to get up into the Ravine to do some field work. Based on yesterday's observations, today's stability issues are centered on the greater Lip area, including the Sluice. The Lip and Bowl are posted at "Moderate" today. As you move farther from this area there a gradual transition to "Low". What this means is that just because Right Gully and the Headwall are posted as Low does not mean avalanche danger is nonexistent. In the Lip and surrounding areas, there is a surface slab that is fairly stiff but varies in thickness. Underneath this is a thinner and slightly softer layer. Below that it goes back to stiffer slab. Most of this top layer is thick and strong enough that your stepping onto it won't impact the weaker layer below enough to trigger a slide. However, in places where it's thinner, or if you were to fall while skiing, your impact has a higher likelihood of reaching a weak layer and initiating a fracture. My guess is that you don't want to find yourself in this situation. How thick is thick enough to alleviate concerns about stability depends a lot on the density and strength of the snow. This is where your ability to assess what's underfoot becomes critical. Moving farther away from the Lip the snow has been beaten down more by the winds, producing harder surfaces with more strength. Hillman's Highway and Left Gully are good examples of this. Right Gully has more varied conditions, with the skier's left side generally being more stable than the skier's right. On the skier's right side, you may find isolated pockets of unstable snow in sheltered lee areas.
As today's clear skies, relatively warm temperatures, and lighter winds make me think of spring, it's worth talking about the effect of warm temps and sun on stability. Up to a certain point, sun and warmth can be good for stability. It has the ability to bake some of the elastic energy out of slabs and round out the snow grains, which leads to better bonding and greater stability. This can be good, but it is possible to have too much of a good thing. Rapid warming of the snowpack can create problems such as wet snow avalanches and icefall. Also, a warm day can create a sun crust which then acts as a future sliding layer for new snow. Today we don't expect to see these problems, but it's important to never be lulled into complacency by good weather.
The Lion Head Winter Route is open. This is a steep and challenging route. Crampons, an ice axe, and the ability to properly use this equipment are necessary for safe travel on this route. The Little Headwall has filled in with snow, however, it is quite a thrash to get into and out of the skiable terrain. The John Sherburne Ski Trail is open and has generally good coverage with some large scoured sections.
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Avalanche Advisory Archives.
United States Avalanche Danger Descriptions.
Échelle Canadienne de risque d’avalanche.
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