The "Extended Column Test"

The promotion of this "test" as something useful in decision making in the field has bothered me for quite a while. I will have to find time to write more about it again later, but here is the short version of my concerns, as well as a suggestion for what to ask anyone promoting this.

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Slabs Vs Loose Snow

Slabs of snow are continuous bodies, and are subject to deformation and the development of internal stresses for that reason. Loose snow without any cohesion does not form a continuous body and its behavior is that of a collection of unconnected grains. Comments in at least one public advisory show a lack of understanding of the fundamental differences.

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The "Critical Temperature Gradient" Myth

For years the figure of 1 C per 10 cm of depth has been called a "critical temperature gradient" and considered the gradient in the snowpack at which faceting of the grains begins. In a recent forum topic the original question was what is most important for facetting and of course this number was presented right away.

What is actually important is the vapor pressure gradient. Depending on the temperature the gradient may need to be much larger than this "critical value" before faceting actually begins to occur.

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Alpha (Runout) Angles and Climate Regimes

The alpha angle is the angle from the end of the runout to the top of the starting zone. For a brief definition including a diagram you can see the avalanche center glossary:

Avalanche Center -> Education Center -> Glossary -> Alpha Angle

Alpha angles (used to measure runout distance) do NOT depend on climatology. Whether a mountain range is maritime or continental (or something else) does not make much difference in alpha angles. Despite what may have found its way into the popular literature. What is important isn't clear, but it's not climate. Every mountain range seems to offer its own behavior regarding maximum runout potentials, and each range must be analyzed separately.

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Welcome / About this Blog

Welcome to my blog on snow avalanches. Over time I've found various issues, comments and claims that I'd like to comment on. This blog will allow me to do that. The comment feature allows a certain amount of feedback, pro and con. More extensive discussion is always welcome in the forums at http://www.avalanche-center.org/phpBB2/

Titles of the most recent posts can also be found on the newsfeeds page at http://www.avalanche-center.org/News/newsfeeds/

While I encourage the use of avalanche-center.org for discussions (as well as for general reference and education) this blog has no formal or official affiliation with that site. Nor any other. Nor is it affiliated with any other individual(s). Everything written here is by me, and I'm responsible for it, unless it is a comment or otherwise attributed to somebody else in particular.

Comments need to be approved, otherwise there is an overwhelming amount of spam. I generally don't believe in approval or editing based on content so disagreements and opposing points of view are welcome as long as they are civil and intelligent. So if you don't see your comment for a little while it's just a matter of me approving it.

I'm also open to guest and invited blog entries, feel free to request a topic or a person to invite by emailing me at snowman@csac.org