Jul 12, 2024: Creep vs. Glide
At some point during the last season a couple of misconceptions arose in the media. One was creep in the snowpack, which was confused with glide in an article which found it's way into Yahoo news as well as at least one ski oriented news site. An amusing aspect of this was that the author, whoever it was, took the opportunity to tell readers that they should take a "Level 1" course to learn about these things. Whether they took such a class is not known of course, but if they did they were probably misinformed on at least this point.
Creep and Glide are two different mechanical phenomena within the snowpack. They are covered in the Avalanche Institute Level 1 course in the modules on Snowpack, but are also simply defined in our glossary.
Creep and Glide are two different mechanical phenomena within the snowpack. They are covered in the Avalanche Institute Level 1 course in the modules on Snowpack, but are also simply defined in our glossary.
Sep 19, 2021: Alpha (Runout) Angles and Climate Regimes
Comments on this post are disabled because the spam bots have now discovered it. If you would like to comment or to arrange a related guest post contact the avalanche center at snow@csac.org
While we don't get many legitimate comments this topic attracts more interest than most, and it is one which is prone to misconceptions. So feel free to comment or request a response post from us.
[Edited for clarity with no change to content on Sept 19, 2021. This first appeared on avalanche-blog.org which has since been transferred to a new site. It has been reposted here and has a courtesy link from that new site.]
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. Despite what may have found its way into the popular literature. What is important isn't entirely 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.
While we don't get many legitimate comments this topic attracts more interest than most, and it is one which is prone to misconceptions. So feel free to comment or request a response post from us.
[Edited for clarity with no change to content on Sept 19, 2021. This first appeared on avalanche-blog.org which has since been transferred to a new site. It has been reposted here and has a courtesy link from that new site.]
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. Despite what may have found its way into the popular literature. What is important isn't entirely 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.
Jan 07, 2008: 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. Here is the short version of my concerns, as well as a suggestion for what to ask anyone promoting this.
[[ Note: This is being reposted on this blog in December 2014, about 7 years after it first appeared on a blog that has been discontinued. I have not followed the technical literature over this period very closely and more work has been done. However, my fundamental concerns remain. Especially for use outside a large data collection operation. (I have reservations about what I consider an over reliance on stability tests in general outside of such programs.) At the end I have added a few comments as of reposting this at the end of 2014. ]]
[[ Note: This is being reposted on this blog in December 2014, about 7 years after it first appeared on a blog that has been discontinued. I have not followed the technical literature over this period very closely and more work has been done. However, my fundamental concerns remain. Especially for use outside a large data collection operation. (I have reservations about what I consider an over reliance on stability tests in general outside of such programs.) At the end I have added a few comments as of reposting this at the end of 2014. ]]
Apr 13, 2007: Slabs, Loose Snow, and Convexities
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.
Feb 27, 2007: The "Critical Temperature Gradient" Myth
Comments are closed since this post is old and has been attracting a lot of spam comments. Real and constructive comments (from any point of view) are still welcome, as are guest posts on any related topic. You can send comments to snow@csac.org and you can also contact us there if you would like to write a guest post. (2022-07-08)
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 faceting 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.
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 faceting 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.
