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Slope
 
 
Slope
 
Shape Slope shape affects avalanche danger to some degree, although factors such as aspect and slope are much more important. Bowl shaped slopes can accumulate wind deposited snow, but convex slopes are statistically much more dangerous for three reasons. First, there is less compressive support at the base of the slope. Second, small rolls and breaks in slope concentrate stresses within the snow pack. This means that it’s much easier to trigger a slide. Third, convex slopes often present route finding challenges. Many skiers and riders assess the angle and snow conditions on top, then travel halfway down a slope before realizing they are in trouble. The best option in this situation is to turn around and hike up slope. An avalanche also may be triggered from below by removing the slab layers compressional support at the base of a slope. Stay out from under and off slopes above 35 degrees when suspicious of instability. It is possible to trigger an avalanche from a distance if the slope you are is attached to any dangerous terrain.http://www.avalanche.org/%7Euac/encyclopedia/concave_slope.htmhttp://www.avalanche.org/%7Euac/encyclopedia/convex_slope.htmhttp://www.avalanche.org/%7Euac/encyclopedia/remote_trigger.htmshapeimage_3_link_0shapeimage_3_link_1shapeimage_3_link_2
Angle If a slope is too steep, snowfall cannot accumulate. Snow simply slides off during a storm in powder avalanches or spindrift. If the slope is too gentle, the snow is not under enough stress to form an avalanche. In between these too extremes exists a happy medium where snow can accumulate on a slope, but it is still under a significant amount of stress. For this reason, slab avalanches typically occur on slopes between 30 to 50 degrees. The magic number for slab avalanche formation is 38 degrees. The closer a slope is to 38 degrees, the more dangerous it is. This number can vary somewhat depending on the type of snow. Wet, sticky snow can form slabs at much higher angles. This type of snow is typical in maritime snowpacks, places like the Cascades or the Sierras. However, the general rule that slopes become more dangerous as they approach 38 degrees holds true in the vast majority cases. How do you judge slope angle? It takes practice! Buy an inclometer or compass and practice measuring slope angles!
 
 
 
 
 
 
 
 
 
                                                                                  
                                                                                   Measuring slope with an inclometer
 
Convexity: Snow is under tensile stress! Snow is under compressional stress!
38° The Magic Number
Do you know the slope angle?
Measuring with a slope meter
            30 degrees is about the steepness of a blue run at a ski area.
           35 degrees
     38 degrees
 
Photo Gellatin National Forest Avalanche Center
Copyright 2008, by the Contributing Authors. Cite/attribute Resource. factcouraud. (2007, May 08). Slope. Retrieved November 24, 2009, from Free Online Course Materials — USU OpenCourseWare Web site: http://ocw.usu.edu/Forest__Range__and_Wildlife_Sciences/avalanche-and-snow-dynamics/AvClass/Terrain/Slope.html. This work is licensed under a Creative Commons License. Creative Commons License
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