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Non-avalanche Terrain
Non-avalanche Terrain
Before trying to understand what is considered avalanche terrain, it’s easiest start by identifying what isn’t avalanche terrain. The simplest way to mitigate avalanche hazard is to avoid avalanche terrain altogether. This can be achieved in several ways:
Travel in the center of the valley floor, well away from any possible debris runout from the slopes above.
Travel in dense forest that is also on a low angle slope.
Use low angle slopes - those with angles of less than 25 degrees.
Travel along ridges, away from cornices or overhangs.
Interactive: Which areas of this terrain would enable you to avoid avalanche terrain? Click on the circles.
Please note: This activity does not work on mobile devices.History of Avalanche Activity
History of Avalanche Activity
The historical or known behavior of a slope or feature in the terrain is important to know and track. Some avalanche paths become active nearly every time they are loaded with new snow. Other avalanches return at a rate much less frequent and predictable. Historical behavior is not an absolute predictor of avalanche size or activity, but local/historical knowledge is an invaluable tool for relating weather events and avalanches in the terrain. Make notes in maps and photos when experienced mentors share historical patterns and make note of major avalanche events as you begin to build more experience.
Use an annotated photo from experts or mentors.
Photo by Colin Zacharias
Avalanche paths are the path an avalanche follows in the terrain. It has three recognizable features:
• The start zone, where avalanches typically initiate. These are often associated with specific trigger points in the terrain.
• The track, where the avalanche typically gains mass and speed as it picks up snow and other debris on its descent.
• The run-out zone, where the avalanche begins to slow down and lose mass as snow and debris are deposited.
An avalanche path may be well defined (left photo) or poorly defined (right photo). Well defined avalanche paths have associated trim lines in the forest and show signs of repetitive activity, season over season. More poorly defined avalanche paths often leave more subtle clues in the terrain, including flagged trees, groups of trees broken at the same height, lumps or chunks in a deposit zone, snow plastered to the uphill side of trees and rocks or unexplained openings in steep terrain.
Vegetation clues
Vegetation clues
Trees and other vegetation can give you clues about where avalanches regularly run. You may be able to see this on maps or satellite images, or in photos from the web or mentors as the annotated one above.
Interactive: Identify the obvious paths you see in this photo by clicking on them.
Please note: This activity does not work on mobile devices.In addition to creating obvious paths, avalanches that have previously run through an area leave clues in the surrounding vegetation. Look for these signs in photos or satellite images. Keep these in mind later as you are identifying avalanche terrain in the field.
Chris Meder
Look for unexplained clearings. Or areas where trees above a certain height are broken or missing.
Liz Riggs Meder
Look for branches missing on the uphill sides of trees
Look for a lack of smaller trees or a large clearing with small trees of similar height.
Or areas where trees are less dense
Check Your Understanding: Vegetation Clues
Check Your Understanding: Vegetation Clues
Can you identify evidence of previous avalanches? Click on the clues in the two photos below:
Please note: This activity does not work on mobile devices.Slope Angle
Slope Angle
Most slab avalanches occur on slopes between 30° - 45°. Loose snow avalanches can occur on steeper terrain. Pay attention to the steepest parts of the slope, even when the average angle could be considerably lower.
Mapping software is capable to a point, but can lack the resolution to show specific steep features in the terrain. Be aware that maps often underestimate slope angle
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