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Questions and Answers
What typically triggers an avalanche?
What typically triggers an avalanche?
At what slope angles do most avalanches occur?
At what slope angles do most avalanches occur?
What role does vegetation play in avalanche dynamics?
What role does vegetation play in avalanche dynamics?
Which factor influences the speed of an avalanche?
Which factor influences the speed of an avalanche?
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How fast can the fastest avalanches travel?
How fast can the fastest avalanches travel?
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What is a common cause of avalanche injuries or fatalities?
What is a common cause of avalanche injuries or fatalities?
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What occurs in the area where an avalanche accelerates?
What occurs in the area where an avalanche accelerates?
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What can the formation of hoar in the snowpack lead to?
What can the formation of hoar in the snowpack lead to?
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Study Notes
Snow Avalanches
- A snow avalanche is a mass of snow, many cubic meters in volume, that separates from a snowpack and moves downslope.
- Rocks, soil, ice, and debris can also move in a similar motion, but "avalanche" is specifically used for snow.
- Avalanche intensity depends on slope steepness, snowpack stability, and weather conditions.
Snow Cover
- Snow cover probability for a white Christmas is considered on December 25th.
- Snow cover maps are updated daily.
Types of Avalanches
- Slab avalanches occur when a snowpack fractures along a weak layer, parallel to the surface.
- These are the most dangerous avalanches, moving as cohesive blocks.
- New snow that hasn't bonded with the layer below is more likely to slide.
- Wet, compacted snow is less likely to slide than dry, powdery snow.
- Snow higher than vegetation and above large boulders is more prone to sliding.
Weak Layers
- Buried weak layers are necessary for slab avalanches.
- Wind can deposit light ice crystals on mountain slopes, forming a weak layer in the snowpack.
- Hoar, a layer of ice crystals, has less strength than other snow layers and can be unstable.
Avalanche Motion
- Fast-moving avalanches (over 35 km/h) often create clouds of powdered snow.
- Avalanche speeds are frequently near 20 km/h but can be much faster.
Avalanche Triggers
- Most avalanches occur after snowstorms.
- Daytime heating from the sun can warm the upper snowpack, leading to avalanches.
- Human activity, such as skiing or snowboarding, can trigger avalanches.
- Explosives are sometimes used to initiate avalanches to prevent dangerous buildup.
Avalanche Paths
- Start zone: where the snowpack first fails.
- Track: where the avalanche accelerates to maximum velocity.
- Run-out zone: where the avalanche slows and deposits snow.
- Slope angle is the most important factor in avalanche formation, occurring most often between 25 and 60 degrees.
- At angles below 25 degrees, snow doesn't readily slide.
- At angles above 60 degrees, little snow accumulates.
Terrain Factors
- Slope orientation (direction slope faces) affects snow accumulation & avalanche potential.
- Snow may consist of interlayered strong and weak layers, particularly on leeward slopes or slopes facing the sun in clear weather.
- Other factors include slope smoothness, vegetation, & the topography.
Regions at Risk
- Avalanches require at least 50 cm of snow to form.
- North America's mountainous regions are most common areas with deep snow.
Effects of Avalanches
- Avalanche deaths frequently occur in the late 1800s and early 1900s.
- Avalanches cause significant economic loss in areas such as B.C. each year due to highway closures and property damage.
- This damage is relative to other events.
- The 1898 Chilkoot avalanche was one of North America's worst, killing over 60 people.
Linkages to Other Hazards
- Avalanches can be triggered by earthquakes.
- Climate change might lead to more winter snowfall, higher intensity storms, and enhanced snowpack instability in some areas.
Natural Service Functions
- Avalanches act as ecological disturbances similar to landslides, increasing local plant and animal diversity.
- They open up areas in forested regions providing habitats.
Human Interaction with Avalanches
- Avalanche risks increase as more human activity occurs in avalanche-prone zones.
- Tourism and recreation, particularly in areas like the Rockies and Alps, have led to a growth in avalanche-related deaths.
- Human activity can lead to significant hazard areas.
- Average fatalities increase based on specific trends in the recreation environment.
Minimizing Avalanche Risk
- Placing infrastructure (buildings, roads, etc.) away from avalanche paths minimizes risk.
- In hazardous areas, structural engineering for buildings and defenses for specific recurrence intervals are vital.
- Mounds and berms are used to channel avalanches away from populated areas.
- Avalanche-shed structures allow snow to pass over roads & railways.
- Controlled triggers use explosives to occur and prevent dangerous buildup.
Avalanche Forecasting
- Avalanche forecasts are based on location data from previous avalanches.
- Snowpack testing and observation, complemented with weather predictions, are integral to accurate reports.
Strength & Stability Tests
- Compression, shovel, and Rutschblock tests are used to evaluate snowpack strengths and identify weak layers.
Avalanche Safety
- Before entering avalanche-prone areas, check the current danger level and any public bulletins.
- Understanding slope angles and terrain is essential.
Avalanche Rescue
- The motion of snow kills a significant portion of avalanche victims.
- Survival depends on the burial depth & time the person is buried. Over 90% of victims survive if rescued within 15 min.
- An immediate search by trained rescuers is more effective than waiting for help.
- Avalanche survivors require essential safety aids.
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Description
This quiz covers the essential aspects of snow avalanches, including their definition, types, and the conditions that influence their occurrence. You'll learn about slab avalanches and the significance of weak layers within a snowpack. Test your knowledge on the factors affecting avalanche intensity and snow cover.
