Avalanche Awareness
The essentials to save YOUR life
What we’ll be covering
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Avalanche types
Natural Factors
Human Factors
Basic travel techniques
Further Resources
Footage
• http://www.youtube.com/watch?v=K8l
_ZpADfsQ
Avalanches Basics
• Avalanches are large masses of snow that
are driven down slope by gravity.
• Different avalanches occur in different
conditions.
• 2 main types
– Loose Snow (Point Release)
– Slab
Avalanche Terrain
• Terrain affects
multiple aspects of
avalanches
– Dictates where
avalanches start
– How far they can
runout
– Can multiply
consequences (terrain
traps)
– Can help stabilize…or
weaken the snowpack
Typical Avalanche Path
Loose Snow (Point Release)
• Made up of loose,
unconsolidated snow
• Start at a point and widen down
slope-characteristic tear drop
shape
• Size: A few square meters to
thousands
• Conditions
– Dry (Sluffs): Cold, dry weather
– Wet: Very Warm periods
• Variable damage, generally
less than slab avalanches
• Typically follow terrain
Slab Avalanches
• Starts out as a cohesive slab
of snow
• Failure is due to a weak
bedding plane beneath the
slab
• Typically has a crown across
slopes with flanks paralleling
slope
• Slabs can range from cm thick
to the thickness of the entire
snowpack
• Size: A few sq. m to entire
mountainsides
Slab Avalanches Cont.
• Conditions: Any
condition, weak layers
can last a few days to an
entire season
• Can destroy entire
villages and vast tracts of
forest
• Wet slabs tend to follow
terrain features
• Dry slabs don’t follow
terrain
• Video:http://www.youtube
.com/watch?v=3HxxzfUfF
Gk
Avalanche Factors:
Weather
Most Avalanches happen during
or soon after snow storms.
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Snowfall intensity is very important
Temperature changes throughout the day
and during a storm
New weight, and hence new stress on
snowpack.
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A 10ftx10ftx10inch slab of snow with a 90% air
concentration weighs 520lbs
WIND
– Wind is a major component of
building slabs
• Strips snow on some aspects and
deposits on others.
• Cross loading in valleys, etc. can
deposit snow in gulley’s and
stream beds making them
avalanche prone
• Snow starts blowing/moving at
wind speeds of around 15mph
• Wind blown snow can be deposited
10 times faster than typical storm
snowfall.
Other Weather Factors
• Other weather factors include
– Sun (melting, sun crusts)
– Temperature (changes snowpack)
– Cloud cover (radiation reflection, can change
snowpack)
Sun and Wind…changes the snow
pack
Avalanche Climates
• Depending on where you
are on the continent, the
climate varies.
• Climate affects
temperature, storm
types, wind, etc.
SNOWPACK!
• 3 main snow climates
– Maritime
– Intermountain
– Continental
• COLORADO!
Continental Snowpacks
Weather
Precipitation
Low Rate, small accumulation
Wind Transport
Little pre-storm
Some to much post-storm
Much post-storm
Temperature
Cold
Snowpack
Depth/ Distribution
Shallow, variable
Layering
Strong over weak, faceted
Temperature
Cold
Avalanches
When
Delayed action: Some during storm, many post-storm
Danger
Slow to rise; Very slow to fall
Snowpack (In extreme brevity)
• Snowpack determines what type of avalanche you might
encounter.
• The temperature, crystal structure, density, and water
content all affect the strength of the snow pack.
• Snow is always changing
– Settlement
– Gravity
– Thermal radiation
• Spatial Variability
– Snow is not uniform across a slope
– Aspect greatly affects sun/wind exposure
– Trees can affect sun/wind exposure on a very localized level
Failure Planes
• Slab avalanches tend to fail along either
weak layers or sliding planes.
• Weak Layers
– Surface Hoar
– Depth Hoar (faceting)
• Sliding Surfaces
– Sun Crusts
– Rain Crusts
– Graupel
Weak Layers
• Surface Hoar
– Forms on clear, cold, calm
nights on snow surface
– Like dew
• Depth Hoar
– Snowpack metamorphism
– Due to large temperature
gradients in snowpack
– Forms during extensive cold
periods or in shallow
snowpacks
– Snow crystals go from a
dense rounded shape to
hexagonal, hollow cylinders
Sliding Surfaces
• Sun Crust: Form from
freeze/ thaw of snow
surface on sunny slopes.
Crust also creates
temperature gradient in
snow pack (creating
faceted grains).
• Rain Crust: Creates very
smooth sliding surface
that can last for long
periods of time.
• Graupel: Spherical balls
of dense snow. Acts like
ball bearings when buried
in the snowpack.
Slope
• Need a slope to have
an avalanche
• Prime slope is 30-45
degrees mid winter,
20-30 in spring
• Shape is also crucial
– Convex or Concave?
– Concave=Compressive
stress
– Convex=Tensile Stress
Aspect
• Aspect creates favorable/ unfavorable
conditions for the formation of weak layers
– Sun Exposure
• Melting/freezing
• Development/ destruction of weak layers
– Wind loading
• Redistributes snow
– Strips snow and loads snow on certain aspects
– Can occur on large and small scale levels
Elevation
• Three main elevations to consider
– Below treeline, treeline, above treeline
• Factors:
– Exposure to sun/wind
– Anchors vs triggers
– Ease of identification of avalanche terrain
• Triggers
– Trees and boulders…sometimes buried
Above Treeline
• High exposure to
sun/wind
– Wind slabs
– Freeze/thaw
cycles
• No anchors
– Buried rocks can
act as weak points
in snow pack
• Avalanche terrain
is not as apparent
– No apparent
avalanche paths
Treeline
• High to moderate
exposure to sun
and wind
• Some anchors but
not much
– Trees tend to act as
weak points due to
wide spacing
• Avalanche terrain is
tricky to recognize
Below Treeline
• Lower Exposure to
sun and wind
• Trees tend to act as
anchors…much
closer together
• Avalanche paths
are easily
recognized
Terrain Traps
• Certain terrain features
can multiply
consequences of
avalanches
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Gullies
Abrupt Transitions
Cliffs
Runouts ending in trees
Lakes/ Rivers
Human Factors
• So far we’ve just looked natural
factors…we can’t control these. Human
factors though, the ones we can control,
are typically the main factor for accidents.
– Powder Lust
– Group Dynamics
– Camera Syndrome
– Experience Arrogance/Ignorance
– Gear Invincibility
So how do we have any fun?
• With proper planning and smart decision
making, the backcountry holds a wealth of
skiing possibilities.
• Being able to recognize and avoid
avalanche terrain is essential to a good
day.
• We have an idea what to look for but how
do we use it to get a great day of turns in
and still be safe?
Before Hitting the Slopes
• Find a good group of experienced people to go
with
– Make sure they have avalanche knowledge, gear and
that they know how to use the gear
• Plan your trip.
– Which routes/ backup routes do you plan to take. Let
someone know where you’ll be.
– Be prepared to change your plans. Avie Conditions
can vary from slope to slope. If a slope has signs of
instability stay off it and have a backup slope in mind.
• Make sure your gear is in good shape and ready
to go
The Day of
• Check the local Weather/Avalanche Forecast
– For Colorado it’s the CAIC:
http://avalanche.state.co.us/index.php
– The forecast typically gives a discussion on the
weather, snowpack, and any other pertinent
information (like recent avalanches).
• ***Avalanche forecasts are given for a large
area, local conditions may be different.***
• If the danger is high…go to a ski area, not the
backcountry!
Avalanche Red Flags
• Recent avalanches
• Signs of unstable snow
– Whumphing
– Cracking
– Hollow sound in snowpack
• Heavy snowfall or rain in the past 24 hours
• Wind blown snow
• Significant warming or rapidly increasing
temperatures
Smart Travel Protocol
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Look for the avalanche Red Flags. Always pay
attention to your surroundings, looking for avalanche
signs and potential dangers…be willing to adapt trip
routes and runs
JUST BECAUSE THERE ARE TRACKS DOES NOT
MEAN A SLOPE IS SAFE!
•
http://www.youtube.com/watch?v=6qVwIuznFW0&feature=related
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Account for changes throughout the day
Communicate with group members
Think ahead
Group decisions should always be made by the most
conservative point of view
Don’t give into the human factors!
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Terrain Considerations
• Route Finding/ Islands of
Safety
– Shortest route not usually
safest, summer routes often
lead through avie terrain.
– Look for Islands of Safety
when crossing
terrain…places you can
retreat to in case of an
avalanche.
– Avoid terrain traps
– Minimize time in Avie Terrain
– Avoid obvious avie
zones…chutes, runouts,
cornices
Backcountry Travel Techniques
Expose only one person to potential
avalanche danger at one time
Be aware of what is above you
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Have an escape route pre-figured
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Remember to identify islands of
safety
Travel with large intervals between
people
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Spindrift
Steep slope
Cornices
Hang fire
Etc
100+ feet, 20-30 feet is
inconsequential because
avalanches are more likely to engulf
the whole party when spaced this
closely
Cross as high up on a slope as
possible
Travel Techniques Continued
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Move from one island of safety to another
Cross in one track
Remove straps
– Ski poles
– Skis
– Ice axes
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Keep pack on and strapped fairly tight to your body
Travel on ridges away from cornices
Try to avoid time in exposed spots
Maintain visual contact
Avoid climbing and skiing above others
Check transceivers at least twice a day
– Check them before you go into the backcountry
– Maybe at lunch or some other time during the day
• AVOIDANCE IS THE BEST SAFETY MEASURE!!! It’s
ok to call it a day and head for the bar.
What went wrong?
• http://www.youtube.com/watch?v=2IItP7d
VoYc&feature=related
• http://www.youtube.com/watch?v=tsyOCF
v2gw4&feature=related
• http://www.youtube.com/watch?v=gBvNpR
FN8Ak
What about the gear?
• You should NEVER go into the backcountry without the essential
avie safety gear. If you don’t have it you are risking yours or your
buddy’s life.
• The essential avalanche safety gear includes the following:
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Beacon
Probe
Shovel
Inclinometer
Compass
• Other gear includes
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Black Diamond’s Avalung
Snow air bags
Snow science kits
Snow saw
A Note on Gear
• Gear does not make you invincible
• In fact, it’s main use is to help someone
else find you AFTER you are buried.
• The ultimate goal is to not use your
equipment outside of practice scenarios
• Your mind does a much better job at
keeping you safe…use it. Gain knowledge
and experience.
Where to get gear
• Bent Gate, REI, Backcountry.com, or other
outdoor stores
• The ORC rents them
– Get a gear pass next semester and you can
have unlimited beacon, probe, shovel rentals
for the spring semester.
Resources
• EDUCATE YOURSELF!
• Classes being offered by the ORC:
– Beacon training next Wednesday night
– Avie 1 course next semester (planning for presidents
day weekend)
• Literature:
– Bruce Tremper’s, Staying Alive in Avalanche Terrain
• Find a group of experienced backcountry skiers
and go on a trip with them
– Join the ORC for a backcountry hut trip or day trip
(next semester)
Websites
• Colorado Avalanche Information Center
(CAIC)
– http://avalanche.state.co.us/index.php
• American institute for Avalanche Research
and Education (AIARE)
– http://avtraining.org/
• Forest Service National Avalanche Center
– http://www.fsavalanche.org/