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Avalanche Seminar
Notes How do people get caught in avalanches? How fast do avalanches go? Dry slab avalanches typically travel 60-80 miles per
hour. They reach these speeds within about 5 seconds after they
fracture. Wet avalanches usually travel much slower, around 20 miles per
hour. What kind of avalanche is most dangerous? Dry slab avalanches account for almost all avalanche
fatalities. A slab avalanche is like a dinner plate sliding off the
table. A cohesive plate of snow slides as a unit on top of weaker snow.
The slab shatters like a pane of glass with the victim in the middle of
the slab and usually there's no escape. What kind of weather produces avalanches? Most of the time, slab avalanches occur because the
weight of new or wind blown snow overloads the strength of the buried
weak-layer. Slab avalanches are a relatively stronger layer of snow on
top of a relatively weaker layer of snow. The weak layer fractures and
the slab becomes the avalanche. The weak layer fractures when stress
equals strength. Snow can only withstand a certain amount of stress at a
certain rate. If the amount of stress is too great or the rate is too
high, then the snow fractures. How do I judge the danger of avalanche
terrain? 1. Steepness. Most avalanches occur on slopes between
35 and 45 degrees. Slopes less than 30 degrees seldom produce avalanches
and slopes steeper than about 50 degrees sluff so often that they tend
not to build up into slabs. So it's the intermediate slope steepness
that produces most of the avalanches. But the bad news is that exactly
the kind of slopes we like to ski; snowboard or snowmobiles usually
produce most of the avalanches. A black diamond slope at a ski resort is
usually around 35 degrees--prime steepness for producing avalanches. How do I judge snow stability? Look for obvious clues: Safe Travel Techniques · One at a time. There always needs to be someone
left behind to do the rescue. Someone always needs to remain in a safe
place while their friend(s) are on the dangerous part of the slope.
Never put everyone on the slope at once. With large groups, split them
in half and stay in visual and voice contact. What do I do if I get caught in an
avalanche? First job should be to avoid this step this is the
first mistake, now you have to fight to survive. If you see your friend get caught in an
avalanche... 1. Watch them closely. Mentally fix the last seen
area and closely watch to see where they end up. This will greatly
reduce the search times if you have a good idea where to begin the
search. How long can you live buried in avalanche
debris? The good news is that even dense avalanche debris is
about 60-70 percent air, and you can breathe that air--at least for a
few minutes. Where do most avalanche fatalities occur? Almost all avalanche fatalities occur in the
"backcountry" areas outside ski area boundaries where no
avalanche control is done. Ski patrollers knock down the avalanches each
morning with explosives before the public arrives. They type of
avalanche hazard mitigation is so successful that only a half of a
percent of avalanche fatalities occur inside of ski area boundaries.
Similarly, few fatalities occur on highways or in buildings. Almost all
occur in the backcountry. Almost all are recreationists and in 95
percent of the fatalities, the avalanche is triggered by the victim, or
someone in the victim's party. Popular myths about avalanches... "Loud noises trigger avalanches" Only in the movies. In 20 years as an avalanche
professional I have never once seen an avalanche triggered by, say, a
shout, even a sonic boom or a low flying helicopter. It's just not
enough force. It needs to be a really loud noise like a bomb going off
at close range. In almost all avalanche fatalities, the avalanche is
triggered by the victim, or someone in the victim's party. "An Avalanche is a bunch of loose snow
sliding down the mountain" Avalanche professionals call these
"sluffs." Loose snow avalanches account for only a very small
percentage of deaths and property damage. What we normally call
avalanches are "slabs" or cohesive plates of snow. Picture a
magazine sliding off the table, with the victim standing on the middle
of the magazine. Avalanches "strike without
warning" I often hear this phrase used in the popular media.
Stock market crashes, meteor impacts and lost love may strike without
warning, but avalanches almost always have obvious signs. Second,
avalanches don't "strike". They happen at particular times and
in particular places for particular reasons. I'll say it again, because
it's so important: In 95 percent of all avalanche accidents, the
avalanche is triggered by the victim, or someone in the victim's party. "If you see an avalanche coming, get
out of the way" Well, at least you can try. An average-sized dry
avalanche travels around 80 mph and it's nearly impossible for someone
to outrun an avalanche or even have time to get out of the way. A fast
snowmobile has some chance but everyone else has a slim chance at best.
Also, avalanches that descend from above kill very few people. Do I
sound like a broken record here; the vast majority of avalanche
incidents are triggered by the victim or someone in the victim's party. "All the avalanche experts are
dead." I'm happy to report just the opposite. Skilled
avalanche professionals enjoy a very low avalanche fatality rate
compared to other groups. Less than half of one percent of all avalanche
fatalities involve avalanche professionals.
Who gets caught in avalanches?
Avalanche victims are almost exclusively backcountry
recreationists--snowmobilers, climbers, snowboarders, snowshoers, skiers
and hikers. Snowmobilers lead the list with twice the number of
fatalities as any other activity.
In 95 percent of avalanche incidents, the VICTIM or someone
in the victim's party triggers the avalanche.
Wind is the most common cause of avalanches. Wind can deposit snow 10
times faster than snow falling from storms. Wind erodes snow from the
upwind side of obstacles and deposits snow on the downwind (lee sides).
We call this "wind loading".
The added weight from snow storms also causes avalanches. If the weight
of new snow is added faster than the buried weak-layer can adjust to its
load, then it fractures and forms an avalanche.
Rapid warming or rapid melting of snow can also cause avalanches. For
instance, rain on new snow almost instantly causes avalanches. Strong
sun or warm temperatures can also cause rapid melting of the snow and
creates wet avalanches.
But wind, snow or rapid warming do not always produce avalanches. It
depends on the condition of the pre-existing snow and the conditions
during the storm. With very stable snow pre-existing snow, even heavy,
new snow with wind can bond well and be perfectly safe in the right
conditions. Stability analysis is a complicated process and it requires
much study and experience to develop good stability analysis skills.
2. Anchors. Trees and rocks that stick up through the snowpack can help
to hold the snowpack in place. But the anchors need to be quite thick to
be effective. For instance a thick, mature grove of evergreen trees
anchor the slab quite effectively while a sparse grove of aspen trees
have very little effect.
3. Aspect with respect to wind. Recently wind-loaded, steep slopes are
almost always very dangerous while recently wind-eroded slopes are
usually fairly safe.
4. Aspect with respect to sun. In the Northern Hemisphere as temperate
latitudes, the direction a slope faces (aspect) is very important. For
instance, north facing (shady) slopes usually produce more avalanches
and more persistent avalanche hazard in mid winter. On the other hand,
in the spring when wet avalanches occur from strong sun, south facing
slopes produce more wet avalanches. At equatorial or Arctic latitudes,
the aspect with respect to the sun has very little effect.
5. Consequences if involved in a slide. What will happen to you if the
slope slides? It's very difficult to survive an avalanche if it strains
you through thick trees or dumps you over a large cliff or deposits you
into a crevasse or dumps you into a narrow gully (creating a very deep
burial). On the other hand you have a fairly good chance of survival on
a small avalanche path, without obstacles and a gentle run-out.
· The best sign of avalanches are other avalanches. You can't get much
more obvious than that. But it's surprising how often people miss this
clue.
· Collapsing snow. When you hear the snowpack collapse catastrophically
with a giant "whoomph", that's the sound of the snowpack
screaming in your ear that it's extremely unstable. Stay off of steep
slopes and stay out from underneath steep slopes.
· Cracking snow. Recent wind loading, especially, creates cracking
snow. The longer the crack, the more dangerous. Stay off of steep
slopes.
· Avalanche weather. Just like people, avalanches do not like RAPID
changes.
o Recent rapid loading of new or windblown snow
o Recent rapid warming
o Recent rapid melting
o Rain on new snow
Active Tests -- What you should be doing:
· Use your avalanche eyeballs
· Use test slopes. Find a small, safe, steep slope and go jump on it to
see how it responds. You can do this on a snowmobile, snowboard, on skis
or on foot.
· Cornice tests. Find a refrigerator-sized cornice and tumble it down
the slope. Hint: ALWAYS wear a belay rope and use a snow saw or thin
avalanche cord to cut the cornice.
· Dig snow pits in representative slopes. You will need to take a
reputable multi-day avalanche class to learn how to effectively do
snowpit tests.
· Have an escape route planned. Always think avalanche. What will you
do if the slope slides. Have a plan first.
· Use slope cuts. Keep your speed up and cut across the starting zone,
so that if the slope slides, your momentum can carry you off the moving
slab into safer terrain. You can do this on skis, snowboards or on
snowmobiles.
· Watch out for cornices. They always break farther back than you
think. Always give them a wide berth. NEVER, NEVER walk out to the edge
of a drop-off without first checking it out. Many people have died this
way.
· If it looks too dangerous, find a safer alternative. Use terrain to
your advantage. Follow ridges, thick trees and slopes with safer
consequences. You can almost always go back the way you came. The route
got you there, it will most likely get you back as well.
· If there's no other choice, go underground. You can almost always
weather out a bad storm or bad avalanche conditions by digging a snow
cave or seeking the shelter of a crevasse. You may be uncomfortable but
you will be alive.
You're first job is to GET OFF THE SLAB, which as you might imagine, is
hard to do.
If you're descending on skis or snowboard, try heading straight down
hill to build up some speed, then angle off to the side of the moving
slab. If you're ascending when the avalanche breaks, there's really not
much you can do. If you're close enough to the crown, you can try
running uphill to get off the slab, or running off to the side.
If you're on a snowmobile you have the advantage of power. Grab some
throttle and use your power to get you off the slab. If you're headed
uphill, continue uphill. If you're headed across the slope, continue
across to safe snow. If you're headed downhill, you're only hope is to
try and outrun the avalanche. Sometimes it works, but usually it
doesn't.
If you can't escape off the slab, try grabbing a tree. But you have to
do it very quickly because avalanches quickly pick up speed. If you
can't grab a tree quickly, then your best friend suddenly turns into
your worst enemy. After about 4 seconds they can easily be traveling at
40 miles per hour, and you can imagine what a tree feels like at 40 mph.
(Almost a third of avalanche victims die from trauma from hitting trees
and rocks on the way down.)
If you can't escape off the slab or grab a tree, then you need to swim
hard. A human body is about three times as dense than avalanche debris
and it tends to sink like a rock unless it's swimming hard. As the
avalanche finally slows down and just before it comes to rest,
1. Try and clear an air space in front of your mouth. This helps delay
the formation of an ice mask, which allows you to breathe longer under
the snow. Try to take a deep breath and hold it. Once the snow sets up
this gives you some breathing room.
2. Push a hand upward. Visual clues allow your friends to find you
faster. You may not know which way is up, but take your best guess.
3. After the avalanche comes to a stop, the debris will instantly set up
like concrete. So any actions you take must occur BEFORE it comes to a
stop. Unless you are very near the surface or have a hand sticking up
out of the snow, it's almost impossible to dig yourself out of an
avalanche.
2. Should you go for help? NO! First, they may not need help and you
would needlessly endanger the lives of rescuers. Second, they only have
a precious few minutes to breathe under the snow, so every minute
counts. If you go for help they most likely will not be alive when you
return with a rescue team. Spend about a half hour or an hour searching
before you go for help.
3. Is it safe to go in? Yes, usually it's safe. But if your friend is
buried in a place with multiple avalanche starting zones looming above
and it's snowing hard or blowing hard or there's rapid melting, then
there's also a good chance of another avalanche coming down on top of
the search area. It's a hard call. If you think it's too dangerous then
it probably is. If it's too dangerous then you should go for help. It's
a job for professionals.
4. Find a safe route to the avalanche debris. Often you can descend down
the avalanche path or come up from the bottom onto the debris.
5. If the victim is wearing a beacon, turn yours to receive and make
SURE everyone in your party is turned to receive. Go fast and cover a
lot of ground. Look carefully for clues, hands sticking out of the snow,
snowmobiles, skies, gloves. In most snowmobile burials, the victim is
usually just uphill of their snowmobile. Explain STOP (Stop Think
Options Plan, Speed up by slowing down)
6. If the victim does not have a beacon then it's a needle-in-a-haystack
situation. You have no choice but to look for visual clues and probe.
Move quickly. Use a ski pole, collapsible probe or tree branch to
randomly probe. Concentrate on debris piled above trees or on benches or
any other area with debris accumulation. Probing is difficult, tiring
and time consuming, so don't get discouraged. If you don't have any
success in the first hour or so, then you need to think about going for
help.
7. With multiple burials, go for the shallow burials first. Get them
breathing but don't take the time to get them completely dug out, just
keep moving and find the next victim and get them breathing, and so on.
Get as many people breathing as possible before returning to treat the
injured.
The bad news is that your breath forms an "ice mask" over your
mouth--a thin layer of ice that forms an impermeable barrier. The latest
statistics show that 93 percent of avalanche victims that survive the
ride are still alive after 15 minutes, but then the numbers drop
catastrophically. After 45 minutes, only eight percent are still alive.
In other words, you don't have much time.
by Bruce Tremper, Director of the Utah Avalanche Forecast Center
System
Natural avalanches occur because new or windblown snow overloads
weak-layers or because of rapid warming, but there's almost always
obvious signs of instability by the time avalanches come down on their
own.
