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"Loud
noises trigger avalanches" |
Although it's a convenient
plot device in the movies (and most recently on Jeep
commercials) noise does NOT trigger avalanches. It's
just one of those myths that refuses to die. Noise is
simply not enough force unless it's EXTREMELY loud noise
such as an explosive going off at close range. Even
sonic booms or low flying helicopter trigger avalanches
only in extremely unstable conditions in which natural
avalanches would likely occur on their own anyway. In
90 percent of avalanche fatalities, the avalanche is
triggered by the weight of the victim, or someone in
the victim's party. |
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"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 that shatter
like a pane of glass and slide as a unit off the mountainside.
Picture a magazine sliding off the table, with the victim
standing on the middle of the magazine. This is why
avalanches are so deadly. |
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Avalanches
"strike without warning" |
We often hear the word
“strike” 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. To repeat again because it's
so important: In 90 percent of all avalanche accidents,
the avalanche is triggered by the victim, or someone
in the victim's party. 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. |
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"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. |
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"All
the avalanche experts are dead" |
We're happy to report
just the opposite. Skilled avalanche professionals enjoy
a very low avalanche fatality rate compared to other
groups. Less than one percent of all avalanche fatalities
involve avalanche professionals. |
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"Spit
to see which way is up" |
It doesn’t matter
which way is up. You can’t dig yourself out of
avalanche debris. It’s like you are buried in
concrete. Your friends must dig you out. |
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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. |
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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. |
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What
causes slab avalanches to fracture? |
Snow is a lot like people.
It doesn’t like rapid change. (Raise taxes slowly
enough and no one notices.) Dry slab avalanches occur
when the weak layer beneath the slab fractures, usually
because too much additional weight has been added too
quickly, which overloads the buried weak layer. Snow
is very sensitive to the rate at which it is loaded
or stressed. Two feet of snow added over two weeks is
not a problem. Two feet of snow in two days is a much
bigger problem. Two feet of snow in two hours is a huge
problem. (Wind can easily deposit two feet of snow in
two hours.) Then, finally the weight of a person can
add a tremendous stress to a buried weak layer, not
in two hours, but in two tenths of a second—a
very rapid change. That is why in 90 percent of avalanche
accidents, the avalanche is triggered by the victim
(or someone in the victim’s party). Wet slab avalanches
occur for the opposite reason. Percolating water dissolves
the bonds between the snow grains, which decrease the
strength of the buried weak layer. |
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What
kind of weather produces avalanches? |
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 snowstorms 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 can also cause dry avalanches but this is much
more rare. Rain or melting of snow surface can also
cause avalanches. For instance, rain on new snow almost
instantly causes avalanches. Strong sun or warm temperatures
can also cause melting of the snow and creates wet avalanches.
Wet avalanches occur because of a decrease in strength
of the buried weak layer because water dissolves the
bonds between the snow grains. 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. |
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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.
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How
do people get caught in avalanches? |
In 90 percent of avalanche
incidents, the VICTIM or someone in the victim's party
triggers the avalanche. |
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How
do people die when buried in avalanche debris? |
The good news is that
even dense avalanche debris is about 60-70 percent air,
but that’s not the problem. People die because
their carbon dioxide builds up in the snow around their
mouth and they quickly die from carbon dioxide poisoning.
Statistics show that 93 percent of avalanche victims
can be recovered alive if they are dug out within the
first 15 minutes, but then the numbers drop catastrophically.
After 45 minutes, only 20-30 percent are still alive
and after two hours almost no one is alive. In other
words, you don't have much time.
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What
it's like to get caught in an avalanche? |
A
personal story by Bruce
Tremper
Unfortunately, I know firsthand. It happened
to me for the first time, I believe, in November of
1978. I was a cocky ex-national circuit ski racer, 24
years old, fresh out of college, and because I needed
the money I was building chairlifts at Bridger Bowl
Ski Area in Montana. I already thought of myself as
a bit of an avalanche expert since I had grown up in
the mountains of western Montana, my father had taught
me the basics of avalanches when I was 10 years old
and I had spent many days skiing backcountry avalanche
terrain without. In other words I was a typical avalanche
victim.
I was skiing alone (first mistake) and not even wearing
a beacon (second mistake). After all, I wasn’t
skiing, I was working, tightening the bolts at the base
of each chairlift tower with a torque wrench. Even in
my ignorance, I could see that it was hardly a subtle
situation. Over a foot of new snow had fallen the night
before and it was blowing hard, loading up the steep
slopes beneath the upper section of the chairlift with
thick slabs of wind-drifted snow.
When I was finished with the tower at the top of the
avalanche paths, I started to walk up the slope so I
could gain the ridge and circle around to the tower
on the other side of the avalanche paths. But since
I didn't bring my backcountry skis or climbing skins
(third mistake), what was an easy ski down was an exhausting
pig wallow back up and the cliffs were too scary to
climb in my slippery plastic boots. So I couldn't help
but notice that there was only a 15-foot wide couloir
that separated me from the safe slopes on the other
side. And naturally enough, I thought that a good skier
like myself should be able to get my speed up and zip
across it before anything too bad happened (fourth mistake).
I did my ski cut according to the book. I build my speed
up and I crossed the slope at about a 45 degree angle,
so that in theory, my momentum would carry me off the
moving slab in case it did break on me. Since I had
never been caught in an avalanche before, I had no idea
how quickly the slab can pick up speed after it shatters
like a pane of glass. I heard a deep, muffled thunk
as it fractured. Then it was like someone pulled the
rug out from under me and I instantly flopped down onto
the snow loosing all the speed I had built up.
So like a startled cow, I sat there on my butt and watched
soft slab instantly shatter into little blocks and the
blanket of snow rocketed down the slope as if sucked
downward by extra heavy gravity.
I jumped to my feet and tried to build up my speed again
so I could jet off to the side. But the blocks were
moving all around me, like skiing on tumbling cardboard
boxes, and nothing seemed to work. It was only two or
three seconds after it broke and the avalanche, with
its unintended passenger, was already moving a good
20 miles per hour. Looking downhill, I saw a line of
small trees coming toward me at a frightening speed,
looking like a line of periscopes slicing through the
water toward me, like an old war movie. I tried to maneuver
to grab one of them. But the avalanche, as I discovered,
pretty much has its way with you, and choice is one
of those things you think you might have before you're
caught in an avalanche, but never afterward. Luckily
it took me directly into the smallest tree and I slammed
it hard and grabbed on with all my strength. The snow
pounded me, like standing under a huge waterfall and
it felt like my neck would snap as each block of wind
slab smashed into my head. But the tree snapped off,
and I quickly rocketed down the slope again.
Then the tumbling started, over and over like being
stuck in a giant washing machine filled with snow. My
hat and mittens were quickly ripped off along with both
my skis. Snow went everywhere, down my neck, up my sleeves,
down my underwear, even under my eyelids, something
I would have never imagined. Every time I opened my
mouth to breathe, the avalanche kind of injection-molded
my mouth and throat full of snow. I spat out the plug
of ice and with the next breath just rammed my throat
full of snow again. Just when I needed to breathe the
most, I couldn't. Drowning to death, high in the mountains,
in the middle of winter and miles from the nearest water.
But after a long while, after I was about to pass out
from lack of air, the avalanche began to slow down and
the tumbling finally stopped. I was on the surface and
I could breathe again. But as I bobbed along on the
soft, moving blanket of snow, which had slowed from
about 50 miles per hour to around 30, I discovered that
my body was quite a bit denser than avalanche debris
and it tended to sink if it wasn’t swimming hard.
I swam hard to stay on the surface, but something was
pulling one of my legs down. This was in the days before
ski brakes and I had safety straps attaching my skis
to my boots. One had already torn free somehow but the
other one felt like a boat anchor tied to my leg. The
ski was beneath me in the slower moving debris and as
the surface debris moved faster, it tipped me forward,
shoving my face in the snow again and I struggled hard
to pull that ski up through the debris with my furious
swimming. Eventually, the swimming worked, and when
the avalanche finally came to a stop I found myself
buried only to my waist, breathing hard, very wet and
very cold.
I remembered from the avalanche books that debris instantly
sets up like concrete as soon as it comes to a stop
but its one of those facts that you don't entirely believe.
But sure enough, everything below the snow surface was
like a body cast. Barehanded, (the first thing an avalanche
does is rip off your hat and mittens) I chipped away
at the rock-hard snow with my shovel for a good 5 minutes
before I could finally work my legs free. On one foot,
the heelpiece of the binding hung from the safety strap
with a six-inch section of the top-skin of the ski still
attached to the screws. It had pulled completely off
the ski. On my other foot, the ski was still intact
but both the tip and the tail were broken. It has always
been a mystery to me how it could have broken both skis,
yet none of my bones.
I decided that day that, no, I wasn't an avalanche expert,
not even close, and that was the real beginning of my
avalanche education. Within a month I luckily landed
a job on the ski patrol doing avalanche control, and
I've been studying controlling, and forecasting avalanches
ever since. One of these days, I may even become an
expert. I don’t think it’s possible to watch
all the snow on a mountainside shatter like a pane of
glass and roar to the bottom at 60 mph, ripping out
trees, without it changing your life, especially if
you triggered the avalanche, and more especially if
you rode it down and survived. Avalanches bit me in
the butt and they haven't let me go. |
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What
do I do if I get caught in an avalanche? |
You're first job is to
GET OFF THE SLAB, which as you might imagine, is not
very easy.
Skiers and boarders technique:
If you're descending on skis or snowboard, try heading
straight down hill to build up some speed, then angle
off to the side off the moving slab. 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
ascending when the avalanche breaks, there's really
not much you can do.
Snowmobilers technique:
If you're on a snowmobile you have the advantage of
power. Grab some throttle and use your power and momentum
to your advantage. If you're headed uphill, continue
uphill. If you're headed across the slope, continue
to the side to safe snow. If you're headed downhill,
you're only hope is to try and outrun the avalanche.
Remember that large avalanches travel 60-80 mph and
they are difficult to outrun. Also remember that a disproportionate
number of avalanche fatalities occur when one snowmobiler
gets stuck on a slope and another person rides up to
help them. Never go up to help a stuck buddy unless
there are several other people in a safe place who can
dig you out. This, of course, requires that everyone
is wearing beacons and shovels and has practiced regularly
with them.
Grab a tree. 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. (A quarter of avalanche victims die from trauma
from hitting trees and rocks on the way down.)
Swim. 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 denser than avalanche debris
and it tends to sink unless it's swimming hard.
Clear an air space in front of your mouth.
As the avalanche finally slows down and just before
it comes to rest, try and clear an air space in front
of your mouth. This helps delay the buildup of carbon
dioxide in the snow around your mouth, which allows
you to live longer under the snow.
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.
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. |
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How
do I judge the danger of avalanche terrain? |
Steepness. Almost all 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 snowmobile usually produce
most of the avalanches. A black diamond slope at a ski
resort is usually around 35 degrees--prime steepness
for producing avalanches.
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Anchors. Trees and rocks that stick
up through the snowpack can help to hold the snowpack
in place. But the anchors need to be fairly 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.
Aspect with respect to wind. Recently wind-loaded, steep
slopes are almost always very dangerous while recently
wind-eroded slopes are usually fairly safe.
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.
Consequences. 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.
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How
do I judge snow stability? |
Look
for obvious clues:
Call the avalanche report. The many
mountainous areas in North America have an avalanche
center that issues regular avalanche advisories. This
gives you an easy, overall view of snow stability for
your area.
Recent avalanches. 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. Recent rapid loading
of new or windblown snow. Recent rapid warming. Recent
rapid melting. Rain on new snow.
Active Tests:
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 test. 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.
Snow Pits. Take a reputable multi-day
avalanche class to learn how to dig in the snow and
do stress tests on the snowpack. These can range from
simply pushing your ski pole into the snow or digging
down with your hand to full-blown pits using a shovel.
These require lots of experience to interpret them effectively.
Integrate the information. Never base
your stability evaluation on just one test or observation.
That’s like deciding to get married after the
first date. Bad mistake. Stability analysis means integrating
many different pieces of information together.
Safe
Travel Techniques:
One at a time. There always needs to
be someone left in a safe spot to do the rescue. Never
put everyone on the slope at once. With large groups,
split them in half and stay in visual and voice contact.
Have an escape route planned. Always
think avalanche. What will you do if you trigger an
avalanche? Have a plan first.
Use slope cuts. Keep your speed up
and cut across the starting zone, so that if you do
trigger an avalanche, 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 needlessly died this way.
What are the alternatives? 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 in a protected
area. You may be uncomfortable but you will be alive. |
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How
do people get caught in avalanches? |
Look
for obvious clues:
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If
you see your friend get caught in an avalanche....? |
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.
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.
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.
Find a safe route to the avalanche debris.
It's almost always safe to descend the avalanche path
but if there is a lot of snow hanging above the fracture,
you should avoid disturbing it. Usually the safest way
to access avalanche debris is to come up from the bottom
onto the debris.
Do a beacon search. 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. If you are descending on
skis or a snowboard, follow a zig-zag pattern so that
you overlap the range of your beacon (usually 40-60
yards, depending on the brand). 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.
If there’s no beacon--probe.
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.
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 completelly dig the victims out or treat
the injured. Remember, finding multiple beacons takes
quite a bit of practice. |
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