Kind: captions
Language: en
this is a video about
avalanches what they are what causes
them how destructive ones can be
prevented and what to do if you're ever
caught in one to actually feel the force
of the avalanche on your body there's
kind of nothing that can prepare you for
that for this video we followed around
the ski patrollers at North America's
biggest ski resort Whistler blackcomb to
trigger avalanches and film them up
close if you've ever driven through the
mountains in Winter or have gone skiing
at a resort you were kept safe by the
knowledge gained by snow scientists
Avalanche forecasters and ski
patrollers if you Google the deadliest
Avalanche the first result will be from
May 1970 when the town of yungi and 10
nearby Villages were destroyed and
estimated 30,000 people were killed but
the Avalanche was triggered by a 7.9 9
magnitude earthquake and the Avalanche
caused a landslide which buried the town
so it wasn't really Avalanche
destruction the deadliest snow
Avalanches happened in December of 1916
during World War I some of the fighting
took place in the dolomites a mountain
range in Northern Italy there thousands
of Italian troops were battling austr
Hungarian soldiers and it had been a
particularly snowy winter over 12 M of
snow had fallen on the mountain range in
the first week of
December on the 13th of December a
single Avalanche wiped out the Austrian
Barracks near Mount marmala killing at
least 275 people but its flow on effects
were far more devastating both sets of
troops realized they could use snow as a
weapon so soldiers on both sides fired
artillery shells into the mountain above
their enemy camps deliberately
triggering Avalanches over the next few
days between 2,000 and 10,000 soldiers
died buried underneath the
snow but most deadly Avalanches aren't
triggered by earthquakes or artillery
shells they're triggered by skiers
snowboarders and snowmobilers recreating
in the back country 93% of fatal
avalanches in the US were triggered by
the weight of the victim or someone in
the victim's party
so how could something so massive and
destructive be triggered by the weight
of just a single human this is Bruce
trer he literally wrote the book on
Avalanches the book which inspired us to
make this video I was a hardcore ski
racer but when I was done racing then I
started building lifts for the Bridger
bow ski patrol and I got caught in my
first Avalanche my job for that day was
tightening of all the bolts at the base
of each chairlift Tower to cuz we were
doing our load test that day and they'd
warn me okay once you get done with this
Tower whatever you do don't cross that
big Avalanche path below it you know and
I made some snide remark like yeah yeah
yeah I I know about all that stuff don't
worry about me you know when I got done
tightening those bolts then I realized I
made a really serious era because I was
just wallowing up to my chest now I
almost needed to take out a shovel and
dig like a tunnel through the snow to
get back up to the Ridge and it was just
exhausting
work and then I got cocky I thought well
I've heard about these ski Cuts I can
just build up my speed and get to the
other side because that's where I wanted
to be anyway like an idiot that's what I
did the first thing that happens when an
avalanche breaks is it just it starts
moving and the first thing you do is
kind of flop over on the snow because
you lose your balance like somebody
pulls a rug out from underneath you and
you fall uphill and there I was just
kind of laying in the snow getting
drugged down the mountain you know I was
caught I couldn't get out of it you know
luckily I was able to grab a small tree
but the snow is just beating me to death
you know and just about snapping off my
neck as it's going by me on this tree
luckily a lot of that snow went by and
that's why I didn't die that day but
then it fin the tree finally snapped off
or something happened and I was uh you
know Tumbling Down the Avalanche path
luckily when I got to the bottom I was
only buried up to my chest I was in the
the tail of the Avalanche and the
Avalanche dies from the tail first so
that slows down while the front part
keeps moving you know I had a lot of
time to think about that for the rest of
the day tightening the rest of those
bolts and thinking holy smokes I should
I could have died I should have died and
I didn't you were tightening bolts you
were caught in an avalanche and then you
went back to Titan bolts that day you
like you went back to work oh yeah yeah
well somebody had to do it I was the guy
that was my job you know this how I was
raised by my father you get the job done
you
know at the most basic level an
avalanche happens when the crystallin
bonds between the snow crystals break
and the force of friction holding the
snow on the mountain isn't enough to
counteract the pull of
gravity Avalanches are categorized by
size on a scale of 1 to five uh one
would not be large enough to bury a
person but size five would involve a
100,000 cubic met of snow traveling many
kilometers causing destruction on a
massive scale the first thing to note is
that snow isn't uniform the snow pack is
built up one storm at a time so it's
layered and these layers aren't all the
same and they change over time due to
the conditions they're exposed to to the
air temperature humidity Sun wind and
rain all affect the structure of the
snow for example after fresh snow has
fallen if there's a warm sunny day the
snow will melt and then refreeze
overnight creating a sheet of ice the
most important condition is the
temperature gradient in the snow pack
but we'll come to that the snow pack
preserves a record of everything that
has happened to it if you dig a pit into
the snow you can read the different
layers to understand its
past nine different Avalanche problems
are recognized but there are two main
types slab and loose there are two types
of loose Avalanches dry loose and wet
loose the snow in dry loose Avalanches
is well loose the snow isn't all stuck
together so after it's triggered it fans
out sometimes loose Avalanches are also
known as as Point release
Avalanches dry loose Avalanches are
commonly known by skiers as Slough and
they usually aren't a serious Hazard
though they can drag a skier off a cliff
it's funny because like in the skiing
Community we've just said like this one
kind of avalanche isn't an avalanche we
just call it something else I had a run
in with SLU uh yesterday at hellbrunner
and you just feel like this wall of snow
pushing you from the back honestly it's
kind of fun it's fun it's like it's kind
of like surfing where it's it's Dynamic
and it's moving and you have to keep
moving with the terrain because you know
that yeah the slough is behind you and
if you're not moving fast enough it's
going to get you another type of
avalanche is wet loose it typically
happens around spring on like southf
facing aspects the sun heats up the snow
and makes it more dense and slushy and
runny the sun's starting to come out I'm
not currently too worried about wet
loose right now but I will be in about
an hour
but the more deadly Avalanches are slab
Avalanches where the top layer of snow
becomes stuck together like a cohesive
slab when the Avalanche is triggered the
snow releases together in big chunks the
prevalence of slab Avalanches depends on
the angle of the ski slope under 25°
there isn't likely to be a slab
Avalanche because gravity just isn't
strong enough to pull the snow down the
mountain any slope steeper than 50° is
also unlikely to have dangerous
Avalanches the slope is so steep that
it's hard for much snow to accumulate
regular small sloughs and slab
Avalanches prevent the buildup of larger
more dangerous slabs 75% of dangerous
slab Avalanches occur between 34 and
45° for comparison a black diamond ski
run is typically around 30° and a double
black diamond is around
40° in other words the the best
conditions for skiing are also the best
conditions for
Avalanches what's really terrifying
about slab Avalanches is you can trigger
them remotely you could be skiing or
walking on a slope that is far less than
30° and trigger an avalanche on a
steeper slope above you and slab
Avalanches are fast they can reach
speeds up to 120
kmph friends of mine have been killed
that way you just don't realize how far
these cracks can PR propagate through
the snow slab Avalanches have three
parts to them a bed surface which is the
lower part of the snow then there is a
weak layer and the overlying slab the
bed surface and the slab are strong
layers that is they're made out of snow
that sticks to itself the kind of snow
that you can make into a snowball the
shape of the snow crystals in strong
layers tends to be rounded in contrast
the weak layer consists of snow crystals
that don't readily cohere one another
these tend to be more angular or faceted
crystals but there are a few different
weak layer types one of the most
worrying is known as surface it's
not made out of snow that falls from the
sky it grows on the surface of the snow
on cold clear nights the surface snow
radiates a lot of its heat away becoming
even colder than the air since warm air
holds more moisture than cold air that
moisture will crystallize at the top top
of the snow creating surface wh surface
wh is formed by condensation it's the
snow equivalent of dew it's really
angular and it doesn't want to stick to
itself usually surface hor is then
broken down by wind or sun melting it
but if a snowstorm occurs just after
these crystals have formed they can
become buried and in that case they
create a very nasty weak layer which is
just perfect for
avalanches another week layer to worry
about are facets snow crystals that used
to be round but that became angular in
the snow pack facets develop when
there's a strong temperature gradient in
the snow A thermal gradient of less than
1° per 10 cm does not produce facets
anything more than that can which is why
the temperature inside a snow pit is
measured if there's a large thermal
gradient there could also be a weak
layer right above and right below crust
there can be really wild temperature
gradients so we had it it down 10 cm it
was - 5.5 and down 20 it was -
3.7 so that's 2 de difference the bottom
of the snow is warmer than the top of
the snow so the warmer snow near the
ground sublimates turning straight from
solid water into water vapor this water
vapor Rises up through the snow pack and
then encounters the colder snow crystals
at this point it refreezes and forms
faceted crystals which like surface
don't stick together creating a
weak layer the bigger the change in
temperature the faster the snow crystals
change and the faster they change if
they change quickly it can promote fting
which promotes instability the other
important factor in slab Avalanches is
the stiffness of the slab since the snow
is cohesive when a force is applied and
the interface between the slab and the
weak layer starts to slip that force and
hence the slippage propagates when while
stiffer slabs might resist initial
triggers better their failure leads to
more propagation leading to larger
Avalanches this also results in more
remote
triggers Avalanches are common after
storms the extra weight of the snow
exerts an additional load onto the snow
pack which can trigger the weak layers
deeper in the snow pack to slide the
vast majority of avalanches occur during
or right after a storm in other words
the best conditions for ski are also the
best conditions for
Avalanches strong winds also increase
the risk of avalanches the wind can pick
up and transport the snow from open to
more sheltered areas as the snow
accumulates the wind pressure compacts
these snow particles as they are
deposited which creates a dense cohesive
layer these newly deposited layers of
snow are called wind slabs wind slabs
can be quite unstable especially shortly
after formation if they've formed over a
weak layer
since they're more cohesive these slabs
can break free as large chunks during an
avalanche making them particularly
hazardous another concern are cornices
cornices form when the wind blows snow
over the top of a ridge and it piles up
on the other side hanging over the edge
cornices can weigh many tons and when
they fall onto a slope they can trigger
massive slab Avalanches one of the ways
that Backcountry skiers test the
stability of the slope they're about to
ride is by dropping a cornice onto it if
the slope didn't slide under the weight
of a cornice it's unlikely to slide
under the weight of a
skier so how are Avalanches prevented in
ski resorts for this video veritasium
producer Peter went out with the ski
patrol team at Whistler blackhome which
is North America's largest ski resort
dude I'm pumped really pumped really
anxious really stoked it should be a
good day there are sections in ski
resorts that are Avalanche terrain
slopes that are greater than 30 or so de
or under Avalanche terrain to keep
skiers safe before a ski area is open
the ski patrols do Avalanche control
work fundamentally it boils down to them
triggering avalanches in a safe way
before there are any skiers on or under
those slopes this is done often enough
so that the snow doesn't get a chance to
build up too much so the Avalanches that
are triggered are
smaller there are a few ways that this
is done but the most common is by by
using explosives explosive charges with
a two-minute fuse are lit and then
detonated on the slopes where they are
likely to produce
Avalanches oh boy really glad I put on
those
goggles sometimes this is done by
throwing the charges out of a helicopter
but a lot of the time this is done on
skis there are even special trams where
the Chargers are attached to a carabiner
and then shuttled across to a hard to
access slope as the charge detonates the
shock wave breaks the weak layer leading
to an
avalanche
yes we got a
slide that wasn't too bad wasn't great
something it was something despite doing
the shoot the day after one of the
biggest storms of the Season we weren't
particularly lucky with getting large
Avalanches we shot all morning and only
got this relatively small slide so I was
getting worried and then we were able to
get this shot
[Music]
oh my God look at
that
[Music]
oh avalan control work is also done on
roads with basically the same idea
trigger Avalanches before they get a
chance to become big and destructive for
example the Trans Canada Highway
connecting the East and West coasts of
Canada goes through Rogers Pass a
mountain pass with 3,000 M tall Peaks on
either side of it the road is right next
to a mountain that's actually called
Avalanche Mountain here Parks Canada and
the Canadian Army conduct Avalanche
control by firing artillery shells at
one of the 270 preset Targets on the
nearby mountains releasing small
Avalanches before they get a chance to
become big and destructive and damage
the
highway deaths from avalanches do
occasionally occur inbounds at Resorts
but they are very rare due to the
diligent work of ski patrollers most
Avalanche injuries and deaths occur in
the back
country it's kind of crazy cuz as a
skier you know you hear so much about
avalanches you realize it's it's deadly
and people die every
year but to actually like feel the force
of the avalanche on your body
like there's kind of nothing that can
prepare you for
that every time I hit the ground I would
just like dig my hands in my feet in
like try to like claw myself down onto
the ground but while also like trying to
protect my head
I knew also like the moment the snow
stopped if I was still in the snow I
would be buried I wouldn't be able to
move I wouldn't
be you know I would be counting on my
buddy to find me and dig me out and save
me
aen pass up the get sced
this wasn't a huge Avalanche this was a
size two so like big enough to you know
bury a car but not like a house so I was
actually able to stop on the slope
before it flattened out where you know
all the snow would accumulate and I
would be buried
[Music]
that but yeah it was intense really
intense and I felt really stupid because
it was uh it was the first Mountain I
ever skied on as a kid was this was this
mountain like this very slope and so I
was just so comfortable with it and like
didn't think twice about the fact that
it was Avalanche train and the snow or I
mean we did check the snow up top but I
don't know I wasn't like fully tuned in
to to the dangers that are present like
the moment you step into Avalanche train
something like that can
happen so the three things that you need
to bring when you go back country skiing
is a beacon which is this thing a probe
which is this big long stick that ends
up collapsing so it does fit in your
backpack and uh shovel if you're buried
in a slab Avalanche it's almost
impossible to dig yourself out during an
avalanche the snow gets mixed around and
friction Heats it up so it melts a
little bit and then when the Avalanche
stops IT refreezes setting like concrete
that's why if you're fully buried you
need someone else to find you and dig
you out
this is why in 1968 the Avalanche Beacon
was invented the beacon is uh a
transceiver so it is both a transmitter
and a receiver of electromagnetic waves
at
457 khz so right now it is in sand mode
so this is the mode it would be on if
I'm skiing in the back country and if
there's an avalanche what would happen
is it'll keep sending out those
electromagnetic waves in all these
directions
then my buddies would change from send
mode to search mode and start looking
for that signal
and what that looks like is that Aaron
is 2 m away from me and her Beacon is on
and it's saying cool there's a person
two 2 met away from me
so around 25% of avalanche fatalities
are from trauma hitting a tree or a rock
or being pushed off a cliff the rest are
from asphixiation if you're buried in an
avalanche and your face is under the
snow there's a small air pocket for you
to breathe the snow is initially porous
but the heat from your body and breath
melts the snow which refreezes forming
an impermeable bubble as you breathe the
concentration of CO2 in that bubble
increases and the amount of oxygen
decreases until you die from
asfixiation if your friends find and dig
you out in the first 10 minutes you have
an 80% chance of survival 15 minutes in
that chance drops to 40% 30 minutes in
you have just a 22% chance of survival
so time is
key there is another invention that
could save your life which is an
avalanche airbag if a skier triggers an
avalanche they can pull on a cord which
activates the airbag the airbag rapidly
inflates historically this was done with
compressed air but newer versions use
battery powered fans the airbag
increases the skier's buoyancy making it
less likely for them to be buried deeply
in an avalanche an added benefit is that
if the skier is buried as the airbag
deflates it leaves a larger air pocket
providing more time to be rescued
Avalanche airbags decrease the chances
of death by nearly
[Music]
half around 30 people in the US die in
Avalanches each year plus an additional
100 in Europe most of them are
Backcountry skiers snowboarders or
snowmobilers and they very likely
triggered the Avalanche that killed them
Avalanches are beautiful Majestic and
completely terrifying if you go into the
back country in Winter please carry a
shovel a probe and a beacon but also
check the avalanche forecast and make
good decisions when heading out to
Avalanche terrain because the best way
to survive an avalanche is not to be
caught in
one we know so much about avalanches
today thanks to people like Bruce people
who followed their curiosity and learned
through Discovery but thankfully you
don't have to go into Avalanche terrain
to experience this kind of learning you
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