All language subtitles for D D S02E07 Avalanches 1080p AMZN WEB-DL DD2 0 H 264-playWEB_track3_[eng]

Avalanches are
mesmerizing killers,

stunning when observed
from afar,

yet fatal when caught
in their trail.

I just thought I would die.

The worst thing, of course,

was to see the people
that were dead

and the people
that were really bad.

Broken legs and stuff, yeah.

It was horrible.

These steamrollers of nature

can travel at incredible speeds

of up to nearly
300 kilometers per hour,

generating pressure waves
strong enough

to knock a bus off a bridge,

with an impact force

powerful enough
to level forests

and deadly enough
to take lives.

If you’re trapped
in an avalanche,

there’s almost certainly
nothing that you can do.

The power and speed

of these mountainside
phenomena,

coupled with
their unpredictability,

makes it particularly difficult

to safeguard
against avalanches.

When the avalanche happens,
it happens so fast,

people could not outrun it.

With fascinating
expert insights

and first-hand accounts
from survivors,

in this episode
we’ll be investigating

two disaster avalanches
that struck Everest

in 2014 and 2015,

resulting in a devastating
number of casualties.

We’ll also be taking a look
at a series

of major avalanche incidents
in the Alps.

So, what exactly are avalanches
and what causes them?

Snow is an extremely dynamic

and complex medium
to understand,

and the same
applies to avalanches.

So from a scientific
point of view,

we can predict a lot,
but not everything,

and we rely
on both historical data

and also snowfall records
to get an idea

on where the danger zones are.

It’s all statistical,
it’s like a weather forecast.

You might say
it’s an 80% chance of rain today

and avalanches are the same.

You could say, you know,
there’s a high risk

of an avalanche happening there
today but you can never predict

exactly when it’s going
to happen.

The Canadian government page

dedicated to mountain safety

describes the forecasting
of avalanches

as being as much an art
as it is a science.

There are two aspects
that are going to decide

when an avalanche will occur.

So there is the strength
of the snow

and there’s the,
the gravitational force on it.

So when the load on the snow
exceeds the strength,

the snow, then it will slide.

The difficulty
with predicting avalanches

is that snow is a very variable
and dynamic material.

The strength of snow
can vary enormously

and it’s very hard
to predict how,

at what point

the snow slope will fail

and that can change
a lot over time

with the weather conditions,

so snow accumulating
on the ground

is really just the beginning
of the story.

But although avalanches come

in a variety
of shapes and sizes

and might be tricky to label,

they always consist
of three key features.

The starting zone,
the avalanche track

and the runout zone.

The starting zone
is usually situated

at a higher point
of a mountain

and is the most unstable point
of the slope.

This is where
the avalanche begins.

The avalanche,
now set in motion,

crashes down
along a natural path,

which is the avalanche track.

Finally,
the avalanche course ends

and it comes to a stop
in a pile of snow and dross

at the bottom of the slope.

This is the runout zone.

But what actually triggers
an avalanche

at the starting zone
in the first place?

A series of factors including
the terrain, snowpack,

and weather conditions

are all key triggers

that can kickstart
an avalanche event.

Avalanches are most prevalent

around the Northern hemisphere
in winter months,

with the highest risk period

usually during
snow storm events.

For an avalanche to happen,
you need a ’cake layer’ effect.

a surface bed of snow,

a weaker layer
that can collapse,

and an overlaying snow slab.

Most avalanches
actually happen

in the middle
of snowstorms

and it’s just
fresh snow accumulation

and they don’t cause
so much trouble mostly.

But then other things
that can trigger them

are the sun
if the snow starts melting

and you get water,
and this can start an avalanche

or if the snow weakens,
so it can happen many weeks

after the snow’s fallen,

if the snow crystals
are continuously changing

and if they get weaker, then
that avalanche can also happen.

And then there are
other effects.

Like, there can be earthquakes
that can trigger them sometimes

and then also animals.

All of these natural variables

affect when and how
an avalanche will occur.

But one of the biggest triggers

are actually the ones
caused by ourselves.

Human activity is responsible

for a staggering 90 percent
of avalanche events.

If you ride a snow scooter
or you ski or snowboard

you can also unfortunately
create an avalanche

at the wrong time and then
you could be caught in it.

I turned on the main part
of the face

before the slide
actually caught up with me.

Basically, after the slide
started to move

and propagated out,
I just got swept down

into the main gutter
of that chute.

Once I went over the cliffs
I was under,

you know, definitely
under the snow.

That was when I started
to get really scared

because I knew
how fast slides consolidate

and how little chance you have
once you’re set up.

So that’s when
I really started to struggle

and really, really fought
as hard as I could for my life.

In North America and Europe,

avalanches kill
around 150 people each year,

a significant increase
since the 1950s.

This rise in fatalities
has been directly linked

to an increase in snow sports,

snow mobiles,
skiers and hikers.

A 29-year-old
snowboarder in the U.S.A.

was tragically buried
and killed

when he and his friends
inadvertently triggered

an avalanche while coming
down the slopes

of Jackson Hole
Mountain Resort in Wyoming.

Backcountry skiers
and snowboarders are advised

to carry avalanche beacons
that emit radio waves,

in case they are buried
beneath the snow,

in order to alert rescuers
who can dig them out.

But the U.S.A. is not
the only region

to experience avalanches
where humans are present.

Mount Everest,
the highest and most famous

mountain on the planet,

attracting world-class
mountaineers

from all across the globe.

But on the 18th of April 2014,

the mountain was
in the spotlight

for a very different
and tragic reason.

There are a lot of avalanches
in the spring

and these are caused
by the longer days

and the increased heat
from the sun

and this melts the snow.

So then the water then
trickles down

to the snowpack
to the bottom of the snow.

And this can lubricate it,
so you can get huge avalanches

because all of the snow
all the way down to the ground

can come down,
and these are often the most,

the most dangerous
and the biggest.

At around 6:45 a.m.,
disaster struck.

A powerful avalanche descended

upon a group
of Nepalese mountain guides,

known as Sherpas,
who were in the middle

of preparing the route
and transporting equipment

for seasonal climbers.

Sixteen Sherpas were killed
by the landslide,

making it one of
the deadliest single incidents

ever recorded
in the history of the summit.

The avalanche struck
at the Khumbu Icefall,

a treacherous passage
between Base Camp and Camp 1

riddled with vast open crevasses

and gigantic columns
of ice known as seracs.

The avalanche was caused

when one of these titanic
seracs dislodged.

The dislodged ice block
would go on to trigger

a powerful avalanche made up
of ice, rock and snow.

This snowslide bombarded
through the Khumbu Icefall,

descended on the Sherpas
and buried them entirely.

Every time you go through
the Khumbu Icefall,

you’re taking your life
in your hands.

You can be hit by avalanches.

You can fall into crevasses
or you can have blocks

of the walls of the crevasses
falling off on you.

And I think in total
there are

hundreds of people
who’ve been killed there.

This type of avalanche

is known as an ice slide
or ice avalanche.

Ice slides
are particularly deadly

due to their unpredictability.

They are birthed
by erratic fractures,

rapidly spreading
through gigantic ice blocks.

Minimal exposure

or complete avoidance
of ice fields

is the only real warning
forecasters can offer.

In the tragic event
of Everest, however,

there was no chance
of a forecast

to prevent the incident.

All that remained
was a community

and families left
to mourn their dead.

The Sherpas are highly skilled
and strong climbers

indigenous to Nepal,

with some of
the most skilled amongst them

called ’Ice Doctors’.

According to the Himalayan database,

an estimated 350 to 450 Sherpas
are hired above the base camp

during climbing peak season
as guides

for Western mountaineering
tourists to Everest.

These guides are charged
with the most dangerous

and laborious tasks
of expeditions.

Such tasks include
hauling heavy equipment

and stock up the slopes,

fixing ropes and carving out
routes in the ice

for their foreign clients,

who are usually stationed
in the base camp below

as these preparations
are underway.

The Sherpas
and the local community

know that each time
they head up

through the glacial crevasses
of Everest’s slopes,

it could well be
their last expedition.

But in one of
the world’s poorest nations,

it’s a risk
that many guides must take

in order to provide
financially for their families.

It is difficult
to get exact figures

on just how much
Mount Everest contributes

to Nepal’s tourism industry,

but estimates suggest that
the great mountain may bring in

over $3 million from climbers
alone every season.

The resulting avalanche tragedy
saw Everest shut down

for the rest of the season,
an economic blow

to both the country’s
tourism industry

and communities
like the Sherpas,

dependent on the mountain
for their livelihoods.

But given the scale
of the disaster,

it was the most appropriate
and safe response

the government could offer.

At the time,
the avalanche of 2014

was the biggest disaster
in the history of Everest

with the highest number
of fatalities

ever recorded on the mountain.

No one could imagine
a tragedy of that magnitude

happening again any time soon.

In April 2015,

the mountain was reopened
again for the season.

Climbers and adventurers
from all across the globe

flocked to the legendary
heights once more,

ready and eager
to scale its peaks.

Everest was back in business.

But almost a year to the day
of the 2014 incident,

disaster struck
the great mountain once again.

A regular Saturday afternoon,
on the 25th of April 2015,

in Nepal’s bustling
capital city of Kathmandu.

Suddenly, the earth moved.

A quake located 225 kilometers
west of Mount Everest

and measuring in
at 7.9 on the Richter scale,

tore through the capital,
killing nearly 9000 people.

For Nepal, still recovering

from the events
of the previous year,

this was a horrific blow.

But up on its highest peaks,

more tragedy was to follow.

Minutes later, on Mount Kumori,

a 7000-meter mountain,

situated just a few kilometers
from Everest,

a powerful avalanche triggered
by the quake roared down

and ripped through the middle
of the busy Everest base camp,

submerging it in snow.

I’m just looking up on my left

and just watching
this huge cloud.

It really was like
an explosion.

Very impressive and then
just basically diving

almost into the tent,
under the table.

I remember telling everyone,
"Get down, get down, get down."

What? You know,

you just listen and I ducked
under the dining table--

It was the dining tent--
And I closed my eyes.

I don’t even remember
hitting the floor

when this sound was just like,

wind just coming

and then just,
it just hits you it’s like,

something hits you,
I don’t know,

and you start rolling,
tumbling

and I remember
hearing the sound like...

things accumulating, like,
falling on top of us

and that’s when
I thought, I said,

"This is it, I’m gonna
be buried alive,"

and panic, just pure panic,
you know, not wanting to die.

When it hit, you think,
"This is it," you know.

"I hope if it ends,

I hope it’s painless,
I hope it’s fast."

Mount Everest
has a tumultuous origin

that can be traced
to the Earth’s

earliest tectonic activities.

Millions of years ago,
the Himalayan mountains

gradually emerged
from the crust

as Earth’s Indian
and Eurasian plates collided.

And today, Everest towers

at 8848 meters
above sea level.

But the seismic activity

which birthed
the great mountain,

continues to have an impact,

specifically on avalanche events.

Earthquakes can act as triggers
for slab-type avalanches

on slopes and mountains
by inducing ruptures

in the weaker layer
of snowpacks.

These ruptures then spread
through the weakened snowpack,

till the slab of snow above
gives way and starts to slide,

becoming the starting zone
of an avalanche.

Some of the biggest
earthquake events

around the world have been
followed by avalanches,

including the 7.1 magnitude
New Zealand earthquake in 2010,

the 7.9 magnitude
Peru earthquake in 1970

and the 9.2 magnitude
Alaska earthquake in 1964.

When an earthquake happens,

we get seismic waves generated

and these are waves
that make the ground move

and actually cause
all of the damage that we see

to buildings and in photographs
and on the news.

But because
the ground is moving,

if the ground
is particularly unstable,

or if snow on top of the ground
is particularly unstable,

that movement of the ground,

and we’re not talking
very much,

we’re talking millimeters
or smaller amounts of movement,

that can
actually destabilize rock

or snow or ground

and cause avalanches
or landslides.

On that fateful day

on the 25th of April,

those two plates

that birthed Everest

collided once again.

April is peak season
on Mount Everest.

Close to 1000 people
were on the mountain

at the time disaster struck,
with a majority of that number

settled down
in the south side base camp,

preparing for expeditions
in the upcoming weeks.

The vast tent city
known as Base Camp

has been described
as a temporary home

to people
from all across the world.

There’s several hundred people
that come together there

every year in spring
and they wait

for the right conditions
and they prepare

for their bit
to climb Mount Everest.

So it’s a big hub of activity.

This was
a particularly busy month,

and there were more people
than usual in the camp.

Figures show it was

an almost record-setting year

for Everest,
in climber numbers,

with nearly 400 climbers

securing permits
for the mountain.

Survivors have remarked

on the relaxed
lunchtime atmosphere

at Base Camp that fateful day,
with groups enjoying meals,

socializing and checking the Internet.

It was an idyllic scene.

But that would all
tragically change

in the blink of an eye.

The ground is shaking.

The whole ground is shaking.

Do you hear that?

One of the guys
from our four-man team

started shouting
"get down, get down,"

and as we looked behind
there was a big powder dust,

you couldn’t see at all,
coming towards us.

Pull. Pull.

Pull!

"Come under my jacket.
Come under my jacket."

Are you okay?

Yeah.

The shaking stopped.

I opened my eyes
and everything was white.

There was just a lot of snow

and I remember trying
to scrape it away

so I could breathe

and my hands
were covered in blood.

Then when you hear it,
there was nothing,

no sound at all,
just pure stillness

and it was pretty haunting.

No, no, wait, wait!

Wait, maybe
there’s coming more.

Maybe in the kitchen tent.
Yeah, maybe.

Stay together, stay together

and we try to find
the kitchen tent.

Oh, no.
There is no kitchen tent left.

The kitchen tent.
"Yeah."

The avalanche appeared
like a nuclear mushroom cloud

and rapidly descended
on Base Camp.

The tent city was buried
in snow.

An estimated 21 people
were dead,

with 120 left injured.

There was over 200 volunteers

and we received
maybe 73 injured climbers

that we safely evacuated
back down to Kathmandu.

And just as we’d finished,
there was another earthquake.

Casualties included
both local Sherpas

and tourists
of various nationalities.

Among the dead
were Sherpa guides,

Nepalese, and tourists
from America and China.

The force of it
was incredible.

It comes over you lightly

and then you’re just
totally entombed

in rock and snow
and everything

like all sorts of propellants
coming at you.

So, like, a lot of them hit me
in the back and took me over

and I started flipping
like a rag doll.

The devastation was extensive.

What had been only
a few hours before,

a functioning settlement,

was turned into a desolate
scene of flattened tents

and blocks of rock,

all scattered around a site

entombed in snow.

Rocks and the winds
had taken them out completely.

I mean, I can’t describe it.
Our kit was everywhere.

Those who were not at base camp

also found themselves
trapped by the avalanche.

These were the Sherpa guides
who had gone ahead

to set up the camps,
and mountaineers

stuck on Camp 1 and 2
above Base Camp.

Although there were
no fatalities,

the group, made up of
approximately 200 individuals,

were struck from above,
with some sustaining injuries.

The earthquake, aftershocks
and avalanche

destroyed the route
through the Khumbu Icefall,

the same hazardous region where
the powerful avalanche of 2014

had barreled through,
killing 16 Sherpas.

There was one positive

for the climbers
on Base Camp 1 and 2.

Due to the multitude
of "up and back" trips

required in preparation
for an Everest Climb,

there were enough provisions

to see the stranded climbers
through several days.

But both those at base camp

and the climbers camped above

were locked
in a desperate attempt

to treat and care
for their wounded comrades.

There are really
three main causes

of fatalities in avalanches.

The first would be trauma.

If you’re hit by something

that is moving fast
and is heavy

and you can be very easily
swept away by a large avalanche

so you’ll also be
bashed against rocks,

possibly swept over cliffs.

If you survive that,
as the avalanche stops,

there is considerable danger
of being buried in the snow

and then the next cause
of death would be suffocation.

Snow is a porous material

with a lot of air
trapped in it.

So it’s not
an immediate suffocation.

Statistically, if people
can be dug out of the snow

within about five minutes

they have a very high chance
of survival.

After half an hour there’s
quite a low chance of survival,

maybe in places where emergency
services would take

more than a half an hour
to get to you.

So in that situation,

people are
really relying on being rescued

by other members
of their own party.

It’s also possible
to be partially buried

by an avalanche

so you may still
be able to breathe.

But the avalanche snow,
once it’s settled,

will set very hard.
It can be very difficult

to dig yourself
out of an avalanche.

So after that there’ll be
a risk of hypothermia.

With numerous
fatalities and injuries,

surviving climbers
sent desperate messages

for helicopter rescue.

According to reports,

22 of the most
seriously injured at Base Camp

were flown to Pheriche village,
the closest medical facility.

However, bad weather
and communications

were hindering
helicopter rescues.

Fortunately, I think,

nobody died
in the higher camps.

They all managed
to be rescued by helicopter

or managed to climb back down.

It also proved
extremely difficult

to evacuate climbers
trapped above Base Camp

as the route back through
the dangerous Khumbu Icefall

was severely damaged.

However, the sheer scale
of the disaster

and the casualties
needing relief

was an enormous task
for rescuers.

Tightly wrapped sleeping bags

containing the bodies
of the dead

lay scattered across
the battered encampment.

Transporting the injured
and the deceased

off Mount Everest
was a monumental endeavor.

Due to the large number
of casualties,

a series of multiple trips
were required

as only two or three people
could be transported at a time.

This was an unforeseen
mass-casualty event

that would put a strain
on even an urban hospital.

In order to effectively treat
the large influx of victims,

those in the most
critical condition

were labeled with an "E"
for "Evacuation" sign.

The entire
rescue helicopter operation

and assignment
of transportation

was a massive
and difficult endeavor.

Eventually, on the Monday,

two days
after the avalanche struck,

most of the climbers who
had been stuck on Camp 1 and 2,

above Base Camp,
were transported down.

There were only
three small helicopters,

making multiple
two-minute trips.

But, at last,

all the survivors
were safely brought back down

to the eerily silent
base camp below.

They might have been
unsuccessful

in fulfilling their ambitions

to reach the top
of the famous mountain,

but, incredibly,

they have all come away
still alive.

Because the avalanche ran
straight through Base Camp,

a lot of the infrastructure
and logistics

of all the crews
that were preparing

for the mountain Everest bit
was destroyed.

And, of course,
there was a lot of...

human suffering,

not only in the local area

where the avalanche happened,

but all through Nepal.

So the entire infrastructure

for the climbing season
disappeared

and the government decided

to close the mountain
that year

and no summit bits occurred.

For some communities,
the threats of avalanches

are an ever-constant feature
in their lives

and one they have had
to adapt to over generations.

This is the case

for alpine inhabitants
and communities.

Avalanches pose a greater
threat to human life

and property in the Alps

than in any other region
in the world.

This is due
to the high population density

of the region
as well as the large number

of visitors to the mountains.

There’s now
a lot more development

in some of these
mountain regions because

they are very attractive
tourist destinations.

So tourist industry
has evolved in the mountains

for skiing and mountaineering.

Like the Himalayas,

the Alps are
a major attraction,

enticing an estimated
tens of millions of tourists

to their slopes every year.

Emerging roughly

44 million years ago,

the Alps are the youngest
mountain range in Europe.

And covering more than
207,000 square kilometers

of the landscape,
they are a prominent feature

of Western Europe’s
physiographic regions.

Human settlement is not

a recent phenomenon
on the Alps,

with humans living amongst
the towering peaks

since prehistoric times.

And with the presence
of human activity,

the tragedy of avalanche
disasters has followed.

In December 1916,

at the height of World War I,

more than 10,000 troops
were killed

in a single-day
avalanche disaster,

triggered by artillery fire
on slopes of unstable snow.

The mortality rate
from avalanches

has remained fairly stable
over the last hundred years.

But the increase

in recreational
winter activities

led to the avalanche deaths
nearly doubling

in uncontrolled terrains
between the 1960s and 1980s.

Between 1950 and 1951, however,

the Swiss-Austrian Alps
experienced a series

of deadly and devastating
avalanche events.

The extreme winter

known as
the "Winter of Terror,"

saw 650 avalanches
strike the region

over a three-month period.

High precipitation
and strong winds

led to the heavy snowfall
piling up on slopes,

till the weak layers
gave way and collapsed.

The winter report

from the Institute
for Snow and Avalanche Research

documented and described

the events
of that terrifying winter.

The report describes
the rolling and crashing sound

of the descending avalanche.

It also describes the darkness
that covered a village

as well as the destroyed
houses and homes

which tragically became
graveyards for entire families.

Several villages
and thousands of acres

of forest were obliterated.

If you think about an avalanche
as it picks up speed,

it also creates friction
and that generates heat,

and with the heat you can have
melting of the ice granules

and they form these icy blocks
or these boulders.

And that makes it
very dangerous

because it’s not
the fluffy white stuff anymore,

It’s actually hard big chunks

that can really damage
structures or hurt people.

In Switzerland,

1000 buildings were destroyed.

At the village of Vals
in Switzerland,

the deadliest single event
of the winter killed 19 people.

In total, 265 people
in Austria and Switzerland

lost their lives
in the disasters.

It was one of
the greatest human tragedies

the nation had experienced
since the World Wars.

But there were
important lessons

around avalanche safeguarding

learnt from
these tragic events.

In 1953, major safety measures
were implemented in the region.

These included
the implementation

of effective
avalanche barriers,

as well as the use
of hazard maps

and the expansion of forecasts

by the Institute for Snow
and Avalanche Research.

These improvements would play
a significant role

in minimizing the number
of fatalities

in a similar major
avalanche disaster in 1999.

In some areas
above settlements

where you know
where the risk is

and you know
where the exposure is

then structures can be built
in the mountains,

so fences high
in the mountains

in the initiation zone
of avalanches

to prevent them from sliding
in the first place,

or large structures
rather like dams

that could divert avalanches
once they have started.

The 1999 Galtur disaster

was the worst avalanche
to strike the Alps in 30 years.

On February 23rd of that year,
a series of massive avalanches

hit the Austrian
alpine village of Galtur.

In just a couple of minutes,

the tiny village
was overwhelmed

and buried
in towering walls of snow.

It was terrible.

What happened?
It was terrible!

The avalanches,
labeled by some newspapers

as "the white deaths,"
caused severe damage.

Thirty-one people were killed,

26 of whom were tourists

and five who were locals.

Many more were injured.

It’s almost a mountain
that came down.

It’s incredible.

One moment, you’ll see nothing,

you’ll hear nothing and then
I get no more air.

After the avalanche,
it had gone, it was silent.

We saw some light shining,
some daylight.

We opened the window,
and as we were in the basement,

we were safe because
the rest of the house,

all the floors
just had vanished.

So it’s a fundamental question,

if we can have
this mass tourism growing.

Ski resorts in the region
were shut down.

This was a huge blow
to the resort industry,

costing more than $6.5 million
for each day of closure.

The avalanche was
the biggest human tragedy

the Alps had witnessed
since the 1951 disaster.

But the snow fences
and avalanche protections

put in place since 1953

helped minimize

the number of fatalities.

And rescue workers managed
to save 26 people

in the 24 hours
following the disaster.

We are here now already
for 60 hours

and I sleep for four hours.

I’m a psychologist
and I’m going to Galtur

and this is my own dog
and he has a good taste

and perhaps
also my dog can help

and perhaps he can find
somebody there.

However, the occurrence
of the avalanche itself

in the village
was a scientific mystery.

Galtur was

a popular mountain village,

known as
a winter sports destination,

and although minor avalanches

were a frequent occurrence
in the region,

they would never usually
reach the village.

This was due to the fact

that Galtur was located
in the Green zone,

designated an avalanche-safe zone.

And yet, paradoxically,
it was this exact area

that had experienced the most
significant avalanche damage.

Nature can do strange things.

There are certain areas where
we know avalanches occur

but then patterns change,
weather patterns change.

Climate is changing,
and therefore,

our historical records
may not be accurate anymore

and our predictions
where there are dangerous areas

may not be correct either.

Scientists got to work

investigating the event

and pointed to a number
of weather phenomena

preceding the avalanche.

Throughout February 1999,

three massive weather fronts

had caused the largest deposits
of snow ever recorded

to amass on the mountain.

The strong winds
piled up the snow

into even deeper drifts.

Deep below,
the melt crust supported

an ever-increasing
weight of snow.

Finally, the crust collapsed,

giving way for the snow mass

to come crashing
down the mountain.

The resulting disaster
would impact the region

for many years to come

and change future understanding

of avalanche events.

Avalanches are inevitable.

There are millions
of avalanches

that happen every year
across the world.

Most of them cause no trouble

and kill nobody
and destroy nothing.

But what’s dangerous is
when people go into places

that are threatened
by avalanches.

In Europe, things
are very well organized.

Areas are being divided

into green, yellow
and red areas.

The red areas,
you’re not allowed

to build any structures.

In the yellow areas,
you can build structures

but they need to be reinforced.

And in the green areas
you can build anything.

And this is instigated
by the local government

or the national government even.

And so people need
to abide by those rules.

The main way to prevent
avalanches from causing trouble

and killing people
and destroying property

is just not to build things

in the places
that are threatened.

The disaster events
on the Alps and Mount Everest

are tragic reminders
of just how devastating

and deadly avalanches can be.

Yet as Professor
Ian Stewart has noted,

we still know less about them

than we do the surface
of the moon.

A process known
as artificial triggering

has been offering
an increasing insight

into the workings
of avalanches.

Artificial triggering
is the practice

of initiating avalanches

through controlled explosions

in order to safeguard against
possible starting zones,

and prevent larger-scale
avalanche events,

which could pose a danger
to the public.

Artificial triggering
of avalanches is generally done

using explosives which could
be dropped out of a helicopter.

It could be simply tossed
by hand onto a slope

by ski patrollers traveling
at the top of the slope

or artillery shells
could be fired at the slope

to trigger the avalanche.

Switzerland has been using
artificial triggering

for many years
as a means of mitigating

avalanche disasters in its Alps

and protecting its communities,

transport links

and winter sports resorts.

So in a ski resort, if there’s
been a lot of fresh snow

or they think
the risk has gone up,

then they’ll go out
and they’ll blast anywhere

that they think
an avalanche might occur.

So that will either trigger
an avalanche

or if it doesn’t
trigger an avalanche

then they’ll think
probably the slope is safe.

So that often happens
early in the morning

before they open the lifts.

There are numerous methods

employed to set off
a controlled avalanches event.

These include hand

and manually-charged
deliveries...

helicopter drop-off of charges,

as well as permanently
installed triggering devices.

Permanently installed devices
are increasingly used

due to their relative safety.

In comparison

with manual
and helicopter detonations,

these devices allow
for remote operating

and remove the need of
a human presence in proximity

to the hazards
of a detonation zone.

An example of these devices
is the Gazex,

an explosive tube containing
an oxygen-propane gas mixture

that can be remotely triggered
to start an avalanche.

As well as offering
increased safety,

the devices have
proved efficient.

The devices create
slab-type avalanches

by effectively making fractures

in the weaker snowpack layer

and thereby creating
a starting zone.

In Switzerland,
there are a few hundred

such preventative systems
that have been set up.

But the choice
of triggering method

is very much dependent

on the specific
topographical need

of each individual peak
as well as costs.

Artificial triggering
can improve safety

and save lives
in many different ways.

The primary thing is that
when you’re triggering,

you keep people
out of the way.

The other thing is that

if an avalanche
doesn’t get triggered

then you can decide
the slope is safe

and people can go back in.

And also, it can prevent
too much snow building up

so it might be a spot

that threatens
a town or something

and then if you
let the snow build up

it could be a really big
avalanche that would hit it.

The control

and proximity to avalanches

offered by artificial triggering

is being harnessed
by scientists

to enable better understanding
of these snow events.

Artificial triggering systems

along with technology-driven
warning devices

and reinforced buildings
may be

effective preventative measures
for avalanches,

but they are
not cheap nor always safe.

For avalanche-prone regions

in low
and middle-income countries

such as Nepal and India,

these measures may not be
the most cost effective

nor sustainable options

to deal with
this natural event.

Mountain forests,
age-old natural barriers

used in Alpine regions,

are increasingly being offered
as cost-effective

and efficient protection

against avalanches
and rockfalls.

Now it’s recognized that

forests can be really important

for preventing avalanches
from happening.

So there’s a big effort

to reforest a lot
of areas of the Alps.

And if you plant a forest

in an avalanche starting zone

this can stop them happening.

If it’s lower down the mountain,

they can also stop
smaller avalanches

but they won’t stop
a really big one.

So the main use of forest

is to prevent avalanches
from happening

rather than to protect
from them directly.

With treetops equalizing
temperature and wind conditions

as well as giving stability
on mountainsides,

forests could be described

as nature’s perfect blanket
against avalanches.

However, natural phenomena
such as storms or wildfires

can put these forests at risk.

Deforestation, climate change
and global warming pressures

are also impacting
on mountain forests

and any protection
they may offer in future.

Some scientists have theorized
that warming temperatures

and climate changes
could also be behind

avalanche disasters on Everest,

regions which might
potentially benefit

from the use
of mountain forests.

But all mountain ranges
have diverse topography

and not all regions
are suited or capable

of sustaining forests
in a similar way to the Alps.

For now, there is
no individual solution

to combat the unpredictable
force of avalanches.

And until we can find

more cost-effective
and accurate methods

of tracking their trajectory,

they will continue to be

one of nature’s
most unpredictable killers.