This is really exciting.
We've been sitting in the UK
waiting for just the right snow conditions for ages.
Then, two days ago, we got the call to say that now is the time.
So, here we are, about to set off an avalanche
just there, on that mountain.
Avalanches are unstoppable forces of nature
that kill hundreds of people every year.
It was kind of a bloodcurdling feeling, really.
I had snow jammed down my throat,
in my eyes, up my nose,
and I really, really needed air.
Even in Britain, around 30 people have lost their lives to avalanches
since the year 2000.
Yet we know surprisingly little about them.
We can't predict when or where they'll strike,
or how big or devastating they'll be.
I'm Danielle George, an engineer and physicist...
Wow!
I've never been in a room where it's snowing.
..and I've gathered an international team of scientists
in the Canadian Rockies for a unique and dangerous mission.
We're going to rig an entire mountain
with cameras and instruments,
and then we're going to load this helicopter with explosives...
Good luck, boys.
Thanks.
..and use it to send a massive avalanche hurtling
down these slopes.
We want to find out why avalanches happen,
where they will strike...
So she's dropping...
..and why some of them become devastating killers.
Are you OK? Big, deep breath. Yeah. You survived an avalanche.
That is a truly...
..frightening experience.
No-one has attempted an experiment quite like this before.
If it works, it will revolutionise our ability to predict
and prevent avalanches.
OK. Here we go.
Wow, look at that!
It's early on a Sunday morning, in March 2018,
and a team of snow scientists arrives in a remote valley
in the Canadian Rockies.
For many, this is their first sight of The Fortress,
a 3,000m peak in the Kananaskis Range.
We've brought these scientists here now
because, for the next few days,
the avalanche risk will be at its highest.
We had about 45cm of snowfall this past week,
and we're heading into another warm-up cycle here.
You know, pretty concerned about the hazard.
I think we'll see a lot of activity in the next couple of days.
OK, so, you see those two trails?
I think that might be a good place for a scan location.
Over the next two days,
the team will be surveying the mountain...
One of the things that's really interesting
is the snow stays so much colder at the top
than lower down the mountain,
that affects how fast it moves.
..trying to learn all they can about the snow conditions,
before we trigger what will be one of the most closely-studied
avalanches of all time.
All right, that's it. Installed.
We've designed this experiment to fulfil three key aims.
First, we want to test our understanding of avalanches
by trying to predict the size, path and power
of the one that we're going to set off.
Second, by studying that avalanche,
we want to learn more about how they work,
why they start and how they do so much damage...
..and thirdly, I want to understand the human cost of avalanches.
Whilst the other guys investigate the avalanche remotely,
I'm going to be getting hands-on with the snow,
finding out what it's really like to be caught in an avalanche.
I want to know what makes them so dangerous,
and if there's anything we can do to survive them.
The star of the show will be this car,
which is going to become a mobile laboratory.
We're going to rig it with sensors,
and then drop it into the surging heart of the avalanche.
If it all works, we will come away with valuable new information
that could help save lives.
We're in a real race against time here.
The slopes above us are covered in fresh snow,
so they are primed for avalanches.
At any time, that snow could come at us,
so we don't want to be down here for longer than absolutely necessary.
So, we need to get this experiment ready and done.
The worst thing that could happen
is that the avalanche triggers spontaneously before we're ready.
So I think, realistically, we've got about 48 hours
to get everything in place.
It's going to be busy.
The next two days will not just be busy,
they'll also be dangerous.
The team will be working in an active avalanche zone.
So, to prepare us for the possibility of being caught
in an avalanche, the day starts with a safety briefing
from local guide and avalanche forecaster Jason Kuruc.
All right, folks,
I just want to take the next few minutes
and show you some of the avalanche safety equipment
that we're going to be using.
We're going to start off with the transceivers.
Danielle, can I ask you to help me out here? Yeah.
So, we're going to put it on underneath your top layer. OK.
So, we're just going to put it over your arm
and then over your head,
and then we'll snug it up, so it's sitting right about here.
I'm going to hand out...
These portable transceivers
are the most important piece of equipment we have.
If any of us are buried in an avalanche,
they'll send out a signal that will alert the rescuers to our position.
For those of us not used to working in the mountains,
it's a daunting prospect.
So, I have a question.
What should I do if I get caught in an avalanche?
So, you want to be trying to do this back crawl swimming motion
to try and keep yourself at the surface of the snow,
and at the very last moment,
when you feel yourself stopping moving,
you want to try and punch a hand up, as well.
That might help us to find you easier.
I feel quite breathless.
You know, when you're talking about it... Mm-hm.
..you know, the feeling of being buried, I'm like...
SHE HYPERVENTILATES You know, panicking.
Yeah, it can be...
..the most exciting and worst few minutes of your life, for sure.
To get some idea of the devastating impact
of being caught in an avalanche, we have to leave The Fortress
and go to the quiet college town of Missoula, Montana.
Avalanches had never been an issue here,
but in early 2014, the town had become a winter wonderland.
It had snowed for 16 of the 28 days of February...
..and everyone wanted to make the most of it.
So, about four o'clock in the afternoon,
I'd just gotten home, I was sitting inside the front room here,
and the kids asked to come out and play.
And I said, "Sure, go play."
And it was about five minutes after that,
I heard a noise coming around the corner here.
And it sounded like a plough truck that was ploughing snow,
like, coming round on this back road, which was really weird,
because they weren't even ploughing the main streets,
the weather was so crazy.
It felt like an earthquake.
It shook the whole house.
You could hear the windows shudder.
And I saw this plume of white snow, it looked like smoke in the air,
just almost like a whiteout.
My wife and I were just sitting in the living room
and thinking about what we were going to do for dinner that night,
and all of a sudden, and instantaneously,
I went from sitting on the couch
to being covered by my house.
It was like a bomb went off,
and my house was sitting on top of me.
And within seconds, I heard my wife screaming,
and, you know, I said, "What's going on?"
and she was just screaming, "My babies, my babies!"
A river of snow had come sweeping off the mountain,
flattening Fred Allendorf's house and burying Casey's kids.
Ten-year-old Coral clambered out unharmed,
but there was no sign of eight-year-old Phoenix.
I saw the lady scrambling about
and wondering what the heck had happened to her son.
I know the statistics.
People don't live that long underneath snow.
You know, it's like, you're sitting there,
you're trying to tell your wife that he's still alive
and, like, really, you know that he's dead.
I was lying there, thinking that either
I was going to suffocate, freeze to death
or somebody's going to find me.
People were coming up with shovels and avalanche probes.
People were shouting out stuff. There was live electric wires.
So, it was quite chaotic.
It was quite a long time before they actually found him -
45 minutes.
He ended up being trapped in this window down here,
in an air pocket.
He was pushed up against the window in an air pocket,
and that's actually what kept him alive.
So, it's almost a miracle that he survived.
And while Phoenix was rushed to hospital,
the search continued for Fred Allendorf and his wife.
We started off five feet away from one another,
and my understanding is she was found about 20m away,
and she was obviously really hypothermic,
and she had lots of internal injuries.
And that was on Friday afternoon, and she died two days later.
The striking thing about the Missoula avalanche
is that it came out of the blue.
No-one had thought the town was in danger.
One of the main reasons we're doing this experiment
is to prevent similar tragedies happening in the future,
by developing a new scientific way of understanding avalanches...
..but there's a worrying trend
that suggests more areas could soon be at risk.
Until recently, we used historical records
to tell us where the danger was.
Mountain valleys were mapped, showing in red the areas
that avalanches had devastated in the past.
It allowed us to say which areas were safe
and which were in danger...
..but these historical records are no longer so useful.
The climate's changing now.
This is changing when the snow falls and when the snow melts,
and in some areas there could be many more destructive avalanches.
Other places, there could be fewer.
It's because we can't rely on the historical records any more
that we desperately need to find new ways of predicting
where avalanches will strike and the amount of damage they'll do...
Hi, Jason.
..but before the serious science can start,
we need to choose the perfect site to trigger our avalanche.
So I've hitched a ride with Jason
to scout out the mountain from the air.
So, how do we choose which avalanche path will be good?
We need a lot of snow up high, in the start zones,
and we need a slope angle greater than 35 degrees, ideally,
up to about 45, 50 degrees.
The first site we look at is called JSP.
Perched on the wide-open slopes of the mountain,
it doesn't look threatening.
There's probably two or three metres of snow just in here.
So, if we were to put explosives across the top here,
that could potentially make it propagate across this whole bowl,
and then all of this snow down here would start falling downhill.
And it's great that we can actually see all the way down,
so we can actually see the path of where the snow might go
on this avalanche as well, all the way down to the road.
So, is that a good site?
It could be a good site, but I'd like to see
a few more options.
The next site we look at is called A Gully.
It looks far more dramatic.
Oh, wow, what about this?
Oh, that's a massive cornice, a couple of metres thick there.
That snow is very, very dense.
You can see how, if we were to put explosives
on the back side of the cornice,
that would cause it to fail and fall onto the slope below it,
to create an avalanche.
Back on the ground, it's time to make the big decision -
where should we set off our avalanche?
You wanted to see the cornices on A Gully. A Gully.
They were massive, what, a few metres?
It is loaded with some snow, but I don't think it has the same
amount of snow as the JSP path. I think...
Oh, well, that's quite interesting, cos I thought on A Gully,
because the cornices were so big, then that would probably be
a really good site, but you're saying you need
more than just the cornice to...
Yeah, you want the whole lot.
If there's slabs at JSP, then it could fracture
across the whole bowl and it could be quite big -
but if it's A Gully,
maybe it's just going to be the local snow, much smaller.
So, it sounds like both of you are saying the same thing, then.
Both of you are saying JSP.
JSP seems like the better bet, but there's no guarantees
in this game. Very true.
JSP looks to be the ideal location for our avalanche.
We know the bowl at the top of the run is filled with deep snow,
but that's not necessarily enough.
If it's going to produce a major avalanche,
that snow needs to contain another critical ingredient.
To find out what that is, I have to travel several hundred
miles south to Bozeman, Montana.
It's home to a unique facility, the Subzero Lab.
OK? Yeah.
It's run by snow scientist Ed Adams.
Wow! I've never been in a room where it's snowing.
What is this room, Ed?
It's a cold lab, and what we're trying to do with it
is simulate nature, as well as we can,
in a winter environment.
Our primary interest is in avalanches.
In the lab today, Ed is performing an experiment
to show how the vast power of avalanches
originates in tiny changes in the structure of ice crystals.
It's something I hadn't appreciated until...until I've come here.
Snow is a very dynamic material.
I call it a shapeshifter.
It's really the hardest stuff to predict.
Ed starts with a typical solid layer of snow...
..but then he dramatically cools the air to -10 degrees
to simulate the conditions on a cold, clear night...
..and within minutes, the surface of the snow
starts to change.
It sprouts feather-like crystals called surface hoar,
the frozen equivalent of dew.
It seems unlikely, but when they're buried under more snow,
these delicate, even beautiful crystals,
become the crucial ingredient needed to trigger avalanches.
To see how that happens, we need to put a sample of the snow
into a CT scanner.
So, this is that first layer that we put in as our base layer -
that's going to be our bottom -
and there's lots of strong interconnections between this.
So, this is a strong layer.
As you said, it appears strong, and it is relatively strong.
The CT scan shows how tightly bonded the strong layer is.
Each crystal forms several sturdy connections to the others around it,
creating a solid slab...
..but the surface hoar is very different.
There's no solid network of bonds.
Instead, each feather-like crystal
only has one delicate point of contact with the layer below.
We've got these large crystals with a very small attachment point,
so they do tend to be very weak, particularly in shear,
so when you put it on a slope, they tend to want to fail.
That's what causes the avalanche?
That's when the avalanche takes off, yep.
Surface hoar is just one of several types of weak layer
that can form in the snow -
and they all trigger avalanches in the same way.
When those fragile crystals start to fracture,
they set off a chain reaction that quickly spreads...
..severing the connection to the layer below
and allowing all the snow on top to slide downhill...
..and when that happens, disaster is never far away.
Ten seconds.
In 2003, snowboarder Johno Verity was in New Zealand
when catastrophe unfolded.
All of the slope was breaking up into cubes of snow.
A hidden weak layer had fractured right underneath him.
It started kind of undulating.
It became a river of snow.
Where's Johno, where's Johno?
It was kind of a bloodcurdling feeling, really.
I had snow jammed down my throat, in my eyes, up my nose,
and I really, really needed air.
Are you OK?
HE PANTS
If we're to succeed in our mission,
we need there to be a similar weak layer
hidden beneath the surface of JSP,
which we can break with our explosives.
Finding it is the next step of our experiment.
The next morning, back on The Fortress,
Scott Havens has climbed to the top of the mountain
in search of that crucial weak layer.
In these conditions, one wrong step
could trigger an avalanche.
So, what we do when we dig a pit...
Cos we're looking for what's happened
over the entire season within the snowpack.
Once they're buried, weak layers are notoriously hard to find.
It's one of the reasons avalanches are so hard to predict.
The most reliable way of finding them is to dig a pit like this.
It reveals the history of the snowpack
that's accumulated over the winter,
and by testing its consistency,
Scott can search for the existence of any weak layers.
So, we have a very dense, very hard slab.
So, barely can get a finger in it -
but as we get further and further down, it's very sugary snow,
it's easier to put my fingers into it.
Take a nice little sample of this...
..and so this is what we're looking for, this is our weak layer.
This is a key discovery.
It's only now that we've found the weak layer that we can be sure
that JSP is capable of releasing a major avalanche...
..and it also gives us another important piece of information.
By sawing along the weak layer, we can make our first estimate
of how large our avalanche could be.
This mini avalanche released about half a cubic metre of snow...
..and it weighs over 100kg.
If, when we drop our explosives, we can get the same weak layer
to fail right across the top of JSP, we can expect up to 100,000 times
more snow to slide out of this bowl.
That would be up to 10,000 tonnes.
A huge avalanche.
But just as Scott is making his discoveries,
there's an alarming development on the other side of the valley.
Hey, check this out. This is real cool. What just happened?
Well, we're starting to see a change in the start zone at the top.
One of our thermal cameras has picked up unexpected movement
in the snow.
So, you see this V in the scan is a lighter colour?
We've got a little different temperature
than the surrounding snow.
It was all dark blue and purple prior,
and then, just in the last couple of minutes,
things started moving. You see it?
It's moving there, yeah, yeah. Pretty neat, hey? Wow.
But, you see, the tail is growing.
I expect it'll be down by here before we're done seeing it.
Wowee!
So, does this mean that the snowpack is really unstable
and this thing could just go at any time? Yeah.
I wouldn't want to be skiing up there right now. Yeah. No way.
So, this is a little bit nerve-racking.
It seems that that avalanche is ready,
and we are nowhere NEAR ready.
We've got more scanning,
we've got an entire experiment to set up.
So, we need that snow to stay up there
for at least another 24 hours.
It seems we may have even less time than we thought.
The scientists desperately need to collect as much data as they can
before the avalanche comes down.
I think this looks good -
we're just going to head up a little bit, and then we'll set up.
It means it's "skates on" time for Chris Hopkinson and his team.
Can I get the tripod first, please? Yeah.
They have just one day to create a map of the mountainside...
It keeps you fit, doing this!
..that we can then use to predict the exact route
our avalanche will take.
There we are.
Their key bit of kit is this yellow box,
which contains a range-finding device called a lidar.
Essentially, what we've got here is a three-dimensional camera,
but instead of using passive light from the sun,
it uses its own active light source.
That light source is a laser,
which it bounces off the mountainside.
The data that's reflected back is then used to build up
this detailed three-dimensional map of the avalanche path.
It reveals every ridge and the steepness of each slope
that will affect the path and speed of the avalanche
as it flows down through this gully and into the valley below.
It's information that will be critical when we try to predict
the size, speed and power of that avalanche.
While the team continue to survey the mountain,
it's time for me to move on to the next part of MY mission.
Because our experiment is about more than just the physics
and mechanics of avalanches.
If we want to save lives, we also need to understand
what being caught in an avalanche does to the human body.
Elyse Saugstad is one of the best skiers in the world,
a former freeride world champion...
..and she knows exactly what it's like to be caught in an avalanche.
In February 2012, she was out with a group of other world-class skiers
on a route called Tunnel Creek,
in Stevens Pass, near Seattle.
What happened that day is a perfect example
of how even the most expert skiers can be caught out
by the hidden risks of avalanches.
I look up to my left,
up into the trees...
..and I see this plume of smoke coming,
like a plume of snow smoke.
My ski partner, Chris Rudolph, yelled at me,
"Elyse, avalanche!
"Elyse, avalanche!"
And I just got flipped over and over and over.
It's a lot like being on a roller-coaster.
The only difference is, in an avalanche,
you don't know when it's going to end and how it's going to end up.
That's when it struck me, "Oh, my gosh...
"This is how I'm going to die."
In just 45 seconds,
Elyse was hurled over 700 vertical metres
down the mountain.
When the slide finally came to rest,
I was mostly buried.
The only thing that was free
was...my face and airway,
which was the most important thing.
But the snow had solidified around me like cement,
and I was so stuck in place, I couldn't even free my head
and lift it up out of the snow.
Elyse was lucky.
She was rescued within minutes...
..but three of her friends died that day.
The thought of being caught in an avalanche is truly horrifying,
and it taps into a genuine fear I have of being buried alive -
but what's it like to be interred in the snow, and why is it so deadly?
Well, much against my better judgment,
I've volunteered to take part in an experiment
which is studying how our bodies react to being buried in snow.
I'm going to have over half a tonne of snow piled on top of me
as part of a trial to test some potentially life-saving equipment.
It's being run by wilderness medicine expert Nic Kanaan.
Nic.
Oh, hey! Hi. How you doing?
Good, thank you. Good to meet you. You too.
Thanks for coming out here.
Oh, well, I was going to say you're welcome,
but you're not really! So...
So, this is it, is it?
This is my grave?
Well, it's not really a grave.
Uh, you're supposed to be coming out of here alive.
It's about a metre deep, and then we're going to be stacking
snow even higher from there.
How do I communicate with you when I'm in there?
You're going to have a radio.
So, you can communicate by radio.
Your feet will not be buried, OK?
Your feet are going to be left free.
If at any point you want out, and you're panicking,
you just start kicking your feet.
Which finger would you like that one on?
This one. OK, great. So this is going to go...
..right here.
The aim of this experiment...
There's nothing nice about this.
..is to find ways to help avalanche victims survive for longer.
We're going to just put this right here,
and then this goes on the forehead.
So, I'm being fitted with sensors that will monitor my vital signs
while I'm under the snow.
Nic's just put this on my finger. See how much my hand's shaking here?
That's bad, isn't it?
But very reflective of how I feel.
One, two. There you go, and I'm going to lower you down, OK?
One, two, three - coming down.
Over three quarters of the people killed by avalanches
die from suffocation.
So, today, I'm helping test a bit of kit called an Avalung.
It's designed to extract the air from the snowpack.
If it works, it should allow me to breathe under the snow
for up to an hour.
Close your eyes.
You're going to have to do some breathing exercises, and...
..all that yoga's going to pay off.
OK?
Cardiac...
Actually, I don't think all the yoga in the world
would help me right now.
I feel utterly terrified, but I guess that's...
..that's the reason we're doing this, cos, you know,
the people caught in an avalanche would feel utterly terrified,
too, so... But I...
Like, my whole body is shaking, and it's not cos I'm cold.
It is truly the most terrifying thing I've ever done, ever.
Or ever wish to do.
I'm only under a metre of snow,
but it really is like being set in concrete.
I can't move.
I can't hear or see anything from the outside world.
OK, can you get on comms and have her wiggle her feet
to indicate that she's OK?
Danielle, wiggle your feet for us.
There we go. Positive - feet.
But already, I'm starting to panic.
Her heart rate has increased to 135.
Her oxygen saturation is dropping a little bit.
She's now at 94% oxygen saturation.
It's soon clear that the survival equipment won't help me
unless I can win my mental battle and remain calm.
After just five minutes under the snow, I lose it completely.
I start hyperventilating and my blood-oxygen level plummets.
So, she's dropping alarmingly...
OK, let's go. Dig her out.
There we go.
There you go.
How you doing?
You OK? Big, deep breath. Yeah.
Big, deep breath. You're doing great.
I'm so sorry. No, you're fine.
You're absolutely fine.
It's just the breathing, I couldn't... There you go.
We got you. We got you.
You're safe.
You're breathing good oxygen.
Your oxygen level is back up to 100, OK? That's good.
OK.
Let's get you out of here, OK? Yeah.
You survived an avalanche.
Up you go!
OK, just stand right there.
That's a truly...
..frightening experience.
It's just the...the sheer panic
of...of the claustrophobia...
..and...and the whole not being able to breathe.
Everything else, I just felt absolutely fine,
but it was... I just...
It's the total mental thing.
I couldn't quite control it mentally,
and so I couldn't...I couldn't control my breathing.
Um...
Yeah.
I can't... And that's just a taste of, obviously, what people feel,
you know, when they're...when they're stuck in an avalanche.
It's truly, truly terrifying.
For many people, the Avalung will be a life-saver,
allowing them to breathe for longer under the snow -
but it wouldn't have saved me.
Unable to control the panic, I inevitably would have suffocated.
That's why we need to conduct experiments like ours.
We need to stop people from being caught by avalanches
in the first place.
Back at avalanche base camp, the team have finished
their survey work...
..and now it's the big moment.
It's time to make our prediction of how the avalanche
will play out tomorrow.
So, Jim McElwaine enters all the data we've collected
into a state-of-the-art computer model,
specially designed to simulate how avalanches behave.
One of the key bits of data for that is a model of the mountain surface,
and that's what we got from Chris's lidar data.
Then Jim adds the details, the depth of the weak layer
and the amount of snow that's lying on top of it.
So, I think there's going to be about 50,000 metre cubed
of snow come down - that's if the whole thing goes.
And we've put all this stuff in,
and then we can run the simulation.
This is the best prediction that current science can make.
It shows the path our avalanche will take
and the distance it will likely travel.
Between 1,000 and 15,000 tonnes of snow will come down the mountain
at speeds of up to 80mph.
The red zones show the areas where the destructive forces
will be the highest...
..and then, after nearly two minutes, it will slide to a halt
right at the bottom of the valley.
We'll see tomorrow how accurate this prediction is,
but we already know that computer models like this one
are fatally flawed.
Sometimes there are some things they can get very wrong.
So, velocities, they're often two or three times larger in avalanches
than the models would predict.
The destructive forces, they can be ten times bigger -
and these can have horrific consequences.
You can design things that you think are going to stand up,
and they get destroyed, many people get killed.
So, the house was right here, as you can see,
where the foundation is.
And so the front door was there, at the head of those stairs.
In Missoula, when the avalanche flowing off Mount Jumbo
struck Fred Allendorf's house, it completely flattened it.
So, this was the driveway.
My office was right there,
and there was a TV room right there.
This is the fatal flaw in our understanding of avalanches.
None of our current computer models would have predicted
this level of destruction.
So, as my good friend - who lives about a block away -
said, "It schmeared the house across the street."
So, the house was completely demolished,
and it was about 100 metres in that direction,
the house was just schmeared all over the landscape.
And Missoula is not a rare case.
Again and again, around the world,
we see avalanches travelling much faster and doing far more damage
than our models can currently explain.
That's why it's so important that we improve our models...
..so we can accurately predict where avalanches will strike
and how much damage they will do...
..but to do that, we must achieve something
that no-one has done before.
We need to find out what's going on
in the heart of the avalanche.
The reason that's so difficult is because,
as they rush down a mountainside,
avalanches throw up a mixture of snow and air...
..creating powder clouds
that can stretch for hundreds of metres in all directions...
..and they are impossible to see through.
If we want to find out why avalanches are so destructive,
we need to find out what's going on inside that powder cloud...
..and that's where our car comes in.
It's going to become a mobile instrument platform
that will let us see inside the avalanche's powder cloud.
Jeff Johnson is a geophysicist from Boise State University in Idaho.
He's a rigging the car with a series of cameras and motion sensors.
It'll then be airlifted onto the mountain
and into the path of the avalanche.
Every year, dangerous avalanches sweep across roads,
swallowing cars whole.
This experiment will give us an unprecedented opportunity
to measure the sorts of forces those vehicles are subject to.
No-one's put a vehicle in the flow path of a snow avalanche
that will be this energetic -
and that's exciting,
because we're going to be able to measure accelerations and forces
that the car is being subjected to
that have not previously been measured.
As it is buffeted down the slope,
it should give us some of the best data ever recorded
from inside an avalanche.
And so that, to me, is very exciting.
We may learn something that we don't know.
But it's not just the car we are going to drop
into the path of the avalanche.
If you get caught in an avalanche,
you are in for a rough ride,
but there are some things we can do to help our survival.
One of them is to wear one of these, an avalanche air bag.
The idea is, if you find yourself caught in an avalanche,
you pull down on this ripcord.
The air bag works in two ways.
First, it acts as a cushion, protecting you from injury
from the power of the snow.
And secondly, it's supposed to take advantage of the way
the different sized chunks of snow in the avalanche behave.
As it churns and rolls, the snow starts to self-organise
so that the smaller particles are on the bottom
and then the much larger snowballs and ice chunks rise to the top.
So the theory is, if you are wearing an air bag,
it makes you bigger, turns you into a larger chunk,
and that should keep you at the top of the avalanche,
and therefore easier to rescue.
To test this, we've got two rescue dummies
about the size and weight of a human,
and we're going to put them in the path of our avalanche.
One of them is wearing an air bag and one of them is not.
In theory, the dummy with the air bag
should stay on the top of the avalanche,
while the other one will be buried deep beneath the snow.
In the morning, we are going to find out if that's true.
Finally, everything is ready.
After two days of surveying and rigging the mountainside,
avalanche day is here...
..and, at sunrise, the whole team gathers.
Morning, everybody, welcome to day three.
Exciting day.
The big sort of theme of it is to remain calm.
Everybody is going to get excited and amped up.
In the end, we need to make proper calls on safety
before anything else happens.
We do the mission, land, regroup
and then see what we have to do to recover.
Calm and slow, measured is the order of the day.
Any other questions, guys?
Awesome. Thanks, gang. Have a good time.
As the final countdown gets under way,
the first thing we need to do is to get the car into place.
So we've got an hour to go, and, for me, this is hugely exciting.
It's amazing to contemplate that this car,
in little more than an hour,
is going to be consumed by an avalanche
that comes down the slope.
It's not something you see every day, is it?
It needs to be lowered with great care.
There are already tracks caused by the snow rolling down the slope...
..and if the car is dropped too violently,
it could set off the avalanche much too early.
You can really see the different bits of the mountain
where it's exposed.
Meanwhile, the scientists gather at the bottom of the slope
to make last-minute checks on their equipment.
Yeah, I'm pretty nervous.
I've got all sorts of bits of kit going on.
Really got to hope I've got it right,
didn't make too many mistakes.
All right, well, here come the dummies.
The next job for Jason, the mountain safety expert,
is to prepare the explosive charges that'll trigger the avalanche.
Only qualified personnel are allowed in here,
so at this point we need to say goodbye for a few minutes
and we'll see you again soon.
It's like perfect conditions for the avalanche.
You know, the sun's been on this all morning,
so it's absolutely ready to go.
So we're nearly there. It's very exciting.
Good luck, boys.
Thanks.
With just six minutes to go, the helicopter takes off
for the final time.
RADIO CHATTER
Jason has to work out precisely where to deploy the explosives
for maximum impact.
He needs to create a shock wave powerful enough to fracture
that weak layer buried a metre under the surface.
I'm confident Jason is going to trigger us an avalanche.
I think he knows what he's doing.
And he's got a big bomb!
Yeah, that's no problem. We're going over to get in position here now.
Then it's a case of lighting the blue touchpaper.
OK, here we go.
Whoo!
At first, not much happens.
It's not clear if the weak layer has fractured...
Come on...
..but then the surface snow starts to slide.
It's coming now, though, look at that. Yeah.
Wow, look at that.
All the time, it is picking up speed, and more and more snow.
Oh, yes.
Look how fast it's going! Yeah.
It's certainly an avalanche you wouldn't want to be in.
If you went over those cliffs, you'd be in a mess.
It's an amazing spectacle -
but was this the avalanche our model predicted?
We can immediately see it made at least one error.
The avalanche didn't reach the valley floor,
stopping several hundred metres short of our prediction.
But just how big and powerful was it?
To find out, we have to go up to the slope
to see the damage the avalanche has caused.
This is the most hazardous part of the entire operation.
There's always the chance of a secondary avalanche
coming down the mountain.
We're going to have somebody acting as avalanche guard
the whole time we're here.
If anybody yells avalanche,
we run HARD towards that treed rib.
HARD.
The first thing we find are the two dummies.
They'd got tangled up and been carried
down the slope together.
But they were sitting safely on the surface,
suggesting the air bag had done its job
and prevented them from being buried.
The next job is to assess how big the avalanche was.
To do that, the lidar team perform another scan.
OK. Looks good so far.
By comparing it to the one before the avalanche,
they can work out exactly how much snow flowed down the mountain.
And so we've got 3,647 cubic metres of loss.
That would give us about 1,300 tonnes
of material, snowpack.
1,300 tonnes is the equivalent of four fully loaded jumbo jets.
But our instruments captured far more
than the size of the avalanche.
These images were taken by our thermal cameras,
and they reveal details that no-one has ever seen before.
When the avalanche starts, it's made up of cold surface snow,
shown in green -
but as it flows, it changes, becoming warmer and more turquoise.
Back at Durham University, the challenge for Jim McElwaine
is to explain what this reveals
about the avalanche's inner workings.
This is radically changing our understanding
of how avalanches behave.
Our old model was that the snow would start off at the top
of the mountain, it would maybe pick up some snow as it moved down,
and then it would deposit it at the bottom.
But what this data shows us is that the snow that starts
at the top probably stops partway down,
and the snow that ends up at the bottom probably started
from somewhere in the middle.
This is very important, because the temperature of the snow
affects how it flows.
This discovery, that the snow at the top of the avalanche
isn't the snow that reaches the bottom,
could have major implications
for our understanding of how far and fast avalanches travel.
It's already helped answer one question.
Whoo!
It might partially explain why our avalanche didn't flow
as far as the models predicted.
Because the snow that reached the bottom was warmer than expected,
it was also slushier and stickier.
And that stickiness contributed to our avalanche stopping
much higher up the slope than the model predicted.
This new knowledge will improve our ability to predict which areas
are under threat from avalanches...
..but what about the really big question?
Why are avalanches so much more devastating than they can predict?
And have we discovered the secret of that vast destructive power?
To answer that, we have to see what our avalanche
has done to the car.
Wow.
It's about 50m below where I think it was set down.
And so... Obviously, it's tilted. It was hit with a lot of force.
The good thing is we have these loggers.
The GPS in here will allow us to figure out how much this has slid.
The car has clearly been seriously damaged.
To see what it went through,
we have to look at the footage from its cameras.
The avalanche starts with a warning of what's to come.
A few large snowballs bouncing down the slope...
..followed by a surging river of snow,
pouring through the gully at around 50mph.
The initial figures from the motion sensors show the avalanche struck
the car with a force of 30,000 newtons,
nearly ten times that needed to break human bone.
Overall, it was nearly four times more powerful
than the computer models would have predicted
for an avalanche this size...
..but can we now explain what generated this extraordinary power?
What current models would suggest
is that the avalanche will hit the car
and it will accelerate smoothly,
move for a bit, and then come to a stop.
But when we look at the acceleration data,
we can see that what actually happened was very different.
What I'm seeing here is there's one big surge...
..the car starts moving -
but then, very surprisingly,
the car gets hit by a second surge,
and then a third surge.
I believe that these surges are most likely why avalanches
have a much greater destructive effect than we would expect.
Until now, our models have assumed
that the snow at the heart of an avalanche
moves like a smoothly flowing river...
..but Jim's theory is that this river is not smooth at all.
That the surges and acceleration are caused by huge waves
in the avalanche.
Like waves on the ocean,
they tower above the rest of the flow
and move much faster and with much greater force.
He believes it was three of these waves
that smashed into our car,
and that they are the source
of the avalanche's unexpected power.
It's potentially a massive breakthrough.
For the first time, we have this direct data
from inside the avalanche -
and this is going to be invaluable for improving our models.
So if we can build these truly predictive models,
then we can really save lives
because we can apply them in areas
where we don't have historical records,
we can apply them if the climate is changing,
and we will know how to design infrastructure
so it can withstand the massive forces that avalanches can generate.
The implications of this experiment could be huge.
For the first time, we are beginning to understand how avalanches move
and why they are so destructive.
It could lead us to a fundamental rethink
in how we assess avalanche risk.
We may find that villages and towns we thought were safe
are actually in danger...
..but armed with that knowledge,
we can now reinforce their defences
to protect them against future calamities.
It may be that these three days in the Canadian Rockies
will one day prove a milestone in advancing avalanche science.
I think this has been really important.
For the first time, we've used portable technology
to look deep inside an avalanche,
and we're just beginning to understand
how these devastating natural phenomena operate.
Now, we are still at the early stages,
we've got a long way to go -
but if we can use this understanding
to improve those models,
then perhaps we can prevent tragedies in the future,
potentially saving thousands of lives.