Secrets of the Earth

We have uncovered

a remarkable planet,

a world of extreme weather,

alien landscapes,

and bizarre phenomena.

It's the most complex system

we know of in the universe.

That planet

is Earth,

and we are only beginning

to unlock its secrets.

When the world turns to white,

a blizzard is in full effect.

The wind is just cranking.

Oh!

You can't see your hand

in front of your face.

There's some snow out here.

Before you know it,

they've got two feet of snow

in 24 hours.

That's unbelievable!

It's almost sensory overload.

The worst ones

can even strike you dead

in a blinding flash.

Listen to that!

Blizzards are one of the most

intense weather phenomena

on planet Earth.

When the surrounding

world disappears,

and death

is a real possibility,

you'll know it's a blizzard...

We're getting upwards

at times of--

...on Secrets of the Earth.

In a galaxy crowded with

frigid, hostile worlds,

planet Earth is

a life-sustaining sanctuary,

unless a blizzard

is suddenly unleashed.

The wind howls,

a three-dimensional

wall of snow

erases the surrounding world,

and life comes

to a sudden halt.

The way a blizzard

can affect a community

is unbelievable.

It can knock out transportation

for days.

Everything comes

to a standstill.

Power outages,

all but a certainty.

February 9, 2013.

Winter Storm Nemo slams

America's Northeast.

Blizzard conditions drop

two and half feet of snow

in some areas,

immobilizing some

40 million people for days.

The principal factor which

makes a blizzard a blizzard

is the strong wind.

A blizzard is essentially

a dust storm with snow.

A storm like this

is a rare event,

and understanding its secrets

means peering directly

into the clouds that

manufacture it.

Overlooking

Steamboat Springs, Colorado,

at an elevation of 10,500 feet,

the wind-ravaged Storm Peak Lab

is the perfect place

to uncover the secrets

of a blizzard.

To qualify as a true blizzard,

a snowstorm must meet

very specific criteria.

We can tell that we're in

blizzard conditions

through this instrument

right here

and wind greater than

35 miles per hour.

As well,

we need to have visibility

less than a quarter of a mile,

which we're witnessing right now

because we have

whiteout conditions here

located at the summit

of this mountain.

If these wind and

visibility conditions persist

for more than three hours,

the National Weather Service

labels the storm a blizzard.

Blizzard warnings in effect.

Scientists

typically study blizzards

by flying weather instruments

through the clouds.

But at Storm Peak Lab,

the scientists

live in the clouds.

This land-based

cloud probe array

uses a continuous laser beam

to sample and decode

the secrets of a blizzard.

These three probes

allow us to study

the inner workings of a cloud.

So by looking at the snowflakes,

looking at the ice droplets,

and looking at the liquid water,

we can determine what's going on

with the blizzard.

A blizzard

starts high in the clouds,

with tiny, super-cooled

water droplets

that seem to defy

the laws of physics.

These are droplets many times

finer than a human hair,

and what happens is that

these droplets stay liquid

even though the temperature is

far below the freezing point.

A water droplet

can remain in this super-cooled

liquid state all the way down

to minus-40 degrees Fahrenheit.

But when that droplet

encounters a small particle

of dust, it freezes

around the particle

and forms an ice crystal.

For that crystal to evolve

into a single snowflake,

it must begin growing

like a tree.

This happens when random bumps

form on the ice crystal.

Water vapor molecules

begin attaching to

and growing branches

on the bump.

More bumps grow

on the branches,

creating a stellar dendrite,

a snowflake.

We have all

heard the phrase that

no two snowflakes are alike,

and of course that is true,

but it is true to

an extraordinary degree.

We start off as these beautiful

symmetric, pristine snowflakes

that you've seen in books.

Thousands of these

will collect together,

because as one snowflake falls,

it collects others.

And then it falls faster

and gets larger,

collects even more,

and there's this runaway

growth process

that leads to a snowflake

falling on the ground.

The result is

powdery snow that's light

and virtually water-free.

In fact, every snowflake

is 90% to 95% air,

taking up ten times as much

space as liquid water.

It's extremely light,

extremely powdery.

It's very dry.

The snowflakes don't have

a lot of moisture.

They haven't

fallen through a cloud

that would give lots

of moisture to the snow.

The surprising