NOVA

Powerful tremors catch millions by surprise.

There was a very violent earthquake.

Collapsing buildings kill thousands.

Many are buried alive.

And we're going to go ahead and have the rescue squad come in

and help extricate that victim out of the hole.

It's the biggest quake to happen here in 80 years.

Major earthquake!

We've never seen anything like it!

Oh, look at that, look at that, look at that!

The quake triggers a huge avalanche on Mount Everest,

killing 20 people.

Whoa, whoa, whoa, inside!

It's the Himalayan peak's most deadly day.

It looks like what you see

when one of these tornadoes runs right through a place.

I've never seen anything come at us like that before.

Millions across Nepal are homeless.

Many are cut off from the world by landslides.

They've lost all the houses that they had.

The whole village is wiped out.

Even scientists are stunned by the powerful aftershocks.

Whoa, that was enormous!

Oh my gosh, it's like the whole mountain's coming down!

We've seen just one fraction of a second

in a 50 million year time interval

of building the Himalayas.

Can they forecast when the next big one will strike?

You know, it's really scary.

There's no reason why one could not occur

in the next ten years or the next ten minutes.

The race is on to unravel the mysteries

of the "Himalayan Megaquake," right now on NOVA.

Major funding for NOVA is provided by the following...

In this hilly terrain, almost all arable land is used.

The slopes stretch up

to eight of the world's ten highest mountains.

Each spring, hundreds of mountaineers come

to climb Mount Everest, the highest point on Earth.

The birthplace of the Buddha,

Nepal is a peaceful haven for both Buddhists and Hindus.

Ancient palaces stand side-by-side

with even older Hindu temples.

April 25, 2015, 11:56 a.m.

The earth begins to move

and doesn't let up for a full minute.

There's no safe place to run.

Whoa, whoa, whoa, inside!

An earthquake rips across the Himalaya...

Get down, get down, get down, get down!

Close the door!

Close the door!

unleashing an avalanche

upon hundreds at Everest's Base Camp.

I've never seen anything come at us like that before.

Oh my God.

Oh my God!

Are you okay?

Yeah!

Are you all right?

Yeah.

Survivors quickly become rescuers.

Makeshift hospitals spring up

to deal with the nearly 18,000 injured.

Many are still buried alive.

Eight-year-old Seema Tamang was trapped under her house.

She can't walk, has a head injury,

but medical care is limited.

There's a race to find anyone alive in the rubble.

Since April 25, seismometers across Nepal

have recorded 400 aftershocks of magnitude four or greater.

Over two million are now homeless.

Shaking isn't the only threat.

Over 5,000 landslides

have left thousands of villages unreachable.

They're cut off from the rest of Nepal,

and they've lost all the houses that they had.

The whole village is wiped out.

They have supplies for about 11 days.

And she's not sure what she's going to do after 11 days,

but she's hoping that the government will come

and give some sort of rescue,

you know, drop some food up here.

So living for them is extremely, extremely difficult

at this stage.

This used to be a cow shed,

and now what you have is people actually occupying this

for their shelters, yes?

So you see there are four little children up here.

They live up here, you see they live in the middle?

That's how they're living.

As the death toll rises toward 8,000,

a few miracles emerge from the dust.

Rescuers dig a baby boy out

from underneath his home on day two.

Remarkably, he's unharmed.

This earthquake came without warning.

People in the central mountain villages felt it first.

Then, just 16 seconds later, the shaking reaches the capital.

The waves rock people like a storm at sea.

The tremors take only a minute to reach Mount Everest,

150 miles away.

The ground is shaking!

Do you hear that?

Irish climber Paul Devaney

picks up his camera to record what's happening.

We realized, "Wow, this is an earthquake

and the whole of the base camp is moving pretty violently."

Then, up above them,

the earthquake dislodges a massive block of snow and ice,

which comes hurtling down.

But they can't see it.

I think probably if it had been a clear day,

people would've seen that avalanche much sooner.

Photographer David Breashears was on the mountain that day.

They had no time by the time they turned around.

Oh, look at that, look at that, look at that.

Oh, look straight ahead.

Ready to go in the tents, or what?

That is immense.

Look, look, look, look, look!

Ready to go in the tent?

The climbers have a few seconds to decide where to run.

I'd say within about 50 feet of our location,

a massive avalanche was bearing down on us.

Oh, oh!

Look, look!

Whoa, whoa, whoa, inside!

At that point in time, you're just focused on,

"How can I survive this, and will I survive this?"

Come under my jacket!

Come under my jacket!

Are you okay?

Yeah, yeah, yeah.

Are you all right?

Yeah.

I've never seen anything like that cloud come at us before.

Are you okay?

We started to learn, three or four hours later,

that there had been loss of life.

Many casualties, people with serious injuries,

multiple broken bones, concussions.

Then every few hours, the death count went up.

These were massive blunt force trauma injuries.

People were blown through the air into rocks.

Ultimately 20 people die on Everest,

and in the rest of Nepal, the total dead nears 9,000.

News of the devastation travels faster

than the seismic waves themselves.

As the earthquake's waves ripple out,

they hit seismic stations at different times.

It takes 24 minutes for them

to reach the other side of the Earth,

in Colorado, where the U.S. Geological Survey

can compare the time they took to reach each station

and then pinpoint where the waves started...

the epicenter.

This one started 50 miles northwest of Kathmandu.

But word travels hundreds of times faster via social media.

We monitor for the word "earthquake" in many languages.

We saw a surge in Twitter traffic.

Realizing it was in a heavily populated area,

an area that we know large earthquakes can do damage,

I was called at home.

Within a few minutes, our seismic sensors

will start seeing this earthquake,

and then we'll locate the earthquake,

determine its magnitude.

Magnitude is the size of the earthquake

at its source.

This one's 7.8... sometimes called a "megaquake,"

an earthquake that's seven or greater.

Earthquake magnitude is not linear.

The 2010 quake in Haiti at 7.0

had the energy of 32 Hiroshima bombs.

Nepal's 7.8 is more than 15 times stronger,

but not as large as this highly active zone can produce.

Geologist Roger Bilham is a first responder

to most of the world's major earthquakes.

I immediately had a look

to see how much money we had in the bank,

and I purchased a ticket on the next flight to Kathmandu.

He's especially interested in the Himalayan region

because of its unique geologic history.

The earth's crust consists of several tectonic plates.

About 50 million years ago, one of them, the Indian plate,

began colliding with Eurasia, gradually forcing it upwards,

creating a massive mountain range...

the Himalayas.

That's what builds the Himalayas.

Where you have compression of two plates,

the plates initially start to fold and fracture.

The Himalayas is probably the largest collision

that we've seen on the planet for the last 500 million years.

The Indian plate continues to converge with Tibet

at the rate of 18 millimeters a year.

In some places, the plates stick,

accumulating stress,

which eventually releases all at once in an earthquake.

This is what scientists believe happened on April 25, 2015.