National Geographic: Tsunami - Killer Wave

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C'mon, Matt!

Attention all stations.

Stand by for

an urgent tsunami warning

for the Big Island and

the islands of Maui, Lanai and Oahu.

This warning is based on a

near Kailua-Kona.

Could it really happen?

Could a giant wave really menace

the beaches of Hawaii?

There is something out there

and it threatens coastlines

around the world.

It's one of nature's

least understood forces: Tsunami!

We often see hurricanes and typhoons

that churn up

higher-than-normal tide.

They can flood

low-lying coastal communities.

But as dangerous

as these storm surges can be,

they are not the worst of

all possible waves.

The real monsters are tsunamis,

freak waves usually produced by

undersea disturbances

like earthquake.

They can race across entire oceans

and swallow cities whole.

And they can leave

tens of thousands dead.

Throughout history,

tsunamis have generated

legendary disasters...

Reversion the shores

nearly every ocean and sea.

Without warning

and without mercy.

killer waves have struck

again and again.

And tsunamis are as mysterious

as they are deadly,

because so few have ever

been observed by scientists.

This extraordinary footage

was shot in 1952,

in the Kuril Islands off

Russia's northern Pacific Coast.

A typical tsunami,

it moved inland like a rising tide,

but with far greater speed

and force.

Fortunately it caused

only minor damage here...

and no deaths.

But tsunamis can be catastrophic.

In the last century alone,

more than 50,000 people

have been killed by tsunamis.

Most had little or no warning.

Few were even aware of the danger.

But for the people of

the Pacific Rim,

deadly tsunamis are not rare events.

They live in the most seismically

active part of the planet,

an area criss-crossed

by earthquake zones

and dotted with volcanoes,

so it's not surprising

that the vast majority

of the world's tsunamis occur here.

In the middle of the Pacific,

the Hawaiian Islands lie isolated

and exposed.

It's people are certainly

no strangers to tsunamis.

But some of them

are acutely aware of the risk.

Dr. Walter Dudley

is director of marine science

at the University of Hawaii at Hilo,

and a leading expert on tsunamis.

We'll have a little

on-site safety briefing.

Today he's taking one of his classes

on a snorkeling field trip.

But first, a few words of caution.

Okay guys, everybody listen up.

We're only about 30 miles

from the epicenter

of two of the largest earthquakes

that have ever struck this island.

In both cases,

they generated

large destructive tsunamis.

The waves took about ten minutes

to get here

and were about 10 to 15 feet high.

So if you are out there on the reef,

and you feel a big earthquake,

drop your gear

and get out of the water

and move ashore

as quickly as possible

Okay, let's have a good lab.

They are among the most catastrophic

of all natural phenomenon.

Unlike things like hurricanes,

there are no warning signs.

The weather doesn't get bad.

You don't feel the earth shake.

It can be just a beautiful day

and then, all of a sudden,

the ocean can come up

and come ashore 30 feet high.

In the Hawaiian Islands,

we've recorded tsunami wave heights

as great as 56 feet on this island

from the 1946 Aleutian tsunami.

In prehistoric times,

wave heights may have reached

over a thousand feet.

Hilo has been struck by tsunamis

as long as there has been a Hilo.

But it was really in 1946

when there was

a built-up downtown Hilo

that we had

a very, very large tsunami

Nineteen forty-six...

after four years of war,

Hawaiians can relax.

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