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WWW.MY-SUBS.CO

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>> Earth, a unique planet,

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restless and dynamic.

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Continents shift and clash,

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volcanoes erupt,

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glaciers grow and recede--

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titanic forces that are

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constantly at work,

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leaving a trail of geological

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mysteries behind.

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This episode investigates

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the deadliest and most

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destructive volcanic event

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in U.S. history.

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Mount St. Helen's,

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a pristine snow-capped mountain,

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suddenly blew 600 feet

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off her summit in a type

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of eruption no one had ever

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witnessed before.

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Scientists trying to understand

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what made this event so lethal

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uncover evidence for one

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of the biggest landslides

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in history, a sideways-directed

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blast that knocked over

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230 square miles of forest

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and mega mud flows that

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thundered down the valleys

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and destroyed everything

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in their path.

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What scientists have discovered

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from this unique event brings

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geologists one step closer

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to understanding

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"How the Earth Was Made."
S02x10 Mt. St. Helens
Original Air Date on February 2, 2010

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-- Sync, corrected by <font color=
-- for MY-SUBS.com ---

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In Washington State,

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100 miles south of Seattle,

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stands Mount St. Helen's,

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one of 20 major volcanoes

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that form part of the Cascade

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Mountain Range at the

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North American West Coast.

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Before May 18, 1980,

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she was at the center

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of a thriving recreational

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paradise and prosperous

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timber industry.

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>> The volcano had

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a beautiful conical form.

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It was called the Mount Fuji

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of North America,

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and the form was a bit concave.

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>> But beneath her beauty

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lay an ominous secret.

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The mountain was brewing

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something that had

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a deadly potential.

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The story began

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on March 20, 1980,

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when a 4.2-magnitude earthquake

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woke Mount St. Helen's

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from a slumber that had lasted

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123 years.

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The last known eruption

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was witnessed in 1857

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by local tribes.

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In 1980, the earthquake

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was an alarming sign because

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warthquakes may be an indication

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that an eruption is building up.

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Earthquakes can happen

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when magma rises from deep

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inside the earth,

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shifting and breaking the rock

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on its journey up.

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>> The very first signals

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we had were earthquakes

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at shallow depth

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neneath the volcano,

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and within a matter

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of just a few days, it was clear

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this was something unusual.

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So the word went out to

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scientists around the country,

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and very quickly we started

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to converge at St. Helen's

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and started trying to understand

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what was going on,

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and what we saw was the volcano

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was becoming more and more

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and more restless.

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>> Volcanoes are dangerous

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because they are hard

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to predict, and in 1980,

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the science of predicting

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volcanic eruptions was still

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in its infancy.

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The most recent explosive

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eruption that occurred

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on the continental U.S.A.

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was Lassen Peak in California

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in 1915. Since then,

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most of the experience

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volcanologists had gained

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came from studying

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quiet lava flows on Hawaii.

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>> Volcanoes are incredibly

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complicated natural systems,

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and they're always full

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of surprises.

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St. Helen's surprises us

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all the time.

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Other volcanoes surprise us.

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But we're learning.

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>> Armed with the latest

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scientific equipment,

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volcanologists were anxious

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to study a possible eruption.

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Little did they know that they

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were about to witness

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the most deadly volcanic blast

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in the U.S. in living memory.

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On Coldwater Ridge, 6 miles

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mortheast of the volcano,

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they installed a trailer

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with highly sophisticated

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equipment and began to closely

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monitor the mountain.

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From there, they had a perfect

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view over the volcano.

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>> We had a front-row seat

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to seeing the evolution

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and reawakening of a major

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Cascade volcano, and we were

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fortunate in that we had people

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here with a lot of energy.

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People were working

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15 to 20 hours a day.

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>> In addition to earthquakes,

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another key indicator

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for volcanic activity

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is gas emissions.

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Magma made out of hot molten

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rock contains gases that come

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from deep inside the earth,

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30 miles down.

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As magma moves up from these

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depths, there is less rock

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weighing down on it from above,

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so the pressure on the magma

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decreases. Gases dissolved

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in the magma escape and rise

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to the surface.

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But gases are not just

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a telltale sign of rising magma.

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They are also responsible

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for the explosiveness

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of the eruption.

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The greater the buildup of gas

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pressure within the volcano,

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the more explosive

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yhe eruption will be.

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>> Well, this is a simple

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experiment to demonstrate

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the importance of gas pressure

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in a magma.

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The bottle is partially filled.

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This is filled about 80%

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with water. This will be

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simulating a volcanic eruption.

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So I'm going to carefully

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place the bottle here.

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We'll tilt it a little bit

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away from me.

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I'm going to put on

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my safety goggles.

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And now I'm about ready

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to start pumping.

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Here we go.

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Oops. There's a little bit

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of gas coming at the bottom.

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A little bit more.

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And the pressures are up to

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about 60 pounds per square inch.

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Whoa!

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Did we get it?

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We got it! Yay!

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>> Like in the bottle,

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the presence of gas

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at the surface of a volcano

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is a sure sign that an explosive

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eruption is building.

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In spring 1980, Casadevall's job

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was to detect these gas

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emissions. The gas he was

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looking for was sulfur dioxide.

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It's a gas that smells like

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rotten eggs and is associated

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with volcanic activity.

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But the key to the measurements

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wasn't the smell. The secret

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was subtle differences

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in the color of the light.

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>> This instrument looks

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at the light in the sky,

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and it looks for the presence

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of certain molecules,

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like sulfur dioxide, which also

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absorb light from the sky.

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And it measures the difference

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between the light absorbed

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by sulfur dioxide and the light

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available in the rest

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of the sky.

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>> In March and April 1980,

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Casadevall and his team

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were using this instrument

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to detect the amount

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of escaping gases.

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They assumed that the gas levels

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would increase prior

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to the eruption as more

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and more magma would rise

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inside the volcano.

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But in 1980, the assumption

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proved wrong.

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Gas emissions didn't change,

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even though earthquakes

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were getting stronger,

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and hundreds of small tremors

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were recorded.

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>> There was really

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no significant variation.

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It was a very low level

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of sulfur dioxide emissions.

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And there was nothing in those

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emission rates that really

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indicated that an eruption

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was just around the corner.

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>> But by late April,

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after 5 weeks of tremors,

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the mountain gave them

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another clue to what

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was brewing inside.

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On the north face, a huge bulge

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was growing outwards.

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>> A casual observer would look

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at the volcano and say,

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"well, it's not longer

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a nice fuji-type shape."

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But in fact, the north side now

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is bulged out, and it was

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obviously deformed in some way.

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And we were trying to understand

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what could have been causing

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that deformation.

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>> It was the first time

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scientists were able to monitor

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the deformation of a mountain.

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On Coldwater Ridge,

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they installed an instrument

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that uses laser technology

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to get precise measurements

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as to how fast the bulge

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was growing.

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>> What we were trying to do

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was to focus a laser beam

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from this instrument

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on a reflector in the volcano,

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receive the returned

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reflected signal, and then

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measure that distance.

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>> The reflectors they used

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were small mirrors

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about 3 inches across

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they had fixed on the bulge.

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>> As was the case in 1980

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before May 18th,

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the north flank of the volcano

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was moving outward.

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It was bulging outward.

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And so the distance

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was getting shorter.

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And what we learned is that

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from Coldwater 2, that distance

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was getting shorter

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about 5 feet a day.

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>> By May 11th, the bulge

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had expanded outward

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a staggering 450 feet.

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Dzurisin had a hunch

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that it was caused

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00:09:22,113 --> 00:09:24,014
by rising magma.

295
00:09:24,082 --> 00:09:25,182
We knew that the north flank

296
00:09:25,250 --> 00:09:26,183
was deforming. We knew

297
00:09:26,251 --> 00:09:27,184
that something had to be

298
00:09:27,285 --> 00:09:28,285
causing it to deform.

299
00:09:28,353 --> 00:09:29,286
What could that be?

300
00:09:29,354 --> 00:09:30,554
Well, it could be magma forcing

301
00:09:30,655 --> 00:09:32,089
its way up into the volcano,

302
00:09:32,157 --> 00:09:33,624
shoving the north flank aside.

303
00:09:33,658 --> 00:09:34,925
That was a possibility.

304
00:09:34,993 --> 00:09:36,360
Well, what else could be

305
00:09:36,427 --> 00:09:37,728
causing it? Well, maybe

306
00:09:37,829 --> 00:09:39,630
the earthquakes were simply

307
00:09:39,731 --> 00:09:42,366
causing the volcano to become

308
00:09:42,467 --> 00:09:44,368
unstable as a result of gravity.

309
00:09:44,435 --> 00:09:45,335
Maybe there was just

310
00:09:45,370 --> 00:09:46,904
a slow landslide going on.

311
00:09:47,005 --> 00:09:47,804
It was very difficult

312
00:09:47,906 --> 00:09:49,006
to understand or to make

313
00:09:49,107 --> 00:09:50,007
a measurement that would

314
00:09:50,108 --> 00:09:51,542
tell you the difference.

315
00:09:51,609 --> 00:09:52,709
The plausible story was

316
00:09:52,744 --> 00:09:53,911
that magma was forcing its way

317
00:09:54,012 --> 00:09:56,280
up under the volcano.

318
00:09:56,347 --> 00:09:57,381
>> As the bulge grew,

319
00:09:57,448 --> 00:09:58,248
the flank of the mountain

320
00:09:58,283 --> 00:10:01,251
became increasingly unstable.

321
00:10:01,286 --> 00:10:03,820
Still, scientists had no idea

322
00:10:03,888 --> 00:10:04,988
how deadly the eruption

323
00:10:05,089 --> 00:10:06,456
would turn out to be.

324
00:10:06,558 --> 00:10:07,624
>> So we didn't know for sure

325
00:10:07,725 --> 00:10:09,626
until... until it happened.

326
00:10:09,694 --> 00:10:11,962
But as the bulge continued

327
00:10:11,996 --> 00:10:13,163
to grow, we knew we were getting

328
00:10:13,264 --> 00:10:14,965
closer to the final outcome.

329
00:10:14,999 --> 00:10:15,832
We just didn't know

330
00:10:15,900 --> 00:10:17,267
what that would be.

331
00:10:17,335 --> 00:10:18,635
>> There were other signs

332
00:10:18,736 --> 00:10:21,271
that an eruption was imminent.

333
00:10:21,339 --> 00:10:23,540
Earthquakes became more frequent

334
00:10:23,608 --> 00:10:26,276
and stronger as time went on.

335
00:10:26,377 --> 00:10:27,644
Authorities feared the worst

336
00:10:27,712 --> 00:10:28,912
and zoned off the area

337
00:10:28,980 --> 00:10:30,447
around the volcano with limited

338
00:10:30,515 --> 00:10:34,351
access for the public.

339
00:10:34,419 --> 00:10:36,186
In spring 1980, geologists

340
00:10:36,254 --> 00:10:37,354
were dealing with a number

341
00:10:37,455 --> 00:10:38,989
of clues that Mount St. Helen's

342
00:10:39,057 --> 00:10:41,892
was building to an eruption.

343
00:10:41,960 --> 00:10:43,994
Earthquakes were an indication

344
00:10:44,062 --> 00:10:48,131
that the volcano was waking up.

345
00:10:48,233 --> 00:10:49,866
Despite low and unchanging

346
00:10:49,968 --> 00:10:52,135
gas emissions, a growing bulge

347
00:10:52,237 --> 00:10:53,503
on the north face suggested

348
00:10:53,571 --> 00:10:54,972
that the magma was indeed

349
00:10:55,039 --> 00:10:57,874
on the rise.

350
00:10:57,942 --> 00:11:00,043
Mysteriously, after May 14th,

351
00:11:00,111 --> 00:11:03,247
the volcano quieted down.

352
00:11:03,314 --> 00:11:04,414
There was hardly any seismic

353
00:11:04,515 --> 00:11:05,949
activity, and the bulge grew

354
00:11:06,017 --> 00:11:09,419
at a slower rate.

355
00:11:09,487 --> 00:11:11,054
On May 17th, officials gave in

356
00:11:11,122 --> 00:11:12,422
to pressure and allowed some

357
00:11:12,490 --> 00:11:13,957
people with property inside

358
00:11:14,025 --> 00:11:15,959
the restricted area to gather up

359
00:11:16,027 --> 00:11:19,029
whatever they could.

360
00:11:19,130 --> 00:11:20,197
Another group was scheduled

361
00:11:20,231 --> 00:11:21,498
to enter for 10 am

362
00:11:21,566 --> 00:11:23,133
the next morning.

363
00:11:23,201 --> 00:11:24,468
But on that day,

364
00:11:24,502 --> 00:11:26,570
disaster struck.

365
00:11:33,939 --> 00:11:35,441
>> On the morning of May 18th,

366
00:11:35,509 --> 00:11:37,143
scientists were about to witness

367
00:11:37,244 --> 00:11:38,511
one of the worst volcanic

368
00:11:38,612 --> 00:11:41,681
disasters in modern history.

369
00:11:41,715 --> 00:11:43,883
For more than 2 months,

370
00:11:43,950 --> 00:11:45,151
a team of volcanologists

371
00:11:45,252 --> 00:11:46,352
had been monitoring

372
00:11:46,420 --> 00:11:48,054
Mount St. Helen's.

373
00:11:48,155 --> 00:11:48,954
>> That's another reason

374
00:11:48,989 --> 00:11:49,889
why May 18 was a surprise,

375
00:11:49,890 --> 00:11:50,923
Because basically in all of this

376
00:11:50,957 --> 00:11:52,558
data we collected before,

377
00:11:52,592 --> 00:11:55,227
there wasn't anything that told

378
00:11:55,295 --> 00:11:56,495
that, you know, May 18th

379
00:11:56,563 --> 00:11:58,631
was going to be the day.

380
00:11:58,632 --> 00:12:00,299
>> David Johnston, a young

381
00:12:00,367 --> 00:12:02,001
volcanologist with the U.S.

382
00:12:02,035 --> 00:12:03,669
Geological survey, was on duty

383
00:12:03,770 --> 00:12:06,038
that day. He had spent the night

384
00:12:06,106 --> 00:12:08,174
on Coldwater Ridge to carry out

385
00:12:08,208 --> 00:12:09,675
measurements of the growing

386
00:12:09,743 --> 00:12:11,277
bulge.

387
00:12:11,311 --> 00:12:12,445
>> It's interesting that even

388
00:12:12,479 --> 00:12:14,046
on the morning of May 18th,

389
00:12:14,114 --> 00:12:15,681
the measurements that Dave made

390
00:12:15,749 --> 00:12:17,550
indicated that that bulge

391
00:12:17,584 --> 00:12:18,818
was still growing at about

392
00:12:18,852 --> 00:12:20,586
the same rate.

393
00:12:20,654 --> 00:12:21,954
>> The same morning, Dan Miller

394
00:12:22,022 --> 00:12:23,255
was on his way to Cowater

395
00:12:23,323 --> 00:12:24,623
Ridge to check on

396
00:12:24,691 --> 00:12:26,158
the time-lapse camera they used

397
00:12:26,259 --> 00:12:29,095
for filming the north face.

398
00:12:29,096 --> 00:12:30,596
>> I was headed to the north

399
00:12:30,630 --> 00:12:32,431
on interstate 5 out of

400
00:12:32,499 --> 00:12:33,899
Vancouver, Washington,

401
00:12:33,967 --> 00:12:34,967
and as I got a few miles

402
00:12:35,001 --> 00:12:36,068
north of town, there's

403
00:12:36,136 --> 00:12:37,636
an overlook point as you go

404
00:12:37,704 --> 00:12:38,704
down the highway where you can

405
00:12:38,772 --> 00:12:39,705
look off to the east

406
00:12:39,806 --> 00:12:41,173
and see Mount St. Helen's,

407
00:12:41,174 --> 00:12:42,074
and I looked over there, and it

408
00:12:42,175 --> 00:12:43,275
was a beautiful clear day,

409
00:12:43,343 --> 00:12:44,610
and there was Mount St. Helen's

410
00:12:44,644 --> 00:12:46,278
with this giant mushroom cloud

411
00:12:46,346 --> 00:12:47,780
going up above it.

412
00:12:47,814 --> 00:12:48,748
At that point, I knew something

413
00:12:48,815 --> 00:12:51,517
very serious was underway.

414
00:12:51,551 --> 00:12:52,618
>> From a safe distance,

415
00:12:52,686 --> 00:12:54,787
35 miles away, Miller witnessed

416
00:12:54,821 --> 00:12:57,156
how the eruption unfolded.

417
00:12:57,224 --> 00:12:57,990
>> The first thing I did

418
00:12:58,091 --> 00:12:59,258
was went to our radio,

419
00:12:59,326 --> 00:13:00,793
our communications radio,

420
00:13:00,861 --> 00:13:02,862
and I made some calls up to Dave

421
00:13:02,896 --> 00:13:04,363
to try to raise him and find out

422
00:13:04,431 --> 00:13:05,698
what was happening.

423
00:13:05,799 --> 00:13:07,700
And not only did I not reach

424
00:13:07,801 --> 00:13:09,702
Dave, but even our repeater,

425
00:13:09,803 --> 00:13:11,804
which was on a mwuntain peak

426
00:13:11,872 --> 00:13:13,072
that was another few miles

427
00:13:13,140 --> 00:13:15,141
to the north of Coldwater 2,

428
00:13:15,175 --> 00:13:17,343
did not answer, indicating

429
00:13:17,411 --> 00:13:19,044
that it had been destroyed.

430
00:13:19,079 --> 00:13:20,346
And that was very scary.

431
00:13:20,414 --> 00:13:21,347
At that point, I realized

432
00:13:21,448 --> 00:13:22,581
that something bad had probably

433
00:13:22,616 --> 00:13:25,351
happened to Dave.

434
00:13:25,419 --> 00:13:26,619
>> Thick dark smoke was

435
00:13:26,686 --> 00:13:28,320
billowing out of the crater,

436
00:13:28,355 --> 00:13:30,322
obscuring the view.

437
00:13:30,357 --> 00:13:31,624
Within hours, daylight

438
00:13:31,691 --> 00:13:33,859
turned murky grey and reduced

439
00:13:33,894 --> 00:13:35,961
visibility up to 300 miles

440
00:13:35,996 --> 00:13:39,432
northeast.

441
00:13:39,533 --> 00:13:42,334
It wasn't until 24 hours later

442
00:13:42,402 --> 00:13:43,669
that the air was clear enough

443
00:13:43,703 --> 00:13:44,904
for scientists to inspect

444
00:13:44,971 --> 00:13:47,706
the devastation.

445
00:13:47,808 --> 00:13:49,074
>> The entire landscape

446
00:13:49,142 --> 00:13:50,443
was almost unrecognizable

447
00:13:50,510 --> 00:13:51,610
to those of us who had spent

448
00:13:51,678 --> 00:13:53,779
almost 2 months before

449
00:13:53,880 --> 00:13:55,781
the big explosion on May 18

450
00:13:55,849 --> 00:13:57,216
working up there every day.

451
00:13:57,250 --> 00:13:58,217
>> Suddenly I realized

452
00:13:58,251 --> 00:13:59,752
that there was complete

453
00:13:59,853 --> 00:14:01,387
and utter silence.

454
00:14:01,488 --> 00:14:02,655
There were no insects.

455
00:14:02,756 --> 00:14:04,290
There were no small animals.

456
00:14:04,391 --> 00:14:05,591
And there were no colors.

457
00:14:05,659 --> 00:14:07,560
The only color was ash grey

458
00:14:07,594 --> 00:14:10,229
for as far as I could see.

459
00:14:10,230 --> 00:14:11,397
>> We made our way up along

460
00:14:11,465 --> 00:14:12,631
the edge of the ridge,

461
00:14:12,666 --> 00:14:14,467
and we found the small quarry

462
00:14:14,501 --> 00:14:15,935
where Dave's trailer

463
00:14:15,969 --> 00:14:17,736
and our vehicle had been parked

464
00:14:17,737 --> 00:14:19,772
on the morning of May 18th,

465
00:14:19,840 --> 00:14:20,673
and we could see

466
00:14:20,774 --> 00:14:21,941
that it was gone.

467
00:14:22,943 --> 00:14:24,210
>> Neither Johnston

468
00:14:24,311 --> 00:14:27,213
nor the trailer were ever found.

469
00:14:27,314 --> 00:14:29,582
A total of 57 people were killed

470
00:14:29,649 --> 00:14:31,650
along with thousands of deer,

471
00:14:31,685 --> 00:14:35,554
elk, bears, and other wildlife.

472
00:14:35,589 --> 00:14:38,023
230 square miles of forests

473
00:14:38,124 --> 00:14:40,626
were destroyed, and the eruption

474
00:14:40,694 --> 00:14:42,461
had torn a 2,000-foot-wide

475
00:14:42,529 --> 00:14:44,630
crater in the summit.

476
00:14:44,631 --> 00:14:46,165
>> It was no longer

477
00:14:46,266 --> 00:14:49,802
a beautiful fuji-type volcano.

478
00:14:49,903 --> 00:14:51,337
And in fact, we could see

479
00:14:51,371 --> 00:14:52,872
that the top of the volcano

480
00:14:52,906 --> 00:14:54,073
appeared to be missing

481
00:14:54,174 --> 00:14:56,542
or was obscured.

482
00:14:56,543 --> 00:14:59,512
>> In the months to come,

483
00:14:59,546 --> 00:15:01,080
scientists faced the difficult

484
00:15:01,147 --> 00:15:02,414
task of finding out

485
00:15:02,449 --> 00:15:03,883
what exactly happened

486
00:15:03,984 --> 00:15:05,885
on that fateful day.

487
00:15:05,986 --> 00:15:07,319
They searched the ground

488
00:15:07,354 --> 00:15:08,988
for clues and methodically

489
00:15:09,089 --> 00:15:10,523
pieced together the chain

490
00:15:10,590 --> 00:15:11,790
of events that had led

491
00:15:11,825 --> 00:15:14,360
to the devastation.

492
00:15:14,427 --> 00:15:15,461
The first important clue

493
00:15:15,529 --> 00:15:17,963
was an earthquake measuring 5.2

494
00:15:17,998 --> 00:15:19,331
that shook Mount St. Helen's

495
00:15:19,366 --> 00:15:21,901
at 8:32 that morning.

496
00:15:21,968 --> 00:15:24,169
The second piece of evidence

497
00:15:24,237 --> 00:15:25,704
came from photographs taken

498
00:15:25,772 --> 00:15:27,172
by tourists who flew over

499
00:15:27,274 --> 00:15:28,541
the mountain around

500
00:15:28,608 --> 00:15:30,876
the same time.

501
00:15:30,877 --> 00:15:31,777
>> They looked down, and they

502
00:15:31,811 --> 00:15:32,978
were able to document,

503
00:15:33,079 --> 00:15:34,313
by a series of photographs,

504
00:15:34,347 --> 00:15:35,447
some shaking on the top

505
00:15:35,515 --> 00:15:36,549
of the mountain,

506
00:15:36,616 --> 00:15:37,716
and then right afterwards,

507
00:15:37,717 --> 00:15:39,184
the whole front of that mountain

508
00:15:39,252 --> 00:15:41,353
started to move sideways.

509
00:15:41,421 --> 00:15:42,454
>> In a series of still

510
00:15:42,522 --> 00:15:43,989
photographs, they documented

511
00:15:44,090 --> 00:15:46,325
how the bulge collapsed.

512
00:15:46,359 --> 00:15:48,360
>> A magnitude-5.1 earthquake

513
00:15:48,428 --> 00:15:50,329
caused the north flank,

514
00:15:50,430 --> 00:15:51,697
which was greatly weakened

515
00:15:51,798 --> 00:15:53,399
by the deformation,

516
00:15:53,433 --> 00:15:54,767
to break loose in the form

517
00:15:54,801 --> 00:15:56,802
of a giant landslide.

518
00:15:56,903 --> 00:15:57,870
>> The volcano just couldn't

519
00:15:57,904 --> 00:15:59,605
take it anymore, and the north

520
00:15:59,673 --> 00:16:01,240
flank became unstable

521
00:16:01,341 --> 00:16:04,243
and slid away.

522
00:16:04,311 --> 00:16:05,344
>> Within seconds,

523
00:16:05,412 --> 00:16:06,812
1,300 feet of the mountain

524
00:16:06,880 --> 00:16:08,414
slid down and destroyed

525
00:16:08,448 --> 00:16:11,584
everything in its path.

526
00:16:11,685 --> 00:16:14,353
What used to be a quiet

527
00:16:14,421 --> 00:16:15,955
mountain valley with the Toutle

528
00:16:15,989 --> 00:16:17,356
River running through it

529
00:16:17,424 --> 00:16:19,224
was now filled with debris

530
00:16:19,259 --> 00:16:21,160
up to 600 feet high,

531
00:16:21,227 --> 00:16:22,428
forming a hilly terrain

532
00:16:22,529 --> 00:16:26,265
known as the hummocks.

533
00:16:26,333 --> 00:16:27,800
From the amount of debris

534
00:16:27,901 --> 00:16:29,168
from the landslide,

535
00:16:29,235 --> 00:16:30,536
scientists calculated

536
00:16:30,604 --> 00:16:32,438
that 2/3 of a cubic mile

537
00:16:32,505 --> 00:16:34,773
of rock slid down the mountain,

538
00:16:34,808 --> 00:16:36,508
enough to bury Washington, D.C.

539
00:16:36,610 --> 00:16:39,979
under 50 feet of rubble.

540
00:16:40,046 --> 00:16:41,146
It was one of the biggest

541
00:16:41,214 --> 00:16:42,615
landslides ever recorded

542
00:16:42,682 --> 00:16:44,416
in history.

543
00:16:44,517 --> 00:16:45,684
It tore a gaping hole

544
00:16:45,785 --> 00:16:47,052
in the side of the mountain

545
00:16:47,120 --> 00:16:48,854
almost 2 miles wide

546
00:16:48,888 --> 00:16:51,957
and over 2,000 feet deep.

547
00:16:52,058 --> 00:16:54,259
To scientists, it was a mystery

548
00:16:54,327 --> 00:16:56,161
why suddenly the entire northern

549
00:16:56,229 --> 00:16:59,398
flank of the volcano collapsed.

550
00:16:59,432 --> 00:17:01,500
Geologists today can still

551
00:17:01,534 --> 00:17:05,971
follow the trail of destruction.

552
00:17:05,972 --> 00:17:07,339
>> What we're looking at here

553
00:17:07,440 --> 00:17:09,308
is a part of a large debris

554
00:17:09,342 --> 00:17:10,342
avalanche. We're looking at

555
00:17:10,410 --> 00:17:11,610
one of the hummocks.

556
00:17:11,711 --> 00:17:13,045
And this is a rock outcrop

557
00:17:13,146 --> 00:17:14,113
that's actually outcropping

558
00:17:14,147 --> 00:17:15,147
in the hummocks,

559
00:17:15,148 --> 00:17:16,148
and the coloration that you see,

560
00:17:16,216 --> 00:17:17,249
first of all is telling you

561
00:17:17,317 --> 00:17:19,885
that this has been altered.

562
00:17:19,953 --> 00:17:21,020
>> This color provides

563
00:17:21,054 --> 00:17:22,187
an important clue

564
00:17:22,288 --> 00:17:23,355
to why the landslide

565
00:17:23,456 --> 00:17:25,090
became so big.

566
00:17:25,158 --> 00:17:26,358
Instead of the usual black

567
00:17:26,459 --> 00:17:27,826
of volcanic lava rock,

568
00:17:27,894 --> 00:17:29,428
it is yellow.

569
00:17:29,462 --> 00:17:30,996
This is a sign that the rock

570
00:17:31,064 --> 00:17:33,365
came in touch with hot water,

571
00:17:33,433 --> 00:17:34,533
turning some of the minerals

572
00:17:34,601 --> 00:17:36,802
in the rock yellow.

573
00:17:36,870 --> 00:17:38,170
Geologists found the same

574
00:17:38,238 --> 00:17:40,272
yellow rock in the crater wall,

575
00:17:40,340 --> 00:17:41,540
suggesting the discoloration

576
00:17:41,608 --> 00:17:42,808
must have happened

577
00:17:42,909 --> 00:17:43,909
on the mountain

578
00:17:44,010 --> 00:17:45,644
before the eruption.

579
00:17:45,712 --> 00:17:46,879
>> So you have rainwater

580
00:17:46,913 --> 00:17:47,780
or glacial water that seeps

581
00:17:47,814 --> 00:17:49,148
down into the mountain,

582
00:17:49,182 --> 00:17:50,449
gets close to the magma,

583
00:17:50,517 --> 00:17:51,617
heats back up, and as it comes

584
00:17:51,718 --> 00:17:52,551
out of the mountain,

585
00:17:52,619 --> 00:17:53,986
then it starts to change

586
00:17:54,087 --> 00:17:55,320
and chemically alter these rocks

587
00:17:55,355 --> 00:17:56,355
and turning them, you know,

588
00:17:56,423 --> 00:17:57,723
into these different colors.

589
00:17:57,824 --> 00:17:58,557
>> But the hot water

590
00:17:58,625 --> 00:18:00,426
didn't just change the color.

591
00:18:00,460 --> 00:18:01,994
More importantly, it also

592
00:18:02,095 --> 00:18:03,896
weakened the rock.

593
00:18:03,963 --> 00:18:04,997
>> So you can see how crumbly

594
00:18:05,098 --> 00:18:07,966
these rocks are just by kind of

595
00:18:08,001 --> 00:18:09,068
digging your hammer through

596
00:18:09,169 --> 00:18:10,002
here, and the reason

597
00:18:10,070 --> 00:18:11,670
they're so crumbly is because

598
00:18:11,771 --> 00:18:13,038
when the hot water moves through

599
00:18:13,106 --> 00:18:15,107
and alters them, they sometimes

600
00:18:15,141 --> 00:18:16,675
altered the clay and some really

601
00:18:16,776 --> 00:18:18,243
soft materials. So if you took

602
00:18:18,311 --> 00:18:19,244
any other rock, it would be

603
00:18:19,312 --> 00:18:20,879
much stronger.

604
00:18:20,947 --> 00:18:22,381
>> This yellow crumbly rock

605
00:18:22,415 --> 00:18:23,782
isn't just found here,

606
00:18:23,850 --> 00:18:25,751
but stretches over 17 miles

607
00:18:25,785 --> 00:18:27,119
throughout the valley,

608
00:18:27,153 --> 00:18:28,754
suggesting that large parts

609
00:18:28,788 --> 00:18:30,856
of the mountain were rotten,

610
00:18:30,924 --> 00:18:33,225
weakened before the eruption.

611
00:18:33,293 --> 00:18:34,126
>> So probably what had been

612
00:18:34,227 --> 00:18:35,327
happening over thousands

613
00:18:35,395 --> 00:18:36,929
of years is magma

614
00:18:36,963 --> 00:18:38,497
down on the volcano

615
00:18:38,565 --> 00:18:39,498
heating up water,

616
00:18:39,599 --> 00:18:41,233
and this acidic water

617
00:18:41,334 --> 00:18:42,868
was gradually rotting out

618
00:18:42,936 --> 00:18:44,403
the center of the volcano.

619
00:18:44,471 --> 00:18:45,304
It couldn't be seen

620
00:18:45,371 --> 00:18:46,505
anywhere at the surface.

621
00:18:46,606 --> 00:18:48,774
>> When the bulge on the north

622
00:18:48,875 --> 00:18:50,743
side finally collapsed,

623
00:18:50,777 --> 00:18:51,944
it pulled along big parts

624
00:18:52,045 --> 00:18:53,512
of the rotten volcano

625
00:18:53,580 --> 00:18:54,580
and left behind

626
00:18:54,647 --> 00:18:55,948
the horseshoe-shaped crater

627
00:18:56,049 --> 00:18:59,985
St. Helen's is famous for today.

628
00:19:00,019 --> 00:19:01,720
>> This volcano is just

629
00:19:01,821 --> 00:19:03,155
a sand pile, if you will.

630
00:19:03,189 --> 00:19:04,890
It had very little internal

631
00:19:04,924 --> 00:19:06,825
integrity or strength,

632
00:19:06,926 --> 00:19:09,561
so that when failure did occur,

633
00:19:09,629 --> 00:19:10,929
literally part of the mountain

634
00:19:10,997 --> 00:19:12,731
slid away.

635
00:19:12,832 --> 00:19:14,533
>> But more destruction

636
00:19:14,567 --> 00:19:16,368
was to come.

637
00:19:16,436 --> 00:19:18,370
Within minutes of the landslide,

638
00:19:18,438 --> 00:19:19,805
Mount St. Helen's channeled

639
00:19:19,839 --> 00:19:21,373
her fury into another

640
00:19:21,441 --> 00:19:23,542
deadly force.

641
00:19:23,610 --> 00:19:24,610
>> The air turned absolutely

642
00:19:24,644 --> 00:19:25,377
black, so nobody could see

643
00:19:25,445 --> 00:19:26,278
anything, but a few of these

644
00:19:26,346 --> 00:19:27,346
witnesses that managed

645
00:19:27,380 --> 00:19:28,914
to survive out in the very edge,

646
00:19:29,015 --> 00:19:30,916
the ground shook intensely,

647
00:19:30,984 --> 00:19:32,251
and they sensed that all

648
00:19:32,285 --> 00:19:33,252
the trees were coming down

649
00:19:33,286 --> 00:19:34,019
at once, even though

650
00:19:34,087 --> 00:19:36,288
they couldn't see it.

651
00:19:36,356 --> 00:19:37,890
>> The landslide had spread

652
00:19:37,924 --> 00:19:40,259
east and west, but this force

653
00:19:40,360 --> 00:19:42,928
surged in a northerly direction.

654
00:19:42,996 --> 00:19:45,063
Within 3 or 4 minutes,

655
00:19:45,098 --> 00:19:46,465
it destroyed everything

656
00:19:46,533 --> 00:19:48,000
on Coldwater Ridge

657
00:19:48,067 --> 00:19:49,334
and ripped out trees

658
00:19:49,369 --> 00:19:50,903
in a 230-square-mile

659
00:19:51,004 --> 00:19:53,372
fan-shaped area.

660
00:19:53,439 --> 00:19:54,239
>> Ao even where we're sitting

661
00:19:54,274 --> 00:19:56,175
here, 8 miles from the volcano,

662
00:19:56,276 --> 00:19:57,276
tou can see this ridge

663
00:19:57,377 --> 00:19:58,510
behind me. This ridge

664
00:19:58,545 --> 00:19:59,378
is 3,000 feet tall,

665
00:19:59,445 --> 00:20:00,279
and all the texture

666
00:20:00,346 --> 00:20:01,446
that you see on this ridge

667
00:20:01,514 --> 00:20:02,447
are the trees, the old-growth

668
00:20:02,515 --> 00:20:03,615
forest trees that were blown

669
00:20:03,650 --> 00:20:05,184
down by the surge that went up

670
00:20:05,251 --> 00:20:06,051
and over this thing

671
00:20:06,085 --> 00:20:07,286
like it wasn't even there.

672
00:20:07,353 --> 00:20:08,253
And so for the surge to have

673
00:20:08,288 --> 00:20:09,288
gone up and over this,

674
00:20:09,355 --> 00:20:10,722
it had to still have been going

675
00:20:10,824 --> 00:20:12,724
roughly 300 miles per hour,

676
00:20:12,792 --> 00:20:13,992
and then it continued

677
00:20:14,093 --> 00:20:15,427
9 miles farther than that

678
00:20:15,461 --> 00:20:17,830
before it finally stopped.

679
00:20:17,897 --> 00:20:18,897
>> To geologists,

680
00:20:18,965 --> 00:20:20,599
this was a surprise.

681
00:20:20,633 --> 00:20:21,867
They had never witnessed

682
00:20:21,901 --> 00:20:25,537
a sideways eruption before.

683
00:20:25,638 --> 00:20:26,705
>> Scientists were intrigued

684
00:20:26,806 --> 00:20:28,006
as to what had caused

685
00:20:28,074 --> 00:20:30,142
this devastating surge.

686
00:20:30,176 --> 00:20:31,176
So they began searching

687
00:20:31,277 --> 00:20:33,612
the ground for evidence.

688
00:20:33,713 --> 00:20:35,414
5 miles northeast of the crater,

689
00:20:35,448 --> 00:20:36,682
Waitt is revisiting

690
00:20:36,716 --> 00:20:39,451
the old deposits.

691
00:20:39,519 --> 00:20:41,186
Mixed with burned wood

692
00:20:41,254 --> 00:20:42,521
from the shredded trees,

693
00:20:42,622 --> 00:20:44,523
he also finds rock.

694
00:20:44,591 --> 00:20:46,425
To the untrained eye, there is

695
00:20:46,459 --> 00:20:48,227
nothing unusual about it,

696
00:20:48,261 --> 00:20:50,429
but not so for the experts.

697
00:20:50,463 --> 00:20:52,865
>> It's clearly young rock.

698
00:20:52,899 --> 00:20:54,066
It's relatively light,

699
00:20:54,133 --> 00:20:55,500
and there's lots

700
00:20:55,535 --> 00:20:56,768
of little voids in here.

701
00:20:56,803 --> 00:20:57,970
In other words, little bubbles

702
00:20:58,004 --> 00:20:59,504
that are frozen in the rock.

703
00:20:59,539 --> 00:21:01,440
So this was the rock that was

704
00:21:01,541 --> 00:21:03,976
growing--there was a hot liquid,

705
00:21:04,043 --> 00:21:05,277
almost solid liquid, that was

706
00:21:05,345 --> 00:21:06,712
growing inside Mount St. Helen's

707
00:21:06,813 --> 00:21:08,080
and causing the bulge

708
00:21:08,181 --> 00:21:09,681
before May 18th.

709
00:21:09,716 --> 00:21:11,483
>> This small rock was

710
00:21:11,517 --> 00:21:13,151
a crucial piece of evidence for

711
00:21:13,253 --> 00:21:14,686
scientists trying to figure out

712
00:21:14,754 --> 00:21:17,222
the chain of events.

713
00:21:17,290 --> 00:21:19,191
After the landslide

714
00:21:19,225 --> 00:21:20,559
tore a gaping hole into

715
00:21:20,593 --> 00:21:22,327
the north flank of the mountain,

716
00:21:22,395 --> 00:21:25,831
it exposed the magma underneath.

717
00:21:25,865 --> 00:21:26,965
Without a cap of earth

718
00:21:27,033 --> 00:21:28,033
to keep it sealed,

719
00:21:28,101 --> 00:21:29,668
the magma suddenly expanded

720
00:21:29,736 --> 00:21:31,403
and surged outwards,

721
00:21:31,504 --> 00:21:32,571
pulling along rock

722
00:21:32,672 --> 00:21:34,940
from inside the mountain.

723
00:21:35,008 --> 00:21:36,308
>> You can envision it

724
00:21:36,376 --> 00:21:37,943
as sort of a colossal-sized

725
00:21:38,011 --> 00:21:40,746
ash hurricane. It was a cloud

726
00:21:40,780 --> 00:21:44,683
of rocks and ash and hot gases

727
00:21:44,751 --> 00:21:46,685
that was maybe several thousand

728
00:21:46,753 --> 00:21:48,320
feet thick that was moving

729
00:21:48,388 --> 00:21:50,122
across the countryside at speeds

730
00:21:50,189 --> 00:21:51,290
of several hundred miles

731
00:21:51,324 --> 00:21:53,492
an hour, a very turbulent

732
00:21:53,593 --> 00:21:54,927
mixture with blocks as large

733
00:21:54,961 --> 00:21:56,862
as 3 or 4 feet in diameter

734
00:21:56,930 --> 00:21:58,196
flying through the air.

735
00:21:58,231 --> 00:22:02,200
It was incredibly destructive.

736
00:22:02,235 --> 00:22:03,769
>> After the initial surge,

737
00:22:03,870 --> 00:22:07,839
Mount St. Helen's turned quiet.

738
00:22:07,941 --> 00:22:09,107
For half an hour, there was

739
00:22:09,142 --> 00:22:11,410
calm and tranquility.

740
00:22:11,477 --> 00:22:12,844
Then the volcano began

741
00:22:12,946 --> 00:22:15,580
hurling its fury skywards.

742
00:22:15,682 --> 00:22:17,382
[explosions]

743
00:22:17,450 --> 00:22:18,951
An enormous mushroom cloud

744
00:22:19,018 --> 00:22:21,119
formed high above the volcano,

745
00:22:21,187 --> 00:22:22,321
3 times as tall

746
00:22:22,388 --> 00:22:24,323
as Mount Everest.

747
00:22:24,390 --> 00:22:25,757
Ferocious explosions

748
00:22:25,825 --> 00:22:27,459
went on for hours, releasing

749
00:22:27,493 --> 00:22:29,628
huge amounts of energy

750
00:22:29,662 --> 00:22:32,364
equal to 27,000 Hiroshima-sized

751
00:22:32,398 --> 00:22:36,668
atomic bombs.

752
00:22:36,736 --> 00:22:39,938
What happened on May 18, 1980,

753
00:22:40,039 --> 00:22:41,673
became a landmark event

754
00:22:41,741 --> 00:22:43,842
for scientists.

755
00:22:43,943 --> 00:22:45,043
It provided them with

756
00:22:45,111 --> 00:22:46,311
an unprecedented chance

757
00:22:46,379 --> 00:22:49,681
to study a lateral eruption.

758
00:22:49,749 --> 00:22:50,849
Discolored rock in the valley

759
00:22:50,950 --> 00:22:52,117
and in the crater wall

760
00:22:52,218 --> 00:22:53,385
were evidence that the mountain

761
00:22:53,453 --> 00:22:57,022
was rotten before the eruption.

762
00:22:57,090 --> 00:22:58,857
Grey volcanic rock

763
00:22:58,925 --> 00:23:01,126
9 miles north of the volcano

764
00:23:01,194 --> 00:23:02,928
was evidence that the landslide

765
00:23:02,996 --> 00:23:04,463
uncorked a massive

766
00:23:04,497 --> 00:23:07,299
lateral blast.

767
00:23:07,400 --> 00:23:09,001
At 5:30 in the evening,

768
00:23:09,035 --> 00:23:11,370
the volcano began to slow down

769
00:23:11,404 --> 00:23:14,306
until it finally quit.

770
00:23:14,374 --> 00:23:15,674
But there was more impending

771
00:23:15,742 --> 00:23:17,209
danger, as the eruption

772
00:23:17,276 --> 00:23:18,543
had caused another

773
00:23:18,578 --> 00:23:20,746
cataclysmic effect.

774
00:23:25,897 --> 00:23:28,232
>> On May 18, 1980,

775
00:23:28,299 --> 00:23:29,533
Mount St. Helen's exploded

776
00:23:29,601 --> 00:23:30,701
in a type of eruption

777
00:23:30,802 --> 00:23:33,704
never witnessed before.

778
00:23:33,772 --> 00:23:36,340
one of the largest landslides

779
00:23:36,408 --> 00:23:38,142
in history triggered a powerful

780
00:23:38,209 --> 00:23:41,679
sideways-directed blast.

781
00:23:41,713 --> 00:23:43,247
Ferocious explosions followed

782
00:23:43,314 --> 00:23:44,515
and formed an immense

783
00:23:44,616 --> 00:23:47,885
mushroom cloud.

784
00:23:47,986 --> 00:23:49,787
Late that afternoon,

785
00:23:49,854 --> 00:23:51,422
the volcano slowed, but more

786
00:23:51,523 --> 00:23:53,691
chaos was about to strike,

787
00:23:53,792 --> 00:23:55,059
as the eruption had triggered

788
00:23:55,160 --> 00:23:59,863
another destructive process.

789
00:23:59,964 --> 00:24:02,232
Hot volcanic ash had melted

790
00:24:02,300 --> 00:24:03,701
the snowfields on top

791
00:24:03,802 --> 00:24:05,869
of Mount St. Helen's.

792
00:24:05,937 --> 00:24:07,871
Hundreds of tons of meltwater

793
00:24:07,972 --> 00:24:09,339
mixed with soil and formed

794
00:24:09,407 --> 00:24:11,041
a series of mud flows

795
00:24:11,142 --> 00:24:15,312
that cascaded down the slopes.

796
00:24:15,313 --> 00:24:17,047
>> Most people don't realize

797
00:24:17,148 --> 00:24:18,515
that this hazard can affect

798
00:24:18,583 --> 00:24:21,318
people living so far downstream

799
00:24:21,319 --> 00:24:23,520
because up to 100 miles

800
00:24:23,588 --> 00:24:25,589
from a volcano can still be

801
00:24:25,690 --> 00:24:27,224
a hazard zone for these kind

802
00:24:27,292 --> 00:24:29,860
of volcanic mud flows.

803
00:24:29,961 --> 00:24:31,161
>> The biggest of the mud flows

804
00:24:31,229 --> 00:24:32,563
came down the Toutle River

805
00:24:32,597 --> 00:24:34,865
Valley. On its way there,

806
00:24:34,933 --> 00:24:36,333
it reached record speeds

807
00:24:36,401 --> 00:24:37,968
of 90 miles per hour

808
00:24:38,036 --> 00:24:39,136
and raced over hills

809
00:24:39,204 --> 00:24:42,239
as high as 20-story buildings.

810
00:24:42,340 --> 00:24:43,507
It destroyed a total

811
00:24:43,608 --> 00:24:46,610
of 27 bridges, nearly 200 homes,

812
00:24:46,678 --> 00:24:49,046
and more than 185 miles

813
00:24:49,147 --> 00:24:54,418
of highway and roads.

814
00:24:54,519 --> 00:24:56,153
Today, its remains are still

815
00:24:56,221 --> 00:24:57,421
preserved on the banks

816
00:24:57,489 --> 00:24:59,656
of the Toutle River.

817
00:24:59,691 --> 00:25:01,125
>> This deposit is an excellent

818
00:25:01,192 --> 00:25:02,860
example of what we scientists

819
00:25:02,927 --> 00:25:04,228
call a lahar, but other people

820
00:25:04,329 --> 00:25:06,396
refer to as a mud flow--

821
00:25:06,498 --> 00:25:09,767
A big massive flow of material

822
00:25:09,868 --> 00:25:11,301
that's much like wet concrete

823
00:25:11,336 --> 00:25:13,036
that was coming down the river

824
00:25:13,138 --> 00:25:14,671
as a huge wall of material,

825
00:25:14,739 --> 00:25:16,140
pushing logs and debris

826
00:25:16,241 --> 00:25:18,242
in front of it.

827
00:25:18,309 --> 00:25:20,110
>> At first, it was a mystery

828
00:25:20,145 --> 00:25:21,578
how this mud flow had become

829
00:25:21,646 --> 00:25:24,381
so big, but the rocks

830
00:25:24,415 --> 00:25:26,950
provided a clue.

831
00:25:27,018 --> 00:25:28,952
>> What we see are rocks of

832
00:25:29,053 --> 00:25:30,220
different types that have come

833
00:25:30,288 --> 00:25:31,855
down from Mount St. Helen's.

834
00:25:31,956 --> 00:25:33,123
Some of these are actually

835
00:25:33,224 --> 00:25:35,392
from the original cone

836
00:25:35,493 --> 00:25:36,960
of the volcano that collapsed

837
00:25:37,028 --> 00:25:39,463
as the debris avalanche.

838
00:25:39,497 --> 00:25:40,564
>> Geologists could now

839
00:25:40,598 --> 00:25:41,865
piece together what caused

840
00:25:41,933 --> 00:25:44,501
these destructive mud flows.

841
00:25:44,569 --> 00:25:46,136
These rocks from high up

842
00:25:46,204 --> 00:25:47,738
in the volcano came from

843
00:25:47,772 --> 00:25:49,039
the landslide that had been

844
00:25:49,140 --> 00:25:50,207
thrown in the valley

845
00:25:50,308 --> 00:25:51,575
in the first minutes

846
00:25:51,676 --> 00:25:53,510
of the eruption.

847
00:25:53,578 --> 00:25:54,578
When meltwater mixed with

848
00:25:54,679 --> 00:25:56,046
the landslide debris,

849
00:25:56,147 --> 00:25:59,283
it formed a gigantic mud flow.

850
00:25:59,317 --> 00:26:00,317
This incredible torrent

851
00:26:00,418 --> 00:26:01,819
lasted till late that night

852
00:26:01,853 --> 00:26:03,954
and dumped more than 65 cubic

853
00:26:04,022 --> 00:26:07,457
miles of mud along the way.

854
00:26:07,492 --> 00:26:08,959
Even 30 years later,

855
00:26:09,027 --> 00:26:10,761
proof of its destructive power

856
00:26:10,862 --> 00:26:12,930
is still in the field.

857
00:26:13,031 --> 00:26:14,498
>> These lahars came down

858
00:26:14,566 --> 00:26:16,400
and totally buried this forest.

859
00:26:16,467 --> 00:26:18,101
We see these standing stumps

860
00:26:18,136 --> 00:26:20,938
of trees that are the remains

861
00:26:21,039 --> 00:26:23,207
of what is often referred to

862
00:26:23,308 --> 00:26:24,408
as a ghost forest.

863
00:26:24,475 --> 00:26:26,476
This was buried by this lahar.

864
00:26:26,578 --> 00:26:27,911
The trees were killed,

865
00:26:27,946 --> 00:26:31,014
and we only see them now because

866
00:26:31,049 --> 00:26:33,217
of the erosion of the river

867
00:26:33,284 --> 00:26:34,218
which has come back in

868
00:26:34,319 --> 00:26:35,586
and eroded into the bank

869
00:26:35,653 --> 00:26:37,020
and uncovered them.

870
00:26:37,088 --> 00:26:39,323
So this is a fantastic clue

871
00:26:39,390 --> 00:26:41,859
of the power and the destruction

872
00:26:41,926 --> 00:26:44,394
of this lahar, which completely

873
00:26:44,495 --> 00:26:46,864
inundated this lower valley.

874
00:26:46,931 --> 00:26:49,499
>> But one deposit farther

875
00:26:49,567 --> 00:26:51,568
upstream was causing confusion

876
00:26:51,636 --> 00:26:53,570
in the investigation.

877
00:26:53,671 --> 00:26:55,939
It looked like a lahar deposit,

878
00:26:56,040 --> 00:26:57,574
but instead of volcanic rock,

879
00:26:57,675 --> 00:26:59,009
it was full of rounded

880
00:26:59,043 --> 00:27:00,944
river pebbles.

881
00:27:01,012 --> 00:27:02,679
>> The scientist who first

882
00:27:02,747 --> 00:27:04,481
studied this wasn't sure

883
00:27:04,549 --> 00:27:05,482
this was a lahar deposit

884
00:27:05,583 --> 00:27:06,650
because it contained so much

885
00:27:06,751 --> 00:27:08,385
of this rounded river rock,

886
00:27:08,486 --> 00:27:09,820
which is characteristic

887
00:27:09,854 --> 00:27:11,288
of streambed deposits

888
00:27:11,389 --> 00:27:12,789
and not lahars.

889
00:27:12,824 --> 00:27:13,724
But then he realized

890
00:27:13,791 --> 00:27:15,525
that it has this very, very hard

891
00:27:15,627 --> 00:27:18,095
compact matrix in it and it was

892
00:27:18,162 --> 00:27:20,731
not bedded or layered in any way

893
00:27:20,865 --> 00:27:22,266
and came to the conclusion

894
00:27:22,367 --> 00:27:24,268
this had to be a huge lahar

895
00:27:24,335 --> 00:27:27,004
that was probably something

896
00:27:27,071 --> 00:27:29,006
on the order of the flow

897
00:27:29,073 --> 00:27:30,607
of the Amazon River.

898
00:27:30,642 --> 00:27:32,542
>> Scientists were stumped.

899
00:27:32,610 --> 00:27:34,077
Not only did this deposit

900
00:27:34,145 --> 00:27:35,612
have rounded river rock,

901
00:27:35,713 --> 00:27:37,447
it was also much bigger than

902
00:27:37,515 --> 00:27:38,916
the deposit from the mud flow

903
00:27:38,983 --> 00:27:40,083
that tore through the valley

904
00:27:40,151 --> 00:27:42,719
on May 18th.

905
00:27:42,820 --> 00:27:44,588
If it wasn't part

906
00:27:44,622 --> 00:27:46,356
of the 1980 lahar,

907
00:27:46,457 --> 00:27:49,059
where did it come from?

908
00:27:49,093 --> 00:27:50,227
Geologists decided

909
00:27:50,261 --> 00:27:52,262
to investigate further and took

910
00:27:52,330 --> 00:27:54,264
samples back to the lab.

911
00:27:54,332 --> 00:27:55,632
Radio-carbon dating showed

912
00:27:55,700 --> 00:27:56,967
that this deposit swept

913
00:27:57,001 --> 00:28:00,337
down the valley 3,000 years ago.

914
00:28:00,438 --> 00:28:01,505
>> If we had been standing on

915
00:28:01,539 --> 00:28:03,273
this spot about 3,000 years ago,

916
00:28:03,341 --> 00:28:04,775
we would have first heard

917
00:28:04,809 --> 00:28:07,077
a very low rumble that would

918
00:28:07,145 --> 00:28:09,346
have gotten louder and louder.

919
00:28:09,447 --> 00:28:10,614
And if we hadn't heeded

920
00:28:10,715 --> 00:28:12,149
that warning, we would have seen

921
00:28:12,250 --> 00:28:15,485
a huge wall of broken trees

922
00:28:15,586 --> 00:28:17,154
and debris coming around

923
00:28:17,221 --> 00:28:18,355
the river bend, probably

924
00:28:18,423 --> 00:28:21,058
at 30 or 40 miles an hour

925
00:28:21,092 --> 00:28:21,892
that would have been

926
00:28:21,993 --> 00:28:23,627
hundreds of feet high.

927
00:28:23,695 --> 00:28:25,329
And that wall of debris

928
00:28:25,430 --> 00:28:26,964
and mud and rock would have

929
00:28:26,998 --> 00:28:28,498
then just swept through here

930
00:28:28,533 --> 00:28:31,034
like a huge freight train,

931
00:28:31,069 --> 00:28:32,803
literally wiping the valley

932
00:28:32,870 --> 00:28:35,973
clean of anything in its path.

933
00:28:36,040 --> 00:28:38,542
>> But where did this ancient

934
00:28:38,609 --> 00:28:40,711
monster flood come from?

935
00:28:40,812 --> 00:28:42,579
The only place that could have

936
00:28:42,613 --> 00:28:44,247
stored that amount of water

937
00:28:44,349 --> 00:28:46,450
and rounded rock was Spirit Lake

938
00:28:46,517 --> 00:28:49,853
35 miles upstream.

939
00:28:49,887 --> 00:28:52,689
This discovery was crucial

940
00:28:52,757 --> 00:28:53,690
because there was

941
00:28:53,791 --> 00:28:55,025
an impending danger that nature

942
00:28:55,059 --> 00:28:58,028
would repeat itself.

943
00:28:58,062 --> 00:28:59,763
Not only did the landslide

944
00:28:59,797 --> 00:29:01,865
that initiated the 1980 eruption

945
00:29:01,899 --> 00:29:03,133
flow west into the Toutle

946
00:29:03,167 --> 00:29:05,669
Valley, it also went east

947
00:29:05,703 --> 00:29:07,704
into Spirit Lake and blocked

948
00:29:07,805 --> 00:29:10,440
its exit. As rivers

949
00:29:10,508 --> 00:29:12,609
and meltwater kept flowing in,

950
00:29:12,710 --> 00:29:15,579
water rose to dangerous levels.

951
00:29:15,613 --> 00:29:16,613
>> It became a very big

952
00:29:16,681 --> 00:29:18,515
wake-up call for the hazards

953
00:29:18,616 --> 00:29:20,584
community, because if this sort

954
00:29:20,618 --> 00:29:22,052
of flood and lahar had happened

955
00:29:22,153 --> 00:29:23,687
in the past, it could happen

956
00:29:23,788 --> 00:29:26,323
again, and the 1980 deposits

957
00:29:26,424 --> 00:29:29,326
dammed Spirit Lake once again

958
00:29:29,394 --> 00:29:31,161
with the same type of weak,

959
00:29:31,229 --> 00:29:33,296
unstable dam that had existed

960
00:29:33,331 --> 00:29:35,699
in the past.

961
00:29:35,767 --> 00:29:36,600
>> Authorities had to act

962
00:29:36,701 --> 00:29:38,135
quickly. Within a couple

963
00:29:38,236 --> 00:29:39,569
of years, Spirit Lake would

964
00:29:39,604 --> 00:29:41,772
have filled up again, and had it

965
00:29:41,839 --> 00:29:43,607
been allowed to overtop,

966
00:29:43,674 --> 00:29:44,508
it would have caused

967
00:29:44,609 --> 00:29:46,143
a catastrophic flood just like

968
00:29:46,210 --> 00:29:49,212
the one 3,000 years ago.

969
00:29:49,313 --> 00:29:50,547
>> The Corps of Engineers

970
00:29:50,581 --> 00:29:52,816
came in. They immediately

971
00:29:52,850 --> 00:29:54,851
devised a plan which involved

972
00:29:54,919 --> 00:29:57,020
pumping water out of the lake

973
00:29:57,088 --> 00:29:59,656
to keep the lake level stable

974
00:29:59,757 --> 00:30:00,924
for the short term.

975
00:30:01,025 --> 00:30:02,025
Their long-term solution

976
00:30:02,126 --> 00:30:03,994
was to drill a boring

977
00:30:04,028 --> 00:30:05,662
through a mountain ridge,

978
00:30:05,763 --> 00:30:07,464
creating a permanent drain

979
00:30:07,532 --> 00:30:09,633
so that Spirit Lake could never

980
00:30:09,667 --> 00:30:12,536
get above that height,

981
00:30:12,570 --> 00:30:13,670
and the danger for

982
00:30:13,738 --> 00:30:15,172
an overtopping flood

983
00:30:15,206 --> 00:30:17,374
was then eliminated.

984
00:30:19,210 --> 00:30:21,078
>> Scientists now understood

985
00:30:21,112 --> 00:30:24,915
what happened on May 18th.

986
00:30:25,016 --> 00:30:27,751
Volcanic rock in mud deposits

987
00:30:27,819 --> 00:30:29,186
along the banks of the Toutle

988
00:30:29,253 --> 00:30:30,854
River valley is evidence that

989
00:30:30,922 --> 00:30:32,923
gigantic mud flows thundered

990
00:30:32,990 --> 00:30:35,659
down Mount St. Helen's,

991
00:30:35,760 --> 00:30:36,993
and rounded river pebbles

992
00:30:37,028 --> 00:30:39,029
in a 3,000-year-old mud deposit

993
00:30:39,097 --> 00:30:40,730
became a warning sign

994
00:30:40,798 --> 00:30:42,165
that Spirit Lake was able

995
00:30:42,200 --> 00:30:43,567
to spill over and cause

996
00:30:43,634 --> 00:30:47,104
an even bigger lahar.

997
00:30:47,171 --> 00:30:48,772
In the summer of 1980,

998
00:30:48,840 --> 00:30:49,906
scientists thought the May

999
00:30:49,941 --> 00:30:51,374
eruption was their chance

1000
00:30:51,476 --> 00:30:53,009
of a lifetime, because

1001
00:30:53,077 --> 00:30:54,377
major volcanic eruptions

1002
00:30:54,479 --> 00:30:56,079
in the Cascades happen only once

1003
00:30:56,114 --> 00:30:58,815
or twice every hundred years.

1004
00:30:58,916 --> 00:31:00,383
But they were soon to be

1005
00:31:00,451 --> 00:31:02,819
proven wrong. After 2 decades

1006
00:31:02,920 --> 00:31:04,721
of inactivity, the mountain

1007
00:31:04,755 --> 00:31:08,024
began to stir again.

1008
00:31:16,378 --> 00:31:17,278
>> The explosion of Mount

1009
00:31:17,379 --> 00:31:19,180
St. Helen's in May 1980

1010
00:31:19,281 --> 00:31:20,248
scarred the mountain

1011
00:31:20,282 --> 00:31:21,549
with a massive crater

1012
00:31:21,617 --> 00:31:23,284
on its north side,

1013
00:31:23,352 --> 00:31:24,752
but in the summer

1014
00:31:24,820 --> 00:31:26,287
after the eruption, the volcano

1015
00:31:26,355 --> 00:31:28,890
began to rebuild itself.

1016
00:31:28,924 --> 00:31:30,658
Thick magma slowly rose

1017
00:31:30,726 --> 00:31:32,160
to the surface and formed

1018
00:31:32,194 --> 00:31:35,163
a dome inside the crater.

1019
00:31:35,197 --> 00:31:36,831
Had the activities continued

1020
00:31:36,899 --> 00:31:38,333
at the same rate, it would have

1021
00:31:38,367 --> 00:31:39,934
taken about 200 years

1022
00:31:40,002 --> 00:31:41,202
to rebuild the mountain

1023
00:31:41,270 --> 00:31:45,373
to its pre-1980 size.

1024
00:31:45,474 --> 00:31:49,544
But in 1986, magma flows ceased,

1025
00:31:49,612 --> 00:31:53,247
and the volcano died down.

1026
00:31:53,282 --> 00:31:55,016
Life returned to normal and

1027
00:31:55,084 --> 00:31:57,652
adapted to the new landscape.

1028
00:31:57,720 --> 00:31:58,920
Plants and trees took hold

1029
00:31:58,988 --> 00:32:02,056
in the fertile volcanic soil.

1030
00:32:02,091 --> 00:32:03,424
Elk and other animals

1031
00:32:03,492 --> 00:32:07,095
migrated back to the mountain.

1032
00:32:07,162 --> 00:32:10,598
Then on September 23, 2004,

1033
00:32:10,666 --> 00:32:13,034
the ominous rumbling began again

1034
00:32:13,068 --> 00:32:14,068
and put volcanologists

1035
00:32:14,136 --> 00:32:16,204
on alert.

1036
00:32:16,205 --> 00:32:17,338
>> The entire Cascade range

1037
00:32:17,406 --> 00:32:18,506
in the western U.S.

1038
00:32:18,607 --> 00:32:19,707
produces on average

1039
00:32:19,775 --> 00:32:22,310
about 2 eruptions every century.

1040
00:32:22,344 --> 00:32:23,778
So you think, well,

1041
00:32:23,846 --> 00:32:25,780
that's one eruption per career.

1042
00:32:25,781 --> 00:32:27,682
and St. Helen's in the 1980's

1043
00:32:27,783 --> 00:32:30,051
qas ours, and we all assumed

1044
00:32:30,119 --> 00:32:31,753
that that was it.

1045
00:32:31,787 --> 00:32:35,323
But we got a second chance.

1046
00:32:35,424 --> 00:32:36,424
>> Mount St. Helen's

1047
00:32:36,492 --> 00:32:39,060
qas cooking up another mystery.

1048
00:32:39,161 --> 00:32:40,428
Small earthquakes became

1049
00:32:40,496 --> 00:32:42,864
stronger and more frequent.

1050
00:32:42,931 --> 00:32:44,432
GPS measurements detected that

1051
00:32:44,500 --> 00:32:45,967
the area around the mountain

1052
00:32:46,035 --> 00:32:47,769
was sinking.

1053
00:32:47,836 --> 00:32:49,337
>> There was one continuously

1054
00:32:49,405 --> 00:32:51,205
recording GPS instrument

1055
00:32:51,240 --> 00:32:52,874
around the volcano,

1056
00:32:52,941 --> 00:32:56,110
and it's code name was JRO-1.

1057
00:32:56,145 --> 00:32:58,146
JRO-1 had not moved

1058
00:32:58,247 --> 00:32:59,947
in any unusual way

1059
00:33:00,049 --> 00:33:01,749
right up until the day

1060
00:33:01,784 --> 00:33:03,584
the earthquakes started.

1061
00:33:03,686 --> 00:33:05,653
And then on that very day,

1062
00:33:05,688 --> 00:33:07,522
it started to move.

1063
00:33:07,589 --> 00:33:10,858
It moved toward the volcano

1064
00:33:10,959 --> 00:33:13,695
and downward, as if that entire

1065
00:33:13,762 --> 00:33:15,296
area of the crust was sagging

1066
00:33:15,330 --> 00:33:19,400
down toward the volcano.

1067
00:33:19,468 --> 00:33:21,235
>> The only plausible

1068
00:33:21,303 --> 00:33:23,504
explanation for the sinking land

1069
00:33:23,572 --> 00:33:24,972
was that the magma reservoir

1070
00:33:25,040 --> 00:33:28,242
deep underground was shrinking.

1071
00:33:28,310 --> 00:33:30,378
In earlier surveys, scientists

1072
00:33:30,412 --> 00:33:31,879
had detected a vast pool

1073
00:33:31,947 --> 00:33:33,648
of molten rock 8 miles

1074
00:33:33,682 --> 00:33:36,150
under the volcano.

1075
00:33:36,218 --> 00:33:37,752
If it was getting smaller,

1076
00:33:37,786 --> 00:33:40,221
magma had to be on its way up

1077
00:33:40,289 --> 00:33:41,322
towards the throat

1078
00:33:41,390 --> 00:33:43,224
of the volcano.

1079
00:33:43,325 --> 00:33:44,425
The renewed activities

1080
00:33:44,493 --> 00:33:46,227
caused widespread concern.

1081
00:33:46,328 --> 00:33:47,395
Scientists feared another

1082
00:33:47,496 --> 00:33:49,497
eruption was building up.

1083
00:33:49,565 --> 00:33:50,865
And they were puzzled what kind

1084
00:33:50,966 --> 00:33:53,668
of eruption it would be.

1085
00:33:53,769 --> 00:33:55,303
In search of an answer,

1086
00:33:55,370 --> 00:33:56,938
scientists turned to St. Helen's

1087
00:33:57,005 --> 00:33:58,873
early days.

1088
00:33:58,874 --> 00:34:00,041
>> Volcanoes are all

1089
00:34:00,109 --> 00:34:01,576
very individual. They have

1090
00:34:01,677 --> 00:34:03,945
individual types of eruptions

1091
00:34:04,046 --> 00:34:06,147
and traits, and what they've

1092
00:34:06,215 --> 00:34:07,415
done in the past is what they're

1093
00:34:07,483 --> 00:34:09,951
going to do in the future.

1094
00:34:09,952 --> 00:34:11,586
>> The key to past eruptions

1095
00:34:11,687 --> 00:34:14,689
is ancient volcanic rock.

1096
00:34:14,757 --> 00:34:16,057
Mike Clynne has specialized

1097
00:34:16,125 --> 00:34:19,026
in mapping these old deposits.

1098
00:34:19,094 --> 00:34:20,328
Southwest of St. Helen's,

1099
00:34:20,395 --> 00:34:21,763
he investigates an area covered

1100
00:34:21,830 --> 00:34:24,999
with large dark boulders.

1101
00:34:25,033 --> 00:34:26,400
A close look reveals the type

1102
00:34:26,468 --> 00:34:28,636
of eruption they formed in.

1103
00:34:28,670 --> 00:34:29,771
>> We know that this rock

1104
00:34:29,838 --> 00:34:30,838
came from a lava flow

1105
00:34:30,873 --> 00:34:32,140
because it has big crystals

1106
00:34:32,207 --> 00:34:33,941
set in a much finer grained

1107
00:34:34,042 --> 00:34:36,110
ground mass of little crystals.

1108
00:34:36,145 --> 00:34:37,211
The big crystals grew

1109
00:34:37,246 --> 00:34:37,845
in the magma chamber

1110
00:34:37,946 --> 00:34:39,046
while the magma was deep

1111
00:34:39,114 --> 00:34:40,748
under the volcano.

1112
00:34:40,849 --> 00:34:42,650
And the fine-grained ground

1113
00:34:42,684 --> 00:34:44,218
mass, which is tiny crystals,

1114
00:34:44,286 --> 00:34:45,920
grew when the lava erupted

1115
00:34:45,954 --> 00:34:48,956
at the surface and froze.

1116
00:34:49,024 --> 00:34:50,958
>> Radio-carbon dating

1117
00:34:51,026 --> 00:34:52,660
established the rock was born

1118
00:34:52,728 --> 00:34:55,296
2,500 years ago.

1119
00:34:55,397 --> 00:34:56,497
The nature of the eruption

1120
00:34:56,565 --> 00:34:59,567
it formed in was slow and quiet.

1121
00:34:59,668 --> 00:35:01,402
>> This kind of lava flow

1122
00:35:01,470 --> 00:35:03,137
erupts from the mountain

1123
00:35:03,205 --> 00:35:05,473
as a liquid, and it flows down

1124
00:35:05,574 --> 00:35:07,675
the mountainside under gravity.

1125
00:35:07,743 --> 00:35:09,110
As it flows away

1126
00:35:09,178 --> 00:35:10,578
from the mountain, it cools

1127
00:35:10,679 --> 00:35:12,747
until it becomes so viscous

1128
00:35:12,848 --> 00:35:14,549
that it can't flow anymore.

1129
00:35:14,583 --> 00:35:16,384
So that's where it stops,

1130
00:35:16,451 --> 00:35:17,752
and that's what you see here,

1131
00:35:17,853 --> 00:35:19,954
is the end result of emplacement

1132
00:35:20,022 --> 00:35:22,356
of this kind of lava flow.

1133
00:35:22,391 --> 00:35:23,224
So they're not dangerous.

1134
00:35:23,292 --> 00:35:24,225
You can stand and watch it

1135
00:35:24,293 --> 00:35:25,860
come down at you.

1136
00:35:25,928 --> 00:35:29,130
From deposits like these,

1137
00:35:29,198 --> 00:35:30,298
scientists could tell

1138
00:35:30,365 --> 00:35:31,299
that Mount St. Helen's

1139
00:35:31,400 --> 00:35:32,366
had produced a number

1140
00:35:32,401 --> 00:35:34,035
of quiet lava outpourings

1141
00:35:34,102 --> 00:35:37,672
in the last 300,000 years.

1142
00:35:37,739 --> 00:35:39,473
They slowly built up

1143
00:35:39,575 --> 00:35:40,675
the mountain from a small

1144
00:35:40,742 --> 00:35:42,009
cluster of rock

1145
00:35:42,077 --> 00:35:45,079
to a conical-shaped volcano.

1146
00:35:45,113 --> 00:35:46,647
But northeast of the mountain,

1147
00:35:46,748 --> 00:35:48,216
Clynne finds a different deposit

1148
00:35:48,283 --> 00:35:49,350
which tells a story

1149
00:35:49,384 --> 00:35:51,485
of a much more dangerous episode

1150
00:35:51,553 --> 00:35:54,222
in St. Helen's past.

1151
00:35:54,289 --> 00:35:55,556
>> We look at this deposit,

1152
00:35:55,657 --> 00:35:56,457
and there's a couple

1153
00:35:56,491 --> 00:35:57,358
of characteristics

1154
00:35:57,392 --> 00:35:58,292
that are important.

1155
00:35:58,360 --> 00:35:59,126
First of all,

1156
00:35:59,194 --> 00:36:00,194
that it's very loose,

1157
00:36:00,295 --> 00:36:01,295
and that it's composed

1158
00:36:01,363 --> 00:36:02,463
of rock fragments that are

1159
00:36:02,564 --> 00:36:04,899
all about the same size.

1160
00:36:04,933 --> 00:36:06,367
Another important characteristic

1161
00:36:06,401 --> 00:36:08,302
is that the rock fragments

1162
00:36:08,370 --> 00:36:09,570
are touching each other.

1163
00:36:09,671 --> 00:36:10,838
There's no material

1164
00:36:10,906 --> 00:36:12,306
in between them.

1165
00:36:12,374 --> 00:36:13,307
Well, that tells us

1166
00:36:13,375 --> 00:36:14,475
that these rock fragments

1167
00:36:14,576 --> 00:36:16,277
came here by falling

1168
00:36:16,345 --> 00:36:17,578
out of the air.

1169
00:36:17,646 --> 00:36:19,547
It's a big explosive eruption

1170
00:36:19,648 --> 00:36:20,648
that sends the material

1171
00:36:20,716 --> 00:36:22,717
very high into the sky,

1172
00:36:22,751 --> 00:36:25,119
and when the wind dies down,

1173
00:36:25,187 --> 00:36:26,020
they start to fall,

1174
00:36:26,121 --> 00:36:28,756
and they pile up here.

1175
00:36:28,824 --> 00:36:30,291
>> The rock fragments are

1176
00:36:30,392 --> 00:36:31,926
very light pumice that formed

1177
00:36:31,994 --> 00:36:33,728
during a violent eruption

1178
00:36:33,829 --> 00:36:34,929
similar to the one that produced

1179
00:36:35,030 --> 00:36:36,564
the huge mushroom cloud

1180
00:36:36,665 --> 00:36:40,735
in May 1980. But age-dating

1181
00:36:40,802 --> 00:36:42,203
revealed that this deposit

1182
00:36:42,271 --> 00:36:46,274
was much older.

1183
00:36:46,341 --> 00:36:47,642
This event happened

1184
00:36:47,709 --> 00:36:50,177
3,500 years ago, and compared

1185
00:36:50,279 --> 00:36:52,079
to the 1980 eruption,

1186
00:36:52,114 --> 00:36:53,247
scientists found evidence

1187
00:36:53,348 --> 00:36:55,182
that it was much more dangerous

1188
00:36:55,250 --> 00:36:57,385
and spewed out 4 times more

1189
00:36:57,452 --> 00:36:59,520
rock and ash.

1190
00:36:59,554 --> 00:37:00,721
>> This is the biggest eruption

1191
00:37:00,756 --> 00:37:02,156
in Mount St. Helen's history,

1192
00:37:02,190 --> 00:37:03,357
and it was about a cubic mile

1193
00:37:03,458 --> 00:37:04,892
of material that was erupted

1194
00:37:04,927 --> 00:37:06,994
at this time. And we know that

1195
00:37:07,029 --> 00:37:08,462
because we trace out

1196
00:37:08,530 --> 00:37:09,830
the deposit, measure

1197
00:37:09,898 --> 00:37:11,799
its thickness and its distance,

1198
00:37:11,833 --> 00:37:13,334
and you add that all up

1199
00:37:13,368 --> 00:37:14,669
together, and you get

1200
00:37:14,736 --> 00:37:16,637
the volume of the eruption.

1201
00:37:16,705 --> 00:37:18,005
This deposit can be traced

1202
00:37:18,073 --> 00:37:20,174
all the way to central Canada.

1203
00:37:20,275 --> 00:37:22,109
>> Studying Mount St. Helen's

1204
00:37:22,177 --> 00:37:23,277
past has revealed

1205
00:37:23,345 --> 00:37:25,112
that she has an unpredictable

1206
00:37:25,180 --> 00:37:27,181
eruptive nature.

1207
00:37:27,249 --> 00:37:28,182
>> Mount St. Helen's had

1208
00:37:28,283 --> 00:37:29,383
everything from relatively

1209
00:37:29,451 --> 00:37:31,185
benign lava flows to quite

1210
00:37:31,286 --> 00:37:33,287
violent eruptions in the past.

1211
00:37:33,355 --> 00:37:34,355
So it's very hard,

1212
00:37:34,423 --> 00:37:36,090
when a volcano starts acting up,

1213
00:37:36,158 --> 00:37:37,091
to know which of these

1214
00:37:37,192 --> 00:37:38,459
possibilities is going

1215
00:37:38,460 --> 00:37:40,361
to happen, and of course,

1216
00:37:40,429 --> 00:37:41,429
the various scientists,

1217
00:37:41,463 --> 00:37:42,463
we discuss and argue

1218
00:37:42,531 --> 00:37:43,531
and all that kind of stuff

1219
00:37:43,565 --> 00:37:44,799
what we think is going on,

1220
00:37:44,833 --> 00:37:45,900
and nobody truly knows

1221
00:37:46,001 --> 00:37:47,835
what's going on.

1222
00:37:47,836 --> 00:37:48,903
>> Scientists investigating

1223
00:37:48,971 --> 00:37:50,338
Mount St. Helen's have found

1224
00:37:50,372 --> 00:37:51,806
clues that show different

1225
00:37:51,907 --> 00:37:54,742
eruptive behaviors in her past.

1226
00:37:54,810 --> 00:37:57,511
Large dark boulders are evidence

1227
00:37:57,546 --> 00:37:58,879
that she is able to produce

1228
00:37:58,914 --> 00:38:02,083
slow and quiet eruptions.

1229
00:38:02,184 --> 00:38:03,784
A thick deposit of white pumice

1230
00:38:03,819 --> 00:38:05,186
is evidence for an ancient

1231
00:38:05,287 --> 00:38:06,988
dangerous eruption 4 times

1232
00:38:07,055 --> 00:38:10,091
larger than the one in 1980.

1233
00:38:10,158 --> 00:38:12,727
Fortunately, the events that

1234
00:38:12,828 --> 00:38:16,464
began in 2004 took a lucky turn.

1235
00:38:16,531 --> 00:38:19,467
The magma did reach the surface,

1236
00:38:19,534 --> 00:38:20,434
but it had lost

1237
00:38:20,469 --> 00:38:22,903
its explosive power.

1238
00:38:22,971 --> 00:38:24,905
It flowed out like toothpaste,

1239
00:38:24,973 --> 00:38:26,374
in a dome-building style

1240
00:38:26,441 --> 00:38:28,809
of eruption. As geologists

1241
00:38:28,910 --> 00:38:30,244
carried on studying

1242
00:38:30,278 --> 00:38:31,445
Mount St. Helen's,

1243
00:38:31,513 --> 00:38:33,280
a volcano 4,000 miles away

1244
00:38:33,348 --> 00:38:35,716
began to stir. Because of

1245
00:38:35,784 --> 00:38:38,052
their experience in 1980,

1246
00:38:38,086 --> 00:38:39,520
scientists were convinced

1247
00:38:39,554 --> 00:38:40,888
a major catastrophe was

1248
00:38:40,922 --> 00:38:43,791
about to unfold, and this time,

1249
00:38:43,825 --> 00:38:47,461
12,000 lives were at risk.

1250
00:38:55,077 --> 00:38:56,344
>> The eruption of Mount

1251
00:38:56,412 --> 00:38:58,346
St. Helen's in May 1980

1252
00:38:58,414 --> 00:39:00,882
took scientists by surprise.

1253
00:39:00,950 --> 00:39:02,116
It was the first time

1254
00:39:02,151 --> 00:39:03,251
they witnessed the failure

1255
00:39:03,319 --> 00:39:05,153
of a massive bulge,

1256
00:39:05,254 --> 00:39:06,488
a huge landslide,

1257
00:39:06,522 --> 00:39:12,126
and a powerful lateral blast.

1258
00:39:12,127 --> 00:39:13,795
>> Prior to 1980, we just

1259
00:39:13,863 --> 00:39:16,231
didn't have the knowledge

1260
00:39:16,298 --> 00:39:18,066
to make those kinds

1261
00:39:18,133 --> 00:39:20,435
of specific predictions.

1262
00:39:20,436 --> 00:39:22,136
We started learning

1263
00:39:22,238 --> 00:39:24,839
in the 1980's at St. Helen's.

1264
00:39:24,874 --> 00:39:25,840
We've continued to learn

1265
00:39:25,875 --> 00:39:27,141
at volcanoes around the world,

1266
00:39:27,209 --> 00:39:29,878
and we've had some successes.

1267
00:39:29,945 --> 00:39:31,579
>> Forecasting volcanic

1268
00:39:31,614 --> 00:39:33,314
eruptions is difficult because

1269
00:39:33,415 --> 00:39:34,949
there is no strict pattern

1270
00:39:35,017 --> 00:39:37,685
to the buildup.

1271
00:39:37,753 --> 00:39:38,887
But as scientists are getting

1272
00:39:38,954 --> 00:39:40,421
more experienced in observing

1273
00:39:40,523 --> 00:39:41,956
volcanic behavior,

1274
00:39:42,024 --> 00:39:42,957
they are getting better

1275
00:39:43,058 --> 00:39:45,226
at their predictions.

1276
00:39:45,327 --> 00:39:49,597
In 1995, Soufriere Hills volcano

1277
00:39:49,665 --> 00:39:50,932
on the Caribbean Island

1278
00:39:50,966 --> 00:39:54,035
of Montserrat became restless.

1279
00:39:54,136 --> 00:39:57,305
It had been quiet for 350 years

1280
00:39:57,406 --> 00:39:58,740
until earthquakes rumbled it

1281
00:39:58,774 --> 00:40:01,743
to life again.

1282
00:40:01,777 --> 00:40:03,311
Residents were used to

1283
00:40:03,412 --> 00:40:04,879
a gently steaming mountain

1284
00:40:04,947 --> 00:40:06,014
and simply hoped

1285
00:40:06,048 --> 00:40:09,317
it would die down, but when

1286
00:40:09,418 --> 00:40:12,320
the earthquakes got stronger,

1287
00:40:12,388 --> 00:40:15,123
officials called for help.

1288
00:40:15,224 --> 00:40:17,325
A team of U.S. Volcanologists

1289
00:40:17,426 --> 00:40:18,760
Flew to the Caribbean

1290
00:40:18,861 --> 00:40:21,696
to monitor the reawakening.

1291
00:40:21,697 --> 00:40:22,830
>> There developed a situation

1292
00:40:22,865 --> 00:40:25,667
there whereby there was a region

1293
00:40:25,768 --> 00:40:27,569
of high seismicity occurred

1294
00:40:27,603 --> 00:40:28,770
just as St. Helen's.

1295
00:40:28,771 --> 00:40:30,305
If you went up on the mountain,

1296
00:40:30,372 --> 00:40:31,406
as we did, they just about

1297
00:40:31,473 --> 00:40:33,241
knocked you to your knees.

1298
00:40:33,309 --> 00:40:35,043
They were very strong events.

1299
00:40:35,144 --> 00:40:36,477
>> Strong earthquakes weren't

1300
00:40:36,512 --> 00:40:38,212
the only warning signs.

1301
00:40:38,280 --> 00:40:39,013
On the south side

1302
00:40:39,048 --> 00:40:40,148
of the mountain, they observed

1303
00:40:40,215 --> 00:40:41,382
how a monstrous bulge

1304
00:40:41,417 --> 00:40:43,952
began to form.

1305
00:40:44,053 --> 00:40:44,919
>> There were cracks

1306
00:40:44,954 --> 00:40:45,587
that were occurring.

1307
00:40:45,688 --> 00:40:46,421
You could see the cracks

1308
00:40:46,488 --> 00:40:47,221
were moving every day.

1309
00:40:47,289 --> 00:40:48,122
It looked like the whole side

1310
00:40:48,190 --> 00:40:49,591
could fall apart, so we could

1311
00:40:49,692 --> 00:40:51,059
get a slope collapse there,

1312
00:40:51,126 --> 00:40:53,828
a major slope collapse.

1313
00:40:53,862 --> 00:40:55,730
>> By October 1997, the bulge

1314
00:40:55,764 --> 00:40:57,398
was growing at a staggering rate

1315
00:40:57,466 --> 00:41:01,869
of 280 cubic feet per second.

1316
00:41:01,937 --> 00:41:04,472
Scientists were alarmed.

1317
00:41:04,506 --> 00:41:05,406
Because of their experience

1318
00:41:05,507 --> 00:41:06,507
on Mount St. Helen's,

1319
00:41:06,575 --> 00:41:07,742
they knew that a collapse

1320
00:41:07,776 --> 00:41:10,945
of the bulge was imminent.

1321
00:41:11,013 --> 00:41:12,547
People living in the proximities

1322
00:41:12,648 --> 00:41:15,216
of the volcano were in danger.

1323
00:41:15,317 --> 00:41:16,551
So they advised the authorities

1324
00:41:16,585 --> 00:41:19,387
to evacuate immediately.

1325
00:41:19,455 --> 00:41:20,955
>> 8,000 people had to leave

1326
00:41:21,023 --> 00:41:23,725
the island. Over 4,000 were

1327
00:41:23,759 --> 00:41:24,959
forced to move to a safer

1328
00:41:25,027 --> 00:41:28,096
location to the north.

1329
00:41:28,130 --> 00:41:32,667
On the 26th of December, 1997,

1330
00:41:32,735 --> 00:41:35,670
the volcano struck.

1331
00:41:35,738 --> 00:41:36,838
After an intense swarm

1332
00:41:36,905 --> 00:41:38,006
of earthquakes, a huge part

1333
00:41:38,040 --> 00:41:40,141
of the bulge broke loose

1334
00:41:40,209 --> 00:41:43,044
and roared down the valley.

1335
00:41:43,112 --> 00:41:45,580
Like at Mount St. Helen's,

1336
00:41:45,648 --> 00:41:46,948
the sudden removal of rock

1337
00:41:47,016 --> 00:41:47,949
released the pressure

1338
00:41:48,017 --> 00:41:51,119
on the magma below.

1339
00:41:51,186 --> 00:41:53,021
A lateral blast surged south

1340
00:41:53,122 --> 00:41:54,222
and spawned a vertical

1341
00:41:54,289 --> 00:41:58,593
ash column 36,000 feet high.

1342
00:41:58,661 --> 00:42:00,294
Within 15 minutes, the eruption

1343
00:42:00,396 --> 00:42:02,296
destroyed 4 square miles

1344
00:42:02,398 --> 00:42:03,831
of the island and completely

1345
00:42:03,866 --> 00:42:05,566
buried the island's capital,

1346
00:42:05,634 --> 00:42:09,270
Plymouth, under 39 feet of mud.

1347
00:42:11,373 --> 00:42:13,041
>> Montserrat is a prime example

1348
00:42:13,108 --> 00:42:14,208
where lessons learned

1349
00:42:14,276 --> 00:42:15,677
from a big catastrophe

1350
00:42:15,744 --> 00:42:17,745
have prevented another one.

1351
00:42:17,846 --> 00:42:18,646
>> Almost everything that

1352
00:42:18,747 --> 00:42:19,480
occurred at St. Helen's

1353
00:42:19,581 --> 00:42:20,581
did occur at Montserrat.

1354
00:42:20,649 --> 00:42:21,482
It replicated St. Helen's

1355
00:42:21,550 --> 00:42:22,450
not only in the lateral blast

1356
00:42:22,484 --> 00:42:23,384
and so forth, but it did

1357
00:42:23,485 --> 00:42:24,819
everything that St. Helen's did

1358
00:42:24,853 --> 00:42:28,489
on a smaller scale.

1359
00:42:28,557 --> 00:42:29,857
>> Scientists studying the

1360
00:42:29,925 --> 00:42:31,759
eruption of Mount St. Helen's

1361
00:42:31,827 --> 00:42:34,295
on May 18, 1980, have uncovered

1362
00:42:34,396 --> 00:42:35,563
a sequence of events

1363
00:42:35,664 --> 00:42:38,666
they had never seen before.

1364
00:42:38,734 --> 00:42:40,935
A growing bulge on the north

1365
00:42:41,003 --> 00:42:42,103
flank of the mountain

1366
00:42:42,204 --> 00:42:43,738
was an alarming sign that a pool

1367
00:42:43,806 --> 00:42:45,206
of magma was building up

1368
00:42:45,274 --> 00:42:47,942
within the volcano.

1369
00:42:48,010 --> 00:42:49,377
Grey volcanic rock

1370
00:42:49,478 --> 00:42:51,846
from the bulge 5 miles away

1371
00:42:51,914 --> 00:42:53,381
was evidence for a powerful

1372
00:42:53,449 --> 00:42:56,451
sideways eruption.

1373
00:42:56,485 --> 00:42:58,119
A 3,000-year-old mud deposit

1374
00:42:58,187 --> 00:42:59,821
became a warning sign that

1375
00:42:59,922 --> 00:43:01,089
the valleys around the mountain

1376
00:43:01,123 --> 00:43:02,557
have been repeatedly swamped

1377
00:43:02,624 --> 00:43:05,426
by huge mud flows.

1378
00:43:05,527 --> 00:43:07,061
A deposit of white pumice rock

1379
00:43:07,162 --> 00:43:08,896
found all the way up to Canada

1380
00:43:08,997 --> 00:43:10,531
showed that Mount St. Helen's

1381
00:43:10,632 --> 00:43:12,166
is able to produce eruptions

1382
00:43:12,234 --> 00:43:13,801
4 times larger than the one

1383
00:43:13,869 --> 00:43:16,370
in 1980.

1384
00:43:16,438 --> 00:43:18,773
As the investigation has shown,

1385
00:43:18,807 --> 00:43:20,341
Mount St. Helen's is full

1386
00:43:20,442 --> 00:43:22,677
of surprises.

1387
00:43:22,711 --> 00:43:24,178
>> St. Helen's, I think of it

1388
00:43:24,246 --> 00:43:25,713
as a teenager among the Cascade

1389
00:43:25,781 --> 00:43:27,682
volcanoes. It's young,

1390
00:43:27,716 --> 00:43:28,950
it's vigorously active,

1391
00:43:28,984 --> 00:43:29,884
it's explosive,

1392
00:43:29,985 --> 00:43:31,419
it's very energetic.

1393
00:43:31,453 --> 00:43:32,720
Even though to our eye,

1394
00:43:32,788 --> 00:43:33,688
as we look at it,

1395
00:43:33,722 --> 00:43:35,423
it appears to be sleeping,

1396
00:43:35,491 --> 00:43:36,491
it's active. It's doing

1397
00:43:36,525 --> 00:43:37,425
what it's been doing

1398
00:43:37,526 --> 00:43:39,761
for tens of thousands of years.

1399
00:43:39,862 --> 00:43:41,062
>> Mount s helen's looks

1400
00:43:41,096 --> 00:43:42,897
set to continue her erratic

1401
00:43:42,998 --> 00:43:45,433
and at times violent outbursts.

1402
00:43:45,467 --> 00:43:47,001
Her deadly potential

1403
00:43:47,069 --> 00:43:48,469
is a stark reminder

1404
00:43:48,537 --> 00:43:51,472
the earth is never at rest.

1405
00:43:52,473 --> 00:43:59,473
-- Sync, corrected by elderman --
-- for MY-SUBS.com ---