NARRATOR: Recently, scientists have collected new data
giving them a better picture of Yellowstone's
Right beneath the caldera, from the last eruption,
sits the magma chamber.
And it's fed by a plume of magma stretching down 465 miles,
northwest into Montana.
It's mostly solid rock, with the potential to liquefy.
And scientists are closely monitoring it.
Magma, or molten rock, is rising through the plume
into the magma chamber at 2 inches a year.
There's no reason for it to stop
or it might come in spurts.
Our images show wider parts and narrower parts.
So it's like slugs of material that
are flowing in a sewer line.
And this restless Yellowstone Caldera
is truly living, breathing.
And every once in a while, it burps.
NARRATOR: The danger is that the plume starts liquefying
and moving up at a faster rate.
Natural systems can throw us a lot of curve balls.
A lot of things can happen that we're not really ready for.
NARRATOR: Scientist Jake Lowenstern
is looking for a pattern connecting
this supervolcano today and its three prior major eruptions,
2.1 million years ago, 1.3 million years
ago, and 640,000 years ago.
JAKE LOWENSTERN: In two of the really large eruptions
at Yellowstone so much material comes out,
entire mountain ranges end up falling into the ground
and essentially disappearing.
NARRATOR: One 50-mile stretch of mountains
simply disappeared by collapsing into the magma chamber.
University of Toronto geologist John Westgate
has tracked the ash from Yellowstone's prior eruptions.
JOHN WESTGATE: It covered much of the United States.
It occurs right out of the Pacific Ocean.
It's even found in the Gulf of Mexico.
Up in northeast Montana is the site that we're working on.
The total is over 7 meters thick.
These eruptions are enormous.
The amount of material erupted from them, huge.
NARRATOR: When Mt.
St. Helens erupted in May 1980, it
blew up one side of the mountain and triggered an avalanche
of snow, mud, ash, and rock.
Driven by the wind, the ash landed in 11 states
and up in into Canada.
But that's nothing compared to the amount
of ash from Yellowstone's last three major eruptions.
In magnitude and volume, each one was far greater than Mt.
Today, there's little evidence of the supervolcano's
The 50 by 30 mile caldera from the last eruption
was covered by lava and ash and smoothed over by glaciers.
Forests now conceal the scars.