Jake Lowenstern: Yes, Yellowstone is a volcano. My name is Jake Lowenstern and I work for
the
U.S. Geological Survey, I'm the Scientist-in-Charge of the
Yellowstone Volcano Observatory. And that's a partnership
with the USGS, the University of Utah who does the actual
monitoring of the earthquakes and ground movement,
and the land manager, Yellowstone National Park.
We're looking here at a geologic map of Yellowstone National Park and the different colors represent
different
geologic units, different rock types, different ages of rocks.
You can see that all of the pink units in here,
these represent the very youngest lava flows, mostly,
that erupted at Yellowstone Volcano.
Most of these are between about 160,000 and 70,000
years old and we see that they're covering up
this area of the park.
It turns out this is the Yellowstone Caldera.
It starts around here and it moves out into the area
over here and it's about 50 miles long, and it formed
when this green material erupted. This is called the
Lava Creek Tuff and the age of this unit, it's found
here in the light green and the dark green also to the
south, the age is 640,000 years.
This was an enormous eruption and it spread ash over
much of the United States.
And a similar eruption to that today would certainly be a big deal.
But since this time, there've been about 80 different
eruptions at Yellowstone. Some of them are very big.
This one is the most recent. It's 70,000 years old
and it's called the Pitchstone Plateau Lava Flow.
In fact, the size of it is about the size of
Washington DC and it's about 100 yards thick in most places.
So this is what we're looking at. We can see volcanic rocks everywhere.
Evidence that this is a really unusual place. It's a massive volcano.
Some of the eruptions from Yellowstone are truly
enormous eruptions. Some of the largest ones that are
known of on earth. And that includes this green unit
here, the Lava Creek Tuff, as well as the purple unit
which is the Huckleberry Ridge Tuff which has erupted 2.1 million years ago.
So these are some of the largest eruptions that we
know of on earth. And because they erupted so much
material, on the order of 1,000 cubic kilometers or 250 cubic miles, then they get
termed as "super eruptions". Really big eruptions. And the way that it works, this is kind of
a new
terminology and super eruptions, if you're a
volcano that has exploded and created one of
these deposits, then you get called a super volcano.
And that's where the word "super volcano" comes from.
So you have this magma that's beneath the surface and
when it erupts and comes out, there's no longer support
for the ground surface up here. And as a result, the
ground surface just caves in. It founders and it falls in.
You're left with what's called a "caldera". It's a subsidence feature or a cave-in feature
that's
caused when it loses its support of the underground magma.
As a result, when it first formed, you had a hole that
was on the order of 50 miles long and even maybe 1,000 or 2,000 or 3,000 feet deep in
places.
We have this deep magma chamber and there's a lot of heat.
The magma is generally at temperatures like 700 or 800
degrees Centigrade or something like 1,200 or 1,300
degrees Fahrenheit. There's a lot of heat.
That heat heats up the rock and that rock then is
conductive cooling. There's water down there.
That water gets heated up and so much of the water
that's near the surface at Yellowstone is actually
at boiling temperature. And as you go down, it gets hotter and hotter.
So that creates a pressurized system of a boiling
aquifer a boiling ground water and that becomes unstable.
It can cause earthquakes and of course it causes the
thermal features that we see everywhere at Yellowstone
that make Yellowstone so famous. The geysers, the
fumaroles or steam vents, the hot springs that are
so beautiful and contains so many different kinds of
life, of thermophile bacteria. So that's what makes
Yellowstone special and it's pretty much all due to this underground magma system.
So we have these massive eruptions that are really
quite rare, and we then we have these lava flows that
happen more frequently but still the last one was
70,000 years ago. But this would be a really big
event if it happened again within the park. It might cause forest fires, it might dam
up rivers
and it would cause a lot of commotion and anxiety
within Yellowstone, but it would have very little
long, long-range effect. It wouldn't affect people
in states that are hundreds of miles away, certainly.
We have other big events that occur at Yellowstone, for example earthquakes. In 1959, there was
a magnitude
7.5 that occurred out near Hebgen Lake. Caused a lot
of damage in the park and also caused a lot of changes
to the thermal areas within Yellowstone. The Teton Fault is on the border of the Teton
Mountains,
south of the park. And it potentially could have a very big earthquake associated with
it.
Beyond that, we have the hydrothermal explosions, or steam explosions, when the ground water
system
becomes too pressurized and erupts during perhaps
an earthquake or due to a change in lake level.
And what happens is the ground water system can
form really large holes in the ground, sometimes
hundreds of feet across. This is Turbid Lake right here; Indian Pond and Mary Bay, all
of these
were created in the last 15,000 years by explosions of the hydrothermal system. In this case,
no magma
has erupted and they're fairly localized events in
terms of their damage, but they're still definitely
relevant for what's going on at Yellowstone and need to be watched.
Almost every year somewhere in Yellowstone there
is a small hydrothermal explosion.
Sometimes they might only be a couple feet across
but we find evidence for them. Sometimes we see a
little bit of smoke coming out or fumes coming out
in a place where we didn't expect it.
Sometimes somebody hears it. And in lucky cases,
we actually get to witness one of these explosions
and that's happened every few years as well. We have no way of predicting these explosions,
especially the smaller ones. But we hope that as
time goes by, we'll get more and more knowledge
about how they work and maybe get the chance that
some day we'll be able to have some predictive
capabilities for these explosions.