Hi, I'm Liz Cottrell,
director of the Global Volcanism Program at the
National Museum of Natural History.
I'm standing here in the
Geology, Gems, and Minerals Hall
in front of the
Earthquakes and Eruptions exhibit.
We know that watching a single volcano erupt is
totally awesome,
but what can watching all volcanoes erupt
throughout the course of earth history tell us
about how the planet works?
Let's take a look and find out.
We're looking here at a map of the world we see the
familiar continents and oceans,
but we don't see the tectonic plates or the
plate boundaries.
Rather than memorizing where they are,
let's collect some data.
I have started a video playing that's recording
earthquakes and eruptions since 1960.
Every time an earthquake happens a dot appears and
every time a volcano erupts a triangle appears.
One of the first things you will notice is that earthquakes
and eruptions are taking place all of
the time.
Way out in the middle of the ocean we see all kinds of
tiny white dots appearing.
Earthquakes are happening 24/7 out in the middle of the ocean,
deep below the water where you can't see it.
What's causing these earthquakes?
Actually it is volcanic eruptions.
Volcanoes are erupting all the time on the sea floor
and they cause earthquakes to take place.
So even though we can't see the volcanic eruptions,
that's what is driving the earthquakes.
What about the middle of the United States?
Or the East Coast?
Nothing is happening.
It doesn't look like that is a plate boundary.
In fact if we look around the entire edge of the
Atlantic Ocean we see hardly any activity.
There are no plate boundaries.
The only plate boundary in the Atlantic runs down the
middle of the ocean, a divergent margin,
the Mid-Atlantic Ridge.
Bang!
We just heard a big symbol crash in 1980 when
Mount Saint Helens erupted in the western United States.
That's a convergent margin,
a subduction zone.
One of the coolest things about this animation is that
is shows you all of the earthquakes and eruptions
taking place all around the globe,
all the time,
that you never hear about.
Let's watch this run for a minute and see if we see any
patterns emerging.
WOW!
We are really starting to see some patterns emerge.
All the white dots in the middle of the oceans tend to
form along a line.
Those are the divergent margins,
where the ocean plates are pulling apart and new crust
is being created at the mid-ocean ridges.
And now, along the edges of the continents all around the
Pacific Ocean Basin we see volcanoes erupting and
more earthquakes.
Those are the convergent margins,
were the plates are coming together and
subduction is taking place.
Where dense, old ocean floor is subducting beneath the
buoyant continents.
All that dense, water-logged plate going down is releasing
its water and causing volcanoes to erupt,
and remember,
volcanoes erupting is synonymous with earthquakes.
So we get we get lots of volcanoes
and lots of earthquakes
at these subduction margins.
These concentrated zones of earthquake and eruption
activity are defining our plate boundaries.
Well, we have arrived at 2011,
and we have some really
striking patterns here.
At this point it is easy to define our plate boundaries.
Just trace with your pencils where the earthquakes and
eruptions take place.
Let the data define the plate boundaries for you.
The earthquakes and eruptions define the plate
boundaries.
They occur in the middles of oceans
and on the edges of continents.
Remember, plate boundaries are located where
earthquakes and eruptions are happening because that
is where tectonic plates are pulling apart
and coming together. 99 00:04:13,833 --> 00:00:00,000