(soft piano music)
- In science you seldom have an aha moment
in which you get the definitive final answer;
this is exactly what's happening and we're confident.
We seldom get that moment.
What you do is you collect information over time,
you develop hypotheses, we get ever closer and closer.
Today I'm here at Three Sisters in Central Oregon
and I'm here to install some monitoring equipment
to keep track of something that's been going on
for 25 years and still goes on today.
Hi my name's Dan Dzurisin,
I'm a geologist with the US Geological Survey.
And I'm here at Three Sisters today
to install some GPS monitoring equipment
that will tell us how much the ground is moving.
Not shaking with earthquakes, but moving ever so slowly,
just a small fraction of an inch per year.
(soft piano music)
Sometime in the mid-1990's, the area around Three Sisters
started going up.
And it was a very, very large area,
more than 10 miles across,
the center of it going up about two inches a year.
Now I'm gonna say that again.
More than 10 miles across,
center of it going up a little more than two inches a year.
One thing that can cause that
is magma moving around underground,
or in particular,
magma rising from greater depth in the earth
up to a shallower depth, which forces the surface
to move upward in a very broad bulge.
And we suspected that might be what was going on.
Colleague of mine used what was then a relatively new system
that makes use of radar satellites orbiting the earth.
They take radar images of the earth's surface,
they go around some additional orbits,
they take another radar image of the same surface.
And by overlaying those and comparing them in a certain way
you can actually get a picture of how much the ground moved
toward or away from the satellite;
down to a fraction of an inch,
it's revolutionary, it's incredible.
And my colleague did that using images
from the late 1990's, 1999, 2000,
and what he saw was this big bulge 10 miles across.
(light acoustic music) And so the USGS,
working with our partners in the Forest Service,
installed a series of monitoring stations out here
to keep track of the rate at which that bulge is growing.
And we measure that in a variety of ways.
We continue to use the radar satellite data
to keep track of it, to give us the broad map.
But then we put GPS stations out at specific locations,
fixed to rock that's rigidly attached to the earth,
and we can measure very, very accurately
how much that particular point has moved.
More accurately than you can measure
using the radar satellites.
The radar satellites give you a picture of the entire bulge,
our GPS stations give us very, very accurate measurements
of how much individual points have moved.
And that's what we're doing here today.
- Hi. Today I am here at Three Sisters,
and we are right near South Sister,
which is right over there.
And today I'm going to show you
how we set up our GPS monitoring system
in order to measure ground deformation.
So we have a pin right here
that is cemented into this lava flow.
And then this is the antenna.
And we're gonna have to set it to true north,
but it just goes right in like this.
And this is what receives the signals from the satellites
in order to collect the data.
This is the receiver,
and this is what's going to store all the data
that we collect over the next two months.
And it is powered by two lithium ion batteries
that look like this.
And we also have this antenna cable
which basically just connects the antenna under here
and it's going to go in through the box through the side
and connect to the receiver.
And then we also have a solar panel over here
which will face south.
And that's just the backup
in case the batteries run out of energy.
Okay, so box right here.
Beside you.
Put this on the side.
(equipment clinking)
We think the most likely cause of the uplift
has been an injection of magma.
Magma has come from deeper within the earth
up toward the surface to a depth of roughly three miles,
a little more than three miles below the surface.
And it's accumulated there over time.
This kind of process has not been documented
very many times anywhere on the earth.
Because I said it made very few earthquakes,
made one earthquakes swarm, relatively small.
But if it's not making earthquakes,
and if you're not using satellite radar data
or some other form of data to look,
episodes like this in the past
probably happened in other places
and maybe here in Central Oregon as well
and we just didn't know it.
So we think it's important to monitor this one
as carefully and thoroughly as we can
for as long as it goes on
to try to get ever closer to that aha moment,
and say okay I'm pretty sure this is what happened,
and this is the process that caused it.