(upbeat music)
Hi, everybody, I'm Mike Poland, the scientist-in-charge
at the Yellowstone Volcano Observatory,
and this is the monthly update for December 1st of 2021.
I thought before we got into talking about
what happened over the past month,
we might talk about deformation at Yellowstone
and specifically uplift.
And this is because we started to think
that maybe there was some uplift happening
at the Norris Geyser Basin area in last month's update.
And that generated a lot of questions,
and I thought this would be a good time to review
what Yellowstone does in terms of its ups and downs
because it does both.
It rises and it falls.
So here's a map of the Yellowstone area.
There's the caldera outlined in the dotted line,
and we've got seismicity from 2021 in red here.
There's about 2,600 earthquakes or so,
not too far off the average for any given year so far.
GPS station here in the east side of the caldera since 2003,
this is the vertical deformation at that site.
And you can see how in 2004, the site went up. In 2009,
then it went down to 2014,
and then up 2014 to 2015,
and down from 2015 to the present.
So the whole ground is rising and falling.
Some people have characterized this
like Yellowstone is breathing.
If we go to the other side of the caldera,
the west side near Old Faithful,
we see the exact same pattern.
It goes up in the early 2000s,
and then from 2009 to 2014 down,
and then up 2014 to 2015,
and then down from 2015 to the present.
So the caldera, again, rising and falling,
and since 2015 it's been going down.
Now, Norris Geyser Basin behaves differently
than these other sites.
You can see these are all on the same scale,
so you can compare them all directly.
Norris had a little bit of down in the early 2000,
didn't do much,
had this little blip of uplift in 2013 to 2014,
and then uplift from 2015 to 2018,
and then it was pretty steady.
But it was this bit of uplift
that we were looking at right at the very end.
Maybe Norris is doing something a bit different.
Well, it turns out it was responding to a seasonal change.
And if we zoom in on these graphs,
we can see exactly what that seasonal trend is.
So this is the vertical deformation
on that east side of the caldera station.
See, it's down, and there's this little bit,
it's sort of a pause in the downward motion or uplift,
and then again, another one there, another one.
Every summer, the caldera sort of bounces up a little bit,
and that's caused by groundwater.
So as the snowmelt percolates into the subsurface,
it actually causes the ground
to sort of expand like a sponge.
And we saw that every summer at this site
in the east side of the caldera.
It turns out at Norris, we see the same thing.
Here's summer of 2019 at Norris.
There's a little bit of pause or uplift
in the overall trends.
Again here in 2020, just a little bit of change.
And here again, it's more strongly expressed in 2021,
but now Norris has started going down,
just like the caldera has started going down.
So the changes we've been seeing at Norris
over the last few months are seasonal in nature
and not an overall trend.
So Norris really isn't deforming all that much.
Now, this is just the last few years, right?
But what's Yellowstone been doing over the long-term?
Now, there we know by looking at past measurements
which go back to the 1920s
that there's a net rise in the ground,
but it has been going up and down over time.
But using geology, we can go back even farther.
So here's a map of the north side of Yellowstone Lake.
And you'll notice in this very detailed topography,
there are these little ridge lines.
Now, these are outlined
with little dashed and dotted lines here,
and the yellow arrows point to some of those.
And here's a picture of what that looks like on the ground.
There's one little terrace here.
There's a bit of a rise and then a terrace beyond that.
Those terraces are caused by changes
in the level of Yellowstone Lake,
which is controlled by the outlet,
the rise and fall of the outlet.
So by looking at the terraces at Yellowstone Lake,
we can understand what's been happening
at Yellowstone deformation-wise,
going back to the last Ice Age 14,000 to 15,000 years ago.
And when we do that, when we date these terraces,
and we can date them based on the presence of ash layers,
we can actually see ash from Crater Lake [OR]
and Glacier Peak [WA] eruptions thousands of years ago
on these terraces.
And archeological sites on the terraces
help us understand their dates.
When we date those terraces, we can see that over time,
Yellowstone has gone up and down over thousands of years.
But over the last 15,000 years or so,
the net motion at Yellowstone has been down.
And in fact, Yellowstone has subsided and deflated
by over 100 feet at the core of the caldera.
So ups and downs at Yellowstone,
that's part of what this caldera does.
That's Yellowstone being Yellowstone.
And frankly it would be kind of strange
if it weren't going up and down.
That's just how Yellowstone behaves.
All right, now let's talk about what happened
during the last months in terms of deformation, seismic,
and geyser activity in Yellowstone.
November saw relatively few earthquakes
in the Yellowstone region.
The University of Utah Seismograph Stations,
which is responsible for the operation and maintenance
of the Yellowstone seismic network,
recorded just 137 events during the month.
The largest was actually south of the park,
just south of the south entrance and north of Jackson Lake.
That was a magnitude 2.5 that occurred on November 10th.
The largest swarm of the month was
about 60 earthquakes that occurred late in November,
just to the north of Old Faithful.
So pretty average month
in terms of seismicity in the Yellowstone region.
Deformation trends have continued as they have since 2015.
This is from the White Lake GPS station,
vertical deformation on the east side of the caldera,
the Sour Creek resurgent dome.
Each one of these dots is one day of data.
Downward trends indicate subsidence,
and upward trends indicate uplift.
And over this two-year period and, indeed, since 2015,
we've seen overall subsidence
with these little summer pauses
or episodes of slight uplift.
And those little summertime episodes are caused
by groundwater recharge.
As all that water from snowmelt percolates
into the subsurface slowly,
the ground soaks it up like a sponge,
and we see pauses in that subsidence
or even a little bit of uplift.
The same pattern is seen on the west side of the caldera
in the Mallard Lake resurgent dome.
This is from a GPS site near Old Faithful.
There's that overall subsidence
with a little bit of summertime uplift
or at least a pause in that subsidence.
Now, you might remember last month we talked
about potential uplift at Norris Geyser Basin.
Now, there hasn't been a whole lot of deformation
that we've seen there,
but then there's this slight 1 to 1 1/2-centimeter up-warp
during the summer, and it really wasn't clear
whether this was real uplift
or some seasonal pattern like we see in the caldera.
Now you can see over the last month, that has turned around,
and so this is almost certainly
just like we're seeing in the caldera,
one of these seasonal signals basically,
the ground charging up with groundwater due to snowmelt.
And if we compare the signal that we get at Norris
to what we see in the caldera,
you can see that the time period
at which the uplift at Norris turns around
matches pretty well with when start seeing subsidence resume
in the caldera.
So that Norris uplift that we were looking at
over the course of the summer,
that very slight up-warping there,
appears related to seasonal groundwater recharge
and is not an overall uplift signal in the Norris area.
So deformation in the Yellowstone region
remains very slight.
Nothing really significant at Norris.
And the caldera system remains in the period of subsidence
as it has since 2015.
And then finally, turning to everyone's favorite geyser,
Steamboat, tallest geyser in the world
in Norris Geyser Basin.
It remains active.
Here is the temperature plot
from the runoff channel with Steamboat.
You can see all these little minor eruptive activity.
It culminates in a major eruption
and then a drop in temperature.
This first eruption of the month occurred on November 12th,
and then there was a second eruption
that occurred very late on November 24th,
and it's looking like we may be ramping
into perhaps another period of eruptive activity.
So Steamboat remains active,
although not erupting quite as frequently
as it has in previous years.
Well, that does it for the December 1st update.
Now, remember, if you you've any questions at all,
you can feel free to email us anytime.
Our address is yvowebteam, all one word, @usgs.gov.
Thanks for joining us.
And until next month, stay safe and stay healthy.
See you later.
(upbeat music)