(upbeat music)
Hi everyone.
I'm Mike Poland, the scientist-in-charge
of the Yellowstone Volcano Observatory.
And this is the monthly update for April 1st of 2022.
Always perhaps a bit tempting to do a practical joke
or something on the April 1st update,
but I think this update, let's talk about earthquakes,
because we had a little seismic swarm at Yellowstone
during the last week of March.
Now, seismic swarms are nothing new in Yellowstone.
We typically have dozens of swarms every year.
And about 50% of all the earthquakes
in Yellowstone are parts of swarms.
And there's typically around 2,000 earthquakes
or so on average every year.
This particular swarm happened
in the northwest part of the park.
You can see West Yellowstone there,
Norris Geyser Basin is here,
Yellowstone Lake down in there.
Now, this swarm started on the evening
of Monday, March 28th.
And in the first 24 hours,
over 100 earthquakes were located as part of the sequence.
All of this location work is done by the seismologists
at the University of Utah Seismograph Stations,
and they maintain all the equipment out there
and do all of the earthquake location work.
This particular area is a real hotbed for seismicity.
In fact, this area in here
is the most seismically active part
of Yellowstone National Park.
Back in 2017, there was a three-month-long swarm
that had over 2,400 located earthquakes in the region.
If we look at the last few decades
of seismicity in the Yellowstone area,
you can see this area of seismicity
right here from, there's West Yellowstone down there,
sort of trending east - west from outside the park,
just into the Norris area.
That's where we see a tremendous number of earthquakes.
Blue ones in this map are seismic swarm events,
and red ones are discreet earthquakes.
Now, there's at least three reasons
that there are so many earthquakes in this region.
The first is that there are faults
all over the place already.
Now, Yellowstone sits right on the eastern edge
of what we call the Basin and Range extensional province.
That stretches from the Tetons in the east
to the Sierra Nevada in the west,
and from central Idaho and central Montana in the north,
down to Mexico in the south,
and this area is being stretched apart.
So there's faults everywhere.
And that's what gives you that very characteristic valley,
mountain range - valley - mountain range
sort of topography in the region.
So there's faults all over the place anyway,
and this region is no exception.
The second reason, there's a lot of water.
Yellowstone sits at the highest elevation,
on average, in the Rockies.
So there's a lot of snow, a lot of rain.
And when that water starts interacting with those faults,
you can get lots and lots of small earthquakes.
And in fact, it's even aided a bit more
by some of that water being hot,
going down towards the cooling magma body,
and then recirculating back towards the surface.
You get a lot of hot water.
So water and fault interactions,
that means lots of small earthquakes.
The third reason is over 60 years old,
and that's this big event that happened
just west of the park in 1959.
The magnitude 7.3 Hebgen Lake earthquake.
This is still the largest earthquake ever recorded
in the Intermountain West Region of the United States.
It caused a tremendous amount of damage in this area.
In fact, a landslide swept into
the Madison River Canyon into a campground,
and over two dozen people were killed during that event.
Big earthquakes like this alter the stress field
in the rock that's around where the earthquake happens,
and it can make small earthquakes more likely.
It created that sort of situation,
trending into Yellowstone National Park.
And so, that means small perturbations
can now cause small earthquakes.
So it's sort of a perfect recipe for earthquakes
in this particular area of Yellowstone.
You've got a lot of preexisting faults,
a lot of water moving around in the sub-surface,
and then the stress state of the area,
because of that 1959 earthquake,
predisposes the area to lots of small earthquakes.
So these kinds of earthquakes are extremely common,
especially in this area here.
They don't really have anything
to do with volcanic activity or magmatic activity.
The magma body, the cooling area, mostly solid anyway,
is to the south of this area here.
So this is really just preexisting faults, water,
and that stress that's left over
from the 1959 Hebgen Lake earthquake.
All right, now, let's talk more detail
about what happened during the month of March
in terms of seismicity, in terms of deformation,
and in terms of geyser activity.
During the month of March,
the University of Utah Seismograph Stations,
which is responsible for the operation
and maintenance of the Yellowstone Seismic Network,
located 254 earthquakes in the Yellowstone region.
And this is pretty typical activity
for a given month in Yellowstone.
The largest event of the month was a magnitude 2.9
that occurred on March 15th,
just north of Yellowstone Lake.
There were also two swarms that occurred during the month.
During the first week of March,
there was a swarm of 38 events
that were located south of Yellowstone Lake,
near Heart Lake.
And the largest event of this swarm was a magnitude 2.2.
And then, of course, there's the swarm
we were just talking about
in the northwest part of the park.
About 115 events have been located
in the last week of March,
the largest being a magnitude 2.6.
So all in all, a pretty average month
for earthquakes in Yellowstone.
Deformation trends have remained pretty steady as well
over the past few years.
This is vertical deformation at the White Lake GPS Station,
which is on the east side of the caldera,
on the Sour Creek resurgent dome.
Each one of these blue dots is one day worth of data.
And the entire plot spans the past two years.
Upward trends indicate uplift,
and downward trends indicate subsidence.
The overall trend during this two-year period,
and in fact, stretching all the way back to 2015,
is one of overall subsidence.
And it's occurring at a rate
of about two to three centimeters,
or about one inch per year.
During the summertime, there are these pauses in subsidence,
or even slight uplift trends.
And this is caused by groundwater from snow melt
that percolates into the subsurface,
and the ground sort of soaks it up like a sponge.
So we see a pause in the subsidence,
or possibly even a little bit of uplift,
but during the winter months
when that snow melt isn't occurring,
we see pretty steady subsidence, as we've seen here
from late 2021 into the beginning of 2022.
If we go over to the other side of the caldera
in the Mallard Lake resurgent dome,
this is near Old Faithful, the same sort of trend shows up.
There's an overall subsidence
of a couple of centimeters per year,
about an inch per year, interrupted during the summer months
by a pause in the subsidence,
even a slight amount of uplift.
The data are kind of noisy during this first part in 2020
due to a lot of trees in the area,
but some of those trees were removed in September of 2020
to reduce the fire load in the area
as a wildfire approached.
There's also a bit of an offset right here.
That's caused by a storm that dropped
quite a lot of snow in the area and obscured the GPS signal.
But otherwise, we see the same sorts of trends
in the caldera that we've seen since 2015,
that of gradual subsidence
of about two to three centimeters, or one inch per year.
And looking at the area of the Norris Geyser Basin,
there really hasn't been much of a change at all
in the last two years.
You can see that the deformation shows quite a steady trend.
There's a bit of uplift here,
apparent uplift in the summer months, again, in 2021.
And that's, again, due to this groundwater recharge
from snowmelt percolating into the subsurface,
and then this big deviation in December.
That's that same storm that affected
the GPS station near Old Faithful.
It also impacted the station near Norris Geyser Basin.
Otherwise we really haven't seen much
in the way of deformation in the Norris area.
Finally, moving to everyone's favorite geyser,
Steamboat Geyser, tallest active geyser in the world.
This is the temperature record
in the Steamboat outflow channel.
It's gets kind of noisy as minor eruptions occur.
And then the major eruption occurs, this one on March 4th.
After that, we see the same regular
sort of diurnal, daily variations in temperature,
no minor eruptions.
Then minor eruptions start picking up again.
That's a sign that we're moving towards a major eruption.
And again, a major eruption did occur on March 30th.
And now, we're back to those normal temperature variations
as the minor activity has not yet resumed.
So Steamboat continues to be active
to eruptions during the month of March.
Hopefully this means it'll continue
putting on a show for us during the summer of 2022.
(uplifting music) Well, that does it
for the April 1st, 2022 update.
Now, remember, if you have any questions at all,
feel free to email us any time.
Our email address is yvowebteam,
that's all one word, @usgs.gov.
Have a happy April Fools' Day,
stay safe, stay healthy, and we'll see you next month.
Bye bye.
(uplifting music)