(upbeat music)
- Hi, everybody, I'm Mike Poland, the scientist-in-charge
of the Yellowstone Volcano Observatory,
and this is the monthly update for March 1st of 2023,
the birthday of Yellowstone National Park.
I thought today we might address
one of the more common questions we get here at YVO,
and that's whether or not an external event
could ever trigger a Yellowstone eruption,
for example a distant earthquake.
This is a question we got quite a lot in 2019
after the magnitude 7.1 Ridgecrest earthquake
in eastern California,
and again in March of 2020
when there was that magnitude 6.5 in central Idaho.
More recently, we've been getting that question quite a bit
about whether or not a nuclear blast
could trigger a Yellowstone eruption.
And the answer to all these questions is no,
that's not the way volcanoes work.
In order to be triggered by some sort of external event,
a volcano would have to be basically about to erupt anyway,
and most of that eruptive pressure comes internally
from the exsolution of gases,
sort of like shaking a soda
and having all those bubbles come out.
That's what drives eruptive activity,
and external events just can't cause that.
So eruptions being triggered by earthquakes
is extremely rare.
You can see this in Yellowstone's history.
The last lava flow eruption was 70,000 years ago,
and there have been hundreds to thousands
of magnitude 7, 8, 9 earthquakes
in the Western U.S. since that time.
The last big explosion was 631,000 years ago.
There would've been thousands of very large earthquakes
in the western U.S. since that time,
none of which triggered eruptions.
The same goes for a nuclear blast.
Most of that energy is actually going into the atmosphere.
Even if an impact were to occur
and drive a weapon into the ground,
we're still talking three miles to the magma chamber.
And so a lot of that energy goes up,
instead of into the surrounding rock.
And perhaps the greatest evidence that this doesn't work
is looking back at the 1959 earthquake.
There was a magnitude 7.3 that occurred
just west of the park near Hebgen Lake.
This occurred several miles deep,
essentially right next to the magma chamber,
and it released the same amount of energy
as a moderate sized nuclear weapon.
And of course nothing happened
in terms of Yellowstone eruptive activity.
The shaking did cause many geysers to change their activity,
but that's sort of like shaking the plumbing
in an old house.
Those geysers have very fragile plumbing systems,
and so the shaking can cause those to break down
and cause many geysers to change their behavior.
But in terms of eruptive activity,
distant earthquakes, local earthquakes, nuclear blasts,
would all be devastating events
but would not trigger Yellowstone to erupt.
That's one of the most common misconceptions
about the system.
Okay, now let's talk about what we observed in Yellowstone
in terms of earthquake and deformation and geyser activity
over the past month.
The University of Utah's Seismograph Stations,
which is responsible for operation
and monitoring of the Yellowstone Seismic Network,
recorded 168 earthquakes in the region
during the month of February.
Now, the largest was a magnitude 2.9
that was about 11 miles to the northeast
of West Yellowstone.
That was part of a swarm of 76 events
that occurred between February 4th and February 11th.
You also see there was a swarm
just to the east of there near Grizzly Lake,
48 events that occurred during the month of February.
And this is actually part of ongoing seismicity.
There's been small earthquake swarms
occurring here since last summer.
And this is not too surprising.
The area between Hebgen Lake
and the north central part of Yellowstone National Park
is the most seismically active area in the region.
And then you can see for the rest of the month,
earthquakes scattered about the region.
This is all pretty normal for Yellowstone.
This represents a background state of activity
in terms of earthquakes.
We also didn't see really significant changes
in the deformation style at Yellowstone.
Now, this is the last two years of vertical deformation
at the White Lake GPS station.
It's on the east side of the caldera
on the Sour Creek resurgent dome.
Each one of these blue dots is a day of data.
Downward trends indicate subsidence,
the ground going down,
and upward trends indicate uplift.
Now, over the last two years,
the gradual trend has been one of subsidence
by a few centimeters, about an inch or two per year,
and this has been ongoing since 2015,
and it's interrupted in the summer months by a pause
or even a little bit of uplift.
This is due to snow melt
that percolates down into the ground
and the ground sort of soaks it up like a sponge.
And then once the summer's over,
we get that return to subsidence.
So we've seen that subsidence going on
over the last few months since the end of last summer.
The same story is true on the west side of the caldera,
near Old Faithful on the Mallard Lake resurgent dome.
Overall subsidence of a few centimeters,
an inch or two per year,
interrupted in the summer months
by a slight amount of uplift,
but then returned to that subsidence
as soon as the summer ends.
There hasn't been much deformation
in the area of Norris Geyser Basin.
Again, there's that summer 2022 bit of uplift,
but then really just a slight amount
of subsidence since then.
There are these occasional drops
that look like really dramatic subsidence.
You can see one right here
in December '21 to January of '22,
and then several in late 2022, early 2023.
These are winter storms
that cover the GPS antenna in snow and ice,
and that causes this apparent subsidence.
But once that snow and ice goes away,
the station returns to normal.
And finally, looking at the world's tallest geyser,
Steamboat Geyser in Norris Geyser Basin.
This is the temperature in the outflow channel.
You can see in about February 10th or so,
we start seeing fluctuations in temperature.
That's due to minor eruptive activity at the geyser.
Often we see minors before a major eruption.
There were two major eruptions in January.
But unfortunately we lost power to the station
starting in mid-February.
We also are not able to access the seismic station
in the area since late February,
so we can't verify whether or not any eruptions occurred
using those datasets.
Power is very fickle in that particular area
since it's in the central part of Yellowstone.
They get an awful lot of snow.
But we do have a stream gage
that monitors all water flow
out of the Norris Geyser Basin area,
and that actually records Steamboat eruptions.
This is the height of the water going past the stream gage
from January 1st to the end of February,
and there are two spikes right here
in early January and in late January,
and these are associated with Steamboat Geyser eruptions.
If we zoom in on that early January spike, you can see it.
It sticks out like a sore thumb.
Really, really obvious spike due to Steamboat eruptions.
Now, we haven't seen a similar kind of spike in February
as these two in January.
These other spikes that are bit broader
are associated with precipitation, rain and snow,
that cause the water flow to increase.
It's possible that there is a Steamboat eruption
perhaps hidden in this spike here.
That's something we'll be able to test
once we reestablish communications
with our monitoring stations in Steamboat,
and are able to download the data that were recorded
during the second half of February.
Well, that does it for the March 1st update.
Now remember, if you have any questions at all,
feel free to email us any anytime.
Our email address is yvowebteam, all one word, @usgs.gov.
Happy birthday to Yellowstone National Park.
Stay safe, stay healthy,
and we'll see you next month.
Bye-bye.
(upbeat music)