(upbeat music)
Hi everyone, I'm Mike Poland,
scientist-in-charge of the Yellowstone Volcano Observatory.
This is the monthly update for October 1st of 2020.
Now, Yellowstone was in the news
during the month of September.
You may have heard there was an earthquake swarm,
centered really around September 10th.
It actually lingered into September 16th.
And before we get into talking about what happened overall
during the month, I wanted to talk about this swarm.
It was a nice little swarm located just south of West Thumb,
south of Yellowstone Lake and North of Mount Sheridan.
Most of it occurred on September 10th.
There were 90 odd earthquakes that occurred that day,
but it lingered on into September 16th.
And overall there were about 125 earthquakes
that occurred in that swarm.
Now that may sound like a lot,
but that's actually par for the course for Yellowstone,
kind of background activity.
Yellowstone has lots and lots of seismic swarms.
There are about 1,5000 to 2,500 earthquakes
every year in Yellowstone.
And about half of these occur as seismic swarms.
This seismicity is related to the fact
that there's faults all over the place in Yellowstone.
This particular swarm here occurred at the intersection
between the caldera, Yellowstone Caldera's bounding faults
and the Mount Sheridan fault zone.
So all of these faults,
plus all of that water moving around the surface,
and the fact that the area is weak overall
because of all the earthquake activity
and magmatic activity over time,
means that earthquake swarms are really common.
These swarms are clusters of earthquakes in time and space.
So rapid-fire sequences of earthquakes,
basically in the same general area.
So they get a lot of notoriety when they happen,
but they happen all the time in Yellowstone.
And really, that's sort of what Yellowstone does.
In fact, in 2017, there was a three month long swarm
that included 2,400 earthquakes.
And one day had 300 of them,
the maximum of which was a magnitude 4.4.
The maximum of this swarm
on September 10th was a magnitude 2.8.
So this is sort of what Yellowstone does.
And these kinds of swarms
happen all the time in Yellowstone.
Okay, let's dive in and talk about
what happened during the month of September.
The University of Utah Seismograph Station,
which is responsible for the operation and maintenance
of the Yellowstone Seismic Network,
recorded 205 earthquakes in the Yellowstone area
during the month of September.
Most of the earthquakes were distributed through the region,
except for that swarm that we just talked about,
of 125 events south of West Thumb
between September 10th and the 16th,
and over 90 of these events
occurred on September 10th alone,
including the largest, a magnitude 2.8.
But this sort of seismicity is very typical
for the Yellowstone region.
So seismicity remains at background levels.
We've seen continued deformation patterns,
that's ground motion patterns, over the past several years
with very little change in the caldera.
This is GPS data vertical deformation
from the White Lake GPS station,
which is on the east side of the caldera,
the Sour Creek Resurgent Dome.
Each one of these points, each one of these circles
is a single day's worth of data.
And this plot spans the last two years.
Downward trends indicates subsidence,
and upward indicates uplift.
So the overall trend
during this two year period is subsidence.
And this dates back to 2015.
Subsidence occurring of a couple of centimeters per year.
That's about an inch per year or so.
And there are small little seasonal changes
that you can see here that happen during the summers.
But overall, that subsidence pattern
has been ongoing since 2015.
The same is true on the western side of the caldera,
where a GPS station near Old Faithful
shows the same pattern, this gradual subsidence
with little seasonal changes here and there,
but gradual substance of a couple of centimeters,
about an inch or so per year.
At Norris, in the Norris Geyser Basin area,
we haven't seen much in the way of deformation
over the past couple of years.
So we have mostly flat from late 2018 to late 2019,
a small subsidence,
and then mostly flat again since early 2020.
So really at Norris, there certainly hasn't been any change
since the beginning of this year.
And finally, turning to Geyser activity.
We had four eruptions of Steamboat Geyser.
This is a plot of the water temperature
for the outflow channel of the geyser.
Anytime you see a spike, that's a major geyser eruption.
These normal oscillations are air temperature,
meaning that there's no water in the channel.
And this sort of jagged lines
are small, minor eruptions of the Geyser.
So each major eruption is preceded by minor activity.
And we had major eruptions on September 1st,
September 9th, September 16th,
and the fourth of the month here on September 26th.
And of course, we did have Giantess Geyser,
which erupted for the first time in six years,
in August erupted again on September 10th.
So geyser activity in Yellowstone,
as usual, remain spectacular.
Well that does it for
the Yellowstone Volcano Observatory monthly update.
Remember, if you have any questions
you can always email us at yvowebteam,
that's all one word, @usgs.gov.
Take care, stay healthy, stay safe,
and we'll see you next month, bye bye.
(upbeat music)