Hello everyone I'm Mike Poland,
the Scientist-in-Charge at the
Yellowstone Volcano Observatory.
And I'm here with the monthly update for Yellowstone
on August 1st of 2019.
There's a lot of interest in Steamboat Geyser, of course,
and as you might remember June was a particularly
spectacular month for eruptions.
July it calmed down a little bit.
It went back to more weekly eruptions.
It had eruptions on July 4th, the 10th,
the 18th, the 24th, and the 30th.
So five eruptions for the month
and that brings the total to 30 for the year.
That's only two shy of the record that was set last year.
Here you can see the July 30th eruption
as recorded at the seismometer that's at
the museum building in the Norris Geyser Basin.
August is also an important anniversary for Yellowstone.
Sixty years ago, the 1959 Hebgen Lake earthquake occurred.
That was on August 17th at about 11:37 at night
local time, back in 1959.
Here's a picture of the fault scarp that formed
during that earthquake.
In fact, you can still visit that fault scarp today.
Now if you're interested in learning more
about the Hebgen Lake earthquake
there are a series of public lectures and other events
that are going to be held at the U.S. Forest Service
Earthquake Lake Visitor Center.
That's just about 27 miles or so to the northwest
of the town of West Yellowstone in Montana.
There's gonna be a couple of Yellowstone
Volcano Observatory scientists speaking.
On August 8th at 3pm local time, Dr. Mike Stickney,
who is the Director of Earthquake Studies
at the Montana Bureau of Mines and Geology,
will be talking about the 1959 earthquake and its geology.
And on August 16th at 2pm local time,
Dr. Jamie Farrell from the University of Utah,
and he's also the Chief Seismologist
of the Yellowstone Volcano Observatory,
will be talking about the impact of the 1959 earthquake
on Yellowstone, including all of the geysers
that make Yellowstone so famous.
So if you're gonna be in the region of West Yellowstone
during that time period, you may wanna check it out.
And I think this anniversary also is a good
reminder to us that earthquake hazards
in the Yellowstone region are pretty significant.
Magnitude six and seven events do happen
and that's something that we all need to be aware of.
Okay, let's get to the data for July.
During the month of July, the University of Utah
seismograph stations, which is responsible for
the maintenance and operation of the Yellowstone
seismic network, located 135 earthquakes
in the Yellowstone region.
You can see a map of those earthquakes here.
The month included a swarm of 78 located earthquakes
about nine miles to the north-northeast of Old Faithful.
This cluster right here included the largest
earthquake of the month, which is a 2.9.
That event was not reported felt by anyone in the park.
This is not unusual.
About half of all earthquakes in Yellowstone
occur as part of swarms.
So this swarm right here, which occurred over the course
of July 19th to the 28th, is pretty normal for the region.
Seventy-eight out of 135 is sort of what we'd expect.
And overall seismicity for the month
was at background levels.
In terms of deformation, we didn't see
that much change either.
This is a plot of the vertical deformation
on the Sour Creek Resurgent Dome
at the White Lake GPS station.
Each dot is a daily measurement of the vertical position.
When it trends down, that means that the ground
is moving down, and up means that the ground is uplifting.
And this over the past two years.
So you can see the overall trend is down
by a few centimeters per year.
There's a couple of places where it looks like
it's popped up a bit and we think that these
are seasonal changes related to the storage
of water beneath the ground due to snow melt
or even lake level changes.
There was one in the late Spring early Summer of 2018
and we see another one that's sort of happening
or just happened over the past few months.
But overall the trend since 2015
has been one of subsidence.
This is at the Old Faithful area, the OFW2 GPS site,
over the same two year period.
And again we see that same subsidence pattern,
perhaps with a bit of a seasonal change
over the last few months since Spring of 2019.
This has also been ongoing since 2015,
this subsidence, and it's been occurring on
the Mallard Lake Resurgent Dome
which is on the west side of the caldera.
In the Norris area, we had been seeing uplifts since 2015
at a rate of a few centimeters per year,
but that stalled in about October of 2018.
And since that time we haven't seen much
in the way of any changes at Norris.
So Norris deformation has largely been static,
no uplift or subsidence for the last many months,
since October of last year.
Now if you'd like more information
you can always go to the Yellowstone
Volcano Observatory website.
We cover all the volcanoes in the southwestern
United States, and Yellowstone.
So if you click on Yellowstone you can get
to current information and background information
about the caldera system.
That includes the current update for Yellowstone,
which is posted on the first of every month.
And also Caldera Chronicles, which is our
weekly article about a different aspect
of Yellowstone history, geology,
current activity, or research.
So we encourage you to check that out
if you'd like more information.
You can also email us if you'd like
at yvowebteam, all one word, at usgs.gov.
We're happy to answer any questions you might have
about Yellowstone current activity, history,
geology, whatever you like.
We love talking about Yellowstone.
Okay, thanks for joining us and next month
we will be coming to you from Yellowstone National Park
where we will be doing some field work.
So we'll see you then, have a good August.