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Inside USGS, No. 6, Ken Pierce, Heavy Breathing of the Yellowstone Caldera

Number 6Ken Pierce U.

S.

Geological SurveyHeavy Breathing of the Yellowstone Caldera TEXT: Heavy Breathing of the Yellowstone Caldera DR.

PIERCE: My name is Ken Pierce, I'm a geologistwith the U.

S.

Geological Survey, actually presently retired and emeritus with the U.

S.

Geological Survey.

And my field of focus-of specialization, is in what's called Quaternarygeology and geomorphology.

Quaternary geology you might think of it asthe time of the ice ages, it's the last few million years, it's the very tag end of geologictime, but it's also the most important part of geologic time because it affects how welive on the Earth and the landscapes around us.

The other part of my field of focus is geomorphology, which is the study of the form of the landand that has a lot to do with what geologic processes are acting on the land, why thelandscape looks the way it does, what were things that happened in the past, or in thepresent or in the possible future that relate to the form of the land.

TEXT: How would you describe the Yellowstonecaldera? DR.

PIERCE: The center of Yellowstone is alarge caldera and calderas around the world are noted for being restless, various kindsof activity going on including uplift, subsidence, volcanic eruptions, all kinds of things happen.

And Yellowstone is no different, it's a restless caldera.

GRAPHIC TEXT: Hot Spot Geoid and SwellMap of major geoid anomaly in the western United States.

Warmer colors indicate higher altitude anomalies, culminating in red at Yellowstone.

Volcanicfields (circles) along the hotspot track are shown with their starting ages.

The dashedwhite circle shows the inferred position of the present hotspot based on a rate of platemovement of 25 km/m.

y.

The dotted line shows the inferred margin of the Yellowstone hotspotswell.

TEXT: Why do you say the Yellowstone calderais restless? DR.

PIERCE: Yellowstone has been deflatedand inflated in the last part of Holocene time or what we might call post-glacial time.

And one of the things that I've been working on is documenting changes in the Yellowstonecaldera through time.

Part of the geology of Yellowstone is set up really nice for this.

There is Yellowstone Lake and a channel of the Yellowstone River that goes across whatis the threshold in the center of the caldera.

If the caldera inflates, this makes YellowstoneLake get higher, if the caldera deflates, this makes Yellowstone Lake get lower.

Andone of the connections between Yellowstone Lake and this threshold area is a channelof the Yellowstone River.

At present, it's acting like a large pool, as an extensionof Yellowstone Lake.

But in the past, when the caldera subsided, this area has actedas a channel of the active Yellowstone River and it actually was so vigorous it was undercuttingits banks, it's acting like a vigorous, normal river.

If you go into an area just beyond the threshold of Yellowstone Lake in this pool section ofthe Yellowstone River and auger down, you go through slack water lake-type deposits, sand deposits and then you go into a gravel, indicating the river was very active at thattime.

If we use these same cores to date the time that the Yellowstone River was actinglike a river instead of a pool, we find that this was about 3, 000 years ago.

So 3, 000 yearsago, Yellowstone was deflated, and now it has inflated.

And this process of deflation, inflation I call heavy breathing of the Yellowstone caldera because it's a big process.

The actualvolume of material involved is quite large.

TEXT IN GRAPHIC TEXT: Elevation of Yellowstoneshorelines (S) near Fishing Bridge from 14, 000 years ago to present.

Transgression indicatesa rise in lake levels, resulting in slack water in the outlet reach.

As lake levelssubside, the Yellowstone River re-establishes its channel.

The historic pattern shows inflationand deflation.

Ages are in thousands of years (ka) from radiocarbon dating of projectilepoints (indicating human occupation on the shoreline) and other geologic relationships.

TEXT IN GRAHIC: LiDAR (Light Detection andRanging) showing the outlet reach of the Yellowstone River from Fishing Bridge to Le Hardys Rapids.

Although the river is now essentially a continuous, low-velocity pool in the outlet reach, steep, high cutbanks on the outsides of the meanders indicate that the older more sinuous channelcontained an energetic river.

The dotted lines are old shorelines.

TEXT: Is there a pattern to the inflationand deflation? DR.

PIERCE: One of the people who surveyedYellowstone is Dan Dzurisin.

And he has shown that both the caldera when it inflates, itswells up, and when it deflates, it's a mirror image of the inflation.

So that we know thatin the short term, the pattern has been very, very symmetrical – inflation and deflation, which again, suggests some symmetrical process.

TEXT: What do you think causes the calderato inflate and deflate? DR.

PIERCE: Whether this is actually the intrusionof magma that somehow is subsiding after that or some process related to geothermal featuressuch as inflation above a geothermal seal – a breaking of the geothermal seal and subsidenceas the hot fluids escape, is part of process.

TEXT: Could it be magma? DR.

PIERCE: If an intrusion of a magma isthought to be the process, it inflates.

Then how do you get the deflation? You can't stuffthe magma back down the hole it came up.

It's going to stay where it is.

It's more likelythat if magmas are coming in, it keeps uplifting, maybe pausing with uplift.

One other thing that we can tell from Yellowstone, is that instead of inflating and then inflatingand then inflating, we can tell that this didn't happen because shorelines of YellowstoneLake are very close to horizontal.

So whatever the process of inflation and deflation is, it's not resulting in a net uplift of the center of the Yellowstone caldera.

The mostlikely cause for that kind of thing is geothermal fluids which can come into the system, escapeout the sides of system, come into the system again and escape out to the side.

TEXT: The research gives us a better understandingof Yellowstone.

When did you join the USGS? DR.

PIERCE: I started with the U.

S.

GeologicalSurvey in Kentucky where I was mapping the Ohio River deposits for the U.

S.

GeologicalSurvey's effort to map the entire State of Kentucky in detail.

After I had been therefor about two years, I got a phone call saying how would you like to come up to Denver andwork on the geology of Yellowstone? And we'll give you a week to think this over.

And Isaid, I don't need a week to think it over, I'm really ready to go.

TEXT: How did you get involved with MontanaState University? DR.

PIERCE: When I was in graduate school, I thought that I would go into teaching because that's the main exposure that I had to othergeologists – the professors.

I started with the Geological Survey thinking, indeed, I'mgoing to get some research done and then I'll be better qualified for a teaching position.

Well, it never worked out that I went into teaching.

I moved up to Bozeman, Montana, with the U.

S.

Geological Survey in 2000.

And since I'vebeen here, I've been affiliate faculty with the Department of Earth Sciences at MontanaState.

And I really enjoyed being able to work with graduate students, to give lectures, to lead field trips at Montana State.

It's very rewarding for me to be able to interactwith students.

Many have graduated and gone into good careers in geology.

And it is veryrewarding to be part of that story.

DR.

PIERCE: We're actually standing on a smallalluvial fan.

The stream came out of the mountainside there and when it got to this flat floor valleyit built a small alluvial fan.

Alluvial fans are one of the easiest things to recognizein the landscape because they are conical shape; they occur where a steep stream coursegets to a flatter place.

And they have this conical fan shape.

My daughter is also a geologist.

She's at Boise State, and she and her students were studying alluvial fans and they formedan alluvial fan club.

TEXT:Special thanks to Students of Montana State UniversityLinda Pierce Jake Lowenstern Images of Yellowstone and Tetons by Dan andLin Dzurisin Video by Liz Westby TEXT:Interview with Ken Pierce Produced by Liz Westby2016 TEXT:For more information on Yellowstone visit theYellowstone Volcano Observatory volcanoes.

usgs.

gov/observatories/yvo/ USGS 5.

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