University Place

[gentle music] – Nancy Larson: Thanks for coming, everybody, tonight.

So, tonight we have the pleasure of hosting a Badger Talk this evening.

The University of Wisconsin’s Badger Talk program carries on a tradition of the Wisconsin Idea by bringing University’s research and expertise to communities across Wisconsin.

Through this free program, more than 600 faculty and staff connect with schools and libraries and community organizations to share knowledge and discuss topics that matter to the people of our state.

Tonight, we have the pleasure of welcoming Sue Swanson, the state geologist and director of the Wisconsin Geological and Natural History Survey.

Sue leads statewide efforts to advance the understanding and use of Wisconsin’s geological resources.

So, this evening, she will provide an overview of the geology of Wisconsin.

So, welcome, Sue.

[audience applauds] – Sue Swanson: It’s a pleasure being here.

Thank you for coming out tonight to learn a little bit about the geology of Wisconsin, and also to learn a little bit about the work of the Wisconsin Geological and Natural History Survey, which we call “the Survey.”

So, if I start talking about the Survey, I’m talking about the work of the Wisconsin Geological Survey.

So, as Nancy said, the Survey is part of UW-Madison Division of Extension, and I’m the director and I’m also your state geologist.

Okay, so we’re gonna jump right in.

And usually, when we start talking about geology, people start thinking about rocks.

And that’s great, think about rocks.

There are rocks in these images that you’re looking at.

But when a geologist looks at a suite of images like this, we also think about the geologic processes that formed the landscapes and outcrops that you’re looking at.

And we think about the long Earth history that led to our landscape that we have today.

And the rocks that are visible at the surface.

And so, you know, geologists actually, you know, we really enjoy studying rocks, but those processes are often where we specialize.

And when I say processes, I mean things like glacial activity, right?

Volcanism, right?

Stream erosion.

So, all of the things that ultimately form geologic materials, help to erode and transport geologic materials.

I’m actually a hydrogeologist.

So, I study groundwater flow.

And all geologists use our knowledge of rocks and Earth history.

We combine other sciences, like physics and chemistry, to better understand some of the processes that we’re most interested in.

And for me, like I said, it’s groundwater flow, but I’m gonna– I’m gonna cover all sorts of different processes and rock types and a lot of Earth history tonight.

Okay?

Okay, so, I’ll also mention some of the landscapes that you’re looking at as we go through the talk tonight.

So, you might recognize some of these places.

In the upper right-hand corner, we’re looking at the Wisconsin River.

In the lower right-hand corner and in the middle, there are some outcrops from the Baraboo area and Devil’s Lake State Park.

In the upper left-hand corner, that’s a rock exposure or outcrop just southwest of Platteville, Wisconsin, in southwestern Wisconsin.

And then, the lower left-hand corner, that’s up on the Lake Superior coast in Bayfield County, the sea caves, if any of you have ever been there.

All right, and here’s what we’re gonna tackle tonight.

We’ll start out by thinking about contributions of geology to the state’s livelihood.

Why should we care about geology, right?

I have to kind of back up really far back, you’ll see, to include a discussion about geologic time.

Geologists need to describe an immense period of time.

And we need language and classification schemes to do so.

So, we’ll talk about geologic time.

Then we’ll be able to talk about the geologic history of what we call Wisconsin today.

And then, finally, I’ll kind of wrap up with some of the current efforts that we have ongoing at the State Geological Survey.

Okay, contributions to the state’s livelihood.

If I were to think about sort of three of the biggest economic endeavors in the state of Wisconsin, hopefully tourism would come to mind, agriculture, and industry.

Okay, so if we start out with tourism, I’m gonna show a series of images from state parks in Wisconsin.

And maybe you’ve been to some of these locations and, you know, not every single state park, but a lot of state parks are set aside for, at least in part, right, for the unique geology or special landscapes within their boundaries, okay?

So, Peninsula State Park, up in the northeastern part of the state, in Door County, Wyalusing in the southwestern part of the state, near the Mississippi River.

Devil’s Lake, I mentioned.

Rib Mountain up near Wausau, okay?

Let’s see, Governor Dodge, just west of Madison, Copper Falls up in Ashland County.

And then, Willow River, just outside of Hudson, Wisconsin, okay?

All right, then agriculture, right?

So, on the right-hand side of the slide, what you can see is a map of soil regions in Wisconsin.

And we know we have world-class agricultural soils in Wisconsin.

And that is in large part due to the underlying geologic materials.

Rocks, right?

But also these processes that shaped the landscape and eroded materials, transported it, and deposited it in Wisconsin.

And then, of course, soils are a combination of that, that geologic material with biological material, and then also taking into account the climate of a region.

But the geology is really important in understanding the distribution of soils and really plays into the fact that we have– we have fantastic agricultural soils in the state.

There’s a picture up in the upper left-hand corner that shows an agricultural landscape, right?

What I really like about this image is if you– if you’ve ever studied a topographic map, then topographic contour lines, they represent elevation.

And when you see them kind of looping around kind of in a bull’s-eye pattern, you know you’re looking at a hill.

Okay?

And so, what’s really neat about this image is that the pattern of the fields are mimicking topographic or elevational contour lines.

And I, when I look at it, I can see, oh, well, there’s, there’s a streamlined hill that is also the result of glacial activity in that region.

We have abundant water resources in the state too.

And, of course, that plays into the agricultural economy.

And so, also as a result of glacial activity, much of Wisconsin had vast wetlands, right?

Low-lying areas in between some of the hills that are depicted in that upper left-hand slide, right, or picture.

And so, some of those wetland areas are used as cranberry bogs today, right?

And then, up in the upper right-hand corner of the images, there’s a picture of a milk house or a spring house on a farm in southern Wisconsin.

And I like to show this one because it touches on a couple of things, right?

So, there’s a natural spring discharging into that milk house or spring house, right?

And so, these types of structures were really important.

You know, even today, right, in keeping food stocks nice and cool in the summer because of the discharging groundwater or keeping food from freezing, right, in the winter.

Because groundwater has a pretty consistent temperature all year long.

Okay, groundwater doesn’t freeze, right?

And in Wisconsin, it’s roughly the temperature that is equivalent to the mean annual air temperature, which is about 10 degrees Celsius or 50 degrees Fahrenheit.

So, it’s great for that purpose.

Discharging groundwater like that also feeds not only this little pond that this particular farmer has stocked with trout, it also feeds trout streams, natural trout streams throughout the state, which we know, you know, brings in, you know, lots of tourism, but then we have, you know, an active aquaculture industry in the state.

Okay, and then, in terms of industry, okay.

Mining is closely tied to geological resources, and the way that we typically think about these geologic materials that are mined and extracted from the Earth are to think about them as nonmetallic resources and metallic resources, okay?

So, for the nonmetallic resources, we have aggregate or sand and gravel, crushed stone that we use in construction, right?

You’ve all seen gravel pits across the state.

Sand is mined from some of the sandstone layers that I’ll talk about later, and that’s used in foundries, in the glass industry.

It’s also used in the oil industry as frac sands, right?

So, we don’t have any petroleum sources really in Wisconsin, we don’t have oil wells, but the sand that is mined gets used as frac sand in the oil industry, okay?

Dimension stone for monuments, right?

We have– You’ll see in our past a volcanic history, okay?

And one volcanic rock type is called andesite.

And it’s mined and crushed and is used as the little pieces on roofing shingles, okay?

And then, of course, peat, right, is used in horticultural and landscaping industry.

So, a variety of nonmetallic mining.

And then, of course, metallic mining.

So, similarly, we’re gonna break metallic mining up, okay, into containing iron, or ferrous resources, or other metals, nonferrous, okay?

In the middle of this slide, I have a picture of what’s called banded iron formation.

And this is the rock type that really formed the basis for a lot of the iron mining in the Upper Peninsula of Michigan, northern Wisconsin, Minnesota.

We’ll talk a little bit about when and how that was– that was formed in that region.

We also– I mentioned already that we had some volcanic activity in our past, and that led to the formation of other types of minerals that contain metals like copper, gold, nickel, silver, right?

So, we have nonferrous metallic mining in Wisconsin, too, or at least we have in the past.

It’s primarily these sites that are getting some attention these days.

And there’s a few sites, one in particular, that is being actively explored in northern Wisconsin today.

I also have on the slide, in southwestern Wisconsin, pointing to this historic lead and zinc district.

Okay, and this was a really important district in the 1800s, actually, all the way up to the 1970s.

It was one of the largest lead mining districts in the 1800s.

Later, zinc was mined.

And like I said, that continued up into the 1970s.

Also with respect to industry, we can’t forget about water, right?

And so, Wisconsin actually has a number of spring resources.

Natural springs, okay?

And again, it’s sort of in the late 1800s, Waukesha, Wisconsin was actually known as Spring City.

And wealthy folks from Chicago would come up and sit next to beautiful gazebos that were built around springs and vacation.

Even then, spring water was bottled.

So, you can see in the image there, Bethesda, the water of quality, right?

And spring water is bottled today still in Wisconsin.

Our abundant groundwater resources have also contributed to the success of some other canned or bottled beverages in the state.

Okay, so, what is geology, all right?

And then, what we’ll do is we’ll kind of get into geologic time, like I said, and then the history within the state of Wisconsin, okay?

So, what is geology?

Broadly, it’s the study of solid earth, right?

And when I say “earth,” I mean both the materials that make up the planet and those processes that I referred to before, whether volcanic or whether seismic, earthquake, right, glacial, stream, wind, coastal, all sorts of great processes, right, that end up shaping the earth.

There’s two main branches of geology, physical geology and historical geology.

I’m gonna be talking mostly about physical geology.

Really is– That’s really much more focused on those processes that I’ve mentioned.

Historical geology gets more into the evolution of the continents and life forms through geologic time.

The State Geological Survey, we, you know, we think about the evolution of the lithospheric plates that make up the upper layer of the Earth.

But we don’t– We kind of rely on it in order to have a better understanding of a broad landscape, okay?

And we don’t do a lot of paleontology.

We use our knowledge of fossils to better understand the age of different rock types.

But we tend to do less historical geology at the State Geological Survey.

All right, deep time, okay?

So, here I’m actually gonna ask you to participate a little bit.

And so, deep time is a concept in the geosciences that tries to capture the vast expanse of time that we have to try to wrap our head around when we are thinking about geologic processes.

And so, I like to always show an image of the Grand Canyon.

I took this picture.

And for me, when I stand in the rim of the Grand Canyon, it’s– I’m sort of speechless.

Right?

The age of the materials is vast, from the base of the canyon up to the rim.

And then, the canyon was formed.

All of this erosion, right, to actually form what we see as the Grand Canyon today.

That took so much time, right?

Geologists call it deep time, okay?

And so, here’s the exercise, right?

So, if I said, do you kind of have a gut feeling for one year of time, like I can kind of reason through how long a year is?

Yeah, sure, okay.

How about 10 years?

Like, I– Like, myself, I get a decade.

Yep.

Fifty years?

Okay, I can wrap my head around that, right?

Seeing a couple fewer hands, but some people are shy.

You don’t have to raise your hands, right?

Let’s really jump, right?

Let’s go to 500 years.

Okay, I can do the math, right?

And I can reason how that compares to 50.

But do I really get 500?

It gets pretty fuzzy for me.

Fifty thousand?

Five million?

How about 3 billion?

[audience chuckles] Right, it’s really hard to wrap our heads around, okay?

And so, what geologists do is sometimes we use sort of analogies to try and describe all of that time.

And this is one that is very well known.

And it’s from a popular intro to geology textbook, right?

This spiral.

And if we look way down at the beginning of that spiral, what that’s supposed to be representing is when the Solar System and Earth formed, right, maybe over 4 billion years ago, the gas and dust came together and formed our planetary body, right?

But even then, it was very different than Earth today.

Different layers needed to differentiate into what we know today as the core, the mantle, and the crust of the Earth.

If you’ve heard of those layers, right?

Life on Earth may have started over 3 billion years ago.

But things that we might recognize more readily as life, you know, much, much later, right?

What’s really, really important is how incomplete our history is.

And so, you know, think about a novel.

We’re surrounded by books here in this library, right?

[laughs] Think about a book, a novel, 350 pages long.

What geologists might have is page 26, okay?

And then, one sentence on page 74, and then a paragraph on page 75, and then a page… Pick a number, I don’t know, 150, right?

You get the pattern.

Very incomplete.

We tend to have more information the closer we are to the present, right?

And so, that also helps kind of explain this spiral.

It’s a lot more detailed near the end, okay?

And another really important thing is that, that over the course of Earth history, some processes happened very slowly, progressively.

But there were other things that were catastrophic, right?

And had a big impact over a short period of time.

Both of those types of processes are very important in Earth history, okay?

In terms of the time periods that we’re gonna be talking about, if you can see where it says Paleozoic Era, right on the top of– on the top layer of that spiral, that’s where we’re gonna spend really most of our time today.

But most of it– most of Earth history is before that, okay?

So, how else do we organize all of this time?

We use a geologic time scale in geology, okay?

And so, just like I said, those bottom three gray rows labeled Precambrian, that’s most of Earth history, okay?

We are gonna get into that middle one, the Archean and Proterozoic a little bit.

And then, we’re gonna spend most of our time in the Phanerozoic, right?

The Paleozoic, Mesozoic, and Cenozoic.

The bars that are hanging down are labeled with life forms that we think evolved around that time, and whether they’re still around today.

Okay?

All right.

So, let’s jump in to Wisconsin’s geologic history, okay?

And so, here’s a poster that you can download from the State Geological Survey website.

And we’ll start with the image on the right-hand side.

And so, in Milwaukee, actually, that’s a location in the state that if you wanted to create a section or drill a really deep well that encompasses pretty much every rock type in Wisconsin, that’s a really good place to do it, right?

So, the oldest rocks are at the base, the Precambrian.

Then we get into Paleozoic rocks, right?

Cambrian, Ordovician, Silurian, Devonian.

Okay?

Then there’s a huge gap in geologic materials, okay?

Between those Devonian Age materials and the Quaternary materials, the, largely the glacial materials, right?

Looser sediment rather than rock, okay?

And we’ll kind of dig in to what I mean by all of that.

But first, let’s look over at the map too.

And on the next slide, we’re only gonna look at the map and then that cross section at the bottom.

It’s really helpful to think about a cross section across the state to understand what’s going on with the patterns in the map, okay?

And so, if I drew a line from western Wisconsin over to the Milwaukee area, and then I took a slice out of the Earth along that line.

You know, think of a layer cake and slicing down vertically.

You see the layers in the layer cake.

That’s kind of what the cross section is doing along that cross section line, okay?

And so, at the base are the oldest rocks, the Precambrian rocks, and then the Cambrian, Ordovician, Silurian, and a little bit of Devonian there over by Milwaukee.

And then, there’s sort of a drape of the Quaternary sediments up on top.

But at this scale, you don’t even– you really don’t even see ’em, okay?

The other thing to note is, on the eastern side of that cross section, the rock layers are dipping ever so slow– not slowly, slightly off to the east, okay?

They’re mostly horizontal through the central part of the cross section.

In western Wisconsin, those rock layers are sloping or dipping ever so slightly off to the west.

In southern Wisconsin, those rock layers are dipping or sloping ever so slightly off to the south, okay?

And so, ultimately, that pattern of rocks has to do with that sloping of these layers, right?

And so, if you– I’m surrounded by books, right?

But if I had a book here, right, and I rotated it a little bit and bent it, which they probably wouldn’t like, then part of the book would be sloping ever so slightly in one direction, ever so slightly in the other direction, ever so slightly towards you.

And I– I’d see the pages on the side, right?

And that’s kind of what we see in Wisconsin, right?

Sort of that happy face pattern.

Those rocks are tilted, so we’re seeing the edges of them as those layers have been eroded off.

Okay, so those Paleozoic rocks sort of flank up onto the Precambrian rocks, which really are topographically higher as well.

So, in this image, it looks like the Precambrian rocks are just one big gray blob, whereas they are highly complex.

There’s a really interesting and long Earth history associated with them.

We are gonna whiz through this, okay?

And so, let’s think about just those materials that are delineated on this map.

You can see that Paleozoic cover that’s– those were the– those layered rocks in the previous slide, right?

Okay, so, the oldest rocks in Wisconsin are 3 billion or more years old and associated with the areas that are labeled the Archean Superior Continent and the Marshfield Continent.

So, the distribution of continents and ultimately lithospheric plates, in the past, it was very different than what it is today.

And we think that there were sort of two different continents, which we’re calling the Superior and Marshfield Continents, okay?

And in between them, there would have been an ocean basin where iron-rich sediments were deposited.

So, I talked about those banded iron formations previously, right?

It’s during this time period that we think the abandoned iron formations, or BIFs that geologists sometimes call them were deposited.

Very, very different environment than today.

We don’t think that there was free oxygen.

As a result, the iron stayed and dissolved in waters and was able to precipitate out with sediments, okay?

There are no places on Earth where banded iron formation are being actively formed today.

Okay, but it worked 3 billion years ago, right?

All right, at about 2 billion years ago, we think there was a major mountain-building event.

And we call this the Penokean mountain-building event.

And so, the– those continents moved closer together.

And a mountain range formed.

For tens of millions of years afterwards, that mountain range was eroded away, okay?

There were other mountain-building events as well.

And one that is probably interesting to you is the Baraboo mountain-building event.

We think that was around maybe 1.7 billion years ago, and that caused the folding and formation of what is today our Baraboo Hills, okay?

The other thing I’ll just point out is the Wolf River complex that’s in red on the slide.

A little bit later, 1.5 billion years ago, there was emplacement of igneous rocks in the subsurface that cooled pretty slowly, allowing individual crystals to be more visible and interlocking.

You know, rocks like granite, right?

In fact, our state rock, the red granite, right?

You can see all the little crystals.

That’s a sign that there was a magma body that cooled pretty slowly and allowed those interlocking crystals to come together tightly and form rocks like granite.

Okay?

Wisconsin also has a history of volcanism, right?

So, the last major event that I’ll mention is the area called the Lake Superior Rift up there.

And in this event, about 1 billion years ago or so, we think that the continent at that time started what geologists call rifting, moving apart, diverging, right?

And volcanism would have been associated with that.

A similar environment today is in East Africa.

If you’ve ever heard of the East African Rift System, okay?

There’s an active rift system along East Africa and into the Red Sea.

So, we have modern analogs for that today.

For whatever reason, the Lake Superior Rift, it never continued.

It failed.

And yet, we have evidence of it in the rock record today, okay?

There were other periods of volcanism too.

I tried to hit the highlights.

We just covered, like, 3 billion years of geologic time.

You can go and see these rocks, you know, at Devil’s Lake to see the Baraboo Quartzite and Copper Falls up in Ashland County.

You can see some of the rift sediments and volcanics, okay?

All right, let’s get into the Paleozoic, right?

And so, and hopefully you can see this okay on the slide, but in addition to having a simplified geologic time scale, I tried to color in time periods for which we have rock material in Wisconsin, okay?

So, we just covered that time period from 3 billion to about 900 million years ago, okay?

And what we’re gonna look at then is roughly from, you know, 500 million to, what, about 400 million years ago, into the Devonian, okay?

And at this time, what we call Wisconsin, it was not in the northern hemisphere, right?

Remember, the configuration of lithospheric plates was very different in the past.

So, it was not in the northern hemisphere and it was actually close to a coastal area.

So, all of these rocks that are associated with Cambrian, Ordovician, Silurian, Devonian time are representative of marine or shallow coastal environments.

Okay?

To get a picture of what I’m talking about, we’re gonna take a look at some paleogeographic maps, okay?

And so, old geography.

[laughs] And geologists always start in the past and work our way to the present.

If we try to do present to the past, we get very confused, okay?

So, we’ll go through this a couple times, right?

But we’re starting in the Cambrian.

And you can see, most of the continental masses are south and, you know, south of the equator here.

One note, too.

Remember, continents don’t slide around over the mantle.

Lithospheric plates slide around.

And lithospheric plates can have continental crustal material and oceanic crustal material.

It’s important to remember it’s not the continents, really, that are moving around.

It’s these larger, larger plates.

Okay?

Okay, so, Cambrian.

Oh, the other thing to point out is, up in the upper left-hand corner, you can kind of see some yellow outlines of today’s geography, right?

The state outlines up there, okay?

So, kind of keep your eye on that because that’s what we’re kind of working towards.

All right, so, Cambrian.

Here we are in the Ordovician.

Silurian.

430 million years ago.

Devonian.

Some of that material is kind of coming together a little bit more.

Here in the Permian, I start to see things that look a little bit familiar to me.

But, granted, I’ve seen these before, right?

But you will too.

So, here we are in the Permian, late Cretaceous.

Starting to recognize things?

And the present, okay?

So, go through it real fast again.

Okay, Cambrian.

So, while it’s really hard to pick out exactly where Wisconsin would be on these Paleogeographic maps, hopefully you get a sense that there was– there was a lot of coastal property [laughs] as the continents and lithospheric plates migrated northward, okay?

And that would have been the environment.

So, what do these rocks look like?

And where can we see them?

The Cambrian rocks, there’s a lot of sandstones, okay?

And they’re very quartz rich, okay?

If you know the mineral quartz, right?

A lot of silicon and oxygen.

Close up, you can see that many of them are really what we call clean.

There’s not much else in ’em besides quartz.

They’re really well rounded.

We call that mature because it means they’ve really been tossed around and edges have been worn off.

They’re almost spherical, right?

And then, you can see what some rock outcrops look like.

It’s this rock material that is really good for frac sands.

Okay.

And there are exposures in southwestern Wisconsin.

But as you drive northward to central Wisconsin, you’ll see some of the active mines that are extracting the quartz-rich sands.

Here’s that outcrop I showed you before, real close to Dickeyville, right before– right between Dickeyville and Platteville in southwest Wisconsin.

And a lot of the Ordovician rocks, slightly deeper water environment.

They have a lot of calcium carbonate in them.

So, limestone or dolomite, which is a calcium magnesium carbonate.

There are some shales, okay?

And you can see that layered nature in this rock outcrop.

Silurian rocks.

Well, you’d need to go over to the Door Peninsula to see them exposed.

They’re buried in most places in eastern Wisconsin.

But if you go to Peninsula State Park and Cape Point in Door County, that’s the Silurian dolomite, and it’s, and it’s also sometimes called the Niagaran dolomite.

Okay, so, recall that now, in Wisconsin, we have what’s called an unconformity.

And what that means is we just simply do not have rock material that represents a vast time period, okay?

There’s not a gap in time.

Time happened.

There’s a gap in the rock record, right?

And the next material that covers much of Wisconsin is largely eroded material, transported material, and deposited material by glaciers and also streams.

Okay?

So, Wisconsin’s glacial past had many phases of glacial activity.

Major advance of an ice sheet, major retreat, okay?

And this map shows some of the major phases of glaciation, called the Pre-Illinoian, the Illinoian, and then the Wisconsinan glaciation.

And it’s named the Wisconsinan glaciation because we have such great examples of landforms and materials, landforms that were formed and materials that were deposited during that particular glacial phase.

Okay?

Even during each one of these phases, there were multiple advances and retreat of the glacial ice.

So, the next slide here, we’re gonna look at a video of this, of the late Wisconsinan glacial time and really just the last 30,000 years or so.

So, I’m going to start the video.

There we go.

Okay, you can see the ice advance across the landscape.

Doesn’t make it to southwest Wisconsin.

Large lakes formed at the margin of the ice at times.

And they disappear and drain away as the ice retreats and melts.

Sometimes it retreats pretty far outside of Wisconsin.

Right, and at about 11,000 or 10,000 years ago, ice exited Wisconsin for the last time.

The last remnants of that ice sheet probably disappeared from Canada, Hudson Bay area, maybe around 7,000 years ago or so.

Okay?

And so, again, it’s the Wisconsinan glaciation because we have such great examples of landforms.

On the right-hand side, there’s an image of these brown lines across the state.

Those are called moraines.

They’re ridges of material that, in this case, if you look at the outermost ridge, we would call that a terminal moraine because that’s the– that’s sort of the farthest that the ice advanced.

And as it paused there, this debris-rich ice material melted out of the ice.

Sometimes it sort of was bulldozed in front of the ice too.

In any case, ridges were developed at that margin, okay?

And if it’s the outermost one, that’s the terminal moraine.

But then, you can see that there are, there are also sort of somewhat concentric lines as you go northward.

I would call those recessional moraines.

So, just like in the previous video, right, we saw that sometimes the ice retreated, paused a little bit, may have built up a little moraine, right?

Maybe retreated a bit.

Maybe re-advanced, built up a moraine in front before finally retreating.

Okay?

Yet, in southwest Wisconsin, not only in the Wisconsinan glaciation, during that phase, but also previous phases, we don’t have evidence of glacial activity.

And so, that’s what we call the Driftless Area of Wisconsin.

And its topography is much more defined by stream erosion and valleys and ridges, okay?

Some other landforms.

There’s a drumlin up in the upper image.

That’s also what I showed you at the very beginning, when there were crops that were concentric around that hill.

These are streamlined hills that indicate the former flow direction of ice.

Okay?

And we have a lot, right, in sort of eastern and central Wisconsin.

The bottom two images, one is a kame and one is an esker.

And both of these landforms form in environments where there’s just a lot of glacial meltwater streams.

Okay?

And so, for a kame, near the margin of the glacier as it’s melting and wasting away, there might be a channel that starts to drain water from the top.

And just like being at the beach when you start to make a little, make a little hill, right, by dripping sediment, right, a kame is a conical hill.

It’s largely sand and gravel.

And it’s because it formed at the base of one of these drainages.

Okay?

An esker is also related to subglacial drainage.

So, if there’s a channel that is bringing water from that– the edge of the ice, right, forward into a meltwater environment, that channel might be weaving back and forth beneath the glacial ice, carrying sediment with it, okay?

But then, once all the– once all the ice melts, you’re left with the sediment that was in the channel.

And now it’s a windy ridge on the landscape, okay?

If you’ve ever been to the Kettle Moraine, the northern unit of the Kettle Moraine State Forest, you’ll see these features.

That’s where these pictures were taken.

Okay.

Okay.

So, now I am going to tell you a little bit about the work of the Wisconsin Geological and Natural History Survey.

And so, our mission… As I said, we are part of the Division of Extension at UW-Madison, and our mission is to conduct education, outreach, and applied research activities on the geology, mineral, and water resources of the state.

We do that to provide baseline information for decision-making, informed decision-making by local government, county government, tribal government, state government, industry, the agricultural sector.

We don’t have any policy forming or regulatory enforcement obligations.

We are there to provide that information for decision-making, okay?

We have about 27 staff members, and this is us.

Once a year, we take a field trip, a staff field trip.

This is from last fall.

It’s in the Baraboo area.

On the left-hand side, there’s a pie chart that shows areas of expertise of our staff.

So, we have a bunch of hydrogeologists, right, studying groundwater, bedrock geologists, Quaternary geologists, that’s that most recent time period.

So, these are the folks who study glaciers and streams and those processes.

We have a large staff of– large for us– [chuckles] staff of geographic information scientists.

At a base level, you can think about this as digital cartography, okay?

Because we make a lot of maps.

But it’s so much more because it’s all of the spatial analysis that can happen with these electronic geological data sets and modeling, computer modeling.

So, important folks in the office as well as outreach, archival geological curation specialists.

We have folks who manage our databases and publications.

And then, there are a few administrators, right?

We’re located about a mile west of the UW-Madison campus in Madison.

But then, we have a second facility too.

It’s our core repository.

So, rock core cylindrical samples collected through drilling methods have been collected for decades and decades and decades in Wisconsin.

Whether it’s for mining exploration, whether it is for foundation drilling, the Department of Transportation sometimes collects core when they’re establishing strength, right, for bridges.

Each one of the dots represents a location where we have core material stored at our core repository out in Mount Horeb.

I like to call this facility Wisconsin’s subsurface library.

These materials, it’s really hard to put a value on.

It’s expensive to collect core, right?

We don’t want to just toss it out.

We don’t know what tomorrow’s questions are gonna be.

We don’t know what new instrumentation might be available so that we can analyze it in different ways.

And so, we want to preserve it.

We also have cuttings.

Cuttings– So, sometimes it’s too expensive to collect core, right?

And so, we use a drilling technique that’s called air rotary.

It’s got a tri-cone roller bit on it, and it– and it basically crushes up the rock as you drill downward.

And then, little chips of rock fly out the borehole with water.

And a geologist leans in with a vegetable strainer, to– this is true– with– to catch that material.

Because little chips of rock are better than no samples, right?

We put them in baggies, we label them, we geolocate them, and we study them.

And that’s what cuttings are.

And then, geologists tend to pick up rocks when we’re in the field.

We call those hand samples.

And so, we have over 15,000 hand samples from across the state too.

We offer tours of the core repository.

Okay, and what do we actually do?

We do a lot of mapping.

So, some of our mapping is geologic mapping.

And you might think, okay, the survey’s been around for over 125 years.

Don’t you have the state mapped yet?

We don’t.

[audience member laughs] Sometimes we redo areas too.

But here’s our progress, right?

And there are areas that do not have bedrock geologic mapping completed yet, right?

We tend to do a lot of mapping at the county scale.

We work with county partners.

It’s also a really useful level of detail for a variety of land use planning questions, water resources questions.

So, we often– We often map counties, okay.

We rarely just produce a geologic map.

We often produce lots of other layers too.

And I’ve got a list of layers for this particular study from Jefferson County, which was published in March of ’24.

Depth to bedrock surface.

This is a area of the state that’s completely covered by glacial material.

So, how deep is the bedrock surface?

And then, we map out the elevation of different geologic layers.

And so, that’s what each one of the other layers are, as well as trying to tie hydrogeologic properties to these rock materials because they serve as aquifers.

This is what a map looks like.

This is remarkable because, as I said, this area is almost completely covered by glacial deposits.

So, we use a lot of borehole data.

Sometimes we drill new boreholes.

But more often, we use existing records from private well records.

So, if any of you have your own private well at your home, the record is stored in a database, and we look at the geology that the driller recorded, and we also make cross-sections.

So, this is a much more detailed cross-section, right, than what I showed you across the entire state at the beginning.

For glacial materials, we also do statewide mapping, not just county scale, right?

And I like to show this because in terms of glacial geologic mapping, a geologist named T.C.

Chamberlin first mapped the glacial geology in 1881.

And you can see that the shape of the glacial formations, like, he did a pretty good job, right?

[laughs] That map wasn’t updated until 1976.

And then, just last year, we published a new Quaternary Geology of Wisconsin map.

And again, all of our map products are available free for download at our website.

We also do county scale glacial geologic mapping too.

And I thought I would just show an example from Burnett County.

Again, you can see our progress throughout the state.

We have a lot in progress, [laughs] but making pretty good progress at the county scale for the glacial and surficial geologic mapping.

And we do a lot of groundwater-related work.

Just one example is a county hydrologic atlas, okay?

And again, just finished this for Burnett County in the northwestern part of the state.

We make use of well construction reports, again, like, we really rely on these.

And you can see the distribution, all those little dots in Burnett County.

Each one is a private well record, okay?

And from that, we’re able to, along with field work, develop a whole suite of maps.

Here’s an image of one of these well construction reports.

And if you can see on the right-hand side, you can see that there’s a series of descriptions for geologic material that the well driller recorded.

There’s also a static water level at the time of drilling.

We use that for water table mapping.

So, again, those records, sometimes we convert that into a depth to bedrock if the well hits the bedrock surface, right, then we can map that out.

Other times, we map the depth to the water table or contour the water table and make a water table elevation map.

We also map groundwater recharge.

So, groundwater recharge.

There’s precipitation, right, that falls onto the land surface.

Some of that precipitation gets utilized by plants.

Some of it runs off, some of it evaporates, right?

That’s the evapotranspiration that’s shown in the diagram.

But some of it infiltrates through the soil zone and makes it to the water table.

That’s recharging our aquifers, okay?

And you know, we– sometimes we’ll talk about, oh, we had a one-inch rainfall, right?

That’s one inch everywhere on the landscape, right?

We talk about recharge in the same sense.

So, how much recharge do we get in a given year, right?

Well, let’s say you get roughly 30 to 32 inches of precipitation.

A good back-of-the-envelope estimate for recharge might be somewhere between a quarter and a third of that.

Okay?

And so, you can see, for Burnett County, the average, the mean is about seven inches per year of recharge.

And then, finally, all of those maps get overlaid, and we produce maps that show the susceptibility of our water, our buried groundwater, our aquifer systems to contamination, okay?

And so, for example, where you have a high recharge rate, that aquifer might be a little bit more susceptible, right, to contamination.

Where there’s a really shallow depth to water, higher susceptibility to contamination, right?

So, we use all of these together and we write up a technical report and we publish it, and it’s free for download.

And so much more, okay?

And so, you can find a lot more on our website, which is up there on the top.

Each year, we write a year in review where we summarize highlights, and there’s lots of great information at the Survey.

So, thank you for listening tonight.

It’s been a pleasure being here.

And, yeah, thank you for coming out to learn about the geology of Wisconsin.

[audience applauds]