cc >> Tom Zinnen: Welcome to
Wednesday Nite at the Lab. I appreciate you all being here
tonight. Our presenter for tonight
is Tom Hooyer. He works both for the Wisconsin
Geological and Natural History Survey and he's got an
appointment with the UW-Madison Department of Geology
and Geophysics. This is his second presentation
to Wednesday Nite at the Lab, and I appreciate him coming
back. Tonight, he'll be talking about
"Once Upon A Lake: The History of the Great Glacial Lakes of
Wisconsin." Please join me in welcoming Tom
to Wednesday Nite at the Lab. ( applause )
Tom Hooyer: Many of you that we are actually in the warmest
period of our climate in the past 125,000 years.
And I'm secretly hoping that this cold weather continues
because as a glacial geologist, I want the ice ages to return.
Tonight, I want to talk about the great glacial lakes here in
Wisconsin. When I mention glacial great
lakes here, a lot of you might think about the old lakes that
were in the Michigan and Superior basins.
However, I don't want to talk about those lakes, those old
lakes. I want to talk about the great
glacial lakes that were within the borders of our state.
Now, as many of you might know, we recently experienced a large
glaciation called the North American Ice Sheet.
It occurred about 21,000 years ago.
A lot of you, when you think about lakes in Wisconsin, you
probably think about Lake Winnebago being the third
largest inland lake, I think, in North America.
You think, well there were certainly were bigger lakes here
at one time. I'm here to tell you there were.
I guess the question is, why aren't those lakes here today.
Well the reason why is that in order to form a lake, you need
to dam up a river, usually. And how do you do that?
If you're an engineer, you build a dam.
Well, how we do it during the ice age, is we build a big ice
sheet, and we advance an ice sheet across the landscape,
damming up surface water drainage ways.
That map I just showed you, the first person to sort of draw the
last great ice sheet was this gentleman here, T.C. Chamberlin,
who was actually a faculty member here at the University of
Wisconsin. He's quite well known, because
he came here, and he was one of the first people to refute that
a lot of deposits that we have in the Midwest were actually not
flood deposits from a Biblical flood, but they're actually the
result of continental glaciations.
He was one of the pioneers here who sort of started off the work
on glacial geology and understanding continental ice
sheets. We had many others, a long line
of famous glacial geologists in the state.
One of the most prominent ones is F.T. Thwaites, who worked at
the department and at the Geological Survey for about
50 years. He pretty much mapped the entire
state. And what we know, 90% of what we
know today about the glacial history of the state can be
attributed to him. So anyway, there was once a
large glacier that actually entered Wisconsin.
And what we do, as geologists, we like to split things up.
What we've done here, there's five different lobes.
The biggest lobe being the Green Bay lobe.
And all these ice lobes actually originated from the Laurentide
Ice Sheet, which had it's center in the Hudson Bay area.
What I want to point out here tonight is one of the large
glacial lakes that formed is this one called Glacial Lake
Wisconsin. I'll talk about that in a few
minutes. So when Chamberlin hopped on
his horse, or in his buggy, eventually in his car, how did
he know that the state had been glaciated?
How did people know? Anyone have any ideas?
How do you know the state's been glaciated?
( inaudible ) Yeah, okay.
I heard moraines and debris. Certainly, when a lot of people
actually looked at those initially, they didn't know
where that was actually from. But one thing, if you go out and
you kick away the soil in some places of Wisconsin, you can see
these things called striations. And how striations form is when
the debris in the bottom of the ice, which is moving, scrapes
across the bedrock. It gives us a good indication
that there was a glacier here once, and the direction that it
actually flowed. Any other ideas?
( inaudible ) Flat sided rocks is a good one.
How about, here's another one. We have a beautiful land form.
They're called drumlins. And here's a relief map
from Jefferson and Dodge Counties.
Here's Highway 94 cutting across toward Milwaukee and 151 up
toward Fond du Lac. What we see is these big drumlin
fields here, or a swarm of drumlins.
These are basically glacial landforms.
But initially, people thought, well, maybe these could be
formed in a large flood. Well, it wasn't until the '50s,
when people discovered radiocarbon dating.
They could go out and they could take a look at, like, buried
wood. In northeast Wisconsin, we have
have a famous layer called the Two Creeks Forest Bed, that's
buried beneath glacial deposits. A lot of these trees, there was
a forest, a glacier came and just mowed down the forest.
I'll talk more about this later. So what we can do is we can go
out and we can cut pieces off these trees.
And there's a big stump sticking out of some glacial sediment
right there. And we can date those.
They'll come back and they're about, I don't know, 13,000
years ago. We knew there was a glacier here
13,000 years ago. But how about prior to that?
Do we have any other records of climate change here in
Wisconsin? Anybody know?
Well, we really don't. We don't have a very good
record. So back in the '80s, I believe
the late '70s, early '80s, to understand what the climate was
here in North America, they said, well, we can do two
things. We can go up onto the ice caps
and we can collect ice cores, with the hopes of getting us a
long-term history of climate change in the world.
And we can go to the ocean and we can collect cores out in the
middle of the ocean, where we know it's a fairly quiet
depositional environment. We can look at those ocean cores
and see if there's a record of climate change.
When we do that, maybe we can get a long-term view of what the
climate has done, at least in North America, or else around
the world. So I just wanted to show this.
One of the most complete climate records comes from the Greenland
Ice Sheet. And what people do, they go
right up to the middle of the ice sheet there, the summit, and
they set up a big drill rig under a large dome there.
They basically collect these ice cores that you see over there on
your right. If you slice one of these ice
cores open, what happens, is that you see a lot of air
bubbles in this ice here. If you take a very detailed, or
a little piece of that and look at it in detail, you can see
that it contains little air bubbles.
And ice, because it's a crystalline material, you can
see the structure of the ice. Those are air bubbles.
So you can go in there and you can extract that air.
You can determine what the content of what CO2 was in the
atmosphere, or the methane content, and whatnot.
But what you can also do is you can chemically analyze the ice
as well, and get a good record of climate change.
I'll talk about that in a little bit.
Here's a portion of that climate record that we have from
Greenland. It's quite interesting.
Down here, we have, this is present.
There's 100,000 ago on the far right.
From the analysis of the ice core, we have temperature here
on this axis. What we see is climate changing
dramatically, the squiggly black line, until about, oh, about
10,000 years ago, when we see this abrupt warming.
Now things are very warm. So we're in the warmest period
that we've been in for the past 125,000 years.
So what happens if you even out this climate change, what we see
is these periods of long cooling, punctuated by very
abrupt warming. So in the past ten years or so,
they've been going down to the South Pole, to the Antarctic Ice
Sheet. They've been drilling ice cores
and doing the same sort of analysis.
The graph on the X-axis here is flipped.
So zero down there is today. And here is 100,000 years ago,
or 150,000 years ago. Once again, we have this
temperature from the isotopes of hydrogen.
But we see the same thing here. We get long periods of gradual
cooling, punctuated by very abrupt warming.
So the question is, how many times has Wisconsin been
glaciated. We know that there were glaciers
here 13,000 years ago because we see trees that were mowed down.
But do you know how many ice sheets have been here?
Has there been one? Five?
Ten? Any idea?
( inaudible ) Three? Four?
It's probably more than that, and I'll show you why.
The ice sheet cores go back about 800,000 years now with the
Antarctic Ice Sheet and the data that's coming out of there.
But we have a longer-term record from ocean sediment cores.
What happens here is you take a ship out into the middle of the
ocean. You dump a big piece of pipe
overboard. It's called a piston core.
It's quite simple. You basically send it down to
the bottom of the ocean and you collect these cores of sediment.
Then you basically crack open those cores and you examine
them. In these cores are these little
creatures, little plankton called foraminifera.
Here's a picture of one Rosalina globularis.
We probably have a foraminifera expert here in this crowd?
No, all right. What happens is that you get the
core and you can look at various species of these forams.
And you can get a climate record from them as well.
I'm going to show you that. I'll explain this in a little
bit more detail. Here's a record from a deep
ocean core. And on this axis, we have depth
from the top of the core to the bottom.
It's about an 11 meter core. On the X-axis, we have
oxygen-isotope ratio. What happens is, what's
important for this slide, and I'll explain oxygen-isotopes in
a minute. What's important to note is that
as you move to the right, you have warmer climate.
And to the left is colder. You can see at the very top, we
have also age or time on this Y-axis right here.
We can see at present, we're actually in a fairly warm
climate. You can see there's our cooling
event right here. We had a long cooling over the
past 100,000 years. We have an abrupt warming event.
What's interesting is when you go down into the sediment cores
and you take a look at these forams here, you see the signal.
You see an abrupt warming, a long cooling, abrupt warming,
long periods of cooling, abrupt warming,
cooling, warming, cooling, warming, and whatnot.
So if we look at the ocean record, and this is quite an old
data set right here from a core that was analyzed back in the
late '60s. We can see that there's been at
least, what, one, two, three, four, five, six major periods of
climate warming and cooling. They have extended this record.
There's at least ten major glaciations that have occurred
over the past million years. So the question is, have we had
ice sheets here in Wisconsin ten times, or not.
I don't have the answer to that. We know that we have extensive
deposits from the last glaciation.
And we have deposits from some glaciation before that, but
we're unable to date them. I want to talk a little bit
about oxygen isotopes. Hopefully this won't put you
guys to sleep. If you remember on the previous
slide, this is how we're getting these old records of
temperature. What happens is that we know
that oxygen has three different isotopes, O-18, O-17 and O-16.
We know that there's a lot of O-18 in that ocean.
I think it's like 99% that's oxygen 18.
One percent is maybe oxygen 16. There's a very minor amount of
oxygen 17. So what I want to tell you here
is that the mass of O-18, obviously, has got an extra
neutron in the atom. If you put a bunch of O-18s on
a balance here, it'd be heavier than let's say, water
made up of O-16. Does that make sense?
Extra neutrons. So we know that in warm
climates, when we're evaporating this water, we get sort of a
proportion of O-16 to O-18 actually evaporating during
warm periods. So when the climate was cold, we
tend to fractionate the oxygen 16, rather than the O-18 here.
What happened is that precipitation actually contains
more oxygen 16. So what we expect, and I'll try
to show that in this diagram here, during glacial periods
when it's cold, we have evaporation precipitation.
What happens is that you get more oxygen 16 stored up here in
the ice sheet on land. And you get more
oxygen 18-enriched ocean. What's interesting, you
remember those bugs I was telling you about?
The forams, what we do is we analyze them for O-16 and O-18.
We actually look at the ratio. So if we were looking right
here at a series of bugs that were living right here over a
long period of time, what we would see is that during
glaciations, we would see-- These bugs are composed of
calcium carbonate shells. What we would see is that
there's a higher ratio of O-18 to O-16, right?
Unlike during interglacial times, basically, O-18 is
relatively depleted compared to this situation here.
And what happens is precipitation now contains a
similar amount of O-18 to O-16. So during periods, these bugs
here, during warm periods, they're going to have a higher
ratio of O-16 to O-18. So what's interesting here is
that we can look at the oxygen isotope ratio of O-16 to O-18 in
those foraminifera in that sea core.
That's how we can extract that climate record.
Here, I just wanted to show you that climate record once again.
This is one specific little foram that these oxygen isotope
ratios is from. That gives you an idea of what a
climate record that we've had, probably in this world.
As geologists, we love to show geologic time sections here,
going back to, that would be 4.4 billion years here.
And the most recent ice age occurred in this period
that we call the Quaternary. It's about
1.8 million years old. So we have good climate records
for the past million years, but how about the 800,000 years
prior to that. How many more glaciations were
there? So a lot of climate scientists
try to figure out what's happened right here in the
Quaternary. It turns out in Wisconsin, large
parts of our geological record are actually missing, like a
period here in the Mesozoic, where the dinosaurs lived.
We have some very old rocks here.
We have a good Quaternary record in this state, although it's
difficult to tell what the age of that glacial sediment is.
I just wanted to show you here, this is the extent of the state
that's been glaciated. We have this area called the
driftless area here. I prefer it be called the
non-glaciated area. As far as we know, there's never
been any ice sheets that have covered this area.
That's quite strange, because if you look at a map of all the
Midwestern states, it's surrounded by glacial deposits,
like I showed you, striations, glacial sediments, drumlins,
whatnot. There's one area of Wisconsin
that's not glaciated. A lot of people speculate as to
why that is. I'm not going to speculate
anything tonight about that. Anyway, if you look at a map of
Wisconsin, a relief, you can actually see this driftless area
here. It's quite obvious.
It has a very different pattern. You can actually see sort of the
outline of the last glaciation, where the glaciers reached.
It kind of stretches across the state.
If you use your imagination on this map, you can draw it across
there. So let's get back to these
glaciers. Hopefully, everyone believes me
now that Wisconsin was glaciated, and that these
glaciers did come from the north.
They dammed up our drainage ways, forming these large
glacial lakes. The first one I want to talk
about tonight is this one, Glacial Lake Wisconsin.
Many of you know of it as the central sand plain today.
What happened here is that the Green Bay lobe advanced down the
Fox River Valley and actually terminated at something we call
a Johnstown moraine, right here.
As many of you drive up north, you come past here and you drive
out on the central sand plain here.
It turns out that right in this area, this is where Glacial Lake
Wisconsin was located. What happened is that as the ice
advanced down here, it pinned up against the Baraboo Hills right
here. You can see the actual moraine
actually wraps around like that and comes down to Madison.
The Wisconsin River comes here, across the Wisconsin Dells, and
down around Portage. What happened was that you
blocked off that drainage way, and then you formed a large
glacial lake that's sitting right here.
And here's a photograph of the northern part of Glacial Lake
Wisconsin. Many of you have driven across
there. It's a very unexciting drive.
And here is just a better relief image of that.
Here you can once again see the lake plain of Glacial Lake
Wisconsin, here at the central sand plain.
But one thing I want to point out now, and I'll talk about it
later on is this Glacial Lake Oshkosh.
It occupied many of these lower areas right here.
So when the ice sheet came down and pinned up against the
Baraboo Hills right here this lake formed.
People ask, where did all this water go.
Well, actually, it went up here, up the east fork of the Black
River to the Mississippi River. This lake was quite large, maybe
about ten to 12 times the size of the existing Lake Winnebago.
We know that once the ice sheet started to retreat as climate
warmed, the lake filled in back here in an area we call the
Lewiston Basin. An outlet formed right here.
We call that the Alloa Outlet. This lake drained
catastrophically down the lower Wisconsin River.
Here's a cross section. I want to back up, but next I'm
going to show you a cross section that runs from the
outlet all the way down to the eastern end of the Baraboo
Hills. This is what the lake probably
looked like. It drained out right here to the
east fork of the Black River. It contained two main basins,
here. And as soon as the ice sheet
backed off of here, this basin, or both basins drained
catastrophically down to the Wisconsin River.
So here's a little detail of that.
I just want to show you this. Here we have the Green Bay lobe
at its maximum extent. The Baraboo Hills are right
here. Many of you can picture Devil's
Lake. It sits right in that gorge
right there. And here we have the lake that
was draining out the east fork of the Black River.
As soon as the ice sheet retreats, this Lewiston Basin
forms. And it ultimately drains over
here, all the way down here. And we have another lake that
forms called Glacial Lake Oshkosh.
I want to talk about that drainage.
Many of you have been to the Wisconsin Dells.
And if you take a look, when the lake drained, it cut down into
the soft Cambrian bedrock. As it was draining, it formed
this unique system of gullies or dells, as people call them.
And there's a picture from H.H. Bennett, I believe from the
early turn of the last century. You can see the water cut down
through the sandstone. Here's a picture of Witch's
Gulch up there. It's a very narrow passageway.
Some people have done calculations of the volume of
water in the lake, and have looked at other geologic
features, and sort of determined that it drained within a period
of about seven to ten days. And some people speculate--
Here's a picture of the lower Wisconsin River--
Is that a lot of the sand that's in the lower Wisconsin River was
actually transported there from the discharge event from Glacial
Lake Wisconsin. Certainly, the existing river
now is transporting a lot of sediment from the central sand
plain. But a lot of this sand is
several hundred feet thick in the valley.
So the source of that may have been from this large flooding
event. One last picture.
It's of the central sand plain, the former lake bed of Glacial
Lake Wisconsin. It is a prime area for growing
cranberries, which Wisconsin is one of the major producers.
The conditions are right because there's a high water table and
it's very poorly drained. Two conditions that are
necessary. What I've been working on more
myself for the past six years since I've been at the Geologic
Survey is that as soon as the ice sheet retreated up into the
Fox River Valley, we have this other lake that is actually
formed, call Glacial Lake Oshkosh.
This green circle here represents the Baraboo Hills.
It turns out that, obviously, the Fox River, which now drains
out Green Bay, couldn't drain out there, so this lake filled
up in the lowlands and drained out here at Portage to the lower
Wisconsin River. The black dashed line here is
simply the extent of the Green Bay lobe at the last glacial
maximum around 20,000 years ago. I want to show you another
shaded relief. Remember I talked about the
Wisconsin Dells, and the river that cut through there.
This blue area that you can see up here, most of that was
occupied by Glacial Lake Oshkosh.
This area shows a large area of Green Lake and Marquette
Counties, not to mention northern Columbia County.
This is kind of what the lake looked like.
This is where its outlets were. We have this outlet here down
through Portage. As soon as the ice sheet backed
up, it cut, it drained out into the Lake Michigan Basin.
As the ice sheet retreated, more and more of these outlets were
cut across the Door peninsula. Two of these outlets that show
up quite dramatically are in Manitowoc and Kewaunee Counties.
One of these major outlets actually carved this valley
right here. A lot of this is through really
solid bedrock. As the ice sheet retreated
northward, another lower outlet opened here called the Kewaunee.
Now if you go up there today, the rivers that occupy these
valleys are very small. So you know that these valleys
could not have been cut by drainage during the Holocene, or
the past 10,000 years. They're actually remnants of big
drainage events from a glacial lake.
This schematic actually shows that drainage sequence.
Here we have the Green Bay lobe. It's actually receding
northward. The outlet opens here to the
Michigan Basin. The lake becomes smaller, lower
outlets open and the lake becomes smaller.
Smaller yet. And then eventually the ice
recedes out of Wisconsin and all we're left with is Lake
Winnebago, Lake Butte des Morts and Lake Poygan, which are
actually rather shallow. I wanted to show this.
( inaudible ) Sure.
( inaudible ) Sure, we know we have some good
dates from the bottom of some geologic cores that show that
it started to recede back about 18,000 years ago.
And receded out of Wisconsin about 15,000 years ago.
It was relatively quickly. But the interesting part of the
story that I'll get to is that there were two sort of major
re-advances of the Green Bay lobe.
The ice sheet must have been responding to oscillations in
the climate. I'll talk about that in a little
bit. Here I just want to show you
those outlets. This is a section of a land
surface, across from left to right.
You can see here is where the Manitowoc outlet is, the
Neshota, the Kewaunee, and the Ahnapee that were used to drain
this glacial lake. What's the evidence for a lake?
Well, if you go up there, you'll find the Fox River Valley a
relatively grim place, because there's not that much
topography. People up there might disagree
with me, because I guess it all depends where you live.
But it's pretty flat. The Fox River Valley is not as
flat as some places of northern Illinois.
So you go up there and you say, what's the evidence for a lake?
Well one thing we can see here is that there's a break right
here. There are a lot of boulders
sitting up here. This turns out to be a lot of
lake sediment. Same here, you can see the sandy
soil right here. This is probably a beach terrace
right here. You come down, the more deep
water, clear lake sediments. It's not very convincing when
you go up there. You'd never believe there was a
lake there. At least I had problems
believing it when I first drove my car across there.
But as I went and visited some quarries and gravel pits, you
can see such a sequence as this. This is about ten meters high,
about 30 feet high. You can see these laminated
sediments right here. You see there's a dark layer,
light layer, dark layer, whatnot.
So there might be 100 such layers here.
What these are is couplets. These each dark layer and each
light layer represent one year of deposition of sediment in the
lake. So if you go up there and
there's of course some sandy material on top, I would
interpret this as lake sediment. This lake is shallowing, so you
have coarser sediment at the top with finer grain sequence.
It's quite impressive. That's a good indication there
once was a large lake there. Of course, as geologists, we
love to go out and drill bore holes into this stuff.
It's what we do to learn about the geology.
We've done so. The red dots represent bore
holes we've drilled recently. There's the drill rig that we
hire to go do this sort of work. Here's a piece of core that
we've actually recovered. It's about one foot across and
about 106 feet in depth. You can see these alternating
layers. It's actually a clay layer, silt
layer, clay layer, silt layer. In some of the cores, we've
counted over 1200 of these bars, which means the lake existed
through at least 1200 years. What we can do is here's a core
or log of one such bore that we drilled.
Here's that sample, that one-foot long core sample again.
What's interesting is the squiggly line, here we have core
depth, or elevation above sea level, but we have a measure of
something called natural gamma radiation.
What's important to notice here is that we notice there's three
different ages of Glacial Lake Oshkosh.
So basically what happens, is that we know Glacial Lake
Oshkosh was reactivated twice after the initial recession of
the ice sheet here. And these white lines here
actually show the extent of those re-advances back into
Wisconsin. The first re-advance we think
occurred, reaches its maximum extent about 15,000 years ago.
It sort of extended down around Fond du Lac, up onto the
escarpment and out into Lake Michigan Basin.
Then the ice sheet totally receded and we had the growth of
our forest here. So climate was warming very
rapidly. When the ice sheet actually
re-advanced to this margin right here, which reached just the
northern tip of Lake Winnebago here.
It actually buried this forest. If you go out, you can actually
find it. This is actually a piece of
beaver-chewed wood that we found.
So a beaver was, you know, operating in that forest.
And you can actually see a thick, it's actually about a
six-inch thick layer of organic material.
So we're very confident of the age of this re-advance.
So the ice sheets are not the sort of stagnant things that we
all think about. Glaciers do move quite slowly,
but in over sort of a 100 year to 1,000 year time period, they
actually move quite rapidly. If you could imagine, from
15,000 years ago, the ice sheet retreated out and actually
re-advanced into Wisconsin. So in a period of 2,000 years,
we've seen a major re-advance, a recession, and a re-advance once
again. I like to think of glaciers as
sort of like a beating heart. They sort of advance and recede,
you know, unless the climate warms and they actually
disappear. This is just a cross section.
I apologize, I know this is quite boring here.
Here we just have elevation. This is a distance from Portage
up to Green Bay. What we have up there is just
this thick sequence of lake sediment and things we call
glacial till, which means that the glaciers deposit these
directly. That's what the landscape is
dominated by, is glacial sediment up there.
One thing I'd mentioned earlier is that, what is the record of
climate change here in Wisconsin.
It's not that great. You guys learned about isotopes.
I talked a little bit about isotopes earlier collected from
the ice cores and the ocean core.
But in one of our cores, which is located right here, we
actually consists of all lake sediment and tills that I talked
about earlier. We went in there and we
extracted the water from the sediment.
We analyzed it for oxygen 18 and oxygen 16.
It turns out what we're after is that there any old glacial water
here in this state? That's the question we're
asking. And the thing is that when we
pump from the aquifers, the bedrock aquifers we have in the
state, are we actually mining ground water?
That is, are we taking a resource that's ultimately a
limited resource, or is actually recharging from water and
precipitation? That's one of the questions we
were asking ourselves here. It turns out that you can see we
have this bow-shaped curve here. And what this values of oxygen
18 here sort of represent that we have very old ground water
within this very thick clay sequence.
So the question remains is that is the water in the aquifers,
which are mainly in the bedrock down here?
Is that real old water? Is that fairly young water?
Are we pumping a source that's actually finite?
That's a real interesting question that I won't get into
much tonight, simply because it's not my expertise, and it
would add another ten minutes to this talk, at least.
But one question that people ask me quite a bit is whether
this thing called isostatic depression will have affected
lake levels in Glacial Lake Wisconsin and Glacial Lake
Oshkosh. Now, if you think about this,
think about the earth as a balloon filled with Jell-O.
That's really what it is. We have the earth's crust, which
is very rigid. And underneath, we have a
mantle, which is actually not very rigid at all.
That's mainly molten rock. So if you imagine a balloon
filled with Jell-O, if you push or apply a force on one side of
the balloon, you're going to displace that Jell-O and it's
going to pop out elsewhere, right?
If you think about this, if you take water out of the oceans and
we load them up on land, we're like poking that balloon.
We cause something called isostatic depression.
When we load these big ice sheets on here, we actually
depress the crust of the earth. Now of course, how much of this
depression actually occurs here depends upon how jelly-like, or
I should say how viscous that Jell-O is in side.
It also depends upon the thickness of the glacial ice
here. So if you can imagine, if we
load Wisconsin with a big ice sheet like this, we're going to
actually depress the land surface.
Actually, this depression is actually felt out way in front
of the ice sheet, as well, maybe by 50 to 100 miles.
It's like, you know, this is something called a forebulge.
The material is squeezed out underneath the ice sheet.
So here's a graph with a lot of lines on it.
But what's important here is this represents the amount of
what I call isostatic rebound or depression over the last 13,000
years. If you take a look at this,
these are a bunch of old glacial great lakes throughout the
Midwest. This is Glacial Lake Oshkosh.
We have a big one here in the Lake Michigan Basin.
We had other ones in the Great Lakes Basin, as well.
As you can see here, in Wisconsin, we have seen 20
meters, which is about 70 feet, of rebound.
The earth's surface is actually coming up over the past 13,000
years. You can see that way up in
northern Canada. They've seen on the order of
about 500 meters of rebound. I should be clear here.
What we do, is that this is actually the result of numeric
models that have been calibrated to fit geologic data.
So we're fairly confident in this project we've doing that
these numbers are fairly right on.
So if we take a look at Wisconsin a bit closer, here we
have Glacial Lake Oshkosh in front of the Green Bay lobe.
Here's a lake that was in the Michigan Basin.
You can see that at right about Portage, which is right here,
basically there's been zero isostatic rebound or actual
depression. If you go to the northern part
of Glacial Lake Oshkosh, there's about 50 meters since 18,000
years ago. So what I'm telling you is that
the shoreline that we find here of Glacial Lake Oshkosh, if we
go all the way up into Oconto County, we should find that at
50 meters higher than it is down in Portage.
We would expect to see over 150 feet of difference between their
shorelines. Does that make sense?
A lot of people ask, well, is Wisconsin still coming up today?
Does anyone know that? Are we still feeling the effects
of the glaciers? Does anyone know that?
Maybe because it doesn't matter, right?
Because this rebound is such a slow thing, it's on a geologic
timescale. It doesn't affect any decisions
we make from year to year. But if we take a transect going
from, let's say Portage, all the way up to the tip of the door
peninsula, and that's that distance right here on the
X-axis, and we take this, what I call deformation relative to
present. What's happened, you can see, is
the ice sheets advance. Well, we'll start here.
The ice sheets advance. We actually depress the crust,
right? Here is at 23,000 years ago, the
ice sheets advance, we're depressing the crust.
Here's 15,000, 13,000, 11,000, and so forth.
So what happened is that we've been depressing the land
surface. In the past, probably 10,000
years, this land surface has actually been on the rebound.
You can see as it comes up during the Halocene period from
about 9,000, all the way up to present, where we are today.
If you recall, I showed you a picture of this thing called a
forebulge in front of the ice sheet.
That's what's happening in Wisconsin today.
We had depression and uplift, so it's doing this sort of motion.
The question is that there's probably over the past 10,000
years, is probably have modified drainage systems in our state.
How drastically, I really don't know.
A lot of people spend time looking at modern gauge records
from Lake Michigan to try to get tilt rates today.
This is significant in some areas, especially if you're
along an ocean coastline. This rebound can have an effect
over say, a couple hundred years.
It can be enough to raise sea level over engineered barriers
and whatnot. Question?
Will those ideas account for the driftless area, like if that
was the bulge ahead of it? >> No, it couldn't.
I mean, when we modeled the ice sheet here, when we calibrate
this model using our lakeshore lines and whatnot, it turns out
that we have, actually, they say on average about 400 meters
thick in the state. So 400 meters is, you know,
1,300 feet, something like that. So the ice sheet is much, much
higher than anything in the driftless area.
So you can imagine with a giant ice sheet that's much higher,
just back from the margin, than anything in the driftless area.
So no, that forebulge wouldn't have been large enough.
Even if it was 50 meters high out in front, it wouldn't have
provided enough topographic relief to divert the glacier
south. That's a good question.
The reason why the driftless area is unglaciated, I don't
have an answer. So anyway, I just kind of
wanted to end up the talk today. When is that lunar eclipse
occurring, Tom? ( inaudible )
Anyway, I just want to say thanks for coming out tonight
on a cold night. Thanks for letting me talk a
little bit about the natural history of the Glacial Lake
Wisconsin, and also this one, Glacial Lake Oshkosh up along
the Fox River Valley. Thanks.
( applause ) >> One question.
Sure. >> I live in Middleton, and we
have two kettle, which means an old source of water.
And they just fill up, then they become silted and we have to
drain them out into Lake Mendota.
The water levels in those kettles are simply an expression
of the water table. So they're recharged by the
ground water. Yeah, there's a lot of those in
Wisconsin, especially up in northern Wisconsin, there's a
lot of small, little kettle lakes that don't have an outlet.
So those are glacial lakes, but they certainly aren't on the
scale of the lakes I've been talking about tonight, which
were much larger, ten or 15 times the size.
We still like them. >> Oh, yeah, they're very nice.
Question? >> Going back to Glacial Lake
Wisconsin and the land form of Wisconsin Dells, is this
something that drained in seven to ten days?
Or was it that quickly? >> It was.
And once the ice sheet quit impinging on the eastern side of
the Baraboo Hills, what happens, you back that ice off just a
little bit, the water breaks through and the water is very
effective at melting that ice. So there's geologic evidence
you're asking is, one it takes quite a bit to erode bedrock
like that, to actually cut down to that sandstone.
But they find good size boulders down along the Wisconsin River
Valley. In order to transport good size
boulders, you have to have a large stream with lots of power.
So that's some of the geologic evidence.
It would be difficult to cut through that sandstone, I
believe, and transport these boulders with any sort of low
flow event that occurred over a long period of time.
There's certainly a lot of assumptions that go along in
those calculations. But it's pretty convincing when
you take a look at some of the geologic features.
I put on here, the volume, if you can wrap your mind around
it, was about 87 cubic kilometers, which is quite big,
compared to Lake Winnebago with a volume of three cubic
kilometers. So this is orders of magnitude,
almost two orders of magnitude larger.
And to give you an idea, that lake was about 4,000 square
kilometers compared to Lake Winnebago that was 600 square
kilometers. The average depth of Glacial
Lake Wisconsin, I'm not sure of that.
I wasn't involved in making those calculations.
But it's probably about, I would imagine 20 meters, or something
like that. Maybe I should actually retract
that. Glacial Lake Oshkosh, the
average was about 17 feet, about five meters deep.
Glacial Lake Wisconsin was quite a bit more, so maybe ten to 15
meters. So if I compare the two lakes,
the volume of Glacial Lake Oshkosh, about 111 cubic
kilometers, compared to 87 for Glacial Lake Wisconsin.
They have done calculations of what the discharge would have
been out to the Wisconsin River and across the Door Peninsula
for Glacial Lake Oshkosh. They've come up with values of
one times ten to the fifth cubic meters per second.
I don't know how this compares, and I meant to check this on the
Web, compared to the floods along the Mississippi River that
occurred back in the early '90s. Does anyone know those discharge
numbers? I don't know.
I think it might be something comparable, like that.
If you can imagine these lakes draining in a period of seven
days, something like that. That's what it would take.
It would take about 15 years to fill Glacial Lake Wisconsin back
again. Yeah?
Your relief maps that you showed, the topographical relief
pictures, where are those from? >> It turns out that the United
States Geological Survey makes these things called digital
elevation models. And if you have the software,
you can download that data right off the Internet and you can
make those. Of course, you have to
manipulate them, color them, and whatnot, and add, you know,
topographic features and whatnot.
They're neat. >> They are neat.
They're fun to show, because it gives you an idea from space.
Are they from space? >> No, the data's actually taken
off their topographic maps. I think most of the data is
taken off of the topographic maps, you know, the quadrangle
maps. That's the source of the data.
( inaudible ) ( laughter )
In the future, what do you do next?
Well, maybe I go to another state.
( laughter ) It's hard to say.
Wisconsin has such a long history starting with
T.C. Chamberlin back in the 1800s, of studying
glacial deposits here. The thing that's really--
When I came here, I thought, what am I going to add?
Right, that these giants in this business haven't known for 100
years. And it turns out that back then,
they didn't have these digital elevation models that we're
looking at here. So we can actually get more
detailed information. It becomes more important when
we're looking for something for sand and gravel resources, or
we're trying to understand groundwater resources.
We need to know the geology quite well.
It turns out that there's plenty of work for geologists still to
do. >> You might find oil.
I wish. ( laughter )
Question? >> Did you say that there is
or is not glacial water, or you still don't know?
There is. There is glacial water in those
thick clay lake sediments up in the Fox River Valley.
The question is that beneath those glacial sediments, we have
what we call a Cambrian bedrock system.
And there's a big, thick layer, and I'll call it the Mt. Simon
sandstone, that comprises the major aquifer for southeast
Wisconsin, but also for Madison, as well.
Tom asked me to talk about this, but I didn't do it
tonight. The question is that many of you
have heard that Waukesha wants to take water from Lake
Michigan. One of the things is that a good
portion of Waukesha County is outside the surface water
drainage basin. That's what determines whether
you can extract water out of Lake Michigan or not.
So Waukesha has been pumping this big productive aquifer for
many decades now, especially as Waukesha County has boomed.
What's happened is that they're depleting the aquifer somewhat.
They've lowered the water table. But they're also getting water
quality as an issue there as well.
They're starting to draw off some brines, and have radium
problems in their water. So Waukesha has been pumping
this aquifer. To give you an idea, they pump
30 million gallons a day in Waukesha.
I think Madison pumps 50 million gallons a day from that aquifer.
So the question that you're getting at, is that old water,
pumping glacial water, are we mining a resource that's not
renewable. And it depends who you talk to.
Some people would say the aquifer is being charged.
Some people think Lake Mendota, for example, is a recharge for
that deep sandstone aquifer. But as that aquifer slopes down
into Lake Michigan Basin, maybe, you know, there's more sort of
impermeable, or less permeable units up in the section that
actually prohibit water, you know, surface water, from
infiltrating and getting down and recharging that aquifer.
Some people would say that some areas of that aquifer contain
very old water, and that we're not recharging it as quickly as
we're using it. You know, of course, I would
say that our water qualities are not very significant compared to
maybe the western states, where they're struggling now in
drought conditions. But it is an issue, because if
we let Waukesha County extract surface water from the Great
Lakes, then we start to establish, supplement what
they're drawing out of the ground water system, we
establish a precedent that anyone can take water that's
outside their "surface water drainage basin."
That' causes all sorts of issues.
Chamberlin discovered this glaciation in Wisconsin.
But was that like a general theory?
You know, people thought there was continental glaciation other
places. I was wondering, nobody thought
of continental glaciation before.
Well, you know, no one thought about them, really.
I mean, if you go back to the 1800s, Louis Agassi is sort of
the main man. He came from Europe.
He was looking at big erratics, what we call erratics.
There's one that sits right up on Bascom Hill now.
There's a big boulder that's an erratic.
Basically, it's a piece of granite.
There's no granite readily available in the Madison area.
So it had to come from far away. The reason, people thought all
those erratics were carried by the great Biblical flood.
And so, what we've seen, and it wasn't until after Agassi and
other folks, took a lot of heat from this back in the early
1800s. And Chamberlin, along with some
other folks around North America, sort of sided with
Agassi, and said, look, there's no way that these boulders are
from this big flood. One, because they're wide
spread. Where did the flood come from?
And all these other land forms, they went and saw these till
sequences. In the Midwest, we see deposits
from a glacier, they went to the modern glaciers and said, oh,
that looks like the deposit from a modern glacier.
What's interesting is that Chamberlin, you know, they sort
of named these tills. There was the Wisconsin, the
Illinoian, the Kansan, and the Iowan.
It turns out that Chamberlin said that there must've been a
big glacier here. And then he started to look
around. This is huge.
It wasn't here, it had to be up in Canada.
And he was actually the first one that made that big map
showing the extent of a continental glacier.
That's what Chamberlin's really well known for, is that he sort
of took that idea. In fact, the last glaciation is
called the Late Wisconsin. The reason why is because
Chamberlin named it such. It was the upper most till unit
that he was looking at, and he called that the Late Wisconsin.
Anything, the lower ones, for those other states.
So those have sort of gone by the wayside, but the Late
Wisconsin has stuck. And that's what's used
throughout the world today. So, I guess our state's quite
honored to have the last glaciation named after us.
Chamberlin really was sort of a pioneer, really.
Agassi was sort of the real pioneer and took a lot of heat,
but Chamberlin hopped on that boat quite quickly when he
realized, when he sort of correctly evaluated the data.
So hats off to him. He certainly, I'm sure, took a
lot of heat from people back in the 1800s.
Back to the idea about Waukesha taking water.
Isn't there a compact among the states surrounding the Great
Lakes about those kinds of issues?
There is. And I don't know much about that
compact. There's others in this room, I'm
sure, who know much more about it.
But what's happening is that Waukesha's argument is that the
surface water divide. You know, in the groundwater
flow system, we also have sort of groundwater, I don't want to
say systems. There's a groundwater divide
that crosses further to the west.
So Waukesha's argument is that the groundwater, within that
groundwater basin, it discharges to Lake Michigan.
So we're saying that this artificial line, this surface
water drainage divide has really got nothing to do with the
ground water. Am I not making sense?
But they're saying that a divide should be based on the
groundwater divide, not the surface water divide.
Because you know, when you put water back into the system,
let's say if you spread it on the land, it actually soaks in.
It goes back into and recharges the aquifer.
The aquifer discharges into Lake Michigan.
That's their argument. So they're challenging that
compact based upon that logic, that it should be based upon the
ground water divides, not the surface water divides.
Does that make sense? >> Is the Laurentide Ice Sheet
below the North American Ice Sheet?
No, that's an old map I put up there.
The Laurentide Ice Sheet was the last great ice sheet that
covered North America. That was kind of an old map I
stuck up there. It was initially just called the
North American Ice Sheet, because no one knew anything
about it. So there was really nothing
called the North American Ice Sheet.
That's sort of a general term that was used very early on.
I don't know where the term Laurentide came from, who named
it that. I have no idea.
I think Chamberlin called it the North American Ice Sheet to
start with, but it's subsequently known as the
Laurentide. We certainly had many of those
ice sheets. And probably many of them came
into Wisconsin over the past two million years.
Yes? >> Am I right in understanding
that as oil is extracted from the ground, the space gets
filled by water? That's my first question.
Is that true? >> It depends.
( laughter ) It depends where you are.
A lot of times, you pump the oil and it may not be, you know, it
takes a while for any sort of water or fluids to recharge.
But a lot of times, oil companies, what I know, they
will actually put up two wells. They'll pump oil out of one.
They'll inject water down one and they'll try to push the oil
out the other one. But naturally, it all depends
what the geologic situation is. >> In so far as that happens, is
there an issue about that water being locked in the earth and
not be evaporated, and does that affect our water supply and our
climate? >> Well, a lot of questions
there. The water, if you think about
ground water, it exists in porous spaces between grains,
right. So what happens is that how well
those pore spaces or those voids are connected determines whether
or not you'll be successful in extracting it or not.
The question is that ground water doesn't evaporate, because
it's not exposed to air. So we don't lose anything to
evaporation in the groundwater. So the question is with climate
change. If we have a reduction in
precipitation, let's say, that's going to possibly mean a
reduction in recharge to our aquifers.
That's possibly what it means. But that depends on where you
are in the world. So once again, that's sort of a
site specific question. Did I answer your questions?
Some of them, yes. ( inaudible )
Thank you all very much. I'll see you next week.
Thank you. ( applause )