- Our first presenter
tonight is David Mickelson,
and he'll be speaking
on The Geology
of the National
Scenic Ice Age Trail.
David retired in 2005
from the Department
of Geosciences at UW-Madison
for 34 years.
He taught,
among other things,
Glacial Geology,
Geomorphology,
and the Geology of
the National Parks.
David and his students
have worked on
the Genesis of Glacial
Deposits in Argentina,
Tibet, Scandinavia,
New England, Utah
Alaska and Wisconsin.
His most recent
co-authored book,
"The Geology Of The
Ice Age National
Scenic Trail", was
published in 2011
by the University
of Wisconsin Press.
And I believe we
have a few copies
here, if anybody
would like to get
a hold of one after the program.
And, David, with that
I'll turn it over
to you and I'll try
to plug in your mic.
- All right, well
thanks very much.
I'm gonna spend the
next 40 minutes or so
talking about the ice
age national scenic
trail, a trail that
runs about 1,200 miles
across Wisconsin,
about half of that is
finished off-road,
the other part is on
road connectors but
the plan is it will
eventually, hopefully
while I'm still able
to walk around on the
trail, to actually fill
in the gaps and have a
complete 1,200-mile trail.
If we climb the tower
of Potawatomi today and
look up to the northeast,
this is the view you get.
But if you had been here
say 14,000 years ago,
this is what you
would have seen.
So this is in Glacier
Bay, Alaska, and you're
looking at a glacier
front that's ending
in water, so ice
bergs are breaking off
and that's called
a carbon margin.
And I'm going to
get my cursor here
so you can see,
you see the cursor?
Yeah, okay, and,
just to give you an
idea of scale, that's
a 21-foot long boat
with three people
in it right there.
So the glacier did a
lot on the land and
obviously because it's
the Ice Age Trail,
it does tend to emphasize
glacial features.
But I want to step
back in time, we gotta
talk a little bit about
Wisconsin's geologic
foundations before we talk
about these later events.
And the oldest rocks
in Wisconsin are about
2.8 billion years old,
that's billion not million.
So that's not the oldest,
there are older rocks.
There are rocks that are
another billion years
older than that, but
they're still very old.
And there was a
mountain range built
at that time, and
the rocks that were,
that we see now at
the ground surface
in northern
Wisconsin were deeply
buried under that
mountain range.
Miles, tens of miles below.
And so they were
heated and under
pressure, and they
became metamorphic rocks.
So most of the rocks
that we see in the
north-central part
of the state, get the
cursor again here,
up in this area are
metamorphic rocks that have been
subjected to heat
and pressure under
a big, high mountain
range like that.
The Ice Age Trail
crosses those rocks,
but you can only see
them in a few places.
Where the Wisconsin
river crosses
the trail, where the
trail crosses the
Chippewa river, and
a few other places.
But for the most
part what you see
up there are glacial
deposits, not the bedrock.
The next memorable event in the
geologic history of Wisconsin is
volcanic activity
in the central part
of the state near
Montello, but it was
fairly localized
and roughly the same
time, within millions of years,
there was a tropical
sea that came
into what is now
Wisconsin from the
South, and in this
tropical sea was
deposited sand, sand
that was being delivered
from what's now North
into this sea by rivers.
And that sand
produced what's called
the Baraboo quartzite,
which I imagine
many of you have
been to Devil's Lake
in the Baraboo area,
and you can see
features that indicate
that this has to
have been deposited
by sandstone.
Ripple marks for
instance, this is the
bottom of Devil's
Lake today, and you
can see the ripples
on the sand under
the water, and then
these are the ripple
marks in the Baraboo quartzite.
And quartzite is just
quartz and grains
welded together by
heat and pressure.
So that's another
metamorphic rock.
You probably know
that it has a purplish
cast to it, it's very
recognizable, very
hard, very resistant
rock, and so through
millions of years,
the Baraboo quartzite
has been more resistant
than the rocks
around, and has
tended to stay up as
a relatively high hill or ridge.
Okay, then we have a
big gap in time again.
We jump up 0.6 billion
years and think
of this geologic
record as sort of like
a book with a lot of
the pages ripped out.
So we get some
information and then
we're missing lots
of pages, and then
we get some more
information, and
then we're missing
lots of pages.
So we're missing
that time between
1.7 billion and 1.1,
and then there's
evidence of a
completely different
geologic environment, instead of
squeezing together
and a mountain
range running across
northern Wisconsin,
what we have now is
the earth's crust
being pulled apart,
being pulled apart
like is happening
along the mid-Atlantic
ridge that you
may have heard of.
It's happening in
Iceland, it's happening
in East Africa,
places where the crust
is being pulled
apart because of this
plate tectonic
movement, and at that
time there was
volcanic activity.
And that was the
time that the Lake
Superior basin actually formed.
The other Great
Lakes didn't even
exist then, but
the Lake Superior
basin formed early
by this process,
by this collapse
of the earth as it
was being pulled apart.
We had volcanoes
that were sort of
localized, not
extensive but there
were volcanoes, and you can see
volcanic rock in places
like Copper Falls
State Park, and
there's actually this
area of these rocks
of this age run
down basically from
the west end of
Lake Superior, down
under Minnesota,
Iowa, Nebraska, and into Kansas.
Now down there, these rocks are
covered by younger ones, but we
can see them at the surface in
Wisconsin and parts of the UP.
So this is at Copper
Falls, associated
with those rocks
from the volcano are
also some sandstones,
but also we can
see this rock, this
volcanic rock called
basalt, right out
at the other end,
the other, the terminus
of the Ice Age Trail.
So the Ice Age Trail
starts here in Potawatomi
State Park, and the
western end is out on
the Minnesota line on
the St. Croix river,
on these basalts, a
very late what's called
Precambrian age, so
the purple and the
lavender there are these
rocks of relatively
young age, and they're
not metamorphic.
They're not buried
deeply, these are
volcanic rocks that
are basically unchanged
since they were deposited.
Then another period
of missing record,
from about a billion years,
to about 500 million.
So 500 million years
of record missing
and then again we
have a record of
tropical seas coming
in and depositing
sand, much like
happened 1,700 million
years ago, rivers
coming from the North.
And in places, you can
actually see these two
different sand deposits,
one on top of the other.
This is on the East Bluff
trail at Devil's Lake,
and the lower rocks
are these older,
welded-together
Baraboo quartzite
sand grains, and just
above it, you can
run your hand right
along it, over that
missing billion years,
we get sandstone
again, but it's not
metamorphic, the
grains haven't been
welded together.
You can actually pick
up pieces of sandstone
and sort of crush it
with your fingers.
So it's very different
and yet it was
deposited in a very
similar ocean basin
just a billion years different.
So if you get down
there, try that.
Walk up and see what it
feels like to put your
hand on that missing billion
years of rock record.
So this is when we
start to see fossils
in Wisconsin, the state
fossil is a trilobite,
as many of you probably know.
And oftentimes these show up as
just little pieces,
fragments, not as
whole fossils,
another fossil that we
get in these
deposits are tunnels
that were produced
by worms, that
have then been
cemented together.
And they are actually cemented
enough so they're more resistant
to weathering than
the sandstone around.
So the black arrows there
are pointing to a ridge
and that represents the
worm tube basically.
And then the low
areas between are the
sandstone that
hadn't passed through
the gullet of the
worm and gotten
cemented together better.
So the geography was
very different then.
This is a map that
shows the little
green Wisconsin as
it moves through
time, from the time
of these sandstones
up until present
time, and of course
it looks like
Wisconsin's floating
as an island out
there, it isn't.
I mean it had North
America around it,
it wasn't just Wisconsin
floating alone.
But notice that 500
million years ago
on the left there
Wisconsin was below
the equator it was
15 degrees below
the equator, and
it was tilted over.
So what's now North
was facing East.
So through that
time, that last 500
million years,
what's happened is
our whole landmass has rotated
90 degrees, so now what's North
is North, and
we've also migrated
from well south of
the equator to well
North of the equator,
basically 45 North.
So substantial changes in where
we sat on the
globe through time.
So those rocks that
I'm talking about
are called Cambrian
rocks, excuse me,
about 500 million
years old, the first
fossils we find in
Wisconsin, not the first
in the world, but the
first we find in Wisconsin.
And they wrap around
those older rocks
so that, let me put the
cursor on here again,
so what you see here
labeled is Cambrian
the gray, that's mostly
sandstone, and they
kind of wrap around
those older rocks
that are shown in
green, and the ice age
trail crosses those up
north of Eau Claire.
And you can actually
see places where
there are exposures
and relatively
close to the trail find
pieces of trilobite.
And there are also
places down in the
Central part of the
state, as you can see,
Dane County, basically
northward up to
say southern edge
of Marathon county.
Around that you can
see some other colors.
You see there's a blue
that's called Ordovician
and there's a purplish
color called Silurian.
In those the dominant rock types
at least have changed,
so by the time
that we get into
the Ordovician Age
so we're talking about
450 million years
ago or something
like that, something
happened to the rivers
that were coming
off the continent to
the north into the sea.
And we had the sand
diverted somewhere else.
And so we changed
from an environment
in the Cambrian
probably somewhat like
the lower Mississippi
delta area and out
into the gulf today,
in other words getting
lots of river sediment,
to a situation
where we are here
in Wisconsin, was
missed by rivers
coming in, and it was
an environment more
like we get in Florida.
So Florida we don't
get sand coming off the
continent, there are
no big rivers there
and so what do we get instead?
We get basically
limestone forming
that basically
ground up sea shells,
coral, and so on,
so when the sand
isn't being dumped
in, then we get those
things that are made
of calcium carbonate.
That's a mineral
that's deposited in the
or, sorry, yeah,
deposited in the ocean
basin, either by microorganisms,
by crushed up shells,
or as I've said corals.
A very early one was
called a stomatolite.
And you can see that
these characteristics
are these concentric
rings here and they're
produced by algae that
secrete calcium carbonate.
And this is what
they look like today
on the coast of
Australia, these are heads
of algae that get
covered in high tide
and the algae are out
and photosynthesizing
and so on, and depositing
calcium carbonate.
And then in low tide,
basically they're
relatively dormant,
and then the tide
comes up and they're
active again.
By about 450 million years ago,
we're starting to
get lots of shells
being preserved as
fossils and those
rocks are called
Ordovician, and those
are the ones in
light blue there.
And actually the fossils don't
change much when we come to the
rocks that are here
under Door County,
the ones of Silurian
Age, the fossils
change somewhat,
here's a wall here
in Sturgeon Bay
that shows curled
mollusk here and
you can see actually
quite a few fossils, some here.
Almost any building
you walk around here,
weathered wall, you
can see those fossils.
So over here in this
part of the state,
near Sturgeon Bay, Door County,
the rocks aren't actually flat,
they're actually
tilted somewhat.
This is very
exaggerated, they're
only tilted a few
degrees but they
tilt downward toward the East
under Lake Michigan.
And so these Silurian rocks, the
rock name is dolomite, it's just
calcium carbonate and magnesium
carbonate, is pretty
resistant to erosion.
And so it's this
fairly hard dolomite
that produces a
feature called the
Niagara escarpment.
And the Niagara
escarpment is really
produces the backbone
of Door County
that you can see
here, and it goes
across the UP, and
then comes back
down, and ultimately
it's what holds
up Niagara Falls,
and that's where
the name originally came from.
So it's a fairly
resistant rock called
dolomite because it's magnesium
and calcium
carbonate, and it was
deposited about 400 to
450 million years ago.
Then we got lots
of record missing.
We jump from there to
30,000 years ago, okay?
So we're talking 400
million to 30,000.
Huge amount of time
missing and that
brings us to ice age Wisconsin.
And the glacier probably came in
here about 30,000 years ago.
It probably came
in through a very
barren environment,
tundra, permafrost
environment like we
get on north coast
shore of Alaska
today and is probably
not trees, but probably
just tundra vegetation.
And we were at the
very southern edge
of this huge ice sheet,
you actually could
have stepped onto
the glacier here in
Wisconsin and gone
on ice all the way
over into central
and southern Russia,
all the way to the
Pacific Ocean, all the
way to the Atlantic Ocean.
Now over the Arctic
Ocean, it would
have been sea ice,
it wouldn't have
been glacier, but
still you would've
been on ice all the
way over to southern Russia.
So a dramatic mass
of ice that was here.
And the next slide
I'm going to show you
is a little movie
that shows the advance
and retreat of that glacier.
So it starts about
30,000 years ago
and that's our best
guess, we don't
have a lot of
information on where
it was at various
times, but this has
been put together
by people at the
Geological Survey
and myself to try
to at least give
an impression of
what it was like.
And what I want
you to see is for
the first 10 or
12,000 years, the
glacier's out pretty much where
the earth's maximum,
but now about
18,000 years it starts
to retreat and advance,
and retreat and advance.
So you get pretty
dramatic changes
and that's pretty
when a lot of the
action of the glacier
was taking place.
A time when the
glacier was moving
back and forth, and
really producing
lots of the land
forms that we see.
So let's take a
minute to talk about
how glaciers operate.
You need more snow
falling in the
Winter than melts in
the Summer in order
to have a glacier,
when that happens,
snow falls and accumulates, year
after year, the
snow, because of the
weight of the
overlying snow, turns
into ice and when ice
gets to a thickness
of about 100 feet,
it's behavior changes.
Now if you drop an
ice cube on the floor,
it's brittle, it breaks,
but glacier ice under
a thickness of about
100 feet, starts to
actually flow, flow
like cold molasses,
or room temperature tar.
It's no longer brittle
so the curvaceous,
the cracks that you
see on top of modern
glaciers, those are the
brittle result of the
plastic movement that's
taking place underneath.
And so as the glacier
then moves, it can
pick up debris, it
slides along, picks up
debris and carries
it out to the outer
edge of the glacier
where melting is
taking place, and that
material gets dropped.
So that's a fundamental
thing is it's
sort of running like
a conveyor belt,
picking up debris,
carrying it out
to the edge and dropping it.
If we look at the
glacier itself,
many times it's very clean ice.
This is in Alaska,
and you're looking
through clear ice,
and you're looking
at debris down on the
bottom of the glacier.
That material is frozen
in through the bottom.
So the bottom of the
glacier is actually
sort of like coarse sand
paper, sliding along
the ground, plowing
up material, grinding
away on rocks, and so
that's what's doing
the work that the glacier does.
The other thing that
happens is we have
lots of water flowing
away from the glacier.
And so that material
has been carried
by the glacier, gets
picked up by steams,
and moved away from the glacier.
And the effect of
the water transport
is to separate sizes,
the glacier tended
to mix things together,
water separates them out.
So you're looking at
a stream here where
the glacier would be off
to the left, and here
it's sort of one-inch
gravel that's being
deposited and the
sand, and the finer
grain material is
going way downstream
out in the distance,
and the coarser
rocks have been
dropped somewhere
closer to the glacier,
where the stream
was starting.
So those streams tend
to separate things
out and that's what
produces sand and gravel.
So the sand and
gravel that we mine
for aggregate, for
asphalt, or for concrete,
that's not deposited
directly by the glacier,
that's deposited by
streams flowing away from
the glacier or maybe in
a tunnel in the glacier.
And because streams
have sorted those
materials out by size,
and that makes it
a desirable material
for aggregate.
The other thing
that is particular
about glacial deposits is that
glaciers pick things up and can
carry them long distances.
So for instance this
is a wall outside
of Picnic Point,
on the UW campus in
Madison, and look
at the mixture of
rock types, those
aren't rocks that
occur naturally around Madison.
And they haven't been
taken here by a truck.
Those were carried
down by a glacier
and they're called
erratics, when they've
been carried a long
distance from one
place to another and dropped.
And so any glaciated
area has erratics
of some kind, and
what determines an
erratic is simply is
it the local bedrock
or is it something
that's been carried
from a distance?
And so the erratics that we have
in this part of
Wisconsin, basically
down the Green Bay lowland,
probably came from
this zone that
you see marked up
here in the east
end of Lake Superior.
So it was coming from somewhere
up in this area and then coming
down this way, it
was not coming,
for instance, from
over in western
Lake Superior this way, at least
during the last glaciation.
So with that little introduction
to geology, let's
talk a little more
about the Ice Age Trail and the
kinds of things that
you can see on it.
The Ice Age Trail
is in red here.
And the Ice Age
Trail was established
by legislation,
congressional legislation,
back in around 1960
and also established
at that time were nine
Ice Age Scientific
Reserve sites, and
you can see those
numbered sites on
the map as well.
I'll mention a
couple of them as we
go along here, in
particular I'll mention
number nine, which
is the one closest
to where we are now.
But as you can see, the Ice Age
Trail starts up in
here in Sturgeon Bay,
runs southward down
a feature called
the Kettle Moraine
that I'm going to
describe in a minute,
and then for the
most part, across the
rest of the state,
it follows a feature
called the moraine.
And a moraine is
a ridge that forms
out at the edge of
a glacier, so this
conveyor belt of a
glacier is bringing
material out to the
edge, the ice melts
and the material gets dropped.
If the edge of the glacier stays
in one place for
a while, then that
material can pile up
and produce a ridge.
So what you're looking
at in this photo
from Greenland is
a ridge on the left
side which is labeled N Moraine,
most oftentimes we just
call them moraines.
It's a ridge that was
deposited when the
edge of the glacier
was sitting out there
for a while, now the
glacier is retreating
and what you're
seeing on the edge
of the glacier is
debris-covered ice.
So that's covered
with rock and soil
material that's melting out.
If the glacier edge doesn't sit
in one place for a while, if it
keeps retreating,
then it will just
deposit a more or
less equal thickness
of material and you
don't get a moraine.
So you only get a
moraine when the
edge of the glacier
stays in one place
for a while, that's what
the moraine indicates.
Oftentimes moraines
end up having
lots of buried glacier
ice underneath.
So you're looking
at, again, the edge
of a glacier in
Alaska and the edge
of the glacier is
really out here.
All of this area
in here is covered
by sand, and gravel,
and rocks, and so on.
It looks like this
if you're down on it.
You see a couple of
people in there for scale.
And yet there's glacier
ice under all of this.
And this material is
slowly melting out.
The ice is melting
out and the material
on that ice is collapsing.
It's sliding off the
slopes into this pond
and then, if there's
ice under the pond,
eventually that will
become a high spot
and material will
slide off that.
So this material is
slipping and sliding
around on the surface,
and then oftentimes
when that happens,
the last pieces of ice
end up melting out and
producing a depression.
So here you could
see diagrammatically
a couple of pieces of
ice that are partly
buried by debris,
the debris melts out
and it produces these
features called kettles.
And we have thousands
of kettles in Wisconsin.
If it weren't for
kettles, we wouldn't
have a tourist industry,
well Door County
would still have a
tourist industry but
up there in Vilas
County and so on,
all of those lakes
are kettles and of
course when you think about it,
southwest Wisconsin,
which was not
glaciated, it's called
a driftless area,
doesn't have lakes, right?
I mean it doesn't
have lakes like
Vilas County or Oneida
County or so on.
So these kettles
are very important.
And in moraines, they're
abundant and deep.
So this is in Langlade
County north of the Antigo.
The Ice Age Trail runs
right through this
landscape, you can't
actually see the trail.
But lots of ups and
downs, ups and downs
through these
kettles, some of them
water filled, some
are dry, but thousands
of them across that
part of the landscape.
So across the northern
tier of counties here
that's characterized
by having very deep
kettles and so on, and
let's see if I can go
back to that, and
then down here, as
we get down closer
to Baraboo and down
toward Madison,
there are kettles
but they're not as deep.
They're much deeper
in northern Wisconsin.
The other part of
the Ice Age Trail,
other than the one
following the moraine,
is one that runs from
down in Walworth County,
down here, and follows
what's called the Kettle
Moraine, up to Door County,
or almost to Door County.
And this is actually
the boundary between
two lobes of ice, so
ice, as it was flowing
plastically, was controlled
by the landscape it
was going over, and
it came down the Lake
Superior basin and
then down into the
Lake Michigan basin,
and then down the
Green Bay a little
bit, Green Bay Basin.
And we call those
lobes, so the Green Bay
lobe came down to
Madison, for instance,
the Lake Michigan lobe
went way down into
Illinois, down past
Champaign Urbana.
So the lobes were
being created by
the underlying
shape of the land.
But where the lobes
came together,
they produced this
feature called
the Kettle Moraine
and the Ice Age
Trail is very well
established there
because lots of
that was public land
to start with, state
forest and so on.
This is just a piece of
it to get you oriented.
Up in the far left
corner of the map
is the corner of Lake Winnebago.
So we're looking
at-- well let's see--
Campbellsport is down here at
the southern--
Yeah, so Campbellsport
is right here, Highway 67--
there's an
Ice Age Visitor Center
here on Highway 67.
And the feature
that you're seeing
running through that map
is the Kettle Moraine.
It's characterized
by having sort of
two ridges in many
places, much like
this moraine forming
between two lobes
of ice in Greenland.
So you can see
there's a lobe of ice
here and another one over here.
And where it comes
together, there's debris
and that's because the two lobes
are bumping into
each other and the
debris they're carrying is being
brought up to the
glacier surface.
And so we ended up with lots of
debris up on top
of the ice surface
and as that debris
melted out between
these two lobes, I
mean the ice melted
out between the
two lobes, we ended
up with a kettle
moraine, that in many
places, especially
in the North here,
ends up being sort
of a double ridge
with a low area in
between that has
glacial features that
are fairly spectacular
and for which the Kettle
Moraine is well known.
One of these features is called
a moulin kame.
A moulin is a
circular, cylindrical
hole in the ice
that collects water,
and mud, and debris
that falls down it.
This is a moulin here in Iceland
and here I'm hoping the students
aren't going to fall down it.
They're seeing who
can get closest
without slipping in,
that kind of thing.
But at the bottom of the moulin
this is what debris
that comes down,
it's water, and
mud, and rocks are
tumbling down and forming a
cone-shaped hill at the bottom.
And these are
common around modern
glaciers as small
features, this one
that you're looking
at is only 10-feet
high or so, but in
the Kettle Moraine,
these are world-class features.
Look at the size of
this one, for instance.
Look at the barn for
scale, that whole
hill is a moulin kame.
So, presumably the ice was
considerably higher than
that, lots of gravel
on top, dropping
down, holes in the
ice to produce these.
And this is a map,
a topographic map
of that area east
of Campbellsport.
And let's see, yeah,
so these dark places
here are places where
these moulin kames are.
And these are world
class, they don't
know of any place
in the world where
there are more,
bigger moulin kames
than you see here,
especially in the Northern
Kettle Moraine, but not
just in the Northern
Kettle Moraine, they're
certainly in the
southern part of the
Kettle Moraine as well.
Lapham Peak for instance
just south of I-94
some of you may have
been to is a moulin kame.
All that water that goes
down through the ice
has to go somewhere, and
it goes through tunnels
like this under the
ice, and oftentimes the
tunnel just remains
empty, but sometimes
the tunnel fills up or
partly fills up with sand
and gravel deposited
by the stream.
And when that
happens, we're left
behind with a ridge
that's called an esker.
Eskers are fairly
common, especially in the
Kettle Moraine and in parts
of northern Wisconsin.
This is one outside
of Campbellsport.
There's some pretty
nice ones in, oh gosh,
western Ozaukee County,
and over into the
Kettle Moraine west
of there.
southern Kettle Moraine has
some and they're
across northern
Wisconsin, as well.
Here's another
one, a smaller one.
So these are ridges of
sand and gravel deposited
by a stream flowing
underneath the glacier.
The Ice Age Trail
follows the tops of these
eskers in a number
of places, this is in
northern Wisconsin,
northwest Wisconsin
actually, up in well
north of Chippewa Falls.
A spectacular esker to hike on.
Whitewater Lake has
eskers running through it.
This is an air-view
of Whitewater Lake,
and all of those winding
ridges are eskers.
So those again are
tunnel fillings,
gravel tunnel fillings.
Yep.
I want to point out
another thing that
happens underneath the ice.
There's these tunnel fillings,
but also back under the glacier,
the glacier is sliding along and
streamlining the landscape.
Okay, it's streamlining whatever
is there, and it
produces elongate hills
like this, that hill
is called a drumlin.
And drumlins are
not stream deposited
in the tunnel, that's an esker.
Drumlins are basically
hills that are
shaped by the ice,
sometimes they
contain some sand
and gravel, but
oftentimes they're
actually glacial deposits.
A material called
till, but they're
elongate hills,
they're shaped by
the flowing of the ice itself.
So they show which way
the ice was flowing.
Sometimes they're
long and narrow
like this, sometimes they're
more equidimensional.
This one is in Jefferson
County, east of Madison.
All right, y'all
still with me here?
(laughter)
All right, so next
time you have a
chance to drive
for instance from
here toward Madison,
when you hit
Beaver Dam, you
start to see these
long drumlins, and
you'll see drumlins
going parallel to
highway 151 all the
way down to Madison,
they're dramatic.
Or if you drive
from Madison, east to
Milwaukee, you're
crossing across them.
So there are many in
that part of the state.
There are also drumlins in
northern Wisconsin, as well.
Well, the thing I want to finish
up with is glacial lakes.
Lakes were very abundant
when the glacier
was here, including a
large one that sat in
the area to the west
of where Lake Winnebago
is now, called Glacial Lake.
I don't know why that
always goes that way.
And that was called
Glacial Lake Oshkosh.
Was extensive, and
if any of you have
driven down around
Appleton in that
area, flat ground
down there and that
flat ground is lakebed
from this Glacial
Lake Oshkosh.
So take 41 down
through around Appleton
and down to Oshkosh
and Fond du Lac,
you're on that flat lake
plain all the way along there.
Lake Michigan itself
was at a higher level
at times in the past,
so for instance the
lowland where say
Two Rivers is was all
under water at that
time, and parts of
the area here around Door County
were under water at that time.
Other times Lake
Michigan was much
lower than it is
today, and we had
rivers flowing from Lake Oshkosh
across the Door
Peninsula and down
into Lake Michigan.
And one of those,
there were a number
of them to the south
here in the Kewaunee River
and so on, but one of
them was Sturgeon Bay
which we are sitting along,
very close to tonight.
The final event in
northeast Wisconsin
was the glacial
advance that deposited
a reddish clay deposit
like this and it's
well exhibited along
the shoreline of
Lake Michigan,
right on Manitowoc
County, Kewaunee County line.
And this is a 14,000-year-old
buried forest.
It's wood, mostly
Spruce, that was growing
and then buried by a
late glacial advance
that came into this
area, went as far south
as the north end of
Lake Winnebago and down
to Two Rivers, and crashed
into a Spruce forest.
So by that time
climate had warmed,
we had forests
growing here, and the
glacier re-advanced
into that, and you
can find pieces of
wood, the wood is as I
said about 14,000 years
old in calendar years.
And it's not petrified,
you could put it in the
fireplace and burn it
just like any other wood.
Here's a rooted
stump, and I've seen
logs, and I think Al
Schneider, who was
a glacial geologist up
there in the Au Dans
has seen them too, up
to like 20, 30-foot long
logs of this Spruce
logs splayed out by the
glacier as it came
into that forest.
So as the glacier
retreated the final time,
lake level here was
higher than it is now.
And the land was
depressed, and so lots
of Door County was
actually under water.
And there are shorelines
that run around
the high parts of Door
County that indicate
those times of
higher lake level.
And if you go up to Potawatomi
State Park, which
is just outside of
town here, this is,
you see the tower
is labeled in that
slide, and there are
raised shorelines,
if you follow the
Ice Age Trail from
its terminus at
the tower, heading south as if
you were gonna march all the way
to Minnesota, one of the first
geologic features you'll see are
these high shorelines that have
been cut into the
dolomite bedrock.
And in this view
from air-born what's
called lidar, you
can see not only
drumlins here on
the west side of
Sturgeon Bay, see
those are indicating
the ice flow direction,
but also very
nice shorelines
here and of course
Sturgeon Bay is this
feature right here.
So with that the
climate was warming.
We quickly went into
a forest vegetation.
We had Paleo-Indians
here by that time.
There were almost
certainly Paleo-Indians
hunting mammoth and
mastodon all along the
ice margin here when it
was here that last time.
So I will leave you
with that thought and
we've got a couple minutes
for your questions.
