SPEAKER: This is a production
of Cornell University Library.
MATTHEW PRITCHARD: Thank
you, Mary, for that kind
introduction, and thank
you guys all for coming out
to hear about this
talk on this snowy day.
But let's get into it.
I'm going to try to
give you a little bit
of an overview of how this
project and book came to be,
and some--
just give you a couple of
vignettes from Art's book
to hopefully pique your
interest into reading more
about his excellent writing.
So I'll just start
by showing you
a picture of Art
on a field trip.
So when I first arrived
here at Cornell in 2005,
a colleague named Don Banfield
from the astronomy department
and I really were
interested in learning more
about the local geology,
and Art graciously
agreed to take us on a
couple of field trips.
I think a couple
people in the room
might have gone on some
of those field trips too.
This is a picture of us up on
Harris Hill, down by Corning,
with Art showing
us some of the maps
and talking about
the discussions.
And out of that discussions,
through the field trips,
we talked a little
bit about the fact
that he was working on a book.
And we'll talk a little bit
about how that book finally
came to be published last year.
But to get to the point of
making that book get published,
we have to thank
a lot of people.
Some of them are in the room.
So first of all,
I'm going to thank
Donna Bloom, who is in the
audience, who was Art's wife.
And their family helped
us to realize this vision.
And lots of other people
helped to pull together
images and graphics
that I'll show you.
So in this book that
we have, it turned out
to be a full color book we
were able to publish thanks
to the work of the
Paleontological Research
Organization, and the figures,
I think, look fantastic.
In particular, thanks to help
from Jonathan Hendricks, who's
in the back of the room.
But lots of other people
helped to make the graphics
in this room, including
some emeritus faculty.
Dan Karig is in the room.
We got help from Brian Isacks,
Rick Allmendinger, and my wife
Rowena Lohman.
Also, all in the Department of
Earth and Atmospheric Sciences
helped to make some of
the images in this book.
And so I also just want to talk
about the legacy of this book,
and the history of the public
understanding about the Finger
Lakes region.
So I have to start with a
couple of cast of characters
of older Cornell faculty
that I never met,
but that Art at least knew
personally or by reputation.
And the first thing
I want to mention
is Oscar von Engeln, who wrote
this book called The Finger
Lakes Region: Its Origin
and Nature, which was really
the best public
understanding book
available for the
general audience that
was available for many years.
It was written first in 1961.
Art Bloom helped to
reissue it in 1988.
And this was really
the best you had
available for
trying to understand
the local geology, written
by this Cornell student,
undergraduate, graduate
student, and faculty
member for many years.
But I have to say,
it's a great book.
It's got a lot of
great details in it,
but it was written in the
language of the early part
of the 20th century,
before we knew anything
about plate tectonics.
And so it really is a bit dated.
But Oscar von
Engeln's name may be
familiar to some of
you that are local.
His bequest allowed
there to be a preserve
of some glacial features
here in Malloryville.
So there's the Oscar
von Engeln Preserve,
which preserves an esker, which
is a subglacial feature we
won't talk a lot
about today, but it's
sort of a very
unique area, and so
this area was named after
von Engeln, whose name still
rings through today.
And von Engeln's teacher was a
guy named Ralph Stockman Tarr,
who was also someone who was
one of the first geologists that
really thought about the origin
of the Finger Lakes area.
And his name comes
up several times
in Art's book because of some
of the early pioneering work
that he did, and he
taught von Engeln.
And so he was a Cornell
professor from 1892 to 1912,
when he died unfortunately
at the young age of 48.
And when he died, there were
several memorials on campus
that you can still go see.
So there's the
Tarr boulder, which
is a glacial erratic
that was moved here
to campus after his death.
This is showing a picture
with Oscar von Engeln taken
in the '60s, but this monument
was put in several decades
before that next to McGraw Hall.
And also in Sage Chapel, there
is a Tiffany stained glass
window that you can go and see
showing some features here,
the glacial features that also--
remember, Ralph Stockman Tarr,
whose oral history and writings
about this area were propagated
through to von Engeln,
and Art was the next one
that carried that forward,
and updated and modernized it
that appears in his book, which
I think is really the
best available book,
and is likely to be the best
available book on understanding
the landscapes of
the Finger Lakes
region for several
decades to come.
All right.
So how do I fit in the story?
I am just an enthusiast.
I haven't done a lot of research
here in the Finger Lakes area.
I just am somebody
who has a long history
of trying to read books
about local geology,
and then trying to
communicate that excitement
to other people.
So this is an
embarrassing picture of me
at age 12 at the New York--
at the Illinois State Fair,
sorry, where I gave
a presentation,
in this case on the geology
of the Grand Canyon,
because that was a place
we went on vacation.
I read local books
about the Grand Canyon,
and I wanted to tell
people about it because it
was such an exciting thing.
And so this is a continuation
of that now, 33 years later,
learning about the
Finger Lakes area.
The geology's a bit different
than the Grand Canyon,
but still spectacular
in so many ways.
All right.
So just a little
more background,
which is how I came to help, and
we all worked together to try
to make this book happen.
So when Art was
cleaning out his office,
he donated these two
bookcases full of materials
about local geology.
All sorts of stuff that's
hard to find in print.
Newspaper clippings,
all sorts of stuff
over his several
decade-long career.
And as I was looking through
this, there was a book.
A book that had
not been published.
And it sort of started
with this thing right
here, which is a
Cornell adult university
guide that Art put
together starting in 1999
that he developed into
a draft manuscript,
and then never saw it
through to publication.
So as I looked through some of
the documents here, I'm like,
oh my goodness,
there's a book here.
And we just need to finish some
graphics, and do some editing,
and we can bring
this to publication.
And so we worked with Art
for several years about that,
and we never quite
got it done before he
passed, unfortunately, in 2017.
But just to give you a
sense of the types of things
that the team of people
we pulled together did,
is Art started with--
this is showing a
map of the New York.
Up here is Lake
Ontario, Lake Erie.
This is an idea he
had for a figure
to go in the book
that was basically
showing the outline of
where there is salt,
and how that outline of
salt below the surface
affects the topography
at the Earth's surface.
And so this was the idea.
The figure, which we decided was
maybe not the greatest figure
for a general audience.
And so with help from Rick
Allmendinger, in this case,
this figure was
remade, hopefully
in a way that you can understand
where the salt is located,
and how that's related
to the edge of where
the valley and ridge topography
is from Pennsylvania.
So the salt has a big control
on the surface expression
of folds throughout the region.
All right.
So now let's talk
a little bit just
about the meat of the book,
just to whet your appetite
for learning more about it.
So this is a question I usually
ask my class in the Earth
Science 101, and that
is, why is Ithaca gorges?
We have as our town motto that
we have this geologic feature,
the gorges.
And usually, what
students answer is, A,
glaciers carved the gorges.
And that's maybe a
common perception.
And in general, as
we'll try to tell you
by the end of the story, the
real story is more like this.
That the rivers
carved the gorges,
but the glaciers had to set
the stage for that to happen.
All right.
So we're going to talk just
about three little questions
about the Finger
Lakes area to give you
a hint of the sort
of information
that Art presents in his book.
And so we'll talk about
these questions in turn.
First of all, why are Cayuga and
Seneca Lakes the biggest finger
lakes?
How does that relate to
the underlying bedrock?
We'll talk about
what joints are,
and joints are fantastically
exposed in many of the gorges
around here.
But why are they not visible
in all of the state parks?
Why do we have joints
important in some state parks
but not in others?
And then we'll also talk about
looking at the gorges itself.
As you hike up them, you might
know some curious things.
That sometimes the gorges
are extremely narrow,
sometimes they're very wide.
And what does that tell us about
the history of those gorges.
So we'll visit those
three questions today.
All right.
So we have to start
with the bedrock.
That's where Art
starts his book.
What is the underlying rock
that makes up this area?
And we had to
understand something
about the formation of the
rocks in this area that
were related to--
this is showing a
paleogeography map.
Here's the equator.
Our area was located in
the Southern Hemisphere
near the equator, and it was
all underwater in this Devonian
time period sometime around
380 to 400 million years ago.
So we lived in a shallow sea.
Shallow tropical sea.
And in that area, the key
story that was going on
was that we were
receiving sediments coming
from the Acadian mountains,
this large mountain range
to our east.
Think of something like
the Andes mountains today
that was sending off eroding
material that was coming
west and deposited in our area.
And the key point
was that when you
were closer to the
mountains, you had
the coarser-grained sediments.
And as you get further
and further away
from that mountains, it
gets finer and finer.
So as you go towards the
Catskills, or go further east,
you're getting into
these areas that
had the coarser gravels and
the larger sediment property--
material.
And also, there would be
a thicker amount of it.
As you get closer to the
source, the amount of sediments
is thicker.
And so as you come
further to the west,
the sediments get
thinner and thinner,
and they get finer
and finer-grained.
So that's a basic story about
our bedrock and the areas,
that in an east-west transect,
the thickness of the beds
changes, and also
their composition.
So here is a picture that
shows that stack of sediments
that eroded off of this
Acadian mountain range.
So in the east here,
we have this thing
that's called the Catskill delta
that's up to three kilometers
thick of this sediments.
And it is made of this
coarser-grained material.
This should say
sandstone and gravels.
And then as you go all
the way west to Buffalo,
it gets down to one
kilometer thick or less.
And so we're here in
between in the Ithaca area.
We're in an area
where there's still
a good thickness to
this pile, but it's
starting to get into the
more fine-grained material.
And so that's going to be very
important for understanding
the erodeability of the bedrock
that might have contributed
to why our finger
lakes in the middle
here, in Seneca and Cayuga
Lakes are the largest.
All right.
So the other thing to
understand about our bedrock
is that besides the fact
that the pile of sediments
change, and the composition
changes from east to west,
there's also sort of a southward
dip to all of these layers.
Such that if you are driving
up towards Lake Ontario,
you get to go deeper and
deeper into the section
to see older and older rocks.
So the rocks that are of
Ordovician and Silurian
age of 417 to 490 million
years ago are exposed up here,
and they are underneath
our feet here in Ithaca.
And so several of
these important layers,
we'll come back to.
So interspersed amongst these
primarily sandstone and shale,
mudstone rocks,
are a few beds that
are very resistant to erosion
that are made out of limestone.
And so we'll talk about
these, the Onondaga limestone
and the Tully limestone are
two very important layers
that show up in several
of the gorges around here,
especially related
to waterfalls.
So this is just a repeat
of that basic idea
of thinking that, there's a
transition in the composition
and thickness of these sediments
as you go from east to west.
All right, so that's
the bedrock story.
The next important--
well, there's
several important events
that happened, but in terms
of thinking about the question
of excavation of our Finger
Lakes area, the next
really important thing
is to think about glaciations.
So over the course of the
last several million years,
there have been several
pulses of glaciation.
The last glacial maximum
was about 24,000 years ago.
It had this extent that--
built up a big pile
of moraines and debris
that made Cape Cod
and Long Island,
and went into a little
bit of Pennsylvania.
And there's one little
part of New York state
that didn't have glaciers,
but the rest of us
were covered in a
mile or more of ice.
And of course, that had a big
impact on global sea levels,
sending the shoreline
all the way out here
to the continental shelf.
So those glaciers,
as they came through
over these multiple
episodes, found certain areas
that were easier to
erode than others.
In this case, areas that used
to be former rivers, and the ice
preferentially helped to
scour out that material.
And so most of these areas
that are now finger lakes
used to be river channels
that have been scoured out
by the ice.
And the basic idea is that
these two biggest lakes, Seneca
and Cayuga, were
not just excavated
in terms of a large length
here, but they are also
extremely deep.
So these were really dug much
deeper than the other finger
lakes down to--
you may have heard that
many of these lakes
are already have the water
bottom that is below sea level.
But with seismic
sounding, the depth
to the bottom of where
the bedrock is exposed
is even deeper still.
So when the glaciers
came through,
through a combination of the
ice and subglacial water,
they eroded these troughs
down to values that are
several meters below sea level.
So they had this
strong erosive ability.
And the key thing
is that in this--
they found a sweet spot in the
area of Cayuga and Seneca Lakes
where there was a thick
pile of sediments,
and the sediments were of
the smaller-grained variety
than they were
further to the east,
and so they were
easier to erode.
So there was this basic
bedrock control on how easy
it was going to be for
the glaciers to erode,
and how big of a
finger lake they
were going to make at the end.
So the other interesting thing
about thinking about, well,
what controlled how
deep those glaciers
dug down into the bedrock?
Well, they basically
stopped at one
of these limestone layers that
was very resistant to erosion.
So if you look again at
the seismic sections of how
deep are the lakes,
basically, this
is a profile here of
Cayuga Lake showing
that you have the water.
Then you have this
sediment fill that
was formed during
the glacial times
and during the
post-glacial time periods.
But the glaciers
themselves stopped eroding.
Basically, the bottom is down
here at the Onondaga limestone.
And so when the
ice came through,
it easily took up this
shale-y sandstone stuff
that was at shallower
depths, but had
a harder time once it got down
to this harder limestone bed.
So most of the
finger lakes' bottoms
are controlled by this
Onondaga limestone.
And it could have been even
deeper if that limestone layer
didn't exist.
All right.
So that's at least
a story as to how
the bedrock that was formed
during the Devonian time period
controlled how big the different
finger lakes were going to be.
So the next thing I
want to talk about
is if you walked in some
of the gorges around here,
you might have noticed
features like this.
These are all joints
that were made
through fracturing of
the rock, primarily
during mountain-building
time periods when
there were large-scale
stresses going across the area.
So basically, the formation
of the valley and ridge
topography in Pennsylvania
several miles to our south.
Those stresses were still
transmitted up to us here
in Central New York.
And in fact, these joints have
been systematically mapped
throughout the area,
and show this pattern
of changing their
orientation as you go around.
That's related to
what's thought to be
this collision, basically, of
Africa with North America that
happened subsequent to the
deposition of these rocks
in the Devonian time period.
So you can see
many of these rocks
at slightly different strata--
different levels
and different ages
if you go and visit a bunch of
different gorges around here.
So we'll talk about a
couple of different ones,
and how the rocks exposed in
these gorges are different.
And then we'll also
make a journey over
to Watkins Glen State Park,
which has a spectacular cross
section that looks very
different than many
of the local gorges.
So again, the basic story as
to why we have gorges here
in Ithaca is related to
these nice series of cartoons
that were made at the
Paleontological Research
Institute for some
of their books.
And the basic idea here was that
when the glacier came through,
it cut this deep trough.
And then you had all
these poor little streams
that were dumping into that
old trough that were now
stranded at a higher elevation.
And so these streams
were abandoned up
at that higher
elevation, and they
started to erode more quickly.
And that's how you basically
created these gorges.
That basically, you
changed the base level
of where the river came into
the gorge by the glaciation,
and then the rivers have
subsequently cut these gorges
back, like this.
And so this is a
hand drawing that Art
made that we put
in the book that
shows the difference on
different parts of the Cayuga
trough of how this looks.
So here's Cayuga lake
with its surface,
its subsurface of where
it had been eroded away.
And then if you go
to different gorges,
you'll notice that there's the
different manifestations of how
these gorges had been created.
So for example, if you
go to Taughannock Creek,
you'll find a single
large waterfall
that everyone gets
the attention.
If you actually pay attention
as you're walking up,
you'll see there's a whole
bunch of little waterfalls
in the lower gorge and
in the upper gorge.
But everyone focuses on the big
one, which-- understandable.
It's beautiful.
But some of the other gorges,
there's not a single waterfall.
There's multiple cascades
as you go up the gorge.
And so that's another
thing to think about as
to why each of these
gorges is different.
So let's just show
some pretty pictures
of these different gorges.
So again, we mentioned
Taughannock Falls right here.
Here's Buttermilk Falls,
which has not a single drop
waterfall, but a
set of cascades.
Watkins Glen.
Trying to remember exactly
how many waterfalls they say
are there in the park.
More than 20,
something like that.
There's multiple
waterfalls going up there.
I just have to include a couple
of super cool old pictures
that a colleague
Bill White just sent.
This is from a book
published in 1869
that shows Taughannock looking
a little bit different than it
does today.
There was this big ledge
over there that fell.
And it'd be maybe hard to
take a picture like this
of Ithaca Falls today
because of how the trees are.
But anyway, this
is another old book
that I just learned about
that is maybe one of the first
that describes the different
gorges around Ithaca that
is available in the
Cornell libraries,
and that's where these
pictures were taken.
All right.
So the key point
is, if you go visit
a bunch of the different
gorges around here,
just really pay attention
to how the gorges are
different and
manifest themselves,
in particular in the
joints that are exposed.
Because-- so this is just
a figure from the book that
shows the different layers
that exist in the local rock
formations.
And the key point
to make here is
that if you go to
Ludlowville Falls,
you're going to be at a
slightly different level
with different formations than
you will if you go to Treman
State Park, for example.
You're going to be
somewhere up here.
And Ithaca Falls,
and Watkins Glen,
and Taughannock lie
somewhere in between those.
So every gorge you go to
visit has slightly different
aged rocks.
And that slightly
different formations
that have different strengths
and different mechanical
properties that
give you slightly
different manifestations,
for example, of joints.
So one of the key
differences is--
I think on the next slide, I got
a picture of Ludlowville Falls.
So here's Ludlowville
Falls, which
is a very different type of fall
than Buttermilk or Ithaca Falls
that we looked at before.
This is a cap rock waterfall.
And this is primarily because
of this Tully limestone,
that's particularly strong
layer locally that also forms
the first waterfall that
you see as you're walking up
the gorge at Taughannock.
So this is a particularly
strong and resistant layer,
and it forms this very
different waterfall
that keeps it
really strong that,
underneath the weak shale,
erodes away preferentially.
And as Art talks about
in the book, some day,
is this large overhang
going to fall over?
He's got some calculations
that show what he thinks
is going to happen next.
But if you look at some of the
other gorges, you can see--
again, there's not these
cap rock waterfalls.
But there's also some
pretty extreme differences.
So this over here is
Treman State Park.
This is a picture that Art took.
Very famous for
its strong control
of joints at right
angles to each other
that some people think
are sort of man-made.
But these are all
natural down here.
But if you go to
Watkins Glen, you
can hardly see
any joints at all.
You can see some, but they're
just not as well-exposed here.
And the primary reason
is both that you're
at a different level
in the local formation,
so you have a slightly
different composition of rock.
And also, as I mentioned before,
you're slightly further west.
You have finer-grained
sediments coming off
of that Catskill delta that
don't form joints as easily.
It's finer-grained.
It's easier to-- when the
stresses are transmitted
into those rocks, it doesn't
form joints as well as
in the coarser-grained rocks
here in the Ithaca area.
So really, pay
attention when you're
walking through the
gorges to look for things
like the formation of joints,
and what the morphology
of the waterfalls looks like.
All right.
So the final point I
wanted to talk about today
is, as you're walking
up the gorges,
you might notice some
changes as you walk upstream.
And so particularly, we'll
look at Fall Creek Valley,
but the story is similar at
Treman State Park and some
of the other gorges
around here that
are reflecting multiple
episodes of glaciation.
So here is a figure that shows a
transect going from Canada down
to Cincinnati, Ohio, showing
basically the maximum extent
of ice at different times.
So as I mentioned before,
the last glacial maximum,
when we had ice all the
way down to Long Island,
was about 24,000 years ago.
That would be right here.
Then we had a period back
here, the Sangamon episode,
that was between the
major glaciations.
And then the previous
maximum glaciation
before that was
150,000 years ago.
But in between
that, the glaciers
do not just walk up to Canada,
come back down in a simple way.
There's a lot of
stutter stepping.
And so when the
glaciers are going--
especially during
the final retreat
is when we have the best
evidence of multiple episodes
of the glaciers going
back to Canada, coming
back down, and back and
forth and back and forth.
And presumably, this was
also happening before that,
but every time the glaciers
override the area, they sort of
erase their previous record.
So the key point
is that glaciers
have come and gone
from this area
multiple times over the
last several million years.
Dozens of times,
most likely, but we
really only have good
evidence for these last couple
of events.
And so what does that mean?
That means that the landscape
gets covered by ice,
and the debris that's
brought by those
glaciations again
and again, and so
the rivers have to get back to
work re-excavating the material
that the glaciers keep
dumping on the area.
And so here's just an example of
the last major glacial advance,
which we call the
Valley Heads moraines,
because this last glacial
advance has a major impact
on our local watersheds.
So this is where it was
about 17,000 years ago.
And you can see, just by
looking at the landscape, where
the edge of the ice was.
So this is showing,
basically, as you're
driving south on
Route 13, and you
go through a very rough area
as you're climbing up the area.
And then around
[INAUDIBLE] Farms,
you get to a smooth area.
And you can also see this if
you were driving on Route 81
up to Syracuse.
You are driving along a
relatively smooth area
here through Cortland
and up through Tully,
and then you may notice,
as you're driving up
to the north out
of your left side,
that basically the
valley bottom drops out.
And all of these areas are
basically the edge of the ice.
The edge of the
ice was right here.
It was right here.
It was right here.
It was right here.
And go back, you can tell
again, it was right here.
Where basically,
that edge of the ice
is very abrupt, where
it's very rough here.
This is called kettle
and cane morphology,
where there was large
rocks, and bits of ice
left behind, leaving
it very rugged.
And this is the edge of the
ice, where there was then
streams and sediments that were
coming off that were deposited
in a smoother surface.
It's a major change that
impacts-- whenever you're
driving up one of
these valleys, you
can tell once you
know what to look
for where the edge
of the ice used
to be during this last advance.
So that's what's called the
Valley Head moraine, where,
basically, this ice is dumped.
And a lot of these features
can be seen now spectacularly
with what's called LIDAR, which
is laser distance ranging.
And that has been
flown for the county,
and we have got some great
examples of this in the book.
This is just an example
showing, again, the von Engeln
Preserve in Malloryville.
This is what it looks
like in a natural view.
And the good thing
about LIDAR is
that you can keep track of when
the laser that you're sending
down from your airplane
hits the top of a tree,
versus when it hits the ground.
And so effectively, you
can remove the trees,
and you get a clearer view
of the underlying landscape.
So this is just showing you
a comparison of the two,
that I think you
can see much more
clearly the famous esker
that von Engeln loved
to take students on
trips to go visit,
as well as some of
the other kettle
and cane features in this
area because of this LIDAR
has revealed many
things in the landscape
that we could only
guess at before,
or you could only see
it in partial relief.
So here is a spectacular
example that Dan Karig
made of looking
at the LIDAR here
for an area near Fall Creek.
You can spend a lot of
time looking at this,
but you can see a lot
of glacial features here
that may not be easy
to see from the ground.
For one, you can see
that these streaks here,
where the ice took a right
turn here up the Fall Creek
valley towards Dryden, when it
was coming down from the north.
Then you can also see on here
several moraines of ice retreat
fronts as the ice was
retreating backwards.
And you can also see a couple
of eskers here in various areas,
and other subglacial features.
So the LIDAR is spectacular.
We've got some good
figures in the book.
And of course, this data
is publicly available
that you can go look
at yourself if you
want to look at your
local glacial features
near your house.
So we have a couple
examples here
of looking at these gorges
that reveals this evidence
for multiple glaciation.
So here is Taughannock.
That shows the lower
park down here, which
is the delta of the stream.
You have to walk 3/4
of a mile up here
to get to Taughannock Falls.
And so here's an example of
Fall Creek and Cascadilla Creek,
showing you--
we'll come back to this
issue here at Fall Creek,
that basically, if you're
walking over on the Cornell
campus, you see here's
Beebe Lake, where
the gorge is really wide.
And then you go upstream, and
the gorge becomes super narrow
before it gets into Forest
Home and becomes wide again.
Here's an example
of Buttermilk Falls.
So you may-- from the
LIDAR, you can clearly see,
here's Buttermilk Falls.
If you were going to
walk up the gorge trail,
you'd be going right here.
But the LIDAR shows, hey, look.
There's another gorge
right next to this
that you may not have
even noticed because it's
covered in trees now.
This is evidence of a
previous gorge that was cut
during a previous glaciation.
So this is one of
several lines of evidence
that, we know these gorge--
every time the ice
comes and covers us up,
it deposits a bunch of debris.
And then the rivers have to get
to work to remove that debris,
and sometimes they find
the exact same course
that they had before,
and sometimes they're
off by a little bit.
And that's effectively
what you're seeing here.
So another spectacular
place to see this
is in Tremon State Park, up
here in Enfield Glen, that you--
again, you have a
fairly wide gorge
that you would come up if you
started at the lower park.
But then you would come to
this very narrow gorge up here
at the top.
And so this is a
zoom-in of that area.
If you come in from
the top, again,
you are also in a
wide zone, and you
enter this super
narrow gorge, and then
you get back into a wide zone.
So what's the story there?
What happened?
How is that-- what
does that tell us
about the glacial
history of the area?
Well, here is the
story that we have
for understanding that area.
Here's, again, a view of the
creek that comes through here,
Lucifer Falls, and then
very narrow Enfield
Glen on top of that.
So the idea was, before the
last glaciation, something
around 120,000 years ago,
there was some sort of stream
that came through here and
had cut a river channel.
The glaciers came
through, filled it all in.
And so then after the
glaciers were gone,
a new stream was starting at the
top of this pile of sediments
and said, I got to find a new
course from myself to make it
back and drain this area.
And it didn't find the exact
same course that it had before.
And so as it starts to cut down
through that glacial debris,
it starts to--
in some places, it had found the
old gorge, but in some places,
it didn't.
And as it cuts through the
easy-to-erode glacial deposits,
it gets cut, it gets
caught in a channel,
and it can't get out when it
starts to reach to the bedrock.
And so as it keeps
the cut cutting down,
it starts to have to cut a
new gorge into the bedrock
in these very narrow zones.
So that gets us to
where we are today.
So this is that narrow
gorge that has just
been cut over the course
of the last 15,000 years
or so, while the upstream
and downstream at this point,
the river had found
its old course,
and so it was able to make
hay down in those areas
because it was
easy for it to cut
through the glacial
deposits, as opposed
to cutting through bedrock.
And so we see that again
and again in various gorges.
So going to Enfield Glen
is a spectacular place
to just see this whole
history laid bare.
You can see the shale
and sandstone rocks
that were deposited during
the Devonian time period.
You can see the joints that were
formed in the late Paleozoic,
during this mountain-building
process down in Pennsylvania.
Then you can see the gorge
that was cut in the last 15,000
years.
And then of course, you can
see what the Civil Conservation
Corps and others have done
so spectacularly to make
it accessible to us today.
Just to mention one other
point, buried gorges
exist all over the state.
A spectacular example
is in the Niagara Gorge.
You might have noticed, if
you've been to Niagara Falls
and walked down the
gorge, that there's
a whirlpool basin that
they send boats down there.
That is part of a buried
gorge that exists here.
So it's the same story
in Niagara Gorge, where
multiple times,
the landscape has
been covered by glaciations.
Gorges have been filled up.
The Niagara River doesn't
always find the exact location
that it used 100,000
years previously
during the last
interglacial time period.
And so in this case, as
it cut this new channel,
it found a little
bit of the gorge
and made this little side
thing, but there is--
the next time
around, when we get
covered by glaciation again
at some point, if we do,
that maybe it will find
that previous gorge.
All right.
And so again, there's
the story here.
In Fall Creek valley,
it's the same,
that there used
to be a gorge that
ran like this through Forest
Home, through Beebe Lake.
And when the Fall Creek started
to cut through here again,
it was going in a slightly
different direction
and had to cut new bedrock.
And so you'll see a much
narrower gorge, basically,
between Forest Home
and Beebe Lake.
All right.
So the final point
I have to mention
is, a question I
sometimes get is, well,
that's all a nice story.
Who cares about any
of this local geology?
Well, let me just give
you two reasons to care.
And that is that there's
an economic impact
from all of the local geology
that we have in the area.
One of the basic ones
is the most important
economic resource that comes
from geology is aggregate.
You may not think
about aggregate a lot,
but gravel, sand, we
couldn't build anything
without those materials.
We need gravel and sand
pits all over the place.
The glacial history of this
area helped to refine and build
deposits of that material.
Some people also don't
know that there's a salt
mine underneath Cayuga Lake.
And so there's a salt mine there
because during an earlier time
period, during the Silurian
time period, before most
of the local rocks
were deposited,
there was also a sea
that was in the area that
evaporated and left
behind huge salt deposits.
So this is why Syracuse
is called the salt
city, because it's where
the salt deposits reached
the surface.
But here below our
lake and Cayuga--
beneath Cayuga Lake,
beneath Seneca Lake,
there are either
mines, a physical mine
beneath Cayuga Lake, and there
are wells beneath Seneca Lake.
And there are also wells all
over Central New York that
have either found natural gas,
or have been used for storage
of natural gas, or for-- there's
a geothermal well up by Auburn,
and there may be future
geothermal wells if the Cornell
Earth Source Heat
Project goes forward,
as well as these brine
wells I mentioned
at the southern
end of Seneca Lake.
So that's at least a reason to
care about the local geology.
All right, so let
me just wrap it up.
If you fell asleep, here's
the answer to the questions
I posed.
Why are Seneca and Cayuga
Lake the biggest finger lakes?
Well, the primary
story that Art tells
in his book-- maybe
some people disagree--
is that it all has to
do with the bedrock.
That we were in an area
where there was very thick
sediments, and those sediments
were relatively fine-grained
compared to the sediments
to the east of us
or to the west of us.
The joints are of
varying importance
in the various local
bedrocks because there
were changes in the bedrock
as you went from east to west.
Watkins Glen has fewer
joints because it's
made out of finer-grained
rocks than we
have here in the Cayuga Basin.
But again, it varies even from
walking up and down one gorge,
you'll see joints more
easily exposed in some layers
than in others.
And then why are Fall Creek
valley so wide at Beebe Lake
but narrow upstream
and downstream?
That's one line of evidence for
multiple cycles of glaciation,
of covering the
landscape, and then
having to re-excavate it
through the process of erosion
from rivers.
All right, so there's a
lot more interesting things
in Art's book.
This is just really
scratching the surface.
But I also will say that
there's a lot of mysteries
that still remain.
Even though this has been
studied for over 100 years,
there's new discoveries
being made all the time.
I'll just mention, Dan Karig has
got a lot of interesting papers
from the research that
he's doing right now.
Not all of it--
maybe a lot of it--
doesn't agree with everything
that Art wrote in his book.
But that just is
indicating that we still
have a lot to learn
about the finger lakes.
So with that, I'll end and
take any questions you have.
Thanks.
[APPLAUSE]
AUDIENCE: I think--
I believe that right down
here, botanic gardens
is in a plunge basin
from a glacier.
If that is true, water
flowing up, and--
right down.
Is that true?
And you didn't highlight
a plunge basin.
MATTHEW PRITCHARD: Yes.
Well, that's a good
question, and there's
a lot of interesting--
so I guess that the short answer
is, I don't know for sure.
But I think it's an
interesting question because--
because we have so many
construction projects here
on campus, we've
had some students
who have started to look
into what we learned
from the boreholes from
those construction projects,
and trying to make a overall map
of where buried gorges might be
on campus, and where
certain areas might
be-- as you say-- deeper
because they had a plunge pool,
compared to some area further
upstream or downstream.
So I guess in short,
it's my ignorance.
I don't know if we've--
we haven't compiled that
yet on a campus-wide basis,
but the records exist over in
the facilities in the Humphries
Building.
And we've had some students
get started on that,
but we haven't quite
finished that to truly make
a map of what we know from
certain areas of campus having
bedrock at a much deeper
level than we would expect
compared to adjacent areas.
So there's clearly,
across campus--
I wouldn't be surprised if
there was a plunge pool there,
and if there were plunge
pools on the arts quad,
where they found-- again, as
those buildings had been built,
bedrock is at deeper
levels than they expected.
Yeah, go ahead.
AUDIENCE: Is there
any particular
reason that these
are finger look like,
not like network of
vasculature or something?
MATTHEW PRITCHARD: Yeah.
Let's see if I got a
good picture of that.
So basically, all of these
gorges are old river basins.
So there is sort of a network--
I really should just go
back to the first slide.
Let's see.
That's it, maybe--
I think this one.
Yeah, maybe this
sort of shows it.
In fact, you can see
remnants of old river--
this is Salmon Creek.
You can see that this is a
tributary that comes together
for a stream that used to
be flowing to the south.
You can just see that by
looking at the landscape.
And so there was an idea that
there was some separate stream
that was a couple streams that
were flowing here to the north.
And you can see that
even from Cayuga Lake
too, sort of is a tributary
that goes to the south.
And so the idea is that the
ice, when it came through,
just found these
troughs that existed
from the previous rivers,
and exploited them.
And so that's why-- it cut
them deep and connected them.
Ones that might have
previously drained
in two separate
areas, the glacier
came through and
just beveled what
used to be the drainage
divide, and connected it
together to make this
longer finger lake.
And so that's the idea, is that
there was a previous landscape
here that was primarily
controlled by rivers that
basically just got trashed and
beveled in the river basins
to make these
longer finger lakes.
Good, you had a question.
AUDIENCE: One I've been
wanting to ask for years.
[CHUCKLING]
MATTHEW PRITCHARD: I might
not be able to answer,
just to warn you.
AUDIENCE: What causes those
perfect right angle fractures?
MATTHEW PRITCHARD: Mm.
So they're not
always right angles.
And so where they
are right angles,
it's really just a coincidence
of having two different forces
coming together to make it.
And so let's see if I can
go back to the slide that
shows the fractures.
Yeah, here we go.
So again, one of the
sets of fractures
is related to the collision
of Africa with Pennsylvania,
and the rest of North America,
that basically sent the stress
pattern such that you--
that's why these
things rotate around,
just like the mountains
do in Pennsylvania.
So that's what
this set of joints
is related to that
collisional process.
And that's why you see
this rotation around.
So that's one set of joints.
What about the
perpendicular ones?
Well, again, if you go
into different gorges,
you will see that they
aren't always perpendicular.
But some places that they are--
and Treman is one example--
where the other set of
joints is often related to--
what these dotted
and dashed lines are
is another manifestation
of that collision
is building a set of folds.
Down in Pennsylvania, they
are super close together
because they're
not above the salt.
But up here, because there's a
layer of salt under the ground,
it sort of affects that
wavelength of the folds.
And so you can imagine at
the top of those folds,
you form another set of joints.
And so the places where,
based on the geometry
of that collision and the
formation of these folds
that allows that
second set of joints
is that they can
be perpendicular.
So it's really just
a coincidence--
because you can see
in some other areas,
they're going to be at a
slightly different angle.
But where they are
basically perpendicular,
it's just these
two sets of forces
that are making the joints
were such that they formed them
at right angles.
Yeah, go ahead, Bill.
AUDIENCE: Very nice talk, man.
Could you go back to your
picture of Niagara Falls?
MATTHEW PRITCHARD: OK.
[CHUCKLING]
All right.
I haven't been to
Niagara Falls in a while.
Maybe I set myself up for a--
AUDIENCE: No, you didn't.
[CHUCKLING]
MATTHEW PRITCHARD: All
right, let's keep going.
AUDIENCE: Near the end.
MATTHEW PRITCHARD: Let's see.
Almost there.
There we go.
AUDIENCE: So see where the
river-- current gorge takes
a bend at Whirlpool
State Park, and you're
suggesting there was a
buried gorge that went off.
There's also a big bend at
the end of the Niagara River
where the current large falls
are, which begs the question--
MATTHEW PRITCHARD: Is there
something that goes like that?
AUDIENCE: Yeah, and
then that extend over
underneath Niagara
Falls, Ontario.
Is there a buried gorge
under there, maybe?
MATTHEW PRITCHARD:
I do not know.
We'll have to ask the Canadians.
[CHUCKLING]
But sometimes-- yeah, that's a
good question, as to whether--
is there a former
trajectory that
went like this that allows
you to come in this direction,
or what is there-- is there
some other factor that's
controlling that?
But again, there
were a series of--
the Great Lakes themselves
are old river basins that
have been essentially cut, and
so it wouldn't surprise me,
I guess, is what I would say.
Yeah, go ahead.
AUDIENCE: I assume that the
thick layers of limestone
are pretty stable.
But what is the possibility
of an earthquake
in this part of the world?
MATTHEW PRITCHARD: OK.
Well, so in addition to the--
so you need two things
for an earthquake.
One you need is
some kind of fault.
And we have lots of these
joints all around us.
And then you also need
some source of stress,
and stress change.
And so because we're
very far right now
from any plate
boundaries, the stresses
are relatively uniform
across our area.
And so we do not have many
earthquakes in New York state.
There are a couple.
There's one out in Attica.
I believe it was in the '30s.
And then there's a couple in
the Adirondacks that happen.
And so there's a huge fault
in Western New York called
the Clarendon-Lifton
fault that's sort of I
think where the
Attica earthquake was.
And I'm not sure if there's
a good understanding of what
the source of stress is there.
In the Adirondacks,
there's an open question
as to why the Adirondacks
exist, and are they
currently uplifting.
And so there's at
least a question there
that there might
be-- the Adirondacks
might continuously be
uplifting right now.
But here in Central
New York, we don't
think that there's any
large source of stress,
and there's no real large
earthquakes above magnitude 3
that have been recorded.
But in fact, we have
a seismic network
that we put out right
now of 15 stations
where we're trying
to better record
those local earthquakes that
might only be magnitude 1 or 2.
And so hopefully
in a year or two,
we'll have a better answer
to the question of where do
earthquakes occur here locally.
But as of right now,
basically, in Tompkins County,
there aren't many.
Yeah, go ahead.
AUDIENCE: So I
have about 15 feet
of the Tully limestone exposed
in my property in Lansing.
And I've noticed that
about five feet up
from the base with the
Moscow shale, there's
a very weak seam
where the glacier was
able to break many feet--
around 50 feet off
the top layer off
before you have another cliff.
And when I pried up the
limes-- and you have
several weak layers like this.
And when I pried it
apart, I got my hands
on some of this material,
it's much softer
than either the Moscow shale
and the shale up above.
And furthermore,
there's sometimes--
the biggest may be an
inch, and some are really
about a 1/16 of an inch.
And there aren't that many.
And you're looking at millions
of years across the 15 feet,
but you only have a few
of these events, really.
Maybe five or six
that are major.
So my question is,
what was happening back
with Devonian era, where it
was just steadily building up
limestone, and then bang, you
have this very different layer
of this other material.
Is it like a volcanic
eruption, or?
MATTHEW PRITCHARD: That
is a great question.
And I've never really
gotten a good answer
to why the Tully
limestone exists at all.
So just think about this.
Why does the Tully
limestone exist?
Because you're in
a Devonian sea.
You're in a relatively--
it's not a super deep sea.
Maybe a few tens
to 100 meters deep.
And you have all
this, again, debris
that's coming off the Acadian
mountains to the east.
And all of a sudden,
you form a limestone,
which usually forms in a
much shallower setting.
And again, we have
a tropical sea here,
so that's not a huge surprise.
But why do you have the
layers of Tully and Onondaga
within this bedding of
shale and sandstone?
And nobody's ever given
me a good answer for that.
So there's that
fundamental mystery.
But again, there
could be small layers.
They could be
volcanic eruptions.
Again, there were
volcanoes to the east of us
that were part of this
Acadian mountain belt.
And you can see--
I've seen some bentonite ash
beds up in the Seneca stone
quarry that's up on the
northwest side of Cayuga
Lake that are
interbedded within this.
I haven't heard of
that happening--
of these ash beds in
the Tully limestone,
but I guess it
wouldn't shock me.
The other thing it could be is
just related to large storms.
So you're in a ocean setting.
You can have large
landslides that
could come from the east that
could bring in small deposits,
either through large storms,
earthquakes that could have
could have made that happen.
So you see these are
usually called turbidites,
and you see evidence of
that in many of the--
and we talk about
that in the book.
Look up the word "turbidite."
But that could be one of the
things that could be mixing in
with the limestone.
Yeah, go ahead in the back.
AUDIENCE: If you go upstream
from Varna along Fall Creek,
in several spots
on the [? wall, ?]
there's areas that are all
blue clay along the bottom.
How did those get there?
MATTHEW PRITCHARD: All right,
well, Dan Karig is the expert.
He can tell you more about that.
Why don't you talk
to him afterwards?
Because anything I say, I'm
going to get an F on, so.
[CHUCKLING]
All right, other questions.
Yeah, go ahead.
AUDIENCE: I don't know
if this is appropriate,
but my house is right down at
the bottom of Fall Creek Falls,
and the water table under
the basement is very high.
It's just a little bit below
the surface of the basement.
If there's a whisper of a
flood, the water just comes up.
It's everywhere.
My neighbor across the
driveway, dry as a bone.
And we always have said, well,
there's underground streams.
But does this give an
explanation for any of that,
or is it just some--
MATTHEW PRITCHARD:
Yeah, it's hard to know.
Basement flooding could be
due to other things related
to construction too.
But it could be a bedrock
change, basically,
either in terms of--
because again, the point
is that it's heterogeneous,
even over a very
small length scale,
that again, you could
have bedrock exposed close
to the surface in some
areas, and right next to it,
previous times that the
stream came through,
it could have cut it through
and given you gravel there
that drains away more easily.
So what you'd want to do is
some kind of geophysical survey
where you're using, for example,
ground penetrating radar
to really try to map the
limits of where that might be.
But that would at least
be a testable idea.
Yeah, go ahead in the back.
AUDIENCE: Could you go
back to the slide that
showed the ancient equator?
MATTHEW PRITCHARD: OK.
Wow, that's a ways back.
[CHUCKLING]
We'll go high tech here and--
all the way back.
Here, I think, yeah?
AUDIENCE: And what
was the relative time
frame of that event?
MATTHEW PRITCHARD: So this
was 385 million years ago
in the Devonian time period.
Basically, this
is inferred from--
we sort of know
what the latitude
was based on the magnetic field
that's recorded in the rocks.
And so that's how you
infer paleo latitude
when the time when these
rocks are being formed.
AUDIENCE: And because
the Earth is not
an exact sphere, wouldn't
there have been a lot of uplift
because of that being
the equator, or no?
MATTHEW PRITCHARD: Yeah.
So there is a potential for--
as the plates move
around the Earth
over the course of hundreds
of millions of years,
there is a vertical
motion that can occur.
So in this case, when you're
closer to the equator,
you're going to be closer to the
Earth's equatorial bulge, which
exists in part because of
the rotation of the Earth
that concentrates
mass down there.
And so there is--
but again, this is happening
over a very long time period.
And so there's going to be--
the process of moving from where
we were 400 million years ago
approximately to
where we are today,
the process of that
long-term movement
is going to be very slow,
I guess is the key thing.
So it's true that the
area here-- and again,
Art in his book goes into this
in great detail, talking about,
well, we were below
sea level here,
and there was a
subsequent time when
there was a long-term
uplift because we don't
have any rocks
that are deposited
when the dinosaurs were alive.
And so that's one evidence
that there was some uplift that
put us above the ground so we
didn't have ocean sediments
accumulating during that time.
All right.
Any final questions?
Go ahead.
AUDIENCE: You showed
the gravel path,
and I've always wondered
where all that stuff went
from these gorges, and from
the finger lakes [INAUDIBLE]..
And thinking about Niagara,
like [INAUDIBLE] Freeville,
none of that stuff
looks for shale-like.
It looks almost like
igneous-type rock.
And in your discussion,
you mentioned that.
So could you straighten
me out on that?
MATTHEW PRITCHARD: Yeah.
So I think, again, I'll
point you to Dan Karig
if you really want to learn,
because he's dug more holes
around here probably
than anybody I know.
He's really looked
at that difference.
So again, a lot of the
local sediments that we get
came down with the
ice from Canada,
and from the Adirondacks.
And so that's why we have
these large glacial boulders
and finer-scale stuff too that
came down with the glaciers.
And that's going to
be eroded, and that's
going to be part
of the story too,
as well as some of the country
rock, the rock in situ of shale
that's going to be
part of the story too.
So depending on
the combination of,
what's the source,
primarily from the ice that
came from Canada, or is it
from the locally-eroded stuff?
In some areas,
I'm going to guess
you're going to find more
one thing than the other.
All right.
Well, thank you guys
all for attending,
and I'm glad to answer
more questions at the end.
[APPLAUSE]
SPEAKER: This has
been a production
of Cornell University Library.
