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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.
Deep lakes, waterfalls, shale, salt deposits, drumlins, and gorges—the unique landscapes of the Finger Lakes captivate locals and tourists alike. In a Chats in the Stacks talk given at Mann Library Matthew Pritchard, professor in the Department of Earth and Atmospheric Sciences (EAS) discusses the book “Gorges History: Landscapes and Geology of the Finger Lakes Region” (Paleontological Research Institution) by the late Art Bloom, also a professor in the Department of Earth and Atmospheric Sciences (EAS), who introduced generations of Cornellians and other inquisitive minds to our beautiful landscapes and the powerful forces that formed them. Pritchard shares some of the fascinating geological stories of the area and discuss the collaborative effort he led to complete the book after Bloom’s passing in 2017.
