Chris Carosa

Previously: How Ice On The Rocks Reveals Our Destiny (Part I) |

You wouldn’t be here if it weren’t for the glaciers.

No, really. You might be somewhere, but you wouldn’t likely be here.

And you can thank the glaciers for that.

You can’t live in Western New York (in general) and our area (specifically) without recognizing the significance of the glaciers. Our neighborhoods contain the remnants of drumlins, kames, and other glacial debris. You see it in the eskers you walk upon in Mendon Ponds Park. You see it in the cobblestone houses that dot our landscape. In fact, you see it every day, only you probably don’t notice it.

As the once majestic Acadia range eroded into what is now the Greater Western New York region, it buried the marine flora and fauna, leaving the fossil record we see today. But it’s not as easy as that, for intervening events would bury these treasures deeper beneath the surface.

“An awful lot of this is later covered by sediments trapped by the glaciers,” says George McIntosh, Paleontologist, RMSC (Emeritus) who specializes in the geology and fossils of the Devonian Period. “The giant continental glaciers that came in here starting about 2 million years ago, or so. But there are some good exposures. People from all over the world – from China, Australia, Europe, and certainly people from North America – come to Western New York to study our fossils in our rocks. There’s good exposure obviously down at Letchworth and there’s good exposures in a variety of different places.”

The Grand Canyon of the East – Letchworth State Park – stands as a testament to the forces of nature that ultimately guide our lives. The gorge itself stands as a monument to nature’s relentless fury – not just the Genesee River’s role in eroding the various Devonian Period (remember that?) shales, sandstones and siltstones. It’s something bigger, something stronger, something with powers and abilities far beyond those of mortal men!

“In this part of New York State, everything above the Devonian Period has been eroded from this part of the world by early rivers, but more recently by the glaciers during what we call the Pleistocene Period or the Pleistocene Era,” says Professor Richard Young (Distinguished Service Professor, Emeritus, SUNY@Geneseo). “And that’s divided into many sub-partitions when the ice advanced across this region, probably at least 10 times roughly every hundred thousand years. But the Pleistocene as it’s defined today is approximately 2.6 million years old.”

Much of the topography we see around us today emerged from beneath the retreating glaciers during the most recent Ice Age. It wasn’t a singular event, but a series of actions over tens of thousands of years.

“The last ice advance during the Pleistocene is called Wisconsin and the Wisconsin is divided into three parts, the early Wisconsin, the middle Wisconsin, and the late Wisconsin,” says Young. “What you see around you and the landscape was all formed pretty much during the late Wisconsin. That was when the ice advanced all the way down to Long Island approximately 25-30,000 years ago.”

Ultimately, two geological forces sculpted the land around us. The pure weight of the mile high ice crushed and depressed the entire landmass and smoothed the ridges. This caused Lake Iroquois – the larger predecessor of Lake Ontario – to empty into the Atlantic Ocean through the Mohawk River rather than the St. Lawrence River as it does today. It’s also why the northern topography of Western New York is much smoother than the jagged landscape of the Southern Tier.

At the same time, moving water chiseled into the earth and carried debris to create new landforms – moraines, eskers, drumlins, kettles, and kames. As the glacier melted its way back to Canada, it unveiled a new landscape, one which would reveal our fate.

“Approximately 16,900 years ago the glacier was in Dansville,” says Young. “Then it slowly retreated northward across the State for about 4,000 years. In the process it created a series of ridges that run east-west. Those regions are places where the ice temporarily was still – it was melting, at the same rate that it was advancing. So it dropped a lot of sand and gravel and there are roughly a dozen moraines between Pennsylvania and Lake Ontario.”

You may recognize some of these familiar features.

“One of the moraines runs through the University of Rochester and that’s called the Pinnacle Hills, where all those radio towers are,” says Young. “One of the more interesting features that formed, along with the moraines, is a whole series of other irregular land forms. We have small ponds which form where ice blocks melted. And we have piles of sand and gravel called kames. Kames are simply places where piles of sand and gravel were dumped more than elsewhere, so they stand above the local landscape. But the moraines are these long ridges and a fairly complex sequence of moraines, kames and kettles formed at the location known as Mendon Ponds.”

Not only do the glaciers reshape the earth, but they can also change the course of mighty rivers.

“The Genesee Valley is formed mostly by the Genesee River, but not only by the modern Genesee River,” says Young. “There was a series of rivers over the last 2 million years. And each time there was a glacier advancing from the north, that would be followed by a reformation of the River after the ice melted.”

“The present course of the River is very complicated,” continues Young. “There are old valleys, like the one at Dansville, and the one through Nunda from the south end of Letchworth Park and Portageville to Nunda. And the newest part of the River system is Letchworth Park, and that’s clear because it’s formed in bedrock.”

We can identify the newly established river paths by the lack of sediment on the ancient rock.

Young says, “The signature for young valleys in this part of the world is that they are formed in bedrock are the ones that formed after the last ice melted. The Genesee River formed a new course that it hadn’t occupied before entirely and that’s the one through Letchworth. Then it continued on past Geneseo and through to the area of Rochester.”

But that’s not the way it used to be.

“There’s also an older channel that is often discussed in the literature and that’s where the Genesee River turns to the east in the area of Rush and then flows north into what is today Irondequoit Bay,” says Young. “But that probably happened more than once, and each time the ice advanced, it made the valleys a little bit bigger or shaped them or carved them a little bit deeper so that some of them are actually below sea level, or at least the bedrock of the valley is below sea level. Since the last Ice Age roughly 13,000 years ago, the Genesee River has never flowed to Irondequoit Bay, although it did, in the long ago distant past and maybe more than once, but the present day channel is the one that formed as the ice retreated northward and the River ended up flowing through Rochester.”