By Kevin Selkregg
When early European explorers reached the Great Lakes, these inland seas were so large that the adventurers hoped they had found part of the famed Northwest Passage to the Pacific Ocean. The Great Lakes region represents the largest freshwater system in the world, and these five lakes were formed in part by the movement of massive ice sheets. The same power of ice can be seen today, albeit on a smaller scale.
A landform that extends over 3 million square miles from eastern to north-central Canada, the Canadian Shield is made up of very old igneous and metamorphic rocks, which form the ancient geologic core of the North American continent. Some 20,000 years ago, glaciers that were part of a large “sea of ice” called the Laurentide Ice Sheet moved southward across the Canadian Shield to the Northeast U.S. For thousands of years, this ice pack, under the weight of the accumulating snow and ice, haltingly pushed southward like a glacial plow. Thousands of feet in thickness, and massive in weight, the overlying ice scoured everything in its path. The glacial grooves on Kellys Island on Lake Erie reflect the immense abrasive power of the glaciers on the limestone bedrock. When the climate warmed, the ice melted and the glacial advance stopped. The underlying topography had been wiped away and new geologic features were revealed, including large grooves in the bedrock, valleys and hills, and the Great Lakes themselves.
Today, these inland waters are fed by a web of rivers and streams that empty into the lakes. Of the many rivers flowing into the Great Lakes, a river closer to my home is Cazenovia Creek, whose confluence with the Buffalo Creek creates the Buffalo River, which then flows into Lake Erie. Just 300 yards from our backyard, Cazenovia Creek is a place of contrasting change through the four seasons of Western New York.
Walking down a gentle slope from our backyard, the path meanders across a small brook through a grove of tall pine trees and thin maples, with fallen trees and waving ferns at their base. Approaching the creek down a steep incline, I have to struggle to negotiate my way through logs, wood piles, and thick growth. Arriving on a sunny day brings the reward of a picturesque view of tree lines on both sides, with a blue sky and puffy white clouds as the backdrop. It is not uncommon to startle a great blue heron into its graceful gliding flight down the tunnel path of the creek view. The softly running water, at its lowest level in late summer, is seemingly in no hurry to reach its destination. Coursing its way over the shale and siltstone base, the waters contain submerged tumbling pebbles and sediment, which have worn grooves and hollows in the creek floor for baby trout and minnows to find rest from the aggressive currents. The Cazenovia waters gracefully migrate around and over rounded algae-covered boulders and cobbles sitting atop the creek bed. Remnants of glacial deposits, glacial ice transported these rocks and boulders thousands of years ago from hundreds of miles to the north.
In a matter of a few months this creek is capped by a snow-covered thick layer of ice, hiding the Cazenovia waters underneath. Snowshoeing to the creek in late January is a trek made easier by the deep snow burying the underbrush. The ice surface has slowly thickened during the winter months, creating a new frozen trail that can support the weight of adventurers headed upstream or downstream. Since the summertime wildlife has vacated the area through migration or hibernation, the silence is deafening, apart from the crunch of the snow under snowshoes.
As spring approaches and the days become longer and warmer, this ice crust over the flowing creek waters does not slowly melt into the creek, but often changes in sudden dramatic fashion in a matter of a few hours. A hidden, subtle strength behind the lazy current of water manifests under the cloak of darkness. One morning in March, I found the once-thick layer of ice covering the 100-foot-wide creek broken up and jumbled in a pile of pieces on the outer creek bank like a trainwreck.
This floe did not follow the path of the creek but instead the mass of ice thrust straight through, ignoring the bend in the creek. Massive pieces of broken sheet ice piled on top of one another. Jagged shards of ice—six to twelve inches thick and ten feet across and approaching one ton in weight—formed ice layers over and under each other. The layer of this jumbled mass was nearly four feet thick, likely a massive load in contact with the ground underneath.
The cause of the break was likely the swelling creek pushing up under the ice crust due to melting snow. The sound of the breaking ice must have been deafening; indeed, icequakes have been recorded from ice breakups along the lakeshore. After the pack ice melted away, the effect of this floe of ice on the creek bank became evident. Much of the soil was stripped away, as if a plow had scraped along the ground, revealing previously buried rocks and boulders. All vegetation was removed, and saplings were stripped of their bark and bent downstream.
After observing the power of this Cazenovia pack ice, I could not help but think of the one-mile-thick glaciers of 20,000 years ago moving south with an unimaginable, massive force behind the migrating ice. Like the trees and bushes on Cazenovia Creek, not much survived the relentlessly advancing ice—geological formations were stripped away leaving little evidence of their existence. And in their place were our five Great Lakes and the rocks and fossils left by the retreating ice.
This article appeared in the Beachcombing Magazine November/December 2022 issue.