During the last great ice age, glaciers nearly a mile thick covered most of the northern portions of North America.
The continental glaciers grew and shrank over a period that began about 110,000 years ago and ended about 10,000 years ago. The maximum extent of glaciation was about 18,000 years ago. Its most southerly reach on the East Coast was right here on Long Island.
As a glacier moves forward, it pushes vast amounts of rock, gravel and soil in front of it, much like a bulldozer. This ridge-like mound of debris is called a terminal moraine. And Long Island was the site of the terminal moraine of the last great period of glaciation.
Drive the length of one of Long Island’s major north/south roadways and you’ll experience the terminal moraine. For example, start at Little Neck’s Long Island Rail Road station and drive south along Little Neck Parkway. You’ll climb a short, steep hill to Northern Boulevard. Keep going and you’ll ascend another hill until you get to Leeds Road.
You’ll drop down a short distance to the Long Island Expressway, but then you’ll be climbing uphill again until you reach the Grand Central Parkway. There you will have reached the top of the terminal moraine.
From there on, it’s all downhill until you reach the Atlantic Ocean. By the time you’ve made it to Union Turnpike, the land is almost pancake flat and very different from the hills and valleys of the north shore.
When our area was covered by glaciers, the moraine was much higher than it is now and sea level was nearly 400 feet lower than it is today. This is due to the fact that so much of the world’s water was locked up in the ice sheets.
As the leading edge of the glacier melted, the water running south to the Atlantic carried away much of the material in the moraine and deposited it on a large “outwash” plain.
As sea level rose when the glaciers retreated back towards the North Pole, much of that plain was inundated. The area that remains makes up the majority of Long Island.
On the north side of the terminal moraine, the melting ice occasionally deposited enormous rocks and boulders that it had picked up on its southward journey tens of thousands of years earlier.
These exotic rocks are called glacial erratics. The best known in our community is “Big Rock,” the large boulder covered with graffiti located just off the Douglaston Point.
Once the ice was gone, small streams flowed down from the top of the terminal moraine in both directions, fed by rain and snow. Each little stream carved its own deep valley into the loose moraine material.
And as the sea level rose, the incoming tide of the newly created Long Island Sound flooded into these valleys at their lower ends, creating the iconic bays of the north shore of the Island such as Little Neck Bay and its companions to the east – Manhasset Bay, Hemstead Harbor, Oyster Bay and so on.
In my next column, I’ll write about the four main streams that formed Little Neck Bay and defined the geography of the Douglaston peninsula and surrounding areas.