Professor Talks Glaciers Abroad and Here at Home

If the scourge of departing winter needs to be placed in some perspective, consider that as early as 10,000 years ago, Connecticut lay under 2,000 feet of glacier. The region’s icy past, as well as glaciers of the present, were part of the conversation when geology professor Douglas Thompson of Connecticut College spoke at Bill Library this week.

Ledyard’s Friends of the Library sponsored the talk as a part of their annual series of eight different presenters. About 30 people attended the lecture.

“A glacier is many years worth of accumulated snowfall,” Thompson told the audience, making it distinct from ordinary ice, which simply freezes from liquid water. Under the pressure of its own weight, the snow begins to re-crystallize into ice, passing first into an intermediate stage called “firn.” Thompson compared this to the dense snow found in plowed mounds at the edge of parking lots.

Thompson’s photographs of glaciers that he’d taken in Alaska, Switzerland and Colorado, showed thin lines in the ice. Each line represented a season’s worth of snowfall, compressed into mere inches.

Other photos that he’d taken included cirque glaciers, which fill out bowls along the side of mountains, hanging glaciers that plunge off the sides and ice-caps that rest atop alpine crags. Glaciers can also be “cold”—frozen all the way through—or “polythermal,” meaning that it will have liquid water beneath that helps it slide along.

The glaciers that rolled through Connecticut were far larger than any mountain glacier and constituted four separate advances and retreats. They started at about 60 degrees north latitude near Hudson Bay, Thompson said.

Over the course of 90,000 years, the heavy snowfall allowed the icy layers to build upon each other and the ice grew taller. Gravity brought it down under its own weight, bringing the mass southward.

“Ice had to build high enough to flow down to Connecticut,” Thompson said. And when it did, it came as a wall that stretched from Cape Cod to North Dakota, dragging boulders and sediment in its wake.

Thompson identified the glacier’s legacy in the shapes of local valleys, often plowed out into the characteristic U-shape. Hills in New England often go up gradually on their north sides before plunging in steeply in the south, evidence of glacial plucking, where the glacier snatches away material from the far ends of outcroppings as it rolls over them.

Places such as the Ledyard Boulder Train off Whalehead Road, are a type of glacial deposit called a moraine. Oftentimes, Thompson said, boulders will not match up with the bedrock, indicating that they had to have been dragged from elsewhere. Even the north-south tendency of rivers in the East is simply duplicating the direction of glacial flow.

Not only did this movement scour the land—“ the equivalent of a giant strip of sand paper”— but it also left deposits, which we know today as Long Island, Fisher’s Island and Martha’s Vineyard. The area that is Long Island Sound today was once a fresh-water “Lake Connecticut,” before it emptied out through The Race, between Long Island and Fisher’s Island.

“There was a time you could’ve walked upon the bottom of Long Island Sound,” Thompson said.

Moving up to the present day, Thompson told the audience that the vast number of today’s glaciers are in retreat, so much so that scientists looking to study advancing glaciers have been hard-pressed to find any.

“The most logical explanation is that the climate is warming,” he said, though he also said that the course of climate change remained unpredictable, and that he was a skeptic of climate modeling.

Retreating glaciers today could disrupt water supplies for populations living beneath the Himalayas and others that depend on glacial runoff to fill their rivers.

Melting glaciers in Greenland and Antarctica could also raise sea levels.

“Just a few feet of rise can make a big difference,” Thompson said. Ecosystems built around the water’s edge such as tidal marshes and the Everglades could be wiped out by even a small change.

In terms of a local impact, he showed pictures of Groton Long Point and Mystic Seaport, both of which are vulnerable to rising seas.

Unlike floating ice, which already displaces water, melting glaciers create a large net rise. “It’s the ice on land that will be a problem.” Thompson said.