A History of Glaciers in Vermont
While it might be difficult to imagine that 25,000 years ago Vermont was covered by a mile thick glacier, evidence of the glaciers rise and fall have had a significant influence on the shape and ecology of our landscape. Careful observation reveals a complex story involving rattails, sea monsters, and isostatic rebound!
I wrote a blog series about the evidence for glaciers, in which I started by describing:
- an overview of glaciers in VT
- how to imagine the time scale on which glaciers operate,
- how glaciers move.
You can start there or just dive right in to the evidence…
But it is more particularly in Great Britain that the most unexpected discoveries have been made. Who could have supposed that in these islands, equally remote from the glaciers of the Alps and the ice of the north, traces of the action of ice should have been found! And nevertheless, all the phenomena which indicate the former existence of glaciers are there just as evident, and just as well preserved, as in the neighbourhood [sic] of the glaciers of the present day.
~ Louis Agassiz in The Glacial Theory and Its Recent Progress 1842
Timeline of Glaciers in Vermont
In broad strokes, the story of glaciers in Vermont goes something like this: Earth entered our most recent glacial period – the Quaternary Glaciation – about 2.6 million years ago. The most recent glaciation, known as the Ice Age (there are 12 glacial periods during the Quaternary Glaciation) began about 110,000 years ago as the climate cooled again. Year after year the glaciers advanced, on the east coast extending as far south to Long Island and down just south of to the northern border of the US out west. They reached their maximum extent 25,000 years ago, at which point the climate changed (the Barents Sea near Norway/Russia burped up some epic methane burps – article) and the glaciers began to retreat. As they retreated, the melt water formed large bodies of fresh water throughout the state, including Glacial Lake Vermont (13,500-12,000 years ago), which filled the Champlain Basin to about 620′ in elevation. Eventually, the Laurentide ice sheet had retreated far enough north exposing the basin to the St Lawrence seaway, allowing the fresh water to drain out (in a matter of hours) and salt water to slowly flow in, mixing in with the remaining water, giving rise to the Champlain Sea was born. The Sea filled the basin to about 320′ with salt water, but by about 10,000 years ago the Sea had reverted to a fresh water body of water, what we know and love as Lake Champlain (more on this later).
|2mya – present||Quaternary or Pleistocene Glaciation|
|111,000ya||Most recent Ice Age|
|25,000ya||Maximum extent of Laurentide Ice Sheet|
|13,500-12,000ya||Glacial Lake Vermont|
Evidence of an Advancing Glacier
Regardless of where on earth we are, in places where there are active glaciers that are advancing (still growing/getting bigger and pushing ice forward at the margins), we find the same features repeated again and again. A glacier is a glacier is a glacier. As the glaciers flows (yes it flows), it transforms the land leaving behind as evidence of its passage:
Evidence of a Retreating Glacier
All good things must come to an end, and as surely as they came, the glaciers left us. And in their wake they left of a whole host of new evidence from which we can reconstruct the past! There are many other features left behind by retreating – or, rather, melting – glaciers (e.g. eskers, kettle ponds, kames, isostatic rebound). And while we definitely have these here in Vermont (e.g. the Passumpsic River eskers), we’ll focus on two prominent bodies of water left behind as the glaciers melted. Here’s a short list of the evidence we see left as the glaciers retreated:
Resources for Glaciers in Vermont
- Glacial Geology of the Burlington/Colchester Quadrangles by Stephen Wright (PDF)
- Glaciers & Glaciation by Benn & Evans
- The Surficial Geology and Pleistocene History of Vermont by Stewart & MacClintock (PDF)
- The Great Ice Age in Vermont by Elbridge Jacobs (PDF)
- Written in Stone by Chet Raymo
- Longstreet Highroad Guide to the Vermont Mountains by Nancy Bazilchuk
- Lake Champlain: A natural history, Mike Winslow
- After the Ice Age by Evelyn Chrystalla Pielou
- The Geology Flannelcast
- BBC Radio 4’s Natural History (occasional stuff on glaciers)
- Chasing Ice (doc) †
- Extreme Ice (Nova doc) †
- Fastest Moving Glacier
- Men of Rock: The Big Freeze (BBC)
There are so many awesome field sites to see evidence of glaciers. Pretty much anywhere you go. For surficial deposits that aren’t till, go anywhere below 700′ (mostly the Champlain Valley). Till is above that.
- Deer Leap summit in Bristol for striations
- Shelburne Bay for glacial polish, striations
- Snake Mountain summit for striations, glacial polish
- your local quarry