WRFH/Radio Free Hillsdale 101.7 FM - History Off Script - Lake Agassiz: The Lost Great Lake

Episode Date: February 2, 2026

Today the Great Lakes are a dominant feature in North America, but roughly 13,000 years ago they would have looked like ponds next to Lake Agassiz. During its existence, this massive body of water dominated the glacial landscape of northern North America, but it wasn't to last. The lake's time was finite, and its fall would shape the world.

That's how history can often feel. Mechanical. One event after the other. But what's in the fine print? What happens if we peel back the layers? What kind of hidden dramas may unfold? It's time we went beyond the textbook. This is history off script.

Here's your host, James Jock. Drowning. That is what you would be if you stood along the Minnesota-Canada border about 12,500 years ago. Under 850 feet of Fridgin's jocke. glacial water, your prospects are just as dim as the faintly lit water that surrounds you. If you make it to the surface, it will be at least 100 miles until you find land, and that's if you are lucky.

In every direction water stretches to the horizon. Welcome to Lake Agassi, the Lost Lake of North America. This is the story of its creation in dramatic fall. The story of Lake Agassi began over a thousand miles away in the northeastern islands of Canada. Here, large quantities of snow accumulated to form massive sheets of ice. As snow continued to pile at the center, the accumulated ice began to push out at its edges and flow. The Laurentide ice sheet was born.

Over thousands of years, it flowed south over much of North America consuming everything in its path. In the south, it reached Indiana, and to the east it reached the Atlantic Ocean. Entire landscapes were buried under miles of ice, and nothing could stop it. Nothing except heat. As the earth began to warm near the end of the last ice age, the Laurentide ice sheet retreated. Where once the wall of ice had plowed through the land, large earthen hills called moraines were left. As the ice sheet continued to melt, the water collected before it.

Hemmed by moraines and glaciers, the water coalesced into an inland sea. This was Lake Agassi. At its height, Lake Agassi likely covered an area the size of the state of California. and contained 30% more fresh water than all the lakes of today combined. It was the king of lakes, but its rain was destined to end. As Agassi rose, so did the pressure it exerted on the earthen banks containing it. Eventually those strains would become too great. Agassi first burst south into Minnesota,

bore in a mile-wide gap into the moraine containing it. The lake began to flow into the Mississippi. It was only a taste of it. things to come. Roughly 12,000 years ago, Agassie blasted through its banks at its northwest shore. This site would have been biblical. Water flooded from the breach at a volume as high as 15 times that of Niagara Falls. The waters gouged out the land as they raced towards the ocean. It was only the beginning. Over the course of six to nine months, five thousand cubic miles of water surged into the ocean as a large portion of the lake drained through the breach.

That is roughly the same amount of water as all the Great Lakes combined. Such a surge of fresh water into the salty oceans is believed to have disrupted global currents, causing a rapid global cooling event known as the younger dryus. And only 20 years, the earth cooled 5 degrees Fahrenheit with more pronounced cooling in the north. The glaciers advanced again, and climatic conditions harsh. But to all of this, there may have been a bright side. Halfway across the world, the drier conditions brought on in the Middle East by the younger dryus are believed to have led to the beginning of the Neolithic Revolution,

a period where hunter-gatherers began to practice agriculture and form settled societies. As conditions became more harsh, individuals were forced to coalesce resulting in organized societies, societies that would begin the progression of civilization as we know it. Eventually, the younger dryness ended. Warming continued, and Lake Agassi continued to ebb and flow as the Laurentide Ice Sheet receded into history. Today, they are distant memories, but their impact lives on in the changes they made upon the earth

and those that inhabit it. This has been History Offscript with your host James Jawsky on Radio Free Hillsdale 101.7 FM.