We think the Great Lakes are big. But 12,000 years ago, there was a "Ghost Lake" in the center of North America that was bigger than all of them combined. Glacial Lake Agassiz. It covered parts of Canada, Minnesota, and North Dakota. The Scary Part: It wasn't held back by dirt. It was held back by a wall of ice. When the ice dam finally broke, it didn't just flood the land—it changed the world. The freshwater rushed into the ocean so fast that it stopped the Gulf Stream and triggered a mini Ice

Glacial Lake Agassiz once held more water than all today’s Great Lakes combined. When it burst, floods 4,000x larger than the Minnesota River carved the land—leaving giant boulders stranded in fields and valleys that still puzzle us today. The story of deep time is written in the stones beneath our feet. | The Randall Carlson