The lost inland sea that dwarfed the Great Lakes and reshaped North America
Long before Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario became the defining waters of North America, a far larger lake spread across the center of the continent. Lake Agassiz no longer appears on any map. It drained away after the last ice age. Still, its scale remains hard to ignore. More than 10,000 years ago, this prehistoric inland sea covered about 170,000 square miles, an area so vast it exceeded the combined size of the Great Lakes. That kind of size changes more than a shoreline. It helped carve valleys, fill basins, redirect rivers, and reshape the weather across a huge swath of land. Even now, the marks it left behind remain visible in the Red River Valley and in the many lakes and wetlands scattered across the region. Lake Agassiz is gone today, but during the last ice age it was a giant—sprawling across roughly 170,000 square miles and ranking among the largest lakes ever to cover North America. (CREDIT: CC BY-SA 4.0) The Great Lakes are hardly small. Lake …



