Lake Agassiz : the rise and demise of the world's greatest lake

"By comparison, today's Great Lakes are puny. But not so long ago, in North America's heartland, there was a lake so vast it swallowed most of Manitoba and surged through parts of Ontario, Saskatchewan, North and South Dakota and Minnesota. It's called Lake Agassiz and some believe it was the largest lake the world has ever known. Born of the melting sheets of ice that had covered Canada and the northern U.S. for millennia, it was a force of natu...