Smithsonian Magazine

The mighty Mississipp­i • Swimming the distance

The secret past and uncertain future of the great river that has defined a nation


IN 1758, THE FRENCH ETHNOGRAPH­ER AntoineSim­on Le Page du Pratz published The History of Louisiana, in which he wrote that the Mississipp­i River’s name meant “the ancient father of rivers.” Though his etymology was off—the Ojibwe words that gave us Mississipp­i ( Misi-ziibi) actually mean “long river”—the idea has proven durable. “Ol’ Man River” buoyed Show Boat, the 1927 musical by Jerome Kern and Oscar Hammerstei­n II. During the 1937 flood, Raymond Daniell wrote in the New York Times about frantic efforts to raise barriers “faster than old man river could rise.”

Now it appears that the Mississipp­i is far older than Le Page thought, and it used to be far bigger than the Ojibwe could have imagined. And it might even become that big again in the future.

These are the extraordin­ary new findings unearthed by geologists including Sally PotterMcIn­tyre at Southern Illinois University, Michael Blum at the University of Kansas and Randel Cox at the University of Memphis, whose work is helping us better understand the monumental events, beginning in late Cretaceous North America, that gave rise to the Mississipp­i, swelling it to gargantuan proportion­s.

In the late Cretaceous, around 80 million years ago, a mountain chain spanned the southern portion of the continent, blocking southbound water flows, so most North American rivers flowed to the Western Interior Sea or north to Canada’s Hudson Bay. Eventually, a gap in those mountains formed, opening a path for the river we now know as the Mississipp­i to flow to the Gulf of Mexico. Scientists call that gap the Mississipp­i Embayment, but the rest of us know it as the Mississipp­i Delta, the vast flood plain that stretches from southern Missouri to northern Louisiana. As recently as 2014, geological consensus held that the Mississipp­i began flowing through the embayment around 20 million years ago. But in 2018, Potter-McIntyre and her team concluded, based on the age of zircon fragments they excavated from sandstone in southern Illinois, that the river began flowing much earlier—some 70 million years ago. The Mississipp­i was thus born when dinosaurs still roamed the planet; one can almost picture an alamosauru­s bending its prodigious neck to drink from its waters. By contrast, the Missouri River, in its current form, dates back a mere two million years. Old Man River, indeed.

Still, 70 million years ago the Mississipp­i was nowhere near as large as it would become. Blum has detailed how the waterway grew as it added tributarie­s: the Platte, Arkansas and Tennessee rivers by the late Paleocene, then the Red River by the Oligocene. Around 60 million years ago, the Mississipp­i was collecting water from the Rockies to the Appalachia­ns; by four million years ago, its watershed had extended


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The Mississipp­i Delta, seen from space in 2001.
By The Mississipp­i Delta, seen from space in 2001.
 ??  ?? An 1832 expedition led by Henry Schoolcraf­t identified the Mississipp­i’s source as Lake
Itasca in Minnesota.
An 1832 expedition led by Henry Schoolcraf­t identified the Mississipp­i’s source as Lake Itasca in Minnesota.

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