USU Geologist Reconstructs Evolution of Mississippi River
LOGAN – Revered in song, literature and lore, the mighty Mississippi River pulses through the heart of North America on a long, winding amble. At first glance, Old Man River, aptly classified by scientists as a meandering river, reveals little of its distant past as a vast glacial stream.
Yet recent findings by Utah State University geologist Tammy Rittenour, bolstered with optically stimulated luminescence or “OSL” dating technology, support earlier speculation that glacial melt, not sea-level change, is largely responsible for the waterway’s evolution during the past 100,000 years.
“Our dating of geological deposits indicates that changes in the river coincided very closely with glacial advances,” said Rittenour, assistant research professor and manager of the USU Luminescence Laboratory.
Rittenour conducted the study, funded by the National Science Foundation and other sources, as part of her doctoral dissertation project at the University of Nebraska with co-investigators Michael Blum, now of Louisiana State University, and Ronald Goble. In a paper published in the May-June issue of the “Geological Society of America Bulletin,” Rittenour’s detailed examination of the river’s fluvial evolution, conducted from the southern tip of Illinois to Baton Rouge, La., builds on findings from 20th century studies.
The Mississippi River spawned from the waters of ancient Lake Agassiz, which dominated present-day central Canada. Rittenour says the waterway has alternately changed from a braided river — featuring multiple, intertwined channels indicative of glacial runoff — to a meandering river, in response to shifting glacial periods. Throughout much of the river valley, the landscape along the Mississippi appears almost flat. But satellite images reveal a web of braided belts throughout the river valley – remnants of glacial melt snaking its way south.
“Our new chronology and longitudinal profiles of the Mississippi offer insights into the response of this continental-scale river system to climatic and sea level changes during the most recent glacial cycle,” said Rittenour, who joined USU as a postdoc researcher in 2005. “This could shed light on the future impact of climate events on the river.”
Rittenour spent four years collecting core samples from braid belts along the river and hauling them back to her alma mater’s luminescence lab for processing. “It was kind of like following Huck Finn’s path,” she said. “I encountered a lot of fried catfish and hush puppies on the menus of old cafes along the way.”
Rittenour was instrumental in the planning and installation of USU’s new luminescence geochronology lab, which the Geology Department formally opened in January on the university’s Innovation Campus. “Luminescence dating offers a wealth of new research opportunities,” she said. “The technology is powerful, accurate and cost-effective.”
Since joining USU, Rittenour notes that she now lives outside the massive Mississippi River watershed, which stretches from western Montana to Pennsylvania. Her focus now, she says, is working with colleagues on study of the American West’s Colorado River.
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