Landslide Investigation in Tennessee River Gorge
Could a landslide have caused a prehistoric megaflood in the Tennessee River Gorge?
Dr. Rachel (Ray) Lombardi, assistant professor in the Department of Earth Sciences, was recently awarded a grant from the Tennessee Valley Authority to investigate potential flood mechanisms of a pre-historic megaflood on the Tennessee River.
The Tennessee River Gorge is a narrow and turbulent reach of the large river, which poses a significant risk of back flooding in Chattanooga, Tennessee. A recent U.S. Geological Survey study reported geologic evidence of a megaflood approximately 375 years ago. When adjusted for the river basin's scale, the estimated size of this megaflood is unprecedented in the southern Appalachian region and ranks among the most extreme floods recorded in the United States. If such a megaflood were to occur today, it would constitute a catastrophic risk to the people and infrastructure in the Tennessee River Valley. So, it is critical to investigate megaflood mechanisms by exploring multiple hypotheses that could explain the patterns of flood deposits found in the gorge to increase resilience to such an unprecedented flood hazard.
Pictured: An example of a rock shelter along the Tennessee River where delicate sediments deposited during high flood stages are preserved in place (top right) for millennia. These flood deposits are identified from their unique geochemical characteristics from local hillslope sediments and provide the basis for estimating flood heights.
The funds awarded to the University of Memphis support a study led by Lombardi and a team of collaborators at the University of Alabama. This collaborative effort explores one hypothesis that local changes in water levels caused by a landslide could explain river sediment deposition at high elevations in the valley. The Tennessee River Gorge has steep slopes and few floodplains, with many landslides showing its history of hillslope failures. Sometimes, large landslides can block the river, creating temporary dams. When these natural dams fail, they release water rapidly, causing what's known as a landslide-lake outburst flood. The study approach evaluates the feasibility of this alternative hypothesis by 1) surveying and estimating the age of a large landslide within the Tennessee River gorge that is directly upstream of the paleoflood deposit and 2) performing a hydraulic dam-break analysis to simulate flows to compare to paleoflood stages.
Pictured: A view from the Tennessee River shows a landslide constricting the river channel to its most narrow point in the gorge.
This research complements previously funded work with collaborators Dr. Lisa Davis and Matthew Gage at the University of Alabama, who investigated regional paleoflood evidence of the 1650 megaflood in major tributaries and below Nickajack Lake near Scottsboro, Alabama, that may provide insight into hydrologic (i.e., rainfall and runoff) mechanisms.
Results from this study will inform future directions for investigating the megaflood, potentially leading to more effective flood management strategies and increased resilience to such catastrophic events.
For more information on this project, contact Lombardi at rlmbardi@memphis.edu.