A river flowing backward seems to defy natural order, yet this unusual phenomenon has occurred in Earth’s history. While rivers typically follow a predictable course dictated by gravity and topography, extreme geological forces can temporarily disrupt this flow. The extraordinary reversal of a waterway like the Mississippi River highlights how sudden shifts can alter established natural features.
The New Madrid Earthquakes of 1811-1812
The Mississippi River famously flowed backward during the New Madrid Earthquakes, a series of powerful seismic events. These intense intraplate earthquakes struck the central United States, specifically the New Madrid Seismic Zone, between December 1811 and February 1812. The first major shock occurred on December 16, 1811, with an estimated moment magnitude between 7.2 and 8.2, followed by a significant aftershock of magnitude 7.4 on the same day.
Two more earthquakes of similar magnitude followed: on January 23, 1812 (7.0–8.0), and February 7, 1812 (7.4 to 8.6). These seismic events were among the most powerful to hit the contiguous United States east of the Rocky Mountains. Their immense scale meant they were felt across vast distances, with reports of church bells ringing as far away as Boston and chimneys toppling in Cincinnati.
The February 7, 1812, earthquake was forceful enough to destroy New Madrid, Missouri. This series of tremors created widespread ground deformation, directly linking to the temporary reversal of the Mississippi River’s flow.
Geological Mechanics of River Reversal
The Mississippi River’s flow reversed due to severe ground deformation from the New Madrid Earthquakes. The quakes’ energy caused violent ground undulation, rapidly changing elevation along the riverbed and banks. This seismic activity led to uplift and subsidence of land, creating temporary obstacles within the river channel.
In some sections, uplift along fault lines formed temporary dams or waterfalls, disrupting the river’s normal southward flow. This sudden change in gradient forced the immense volume of water to temporarily flow upstream, against its usual direction, as it sought a new path or adjusted to the altered topography. Boatmen described the Mississippi running backward for several hours, a visual representation of this dramatic geological shift.
The intense shaking also generated large “river waves” or fluvial tsunamis within the Mississippi. These waves, propelled by seismic energy, moved upstream, contributing to the perceived backward flow and causing boats to wash ashore. The combination of land uplift creating temporary barriers and the powerful upstream surge of water due to seismic seiches led to the river’s temporary reversal.
Impact and Lasting Effects
The New Madrid Earthquakes and river reversal had immediate and lasting consequences on the landscape and communities. One permanent change was the formation of Reelfoot Lake in northwestern Tennessee. This 18,000-acre natural lake formed when extensive land subsidence, sinking 1.5 to 6 meters, allowed Mississippi River water to flood the depressed area. The lake still features submerged cypress trees, remnants of the former forest.
River navigation was significantly disrupted, challenging steamboats and flatboats. Boatmen described confronting disappearing islands, collapsing riverbanks, and widespread floating debris. Historical accounts detail how the quakes caused fissures to open, ejecting sand and coal, and creating temporary waterfalls in the river.
The New Madrid Seismic Zone remains active today, though most seismic events are minor and often undetectable by humans. Scientists monitor the zone, located in southeastern Missouri, northeastern Arkansas, western Tennessee, western Kentucky, and southern Illinois. While a repeat of the 1811-1812 events is unlikely, ongoing activity reminds us of the region’s dynamic geological past.