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Hurricane Ida Is So Strong It Reversed the Mississippi's Current

The Mississippi flowed in the wrong direction for approximately four hours on Sunday.

Since Hurricane Ida made landfall in Port Fourchon, Louisiana on Sunday afternoon it has left more than a million people without power and caused hospital closures due to its dangerous 150 mph (240 km/h) winds.

The hurricane is so powerful that it even made the Mississippi flow in the wrong direction for approximately four hours according to data from the United States Geological Survey (USGS) initially reported by CNN.

Hurricanes, earthquakes, and the Mississippi

Rivers can change their direction of flow due to a number of reasons ranging from tidal forces, erosion, and earthquakes, but river flow reversal caused by hurricanes is "extremely uncommon" according to the USGS. 

Sunday's river flow reversal at the Mississippi joins a short list of only a handful of times where the multiple state-crossing river has changed direction: "I remember, offhand, that there was some flow reversal of the Mississippi River during Hurricane Katrina [in 2005], but it is extremely uncommon," Scott Perrien, a supervising hydrologist at USGS told CNN. The river flow of the Mississippi was also momentarily reversed by a so-called fluvial tsunami in 1812. This was caused by the strongest of a series of earthquakes that hit the region of Missouri between December 1811 and March 1812.

Three-way tie for Louisiana's strongest-ever hurricane

According to Perrien, the river level rose approximately 2 meters (7 feet) on Sunday due to a storm surge pushing upriver. During that time, the river went from flowing about 2 feet per second to roughly half a foot per second in the opposite direction. Perrien did point out, however, that the USGS's river gauge does not measure the deepest portions of the Mississippi, so it is possible that those parts of the river were still flowing in the right direction.

Ida is currently classified as a Category 4 storm, which means it falls in the wind speed range of 130 to 156 mph. It is set to go down in history as part of a three-way tie for the most powerful storm to his Louisiana since records began alongside 2020's Hurricane Laura and the 1856 Last Island Hurricane. All of these storms reached top wind speeds of 150 mph meaning they were just shy of being Category 5 hurricanes.

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Projections show that Hurricane Ida will continue to progress inland over parts of Louisiana and western Mississippi on Monday, a statement from the National Hurricane Center explains. The incredibly powerful Ida will likely result in the occurrence of other uncommon phenomena, though we likely won't see the Mississippi's river flow reverse again for quite some time.

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