A 158-car pileup on Louisiana’s Interstate Highway 55 killed at least seven people and injured at least 25 more on Monday. 

The cause? Super fog.

Super fog refers to the dangerous weather condition resulting from the combination of fog and smoke. The weather phenomenon created near-zero visibility for a six-hour period on parts of I-55 west of New Orleans. 

Harsh smoke from wildfires near Jean Lafitte and Bayou Sauvage — to the south and east of New Orleans — along with dense, seasonal fog typical for this time of year created the super fog that led to the crashes. 

The first crashes occurred close to the highway’s Manchac exit, and reports came in before 9 a.m. on Monday. As drivers approached the crashes, lack of visibility created a chain reaction of accidents, which settled into three main clusters in a mile-long stretch. 

Witnesses told The Times-Picayune they heard crashing for over 30 minutes.

One vehicle went over the side of the interstate, although its driver survived.

Hundreds of cars crash on I-55, killing 7. ‘The worst I’ve seen’ https://t.co/j5KnybamGT

— NOLA.com (@NOLAnews) October 24, 2023

An intense fire involving two 18-wheeler trucks broke out on a section of the highway. As smoke further clouded the scene, drivers and passengers attempted to help those trapped in their vehicles; others waited for rescue crews to free them from damaged cars. 

Louisiana State Police and the St. John Sheriff’s Office, along with deputies from St. Charles and Jefferson Parish, responded to the crash scenes. Fire Departments from Hammond, Manchac and St. John extinguished the fires. 

Authorities closed the Bonnet Carre Spillway in both directions for five hours, diverting traffic away from the crashes until they reopened later on Monday. Around 20 miles of the highway running alongside Lake Maurepas remained closed as of Tuesday morning. 

While wreckage continues to be dealt with, residents should expect I-55 to remain closed for “the foreseeable future,” Louisiana State Police said. 

Several New Orleans schools canceled classes or issued delays Tuesday morning, expecting the super fog to create dangerous driving conditions. 

A high pressure dome sitting over Louisiana blocked wind’s ability to move fog out of the area. But fog conditions improved Tuesday morning due to slightly stronger winds in the region.

Given that the marsh fires are still burning, though, the super fog may return this weekend if winds subside. 

Today’s #TimelapseTuesday imagery via @NOAA‘s #GOESEast 🛰️ shows “super fog” dissipating over ~6 hours in Louisiana yesterday. This formed from a combination of dense fog and smoke from nearby marsh fires, and caused a tragic multi-vehicle accident in St. John the Baptist Parish. pic.twitter.com/JvAzPl7SKo

— NOAA Satellites (@NOAASatellites) October 24, 2023

Fire crews are working to extinguish the fires near Jean Lafitte. New Orleans firefighters are collaborating with the Sewerage and Water Board of New Orleans to flood the site of the Bayou Sauvage fire with water from a nearby drainage canal. 

If flooding efforts fail to stop the Bayou Sauvage fire, rain remains a solution. However, clear weather conditions are expected through the next week, and southeast Louisiana receives its lowest rainfall totals in October.