Dense ‘Super Fog’ Causes Deadly Car Crashes in Louisiana

The thick haze lowers visibility to less than ten feet and forms when smoke from smoldering leaves, brush or trees mixes with moisture in cool air

Crash along a highway
The aftermath of a multi-vehicle pileup on I-55 on Oct. 23, 2023 that occured because "super fog" lowered visibility. AP Photo / Gerald Herbert

An unusual weather phenomenon known as “super fog” has created dangerous driving conditions on several Louisiana roads over the past few weeks, leading to a series of deadly car accidents that left a total of eight dead and dozens injured. 

Visibility dropped to near-zero on I-55 near New Orleans during the first of the crashes, which led to a 158-car pileup on October 23 with seven fatalities. Photos of the aftermath show charred and smashed vehicles and a car that had fallen off a bridge into the water below. 

“I’m shocked still. There were explosions happening from the 18-wheeler that was way farther ahead that was on fire,” Kylie Cuevas, a survivor of the crash, tells Maddie Kerth of WVUE. “They were trying to put it out. We just kept hearing explosions, which was very scary for all of us.”

The second crash occurred on I-10 in Louisiana earlier this week, causing one death and several injuries. City officials urged drivers to use extreme caution over the next few days while super fog remains a threat.

Super fog forms when smoke from smoldering organic material—such as leaves, brush and trees—mixes with moisture in cool air. Smoke particles attach to water molecules in the fog, creating a denser haze that lowers visibility to less than ten feet, reports Mike Bedigan for the Independent. The phenomenon differs from smog, which forms as smoke from human-made air pollutants mixes with cooler, saturated air. 

These latest bouts of super fog have been aided by several marsh fires burning in the New Orleans metro area, including one on a 200-acre remote private property near Bayou Sauvage that’s been smoldering since mid-October, reports Carlie Kollath Wells for Axios. Firefighters have been unable to use heavy equipment to fight the blaze out of fear of damaging underground gas pipelines on the property.

Such fires are usually put out with rainwater, but most of Louisiana has been in a state of drought for months, with an average of just five inches of rain falling across the state since the beginning of August. 

“88 percent [of Louisiana] is in either extreme or exceptional drought, these are the two worst classes,” state climatologist Barry Keim tells Jeff Palermo of the Louisiana Radio Network. “Normal rainfall for this time period would be about 13.5 inches, so we are at about 40 percent of normal rainfall for the last three months.” 

Marsh fires usually occur every year in southern Louisiana, and they’re often sparked by lightning strikes or by human activity, report Isabella O’Malley and Kevin McGill for the Associated Press (AP). The fires smolder for weeks or months at a time, and they produce a lot of smoke.

“It’s one of those phenomena that, with climate change, we might see it more often,” Stephen Murphy, director of the disaster management program at Tulane’s School of Public Health and Tropical Medicine, tells the AP. “The drought conditions down here certainly fueled, no pun intended, all that marsh fire.”

Low visibility from precipitation, fog, snow, dust and smoke can lead motorists to vary their speed on roads, increasing the risk of a crash. More than 38,700 vehicle crashes occur each year in fog, resulting in over 600 deaths and 16,300 injuries.

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