The number of casualties from a multi-car pileup on Monday caused by a "super fog" on Interstate 55 near New Orleans has risen to eight dead and 63 injured, according to Louisiana State Police.
While the death toll initially stood at seven, one of the injured died in the hospital overnight, state police said.
The crash, involving at least 168 vehicles, occurred on Monday morning as heavy fog conditions severely lowered visibility, according to Louisiana State Police. A long stretch of Interstate 55, a 24-mile-long highway over Lake Pontchartrain near New Orleans, is expected to be closed "for the foreseeable future," police said.
Interstate 10 and Interstate 310 were also closed as a result of the crash, police said. Louisiana Gov. John Bel Edwards confirmed the accident in a statement Monday.
For hours after the crash, emergency crews worked to clear debris from both northbound and southbound lanes, according to state police. A portion of the crash scene on I-55 caught on fire shortly after the initial incident, authorities said.
A comprehensive structural inspection will take place once the bridge surface is completely clear of debris, diesel and other chemicals, police said.
The super fog was caused by smoke from marsh fires burning in the region combined with dense fog developing in the area early Monday morning bringing extremely low visibility. In some spots, visibility was near zero, creating dangerous driving conditions.
Super fogs typically form when condensed water vapor mixes with the smoke and moisture released from damp organic material smoldering from a nearby fire, such as brush, leaves and trees, according to the National Weather Service. Visibility can be lowered to less than 10 feet as a result, according to the NWS.
This has been occurring in the region over the past several mornings, with the location of the densest fog and most dangerous conditions varying day to day, forecasts show.
Super fogs can be especially dangerous when they develop near and over highways. The localized nature of the weather phenomenon means that visibility conditions can worsen rapidly within a very short distance, which can lead to a hazardous combination of sudden low to near-zero visibility and vehicles traveling at a high speed on a highway.
The very limited visibility then hinders a driver's ability to react to changing conditions on a roadway.
The National Weather Service issued a dense fog advisory for much of southeastern Louisiana on Monday morning, including from Baton Rouge to New Orleans.
Over the past several days, the National Weather Service has been warning of the threat of dense fog during the early mornings in the region that would be worsened in some areas by nearby marsh fires. State police advised drivers to use their low-beam headlights if they can't see at least 500 feet in front of them.
The fog dissipated by mid Monday morning, and all fog alerts have since been canceled.
Morning fog is not uncommon this time of the year for the region, but more than 86% of the state is currently battling extreme drought conditions, which is elevating fire danger. This could mean more instances of super fog in the coming days and weeks as cooler temperatures settle in, but the drought and wildfire risk persist.
In addition, devastating drought and wildfire conditions continue to impact Louisiana. More than 60% of the state is now categorized at exceptional drought, the highest category of concern, according to the U.S. Drought Monitor. Just three months ago, 0% of the state was listed under exceptional drought.
"The combination of wildfire smoke and dense fog is dangerous, and I want to encourage all Louisianans in affected areas to take extreme caution when traveling," Edwards said in a statement.
The St. John the Baptist Parish Sheriff's Office, which initially responded to the crash, directed media requests to Louisiana State Police.
8 dead, 63 injured in 'super fog' multi-car pileup on Louisiana highway: Police originally appeared on abcnews.go.com