‘Superfog’ Caused a Deadly Multi-Car Pileup on Louisiana; Scientists Investigate the Role of Wetland Fires

In south Louisiana, thick smoke from fires in marshy wetlands mixes with the fog that often appears on cool, windless mornings. This combination is referred to by experts as "super fog."

What is a Super Fog?

Super fog is a phenomenon that results when smoke and moisture released from damp, smoldering organic materials such as leaves, trees, and brush get mixed with cool, nearly saturated air. It can reduce visibility to less than 10 feet (3 meters), according to the National Weather Service.

Under light wind conditions, super fog can wind through low terrain areas like creek beds or drainage ditches. It can be hazardous, especially when it is present over highways.

Just like smog, super fog is a type of fog that can pose problems to urban areas. Smog is formed when fog combines with smoke from pollutants from heavy car traffic or industry. It not only leads to limited visibility, but it also poses a serious health hazard.

Super fog is not necessarily like enormous out-of-control wildfires, but they smolder and produce smoke that can last for weeks or months at a time. Because of climate change, this phenomenon is likely to happen more often since drought conditions can fuel all the marsh fires.

A Deadly Combination

This week, super fog has become deadly as it reduced visibility on highways to near zero. On October 23, the superfog caused a series of accidents that turned a section of Interstate 55 near New Orleans into a virtual junkyard of damaged and charred vehicles.

A total of 158 vehicles got involved in the accident, according to local officials. There are also 25 reported injuries, with seven confirmed deaths as of October 24. The super fog was thickest on Monday morning. It had lifted by afternoon as increasing wind and high pressure moved towards Georgia, eliminating any threat of a repeat superfog event. However, fog advisories remained over a small area of the state on Tuesday.

According to meteorologist Tyler Stanfield, superfog events are not overly rare, but they need a perfect set of conditions for them to materialize. For instance, fireworks can contribute to the conditions, and super fog has occurred during Fourth of July and New Year's celebrations. The incident that happened last Monday is characterized by very light winds and high pressure over the regions which trapped moisture near the ground. Stanfield described it as "a pretty typical fog setup."

Marshes may be considered wetlands, but they can dry out. In Louisiana, this happens when the state suffers from a drought that has contributed to wildfires in marshes and timberland. As the dry grass ignites, it does not only burn the grass on top, but it also burns through the crust and the peat layer underneath.

Such types of fires occur every year in south Louisiana. They can be due to lightning strikes or people such as arsonists, hunters looking for a game, or wildlife officials conducting controlled burns to promote new growth. The fires usually happen in remote, hard-to-access areas where they could get out of control.