As the sun rose Thursday morning, the super fog began to dissipate and a series of crashes could be seen left along Interstate 95 in Volusia County, Florida.
CNN  — 

Five crashes, two of which killed three people, occurred along a stretch of I-95 in Volusia County, Florida, early Thursday, shutting down an 18-mile stretch of the interstate in both directions.

The highway was re-opened Friday after repairs were completed overnight, said Lt. Kim Montes, a public information officer for the Florida Highway Patrol.

“Super fog,” a combination of dense fog and smoke, brought visibility down to less than 10 feet and contributed to the crash, the Melbourne National Weather Service (NWS) tweeted.

“This is a very complex fatal crash scene,” Montes said.

According to Montes, the accidents occurred around 1:30 a.m., with 17 vehicles involved.

Two of the five crashes were fatal, with one death in a crash on the northbound side and two on the southbound side of the interstate.

“That’s very unusual to have something like that. We typically only have one side affected,” Montes said.

“Miraculously, when you look at some of these cars in the northbound lanes, there are people that survived that (you) don’t know how that happened.”

The cause of the accident is under investigation, but according to Montes, dense fog and smoke from a prescribed burn in the area brought visibility to zero on the interstate overnight.

“When I came out here two hours after this crash happened, I was doing one mile an hour creeping along the interstate because I could not see in front of my vehicle,” Montes said.

Fog could still be seen near one of the crash sites early Thursday morning.

As the sun rose Thursday morning, CNN affiliate WESH had aerials of the crash site and the super fog was still visible near the crash site.

“This is a phenomenon that happens throughout central Florida with our weather when we have the smoke in the fog,” Montes added. “Especially when it’s cooler, especially the overnight hours.”

Super fog forms when smoke combined with moisture released from damp smoldering organic material such as brush, leaves and trees, mixes with cooler, nearly saturated air.

Smoke from the prescribed burn in the area would be necessary for creating super fog.

“The area was under what is called a temperature inversion,” explained CNN meteorologist Chad Myers. “Normally, air gets colder as you go up in altitude, but in this case, the temperature actually rose significantly just above the surface. This created a trap, of sorts, that did not allow the smoke to rise up from the ground, making the fog even denser. “

A recent study aimed at better understanding how super fog forms may help forecasters adjust criteria in planning future prescribed burns.

While it is now known how super fog forms, co-author of the study Marko Princevac cautioned, “It is still early to claim that super fog can be predicted with any certainty.”

Super fog has caused several large pileups in Florida, including on I-4 near Davenport in 2008 and one on I-75 south of Gainesville in 2012, the NWS in Melbourne said.

CNN’s Chris Boyette and Tina Burnside contributed to this story