ST. LOUIS – At least 20 power pole fires sparked thousands of power outages across the St. Louis area Wednesday, and the cause is a rare weather phenomenon, Ameren Missouri said.

"I’ve not heard of it before, and I'm hearing other people haven't heard of it before either,” Jo Logan said, while she watched a pole burn in Crestwood. "It was kind of scary at first seeing that on fire."

Ameren said cars are grinding up all of the salt on the roads, sending salty sediment into the air. That sediment is settling on devices called insulators on high-voltage power poles.

Wednesday morning, there was also light mist in the air, and that created a formula for electricity.

"It's allowing electricity to be conducted across the insulators, and it's heating up the wood structure, causing it to catch on fire,” Kevin Anders of Ameren said.

Anders said if the mist was heavier rain, then it would have just washed away the salt, and there wouldn’t have been any problems.

Instead, the conditions created a perfect storm for this phenomenon, leaving 9,000 people in the dark at the peak of the outage.