What caused the deadly California wildfires?

Investigators are considering an array of possible ignition sources for the huge fires that have killed at least 10 people and destroyed thousands of homes and businesses in the Los Angeles area.

In hilly, upscale Pacific Palisades, home to Hollywood stars like Jamie Lee Curtis and Billy Crystal who lost houses in the fire, officials have placed the origin of the wind-whipped blaze behind a home on Piedra Morada Drive, which sits above a densely wooded arroyo.

While lightning is the most common source of fires in the U.S., according to the National Fire Protection Association, investigators were able to rule that out quickly. There were no reports of lightning in the Palisades area or the terrain around the Eaton fire, which started in east Los Angeles County and has also destroyed hundreds of homes.

The next two most common causes: fires intentionally set, and those sparked by utility lines.

John Lentini, owner of Scientific Fire Analysis in Florida, who has investigated large fires in California including the Oakland Hills fire in 1991, said the size and scope of the blaze doesn’t change the approach to finding out what caused it.

“This was once a small fire,” Lentini said. “People will focus on where the fire started, determine the origin and look around the origin and determine the cause.”

So far there has been no official indication of arson in either blaze, and utility lines have not yet been identified as a cause either.

Utilities are required to report to the California Public Utilities Commission when they know of “electric incidents potentially associated with a wildfire,” Terrie Prosper, the commission's communications director, said via email. CPUC staff then investigate to see if there were violations of state law.

The 2017 Thomas Fire, one of the largest fires in state history, was sparked by Southern California Edison power lines that came into contact during high wind, investigators determined. The blaze killed two people and charred more than 440 square miles (1,140 square kilometers), according to the investigation headed by the Ventura County Fire Department.

So far no such reports for the current fires have been posted to the CPUC website that tracks such filings.

While lightning, arson and utility lines are the most common causes, debris burning and fireworks are also common causes.

But fires are incited by myriad sources, including accidents.

In 2021, a couple's gender reveal stunt started a large fire that torched close to 36 square miles (about 90 square kilometers) of terrain, destroyed five homes and 15 other buildings and claimed the life of a firefighter, Charlie Morton.

The Eaton and Palisades fires were still burning with little to no containment on Thursday. Winds softened, but there was no rain in the forecast as the flames moved through miles of dry landscape.

“It’s going to go out when it runs out of fuel, or when the weather stops,” Lentini said. “They’re not going to put that thing out until it’s ready to go out.”