Investigators are considering an array of possible ignition sources for the huge fires that ripped through the Los Angeles area.
The blazes broke out last Tuesday and so far more than 12,000 structures have been destroyed and at least 24 people killed. They were fuelled by fierce Santa Ana winds, which forecasters expect to remain strong at least until midweek.
However, a cause for the fires has yet to be determined and early estimates indicated they could be costliest fires ever for the US. Preliminary estimates by AccuWeather put the damage and economic losses at between $135 billion (£111 billion) and $150 billion (£123 billion).
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 do not 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.”
Here’s a closer look at theories that have been circulating online and on social media about what sparked the LA fires.
Lightning
Lightning is the most common source of fires in the US, according to the National Fire Protection Association, but investigators have been quick to dispel any suggestion it caused the LA fires.
There were no reports of lightning in the Palisades area or the terrain around the Eaton Fire that started in east Los Angeles County.
Utility lines
So far, utility lines have not yet been identified as a cause either.
Utilities are required to report to the California Public Utilities Commission (CPUC) when they know of “electric incidents potentially associated with a wildfire”, said Terrie Prosper, the commission’s communications director. 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 burnt more than 1,140 square kilometres.
On Friday, Southern California Edison filed a report with the CPUC related to the Eaton Fire in the hills near Pasadena, an area the utility serves.
Edison said it has not received any suggestions that its equipment was involved in the ignition of that fire but that it filed the report with state utilities regulators out of “an abundance of caution” after receiving evidence preservation notices from insurance company lawyers.
“Preliminary analysis by SCE of electrical circuit information for the energized transmission lines going through the area for 12 hours prior to the reported start time of the fire shows no interruptions or electrical or operational anomalies until more than one hour after the reported start time of the fire,” the utility reported.
New Year’s Eve blaze
Evidence reviewed by the Washington Post suggested that the Palisades Fire started in the area where firefighters had spent hours using helicopters to put out a blaze six days earlier on New Year’s Eve.
Further analysis yielded results that showed the new fire started in the vicinity of the old fire, raising the possibility that the New Year’s Eve fire reignited.
“The foot of the fire started real close to where the last fire was on New Year’s Eve,” said a Los Angeles County firefighter, according to a Post review of archived radio transmissions.
“It looks like it’s going to make a good run,” another added.
Residents at the scene of the wildfires told the Washington Post and investigators that firefighters’ response last Tuesday was much slower than on New Year’s Eve, which the radio transmissions later corroborated.
Climate change
Climate change has made the grasses that are fuelling the LA fires more vulnerable to ignition, scientists have said in a new study.
Decades of drought in California were followed by extremely heavy rainfall for two years in 2022 and 2023, but that then flipped again to very dry conditions in the autumn and winter of 2024 – with a now record dry start to the 2025 rainy season.
Scientists said in the report, published in the journal Nature, that the massive swings from wet to dry has caused “whiplash” conditions globally. The report added that further whiplash increases are anticipated with more global warming.
“This whiplash sequence in California has increased fire risk twofold,” said lead author Daniel Swain from UCLA.
“First, by greatly increasing the growth of flammable grass and brush in the months leading up to fire season, and then by drying it out to exceptionally high levels with the extreme dryness and warmth that followed.”
“It’s clear from the devastation caused by the current wildfires in LA that rapid changes in the volatility of precipitation and evaporation can have a large impact,” said Prof Sir Brian Hoskins, chair of the Grantham Institute for Climate Change at Imperial College London.
Was it an accident?
Fires can be caused by a myriad of sources, including accidents.
A couple’s gender reveal stunt in 2020 started a large fire that spread over seven acres, tore through five homes and 15 other buildings and claimed a firefighter’s life.
A smoke-generating pyrotechnic device was reportedly set off in a field and quickly ignited dry grass on a scorching day.
The couple frantically tried to use bottled water to douse the flames and called 911, authorities said.