Just before midnight last New Year’s Eve, an Uber driver in his late 20s, the French-born son of Baptist missionaries, dropped a passenger in the Pacific Palisades on the west side of Los Angeles. Then he took a short hike up the Temescal Ridge trail to a clearing he knew as Hidden Buddha, and according to charging documents made public last week, started the fire that became the most destructive in the city’s storied history of catastrophic burns: 12 people killed and nearly 6,000 homes destroyed, an entire neighborhood incinerated in hours, leaving $25 billion in damage behind, an ash heap of American dreams deposited by the sea.
But none of that happened immediately. In fact, almost none of it happened on New Year’s Day, under the particular fire conditions into which Jonathan Rinderknecht may or may not have flicked a cigarette or a lighter.
A network of local monitors first captured a sign of ignition on the trail just after 12:12 a.m., according to the criminal complaint, and Rinderknecht called 911 just 30 seconds later. Out of cellphone service, he couldn’t connect, and so he tried a second time and a third time, walking back toward his car, and finally reached a dispatcher from the bottom of the trail — at which point the Los Angeles Fire Department was already on its way.
The fire spread quickly, but the firefighters arrived quickly, too, and in great numbers — exactly what you would want a wildfire response to be. By the time the department declared the fire dead and left the site on Jan. 2, what was formally called the Lachman fire had burned just eight acres — a small scar, by California standards, and none of it beyond Topanga State Park. It was over; the fire was out.
Except it wasn’t. The Lachman fire hadn’t been fully extinguished. It had just disappeared underground, where it continued to smolder, burning through buried organic material below those eight acres in an unsettlingly surreptitious pattern that is known to most fire scientists and firefighters but that civilians are only now beginning to appreciate. The charging document used the term “holdover fire.” The more colorful phrase is “zombie fire,” and it heralds a disconcerting risk calculus for anyone staring down or trying to mitigate the terrifying threat of a catastrophic burn.
In recent years, fire-conscious Americans across the arid West would look out on parched landscapes, knowing that nearly everything they saw was ready fuel and worrying about what would happen if some accident — a downed power line, a spark thrown by heavy machinery, a reckless cookout or even outright arson — should happen to ignite it. Perhaps it will take decades to thin the landscape of all that fuel, but in the meantime, you might tell yourself, we can reduce, or even eliminate, the number of ignitions, at least on those days of highest fire risk.
Zombie fires offer a different perspective: that the landscape itself could yield the ignition, at almost any point, no matter the precautions. The earth below our feet is now a wick and can burn for days or weeks or even months without our knowing, waiting to explode. The Lachman zombie came alive again on Jan. 7 — what had been an underground burn so calm it produced only little puffs of smoke turned into a fire monumental enough to engulf large swaths of the spectacular Santa Monica mountains, threatening several neighborhoods adjacent to the one and a half it utterly destroyed.
To fire experts, holdover fires are not exactly new. Many lightning-caused fires begin this way — a tree is struck in the midst of a thunderstorm wet enough to stop the trunk from burning, while underground the root system begins to smolder.
Historically, wildland firefighters were taught to stay with a fire “until the last smoke,” afterward testing for underground fire by pressing the ground with a bare hand, then sometimes digging up the several yards of ashen earth to expose the fire to water, like tilling multiple feet of burning soil. More recently, they’ve begun using infrared imaging to do that monitoring — though, in the Palisades, they did not, even after returning to the site on Jan. 3 to respond to a report of smoke in the area. (This is one reason that while some climate skeptics took the Rinderknecht arrest as permission to believe that arson rather than warming is driving the new age of American wildfire, many of those in the Palisades raging about local response saw it as confirmation of their own suspicions.)
But perfect-storm conditions require something like perfect performance and perfect foresight from firefighters, and it is not at all unheard-of for them to declare a fire contained or extinguished only to watch it flare up again, sometimes spectacularly. That’s what happened with the Oakland firestorm of 1991, also known as the Tunnel fire, which killed 25 and injured 150, burning more than 1,500 acres and destroying almost 3,000 homes in the Berkeley Hills. And it’s what happened in Maui in 2023, when firefighters scrambling to address dozens of reported ignitions in extremely dangerous wind conditions left behind one patch of fire that they judged to be fully contained, but that exploded just minutes later, ultimately tearing through Hawaii’s former capital, Lahaina, destroying several thousand structures and killing more than 100 people in what became the deadliest American wildfire in more than a century.
But zombies also loom larger now because they seem to be producing more of our catastrophic fire disasters — even when the initial ignition was intentional. In New Mexico, in 2022, the U.S. Forest Service undertook a controlled burn of dead lumber, intended to reduce the risk of future fire by thinning the landscape of fuel. The firefighters thought the fire had been fully extinguished in January; instead, it went underground, burning through the winter and several snowstorms and emerging again in April, when it began spreading rapidly and merged with another out-of-control controlled burn.
Altogether, the Calf Canyon and Hermits Peak fire burned nearly 350,000 acres — more than 500 square miles across three counties. It was the largest fire in the state’s entire burn-scarred history, and it had been hiding underground, waiting to explode, for four whole months.
These days, across the West, you still routinely come across adorably chunky wooden signs showing the day’s fire risk, many of them bearing the admonition from Smokey Bear: “Only you can prevent wildfires.” (Many others merely imply it.) The claim is about ignition — that vigilance on the riskiest, windiest days can stop even the ripest fuel from exploding. But can it? For decades now, fire people have argued that wildfire suppression itself was actually a kind of disaster, because some fire is good fire and these landscapes need it, and that a half century of suppression in Smokey’s name (and the name of real estate development) has left huge swaths of the landscape desperate to burn.
Holdover fires add another complication: It is much more complicated to fight fire at the point of ignition if a match dropped on Monday can have the same effect as a match dropped on Friday, a power line downed one week can cause problems a fortnight later or a spark thrown by logging equipment in March can prove responsible for a catastrophic megafire in August.
But, of course, zombie fires suggest another form of firefighting as well: more underground and perhaps less in the trees; more in the wake of fires and perhaps less on its advancing front; more fastidious about “mop-up,” which many firefighters consider dreary drudgery, with perhaps much wider perimeters to monitor on foot; more monitoring of old burn scars, including by drone; more watering of smoke spots, also by drone; and an awful lot more churning up of burned land to reach the hot spots underneath. Perhaps putting a lot more chemical retardant down into the earth, too.
In Canada, where dry peatland in the boreal forest can shelter slow burns for months on end, zombie fires burning underground through the winter are merely unusual — “overwintering,” it’s called. But the Canadian fire scientist and wildland firefighter Sonja Leverkus tells me she has been fighting a fire that is now heading into its third straight winter, just 25 miles from her home in Fort Nelson. In her research she has identified another way zombie fires complicate things: not just by smoldering underground, waiting for ideal conditions above, but also by contributing to the fuel load on the surface, doing enough damage to root systems that the trees die and collapse, drying and ready to burn.
“When I listen to what the land is telling us, the land is telling us,” she says, “we’re definitely in the ‘pyrocene’ — the time when fire dominates Earth.”
Michael Wara, who studies wildfire at Stanford, says, “It’s so tempting for people to think that the cause of these enormous catastrophes is the person who drops the match, who drops the cigarette.” But, he says, “that’s just wrong.” What holdover fires teach us more than anything else is that the ignition doesn’t matter nearly as much as the buildup of fuel does. “What can burn will burn.”
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