In summary
San Gabriel Valley areas scarred by the Eaton Fire are at “high to very high risk” of debris flows this week. How do they happen? What is being done to prepare? And what do survivors of a catastrophic one that killed 23 people remember about the day that the hills came down?
Sterling Klippel is awed by the beauty of nature but spends his working days resisting its power.
Casting worried glances at a gray sky above the Sierra Madre Dam in the foothills of the San Gabriel Mountains, Klippel, a beefy and upbeat man, was patiently describing the complexities of Los Angeles County’s flood protection system.
As a principal engineer for the county’s Public Works Department, Klippel’s job is to try to stop catastrophic flows of mud, debris and boulders that could rush into fire-stricken neighborhoods in Altadena and surrounding communities. Klippel and his stormwater crews must ensure that the county’s network of dams, debris basins, channels and storm drains are up to the task.
Emergency teams from multiple agencies have cleared out flood basins beneath the Eaton Fire’s 14,000-acre burn scar, rushed to distribute sandbags and placed long concrete barriers to redirect potential flows.
But the work to hold back fire-scarred mountains that no longer have vegetation to stabilize them can be futile and humbling.
While the Eaton Fire is contained, the danger to foothill communities is not.
Nearly 170,000 people live in Altadena, Pasadena and Sierra Madre at the foot of the San Gabriel Mountains, and many are potentially in the path of debris flows.
Heavy rainfall expected on Thursday and Friday has triggered warnings about fire-scarred hillsides unleashing torrents of mud, boulders and debris from the torched slopes. The National Weather Service issued a flash flood watch for late Thursday, with the greatest risks in areas burned by the Eaton, Palisades, Franklin, and Bridge fires. In Santa Barbara, people in the Lake Fire’s burn areas were told to prepare to evacuate as a storm approaches today.
Neither flood nor landslide, debris flows are creatures all their own. Often holding more sediment and rock than water, they usually begin with torrential rain on dry, impervious and unstable earth — conditions often created by wildfires.
The droplets kick up sand and gravel, and the water accumulates much faster than it can sink into the ground. Within minutes, the runoff can snowball into an ashy-gray torrent of tumbling rocks and boulders that blow through bridges, macerate structures and carry away houses and vehicles.
The highest danger of a debris flow can persist for years after a fire, and right now, the southern flank of the steep, crumbly San Gabriels is considered especially vulnerable.
Throughout Southern California, the bases of mountain ranges are strewn with the effluent of past debris flows — called alluvial fans — and cities in the sprawling Los Angeles basin have been built on top of them.
The Eaton Fire damage assessment report, released by the National Forest Service on Tuesday, warns that “the probabilities of hyper-concentrated flows and/or debris flows are high to very high in most channels in the Eaton Fire burn area.” The report projects potentially massive debris flows spilling into Altadena from Eaton Canyon and several other watersheds scarred by the fire.
Throughout Southern California, the bases of mountain ranges are strewn with the effluent of past debris flows — and cities in the sprawling Los Angeles basin have been built on top of them.
Southern California has a history of such catastrophic events.
A disastrous debris flow in 1969 killed 100 people after a 20-foot wave of mud rushed through Azusa in the foothills of the San Gabriels. In 1994 a man and his 9-year-old son were killed during a flash flood in a park in Sierra Madre, where a canyon had burned a year before. And to the east, in San Bernardino County, 16 people died in debris flows after 2003’s Old and Grand Prix fires.
The most recent devastation was in 2018, when a debris flow in Montecito after the Thomas Fire killed 23 people, many of them drowned in waves of mud or crushed by debris.
In the areas scarred by the Eaton Fire, just a fifth of an inch of rain could trigger a disaster if it falls within15 minutes, said Jeremy Lancaster, the state geologist who heads the California Geological Survey. The federal report pegged a higher threshold — with 1.57 inches of rain per hour or less than half an inch in the critical 15-minute span — very likely to initiate debris flows in the burned canyons.
“We’re worried about short-duration, high-intensity rainfall, like thunderstorms,” Lancaster said.
This week’s storm will test the capacity of the county’s system to handle the force of what might be unleashed later this week.
Klippel knows the race is on.
“We work with the weather service and look at modeling 48 hours ahead of a storm,” he said. “Things start to come into focus. We want all of our flood control facilities to be ready. We’ve got to get everything cleared out.”
Hundreds of feet below the spot where Klippel was standing, bulldozers and other heavy equipment scraped and pushed the canyon’s sediment and rock and loaded heavy piles into dump trucks lined up to haul it away,
This site, built in 1928, no longer operates as a dam, but its solid concrete sweep is designed to stop the advance of mud and debris and allow only water to pass through culverts to open areas where the water percolates back into the aquifer.
These and dozens other structures are critical safety barriers — the roof of a home is visible through trees behind the dam and many cherished neighborhoods are tucked away downstream in wooded ravines.
Of particular concern is the secluded enclave known as Pasadena Glen, a quirky mix of ultra-modern designer homes and rustic cabins. Running through the community is a deep, rocky cleft that carries water coming from higher elevations past the live oaks and sycamores into collection basins below.
In an unburned landscape, roots and other flammable organic material help hold sand, gravel and rock together, explained Benjamin Hatchett, a Colorado State University fire meteorologist based in Northern California who has assessed landscapes after wildfires. The overhead canopy, he said, also absorbs the shock of raindrops before they land.
But after a severe fire, much of the ground is burned down to nothing but bare mineral earth, ready to come unzipped at the first torrent of water.
That’s where things stand in the charred footprint of the Eaton Fire.
The state response team that handles watershed emergencies reported that “the Eaton Fire has a high likelihood of generating large magnitude post-fire flood and debris flow events,” adding that “the risk is very high” because of the “critical values exposed.”
In other words: This is an emergency — and people’s lives and the places they care about are in danger.
Mountains can fall apart
If you wanted to purposefully design a mountain range to come apart and sluff off its rocky flanks, you could do no better than the San Gabriels. Their steep slopes efficiently funnel storm runoff through narrow cuts from peaks that widen at the bottom.
This extreme architecture enhances fire: deep, narrow clefts transport flames like chimneys. And those broad alluvial fans are expert at what geologists call entrainment — water, mud, sediment and boulders coalesce and gain speed and mass as they race downhill, hitting the bottom and spreading debris flows across a wide area.
The speed of the flows can reach 30 to 40 miles an hour and are urged along by the slopes’ steepness and lack of vegetation. Severely burned soils coated with ash become hydrophobic, meaning rather than soaking into the hillsides, the water rolls easily off the surface.
For example, water dumped from the local peak, Mt. Wilson, at 5,700 feet, will come down the mountain seven times faster after a severe fire, said Sean Norman, a Cal Fire team leader on the Eaton Fire.
That acceleration is unwelcome news for communities nestled in the foothills. In the same way that trees are fuel for wildfires, steep hillsides clogged with boulders become fuel for debris flows.
Most debris flows dissipate in minutes or less, often when a leveling of the land diffuses the energy and brings the torrent of rubble to a standstill. This often happens where a canyon opens onto a wide plain or river valley, creating an alluvial fan — one of the most visually compelling and dynamic features of geology.
In the case of the San Gabriel Mountains, debris flows are a scenario that’s been explored many times, none so closely as in John McPhee’s 1989 book, “The Control of Nature,” in which he vividly details a devastating debris flow from the San Gabriels that plowed through homes, washed away automobiles and carried off disinterred coffins.
The book’s title is more a wry oxymoron than a confident statement of humankind’s ability to impose its will on natural systems. “In Los Angeles versus the San Gabriel Mountains, it is not always clear which side is losing,” McPhee wrote.
In geological reckoning, the San Gabriel Mountains are immature, unruly teenagers. Sitting at the intersection of the Pacific and North American plates meeting at the San Andreas Fault, the mountains are still fitfully growing — the western end of the range lifted several feet during the 1971 Sylmar earthquake.
The average slope gradient in the San Gabriel Mountains is over 65%.
Their steepness defines their “angle of repose,” a geologic concept critical to catastrophic debris flows. It’s the steepest angle at which material starts to fall — the point at which too many shovels of sand collapse the whole pile.
The San Gabriels are unique in California. They are part of the Transverse Ranges with a West-East orientation, not the North-South run of California’s Sierra Nevada and other mountain spans. North-facing slopes of the San Gabriels offer a glimpse of the Sierra-like ponderosa pines, rugged hillsides and wild country. The south-facing slopes overlook a teeming metropolis and offer a spare Mediterranean array of gnarled shrubs and hard-scrabble plants.
“You feel like you could extend one arm in one direction and one arm in another and touch completely different things. It’s amazing,” said Jason Collier, acting manager of the San Gabriel Mountains National Monument. “There are extremes in temperatures and elevation. Here in the L.A. basin we go from sea level to Mt. Baldy at 10,000 feet. And you can do it in an hour on Hwy 2.”
Collier sees a rich geologic history and others see recreational opportunities.
Ben White, 79, is in his 35th year as a member of the San Gabriel Mountains Trailblazers, a hardy group of volunteers that trek through the range, repairing fences and Forest Service trails.
The group goes out three Saturdays a month. Before the fire, White had missed only three outings.
“Hiking up there takes your mind off your problems,” he said. The fire has damaged a place he loves. “If I look at it as a loss, I would be depressed, permanently.”
Not all rain is created equal
The flash flood watch for late this week is nothing to take lightly. Forecasters only issue such alerts when they are more than 50% confident that the incoming rain will reach critical rates, said Jayme Laber, a senior hydrologist with the National Weather Service’s weather forecast office in Oxnard.
For residents living in or near a fresh burn area, the flood watch means it’s time to prepare for a possible evacuation.
“That’s their heads-up to make preparations,” Laber said. “That’s the time to start thinking about making an evacuation call, not when it’s already raining.”
When a fast flood watch turns into a warning, there’s little time for preparation. In most cases, it’s too late.
When weather forecasters see live rainfall levels reach or exceed critical thresholds in or near a high-hazard zone, then they issue a flash flood “warning.”
When a watch turns into a warning, there’s little time for preparation. In most cases, it’s too late.
Warnings “can have from zero lead time up to maybe an hour’s worth of lead time, depending how confident we are in what we’re seeing in our radar,” Laber said.
The neighborhoods within sight of the burn scar are teeming with workers fixed on preparing for the deluge: The state has stockpiled 271,000 burlap sandbags, 777 sheeting rolls and 17,790 wood stakes, among other items. Others from the California Conservation Corps have placed fencing, straw wattles and other means to filter contaminants contained in the runoff. The National Guard sent an engineering crew with heavy equipment to move debris.
There is a feeling of urgency with all of the preparations. Many people recall what happened in similar circumstances in Montecito seven years ago.
The night the hills came down in Montecito
By the time the rains came, everyone had pretty much had it with emergencies. In early January of 2018 residents of Santa Barbara and neighboring Montecito were back in their homes, exhausted after extended evacuations from the Thomas Fire, a monstrosity that blazed for five and a half weeks and was at the time the largest fire in California history.
“We had a month of evacuations and fear. Firefighters saved Montecito. We were so grateful and happy to be home,” said Abe Powell, who was the director of the Montecito Fire Protection District at the time.
But emergency officials were huddling, poring over worrying reports. Meteorologists predicted a significant rain event — soon. And the teams dispatched to assess the stability of the hillsides denuded by fire warned Montecito officials in plain language: “Between friends, if rain comes through, you will be f*cked,“ Powell said, using the team’s salty language.
Powell, whose family had been evacuated for a month, worked with emergency authorities to craft an urgent message: Be prepared to leave your homes again, there could be massive mud flows off the Santa Ynez Mountains.
Crews cleared debris basins, moved in heavy concrete barriers and stacked sandbags. All emergency personnel were called back to work. Residents watched the feverish preparations but also took note of the scant rainfall forecast and appeared to collectively shrug.
Emergency officials began to consider the likelihood that “evacuation fatigue” had set in and that residents might not heed warnings to get out. Powell said door-knocking was not going well, with some homeowners insisting they would ride it out.
“A number of people I argued with at the sandbag pile lost their homes, and not all of them survived,” he said.
Powell estimated that only about 20% of those living in the mandatory evacuation zone actually left their homes.
Authorities pre-positioned search and rescue teams on high ground and deployed swiftwater rescue squads.Then they hunkered down and waited.
“A number of people I argued with at the sandbag pile lost their homes, and not all of them survived.”
Abe Powell, former director of the Montecito Fire Protection District
Aaron Briner, then a fire engine captain, went to sleep just before midnight at Station 2 in Montecito on Jan. 8. It was sprinkling. A call came into the station at 3:30 a.m. reporting a building was on fire. Briner looked out and heavy rain was falling.
“We prepared for the potential, but I don’t know that we could truly grasp the scope of what happened,” said Briner, now the city’s fire marshall.
Briner’s engines tried multiple routes to get to the fire but were cut off by roads subsumed by mudflows and boulders the size of the fire engines themselves.
“We came across people who were trying to pull themselves out of chest-deep mud,” he said. “We had no idea of the scope.
“It was dark, there was no power, most of the cell service was gone. There were no landmarks, no trees, we almost got lost a few times. Some of our guys ended up in swimming pools. I saw a mudline on trees up to 20 feet.”
Elsewhere in Montecito, Powell also woke up to the roar of heavy rain. And another peculiar sound: Boulders the size of SUV’s were careening down the mountain, their collisions sounding like massive billiard balls smashing into each other.
He rushed to a window and saw an explosion and bright lights in the sky. He briefly thought it looked like an alien invasion. It turned out to be a fire.
“We came across people who were trying to pull themselves out of chest-deep mud…It was dark, there was no power, most of the cell service was gone. There were no landmarks, no trees, we almost got lost a few times.”
Aaron Briner, former fire engine captain in montecito
The burst of torrential rain caused the watershed behind the San Yisidro Creek Bridge to give way. The debris flow rushed toward town going 40-miles-an-hour and carrying with it anything in its path. Including the bridge.
The boulder-filled mudslide hit the bridge and took it out, smashing a gas line that erupted in flames. That wall of mud and rocks, now ablaze, crashed into a house containing a sleeping couple.
With mud and flames quickly rising, their pajamas on fire, the pair rushed to the home’s second story. They had a choice: stay above the flood in a burning house or jump from the fire into the darkness and onto a fast-moving, roiling river of mud.
They leapt from the upper floor onto the debris flow, clothes burned off, and badly injured. A firefighter heard their screams and waded into the moving mud to pull them to safety. A helicopter took them to a hospital. They survived. Twenty-three others in Montecito did not.
Suzanne Hyde, a live-in private chef, said her first reaction to evacuating the home she shared next to Montecito Creek was “I’m not leaving,” she said, having just returned home and unpacked from the fire evacuation. She wanted to do her laundry, and it wasn’t even raining.
But her client convinced her, saying, “We really need to leave, we can’t control water.”
“I would have been killed, probably while still in bed. It still blows my mind to think of the power of water.”
Suzanne Hyde, Montecito resident
Hyde reluctantly left with her two cats and pet rabbit. “Then, obviously, all hell broke loose.” A boulder “the size of a VW bug” crashed through Hyde’s bedroom, apparently rolling over her bed on its way through the wall.
“I would have been killed, probably while still in bed,” she said. “It still blows my mind to think of the power of water.”
Aftermath of the Montecito disaster
Scores of daring rescues played out in the early morning, with ruptured gas lines hissing loudly. As the sun came up the light revealed a changed landscape. The painstaking search for survivors went on for nearly two weeks, through layers of muck and boulders so large that it took dynamite to clear them.
Until that night, Briner hadn’t given much thought to the full implications of debris flows. Once geologists began to look around the region, they found evidence of historic landslides of such volume that rocks were dragged all the way to the Pacific. Present-day ocean reefs were formed with boulders from the surrounding mountains, he said.
There’s no reason to believe that the risk will ever go away.
“We mitigate risk, we don’t prevent risk,” Briner said. “It will always be here. We choose to be in these areas, we have to recognize risk comes with that.”
Kelly Hubbard, director of the Santa Barbara County Office of Emergency Management, said most of the remediation began immediately: Federal funding enabled authorities to buy out willing property sellers to expand debris basins.
And the difficult public conversation about rethinking living in harm’s way began. “We talked about maybe not rebuilding in the same location, maybe rebuilding better,” Hubbard said. “We had a homeowner who literally survived by riding in his home down the mudslide. He became an advocate in the community.”
This year’s annual vigil to remember the lives lost in the Montecito debris flow was held, as usual, on Jan. 9, two days after the fires in Los Angeles ignited. Community members said prayers, lit candles and expressed support for those in the path of the Eaton Fire.
“We know all too well what can happen,” Powell said.
