A man stands at the base of stairs on a steep slope in burned land.
Bill English stands next to a burned-out site on his property in Boulder Creek. He lives in one of the highest-risk areas identified by Santa Cruz County.
(Kevin Painchaud/Lookout)

As ‘mudslides on steroids’ threaten, Santa Cruz Mountain dwellers ponder new normal

Santa Cruz Mountain residents are bracing for more evacuations because of debris flows this winter, with potentially no end in sight to annual cycles of wildfires and heavy rains.

Kathleen Miller Thomas lived in Boulder Creek for 39 years. The 82-year-old artist loved to hike the steep slopes behind her home, tend her garden with her husband and care for their eight pets: three cats, a dog and four chickens. “It was perfect,” she said. “And my idea has been to live there for the rest of my life.”

But now Thomas — along with her husband, dog, and two of those cats — is crammed into a 2-bedroom apartment on the westside of Santa Cruz. They fled the CZU Lightning Complex Fire and never returned.

It’s not fires they are afraid of, though. It’s debris flows — a deadly geological phenomena akin to a mudslide on steroids.

The Lightning Complex fire was so big, so intense, and its range so unprecedented, that the risk of debris flows during this year’s rainy season will be unlike any other in the region’s history. The oft-repeated warning about one is, “If you hear it, it’s too late.”

“I’m not moving back, and neither is he, until we know it is safe,” Thomas said. “It could very well take a couple of years, and we know that.”

A white woman with blonde hair pictured in front of a house in the forest.
Kathleen Miller Thomas pictured near her home in Boulder Creek.
(courtesy of Kathleen Miller Thomas)

This situation could become the new normal for dwellers of the Santa Cruz Mountains. The combination of twinned catastrophes — massive wildfires followed by intense rain — might permanently alter life for the thousands of people who live there.

Climate scientists say projections show fire season will be bigger and last longer, while rain intensity will likely also increase. This year might be the first time, but it probably won’t be the last, that residents are forced to evacuate for fires and debris flows in the same year.

“I think it is likely that based on just having more conditions that could lead to debris flows, it is likely that they could occur more often,” said Danielle Touma, a postdoctoral scholar at UC Santa Barbara, who is studying the effects of climate change on debris flows. “If we just look at the climate side of things, based on previous studies and what we’re seeing in our studies so far, these conditions could become more likely in the future.”

Santa Cruz County Evacuation Zone Map

A deadly history, including in Santa Cruz

The most famous debris flows in recent history killed 23 people and destroyed 408 houses in Montecito, near Santa Barbara, in winter 2018. A massive fire had just hit the area, creating conditions akin to what Santa Cruz County faces now.

Similar events also have hit the county in the past: the 1982 Love Creek landslide near Ben Lomond destroyed nine houses and killed 10 people.

A debris flow is distinct from a landslide in that it’s made up of a bunch of “particles” — things like loose soil, vegetation, trees and boulders — that move independently of each other, versus a landslide in which a chunk of land or mud moves as one piece, or a mudslide, when land on a slope gets so wet it begins to flow like water. Jim Olson, a private consulting geologist who has worked frequently in the Santa Cruz Mountains, says debris flows can be thought of like a massive flood.

“It picks up a lot of material, meaning soil, literally boulders the size of houses, huge redwood trees,” he said. “It buries whatever is in its way.”

photo of a white man with a tree and fence in the background
Jim Olson, a geologist who works in the Santa Cruz Mountains.
(Kevin Painchaud/Lookout)

Fires increase the likelihood of flows because they bake the soil, making it less absorbent, and ravage the vegetation, leaving it completely uprooted or with weakened roots.

“This is a new thing in Santa Cruz County,” said Jeff Nolan, the county geologist. “If we have a bunch of gentle, small, rainstorms this winter, the landscape will heal itself relatively quickly. But if we have high intensity rainfalls, as predicted, there may be a few evacuations.”

Nolan says if he lived in one of the high risk areas identified by the county, he would rent a house somewhere else for the rainy season. “Partially because of the hazard, and partially because of the level of disruption to your life that may happen if you do end up getting evacuated.”

Map showing the extent of the CZU Lightning complex fire compared to previous fires in the area.
Map of previous fires in the CZU Lightning Complex burn area. The size of the CZU fire was historically unprecedented.
(CALFire and California Department of Conservation.)

Beloved mountain life threatened

At least a dozen houses on Thomas’s street were destroyed by the fire, and she says many of her neighbors have also fled, or may leave soon. But doing so can be a financial sacrifice: it requires either selling one’s house, or trying to keep it while renting elsewhere.

Olson says a lot of areas in the Santa Cruz mountains were built up prior to the strict geology requirements now in place for anyone wanting to build a home. “They’ve been built in places where [now] we might not recommend building at all,” he said.

The county has released a map of potential debris flow danger with areas in or below the CZU burn area broken into zones with risk levels deemed elevated or high, and likely to see evacuations. Key infrastructure threatened by flows includes Boulder Creek Elementary and several state parks.

Bill English, an engineer who also lives in Boulder Creek, didn’t want to evacuate for the fire in August. He waited until the very last minute, when he could see the glow of the flames from his house.

When he returned, his house was still standing, but he was shocked by the destruction around it. Five of the seven houses bordering his property were destroyed.

Properties destroyed by the fire near Bill English's house in Boulder Creek.
(Kevin Painchaud/Lookout Santa Cruz)
Bill English in Boulder Creek.
(Kevin Painchaud/Lookout Santa Cruz)

Now, his home is in one of the highest-risk areas identified by the county. He thinks the particular geology of his property will keep it safe, but his confidence is beginning to waver. “I’m hoping that whatever happens above us decelerates before it ever impacts where we are,” he said. “But then again, I never thought the fire would ever reach this far down towards the river.”

English and his family settled in Boulder Creek partly out of “sticker shock,” as houses in town were out of their price range when they moved to Santa Cruz in 1997, but also because they loved the community and the proximity to nature. Like Thomas, he’s never wanted to move.

What Can be Done

Santa Cruz County officials have held a series of town halls, blasted social media with notices, set up flashing road signs, and will be going door-to-door in affected areas, all encouraging people to check the county’s map to“know their zone,” sign up for emergency warnings, and heed evacuation orders.

Some of their big concerns are evacuation fatigue, or that residents won’t consider debris flows as serious as fire. County officials, in town halls and presentations to the Board of Supervisors, highlighted the fact that only an estimated 23 percent of Montecito residents heeded debris flow evacuation warnings, while 75 percent evacuated for the preceding fire.

Getting through this winter is just the first hurdle: the risk of deadly flows could remain elevated in burned areas for two to five years. Future fires, and future rain, will begin the cycle all over again. Infrastructure can be built to permanently mitigate the risk, but it can’t easily be done by individual property owners.

“If we have somebody come to us and say, ‘I want to do something about the debris flow hazard here,’ we need to actually study areas that are off of their property,” said Olson. “These are basin wide analyses that would need to be done, and then to remediate that hazard, you need a whole community-wide development plan.”

Developments in southern California, Japan, and Europe, have built huge catchment basins, or installed debris nets, to try to permanently protect communities.

An aerial image of a debris-flow basin built at the bottom of a hillside in San Bernardino, California.
An aerial image of a debris-flow basin built at the bottom of a hillside in San Bernardino, California.
(Doug Morton, US Geological Survey)

Nolan says the county is talking to FEMA and the National Resources Conservation Service to see if it’s possible to secure funding to protect some high risk areas in the Santa Cruz Mountains. “I can’t say that it’s going to work out,” he said. “But we’re certainly talking to people.”

English and Thomas both say they feel incredibly lucky that their families and homes escaped destruction by the fire. But both are also drained by the disasters this year has thrown at them, and by contemplating years of disruption ahead.

“We loved our home. Absolutely loved it,” said Thomas. “We just didn’t feel like it was safe enough to stay there.”