Rapid Response: Caltech Scientists Mobilize After Eaton Fire

With the creation of the Eaton Fire Research Fund, Caltech scientists have launched a rapid-response effort to study toxic ash and debris flow risks after Los Angeles wildfires.

The night before the Eaton Fire broke out in January 2025, Professor of Geochemistry François Tissot evacuated his Altadena home with his wife and two young children—not because of flames, but because powerful winds threatened to topple a massive tree onto their house. The next morning, as fire tore through east Altadena, the family briefly returned to check on their home.

"I just needed to know if the house had burnt or not," Tissot says. It was damaged but still standing—the only house on their street to survive the fire. Then the winds picked up again, and they drove away.

Even as his own life was upended, Tissot was already thinking about the broader risks the fire posed. The Eaton fire wasn't a typical wildfire, he explains, it was an urban firestorm, fueled by homes, electronics, and construction materials that released toxins like lead and asbestos. High winds didn't just spread the flames; they carried these contaminants far beyond the burn zone.

Despite feeling personally overwhelmed, Tissot mobilized members of his research lab. Within 30 minutes, every team member had replied, ready to assist however they could.

Tissot, a Caltech Heritage Medical Research Institute (HMRI) investigator, says he felt a responsibility to step up. "We're sitting on all this instrumentation and expertise. If we're not using it to help our community, I think that would be morally unacceptable," he says. "I don't think I could look at myself in the mirror if we didn't act."

Support from the newly created Eaton Fire Research Fund, an initiative launched by the Division of Geological and Planetary Sciences (GPS) that raised more than $250,000, allowed Tissot and group to respond immediately.

Within days, Tissot's team was swabbing ash from window sills, rooftops, and sidewalks, looking for toxic metals that could pose long-term health risks, especially to children. Their study would go on to analyze more than 500 samples and help inform public health messaging and policy decisions in Los Angeles County.

"Just Start Doing It"

The fund was initiated by John Eiler, Robert P. Sharp Professor of Geology and Geochemistry and the Ted and Ginger Jenkins Leadership Chair of the division.

Eiler felt the fire demanded an immediate, community-focused scientific response. "I told our faculty, 'Don't wait. Just start doing it. I'll figure out how to pay for it later,'" he says. "We should just do it."

He reached out to the GPS Chair's Council and other philanthropic supporters with an interest in the division. Eiler didn't make a formal funding ask; he simply shared how faculty were rapidly mobilizing in response to the fire.

Within 48 hours, Eiler had raised over a quarter million dollars in current-use funds from donors, including retired energy executive and Chair's Council member Frank Hu.

"I thought this was a great example of Caltech at its best," Hu says. "They didn't wait because they couldn't. The data had to be collected immediately. I just thought, this is real science that's relevant to the community."

Hu says he was especially impressed by Eiler's leadership and initiative. "He didn't wait for us to fund him. He said, 'I'm going to do this—can you help?' That made a big impact on me," Hu says.

Chairs Council member and Pasadena resident David Rogers says he donated to the Eaton Fire Research Fund because he appreciated Caltech's problem-solving approach and its focus on addressing community impacts after the fire.

"Caltech is such a high quality, no nonsense, just get it done kind of place. It's a good, efficient way to put charitable money to work," Rogers says.

Mapping Ash, Tracking Lead

Tissot's background in ultra-clean geochemical analysis made him uniquely suited to study the toxic dust left behind. His lab, a descendant of the cleanroom practices pioneered at Caltech by geochemist Clair Patterson who famously exposed the dangers of leaded gasoline, allowed for extremely precise detection of trace metals like lead.

His group analyzed the material using some of the same ultra-sensitive instruments used to study ancient meteorites. Tissot says he appreciates the ability to shift between "hardcore cosmochemistry" and research with immediate human impact. "That's one of my favorite things about this work," he says. "The tools are so flexible."

With support from the fund, Tissot and his team launched one of the most comprehensive post-fire ash surveys in the region, gathering data from Caltech buildings and private homes. The results were troubling: surfaces that hadn't been cleaned often showed lead levels far exceeding EPA limits.

"If we didn't have that support, maybe we could have tested 40 samples," Tissot says. "Instead, we tested 500—and that let us say, 'Here's where the lead is.' That's a public health tool."

Debris Flows and Drone Flights

While Tissot studied the fire's toxic residue, geology graduate student Emily Geyman focused on a different kind of danger: the potential for deadly debris flows triggered by winter rains. Though some neighborhoods had been spared by the flames, their position directly below burned mountain slopes left them vulnerable.

The day the fire broke out, Geyman had just met with her thesis advisory committee who suggested that she stay focused and avoid taking on new projects. "And then five hours later, I was walking home through the smoke, looking up at burning ridgelines," she says.

Geyman's apartment in Pasadena wasn't in the burn zone. Yet that night, she began to wonder whether her expertise, normally applied to mountain sediment cycles, could help the neighborhoods below the scorched hills.

Historically, agencies have used empirical models to predict debris flows, based on a limited dataset of past events. Geyman and her advisor, Professor of Geology Mike Lamb, wanted to improve on that with physical models and high-resolution topographic surveys. With the fund's support, they quickly purchased fireproof field gear and a high-performance computer to process drone-collected LiDAR (Light Detection and Ranging) data.

"It made it so that money was not an obstacle," Geyman says. "We needed to fly the drone right away. We needed to analyze the data right away. The fund let us act fast, when every hour counted."

Their results confirmed a theory that Lamb's research group had been investigating for about a decade: that most debris flows stem not from runoff scouring hillsides, but from sediment that had already been mobilized and deposited in mountain channels during the fire. That insight allowed them to estimate debris flow volumes more accurately and provide real-time data to the state and local officials for evacuation planning.

"I saw Emily present her findings after the rain that confirmed the predictions. It was amazing," Hu says. "This was something that had stumped geoscientists for decades. The fact that she was able to validate the model within months was just incredible."

Public Health and the Next Chapter

Tissot is continuing to share his findings with the public and policymakers. The team's research helped shape guidance from city and county officials and led to a sit-down with California State Senator Sasha Pérez to discuss how state policy might respond.

"One of the main things that needs to happen now is making sure families—especially those with young children—understand the importance of cleaning their homes thoroughly," he says. "There's no safe level of lead, and if people don't take steps to clean, there's a risk of ongoing exposure."

Los Angeles County is now offering free blood lead testing for residents. Tissot urges families in affected areas to take advantage. "There's a short window in which intervention can make a difference," he says.

A New Way of Doing Science

For Eiler and Hu, the impact of the Eaton Fire Research Fund goes beyond the scientific insights it generated. It demonstrated the power of Caltech's unique combination of proximity, infrastructure, and culture.

"If you were going to create a tiger team of labs and field expertise and drop it into an emergency zone, you'd put it here," Eiler says. "Except we were already here. And we were ready."

"Every time I encounter Caltech, I'm reminded that it's an institution that can change the world," adds Hu. "It's a very special place—small, multidisciplinary, and home to truly world-class science. I'm proud to support it."

For Geyman, the experience reshaped her view of what it means to do meaningful research.

"Usually, I feel as though I have months or years to answer a research question," she says. "No one's checking in daily. But here, we were working with emergency responders who were saying, 'We have a meeting with LA County tomorrow—can you send numbers today?'"

That urgency rewired Geyman's sense of scientific purpose. "It was a reminder of how gratifying it is to see research translate into real change," she says. "In the future, I want to think more about taking that extra step—about how answering a hypothesis can become something people can actually use."

The following donors contributed to the Eaton Fire Research Fund: The Agouron Institute; Terence Barr (BS '84); David Hadley (PhD '78); Jose Helu (BS '79); Frank Hu; David and Victoria Rogers; Dayna Salter (BS '76); and Caltech Trustee Charles Trimble (BS '63, MS '64, DDA '95).

Read more about Caltech's response to the Eaton fire in the Caltech Science Exchange and in the After the Fires podcast.