by Spencer Patrick, GSA Science Communication Intern – Undergraduate at Occidental College

Burning forests and humans do not mix well, especially when individuals understand only some of the dangers. Flames racing across a mountainside make for gripping television, but a second wave of tragedy often lies just beyond the camera’s view.

As the fire rages, the vegetation that normally provides structure to the top layers of a hill-slope’s soil becomes a source of natural fuel. After hours of flame and choking smoke, an extinguishing rain can seem like a godsend. However, the inferno has modified the physical and chemical properties of the soil, transforming it from a sponge into a hydrophobic raincoat that diverts water and carries surface material downhill. This relationship between wildfires and landslides increases the potential for both property damage and loss of life.

As the size and severity of wildfires increase in the American West, communities and governments look to scientific research, new technologies, and more targeted communication to mitigate the dangers. Clear communication in the fields of fire science, risk assessment, and landslide mapping is an essential component in keeping the public safe. The ultimate purpose of science communication is to help the public make informed decisions: whether or not to build a house on a scenic cliff face, how soon to return home after a devastating fire, and so on.

At the 2018 GSA Annual Meeting, several geologists took time to address directly this need for clear communication. U.S. Geological Survey research hydrologist Jason Kean detailed the types of debris flow dangers that can occur after a violent fire. “A debris flow is a flood on steroids,” he warned. “Not only do you have all the water in a flood, but you double it with the sediment.” And it’s not just the amount of material, but the size of its components. “It’s as if you have a jar of mixed nuts and you shake it. Just as the big nuts come to the top, the big boulders come to the front of the debris flow. And when they come, they create a moving dam. The standard tools that we use to predict floods don’t exactly work with debris flows,” says Kean, “because they have different dynamics.”

Last year, during the Thomas Fires in Montecito, California, Kean worked with emergency response teams and the National Weather Service to create a post-fire debris flow hazard assessment. The map shows the probability of a debris flow inundating basins in Ventura and Santa Barbara counties. “The Thomas fire was tough because it came in December,” Kean explained. “It was really late in the year, and there is very little time between the fire and the rain. Our hazard assessment came out five days before the rainstorm that caused the debris flows.”

Coordinating hazard assessments across multiple agencies and government services —especially for a blaze that “was a quarter the size of Rhode Island”— requires not only lightning-fast communication from all parties, but also a great deal of forethought. Kean described some of the limitations they found in the current system of information dissemination. “We say where the debris flows start; we say how much rain it takes to cause a problem; we say how big that problem is going to be. But we don’t say where it is going to go. Montecito highlighted that gap in our hazard assessment.”

When the public is in immediate danger, they need to clearly understand that danger and the risk they mitigate when evacuating. “We didn’t have maps of [the debris flow] run-out. If we had maps of run-out, maybe people would have listened to those evacuation notices more because they would have seen what the potential was.”

Here Kean touches on something echoed by other landslide researchers. While the value of producing fire and landslide hazard assessment maps for the public is obvious, inundating citizens with multiple evacuation notices can have unintended consequences. In the case of the Thomas Fire, citizens received evacuation notices concerning the wildfire, followed by more evacuation notices for the debris flows. This may have led to a kind of evacuation fatigue, where some citizens decided to ignore the later notices and ride out the danger at home. As a result, “twenty-three people died, and over four hundred houses were damaged or destroyed.”

The need for nuanced communication from scientists and researchers is paramount in these types of situations. Rick Wooten, a senior geologist with the North Carolina Geologic Survey, describes when citizens regard information with incredulity rather than fatigue. “In western North Carolina, where I work, there may be decades between landslide events in specific locations; in general areas it may be hundreds of years.” This makes it difficult to convey the seriousness of the threat. “People that live there now have no idea that this was something that could happen. There’s the other end of it where it’s a fairly frequent thing, as in California and places like that. The problem that we face here is that it doesn’t happen very often and is off the radar completely.”

Wooten describes a particularly devastating case in 2004, where major flooding and debris flows destroyed sixteen homes and resulted in five fatalities. In response, the state survey began hazard assessments, county by county, year by year. “By the time 2011 came around, seven years later, the memories of what happened had faded.” Instead of thinking about the danger that such landslides could bring, those at the highest risk looked to the bottom line. “The perception by some is that the landslide hazard maps we were producing could reduce property values [because] some model shows that part of my property may or not be safe.”

Wooten describes these hazard maps as proactive approaches to mitigate the damage derived from landslides, identifying areas that would benefit from site-specific analysis. Ideally, homeowners would contract with a geologist before construction to assess whether their homes were in high-risk landslide areas. In crisis situations, where the hazard of a wildfire or landslide is days away at most, first responders make the hard decisions about what structures to save. However, when long-term timelines are available, that responsibility can shift to the homeowner.

Steven Slaughter, a program manager for landslide hazards with the Washington State Department of Natural Resources, describes how such expectations work in his state. “When someone builds a house, that house is there for potentially generations. Our susceptibility maps are overly general, but the idea is that it’s a triggering system. The planner knows that if someone wants to build a house in this spot, they need to call a geologist to assess the site and write a geotechnical report to help the homeowner understand what the hazards may be.”

Homeowners Guide to Landslides - Cover Image
‘Homeowners Guide to Landslides’, courtesy Washington Geological Survey and Oregon Department of Geology and Mineral Industries

Such geotechnical reports can be helpful in knowing whose responsibly it is when a house is destroyed in a known high-risk location, yet Slaughter worries that not enough is being done. “Unfortunately, it comes down to money. In the Puget Sound area, people are willing to trade risk for views.” He gives the example of Perkins Lane, on the edge of Seattle’s upscale Magnolia neighborhood.

“Perkins Lane has been a known hazard since the ’20s or ’30s. Yet people build houses there. In 1996, six or seven houses went down the hill.” But in Slaughter’s experience, as with Wooten in North Carolina, people tend to forget. “The property [on Perkins Lane] all went up for sale again, and just sold this last eighteen months. They’re doing the same thing again.”

Beyond the amazing views from the street, much of the allure stems from money. “The lots are probably $250,000,” says Slaughter, “which is a steal when you have amazing views of the Sound and Seattle,” especially given that houses just above them “are worth $1.5 to $2 million apiece.” At those prices, these new homeowners are perhaps willing to put up with a bit of shifting sand. But Slaughter worries that they don’t understand the full extent of the risks. “Literally the houses that were there in 1996 are at the bottom of the beach in piles.”

To help emphasize the dangers, Jason Kean worked with fragility curves to tie debris flow characteristics to dollar figures, a convention already employed in the earthquake-hazard industry. However, it’s clear from Perkins Lane that some deals seem too good to pass up. How can hazard and risk be properly communicated, and whose job is it to enforce compliance with such warnings, be they proactive geotechnical reports or immediate evacuation notices?

Although the evidence of danger exists—consider the destroyed homes below Perkins Lane—people are still choosing to take a chance, sometimes at the highest cost. As scientists who understand the dangers first-hand, geologists can play a key role in helping the public understand the hazards and make more informed choices. Improved communication with the general public can go a long way in overcoming the complacence of warning fatigue, and the siren call of cheap land on crumbling cliffs.

Replacing vague terms and domain-specific jargon with clear descriptions can go a long way in cementing an image of risk in the minds of homeowners. Maybe the deal is too good to pass up, or the view too scenic. But with clear assessments, at least they will be making those decisions with an adequate level of fear and honesty. The danger of wildfires is well understood by the public. But they are less informed about the dangers of post-fire landslides. Fortunately, geologists and hydrologists have a key role to play in helping communities understand the hazards. They already provide some of this function through the development of hazard maps. But their assistance can go beyond the raw numbers of such documents. As the details of hazard mapping and risk assessments grow to meet the increasing risk of landslides and wildfires, the responsibility of researchers must be also reviewed. In a variation of the Hippocratic oath, soil scientists should help citizens grasp the information they are introduced to, both now, and as our environment rapidly changes.