Wildfires are increasing the risk of dangerous landslides

The risk of dangerous landslides is increasing as forest fires devastate more landscapes across the West, a UO researcher finds, but it can be hard to predict in the aftermath of a fire, especially given environmental variations across geographic regions.

UO geologist Josh Roering studies landslides in the Pacific Northwest and aims to better understand how they are different from those in drier regions. His research was just featured in an article in Nature looking at the issue of landslides in the wake of forest fires.

The Nature article highlighted one of Roering’s current research projects that shows how landslides can behave differently in the Pacific Northwest and emphasizes why it’s important to understand these geographic nuances.

This research project is in the Columbia River Gorge, where the Eagle Creek Fire burned across 20,000 acres in 2017. But it was not until 2021 that a massive rain event triggered a huge mudslide and resulted in a fatality as the mud swept a car off the road.

The delayed activity was in keeping with Roering’s research findings from his project in the area, which show that the risk of debris flows can be delayed on steep and heavily treed slopes like those in the Columbia River Gorge. This delayed risk is largely due to the fact that tree roots decay over time and are more susceptible to contributing to debris flows a few years after a fire.

Roering explains that the roots in the upper meter of the soil lose approximately 90 percent of their strength after 3-5 years.

“We’re sort of sitting on this ticking time bomb in terms of badly burned areas with steep slopes, perched above major travel corridors and freeways,” Roering told Nature.

Roering’s research has implications for how scientists and emergency managers prepare for storms in heavily wooded burn areas. His research group is continuing to examine landslide activity after forest fires in the Pacific Northwest through hydrologic monitoring and root strength measurements.