Landslide risk is on the rise thanks to climate change, and states seek to identify hazards | State and Region

For years, small planes have buzzed the skies over Washington carrying sets of specialized instruments that peer through the belly of the plane. As they fly over mountains, rivers and valleys, the machines paint the topography below with laser light thousands of times per second, reflecting the contours of the landscape back to onboard sensors as data, which is then processed. to create detailed scans of the terrain.

This technology is known as LiDAR – Light Detection And Ranging – and the flights are the work of the state’s Landslide Hazards and LiDAR programs. The initiatives were born out of tragedy: In 2014, a massive landslide erupted over the small community of Steelhead Haven near Oso, Washington, at the foot of the Cascades. Forty-three people were killed, making it the deadliest landslide in US history.

Subsequently, an influx of funding rapidly expanded the fledgling programs, and the mandate was clear: to map the slides and identify potential danger zones. “I don’t think we’ll ever reach a place where there’s no destruction of property from landslide, because you can’t predict when it’s going to happen,” said program manager Kate Mickelson. Landslide Hazards Program. with the Washington Geological Survey. “But I would like people to know that there is that risk there, because I think a lot of people are caught off guard.”

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This is where LiDAR comes in. The laser light filters through the gaps between the branches and leaves of thick vegetation, producing sharp images of the ground below. In Washington, he revealed thousands of past slides, which Mickelson’s team then maps to identify areas at risk. On subsequent visits, LiDAR scans may even show small movements over time that could indicate instability. Several states, including Oregon and Colorado, have similar initiatives, though the Oso tragedy has given Washington’s work a distinct sense of urgency. Staff also provided support to counterparts in Alaska during a program launch, Mickelson said.

LiDAR data is also used by state officials in a variety of other ways: to assess hillside stability before timber sales, to identify landslides along shorelines that could harm fragile ecosystems or critical infrastructure, and to ensure that disaster evacuation routes are safe and reliable. The data is also available to local governments for land use decisions, including new construction or renovations, and even individual homeowners. “We had several homes that were destroyed last winter by landslides, and I don’t know if those people knew they were in a hotspot,” Mickelson said. “We would really like to get the message out.”

Climate change makes landscape hazard mapping increasingly important as more intense rainfall events, which can saturate and destabilize the ground, become more likely. On top of that, Washington’s retreating glaciers reveal eroded rocks that can exacerbate runoff. Factor in the existing challenges of steep grades in a wet climate and it’s a recipe for trouble. “We have this conducive setting for landslides to happen, and then you add the impacts of climate change to that,” said Ronda Strauch, a University of Washington PhD researcher and climate adaptation adviser. for the Seattle City Light utility.

Fire can also increase danger: after an area burns, communities downstream remain at higher risk for several years, despite the perception that the threat has passed with the flames. Washington’s program includes post-wildfire debris flow assessments, during which teams survey infrastructure and homes in potential flow paths and report the results to residents. That work — already well established in fire-prone states like Arizona, Colorado and California, Mickelson said — is becoming increasingly necessary in the warming Northwest.

Despite the perspective offered by LiDAR, it is still difficult to predict individual landslides, given the complicated interplay between geology, precipitation, groundwater, and even the triggering of earthquakes. Earlier this year, Washington removed an online shallow landslide forecast map based on precipitation thresholds, fearing it was not accurate enough. The Geological Survey hopes to revive it in a few years, but in the meantime, the hazard program is directing people to federal resources, a LiDAR technical portal and another interactive map it launched late last year.

This map lets people explore surreal LiDAR composite art created by Geological Survey graphic editor Daniel Coe, showing winding river paths and obscured slides. And that aligns with the landslide program’s focus on education: connecting people to the earth’s long geological history and the hidden threats it may contain.

For Mickelson and his colleagues, the work will continue. Washington has scanned between 70% and 75% of the state so far, and is on track to reach nearly 100% in the next few years. But once that first pass is complete, they’ll start over from scratch – to improve the resolution of certain areas, monitor changes over time, and ultimately gain a better understanding of the landscape.

Michael Crowe is a Seattle-based science and environmental journalist.

Teresa H. Sadler