Minimizing the dangers posed by landslides to people, roads, utilities and rail lines will likely become easier and cheaper thanks to the work of professors at Portland State University and Oregon State University.

Adam Booth, assistant professor of geology at PSU, is working with Oregon State professors Ben Leshchinsky and Michael Olsen to perfect a landslide prediction method that relies on a LIDAR (Light Detection and Ranging) system.

“LIDAR has been around for 15 years now,” Booth said. “It lets us see what the bare earth looks like.”

The system has been used largely by aircraft to help geologists map the surface below a tree canopy. That visual record shows where landslides have struck. However, this new method is able to help scientists identify when the slide struck, not just where.

“Once you date the landslides, you know how likely it is in a given year,” Booth said.

In the past the only way to date landslides in a given area was through the time-consuming and expensive process of radiocarbon dating rocks from a debris field.

The process that Booth and his colleagues use is a combination of radiocarbon dating and LIDAR scanning. When an area is found with multiple landslides, samples are taken from a small number of slide areas; their ages are determined using traditional radiocarbon dating.

For nearby slides, LIDAR then conveys ages that correspond to radiocarbon dating. LIDAR measures the relative variability in the topography that tells geologists how weathered rocks and debris are within the slide. A debris field with a smoother surface is older because erosion and weather dull rough edges over time. A rougher debris field has undergone less wear and therefore is younger.

Combining that data with the information from the radiocarbon dating gives scientists a complete picture of slide ages within a given area. Knowing the age of a range of landslides can tell scientists how often slides happen historically in an area. That information can be combined with a historical database of landslides kept by the Oregon Department of Geology and Mineral Industries (DOGAMI) to get an even clearer picture of the frequency and causes of slides.

“We can narrow (the age of a slide) to between a few hundred to a few thousand years,” Booth said. “We can compare it to climate info and figure out (whether) we get a higher landslide frequency during a cooler and wetter climate.”

The method does have limitations. The process can estimate slide frequencies only over a large area, usually at least around 15 miles. It can’t determine where a specific landslide will occur or if a specific acre or square mile of land is any more susceptible to landslides than the one next to it.

“It has to be a large enough area where you have a number of landslides to study,” Booth said.

It also has to be an area that has been historically active. The process can’t determine the level of increased risk for a scorched area, such as the Columbia River George. That still requires expensive drilling to see what is happening under the surface.

“We have to find out where is the water,” Leshchinsky said. “That has to be done by drilling to characterize the subsurface. Until we develop X-rays that will get us under the surface, we have to use these expensive methods.”

The new process can still be helpful for parties that plan, build and maintain transportation, utility and rail lines. Currently, the process is being used on the southern Oregon coast to help Oregon Department of Transportation officials determine where they should direct equipment and personnel to clear potential slides this winter.

“They have an interest because they have a lot of linear infrastructure,” Leshchinsky said. “We are in a very mountainous state with quake hazards. This can help ODOT to prioritize the roads.”

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