Experts warn Oregon: ‘Be prepared for rockfalls, landslides’


Small landslides and debris flows can happen years after a fire, experts say

PORTLAND, Ore. (KOIN) –– Forestry and geological experts continue to warn people about the danger of rockfalls and landslides in parts of Oregon as areas torched by wildfires brace for more thunderstorms. 

Some areas saw heavy rain Friday but the sun was shining in Marion County, glistening off blackened needles and tree debris along the banks of the North Santiam River as ash settled in nearby pools and puddles. 

The smoke and haze briefly lifted in Stayton earlier in the day, revealing distant hills and forests –– some of which were still smoldering. 

Many people were also getting their first look at rockslides and damage to roads like Highway 224. 

Scott Burns, a geology professor at Portland State University, said experts in the region have a better idea of what residents and drivers need to be aware of after studying the effects of fires in the Columbia River Gorge. 

“We tell people to be prepared for rockfalls, small landslides and then there will be water in the streams and it’s going to be dirty,” Burns told KOIN 6 News. 

Burns said areas weakened by fires are prone to rockslides, followed by erosion. 

“As the rains come in, there will be a lot of surface erosion of all of the charcoal and ash that is on the ground, so that’s going to get into the stream,” he said. 

Small landslides and debris flows are then likely occur years after a wildfire, especially in high-drainage areas. 

“There is a 5-10 year delay because the roots that are holding all the trees they are still in the ground,” Burns explained. “The top of the trees burned off but the roots are still there. It takes 5-10 years to disintegrate.” 

In Mill City, transportation officials were working feverishly to remove dangerous trees from the immediate roadside. The town’s mayor said that while the community is mostly focused on rebuilding lives right now, he’s aware of other challenges ahead. 

“The washing out of all the burned-out residences is going to put all kinds of toxins into the river,” Tim Kirsch said. “So we want to be able to secure and start our cleanup process as quickly as possible.” 

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