A team of researchers led by Oregon’s Department of Geology and Mineral Industries recently lasers surveys of the area burned by the Eagle Creek fire in 2017 to better understand how frequent and severe landslides can be after wildfires. Much of the landslide research that has been done previously is in dryer desert climates. This new research will help communities understand landslide dangers after severe wildfires in wetter, forested ecosystems like Western Oregon. Bill Burns, engineering geologist for DOGAMI, joins us to expand on why the research matters.
Note: The following transcript was transcribed digitally and validated for accuracy, readability and formatting by an OPB volunteer.
Dave Miller: From the Gert Boyle studio at OPB, this is Think Out Loud. I’m Dave Miller. In September of 2017, a wildfire caused by a teenager’s fireworks ripped through the Columbia River Gorge. 50,000 acres eventually burned in what became known as the Eagle Creek Fire. We now know more about the aftermath of the fire.
A team of researchers led by Oregon’s Department of Geology and Mineral Industries, or DOGAMI, recently did laser surveys of the Eagle Creek area to better understand the likelihood and the severity of post-fire landslides. Much of the previous research had been done in drier climates. This new study could help communities understand these dangers in wetter, forested ecosystems like western Oregon.
Bill Burns is an engineering geologist for DOGAMI, and he joins us now. It’s great to have you on Think Out Loud.
Bill Burns: Yeah, hi Dave. Thanks for having me.
Miller: What were the biggest questions that you had going into this study?
Burns: Some of the questions we had were, “are we even gonna have post-fire debris flows in western Oregon?” It is just so different here than it is in these other drier, arid regions of the United States that we see these types of events happening.
Miller: You say debris flows. I used the word landslides. I’ve seen mudslides. I’ve seen debris flows. Is there a distinction here? Are we talking about the same thing?
Burns: Yeah, great question. Debris flows are a little different. They are kind of a unique type of landslide that enters the channel system and then comes down the channel system entraining more material, growing in size and speed. And then they tend to flow out of the channel at the mouth of the channel and engulf anything that’s there. The real issue is that they can move very fast, and what that does is unfortunately presents a life safety threat.
Miller: Is a channel system different from, say, a side of a mountain just sloughing off?
Burns: Yeah, it is. The channel kind of provides what we call confinement, which is the edges of the channel that keep the material together and moving together as a single mass instead of allowing it to kind of spread out.
Miller: So you had said that one of your big questions is, would there even be these debris flows in the historically wetter side of the Cascades, a place like the Columbia River Gorge. What did you find out? Did these slides happen post-fire?
Burns: Western Oregon is very prone to these types of landslides and debris flows, without a fire. And so what we were trying to find out is how does the fire affect this? What we saw was that the fire does affect these types of landslides in western Oregon, but it’s different than what we see in these arid climates, like in Southern California and other places like Arizona.
An example would be, if you think about the hazard curve in these arid climate regions, what happens is right after the fire, the hazard curve goes way up, and then it kind of quickly comes back down within a year or two, back down to the background rate. And what we’re finding is that in western Oregon, it may take several years for that hazard curve to get up to where it’s at this increased level, and then unfortunately it may stay up there for several decades.
Miller: Wow, that’s really different. It actually seems maybe silly to compare relative risks, but if the question is bad for a year versus a delay and then bad for decades, I think I would prefer the former. Is it possible for you to explain the difference in those, as you say, hazard curves to those of us who are not geologists?
Burns: So there are some kind of significant differences between western Oregon and these drier climate areas. So for example, the geology is very different. In the Cascades, we have these deeply weathered volcanic soils. The biodiversity that we have up here is extremely different. We have dense forest and understory and huge trees. And then finally, the climate is different, right? It tends to be very dry there, and then they get kind of convection storms once in a while. Whereas, as we’re all very familiar, it rains here all winter.
And then occasionally we have these atmospheric river type storms, which can give us kind of a one-two punch. And what they can do is they can rain really hard, intense rainfall for several days, but then they also bring this temperature increase which can melt snow, and that’s where you get that one-two punch. You get kind of all this rainfall and that added precipitation, that added water from the snow melt, and it’s just too much water for our system to handle.
Miller: Climate change is obviously leading to more severe fires. Will it also lead to more landslides or debris flows?
Burns: What this study found was that if we have fires, it’s very likely to increase landslides and debris flows. And what a lot of the climate scientists are saying is that they predict that we’re going to have more fires. So with more fires we’ll likely unfortunately come more landslides and debris flows.
Miller: What do you see as the potential practical applications of your findings?
Burns: It’s interesting because just understanding the process better helps us understand how to reduce future risk. An example would be now that we are starting to understand that the elevated hazard may not just be for a couple of years, it may be for decades, what that’s gonna help us do is, you know, not let our guard down after only a couple of years, to be more on alert for a longer time period.
Miller: That sounds like it’s still about being aware that there could be a debris flow, as opposed to stopping it. Is there a way post-fire and going on for decades to make these flows less likely, or is it more let’s not be under it when it happens?
Burns: I think it’s a combination of both. In some places, it’s very difficult to move things, like roads that are already in place. And so in those cases, we need to be aware of these time frames when this hazard is increased, which is like I was saying, during periods of heavy rainfall.
But then there’s other things we can do, like planning activities to try and keep future development from happening in these areas. Or at least when it happens, maybe thinking about mitigation and reducing risk as we do that.
Miller: Bill Burns is an engineering geologist for DOGAMI. We talked last week.
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