Geologists investigating Ketchikan landslide causes, after four fatal Alaska slides in a decade

Landslides like the one that killed a man in Ketchikan on Sunday can strike with little warning, sending earth and trees crashing down a mountainside as fast as a car on a highway.

Scientists are still looking into what factors were at play in the deadly Ketchikan landslide, but rainfall saturating the ground, potentially triggered by wind, are common culprits in landslides in Southeast Alaska. There’s also the increased frequency and severity of weather events associated with climate change.

Gabriel Wolken is manager of the Climate and Cryosphere Hazards Program for the state Division of Geological and Geophysical Surveys. Wolken says landslides are often the result of a complicated series of events.

Listen:

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This interview has been lightly edited for length and clarity.

Gabriel Wolken: Several factors contribute to the development of a landslide, and then triggering is something else, too. Saturated ground can elevate landslide susceptibility, and this causes a reduction in the stresses that hold the soil particles together, the rock together, just inserting water in between different soil particles, and it causes those particles to separate, no longer interlock. And so that’s typically what happens during precipitation events, especially extreme precipitation events, when there is a lot of moisture falling to the ground. And this is especially the case when soils are already saturated.

And then several factors contribute to the development of landslides. You know, rainfall, snowfall, temperature changes, and of course, wind is one of those. Typically, wind’s influence on the development of landslides has to do with the wind’s impact on trees, and then how the tree acts as a lever on the soil,and the different physical interactions that happen at that point.

I just want to underscore that we really don’t know enough about the landslides in Ketchikan to make any sort of statements about the causes, the triggers, at this point, but we’re really investigating it right now. We have many of our folks, partners on the ground, investigating the landslide right now, assessing it, assessing the stability of the slope, and then later, you know, we’ll really dive into trying to understand what actually happened.

Casey Grove: Yeah, that makes sense. So I wanted to ask you about something that has come up. I think it’s been four fatal landslides in the last 10 years or so. And, you know, folks are talking about how it seems like these are happening more frequently. Is that true? And do we have any kind of sense of why that might be?

GW: Yeah, I mean, it does. It does seem that way. I agree, 12 fatalities in the last decade or so is a lot, and this is hard to deal with. And, you know, our thoughts go out to the people who are impacted by these disastrous events. But in terms of determining whether or not landslides in Alaska are occurring more frequently in recent decades or in recent time compared to those in the past, is really quite difficult, if not impossible, to answer at this time, really due to a few factors. And really the most influential, perhaps, is the inconsistencies in landslide reporting. And so it means that we really don’t have a detailed enough historical record in Alaska, the records really don’t go back far enough for us, to be able to fully assess whether or not there has been an increase in landslides in recent time.

CG: Hypothetically, I mean, seeing the effects of climate change on so many different parts of our lives and so many different parts of the terrain out there, would you expect that that could be something that would increase, maybe, the frequency of landslides?

GW: Right, yeah, so again, the caveat is always (that) Alaska is fairly data sparse, and so it’s really hard to answer this question directly. But what is clear is that as the world warms, climate change is making adverse and extreme weather events both more likely and worse.

And so while these areas, such as Southeast Alaska, are already quite damp and windy at times, increases in temperature, precipitation and wind likely will have noticeable effect on the landscape, and that could include a change to what we consider to be the frequency and magnitude of natural hazards right now. And so in other places in the world, there have been connections to increases in the frequency of landslides with increasing temperature and precipitation. That’s entirely likely for Alaska, but we cannot say definitively that that’s that’s indeed the case at this point.

CG: So I appreciate you being the one to step forward and talk to me about this today, and I don’t mean to put this huge question just on you alone, but what are we supposed to do about that? I mean, what can local, state, federal agencies do? What sort of things are underway, maybe already, to help people avoid the adverse impacts of of landslides?

GW: Right, well, I think what’s really important is that we have very good relationships going on right now between state, federal agencies, local government agencies, universities, all really good relationships. We have partnerships in play, and the goal really is to try to work together to make sure that we’re doing all we can with what we have to provide a resilient state, resilient communities, by increasing the knowledge of the conditions that create landslides and to try to just generally make things safer for people.

And what this ends up being is a very challenging area to work, and we cannot with absolute certainty, you know, provide predictions about landslides, or anything even remotely close to that. But what we can do is evaluate landslides that have happened. We can make sure that we’re recording landslides and specific events properly so that we can use that to increase our knowledge and hopefully predict how landslides might occur in the future.