Geologist explains science of landslides in Southeast Alaska

KETCHIKAN, Alaska (KTUU) – Geologists with the State of Alaska are currently in Ketchikan researching slope conditions in an effort to ensure the area is safe before looking into the actual cause of Sunday’s deadly landslide.

“When talking about this, it’s really difficult to imagine what the residents are going through, and our thoughts are really with the families impacted by the recent landslide,” Dr. Gabriel Wolken, the manager of the climate and hazards program with the Alaska division of geological and geophysical surveys, said on Wednesday.

Wolken is also a research professor at the University of Alaska Fairbanks.

“[Geologists are] making sure that the area is safe for the responders and the people trying to put their lives back together. And then soon after this, we will thoroughly analyze the information and the data that are being collected by the geoscientists on the ground, and come up with some causal mechanisms for this event.”

While not sure of the root cause of the landslide — which claimed the life of 42-year-old Sean Griffin — Wolken says that landslides are nearly impossible to predict.

Wolken said geoscientists are gaining a better understanding of what conditions need to be present in order for landslides to occur.

“One thing that is certain is that extreme weather can play a large role in how landslides develop, and intense, prolonged rainfall can play a really large role in this. It can weaken the stability of the slopes,” Wolken said. “This is especially true if the slope’s already saturated, [rainfall] can change the condition of the soil, causing the pore pressure in the soil to increase, which really weakens the stability of the slope. So whenever there’s a lot of rain, a lot of extreme weather, then that can be problematic.”

Wolken says there are warning signs that a landslide is imminent, particularly in Southeast Alaska, where people can keep an eye out for springs in the soil.

That, he says, is an indication the soil is quite saturated. New cracks in the ground or unusual bulges are something to watch out for as well.

“Another thing to keep a lookout for is any precursor indications that movement is occurring, perhaps in a creep fashion,” Wolken explained. “So if you’re in your house, you might notice that there’s cracks that have developed in the drywall or plaster — if you have that in your house — or maybe the door is not closing properly.

“These are all indications that things are kind of changing in the structure of the house, and those are things to look out for in the event that a slow creep might be occurring on the slope.”

Wolken is leading a study on landslide hazards in Haines, 364 miles northwest of Ketchikan. The project is analyzing data from the spring of 2021, taken one year after a deadly landslide claimed two lives.

“There have been too many destructive and deadly events, resulting in 12 fatalities in the last decade,” he said. “So determining whether landslides in Southeast Alaska are occurring more frequently in recent years than in the past is very difficult, if not impossible, to answer at this time.”

He says it’s difficult to determine if landslides are happening more frequently because of a lack of data, as well as inconsistencies in landslide reporting. He explained that the research in Haines is ongoing and reports are currently being prepped.

That’s the work that’s happening now. Scientists and geologists are collecting data that will provide future generations with a better understanding of why these landslides occur.

“Our work is really aimed at generating the actionable science that is needed to improve decision-making across the state, across multiple sectors of society,” Wolken said. “And this doesn’t stop at one landslide. This doesn’t stop at one location of the state.

“So we’re really focused broadly on a statewide landslide hazard preparedness, which means that we’re focused on lots of different places at a single time to try to understand, characterize and assess these different places.”

The work now is happening in Ketchikan, as people like geologist Martin “Mort” Larson are collecting data.

“They’re very busy on the ground, going to different places in the high elevation terrain, looking for different signatures on the landscape that would indicate unstable slope conditions, and that can vary across the board, but certainly looking at saturated ground issues, any scarps that are on the landscape, and doing some preliminary mapping of the area,” Wolken said. “We have deployed personnel to the area to work with our partners from both state and federal agencies. I know that the Department of Transportation is collecting some airborne drone-based remote sensing that’s helping with the folks on the ground in a rapid response sort of way, we have deployed a remote sensing specialist to go down and collect some broader Lidar of the area so that we can use that in our analysis.”

Copyright 2024 KTUU. All rights reserved.