New study provides insight into 2020 Beach Road landslide

There will be an uptick in helicopter activity this week near town as geologists collect data to map past and potential landslide areas across the Haines Borough.

The researchers, from the University of Alaska, Fairbanks (UAF) and the Alaska Department of Geological and Geophysical Surveys (DGGS), are seeking to understand geologic hazards and provide information to the borough that could help avert future damage.

Their project involves capturing high-resolution images, conducting helicopter surveys and taking soil samples — data they will use to assess slope stability along Lutak Road, Haines Highway and Beach Road, among other slide-prone areas.

Geological engineering professor Margaret Darrow is the lead researcher in town from UAF. She has been studying Haines’ geology since the December 2020 weather event; her research led to publication of a paper last month investigating causes of the deadly Beach Road landslide and underscoring the importance of geologic mapping to assess risk and warn residents.

“When the Beach Road slide happened in 2020, I was sitting in my house in Fairbanks listening to the radio, and I gasped when I heard what had happened,” Darrow said. “And I started thinking, ‘Gosh, what could I do to help the community?”

Darrow and her fellow researchers use LiDAR (Light Detection and Ranging) imagery to inspect the geologic structure of hillsides. The technology is like a geologist’s x-ray machine; it lets scientists see through vegetation, giving a glimpse of the ground’s anatomy.

Darrow’s paper, titled “Geomorphology and initiation mechanisms of the 2020 Haines, Alaska landslide,” determined that the Beach Road slide wasn’t the first slide on Mount Riley’s north ridge. Using LiDAR she examined head scarps — steep sections of rock that indicate past slides. (“Scarp” is short for “escarpment”; a head scarp is the area at the top of a landslide.)

Darrow said she was able to determine that there was a slide at the end of Beach Road between 250 and 11,000 years ago. More research — such as rock sampling — would be needed for more precise dating. Landslides are more likely to occur where they have already happened, Darrow said.

The research outlined in her paper — which had six co-authors including local geologist Cindy Buxton — “illustrates the importance of identifying pre-existing landslide features and source areas likely to produce future landslides,” the authors wrote.

They estimated that 187,000 cubic meters of material moved during the Beach Road slide. That’s enough to fill 48 dump trucks, each carrying 14 tons of debris, every day for an entire year, Darrow said. About 58,000 cubic meters settled on the hillside and the rest washed into the ocean, she estimated.

The paper also summarizes weather, noting that the slide occurred during a rain-on-snow event caused by an atmospheric river. Given that Southeast Alaska is projected to get warmer and wetter, with increasing likelihood of rain on snow, the researchers recommended developing an atmospheric river scale, to measure rainfall intensity, “coupled with geological information for the region, to enhance warnings to residents in landslide-prone areas.”

The current mapping project is an extension of Darrow’s Beach Road research, funded by a National Science Foundation grant.

While Darrow was researching the Beach Road slide, which stole regional and national headlines, she said she heard from Haines residents that there was also a lot of damage elsewhere.

“There were so many events all over Haines, and you really need to capture that,” she said.

One of her graduate students is now working to map all the slide events that occurred near borough infrastructure. They plan to make the map available to the community, Darrow said.

This summer’s work will set the stage for a bigger geologic mapping campaign next summer, Darrow said.

Borough manager Annette Kreitzer said geologists are also doing a LiDAR analysis of the future Mount Riley subdivision area — dozens of forested acres north of Carrs Cove.

After a fatal 2015 landslide in Sitka, DGGS mapped and modeled geologic hazards there, which resulted in controversy over the maps’ impact on property values, insurance and the ability to acquire bank loans.

Once the state’s mapping in the Chilkat Valley is finished, residents and officials will have to reckon with how to respond to landslide risks.

Darrow said she’s not sure another paper will come out of her research in Haines but she is interested in compiling information about the community’s emergency response.

This summer’s data collection, and associated helicopter activity, will end July 30.

Darrow said residents with questions could contact her at [email protected].