Eyewitness account of landslide presents research interest

Published: Jan. 23, 2021 at 8:31 PM AKST
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ANCHORAGE, Alaska (KTUU) - An eyewitness account of a December landslide presents research interest which Alaska may soon get more of since former President Trump recently signed the National Landslide Preparedness Act.

On December 24, a mountainside gave way about 50 miles from Juneau just over the Canadian border in the Taku River Valley.

“I would imagine it would be felt similar to an earthquake,” Natalia Ruppert, seismologist at the Alaska Earthquake Center said. “Like very weak shaking considering how far it was and how it wasn’t really large as far as the magnitude. I would imagine, it was very weak, mild-to-weak shaking and that people felt.”

Ruppert said the landslide was picked up on sensors, and registered somewhere near a magnitude 2.9 earthquake. However, the rumble was from the landslide falling, not faults moving.

It’s common for landslides to be picked up by seismic sensors, but many found in data aren’t seen in nature, Ruppert said.

“We do absorb landslide signals on our seismic cycles sensors quite frequently actually,” Ruppert said. They can be very small, or up to the equivalent of a magnitude five earthquake.

However, this is a rare instance where there were eyewitness accounts. “We were able to find it in our seismic records, so it’s just interesting for us,” she said.

Pilot Jamie Tait didn’t see the landslide fall, but he got a birds-eye view of the aftermath a few days later on December 26.

Landslide in the Taku River Valley
Landslide in the Taku River Valley(Jamie Tait)

“It’s pretty massive. It looks like a very large chunk of the mountain came off and fell down the mountainside,” Tait said.

The landscape near the slide isn’t new to Tait. He was able to spot it from about 10 miles away.

“I’ve flown up and down that river for the better part of 40 years and recognize pretty much every corner of it. The slide was pretty, pretty immense. So it was pretty obvious from a long ways away,” Tait said.

A few days after he first saw the slide, Tait went back to check it out. He landed his helicopter at the foot of the mountain. When he saw the destruction from the ground, he had one word.

Pilot Jamie Tait visits a landslide in the Taku River Valley days after it fails. A man is...
Pilot Jamie Tait visits a landslide in the Taku River Valley days after it fails. A man is standing in front of a rock at the base of the slide for size.(Jamie Tait)

“Wow,” he said with a chuckle. “It’s hard to describe because Mother Nature is out there doing her thing. And we absolutely have no way to manage what she does.”

But this isn’t the first time Tait has seen Mother Nature at work from his helicopter.

Tait said several years ago he saw a landslide that blocked the Inklin River, which feeds into the Taku River.

“It had backed up for a day or so before it let go,” he said.

Tait was also able to see Russel Fjord when Hubbard Glacier dammed it years ago. He said it was a significant event.

But he said the Taku River Valley landslide is by far the largest he has seen.

Ruppert said Tait’s eyewitness account presents research interest. Geologists and seismologists are always looking for data where they have pictures.

“It’s just another case study that in the future it can be used to model or as an example of what can happen with this landslide phenomenon,” she said.

Alaska may soon get more research opportunities. Former President Trump recently signed the National Landslide Preparedness Act. For Alaska, it could mean many things, including much needed mapping.

“We are a big state, and we are a fairly young state. And when you look at the status of geologic mapping of many kinds across our state, there’s large gaps. The resources are not sufficient to do all the work that needs to be done to fill any of those maps,” Steven Masterman, director of the Division of Geological and Geophysical Survey said.

That applies in Prince William Sound and the Southeast. It could help identify more landslides like what’s in Prince William Sound’s Barry Arm, which is threatening to release into the water and create a destructive tsunami that could hit Whittier and nearby towns.

“The terrain in Southeast Alaska, and in Prince William Sound, it’s so rugged, it’s so steep. And many areas are steeper than the angle of repose of the material that the hills are made out of,” Masterman said.

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