Alaska's Landslide Zones: Where They Are, How Large They Are
New report identifies and maps thousands of documented Alaska landslides FROM THE ALASKA BEACON https://alaskabeacon.com/ BY: YERETH ROSEN ...
New report identifies and maps thousands of documented Alaska landslides
The source area and upper portion of a landslide runout at Pedersen Lagoon near Seward are seen on Aug. 9, 2024. The landslide that occurred two days earlier caused a local tsunami that reached a height of about 56 feet. This type of landslide is among many different types described in a newly published state landslide inventory. (Photo by Jeff Pedersen/Alaska Wildland Adventures/Provided by the U.S. Geological Survey)
More than 10,000 known Alaska landslides or landslide-related events are documented in a new state inventory intended to help improve understanding of risks and what can be done to improve safety.
The inventory, published by the Alaska Division of Geological and Geophysical Surveys, is intended to be integrated into a national landslide inventory maintained by the U.S. Geological Survey.
It will be updated as more information is collected, said Jillian Nicolazzo, a geologist who leads the division’s landslide hazards program.
“This is the first step just to sort of get everything in one place,” Nicolazzo said. “Now that we see what we have, we can start looking at what we don’t have and start filling in the gaps.”
To compile the inventory, state scientists pored over more than 1,000 USGS maps and reviewed aerial imagery, published news accounts and other information on where landslides have occurred in the past. Many of those USGS maps dated back to the 1950s, when the agency was trying to scope out opportunities for mineral extraction or infrastructure development, Nicolazzo said.
“They weren’t looking for landslides. They were just trying to map the geology. And if they happened to see landslides too, they might have noted it on the maps, but they also might not have,” she said.
One map that contributed to the inventory is even older; it was created in 1915.
The new searchable landslide inventory features an Alaska map with colored dots representing the type of event that occurred at each site. Some are slides in which unstable upper layers detach from more stable lower layers. Some are abrupt falls that send rocks or boulders tumbling. Some are considered “flows,” a category that includes the continually moving frozen debris lobes dotting the Brooks Range. Some are considered thaw events. Those and other types of events are described in the inventory.
The dots on the map fill most of the southern half of the state, from the eastern Interior to the eastern Aleutian Islands, and are spread across the Brooks Range in the Arctic. The relatively empty spaces do not necessarily represent a lack of landslides, Nicolazzo said. Rather, those reflect a lack of reports, she said.
So far, the inventory includes only some of the events that have occurred in Southeast Alaska, where slides have killed 12 people in the past decade. That region of the state is already covered by an extensive and periodically updated inventory of landslides in the Tongass National Forest, which comprises most of the Southeast region.
While much of the information used for the inventory is old, Alaska’s landslide monitoring work is relatively new, at least when compared to the programs that have been underway for decades in countries like Norway and Switzerland.
The Division of Geological and Geophysical Surveys’ landslide hazards program was established only three years ago, and the inventory has been one of its major projects.
Compared to those other countries, “we’re in the beginning stages. But we have to start somewhere,” Nicolazzo said.
To meet the challenge, agencies have mounted a group effort, she said.
“The state is very large, and we don’t have a lot of state employees working on it. There aren’t a lot of federal employees working on it,” she said. “We tag-team different tasks to each of our strengths.”
Funding to support the effort is also limited, she said. She pointed to the multiagency work monitoring the high-risk Barry Arm landslide site in Prince William Sound as evidence of that.
“There is a lot of money spent on equipment looking just at that one landslide, and we know it’s not the only one in the area,” she said. “It would require a lot more money than we have available to monitor everything the same as we’re monitoring that one.”
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