Geologists find tsunami hazard in eastern Aleutian Islands

  • By Dan Joling
  • Wednesday, January 13, 2016 11:02pm
  • News

ANCHORAGE — Geologists in Alaska have found evidence that a 125-mile section of the eastern Aleutian Islands that was once considered unlikely to generate earthquakes may be a future source of temblors — as well as potentially devastating tsunamis that could hit Hawaii.

Field work by U.S. Geological Survey scientists on Sedanka Island near Dutch Harbor, a major U.S. fishing port, revealed “sand sheets,” or deposits of sand lifted off beaches and moved a half-mile inland. The sand sheets indicate large tsunamis had hit frequently — in geologic time.

“This is the first Aleutian study to report evidence for prehistoric tsunamis, and the recurrence intervals are in geologic perspective very short at 300 to 340 years,” said USGS geologist Rob Witter.

The Aleutians, stretching about 1,200 miles, are part of a subduction zone where two great tectonic plates collide. The Pacific Plate, beneath the Pacific Ocean, is slowly being subducted, or pushed below, the North American Plate that covers most of North America.

Prevailing models show that friction locks up the two plates, and elastic energy builds until the strain is too great and there’s an earthquake. The largest releases in the form of megathrust earthquakes shift hundreds of miles of earth and create devastating tsunamis.

A 1946 earthquake 90 miles south of Unimak Island in the eastern Aleutians stopped before it reached the area near Dutch Harbor. The earthquake created a tsunami that killed six people in Alaska, including five Coast Guardsman at a lighthouse on Unimak Island, and 159 people in Hawaii.

A 1957 quake tore 745 miles of ground near Adak in the western Aleutians but stopped short of the area around Dutch Harbor. A tsunami took no lives but caused widespread damage in Hawaii.

The 125-mile-long area in the eastern Aleutians has been an enigma, Witter said. It was thought to be over a “creeping” fault where the plates move continuously without building up strain.

A tip from a retired Humboldt State University geologist, Gary Carver, who saw sand sheets on Sedanka Island led to the study by Witter and other researchers. The oldest sand sheet appeared to be deposited 1,700 years ago. The newest was deposited in 1957.

“In this particular area, what’s surprising is that it’s creeping, yet we have evidence for large tsunamis that may have been caused by megathrust earthquakes in the past,” Witter said.

The USGS researchers made no recommendations for earthquake modeling affecting Hawaii, but officials there have used the information to broaden tsunami evacuation zones, Witter said.

More in News

Soldotna City Hall is seen on Wednesday, June 23, 2021 in Soldotna, Alaska. (Ashlyn O’Hara/Peninsula Clarion)
Soldotna bumps vote on use of accessory housing as short-term rentals

An accessory dwelling unit is a subordinate, detached dwelling unit located on a lot or parcel with an existing residence

Foliage surrounds the Soldotna Police Department sign on Tuesday, Aug. 30, 2022 in Soldotna, Alaska. (Ashlyn O’Hara/Peninsula Clarion)
Foliage surrounds the Soldotna Police Department sign on Tuesday, Aug. 30, 2022, in Soldotna, Alaska. (Ashlyn O’Hara/Peninsula Clarion)
Law enforcement to host women’s self-defense class in January

Within 48 hours of the course being advertised, 120 women had signed up to participate

Alaska State Troopers logo.
Local hunter credits community members for Thanksgiving rescue

Glover said he didn’t even strike out from his home to go hunting

In this July 13, 2007, photo, workers with the Pebble Mine project test drill in the Bristol Bay region of Alaska, near the village of Iliamma. (AP Photo / Al Grillo)
EPA proposes restrictions to block Pebble Mine

Mine developer Pebble Limited Partnershi called the EPA’s decision a preemptive veto

Architect Nancy Casey speaks in front of a small gathering at this year’s final Fireside Chat presented by the Kenai Watershed Forum on Nov. 30, 2022, at Kenai River Brewing in Soldotna, Alaska. (Jake Dye/Peninsula Clarion)
Building with the environment in mind

Kenai Watershed Forum’s Fireside Chats conclude

Johni Blankenship signs her name after being sworn in as Soldotna City Clerk at a city council meeting on Wednesday, Nov. 30, 2022, in Soldotna, Alaska. (Ashlyn O’Hara/Peninsula Clarion)
Blankenship sworn in as Soldotna city clerk

Blankenship comes to the City of Soldotna from the Kenai Peninsula Borough

Demonstrators hold signs supporting Justin Ruffridge and Jesse Bjorkman for state office on Election Day, Nov. 8, 2022, in Kenai, Alaska. (Jake Dye/Peninsula Clarion)
Nov. 8 election results certified

The outcomes of local races for state office remain unchanged

The Kenai Peninsula Borough administration building is photographed on Tuesday, March 17, 2020, in Soldotna, Alaska. (Photo by Victoria Petersen/Peninsula Clarion)
4 candidates vie for borough mayoral seat

The special election is slated for Feb. 14

Spruce trees are dusted with snow on Dec. 22, 2020, in the Kenai National Wildlife Refuge near Soldotna, Alaska. Some areas of the refuge are open to harvest of holiday trees for non-commercial uses beginning Thanksgiving. (Photo by Jeff Helminiak/Peninsula Clarion)
Snowmachine use permitted in Kenai National Wildlife Refuge beginning Dec. 1

Areas now available include those “traditionally open to snowmachine use”

Most Read