Eight years ago, Portland State archaeologist Sarah Sterling came across an unusual find in the ancient tribal village site of Tse-whit-zen, near Port Angeles, Wash.
Courtesty of Brian Atwater
Sarah Sterling (right), a PSU archaeologist, and Ian Hutchison, a professor at Simon Fraser University, examine possible tsunami deposits near the mouth of Salt Creek in Clallum County, Wash.
The village appeared to have been abandoned every few hundred years, according to gaps in her radiocarbon sequencing.
The curious find led her to develop a hypothesis that caused a surge of research to follow it.
Her explanation: more than one tsunami, spaced hundreds of years apart.
Since then, the area has been the major focus for researchers from across various disciplines interested in the region’s earthquake and tsunami history.
In May 2012, Sterling went back to Salt Creek Marsh, 17 miles west of Port Angeles along the Strait of Juan de Fuca shoreline, to look for more evidence in the layers of sand tsunamis left behind.
“They show up very clearly in organic, rich marsh sediment,” Sterling said.
With her was geologist Ian Hutchinson of Simon Fraser University in Vancouver, British Columbia. The research was made possible by a PSU Faculty Enhancement Grant.
“When it comes to finding evidence for tsunamis, you need a geologist,” Sterling explained.
The method for examining ancient tsunami evidence involves a process known as coring, which uses a cylinder to bore into the ground and bring up a sample of earth.
COURTESY OF Sarah Sterling
AT SALT Creek Marsh, radiocarbon dating shows when sand layers were deposited.
The sediment “core” is then examined and assessed—in this case, by Sterling and Hutchinson—for deposits left behind by tsunamis. The team examined target sand sheets for evidence of marine shell fragments. Through radiocarbon dating, these shell fragments provide the evidence for marine surges, indicating a tsunami.
Sterling was hoping to find a link between the abandonment dates at the village and the patterns found in the marsh sediment.
“We went with the goal to see if we could prove if ancient tsunamis previously recorded in the region correlated with the measurable gaps in the radiocarbon sequence I found,” Sterling said.
After collecting their data, the team came up with two estimated dates of ancient tsunamis.
“Right now, we are finishing up the draft for publication, and it will hopefully pass to a journal in the not-too-distant future,” Sterling said.
Currently, Sterling is working with professor Virginia Butler on a National Science Foundation grant to study how large earthquakes and tsunamis affected resource availability and subsistence practices in
Tse-whit-zen.
Portland State geologist professor Curt Peterson led a separate study at Neah Bay, on the tip of the Washington Olympic Peninsula.
“The work on Neah Bay is separate from the work in Port Angeles conducted by [Sterling], but the common link is in examining the possibility that native peoples were impacted by Cascadia earthquakes and associated tsunamis,” Peterson said.
His findings, will be published in the Journal of Coastal Research early next year, reporting the dates of four tsunamis in the area.
Peterson and his team have also completed a paper on major paleotsunami recurrence intervals in the Cascadia area that will be submitted to the science journal Natural Hazards at the end of this week.
The time between the tsunamis varies from a couple hundred years to 800 years, with the most recent tsunami date estimated to be 300 years ago.