322 Years Ago This Week: Cascadia Tsunami Hits Oregon Coast, Washington Coast

Published 01/27/22 at 12:06 AM PST
By Oregon Coast Beach Connection staff

(Pacific City, Oregon) - 322 years ago, on January 26 in the year 1700, the Oregon and Washington coast, along with parts of Japan, were absolutely deluged by a massive tsunami. In the case of the Pacific Northwest, the reach was miles inland in some areas. (Above: ghost forest tree near South Beach, courtesy Robert Dziak, Hatfield Marine Science Center)

The cause was a great subduction event off the west coast of the future United States, taking place at a spot where the two continental plates collide and butt up against each other. Every once in awhile, something has to give and what's called the Cascadia Subduction Zone erupts in a violent submarine earthquake. What happened afterwards was a gargantuan displacement of ocean water, leading to a tsunami on the shores of more than one continent.

To native tribes in the region at the time, it created an epic tale of struggle between two powerful entities, Thunderbird and Whale. The stories vary as to which one was the villain, but the end result was shaking Earth and an ocean that suddenly retreated, then just as abruptly came screaming inland, wiping out whole villages and leaving canoes in trees.

Above: ghost forest stump near Coos Bay, courtesy Brent Lerwill

On the other side of the world, written history by the Japanese confirms a similar story and provided the date. It took scientists and historians awhile to piece all that together, but with carbon dating of Oregon and Washington coast ghost forests in estuaries just inland – as well as parts of the soil – the late 20th century started to put various puzzle parts into place.

There had been a subduction zone event that was cataclysmic, and at one point scientists had the date.

After all, geologists poking into the Washington coast and Oregon coast had long been finding tsunami evidence in ancient dead trees as well as the layers of ground just inland from the beaches. Along the estuaries, in places like Coos Bay, Pacific City, Grays Harbor or near Cape Lookout, the cutaway cross sections of riverbanks showed a variety of layers, each looking back in time. Scientists could see the layers of old campfires and discarded debris from native tribes, and on top of that there were sandy and soil layers belonging to the stuff closer to the ocean. That had been transported by some powerful means: many of these research sites were miles inland from the coast.

Ghost forest stump near Coos Bay, courtesy Brent Lerwill

In fact, researchers could see more than one such apocalyptic event. According to the Oregon Department of Geology and Mineral Industries, regarding Nestucca Bay at Pacific City:

“Three tsunamis triggered by great earthquakes on the Cascadia subduction zone have inundated Nestucca Bay, Oregon over the past 2000 years. The primary evidence includes layers of sandy sediment that bury tidal marshes submerged by earthquake-related subsidence. Additional tsunami evidence includes: the spatial extent of sandy deposits, clear trends in deposit thickness and mean particle size that decrease with increasing distance inland, the presence of brackish-marine diatoms within the deposit and normally graded layers within each deposit.”

There, scientists discovered the tsunami waves had reached over 4 km inland from town.

Near Copalis on the Washington coast, ghost forests have long been giving clues to the same tsunami. That set is about one mile upriver from the beach.

Over the last 40 years or so, scientists helped put a date on this tsunami by noting the rings of dead trees they found in estuaries. Matching them to similar trees farther inland that hadn't been turned to ghost forests by a sudden drop, they counted the rings inside the trees in the estuaries of areas like Coos Bay, Seaside, near Newport or Copalis. That, plus carbon dating of trees and soil layers, brought them to 1700.

These ghost forests aren't quite as spectacularly spooky as those found on the beaches: ghost forest stumps found in places like Neskowin, Newport, Seal Rock or Arch Cape are far older than 1700, sometimes by thousands of years. Regional media still mix up beach ghost forests with the 1700-era trees found just inland. (See Explanations of Neskowin Ghost Forest Wrong, Say Oregon Coast Geologists)

Such new ghost forests are discovered periodically. Last year, a Hatfield Marine Science Center researcher found a set of 40 trees near South Beach that were leftover from that quake. Also in 2021, Oregon Coast Beach Connection helped identify another set near Coos Bay that researchers had not yet documented, as well as in Netarts Bay.

Nature is unforgiving with its earthquake predilections, and history is doomed to repeat itself here on the Washington and Oregon coastlines. The last big one was estimated at a magnitude 9 or so, and that will again happen offshore. Scientists say the average frequency for the Cascadia Subduction Zone is every few hundred years – and it's already been 300 years.

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Netarts ghost stump, courtesy Dillon West

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