TECHNOLOGY

The long-lost story of the 18th century tsunami, as the trees told it


And don’t forget the trees. In the 1990s, researchers identified a “ghost forest” of dead cedars off the Washington coast; Tri-ring dating has confirmed that they actually died in 1700. Survived. The rings of those trees may contain evidence of the stress caused by living through a massive flood.

Finding them was not easy. “It takes a little relief to find some old growth forests near the coast,” Ziak said, and there’s good reason for that. “Large, accessible trees near the coast were like gold for loggers who colonized the area in the centuries after the earthquake. The fires extinguished others. Still, the team found trees that seemed to match the bill: about a mile off the coast of Oregon’s South Beach.” Old-growth Douglas Fars gathered at a stand in Mike Miller State Park.

If you were standing next to the then young Fars in 1700, you would probably feel the ground rolling. After a few minutes, the water would roll. It’s not the Bible’s water wall, but “like the rapid flow of a high tide,” says Ziak. (Here is a video of Japan’s 2011 tsunami for reference.) Her model offers speeds of up to two to 10 meters per second and depths of up to 10 meters per second in this park. Nearby sand dunes tell Zia that the tsunami would probably have ended quickly; A nearby pond tells him that the water may fry the roots for a long time. In either case, this rush of seawater will be enough to do some damage to the unaccustomed plants of such salt.

To find evidence that the trees had dealt with tsunami-related damage, Black pulled out a cylindrical core from the tree at the site, finally identifying seven that were old enough at the time of the earthquake. He sanded the cores, each as wide as a pencil, revealing the remaining concentrated patterns by annual growth. An unusually productive year appears as a wide space between tree rings; A bad year seems to be narrow. Each tree’s calendar year is consistent with its neighbors, who have combined every part of the black to rest to ensure that they have experienced the same climate over the past three centuries. “It’s like doing a puzzle,” Black said. And this reveals a clear trend: trees in the flood zone predicted by the model grew poorly during the 1700s.

Now he and Dziak are interested in testing the chemical differences in the rings of each tree, which can unmistakably describe the motion of seawater. Will Strabble, a geologist at the University of Arizona who was not involved in the work, agrees with the team’s caution. (Strabble and Black worked together, but he was not involved in the study.) Mike Miller destroyed the stand in 1700 – salt water – not earthquakes or climate change – it is important to have chemical evidence to prove this theory.

Nevertheless, Strabble emphasizes how valuable such evidence is to support simulations of tsunami flooding, since 1700 soil data are so difficult to obtain. “I really think these models are groundbreaking for ground truth to go to the field and use datasets like tree rings,” Strubble said.

Other old-growth tree pockets along the currents in Oregon and Washington were also flooded. If the chemical analysis is turned off, this tool can also determine the magnitude of the 1700 tsunami outside the Mike Miller stand.

It can also be valuable to find out which trees have survived the effects of saltwater, Pearl suggests: “Are older trees more likely to perish?” Smaller trees have more roots, so they rely more on rainfall than groundwater. If the long sun-blocking canopy dies, they can return quickly, or even improve later. “And not only will there be tsunamis in the future, sea levels will also rise-what species can face saltwater?” He asked.



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