The long lost story of the 18th century tsunami told by trees

The trees will not forget. In the 1990s, researchers discovered a “ghost forest” of dead cedar near the Washington coast; tree-ring dating comfirmed They did die in 1700.But Black and Diak found the trees that had experienced the tsunami-and SurvivedThe growth rings of these trees may contain evidence of the stress caused by living in huge floods.

Finding them is not easy. “It takes some investigation to find some ancient forests close enough to the coastline,” Dziak said. “This is for good reason.” The large trees that are accessible near the coastline are important for the loggers who colonized the area in the centuries after the earthquake. It’s like gold. The fire has destroyed others. Despite this, the team found trees that seemed to meet the requirements: old growing Douglas firs gathered in a stand in Mike Miller State Park, nearly a mile from the coast of South Beach, Oregon.

If you were standing next to a young fir in 1700, you might feel the ground rumbling. After a few minutes, the water will roll in. It will not be a wall of water as the Bible says, but “like the rapid influx of high tide,” Dziak said. (This is a video Take the 2011 tsunami in Japan as an example.) His model shows that the speed of this park is between 2 and 10 meters per second and the depth can reach 10 meters. The nearby sand dunes told Dziak that the tsunami might disappear soon; a nearby pond told him that the water might make the roots soak for longer. In either case, the influx of seawater is enough to cause some damage to trees that are not accustomed to this salt.

In order to find evidence that the trees had dealt with tsunami-related damage, Black extracted cylindrical cores from the trees on the scene and finally identified seven trees that were old enough during the earthquake. He polished the cores with sandpaper, each of which was about the width of a pencil, revealing the concentric patterns left by the annual growth. An exceptionally prolific year is manifested as a wide space between the tree rings; a bad year appears narrow. Black juxtaposes each core with the rest to ensure that the calendar year of each tree is consistent with its neighbors who have experienced the same climate in the past three centuries. “It’s a bit like a puzzle,” Black said. It reveals a clear trend: the trees in the flood zone predicted by the model grew slowly during the 1700’s.

Now, he and Dziak are eager to test the chemical differences in each annual ring, which can irrefutably attribute the slowdown to sea water. Will Struble, a geomorphologist at the University of Arizona who was not involved in this work, agrees with the team’s cautious approach. (Strubull and Black worked together, but he was not involved in this research.) Having chemical evidence is essential for proving that salt water—not earthquake vibrations or climate change—has hindered Mike Miller’s position in 1700. Theory is very important.

Nevertheless, Struble emphasized the value of such evidence in supporting simulations of tsunami inundation, as field data for 1700 are difficult to obtain. “In order to really be able to enter the field and use data sets like tree rings to determine the truth, these models are indeed what I think is novel,” Struble said.

Other ancient trees along streams in Oregon and Washington state will also be submerged. If the chemical analysis is successful, this tool can map the range of the 1,700 tsunami, far beyond Mike Miller’s position.

It may also be valuable to figure out which trees survived the pressure of the sea, Pearl suggested: “Are old trees more likely to die?” Younger trees have shallower roots, so they rely more on precipitation than groundwater. . If the taller awnings disappear, they may also rebound faster and may even thrive later. “Not only the future tsunamis, but also sea level rise-in the face of salt water, which species may be the most resilient?” she asked.