Elleda Wilson: Yes, they happen here
Jan. 26—Warning rerun: Researchers from the U.S. Geological Survey have an ongoing project at the mouth of the Lewis and Clark River, Coastal Hazards Specialist Patrick Corcoran, who is the Oregon Sea Grant county leader at the Oregon State University Clatsop County Extension, said.
"They excavated a small section of the river bank to reveal the history of tsunami inundations," he explained, describing the photos shown, which were taken in April.
"The horizontal brown 'lines' in this cross-section indicate the last four tsunamis. While finding of tsunami layers in this location is not a new discovery, it is still dramatic to actually look at these deposits," he added. Not to mention scary.
"The key message is: 'Yes, they happen here. We get what Japan got (in 2011),'" he warned. "It's easy to be complacent ... However, this image shows that we get large earthquakes and tsunamis fairly regularly in geologic time. The dates of these tsunamis are roughly 1700, 1400, 900, and 400 A.D."
This is how it works: When tsunamis hit the coast, they drag marine sand and debris upriver. Then, as the tsunami wanes, a layer of sand is deposited over the flooded area.
The researchers are gathering information to make new, updated tsunami inundation maps. One of the things they look for, Corcoran said, is foraminifera, ocean-dwelling protozoa that get deposited inland by large tsunamis. By mapping where they find the foraminifera, they can tell how far inland the tsunami came.
"The vegetation, the sand composition and the marine critters reveal a long history of big earthquakes and tsunamis in the region," Corcoran observed. "Understanding our natural history can better prepare us for the next time the foraminifera come to town." (In One Ear, 5/25/2012)
Note: The current tsunami inundation maps are available at bit.ly/TsuMaps, so you might want to take a look.