The Core Story of Beaver Creek and the 1700 TsunamiDid the 1700 Cascadia Earthquake and Tsunami effect

Beaver Creek?

Our class wanted to find out, so we decided to take core samples from the ground at five different locations. To take core samples, we took 2 meter long 4” pvc pipe. We drove the pipe into the ground with a sledge hammer. Next, we used a truck jack to pull it out of the ground. Once we returned to school we used a special saw to cut the pipes in half (long ways) so we could look at the layers inside. We thought that the closer to the ocean, we would find a layer of sand from the tsunami and further up the creek we would not find any evidence of the earthquake or tsunami.

This picture shows our different coring locations

A student driving in the pvc pipe to take the core sample

What did we find?In our first core sample(core 1) we found a layer of sand we believe to be deposited by the 1700 tsunami. The sign of this is that the sand is deposited over a layer of silt and peat. You can even see the imprint of a beach grass right below the layer of sand with is strong evidence of subsidence after an earthquake .When two tectonic plates collide and one is being shoved under the other, they lock up building pressure, as the pressure builds the top plate begins to bulge up.Subsidence results from the the pressure of two locked tectonic plates being released, then the land drops back to its original level, sometimes up to a meter or more.

Core 1

In our second core (core 2), the results was not as clear. We took this core pretty close to the road, As you can see in the photo , we have a dark peat layer, but on top of that is a clay layer that has chunks of clay and small pieces. We have two theories on this. The first theory is that when the road was built, they used fill to bring up the grade, so that the road would be out of the marsh. The second theory is, that when the earthquake happened, there was a landslide from the hill just above the coring site.

Core 2 Core 3 Core 4 Core 5

In our third core (core 3) We got a real surprise. This core wastaken a couple of miles inland directly below the Interpretive Center. As you can notice from the picture, there was what we believe to be alarge layer of sand from the tsunami. You have the sand directly abovethe peat layer, which is a strong evidence of subsidence followed bya tsunami. The amazing part is that the layer is so thick. We believe the way the hill juts out into the estuary, created an eddy effect while thetsunami was rushing in and out. When the water slowed down in the eddy it allowed the sand to drop out of the water and build up by the hill.

The fourth core (core 4), supported the case even further of a massiveEarthquake. This core revealed strong evidence of subsidence. If you lookclosely you can see pieces of plant material on the dark horizon line tothe light. This shows the old level of the surface where plants were growing but a dramatic event caused them to stop growing instantly and were buried overtime due to deposition from the creek. This is strong evidence of subsidence due to an earthquake. The amount of subsidence could have been close to a full meter.

Inage courtesy of Oregon State University

The fifth core (core 5), was also a bit of a surprise. We expected to see some evidence of subsidence, but we found nothing. I was all one continuous layer of silt dropped by the creek. This sample was taken a good ways up on the south fork of Beaver Creek. We saw no evidence of subsidence or the tsunami. We thought that maybeThe tsunami didn’t reach up there because it was not directly in line with the ocean like the main stem of Beaver Creek. We also thought that maybe some dike building or other construction may have destroyed what little evidence there may have been.

What does it all mean?

Each core tells a story and when you put them all together, they tell a pretty compelling story. In the recent past, Beaver Creek was impacted by a major earthquake and tsunami. Based on other research the exact date was January 26, 1700. How were the native people effected that lived on Beaver Creek? We may neverKnow, but the land bares the scars. What we do know is that the Cascadia earthquake was over three hundred years ago and the odds of it happening again in the near future are strong. When will the next earthquake happen? Nobody knows for sure, butscientist agree it will happen again.

What can we do?

Being aware of what to do when you are in an earthquake is important. 1. If you feel the ground shake, duck, cover, and hold.2. If you are near the coast and you feel an earthquake , go immediately to the nearest high ground. 3. Be prepared for aftershocks.4. Carry an emergency bag in car that contains food, water, and a first aid kit

We would like to thank:Dale Hubbard with Oregon State University

By the 6th Grade students at Eddyville Charter School

The WetlandsConservancy