Transcript tsunami poster - The Wetlands Conservancy

The Core Story of Beaver Creek and the 1700 Tsunami
By the 6th Grade students at Eddyville Charter School
Did 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.
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 1
Core 2
Core 3
Core 4
Core 5
This picture shows our different
coring locations
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 maybe
The 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 never
Know, 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, but
scientist agree it will happen again.
A student driving in the pvc pipe to
take the core sample
What can we do?
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.
Inage courtesy of Oregon State University
In our third core (core 3) We got a real surprise. This core was
taken a couple of miles inland directly below the Interpretive Center.
As you can notice from the picture, there was what we believe to be a
large layer of sand from the tsunami. You have the sand directly above
the peat layer, which is a strong evidence of subsidence followed by
a 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 the
tsunami 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 massive
Earthquake. This core revealed strong evidence of subsidence. If you look
closely you can see pieces of plant material on the dark horizon line to
the 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.
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
The WetlandsConservancy