When the next Cascadia earthquake happens, coastal communities in the Pacific Northwest are in trouble.
Intense shaking, a massive tsunami,
but also a near instantaneous
drop in elevation.
Yet it's been so long since the last big earthquake, it's hard to know exactly what we should expect.
Well, what if we could look back in time to learn from past earthquakes
using tiny
fossils from 100,
even 1000 of years ago.
They could tell us a story about how our coast will be forever changed when the next big one hits,
and that's
all science, no fiction.
You'd be surprised what you can find lurking under the surface of an Oregon salt marsh.
So should we core? Yeah.
Yeah.
One way of learning what's there is by taking a core.
The Oregon coast is one of the best places in the world
with the longest record of marsh history, which makes it a great candidate to study old tsunamis.
A core sample reveals the history of a place in layers of sediment.
Nice. Yeah. It's a nice sand.
Generally, the deeper you go, the further back in time you travel.
Dave's in there.
Becoming one with the mud.
Yeah. It smells
nice and decomposed too. David Bruce will do more than just smell the dirt for his PhD project. Woof.
Decompose Pete.
He'll use what he finds to help coastal communities prepare
for when the next big Cascadia subduction zone earthquake hits the Pacific Northwest.
Subduction zone earthquakes can be devastating.
Out in the Gulf of Alaska, the ocean bottom seems to sink.
In Anchorage,
Alaska's largest city, buildings collapse,
streets and homes slip into the earth.
In Alaska, in 1964,
a 9.2
magnitude quake caused tsunamis
in parts of the coast to drop at elevation more than 5 feet,
a phenomenon
called subsidence.
With good information,
northwest communities could plan for the worst by bolstering
infrastructure where they can and not building in low areas.
1, 2, 3, 6.
What separates these seismologists
from other earthquake scientists
is that they're looking for tiny fossilized
algae entombed in the sediment.
They're called diatoms.
Diatoms
are a unicellular
photosynthetic
algae,
and they are in all aquatic environments. So freshwater, brackish, and marine. You can find them anywhere where there's water, anywhere where it's even damp.
Diatoms have shells made of silica. They're tough. When they die, they can stick around intact in the sediment for 1000 of years
just waiting to be captured in a core sample.
Oh, yeah.
This core sample is a thing of beauty. That's what it should look like. Mike's gonna pass
out. I've got the vapors.
It perfectly shows the tsunami from the last Cascadia earthquake
more than 300 years ago.
The evidence is this thick layer of sand,
which was washed inland by the wave.
That's the trinity right there, the soil,
the tsunami, the mud.
I'm gonna take a picture.
This one's going viral.
We gotta get it. That takes away all your question. Land level change, tsunami,
land level change.
The
Cascadia subduction fault runs north south, about a 100 miles off the Pacific Northwest coast.
Here, the Juan de Fuca plate and the North American plate collide,
with Juan de Fuca being forced down or subducted underneath the continent.
But the plates don't slide past each other easily. They lock together where they meet, causing the top plate to bend up.
Our coast rises out of the ocean. But at some point, the pressure at the fault becomes too much.
The plates grind past each other, triggering the Cascadia earthquake and a tsunami.
On the coast, in the span of just a few minutes, the land drops or subsides,
raising relative sea level as much as 6 feet or maybe even more,
which makes tsunamis
all the more powerful.
It's not a hypothetical.
2,011
earthquake and tsunami
Japan left around 20,000
people dead.
It destroyed coastal communities, and the subsidence
left some low lying areas permanently flooded.
Evidence of this up and down motion on the coast is what the geologists
are looking for in the core.
Specifically, we're looking for the tidal wetland signature of subduction zone earthquakes, And that's,
land level change where you see this
old marsh that's, peat kinda. And then on top of that is sand, which is a tsunami that came in. Then right above that
is,
tidal muds.
Not only does the type of sediment change as the land rises and falls with the Cascadia earthquake cycle,
but so do the tiny fossil diatoms
connected with those environments.
This is the key. Different species of diatoms like different areas of the marsh.
The diatoms that like lots of saltwater
won't live in the high marsh where groups of freshwater diatoms live,
And there are other communities that live in the more brackish spaces in between.
The communities are distinct.
There we go. We can see some diatoms there.
Just get on the microscope and you you start looking at who's there.
The diatom species they find in the core samples are as diverse as they are beautiful.
It's really fun. I get lost on the on the microscope. Yeah. You really can.
They're different sizes and shapes.
The limit.
The croissant.
The football.
How about a round of golf,
the snow tire?
And they use the intricate patterns on their surfaces to help tell one diatom hot dog from another.
The team will identify and count 3 to 600 diatoms from each sediment layer, and then compare the communities of fossil diatoms to what's living in the marsh now.
This is how they convert a bunch of fossils to knowing the actual elevation change from the
diatom communities found right below the tsunami sand match modern diatoms living in the high marsh, say 4 feet above sea level, they know that was the elevation
diatoms in the sediment after the earthquake. Let's say those match diatom groups that now live 2 feet below sea level.
From 4 feet above to 2 feet below,
they can conclude that the earthquake caused the land to drop
6 feet in elevation.
Yes.
Ready?
1, 2, 3.
And the beauty of taking core samples is that if you find the right spot Here we go. Here we go. And go deep enough,
you can figure out how much the land dropped with earthquakes that happened 1000 of years ago.
One of the things I really wanna do is, like, take that record back and say, like, how does this
change over time?
Does it drop 1 meter every time? Or is it different? Or, like, what's causing the change?
Based on what these researchers have found in the cores
Ugh. They know the area around Oregon's Salmon River Estuary dropped more than 4 feet during the last Cascadia earthquake.
And, of course, that's not the only sea level change that coastal communities need to plan for.
Climate change is causing ocean levels to rise around the world,
and it's important we're planning for both.
We think about sea level rise on the Oregon coast, but we don't think about it in the context of the earthquake cycle where we could have 2 meters of sea level rise tomorrow.
Add all that sea level rise together,
and you get more erosion,
crumbling roads, and saltwater in places it definitely
shouldn't be.
And these tiny, beautiful
fossils from the past
may be one of our best clues to understanding how to safeguard the future of the Pacific Northwest Coast.
You count it. Alright.
123.
Fun fact, up to half the oxygen we breathe is produced by diatoms.
Another fun fact,
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