(pensive music) - When the next Cascadia earthquake happens, coastal communities in the Pacific Northwest are in trouble, (earth rumbling) 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 hundreds, even thousands 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."

(upbeat pensive music) (upbeat pensive music continues) (wheat rustling) You'd be surprised what you can find lurking under the surface of an Oregon salt marsh.

- [Tina] So, should we record?

- [David] Yeah, let's do it.

- [Mike] Yeah.

- [Narrator] One way of learning what's there is by taking a core.

(ground rumbling) (water gurgling) - [David] One, two, three.

- 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.

- [Narrator] A core sample reveals the history of a place in layers of sediment.

- [Tina] Nice, yeah, that's a nice sand.

- [Narrator] Generally, the deeper you go, the further back in time you travel.

- [Tina] Dave's in there becoming one with the mud.

- Yeah, it smells nice and decomposed too.

- [Narrator] David Bruce will do more than just smell the dirt for his PhD project.

- Oof!

Decomposed peat.

- [Narrator] He'll use what he finds to help coastal communities prepare for when the next big Cascadia subduction zone earthquake hits the Pacific Northwest.

(film reel racketing) Subduction zone earthquakes can be devastating.

- [Narrator 2] Out in the Gulf of Alaska, the ocean bottom seems (tense music) to sink.

In Anchorage, Alaska's largest city, buildings collapse.

Streets and homes slip into the earth.

- [Narrator] In Alaska in 1964, a 9.2 magnitude quake caused tsunamis in parts of the coast to drop an elevation more than five feet, a phenomenon called subsidence.

(helicopter blades whirring) With good information, Northwest communities could plan for the worst by bolstering infrastructure where they can and not building in low areas.

- [David] One, two, three, okay.

- [Narrator] What separates these seismologists from other earthquake scientists is that they're looking for tiny fossilized algae entombed in the sediment.

(water gurgling) They're called diatoms.

- Diatoms are a unicellular, (pensive music) 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.

- [Narrator] Diatoms have shells made of silica.

They're tough.

When they die, they can stick around intact in the sediment for thousands of years, just waiting to be captured in a core sample.

- [Mike] Oof.

- [Tina] Oh yeah.

- [Narrator] This core sample is a thing of beauty.

- [Tina] That's what it should look like.

Mike's going to pass out.

- Oh, I've got the vapors.

- [Narrator] 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.

- [Dave] That's the trinity right there.

The soil, the tsunami, the mud.

- I'm going to take a picture.

This one's going viral!

(everyone laughs) Okay, we got it.

- That takes away all your question.

Land level change, tsunami, land level change.

(ethereal music) (quirky pensive music) - [Narrator] The Cascadia Subduction fault runs north-south, about a hundred 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, (earth rumbles) raising relative sea level as much as six feet (waves crashing) or maybe even more, (water burbling) which makes tsunamis all the more powerful.

(seagulls cawing) It's not a hypothetical.

(sirens blaring) We've seen this happen, and recently.

(people speaking Japanese) - [Narrator] The 2011 earthquake and tsunami in Japan left around 20,000 people dead.

It destroyed coastal communities and the subsidence left some low-lying areas permanently flooded.

(wind whistling) 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 a land level change where you see this old marsh that's peat, kind of.

And then on top of that is sand, which is a tsunami that came in, and then right above that is tidal muds.

- [Narrator] Not only does the type of sediment change as the land rises (pensive music) 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 salt water (water burbling) won't live in the high marsh (insects chirping) where groups of freshwater diatoms live, and there are other communities that live in the more brackish spaces (water burbling) in between.

The communities are distinct.

(A/C humming) (droplet burbling) - [Dave] There we go.

We can see some diatoms there.

Just get on the microscope and you start looking at who's there.

- [Tina] The diatom species they find, and the core samples are as diverse as they are beautiful.

(pensive music) - It's really fun.

I get lost on the microscope.

- [David] Yeah, you really can.

(water sloshing) - [Narrator] They're different sizes and shapes.

The lemon, 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 300 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 earthquake.

If the diatom communities found right below the tsunami sand match modern diatoms living in the high marsh, say, four feet above sea level, they know that was the elevation right before the earthquake.

Then they look at the diatoms and the sediment after the earthquake.

Let's say those match diatom groups that now live two feet below sea level.

From four feet above to two feet below, they can conclude that the earthquake caused the land to drop six feet in elevation.

(water sloshing) - [Mike] Ready?

One, two, three.

(water sloshing continues) - [Narrator] And the beauty of taking core samples is that if you find the right spot- - [Dave] Here we go!

Here we go!

- [Tina] And go deep enough, you can figure out how much the land dropped with earthquakes (David and Mike grunting) that happened thousands of years ago.

- [Tina] Boom.

That's just going to catch it.

- One of the things I really want to do is like take that record back and say like, (Mike grunting) how does this change over time?

Does it drop one meter every time or is it different?

Or what's causing the change?

- [Narrator] Based on what these researchers have found in the cores- (uplifting music) - [Dave] Oh!

(upbeat music) - [Narrator] They know the area around Oregon's Salmon River Estuary dropped more than four 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 coasts, but we don't think about it in the context of the earthquake cycle, where we could have two meters of sea level rise tomorrow.

(waves lapping) - [Narrator] Add all that sea level rise together and you get more erosion, crumbling roads, (traffic humming) and salt water 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.

(upbeat music continues) - [Jes] You count it.

- [Tina] All right.

One, two, three.

- [Narrator] Fun fact, up to half the oxygen we breathe is produced by diatoms.

Another fun fact, OPB members provide more than half the support for our local news and shows like "All Science.

No Fiction."

- [Tina] Oh my God.

Grad students.

- [Jes] Awesome.

Thank you members!

Oh!

- Hey, that one might work.

- [Narrator] And don't miss out on any of OPB's science, environment, and arts programs by subscribing to OPB Insider at opb.org/allscience.

- [Tina] Good effort you all, extra IPAs for you!

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