helped us stay comfortable during filming.

[♪INTRO]

Stefan: Welcome back to Washington! This is the final

episode in our mini-series about the geology of Olympic National Park!

Alexis: So far, we've talked about Mt. Olympus and

an ancient that transformed Washington and now, it's time for one last story.

Stefan, let's hit the beach!

Stefan: Oh yeah!

Stefan: Last week when we were at Rialto Beach, you

might have noticed a bunch of cool rock towers in the background. Those are called sea stacks,

and these beaches in western Washington are famous for them.

Alexis: But these rocks don't just look cool. They

also tell a fascinating story about how this landscape has changed over the last few centuries.

Alexis: Welcome to Ruby Beach!

Stefan: We figured that while we were in Washington, we should

visit at least two place that have sea stacks. I mean, like, when in Rome…right?

Alexis: Something like that. Anyway!

Alexis: So, behind us, are some of Ruby Beach's

famous sea stacks. Sea stacks can be made of all kinds of rock, but the ones here are

generally made of the sedimentary rock breccia and mostly-volcanic conglomerate.

Basically, that means they're made of a bunch of rocks that got cemented together.

Stefan: Meanwhile, the ones over at Rialto Beach are made

of volcanic basalt, sedimentary sandstone, and conglomerate, depending on

where you look.

Alexis: Exactly what the stacks are made of doesn't

matter that much, but the important thing to know is that these sea stacks are made

of harder rock than the stuff you tend of finding on the mainland. And that's important because

of how sea stacks are formed in the first place.

Stefan: Sea stacks form because of something called

preferential erosion.

You start off with a headland, or a piece of the coast that juts out into the ocean.

As the ocean waves come in, they get bent around the headland and end up hitting the

coast in specific spots. And that's where the trouble starts. Or the fun.

If the area where the waves hit is made of softer rock, or made of a rock that contains

some kind of fracture, the waves will erode it.

That leads to small indents in the headland, and then small caves, and then eventually,

the water cuts straight through. And then you're left with a sea arch!

Stefan: You can find sea arches all over the place,

but it's not like erosion stops once that arch is formed. The waves continue to

erode the rock, and over time the arch can get bigger until it eventually collapses into sea stacks.

Alexis: But the rock composition isn't the only

variable. According to a cool model published in 2014, the beach in front

of the sea stack is important, too.

The model found that really wide beaches tend to prevent sea stacks from forming, because they

act as protective barriers. Basically, the waves crash against the beach and don't

actually hit the headland.

Meanwhile, really narrow beaches can encourage sea stacks to form. In that case, the water

picks up all the sand and other sediment, and it rubs against the headland kind of like sandpaper.

So erosion happens faster.

Over all, this means that, if Ruby Beach were a lot wider, we might not have these rocks

to look at!

Stefan: So, the sea stacks at Olympic National Park

are really cool, but that's not the only place you can find them.

They're all over the world, from Scotland to Australia. And when you do find them, they can tell you somethings about the place you are visiting.

Alexis: For one, at the most basic level, you can

learn where the coastline used to be. Because anywhere there's a sea stack — well, that

used to be part of the mainland!

Stefan: Sea stacks also tell you that waves are mainly

approaching the coast head-on, rather than on an angle. When the waves come in sideways,

they erode mostly one side of a headland, and that makes it a lot harder for sea stacks to form.

Alexis: And finally, sea stacks tell you that there's

a sort of balanced system happening here. Kind of like we talked about in the Mt. Olympus

episode earlier on this trip!

If you find a sea stack, you know there's a good amount of sediment moving around

and eroding the cliffs, but not so much that it forms a wide protected beach that prevents erosion.

So, generally, when you find a sea stack, there won't be some kind of huge sprawling

beach stretching way out into the water.

Stefan: Instead, you're more likely to see something

like this!

Stefan: So while sea stacks are pretty cool, but they won't

last forever — probably not more than a few hundred years, depending on how big they are

and what they're made of.

Alexis: They're a reminder that the land around

you is constantly changing, and that there's a lot you can learn if you know what to look for.

Stefan: But… there's one more thing we

should mention about sea stacks. Because while they are really nice to look at, they are

also kind of dangerous.

Alexis: It's true. Like, in the late 1800s, one

ship near Rialto Beach got caught in some rough waves and foggy weather. Someone on

the board saw a sea stack through the fog and thought it was another boat, so they decided

to steer toward it… and ended up crashing.

Stefan: There have actually been over a hundred

shipwrecks off the coast of Washington, due to sea stacks, rough waters, tons of fog,

and reefs are hiding just under the waves. So while these are nice

to look at during the daytime…

Alexis: We're going to stick to dry land. And on

that note, we should probably head back to the car and tell Hank we're about done here!

Stefan: That sounds great! So until next time, thank you

for joining us on our road trip!

Alexis: Thanks to Subaru for partnering with us for this three-part road trip series, and for lending the support of an all-new 2020 Subaru Outback.

Stefan: We had to drive a lot to make these episodes, both

inside Olympic National Park and out, and all the features of the outback help make our trip a lot easier.

My favorite feature was the roomy cargo space! We fit our luggage and even film gear easily.

And with the hands-free power rear gate, I didn't have to put my bags down on the wet

ground to open the door. Which is always a struggle, right?

Alexis: If you want to learn more about the 2020 Subaru

Outback, you can check out the link in the description.

[ ♪OUTRO ]