Thanks to Subaru for partnering with us on SciShow mini series.

The all new 2020 Subaru Outback helped us stay comfortable during filming. If you want to learn more about the 2020 Subaru Outback and its features, you can check out the link in the description. [♪INTRO].

Stefan: Welcome to a very special episode of SciShow! We're going on a road trip! I'm Stefan Chin, one of your usual hosts, but today I'm here with Alexis Dahl, SciShow's content manager!

Alexis: Thanks for having me, Stefan! This is not the side of the camera I usually end up on. Over the next three episodes, Stefan and I will be exploring Olympic National Park in. Washington to bring you some of the coolest geology stories there.

We've been doing lots of research to prepare for this trip, and we're excited to finally see the park!

Stefan: So, shall we get going?

Alexis: Let's go! [ ♪MUSIC ].

Alexis: Even if you've lived in Washington State your whole life, there's a chance you've never seen Mt. Olympus. It's tucked away on the Olympic Peninsula, and there aren't many places to get a good view of it.

Stefan: That's why we're headed up to Hurricane. Ridge. Partly to show you the view, and partly because there's a really good story here.

Alexis: See, here's the thing about Mt. Olympus. Every year for millions of years, new material has been added to the bottom of the mountain and the mountain range. Except… Mt.

Olympus hasn't noticeably grown in more than 10 million years.

Stefan: And as for why… that requires a cool geology lesson.

Stefan: The Olympic Mountains started forming somewhere between 5 and 20 million years ago, largely thanks to the work of two tectonic plates. Tectonic plates are the huge slabs of rock that make up Earth's crust, and they move over time, changing the landscape as they go. There are a bunch of them, but the two plates to know here are the Juan de Fuca plate and the North American plate. Juan de Fuca is an oceanic plate, meaning it's made of dense rock and tends to hang out below sea level.

And the North American plate is continental, so it tends to be above sea level. In any case, millions of years ago, this oceanic plate started subducting, or traveling underneath, the North American plate. And during that process, material from Juan de Fuca got scraped off and piled onto the.

North American plate.

Alexis: It was kind of like stuff piling up at the end of a conveyor belt. And over time, that material kept building, getting taller and taller until, finally… the Olympic Mountains were born!

Alexis: Now, to be clear, the mountains didn't get so tall just because a tectonic plate subducted underneath this area. Geologists are still trying to figure out exactly how they got their height, and they do have a few other ideas.

Stefan: Like, one hypothesis is that in this part of Washington, the Juan de Fuca plate is subducting at a shallower angle than average and is making the crust above it curve upwards, like a dome.

Alexis: Another idea is that it might have to do with how other geologic features around here are moving.

Stefan: Honestly, when you're trying to study things that have happened over millions of years, the research is… kind of tricky.

Stefan: Regardless of why the mountains are so tall, though, one thing is for sure: They're not done growing. For example, the Juan de Fuca plate is still subducting, so new material is being added to the mountains all the time.

Alexis: Also, this area is currently undergoing something called isostatic rebound. During the last Ice Age, this part of Washington was covered by a large ice sheet that's mostly disappeared.

Stefan: Yeah mostly. But we're here and it's January, and it's pretty cold as you can see among other things. So why don't we get back inside?

Alexis: Good idea! [ ♪MUSIC ].

Stefan: Well, this is a little bit nicer.

Alexis: It is! Weather aside, thousands of years ago, when that ice sheet existed, it was really heavy. So heavy that it pushed down the Earth's crust underneath it. Now that the ice is gone, the crust is rebounding and rising up again.

So besides the Juan de Fuca Plate and everything else, that's contributing to the growth of the Olympic Mountains as well.

Stefan: Except the kicker is, even though these processes are still going, geologists think Mt. Olympus and the Olympic Mountains have been about this high, with the same overall shape, for 14 million years.

Alexis: Which is a surprisingly long time. It's like this because there's actually a really cool system happening here, where the uplift of the mountains seems to be balanced by the rate they're eroding. Let's use Mt. Olympus as an example.

Stefan: Actually, why don't we head into the Hoh. Rain Forest? That seems appropriate, given what's going on.

Alexis: Oh yeah! Let's do that. [ ♪MUSIC ].

Stefan: So, as you might have noticed, Olympic National. Park is wet. One of the reasons it happens is the Olympic Peninsula is the first land rainclouds encounter after they cross the Pacific Ocean. Over time, that rain hits the mountains and wears away the landscape.

It's like how you can erode a sandcastle by dumping water on it, but on a much larger scale.

Alexis: But that's not the only thing happening here. Mt. Olympus is also eroded by rivers and streams running down its slopes, and that's where the balance comes in. See, as the mountain gets taller and steeper, water can flow down it faster and cut deeper channels into the rock.

Those channels wear away the mountain. And thanks to them — along with sudden events like landslides — the mountain becomes shorter and less steep. As a result, water flows down it more slowly and erodes the mountain less.

Then, over time, Mt. Olympus gets taller and steeper again, the process repeats.

Stefan: This is a stable or near-stable system, so we don't really see Mt. Olympus or any of its buddies getting noticeably taller over the years. And unless something drastic changes, we probably won't. It will just exist in a nice, even balance, frozen around 2400 meters tall.

Alexis: So, that's the story! There's a careful balance here between the rising mountains and the erosion that wears them down. And thanks to that, Mt. Olympus doesn't really grow — even though it gets new material all the time.

But hey, that's not the only story in Olympic National Park.

Stefan: Oh, definitely not. Next up, we're going to head to the beach to learn about the ancient island that transformed Washington. So, stay tuned next week! But for now…

Alexis: Thanks for watching this episode of SciShow! Hey, I never get to say that. This adventure wouldn't have been possible without the 2020 Subaru Outback, so we'd like to give the team at Subaru a big “Thank You”.

Stefan: From the comfy seats to the Subaru Starlink. Touchscreen Navigation, the Outback helped us get to Olympic National Park and navigate the roads to Hurricane Ridge.

Alexis: We also got to take advantage of some features like X-mode, which were super helpful on all those hills and winter roads.

Stefan: If you want to learn more about the 2020 Subaru. Outback, you can check out the link in the description. [ ♪OUTRO ].