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  • Thanks to Subaru of America for supporting this series of SciShow. Their all new 2020

  • Subaru Outback helped us stay safe and warm during filming.

  • [♪INTRO]

  • Stefan: Welcome back to our road trip! We're in

  • the middle of a three-part series about the geology of Olympic National Park.

  • Alexis: Last week, we talked about the Mt. Olympus,

  • the tallest mountain on Washington's Olympic Peninsula. But now, let's switch gears and

  • talk about one of my favorite stories here: the story of an ancient island called Siletzia.

  • Stefan: Oh right, let's go!

  • Alexis: So, here's a question for you. There are

  • no volcanoes on the Olympic Peninsula, but there is a ton of basalt, which is a type

  • of volcanic rock. So, how did it get here?

  • Well, it wasn't the Cascades off to the east. Instead, scientists believe it got there

  • because about 50 million years ago, a volcanic island called Siletzia collided with North

  • America.

  • Stefan: The story goes like this.

  • More than 50 million years ago, in the northeast Pacific Ocean, an island made primarily of

  • volcanic rock appeared. Today, geologists call it Siletzia.

  • Siletzia was attached to an oceanic tectonic plate. And over time, that plate movedas

  • they tend to do. Specifically, this one went east and was slowly traveling underneath the

  • North American tectonic plate.

  • Alexis: Or subducting, if you watched our Mt. Olympus

  • episode.

  • As the tectonic plate moved, Siletzia moved along with it. And eventually, about 50 million

  • years ago, Siletzia ran up against North America.

  • In other scenarios, this might have actually been the end of the story. Siletzia might

  • have just disappeared under the North American plate, melted, and never been heard from again.

  • Which happens.

  • Stefan: But! Recent studies suggest that Siletzia

  • was too hot and buoyant for it to subduct. So instead, it accreted onto North America

  • meaning that it got stuck to the side of the tectonic plate and eventually spread

  • throughout the landscape.

  • Alexis: That's why the Olympic Peninsula and the

  • Pacific Northwest have a bunch of volcanic basalt! Not because of a bunch of volcanoes,

  • but because of an ancient, traveling, volcanic island!

  • Stefan: Geologists have figured most of this out by

  • studying the rocks around here and by using models, like one published in 2014 that used

  • a bunch of data from rocks in Washington and Oregon.

  • Alexis: And you can see evidence of this all over

  • the place.

  • Alexis: The Siletzia basalt stretches from Oregon

  • to British Columbia, and it varies from 10 to 32 kilometers thick. If you know what to

  • look for and have a good map, you can see it for yourself on certain hiking trails or

  • other rock outcroppings around here.

  • Stefan: So this is all so really cool, especially

  • if you know the story behind what you're looking at. But there's one question we

  • haven't answered yet: Where did Siletzia come from? How did that island get there in

  • the first place?

  • Alexis: Stefan, I am very glad you asked! Because

  • that is one of my favorite parts of this story!

  • Okay, so tectonic plates are moving all the time. Which means that 50 million years ago the

  • North American plate and the oceanic plate that containes Siletzia were on the same place

  • on the globe as they are today. They were actually much farther east.

  • Stefan: Okay, okay.

  • Alexis: So, about 50 million years agooff the

  • west coast of what's now Washingtonwas the Yellowstone hotspot.

  • Stefan: Wait, Yellowstone as inYellowstone National

  • Park?”, like no where near Washington!

  • Alexis: Yes! 50 million years ago, the same hotspot

  • that powers all of the cool thermal features at Yellowstone National Park was most likely

  • located under the eastern Pacific Ocean.

  • And over time, it released a bunch of volcanic material that became the Siletzia basalt.

  • Stefan: That is wild!

  • Alexis: Admittedly, this is somewhat up for debate

  • because it's pretty hard to prove, and there are other hypotheses. But there's a lot

  • of good evidence for this. And it's just mind-blowing to think about.

  • Stefan: So, the story of Siletzia is super cool, because

  • if you didn't know the story behind itwell, you could just look at a bunch of basalt and not

  • think twice about it. But if you do know what you're looking at, it's seriously amazing.

  • Alexis: And there are more stories like that out here too,

  • too! So, before we head home, let's make one more stop.

  • Stefan: Before we wrap up, though, we'd like to

  • say thanks to Subaru for making this road trip adventure possible!

  • Alexis: When we filmed this series, it was the beginning

  • of January, and we got a chance to take advantage of the Outback's all-wheel drive, ground

  • clearance, andof coursethe heated seats and steering wheel.

  • Stefan: We are so glad we had heated seats.

  • Alexis: Seriously. After a cold day of filming, it

  • was very nice to get into a warm car.

  • Stefan: If you want to learn more about the 2020 Subaru

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

  • [♪OUTRO]

Thanks to Subaru of America for supporting this series of SciShow. Their all new 2020

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ワシントンを変えた古代の島サイショーフィールドトリップ #2 (The Ancient Island That Transformed Washington: A SciShow Field Trip #2)

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    林宜悉 に公開 2021 年 01 月 14 日
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