Hey everyone.

My name is Chris Anderson and I'm at Arches National Park, home to over 2000 natural arches, some of which span over 300ft.

It's the densest concentration of natural stone arches in the entire planet, so how did they get here?

Let's find out today on OutSCider Classroom!

[Intro music] [Music] To understand why we see all these arches, let's take a trip back to around 300 million years ago.

This was a time of big geologic change.

Supercontinents were splitting up, and tectonic plates are on the move.

Where we're standing at today was a tropical sea.

Well, at least sometimes.

You see, Earth's climate tends to go through cycles, often lasting millions of years.

Sometimes this area was underwater, but sometimes when the climate got cooler, more water was in the polar ice caps and the seas retreated.

But when seas retreat, they leave a little something to remember them by salt.

Over 15 million years, sea levels rose and fell almost 30 times.

Each time the seas retreated, they left behind this salt that was dissolved in the water and a lot of it.

The salt deposits under Arches National Park is over 5000ft thick.

That's enough salt to season enough pretzels to feed... Okay, well, let's just say that's a lot of pretzels.

So how did a giant slab of salt result in all these sandstone arches?

Let's check in with doctor Tamsin McCormick and learn more.

What happens is we get we get the different layers.

Some of them are soft and some of them are hard.

And the salt rising up and it forms these antique lines.

Gaps between the fins start to widen.

Water can then percolate down through those fractures and reach the salt bed.

Salt is, soluble in water and so it will dissolve.

That salt then could get moved out.

And it leaves us with a bit of a space problem.

And so the roof collapses.

And so that forms these valleys which are not formed by rivers, they're rather unusual and right on the edge of the valleys as that salt layer has been excavated, you can start to see those, the sandstone sort of rolling a little bit into the, into the valley on the edge here.

And that's where those, many, many arches form, right in those fins on the edge of those valleys.

Salt played a big role in creating these amazing arches, but that's only half the story.

The other half, good old H2O.

When it rains, water dissolves a little bit of carbon dioxide in the atmosphere, creating a weak acid called carbonic acid.

It's the same acid in soda.

Over time, that rain reacts with the rock, breaking it down bit by bit, grain by grain.

That's exactly what happened here.

Over millions of years, the sandstone was carved by rain, creating these beautiful arches.

Scientists call this chemical weathering.

When a chemical reaction breaks down rock, the same thing happens when oxygen in the atmosphere reacts with minerals or when plants secrete enzymes to let them get a better hold on hard surfaces.

These are all chemical reactions, but chemistry isn't the only way to break apart rock.

Sometimes you need a little muscle work.

Breaking rocks apart takes a lot of work, but the elements are at it 24/7.

Blunt forces like wind or rain can, over time, break down rocks.

Wind plays an important role in shaping the landscape of arches, in particular because it picks up sand grains from the desert and blows them across a mostly treeless landscape, basically acting like a sand blaster.

And while we are in a desert, it does rain and it does get below freezing, especially at night.

When rainwater seeps into the cracks of the rocks and freezes, it expands, pushing the rocks apart.

Over time, these cracks get bigger, which allow for more rainwater to get in.

When that freezes and expands, it pushes the rock apart even further, creating this vicious cycle that breaks apart the rocks.

These processes are called physical or mechanical weathering because they involve physical forces breaking apart the rocks.

Chemical and physical weathering work together to shape Earth's surface.

Here and well, everywhere else on the planet, but it's been a particular set of circumstances that have led to the creation of all these arches.

First, the salt valley formed, which created all those sandstone fins that were eventually weathered away.

There's a few other factors here as well.

This is a desert, so we don't get much rain.

So the chemical weathering process happens pretty slowly.

We're also in the middle of a tectonic plate.

Earthquakes are rare and arches aren't destroyed or collapsed before they're done forming.

All these geologic processes have worked together to make thousands of arches in the park.

There's lots of fun things to do and explore arches, hiking, mountain biking, rock climbing.

But it gets pretty hot during the day, so make sure you got plenty of water, extra snacks, a good map, and sun protection.

Okay class pop quiz!

You should always stay on the mark trails because A: there may be rock formations that are unstable and blocked for your own protection.

B: wandering off trail can destroy fragile habitat, or C: it's super easy to get lost in the desert.

That's right, it's D: all of the above.

Congratulations!

You aced that quiz.

Remember, this park is protected if all of us work to keep it that way.

So stay on the trails and follow all the park regulations.

And if you have any questions, ask a ranger.

Now get out there and start exploring.

[Music] So, Lydia, you're a soil scientist, what the heck is weathering?

Oh, okay.

So weathering generally is the process of the soil, so we have a soil separation here, but it's a process of a detached soil or a rock, I should say, is a process of it detaching from the surface in which it lies and then getting moved in a variety of different types of ways.

Now there are different types of weathering.

So there is a biological weathering, which we can see here by the vegetation really kind of eroding into that rock material.

And there's also chemical weathering.

And so that can be from water and a chemical compound and the rock material, soil material that then causes it to further, basically, separate.

So really, you want to think about the process of weathering as really one of detachment and separation.

Okay.

So weathering is detaching or breaking something apart.

Yes.

So how is that different than erosion?

So erosion is a type of transport mechanism.

So that's the next really step after the detachment is a transport step.

And so erosion is a type of transport.

And there are multiple types of erosion.

So there's erosion that can be caused by water.

Which, you know, we're standing here in a stream bed.

We can see a lot of these areas, these surfaces over here that have been eroded down.

So that's really something that's caused by water, but also can be wind erosion.

And so I like to think about when we're in the desert southwest that really all of these amazing landscapes that we see, like arches are really shaped by the power of water and wind.

Over time, creating these really amazing shapes and landscapes that we observe, and really eroding different parent material to expose these beautiful colors.

But really, that is a process of the transport of material itself.

Okay.

So weathering, detaching or breaking apart.

Erosion is moving things, so transporting... Transporting so how are those two things different than deposition?

So deposition is kind of like the last phase of that.

So deposition is really when the material is being transported to stop moving and it settles in, in a place.

So, for example, if we're just going to look at our landscape here, after that material has detached and been transported, it actually gets a lot of times transported in these types of stream channels or stream beds that we're in.

And so as you can see, it's settled out and it's a lot of this finer material, -Oh, yeah.

That tends to travel a lot further than heavier material, but that is really it being deposited in place and settling down.

So this kind of gritty, dirty, it's almost like sand.

This was weathered from these hills, then eroded by the water and then deposited down here where we're standing.

And you can even see some of the colors from these landscapes really kind of getting deposited into this riverbed, which is part of what makes it really cool.

But yeah, it's kind of sandy.

You can feel the texture.

Yeah.

That is all from this, just the water as it is transporting it, the smaller particles will move further, further along.

And that tends to be why, you can feel a little bit more sandy than some of these bigger pebbles.

Weathering, breaking apart, erosion, transporting.

Deposition.

Dropping it, settling down.

- Settling down.

Is there a way that I can remember the difference between all three?

I'm so glad you asked.

There's a little dance.

Do you want to do with me?

Yes, I do.

You have to do with me, though, because I don't want to dance alone.

No, no, no.

- Okay.

We never dance a lot on this show.

Okay?

So start.

Right?

This is like your soil surface and you detach... Detach.

And then you want to do the transport... Slide to the right.

You gotta do the hill movement.

- Yeah.

Oh yeah.

- Hill movement.

And then you want to deposit down.

That was good.

That was good.

But I got to do it faster.

Yeah.

We gotta do one more time.

Okay and detach, transport and deposit.

[Detach, Transport and Deposit Remix Music] [Music] So hi, I'm Lydia.

I am a soil microbiologist.

[Woosh, pops] [Ding] Generally, a soil microbiologist studies the microbes and the fungi, and the archaea and bacteria that are in the soil system.

So initially I did study water, but I found that soil has to interact with the water system in some cells, and it's a lot.

And soil is really complicated because it has so many more compounds in there, so many more chemical interactions than water.

And I found a lot of beauty in that complexity.

And that's why I study soils and soil microbiology specifically, because it's just so under-understood.

And I think that is a really exciting part is there's this ability to be able to learn more and create new knowledge around soil microbes.

So I had to think about who got me excited about science.

I think it's just been a variety of different teachers throughout my life, but my dad is definitely a big one.

He's kind of a mad scientist, and not that he's had this formal school training, but he's just always been a someone who's really good about fixing things, and is always really intellectually curious.

I feel like he's really self-taught.

And so, he eventually went on to be to design rainwater harvesting systems, but he was always like, "look at these cool bugs!

Like, look at them!"

And I'd be like, "Oh, cool," you know.

So those types of things are just getting you really excited.

I love science and the variety of ways that it can be expressed.

I love running and so being able to mix running in with science is something I'm super excited about.

And then also just amplifying native communities.

And so I'm continuously trying to find ways to braid those three interests together.

Well, I think there's multiple best parts of my job, but one of the best ones is the ability to be outside.

The other one is that I, I get paid to ask questions that I think are interesting and have the tools at my fingertips to answer them.

And I think that's the coolest part, is that you're continuously developing new questions, finding half answers for them, and then continuing to just pursue that.

How the pursuit of science and knowledge and how the ability to do so.

Because how many times in your life have you been like, I wonder how this works.

We actually get to do that and get paid for it.

I think that part is really awesome.

But also just if you're interested in something, continue to pursue it, continue to find mentors in it in a variety of different ways.

Whether that's academic or community mentors, because those are really people who are going to foster your passion for that, and you want to follow that passion for these subjects because it can lead to really fun careers, but also making meaningful change in the world that we need.

[Music] Did you know the soil in Arches National Park is alive?

IT'S ALIVE!

That's right.

The soil is teeming with life.

They're called biological soil crust.

And in some places, up to 70% of the soil is alive, filled with lichens, mosses, fungi and bacteria.

But most importantly, blue green algae.

Yeah!

Algae in the soil.

Blue green algae is also known as cyanobacteria and is one of the oldest forms of life on Earth.

Scientists think these were one of the first organisms to live on dry land, which makes a ton of sense that they're right at home in the dirt.

Normally, in a biological soil crust, cyanobacteria are dormant.

That is, until it rains.

When soil gets wet, they move through the soil, leaving behind gooey, sticky fibers.

These fibers form a web that keep the soil together, creating a thick layer that has the consistency of the mat in your bathroom.

Young crusts are flat and brown.

It can be a little hard to distinguish from bare earth, but older, more mature crusts are bumpy and black and can be thousands of years old.

So other than being cool, what's so great about a biological soil crust?

Hi, I'm Doctor Jennings, and let me tell you about why biological soils are so cool.

So one of the most important things is how soils can help prevent erosion.

So what we have here is a really beautiful soil profile.

And what you can see is how this has really kind of gotten just, gotten disturbed.

And you can see the areas where the water has really flowed through them.

That's erosion, right?

But when you have that detail like that on top, or even this little over here, or like this tree over here, that really helps protect and hold in the water so that the erosion doesn't, you know, disturb and, impact the soil.

Because what happens when a lot of erosion happens is that, we're here in a stream bed, I can pull all of that sediment out of here and move it to somewhere else.

And while that's important, it's an important movement of sediments, it's really important that we have vegetation here to stabilize that, because it can cause a lot of, infrastructure damage to our homes.

It can impact the water quality.

So it's really important that we do have vegetation here to prevent erosion.

Now, another really important part of soils is how they impact nutrients.

And so we talked a little bit about erosion and kind of the water pushing all of these nutrients or all of these soils away.

You can also have nutrient flow.

Now why are nutrients important?

Nutrients help give vitamins to you and I, to the plants, vegetation, to Salchicha over there.

So nutrients are really important, but we want to keep nutrients in the soil so the plants keep on growing.

Water is a really rare resource.

And so we have a lot of periods of drought.

And when we do get rain it can rain really, really intensely.

So we want to have that vegetation here to hold in that water when we do get it because it is such a rare nutrient or such a rare resource to have here.

Soil, biological crust and living crust, living soils, those are really important not only for this plant, you know, maintaining the plant structure, but also for the types of nutrient cycling that they have going in there.

So we talk about nutrient cycles.

Some of the biggest ones, the most important are carbon and nitrogen cycling.

And those are really important macro nutrients that plants need, what we need, and plants are really important help stabilizing them and then helping the cycling that happens in the soil.

Unfortunately, we humans tend to destroyed this super important but also super fragile ecosystem.

How?

Mountain bikes, ATVs, even your footprints can kill the soil, allowing the wind to scatter the microorganisms.

Worst of all, it can take over 50 years for the soil to regenerate.

Good news is you can do your part in protecting living soils and it's super easy.

Just stay on the trails.

And if you're on a bike or in a motorized vehicle, stay on the designated roads.

Even if you're not in Arches and you're just going for a hike in your neck of the woods, stay on the trails.

You don't want to get lost and you certainly don't want to be that person who destroys a thousand year old community of microorganisms.

[Music] Hey, everyone, I'm Chris Anderson, and I'm Doctor Rachel Bosch, and I'm Doctor Dylan Ward.

We are geomorphologists at the University of Cincinnati, working on a project supported by the National Cave and Karst Research Institute and the National Park Service.

And they're going to show me how they're learning, how Mammoth Cave is continuing to form.

So grab a pair of hiking boots, a good headlamp.

We're going on a science adventure.

[Music] Guys, We know a bit about how chemical weathering breaks down the limestone with all the rainwater.

How does physical weathering work here?

So when you have water flowing through a cave or through a river, you are transporting sand and gravel and sometimes boulders through these rivers.

And as you're doing that, they're kind of hopping along the surface and bouncing and crashing into the rocks and things, and they break off little bits of the rock that they impact into.

So as these as water is eroding sediment away, and it kind of smacks into the walls of the cavern and kind of continues to break stuff down, continues to weather stuff.

So, there's actually a lot of sand here too, but I thought this cave was limestone.

How did this sand get here?

Well, there's rivers on the surface up above us that are carrying all this sand from areas that have sandstone.

And some of those rivers disappear into sinkholes, and they become underground rivers that flow through these caves.

So those rivers are depositing the sand, down here in, in, in the cave, even though this was at the surface.

They're depositing, the sand was, started at the surface and has been carried into the cave and then deposited here.

So I guess what, you guys, because what you guys are studying is how the surface erosion and weathering and deposition all impacts the cave.

How does that work, really?

Well, one of the major things is that, the caves are only here because the Green River has cut down, like, like a knife through a layer cake, of the Kentucky geology.

So the Green River's kind of cut through all these layers of rock, and it brings all this stuff kind of with it.

Yeah, it's, it's cut down.

And the rivers that flow into the Green River, some of which, you know, still flow into the Green River, like the Barron River.

Others now flow into this limestone layer and through the caves to the Green River.

Now you guys are going down to the cave to take a take a little bit of data today, right?

Yes we are.

We're going to one of those rivers that Dylan was just talking about that comes from the surface and goes through Mammoth Cave and then exits out through spring into the Green River.

Well, that's pretty cool.

Do you mind if I tag along?

Not at all.

All right, well, let's go.

You guys lead the way.

[Music] [Music] What has your data that we collected down in the cave, how does I told you how the cave is changing?

So when we were down in Roaring River, we measured that the bedrock surface, that limestone floor of the Roaring River passage has lowered by 0.014in over the past year, which is about 1/100 of an inch.

1/100 of an inch, that's not that much, is it.

It doesn't really sound like that much, but if that happens for hundreds or thousands of years, it adds up.

I mean, I can imagine there's let's say it'd be about 100 years then to for it to erode or for it to whether one inch.

But if there's millions and millions of years, that's a lot of that's a lot of weathering.

Yes, it is.

But that wasn't the only thing that we learned down there, that there looked like there was some really big changes over time.

So it's not like these weathering patterns like happen like consistently across time, right?

No, no, they're very punctuated.

And sometimes you have big floods that come through and rearrange all of the furniture in the cave passage, so to speak, all of the all of the loose rocks and all of the sand, but the different piles of sand and stripped all the mud off of the, of the fallen rocks that had been there before.

Yeah, so it's almost like very little erosion, then boom, erosion events and then really little erosion, then erosion events of some longer time, Right?

- Yeah.

The Earth's surface is super dynamic.

Things are always changing.

And so even if this rock over here is only eroding by 100th of an inch each year, you know, there are still these catastrophic events sometimes.

Things get buried under huge piles of sand.

Things get carried away and move someplace else.

Dylan and Rachel, thank you guys so much for taking me into the cave and letting me tag along, and we'll see how you measure how this incredible cave system changes over time.

Like you said, it's super dynamic when it's really, really cool.

You're welcome!

- You're very welcome!

And for those of you at home, see what you can find around where you live.

See if you can find examples of erosion and weathering and deposition.

How it's changing the surface of the earth near you.

[Music] Major funding is provided by the National Geographic Foundation.

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