[00:00:08.04] - Speaker 1

Hi, I'm Ranger Sarah, and welcome to Grand Canyon National Park. I'm standing here on the South Rim of Grand Canyon, within the village area. However, this is not the only area you can access the park from. You can experience the park from the North Rim, the South Rim, and even the bottom of the Canyon. On the North Rim, you can view the Canyon from Bright Angel Point or here from Point Imperial, which provides a whole new perspective. Lastly, if you're up for the ultimate hiking challenge or rafting adventure, you can experience the Canyon from the bottom. Now, the Canyon didn't always look this way. It had to start its formation at some point. Well, the rocks tell a story that start 2 billion years ago when igneous and metamorphic rock formed at the bottom, followed by sedimentary rocks layered on top. And after many different environments existing on this landscape, from oceans to arid sand dunes, a big uplift occurred through plate tectonics. Now, today we call that uplift the Colorado Plateau. And after this plateau was formed, the Colorado River, which was formed 6 million years ago, began to carve the canyon out, ultimately revealing the many rock layers that you see here today.

 

[00:01:44.13] - Speaker 1

Since its formation, many people have developed strong connections to this place, and not just for those that visit today, but for those who have been in the area for over 10,000 years. Some of the first people to recognize this special place are the 11 associated tribal communities. From time immemorial, these tribes have continued to create strong cultural and historical connections to the Canyon. We gratefuly acknowledge the native peoples on whose ancestral homelands we gather on, as well as the vibrant and diverse native communities who continue to call this place home.

 

[00:02:59.27] - Speaker 1

As we continue to learn, you'll begin to see that the Canyon holds so much history. So today we're going to be investigators, and we're going to dive deeper into the formation of the Canyon. We're going to learn, we're going to discover why the Canyon is still continuously shaping today.

 

[00:03:25.01] - Speaker 1

Oh, hey, everyone.

 

[00:03:27.09] - All

Hi, Ranger Sarah.

 

[00:03:28.22] - Speaker 1

Well, with the help of my ranger friends here, we're going to make observations to find a bunch of pieces of evidence of why the canyon is still shaping.

 

[00:03:38.16] - Speaker 2

Hi, I'm ranger Joelle, and I'll be talking to you about small pieces of evidence and the Colorado River.

 

[00:03:44.26] - Speaker 1

You heard that right, the Colorado River, woo!

 

[00:03:46.08] - Speaker 3

Hi, I'm Ranger Lucy. I'll be talking to you about large scale evidence that we see here in the canyon.

 

[00:03:53.15] - Speaker 1

Sweet, I'm looking forward to those panoramas of the canyon.

 

[00:03:57.11] - Speaker 4

Hi, I'm Ranger Alejandro, and I'll be talking about humans and human-driven impacts in the Grand Canyon landscape.

 

[00:04:03.12] - Speaker 1

All right. Well, there you have it. As you can see, we are going to be making lots of observations today to find evidence of why the Grand Canyon is still changing today. All right, see you soon!

 

[00:04:30.01] - Speaker 2

Hi, my name is Ranger Joelle, and we are going to be looking for small pieces of evidence of what forces are shaping the Grand Canyon. Small pieces of evidence are often overlooked when talking about what made the Grand Canyon, but they're just as important, and they still have a big impact in our landscape. When we're looking for small pieces of evidence, we are going to be looking for signs of weathering and erosion, which are two geologic processes that shape our landscape. Weathering is when rocks and minerals break down as a smaller piece based on physical, biological, or chemical means. Meanwhile, erosion is when weathered rocks and minerals are transported from one location to another via natural forces like wind or water. Together, these geologic processes play a big role in creating and shaping landscapes, from beaches to valleys to mountains to the Grand Canyon.

 

[00:05:29.02] - Speaker 2

Let's zoom up on these rocks. Do you see that? That fuzzy stuff is called lichen. Lichen is made from a symbiotic relationship of two organisms: fungus and algae. So how is it a part of Grand Canyon geology if it's not a rock? Well, lichens are hardy organisms that can adapt well to desert climates and easily soak up water into their cells. So when lichen grows on rock, it buries into the rock's surface with tiny little hairs called hyphae. As those hairs anchor deeper into the rock, the rock slowly dissolves and weakens from the lichen releasing weak acids. The lichen will also expand during wet seasons and then contract during dry seasons, further weakening the rock that it lives on. So after the lichen eventually dies, the rock is going to erode away.

 

[00:06:30.28] - Speaker 2

Now, let's explore some more evidence. Do you see all of the small craters in the rocks around me? Similar to lichen's weathering process, these craters were also created from acid breaking down the rock. Rainwater is slightly acidic. This naturally occurs when carbon dioxide in the atmosphere dissolves into rain. When rainwater pools on top of limestone rock, it slowly dissolves, creating holes or craters in the rock. Over time, the rock erodes more and more because of the monsoon rains we get in the summer. You can see examples of this all throughout the park.

 

[00:07:09.19] - Speaker 2

All right explorers, let's look at our last piece of evidence. This is chert. Stuck in the rock. Chert is a harder rock that can be found in limestone. So just like the limestone that we walk on the rim of the canyon in the Kaibab formation. Back when this rock layer was forming, about 270 million years ago, this area was actually part of an ocean. Within that ocean lived sponges that once they died off, they became fossils. And those fossils formed the chert that we see today. So with so many sponges in that ancient ocean, layers like the Kaibab formation are actually more resistant to erosion because of the chert. Since chert is harder than the limestone rock, it's embedded deep within the rock, causing these massive chunks of chert to stick out from the rock as the rock erodes away. So how does this play a role in the changing canyon? Since chert itself isn't actually causing the canyon to erode, for us, it's more of an indicator that erosion has happened in an area. This is an of how weathering and erosion can reveal new parts of the canyon to us.

 

[00:08:50.08] - Speaker 3

Hi, I'm Ranger Lucy. So, so far, we've covered the small-scale evidence. We've gone over how weathering and erosion work, and we've begun to form an understanding of how the canyon formed. Now it's time to step back, zoom out, and take a look at some of the bigger picture evidence.

 

[00:09:07.07] - Speaker 3

All right, so let's focus on these upper few layers of rock here. At the Grand Canyon, we see a lot of different minerals make up the rock layers. But the two we see the most are called iron and oxygen. When iron and oxygen mix together, they do something cool. They create a totally new compound. That compound is called iron oxide. It's just a mix of their names. Here, the most common form of iron oxide that we see in the canyon is called hematite. Hematite is actually one of the most common compounds in the entire world. Now, hematite does something interesting when it's exposed to even more oxygen or water. It creates rust. It's like when you're looking at a really old penny, it's not shiny and new. It has that dark film on it. When water moves over these rock layers at the canyon, we see that water react with the hematite to form these beautiful red, rusty cliffs. So when you look into the canyon, you're not actually seeing the natural color of the rock. You're looking at the red rust on top of the rock layer to create this beautiful color.

 

[00:10:15.06] - Speaker 3

So water does more than just cause rust on rocks. Water also has the power to break boulders. If we zoom in on some precarious-looking rocks behind me, you might just see some that look like they could topple over. These towers of rock form when water changes states into ice. That ice builds up and expands inside of the rock, pushing outwards and forcing the rock to break. These breaks will fall from the rim of the canyon over time, and slowly we're left with these towers of rock that are still standing strong. So as erosion continues to shape this landscape, these rocks are most likely going to collapse one day, and you won't be able to see these towers. So come to the Grand Canyon and see them while you can.

 

[00:11:24.24] - Speaker 3

There's one more important way that water shapes the landscape here at Grand Canyon. Obviously, we all know about the Grand Canyon, but did you know there are many multiple side canyons branching off of this main area we see?

 

[00:11:41.25] - Speaker 3

Let's take a closer look at one. This is Bright Angel Canyon. If you're planning on visiting and completing a rim-to-rim hike, then you'll have to traverse through this area here. But how did water move to form yet another canyon? Canyon branching off from the main area we see? Water from various points along the rim, like snow melting or rainwater falling, gather to form creeks. These creeks flow over the rocks, and it breaks them down so we can carve out new areas of the canyon. These areas become wider over time as water tries to flow towards the primary source at the bottom of the canyon, the Colorado River.

 

[00:12:44.22] - Speaker 4

Hi, I'm Ranger Alejandro, and today I'm wondering, how many human footprints can be found in the Grand Canyon landscape? While we might not be able to find an exact answer to this question, we know that humans' presence and impact on this land can still be felt and observed today. As we look out at the canyon, think about in what ways have humans changed and impacted this landscape, and how many of those are actively happening today? Turn and talk to the person next to you and talk about two ways in which you think humans impact this landscape. By now, we've learned about the small and big pieces of evidence that can help us understand how geologic processes are continuing to the Grand Canyon landscape. These processes, however, often don't work alone. Human-led actions paired with geologic processes have the ability to bring major changes to this landscape. We've also learned that human activity and connections to the Grand Canyon landscape predate the park itself. Humans have lived in, changed, and impacted this landscape for over 10,000 years, from those that call this place their ancestral home to those that visit every year. Since its inauguration in 1919, Grand Canyon National Park has grown to be a popular destination for people visiting from all over the country and world.

 

[00:14:10.14] - Speaker 4

Increased use in visitation means increased impact on the landscape, which can bring physical changes to the world all around us, especially here at the Grand Canyon. Now, here you'll find three primary ways in which humans impact the Grand Canyon landscape: recreation, transportation, and land development. All three of these actions are connected to the processes of weathering and erosion. Let's explore each of these more closely and figure out how they impact the Grand Canyon landscape. Recreation is a big way people can experience the Grand Canyon. Grand Canyon National Park has over 700 miles of hiking trails, which can allow visitors to explore this landscape through a variety of habitats and terrains. Maintained trails like the South Kaibab Trail here is considered an official hiking path by the National Park Service. With over 6 million visitors each year, many of these trails receive heavy foot traffic, which can contribute to human-led erosion of them. As more and more people hike the same path, the rocks and soil underneath can wear away faster. Over time, these changes can bring significant alterations to the landscape. To help manage the impacts of human-driven erosion here, certain areas may be paved, including trails along the canyon rim, as well as more heavily trafficked paths, like this one along the visitor center.

 

[00:15:40.03] - Speaker 4

This not only reduces the impact and speed of erosion, but also increases more accessibility for people by having stable and durable surfaces. Now, another form of human-driven impact we can find here at the park are unofficial trails, often called social or desired trails. Because these trails are not official, they often go unmaintained, which can lead to the degradation and damage of fragile ecosystems and vegetation. Let's go find out what other forms of human-driven impact we can find here at the Grand Canyon landscape. Paths of travel, like those used by mules and vehicles, can also contribute to erosion. The weight and movement of mules on trails, as well as the weight of tires on dirt roads, can accelerate the erosion process. Continuation of these actions means continuation of erosion, creating deeper paths, and sometimes even changing the course of water runoff during heavy rains, further changing the landscape. To help manage the impacts of different forms of transportation in the park, from mules on trails to vehicles on dirt roads, different measures may be taken by park management, including constant trail maintenance, as well as the issuing of permits to limit overuse of certain areas along dirt roads containing fragile ecosystems and vegetation.

 

[00:17:05.22] - Speaker 4

All of this in an effort to help reduce the erosion of those areas. Now, human-led impacts can even be found in the deepest parts of the canyon, once again bringing change to the Grand Canyon landscape. Now, let's talk about human-led land development, specifically dams. These human-made structures, like the Glen Canyon Dam up-river and the Hoover Dam down-river, have a profound impact on the changing of the Grand Canyon landscape. Now, these structures have the ability to control the flow of the Colorado River, which can either result in a slower erosion process or a faster erosion process depending on where the canyon is being impacted. Historically, these dams have slowed down the flow of the Colorado River, which has resulted in a slower erosion process of the canyon walls. However, low-lying areas like sandbars can also be impacted by dams by increasing their erosion because the river isn't able to deposit as much sediment as it used to prior to the dam's construction. So we've seen how this amazing landscape has been shaped not only by natural forces, but by humans and human-driven activities as well. Think about all the footprints, both literal and figurative, we've left here through time.

 

[00:18:30.28] - Speaker 4

From the communities that have considered this place their ancestral home since time immemorial, to the millions of visitors who travel from all across the globe each year to experience a site like this. Our presence is everywhere. So let's review. We learned about how recreational activities, like hiking on trails, can contribute to the erosion of them, and how the weight of mules and vehicles can also add on to this through different parts of the park. Plus, we learned how dams along the Colorado River can control the flow of the river, which can influence and alter how sediment is deposited and formations like sandbars eroding away. Now, it's important to remember that change is a constant force in a place like the Grand Canyon, neither good or bad by definition. In fact, one of the most influential forces of change is responsible for the creation of the Canyon a long time ago. It's right behind me, isn't it? Let's learn more about the Colorado River's history and the Grand Canyon landscape.

 

[00:19:52.19] - Speaker 2

The history of the Grand Canyon is the history of the Colorado River. This river has been carving the Canyon for 6 million years and is the main reason for the canyon's depth and width. The Colorado River is also the main source for transporting rocks and sediment through the canyon. As the Colorado River flowed through the elevated plateau, it began to erode the rock through a process called downcutting. The river's powerful flow, strengthened by melting snow and seasonal rains, increased its erosive power. The Colorado River carried sediment, rocks, and other debris, which acted like sandpaper, grinding and scraping the river bed and canyon walls, gradually deepening the canyon. But why isn't other rivers making similar canyons? Why is there no Grand Canyon of the Mississippi River? We're going to explore three reasons why the Grand Canyon of the Colorado River came to be.

 

[00:20:55.01] - Speaker 2

The first reason is the Colorado River's steep slope. Let's imagine that you're sledding. If you're going sledding down a smaller hill, you won't gain much speed. However, if you're going down a bigger, steeper hill, the steeper slope of that hill will mean that you go down it faster. About 70 million years ago, tectonic plates started to raise the Colorado Plateau, elevating the area and creating a steeper area for the Colorado River to flow.

 

[00:21:25.14] - Speaker 2

On its 278-mile journey through the Grand Canyon, the Colorado River descends about 2,000 feet in elevation. This steep slope gives the river a tremendous amount of speed and the ability to transport big rocks during floods. The second reason of how the Colorado River is forming the Grand Canyon is with the force of its moving water. The fast moving water of the Colorado helps to break down and remove rock material from the river's path. The average flow is between 12,000 and 15,000 cubic feet per second. That's as if 12,000 to 15,000 basketballs came barreling past you each second. During a flood, the increased volume of water flowing in the river can flow at a rate of 300,000 cubic feet per second. Imagine 300,000 basketballs barreling past you each second. Ouch! That's how fast the Colorado River's water is. The third reason for how the river is creating this canyon is because of this area's dry environment. The dry desert of the Grand Canyon slows the erosion process because there isn't as much vegetation to slow down the movement of rocks and sediment. Weather from wind and water happens relatively quickly in arid regions. In more humid regions, plants cover the land and help slow erosion.

 

[00:22:59.10] - Speaker 2

In arid climates, there's often little soil and few plants keeping that soil in place, thus leaving bedrock exposed. The exposed rocks are more easily eroded by precipitation, daily changes in surface temperature, and ice during winter months. Rivers flowing through arid landscapes can carve through rock more easily because the rock is exposed and weathered.

 

[00:23:30.04] - Speaker 1

Hey, welcome back, investigators. So today we learned a lot about the canyon. We learned how weathering and erosion, along with the human impact, and even the river, shape this landscape.

 

[00:23:43.22] - Speaker 3

We've covered everything from small pieces of evidence, like holes in rock, to larger scale evidence, like red rust on a cliff face. We've even covered human impact, like the creation of trails and roads, all the way down to the bottom of the canyon at the Colorado River, which is why we have this beautiful canyon here today.

 

[00:24:04.10] - Speaker 4

Now, as we come to the end of our time together, we'd like to ask you to take some time to reflect on everything we learned today. From the forces and processes that you discovered today, which ones were your favorite? Which ones were the most interesting? And which ones would you like to continue to learn more about? In a place like the Grand Canyon, the questions and curiosity are never-ending. We could be here all day.

 

[00:24:27.29] - Speaker 2

But remember, these processes and forces all work together to create this Grand Canyon landscape. Thank you for being investigators with us today, we're signing off from Grand Canyon National Park!