Learn about how streams develop and affect the landscape, the causes and mitigation of flooding, and why landslides happen.

How Was the Grand Canyon Formed?

A video from It’s Okay to Be Smart. The resources accompanying this video were created by Diane Schuetz and are shared with a CC BY-NC-SA license.

Summary

The science behind one of Earth’s greatest natural wonder. How did the Grand Canyon get so big? Learn about the geological processes that helped create the Grand Canyon: Vishnu Mountains (basement rocks), erosion and weathering (flattening the mountains), Cambrian Sea (limestone and fossils), colliding tectonic plates (create the Colorado Plateau), and the Colorado River carving through the plateau exposing the ancient rock layers.

Why Watch This Video?

• Have you ever wondered why the Colorado River was able to form the Grand Canyon even though the Colorado River isn’t as big as the Mississippi or Amazon River?
• Would you like to know how the forming of the Colorado Plateau and the Colorado River aided in the creation of the Grand Canyon?
• Have you ever been confused by why there are so many different layers of rocks in the Grand Canyon?

Key Terms

Erosion. The process that removes gravel, rocks and ions from the parent rock or mountain due to weathering, causing these smaller particles or ions to break off. This is what happened to the Vishnu mountains, as well as side effects from the Cambrian sea, colliding tectonic plates and the Colorado River that moves gravel, silt and sediment.

Geological time (deep time). The time used by geologist to explain how geological processes happen over a very long time (millions to billions of years.)

Tectonic plates. The lithosphere—Earth’s crust plus the top part of the mantle—is broken into fragments called plates.  Two tectonic plates collided to create the Colorado Plateau which led to the Colorado River being formed.

Loose Ends

What is a “tectonic elevator ride?”

When two tectonic plates collide also known as a convergent boundary. At a convergent boundary one of the plates will buckle beneath the other, pushing the opposing plate up which creates mountains and plateaus. The mountains created were the Rockies, which played a part in creating the Colorado River.

“At convergent boundaries, plates collide with one another. The collision buckles the edge of one or both plates, creating a mountain range or subducting one of the plates under the other, creating a deep seafloor trench. At convergent boundaries, continental crust is created, and oceanic crust is destroyed as it subducts, melts, and becomes magma.” (Cowan, 2013)

Oldest rocks are located at the bottom of the canyon due to weathering and erosion of the Vishnu mountain range.

The Vishnu mountain range formed when tectonic plates collided approximately 2 billion years ago. These tectonic plates and the mountain range they built laid the foundation for more rock layers to build above them. Each layer the Colorado river cut through, helps geologists with their studies. The geologists can differentiate the layers and estimated the years for when rocks could have been deposited there.

“In the Grand Canyon, there are clear horizontal layers of different rocks that provide information about where, when, and how they were deposited, long before the canyon was even carved. The Law of Superposition states that sediment is deposited in layers in a sequence, the oldest rocks are on the bottom and the youngest rocks are on the top.” (Timmons, 2013)

The Colorado river is a major part of the Grand Canyon’s history.

After the layers of sediment, limestone, shale, and sandstone were deposited (over a few hundreds of millions of years), roughly 70 million years ago the tectonic plates collided again. This collision formed the Rocky Mountains and the Colorado Plateau, which would eventually produce the Colorado River. Even though the Colorado river isn’t very big compared to the Amazon or Mississippi river due to the limestone, shale and sandstone layers the Colorado river was able to cut into the Earth and create the stunning canyon that we see today.

“By around 6 million years ago, waters rushing off the Rockies had formed the mighty Colorado River. As the plateau rose, the river cut into it, carving the canyon over time. Smaller rivers eventually cut the side canyons, mesas and buttes that are so characteristic of the canyon today.” (Witze 2019)

Self-Test

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References

Cowan, A. M. (2013, March 05). Plate Tectonics. Retrieved November 17, 2020.

Timmons, S. (2013). Grand Canyon Geology. Retrieved October 14, 2020.

Witze, A. (2019, February 26). A deeper understanding of the Grand Canyon. Retrieved November 14.

What Rivers Can Tell Us About the Earth’s History

A talk by Liz Hajek for TED. The resources accompanying this video were created by Maeve Chidwick and are shared with a CC BY-NC-SA license. This video starts at the 4 minute mark.

Summary

In the Ted Talk What rivers can tell us about the earth’s history Geologist Liz Hajek argues that Earth is an incredibly dynamic place. Liz Hajek constructs her argument by explaining how rivers constantly change by quite literally jumping locations. This jumping movement of rivers is one of the many factors that produces the dynamic environment of Earth. She argues that to manage our resources sustainably and effectively on this dynamic planet it is critical that we understand how landscapes have evolved and continue to alter with respect to climate and land use events.

Why Watch This Video?

• Have you ever wondered how you could time-travel to see what past landscapes looked like millions of years ago?
• Would you like to know how a rapid release of C0₂ would affect Earth’s landscape particularly the waterways and rivers near you? The past is the key to understanding what the future climate change will look like for us.
• Have you ever been confused by the concept that Earth’s landscapes are dynamic (constantly changing)? When the landscapes around you seem constant and unchanged on a day to day basis.

Key Terms

Sedimentary rock is rock that has formed from moving water transporting materials  (i.e. sand, clay) downstream over time. These materials accumulate, compact and become rock.

Fossil rivers are deposits of sedimentary rock laid down millions of years ago by past rivers. These layers of sedimentary rock show how rivers flowed and what landscapes looked like million of years ago.

Paleogeography is the study of historic records left in Earths landscapes. In this particular video Liz Hajek is looking at sedimentary rock river fossils to understand what past rivers and landscapes looked like.

Loose Ends

Rivers wiggle and jump over time.

Rivers out on open plains can change direction (i.e. wiggling/ jumping) with a just a little disturbance to the river and a lot of time. An example of a disturbances would be something like a beaver’s dam in a river. The dam will change the flow of the river and force the river to take an easier route. Rivers may cut off loops. As noted by Liz Hajek, these U-shaped water ways left behind by the river are called oxbow lakes.

What is a flood plain?

The term flood plain was briefly used in this Ted Talk. A flood plain is the area of land covered by water in flooding season. When the flooding has passed, there is fertile land as the fine sediment in left over on the land. This sediment is ideal for agriculture. An example of a flood plain is the Fraser Valley  in British Columbia.

What is tectonic plate movement?

At the 7:15 mark, Liz Hajek  shows tectonic plate movement for the last 600 million years of Earth’s surface. Earth’s plate tectonic movement is due to the fact that Earth is made up of many different tectonic plates (fragments of the lithosphere) that fit together like puzzle pieces and sit atop a weak layer called the asthenosphere that allows the tectonic plates to move. These tectonic plates are in constant motion, moving away form each other (divergent), towards each other (convergent), and beside each other (transform) due to the heat of Earth’s core. Plates can move centimetres per a year, and over millions of years leads to the reconfiguration of contents seen in the video.

Additional note: time on a large scale such as 600 million years is referred to as geological time.

Self-Test

Try these questions to test your understanding.

References

Hajek, L. (2014, March). What rivers can tell us about the earth’s history [Video]. TED Conferences.

Panchuk, K. M. (2019). Physical Geology, 1st USask Edition.

Why Isn’t the Netherlands Underwater?

A video by Stefan Al for TED-Ed. The resources accompanying this video were created by Amelia Russell and are shared with a CC BY-NC-SA license.

Summary

This video explains how the Netherlands is very susceptible to flooding due to intense storms, as a large portion of its territory is below sea level. However, the government of this coastal country has implemented considerable amounts of precautionary measures and protective technologies to avoid the damaging effects of these natural disasters. The Netherlands sets an example for flood prevention with its use of protective dikes, artificially elevated neighbourhoods, and many more engineered solutions.

Why Watch This Video?

• Have you ever wondered how coastal countries are preparing for rising sea levels?
• Would you like to know how flood prevention techniques work, and if they are actually effective?
• Have you ever been confused by the fact that a large portion of the Netherlands’ territory is below sea level, yet it doesn’t undergo any more damages from floods than the average coastal country?

Key Terms

A delta is the landmass that occurs at the mount of a river when fragments of rock and other material accumulate as a river flows into another body of water. This happens because the flow of the river slows down as it reaches its end, so the material will sink to the bottom of the riverbed instead of emptying into the new body of water.

A dike is a wall made out of earth or stone, built to hold back water and prevent flooding. They can be naturally occurring, but they are mostly man-made structures.

An estuary is a transition zone where a river and the ocean meet. It contains a mix of freshwater from the river and saltwater from the ocean.

Loose Ends

How do floods actually occur, and can they occur in places that aren’t located on a coast?

The video explains the many devastating effects of floods as well as the ways the Netherlands is built to protect against them, but how do these destructive natural disasters develop? A big storm or a tsunami can cause flooding in coastal cities by forcing the ocean to flow into the mainland. However, flooding can also happen further inland when a river gets overwhelmed by the amount of water flowing through it. This can happen through precipitation, melting ice, or other factors that raise water levels. It is important to note though, that many floods actually progress over somewhat large periods of time, giving people hours, or sometimes days to evacuate the area. Of course, flash floods, which are the result of excessive rainfall in less than six hours, can still occur, leading to more dangerous flooding and more damage.

Are there any negative environmental impacts of blocking off rivers and estuaries?

Even though dams are effective tools used to prevent flooding, they can be a nuisance to aquatic animals who are trying to travel down the river or stream they block off. For example, species like fish who travel between rivers and the ocean, can have their whole life-cycles disrupted by these dams, killing large amounts of them. However, this was considered by the Delta Works committee when they built a storm surge protector called Oosterscheldekering. It was originally supposed to be a completely closed off dam, but the potential negative impacts on the ecosystem in the area forced the organization to make a barrier of floodgates that could open and close depending on when they need to be closed.

If these preventative measures are so effective for the Netherlands, are other coastal cities using them? If not, how come?

Other countries are indeed using the Netherlands’ advanced engineering as a blueprint for their own designs. City planners and engineers from countries like the U.S. have visited the Netherlands to look at their designs and collaborate with Dutch officials in discussions about how they can use similar technology to minimize the damage of natural disasters. However, the U.S. is also known for its post-disaster management, and not so much their disaster prevention. This means that they would have to completely change their methods and fund more flood prevention programs rather than putting money into the cleanup after the flood. Also, other cities don’t have to focus on the danger of flooding as much because it is nowhere near as great as it is for the Netherlands.

Self-Test

Try these questions to test your understanding.

References

Higgins, A. (2012, November 14). Lessons for U.S. From a Flood-Prone Land. The New York Times.

Kimmelman, M. (2017, June 15). The Dutch Have Solutions to Rising Seas. The World is Watching. The New York Times.

Miner, L. & Wilks, J. (2020, February 25). Rising sea levels- how the Netherlands found ways of working with the environment. Euronews.

National Geographic. (2013, December 12). Delta. National Geographic.

Tahmiscioglu, M. S., Anul, N., Ekmekçi, F., Durmus, N. (2011, February). Positive and Negative Impacts of Dams on the Environment. CVC.

When Nature Strikes- Landslides

A video by the National Science Foundation. The resources accompanying this video were created by Jake Beutle and are shared with a CC BY license.

Summary

This video is a case study that follows geologist David Montgomery and a team of scientists as they analyze the 2014 Oso landslide in Washington to determine how and why the landslide occurred. Past and present data of the Oso area is used to gain insight into the environmental factors that went towards triggering this landslide and potential future slides. This video also provides an inside look into the lab and fieldwork performed by geologists as they conduct surveys and generate maps based on the terrain where the landslide took place.

Why Watch This Video?

• Have you ever wondered why certain sloped surfaces fail and trigger landslides, but others don’t?
• Would you like to know how the history of a landscape can be used to predict future landslides?
• Have you ever been confused by how geologists use their field data and apply it to further their understanding of natural disasters?

Key Terms

Slurry. In a landslide, the terrain can become disrupted due to an excessive amount of water from heavy rainfall or from the rapid melting of snowpack or glaciers. With the ground oversaturated, mass amounts of dirt, rock, and debris mix together to form a muddy, semi-liquid material known as slurry¹. The slurry is pulled downhill by gravity and can flow at speeds faster than humans can run¹, leaving the destructive path landslides are known for.

Topography. When looking to understand a natural disaster, scientists use topography to get a better idea of the landscape they’re working with. Topography is the study of the physical features of a landscape such as valleys, rivers, mountains, etc². These features can be both natural or man-made and are described by their relative positions and elevation. This data can be placed into a topographical map to describe how the landscape features relate to each other in the environment.

Degrade. When natural materials degrade, it means they are being broken down and weakened over time. Natural materials degrade as a result of exposure to weathering processes (like extreme temperatures or rainfall) which can cause the structure of soil and rock to deteriorate. Landslides can be triggered by the material on a slope degrading to the point where it is so weak and unstable that it is incapable of holding itself together and proceeds to slide.

Loose Ends

Are all landslides considered the same?

No. There are many different kinds of landslides that are differentiated based on the material in the slide (rock, earth, or debris) and the way the slide moves. The two main types of landslides are rotational slides and transitional slides³. Rotational slides occur when the ground that the surface slides on is curved upward, and when the material slides, it moves down along the curve (like sliding in a bowl)³.  A transitional landslide occurs when the ground that the surface slides on is along a flat plane, and the material on the surface instead slides straight downhill (like sliding down a ramp)³.

What is a scarp and how do we use them to predict landslides?

A scarp is a very steep part of a slope with exposed rock and soil. Scarps form when material from the landscape is displaced due to movement by plate tectonics or gravity, creating an offset in the terrain where one side of the terrain is higher than the other. In the video, the geologists pointed out how different scarps were left over after slides had occurred throughout history and were the starting point of future slides that haven’t happened yet. This is because scarps are key in the formation of landslides since the slope of a scarp is very steep and can be easily eroded by weathering processes which makes it easier for gravity to pull it down.

Are all landslides triggered by water?

Even though water is one of the main factors that cause a slope to fail, there are still various other natural and human influences that can trigger a landslide. In nature, seismic activity from earthquakes causes frequent landslides to occur around the world. Seismic activity results in the ground shaking from the movement of tectonic plates with forces that can loosen the earth on steep slopes, leading to gravity pulling it down. Humans are also capable of triggering landslides through different activities like the removal of slope material to build new developments or by altering where water naturally drains, which causes water to pool and generate erosion.

Self-Test

Try these questions to test your understanding.

References

1. The Ready Campaign. (n.d.). Landslides & Debris Flow | Ready.gov. Ready.Gov. Retrieved October 13, 2020.

2. Earth Science for Kids: Topography. (n.d.). Ducksters. Retrieved October 13, 2020.

3.  U.S. Geological Survey, U.S. Department of the Interior. (2004, July). Landslide Types and Processes. Usgs.Gov.