Erosion

Erosion

Every year, millions of tourists ​flock to the Grand Canyon in the western United States to stand on the edge and admire the steep cliff face cascading down thousands of feet. Layers of beautiful red and orange rock line the walls of the canyon as it slopes toward a narrow, muddy river. What force could have created such a monumental natural wonder? What if I told you it was that somewhat unimpressive river, barely noticeable, at the bottom? Would you believe me?

To explain ​how the Colorado River is responsible for creating the Grand Canyon, we have to understand erosion. Erosion is the process of moving tiny pieces of rock, called sediment, over time. Before rock can be eroded, it must be weathered. Weathering happens when rock is broken down in smaller pieces or dissolved in water. Once weathered, the small pieces of rock can be carried away. There are four ways that rock can be eroded: gravity, wind, ice, or moving water.

Gravity can cause ​serious and sometimes dangerous erosion. Landslides, mudslides, and rock falls happen when large amounts of rock and sediment slide or fall down a steep hill or mountainside. These events can destroy buildings and endanger the lives of anyone in the path of the falling debris.

Wind picks up dust and fine​ sand and moves it somewhere else. This causes problems for farmers as soil for planting crops is removed from their fields. Whole towns have been covered in sediment after dust storms caused by wind erosion. This type of erosion is also a problem in coastal communities when sand dunes are blown away, leaving buildings in danger from the ocean waves.

Ice also causes erosion on a massive scale. Glaciers are rivers of ice that move slowly across the land. As they move, rocks and sediment get stuck in the ice. The glacier drags the rocks along, scraping off more rock as it goes and leaving behind a deep valley.

​Moving water, like rivers and ocean waves, are a major cause of erosion. As the water moves, it picks up small rocks and sediments. The sediment in the water then causes abrasion, like sand paper wearing away more and more rock. This type of erosion is precisely what created the Grand Canyon. Millions of years ago, the wide Colorado River ran on flat ground, at what is now the top of the canyon. It slowly wore away bits of rock and carried them downstream, carving the Grand Canyon, thousands of feet deep, out of solid rock.

​On the next slide, get ready for some questions!

Multiple Choice

Where is the Grand Canyon?

• Canada

• The western United States

• Europe

• South Africa

Multiple Choice

What made the Grand Canyon?

• A meteor

• Tectonic plates

• A river

• A glacier

Multiple Choice

True or False: Rock breaking down into smaller is called weathering.

• True

• False

Multiple Choice

Erosion is caused by ____________________.

• Gravity, wind, trees, and sand

• Gravity, wind, sediment, and snow

• Gravity, rain, ice, and hail

• Gravity, wind, ice, and water

Multiple Choice

Which is not an example of erosion caused by gravity?

• Landslides

• Mudslides

• Dust storms

• Rock falls

Multiple Select

Wind erosion causes problems for _________.

• Farmers

• Coastal Communities

• Glaciers

Multiple Choice

True or False: Glaciers can move.

• True

• False

Multiple Choice

What are glaciers?

• Giant dust storms

• Mountains of rock

• Rivers of ice

• Deep valleys

Multiple Choice

Sandpaper is used to describe ___________.

• Glaciers

• Sediment

• Abrasion

• Gravity

Multiple Choice

How long did it take for the Colorado River to carve the Grand Canyon?

• Hundreds of years

• Thousands of years

• Millions of years

• Billions of years

Poll

Did you understand the lesson? Choose 1 answer choice.

• 😃 Yes. I feel like an expert!

• 🙂 Almost yes. I feel great.

• 😐 Partly. I feel okay.

• 😕 Almost no. I feel confused.

• ☹️ No. I feel very frustrated.

Open Ended

Explanatory Writing: Explain how erosion moves and deposits rocks. Make sure you have checked your work.

Thanks for completing this lesson!​