Erosion and Deposition

Erosion and Deposition

Middle School

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Learning Objectives

• Define erosion, deposition, and mass movement as key processes that shape the Earth's surface.

• Identify the four main types of mass movement: landslides, mudflows, slumps, and creep.

• Explain how wind acts as an agent of both erosion and deposition.

• Analyze how gravity, water, and wind contribute to the continuous reshaping of landforms.

Key Vocabulary

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Sediment

Material like rock pieces, or the remains of plants and animals, transported by erosion.

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Deposition

The process where agents of erosion, like wind or water, lay down carried sediment.

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Mass Movement

The downhill movement of rock and other earth materials, caused by the force of gravity.

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Deflation

The process by which wind removes loose surface materials, such as particles of clay and silt.

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Sand Dune

A deposit of windblown sand that forms when the wind slows or meets an obstacle.

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Loess

Fine, nutrient-rich, wind-deposited sediment that is finer than sand but coarser than clay particles.

The Cycle of Change: Erosion and Deposition

• Erosion carries away sediment using water, ice, wind, and gravity.

• Deposition drops sediment in new locations, building new landforms.

• Erosion wears down the land, and deposition builds it up.

Multiple Choice

What is the primary role of erosion?

• It carries away sediment from one place.

• It drops sediment to build new landforms.

• It causes rocks to become hotter.

• It holds sediment in a single location.

Multiple Choice

What is the relationship between erosion and deposition?

• Erosion is the process of wearing down land, while deposition is the process of building it up.

• Erosion and deposition are two words for the exact same process.

• Erosion only happens with water, and deposition only happens with wind.

• Deposition must always happen before erosion can begin.

Multiple Choice

If a river carrying a large amount of sediment suddenly slows down, what is the most likely outcome?

• Deposition will increase, and a new landform like a delta might begin to form.

• Erosion will speed up, carrying away more sediment.

• The water, ice, and wind will disappear.

• The sediment will be converted into rock by gravity.

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What Is Mass Movement?

• A landslide is a rapid slide of rock and soil down a steep slope.

• A mudflow is the quick downhill movement of a water, rock, and soil mixture.

• A slump is when a large mass of rock and soil suddenly slips downhill.

• Creep is the very slow downhill movement of rock and soil over time.

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Multiple Choice

Which statement best defines mass movement?

• The downhill movement of rock and soil due to gravity

• The formation of mountains from underground pressure

• The slow process of rocks breaking down into soil

• The shaking of the ground caused by earthquakes

Multiple Choice

What is the primary difference between a landslide and a creep?

• The type of rock involved

• The season in which it occurs

• The speed of the movement

• The steepness of the slope

Multiple Choice

After a week of heavy storms, a mixture of water, soil, and rock begins to move quickly down a hill. Which type of mass movement does this describe?

• A landslide

• A mudflow

• A slump

• A creep

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How Wind Causes Erosion

Deflation

• Wind lifts and removes loose particles like clay and silt from the ground.

• Heavier sand particles are bounced along the surface, while larger pebbles are rolled.

• This process can leave behind a rocky surface known as desert pavement.

Abrasion

• This occurs when wind-blown particles, like sand, scrape against rock surfaces.

• The constant impact of these particles acts like sandpaper, slowly wearing the rock away.

• Over time, abrasion can carve rocks into unique shapes and smooth their surfaces.

Multiple Choice

What is the primary way wind causes erosion through the process of abrasion?

• By wind-blown particles scraping against rock surfaces.

• By wind lifting and removing loose soil from the ground.

• By wind rolling large pebbles to form new rocks.

• By wind depositing sand and silt in a new location.

Multiple Choice

What is the main difference between the processes of deflation and abrasion?

• Deflation removes loose particles from the ground, while abrasion uses those particles to wear away rock surfaces.

• Deflation carves rocks into new shapes, while abrasion creates rocky desert pavement.

• Deflation only moves heavy pebbles, while abrasion only moves light sand and clay.

• Deflation is caused by wind, while abrasion is caused by water.

Multiple Choice

A windy desert landscape has many large rock formations and a great deal of loose sand. What is the most likely appearance of this landscape after many thousands of years?

• The ground will become rocky as sand is removed, and the rock formations will be smoothed and carved.

• The sand will pile up against the rock formations, making them larger and rougher.

• The rock formations will be broken down into sand, covering the entire landscape.

• The wind will have no effect on the rock formations but will create large sand dunes.

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Wind Deposition

Sand Dunes

• ​Sand dunes are mounds of sand formed when wind deposits sand around an obstacle like a plant.

• ​​The shape and size of a sand dune depend on the wind, sand amount, and nearby plants.

• ​These large mounds of sand are not static; they often shift and move with the wind.

Loess Deposits

• ​Wind can carry very fine sediment, such as silt, over extremely long distances before dropping it.

• ​​When this fine sediment is deposited, it builds up into thick layers of soil called loess.

• ​Loess deposits are very rich in nutrients, which makes them incredibly fertile and excellent for farming.

Multiple Choice

Which statement best defines wind deposition?

• The process of wind carrying and dropping sediment in a new location.

• The process of water freezing and breaking rocks apart.

• The process of glaciers carving out valleys and lakes.

• The process of volcanoes erupting and creating new land.

Multiple Choice

What is a key difference between the sand that forms sand dunes and the sediment that forms loess deposits?

• Sand dunes are made of larger particles, while loess is made of very fine sediment.

• Sand dunes are rich in nutrients, while loess is not fertile.

• Sand dunes are permanent and static, while loess deposits move with the wind.

• Sand dunes are formed by water, while loess is formed by wind.

Multiple Choice

A farmer needs to decide where to plant a new field. One area has large, shifting sand dunes, while another has thick layers of loess. Which area is the better choice for farming and why?

• The area with loess deposits, because they are very fertile and rich in nutrients.

• The area with sand dunes, because shifting sand is easier to plow.

• The area with loess deposits, because fine sediment holds less water.

• The area with sand dunes, because nearby plants make the soil better for farming.

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Common Misconceptions

Misconception	Correction
Erosion and weathering are the same.	Weathering breaks down rock. Erosion moves the broken pieces.
All geological changes from erosion are extremely slow.	Some changes like landslides happen very quickly.
Sand dunes are permanent, stationary landforms.	Sand dunes are constantly moved and reshaped by wind.
Gravity only causes rocks to fall straight down.	Gravity drives all mass movement, including slow creep.

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Summary

• Erosion removes sediment; deposition builds land, forming a continuous cycle.

• Gravity drives mass movements like landslides, mudflows, slumps, and creep.

• Wind erodes land by deflation and abrasion, then deposits sand dunes and loess.

• These processes reshape Earth's surface and help predict natural hazards.

Poll

On a scale of 1-4, how confident are you about explaining the difference between erosion and deposition?

• 1

• 2

• 3

• 4