Science · 7th Grade · Earth's Changing Surface · Weeks 28-36

Erosion and Deposition: Moving Earth Materials

Students investigate how water, ice, wind, and gravity transport weathered materials and deposit them in new locations.

• Common Core State Standards
• MS-ESS2-1
• MS-ESS2-2

About This Topic

Erosion is the transport of weathered rock and sediment by water, wind, ice, or gravity from one location to another. Deposition occurs when the transporting agent loses energy and drops its sediment load. Running water is the dominant erosion agent on most of Earth's surface: rivers cut valleys, carry sediment toward the ocean, and deposit it as alluvial fans, floodplains, and deltas. Glaciers are extraordinarily effective at large-scale erosion, carving U-shaped valleys, fjords, and high-mountain features like horns and cirques. Wind erosion is most significant in arid environments with sparse vegetation. Gravity alone moves material through mass wasting events including landslides, mudflows, and rockfalls. The MS-ESS2-1 and MS-ESS2-2 standards ask students to develop models and construct explanations for how Earth's surface is shaped by these processes.

Human activities dramatically accelerate natural erosion rates. Clearing forests removes root systems that bind soil, and construction sites expose bare ground to rain and wind. In the US, the Mississippi River delivers roughly 500 million tons of sediment to the Gulf of Mexico annually, much of it from agricultural land in the Midwest. The Dust Bowl of the 1930s remains the most dramatic domestic example of agriculture-accelerated erosion.

Active learning investigations that give students control over erosion variables in a stream table produce much stronger causal understanding than reading about these processes.

Key Questions

1. What role does vegetation play in preventing the loss of soil?
2. How do human activities accelerate the natural process of erosion?
3. Compare and contrast the erosional and depositional features created by glaciers and rivers.

Learning Objectives

• Compare and contrast the erosional and depositional landforms created by glacial and riverine processes.
• Explain the role of vegetation in mitigating soil erosion by analyzing case studies.
• Analyze how specific human activities, such as deforestation and urbanization, accelerate natural erosion rates.
• Design a model that demonstrates the transport and deposition of sediment by wind or water.

Before You Start

Weathering: Breaking Down Earth Materials

Why: Students must understand how rocks and minerals are broken down before they can investigate how these materials are transported.

Introduction to Earth Systems

Why: A basic understanding of Earth's major systems (geosphere, hydrosphere, atmosphere) is necessary to grasp how erosion and deposition interact across these spheres.

Key Vocabulary

Erosion	The process by which soil, rock, and sediment are worn away and transported by natural forces like water, wind, ice, or gravity.
Deposition	The geological process in which sediments, soil, and rocks are added to a landform or landmass, occurring when the transporting agent loses energy.
Mass Wasting	The downslope movement of rock, regolith, and soil under the direct influence of gravity, such as landslides and mudflows.
Alluvial Fan	A fan-shaped deposit of sediment formed where a stream emerges from a narrow valley onto a plain.
Glacial Till	Unsorted sediment deposited directly by a glacier, often containing a wide range of particle sizes from clay to boulders.

Watch Out for These Misconceptions

Common Misconception

Erosion only happens near rivers and oceans.

What to Teach Instead

Wind erosion is highly significant in deserts and recently disturbed soils. Glacial erosion shaped large portions of the northern US. Mass wasting occurs on any slope steep enough to destabilize accumulated material. Examining photographs of glaciated valleys in the Rockies, sand dunes in the Southwest, and hillside landslide scars helps students see the full geographic range of erosion agents.

Common Misconception

Deposition only happens in water.

What to Teach Instead

Wind deposits sediment as dunes and as fine-grained loess, which forms thick layers covering large parts of the Midwest. Glaciers deposit unsorted material as till and as terminal moraines when they melt. Identifying these non-water depositional features on a regional geologic map shows students the full scope of depositional processes.

Active Learning Ideas

Simulation Game: Stream Table Erosion and Deposition

Groups use sand trays with a slight slope and add water to simulate a stream. First, they observe erosion and deposition patterns on bare sand. Then they add moss, grass plugs, or sponge pieces as 'vegetation' for a second run. Students compare channel shape, amount of material removed, and deposition patterns between runs and connect their findings to the role of vegetation in preventing soil loss.

55 min·Small Groups

Think-Pair-Share: Human Acceleration of Erosion

Show before-and-after satellite images of an area before and after deforestation or major construction. Students individually estimate the change in erosion rate and list the specific factors responsible, then share with a partner. The class discusses management practices (cover crops, silt fences, terracing, riparian buffers) that could reduce the erosion rate.

25 min·Pairs

Gallery Walk: Erosional and Depositional Landforms

Post eight stations with photographs and brief descriptions of landforms created by different agents: a river delta, a glacial U-shaped valley, a desert sand dune, an alluvial fan, a sea stack, a loess deposit, a landslide scar, and an oxbow lake. Groups rotate and match each landform to its erosion agent, noting one observable feature that distinguishes it from a landform made by a different agent.

40 min·Small Groups

Real-World Connections

• Civil engineers and geologists work together to design and implement erosion control measures for construction sites and along coastlines, using techniques like retaining walls and vegetation buffers to prevent soil loss and protect infrastructure.
• Farmers utilize conservation tillage and cover cropping practices, informed by soil science, to reduce the impact of wind and water erosion on agricultural lands, preserving soil fertility for future harvests.
• National Park Service rangers monitor and manage natural erosion processes in areas like the Grand Canyon, balancing visitor access with the preservation of delicate geological features formed over millennia by river erosion.

Assessment Ideas

Quick Check

Provide students with images of different landforms (e.g., U-shaped valley, delta, sand dune, landslide scar). Ask them to identify the primary agent of erosion and deposition responsible for each landform and write a brief explanation.

Discussion Prompt

Pose the question: 'Imagine a large forest is cleared for a new housing development. Describe at least two ways erosion will be accelerated and one method that could be used to mitigate this increased erosion.' Facilitate a class discussion where students share their ideas.

Exit Ticket

Students receive a card with one of the key questions from the unit (e.g., 'How do human activities accelerate erosion?'). They must write a 2-3 sentence answer, citing at least one specific example discussed in class.

Frequently Asked Questions

What role does vegetation play in preventing the loss of soil?

Plant roots physically bind soil particles together, resisting transport by water and wind. Leaf canopy intercepts rain, reducing the impact of water drops on bare soil (splash erosion). In the absence of vegetation -- on a construction site or deforested slope -- erosion rates can increase by ten to one hundred times compared to well-vegetated land of the same slope and soil type.

How do human activities accelerate the natural process of erosion?

The main drivers are deforestation (removing root anchoring and canopy protection), agriculture on steep slopes without terracing or cover crops, construction that strips vegetation from large areas, and stream channelization that increases water velocity and erosive power. The 1930s Dust Bowl is the most dramatic US example of wind erosion accelerated by large-scale removal of native grassland.

How do glaciers create different landforms than rivers?

Glaciers carry all particle sizes indiscriminately (ice does not sort by weight) and exert enormous lateral and downward force, carving U-shaped valleys with broad, rounded floors. Rivers sort sediment by size and cut V-shaped valleys. Glaciated terrain is recognizable by U-shaped valleys, polished and grooved bedrock, hanging valleys, and glacial erratics -- large boulders transported far from their source.

How does active learning help students understand erosion and deposition?

Erosion and deposition are process-driven, and understanding them requires seeing how variables interact in real time. Stream table simulations let students test one variable at a time and observe the effects directly, building causal explanations grounded in their own evidence. This is far more durable than reading a description of what rivers do, and it mirrors the investigative practice at the core of MS-ESS2-1.