Science · 6th Grade · Earth's Changing Surface · Weeks 28-36

Erosion and Deposition

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

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

About This Topic

Erosion and deposition are the transport and accumulation phases of the sediment cycle, and together with weathering they explain how landscapes are continuously reshaped. This topic supports MS-ESS2-1 and MS-ESS2-2 in the 6th grade US curriculum. Erosion is the detachment and movement of weathered material by water, ice, wind, and gravity. Deposition occurs when these agents lose energy and release their sediment load, building new landforms in new locations.

Water erosion spans enormous scales, from sheets of runoff during rainstorms to the canyon-cutting power of rivers over millions of years. The Colorado River carved the Grand Canyon over approximately 5 to 6 million years, removing vast volumes of rock. US examples at every scale include beach erosion on Atlantic and Pacific coastlines, gully formation in agricultural fields, and delta building at the Mississippi River mouth. Glaciers carved the Great Lakes basins and the U-shaped valleys of Yosemite during the last ice age. Wind erosion shapes the dunes of the Great Sand Dunes National Park and the scoured plains of the western interior.

Understanding the relationship between agent energy and deposition order is central to this topic. As water slows, it deposits progressively finer material, with boulders settling first and clay last. This grain-size sorting creates the layered sedimentary record geologists use to reconstruct past environments. Active learning through stream table experiments and landform mapping directly puts these processes in students' hands at classroom scale.

Key Questions

1. Explain how glaciers reshape landscapes over long periods.
2. Analyze how the rate of erosion changes based on the type of soil or rock.
3. Differentiate between erosion and deposition and their resulting landforms.

Learning Objectives

• Compare the depositional patterns of different agents of erosion (water, ice, wind, gravity) based on energy levels.
• Analyze how specific landforms, such as deltas, moraines, and sand dunes, are created by deposition.
• Explain the role of gravity as both an agent of erosion and a contributing factor to mass wasting.
• Differentiate between the erosional and depositional features created by flowing water versus glacial ice.

Before You Start

Weathering: Breaking Down Rocks

Why: Students need to understand how rocks are broken down before they can investigate how those broken pieces are transported and deposited.

Properties of Water and Wind

Why: Understanding the basic characteristics of water and wind as fluids is foundational to comprehending their erosional and depositional capabilities.

Key Vocabulary

Sediment Load	The material (rocks, sand, silt, clay) that is being transported by water, wind, ice, or gravity.
Deposition	The geological process in which sediments, soil, and rocks are added to a landform or landmass, often by a slowing agent of erosion.
Mass Wasting	The downslope movement of rock, regolith, and soil under the direct influence of gravity, such as landslides and rockfalls.
Glacial Till	Unsorted, unstratified sediment deposited by glacial ice, often containing a mixture of clay, sand, gravel, and boulders.
Alluvium	Sediments deposited by flowing water, typically found in riverbeds, floodplains, and deltas.

Watch Out for These Misconceptions

Common Misconception

Erosion only happens during dramatic events like floods or landslides.

What to Teach Instead

Erosion is a continuous process. A single raindrop striking bare soil causes splash erosion. Normal stream flow erodes banks and the streambed every day. Wind removes fine particles from exposed soil constantly. Dramatic events are simply the visible extreme of processes that operate at low intensity all the time, making the cumulative effect very significant.

Common Misconception

Glaciers erode landscapes the same way rivers do.

What to Teach Instead

Glaciers and rivers erode very differently and leave distinct evidence. Rivers carve V-shaped valleys by downcutting. Glaciers carve U-shaped valleys by grinding rock from all sides under immense pressure, using embedded rocks as abrasive tools and plucking material from valley walls. The valley cross-section shape is one of the key clues geologists use to identify which agent was responsible.

Common Misconception

Deposition only happens when a moving agent stops completely.

What to Teach Instead

Deposition begins whenever an agent loses enough energy to drop a particle, not only when it stops entirely. A slowing river drops its coarsest sediment first, then finer material farther downstream. Deposition in a river delta begins where the current disperses into the ocean, not where the river stops flowing. This energy-gradient relationship is what creates the layered structure of sedimentary deposits.

Active Learning Ideas

Inquiry Circle: Stream Table Experiment

Groups use stream tables or plastic bins with sand and a water source to model erosion and deposition. They systematically vary slope angle and water flow rate, recording how each change affects the rate of erosion and the location where sediment is deposited. Groups present their findings as a cause-and-effect explanation.

50 min·Small Groups

Think-Pair-Share: How Did That Canyon Form?

Show a cross-section diagram of the Grand Canyon layers alongside a present-day photograph. Partners discuss the agents of erosion and deposition involved, the time required to produce each layer, and what the area might have looked like before carving began.

20 min·Pairs

Gallery Walk: Erosion Agents

Post photographs of landforms produced by each major erosion agent: river, glacier, wind, ocean waves, and mass movement (landslide). Students identify the agent responsible, the resulting landform type, and one US location where this process is actively occurring.

25 min·Small Groups

Sorting Activity: Grain Size and Deposition Order

Groups receive mixed samples of gravel, sand, silt, and clay. They predict and then test the deposition order by adding the mixed sample to a water column in a clear tube and timing when each size class settles. Groups connect their results to real-world river delta and floodplain formation.

30 min·Small Groups

Real-World Connections

• Civil engineers and geologists study erosion and deposition to design effective flood control systems, like levees and dams along the Mississippi River, and to predict where coastal erosion might impact infrastructure.
• Park rangers at places like Badlands National Park or Zion National Park explain to visitors how water and wind erosion have sculpted the dramatic landscapes over millions of years, shaping hiking trails and visitor viewpoints.
• Farmers and land managers implement conservation techniques, such as terracing and cover cropping, to reduce soil erosion on hillsides and prevent valuable topsoil from being washed away into local streams and rivers.

Assessment Ideas

Exit Ticket

Provide students with images of three different landforms (e.g., a delta, a sand dune, a U-shaped valley). Ask them to identify the primary agent of erosion/deposition for each and write one sentence explaining how that landform was created.

Quick Check

Present students with a scenario: 'A fast-moving river carries a heavy load of sediment and then enters a wide, slow-moving lake.' Ask them to list, in order, the types of sediment (e.g., boulders, sand, silt, clay) that would be deposited as the river slows down and explain why.

Discussion Prompt

Pose the question: 'How might a landslide (mass wasting) change the landscape of a mountain region, and what happens to the deposited material afterward?' Facilitate a class discussion, guiding students to connect gravity's role in erosion with the subsequent deposition of debris.

Frequently Asked Questions

What is the difference between erosion and deposition?

Erosion is the picking up and moving of weathered rock and soil by water, wind, ice, or gravity. Deposition is the dropping of that material when the agent slows or loses energy. They are two stages of the same transport system: erosion removes material from one location and deposition builds it up somewhere else, creating the variety of landforms we see across Earth's surface.

How do glaciers reshape landscapes?

Glaciers erode by plucking loose rock from valley walls and floors and grinding it under their enormous weight, using embedded rock fragments as abrasive tools. This produces U-shaped valleys, polished rock surfaces, and mixed sediment deposits called till. When glaciers melt, they leave behind lakes, moraines, and drumlins. The Great Lakes basins were shaped largely by glacial erosion during the last ice age.

How does water speed affect erosion and deposition?

Fast-moving water carries more energy and can transport large particles including gravel and cobbles. As water slows, it progressively loses the energy to carry heavy particles, which settle first. Clay and silt travel farthest because they are lightest. This is why river deltas and floodplains are composed of fine-grained sediments while riverbeds contain coarser gravel and sand.

Why is a stream table experiment a good active learning tool for erosion and deposition?

A stream table lets students manipulate the variables controlling erosion and deposition, including slope, flow rate, and sediment type, and directly observe results at a manageable scale. When students see sediment transported and then deposited by simply adjusting slope angle, they build an intuitive, evidence-based model that maps onto real river and delta systems covered by MS-ESS2-1 and MS-ESS2-2.