Shaping the Earth: Landscapes and Change · Term 3

Weathering and Erosion

Examining the slow and rapid processes that break down rocks and move sediment across the landscape.

About This Topic

Weathering and erosion are the twin processes that shape the Earth's surface over time. In this unit, students distinguish between the breaking down of rocks (weathering) and the movement of those materials (erosion). The Ontario curriculum emphasizes how these processes affect the local landscape, from the rugged Canadian Shield to the eroding bluffs of Lake Ontario. Students will investigate the roles of water, ice, wind, and living things in these changes.

This topic also introduces the concept of 'deep time' and how small changes can lead to massive geographical features like the Niagara Falls. Understanding erosion is also critical for discussing human impacts on the environment, such as how deforestation leads to soil loss. Students grasp this concept faster through structured discussion and peer explanation of their erosion models.

Learning Objectives

• Classify different types of weathering as mechanical or chemical.
• Explain how gravity, water, wind, and ice contribute to erosion.
• Compare the effects of weathering and erosion on different types of rock formations.
• Analyze how human-made structures can alter natural erosion patterns.
• Predict the long-term impact of increased erosion on a local landscape.

Before You Start

Properties of Rocks and Minerals

Why: Students need to understand the basic composition and properties of rocks to analyze how they break down and are transported.

The Water Cycle

Why: Understanding how water moves through the environment is fundamental to grasping its role as a primary agent of weathering and erosion.

Forces and Motion

Why: Students should have a foundational understanding of forces like gravity and motion to comprehend how wind, water, and ice move sediment.

Key Vocabulary

Weathering	The process that breaks down rocks and minerals into smaller pieces, either by physical means or chemical reactions.
Erosion	The process by which weathered rock and soil particles are moved from one place to another by agents like water, wind, or ice.
Sediment	Loose particles of rock, soil, and organic material that are moved by wind, water, or ice.
Deposition	The geological process in which sediments, soil, and rocks are added to a landform or landmass.
Mechanical Weathering	The physical breakdown of rocks into smaller pieces without changing their chemical composition.
Chemical Weathering	The breakdown of rocks through chemical reactions, often involving water and air, which changes the rock's composition.

Active Learning Ideas

Inquiry Circle: Sugar Cube Weathering

Students shake sugar cubes in a container to simulate physical weathering and drop water on them to simulate chemical weathering. They compare the results and discuss which process was faster and why.

⏱ 30 min·Small Groups

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Simulation Game: The Erosion Stream Table

Using a tray of sand and a gentle flow of water, students observe how a river carves a path. They then add 'trees' (twigs) or 'houses' (blocks) to see how vegetation or human structures change the rate of erosion.

⏱ 50 min·Small Groups

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Gallery Walk: Ontario Landforms

Students look at photos of famous Ontario sites (Niagara Falls, Cheltenham Badlands, Flowerpot Island). They must identify whether weathering or erosion was the primary force at work and explain their reasoning on a shared chart.

⏱ 30 min·Whole Class

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Real-World Connections

Geologists and environmental scientists study erosion patterns to understand how landscapes change, predict natural hazards like landslides, and plan for land conservation. They use tools like GPS and satellite imagery to map changes over time.

Civil engineers consider erosion when designing infrastructure such as bridges, dams, and roads. They must implement strategies to prevent soil loss and protect structures from being undermined by moving water or wind.

Park rangers at places like Niagara Falls monitor the rate of erosion to ensure visitor safety and to understand the geological history of the area. They use this information to manage trails and protect natural formations.

Watch Out for These Misconceptions

Common Misconception

Weathering and erosion are the same thing.

What to Teach Instead

Weathering is the 'breaking' and erosion is the 'taking.' Using a 'break it and move it' mnemonic during hands-on activities helps students keep the two processes distinct.

Common Misconception

Erosion only happens during big storms.

What to Teach Instead

Erosion is a constant, often slow process. Time-lapse videos combined with classroom models help students see that even a tiny drip of water causes change over time.

Assessment Ideas

Quick Check

Present students with images of different landscapes (e.g., a desert with sand dunes, a river valley, a rocky coastline). Ask them to identify the primary agent of erosion visible in each image and write one sentence explaining why.

Discussion Prompt

Pose the question: 'Imagine a large dam is built on a river near your town. How might this change the amount of sediment that reaches the land downstream?' Facilitate a class discussion, encouraging students to use vocabulary terms like erosion and deposition.

Exit Ticket

Provide students with two scenarios: 1) A rock is exposed to freezing and thawing cycles. 2) A rock is exposed to acid rain. Ask them to identify the type of weathering occurring in each scenario (mechanical or chemical) and briefly explain their reasoning.

Frequently Asked Questions

What are the best hands-on strategies for teaching weathering and erosion?

Stream tables are the gold standard for erosion, as they allow students to manipulate variables like slope and water speed. For weathering, 'freeze-thaw' experiments using plaster of Paris and water in a freezer can show how ice breaks rock, which is very relevant to the Canadian climate.

How does the Niagara Escarpment show erosion?

The soft shale at the bottom of the falls erodes faster than the hard limestone on top, causing the top layer to eventually collapse. This process has moved the falls several kilometers back from their original position.

How do plants help prevent erosion?

Roots act like a net that holds the soil together, and leaves break the fall of raindrops so they don't hit the ground with as much force.

Why is soil erosion a problem for farmers in Ontario?

The top layer of soil contains the most nutrients for crops. If it erodes away due to wind or water, the land becomes less fertile and harder to farm.