Weathering and Erosion

Weathering and Erosion

Middle School

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Learning Objectives

• Define weathering, erosion, and deposition, and explain how they are different.

• Compare mechanical and chemical weathering and provide examples of each type.

• Identify the primary causes of erosion and the landforms created by deposition.

• Explain how factors like climate and topography shape the Earth's landscape.

Key Vocabulary

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Weathering

The process by which rocks are broken down into smaller pieces called sediments over a long period.

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Erosion

The process that moves weathered rocks and sediments from one location to another by different agents.

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Deposition

The process where eroded sediments, rocks, and soil settle in a new location after being transported.

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Mechanical Weathering

The physical breakdown of rocks into smaller pieces without changing the rock's chemical makeup at all.

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Chemical Weathering

The breakdown of rocks through chemical reactions that alter the rock's composition and create new substances.

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Sediments

Small pieces of rock that have been broken down by the long and slow process of weathering.

Key Vocabulary

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Topography

The surface features of a region, including its mountains, valleys, and other natural landforms and features.

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Differential Weathering

The process where less resistant rocks weather away faster than more resistant rocks, shaping the landscape.

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Weathering: The Breakdown of Rocks

• Weathering is the process that breaks rocks down into smaller pieces called sediments.

• Climate and topography influence the rate and type of weathering that occurs.

• Weathering helps form soil and provides material for erosion and deposition.

• The two fundamental types are mechanical weathering and chemical weathering.

Multiple Choice

What is the process that breaks rocks into smaller pieces called?

• Erosion

• Weathering

• Deposition

• Sedimentation

Multiple Choice

Which factors influence the rate and type of weathering?

• Climate and topography

• Latitude and longitude

• Population and industry

• Time of day

Multiple Choice

How does weathering contribute to ecosystems?

• It destroys all plant life.

• It forms soil and provides material for erosion and deposition.

• It stops rainfall from reaching the ground.

• It creates earthquakes.

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Types of Weathering: Mechanical vs. Chemical

Mechanical Weathering

• Rocks are physically broken into smaller pieces without any chemical changes to the rock itself.

• This is caused by the force of wind, water, ice, growing plant roots, and temperature changes.

• Ice wedging is when water freezes in cracks, expands, and breaks the rock apart.

Chemical Weathering

• Rocks are broken down by chemical reactions that change what the rock is made of.

• For example, carbonic acid in rainwater can dissolve rocks such as limestone over a long time.

• Oxygen in the air or water can cause iron in rocks to rust and crumble away.

Multiple Choice

What is the main difference between mechanical and chemical weathering?

• Mechanical weathering involves chemical reactions, while chemical weathering is a physical process.

• Mechanical weathering breaks rocks into smaller pieces, while chemical weathering changes what the rock is made of.

• Mechanical weathering is caused by rain, while chemical weathering is caused by wind.

• Mechanical weathering happens quickly, while chemical weathering happens slowly.

Multiple Choice

Which of the following describes a rock being broken down by a physical force without changing the rock's composition?

• Iron in a rock rusting and turning reddish-brown.

• A limestone statue slowly dissolving from acid rain.

• Plant roots growing in the cracks of a sidewalk and breaking it apart.

• A rock changing color due to exposure to oxygen.

Multiple Choice

A statue made of limestone with an iron frame is placed in a city that has cold winters and frequent acid rain. Which statement best explains how the statue will weather?

• The force of the rain and ice wedging would physically break both the limestone and the iron apart.

• The limestone would dissolve from acid in the rain, and the iron would rust from exposure to oxygen and water.

• Only the limestone would weather, because iron is a metal that does not change.

• The cold winters would cause the iron to rust, while the rain would physically break the limestone.

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Erosion: Moving the Pieces

Long-Distance Travel

• Sediments are carried over long distances by agents like flowing water or glaciers.

• During their journey, the rocks are broken down into smaller and smaller pieces.

• Constant tumbling and collision with other rocks makes them smooth and well-rounded.

Short-Distance Travel

• Sediments are moved over short distances, often by gravity, like a rockfall.

• Because the journey is brief, the rocks do not break down much and remain large.

• They have not traveled far enough to become smooth, so they have sharp, angular edges.

Multiple Choice

What does the process of erosion do to sediments like rocks and sand?

• They are carried from one place to another by forces like water or gravity.

• They are formed from the heat and pressure deep inside the Earth.

• They are created when lava from a volcano cools and hardens.

• They are permanently fixed in one location and do not move.

Multiple Choice

What is the relationship between the distance a rock travels during erosion and its physical appearance?

• The longer the journey, the smoother and more rounded the rocks become.

• The longer the journey, the larger and more angular the rocks become.

• The distance of the journey does not affect the shape or size of the rocks.

• Only rocks that travel short distances are moved by flowing water.

Multiple Choice

A geologist discovers a large rock with sharp, angular edges at the base of a mountain. What is the most likely conclusion about the rock's history?

• The rock was likely moved a short distance by gravity, such as in a rockfall.

• The rock must have been carried for many miles at the bottom of a glacier.

• The rock spent thousands of years tumbling along a fast-flowing river.

• The rock's sharp edges were formed by wind and rain over a long period.

Deposition: Building New Landforms

• Deposition occurs when sediments are dropped and settle in a new location.

• This happens when agents like wind or water lose their energy.

• This process creates landforms like deltas, dunes, and beaches.

Multiple Choice

What is the process of deposition?

• Sediments being dropped and settling in a new place

• Rocks being broken down into smaller pieces

• Sediments being carried from one place to another

• Landforms being created by volcanic eruptions

Multiple Choice

What causes agents like wind or water to deposit the sediments they are carrying?

• A loss of energy

• An increase in speed

• A change in the sediment type

• A decrease in the Earth's gravity

Multiple Choice

If a fast-moving river carrying sediment flows into a calm ocean, which landform is most likely to be created where the river meets the ocean?

• A delta

• A sand dune

• A deep canyon

• A mountain range

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Special Cases: Differential Weathering & Barrier Islands

Differential Weathering

• Different rock types weather at different rates, which creates irregularly shaped landscapes.

• Harder, more resistant rock, like quartz, withstands weathering for a much longer time.

• Softer, less resistant rock, such as limestone, weathers away more quickly.

Barrier Islands

• These are long, narrow islands formed by sediment that runs parallel to the mainland.

• They act as a natural buffer, protecting the mainland from waves and storms.

• Made of loose sediment, they are vulnerable to being washed away by major storms.

Multiple Choice

Which statement best defines differential weathering?

• When different types of rock weather at different rates.

• When all rocks are broken down by storm activity.

• When sediment forms long, narrow islands.

• When hard rock and soft rock weather at the same speed.

Multiple Choice

What is the primary function of a barrier island?

• It is made of hard, resistant rock that is difficult to erode.

• It protects the mainland from the impact of waves and storms.

• It is a source of new sediment for the mainland coast.

• It causes different types of rock to weather at different rates.

Multiple Choice

Imagine a landscape made of both hard quartz and soft limestone. Over a long period, what would be the most likely appearance of this landscape?

• The limestone would wear away, leaving the quartz behind as hills or cliffs.

• The quartz and limestone would erode at the same rate, creating a flat plain.

• The quartz would wear away quickly, leaving the softer limestone behind.

• A barrier island would form in front of the landscape from the eroded rock.

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Common Misconceptions

Misconception	Correction
Weathering and erosion are the same thing.	Weathering breaks rock; erosion carries away the broken pieces.
Only dramatic events like floods cause erosion.	Most erosion is a slow, continuous process.
All rocks are equally strong and resist weathering.	Softer rocks erode faster than harder rocks.
Human actions don't impact natural weathering.	Human pollution can create acid rain, accelerating weathering.

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Summary

• Weathering breaks rock, erosion carries it away, and deposition drops it in new locations.

• Mechanical weathering is a physical break, while chemical weathering involves a chemical change.

• The primary agents of erosion are flowing water, wind, glaciers, and gravity.

• Deposition builds new landforms, like deltas, dunes, beaches, and protective barrier islands.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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