Denudation, Types, Sequence and Weathering Factors for SS 3

Class: Senior Secondary School 3 (SS3 / SSS3)
Term: 1st Term
Week: 4
Age: 17 years
Duration: 45 minutes
Subject: Geography
Curriculum Theme: Geography
Previous Lesson: Karst Limestone Topography, Features and Importance
Topic: Denudational Process
Subject Matter: Meaning of denudation, types of denudation such as weathering and mass movement, sequence of denudation, factors affecting denudation, definition of weathering, factors affecting weathering, types of weathering, physical or mechanical weathering

Specific Objectives

By the end of the lesson, students should be able to:

Cognitive Domain:

• Define denudation and weathering.
• List the types of denudation.
• Explain the factors affecting denudation and weathering.
• Describe the different types of physical or mechanical weathering.

Affective Domain:

• Appreciate the importance of denudational processes in shaping landforms.
• Participate actively in class discussions about denudation.

Psychomotor Domain:

• Observe and identify signs of weathering in the environment.
• Differentiate between various types of physical weathering processes.

Social Domain:

• Collaborate with peers during field observations or discussions.

Reference Materials

The following resources were used in planning this lesson:

• FCT-ERC SS 3 Scheme of Work, September 2014 curriculum.
• Relevant State Unified Scheme of Work.
• A suitable Geography textbook for SS 3.

Instructional Materials

The teacher will teach this lesson with the aid of:

• Films
• Pictures of eroded landforms
• Models illustrating denudation
• Diagrams and sketches of weathered rocks
• Access to a quarry site (if guided fieldwork is possible)

Rationale for the Lesson

Understanding denudation helps students know how the Earth’s surface is constantly changing. This knowledge is important for understanding landforms around them and how human activities can influence these natural processes.

Prerequisite/Previous Knowledge

Students have basic knowledge of rocks, soil, and the general features of the Earth’s surface from earlier geography lessons.

Lesson Content/Board Summary

Denudational Process

Meaning of Denudation

Denudation is the general lowering of the Earth’s surface by agents of erosion. It involves the removal of rock and soil material from higher elevations to lower elevations. It is a combined process of weathering, mass movement, erosion, and transportation.

Types of Denudation

Denudation is broadly classified into the following types:

1. Weathering: The disintegration and decomposition of rocks in situ (in place) without significant movement of the weathered material.
2. Mass Movement: The downslope movement of rock and soil under the direct influence of gravity.
3. Erosion: The active removal and transportation of weathered material by agents like running water, wind, glaciers, and waves.
4. Transportation: The movement of eroded material from one place to another.
5. Deposition: The laying down of transported material when the carrying agent loses energy.

Sequence of Denudation

Denudation generally follows a sequence:

1. Weathering: Rocks are broken down into smaller pieces.
2. Mass Movement: Loose weathered material moves downslope, primarily by gravity.
3. Erosion: Agents like water, wind, ice, and waves pick up and carry away the weathered material.
4. Transportation: The carried material is moved from one place to another.
5. Deposition: The transported material is laid down in new locations.

Factors Affecting Denudation

Several factors influence the rate and type of denudation:

1. Climate: Temperature and precipitation levels influence weathering and erosional agents.
2. Topography/Relief: Steep slopes promote faster mass movement and erosion.
3. Rock Type and Structure: Hardness, jointing, and chemical composition of rocks affect their resistance to weathering and erosion.
4. Vegetation: Plant cover protects soil from erosion and promotes certain types of weathering.
5. Human Activities: Deforestation, mining, and construction can accelerate denudation.

Definition of Weathering

Weathering is the process by which rocks are broken down, dissolved, or altered on the Earth’s surface. It is a static process, meaning the weathered material generally remains in place until it is removed by agents of erosion or mass movement.

Factors Affecting Weathering

The following factors influence the rate and type of weathering:

1. Climate: High temperatures and rainfall promote chemical weathering, while freeze-thaw cycles are important for physical weathering.
2. Rock Composition: The minerals present in a rock determine how it will weather.
3. Rock Structure: Joints, cracks, and bedding planes provide surfaces for weathering agents to penetrate.
4. Topography: Slopes affect water runoff and exposure to weathering agents.
5. Vegetation: Roots can cause physical breakdown, and decaying organic matter can produce acids that cause chemical weathering.
6. Time: Longer exposure to weathering agents results in more extensive weathering.

Types of Weathering

Weathering is generally divided into three main types:

1. Physical or Mechanical Weathering: The disintegration of rocks into smaller fragments without any change in their chemical composition.
2. Chemical Weathering: The decomposition of rocks through chemical reactions, altering their mineral composition.
3. Biological Weathering: The breakdown of rocks by living organisms (plants, animals, microorganisms).

Physical or Mechanical Weathering

Physical weathering involves processes that break rocks into smaller pieces without changing their chemical makeup. Common types include:

1. Exfoliation (Onion-peeling/Spheroidal Weathering): This occurs in areas with large diurnal temperature ranges. The outer layers of rocks expand when heated and contract when cooled, causing them to peel off in concentric sheets like an onion. It is common in massive, homogeneous rocks like granite.
2. Block Disintegration: This is common in rocks with well-defined joints or cracks (e.g., granite, basalt). Repeated heating and cooling cause the rock blocks to expand and contract, widening the joints until the blocks separate.
3. Granular Disintegration: Occurs in coarse-grained rocks where different minerals have different expansion and contraction rates. The grains loosen and fall apart, turning the rock into sand or gravel.
4. Frost Action (Freeze-Thaw Weathering): Water seeps into cracks in rocks and freezes. As water turns to ice, it expands by about 9%, exerting pressure on the crack walls. Repeated freezing and thawing eventually widen the cracks and shatter the rock. This is prevalent in cold, humid climates.
5. Salt Crystal Growth (Salt Weathering): In arid and semi-arid regions, water containing dissolved salts penetrates rock pores and cracks. As the water evaporates, salt crystals grow, exerting pressure on the rock and causing it to disintegrate.

Illustrative Examples and Applications

1. Exfoliation, freeze-thaw action and temperature changes are examples of physical weathering processes.
2. Carbonation, oxidation and hydrolysis are important chemical weathering processes.
3. Soil creep, landslides and rockfalls are examples of mass movement down a slope.

Quick Revision Table

Area	Key Point
Meaning of Denudation	Denudation refers to the general lowering of the Earth’s surface by various natural agents. It involves the removal of rock material from higher…
Types of Denudation	Denudation is broadly classified into the following types: Weathering: The disintegration and decomposition of rocks in situ (in place) without…
Sequence of Denudation	Denudation typically follows a sequence of processes: Weathering: Breaks down rocks into smaller pieces. Erosion: Removes these pieces from their…
Factors Affecting Denudation	Several factors influence the rate and type of denudation: Climate: Temperature and precipitation levels influence weathering and erosional…
Definition of Weathering	Weathering is the process by which rocks are broken down, dissolved, or altered on the Earth’s surface. It is a static process, meaning the…
Factors Affecting Weathering	The rate and type of weathering are influenced by: Climate: Temperature fluctuations, rainfall, and humidity are key. Rock Characteristics:…

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction and Recall

Time: 4 minutes

Teaching Skill: Set Induction

Teacher’s Activity: The teacher greets the students and asks them to observe the school compound or a picture of a rocky landscape, asking what changes they notice over time or what might cause rocks to break.

Students’ Activity: Students respond by mentioning things like cracked pavements, broken rocks, or worn-out surfaces.

Learning Point: Prior denudation knowledge.

Step 2: Explanation of Meaning of Denudation

Time: 5 minutes

Teaching Skill: Explanation/Definition

Teacher’s Activity: The teacher defines denudation, explaining it as the overall process of lowering the Earth's surface through weathering, mass movement, and erosion. The teacher uses diagrams or models to illustrate.

Students’ Activity: Students listen attentively, observe the diagrams/models, and take notes.

Learning Point: Meaning of denudation.

Step 3: Types and Sequence of Denudation

Time: 5 minutes

Teaching Skill: Elucidation/Categorization

Teacher’s Activity: The teacher explains the two main types of denudation (weathering and mass movement) and describes the general sequence of denudational processes (weathering, mass movement, erosion, transportation, deposition).

Students’ Activity: Students listen, ask questions for clarity, and note down the types and sequence.

Learning Point: Types of denudation.

Step 4: Factors Affecting Denudation

Time: 5 minutes

Teaching Skill: Listing/Explanation

Teacher’s Activity: The teacher lists and briefly explains the factors that influence denudation, such as climate, topography, rock type, vegetation, and human activities.

Students’ Activity: Students listen and copy the factors into their notebooks.

Learning Point: Factors Affecting Denudation.

Step 5: Definition of Weathering and Factors Affecting it

Time: 5 minutes

Teaching Skill: Definition/Analysis

Teacher’s Activity: The teacher defines weathering and distinguishes it from denudation. The teacher then discusses the key factors that affect the rate and type of weathering, using examples.

Students’ Activity: Students listen, contribute examples, and write down the definition and factors.

Learning Point: Meaning of denudation.

Step 6: Types of Weathering (Physical or Mechanical Weathering)

Time: 5 minutes

Teaching Skill: Demonstration/Illustration

Teacher’s Activity: The teacher explains the concept of physical weathering and details its various types: exfoliation, block disintegration, granular disintegration, frost action, and salt crystal growth. Pictures or short video clips are used to demonstrate each type.

Students’ Activity: Students observe the illustrations, ask questions, and take detailed notes on each type of physical weathering.

Learning Point: Types of denudation.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. What is denudation?
2. Mention two types of denudation.
3. List three factors that affect denudation.
4. Define weathering.
5. Describe two types of physical or mechanical weathering.

Students’ Activity: Students answer orally and in writing, showing working or giving examples where the lesson requires it.

Learning Point: Denudation skills assessed.

Step 8: Note-Taking

Time: 8 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides students to copy the essential Board Summary on denudation into their notebooks, drawing attention to the key rules, examples, diagrams or distinctions already taught.

Students’ Activity: Students copy the essential notes carefully into their notebooks and correct any errors in their earlier work.

Learning Point: Denudation notes recorded.

Step 9: Conclusion

Time: 3 minutes

Teaching Skill: Reinforcement/Summarization

Teacher’s Activity: The teacher briefly summarizes the key points of the lesson, emphasizing the continuous nature of denudational processes. The teacher then gives an assignment: "Research and bring examples of landforms created by different types of physical weathering in Nigeria."

Students’ Activity: Students listen to the summary.

Learning Point: Denudation concepts consolidated.

Continuous Assessment/Further Study

Type: Homework / Map Work

Instruction: Complete the following tasks using the Board Summary, relevant maps or diagrams, and examples from the lesson.

1. Prepare a one-page revision note on Meaning of Denudation, using at least two examples from the Board Summary.
2. Draw a labelled diagram, sketch or outline map that illustrates Types of Denudation where appropriate, and add a short explanation.
3. Construct a two-column table comparing key points from Types of Denudation and Sequence of Denudation.
4. Use a Nigerian, African or world example within the lesson scope to explain Factors Affecting Denudation.
5. Write one examination-style paragraph explaining an important relationship or application in denudation.

Lesson Keywords

• Denudation – The general lowering of the Earth’s surface by processes like weathering, mass movement, and erosion.
• Weathering – The breaking down and decomposition of rocks and minerals on or near the Earth’s surface.
• Mass Movement – The movement of rock, soil, and regolith down slopes under gravity.
• Exfoliation – A type of physical weathering where outer layers of rock peel off due to thermal expansion and contraction.
• Frost Action – Physical weathering caused by the repeated freezing and thawing of water in rock cracks.
• Block Disintegration – Physical weathering where rocks break into angular blocks along joints due to temperature changes.
• Granular Disintegration – Physical weathering where coarse-grained rocks crumble into individual grains.

Differentiation

The teacher will provide additional visual aids and simplified explanations for struggling students, while more advanced students will be encouraged to research specific local examples of denudation and present their findings.

Suggested Lesson Videos

Search YouTube for Denudation, Types, Sequence and Weathering Factors Geography SS 3