Denudational Processes, Chemical Weathering and Mass Movement for SS 3

Class: Senior Secondary School 3 (SS3 / SSS3)
Term: 1st Term
Week: 5
Age: 17 years
Duration: 45 minutes
Subject: Geography
Curriculum Theme: Geography
Previous Lesson: Denudation, Types, Sequence and Weathering Factors
Topic: Denudational Processes Cont
Subject Matter: Chemical weathering, meaning of mass movement or mass wasting, factors affecting mass movement, types of mass movement, effects of mass movement on landforms, field evidence of weathering effects

Specific Objectives

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

Cognitive Domain:

• Define chemical weathering and mass movement.
• State the factors affecting mass movement.
• List different types of mass movement.
• Explain the effects of mass movement on landforms.

Affective Domain:

• Appreciate the impact of denudational processes on the environment.
• Participate actively in discussions and fieldwork observations.

Psychomotor Domain:

• Observe and identify weathering effects in the field.
• Draw sketch diagrams showing effects of weathering and mass movement on landforms.

Social Domain:

• Collaborate with peers during fieldwork and group activities.
• Ask and answer questions effectively during the lesson.

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
• Models
• Diagrams and sketches
• Drawing paper

Rationale for the Lesson

Understanding chemical weathering and mass movement helps students to know how landforms change over time. This knowledge is important for understanding natural hazards and the environment around them.

Prerequisite/Previous Knowledge

Students have prior knowledge of denudation and other forms of weathering from previous lessons.

Lesson Content/Board Summary

Denudational Processes (Continued)

Chemical Weathering

Chemical weathering is the breakdown of rocks through chemical reactions that change their mineral composition. This process often occurs in the presence of water, oxygen, and acids.

The following are types of chemical weathering:

1. Solution: This involves the dissolving of soluble minerals (like rock salt or limestone) in water, especially acidic water, leading to their removal.
2. Carbonation: This occurs when carbon dioxide dissolves in water to form carbonic acid, which then reacts with minerals (especially calcium carbonate in limestone) to form soluble bicarbonates, leading to dissolution.
3. Hydration: This is the absorption of water by minerals, causing them to swell, increase in volume, and become weaker. For example, feldspar can hydrate to form clay minerals.
4. Oxidation: This is the reaction of minerals, particularly those containing iron, with oxygen in the presence of water. This forms iron oxides (rust), which weaken the rock and give it a reddish or yellowish-brown colour.
5. Hydrolysis: This is a chemical reaction between water and rock minerals to form new compounds. It is common in silicate minerals, where hydrogen ions from water replace metallic ions in the mineral structure, leading to the formation of clay minerals.

Meaning of Mass Movement or Mass Wasting

Mass movement, also known as mass wasting, is the large-scale downward movement of rock debris, soil, and regolith (loose unconsolidated material) on slopes under the direct influence of gravity. It does not necessarily involve a transporting agent like water, wind, or ice.

Factors Affecting Mass Movement

The following factors influence the occurrence and type of mass movement:

1. Slope Angle (Gradient): Steeper slopes are more prone to mass movement as gravity has a stronger pull.
2. Water Content: Water acts as a lubricant and adds weight to the soil and rock, reducing cohesion and increasing the likelihood of movement.
3. Vegetation Cover: Plant roots bind soil particles together, stabilizing slopes. Removal of vegetation (e.g., deforestation) increases susceptibility to mass movement.
4. Nature of Rock and Soil (Geology): Weak, fractured, or unconsolidated rocks and soils are more easily moved than strong, solid bedrock.
5. Presence of Discontinuities: Faults, joints, and bedding planes in rocks can provide surfaces along which movement occurs.
6. Seismic Activity (Earthquakes): Ground vibrations during earthquakes can dislodge unstable material and trigger mass movements.
7. Human Activities: Construction, mining, road cutting, and irrigation can destabilize slopes and induce mass movement.

Types of Mass Movement

Mass movements are classified based on the speed of movement, the type of material, and the nature of the movement.

1. Creep: This is the slowest form of mass movement, involving a gradual, continuous downhill movement of soil and regolith. Evidence includes leaning fences, tilted utility poles, and curved tree trunks.
2. Flow: This involves the movement of saturated soil and regolith as a viscous fluid. Examples include:
   1. Mudflow: Rapid flow of water-saturated fine-grained material down a slope.
   2. Earthflow: Slower, tongue-like flow of fine-grained, water-saturated material.
3. Slide: This involves the movement of a coherent mass of rock or soil along a well-defined shear plane or surface. Examples include:
   1. Landslide/Rockslide: Rapid movement of rock or earth down a slope.
   2. Slump: Rotational movement of a block of material along a concave-upward slip surface, creating a series of terraces.
4. Fall: This is the most rapid type of mass movement, involving the free-falling of rock fragments from a steep cliff or overhang. This leads to the accumulation of talus or scree at the base.

Effects of Mass Movement on Landforms

Mass movement significantly alters landforms in various ways:

1. Formation of scree slopes or talus cones at the base of cliffs and steep slopes.
2. Creation of scars, bare patches, and hummocky terrain on slopes where material has moved.
3. Displacement and redistribution of soil and rock, changing the local topography.
4. Blocking of rivers and streams, leading to the formation of temporary lakes.
5. Damage to human infrastructure such as roads, railways, buildings, and agricultural land.
6. Formation of terraced features on slopes due to slumping.

Field Evidence of Weathering Effects

When observing landforms, students can identify several signs of weathering:

1. Cracks and fissures in rocks, indicating physical breakdown.
2. Discoloration or staining of rock surfaces, often reddish-brown from oxidation.
3. Exfoliation or peeling of rock layers, common in granite due to pressure release.
4. Presence of loose rock fragments (scree or talus) at the base of cliffs.
5. Rounded boulders and pebbles in riverbeds, showing abrasion and chemical alteration.
6. Leaning fences, poles, or trees, indicating slow soil creep.
7. Undercutting of river banks or cliff bases by water action.
8. Presence of caves and sinkholes in limestone areas, evidence of solution and carbonation.

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
Chemical Weathering	Chemical weathering is the breakdown of rocks through chemical reactions that change their mineral composition. This process often occurs in the…
Meaning of Mass Movement or Mass Wasting	Mass movement, also known as mass wasting, is the large-scale downward movement of rock debris, soil, and regolith (loose unconsolidated material)…
Factors Affecting Mass Movement	The following factors influence the occurrence and type of mass movement: Slope Angle (Gradient): Steeper slopes are more prone to mass movement…
Types of Mass Movement	Mass movements are classified based on the speed of movement, the type of material, and the nature of the movement. Creep: This is the slowest…
Effects of Mass Movement on Landforms	Mass movement significantly alters landforms in various ways: Formation of scree slopes or talus cones at the base of cliffs and steep slopes….
Field Evidence of Weathering Effects	When observing landforms, students can identify several signs of weathering: Cracks and fissures in rocks, indicating physical breakdown….

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 reviews the previous lesson on denudational processes, specifically physical weathering. The teacher then introduces the day's topic, "Chemical Weathering and Mass Movement," explaining that these are also important ways landforms change.

Students’ Activity: Students respond to greetings, recall the previous lesson, and listen attentively to the introduction of the new topic.

Learning Point: Prior denudation knowledge.

Step 2: Chemical Weathering

Time: 5 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher explains the meaning of chemical weathering using pictures and models to illustrate processes like solution, carbonation, and oxidation. The teacher gives examples of how these processes affect different rock types.

Students’ Activity: Students watch the films and observe the pictures and models. They take notes and ask questions for clarification.

Learning Point: Chemical Weathering concepts.

Step 3: Meaning and Factors Affecting Mass Movement

Time: 5 minutes

Teaching Skill: Explanation/Discussion

Teacher’s Activity: The teacher defines mass movement (or mass wasting) and discusses the various factors that influence its occurrence, such as slope angle, water content, vegetation, and human activities. The teacher encourages students to give local examples.

Students’ Activity: Students listen, take notes, and contribute to the discussion by sharing their observations or experiences related to mass movement factors.

Learning Point: Meaning of denudation.

Step 4: Types of Mass Movement

Time: 5 minutes

Teaching Skill: Visualisation/Categorisation

Teacher’s Activity: The teacher uses diagrams, pictures, and short film clips to explain and differentiate between various types of mass movement, including creep, flows, slides, slumps, and falls. The teacher highlights key characteristics of each type.

Students’ Activity: Students observe the visual aids, identify the different types of mass movement, and note their characteristics. They may ask questions about specific examples.

Learning Point: Types of denudation.

Step 5: Effects of Mass Movement on Landforms

Time: 5 minutes

Teaching Skill: Guided Discussion

Teacher’s Activity: The teacher guides a discussion on the effects of mass movement on landforms, emphasizing how they alter the landscape and create new features. The teacher encourages students to think about both destructive and constructive effects.

Students’ Activity: Students actively participate in the discussion, sharing ideas and examples of how mass movement affects landforms.

Learning Point: Effects of denudation.

Step 6: Field Evidence of Weathering Effects

Time: 5 minutes

Teaching Skill: Observation/Application

Teacher’s Activity: The teacher shows pictures or films of real-world examples of weathering and mass movement effects, such as tilted poles, cracked roads, or areas of rockfall. The teacher explains how students can identify these features during fieldwork.

Students’ Activity: Students observe the examples and discuss what they would look for when observing weathering effects in their local environment. They prepare to participate in fieldwork or sketch diagrams.

Learning Point: Effects 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 chemical weathering?
2. Mention three processes involved in chemical weathering.
3. Define mass movement.
4. List three factors that affect mass movement.
5. Name two types of mass movement.
6. State two effects of mass movement on landforms.

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 summarises the key points of the lesson on chemical weathering and mass movement.

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

Lesson Keywords

• Chemical Weathering – The breakdown of rocks by chemical reactions, altering their mineral composition.
• Mass Movement – The downslope movement of rock, soil, and regolith under gravity.
• Creep – The very slow, continuous downslope movement of soil.
• Landslide – The rapid movement of a mass of rock or soil down a slope.
• Solifluction – Slow flow of water-saturated soil over frozen ground.
• Oxidation – Chemical reaction involving oxygen, often leading to rust.

Differentiation

The teacher will provide additional support to struggling students through one-on-one explanations and simplified diagrams. Advanced students will be encouraged to research specific case studies of mass movement in Nigeria and present their findings.

Suggested Lesson Videos

Search YouTube for Denudational Processes, Chemical Weathering and Mass Movement Geography SS 3