Mass Movements – SS3 Geography Lesson Note (First Term)

Mass movement is the downslope movement of earth materials, such as soil, rock and debris, from higher to lower ground under the influence of gravity. It can be slow, as in soil creep, or rapid, as in landslides and rock avalanches. Its effects on people include loss of lives, damaged property and infrastructure, and reduced farm productivity.

Behavioural objectives

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

1. Explain the concept of mass movements.
2. Identify types of mass movements.
3. Describe the processes involved in the different types of mass movements.
4. Analyse the effects of mass movements on people.

Instructional techniques and materials

Instructional techniques

• Identification
• Explanation
• Questions and answers
• Demonstration
• Videos from the source

Instructional materials

• Videos
• Loudspeaker
• Textbook
• Pictures

What is mass movement?

Mass movements refer to the downslope movement of earth materials under the influence of gravity. These movements involve the transfer of soil, rock and debris from higher elevations to lower elevations and are typically driven by the force of gravity acting on the Earth’s surface. Mass movements can occur slowly over long periods or rapidly during events like landslides.

What are the types of mass movements?

1. Landslides: A landslide is a mass movement of rock, soil and debris down a slope, often triggered by factors such as heavy rainfall, earthquakes, volcanic activity or human activities. Landslides can range from slow, gradual movements to rapid, destructive events, and they can occur on various scales, from small localised occurrences to large, landscape-altering events.
2. Rock avalanches: A rock avalanche is a more significant and chaotic mass movement involving the rapid descent of a large volume of rock material. Rock avalanches typically occur when a massive amount of rock detaches from a mountain or cliff, often triggered by factors like earthquakes, volcanic activity or human activities.
3. Soil creep: Soil creep is a slow, continuous downslope movement of soil and regolith. It is characterised by the gradual displacement of individual soil particles, typically in response to the expansion and contraction caused by temperature changes. While soil creep may be imperceptible over short periods, its cumulative effect can lead to noticeable changes in the landscape over time.
4. Slumps: Slumps are a type of mass movement involving the rapid movement of a mass of rock or soil along a curved slip surface. Unlike slides that move along a flat plane, slumps occur along a concave surface. Slumps are often triggered by saturation of the soil, which reduces its stability. They can result in the tilting or rotation of the affected material, leading to distinct features in the landscape.

What processes are involved in the different types of mass movements?

The following are the processes involved in different types of mass movements:

1. Rockfalls: Individual rocks detach due to weathering or seismic activity, free-falling or bouncing downslope.
2. Rockslides: Blocks of rock move as a unit, often along pre-existing fractures, sliding downslope.
3. Debris flows: Rapid downslope movement of a mixture of soil, rock and water, often triggered by heavy rainfall or rapid snowmelt.
4. Rock avalanches: Swift and chaotic descent of large volumes of rock. It is triggered by factors like earthquakes, volcanic eruptions or oversteepening of rock slopes.
5. Creep: Slow, continuous downslope movement of soil and regolith. Expansion and contraction of soil particles due to temperature changes cause gradual displacement.
6. Slumps: Rapid movement along a curved slip surface. It is often initiated by saturation of the soil, causing the overlying material to slide along a curved plane.

What are the effects of mass movements on people?

The following are the effects of mass movements on people:

1. Rapid mass movements, such as landslides and mudflows, can lead to the loss of human lives and cause extensive damage to infrastructure, homes and agricultural land.
2. Communities living in areas prone to mass movements may face forced relocation due to the destruction of their homes and the risk of future hazards.
3. Roads, bridges and other infrastructure may be severely damaged or destroyed, hindering transportation and access to affected areas.
4. Mass movements can have significant economic consequences, including the cost of rebuilding, loss of livelihoods and disruptions to local economies.
5. Mass movements can lead to environmental degradation, affecting ecosystems, water quality and biodiversity in the affected areas.
6. Areas affected by mass movements may experience reduced agricultural productivity due to soil erosion, loss of topsoil and disruption of farming practices.

Evaluation

1. What is mass movement?
2. Mention and discuss the types of mass movement.
3. Discuss five processes that take place in mass movement.
4. Mention five effects of mass movement on people.

Classwork: As in the evaluation.

The teacher commends the students positively.

Assignment

1. Explain soil creep and slumps.
2. State three effects of mass movements on people.