Factors that Affect Mass Movements

Quick Summary

• Steep slopes increase gravitational pull causing faster mass movement
• Water adds weight and reduces friction between soil particles
• Lack of vegetation removes root systems that bind soil together
• Human activities like mining, construction, and deforestation trigger movements
• Earthquakes and volcanic eruptions cause sudden mass movements

Natural Factors Affecting Mass Movement

1. Slope Gradient (Steepness)

The steeper a slope, the stronger gravity’s downward pull on materials. On gentle slopes below 15 degrees, soil remains stable. Between 15-30 degrees, movement risk increases. Above 30 degrees, even small disturbances can trigger landslides.

In Nigeria, steep slopes on the Jos Plateau in Plateau State experience frequent rockfalls during rainy season. The Mambilla Plateau in Taraba State also has steep escarpments where soil creep occurs slowly over time. Flat areas like the Niger Delta have minimal mass movement because gravity’s effect is weak.

2. Water Content and Saturation

Water affects mass movement in several ways. First, it adds weight to soil, increasing downward pressure. Second, water fills spaces between soil particles, acting as lubricant that reduces friction. Third, saturation weakens cohesion between particles, making soil flow like thick liquid.

During heavy rains in southeastern Nigeria, soil on hillsides becomes waterlogged. The added weight and reduced friction cause mudslides that destroy farms and block roads. In Abuja, rainstorms trigger debris flows in areas where construction exposed bare slopes. The 2012 flooding in many Nigerian states caused widespread mudslides and landslips.

3. Vegetation Cover

Plant roots bind soil particles together like underground nets. Trees, shrubs, and grass create mechanical stability. When vegetation is removed, soil loses this binding force. Roots also absorb water from soil, reducing saturation that could trigger movement.

Areas with thick forest in Cross River State experience less mass movement than cleared farmland in the same region. Deforestation on slopes in Imo and Anambra states has increased gully erosion and landslides. Overgrazing in northern states removes grass cover, making slopes vulnerable to soil creep and earthflows.

4. Rock Type and Soil Composition

Different rocks and soils resist movement differently. Clay soils expand when wet and contract when dry, creating cracks that weaken slopes. Sandy soils drain quickly but lack cohesion. Weathered rock crumbles easily compared to solid granite or basalt.

Clay-rich soils in parts of Edo State become unstable when saturated. Loose sandy soils in riverbank areas collapse easily during floods. Weathered basement complex rocks in southwestern Nigeria are more prone to movement than the hard granite outcrops found in some northern states.

5. Climate and Weather Patterns

Heavy rainfall is the most common climate trigger for mass movement. Rapid snowmelt in cold regions has similar effects. Freezing and thawing cycles break rock apart. Areas with high annual rainfall experience more frequent movements.

Southern Nigeria’s heavy rainy season (April to October) coincides with peak mass movement activity. States like Cross River, Akwa Ibom, and Rivers experience landslides during intense storms. In contrast, dry season months (November to March) see fewer movements because soil remains relatively stable.

Temperature changes also matter. In highland areas like Jos and Mambilla Plateau, nighttime cooling causes rock contraction. Daytime heating causes expansion. This freeze-thaw cycle (though mild in Nigeria) gradually breaks rocks, making them vulnerable to sliding.

6. Earthquakes and Earth Tremors

Seismic activity shakes the ground, dislodging unstable materials. Even small tremors can trigger avalanches on steep slopes. The vibration reduces friction between particles, similar to shaking sand in a container.

Nigeria experiences occasional earth tremors, though major earthquakes are rare. The 1984 earthquake in Ijebu-Ode area (Ogun State) caused some landslips. The 2016 tremor in Abuja shook buildings but caused limited mass movement because the terrain is relatively flat. Areas near fault lines face higher earthquake-related movement risk.

7. Volcanic Activity

Volcanic eruptions melt snow and ice on mountains, creating massive mudflows called lahars. Ash deposits add unstable material to slopes. Lava flows can destabilize surrounding areas.

Nigeria has no active volcanoes currently, but the Biu Plateau in Borno State shows evidence of ancient volcanic activity. In other parts of Africa, Mount Cameroon (near Nigeria’s border) experiences occasional eruptions that trigger debris flows. Understanding volcanic triggers helps explain mass movements in volcanic regions worldwide.

Human-Induced Factors

1. Mining and Quarrying

Removing rock and soil for mining creates steep, unstable slopes. Quarrying weakens rock structure. Mine waste heaps can collapse under their own weight or during rains.

Tin mining activities on the Jos Plateau created numerous abandoned pits and waste dumps. Some of these spoil heaps slide during heavy rains, burying farmland and houses. Stone quarries in Ogun, Oyo, and Edo states cut vertical slopes that sometimes collapse, endangering workers. Sand mining along riverbanks in Lagos destabilizes banks, causing slumping.

2. Construction and Infrastructure Development

Road construction through hills requires cutting slopes, often making them steeper and less stable. Building foundations add weight to slopes. Poor drainage systems concentrate water, triggering movements.

Highway construction through hilly areas in southern Nigeria has triggered numerous landslides. The Enugu-Onitsha expressway passes through sloped terrain where road cuts have caused instability. Housing developments on Abuja hillsides sometimes experience foundation problems when slopes move. Poorly designed drainage along the Lagos-Ibadan expressway contributes to slope failures during rainy season.

3. Deforestation and Agricultural Activities

Clearing forests for farming removes root systems that stabilize soil. Plowing breaks up soil structure. Overgrazing by livestock strips vegetation cover. These activities leave slopes vulnerable to erosion and mass movement.

Slash-and-burn farming on slopes in southeastern states has increased landslide frequency. Fulani herders’ cattle overgraze hillsides in central Nigeria, removing protective grass cover. Logging in Cross River State exposes slopes that previously had forest protection. Cocoa and cashew farmers in southwestern states who farm on slopes without terracing face soil loss.

4. Irrigation and Water Management

Excessive irrigation saturates soil beyond its carrying capacity. Leaking water pipes add moisture to slopes. Improperly designed drainage concentrates water flow, increasing erosion and movement risk.

Irrigation projects in northern Nigeria sometimes create waterlogging that weakens slopes. Broken water pipes in Abuja’s hilly neighborhoods have contributed to localized slumping. Communities that redirect streams for farming purposes may inadvertently increase mass movement downstream.

5. Urban Development and Land Use Changes

Replacing vegetation with impermeable surfaces (concrete, asphalt) increases runoff. Buildings add weight to slopes. Underground utilities like sewers can create pathways for water infiltration.

Rapid urbanization in cities like Port Harcourt, Calabar, and Enugu has replaced stabilizing vegetation with buildings and roads. This change increases both the likelihood and consequences of mass movements. Settlements built on steep slopes in these cities face higher risks during heavy rains.

Comparison of Mass Movement Triggers

Interaction of Multiple Factors

Mass movements rarely result from a single factor. Usually, multiple conditions combine to trigger movement. For example, a slope might have these conditions:

1. Pre-existing weakness: Steep slope with clay-rich soil
2. Preparatory factors: Deforestation removed stabilizing roots
3. Triggering event: Heavy rainfall saturates soil
4. Result: Landslide occurs

Understanding this sequence helps predict and prevent mass movements. Engineers assess all relevant factors before constructing roads or buildings on slopes. Farmers who maintain vegetation cover on sloped land reduce movement risk even during heavy rains.

Prevention and Control Measures

• Slope Stabilization: Build retaining walls, install drainage systems, reduce slope angles
• Vegetation Planting: Establish grass, shrubs, and trees to bind soil with roots
• Proper Drainage: Direct water away from slopes using gutters, channels, and subsurface drains
• Terracing: Create level platforms on slopes for farming, reducing steepness
• Building Codes: Restrict construction on very steep slopes or unstable ground
• Monitoring Systems: Install sensors to detect early signs of movement in high-risk areas
• Land Use Planning: Avoid removing vegetation on critical slopes

Common Exam Mistakes

WAEC Chief Examiners report that students often:

• Confuse mass movement with erosion: Mass movement is gravity-driven downslope; erosion is removal by water, wind, or ice. Don’t use them interchangeably
• List factors without explanation: Saying “water causes mass movement” is incomplete. Explain HOW: water adds weight and reduces friction between particles
• Ignore Nigerian examples: Don’t write “mountains” – specify “Jos Plateau” or “Mambilla Plateau”
• Forget human factors: Many students list only natural factors (rain, slopes) but omit mining, construction, and deforestation
• Mix up cause and effect: Steep slopes don’t cause earthquakes; earthquakes trigger movements on steep slopes. Keep relationships clear
• Poor question interpretation: “State” needs brief points; “Explain” requires cause-and-effect details; “Describe” needs characteristics and processes

Practice Questions

Multiple Choice Questions

1. Which of these human activities most directly triggers mass movement?
a) Fishing in rivers
b) Mining on hillsides ✓
c) Growing crops on flat land
d) Trading in markets

2. Water increases mass movement primarily by:
a) Making plants grow faster
b) Adding weight and reducing friction ✓
c) Cooling the rock surface
d) Attracting more rainfall

3. Vegetation helps prevent mass movement by:
a) Increasing rainfall in the area
b) Making slopes steeper
c) Binding soil with roots ✓
d) Attracting animals to the slope

4. Which Nigerian location experiences frequent mass movements due to steep terrain?
a) Niger Delta swamps
b) Lagos coastal plains
c) Jos Plateau highlands ✓
d) Sokoto plains

Essay Questions

1. Explain five factors that affect mass movement. (10 marks)

Tip: Choose a mix of natural (slope, water, earthquakes) and human factors (mining, construction). For each factor, explain HOW it causes or increases mass movement. Use Nigerian examples like Jos Plateau or southeastern hillsides.

2. Describe three ways human activities trigger mass movements in Nigeria. (6 marks)

Tip: “Describe” needs more detail than “state” but less than “explain.” Focus on mining, construction, and deforestation with specific examples.

3. State four methods of preventing mass movement on slopes. (4 marks)

Tip: “State” means brief points only. Include: planting vegetation, building retaining walls, proper drainage, terracing slopes.

4. Explain how rainfall contributes to mass movement. (5 marks)

Tip: Cover three main mechanisms: adds weight to soil, acts as lubricant between particles, weakens cohesion when soil saturates. Mention Nigerian rainy season examples.

Memory Aids

WASHED mnemonic for mass movement factors:

• Water content (saturation)
• Activities of humans (mining, construction)
• Slope steepness (gradient)
• Human removal of vegetation
• Earthquakes and tremors
• Different rock types (weak vs strong)

Remember the sequence: “Steep Wet Naked slopes Shake and Slide” = Steep slopes + Water + No vegetation + Earthquake = Mass movement

Nigerian highland areas prone to mass movement: “Just Make Plans” = Jos plateau, Mambilla plateau, Plateau State generally

Related Topics

• Meaning of Mass Movement – Definition and basic concepts
• Types of Mass Movements – Landslides, mudflows, rockfalls, soil creep
• Meaning of Weathering – How rocks break down before moving
• Types of Weathering – Physical, chemical, and biological processes
• Factors that Affect Weathering – Conditions that weaken rocks