Landslides are among the environmental disasters that can occur when soil, rocks and other materials suddenly or gradually move downhill under the force of gravity. Although landslides are not as widespread across Nigeria as flooding, they can cause serious damage when they occur, particularly in areas with steep slopes, unstable ground and intense rainfall.
A landslide can happen naturally, but human activities can increase the likelihood of one occurring. Removing vegetation, cutting into hillsides for roads or buildings, changing natural drainage patterns and poorly planned construction can all weaken slopes.
For Nigeria, therefore, landslide management should not begin after a slope has collapsed. Identifying vulnerable areas and reducing the factors that make slopes unstable are important parts of disaster prevention.
What Causes a Landslide?
A landslide occurs when the forces holding soil, rock or other materials in place are no longer strong enough to resist gravity.
Rainfall is one of the major triggers.
When heavy or prolonged rain enters the ground, soil can become saturated. Water increases the weight of the material and can reduce the strength holding soil particles together. On a steep slope, this can eventually cause the material to move downhill.
However, rainfall alone does not explain every landslide.
The geology of an area, slope angle, vegetation, drainage, construction and human disturbance can all influence whether a slope becomes unstable.
The United Nations Office for Disaster Risk Reduction identifies heavy rainfall, earthquakes and human activities such as deforestation and inappropriate land use among factors that can contribute to landslides (UNDRR, 2020).
Why Nigeria Is Vulnerable in Some Areas
Nigeria has a wide variety of landscapes.
Much of the country consists of relatively low-lying terrain, but there are also mountainous and hilly areas, particularly in parts of the southeast, east-central region and along some highland areas.
The risk is therefore not evenly distributed.
Research has identified landslide-prone locations in parts of southeastern Nigeria, where steep terrain, intense rainfall, weathered rocks and human activities can interact to produce unstable slopes.
A study of landslide susceptibility in southeastern Nigeria found that factors including slope, geology, rainfall, land use and drainage influence landslide occurrence (Okonkwo et al., 2022).
This demonstrates an important point: disaster prevention requires knowledge of the local environment.
A Nigerian Case Study: Enugu State
Enugu provides a useful Nigerian example because of its combination of hills, slopes, urban development and intense rainfall.
Research has documented landslide occurrences in parts of Enugu State and linked susceptibility to geological and environmental conditions.
The Enugu escarpment contains areas where roads, settlements and other infrastructure have been developed around slopes. When vegetation is removed or slopes are modified without adequate stabilization, natural resistance can be reduced.
This is particularly important when roads are constructed through hilly terrain.
Cutting into the lower portion of a slope can remove material that was helping support the upper section. If drainage is then poorly managed, water can accumulate within the slope and further weaken it.
What Happens During a Landslide?
The effects can be immediate and severe.
A landslide can:
- Destroy houses.
- Block roads.
- Damage bridges and drainage structures.
- Bury farmland.
- Damage electricity and communication infrastructure.
- Injure or kill people.
- Block rivers and streams.
- Isolate communities.
A landslide can also create secondary hazards.
For example, material falling into a river can temporarily block the channel. If water accumulates behind the blockage and the barrier later fails, a sudden downstream flow can occur.
This is why landslide risk should not be considered only at the location where the ground movement begins.
The Role of Vegetation
Vegetation is an important part of slope stability.
Plant roots can help bind soil together, while vegetation can reduce the speed at which rainfall reaches and moves across the ground.
Removing vegetation from a steep slope can therefore increase vulnerability.
This does not mean that vegetation can prevent every landslide. Extremely heavy rainfall, geological weaknesses and other factors can overwhelm natural protection.
However, maintaining appropriate vegetation is one of several measures that can contribute to slope stability.
This is especially relevant when land is being cleared for farming, roads or buildings.
Construction Can Increase Risk
Urban development needs to consider the stability of the land before construction begins.
Building on or immediately below unstable slopes can place people and infrastructure in danger.
Road construction is another important consideration.
When engineers cut into a hillside, the original balance of the slope changes. Without appropriate retaining structures, drainage and slope stabilization, the modified slope may become vulnerable.
The problem becomes worse when rainwater is allowed to flow uncontrolled across exposed soil.
This is why environmental assessment and geotechnical investigation are important before major construction projects in hilly areas.
Drainage Is Important
Water management is one of the most important aspects of landslide prevention.
A slope does not necessarily fail because rain falls on it. Problems can arise when water enters the slope and is unable to drain safely.
Properly designed drainage can reduce uncontrolled water accumulation.
Roadside drains, channels and other drainage structures should therefore be designed to safely manage runoff without causing additional erosion or directing excessive water into vulnerable slopes.
This requires cooperation between environmental-health professionals, engineers, planners and local authorities.
Technology Can Identify Vulnerable Areas
Modern technology provides useful tools for landslide-risk assessment.
Geographic Information Systems (GIS) can combine information about slope, geology, rainfall, vegetation, drainage and land use.
Satellite imagery can identify changes in vegetation and land cover.
Digital elevation models can show where steep slopes occur.
Rainfall-monitoring systems can also help identify periods when the likelihood of slope failure may increase.
Researchers have used GIS-based methods to produce landslide-susceptibility maps in Nigeria. Such maps can help authorities identify areas that require closer monitoring or stricter development controls.
This is an important application of environmental technology.
Instead of waiting until a landslide destroys a road or house, authorities can use spatial information to identify areas where preventive action is more necessary.
Warning Signs Residents Should Watch For
Communities living around slopes should take changes in the ground seriously.
Warning signs can include:
- New cracks appearing in the ground.
- Cracks developing in walls or foundations.
- Trees or poles beginning to lean.
- Doors or windows suddenly becoming difficult to open.
- New water appearing from the ground.
- Small movements or bulges developing on a slope.
- Unusual sounds such as cracking or movement.
- Soil or rocks beginning to fall from a hillside.
A single warning sign does not necessarily mean a landslide is imminent, but unusual changes should not be ignored.
Residents should report serious ground movement to relevant authorities and avoid remaining directly below an unstable slope.
What Can Nigeria Do?
Landslide prevention requires a combination of measures rather than one solution.
First, high-risk areas should be identified through geological surveys, GIS mapping and field assessments.
Second, construction regulations should be properly enforced in vulnerable areas.
Third, vegetation should be protected where it contributes to slope stability.
Fourth, drainage systems should be designed and maintained to prevent uncontrolled water infiltration and runoff.
Fifth, communities should receive information about landslide warning signs and evacuation procedures.
Finally, roads and other infrastructure in mountainous or hilly locations should be regularly inspected.
Prevention is considerably cheaper and safer than waiting until a landslide destroys infrastructure and then attempting emergency repairs.
An Environmental Health Perspective
Landslides are sometimes viewed purely as geological or engineering problems. They are also environmental-health concerns.
When a road is blocked, people can lose access to hospitals, schools, markets and workplaces.
When houses are destroyed, families may require emergency shelter, water and sanitation services.
When a landslide blocks a watercourse, the consequences can extend beyond the original location.
This illustrates why environmental health looks at the relationship between environmental conditions and human wellbeing.
My Environmental Health Science training has encouraged me to view environmental hazards from this broader perspective. The objective is not simply to understand what happened but to identify how exposure can be reduced before people are harmed.
Conclusion
Landslides are not Nigeria’s most widespread environmental disaster, but where they occur, their consequences can be devastating.
They result from the interaction of factors such as slope, geology, rainfall, soil conditions, vegetation, drainage and human activity.
Nigeria can reduce the risk by identifying vulnerable slopes, controlling inappropriate development, maintaining vegetation, improving drainage and using GIS and remote sensing to monitor areas of concern.
For communities in hilly parts of the country, awareness is equally important.
A crack in the ground, a leaning tree or unexplained movement on a slope may appear insignificant at first. But recognizing these warning signs early can provide an opportunity to act before the ground gives way.
The lesson is straightforward:
We cannot control gravity or stop every heavy rainfall event, but we can reduce the number of people and structures exposed to unstable slopes.
Good environmental planning means understanding the land before building on it.
References
- United Nations Office for Disaster Risk Reduction (UNDRR). (2020). Landslide. Sendai Framework Terminology on Disaster Risk Reduction.
- Okonkwo, C. C., et al. (2022). Research on landslide susceptibility and environmental factors in southeastern Nigeria.
- Federal Republic of Nigeria. National Disaster Management Framework. National Emergency Management Agency (NEMA).
- National Emergency Management Agency (NEMA). National Disaster Risk Assessment and Management resources.
