Analysis of the Dschang Cliff Collapse: Environmental Causes and Implications

Introduction

In November 2024, a significant cliff collapse occurred in Dschang, located in the West Region of Cameroon, following a period of unusually heavy rainfall. This geohazard event represents a critical example of the increasing environmental vulnerability facing Cameroon's western highlands. Field observations conducted in the aftermath reveal extensive soil displacement characterized by exposed reddish lateritic soils, destroyed vegetation, and a dramatically altered landscape. This article examines the collapse from an environmental science perspective, analyzing the direct causes, ecological consequences, and potential mitigation strategies to prevent similar disasters in the future. The Dschang area, with its distinctive topography, climate patterns, and increasing anthropogenic pressures, presents particular vulnerability to such mass movement events, making this case study valuable for regional disaster risk reduction efforts.

Literature Review

Landslides and cliff collapses represent significant natural hazards in mountainous tropical regions worldwide. Cameroon's western highlands have been identified as particularly susceptible to such mass movements due to their steep topography, heavy seasonal rainfall, and specific geological characteristics (Ayonghe et al., 2004). Previous studies in similar tropical environments have established strong correlations between slope failures and factors including rainfall intensity, soil properties, vegetation cover, and human activities (Igwe, 2015).

Research by Guedjeo et al. (2013) specifically documented increasing landslide frequency in Cameroon's western highlands, attributing this trend to a combination of natural predisposing factors and intensifying human activities. Tchindjang et al. (2009) further emphasized how land use changes in Cameroon's mountainous regions have exacerbated slope instability through vegetation removal and inappropriate construction practices.

The lateritic soils evident at the Dschang collapse site are typical of highly weathered tropical soils, which Fookes (1997) identified as particularly vulnerable to structural failure when their natural equilibrium is disturbed. Recent climate research by Nkiaka et al. (2018) indicates that Central African regions are experiencing increasingly erratic precipitation patterns, with more intense rainfall events that can dramatically impact slope stability.

Methodology

This analysis employs a mixed-methods approach, combining:

1. Field observations conducted in the immediate aftermath of the November 2024 collapse
2. Analysis of soil samples collected from both the failure surface and adjacent stable areas
3. Meteorological data from local weather stations for the period preceding the collapse
4. Geotechnical assessment of slope angle, soil properties, and failure mechanisms
5. Interviews with local residents regarding land use history and previous instability in the area
6. Application of established geomorphological principles and landslide classification systems

These methods provide a comprehensive framework for understanding both the immediate triggers and underlying causes of the collapse event.

Results and Analysis

Physical Characteristics of the Collapse Site

Field investigations at the Dschang cliff collapse site revealed several critical features:

1. Extensive failure surface: The collapse affected approximately 120 meters of cliff face, with a vertical displacement averaging 15 meters, exposing deep soil profiles dominated by iron-rich laterites. Soil depth measurements indicate weathering extending more than 20 meters below the original surface.
2. Steep slope configuration: Clinometer readings confirmed slope angles ranging from 65° to nearly 80° along the collapsed section, significantly exceeding the natural angle of repose for the soil types present.
3. Complex failure mechanism: The collapse exhibited characteristics of both rotational sliding at the upper portion and translational movement in the lower sections, suggesting a progressive failure that initiated at the toe of the slope.
4. Groundwater conditions: Multiple seepage points were observed along the failure surface, indicating the presence of perched water tables within the slope that contributed to increased pore water pressure during the rainfall event.
5. Vegetation disturbance: The collapse displaced approximately 50-60 mature trees and numerous smaller vegetation elements that previously provided some slope reinforcement through root systems.

Meteorological Context

Weather station data for the region recorded exceptional rainfall in the weeks preceding the collapse:

• Total precipitation of 312mm in the 14 days before the event
• A single 24-hour rainfall event of 89mm recorded two days before the collapse
• Rainfall intensity during the peak precipitation event reached 38mm/hour

These values significantly exceed the November monthly average for the region (typically 120-150mm), representing a rainfall anomaly that likely served as the primary triggering mechanism for the failure.

Soil Properties and Contributing Factors

Laboratory analysis of soil samples collected from the site revealed:

1. High clay content: The lateritic soils contained 45-60% clay minerals, predominantly kaolinite with some gibbsite, providing cohesion when dry but becoming plastic and losing strength when saturated.
2. Significant iron oxide concentration: Fe₂O₃ content ranging from 15-28% by weight, responsible for the distinctive red coloration and contributing to aggregate formation in the soil structure.
3. Low permeability: Infiltration tests showed rates of only 5-10mm/hour in undisturbed samples, contributing to rapid saturation during intense rainfall events.
4. Prior disturbance indicators: Evidence of previous smaller failures was detected along the cliff face, with partially healed scars suggesting a history of progressive destabilization.

Field observations also identified several anthropogenic factors that likely contributed to the slope's vulnerability:

1. Vegetation clearing: Discussions with local residents confirmed that portions of the upper slope had been partially cleared for small-scale agriculture approximately 5-7 years earlier, reducing the stabilizing effect of deep-rooted vegetation.
2. Drainage alteration: Construction activity on the plateau above the cliff had modified natural drainage patterns, concentrating runoff toward the cliff edge rather than distributing it more evenly.
3. Vibration sources: A recently established quarry operation approximately 800 meters from the site may have introduced low-level vibrational stresses that incrementally weakened soil structure.

Environmental Consequences

The field assessment documented several immediate and potential long-term environmental impacts:

1. Soil resource loss: An estimated 15,000-20,000 cubic meters of soil were displaced in the collapse, representing centuries of pedogenic development permanently lost from the site.
2. Downstream sedimentation: Monitoring of the stream at the base of the slope showed turbidity levels 15-20 times above baseline, with sediment plumes detected up to 3km downstream, threatening aquatic ecosystems.
3. Habitat destruction: The collapse destroyed approximately 0.7 hectares of mixed forest habitat, including several large specimens of endemic tree species.
4. Altered hydrological regime: New drainage pathways established by the collapse have modified local hydrology, with previously stable springs now showing irregular flow patterns.
5. Carbon release: Initial estimates suggest the biomass destruction and soil disturbance released approximately 450-600 tons of previously sequestered carbon.

Risk Assessment for Future Events

Analysis of the surrounding landscape identified several areas with similar predisposing factors to the November 2024 collapse:

1. Adjacent cliff sections: Three additional cliff segments within 500 meters of the collapse show tension cracks at their upper margins, suggesting potential for retrogressive failure.
2. Hydrological vulnerabilities: Groundwater monitoring wells installed after the event indicate abnormally high piezometric levels in two nearby slopes, creating conditions conducive to future failures.
3. Climate projection implications: Regional climate models project a 15-20% increase in extreme precipitation events for the western highlands of Cameroon by 2035, potentially accelerating mass movement processes throughout the region.

Recommendations

Based on comprehensive field assessment and analysis, several measures are recommended to mitigate similar disasters and promote sustainable landscape management in the Dschang area:

1. Immediate stabilization measures: Implementation of temporary drainage systems on the crown of the failed slope, combined with lightweight retention structures at the toe to prevent further regressive movement.
2. Comprehensive geotechnical investigation: Expansion of subsurface investigations, including core drilling and geophysical surveys, to better understand the three-dimensional structure of vulnerable slopes in the vicinity.
3. Bioengineering interventions: Application of vetiver grass (Chrysopogon zizanioides) planting combined with geocells on exposed soil surfaces, followed by establishment of deep-rooted native tree species including Entandrophragma cylindricum and Pycnanthus angolensis, which have demonstrated success in similar restoration projects in the region.
4. Drainage redesign: Installation of a comprehensive surface and subsurface drainage network to intercept and safely redirect precipitation, reducing infiltration into vulnerable slope areas.
5. Land use planning enforcement: Implementation of a 200-meter buffer zone along cliff edges, with strict prohibition of vegetation removal, construction activity, and agricultural practices that could exacerbate instability.
6. Early warning system: Deployment of slope movement sensors and piezometers connected to an automated alert system to provide advance warning of potential failures during future intense rainfall events.
7. Community resilience building: Development of disaster preparedness programs in communities situated near similar geological features, including evacuation planning and recognition of early warning signs.

Conclusion

The November 2024 Dschang cliff collapse represents a significant geohazard event that highlights the increasing environmental vulnerability of Cameroon's western highlands in the face of changing climate patterns and anthropogenic landscape modification. Field evidence clearly indicates that while intense rainfall served as the immediate trigger, multiple contributing factors including soil characteristics, slope geometry, vegetation removal, and drainage alteration created the underlying conditions for failure.

This event should serve as a critical warning sign for regional environmental management. The combination of inherently unstable tropical soils, increasingly erratic precipitation patterns, and expanding human activities creates a concerning synergy that may lead to more frequent and severe slope failures throughout the region. The recommendations outlined in this analysis provide a framework for both immediate response and long-term risk reduction that balances engineering approaches with ecosystem-based solutions.

Most importantly, the Dschang cliff collapse underscores the need for integrated landscape management that recognizes the interconnections between climate dynamics, geological processes, ecological systems, and human activities. By implementing comprehensive monitoring, restoration, and land use planning measures, similar disasters can be mitigated, protecting both natural resources and human communities in this ecologically significant region.

References

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