Why Durban's geology makes it vulnerable to devastating landslides

The catastrophic landslides that struck Durban and the eThekwini region of South Africa in 2022 were a stark reminder of the power of nature. While climate change and urban planning played a role, the region's geology is a major factor in its vulnerability to landslides.

Understanding Durban's Geological Landscape

Durban and its surrounding areas sit on a diverse geological tapestry, with each formation contributing to the landslide risk:

The Berea Formation: A Coast of Ancient Sand Dunes
- Stretching from Durban to Mtunzini, the coastline is dominated by the Berea formation, characterized by steep, ancient red sand dunes.
- These sands, while strong, are highly susceptible to erosion, especially when exposed to concentrated water flow.
- Torrential rains can quickly erode the sands, forming gullies and triggering landslides.
The Pietermaritzburg Formation: Inland Shales Prone to Instability
- Inland, the landscape transitions to the Pietermaritzburg formation, composed of shales formed from layers of clay and silt.
- When weathered, these shales can become extremely slippery, increasing landslide susceptibility.
- Even a small rise in water pressure within these layers, often due to prolonged rainfall or leaking pipes, can be disastrous.
- The residential area of Clare Estate, tragically affected by landslides in 2022, is a case in point, highlighting the historical recurrence of landslides in areas underlain by these shales.
The Natal Group Sandstones: A Recipe for Liquefaction
- The Natal group sandstones, interspersed with layers of clay, introduce another layer of complexity.
- Heavy rainfall can saturate the sandy layers. When trapped by the clay layers, the excess water pressure can liquefy the sand, causing it to flow like a liquid, leading to ground instability and landslides.

The 2022 Floods: A Perfect Storm for Disaster

The devastating 2022 floods saw over 300mm of rain deluge the region in just four days, far exceeding the typical rainfall thresholds for landslides. The ground, already saturated from the rainy season, simply couldn't cope, leading to widespread landslides and devastation.

Mitigation: A Complex Challenge

While Durban has implemented zoning regulations and early warning systems in some areas, the 2022 events highlight the need for more comprehensive action. However, landslide mitigation is not just a technical challenge; it involves navigating complex social and political landscapes:

Zoning Regulations: Expanding zoning regulations to cover more areas at risk is crucial. However, this often faces resistance due to concerns about property devaluation.
Early Warning Systems: Investing in and improving early warning systems can provide residents with valuable time to evacuate. Yet, these systems can be expensive and may not always provide sufficient warning.
Social and Political Considerations: Addressing the social and political dimensions, such as community engagement, education, and equitable implementation of regulations, is vital for long-term success.

Durban's geology makes it inherently vulnerable to landslides. By understanding the specific geological risks and proactively addressing them through a combination of technical solutions, social awareness, and political will, the city can work towards mitigating the devastating impacts of future landslides.