Causes of landslides in urban areas

Landslides are a significant hazard in hilly or mountainous regions, particularly in urban settings where human activities can exacerbate natural risks.

Factors contributing to landslide risks

• Poor water management - Uncontrolled discharge of water into natural channels or gullies, especially during heavy rainfall, increases slope instability. Without proper sewers or storm drains, large volumes of water flow unregulated, heightening erosion and landslide risks.
• Slope disruption - Excavating slopes to create terraces for building houses often results in steeper, less stable slopes behind the terrace. This human-induced alteration significantly increases the likelihood of landslides.
• Construction waste dumping - Disposing of construction debris on slopes adds extra weight, particularly on already unstable or active landslide areas, worsening stability issues.
• Vibrations from traffic - Heavy traffic or construction activities can generate vibrations that destabilise slopes, triggering landslides in vulnerable areas.

Impacts and costs of landslides

Landslides cause a wide range of impacts, from personal loss to economic burdens. These effects can be immediate or long-term, affecting individuals, communities, and governments.

Categories of costs associated with landslides

Case study: Urban landslides in Kalimpong, India

Kalimpong, a hill station in West Bengal, India, sits at an elevation of 1,250 m above the Teesta river. The area of Dumsi Pakha, located below the main town, exemplifies how urban mismanagement in steep terrains can lead to devastating landslide issues.

Key issues in Kalimpong

• Water management failures - In Kalimpong town, water is released without regulation into gullies passing through Dumsi Pakha. These channels, often clogged with rubbish, are dry at the end of the dry season but experience massive flows during the monsoon, causing extensive instability along their banks.
• Slope alterations - Many houses in the settlement are built on mini-terraces created by cutting into the slope. This practice steepens the slope behind the terrace, significantly increasing the risk of landslides.
• Construction waste issues - Uncontrolled dumping of construction debris near the town adds weight to already unstable slopes, aggravating landslide risks.
• Lack of infrastructure - The absence of proper sewers and storm drains means that heavy rainfall results in unregulated water flows, further destabilising slopes downstream.

Case study: Landslides in Sri Lanka, 2016

In May 2016, Sri Lanka experienced severe landslides and torrential rain, particularly in the Central Hills region, demonstrating the devastating potential of such hazards in vulnerable areas.

Details of the event

• Scale of impact - Over three days, the death toll reached 37, with more than 150 people reported missing. The heavy rains forced over 137,000 individuals to evacuate their homes.
• Rainfall intensity - The affected area received over 100 mm of rain between 15 and 16 May, triggering widespread slope collapses.
• Destruction - Dozens of homes were destroyed as mountain slopes gave way, displacing hundreds of villagers.
• Challenges in response - Rescue operations faced significant obstacles due to treacherous road conditions leading to the mountainous region, as reported by the Red Cross.

Common misconceptions about landslide causes

Landslides are often misunderstood, with many assuming they are solely natural events.

Correcting misunderstandings about landslides

• Misconception: All landslides are caused by natural processes - While natural factors like heavy rainfall or earthquakes can trigger landslides, human activities play a significant role. Actions such as road building, and vibrations from heavy traffic often contribute to or directly cause landslides.
• Reality: Human influence matters - Urban mismanagement, including poor water drainage systems and improper construction practices, can significantly increase landslide risks, often more than natural processes alone.