Study: Wayanad Landslides Were a Product of Climate and Geology Together

The catastrophic landslides that struck Wayanad in July 2024 were not caused by extreme rainfall alone. A new international study says the disaster was also shaped by the region's geological and structural characteristics, which determined where the slope collapsed and how the debris moved.

The study, published in the peer-reviewed journal Landslides, was conducted by researchers from the University of Kerala, the Indian Institute of Science Education and Research (IISER) Mohali, and Savitribai Phule Pune University. It notes that intense monsoon rain acted as the immediate trigger, but the underlying geology played a critical role in making the event one of the most destructive recorded in the Western Ghats.

On the night of July 30, 2024, nearly 573 mm of rainfall in 48 hours triggered a massive slope failure in the upper catchment of the Punnapuzha river. The resulting debris flow travelled about 8 km, descending roughly 768 metres while sweeping through Punchirimattam, Mundakkai and Chooralmala. It carried enormous volumes of rock, soil and vegetation, causing extensive destruction in the area.

To understand why the landslide became so destructive, the research team carried out field investigations across the affected valley in April 2025. They mapped the geology from Chooralmala to Punchirimattam and analysed rock samples in the laboratory. Because the landslide crown remained unsafe to approach, drone-mounted LiDAR and high-resolution aerial imagery were used to examine the upper failure zone.

The study found that the hills in the affected area are underlain by ancient crystalline rocks that have undergone repeated deformation for hundreds of millions of years. These processes created natural weak planes, including shear zones, fractures and foliations. Rainwater penetrating these fissures caused extensive chemical weathering, turning hard rock into soft, deeply weathered material underground.

The landslide likely originated within a highly weathered shear zone near the crown, where a first-order stream crossed the weakened rock. During the extreme rainfall, water rapidly infiltrated the interconnected fractures, increasing water pressure inside the slope. When the rock mass could no longer withstand this pressure, a large block detached and set off the landslide.

As the debris rushed downhill, narrow valley sections underlain by harder rocks such as metagabbro and granite functioned as natural barriers. Debris temporarily piled up behind these constrictions, forming short-lived natural dams. When those dams broke, powerful surges of water, mud and boulders were released, greatly increasing the damage downstream.

The study highlights the interplay of climate and geology. "Extreme rainfall acted as the immediate trigger, but the pre-existing geological framework determined where the slope failed, how the debris moved and why the event became exceptionally destructive," said Y. Anilkumar and K.S. Sajinkumar, assistant professors at the Department of Geology, University of Kerala, who led the study.

The findings underscore the need for landslide hazard assessments that consider both meteorological and geological factors, particularly in hilly regions where climate change is increasing the frequency of extreme rainfall events. Understanding the dual role of climate and geology can help authorities better identify vulnerable slopes and plan mitigation measures.