THIRUVANANTHAPURAM: The landslide that devastated a few villages of Wayanad a month ago is the biggest in India’s recorded history, according to a study commissioned by the Kerala State Disaster Management Authority. The July 30 landslide resulted in a debris flow of nearly six million cubic metres -- capable of filling 2,400 Olympic-sized swimming pools stretching eight kilometres downhill, the study found.
Previously, the 1998 Malpa landslide in Uttarakhand held the record for the largest debris flow in the country. The Wayanad landslide was five times larger than Malpa and 300 times the size of the 2020 Pettimudi landslide in Munnar.
The study conducted jointly by researchers from the Indian Institute of Science Education and Research-Mohali, Kerala University, and the Kerala University of Fisheries and Ocean Studies used LiDAR technology and photogrammetric methods to arrive at its conclusion.
The origin of the landslide has been pinned to the upstream area of Punnapuzha, deep within the forest on the eastern slope of the Western Ghats. “The scale of the debris avalanche, which travelled eight kilometres from the landslide’s crown, underscores its enormity. The generation of 5-6 million cubic metres of sediment is significantly larger than the Malpa landslide,” said lead researcher Sajinkumar K S, an assistant professor with Kerala University’s geology department.
He noted that intense rain triggered the landslide, and the area’s geology contributed to its scale. “The landslide started as a rock slide and transformed into a debris flow. It was obstructed at Seethamma Kund, creating a damming effect before it burst into a debris avalanche,” he pointed out.
The debris’ force was so powerful that it filled the entire riverbed, causing rocks the size of two trucks to be displaced 50 metres. These rocks, formed 250 crore years ago, had been weathered by water and sun over the years. Landslides since 1984 had already removed the topsoil, making these rocks vulnerable, the study said.
“Typically, landslides halt at the surface of the rock. But here, the weathered rocks under the riverbed, oriented against the water flow, allowed the water to infiltrate and exacerbate the weathering,” Sajin said.
Analysis by Adin Ishan from IISER Mohali revealed that sediment levels in the Chaliyar surged by 185% during the event, highlighting the landslide’s magnitude. The team comprised senior researchers Yunus Ali Pulpadan and Gireesh Gopinath, along with students Sahil Kaushal, Jiyadh Thanveer, Achu Ashok, Krishnapriya and Rajaneesh, besides Sajinkumar.