What caused Wayanad landslides? Geoscientist points to unchecked human interventions, climate vagaries
C.P. Rajendran goes into the factors that caused the Wayanad landslides and what the government can do to reduce the impact on people in future
File picture of geoscientist C.P. Rajendran
| Photo Credit: The Hindu
Human interventions including deforestation, unplanned construction activities and climate vagaries caused the devastating landslides in Wayanad, says C.P. Rajendran, geoscientist and adjunct professor at the National Institute of Advanced Studies, Bengaluru, in an e-mail interview to The Hindu as the State continues to reel under the deadly disaster.
On the worst-ever tragedy to hit Kerala since the 2018 deluge.
The landslide at Mundakkai that occurred on July 29 causing more than 150 deaths is one of the worst natural disasters in Kerala’s recent history. The landslide in Mundakkai and Chooralmala in Wayanad occurred about 2-3 km from Puthumala, where a similar type of mass wasting occurred on August 29, 2019.
Studies conducted by a group of researchers from Central Coastal Agricultural Research Institute, Goa, published in 2020 indicated that the Puthumala landslide started as one of those smaller landslides that occurred deep inside the forest, and the landslide gained momentum as it reached the lower reaches of the hill as the soil structure in the lower parts was fragile and saturated with rain. It turned into a massive slide filled with rocks and mud bringing down a part of the hill. The high-intensity rainfall was the major trigger that acted as a tipping point.
What may have been the causative factors this time?
Factors like deforestation which started in the 1980s to clear the land for tree plantations must have gradually changed the soil conditions in the region. The root systems of the forest trees left out within the soil must have decayed, leaving huge cavities. Similar soil conditions with cavities under the soil cover must exist in the Mundakkai/Chooralmala area. It is possible that the water seeped into the cavities and interconnected underground channels formed by soil piping phenomena.
The area must have received on average close to 1830 mm of rain in the last 30 days, according to rain gauge data reported from Kalladi, a site located about 5 km from Mundakkai. Along with these factors, unscientific construction practices and quarrying may have also contributed to the evolution of this hazard. A similar soil piping mechanism must have worked in Mundakkai/ Chooralmala as these sites share similar geology and soil structure. It is also reported that about 102 sqkm and 196 sqkm areas in Wayanad are extremely landslide prone and moderately landslide prone respectively with some locations also vulnerable to soil piping effect.
What is the way forward now?
Climatic conditions are expected to worsen in the future because of the emerging global warming scenario. The frequency of landslides is likely to go up in hilly regions like Wayanad. The agencies involved in landslide susceptibility maps like the State Disaster Management should be involved in updating the existing maps. It is not clear if the Mundakkai area is part of the high-risk area in the available map. The satellite observations and digital elevation models are now widely used to map the landslide risk mapping. The government must frame clear policies on land management based on such zoning maps by taking the people into confidence.
It also has to evolve long-term strategies to address annual floods and landslides that affect poor people, who are forced to live in ecologically-fragile lands. Kerala with a high-density population should initiate imaginative but humane initiatives on environmental management and new guidelines for land utilisation.
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