‘Erratic monsoon, old fault lines surge landslides in Garhwal Himalayas’

Dehradun: A sharp rise in landslides across the Garhwal Himalayas during the 2025 monsoon was "primarily driven by intense and erratic rainfall that reactivated old, dormant landslide zones", according to a new scientific study published in ‘Landslides', a peer-reviewed journal of Springer Nature. The study found that "areas which had remained relatively stable for years failed again after prolonged rainfall saturated soil and rock material, reducing shear strength along pre-existing slip surfaces".The research, titled ‘Preliminary assessment of heavy rainfall-induced landslides and reactivation of old landslides in the Garhwal Himalayas', highlighted the "inherent vulnerability" of the region, characterised by fragile geological formations, steep slopes and active tectonics. "These natural factors were further aggravated by human activities such as road widening, hill cutting, unplanned construction and poorly designed drainage systems, all of which weakened slope stability," stated the study authored by Soumik Saha and Biswajit Bera of the department of geography, Sidho-Kanho-Birsha University in West Bengal.Based on field investigations and post-event analysis, the researchers documented a marked increase in landslide activity during Aug and Sept 2025, with Chamoli, Rudraprayag and Uttarkashi emerging as the "worst-affected districts". Several known landslide-prone locations, including Pagalnala, Langsi, and stretches along the Gangotri and Yamunotri highways, witnessed repeated slope failures. The incidents disrupted traffic for extended periods, cut off villages and severely affected the Char Dham Yatra, with pilgrim movement impacted for weeks, the research said.Using rainfall data from India-WRIS and official disaster reports, the study found that monsoon rainfall in 2025 was among the "highest recorded in the past five years at several locations". Gaurikund in Rudraprayag district received more than 4,800 mm of rainfall during the monsoon months, while Uttarkashi, Pipalkoti and Kalagarh also experienced significantly above-normal precipitation. Short-duration extreme rainfall events, combined with prolonged wet spells, played a critical role in triggering slope failures across the region, according to the authors.Field observations revealed frequent debris flows and shallow landslides along highways, rural roads and near settlements. The concentration of infrastructure and habitation in known landslide-prone zones significantly increased exposure and risk, particularly when old landslides were reactivated. The researchers also pointed to changing monsoon rainfall patterns linked to climate variability, noting that "intense, short-duration rainfall events are becoming more frequent and are likely to further escalate landslide hazards in the Himalayas".The study called for detailed landslide inventory mapping, continuous monitoring of vulnerable slopes and the integration of rainfall thresholds into early-warning systems. It also stressed the need for scientifically planned slope-stabilisation measures and stricter regulation of construction activities in fragile mountain terrain. "Without urgent mitigation measures and improved land-use planning, landslide risks in the Garhwal Himalayas will continue to rise, with serious consequences for lives, livelihoods and regional connectivity," the authors warned.