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Abstract Investigating the preferential flow path of a debris flow is crucial for quantifying the risk and developing mitigation strategies. Here, we examined 66 debris flows from the Western Ghats in India employing Rapid Mass Movement Simulation (RAMMS)::Debris Flow software to understand the kinematics of run-out. Our analysis revealed that the debris flow run-out in the study area follow two main routes: 60 along the existing stream channels (SC) and six following the steepest hill slope (SH). We further simulated these debris flows to identify their drivers, and derived a threshold that distinguishes between SC and SH-type debris flows. Our results indicate that the debris flow volumes greater than 7072 cu. m is SH-type, whereas those with smaller volumes are more likely to follow SC paths. The model’s accuracy was validated against field observations, achieving a success rate of 93% for SH-type flows and 85% for SC.

Abstract The long run-out debris flows caused by oversaturated soil systems during the aggravated monsoon period in the Western Ghats raise questions about the hill community’s future. Here, we report the catastrophic long run-out Wayanad debris flow that occurred on 30th July 2024, which resulted in 231 fatalities and 128 people missing, and caused widespread destruction to infrastructure. This involved a maximum flow height of 10.66 m and maximum flow velocity of 18.7 m/s, simulated using RApid Mass Movement Simulation.