<p>Climate change has increased the frequency and intensity of extreme rainfall events across humid tropical mountain regions, making steep landscapes more vulnerable to large geomorphic disturbances. Extreme rainfall-triggered landslides in these environments often produce impacts that extend well beyond the initial slope failure zone, yet the processes controlling downstream geomorphic amplification remain poorly understood. This study investigates the Mundakkai–Chooralmala landslide (MCL) in the Western Ghats and proposes a new process framework termed cascading hillslope–channel coupling with dam-amplified erosion. High-resolution longitudinal profile metrics, including the valley confinement ratio (VCR), stream length–gradient (SL) index, normalized channel steepness (k_sn), concavity (θ), χ-transformation, and a geomorphic amplification index (GAI), were integrated with field-based geomorphic observations to quantify transient channel response. Results show that erosion amplification was strongly influenced by three temporary debris dams formed within the first ~ 4&#xa0;km of the channel network. These obstructions developed from the accumulation of boulder-rich landslide debris and large volumes of woody material derived from uprooted forest vegetation, which increased dam stability and enhanced water impoundment. Intense monsoonal rainfall rapidly increased discharge, causing hydraulic pressure to build behind these temporary dams before successive breach events occurred. Morphometric analysis revealed localized SL anomalies, elevated k_sn peaks, and strong χ-profile deviations associated with these dam-break locations, indicating the propagation of transient erosion waves through the basin. Valley confinement exerted a major control on erosion style, with confined upstream reaches dominated by vertical incision and bed scour, moderately confined reaches showing severe lateral bank erosion and channel widening, and downstream unconfined reaches characterized by sediment redistribution and profile smoothing. The basin-scale GAI value (5.73) indicates strong localized geomorphic amplification concentrated within downstream sectors, demonstrating that erosion intensity was controlled by repeated sediment storage and release rather than gradual fluvial adjustment. The findings highlight the important geomorphic role of woody debris in stabilizing temporary dams, prolonging impoundment, and increasing erosive power during dam failure events. This study demonstrates that longitudinal channel metrics commonly applied in tectonic geomorphology can effectively identify and quantify event-scale geomorphic disturbances in tropical mountain environments. The results further emphasize the need for improved geomorphic classification frameworks that distinguish isolated slope failures from amplification-driven fluvial cascades. Overall, the proposed framework provides a process-based basis for understanding the interaction between landslide activity, temporary damming, and downstream erosion hazards in extreme rainfall environments.</p>