Amplified Risks of the Yarlung Zangbo–Brahmaputra River to Glacier Hazard Chains due to Multi-Hazard Transformation

A glacier hazard chain can form a long-runout mass flow and generate a large flood, affecting downstream areas hundreds of kilometers away from the initiating hazard site. This study focuses on the Yarlung Zangbo Daxiagu. The objective is to address two key unresolved issues: the evolution of detached glacier materials into debris flows or debris floods and the amplification of the impact range and threats. A comprehensive framework is developed that considers the impacts of near-field and far-field hazards. Numerical modeling, remote sensing, and field investigations were integrated to understand the interactions, transformations, and amplifications of hazards in the glacier hazard chain. The results indicate that extensive, nearly saturated sediments on the glacier valley floor, when entrained, amplify the magnitude of the mass flow. The topography plays a crucial role. When the valley outlet is perpendicular to the river course, topographic obstacles cause immediate halting, resulting in the formation of high barrier dams. Conversely, when the glacier valley aligns nearly parallel to the river course, the mass flow can travel a much longer distance upon entering the river, causing an enlarged affected area. The barrier dams can breach rapidly, causing breaching floods that amplify the downstream impact from several kilometers to hundreds of kilometers. Our analysis reveals that the overall impacts remain spatially limited. Specifically, downstream areas along the Yarlung Zangbo–Brahmaputra River are unlikely to face greater threats from the upstream floods than local monsoon floods. Our findings provide the foundation for the management of glacier hazard chains.