The Hazard of Glacial Lakes: Case Studies from Nepal and Peru

The last half century has witnessed considerable glacier melt that has led to the formation of large glacial lakes in high mountain regions.  These glacial lakes typically form behind terminal moraines comprising loose boulders, debris, and soil, which are susceptible to fail and cause a glacial lake outburst flood (GLOF).  These lakes also act as a heat sink that accelerates glacier melt and in many cases is accompanied by rapid lake areal expansion.  As these glacial lakes grow, their hazard also increases due to the increase in potential flood volume and the lakes’ proximity to triggering events such as avalanches and landslides.  

    Understanding the existing and future hazard and risk associated with these lakes is important for downstream communities and other stakeholders, e.g., hydroelectric companies. Unfortunately, in many cases existing methods used to assess GLOF hazards have yielded conflicting classifications, leading to confusion amongst stakeholders whom the studies are meant to assist. This talk will discuss the development of an objective and holistic risk and action framework for characterizing potentially dangerous glacial lakes in Nepal that may be used to assist and prioritize risk-mitigation actions. Imja Lake in Nepal is the primary focus, but the technique is transferable to other potentially dangerous glacial lakes in the Himalaya and other regions, e.g., the Cordillera Blanca of the Andes.   

    GLOFs are often triggered by avalanches falling into glacial lakes, initiating a chain of processes that may culminate in significant inundation and destruction downstream. This talk will also discuss the simulation of the potential GLOF process chain originating from Lake Palcacocha in the Cordillera Blanca of Peru, the source of a previously catastrophic GLOF on December 13, 1941, killing about 1800 people in the city of Huaraz. The chain of simulated processes includes: (1) avalanches above the lake; (2) lake dynamics resulting from the avalanche impact, including wave generation, propagation, and runup across lakes; (3) terminal moraine overtopping and dynamic moraine erosion simulations to determine the possibility of breaching; (4) flood propagation along downstream valleys; and (5) inundation of Huaraz. The results are converted into flood intensity and hazard maps useful for city planning and regulation.