Modeling a glacial lake outburst flood process chain: the case of Lake Palcacocha and Huaraz, Peru

Abstract

Abstract. One of the consequences of recent glacier recession in the Cordillera Blanca, Peru, is the risk of glacial lake outburst floods (GLOFs) from lakes that have formed at the base of retreating glaciers. 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 paper presents simulations of all of the processes involved in a potential GLOF originating from Lake Palcacocha, the source of a previously catastrophic GLOF on 13 December 1941, killing about 1800 people in the city of Huaraz, Peru. The chain of processes simulated here includes (1) avalanches above the lake; (2) lake dynamics resulting from the avalanche impact, including wave generation, propagation, and run-up 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 populated areas. The results of each process feed into simulations of subsequent processes in the chain, finally resulting in estimates of inundation in the city of Huaraz. The results of the inundation simulations were converted into flood intensity and preliminary hazard maps (based on an intensity-likelihood matrix) that may be useful for city planning and regulation. Three avalanche events with volumes ranging from 0.5 to 3 × 10 6 m 3 were simulated, and two scenarios of 15 and 30 m lake lowering were simulated to assess the potential of mitigating the hazard level in Huaraz. For all three avalanche events, three-dimensional hydrodynamic models show large waves generated in the lake from the impact resulting in overtopping of the damming moraine. Despite very high discharge rates (up to 63.4 × 10 3 m 3 s −1 ), the erosion from the overtopping wave did not result in failure of the damming moraine when simulated with a hydromorphodynamic model using excessively conservative soil characteristics that provide very little erosion resistance. With the current lake level, all three avalanche events result in inundation in Huaraz due to wave overtopping, and the resulting preliminary hazard map shows a total affected area of 2.01 km 2 , most of which is in the high hazard category. Lowering the lake has the potential to reduce the affected area by up to 35 %, resulting in a smaller portion of the inundated area in the high hazard category.

Compiling an Inventory of Glacier-Bed Overdeepenings and Potential New Lakes in De-Glaciating Areas of the Peruvian Andes: Approach, First Results, and Perspectives for Adaptation to Climate Change

“…A corresponding priority list could then be derived for further and more detailed investigations such as field measurements and more complex modelling of potentially dangerous processes and process chains. In critical cases, the assessment of hazard potentials and risks can be done with sophisticated model chains [45][46][47][48]. Such further steps and improvements necessitate better data, especially higher-resolution DEMs, and continued monitoring, mainly with high-resolution remote sensing, of glacier changes, corresponding acceleration trends, and the detailed formation of new lakes.…”

Decision-Making Methodology for Risk Management Applied to Imja Lake in Nepal

“…Constraining prices for expected avoided damages under which lake lowering (10 or 20 m) is efficient. As discussed by Somos-Valenzuela et al [13], the general lack of field data regarding actual GLOF events leads to many unknowns about the processes, particularly those related to avalanches, lake dynamics and moraine erosion. There is very little information on avalanche characteristics, magnitude of avalanche-generated waves, or erosive capabilities of overtopping waves on which to base validation of these simulated processes.…”

“…The results of the full breaching scenario are used since they represent the worst-case scenario which should be communicated to decision makers and stakeholders. For the sake of providing complete information, the probable maximum inundation [13] as a result of a full breach of the damming moraine at Imja Lake was used, assuming this event is the worst possible scenario that could conceivably occur. This probable maximum inundation was estimated by modeling the event of a full collapse of the moraine following an internal self-destructive piping event that erodes the moraine to the extent that the release of the lake water can maintain the erosion and create a full breach of the moraine [18].…”

“…Stability of the slopes above the glacial lake and of the moraines (terminal and lateral), dynamics of the glacier and lake over time and hydrodynamics in the lake and of the flood downstream converge to produce a GLOF event [5,7,13]. Understanding and predicting the chain of events that lead to a GLOF is highly complex and uncertain.…”

“…By lowering the lake level, pressure on the moraine decreases and the potential surge of water flowing downstream in the event of a flood is decreased, resulting in a smaller inundated area [7,13,18]. A less costly and invasive option is to install early warning systems and community outreach efforts.…”