Reconstruction of the 1941 GLOF process chain at Lake Palcacocha (Cordillera Blanca, Peru)
Reconstruction of the 1941 GLOF process chain at Lake Palcacocha (Cordillera Blanca, Peru)
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DOI：
10.5194/hess-24-93-2020
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发表时间：
2020-01-09
影响因子：
6.3
通讯作者：
Frey, Holger
中科院分区：
文献类型：
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作者：
Mergili, Martin;Pudasaini, Shiva P.;Frey, Holger
秘鲁的布兰卡山脉几十年来一直是冰川迅速消融的地方。在冰川消退的前方形成的众多湖泊之一是冰碛坝的帕尔卡科查湖，由于不明原因，该湖于1941年突然干涸。由此产生的冰川湖溃决洪水导致大坝倒塌，下游的Jircacocha湖完全排水，并在23公里外的瓦拉斯市造成重大破坏和数千人死亡。我们选择了一种综合的方法来重新审视1941年的事件，在地形重建和基于GIS的开源质量流/过程链模拟框架r.avaflow的数值反算方面，该框架建立在Pudasaini（2012）两相流模型的增强版本上。因此，我们认为四种情况：（A）和（AX）由于退化侵蚀，假设两种不同的流体特性的帕尔卡科查湖的冰碛坝的突破;（B）湖上的滑坡的影响所造成的冰碛坝的故障;和（C）地质力学故障和冰碛坝的崩溃。模拟在很大程度上产生了经验上足够的结果，物理上合理的参数，以1941年事件的文件和以前对未来情景的计算作为参考。大多数模拟情景表明，到达瓦拉斯的行程时间在36到70分钟之间，峰值流量超过10 000 m（3）s（-1）。情景的结果表明，最有可能的启动机制将是退行性侵蚀，可能引发的轻微冲击波和/或促成了一个薄弱的稳定条件的冰碛坝。然而，Jircacocha湖的参与掩盖了下游进程启动的部分信号。未来可能发生的事件的预测模拟必须基于一组较大的反算GLOF过程链，同时考虑到预期的参数不确定性和处理临界阈值效应的适当策略。
The Cordillera Blanca in Peru has been the scene of rapid deglaciation for many decades. One of numerous lakes formed in the front of the retreating glaciers is the moraine-dammed Lake Palcacocha, which drained suddenly due to an unknown cause in 1941. The resulting Glacial Lake Outburst Flood (GLOF) led to dam failure and complete drainage of Lake Jircacocha downstream, and to major destruction and thousands of fatalities in the city of Huaraz at a distance of 23 km. We chose an integrated approach to revisit the 1941 event in terms of topographic reconstruction and numerical back-calculation with the GIS-based open-source mass flow/process chain simulation framework r.avaflow, which builds on an enhanced version of the Pudasaini (2012) two-phase flow model. Thereby we consider four scenarios: (A) and (AX) breach of the moraine dam of Lake Palcacocha due to retrogressive erosion, assuming two different fluid characteristics; (B) failure of the moraine dam caused by the impact of a landslide on the lake; and (C) geomechanical failure and collapse of the moraine dam. The simulations largely yield empirically adequate results with physically plausible parameters, taking the documentation of the 1941 event and previous calculations of future scenarios as reference. Most simulation scenarios indicate travel times between 36 and 70 min to reach Huaraz, accompanied with peak discharges above 10 000 m(3)s(-1). The results of the scenarios indicate that the most likely initiation mechanism would be retrogressive erosion, possibly triggered by a minor impact wave and/or facilitated by a weak stability condition of the moraine dam. However, the involvement of Lake Jircacocha disguises part of the signal of process initiation farther downstream. Predictive simulations of possible future events have to be based on a larger set of back-calculated GLOF process chains, taking into account the expected parameter uncertainties and appropriate strategies to deal with critical threshold effects.