The Bering-Bagley Glacier System (BBGS), Alaska, Earth's largest temperate surging glacier, surged in 2008–2013. We use numerical modeling and satellite observations to investigate how surging in a large and complex glacier system differs from surging in smaller glaciers for which our current understanding of the surge phenomenon is based. With numerical simulations of a long quiescent phase and a short surge phase in the BBGS, we show that surging is more spatiotemporally complex in larger glaciers with multiple reservoir areas forming during quiescence which interact in a cascading manner when ice accelerates during the surge phase. For each phase, we analyze the simulated elevation-change and ice-velocity pattern, infer information on the evolving basal drainage system through hydropotential analysis, and supplement these findings with observational data such as CryoSat-2 digital elevation maps. During the quiescent simulation, water drainage paths become increasingly lateral and hydropotential wells form indicating an expanding storage capacity of subglacial water. These results are attributed to local bedrock topography characterized by large subglacial ridges that dam the down-glacier flow of ice and water. In the surge simulation, we model surge evolution through Bering Glacier's trunk by imposing a basal friction representation that mimics a propagating surge wave. As the surge progresses, drainage efficiency further degrades in the active surging-zone from its already inefficient, end-of-quiescence state. Results from this study improve our knowledge of surging in large and complex systems which generalizes to glacial accelerations observed in outlet glaciers of Greenland, thus reducing uncertainty in modeling sea-level rise.

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从观测和数值模拟看白令-巴格利冰川系统的涌动周期的演变

阿拉斯加的白令-巴格利冰川系统 (BBGS) 是地球上最大的温带汹涌冰川，在 2008 年至 2013 年期间激增。我们使用数值模型和卫星观测来研究大型复杂冰川系统中的涌动与较小冰川中的涌动有何不同，这是我们目前对涌动现象的理解的基础。通过对 BBGS 中长静止期和短涌动期的数值模拟，我们表明，在较大的冰川中，涌动在时空上更加复杂，在静止期间形成多个库区，当冰在涌动期加速时，这些库区以级联方式相互作用。对于每个阶段，我们分析模拟的海拔变化和冰速模式，通过水势分析推断不断变化的基础排水系统的信息，并用 CryoSat-2 数字高程图等观测数据补充这些发现。在静态模拟过程中，排水路径变得越来越横向，水势井的形成表明冰下水的储存能力不断扩大。这些结果归因于当地的基岩地形，其特征是大型冰下山脊阻碍了冰和水的向下流动。在浪涌模拟中，我们通过施加模仿传播浪涌波的基础摩擦表示来模拟白令冰川干线的浪涌演化。随着浪涌的进行，活跃浪涌区的排水效率从本来就低效的静止状态进一步下降。这项研究的结果提高了我们对大型复杂系统中涌动的认识，该系统可推广到格陵兰岛出口冰川中观察到的冰川加速，从而减少海平面上升建模的不确定性。