The influence of a poroelastic till on rapid subglacial flooding and cavity formation
The influence of a poroelastic till on rapid subglacial flooding and cavity formation
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DOI：
10.1017/jfm.2018.624
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发表时间：
2018-09-24
影响因子：
3.7
通讯作者：
Neufeld, Jerome A.
中科院分区：
文献类型：
--
作者：
Hewitt, Duncan R.;Chini, Gregory P.;Neufeld, Jerome A.
我们开发了一个模型，在弹性冰川冰和多孔弹性冰下冰碛之间的接触水的快速传播，在格陵兰岛的冰上湖泊的快速排水观测的动机。通过将冰视为弹性弯曲梁，可以详细研究与冰下水文网络（模拟为饱和多孔弹性冰碛物）接触的流体动力学。该模型描述了一个轴对称的冰下洞穴的形成和动力学，以及孔隙压力的传播，响应于注入流体。数值模拟和渐近分析的组合被用来描述这些动态的刚性和可变形的多孔直到，层流和湍流流体流动。对于恒定的注入速率和层流，空腔是均衡的，并且其扩展由冰的弯曲和冰-冰碛接触附近的孔隙水的吸力控制。对于一个可变形的直到，这种控制可以修改：一般来说，一个弯曲波，最初被困在接触点的前面松弛随着时间的推移，通过扩散的孔隙压力提前的空腔。虽然动态被发现是相对不敏感的冰下直到在注射过程中具有恒定的流量的属性，显着的依赖性直到属性是在随后的传播过程中表现出一个恒定的体积。一个简单的混合动力的湍流层流模型来考虑快速注入速率的水：在这种情况下，自相似的湍流传播最初可以控制蔓延的空腔，但有一个过渡到层流控制附近的冰，直到接触点的流动减慢。最后，模型的结果进行了比较，最近的地球物理观测的快速排水的冰上湖在格陵兰岛的比较提供了定性的协议，并提出了建议，为今后的定量比较。
We develop a model of the rapid propagation of water at the contact between elastic glacial ice and a poroelastic subglacial till, motivated by observations of the rapid drainage of supraglacial lakes in Greenland. By treating the ice as an elastic bending beam, the fluid dynamics of contact with the subglacial hydrological network, which is modelled as a saturated poroelastic till, can be examined in detail. The model describes the formation and dynamics of an axisymmetric subglacial cavity, and the spread of pore pressure, in response to injection of fluid. A combination of numerical simulation and asymptotic analysis is used to describe these dynamics for both a rigid and a deformable porous till, and for both laminar and turbulent fluid flow. For constant injection rates and laminar flow, the cavity is isostatic and its spread is controlled by bending of the ice and suction of pore water in the vicinity of the ice-till contact. For a deformable till, this control can be modified: generically, a flexural wave that is initially trapped in advance of the contact point relaxes over time by diffusion of pore pressure ahead of the cavity. While the dynamics are found to be relatively insensitive to the properties of the subglacial till during injection with a constant flux, significant dependence on the till properties is manifest during the subsequent spread of a constant volume. A simple hybrid turbulent-laminar model is presented to account for fast injection rates of water: in this case, self-similar turbulent propagation can initially control the spread of the cavity, but there is a transition to laminar control in the vicinity of the ice-till contact point as the flow slows. Finally, the model results are compared with recent geophysical observations of the rapid drainage of supraglacial lakes in Greenland; the comparison provides qualitative agreement and raises suggestions for future quantitative comparison.