RHEOLOGICAL NONLINEARITY AND FLOW INSTABILITY IN THE DEFORMING BED MECHANISM OF ICE STREAM MOTION
RHEOLOGICAL NONLINEARITY AND FLOW INSTABILITY IN THE DEFORMING BED MECHANISM OF ICE STREAM MOTION
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冰流运动变形床机制的流变非线性和流动不稳定性
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发表时间：
1991
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通讯作者：
B. Kamb
中科院分区：
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作者：
B. Kamb
根据土壤力学和冰流B底部冰碛的初步实验资料，与最近在模拟南极冰流快速运动的变形床机制时所假设的相反，水饱和冰碛的流变学可能是高度非线性的。等效流动定律指数n可能高达1000，并且剪切应力和有效压力依赖性的非线性是密切相关的。高非线性对变形床机理有重要影响。通过这种机制操作的流动系统可能是不稳定的，这是由于通过基底冰碛物的剪切加热产生基底水的反馈。短期的反馈效应进行了分析，在一个模型冰流中的基础融水是通过一个分布式系统的狭窄的间隙导管在冰，直到界面的扰动。虽然分析是近似的，一些系统参数知之甚少，结果表明，变形床机制是不稳定的n > 20。在目前活跃的冰流中明显缺乏这种不稳定性，这意味着它们的运动不是由变形床机制控制的，而是由其他一些尚未确定的机制控制的。
Contrary to what has recently been assumed in modeling the proposed deforming bed mechanism for the rapid motion of Antarctic ice streams, the rheology of water saturated till is probably highly nonlinear, according to information from soil mechanics and preliminary experiments on till from the base of Ice Stream B. The equivalent flow law exponent n is probably as high as ∼100, and the nonlinearities of the shear stress and effective pressure dependences are closely linked. The high nonlinearity has important consequences for the deforming bed mechanism. A flow system operating by this mechanism can be unstable as a result of feedback from the generation of basal water by shear heating of basal till. The short-term feedback effect is analyzed for a perturbation in a model ice stream in which the basal meltwater is transported through a distributed system of narrow gap-conduits at the ice-till interface. Although the analysis is approximate and some of the system parameters are poorly known, the results suggest that the deforming bed mechanism is unstable for n > ∼ 20. The apparent lack of such an instability in the currently active ice streams implies that their motion is controlled not by the deforming bed mechanism but by some other as yet unidentified mechanism.