Drainage pathways beneath ice sheets and their implications for ice sheet form and flow: the example of the British Ice Sheet during the Last Glacial Maximum
Drainage pathways beneath ice sheets and their implications for ice sheet form and flow: the example of the British Ice Sheet during the Last Glacial Maximum
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冰盖下的排水路径及其对冰盖形式和流动的影响：以末次盛冰期英国冰盖为例
DOI：
10.1002/jqs.1407
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发表时间：
2010
影响因子：
2.3
通讯作者：
Boulton G
中科院分区：
文献类型：
--
作者：
Boulton G
冰盖下的排水系统知之甚少，即使它是一个主要的决定因素，其基础边界条件，其形式，流动和稳定性的影响，特别是冰流是关键的动态组件。从以前的冰原上得到的证据可以加强对这一问题的了解。冰川学原理应用于约克谷的地质证据，证明英国冰盖的主要冰流占据，推断重力剪切应力在4-24千帕范围内，而典型的冰川剪切应力约为80-100千帕，终端区的水平速度在400-950千帕范围内。结果表明，冰流是在一个几乎漂浮的状态，与有效的压力在50-100 kPa的范围内的冰压力在2000和5000 kPa之间的范围。英国冰盖南翼的其他冰流也有类似的推论。冰流区域的埃斯克系统代表了冰下排水隧道的位置，这些排水隧道被认为是冰盖中多余的地表水渗透到河床的关键排水要素。河道-地下水耦合的理论，自组织响应水补给率和冰下河床的transmittance被应用到冰下溪流esker系统。当与当地地质证据相匹配时，该理论预测了基底水压力的分布、地表水向冰川床的补给速率、局部剪切应力、沉积过程的区域模式（包括河床变形）及其季节性波动。950 mm年补给率的预测与乌塞（约克谷）流域906 mm现代平均年降雨量的现代值一致。计算出的四条主要冰下河流的平均年流量为55 m3 s-1，而现代乌塞河的平均流量为49 m3 s-1。瞬态分析表明，地下含水层中的水压对地表补给变化的响应时间约为10-100天，这表明冰床界面可能存在不稳定性。然而，不可能确定约克谷冰流的特征是稳定的还是不稳定的（涌动的）流动。版权所有© 2010约翰威利父子有限公司.
The drainage system beneath ice sheets is poorly understood, even though it is a major determinant of their basal boundary condition, with implications for their form, flow and stability, and particularly of the ice streams that are crucial dynamic components. Understanding can be enhanced by evidence from the beds of former ice sheets. Glaciological principles are applied to geological evidence in the Vale of York that demonstrate occupancy by a major ice stream of the British ice sheet, with deduced gravitational shear stresses in the range 4–24 kPa, compared with a typical glacier shear stress of about 80–100 kPa, and horizontal velocities in the terminal zone in the range of 400–950 ma1. It is shown that the ice stream was in an almost buoyant state, with effective pressures in the range 50–100 kPa for a range of ice pressures between 2000 and 5000 kPa. Similar deductions are made for other ice streams on the southern flank of the British ice sheet. The esker system in the area of the ice stream represents locations of subglacial drainage tunnels that are suggested to be the key drainage elements in ice sheets where excess surface water penetrates to the bed. A theory of channel‐groundwater coupling which self‐organises in response to the rate of water recharge and the transmissivity of the subglacial bed is applied to the sub‐ice stream esker system. When matched to local geological evidence, the theory predicts the distribution of basal water pressures, the rate of recharge of surface water to the glacier bed, local shear stresses, the areal pattern of sedimentary processes including bed deformation, and their seasonal fluctuations. Predictions of the annual recharge rate of 950 mm are consistent with the modern values of modern mean annual rainfall in the Ouse (Vale of York) catchment of 906mm. The calculated mean annual discharge of the four major subglacial rivers in 55 m3s−1, compared with a mean flow of the modern Ouse of 49 m3s−1. A transient analysis shows the response time of water pressures in the underlying aquifer to changes in surface recharge to be of the order 10–100 days, suggesting the possibility of instabilities at the ice‐bed interface. It is not possible, however, to determine whether the Vale of York ice stream was characterized by stable or instable (surging) flow. Copyright © 2010 John Wiley & Sons, Ltd.
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