The effect of discrete recharge by moulins and heterogeneity in flow-path efficiency at glacier beds on subglacial hydrology
The effect of discrete recharge by moulins and heterogeneity in flow-path efficiency at glacier beds on subglacial hydrology
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DOI：
10.3189/2012jog11j189
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发表时间：
2012-01-01
影响因子：
3.4
通讯作者：
Glowacki, P.
中科院分区：
文献类型：
--
作者：
Gulley, J. D.;Grabiec, M.;Glowacki, P.
冰川下管道系统被认为是由树枝状网络组成的，树枝状网络存在的压力低于分布式系统，其位置由理论水力潜力确定。然而，在有冰山的冰川上，融化的水在离散的点被输送到冰川床上，这违反了计算潜力所需的均匀补给的假设。为了了解冰川对冰下管道水文的影响，我们使用洞穴技术绘制了斯瓦尔巴特群岛汉斯布林冰川底部0.4公里的冰下管道，并将我们的观测结果与理论预测进行了比较。导管开始于一个预计缺乏引流的区域，以斜角而不是直角穿过等势线，局部吻合而不是树枝状。由冰上河流和冰缝的位置决定的冰川位置控制着冰下补给的位置。由于管道与有效压力的梯度没有直接的因果关系，这种补给可以在冰川床地区形成管道，而水力势能理论可能无法预测这些区域有管道。通过冰下管道的补给，使得管道中的水头增加得更快，并达到比邻近分布式系统中更高的值，从而导致冰川在冰下管道上方的滑动速度增加而不是减少。
Subglacial conduit systems are thought to consist of dendritic networks that exist at lower pressure than distributed systems and have locations that are determined by theoretical hydraulic potential. On glaciers with moulins, however, meltwater is delivered to glacier beds at discrete points, violating assumptions of uniform recharge needed to calculate potential. To understand how moulins affect subglacial conduit hydrology, we used speleological techniques to map 0.4 km of subglacial conduit at the base of a moulin in Hansbreen, Svalbard, and compared our observations with theoretical predictions. The conduit began in an area predicted to lack drainage, crossed equipotential contours at oblique rather than right angles and was locally anastomotic rather than dendritic. We propose moulin locations, which are determined by the locations of supraglacial streams and crevasses, control locations of subglacial recharge. Because conduits have no direct causal relationship with gradients in effective pressure, this recharge can form conduits in areas of glacier beds that may not be predicted by hydraulic potential theory to have conduits. Recharge by moulins allows hydraulic head to increase in conduits faster and to higher values than in adjacent distributed systems, resulting in an increase rather than a decrease in glacier sliding speeds above subglacial conduits.