Mechanisms of englacial conduit formation and their implications for subglacial recharge
Mechanisms of englacial conduit formation and their implications for subglacial recharge
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冰河管道形成机制及其对冰下补给的影响
DOI：
10.1016/j.quascirev.2009.04.002
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发表时间：
2009
影响因子：
4
通讯作者：
Jonathan B. Martin
中科院分区：
文献类型：
--
作者：
J. Gulley;D. Benn;E. Screaton;Jonathan B. Martin
Shreve[1972]发展的理论模型深刻地影响了人们对河流排水系统的特征和演变的看法。冰川中的水的运动。冰川学杂志11(62)，205-214]。Shreve模型基于三个主要假设：(1)冰川排水处于稳定状态；(2)冰川水将沿着冰川内最陡峭的水力坡度流动；(3)由于冰墙融化，压力水头等于周围冰的压力减去一个小分量。Shreve模型作为流域排水理论的基本组成部分已被广泛采用。然而，没有证据表明该模型提供了实际冰川排水系统的真实图景。为了评价史瑞夫的理论，我们使用洞穴学技术直接调查了冰川管道。我们绘制了2005至2008年间在温带、多热、寒冷和残骸覆盖的冰川中27条不同的冰川上总计8.25公里的通道。除了这里报道的新信息外，还公布了世界各地其他40条输气管道的数据，这些管道使用洞穴技术对176米深的冰层进行了勘测。在所有情况下，排水系统都由一根不分叉的管道组成。冰川管道形态被发现与冰川主应力的方向或先前存在的高水力传导性线路的存在密切相关。如果有足够的水供应，水力压裂就会在纵向应力为压应力的纵向延伸区和水平以下的管道中形成垂直管道。在未破裂的冰川表面，相对较浅的水平以下的导管和迁移的镍点形成切割和关闭，如果渠道切割明显快于地表下降。管道也可以沿着可渗透的碎片填充的裂缝痕迹形成，这些裂缝连接着不同潜力的冰上湖盆。我们的结果表明，Shreve类型的冰川排水系统并不存在，这意味着冰川管道只能穿透厚厚的冰来为冰上水体与加速带相交或平流处的河床补给。
Ideas about the character and evolution of englacial drainage systems have been deeply influenced by the theoretical model developed by Shreve [1972. Movement of water in glaciers. Journal of Glaciology 11(62), 205–214]. The Shreve model is based on three main assumptions: (1) englacial drainage is in steady state; (2) englacial water will flow along the steepest hydraulic gradient within the glacier; and (3) pressure head equals the pressure of the surrounding ice minus a small component due to melting of the walls. The Shreve model has been widely adopted as a fundamental component of englacial drainage theory. There is no evidence, however, that the model provides a realistic picture of actual glacial drainage systems. To evaluate Shreve's theory, we used speleological techniques to directly survey englacial conduits. We mapped a total of 8.25km of passage in 27 distinct englacial conduits in temperate, polythermal, cold-based and debris-covered glaciers between 2005 and 2008. New information reported here is supplemented by published data on 40 other englacial conduits located worldwide and surveyed to ice depths of 176m using speleological techniques. In all cases, englacial drainage systems consisted of a single unbranching conduit. Englacial conduit morphologies were found to be intimately linked to the orientation of a glacier's principal stresses or the presence of pre-existing lines of high hydraulic conductivity. If a sufficient supply of water is available, hydrofracturing forms vertical conduits in zones of longitudinal extension and subhorizontal conduits where longitudinal stresses are compressive. On unfractured glacier surfaces, relatively shallow subhorizontal conduits with migrating nickpoints form by cut-and-closure provided channel incision is significantly faster than surface lowering. Conduits can also form along permeable debris-filled crevasse traces that connect supraglacial lake basins of different potential. Our results suggest that Shreve-type englacial drainage systems do not exist and implies that englacial conduits can only penetrate through thick ice to recharge the bed where supraglacial water bodies either intersect, or are advected through, zones of acceleration.