BOREHOLE WATER-LEVEL VARIATIONS AND THE STRUCTURE OF THE SUBGLACIAL HYDROLOGICAL SYSTEM OF HAUT GLACIER DAROLLA, VALAIS, SWITZERLAND
BOREHOLE WATER-LEVEL VARIATIONS AND THE STRUCTURE OF THE SUBGLACIAL HYDROLOGICAL SYSTEM OF HAUT GLACIER DAROLLA, VALAIS, SWITZERLAND
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DOI：
10.3189/s0022143000034894
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发表时间：
1995-01-01
影响因子：
3.4
通讯作者：
SMART, CC
中科院分区：
文献类型：
--
作者：
HUBBARD, BP;SHARP, MJ;SMART, CC
夏末冰下水的压力已被测量在一个密集的阵列钻孔的消融区的Haut冰川d 'Arolla，瑞士。内插表面的最小昼夜水压和昼夜水压变化表明存在一个冰下通道内一个更广泛的，分布式排水系统。该水道沿着可变压力轴（VPA）的中心流动，有些宽达米，其特征是昼夜最小水压（通常为大气压）低，昼夜水压变化高。这些特征在横向距离c以上是过渡性的。70米，以更高和更稳定的冰下水压力在邻近的分布式系统。位于靠近瓦VPA中心的钻孔中记录的水压变化反映了地表融水向冰川床的输送，并导致了一个昼夜逆转的横向水力梯度，该水力梯度在下午将水从通道中排出进入分布式系统，并在夜间返回通道。冰下观测表明，这种流动是通过垂直封闭的沉积层发生的。钻孔浊度记录表明，由此产生的昼夜水流是负责动员和运输悬浮液中的细碎屑。通过对周日压力波传播速度和振幅衰减的分析表明，沉积层的导水率随距河道距离的增加呈指数下降，从c. 10（-4）m s（-1）在区块通道边界到c。10（-7）m s（-1）70 m au-av.这些表观水力传导率是一致的达西流通过干净的沙子和典型的冰川till，分别。我们认为，细料是系统地冲洗从位于附近的大型，融化季节排水通道下温暖的冰川底部的基底沉积物。这一过程马！对冰川侵蚀模式、水化学和动力学有重要影响。
Late-summer subglacial water pressures have been measured in a dense array of boreholes in the ablation area of Haut Glacier d'Arolla, Switzerland. Interpolated sur faces of minimum diurnal water pressure and diurnal water-pressure variation suggest the presence of a subglacial channel within a more widespread, distributed drainage system. The channel flows along the centre of a variable pressure axis (VPA), some tells of metres wide, that is characterized by low minimum diurnal water pressures (frequently atmospheric) and high diurnal water-pressure variations. These characteristics are transitional ol-er a lateral distance of c. 70 m to higher and more stable subglacial water pressures in the adjacent distributed system. Water-pressure variations recorded in boreholes located close to the centre of tile VPA reflect the delivery of surface-derived meltwater to the glacier bed and result in a diurnally reversing, transverse hydraulic gradient that drives water out from the channel into the distributed system during the afternoon and back to the channel overnight. Subglacial observations suggest that such flow occurs through a vertically confined sediment la)er. Borehole turbidity records indicate that the resulting diurnal water flows are responsible for the mobilization and transport of fine debris in suspension. Analysis of the propagation velocity and amplitude attenuation of the diurnal pl es;sure waves suggests that the hydraulic conductivity of the sediment layer decreases exponentially with distance from the channel, falling fr om c. 10(-4) m s(-1) at tile channel boundary to c. 10(-7) m s(-1) 70m au-av. These apparent hydraulic conductivities are consistent with Darcian flow through clean sand and typical glacial till, respectively.We suggest that fine material is systematically flushed from basal sediments located adjacent to large, melt-season drainage channels beneath warm-based glaciers. This process ma! have important implications for patterns of glacier erosion, hydrochemistry and dynamics.