Collaborative Research: Investigation of Englacial Conduit Formation and Evolution

这是波特兰州立大学和圣奥拉夫学院的主要研究人员合作提出的一项建议。水在冰川中的运动通过影响冰川床上的应力分布而深刻地影响冰的运动。因此，对冰下输水的水力性质进行了大量的研究。对于温带冰川，水的主要来源是地表产生的融水。这些水如何到达冰川床是至关重要的。地表和冰川条件可能优先引导水流到冰川床的某些部分，而使床的其他部分挨饿。因此，对冰下水力条件空间格局控制的理解将取决于对将水输送到河床的地表和冰川条件的理解。现有的关于冰川管道的知识在很大程度上是对冰下条件研究的副产品。本项目的目的是研究高山冰川中冰川导管的位置、大小和水力特性。该项目将在瑞典Tarfala的Storglaciaren进行，那里有广泛的科学工作背景，并且积极的研究计划仍在继续。主要研究人员将进行为期两年的实地项目，直接探测冰川管道，并使用冰雷达识别和跟踪管道路径。低频雷达测量（5mhz）将定位具有强烈冰川散射的区域，这表明存在冰川水袋和潜在的钻井生产区域。该雷达还将用于绘制当地的地层深度和地形。传统的热水钻探将穿透冰川，与冰川管道相交。在遇到管道后，他们将使用井下仪器测量管道直径、水压和水流速度。他们将尝试确定管道之间的互联性，以测量其在流道上的综合水力性能。管道的路径将使用100兆赫的高分辨率探地雷达进行跟踪，该频率既可以分辨单个管道，也可以监测随时间变化的水文变化的回波特征变化。这项研究的结果将进一步加深我们对管道起源和对水流向河床的控制的理解。用已知大小和位置的导管识别高分辨率雷达信号，将对今后使用冰雷达探测和绘制冰川导管位置取得重大进展。我们将直接测量冰川导管的几何和水力学。探测冰川导管的主要方法是钻入冰川直接与导管相交。我们将使用钻速为每分钟1米的热水钻头。我们将尝试在3个不同的阵列中钻20个井眼，总共钻60个孔。在钻探过程中，我们将监测钻探深度和水位。如果井眼两侧出现开口，并且通过水中的自然颗粒移动或通过悬挂在摄像机上的线的偏转检测到流动，则不会在井眼中进行进一步钻探。如果检测到流量，将进行仔细的水力测量。开口的形状将被记录下来，流速将被测量。在每个井眼阵列和阵列之间，我们将通过在一个井眼中置换水并测量其他井眼的响应来测试互连性。该项目的数据将测试管道起源和演变的模型。另一项试验将对充水管道的测量深度及其水力特性与理论预测进行比较。管道的流动数据和几何形状将用于检验Rothlisberger（1972）的理论。如果我们能够长期监测管道，我们也将测试Spring（1980）的非稳态理论。从钻孔阵列和雷达成像（Jacobel）中，我们将推断冰川中6个不同位置（超过2年）管道网络的三维拓扑结构。这些结果将有助于解决Shreve（1972）和Fountain and Walder（1998）模型之间的差异。更一般地说，管道网络的空间差异意味着流向河床不同区域的水通量的差异，因此对冰下水力系统的发展施加了外部条件。这些结果将在几篇期刊文章中报道。

ABSTRACTOPP-00-97137FountainOPP-OO-97095JacobelThis is a collaborative proposal from Principal Investigators at Portland State University and St. Olaf College. The movement of water through glaciers profoundly affects ice motion by influencing the stress distribution at the bed of the glacier. Therefore, a great deal of research has focused on the hydraulic nature of subglacial water transport. For temperate glaciers, the main source of water is surface-generated melt water. How this water reaches the glacier bed is of critical importance. Surface and englacial conditions may preferentially direct water flow to certain parts of the glacier bed and starve other parts of the bed. Therefore, an understanding of the controls on the spatial pattern of subglacial hydraulic conditions will depend on an understanding of the surficial and englacial conditions routing the water to the bed. Existing knowledge of englacial conduits has largely been a by-product of investigations into subglacial conditions. The goal of this project is to investigate the location, size, and hydraulic character of englacial conduits in an alpine glacier. This project will take place on the Storglaciaren in Tarfala, Sweden, where an extensive background of scientific wok exists and an active research program continues. The Principal Investigators will undertake a two-year field program that directly detects englacial conduits and uses ice radar to identify and trace the conduit paths. Low frequency radar measurements (5 MHz) will locate regions with strong englacial scattering suggestive of englacial water pockets and potentially productive areas for drilling. The radar will also be used to map the local bed depth and topography. Conventional hot-water drilling will penetrate the glacier to intersect englacial conduits. After a conduit is encountered, they will measure conduit diameter, water pressure, and water flow speed using down-hole instruments. They will attempt to determine the interconnectivity between conduits to measure their integrated hydraulic properties over the flow path. The path of the conduits will be traced using a high-resolution ground penetrating radar operated at 100 MHz, a frequency chosen both resolve individual conduits, and to monitor changes in echo characteristics corresponding to hydrologic changes over time.The results from this study will further our understanding of conduit origin and the controls on water routing to the bed. Identification of high-resolution radar signals with conduits of known sizes and locations will make significant progress towards future use of ice radar for detecting and mapping the location of englacial conduit. NSF Proposal Number: 0097137PI: FountainStatement of WorkWe will directly measure the geometry and hydraulics of englacial conduits The principle method of detecting englacial conduits will be drilling into the glacier to directly intersect the conduits. We will employ a hot-water drill capable of penetrating at rates of 1 m min-1. We will attempt to drill 20 boreholes in 3 different arrays for a total of 60 holes. During drilling we will monitor both drill depth and water levels. If openings appear on both sides of the borehole and flow is detected, either by natural particulates moving in the water or by a deflection of thread hanging from the camera, no further drilling in the hole will occur. If flow is detected careful hydraulic measurements will be made. The shape of the opening will be recorded and flow velocities will be measured. Within each borehole array and between arrays, we will test for interconnectivity by displacing the water in one borehole and measuring the response in other boreholes. The data from this project will test a model for the origin and evolution of conduits. Another test will compare the measured depth of a water-filled conduit and its hydraulic characteristics to that predicted by theory. The flow data and geometry of the conduits will be used to test Rothlisberger's (1972) theory. If we are able to monitor conduits over time we will also test Spring's (1980) non-steady state theory. From the borehole arrays and the radar imaging (Jacobel) we will infer the 3-dimensional topology of the conduit network at 6 different locations (over 2 years) in the glacier. These results will help to resolve the differences between the models of Shreve (1972) and Fountain and Walder (1998). More generally, spatial differences in the conduit networks imply differences in the flux of water to different areas of the bed and therefore impose an external condition on the development of subglacial hydraulic systems. These results will be reported in several journal articles.