Collaborative Research: Investigation of Englacial Conduit Formation and Evolution

ABSTRACTOPP-00-97137FountainOPP-OO-97095JacobelThis是波特兰州立大学和圣奥拉夫学院首席研究人员共同提出的建议。水在冰川中的运动通过影响冰川底部的应力分布，深刻地影响着冰的运动。因此，大量的研究集中在冰下水运输的水力性质上。对于温带冰川，水的主要来源是地表产生的融化水。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会优先将水引导到冰川床的某些部分，并使冰川床的其他部分挨饿。因此，对控制冰下水力条件空间格局的了解将取决于对将水输送到河床的地表和冰川条件的了解。现有的关于冰河管道的知识在很大程度上是对冰下条件调查的副产品。该项目的目标是调查高山冰川中的冰川管道的位置、大小和水力特性。这个项目将在瑞典塔尔法拉的斯托格拉斯亚伦进行，那里有广泛的科学研究背景，一个活跃的研究计划仍在继续。首席调查员将开展一项为期两年的实地方案，直接探测管道，并使用冰雷达识别和追踪管道路径。低频雷达测量(5 MHz)将定位具有强烈冰川散射的区域，暗示着冰川水袋和潜在的钻探生产区域。雷达还将用于绘制当地海床深度和地形的地图。传统的热水钻探将穿透冰川，与冰川管道相交。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连性，以测量其在流道上的综合水力特性。这项研究将利用100兆赫的高分辨率探地雷达追踪管道的路径，选择的频率既能分辨单个管道，又能监测与水文变化相对应的回波特性的变化。这项研究的结果将加深我们对管道来源和对输水到河床的控制的了解。识别具有已知大小和位置的导管的高分辨率雷达信号将在今后使用冰雷达探测和测绘管道位置方面取得重大进展。NSF建议号：0097137PI：FountainStatement of Work我们将直接测量冰川管道的几何形状和水力学，探测冰川管道的主要方法是钻入冰川直接与管道相交。我们将使用一台能够以1m/min-1速度穿透的热水钻机。我们将尝试在3个不同的阵列中钻20个孔，总共60个孔。在钻井期间，我们将监测钻井深度和水位。如果钻孔的两侧出现开口，并检测到水流，无论是通过水中移动的自然颗粒还是通过悬挂在摄像头上的丝线偏转，将不会在孔中进行进一步的钻孔。如果检测到水流，将进行仔细的水力测量。将记录开口的形状，并测量流速。在每个钻孔阵列内和阵列之间，我们将通过置换一个钻孔中的水并测量其他钻孔中的响应来测试互连性。该项目的数据将测试管道起源和演化的模型。另一项测试将把充满水的管道的测量深度及其水力特性与理论预测的深度进行比较。管道的流动数据和几何形状将被用来检验罗斯伯格(1972)的理论。如果我们能够随着时间的推移监测管道，我们也将测试Spring(1980)的非稳态理论。根据钻孔阵列和雷达成像(Jacobel)，我们将推断出冰川中6个不同位置(超过2年)的管道网络的三维拓扑。这些结果将有助于解决Shreve(1972)和Fountain和Walder(1998)模型之间的差异。更广泛地说，管道网络的空间差异意味着流向河床不同区域的水的流量不同，因此对冰川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发表。

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.