Seismological Investigation of Columbia Glacier Calving Mechanics

冰山崩解是许多海洋冰川质量损失的主要组成部分，并与潮水冰川退缩的动力学密切相关。尽管它很重要，但人们对产犊过程知之甚少。随着人们更好地了解阿拉斯加冰川在现代全球物质平衡中的重要性，以及认识到现代潮水冰川作为海洋古冰盖快速消退的类比的作用，了解崩解和潮水冰川动力学的必要性变得更加紧迫。自20世纪80年代初S以来，人们对哥伦比亚冰川进行了研究，并获得了大量有用的数据。然而，随着哥伦比亚冰川消退的加速，研究它的重要性增加了。它是阿拉斯加主要潮水冰川中最后一条从延伸位置退缩的冰川，也是目前世界上最快的冰川(年产12公里)，每年通过崩解向海洋排放大约22公里的冰，并可能在25年内或更短的时间内完成退缩。首席调查员将追求三个目标：1)对1997-1999年拍摄的照片确定的运动学进行详细分析，描述冰川航道在终点处约4公里范围内的水流状况、应变率特征、边界牵引力和河床深度。将在1999年地面摄影测量的基础上，完成对冰川最低5公里处应变率空间不均一性的地质统计分析。这项工作将由2000年至2001年期间的额外航空摄影补充。对与不可逆潮水退缩有关的运动波的上游传播的理论分析将说明，基底滑动可能是潮水退缩的间歇性和一般不可逆性的最终原因；2)使用现代地震记录设备对冰川冰川和崩解活动的观测相对不成熟。首席调查员将分析这些数据集，以开发改进未来部署和数据分析的技术。目标是利用已知震源确定一阶时频域震源特性。他还将把烟纸记录数字化，以便在标准软件包中进行分析，并将改进的事件探测软件应用于数字化数据集；3)2002年8月的照片飞行是1976年开始的不间断航空摄影系列中的第124次和第125次飞行，我们关于1980年左右以来的撤退模式的大部分知识都是基于这些飞行。未来的摄影测量分析现在成为他的责任，因为摄影测量程序相当简单，但识别摄影中正确特征的实际过程并非如此。因此，这个问题最难的部分适合冰川学家的技能，而不是摄影测量学家，所以他将购买新的数字(‘软拷贝’)摄影测量软件。

ABSTRACTOPP-024072PfefferIceberg calving is a major component of mass loss from many marine glaciers and is intimately connected with the dynamics of tidewater glacier retreat. Despite its importance, the calving process is very poorly understood. The need to understand calving and tidewater glacier dynamics becomes more pressing as the importance of Alaskan glaciers in modern global mass balance is better understood, and as the utility of modern tidewater glaciers as analogs for rapid retreat of marine-based paleo ice sheets is recognized. The Columbia Glacier has been studied since the early 1980's, and has yielded a large volume of very useful data. The importance of studying Columbia Glacier increases, however, as its retreat accelerates. It is the last of Alaska's major tidewater glaciers to retreat from its extended position, and currently the world's fastest glacier (at 12 km yr-1), which discharges approximately 22 km3 per year of ice into the ocean via calving, and may complete its retreat within 25 years or less.The Principal Investigator will pursue three objectives: 1) a detailed analysis of kinematics determined from the 1997- 1999 photography which describes the flow regime, strain rate characteristics, boundary tractions, and bed depth in the glacier channel within about four km of the terminus will be done. Geostatistical analysis of spatial heterogeneity of strain rates in the lowest five km of the glacier, based on terrestrial photogrammetry from 1999 ground-based photography will be completed. This work will be supplemented by additional aerial photography from 2000 and 2001. Theoretical analysis of upstream propagation of kinematic waves associated with irreversible tidewater retreat which shows how basal sliding may be the ultimate cause of the episodic and generally irreversible character of tidewater retreat will be addressed; 2) Observations of glacial icequake and calving activity using modern seismic recording equipment is relatively immature. The Principal Investigator will analyze these data sets to develop techniques that will improve future deployment and data analysis. The goal is to determine first-order time and frequency domain source characteristics, using known seismic sources. He will also digitize the smoked-paper records to enable analysis in standard software packages and apply the refined event detection software to the digitized data set; and 3) The August 2002 photo flights are the 124th and 125th flights in an unbroken series of aerial photography started in 1976, and from which most of our knowledge on the pattern of retreat since around 1980 is based. Future photogrammetric analysis now becomes his responsibility because the photogrammetric procedures are fairly straightforward, but the actual process of recognizing the correct features in the photography is not. Thus, the most difficult part of the problem is suited to the skills of a glaciologist than a photogrammetrist, so he will purchase new digital ('softcopy') photogrammetric software.