Seismological Investigation of Columbia Glacier Calving Mechanics

冰山崩解是许多海洋冰川质量损失的重要组成部分，与潮汐冰川退缩动力学密切相关。尽管它很重要，但人们对产犊过程知之甚少。随着阿拉斯加冰川在现代全球物质平衡中的重要性得到更好的理解，以及现代潮汐冰川作为海洋古冰盖快速退缩的类似物的效用得到认识，了解冰裂和潮汐冰川动力学的需求变得更加迫切。自20世纪80年代初以来，人们一直在研究哥伦比亚冰川，并获得了大量非常有用的数据。然而，随着哥伦比亚冰川的加速消退，研究它的重要性也在增加。它是阿拉斯加主要的潮汐冰川中最后一个从其延伸位置退缩的冰川，也是目前世界上最快的冰川（以每年12公里的速度），每年通过崩解向海洋排放约22立方公里的冰，并可能在25年内或更短的时间内完成退缩。首席研究员将追求三个目标：1)对1997- 1999年拍摄的照片进行详细的运动学分析，其中描述了冰川终点站约4公里范围内的流动状况、应变速率特征、边界牵引力和河床深度。将完成基于1999年陆基摄影测量的冰川最低5公里应变率空间异质性的地质统计学分析。在2000年和2001年，将会有额外的航空摄影作为补充。对与不可逆退潮有关的运动波的上游传播进行理论分析，表明基底滑动可能是退潮的偶发性和一般不可逆特征的最终原因；2)利用现代地震记录设备对冰川冰震和冰裂活动的观测相对不成熟。首席研究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间和频域震源特性。他还将把烟纸记录数字化，以便在标准软件包中进行分析，并将改进的事件检测软件应用于数字化的数据集；2002年8月的照片飞行是1976年开始的不间断航空摄影系列的第124次和第125次飞行，我们对1980年左右以来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了他的责任，因为摄影测量程序相当简单，但在摄影中识别正确特征的实际过程却不是这样。因此，这个问题最困难的部分更适合冰川学家的技能，而不是摄影测量师，所以他会购买新的数字（“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.