Seismological Investigation of Columbia Glacier Calving Mechanics

山地冰川和小型冰帽共同构成了全球陆地冰的重要组成部分（阿拉斯加和邻近的加拿大冰川占世界冰川面积的13%，不包括南极洲和格陵兰岛）。 尽管没有很好地解决质量平衡，最近的证据表明，阿拉斯加冰川，凭借其大的集体面积，快速响应的特点，和高质量通量，有助于现代海平面上升的速度比以前认为的大约7倍。 阿拉斯加冰川的大部分质量损失来自于间歇性的冰川，它们的前进和后退是间歇性的，长时间的前进和稳定被快速的、显然不可逆转的后退所打断。在退缩过程中，冰川物质平衡主要是由人们知之甚少的冰山崩解过程控制的，而不是直接的气候强迫，流入海洋的冰流量可能非常大。 哥伦比亚冰川目前正以每年约22立方公里的速度向海洋排放冰山。 因此，冰川崩解是现代冰川变化和海平面上升的一个重要但知之甚少的因素。 主要研究人员目前在哥伦比亚冰川的工作计划有两个重点，每一个致力于增加理解的作用，冰解在冰川退缩。 首先，他们将继续他们的航空摄影计划，因为冰川终点通过一个主要的通道收缩撤退。其次，他们将对产犊过程进行被动地震学调查。 这项工作的动机是小冰川（特别是阿拉斯加的冰川）的重要性，现代全球冰川质量平衡和海平面变化，需要更好地了解在冰川动力学的作用，冰解。 此外，哥伦比亚冰川是阿拉斯加冰川中最后一个退缩的冰川，部分处于退缩阶段，并处于其通道几何形状的关键位置。 这种研究定时产犊的机会将在几十年内消失，所以现在利用它很重要。 潮水崩解是冰川动力学和冰/海洋相互作用的重要组成部分，但仍然知之甚少。 由于缺乏相关的观察和缺乏相关观察的知识，更好地了解产犊的进展受到阻碍。 这项研究将提供一个非常成功的航空摄影观测计划的延续，该计划已经产生了有史以来最长和最详细的冰川运动学观测记录，并形成了目前已知的大部分关于冰川动力学的基础。主要研究人员将开始对哥伦比亚冰川进行一系列新的地震观测，试图详细发现导致冰解的断裂事件的时间、位置和几何形状。以前对包括哥伦比亚冰川在内的冰川进行了有限的地震调查，但数据采集和处理方面的现代进步将使他们能够更有效地利用地震学，并更详细地观察断裂和冰解。 拟议活动产生的更广泛影响：除了在现代海平面变化中的作用外，冰川崩解在过去对全球冰盖和气候动态也发挥了关键作用。 来自北大西洋的充分证据表明，被动的情景产犊是必不可少的快速解体的劳伦泰德冰盖（LIS），但目前的LIS重建不试图纳入产犊过程，由于缺乏一个数学产犊关系。 然而，冰盖建模者渴望有关产犊过程的输入，以纳入LIS模型。 此外，对定时产犊的了解为南极和格陵兰的海洋终结冰提供了有用的交叉知识 产犊发生频率低得多的地方。

Mountain glaciers and small ice caps collectively constitute a significant fraction of global land ice (Alaska and adjacent Canadian glaciers comprise 13% of the world's glacier area, exclusive of Antarctica and Greenland). Despite poorly resolved mass balances, recent evidence shows that Alaskan glaciers, by virtue of their large collective area, rapid response characteristics, and high mass fluxes, contribute to modern sea level rise at a rate approximately seven times greater than previously thought. Much of the mass loss from Alaskan glaciers comes from tidewater glaciers, which advance and retreat episodically, with long periods of advance and stability punctuated by rapid, apparently irreversible retreat. During retreat, tidewater glacier mass balance is dominated by the poorly understood process of iceberg calving, rather than direct climate forcing, and the magnitude of ice flux into the ocean can be very large. Columbia Glacier is presently discharging icebergs into the ocean at a rate of approximately 22 km3 yr-1. Thus, tidewater calving is an important, but poorly understood element of modern glacier change and sea level rise. The Principal Investigators present work plan at Columbia Glacier with two points of focus, each dedicated to an increased understanding the role of calving in tidewater glacier retreat. First, they will continue their program of aerial photography as the glacier terminus retreats through a major channel constriction. Second, they will conduct a passive seismological investigation of calving processes. This work is motivated by the importance of small glaciers (especially Alaskan tidewater glaciers) to modern global glacier mass balance and sea level change and by the need to better understand the role of calving in tidewater glacier dynamics. Additionally, Columbia Glacier is the last of the Alaskan tidewater glaciers to retreat, and is partly through its retreat phase and at a critical location in its channel geometry. This opportunity to study tidewater calving will be gone in a few decades, so it is important to take advantage of it now. Tidewater calving is an important part of glacier dynamics and ice/ocean interaction, but is still poorly understood. Progress toward a better understanding of calving is handicapped by a lack of relevant observations and lack of knowledge of what the relevant observations should be. This research will provide a continuation of a highly successful observational program of aerial photography that has yielded the longest and most detailed observational record of tidewater glacier kinematics ever assembled, and has formed the basis of much of what is presently known about tidewater dynamics. The Principal Investigators will start a new series of seismic observations on Columbia Glacier in an attempt to discover in detail the timing, location, and geometry of fracture events leading to calving. Limited seismic investigations have been previously made on tidewater glaciers, including on Columbia Glacier, but modern advances in data acquisition and processing will allow them to use seismology much more effectively and to look at fracture and calving in much greater detail. Broader impacts resulting from the proposed activity: In addition to its role in modern sea level change, tidewater calving played a critical role in global ice sheet and climate dynamic in the past. Ample evidence from the North Atlantic Ocean suggests that passive episodic calving was essential in the rapid breakup of the Laurentide Ice Sheet (LIS), but current LIS reconstructions do not attempt to incorporate calving processes due to the lack of a mathematical calving relationship. However, ice sheet modelers are eager for input concerning calving processes to incorporate in LIS models. Additionally, an understanding of tidewater calving provides useful crossover knowledge for Antarctic and Greenland marine-ending ice masses where calving occurs much less frequently.