Investigating the Dynamics of Tidewater Glaciers with Application to Columbia Glacier, Alaska and Kangerlussuaq Glacier, East Greenland

预测未来海平面的不确定性受到对冰川崩解行为缺乏了解的影响。在地质记录中有许多例子表明冰川崩解时经历了迅速的变化。这种行为最著名的例子是海因里希事件，标志着劳伦泰德冰盖的冰山产量显著增加的短暂时期。首席研究员将应用数值模型来描述和解释观测到的阿拉斯加哥伦比亚冰川和格陵兰康克鲁斯瓦格冰川的退缩。从研究这些冰川中获得的经验教训可以应用于其他正在崩解的冰川，以解释过去的变化以及预测可能的未来变化。哥伦比亚冰川是一个潮汐冰川，自20世纪80年代初以来一直在加速退缩。自1976年以来，美国地质勘探局每年大约进行五次航空摄影测量，记录了撤退前和撤退后的这段时间。该数据集是所有冰川崩解过程中最完整的数据集，涵盖了冰川速度和几何形状的季节变化和长期变化。康克鲁斯瓦格冰川是一个快速移动的冰解冰川，在20世纪90年代经历了快速变薄，从20世纪30年代开始收集了表面海拔和冰川速度的数据。虽然没有哥伦比亚冰川的数据集那么广泛，但现有的数据足以约束数值模型，并研究最有可能对这个出口冰川的行为负责的过程。关于哥伦比亚冰川和其他正在崩解的冰川，最重要的问题是什么过程可能导致退缩，什么反馈机制在维持退缩中是重要的。为了回答这个问题，首席研究员建议采用一种启发式的方法，根据裂冰标准估计冰山的产生速度。两种不同的公式将被纳入模型，并根据现有数据对它们的预测进行检验。同样地，通过结合简单而现实的滑动关系，该模型将被用来检验一个假设，即后退过程中的加速可能与冰川变薄和浮选方法有关，降低了有效的基础压力。最后，他将调查沉积物循环的作用和终端冰碛岸的形成，以及这个过程是否对终端向峡湾推进至关重要。科学价值：该项目的主要目标是确定在控制冰解冰川生命周期中最重要的过程，其典型特征是冰川末端缓慢前进到位于峡湾口的相对稳定的末端，随后是下游快速后退和解体的短暂时期。到目前为止，大多数关于潮汐冰川的研究都集中在特定的方面，如产犊、沉积物沉积等，但很少有人尝试将各种想法和建议整合到一个单一的模型中，并应用于一个有充分记录的冰川。更广泛的影响：虽然拟议的工作主要集中在哥伦比亚冰川上，但更好地了解冰川崩解的动力学将具有更广泛的应用，特别是减少未来海平面上升情景的不确定性以及冰川崩解对海平面上升的贡献。

ABSTRACTvan der VeenOPP-0520427Uncertainties in predicting future sea level are affected by a lack of understanding thebehavior of calving glaciers. There are many examples in the geological record of calving glaciers that underwent rapid change. The best-known examples of such behavior are the Heinrich events, marking short-lived periods of significantly increased iceberg production from the Laurentide Ice Sheet. The Principal Investigators will apply a numerical model to describe and explain the observed retreat of Columbia Glacier, Alaska, and of Kangerlussuaq Glacier, Greenland. The lessons learned from studying these glaciers can be applied to other calving glaciers, to explain past changes as well as predict possible future changes. Columbia Glacier is a tidewater glacier that has been retreating at an increasing rate since the early 1980s. The period prior to, and the subsequent retreat, have been documented by aerial photogrammetry, conducted by the U.S.G.S. for about five times a year since 1976. This data set is the most complete for any calving glacier and covers both seasonal variations and long-term changes in glacier speed and geometry. Kangerlussuaq Glacier is a fast-moving calving glacier that underwent rapid thinning during the 1990s and data has been compiled on surface elevation and glacier speed from the 1930s. While not as extensive as the Columbia Glacier data set, available data are sufficient to constrain numerical models and investigate processes most likely responsible for the behavior of this outlet glacier. The most important question concerning Columbia Glacier and other calving glaciers is what processes may initiate retreat and what feedback mechanisms are important in sustaining retreat. To answer this question, the Principal Investigator proposes to adopt a heuristic approach in which the rate of iceberg production is estimated from a calving criterion. Two different formulations will be incorporated into the model and their predictions tested against the available data. Similarly, by incorporating simple yet realistic sliding relations, the model will be used to test the hypothesis that the speed up during retreat may be associated with glacier thinning and approach to flotation, lowering the effective basal pressure. Finally, he will investigate the role of sediment recycling and the formation of a terminal moraine bank, and whether this process is essential for allowing the terminus to advance down the fjord.Scientific Merit: The main goal of this project is to identify processes most important in controlling the life cycle of calving glaciers, typified by a prolonged period of slow terminus advance to a relative stable terminus located at the mouth of the fjord, followed by a brief period of rapid retreat and disintegration of the lower reaches. Until now, most studies concerning tidewater glaciers have focused on specific aspects, such as calving, sediment deposition, etc., but few attempts have been made to integrate the various ideas and suggestions into a single model with applications to a well-documented glacier.Broader Impact: While the proposed work focuses on Columbia Glacier primarily, betterunderstanding of the dynamics of calving glaciers will have broader applications, in particular reducing uncertainties in future sea-level rise scenarios and the contribution of calving glaciers to this rise.