Collaborative Research: Glacial Valley Profile Evolution

这是加州大学圣克鲁兹分校和华盛顿大学的主要研究人员合作提出的一项建议。地球科学部（地质学和古生物学）提供了大约三分之一的资金。我们对冰川如何雕刻高山景观的了解很少。尽管在发展冰川床的磨损和雕刻物理方面取得了重大进展，但冰川侵蚀在景观模型中的作用在很大程度上被忽视了。我们知识库中的这一空白是由于很难建立一个模型来捕捉：1)冰川的生长和衰退；2)冰川融水的产生和暂时储存；3)河床侵蚀的空间分布。首席研究人员将对阿拉斯加中南部楚加奇山脉的Bench冰川进行实地测量，并开发一个模型，以确定冰川如何作为景观侵蚀的媒介。他们将把重点放在长谷剖面的演化上，这是继Harbor最近完成的跨谷剖面演化建模之后的一个合乎逻辑的步骤。首席调查员的实地项目将提供与冰川床上侵蚀的时间、空间分布和程度相关的数据集。他们将使用一个直接的一维模型，并逐渐增加更复杂的因素，如气候强迫和冰川的拓扑结构。他们将：1)记录质量平衡剖面；2)利用冰面上的多个反射器测量地表速度的时空分布；3)利用声传感器测量河段水沙输出；4)对悬浮物进行采样和浊度测量相结合。滑动速度和水平衡数据将指导侵蚀时间和模式的建模，而年产沙量将提供整体约束。沉积物产量使两者之间的关系变得复杂，但一个为期三年的监测项目将最大限度地减少储存的变化。交错有限的一维冰川模型将随着时间的推移在范围和厚度上发生变化，这是由质量平衡剖面或决定降水和融化模式的气象成分的变化所驱动的。这种方法将使首席研究人员能够在系统中纳入重要的反馈，包括随着山谷加深而变化的山谷阴影，以及如果冰表面被碎片覆盖，融化速度的降低。他们将关注冰川系统中的水平衡，因为水压调节了滑动。瞬时侵蚀速率由冰川侵蚀规律决定，该规律与计算出的局部滑动速率和河床的可蚀性有关。首席研究员将使用他们的模型来探索过深山谷和悬空山谷的形成。这个冰川谷演化模型将有广泛的应用，因为它是解决山脉演化中气候-侵蚀-隆起反馈的迫切需要。它还将提供冰川地形的沉积物和水通量的历史，这调节了下游地区的化学风化、阶地发育和盆地填充。悬谷问题所需要的冰川-支流相互作用模型，将为研究对危险现象了解甚少的jokulhlaus提供基础。

This is a collaborative proposal by the Principal Investigators at the University of California-Santa Cruz and University of Washington. The Division of Earth Sciences (Geology and Paleontology) is contributing about one-third of the funding. Our understanding of how glaciers carve and sculpture alpine landscapes is poor. Although significant progress has been made on developing the physics of abrasion and sculpturing of glacial beds, glacial erosion into landscape models has largely been ignored. This void in our knowledge base is due to the difficulty in developing a model that captures the: 1) growth and decay of the glacier; 2) generation and temporary storage of meltwater within the glacier; and 3) spatial distribution of erosion over the bed. The Principal Investigators will make field measurements on the Bench Glacier in the Chugach Range of south-central Alaska and develop a model to determine how glaciers function as agents of landscape erosion. They will focus on the evolution of the long valley profile which is a logical step after the modeling of cross-valley profile evolution recently done by Harbor. The Principal Investigators' field program will provide data sets relevant to the timing, spatial distribution and magnitude of erosion over the glacier bed. They will use a straight one-dimensional model and incrementally add more complex factors such as climate forcing and topology of the glacier. They will: 1) document the mass balance profile; 2) measure the pattern of surface speed in time and space using multiple reflectors on the ice; 3) measure the water and sediment output using acoustic sensors for river stage; and 4) make a combination of sampling and turbidity measurements for suspended sediments. Sliding speed and water balance data will guide modeling of timing and pattern of erosion, while annual sediment yield will provide an integral constraint. The sediment yield complicates the relationships, but a three-year monitoring program will minimize variations in storage.The staggered finite one-dimensional glacier model will vary in extent and thickness through time, driven by variations in the mass balance profile or the meteorological constituents that dictate precipitation and melt patterns. This approach will allow the Principal Investigators to incorporate important feedbacks in the system, including evolution of the valley shading as the valley deepens, and reduction of melt rate if the ice surface becomes mantled with debris. They will focus on water balance in the glacial system as water pressure modulates sliding. The instantaneous erosion rate is dictated by a glacial erosion rule that is tied to the calculated local sliding rate and the erodibility of the bed. The Principal Investigators will use their model to explore the formation of overdeepening valleys and hanging valleys. This glacier valley evolution model will have broad applications because it is critically needed to address climate-erosion-uplift feedbacks in mountain range evolution. It will also provide the history of sediment and water flux from glaciated terrain, which modulates chemical weathering, terrace development and basin filling in regions downstream. A model of glacier-tributary interactions, required for the hanging valley problem, will provide the basis for studying jokulhlaups which are poorly understood hazardous phenomena.