Development of a glacial abrasion rule for landscape-evolution models

冰川景观是由上面滑动的冰雕刻而成的。持续不断的冰流磨损着下面的基岩，随着时间的推移侵蚀着它。这种磨损的速度和模式部分源于一种叫做磨蚀的过程，这种过程是由基底冰中携带的沉积物被压入下面的岩石并被冰川带走而产生的。已经提出了许多理论来估计磨损率，这取决于许多参数。为了准确地模拟冰川景观的演变，需要一个数学上的“磨损定律”来准确地捕捉与磨损有关的物理现象。在真正的冰川下，磨损规律的形式很难确定，因为它们的床通常是难以接近的，而且控制因素很难在实地测量。使这些困难进一步复杂化的事实是，磨损率很小，因此需要几十年或几个世纪才能测量到侵蚀体积。该项目的目标是利用一套新颖的实验室仪器建立一种描述冰川磨损物理的数学关系，从而可以在数值景观演化模型中实现。在实验室中，可以控制和测量条件，达到准确确定磨损规律所需的精度。该项目将支持威斯康星大学麦迪逊分校的一名研究生和一名本科生，并为梅诺米尼民族学院的代表性不足的学生提供培训。威斯康星大学麦迪逊分校的一个大直径环剪切装置和一个直接剪切装置将用于在压力熔点上滑动含有碎片的冰，这些冰在形状和成分上都有所不同。磨损产生的条纹将使用白光干涉仪进行分析，该干涉仪能够测量侵蚀材料的体积，最小可达10-18立方米。由于能够测量这些微小的体积，滑动实验可以在相对较短的时间内进行（每次不到一个月），并且仍然产生足够的磨损体积来确定磨损规律。使用这些仪器，将开发出一个将侵蚀速率与独立变量（如滑动速度、基底熔化、床形、碎屑硬度和碎屑浓度）联系起来的磨损规律。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Glacial landscapes are sculpted by the ice that slides above them. The constant flow of ice wears away at the underlying bedrock, eroding it through time. The rates and patterns of this wear stem in part from a process called abrasion, which results from sediment entrained in basal ice being pressed into the underlying rock and drug along by the glacier. A number of theories have been proposed to estimate abrasion rates, which depend on a multitude of parameters. In order to accurately model the evolution of glacial landscapes, a mathematical “abrasion law” is needed that accurately captures the physics relevant to abrasion. The form of the abrasion law is difficult to determine beneath real glaciers because their beds are often inaccessible and the controlling factors are difficult to measure in the field. Further compounding these difficulties is the fact that abrasion rates are miniscule and therefore require decades or centuries to pass before the eroded volume is measurable. The goal of this project is to develop a mathematical relationship that describes the physics of glacial abrasion using a novel set of laboratory instruments, so that it can be implemented in numerical landscape evolution models. In the laboratory, conditions can be controlled and measured with the precision needed to accurately determine the abrasion law. The project will support a graduate and an undergraduate student from UW-Madison and provide training for underrepresented students from the College of Menominee Nation.A large-diameter ring shear device and a direct shear device at UW-Madison will be used to slide debris-laden ice at the pressure melting point over rock beds that vary in shape and composition. The striations produced by abrasion will be analyzed using a white light interferometer capable of measuring the volume of eroded material down to 10-18 cubic meters. With the ability to measure these miniscule volumes, the sliding experiments can be conducted in relatively short timeframes (less than one month each) and still generate sufficient abraded volume to determine the abrasion law. Using these instruments, an abrasion law will be developed that relates the rate of erosion to independent variables, such as sliding speed, basal melting, bed shape, debris hardness, and debris concentration.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.