Laboratory Study of Substrate Control and Cryoseismicity of Glacier Basal Motion

气候变化最具破坏性的潜在影响之一是海平面上升。根据目前的预测，到本世纪末，海平面将上升1米。 这样的规模将淹没世界上一些人口最稠密的地区，但预测的不确定性需要降低。约束良好的海平面预测可以为基础设施保护和规划提供指导，部分取决于准确模拟冰川冰通过快速移动的冰体（称为冰流）从积雪区输送到海洋的速度。对冰流流速的控制，特别是那些影响冰流底部难以进入的过程的控制，受到观测的限制很差。为了阐明这些重要的控制措施，项目团队将进行实验室实验，隔离和约束特定的滑动行为。 实验旨在确定哪些因素（例如，温度、水压、速度、作用力幅度）控制滑动响应，使结果可以从实验室规模扩大到冰流规模，并为冰盖模拟模型提供更好的预测能力。为了隔离冰流基底滑动过程，项目团队将在低温条件下进行材料摩擦实验。该团队将应用速率和状态相关摩擦的数学框架，该框架已在岩石力学中成功使用数十年来描述地震现象。基于该团队过去对冰-岩摩擦对正应力、温度、滑动速度和驱动应力振荡的依赖性的测量，该项目将扩展参数空间，以包括排水和不排水条件下的层厚度和孔隙流体饱和度。摩擦熔化、润滑和孔隙压力之间的耦合将使受力复杂化，并可能大大增加行为的范围。实验将测试速率-状态摩擦公式描述这一全方位观察到的行为的能力，从粘滑事件到缓慢滑动和震颤到稳定的无摩擦蠕变。除了测量摩擦剪切应力外，该团队还将实施声学表征技术，以记录变形过程中的声发射和超声波传播特性。虽然直接的可比性，从外地的地震数据是不可能的，如何实验条件影响波形特性，如极性，频率和形状的观察可以帮助解释cryoseismic数据集。研究结果还将提供用于冰盖模型的基底滑移和河床变形本构关系和参数，这些模型对预测冰盖系统的变化至关重要。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

One of the most devastating potential impacts of climate change is sea-level rise. Current forecasts predict sea level to rise by as much as a meter by the end of this century. Such a magnitude would inundate some of the world's most populated areas, but uncertainties in the predictions need to be lowered. Well-constrained sea-level projections that can provide guidance to infrastructure protection and planning are dependent in part on accurately modeling the rate that glacier ice is transported from snow accumulation zones to the oceans by fast-moving bodies of ice called ice streams. Controls on ice-stream flow rates, particularly those influencing processes at the hard-to-access base of ice streams, are poorly constrained by observation. To shed light on these important controls, the project team will conduct laboratory experiments that isolate and constrain particular sliding behaviors. The experiments aim to identify which factors (e.g., temperature, water pressure, velocity, amplitude of forcing) control the sliding response so that outcomes can be scaled up from the laboratory to the ice-stream scale and provide better predictive power to ice-sheet simulation models.To isolate the ice-stream basal sliding process, the project team will conduct friction experiments of materials at cryogenic conditions. The team will apply the mathematical framework of rate- and state-dependent friction that has been successfully used for decades in rock mechanics to describe earthquake phenomena. Building on the team's past measurements of ice-on-rock frictional dependence on normal stress, temperature, sliding velocity, and driving stress oscillation, this project will extend the parameter space to include till-layer thickness and pore-fluid saturation under drained and undrained conditions. Coupling among frictional melt, lubrication, and pore pressure will complicate the forcing and may greatly increase the range of behaviors. The experiments will test the rate-state friction formulation's ability to describe this full range of observed behaviors, from stick-slip events to slow slip and tremor to steady aseismic creep. In addition to measuring frictional shear stress, the team will implement acoustic characterization techniques to record acoustic emissions and ultrasonic wave propagation properties during deformation. Although direct comparability to seismic data from the field is unlikely, observations of how experimental conditions influence waveform properties such as the polarity, frequency, and shape can help in the interpretation of cryoseismic datasets. The results will also provide basal slip and bed deformation constitutive relations and parameters for use in ice-sheet models that are vital for predicting changes in ice-sheet systems.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.