NSFGEO-NERC: Ice-shelf Instability Caused by Active Surface Meltwater Production, Movement, Ponding and Hydrofracture

南极洲周围的漂浮冰架提供了一个缓冲区，防止冰从大陆内部快速流入海洋。如果这种缓冲作用减少或消失，将有更多的冰快速流向海洋，导致海平面上升。因此，了解冰架稳定性的控制因素，对于评估和预测可能的冰架收缩或崩溃是很重要的。有证据表明，冰架不稳定性的一个来源是表面融化和融水的运动。拉森B冰架上超过2500个表面湖泊长达十年的发展，以及随后的突然排水，是2002年冰架突然崩溃的两个最明显的前兆。该项目将利用对南极半岛乔治六世冰架（GVIS）的一系列地球物理观测，研究冰架在强烈的表面融化时是如何断裂的。要观察到的主要过程是粘弹性冰架弯曲和断裂的表面融水运动，加载和卸载。该团队之前的实地考察提供了对麦克默多冰架（McMIS）上这些过程的第一次直接测量。然而，结果在应用于其他冰架时受到一定的限制，这是由于不均匀的碎片覆盖，因此不典型的消融率，稀疏分布的池塘，以及靠近活动裂谷的冰弯曲测量。与McMIS相比，GVIIS提供了一个近乎完美的机会来观察融水加载过程，正如卫星图像显示的那样，它拥有数百个湖泊，并显示出对湖泊排水的粘弹性反弹特征。此外，由于其压缩应力状态，GVIIS被认为没有即将破裂的风险，使冰架成为安全的工作环境。建议的四年计划将对GVIIS进行为期27个月（2019年11月至2022年1月）的测量。地震仪，全球定位系统（GPS），水压传感器，两个自动气象站，和热敏电阻串将被部署到记录断裂地震，冰架弯曲，水深，表面和地下融化，分别在和周围确定的融水功能。这些仪器将部署在紧邻BAS化石海崖站的20 x 20 km的野外区域。现场数据将用于验证和扩展该团队现有的方法，以模拟可能导致水力压裂的冰架弯曲和应力，地表水排放到下面的海洋，以及可能的Larsen-B型冰架不稳定性。

The floating ice shelves around Antarctica provide a buffer against rapid ice flow from the continent's interior to the ocean. If that buffer is reduced or removed, there will be more rapid ice flow to the ocean contributing to sea level rise. Understanding the controls on ice shelf stability, therefore, is important for the assessment and prediction of possible ice shelf shrinkage or collapse. Evidence shows that one source of ice shelf instability comes from surface melting and the movement of the meltwater. The decade-long development of >2500 surface lakes on the Larsen B Ice Shelf, followed by their abrupt drainage, were the two most conspicuous precursors to the ice shelf's sudden collapse in 2002. This project will investigate how ice shelves fracture when subjected to strong surface melting using a suite of geophysical observations on the George VI Ice Shelf (GVIIS) of the Antarctic Peninsula. The leading processes to be observed are viscoelastic ice-shelf flexure and fracture in response to surface meltwater movement, loading, and unloading. The team's prior fieldwork provided the first direct measurements of these processes on the McMurdo Ice Shelf (McMIS). However, the results were somewhat limited in their application to other ice shelves due to a heterogeneous debris cover and therefore atypical ablation rates, sparsely-distributed ponds, and ice-flexure measurements made close to an active rift.Compared to the McMIS, the GVIIS provides a near-perfect opportunity to observe meltwater loading processes, as satellite imagery shows it hosts hundreds of lakes and displays features of viscoelastic rebound in response to lake drainage. Furthermore, GVIIS is thought not to be at risk of imminent breakup due to its compressive stress regime, making the ice shelf a safe working environment. The proposed 4-year project will conduct a 27-month period (November 2019 - January 2022) of measurements on the GVIIS. Seismometers, global positioning system (GPS), water pressure transducers, two automatic weather stations, and thermistor strings will be deployed to record fracture seismicity, ice shelf flexure, water depths, and surface and subsurface melting, respectively, in and around identified meltwater features. These instruments will be deployed in a 20 x 20 km field area immediately adjacent to BAS's Fossil Bluff Station. Field data will be used to validate and extend the team's existing approach to modelling ice-shelf flexure and stress that can lead to hydrofracture, drainage of surface water to the ocean below, and possible Larsen-B style ice-shelf instability.