Incorporating Glacial Blisters into Models of Subglacial Drainage

由于气候变化，冰川的结构正在发生重大变化；新的特征正在出现，而这些特征还没有被很好地理解，因此需要更好的模型。随着全球气候变暖，在变暖的季节波动期间，冰川表面上的融水湖也普遍变暖。这样的“冰川上”湖泊可以通过冰的裂缝迅速（以小时为单位）流失，融化的水随后聚集在“冰川下”湖泊中。这些，反过来，迫使冰和基岩之间出现一个缺口，导致冰川局部上升，水在压力下储存在下面的水池中——这种特征由于它们的结构而被称为“冰川水泡”。这些突然的排水事件可能会淹没原有的冰下排水系统，导致大量的水涌入。在冰川终点附近，排水系统中的大型渠道能够迅速将水带走，从而减少了此类事件的影响。然而，在更远的内陆，通常不存在这样广阔的渠道。因此，内陆水疱可以在几天内排出，比它们最初形成的速度要慢得多。人们认识到，由于冰川底部的润滑作用，流经冰下排水系统的水量可以显著影响冰盖的运动。然而，如何将水泡排水纳入冰川水文模型仍然是一个开放的领域，并且它与冰速增加之间的任何潜在联系尚未通过数学模型建立。该项目的目的是扩展目前的冰下排水系统模型，以纳入由冰上排水驱动的湖泊的影响。在扩展模型的过程中，我们可以尝试观察整体冰川行为是否有任何重大变化。例如，在排水过程中，人们可能会看到更深的内陆形成更大的渠道，使水更快地从水泡中排出。或者，人们可以观察到，长期的排水导致冰川底部更大的润滑，从而导致表面更快的运动。在水泡的长度尺度上，冰可以在弹性变形下建模，但在冰川的尺度上，更明智的选择是将冰视为粘性的。将这两个模型结合起来，或者实际上使用更复杂的粘弹性设置，将成为这个项目的主要部分。该项目属于EPSRC连续介质力学研究领域，特别是与流体和固体力学建模有关。它将涉及多孔介质中流体流动和变形的基本方面。它有可能让我们更好地理解是什么导致了冰川速度的增加，从而导致了全球海平面上升的整体冰川融化和崩解速度。鉴于快速变化的气候增加了冰川池塘的发生，对排水的影响进行建模（从而改进我们的模型）将使我们能够更好地预测大气变暖对全球冰川覆盖减少的影响。

Glaciers are currently undergoing major changes in their structure due to climate change; new features are appearing which are not well understood for which better models are needed. As the global climate has warmed, so has the prevalence of meltwater lakes on the surfaces of glaciers during warmer seasonal fluctuations. Such 'supraglacial' lakes can drain rapidly (on the order of hours) through fractures in the ice with the meltwater then collecting in 'subglacial' lakes. These, in turn, force a gap between the ice and bedrock causing the glacier to rise locally with the water stored below in a pool under pressure - such features are known as 'glacial blisters' due to their structure.These sudden drainage events can flood a pre-existing subglacial drainage system with an overwhelming influx of water. Near the glacier terminus large channels in the drainage system are able to carry water away quickly, reducing the effects of such events. However, further inland such expansive channels don't usually exist. Thus, inland blisters can drain on the order of days, at a much slower pace than they are initially formed.It is recognised that the quantity of water flowing through a subglacial drainage system can significantly affect the ice sheet motion due to lubrication at the base of a glacier. However, how to incorporate blister drainage into glacial hydrology models remains an open area and any potential link between this and increased ice velocity has not yet been established through mathematical models. The aim of this project is to extend current subglacial drainage system models to incorporate the effects of lakes driven by supraglacial drainage. In extending the models we can then attempt to observe if there are any significant changes on the overall glacier behaviour. For example, during drainage, one might see that larger channels are formed further inland to enable water to drain form blisters more quickly. Alternatively one might observe that longer term drainage leads to greater lubrication at the base of the glacier hence resulting in faster motion at the surface.On the length scale of a blister, the ice can be modelled under an elastic deformation but on the scale of the glacier a more sensible choice would be to treat the ice as viscous. Marrying these two models, or indeed using a more complex visco-elastic setup, will form a major part of this project.This project falls within the EPSRC Continuum Mechanics research area, specifically in relation to modelling fluid and solid mechanics. It will involve fundamental aspects of fluid flow and deformations within a porous medium. It has the potential to better our understanding of what causes an increase in glacier velocity and thus overall glacier melting and calving rates that lead to global sea level rise. Given the rapidly changing climate has increased the occurrence of glacier ponding, modelling the effects of drainage (and hence refining our models) will enable us to better predict the effects the warming atmosphere will have on the reduction of global glacier coverage.