Processes of fast glacier flow

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Ice sheets and glaciers are the biggest potential source of future sea level rise. Mountain glaciers also play an important role in regional water supplies, especially through providing water during dry summers, while continent-sized ice sheets such as those in Greenland and Antarctica have multple impacts on the world's climate system beyond sea level change. Ice flow is a key component in determining how much ice there is on the planet: faster ice flow tends to lead to thinner, smaller ice masses, and potentially even to the complete disappearance of a glacier or ice sheet. Yet relatively little is known about how the fastest glacial flow phenomena on Earth work - ice streams in Antarctica, surging glaciers, and fast-flowing glaciers that teminate in the ocean. The proposed research aims to unravel the physics behind these phenomena. It will focus on the role that melt water plays in speeding up ice flow. Most fast glacier flow is caused by lubrication of the base of the ice by melt water that reaches the bed. To quantify the effect of water, it is however not enough to know how much of it reaches the bed: we also have to know how it drains along the bed. Highly pressurized water will weaken the contact between ice and rock, and permit faster sliding. My research will use mathematical modelling techniques in combination with direct observations at the bed of a valley glacier to determine the physics that controls water pressure under the ice, and to introduce that physics into ice flow simulations to better predict its effects on fast ice flow phenomena. Alongside this focus on water, I will develop novel modelling techniques to capture the breaking-off of icebergs, and the effect that this has through removing constrictions on ice flow that slow ice discharge into the oceans. I am motivated in this effort by the fact that the parts of Greenland and Antarctica that are losing mass fastest are invariably outlet glaciers that terminate in the ocean, where the loss of a floating ice tongue (or `ice shelf') has removed a constriction to ice flow. Future projections of ice discharge will crucially depend on being to understand how and why floating ice tongues break off, and my work will aim to produce predictive models for the underlying physics.