Hydraulic and mechanical controls on fast glacier flow

点击翻译按钮获取中文摘要

Accelerating and retreating outlet glaciers in Greenland, large icebergs calving off Antarctica, shrinking glaciers in the Alps, the Rockies and the Himalayas: all these have been shining a spotlight on glaciers and ice sheets over the last decade. How fast will sea levels rise? How fast will glaciers disappear as virtual "water towers", providing water resources during dry summers? Can we extrapolate from current trends? Answering these questions requires process understanding, because land ice evolves slowly and the detailed instrumental record is short. Without understanding the physics driving observed change, we cannot know if and how it will continue. The proposed research tackles four interlinked questions in glacier and ice sheet dynamics, all motivated by the role melt water plays in changing ice flow. In relatively temperate climates, surface melt occurs widely in summer: not only on mountain glaciers, but also the vast Greenland ice sheet. That melt does not stay at the glacier surface, but is routed to the bed. How does it affect sliding once there? This is the first question we tackle. The configuration of the drainage system under the ice is the key to sliding: if it sustains high water pressure, faster ice motion occurs. However, recent observations by my group and others underline the importance of a patchy drainage system. Water does not flow everywhere. How water routing changes over time is central to the response of the glacier bed to surface water input. Using an eight-year data set created at UBC, we will construct a fully calibrated model that captures all essential aspects of drainage system evolution. Such a model faces its sternest test in trying to predict glacier outburst floods and glacier surges. To this day, a full explanation of glacier surges - episodic accelerations of certain glaciers, often by orders of magnitude - remains one of the longest-standing problems in glacier dynamics. We will undertake a systematic theoretical and observational exploration of these phenomena in order to refine our models further. A key question we will study is how englacial water storage interacts with the drainage system, and whether feedbacks between the two can cause glacier surges. Water production is however not limited to mountain glaciers and Greenland. Building on a three-year field project studying surface melt features on an Antarctic outlet glacier and their relationship with ice dynamics, we will develop models for water storage and drainage in much colder climates, where melting often occurs in the shallow subsurface, shielded from frigid air temperatures by a thin layer of ice. Our goal is ultimately to understand how enough water can pool to encourage hydrofracturing to occur as a precursor to calving. The last question we tackle is that of calving mechanisms themselves: how does the process that dominates mass loss in most polar ice caps work, and how can it be modelled?