Ice sheet dynamics and ice quakes in Antartica.Ice sheet dynamics is no longer thought of as giant slabs of slow-moving frozen water, ice sheets are energized by a complex system of sub-glacial lakes, floods, streams and ice quakes. Glaciologists have long been fascinated by the way a mountain glacier might suddenly give up its usual slow creeping, to race forward at a rate of hundreds of meters a day. This rapid acceleration is proposed to occur when the pressure at the bottom melts ice so that water lubricates the flow. As the ice begins to move, friction melts more water and the flow accelerates. Could the ice in Antarctica become unstable in this fashion? Scientists have discovered that a kilometer-thick Antarctic ice stream rested not on bedrock but on a layer of slippery mud. Another unsettling discovery is that in recent centuries some of the great ice streams had stopped or started moving, for no clear reason. The dynamics of ice sheets and the streams that feed them turns out to be, like most things geophysical, a complicated snarl of influences.
Long period seismic events can be related to the stick and slip nature of glacial ice movement. The seismic signals raise the possibility that discharge processes include episodic increases in the sliding of the ice that operate in a failure mode. This type of episodic sliding or sticking over large areas to the rock and sediment that make up the glacier bed emphasizes the difficulties inherent in modelling rapid ice discharge. The factors that might control the rate of ice flow range from long-term changes in ice properties (dust content, thermal profiles, rates of accumulation of snow) to water-modulated sliding over a bed of complex composition and geometry. If episodic motion makes up a significant component of total ice flow, then ice models will require a broadened scope to deal with the processes that may be involved. This project aims to develop and test these ideas further. Further identification of the patterns of episodic motion and the relationship between it and known forcings, such as meltwater input pulses and ocean tides, may help to constrain the problem. The indicated coupling between surface meltingand ice-sheet flow provides a mechanism for rapid, large-scale,dynamic responses of ice sheets to climate warming.
Ref: Science 302, 622 (2003); Ekström et al.
Science 302, 5645 (2003); Fahnestock.
Advisor: Dr Louise Olsen-Kettle
Level of Project: Honours/MSc/PhD