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Ice streams are the primary determinant of ice sheet mass balance and stability. To understand and predict ice sheet behaviour, the mechanisms controlling ice streaming must be understood. Using a new inventory of Laurentide palaeo-ice streams, a fundamental, unresolved question is addressed: what determines the location of ice streams?
From the literature eight hypothesised controls on ice stream location have been identified: topographic focusing, topographic steps, macro-scale bed roughness, subglacial geology, meltwater routing, geothermal heat flux, calving margins and internal self-regulation. Each control was tested to determine its influence on ice stream location. This was assessed based on the degree of spatial coincidence between the control and Laurentide palaeo-ice streams.
No single factor, or combination of factors was found common to all ice streams, but topographic focusing, subglacial geology, meltwater routing and calving margins were most frequently associated with ice streaming. Topographic steps, macro-scale bed roughness, geothermal heat flux and internal self-regulation were rarely found in association with ice streaming. It is proposed that a hierarchy of factors control the location of ice streams.
Factors occurring at the top of the hierarchy exert a strong influence on ice stream location, and where present beneath an ice sheet, are likely to be associated with fast flow. Those factors occurring lower down the hierarchy are only likely to be associated with ice streaming in the absence of other favourable conditions. Two hierarchies were proposed, one for ice streams with calving margins, and a second for non-calving ice streams.
These hierarchies provide a tool for predicting the likely location of ice streams within an ice sheet. They can also explain the location of ice streams in contemporary ice sheets, and offer a means of predicting the likely fate and location of ice streams under possible retreat scenarios.
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