Mathematical Models of ice stream dynamics and supraglacial drainage
Patterning is a recurrent feature of glacial systems, which characterizes as much subglacial and supraglacial environments as the flow of ice itself. Some examples include bedforms developing at the contact between ice and bed, spatial organization in subglacial and supraglacial drainage networks, t...
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| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
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Politecnico di Torino
2016
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| Online Access: | http://hdl.handle.net/11583/2640231 https://doi.org/10.6092/polito/porto/2640231 |
| Summary: | Patterning is a recurrent feature of glacial systems, which characterizes as much subglacial and supraglacial environments as the flow of ice itself. Some examples include bedforms developing at the contact between ice and bed, spatial organization in subglacial and supraglacial drainage networks, the narrow corridors of fast flowing ice known as ice streams that form the arterial drainage system of large ice sheets, and temporal switches between slow and fast flow regimes in glacier and ice stream flow. This thesis focusses on two types of glacial patterns, namely ice streams and channelization in supraglacial drainage networks. Ice flow within ice sheets is far from uniform, with the narrow bands known as ice streams flowing at velocity two order of magnitude larger than the rest of the ice sheet. In the Siple Coast region of West Antarctica ice streams experiance weak topographic confinement, thus suggesting that they may originate spontaneously from an otherwise uniform flow as a fingering instability. Motivated by observations suggesting that the marked contrast in velocity between ice streams and surrounding ice is due to a transition from frozen, thus sticky bed underneath slow flowing regions, to molten, thus well lubricated bed under ice streams, we investigate the role of basal thermal transitions in relation to the onset of ice streams. Our findings suggest that basal transitions from frozen to molten bed (or vice versa) can undergo an instability potentially leading to the onset of streaming. An asymptotic analysis for short wavelenght perturbations shows that, at wavelengths of few ice thicknesses, such instability is controlled by the interplay between strain heating and heat advection from the region upstream of the transition. We also find that the background structure of the ice sheet is key to pattern formation. In particular, in the case of ice flowing from molten to frozen regions we find an instability at the ice sheet thickness scale or smaller, which is not resolved by most ice sheet ... |
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