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Microscale evidence of liquefaction and its potential triggers during soft-bed deformation within subglacial traction tills

Phillips, E.R.; Evans, D.J.A.; van der Meer, J.J.M.; Lee, J.R.

Microscale evidence of liquefaction and its potential triggers during soft-bed deformation within subglacial traction tills Thumbnail


Authors

E.R. Phillips

J.J.M. van der Meer

J.R. Lee



Abstract

Published conceptual models argue that much of the forward motion of modern and ancient glaciers is accommodated by deformation of soft-sediments within the underlying bed. At a microscale this deformation results in the development of a range of ductile and brittle structures in water-saturated sediments as they accommodate the stresses being applied by the overriding glacier. Detailed micromorphological studies of subglacial traction tills reveal that these polydeformed sediments may also contain evidence of having undergone repeated phases of liquefaction followed by solid-state shear deformation. This spatially and temporally restricted liquefaction of subglacial traction tills lowers the shear strength of the sediment and promotes the formation of “transient mobile zones” within the bed, which accommodate the shear imposed by the overriding ice. This process of soft-bed sliding, alternating with bed deformation, facilitates glacier movement by way of ‘stick-slip’ events. The various controls on the slip events have previously been identified as: (i) the introduction of pressurised meltwater into the bed, a process limited by the porosity and permeability of the till; and (ii) pressurisation of porewater as a result of subglacial deformation; to which we include (iii) episodic liquefaction of water-saturated subglacial traction tills in response to glacier seismic activity (icequakes), which are increasingly being recognized as significant processes in modern glaciers and ice sheets. As liquefaction operates only in materials already at very low values of effective stress, its process-form signatures are likely indicative of glacier sub-marginal tills.

Citation

Phillips, E., Evans, D., van der Meer, J., & Lee, J. (2018). Microscale evidence of liquefaction and its potential triggers during soft-bed deformation within subglacial traction tills. Quaternary Science Reviews, 181, 123-143. https://doi.org/10.1016/j.quascirev.2017.12.003

Journal Article Type Article
Acceptance Date Dec 3, 2017
Online Publication Date Dec 16, 2017
Publication Date Feb 1, 2018
Deposit Date Dec 6, 2017
Publicly Available Date Dec 16, 2018
Journal Quaternary Science Reviews
Print ISSN 0277-3791
Electronic ISSN 1873-457X
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 181
Pages 123-143
DOI https://doi.org/10.1016/j.quascirev.2017.12.003
Public URL https://durham-repository.worktribe.com/output/1338870

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