The influence of a poroelastic till on rapid subglacial flooding and cavity formation

Hewitt, D. R. and Chini, G. P. and Neufeld, J. A. (2018) The influence of a poroelastic till on rapid subglacial flooding and cavity formation. Journal of Fluid Mechanics, 855. pp. 1170-1207. ISSN 0022-1120, ESSN: 1469-7645 DOI https://doi.org/10.1017/jfm.2018.624

[img] Text
influence_of_a_poroelastic_till_on_rapid_subglacial_flooding_and_cavity_formation.pdf - Published Version
Restricted to Registered users only

Download (2MB)

Abstract

We develop a model of the rapid propagation of water at the contact between elastic glacial ice and a poroelastic subglacial till, motivated by observations of the rapid drainage of supraglacial lakes in Greenland. By treating the ice as an elastic bending beam, the fluid dynamics of contact with the subglacial hydrological network, which is modelled as a saturated poroelastic till, can be examined in detail. The model describes the formation and dynamics of an axisymmetric subglacial cavity, and the spread of pore pressure, in response to injection of fluid. A combination of numerical simulation and asymptotic analysis is used to describe these dynamics for both a rigid and a deformable porous till, and for both laminar and turbulent fluid flow. For constant injection rates and laminar flow, the cavity is isostatic and its spread is controlled by bending of the ice and suction of pore water in the vicinity of the ice-till contact. For a deformable till, this control can be modified: generically, a flexural wave that is initially trapped in advance of the contact point relaxes over time by diffusion of pore pressure ahead of the cavity. While the dynamics are found to be relatively insensitive to the properties of the subglacial till during injection with a constant flux, significant dependence on the till properties is manifest during the subsequent spread of a constant volume. A simple hybrid turbulent-laminar model is presented to account for fast injection rates of water: in this case, self-similar turbulent propagation can initially control the spread of the cavity, but there is a transition to laminar control in the vicinity of the ice-till contact point as the flow slows. Finally, the model results are compared with recent geophysical observations of the rapid drainage of supraglacial lakes in Greenland; the comparison provides qualitative agreement and raises suggestions for future quantitative comparison.

Item Type: Article
Uncontrolled Keywords: 2018AREP; IA74
Subjects: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Divisions: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Journal or Publication Title: Journal of Fluid Mechanics
Volume: 855
Page Range: pp. 1170-1207
Identification Number: https://doi.org/10.1017/jfm.2018.624
Depositing User: Sarah Humbert
Date Deposited: 11 Apr 2019 11:45
Last Modified: 11 Apr 2019 11:45
URI: http://eprints.esc.cam.ac.uk/id/eprint/4441

Actions (login required)

View Item View Item

About cookies