Hydraulic properties of subglacial sediment determined from the mechanical response of water-filled boreholes

The hydraulic properties of basal sediments must be known if the surge mechanism of soft-bedded glaciers is to be understood. Freezing of water-filled boreholes drives water into the subglacial bed and the associated pressure effects give information about subglacial hydraulic properties. A numerical model describing the mechanical response of an unconnected borehole and the bed beneath it to this freezing forcing was developed, using a non-linear transient viscoelastic ice rheology and an approximate model of top-down freezing. The resulting system of equations was solved using the method of lines. Results agree well with analytic solutions, if parameters are correctly chosen. Forward modelling of pressure records from three 1992 boreholes and three from other years indicates that the till underlying Trapridge Glacier has a hydraulic conductivity of 1.3 x 10⁻⁹-1.35 x 10⁻⁸ ms⁻¹, in agreement with previous indirect estimates. The model was also used to investigate the response of a borehole to sudden pressure changes. The response is very fast compared to pressure sensor sampling rates: thus the "true" basal signal is essentially unaffected by the presence of the borehole, except during the initial freeze-in. The decay events seen in Trapridge Glacier pressure records are caused by the response of the basal drainage system, not the borehole.

Name thesis:degree_name

Master of Science - MSc

Level thesis:degree_level

master's

Discipline thesis:degree_discipline

Geophysics

Grantor dc:publisher

University of British Columbia

Year dc:date

1993

Author dc:creator

• Waddington, Brian Stewart

Statement dc:rights

• For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.

Language dc:language

eng

Handle dc:identifier

http://hdl.handle.net/2429/1527

OAI identifier oai:identifier

oai:circle.library.ubc.ca:2429/1527