Earth Tidal Controls on Basal Dynamics and Hydrology

Details Earth Tidal Controls on Basal Dynamics and Hydrology Earth Tidal Controls on Basal Dynamics and Hydrology

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmip21a0664k&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #IP21A-0664

Mathematics

Logic

0915 Downhole Methods, 1249 Tides: Earth, 1827 Glaciology (1863), 1863 Snow And Ice (1827)

Scientific paper

We appraise earth tidal forcing of coupled mechanical and hydrological processes beneath warm-based ice masses, which have to date been poorly documented but represent exciting phenomena that have important implications for future studies of glacier dynamics. Regular cycles in winter and early spring electrical self-potential (SP), water pressure (PW) and electrical conductivity (EC) were recorded at the bases of several boreholes drilled through Haut Glacier d'Arolla, Switzerland. Fourier power spectra of these data reflect the presence of diurnal and semi-diurnal cycles, and comparison with the earth tidal spectrum indicates that at least four components of the latter are visible in the borehole spectra: the luni-solar diurnal, the principal lunar diurnal, the principal solar semi-diurnal, and the principal lunar semi-diurnal. This correspondence suggests that earth tides exert a strong control over water flow at the bed of the glacier, at least during winter and early spring. We envisage a mechanism that involves earth-tide induced deformation of the bedrock and the unconsolidated sediments beneath the glacier, and to a certain extent probably also the overlying ice body. Basal water pockets, including those containing our sensors, located within these media are in turn also likely to be deformed periodically. We believe that PW gradients induced by such deformation may result in transient water flow and SPs in the pockets. Since PW and EC are typically out-of-phase, injection of waters of lower EC into the pockets during times of peak water flow is likely. Several lines of evidence suggest that such injection was caused by melting of the ice wall due to frictional heating, balancing creep closure which sustained some pockets through the winter. Further, the first annually-repeated post-winter reorganization event, termed the May event, may well be triggered by tidally-induced releases of waters from storage. This implies that the May event marks the opening of the subglacial drainage conditions at the start of the summer, and not the Spring event, as commonly assumed to date.

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