We demonstrate that high-frequency observations of subglacial hydraulic processes provide new insights into this evolving dynamic system. Using both the resonance frequencies and attenuation of recorded crack waves we estimate thickness, aperture and length of the resonating basal water layer patch into which we drilled. Our borehole observations confirm the occurrence of both sound and crack waves within the basal water layer. Long-wavelength resonances, in contrast, experience restoring forces due to elasticity and are composed of anomalously dispersed crack waves or Krauklis waves. Within such structures, short-wavelength waves experience restoring forces due to compressibility and are composed of sound waves. We apply a previously established theory of wave propagation along thin, water-filled structures such as water-filled voids, basal water layers, or hydraulic fractures. Here, we explore these mechanics using observations from a kHz-sampled pressure sensor installed in a borehole directly above the hard granite bedrock of a temperate mountain glacier in Switzerland. Within the subglacial system, rapid changes in these processes may excite resonances whose interpretation requires an understanding of the underlying wave mechanics. Hydraulic processes within and beneath glacial bodies exert a far-reaching control on ice flow through their influence on basal sliding.
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