Mapping the Subglacial Drainage System from Dense Array Seismology: a Multi-method Approach.
Abstract
Subglacial hydrology strongly modulates glacier basal sliding, and thus likely exerts a major control on ice loss and sea-level rise. However, the limited direct observations of the spatial organisation of the subglacial drainage system make difficult to assess the physical processes involved in its development. Recent work shows that detectable seismic noise is generated by water flowing subglacially, such that seismic noise analysis may be used to retrieve subglacial channelized water flow physical properties. Yet, such approach has essentially been applied to investigate changes in subglacial channels physics with time, but the capability of using seismic observations to investigate the spatial organisation of the drainage system (e.g. channels number and positions) remains to be investigated. The objective of this study is to do so using dense array seismic observations. We use 1-month long ground motion records at a hundred of sensors deployed on the Argentière Glacier (French Alps) during the onset of the melt season, when the subglacial drainage system is expected to strongly evolve in response to the rapidly increasing water input. We conduct a multi-method approach based on the analysis of both amplitude and phase maps of seismic signals. The amplitude content is evaluated after correction from site effects, and the phase content is evaluated through two approaches, which are cross-spectral density analysis and event-location from beamforming analysis. We observe characteristic spatial patterns that are consistent across those three independent techniques, which we attribute to the underlying subglacial drainage system.
Our approaches present results with very high temporal day-to-day variability. During periods of rapid changes in water input, we identify two main subglacial channels whose positions are coherent with those expected from hydraulic potential calculations. During the rest of the survey, we both observe period with homogeneous and heterogeneous spatial patterns. Seismic noise can therefore reveal how the subglacial water flow spatial properties (pressure conditions, channels geometry) changes in response to water input. Our spatialized observations may help tackle long-lasting questions on the spatiotemporal variability of the physics of subglacial water flow.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S31A..05N
- Keywords:
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- 0799 General or miscellaneous;
- CRYOSPHERE;
- 9810 New fields (not classifiable under other headings);
- GENERAL OR MISCELLANEOUS;
- 1895 Instruments and techniques: monitoring;
- HYDROLOGY;
- 7299 General or miscellaneous;
- SEISMOLOGY