By modulating the effective pressure at the glacier bed, glacier hydraulics play a key role in ice flow dynamics ( Iken and Bindschadler, 1986). In addition, drainage events of glacier-dammed lakes can inject large volumes of water on short timescales, exceeding the capacity of the subglacial conduits and causing a pressurization of the system ( Roberts, 2005).
Such a configuration is often encountered in the early melt season ( Iken and Bindschadler, 1986 Werder et al., 2013). In the case that the drainage system does not adapt fast enough to meltwater input, subglacial water pressures increase.
During the melt season with increased meltwater input, the subglacial drainage system typically transitions from the distributed to a channelized system allowing for more efficient water evacuation ( Fountain, 1993 Hock and Hooke, 1993 Bartholomew et al., 2010). Subglacially, the water flows in a drainage system often described by the two end-member scenarios of distributed and channelized flow ( Fountain and Walder, 1998 Cuffey and Paterson, 2010). On high-melt glaciers, meltwater produced at the surface is routed through moulins and crevasses to the glacier bed. Our results highlight the use of cryo-seismology for monitoring glacier hydraulics. The pressurization is in phase with the drop in the lake level, and its retrieved maximum coincides with ice uplift measured via GPS. Our analysis suggests a pressurization of the subglacial environment at the drainage onset, followed by an increase in the hydraulic radii of the conduits and a subsequent decrease in the subglacial water pressure as the capacity of the drainage system increases. To estimate the hydraulics associated with the drainage, we use tremor–discharge scaling relationships. The ice-marginal lake likely connects to this drainage system via hydrofracturing, which is indicated by sustained icequake signals emitted from the proximity of the lake basin and starting roughly 24 h prior to the lake drainage. Consistent with field observations, continuous source tracking via matched-field processing suggests a gradual up-glacier progression of an efficient drainage system as the melt season progresses. The dominating process can vary on sub-kilometer and sub-daily scales. We find that the tremors are generated by subglacial water flow, in moulins, and by icequake bursts. Together with our seismic data, discharge, lake level, and ice flow measurements provide constraints on glacier hydraulics. Data were recorded during the 2016 melt season including the sudden subglacial drainage of an ice-marginal lake. In this study, we analyze glaciohydraulic tremors recorded by four seismic arrays installed in different parts of Glacier de la Plaine Morte, Switzerland. Water-driven fracturing as well as turbulent water flow within and beneath glaciers radiate seismic waves which provide insights into otherwise hard-to-access englacial and subglacial environments. Have information we can use to flesh out or correct this record let us know.Hydraulic processes impact viscous and brittle ice deformation. This description of a site outside SERC has not been vetted by SERC staff and may be incomplete or incorrect.
STATE THAT SEISMAC TREMORS SOFTWARE
The site features a link to download the software and a link to help files for installing and using it. Time labels tell exactly when an event occurred, the sampling rate can be adjusted, and acceleration data can be smoothed. The software allows users to pause the display to study an event scroll back in time to see older data enlarge or contract the graph, both vertically and horizontally and copy, print or save the screen. The resizable, real-time scrolling display lets students see the seismic waves from tapping their toes on the floor, lay the laptop on their chests to see their heartbeats, or see seismic waves from real earthquakes. It uses the Sudden Motion Sensor (accelerometer) that these machines are equipped with to create and display real-time, three-axis acceleration graphs (seismograms).
STATE THAT SEISMAC TREMORS MAC OS X
SeisMac is a free Mac OS X application that turns MacBook or MacBook Pro laptops into seismographs.
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