Exploring glacier dynamics with subglacial water pressure pulses: Evidence for self‐organized criticality?

In order to determine whether brief excursions, or “pulses,” in subglacial water pressure inferred by Kavanaugh and Clarke (2000, 2001) occur, water pressures at the bed of Trapridge Glacier, Yukon, Canada, were recorded using an interface board that continuously monitored a pressure transducer. During the 231 day period between 16 July 2005 and 4 March 2006, more than 7000 pressure pulses were recorded, with magnitudes reaching nearly 3 times the flotation value. Comparison of the pressure pulse record with those from a number of other instruments installed in this soft‐bedded glacier indicates that these pulses are generated by stress transients that compress the water within the borehole; calculations suggest that these transients are as large as 75 times the nominal driving stress. Both the magnitudes and interevent times for these pulses are well fitted by power law distributions that are remarkably similar to those exhibited by earthquakes. These similarities suggest that the ice‐bed interface of a soft‐bedded glacier behaves much like an earthquake fault and raises the possibility that such glaciers self‐organize to a critical state. Further evidence for self‐organized criticality (SOC) of soft‐bedded glaciers is suggested by an examination of well‐known ice dynamical properties and the rheological properties of subglacial sediments, which suggests that SOC might be a natural consequence of the rate‐independent behavior of subglacial sediments.