Using pressure pulse seismology to examine basal criticality and the influence of sticky spots on glacial flow

Abstract

[1] Here we report results of water pressure pulse studies conducted at Storglaciären (Sweden) and West Washmawapta Glacier (British Columbia, Canada). Comparison of pressure pulse records with meteorological conditions at Storglaciären indicates that several periods of increased basal slip activity observed during a 10 day interval of summer 2008 were due to precipitation loading of the glacier surface, rather than to infiltration of surface water to the glacier bed; this indicates that the glacier bed was close to the failure strength for much of this interval. Pressure pulse magnitudes for the two glaciers were well-fit by power law distributions similar to those earlier observed at Trapridge Glacier (and similar in form to the Gutenberg-Richter relationship commonly used in seismology), suggesting that the mechanical processes that give rise to these distributions are robust features of soft-bedded glaciers. In contrast, interevent time distributions for both glaciers diverge from those observed at Trapridge Glacier for short recurrence intervals, suggesting that the factors that govern the rate at which these processes occur differ between glaciers. An examination of pressure pulse characteristics at West Washmawapta Glacier indicates that the establishment of a basal drainage system in summer 2008 resulted in increased stability and reduced sensitivity to meltwater input, suggesting that common assumptions about the relationship between meltwater production and ice flow are oversimplified. These results demonstrate that water pressure pulse observations can provide valuable insight into the dynamics of soft-bedded glaciers.Citation: Kavanaugh, J. L., P. L. Moore, C. F. Dow, and J. W. Sanders (2010), Using pressure pulse seismology to examine basal criticality and the influence of sticky spots on glacial flow,

Short duration water pressure transients in western Greenland's subglacial drainage system

“…During a 231 day period on Trapridge Glacier, Kavanaugh (2009) measured 1467 pressure pulses in one borehole with magnitudes >4.7 m; 70 of these had magnitudes greater than the local ice overburden pressure of 47.2 m. On West Washmawapta Glacier, a total of 199 260 pulses were measured in a single borehole with magnitudes >0.5 m over a 290 day period (Kavanaugh and others, 2010). Visual inspection shows that more than 1000 of these pulses had magnitudes >5 m (see Kavanaugh and others, 2010, Fig. 8c).…”

“…If the local system is closed, then it is possible to generate pulses through small volume changes in water cavity volume at the bed (Kavanaugh, 2009; Kavanaugh and others, 2010). Explaining the pressure drops we measure through volume change requires an expansion of ~10 −2 %.…”

“…Attempts to measure short duration pressure changes in the subglacial drainage system are rare, but in all cases where pressure has been measured at high frequency, transient pressure pulse behavior has been common. Kavanaugh (2009) and Kavanaugh and others (2010) measured thousands of subglacial pressure pulses on Trapridge and West Washmawapta glaciers that were pervasive through both winter and summer seasons, and with magnitudes exceeding the local ice overburden pressure. In other studies, pulse behavior was not directly measured, but inferred from pressure changes that were large enough to permanently deform the pressure transducer measurement diaphragm (Kavanaugh and Clarke, 2000) or induce transducer failure (Kavanaugh and Clarke, 2001).…”

“…All existing measurements have been made beneath Canadian alpine glaciers with till beds. Frequent pulse behavior therefore appears to be a robust feature of soft-bedded glaciers, and may be a potential indicator of basal conditions (Kavanaugh and others, 2010). Furthermore, such changes in water pressure may influence glacier erosion rates by changing basal stress conditions that drive quarrying processes (Iverson, 1991; Hallet, 1996; Cohen and others, 2006).…”

The crystal fabric of ice from full‐waveform borehole sonic logging

“…In this section we briefly review common practice of correcting for temperature and pressure. For temperature (Table 2), a number of published glacio‐seismological studies [ Blankenship and Bentley , 1987; Anandakrishnan and Bentley , 1993; Mayer et al , 2000; Studinger et al , 2003; Dahl‐Jensen et al , 2003; Benjumea et al , 2003; Nøst , 2004; Navarro et al , 2005; King and Jarvis , 2007; Horgan et al , 2008; Kavanaugh et al , 2010] use the ‐2.3 m s −1 K gradient of Kohnen [1974]. The Kohnen [1974] gradient was derived empirically from seismic refraction studies in Antarctica and Greenland.…”