Short-period observations of speed, strain and seismicity on Ice Stream B, Antarctica

Abstract

ABSTRACT. The speed ofIce Stream B, Antarctica, was measured twice a day over a 1 month study period, and found to be steady at about the ±3 ~% level, the sensitivity of the measurements. The vertical strain was measured at three sites over a 1 year period at 1 h intervals with sensitivities of 2 or 0.2 ppm. The strain rate varied on all time-scales. Events of high strain rate were observed, but never at more than one site at a time. They can probably be understood in terms oflocal modification of the strain field associated with crevassing. Diurnal variation in strain rate was observed at one and possibly two sites during two summers. The seismicity was measured at all three sites, and diurnal and seasonal variations were prominent at all, the seismicity being much more intense in winter. Several possible causes of the diurnal variations in strain and seismicity are considered: thermal and atmospheric effects, and the effects of tides in the Ross Sea.

Modeling the elastic transmission of tidal stresses to great distances inland in channelized ice streams

“…Seismic studies on several Siple Coast ice streams correlate fluctuations in basal seismicity with the semidiurnal and/or fortnightly ocean tides, suggesting a link between ocean tidal loading and basal stress in these ice streams (Harrison et al, 1993;Anandakrishnan and Alley, 1997;Bindschadler and et al, 2003;Wiens et al, 2008;Walter et al, 2011). Furthermore, continuous GPS (CGPS) surveys on some Antarctic ice streams find surface velocities modulated at tidal frequencies (Rutford Ice Stream: Gudmundsson, 2006Gudmundsson, , 2007Bindschadler Ice Stream: Anandakrishnan et al, 2003) or stick-slip motion correlated with extremes in Brunt et al (2010); 3 Heinert and Riedel (2007); 4 Anandakrishnan and Alley (1997); 5 Scott et al (2009);6 Rignot (1998); 7 Gudmundsson (2006); 8 Gudmundsson (2007); 9 Stephenson (1984); 10 Weins and et al (2008); 11 Winberry et al (2009); 12 Walter et al (2011); 13 Winberry et al (2014); 14 Harrison et al (1993).…”

Insights into ice stream dynamics through modelling their response to tidal forcing

“…Since the discovery of tidal effects on ice streams (Harrison, 1993;Anandakrishnan and Alley, 1997;Engelhardt and Kamb, 1998;Bindschadler et al, 2003a, b;Anandakrishnan et al, 2003;Gudmundsson, 2006), the interpretation and understanding of the mechanisms and impacts has continued to develop. Initial measurements of tidal forcing on ice were limited to the surface of the ice shelves (Williams and Robinson, 1980) and the hinging zone where ice flexure occurs near the grounding line (Smith, 1991;Doake et al, 1987).…”

Earth tide forcing of glacier drainage

“…Earth tide forcing of subglacial P W can therefore be expected to cause periodic variations in the strength of the sediment layers underlying affected ice masses. This implies that the motion speed of the ice mass itself could be modified on a similar time scale, complementing the effects of ocean tides on motion speed where ice masses terminate on water [ Echelmeyer and Harrison , 1989; Harrison et al , 1993]. Second, the character and precise timing of subglacial drainage reorganization events could be influenced by earth tidal cycles.…”

“…However, no empirical evidence of either earth or atmospheric tide forcing of subglacial aquifers has yet been reported. In contrast to ocean tides [ Walters and Dunlap , 1987; Echelmeyer and Harrison , 1989; Harrison et al , 1993; Anandakrishnan and Alley , 1997; Bindschadler et al , 2002], earth tides would affect any grounded ice mass ubiquitously, and could therefore represent an important control on basal drainage and motion at a global scale. In this study, we interpret borehole‐based subglacial hydrological data recorded through the winter months at Haut Glacier d'Arolla, Switzerland, in terms of earth tide forcing.…”