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Basal hydraulic system of a West Antarctic ice stream: constraints from borehole observations

  • Hermann Engelhardt (a1) and Barclay Kamb (a1)


Pressure and tracer measurements in boreholes drilled to the bottom of Ice Stream B, West Antarctica, are used to obtain information about the basal water conduit system in which high water pressures are developed.These high pressures presumably make possible the rapid movement of the ice stream. Pressure in the system is indicated by the borehole water level once connection to the conduit system is made. On initial connection, here also called “breakthrough” to the basal water system, the water level drops in a few minutes to an initial depth in the range 96–117 m below the surface. These water levels are near but mostly somewhat deeper than the floation level of about 100 m depth (water level at which basal water pressure and ice overburden pressure are equal), which is calculated from depth-density profiles and is measured in one borehole. The conduit system can be modelled as a continuous or somewhat discontinuous gap between ice and bed; the thickness of the gap δ has to be about 2 mm to account for the water-level drop on breakthrough, and about 4 mm to fit the results of a salt-tracer experiment indicating downstream transport at a speed of 7.5 mm s−1. The above gap-conduit model is, however, ruled out by the way a pressure pulse injected into the basal water system at breakthrough propagates outward from the injection hole, and also by the large hole-to-hole variation in measured basal pressure, which if present in a gap-conduit system with δ = 2 or 4 mm would result in unacceptably large local water fluxes. An alternative model that avoids these objections, called the “gap opening” model, involves opening a gap as injection proceeds: starting with a thin film, the injection of water under pressure lifts the ice mass around the borehole, creating a gap 3 or 4mm wide at the ice/bed interface. Evaluated quantitatively, the gap-opening model accounts for the volume of water that the basal water system accepts on breakthrough, which obviates the gap-conduit model. In order to transport basal meltwater from upstream it is then necessary for the complete hydraulic model to contain also a network of relatively large conduits, of which the most promising type is the “canal” conduit proposed theoretically by Walder and Fowler (1994): flat, low conduits incised into the till, ∼0.1 m deep and perhaps ∼1 m wide, with a flat ice roof. The basal water-pressure data suggest that the canals are spaced ∼50–300 m apart, much closer than R-tunnels would be. The deepest observed water level, 117 m, is the most likely to reflect the actual water pressure in the canals, corresponding to a basal effective pressure of 1.6 bar. In this interpretation, the shallower water levels are affected by loss of hydraulic head in the narrow passageway (s) that connect along the bed from borehole to canal(s). Once a borehole has frozen up and any passageways connecting with canals have become closed, a pressure sensor in contact with the unfrozen till that underlies the ice will measure the pore pressure in the till, given enough time for pressure equilibration. This pressure varies considerably with time, over the equivalent water-level range from 100 to 113 m. Basal pressure sensors 500 m apart report uncorrelated variations, whereas sensors in boreholes 25 m араrt report mostly (but not entirely) well-correlated variations, of unknown origin. In part of the record, remarkable anticorrelated variations are interspersed with positively correlated ones, and there are rare, abrupt excursions to extreme water levels as deep as 125 m and as shallow as 74 m. A diurnal pressure fluctuation, intermittently observed, may possibly be caused by the ocean tide in the Ross Sea. The lack of any observed variation in ice-stream motion, when large percentagewise variations in basal effective pressure were occurring according to our data, suggests that the observed pressure variations are sufficiently local, and so randomly variable from place to place, that they are averaged out in the process by which the basal motion of the ice stream is determined by an integration over a large area of the bed.

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Alley, R. B. 1989a. Water-pressure coupling of sliding and bed deformation; I. Water system. J. Glaciol., 35(119), 108118.
Alley, R. B. 1989b. Water-pressure coupling of sliding and bed deformation: II Vocity–depth profiles. J. Glacial., 35(119), 119129.
Alley, R. B. 1990. West Antarctic collapse—how likely? Episodes, 13 (4). 231238.
Alley, R. B. 1993. In search of ice-stream sticky spots. J. Glaciol., 39(133), 447454.
Alley, R.B. and Bentley, D. R. 1988. Ice-core analysis on the Siple Coast of West Antarctica. Ann. Glariol., 11, 17.
Alley, R. B. and MacAyeaL, D. R. 1994 West Anlarelie ice sheet collapse: chimera or clear danger? Antarct J. U.S., 28(5), 1993. 5960.
Alley, R.B.. Blankenship, D. D Bentley, C. R. and Rooney, C.R. 1986. Deformation of till beneath ice Stream B West Antarctica. Nature 322(6074), 5759.
Alley, R.R. Blankenship, D.D. Rooney, S.T. and Bentley, C.R. 1987. Till beneath Ice Sueam B. 4. A coupled ice–till flow model. J. Geophys Res., 92 (B9). 89318940.
Alley, K. R. Blankenship, D. D. Rooney, S. T. and Bentley, R. 1989. Water-pressure coupling of sliding and bed deformation: III. Application to Ice Stream B, Antarctica. J. Glaciol., 35(119), 130139.
Bentley, C.R. 1987. Antarctic ice streams: a review. J. Geophys. Res., 92 (B9), 88438858.
Bindschadler, R. 1983. The importance of pressurized subglacial water in separation and sliding at the glacier bed. J. Glaciol., 29(101), 319.
Bindschadler, R.A., ed. 1991. West Antarctic Ice Sheet Initiative. Volume 1. Science and implementation plan. Washington, DC, National Aemnautics and Spaee Administration, (NASA CP-3115.)
Bindschadler, R. A. and Scambos, T. A. 1991. Satellite-image-derived velocity field of an Aniareiic ice stream. Science, 252(5003), 242246.
Blankenship, D.D., Bentley, C. R. Rooney, S.T. and Alley, R. B. 1986. Seismic measurements reveal a saturated porous layer beneath an active Autaretic ice stream. Nature, 322 (6074). 5457.
Blankenship, D.D.. Bentley, C. R. Rooney, S.T. and Alley, R. B. 1987. Till beneath Ice Stream B. 1. Properties derived from seismic travel times. J. Geophys. Res., 92 (B9). 89038911.
Boulton, G.S. and Hindmarsh, R.C.A. 1987, Sedimem deformation beneath glaciers: rheology and geological consequences. J. Geophys Res., 92 (B9), 90599082.
Bronstein, I.N. and Semendjajew, K. A. 1987. Taschenbuch der Mathematik. Frankfurt/Main. Verlag Harri Deutsch.
Engelhardt, H. 1978. Waler in glaciers: observations and theory of the behaviour of water levels in boreholes. Z. Gletscherkd. Glazialgeol., 14 (1),3560.
Engelhardt, H., Humphrey, N. Kamb, B and Fahnestock, M. 1990. Physical conditons at the base of a fast moving Antarctic ice stream. Science, 248 (4951) 5759.
Fowler, A. C. 1987. Sliding with cavity formation. J. Glaciol., 33(155), 255267.
Gow, A.J. 1970. Preliminary results of studies of ice cores from the 2164m deep drill hole, Byrd Station, Antarctica. International Associaliim of Scientific Hydrology Publication 86 (Symposium at Hanover. New Hampshire, 1968 — Antarctic Glaciologieal Exploration (ISAGE)), 7890.
Harrison, W. D., Echelmeyer, K. A. and Engelhardt, H. 1993. Short-period observations of speed, strain and seismicity on Iee Stream B, Antarctica. J Glaciol., 39(133), 463470.
Hodge, S.M. 1976. Direct measurement of basal water pressures: a pilot study J. Glaitol., 16(74), 205218.
Hodge, S.M. 1979. Direct measurement of basal water pressures: progress and problems. J. Glaciol., 23 (89). 309319.
Iken, A. 1981. The effect of the subglacial water pressure on the sliding velocity of a glacier in an idealized numerical model. J. Glaciol., 27 (97). 407421.
Been, A. and Bindschadler, K. A. 1986. Combined measurements of subglacial water pressure and surface velocity at Findelengletscher, Switzerland: couclusions about drainage system and sliding mechanism. J. Glaciol, 32(110), 101119.
Kamb, B. 1991. Rheological nonlinearity and flow instability in the deforming bed mechanism of ice stream motion. J. Geophys. Res., 96 (B1), 16,585–16,595.
Kamb, B. 1993. Glacier Ilow modeling. In Stone, D.B. and Runcorn, K. eds. Flow and creep in the Solar system: observation, modeling and theory. Dordrecht, etc., Kluwer Academic Publishers. 417506. (NATO ASI Series E: Applied Sciences 391).
Kamb, B. and Echelmeyer, K. A. 1986. Stress-gradient coupling in glacier flow: I. Longitudinal averaging of the influence of ice thickness and surface slope. J. Glaciol., 32(111), 267281.
Kamb, B. and Engelhardt, H. 1987. Waves of accelerated motion in a glacier approaching surge: the mini-surges of Variegated Glacier. Alaska. U.S.A. J. Glariol., 33(113), 2746.
Kamb, B. and 7 others 1985. Glacier surge mechanism: 1982–1983 surge of Variegated Glacier. Alaska. Science, 227(4686), 469479.
Kamb, B., Engelhardt, H, Fahnestock, A. Humphrey, N. Meier, M and Stone, D. 1994. Mechanical and hydrologic basis for the rapid motion of a large tidewater glacier. 2. Interpretation. J. Geophys. Res., 99 (B8), 15,231–15,244.
Lingle, C. S. and Brown, T.J. 1987. A subglacial aquifer bed model and water pressure dependent basal sliding relationship for a West Antarctic ice stream. In Van der Veen, C.J. and Oerlemans, J. eds. Dynamics of the West Antarctic ice the sheet. Dordrecht, etc. D. Reidel Publishing Co., 249285.
MacAyeal, D.R. 1992. Irregular oscillations of the West Antarctic ice sheet. Nature 359(6390), 2932.
Meier, M. and 9 others 1991. Mechanical and hydrologic basis for the rapid motion of a large tidewater glacier. 1. Observations, J. Geophys. Res., 99 (B8), 15,219–15,229.
Murray, T. and Clarke, G. K. C. 1995. Black-box modeling of the subglacial water system. J. Geophys Res.. 100 (B7) . 10,231–10,245.
Paterson, W S. B. 1994. Thre physics of glaciers. Third edition. Oxford, etc.. Elsevier.
Retzlaff, R., Lord, N. and Bentley, C.R. 1993. Airborne-radar studies: Ice Streams A, B and C, West Antarctica. J. Glaciol., 39 (133). 495506.
Rose, K.E. 1979. Characteristics of ice flow in Marie Byrd Lan, Antarctica. J. Glaciol., 24 (90). 6375.
Stone, D. B. and Clarke, G. K. C 1993. Estimation of subglacial hydraulic properties from induced changes in basal water pressure: a theoretical framework for borehole-response tests, J. Glaciol., 39(132), 327340.
Sunder, S.S. and Wu, M. S. 1990. On the constitutive modeling of transient creep in polvcry stalline ice. Gold Reg. Sei. Technol., 18(3), 267294.
Timoshenko, S.P. and Goodier, J.N. 1951. Theory of elacticity. New York, McGraw-Hill Book Co.
Waddington, B.S. and Clarke, C. K. C 1995. Hydraulic properties of subglacial sediment determined from the mechanical response of water-filled boreholes. J Glacial., 41(137), 112124.
Walder, J.S. and Fowler, A. 1994. Channelized Subglacial drainage over a deformable bed. J. Glaciol., 40 (134),. 315.
Weertman, J. 1969. Water lubrication mechanism of glacier surges. Can. J. Earth Sci., 6 (4, Part 2), 929942.
Weertman, J. 1970. A method for setting a lower limit on the water layer thickness at the bottom of an ice sheet from the time required for upweling of water into a borehole. International Association of Scientific Hydrology Publication, 86 (Symposium at Hanover, New Hampshire. 1968 — Antarctic Glaciological Exploration (ISAGE), 6973.
Weertman, J. 1972. General theory of water flow at the base of a glacier or ice sheet. Rev. Geophys, Space Phys., 10 (1). 287333.
Weertman, J. and Birchfield, G. E. 1982. Subglacial water flow under ice streams and West Antarctic ice-sheet stability. Ann. Glaciol., 3, 316320.
Whillans, I.M. 1984. Ice stream dynamics. Antarct J. U.S. 19 (5) 5153.
Whillans, I.M and van der Veen, C.J 1993. New and improved determinations of velocit of Ice Streams B and C, West Antarctica. J. Glaciol., 39(133), 483490.
Whillans, I.M., Bolzan, J and Shabtak, S 1987. Velotity of the Streams B and C, Antarctica. J. Geophys. Res., 92 (B9), 88958902.


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