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Derivation Of Flow-Law Properties From Bore-Hole Tilt Data: Discussion Of The Dye 3, Camp Century, And Byrd Station Bore-Hole Results

Published online by Cambridge University Press:  20 January 2017

D. Dahl-Jensen  and
N.S. Gundestrup
D. Dahl-Jensen
Affiliation:
Department of Glaciology, Geophysical Institute, University of Copenhagen, Haraldsgade 6, DK -2200 Copenhagen N, Denmark
N.S. Gundestrup
Affiliation:
Department of Glaciology, Geophysical Institute, University of Copenhagen, Haraldsgade 6, DK -2200 Copenhagen N, Denmark
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Abstract

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Type
Abstracts of Papers Presented at the Symposium but not Published in this Volume
Information
Annals of Glaciology , Volume 12 , 1989 , pp. 200 - 201
Copyright
Copyright © International Glaciological Society 1989

Derivation of flow properties from bore-hole tilts is a popular way of determining flow properties of “real” glacier ice. Many interpretations have been made of the measurements from the Camp Century bore hole (Reference PatersonPaterson, 1983; Reference Wolff and DoakeWolff and Doake, 1986), the Byrd Station bore hole (Reference PatersonPaterson, 1983; Reference Doake and WolffDoake and Wolff, 1985), and the Dye 3 bore hole (Reference Dahl-Jensen and GundestrupDahl-Jensen and Gundestrup, 1987; Reference Pimienta and DuvalPimienta and Duval, 1987) where the flow-law exponent in Glen's flow law has values ranging from 1 to 3. The great allowance for variations in the exponent is primarily due to the experimental error in the tilt measurements.

The high-quality bore-hole tilt data from the 2037 m deep Dye 3 bore hole are used to illustrate some of the difficulties which are connected with the use of field measurements to determine flow-law parameters. In the 250 m thick bottom layer of Wisconsin ice, where 80% of the deformation occurs, the deformation rates are enhanced by the varying impurity concentrations and crystal sizes.

The data from this region cannot be used to determine flow-law properties until the enhanced flow is quantitatively explained. In the remaining 1785 m of ice, the experimental error on the tilting rates in the upper 890 m are of the same order of magnitude as the measurements themselves. This leaves us with 900 m of ice, in which only 20% of the deformation occurs, to determine the flow-law parameters. In this region, the importance of including the longitudinal stress deviators and using stress fields that include variations due to the rough bedrock are discussed.

The experience from the Dye 3 bore-hole tilt data is used to discuss the Camp Century and Byrd Station bore-hole results.

One of the most obvious suggestions for future work is the need for re-surveying the existing bore holes. This would allow determination of significant tilt rates in the upper parts of the ice even though the lower part of the bore hole is inaccessible.

References

Dahl-Jensen, D. Gundestrup, N.S.. 1987 Constitutive properties of ice at Dye 3, Greenland. International Association of Hydrological Sciences Publication 170 (Symposium at Vancouver 1987 — The Physical Basis of Ice Sheet Modelling), 31–43. Google Scholar
Doake, C.S.M. Wolff, E.W.. 1985 Flow law for ice in polar ice sheets. Nature, 314(6008), 255–257. Google Scholar
Paterson, W.S.B. 1983 Deformation within polar ice sheets: an analysis of the Byrd Station and Camp Century borehole–tilting measurements. Cold Reg. Sci. Technol., 8(2), 165–179. Google Scholar
Pimienta, P. Duval, P.. 1987 Rate controlling processes in the creep of polar glacier ice. J. Phys. (Paris), 48, Colloq. C1, 243–248. (Suppl. au 3.) CrossRefGoogle Scholar
Wolff, E.W. Doake, C.S.M.. 1986 Implications of the form of the flow law for vertical velocity and age–depth profiles in polar ice. J. Glacial., 32(112), 366–370. Google Scholar