Thermomechanical behavior of large ice masses
wich Islands (Baker 1978), we find that an aphyric andesite from northern Candlemas Island is almost identical to the Vostok tephra (table). Lavas from Candlemas Island are exceptionally low in potash (K20) (Tomblin 1979), a characteristic feature of the Vostok tephra. All available data at this time strongly suggest that the South Sandwich Islands-and in particular Candlemas Island-is the source of the Vostok tephra. Vostok Station is over 4,000 kilometers in a direct line from Candlemas Island, and yet the Vostok tephra is clearly visible and 0.05 meter thick. It is highly prob able that the Vostok tephra is widespread over the east antarctic ice sheet, and has the potential to act as an important stratigraphic marker horizon. We wish to thank Crank Heikan and the Los Alamos National Laboratory for their assistance. This work is supported by National Science Foundation grant DPP 80-21402. References Baker, P.E. 1968. Comparative volcanology and petrology of the Atlantic island-arcs. Bulletin Volcanologique, 32, 189-206. Baker, P.E. 1978. The South Sandwich Islands: III Petrology of the volcanic rocks. (British Antarctic Survey Scientific Reports No. 93.) Cambridge, England: British Antarctic Survey. Delmas, R., and C. Boutron. 1980. Are the past variations of the stratospheric sulfate burden recorded in central Antarctic snow and ice
Thermomechanical behavior of large ice masses D. A. YUEN and M. R. SAARI Department of Geology Arizona State University Tempe, Arizona 85287 C. SCHUBERT
Department of Earth and Space Sciences University of California Los Angeles, California 90024
The simulation of the thermomechanical structure of large ice sheets is complicated by the coupling between the temperature and the deformation due to the strong temperature-dependence of ice rheology. We have proposed (Yuen and Schubert 1979; Schubert and Yuen 1982) that instabilities may arise from viscous dissipation, leading to basal melting and foundering of the antarctic ice sheets. We have continued our work on this problem by developing: (1) a faster way of obtaining one-dimensional steady-state velocity and temperature profiles of large ice masses, (2) a numerical code that can be used to
1984 REVIEW
layers? Journal of Geophysical Research, 85, 5645-5649. Gonzalez-Ferran, 0. 1982. The Antarctic Cenozoic volcanic provinces and their implications in plate tectonic processes. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Cow, A.J., and T. Williamson. 1971. Volcanic ash in the Antarctic ice sheet and its possible climatic implications. Earth and Planetary Science Letters, 13, 210-213. Hammer, C.U. 1980. Acidity of polar ice cores in relation to absolute dating, past volcanism, and radio-echoes. Journal of Glaciology, 25, 359-372. Hammer, C. U., H. B. Clausen, and W. Dansgaard. 1981. Past volcanism and climate revealed by Greenland ice cores. Journal of Volcanology and Geothermal Research, 11, 3-10. Katsui, Y. 1982. Late Cenozoic petrographic provinces of the volcanic rocks from the Andes to Antarctica. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Kyle, P.R., J.M. Palais, and R. Delmas. 1982. The volcanic record of Antarctic ice cores: Preliminary results and potential for future investigations. Annals of Glaciology, 3, 172-177. Mosley-Thompson, E. 1980. 911 years of microparticle deposition at the South Pole: A climatic interpretation. (Institute of Polar Studies, Report 73.) Columbus: Ohio State University Press. Parker, B.C., E.J. Zeller, and A.J. Cow. 1982. Nitrate fluctuations in Antarctic snow and firn: Potential sources and mechanisms of formation. Annals of Glaciology, 3, 243-248. Tomblin, J.F. 1979. The South Sandwich Islands: II The geology of Candlemas Island. (British Antarctic Survey Scientific Reports No. 92.) British Antarctic Survey, Cambridge, England.
monitor the time history of shear heating instabilities of ice flows, and (3) an essentially analytical model to account for the role played by the thinning of the ice sheet in glacial surges. In the course of constructing steady-state profiles, we have found a new class of solutions associated with large accumulation rates. The character of the new solutions arises physically from a thermal blanketing effect produced by advection of cold material toward the base of the ice sheet. For representative values of ice rheological parameters and typical surface conditions, the new solutions are obtained whenever the accumulation rate exceeds a few tenths of a meter per year. This solution branch is characterized by its relative stability to finite-amplitude perturbations. For accumulation rates smaller than a few tenths of a meter per year, the solutions are unstable to finite-amplitude perturbations. Because accumulation rates are on the order of 0.1 meter per year, it is important to delineate better the boundary separating these two families of solutions. This research was supported by National Science Foundation grant DPP 82-15015. References Schubert, C., and D.A. Yuen. 1982. Initiation of ice ages by creep instability and surging of the East Antarctic ice sheet. Nature, 296, 127-130. Yuen, D.A., and C. Schubert. 1979. The role of shear heating in the dynamics of large ice masses. Journal of Glaciology, 24, 195-212.
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Thermomechanical behavior of large ice masses D. A. YUEN and M. R. SAARI Department of Geology Arizona State University Tempe, Arizona 85287 C. SCHUBERT
Department of Earth and Space Sciences University of California Los Angeles, California 90024
The simulation of the thermomechanical structure of large ice sheets is complicated by the coupling between the temperature and the deformation due to the strong temperature-dependence of ice rheology. We have proposed (Yuen and Schubert 1979; Schubert and Yuen 1982) that instabilities may arise from viscous dissipation, leading to basal melting and foundering of the antarctic ice sheets. We have continued our work on this problem by developing: (1) a faster way of obtaining one-dimensional steady-state velocity and temperature profiles of large ice masses, (2) a numerical code that can be used to
1984 REVIEW
layers? Journal of Geophysical Research, 85, 5645-5649. Gonzalez-Ferran, 0. 1982. The Antarctic Cenozoic volcanic provinces and their implications in plate tectonic processes. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Cow, A.J., and T. Williamson. 1971. Volcanic ash in the Antarctic ice sheet and its possible climatic implications. Earth and Planetary Science Letters, 13, 210-213. Hammer, C.U. 1980. Acidity of polar ice cores in relation to absolute dating, past volcanism, and radio-echoes. Journal of Glaciology, 25, 359-372. Hammer, C. U., H. B. Clausen, and W. Dansgaard. 1981. Past volcanism and climate revealed by Greenland ice cores. Journal of Volcanology and Geothermal Research, 11, 3-10. Katsui, Y. 1982. Late Cenozoic petrographic provinces of the volcanic rocks from the Andes to Antarctica. In C. Craddock (Ed.), Antarctic geoscience. Madison: University of Wisconsin Press. Kyle, P.R., J.M. Palais, and R. Delmas. 1982. The volcanic record of Antarctic ice cores: Preliminary results and potential for future investigations. Annals of Glaciology, 3, 172-177. Mosley-Thompson, E. 1980. 911 years of microparticle deposition at the South Pole: A climatic interpretation. (Institute of Polar Studies, Report 73.) Columbus: Ohio State University Press. Parker, B.C., E.J. Zeller, and A.J. Cow. 1982. Nitrate fluctuations in Antarctic snow and firn: Potential sources and mechanisms of formation. Annals of Glaciology, 3, 243-248. Tomblin, J.F. 1979. The South Sandwich Islands: II The geology of Candlemas Island. (British Antarctic Survey Scientific Reports No. 92.) British Antarctic Survey, Cambridge, England.
monitor the time history of shear heating instabilities of ice flows, and (3) an essentially analytical model to account for the role played by the thinning of the ice sheet in glacial surges. In the course of constructing steady-state profiles, we have found a new class of solutions associated with large accumulation rates. The character of the new solutions arises physically from a thermal blanketing effect produced by advection of cold material toward the base of the ice sheet. For representative values of ice rheological parameters and typical surface conditions, the new solutions are obtained whenever the accumulation rate exceeds a few tenths of a meter per year. This solution branch is characterized by its relative stability to finite-amplitude perturbations. For accumulation rates smaller than a few tenths of a meter per year, the solutions are unstable to finite-amplitude perturbations. Because accumulation rates are on the order of 0.1 meter per year, it is important to delineate better the boundary separating these two families of solutions. This research was supported by National Science Foundation grant DPP 82-15015. References Schubert, C., and D.A. Yuen. 1982. Initiation of ice ages by creep instability and surging of the East Antarctic ice sheet. Nature, 296, 127-130. Yuen, D.A., and C. Schubert. 1979. The role of shear heating in the dynamics of large ice masses. Journal of Glaciology, 24, 195-212.
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