Structural Glaciology of an Ice Layer in a Firn Fold, Antarctica

  1. Malcolm Mellor
  1. John R. Reid Jr.

Published Online: 14 MAR 2013

DOI: 10.1029/AR002p0237

Antarctic Snow and Ice Studies

Antarctic Snow and Ice Studies

How to Cite

Reid, J. R. (1971) Structural Glaciology of an Ice Layer in a Firn Fold, Antarctica, in Antarctic Snow and Ice Studies (ed M. Mellor), American Geophysical Union, Washington, D. C.. doi: 10.1029/AR002p0237

Author Information

  1. Department of Geology, University of North Dakota, Grand Forks

Publication History

  1. Published Online: 14 MAR 2013
  2. Published Print: 1 JAN 1971

ISBN Information

Print ISBN: 9780875901169

Online ISBN: 9781118669808

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Keywords:

  • Firn fold;
  • Glaciology;
  • Ice layer;
  • Petrofabric analysis procedure;
  • Ross ice shelf

Summary

Firn folds up to 8 meters high and with a wavelength approximating 100 meters are present in the vicinity of the Bay of Whales, Ross ice shelf, Antarctica. They were formed through the convergence of two ice masses flowing around Roosevelt Island about 20 miles to the south. In one of the folds an ice layer formed through the refreezing of meltwater produced during the summer season 1952–1953. This layer, and another formed in 1913–1914, were studied in detail to determine (1) the relationship of crystal size to the proximity to the snow surface and the crevasse wall along which the layers were exposed; (2) the relationship between crystal size and the stresses within the fold; and (3) the density and pattern of preferred crystal orientation as related to the crystal size and the fold stresses.

The crystal grains range from 4.5 to 2.5 mm in median diameter, the diameter being controlled by the intensity of solar radiation, the type and the amount of stress, and the content of air bubbles in the ice. The largest crystals occur where the solar radiation is most effective and where shear stress and air bubble content are at a minimum.

The strongest preferred orientation of c axes (8–9 per cent per 1 per cent area) occurs approximately midway from the crest to the adjacent trough, where shear stress is theoretically greatest. Microfolds also exist at this site. The ‘ideal' ice fabric pattern at this location consists of four c-axis maxima, centered at 21°, 26°, 27°, and 32°, respectively, from the pole to the shear plane. The major strain directions were determined from measurements in the anticlinal area. This fabric pattern does not correspond to any other observed or theoretical pattern, with one possible exception, and appears partially to reflect some rotation of the stresses relative to the present fold axis.

The c axes of crystals in an isolated secondary fold along the limb of the major fold are parallel to the bedding plane of each limb, a situation suggesting that the ice layer deformed by translation glide along the basal glide planes of the ice crystals.