• The petrofabrics of aufeis in a turbulent Alaskan stream

      Kreitner, Jerry D. (1969-05)
      The growth, form, and decay of ice in turbulent Goldstream Creek, Alaska, has been observed each year since 1964. Overflows which occur throughout the early part of the winter deposit layers of ice (aufeis) upon the pre-existing ice surface. Vertical and horizontal thin sections of the stream ice from the years 1965-66, 1966-67, and 1967-68 were examined and photographed under ordinary and polarized light. The c-axes of the crystals were oriented with a Rigsby four-axis stage and plotted on Schmidt equal-area nets. Examination of photographs and stereograms revealed five basic types of ice in Goldstream Creek: (1) clear, massive, original stream ice composed of elongate, tapered crystals in which the c-axes are primarily horizontal and randomly oriented; (2) bubbly overflow ice layers (aufeis) with horizontal c-axes which are sometimes aligned parallel to the stream flow; (3) skim ice layers with vertical to horizontal c-axis crystals; (4) fine-grained equigranular snow ice; and (5) underwater ice masses of slightly coherent, rounded plates with the c-axes normal to the plates and randomly oriented. During break-up the melt-water flows on top of the stream ice and slowly erodes the ice layers in the stream by a combination of melting and mechanical fragmentation. The layers are eroded away in descending order from the top to the bottom of the stream.