Studies of crystal fabrics and structures in glaciers

• Main Author: Rigsby, George P.
• Format: Others
• Published: 1953
• Online Access: https://thesis.library.caltech.edu/1735/1/Rigsby_gp_1953.pdf; Rigsby, George P. (1953) Studies of crystal fabrics and structures in glaciers. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/03RC-6663. https://resolver.caltech.edu/CaltechETD:etd-05122003-112509 <https://resolver.caltech.edu/CaltechETD:etd-05122003-112509>

Optical orientation of approximately 5000 ice crystals was determined on the Emmons Glacier in 1950, the Malaspina Glacier in 1951, and the Saskatchewan Glacier in 1952, by means of a 6-inch universal stage mounted between crossed polaroid sheets. The crystals measured were 0.2-6 inches across, and from three to eighty were included in each 4 ? x 6-inch thin-section. The optic axes when plotted on a Schmidt equal-area projection, form consistent patterns which appear to be related to the foliation in the ice. The patterns usually feature strong maxima at the corners of diamond shaped quadrangles. Concentrations of axes as high as 26 per cent in 1 per cent of the area were recorded. Two possible mechanisms for producing common orientation of the crystals in glacier ice seem plausible. One is ?instantaneous recrystallization? by means of which the atoms in a lattice become energized under stress and rearrange themselves into more comfortable positions. The second is the growth of crystals favorable to deformation on glide planes at the expense of those which are unfavorably oriented for gliding and consequently become strained and develop higher free energy. From the study of fabric patterns in glaciers it seems likely that the two crystals are oriented in such a way as to allow gliding either on two glide planes other than the well-known basal plane, or on the basal glide plane with the pattern later being changed by recrystallization, possibly by an ordered response within the crystals to the relaxation of stresses. This might be compared to annealing behavior in metals. It is postulated that ?solid flow? occurs in ice by deformation on glide planes and continuous recrystallization with migration of grain boundaries as local stresses on each crystal slowly change. The preferred orientation of crystals is probably developed by growth of crystals favorably oriented for gliding at the expense of the others.