Abstract
Abstract. Crystal orientation fabric (COF) analysis provides information about the c-axis orientation of ice grains and the associated anisotropy and microstructural information about deformation and recrystallisation processes within the glacier. This information can be used to introduce modules that fully describe the microstructural anisotropy or at least direction-dependent enhancement factors for glacier modelling. The COF was studied at an ice core that was obtained from the temperate Rhonegletscher, located in the central Swiss Alps. Seven samples, extracted at depths between 2 and 79 m, were analysed with an automatic fabric analyser. The COF analysis revealed conspicuous four-maxima patterns of the c-axis orientations at all depths. Additional data, such as microstructural images, produced during the ice sample preparation process, were considered to interpret these patterns. Furthermore, repeated high-precision global navigation satellite system (GNSS) surveying allowed the local glacier flow direction to be determined. The relative movements of the individual surveying points indicated longitudinal compressive stresses parallel to the glacier flow. Finally, numerical modelling of the ice flow permitted estimation of the local stress distribution. An integrated analysis of all the data sets provided indications and suggestions for the development of the four-maxima patterns. The centroid of the four-maxima patterns of the individual core samples and the coinciding maximum eigenvector approximately align with the compressive stress directions obtained from numerical modelling with an exception for the deepest sample. The clustering of the c axes in four maxima surrounding the predominant compressive stress direction is most likely the result of a fast migration recrystallisation. This interpretation is supported by air bubble analysis of large-area scanning macroscope (LASM) images. Our results indicate that COF studies, which have so far predominantly been performed on cold ice samples from the polar regions, can also provide valuable insights into the stress and strain rate distribution within temperate glaciers.
Highlights
Since the second half of the last century, ice cores have been regarded as extremely valuable archives for reconstructing the climate history of the past hundreds of thousands of years (Robin et al, 1977; Petit et al, 1999; Thompson et al, 2002)
The stresses and strain rates occurring within the ice mass cause glacier flow and induce the development of a characteristic crystal orientation fabric (COF) and microstructural anisotropy (Gow and Williamson, 1976; Herron and Langway, 1982; Alley et al, 1995, 1997) and are summarised in Faria et al (2014a)
The Crystal orientation fabric (COF) results are displayed in the form of Schmidt equal-area stereo-plots on the lower hemisphere
Summary
Since the second half of the last century, ice cores have been regarded as extremely valuable archives for reconstructing the climate history of the past hundreds of thousands of years (Robin et al, 1977; Petit et al, 1999; Thompson et al, 2002). Microstructural investigations have been conducted to reconstruct the ice flow of ice sheets in Greenland and Antarctica as well as in glaciated mountain areas (Russell-Head and Budd, 1979; Alley, 1992; Azuma, 1994). For those investigations, the focus has been on the crystallographic orientation of the ice grains. The stresses and strain rates occurring within the ice mass cause glacier flow and induce the development of a characteristic crystal orientation fabric (COF) and microstructural anisotropy (Gow and Williamson, 1976; Herron and Langway, 1982; Alley et al, 1995, 1997) and are summarised in Faria et al (2014a)
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