ICE CRYSTAL ORIENTATION DISTRIBUTIONS IN LARGE ICE MASSES

• Main Authors: ショウジ ヒトシ, ミヤモト アツシ, ナリタ ヒデキ, Hitoshi SHOJI, Atsushi MIYAMOTO, Hideki NARITA
• Format: Report
• Language: English
• Published: ABSTRACT 1997
• Subjects: Byrd; Mizuho; Dye 3; Dye-3; Polar meteorology and glaciology; Proceedings of the NIPR Symposium on Polar Meteorology and Glaciology
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=3990; http://id.nii.ac.jp/1291/00003990/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3990&item_no=1&attribute_id=18&file_no=1

Flow behavior of large ice sheets is affected mainly by c-axis orientation fabric, and the fabric formation is caused by the anisotropic characteristics in the plastic deformation property of ice crystal. There are three processes involved in fabric formation; i.e. crystal rotation (AZUMA and HIGASHI, 1985), recrystalization and polygonization. Two types of crystal fabric development with depth have been observed in deep polar ice cores. Type A shows crystal fabric changes from a random distribution near the surface to vertical cluster development with depth under vertical compression and to a strong single maximum pattern near the bottom under simple shear deformation (Camp Century, Dye 3,GRIP and Byrd ice cores). Type B shows fabric changes from a random distribution near the surface to a large girdle development with depth, where the c-axis direction is almost perpendicular to the uniaxial tensile strain axis along the ice flow direction (Mizuho and Vostok ice cores). To estimate vertical compressive strain, ε and uniaxial tensile strain, γ, the following equations were assumed : ε=-ln(y/H), γ=-2ln(y/H), where y is height from the bottom and H is ice thickness. For Type A cores, the c-axis lies mainly along the vertical core direction with depth and a single maximum fabric appears at depth for about ε=150%, except for Byrd core samples which shows single maximum fabric appearance for about ε=80%. For Type B cores, crystal fabrics developments with an increase in γ are quite similar to each other.