Stress-induced foliation in the terminus of Variegated Glacier, Alaska, U.S.A, formed during the 1982–83 surge

Two sets of bubble-density foliation, one vertical and transverse to flow and one vertical and parallel to flow, developed in the ice of the terminus lobe of Variegated Glacier, Alaska, during the passage of the final stages of the 1982–83 surge in June and July 1983. The transverse foliation is ubiquitous in the lower part of the terminus lobe affected by the surge, but disappears abruptly over a 5 m wide zone at the boundary of the surge, as delineated by measurable strain rates during the surge. The ice at the outermost limit of the transverse foliation experienced compressive total strains no greater than −0.10 (logarithmic), but did briefly experience high strain rates, corresponding to compressive stresses in excess of 0.6 MPa. It is concluded that the transverse foliation was developed as a consequence of high compressive stress rather than high total strains. Experimental evidence of Kamb indicates that bubble migration occurs under similar tectonic conditions to those in the terminus lobe during the surge, and that bubble migration is related to stress rather than finite deformation or rotation of pre-existing structures. Bubble migration may be the mechanism by which the transverse foliation developed during the passage of the surge front.