1Glacier motion dominated by processes deep in underlying till

• Main Authors: Martin Truffer, William D. Harrison, Keith A. Echelmeyer
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: alaska range; glacier; Alaska
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.505.829; http://www2.gi.alaska.edu/~truffer/publications/deform.pdf

Black Rapids Glacier is a 40 km long, surge-type glacier in the central Alaska Range. In spring 1997 a wire line drill rig was set up at a location where the measured surface velocities are high and seasonal and annual velocity variations are large. The drilling revealed a layer of subglacial `till', up to 7 m thick, that is believed to be water saturated. At one location a string of instruments, containing three dual-axis tiltmeters and one piezometer, was successfully introduced into the till. The tiltmeters monitored the inclination of the borehole at the ice-till interface, 1 m into the till, and 2 m into the till for 410 days. They showed that no signi¯cant deformation occurred in the upper two meters of the till layer, and no signi¯cant amount of the basal motion was due to sliding of the ice over the till. The measured surface velocity at the drill site is about 60 ma¡1, of which 20-30 ma¡1 can be accounted for by ice deformation. Almost the entire amount of basal motion, 30-40 ma¡1, was taken up at a depth in the till greater than 2 m, possibly in discrete shear layers, or as sliding of till over the underlying bedrock. We propose that the large-scale mobilization of such till layers is a key factor in initiating glacier surges. 2INTRODUCTION