Former dynamic behaviour of a cold-based valley glacier on Svalbard revealed by basal ice and structural glaciology investigations

• Published in: Journal of Glaciology
• Main Authors: Lovell, H., Fleming, E.J., Benn, D.I., Hubbard, B., Lukas, S., Naegeli, K.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2015
• Subjects: Arctic glaciology; Basal ice; Ice dynamics; Structural glaciology; Subglacial sediments; Arctic; Svalbard; Tellbreen; glacier; Journal of Glaciology; Spitsbergen
• Online Access: https://research-portal.st-andrews.ac.uk/en/publications/4de31780-5439-4c88-9d39-f0a15bf8c420; https://doi.org/10.3189/2015JoG14J120; https://research-repository.st-andrews.ac.uk/bitstream/10023/7724/1/Benn_2015_JoC_Former.pdf

Large numbers of small valley glaciers on Svalbard were thicker and more extensive during the Little Ice Age (LIA), demonstrated by prominent ice-cored moraines up to several kilometres beyond present-day margins. The majority of these glaciers have since experienced a long period of strongly negative mass balance during the 20 th century and are now largely frozen to their beds, indicating they are likely to have undergone a thermal transition from a polythermal to a cold-based regime. We present evidence for such a switch by reconstructing the former flow dynamics and thermal regime of Tellbreen, a small cold-based valley glacier in central Spitsbergen, based on its basal sequence and glaciological structures. Within the basal sequence, the underlying matrix-supported diamict is interpreted as saturated subglacial traction till which has frozen at the bed, indicating that the thermal switch has resulted in a cessation of subglacial sediment deformation due to freezing of the former deforming layer. This is overlain by debris-poor dispersed facies ice, interpreted to have formed through strain-induced metamorphism of englacial ice. The sequential development of structures includes arcuate fracture traces, interpreted as shear planes formed in a compressive/transpressive stress regime; and fracture traces, interpreted as healed extensional crevasses. The formation of these sediment/ice facies and structures is indicative of dynamic, warm-based flow, most likely during the LIA when the glacier was significantly thicker.