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, Harold, Fleming, Edward J., Benn, Douglas I., Hubbard, Bryn, Lukas, Sven, Naegeli, Kathrin
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2015
• Subjects: /dk/atira/pure/core/subjects/geography; Geography; Svalbard; Tellbreen; glacier; Journal of Glaciology; Spitsbergen
• Online Access: https://doi.org/10.3189/2015JoG14J120; https://researchportal.port.ac.uk/portal/en/publications/former-dynamic-behaviour-of-a-coldbased-valley-glacier-on-svalbard-revealed-by-basal-ice-and-structural-glaciology-investigations(9810cdf7-0160-467c-8f57-21e9288a1e94).html; https://researchportal.port.ac.uk/ws/files/2274580/Lovell_et_al._2015_.pdf; http://www.igsoc.org/journal/61/226/j14j120.html

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 20th 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.