Rising ELA and Expanding Proglacial Lakes Lead to Initiation of Rapid Retreat of Brady Glacier, Alaska

• Main Authors: M. Pelto, D. Capps, J. J. Clague, B. Pelto
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: glacier retreat; Glacier Bay; equilibrium line altitude; Ela; Western Glacier; glacier; glaciers; Tidewater; Yakutat; Alaska
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.372.9856; http://www.nichols.edu/departments/glacier/ESC2012.pdf

Brady Glacier, Alaska, is a large tidewater glacier that is beginning a period of substantial retreat. Examination of 27 Landsat and MODIS images from the period 2003–2011 indicates that Brady Glacier has a mean ELA (equilibrium line altitude) of 745 m and AAR (accumulation area ratio) of 0.40. The zero balance ELA is 600 m and equilibrium AAR 0.65. The negative mass balance associated with the increased ELA has triggered thinning of 20–100 m over most of the glacier below the ELA from 1948 to 2010. The thinning has caused substantial retreat of seven calving distributary termini of the glacier. Thinning and retreat have led to an increase in the width of and water depth at the calving fronts. In contrast, the main terminus has undergone only minor retreat since 1948. In 2010 several small proglacial lakes were evident at the terminus. By 2000, a permanent outlet river issuing from Trick Lake had developed along the western glacier margin. Terminus lake development combined with continued mass losses will lead to expansion of the lakes at the main terminus and retreat by calving. The glacier bed is likely below sea level along the main axis of Brady Glacier to the glacier divide. Retreat of the main terminus in the lake will likely lead to a rapid calving retreat similar to Bear, Excelsior, Norris, Portage, and Yakutat glaciers.