| Abstract/Description or Keywords |
Bridge Glacier is a lacustrine calving glacier located in the southern Coast Mountains and terminates in a 6.2 km² proglacial lake. The glacier has retreated more than 3.55 km up-valley since 1984, the majority of the retreat having occurred since 2003. While surface melt may have contributed to the retreat, calving allowed for an additional annual volume of ice loss. The relative contributions from surface melt and calving to the total volume of ice loss is examined for the 2013 melt season. Surface melt is quantified using on-glacier meteorological data to drive a distributed energy balance model. The calving flux is quantified using field measurements of lake bathymetry, terminus area change, and ice thickness. Calving flux estimates are completed by daily measurements of terminus surface velocity derived from manual feature tracking using oblique time lapse camera imagery. Calving accounts for 23% of the total ice loss in the 2013 melt season, suggesting that surface melt is the main driver of mass loss at Bridge Glacier. Data from the 2013 field season is used to inform historical calving flux and surface melt estimates from 1984 to 2013. The calving flux is minor until 1991, at which point the glacier terminus achieves flotation, and begins to discharge large tabular icebergs. Calving was characterized by large, multi-annual retreats, alternating with periods of relative stability. The calving flux peaked from 2005 to 2010, when it was roughly equal to the mass loss due to surface melt. Calving was a much smaller contributor of mass loss from Bridge Glacier, except for a transient high-calving period in the late 2000s. Looking forward, Bridge Glacier will retreat into shallower water where the terminus will no longer float, and calving losses should decrease substantially. Although calving losses will become an increasingly minor portion of the mass balance, future retreat is expected at Bridge Glacier due to a legacy of dynamic thinning brought about by its transient calving phase. |
