Ablation from calving and surface melt at lake-terminating Bridge Glacier, British Columbia, 1984–2013

M Chernos,R D Moore,M Koppes

doi:10.5194/tc-10-87-2016

Abstract

Abstract. Bridge Glacier is a lake-calving glacier in the Coast Mountains of British Columbia and has retreated over 3.55 km since 1972. The majority of this retreat has occurred since 1991. This retreat is substantially greater than what has been inferred from regional climate indices, suggesting that it has been driven primarily by calving as the glacier retreated across an overdeepened basin. In order to better understand the primary drivers of ablation, surface melt (below the equilibrium line altitude, ELA) and calving were quantified during the 2013 melt season using a distributed energy balance model (DEBM) and time-lapse imagery. Calving, estimated using areal change, velocity measurements, and assuming flotation were responsible for 23 % of the glacier's ablation below the ELA during the 2013 melt season and were limited by modest flow speeds and a small terminus cross-section. Calving and surface melt estimates from 1984 to 2013 suggest that calving was consistently a smaller contributor of ablation. Although calving was estimated to be responsible for up to 49 % of the glacier's ablation for individual seasons, averaged over multiple summers it accounted between 10 and 25 %. Calving was enhanced primarily by buoyancy and water depths, and fluxes were greatest between 2005 and 2010 as the glacier retreated over the deepest part of Bridge Lake. The recent rapid rate of calving is part of a transient stage in the glacier's retreat and is expected to diminish within 10 years as the terminus recedes into shallower water at the proximal end of the lake. These findings are in line with observations from other lake-calving glacier studies across the globe and suggest a common large-scale pattern in calving-induced retreat in lake-terminating alpine glaciers. Despite enhancing glacial retreat, calving remains a relatively small component of ablation and is expected to decrease in importance in the future. Hence, surface melt remains the primary driver of ablation at Bridge Glacier and thus projections of future retreat should be more closely tied to climate.

Highlights

Since the end of the Little Ice Age, glaciers across the globe have been shrinking at an accelerated rate (e.g. Dyurgerov and Meier, 2005; Radicand Hock, 2011; Gardner et al, 2013; Zemp et al, 2015)
Terminus velocities increased at Tasman from 69 to 218 m a−1 (Dykes and Brook, 2010; Dykes et al, 2011), while the calving rates for both glaciers increased from 50 m a−1 to between 227 and 431 m a−1 (Boyce et al, 2007; Dykes et al, 2011); these rates are consistent with what we found at Bridge Glacier
Bridge Glacier is a lake-terminating glacier in the Coast Mountains of British Columbia that has retreated over 3.55 km since 1972, with the majority of retreat occurring after 1991

Summary

Introduction

Since the end of the Little Ice Age, glaciers across the globe have been shrinking at an accelerated rate (e.g. Dyurgerov and Meier, 2005; Radicand Hock, 2011; Gardner et al, 2013; Zemp et al, 2015). While recent glacier retreat is well documented (e.g. Kaser et al, 2006), the projection of future retreat is critical to the management of water resources and understanding the evolution of riparian and aquatic habitats (Milner and Bailey, 1989; Cowie et al, 2014). Due to their sensitivity to air temperatures and precipitation, variations in glacial size and volume serve as important high-altitude climate change indicators (Oerlemans, 2005; Kaser et al, 2006). Glaciers that terminate in bodies of water have been shown to exhibit changes in mass balance that are at least partially independent of climate on decadal timescales

Results

Discussion

Conclusion