Hydrologic and Thermal Responses to Rapid Retreat of a Lake-Terminating Glacier

English Abstract:

There has been increasing concern about the effects of ongoing glacier retreat and its influences on downstream river flows and aquatic habitat, including water temperature. Few studies have focused on the downstream effects associated with the formation of proglacial lakes, and no studies to our knowledge have focused on the effects of icebergs calved from lake-terminating valley glaciers. To address this knowledge gap, we are studying Bridge Glacier in the Coast Mountains of British Columbia, Canada, which currently terminates in a proglacial lake with a maximum depth of ~180 m. Analysis of Landsat imagery and application of an inverse linear response model indicate that the rate of retreat increased by two- to three-fold over predicted rates when the glacier terminus retreated into an over-deepened basin ca 1991. Field observations and energy-balance analysis for summer 2013 demonstrate that the presence of icebergs reduced summertime warming of the lake, as a result of a) the reduced area of water surface exposed to energy exchange and b) the consumption of thermal energy to drive sub-aqueous melting. During the 2013 field season, iceberg calving represented about 25% of the total mass loss of the glacier, and an energy balance analysis suggested that iceberg melting accounted for 6-7% of the total discharge recorded downstream of the lake. Once Bridge Glacier retreats to the point it becomes land-terminating, the loss of iceberg production will result in increased summertime lake warming and a reduction in meltwater runoff, with implications for downstream aquatic environments. Ongoing research is focused on generating longer-term estimates of iceberg dynamics and their influence on summer streamflow trends.