| Contribution to sea-level rise from glacier mass loss has increased over recent decades. Current research suggests that the response of glacier mass balance to changes in climate is a function of glacier size, but local topographic factors such as aspect and insolation may have greater effects than size alone. With high quality aerial photography and well-distributed ground control points, digital photogrammetry can be used to develop high-resolution geodetically-derived records of glacier mass balance over time to examine intra- to inter-decadal patterns of glacial change. Stereo pairs of scanned historical aerial photography were viewed in 3D with the Vr Mapping software (Cardinal Systems) and gridded surface elevations were digitized for years between 1965 and 2009. Mass balances were calculated for two small glaciers, Joffre (0.4 km2) and Unnamed (0.15 km2) glacier, in the south Coast Mountains, British Columbia, Canada, over four different intervals within 1965-2009, and over the entire study period. These mass balance measurements were compared to those measured for the larger, and adjacently located Place Glacier (3.31 km2) as calculated by Menounos and Schiefer (2009) using the same geodetic method. All three study glaciers experienced consistently negative mass balances. Over the entire 1965-2009 period, water equivalent mass balances were calculated as -38.0 m, -40.4 m, and -11.6 m for Place, Joffre, and Unnamed glaciers, respectively. Proportional area losses over the time period were 31%, 59%, and 38%, respectively. There was no clear trend in response of either glacier mass balance or areal extent to climate changes over the study period based solely on size. Some differences in glacier response to climate were likely attributable to differences in glacier aspect and insolation, with south-facing, higher insolation Joffre Glacier losing the most mass, and north-facing, lower insolation Unnamed Glacier losing the least mass. Influences such as accumulation through blowing snow and avalanching did not have a visible effect on any glacier's mass balance. Small glaciers, such as Unnamed Glacier, may be able to sooner take advantage of local topographic influences than larger glaciers by retreating into high elevation, north-facing, low insolation niche environments that promote ice maintenance. Most glaciers in the region are likely retreating towards an extent that is nearer to an equilibrium condition for the modern climate regime, however small glaciers may be closer to reaching this state. |
