SPATIAL MODELLING OF ALPINE GLACIERS DURING THE LITTLE ICE AGE AND MODERN VARIABILITY IN GLACIER EXTENT

Digital data sets are used to investigate glacial changes occurring in the Columbia and Canadian Rocky Mountains since the Little Ice Age (LIA) maximum. We use a geospatial approach to reconstruct former glaciers and measure both modern glacier elevation and areal extent. The availability of higher resolution digital datasets enables landscape modelling and analysis at a finer scale than previously possible. This makes it feasible to model small niche and cirque glaciers that are sensitive to environmental changes over short time periods.

Using photogrammetric techniques, 10 m digital elevation models and orthorectified air photos were created for use in glacial reconstruction models. Glacier surfaces at 16 sites were modeled from trimline and LIA moraine elevations using a spline interpolation technique in a geographic information system (GIS). These LIA glacier surfaces yield a regional equilibrium line altitude (ELA) of 2500 m ± 25 m and a modern ELA of 2615 m± 25 m, using an accumulation area ratio of 0.6. Although ELA values vary widely within each basin, a regional trend does exist with higher ELAs found farther east in the Rockies.

In 2005 these glaciers occupied 0-67% of their maximum LIA extent. Overall, glaciers smaller than 1 km² during the LIA have experienced the most severe changes in areal extent and ice thickness. Observations show that their relative extents are strongly affected by glacier size and topographic conditions, such as shading and exposure. Hypsometric curves and spatial statistics indicate that glacier response is influenced by topography, and suggest that although microclimate characteristics may play an important role for the existence of small glaciers, the effect of topography is paramount. Glaciers situated in areas of the most favorable topographic conditions will reach greater maximum extents and persist longer than their counterparts.