USE OF A DIGITAL ELEVATION MODEL TO MEASURE DEFLATION OF A ROCK GLACIER IN OPABIN BASIN, YOHO NATIONAL PARK

Adjacent to the Opabin Glacier in Yoho National Park is a rock glacier that geomorphologically appears to be a debris-covered glacier. However, this interpretation conflicts with geophysical analyses that suggest that there is no massive ice under large areas of this debris. This study presents a method of (a) detecting the recent presence of massive ice under a debris cover; (b) roughly quantifying the deflation of this rock glacier over several decades; and (c) illustrating the areal distribution of this deflation.

Rock glaciers remain poorly understood, in spite of numerous studies, in part due to the lack of practical methods to measure volume and distribution of ice under and within rock debris. For two years, the Opabin Basin in the Lake O’Hara watershed has been monitored by an international team of hydrogeologists and geophysicists to gain an understanding of hydrological responses of alpine basins to climate warming. A large contribution to the basin’s runoff is glacially derived, but difficult to predict due to the large debris-covered component of the Opabin Glacier.

In this study, photogrammetrically derived digital elevation models (DEMs) of the rock glacier surfaces in 1962 and 2006 are compared. This is the first study in Canada that attempts to moniter a rock glacier with this methodology. Aerial photographs are used to generate stereo images and DEMs with remote sensing and GIS programs. Comparison of the DEMs provides a method of identifying areas where significant deflation has occurred over the four decades, as well as serving to quantify this deflation.

Results suggest (1) development of localized depressions that are interpreted to be thaw pits, as well as significant uniform melting of large areas, particularly along parts of the north-east edge of the rock glacier; and (2) average deflation over the surveyed area of ~6±3m, with maximum deflation values of ~40±3m. The DEM comparison shows reasonable congruence with the geophysical survey completed for most areas of the rock glacier, although interpretations differ as to the nature of the ice at the toe: the results of the DEM comparison suggest the presence of massive ice, in contrast to geophysical interpretations which suggest interstitial ice.