Arctic GIS Workshop Poster Abstract
The Use of GIS Methods for Determining Changes in Mountain Glaciers
Glaciers all over the world have been changing noticeably in the last 50 years. Mountain glaciers are particularly sensitive to a changing climate, and their status has direct relevance to regional climatology, streamflow and global sea level change. As a measure of how glaciers are changing, one can easily determine changes in terminus position. However, these changes are difficult to interpret in terms of mass balance and climate change because they require knowledge of glacier dynamics and its associated response times. Glacier volume changes are more easily and directly related to climate change and sea level, but such changes are typically difficult and expensive to determine. For this reason, there have been relatively few studies of glacier changes in North America (for example, there are only three or four ongoing mass balance studies in Alaska, and these are not necessarily on 'representative' glaciers). Recently, we have developed an airborne laser altimetry system which, when combined with GIS techniques, enables us to more easily determine surface elevation, area and volume changes. We have applied these methods to over 90 glaciers in Alaska, Washington and Canada. By comparison of our altimetry profiles with existing maps we can determine changes over the last 40 years or so. By making repeat profiles we can also determine changes over the last decade and even ongoing changes over seasonal and annual time scales. The glaciers in our dataset represent a variety of climatological regions, glacier sizes and types.
We use GIS methods to integrate Digital Elevation Models over prescribed glacier outlines. This gives us the surface area of the glacier, and changes in this area due to advance or retreat. We also determine the distribution of glacier area as a function of elevation. These GIS results can then be combined with our elevation change measurements to determine volume changes and long term glacier mass balances. The changes we are seeing on Alaska and Canadian glaciers are quite significant. We have measured glacier-wide thinning rates of 0.2 to 1.5 m per year over the last 40 years, with near-terminus thinning rates of up to 6 m/yr over this interval. Repeat profiling of these glaciers shows that, in many cases, ongoing rates of thinning have increased, with glacier-wide thinning rates of up to 3 m/yr over the last five years. These large thinning rates give important information on regional changes in arctic climate and on the contribution of mountain glaciers to sea level change.
Our results are of interest not only to other glaciologists, but also to climatologists, oceanographers, and others interested in the ice-climate system. We would like to see our data disseminated to these wider scientific audiences. As the majority of our data is spatially distributed, we suggest that our results could ideally be presented within an arctic GIS framework, making it readily available to others. The datasets would consist of elevation change along the different glaciers, areal extent and changes thereof, as well as overall volume changes for a large number of glaciers.