CONTERMINOUS UNITED STATES
Status of Glacier Monitoring and the Remote Sensing Snow-and Ice-Data Base
in the Conterminous USA
Robert Krimmel, USGS
More glaciers are presently monitored in the conterminous USA than ever before. Most glaciers are in National Parks, and since the early 1990's the National Park Service has begun a program to monitor glaciers in the National Parks. In 1996, 4 glaciers in North Cascades NP were monitored for the 4th year with seasonal balance measurements and annual vertical photography. Two of these glaciers will continue to be monitored indefinitely. In Olympic National Park, the Blue glacier has been continuously monitored since 1958, primarily by the University of Washington, and present efforts are to continue simple seasonal balance measurements, and to determine ice volume changes between several mapped dates. At Mt. Rainier National Park sequential vertical photography is done about every 5 years to measured ice surface levels and terminus changes. A program to measure altitudes along 3 transverse profiles of Nisqually Glacier, begun in the early 1930's, is continuing. In Glacier National Park, vertical photography of all the glaciers is obtained every 3 years, and a GIS data base including all available information about the changes is size of the glaciers has been developed. In Yosemite, McClure Glacier data from 1968-1974 has been assembled for publication, and a volunteer program is ongoing to monitor a nearby glacier. The US Geological Survey is continuing a program begun in 1958 to monitor South Cascade Glacier in Washington State with seasonal mass balance measurements combined with meteorological and hydrological measurements.
The glaciers within the conterminous USA are scattered over a large area, and tend to be small. Most glaciers taken individually are insignificant, but these small glaciers are very important hydrologically when taken as a whole, and should not be ignored in glacier inventories. Because of the small size of these glaciers, the present synoptic remote sensing data from Landsat and SPOT are of marginal use for glacier monitoring. Recent satellite sensors with less than 15 m resolution have potential utility, as does a plethora of still-to-be released classified intelligence data. Presently, the most informative glacier data base is the USGS 7.5 minute (1:24,000 scale) topographic map set. Many of these maps are now 30-40 years old, and show the glaciers as they were at that time. Despite the passage of time, these maps are often the most accurate portrayal of the snow and ice available. More recent mapping-quality photography is sometimes available through the National High Altitude Photography program, or within other agencies archives (such as state Department of Natural Resources, or the Forest Service), but are often difficult to locate. The USGS Ice and Climate Project also has acquired a collection of vertical and oblique photographs of glaciers of western North America, which are indexed by glacier name, and spans a time of 1960-1996. Only a small portion of this collection has been used to produce new glacier maps. Glacier inventories, which are a compilation of all the snow and ice areas within a specified geographic area, have only been completed for the North Cascades of Washington. We presently can not give an area of snow and ice cover within most geographic areas simply because the inventories have never been completed. The data base exists, that being the previously mentioned topographic map series, combined with more recent photography which is usually available. A potentially extremely useful outfall from the topographic map series is a compilation of all snow and ice masses into a digital data base. Each snow patch could be defined by a polygon around its perimeter, with a low density digital elevation model of its topography, and geo-referenced with name (if there is one), latitude and longitude, date of the photography from which the map was made, and other relevant data. This would become a "snapshot" of snow and ice from several decades ago, would allow changes between that time and more recent measurements (whether aerial photography, satellite, or other means), and would allow simple searches and statistics to be used to make general statements concerning regional glacier areas. The glacier areas in the accumulation zone, which may change dramatically year-to-year, independently of the long-term "glacier fluctuation" change, must be "locked" to a specific value so that only the terminal changes are monitored. Snow and ice identification algorithms must be developed so that small changes in end-of-balance-year snow albedo, or other conditions that may artificially change the apparent area of snow or ice do not dominate results derived by massive processing of remote sensing data.
Careful analysis of the dual data set of topographic maps and recent aerial photography or other remote sensing material will allow the interim change in glacier area to be measured, and will supply vital global change measurements. [an error occurred while processing this directive]