Glacier Monitoring Studies

Monitoring and Assessing Glacier Changes and Their Associated Hydrologic and Ecologic Effects in Glacier National Park

Purpose: To systematically monitor changes in Glacier National Park’s namesake glaciers and to determine the causes of changes, assess their ecological and hydrological effects, and predict future changes and effects.

Glacier National Park’s namesake glaciers have receded rapidly since the Park’s establishment in 1910, primarily due to long-term changes in regional and global climate. These changes include warming, particularly of daily minimum temperatures, and persistent droughts. This warming is ongoing and the loss of the Park’s glaciers continues, with the park’s glaciers predicted to disappear by 2030.

In the past decade, Glacier NP has experienced dramatic climate variability that includes record winter and summer droughts, near record summertime temperatures, as well as near-record winter snowfall. While the park’s glaciers continue to shrink, it is not clear whether these dramatic fluctuations have accelerated or slowed glacier recession and downwasting. In part this is because studies of glaciers in Glacier NP to date have focused on changes in the area of individual glaciers and the extent of glaciers in the park. Few measurements of glacier volume or mass have been made. Measurements of area alone can be misleading; changes in mass and/or ice flux can result in significant changes to the glacier and to streamflow below the glacier even when glacier area remains stable. Though hydrologic changes such as these can have important ecologic effects downstream of the glaciers, the nature and extent of changes in runoff volume, and stream temperature have not been measured or analyzed.

	Monitoring Summary: The USGS proposes a nested strategy in which an intensively studied glacier is surrounded by less intensively studied glaciers. Concentrated study of one glacier (a benchmark glacier) provides detailed data about physical processes that control glacier mass and area throughout the region. Less intensive study of secondary glaciers provides data about variability of such processes within the region. Data about the benchmark glacier is typically collected annually, with the secondary glaciers studied less frequently or with remote sensing. This monitoring program applies the strategy outlined in A Strategy for Monitoring Glaciers (Fountain, et al, 1997) to the region in and around Glacier NP (approx. 600,000 hectares), keeping in mind the difficult access and small size of glaciers in the area.
	Detailed Site Information: Benchmark Glacier – Sperry Glacier Secondary Glacier Network Sites

Monitoring Methods

Seasonal Mass Balance Measurements: Documenting glacier mass changes is a critical step in defining the responses of glaciers to regional weather and climate variations. Seasonal mass balance measurements are conducted twice each year on the benchmark glacier (Sperry) and every 2-3 years on the secondary glaciers in the network.

Mass balance is determined by measuring the mass of water gained or lost each summer at the glacier's surface. The height of the glacier surface is measured twice yearly, at the accumulation and ablation peaks (late spring and late summer). The initial measurement defines how much water mass, in the form of snow, was deposited on the glacier over the previous winter. The second measurement shows how much water mass - as snow and ice - was lost through melting over the summer. The difference between the two measurements is an estimate of whether the glacier is gaining or losing ice. This mass balance is usually expressed in meters of snow water equivalent. A number close to zero indicates the glacier is in balance - it's neither gaining nor losing mass and would thus likely not be advancing or retreating. A glacier with a negative mass balance is losing more ice each year than is replaced by snow, so it will either recede or thin. The opposite is true for a glacier with a positive mass balance; it will advance or thicken.

The initial mass is calculated by measuring the depth and density of the snow sitting on the glacier. Snow depth is measured by probing through the snow to the ice below. Density is measured in snow pits. The depth and density measurements are combined to calculate the mass of water sitting on the glacier. Stakes are placed in seven meter deep holes drilled through the snow and into the ice below. The stakes are made of 1.5m sections of 2.5cm diameter pvc pipe connected by cable ties, and are removed after each season. When snow or ice melts enough to expose a joint between sections of pipe, the section of the pipe above the joint falls onto the snow surface. At the end of the summer, the length of stake exposed shows how much snow and ice - and thus mass - that's melted over the season at each point. The point measurements are extrapolated across the surface of the glacier to get an overall estimate of how much mass the glacier as a whole is gaining or losing.

Area Measurements:Conducted to quantify changes in the extent of individual glaciers and the regional glacier extent. Measurements are made by mapping the perimeter of glaciers using high resolution GPS receivers. Measurements are made in late summer, when the extent of glacial ice is most evident. Area measurements would be conducted annually on the benchmark glacier, and every 2-3 years on the network’s secondary glaciers.

Repeat Photography: This technique is used as a visual indication of change in glacier area. A collection of historic photos has already been started and some repeats have been taken. Photos are repeated on a 5 year interval unless dramatic changes are noticed sooner. Photos are taken on both the benchmark and secondary glaciers. A collection of repeat photographs of glaciers can be viewed and downloaded at the Repeat Photography Project website.

Hydrology Measurements: Water temperatures in the outflow streams are measured throughout the melt season (May – Sept.) and compared to streams from non glaciated basins. This would determine the impacts that glacial runoff has on stream temperature and also on how far downstream these impacts reach. These measurements are taken with temperature loggers that are about the size of a roll of lifesavers and are tied to a rock in the stream. There are about 3 loggers per stream placed at intervals from just below the glacier, midway downstream, and near the mouth of the stream. Discharge measurements are taken from streams draining the benchmark and secondary glaciers. Grinnell glacier already has a stream gauging station near the lake outlet, but the others will have stream depth and profile measurements taken to determine discharge.

Remote Sensing: This technique is used to see how changes in glaciers not included in our measurement strategy compare to what we know of changes in glaciers which are being monitored. This includes the use of aerial photography and satellite imagery.