Module 13 | Scenario 2: Exploring Glacier Change

Key Concepts

Glaciers create beautiful mountain landscapes, enable snow-sure skiing, and provide vital freshwater resources. Today, glaciers worldwide are monitored from space using satellites, but there are 41 glaciers on which scientists have collected extensive observations over a period of more than 30 years. The World Glacier Monitoring Service recognizes these as reference glaciers because they provide longer-term observations of glacier change and variability. 

The observations collected on these reference glaciers enable one to calculate the long-term or year to year glacier mass balance, which is the change in the amount of water stored as ice in the glacier. If the glacier mass balance is positive, the glacier is gaining mass, with more water stored as ice in the glacier. This might occur, for example, after a cold, snowy year. Conversely, if the glacier mass balance is negative, the glacier is losing mass, with less water stored as ice in the glacier, as might happen after a warm, dry year when the glacier loses more mass to melting than it gains from snowfall.  

These glaciers also have long records of the position of the lowest end of the glacier, known as the front or terminus. Changes in the position of the front are known as front variations and are positive if the glacier is advancing and negative if the glacier is retreating. Cumulative front variations show the total change in the position of the front (typically in meters) since the beginning of the observational record or a specified time.

The photo below of the Emmons Glacier on Mount Rainier in Washington State provides an example of a typical glacier. High on the mountain is the accumulation zone where the mass gained from snowfall exceeds the loss from the melt. The glacier flows to a lower elevation where the ablation zone is found. Here, the mass lost to melting exceeds that gain from snowfall.  

The lower portion of the Emmons Glacier is debris-covered and buried by dirt and rocks. About 15% of all glaciers are debris-covered. Eventually, the glacier ends at the front or terminus.  

Over the course of a year, a glacier can lose or gain mass if there is a difference between the mass gained from snowfall compared to that lost from the melt or other processes like sublimation. Glacier mass balance thus reflects the cumulative effect of precipitation, temperature, and radiation, with glaciers serving as a natural thermometer of climate change.  

a. Annual glacier mass balance

Below is an example of the annual mass balance of the Silvretta Glacier, a small glacier in northeast Switzerland (Google Maps Link) with a long record extending back to 1918/1919. Blue bars indicate positive values, which means the glacier gained mass.  Red bars indicate negative values, which means the glacier lost mass. Values are expressed in units of millimeters of water equivalent (mm w.e.), which represents the depth of water contained in the ice gained or lost if it were spread out over the area of the glacier. Fluctuations from annual mass gains to annual mass losses occurred until the early 1980s, although mass loss years were more frequent and sometimes greater than mass gain years. After the early 1980s, mass loss has dominated. In 2020/2021 a record mass loss of over 3,000 millimeters w.e. occurred, which means that the water contained in the ice loss was enough to cover an area equal to that of the glacier to a depth of over 3,000 millimeters (3.0 meters, about 10 feet). That water flowed away from the glacier or was lost through sublimation to the atmosphere, but this illustrates that a tremendous amount of ice was lost by the glacier.  

Annual mass balance of the Silvretta Glacier

b. Cumulative front variations

Another sign of glacier change is variations in the position of the glacier front. The change in position of the glacier front from some reference time is known as the cumulative front variation and is typically given in meters. The cumulative front variation is negative if the glacier is retreating and positive if the glacier is advancing. A retreating glacier doesn't mean that the glacier is moving uphill, but instead that the glacier is melting (and sublimating) faster than it flows, resulting in a retreat of the glacier front.  

Records for the cumulative front variation of the Silvretta Glacier are shorter than those for annual mass balance and begin in 1956/1957. Through the end of the record in 2022 this glacier, which is about 3,000 meters (3 kilometers) long, has retreated about 500 meters (0.5 kilometers). There was a period in the late 1970s and early 1980s when the glacier front neither retreated nor advanced much from year to year. Comparison with the glacier mass balance graph above shows this was a period during which the frequency and size of the positive and negative mass balance years were relatively similar.  

Cumulative front variation of the Silvretta Glacier

c. Glacier Data

Observations from the World Glacier Monitoring Service reference glaciers are available at this site. Click on the glacier name in the list of reference glaciers on that site to access the data. Annual mass balance graphs usually appear on each glacier's site, but if not, can be accessed at the bottom of the page by clicking on the MB graph icon near the bottom of the page. Cumulative front variation graphs can be accessed by clicking on the FV graph icon near the bottom of the page (not available for all glaciers).