State glaciers shrink

The South Cascade Glacier, pictured in 2006, has decreased by more than a third. A report released last month looks at the data and models that track these changes. - U.S. Geological Survey, Washington Water Science Center
The South Cascade Glacier, pictured in 2006, has decreased by more than a third. A report released last month looks at the data and models that track these changes.
— image credit: U.S. Geological Survey, Washington Water Science Center

A new computer model by the United States Geological Survey (USGS) has confirmed what few will be surprised to hear.

The giant glaciers that encase the mountains of western Washington in ice are melting. A study by the USGS shows that the mammoth mound of ice known as the South Cascade glacier has shrunk by more than a third. Like a canary in a coal mine, its demise signals dire implications for our climate and our water supplies.

The report found that the retreat and loss of mass of the South Cascade Glacier during 2006 and 2007 was consistent with data from the collected from the glacier since 1958. The new report finds that glacier has been responding to “climate conditions that will not support the glacier in its recent size and position on the landscape,” the report said.

In other words, it is shrinking.

In 1958, the glacier was 2.71 square kilometers in size. In 2007, its size had diminished more than one-third, down to 1.73 kilometers.

The glacier is located in the North Cascades Mountain range 25 miles north-northeast of the town of Darrington, Wash.

The mass of a glacier is the combined masses of its snow and ice, changes over the seasons as it gains snow and ice or loses them through melting or evaporation. The quantity of snow gained minus ice and snow lost is called the mass balance. Scientists use the mass balance as the best way to know if the glacier is growing or shrinking.

The USGS studies the glacier to understand the variability of the region’s water resources and climate change. The USGS monitors the annual accumulation, ablation, and net mass balance at the glacier itself and examines the snowpack by means of satellite passive microwave and other observations.

A new computer model has been developed to help researchers keep better track of South Cascade Glacier’s mass balance. The model is designed to supplement traditional field measurements and gives researchers a way to reliably estimate the glacier’s annual gains and losses.

“Glaciers are especially tough places to collect data,” said Bill Bidlake, USGS hydrologist and lead author of the report, “and this new mass-balance model helps us to reliably fill in the measurement gaps caused by bad weather and dangerous travel conditions on the ice.”

Glaciers, snow and ice sheets are important components of the Earth’s water and climate. They respond to and indicate changes in climate, as well as exerting an influence on global and regional climate. They also serve as water resources, serving as natural reservoirs. Measuring changes in the size and volume of glaciers and snowpacks provides one direct way of knowing what kind of effects are caused by variations in the global climate. What is not well understood is the relation of snow and ice to climate change and water resources.

Long-term records of glacier changes provide information about climate variability as well as the water available to basins through meltwater. Snowpacks have a great impact on atmospheric circulation and are an important source of water not only for climate and hydration but for hydropower: electrical energy for homes and businesses .

The “mass balance program” at South Cascade Glacier is part of the USGS monitoring of glacier mass balances throughout the Western States. South Cascade Glacier in Washington and Gulkana and Wolverine Glaciers in Alaska are considered “benchmark glaciers.” Records for these glaciers form the basis for examining connections between glaciers and climate.

To see the entire report and other USGS studies, go to

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