Better imaging maps Glacier Park’s ice field shrinkage.

The fact that Glacier National Park’s namesake ice fields keep melting doesn’t qualify as breaking news anymore, but the precision with which we can track the shrinkage does.

Improved satellite imaging techniques helped a team of U.S. Geological Survey and Portland State University scientists confirm that 39 named glaciers in the park and adjacent Bob Marshall Wilderness Complex have lost an average 39 percent of their surface area since 1966, with some losing 85 percent. That’s left just 26 ice fields larger than the 25-acre threshold generally needed to be considered a glacier.

The latest periodic glacier analysis was released on May 10. USGS lead scientist Dan Fagre said improved satellite resolution helped his researchers reveal parts of the glaciers that site visits can’t pick up.

“Siyeh Glacier had a lot of rock piled on top that obscured lots of its surface,” Fagre said. “We were tipped off to that because of the resolution of the satellite imagery.”

But ground teams still need to visit the actual mountain basins to examine the mass of the ice fields. One team just returned last week from Sperry Glacier, Glacier Park’s largest remaining ice field at 215 acres. Fifty years ago, it covered nearly 300 acres beneath Mount Edwards and Gunsight Mountain.

“Toward the top, they measured close to 40 feet of snow,” Fagre said of the 2016-17 winter accumulation. “That bodes well for this year, although it depends on how the summer shapes up. It could all disappear. So it remains to be seen whether the positive snow balance gets maintained through September.”

Glacier Park had about 150 glaciers larger than 25 acres when it was originally surveyed a century ago. All were considered small alpine glaciers, which formed about 7,000 years ago. They are very different from the massive Pleistocene epoch glaciers that carved the park’s major valleys and peaks.

“Tracking these small alpine glaciers has been instrumental in describing climate changeClimate change is a lasting change in weather patterns over long periods of time. It can be a natural phenomena and and has occurred on Earth even before people inhabited it. Quite different is a current situation that is also referred to as climate change, anthropogenic climate change, or ... effects on Glacier National Park to park management and the public,” said Lisa McKeon, USGS scientist who has been documenting glacier change since 1997. The high-elevation ice fields store and deliver cold waterClimate change is expected to exacerbate current stresses on water resources from population growth and economic and land-use change, including urbanisation. On a regional scale, mountain snow pack, glaciers and small ice caps play a crucial role in freshwater availability. Widespread mass ... to creeks, lakes and rivers below the peaks, regulating temperatures well into late summer and fall. Many species of fish and insects directly depend on cold-water supplies for survival, including native cutthroat and bull trout.

“While the shrinkage in Montana is more severe than some other places in the U.S., it is in line with trends that have been happening on a global scale,” Portland State geologist Andrew G. Fountain said. “The glaciers in Olympic National Park are not receding as fast, but California’s are receding faster.”

Montana has about 49 square kilometers of glacial ice fields statewide, or about 12,100 acres. California has just 23 square kilometers of glacial ice. Washington, with its greater snowfall and tall volcanic peaks, has 400 square kilometers of glacial ice.

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