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Prouty Glacier icefall.jpg



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Figure showing the accumulation and ablation zones on a glacier that are separated by the equilibrium line (dashed line). Note that glaciers calve icebergs only if they terminate in a body of water. 


Figure showing the loss of glaciers in western North America from 100% at 2000 (1.0) to 0% at 2100 (0.0). Results are from Hock et al. (2019, J. Glaciology)

A glacier is an ice body that deforms under its own weight. To do this, the ice must be at least 30 m (100 feet) thick so that its weight causes the bottom ice to deform like toothpaste. 

A glacier forms when snow lasts through the summer for many summers. Overtime, that snow compacts into ice and the ice turns into a glacier once it is over 30 m thick. At that point, the ice then flows down slope to a lower and warmer elevation where it melts. 

A glacier is divided into two zones: the accumulation and ablations zones. The accumulation zone is where snow survives through the summer, which will eventually turn into ice and feed the glacier. The accumulation zone is where the glacier gains mass. 


The ablation zone is the region where all prior winter snow is melted and the underlying glacial ice is also melted (and sublimated directly into the atmosphere). If there is a lake in front of the glacier, then it can calve off icebergs as well. The ablation zone is where the glacier loses mass.


The dividing line between the accumulation and ablation zones is called the equilibrium line. The equilibrium line altitude (ELA) roughly corresponds with the summer snow line as well as the elevation where the mean annual temperature is 0 degrees Celsius (32 degrees Fahrenheit). 

When a glacier gains more mass in its accumulation zone than loses in its ablation zone, its mass balance is positive. After several years of positive mass balance, the glacier will grow and advance down slope, increasing in size and length. If a glacier loses more mass than it accumulates, then it will retreat. This is what is occurring across much of Western North America. Depending on the model used, Western North America could lose 60 to 90% of its glaciers by 2100. 

For more, see Mazama article "What is a glacier?"


The loss of glaciers will have a profound effect on the ecosystem and dependent economies. In Oregon, glaciers provide crucial summer meltwater that keeps streams flowing long after the snow has melted away. This sustains agriculture, ranching and fisheries. Hydroelectric dams depend on summer glacier melt to keep power production. 

The Oregon Glaciers Institute will place the changes in Oregon's glaciers and their impacts within this larger regional to global context. 

A cartoon showing the effects that will come from global warming's impacts on mountain regions and glaciers from Hock et al. (2019; IPCC Special Report). 

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