Page 579 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

17.2
GLACIAL MASS BALANCE
The diagram shows the annual mass balance of a glacial system, which determines the location of the equilibrium line. Generally, a glacier with a positive mass balance will expand, while a glacier with a negative mass balance will retreat.
PORTRAIT OF A RETREATING GLACIER, 1979–2010
[Leksele/Shutterstock]
Accumulation zone
+ Positive balance
Equilibrium line
– Negative balance
Direction of flow
Bedrock
Ablation zone
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17.3
South Cascade Glacier in Washington State is one of three glaciers that the United States Geological Survey (USGS) monitors intensively (the other two are in Alaska) to obtain long-term, benchmark data on changes in glaciers in relation to climate. These photographs and other USGS data show that, as temperatures warmed, South Cascade Glacier retreated up its valley and its mass balance declined steadily. [USGS.]
Infer: Based on what you can see in the photos, outline the largest area formerly occupied by South Cascade Glacier. What evidence helped you arrive at this conclusion?
Ice calving off the Perito Moreno glacier, Patagonia, Argentina. [PSD Photography/Shutterstock.]
GEOquiz
2010
1979
1. Predict: How would the position of the firn line change if a glacier receives more snowfall at higher elevations for several years in a row? Explain.
2. Explain: Thinking of a glacier as a system, explain how changes to inputs and outputs result in a glacier’s having a positive or negative mass balance.
geosystems in action 17 GLACIERS AS DynAMIC SySTEMS
(gain)
(gain)
(loss)
(loss)