Page 578 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

542
As an open system, a glacier is in equilibrium if it is neither advancing nor retreating. But if inputs of snow are greater than losses through melting, deflation by wind, sublimation, and calving, the glacier will expand. If ice losses exceed inputs, the
glacier will retreat (GIA 17.1). Whether a glacier is in equilibrium can be determined from its mass balance (GIA 17.2). Today, many alpine glaciers worldwide are retreating as they melt because of warming related to climate change (GIA 17.3).
CROSS SECTION OF A TYPICAL RETREATING ALPINE GLACIER
The diagram shows the relationship between the zone of accumulation, the equilibrium line, and the zone of ablation in a retreating glacier. Ice continues to slide downhill as the glacier’s terminus retreats upslope, depositing material and creating terminal and recessional moraines. Additional inputs of ice can come from tributary glaciers as glaciers merge. [Bobbé Christopherson.]
17.1
At least four tributary glaciers flowing into a valley glacier, Greenland
Accumulation zone:
Snow and firn build up in this zone, are compressed by their own weight, and change to glacial ice as the glacier increases in thickness.
Merging glaciers, Nordaustlandet Island
Terminal moraine, Nordaustlandet Island, Arctic Ocean
Snow and firn
Plucking Abrasion
Firn line:
The accumulation zone ends; summer melting occurs below this line.
Cirque basin
Tributary glacier
Medial moraine
Lateral moraine
Recessional moraine Melting and
evaporation
Till
Meltwater stream
Ablation zone:
In this zone the glacier loses mass through melting and other processes.
Crevasses
(a)
Glacier ice
Bedrock
Equilibrium line:
Accumulation and ablation are in balance; generally matches the firn line.
Terminal moraine
Outwash plain
Compare: How are the accumulation zone and the ablation zone similar? How are they different?
Visit the Study Area in MasteringGeographyTM to explore glacial mass balance.
Visualize: Study a geosciences animation of Assess: Demonstrate understanding of a glacial processes. glacier’s mass balance (if assigned by
instructor).
geosystems in action 17GLACIERS AS DynAMIC SySTEMS