Anatomy of a Glacier DefinitionsAnatomy of a GlacierDefinitions1. The accumulation (input)zoneis where a glacier gains snow and ice through snowfall andcompression. Ice begins to flow like a conveyor belt, driven bygravity and ever mounting snows.
2. In the lower region, or ablation (output)zone, the glacier loses ice through melting andevaporation. Older ice is carried down to greater and greaterdepth.
3. An equilibriumline divides the two areas. Thisspot is like an old fashioned pair of scales used to weigh golddust.
4. Advancing ice scrapes and grinds the bedrock,boulders, and gravel beneath it and pushes a ridge of terminalmoraine in front.
5. Another, or tributary, glaciersometimes joins the main flow, adding another strip of lateralmoraine debris. The two lateral moraines combine to form a singlemedial moraine, which now extends down the middle of the glaciertowards the snout.
6. When two lateral moraines combine, they form asingle medial moraine, which extends down the middle of the glaciertowards the snout. When medial moraines come close to one anothernear the terminus, a glacier may look multicolored or striped.
7. Glacier ice melts and fractures, and the sea oftenbatters it. Finally, chunks of ice break off as icebergs in a processcalled calving, which balances the flow of ice from behind.
8. Near the terminus (end) of aglacier, its surface thins and stretches and breaks into a mosaic ofcrevasses.
9. Meltwater flows through hidden channels andtunnels.
10. Snow to Ice: Water seeps through accumulated snow and graduallyforms horizontal "ice lenses" and vertical "glands." Eventually, thewhole mass compresses into a deep bed of dense ice.
11. Ice Flow: Bending of a vertical bore hole (left) shows how aglacier moves by internal deformation and sliding at the base (redarrow).
12. Glacier Bed: Glaciers move by sliding over bedrock or underlyinggravel and rock debris. With the increased pressure because of theweight, the individual ice grains slide past one another and the icemoves slowly downhill. Water lubrication is crucial to eitherprocess. The sliding of the glacier over its bed is calledbasal slip.
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