2. In the lower region, or ablation (output)
zone, the glacier loses ice through melting and
evaporation. Older ice is carried down to greater and greater
depth.
3. An equilibrium
line divides the two areas. This
spot is like an old fashioned pair of scales used to weigh gold
dust.
4. Advancing ice scrapes and grinds the bedrock,
boulders, and gravel beneath it and pushes a ridge of terminal
moraine in front.
5. Another, or tributary, glacier
sometimes joins the main flow, adding another strip of lateral
moraine debris. The two lateral moraines combine to form a single
medial moraine, which now extends down the middle of the glacier
towards the snout.
6. When two lateral moraines combine, they form a
single medial moraine, which extends down the middle of the glacier
towards the snout. When medial moraines come close to one another
near the terminus, a glacier may look multicolored or striped.
7. Glacier ice melts and fractures, and the sea often
batters it. Finally, chunks of ice break off as icebergs in a process
called calving, which balances the flow of ice from behind.
8. Near the terminus (end) of a
glacier, its surface thins and stretches and breaks into a mosaic of
crevasses.
9. Meltwater flows through hidden channels and
tunnels.
10. Snow to Ice: Water seeps through accumulated snow and gradually
forms horizontal "ice lenses" and vertical "glands." Eventually, the
whole mass compresses into a deep bed of dense ice.
11. Ice Flow: Bending of a vertical bore hole (left) shows how a
glacier moves by internal deformation and sliding at the base (red
arrow).
12. Glacier Bed: Glaciers move by sliding over bedrock or underlying
gravel and rock debris. With the increased pressure because of the
weight, the individual ice grains slide past one another and the ice
moves slowly downhill. Water lubrication is crucial to either
process. The sliding of the glacier over its bed is called
basal slip.