Download The action of glaciers

UNIT
8
Surface processes
THE ACTION OF GLACIERS
Biology and Geology 3. Secondary Education
UNIT
8
The action of glaciers
• Glaciers are enormous masses of ice which are formed due to
accumulation, compaction and re-crystallisation of the snow deposited in very
cold regions (the majority of them remote) of the earth’s surface.
• The ice in the glaciers can flow and, like all moving objects, it has energy
which enables it to cause erosion, transportation and sedimentation on the
materials that make up the terrain. This enables glaciers to modify the land
relief.
• As it slides along, the ice rips off fragments of
rock (erosion).
• The fragments of rock are
carried to lower areas
(transportation).
• At the end of its course,
the glacier deposits the
transported fragments
(sedimentation).
Biology and Geology 3. Secondary Education
UNIT
8
The action of glaciers
EROSION
• Glaciers erode the terrain in two ways:
By entrainment: as the ice moves down-slope across a surface with
fractures, due to frost weathering, it lifts up blocks of rock of all sizes,
which are incorporated into the mass of ice.
By abrasion: the fragments of rock carried by the glacier rub against
the surface, smoothing it and polishing it (like sandpaper) or creating
grooves called glacial striations, which make it possible to know the
direction of movement of the ice after it has receded.
• The speed of erosion by the glacier depends on how fast the ice moves,
the size of the fragments it carries and the type of soil the glacier moves
across.
Biology and Geology 3. Secondary Education
UNIT
8
The action of glaciers
FORMS CREATED BY EROSION
Once the glaciers have receded, we can identify the following forms of erosion:
• Glacial valleys. They are wide and U-shaped. They transform into V-shaped
river valleys as watercourses flow down them.
U-shaped glacier valley
Biology and Geology 3. Secondary Education
V-shaped river valley
UNIT
8
The action of glaciers
FORMS CREATED BY EROSION
Once the glaciers have receded, we can identify the following forms of erosion:
• Glacial valleys. They are wide and U-shaped. They transform into V-shaped
river valleys as watercourses flow down them.
Terrain after the glaciers
have receded
Valley glaciers during
glaciation (30,000 years
ago)
Biology and Geology 3. Secondary Education
UNIT
8
The action of glaciers
FORMS CREATED BY EROSION
Once the glaciers have receded, we can identify the following forms of erosion:
• Glacier valleys. They are wide and U-shaped. They transform into V-shaped
river valleys as watercourses flow down them.
• Glacier cirques. They are large depressions which remain in the former area
of accumulation of the glacier. They often have lakes.
• Horn and arêtes. These
are the sharp peaks and
crests of the mountains
around the cirque, formed
by erosion.
Horn
Arête
• Roche moutonée. These
are the rocks on the valley
bottom, polished by the
glacier.
• Fjords. They are former
glacial valleys whose final
section is flooded by the
sea.
U-shaped valleys
Biology and Geology 3. Secondary Education
Glacial
cirques
UNIT
8
The action of glaciers
TRANSPORTATION AND SEDIMENTATION
• As the glaciers move slowly, eroding the valleys, they incorporate and
transport a large quantity of rock fragments.
• When the ice of the glaciers recedes, all those materials are
deposited, creating different forms of glacial sedimentation,
general known as tills o tillites.
Biology and Geology 3. Secondary Education
UNIT
8
The action of glaciers
TRANSPORTATION AND SEDIMENTATION
• As the glaciers move slowly, eroding the valleys, they incorporate and
transport a large quantity of rock fragments.
•.When the ice of the glaciers
recedes, all those materials are
deposited, creating different forms of
glacial sedimentation, generally
known as tills or tillites.
•Tills are an unsorted mixture of
angular fragments of different sizes,
from sands or gravels to large
blocks.
Biology and Geology 3. Secondary Education
UNIT
8
The action of glaciers
TRANSPORTATION AND SEDIMENTATION
•As the glaciers move slowly, eroding the valleys, they incorporate and
transport a large quantity of rock fragments.
When the ice of the glaciers
recedes, all those materials are
deposited, creating different forms of
glacial sedimentation, general
known as tills o tillites.
Lateral moraines
Central
moraine
•Tills are an unsorted mixture of
angular fragments of different sizes,
from sands or gravels to large
blocks.
•The most common forms of
transportation and deposition are the
moraines, which may be lateral,
central, terminal or ground.
Biology and Geology 3. Secondary Education
Terminal
moraines
Ground
moraine