Diapositiva 1

1
UNIT
Surface processes
8
THE ACTION OF GLACIERS
Biology and Geology 3. Secondary Education
2
UNIT
The action of glaciers
8

• 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
  earths 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.

Biology and Geology 3. Secondary Education
3
UNIT
The action of glaciers
8
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
4
UNIT
The action of glaciers
8
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
V-shaped river valley
Biology and Geology 3. Secondary Education
5
UNIT
The action of glaciers
8
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
6
UNIT
The action of glaciers
8
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. 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.
Biology and Geology 3. Secondary Education
7
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
8

• 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
9

• When the ice of the glaciers recedes, all those
  materials are deposited, creating different forms
  of glacial sedimentation, general known as tills
  o tillites.
• 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