Physical Geography Essay: Glaciers Essay

This essay has a total of 1198 words and 6 pages.

Physical Geography Essay: Glaciers

a) In what ways do glaciers erode? (8)

The almighty glacier can be very powerful when it moves, eroding anything that gets in its
way. The glacier erodes in a number of ways, be it by abrasion, plucking or dilation,
their paths of erosion rarely go unnoticed.

Abrasion occurs when there are debris between the bedrock and the icesheet or in the lower
layer of ice. This layer of debris is pressed against the ice and grinds away material
from the bedrock as the glacier moves. The rate of abrasion depends on a number of
factors. The speed of the ice’s movement is an important factor, since if the ice were to
move slowly, the rate of abrasion would be low. Another pivotal factor is the amount of
debris there is. Obviously clean ice or one with very little debris will have little
effect. The angularity of the debris is also important, as jagged debris will increase the
rate of abrasion. The relative hardness of the bedrock to the debris is crucial since if
the bedrock were to be much more resistant or harder than the debris then the debris will
be worn down, as opposed to the bedrock being eroded. A more obscure but vital factor is
the rate of removal of the debris. If the ice were already full of debris hence the rate
of removal low, th!

e debris will form a quasi-protective layer shielding the bedrock from any abrasive
action. The thickness of ice is the final factor that plays a role in abrasion rates. The
graph below shows how the rate of abrasion changes with increasing ice thickness. At a),
there is increasing friction as pressure increases hence increased abrasion. At b),
however, increased pressure leads to pressure melting at the glacier base. Water reduces
the friction, therefore reduces the abrasion. At c), the pressure increases to a point
where friction is so great that material does not move and lodgment occurs.

Plucking, or quarrying, occurs when glaciers freeze around loosened rock and ‘pluck’ them
out when the glacier moves. The rock may be have been loosened due to a variety of
reasons, for example, freeze thaw weathering within the glacier. This is known as
regelation. Plucking may also take place away from a valley wall, e.g., when the glacier
is upstream of a large bolder, pressure will build up behind the bolder. This will cause
pressure melting hence allows the glacier to flow around the bolder and refreeze. Now the
bolder is more susceptible to plucking.

Dilatation or pressure release occurs when ice takes the place of the rock it previously
eroded. Since the ice is less dense than the previous rock, the rock is allowed to expand
and ‘release’ the pressure that it was once subjected to, hence the name: pressure
release. This expansion will cause cracks to form in the rock that will encourage future
plucking and abrasion.

Frost shattering takes place where the water enters cracks and freezes. Since ice expands,
this causes the joint to be widened and makes it more vulnerable to future erosional

Rock fracture is a very rare form of erosion, which occurs when the sheer force of the ice
slamming into the bedrock erodes it. Since ice rarely moves at such a speed, this form of
erosion is rarely seen.

Rotational movement occurs when large amounts of snow fall on the ice. The weight of the
snow makes the ice readjust its mass. The rotational slumping that occurs is thought to be
responsible for the over-deepening of corrie floors.

b) What landscape evidence would indicate that glacial erosion has occurred. (17)

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