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Physical Geography Essay: Glaciers

Term Paper Title: Physical Geography Essay: Glaciers
Word Count: 1198
Page Count: 4.79 (250 words per page double spaced)

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 processes.

     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...

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