Factors Affecting Rates of Abrasion Flashcards
What is glacial abrasion?
Glacial abrasion is the process of erosion in which a glacier wears away the bedrock over which it moves through the grinding action of the debris embedded in its base.
What is the role of basal debris in glacial abrasion?
The presence of basal debris is essential for glacial abrasion. Pure ice is unable to carry out abrasion of solid rock, and the rate of abrasion increases with the amount of basal debris up to a point where it produces great friction, which slows down rates of movement.
What is the significance of debris size and shape in glacial abrasion?
Particles embedded in ice exert a downward pressure proportional to their weight, and so larger debris is more effective in abrasion than fine material. Angular debris is also more effective as the pressure is concentrated onto a smaller area of debris-bedrock interface.
What is the role of the relative hardness of particles and bedrock in glacial abrasion?
Abrasion is most effective when hard, resistant rock debris at the glacier base is moved across weak, soft bedrock. If the bedrock is more resistant than the debris, then little abrasion will be accomplished.
What is the effect of ice thickness on glacial abrasion?
The greater the thickness of overlying ice, the greater the pressure exerted on the basal debris and the greater the rate of abrasion. However, beyond a certain thickness, the pressure becomes too great and there is too much friction between the debris and the bedrock for much movement to occur. This is typically 100-200 m, but it depends upon ice density and the nature of the debris.
What is the role of basal water pressure in glacial abrasion?
The presence of a layer of meltwater at the base of a glacier is vital if sliding and therefore abrasion is to take place. However, if the water is under pressure, perhaps because it is confined, the glacier can be buoyed up, reducing pressure and erosion.
Why is sliding of basal ice important in glacial abrasion?
Abrasion requires basal sliding to move the embedded debris across the rock surfaces. The greater the rate of sliding, the more potential there is to erode as more debris is passing across the rock per unit of time.
What is the significance of the movement of debris to the base in glacial abrasion?
Abrasion does not only wear away the bedrock, it also wears away the basal debris. Debris needs to be replenished (by glacial erosion and weathering processes) if abrasion is to remain effective.
