Harbor 2013 (6) Flashcards
What is abrasion?
The small-scale mechanical breakdown of rock surfaces caused by stress and motion at the contact point between a clast embedded in a glacier and the underlying bedrock.
What does abrasion produce?
Abrasion produces fine rock particles (glacial flour) that are transported away in meltwater and leaves erosional traces that include striations and polish on a rock surface.
What is entrainment?
Refers to the processes that result in rock particles or sediments being incorporated within, attached to, or moved by the glacier ice.
What is erosion?
Refers to the removal of soil or rock from a location and includes both processes that breakdown or reduce the strength of the material and processes responsible for the movement of the material from its original location.
What are paraglacial environments?
These are transient, nonglacial environments that are not, at present, directly impacted by glaciation, but have process types and rates that are responding to recent deglaciation.
What is plucking?
Also sometimes termed as quarrying, it includes both the fracture of underlying rock as well as the entrainment of rock fragments that result from either fracture due to glacial action or those that have been isolated by preexisting bedrock cracks.
What is regelation?
Is the refreezing of water that was originally ice.
What is glacial erosion?
Glacial erosion includes processes that occur directly in association with glacial ice, such as abrasion, plucking, physical and chemical erosion by subglacial meltwater, as well as processes that are enhanced or modified by glaciation.
Traditionally, the primary processes of glacial erosion have been described as:
1) abrasion, (2) plucking (quarrying), and (3) physical and chemical erosion by subglacial meltwater
How does plucking occur?
Stresses may cause rock failure at the tip of the crack.
Cracks in underlying rock actually acts to concentrate the stress at the tip of the crack, magnifying the force that is applied, and this effect increases with crack length.
As fracture occurs, stored strain energy is released.
At the base of a glacier moving over bedrock, stresses are concentrated at the contacts between the bed and clasts (rock fragments or particles), allowing for abrasion, and on bumps and steps where the bed is not smooth, allowing for plucking.
What is plucking?
Plucking, also sometimes termed as quarrying, includes both the fracture of underlying rock as well as the entrainment of rock fragments that result from either fracture due to glacial action or those that have been isolated by preexisting bedrock cracks.
When does abrasion occur?
Abrasion occurs when clasts embedded in the basal layers of a glacier scratch, score, polish, and wear down the bedrock over which they pass
An apparent paradox in glacial erosion is how ice, which is mechanically weaker than rock, can produce abrasion.
One of the primary reasons for this is that the ice is in contact with the clast over a large area, whereas the clast is in contact with the underlying bedrock at a small point, thus, a small force per unit area over the large contact surface between the ice and the clast is then applied to a very small contact area between the clast and the bedrock, resulting in a very large force per unit area.
High abrasion rates occur when…
basal melting rates are high and clast concentrations are low enough that they do not impede ice flow toward the bed.
