Weathering And Slopes Flashcards
What is weathering?
It is the disintegration and decomposition of rock in situ (the original position). It does not involve the movement of any material.
What are the two types of weathering?
Mechanical (physical) and chemical
Where does mechanical weathering occur? And what does it produce?
In areas of devoid vegetation (deserts), high mountains and arctic regions. It usually produces sands.
Where does frost shattering occur and and how does it take place?
It occurs in rocks that contain crevices and joints where there is limited vegetation cover and where temperatures fluctuate around 0•c.
In the daytime when it is warmer water enters the joints but during cold nights it freezes.
What is physical weathering?
It is the disintegration of rock into smaller particles by mechanical processes but without any change in the chemical composition of the rock
What is chemical weathering?
It is the decomposition of rock resulting from a chemical change.
Where does chemical weathering occur?
Takes place in warmer, more moist climates where there is vegetation cover.
What are the two ways that frost shattering leads to mechanical break down?
- As ice occupies 9% more volume than water, it exerts pressure within the joints
- When water freezes within the rock it attracts small particles of water, creating increasingly large ice crystals
What does frost shattering or freeze thaw lead to?
It slowly widens the joints and in time causes pieces of rock to shatter of from the main body. Because of this block disintegration occurs on steep slopes, large angular rocks collect at the foot of the slope as scree or talus. On gentler slopes, large blockfields tend to develop.
What is salt crystallization? And how does it occur?
When slight saline water evaporates in cracks then salt crystals form. As the crystals become larger they exert stresses upon the rock causing it to disintegrate. It occurs in hot deserts by granular disintegration.
What is pressure release and how does it occur?
When intrusive rocks have developed under great pressure they are very strong due to the confining pressure. If at a later stage they are exposed to the atmosphere then there will be a substantial release of pressure which weakens the rock allowing other agents to enter it and other processes to develop. Where cracks develop parallel to the surface, sheeting causes the outer layers of rock to peel away. Thus causing exfoliation domes
What is thermal expansion insolation weathering?
Caused by the expanding and contracting of the rock. Causes exfoliation and granular and block disintegration
What is biological weathering?
Tree roots grow along bedding planes and extend into joints widening them until blocks of rock become detached. Also burrowing creatures
What is oxidation? And give examples
When rocks are exposed to oxygen in the air or water.
