Chapter 14: Weathering Flashcards
Weathering
The breaking down or disintegration of material by way of chemical and physical processes
Physical weathering common processes
THERE ARE FOUR:
- Frost action
- Crystallization
- Hydration
- Pressure-release jointing
FROST ACTION
when water in a confined space freezes and expands.
I.e water in a crack in rock freezes, exerting a force outwards and expands and breaks the rock
CRYSTALLIZATION
Occurs when new minerals precipitate in a confined space
A crack in a rock - exerts an outward force and breaks the rock apart
HYDRATION
the expansion of some minerals when they get wet
If this process takes place in a confined space it can break a rock apart
PRESSURE-RELEASE JOINTING
Occurs when a rock that formed deep underground is exposed at the surface.
(When exposed at the surface it is under much less pressure and it expands. As a result, the outer layers will break off)
Chemical Weathering processes
- Oxidation
- Hydrolysis
- Solution
- Carbonation
OXIDATION
Iron-bearing rock (usually a black mineral), added to oxygen –> Rust
HYDROLYSIS
A chemical reacting involving water
Original or Primary Mineral + H2O –> New secondary mineral
SOLUTION
The way in which minerals dissolve in water
Salt (NaCl) added to water to create Na + Cl
CARBONATION
The dissolution of carbonate minerals (i.e. limestone) in a weak acid.
How does the weak acid in carbonation processes come from
The weak acid can come from the combination of water and carbon dioxide
The most important thing about almost weathering processes is _________!
WATER
Water is important to weathering because
- A universal solvent
- It is common in all three phases: liquid, solid and gas
- It expands by 9% when frozen
- It is a polar molecule
- If water is not part of the reaction, then it provides a place for the reaction (i.e. solution process)
Universal solvent
It will dissolve anything given enough time
How is water a “polar molecule”
Hydrogens at one end of the molecule contribute a positive charge, while the other end has a negative charge.
Although it does not have a chemical charge it behaves as if it does.
What is one of the most common results of weathering?
Soil.
Soil (6)
- A dynamic natural body
- made up of fine materials
- covering Earth’s surface
- in which plants grow.
- composed of both mineral and organic matter
- A layer of weathered mineral and organic material on the Earth’s surface.
Soil profile
A vertical section of soil extending from the surface to the deepest extent of plant roots or to regolith or bedrock.
How does the environment affect soil composition?
Depending upon the soil forming environment, a soil profile may have different internal layers or horizons.
Soil Horizons
The various layers exposed in a pedon, roughly parallel to the surface.
O A B C R (bedrock)
O soil horizon
Surface organic horizon
A soil horizon
Light in colour due to a net loss of minerals. What is weathered here is carried downward
B soil horizon
Dark coloured layer because at this level there is a net gain of material.
- What is removed from above ends up here
C soil horizon
Made of weathered bedrock or weathered parent material. Zone is identified as the regolith
Which way do minerals travel through soil?
Downward, due to gravity and water
Which way do minerals travel through soil?
Downward, due to gravity and water
Factors affecting soil formation
5
- SOIL BIOLOGY (plants and animals)
- TOPOGRAPHY
- PARENT MATERIAL
- WEATHER. frequency and duration of precipitation in particular, and the frequency and range of temperature changes
- TIME. more time means more soil
How does topography affect soil formation?
It affects the amount of sun the surface gets and how water drains. It also affects vegetation.
