Soil Parent Material Flashcards
What is the first step in soil formation?
When mineral material and organic matter from plants and animals are combined together.
What is the general ratio of solids/void space in soils? `
50/50
What are the 3 broad classes of rock?
- Igneous (Molten magma)
- Metamorphic (Altered by heat and pressure)
- Sedimentary (Sedimentary deposits)
What distinguishes parent material?
Type and/or ratio of the type of mineral quantities.
In most cases, rocks are mainly composed of what element?
Silica
A higher or lower concentration of silica will cause rocks to break up more quickly at the surface of the earth?
Lower
(Rocks with higher % of Silica are more resistant to breaking up at the climatic conditions of the earth’s surface.)
The correct term for the ‘breaking-up’ of soils is?
Weathering
What are the two main groups of weathering?
- Physical
- Chemical
What are the different types of physical weathering?
- Thermal
- Mechanical
- Plant pressure
What is the main concept of Thermal Weathering?
Different minerals have varying rates of expansion when exposed to heat. Where these rates differ withing the rock, stress is caused and fracturing can occur in areas of weakness.
Explain the second form of thermal weathering in rocks…
Temperature differences within the rock itself (outer and inner sections) can cause exfoliation weathering as the outer layers of the rock are fractured and peeled away.
(AKA ‘onion skin’)
Explain the process of ‘frost shattering’ ?
Water can penetrate small cracks in the rocks. When the water freezes, it expands by 10% and the expanding ice forces the cracks to break open.
What is the other effect that water infiltration into a rock can have?
Different materials have different rates of swelling and shrinkage. This can initiate stress within the rocks.
Biological weathering is…
The process by which plants and animals contribute to the weathering of plants. Either by physical actions of animals or where root growth from plants infiltrates rock and causes damage to its structure.
What is the function of exudates in relation to chemical weathering?
Plant roots release exudates that are metabolised by micro-organisms thereby increasing the rate of chemical weathering.
Name the (5) types of Chemical Weathering?
- Hydrolysis
- Carbonation
- Hydration
- Dissolution
- Oxidation & Reduction
What is the most common form of Chemical Weathering?
Hydrolysis
Explain the steps of Hydrolysis.
H2O dissociate into H+ and OH-
These charged particles attack the bonds that hold minerals together.
This causes disintegration of the rocks and changes the nature of the minerals.
The respiration of biological activity leads to CO2 being respired. This dissolves in soil water producing a weak acid that attacks minerals.
Carbonation is an accelerated form of?
Hydrolysis
Explain the process of Carbonation
- Majority of soil organisms respire Carbon Dioxide.
- When CO2 contacts with water, a portion of it dissolves to form carbonic acid.
- The acid attacks the mineral, degrading it.
Plant roots excrete sugars that are then used and converted to acids by micro-organisms. All acids are rich sources of hydrogen ions; carbonation, therefore, enhances hydrolysis.
