4 - Soil Formation Flashcards
What are the 5 factors affecting soil formation?
1) Parent Material
2) Climate
3) Organisms
4) Topography
5) Time
What characteristics of soil does parent material influence?
- pH
- Texture
- Fertility
How is igneous rock formed?
Igneous rocks are formed when magma cools and hardens.
How does the rate of cooling of magma influence the formation of crystals in igneous rocks?
If the magma cools slowly, lagre crystals are formed.
If magma cools quickly, small crystals are formed.
Describe the formation of sedimentary rocks?
As sediment becomes deposited on sea and lake beds, layers begin to form. As these layers build up, pressure is put on the lower layers and the sediment becomes compressed into rocks.
E.g. limestone and sandstone.
How are metamorphic rocks formed?
Metamorphic rocks form when other rocks (igneous & sedimentary) are placed under great heat and/or pressure. This changes the rocks into a new type of rock.
What metamorphic rocks are formed from i) limestone, ii) sandstone, and iii) granite?
i) Marble
ii) Quartzite
iii) Gneiss
What are the 2 types of weathering? Name and explain.
1) Mechanical weathering is the physical breakdown of large particles into smaller particles.
2) Chemical weathering is the chemical breakdown of large particles into smalller particles.
Name the 5 types of mechanical weathering.
1) Heating and cooling
2) Freeze-thaw action
3) Abrasion
4) Roots
5) Animals
Explain at least 3 types of mechanical weathering.
1) Heating and Cooling: Heating causes expansion of material, and cooling causes shrinking/contraction of material. As the minerals in rocks heat and cool they expand and contract at different rates causing the rock to shatter.
2) Freeze-thaw action: Water expands as it freezes. The water in cracks in rocks expands, putting pressure on the rock. When the water thaws, this pressure is released. As this repeatedly happens, the pressure and release on the rock causes it to shatter.
3) Abrasion: As rocks move around (by water, gratuity, wind) they hit off eachother. This causes them to wear down.
4) Roots: Roots can enter cracks in rocks and as the roots grow, they put pressure on the rocks, contributing to then prying apart.
5) Animals: Burrowing animals can cause rocks to breakdown when they dig for food or shelter.
Name and explain the 3 types of chemical weathering.
1) Oxidation: Minerals react with oxygen and water. The oxidation of iron gives a rust colour to rocks.
2) Solution/Carbonation: As rain falls, carbon dioxide from the air dissolves in it, forming a weak carbonic acid. This acidic rain reacts with the rock and wears it away.
3) Hydrolysis: Rocks are broken down when substances react with water.
How does climate affect soil formation?
Temperature and rainfall contribute both to mechanical and chemical weathering of rocks. They also influence the rate of reactions in soils and the proportions of water and air in the soil.
How do organisms affect soil formation?
Decomposers in the soil breakdown organic matter to provide nutrients in the soil.
How does topography affect soil formation?
Soils that develop on slopes tend to be shallow, as the soil moves down with gravity, resulting in deep soil in the valley.
How does time affect soil formation?
It takes time for rocks and organic matter to break down, and so time is needed for soils to develop. Older soils tend to be deeper, while young soils are usually more shallow.
What are the 5 layers in a soil profile (horizons)?
O - Made up of organic matter.
A - Topsoil. Organic matter and minerals from parent material.
B - Subsoil. Rich in minerals that have leached through the O and A horizons.
C - Parent material. Mostly consists of parent material from which the soil has developed.
R - Bedrock.mass of parent material, not soil.
