Lithosphere III Flashcards
What are the 3 steps involved in weathering?
- Rock begins to disintegrate due to physical factors.
- Parent materials develops and there is early colonization of the surface by small plants, such as lichen.
- Development of soil horizons in a soil profile.
What is weathering?
Weathering is any of the chemical, biological, or mechanical processes by which rocks exposed to the weathering undergo chemical decomposition and physical disintegration.
Rate of weathering depends on […]
Temperature, moisture, organisms, and the strength of the material parent.
What are the two types of weathering? Explain the difference between them.
Mechanical/physical: physical breakdown of rocks without changing their chemical composition
Chemical: breakdown of minerals by chemical reactions with air, acids, or water
Give an example of how parent material affects weathering.
Metamorphic rocks are stronger than sedimentary rocks
Give 2 examples of mechanical weathering.
Wind abrasion and freezing and thawing.
Explain how wind abrasion works and where it is more prevalent.
Particles like sand get picked up by the wind and degrade the rock. Because lifting particles off the ground requires energy, we expect more abrasion to occur closer to the ground vs higher up.
Explain how freezing and thawing works.
An area filled with water will freeze. The ice will expand and put pressure on the cracks, pushing them to crack further and eventually break.
Give 2 examples of chemical weathering.
Hydrolysis and dissolution.
What is hydrolysis?
Hydrogen ions in water react with rock minerals, making them weaker.
Explain why granite is particularly vulnerable to chemical weathering.
Because it contains feldspar, which is reactive with hydrogen.
What is dissolution?
Water containing small amounts of carbonic acid will react with rock minerals (usually limestone) to pull them away from the rock and into solution.
How do organisms contribute to weathering?
The presence of organisms will increase the rate of weathering on top of other drivers like rain, moisture, and temperature. They can contribute to both physical weathering and chemical weathering.
Give an example of how organisms can contribute to both physical and chemical weathering.
Physical: pressure exerted by tree roots
Chemical: roots producing CO2 and organic acids that acidify soil and promote weathering, weathering from acids produced by plants and microbes.
Describe the relationship between climate and weathering.
Warm, wet climates promote chemical weathering, while cold, semi-moist climates promote physical weathering (notably frost). Dry climates give low rates of weathering, especially chemical weathering.
Climate also affects weathering indirectly through the type of vegetation present.
Do soil horizons form from bottom to top or from top to bottom?
From top to bottom.
Describe the limits/boundaries of the soil profile.
Upper limit: consists of air, shallow water, live plants, or plant material that has not yet started to decompose.
Lower limit: the depth at which soil weathering stops being effective and there is no alteration of the original material.
Between the upper and lower limit are horizons.
Name the major soil horizons from top to bottom.
O (organic), A (topsoil), E (leaching layer), B (subsoil), C (substratum), bedrock (parent material)
What is the O horizon made up of?
It is made of an accumulation leaves, twigs, moss, and woody materials.
Where are soils with O horizons typically found? Why?
They are not found in all soil profiles. They are associated with forested soils or places with high little inputs and low decomposition rates. They would not be found in managed ecosystems because the decomposition rates are higher there.
What is the first soil horizon to be formed?
In soils with an O horizon, it’s the O horizon followed by the A horizon. Otherwise, the A horizon forms first.
What is the A horizon made up of?
It contains a high concentration of carbon, nutrients, and organisms, and is also where plant roots are located. It also has minerals, such as sand, silt, etc.
How big is the A horizon? What effect does this have on soil function?
It can vary from a few cm to >100 cm deep. Given that this part of the soil contributes heavily to soil ecosystem services, a shallower A horizon leaves the soil vulnerable to rapid erosion and degradation.
Where are soils with an A horizon typically found? Why?
All soils have an A horizon, because it’s the first horizon that forms (barring the O horizon sometimes).
Where are soils with an E horizon typically found? Why?
Soils with an E horizon tend to be highly weathered older soils, acidic soils, or in wet climates.
Another name for the E horizon is […]
The Ae horizon
What is the E horizon made up of?
It is a zone of eluviation where materials from the A horizon, including clay, organic matter, iron, and/or aluminum, move down and through, eventually ending up in the B horizon. It is quite depleted and is often grey in colour
