1. Weathering Processes by Honey 12CS

2. What is weathering?
The process of breaking down rocks, soils and their minerals at or near the ground surface when it is exposed to air, moisture, and organic matter.
Occurs 'without movement'
2 classification-Physical and Chemical

3. Freeze-thaw Biological weathering
Physical weathering
Freeze-thaw
Biological weathering

4. What is Freeze-Thaw (frost shattering) ?
A form of physical weathering.
Occurs when there are fluctuations of temperature above and below the freezing point. (0°C/32°F. )
Water collects in a crack, freezes and expands in volume by 9% as it turns to ice. This expansion exerts great pressure on the rock, causing the crack to enlarge.
Most likely in areas of extreme and perpetual cold, such as the polar regions.
At high altitudes

5. What is the end product of Freeze-thaw?
Scree slope (broken fragments of rock).
Smaller, often angular particles.
No vegetation grow.

8. What is the Biological weathering?
Resulting from the action of organic materials, the activities of living organisms.
Can lead to both physical (expanding tree roots) and chemical weathering (chelation)
Occurs most in humid (warm-wet) chemical microenvironment. (tropical climates-the heavier rainfall, plants grow well)-mostly have chemical reaction.

9. Some burrowing animals e. g
Some burrowing animals e.g. mole, rabbit, ants always dig a hole in soil or rocks.
These turn over soil and expose it and the underlying rock to more chemical weathering.
This exerts a destructive pressure as they grow.
Plant grows bigger on the rock. As rock can’t absorb much water in, plant roots grow further to find water in cracks and weaknesses. This enlarges cracks.
Roots grow bigger and widen the rocks. When they rot, they release acid to weather rocks.
Plant grows resulting from wind blows seed to grow on the rock.

10. Biological weathering factors
Lichen, fungus, mold, etc.
Secrete acids which "etch" the rock
Make subtle irregularities
Lichen can extract irons from rocks (chelation)
Plant roots/Weeds
Can grow into cracks - force them apart
Breaks rock - a physical process
Increases surface area - leads to increased chemical attack
Organic acids (humic acid)
Rotting plants giving off organic acids .
These can chemically weather the minerals
Organic debris
Falls and decomposes
Releases carbon which can combine with water and the atmosphere to make acids (rain)

11. What is the end product of biological weathering?
Affects limestone , chalk and granite
Can assist in breaking down rock into sediment or soil.
May lead to Podsolisation of soils.