Transcript Chapter 6 Weathering and Soil

Chapter 6
Weathering and Soil
Types of Weathering
• Mechanical Weathering – Breaks apart rock
without changing its chemical composition
• Examples
– Plant roots grow into the cracks of rocks
– Animals burrowing
– Ice Wedging
Types of Weathering
• Chemical Weathering – Breaks up rocks due
to a change in their chemical composition.
(Water and Oxygen are factors)
• Examples
– Acid Rain
– Rust
Mechanical vs. Chemical
Chemical
Mechanical
Ice Wedging
• Type of mechanical weathering
• This happens when water gets inside rocks,
freezes, and then expands causing the rock to
break.
Carbonic Acid
• When water mixes with carbon dioxide in the
air, carbonic acid forms.
• Type of chemical weathering
• Comes in contact with different rocks, and
reacts with the minerals in them.
Oxidation
• Oxidation occurs when a material is exposed
to water and the oxygen in the air.
• This causes “rust”
• Type of chemical
weathering.
Climate and Weathering
• Cold climates – mechanical weathering
breaks down rocks rapidly through ice
wedging
• Chemical weathering is more rapid in warm,
wet climates. (tropical areas)
• Lack of moisture and cold climates keeps
chemical weathering at a minimum.
What is Soil?
• Soil – A mixture of weathered rocks, decaying
organic matter (plants & animals), mineral
fragments, water, and air.
• Sediments + Organic Matter
= Soil
What is Humus?
• Humus – Dark colored organic matter found
in soil; made of decayed plants and animals.
• Soil Profile – Vertical section
of the different soil layers.
• Horizon – Each layer in the
soil profile. (Three Horizons:
A, B, and C)
Horizons
• Horizon A
– Most evolved
– Known as topsoil
– More humus and smaller rock and mineral
particles than other layers.
• Horizon B
– Less evolved
– Lighter in color
– Some plant roots reach here
Horizons Continued
• Horizon C
– Bottom layer of soil profile
– Contains partly weathered rock
– Solid rock
Layers of Soil
Leaching
• Removal of soil
materials dissolved in
water.
• Occurs throughout all
three Horizons.
When does Desertification occur?
• When soil is dry due to lack of rain combined
with poor farming practices and over –
grazing.