Download Weathering and Erosion

Weathering and Erosion
Natures way of tearing down
everything that has been built up
over billions of years.
What is mechanical weathering?
Objective- explain the ways that Earth’s surface is worn
away by mechanical weathering.
Weathering- breaking down of rocks and other materials
on Earth’s surface.
Mechanical weathering- weathering in which the chemical
makeup of rocks does not change.
* Involves only physical changes, such as size and shape.
Mechanical weathering occurs as a result of;
– temperature changes.
– Ice wedging
– Root action
Mechanical Weathering
Temperature Changes
• Rocks may be broken apart by temperature changes.
– Heat makes them expand. (daytime)
– Cooling makes them contract. (night time)
Exfoliation- the peeling of rock layers, created by temperature
extremes. (creates domed rocks)
Ice wedging- mechanical weathering caused by the freezing and
melting of water.
When water freezes it expands by 10%.
Water enters cracks in the rock freezes, expands and widens
the crack. Repeated actions cause rocks to split apart.
*Root wedging- Plant root in search of minerals and water can
grow in cracks of rocks.
Roots force rocks apart, breaking them into smaller pieces.
*Burrowing animals- animals that dig next to rocks, exposing
them to the elements of weather.
Mechanical Weathering
Exfoliation
Mechanical Weathering
Ice wedging (frost wedging)
Mechanical Weathering
Root Wedging
Mechanical Weathering
Burrowing Animals
What is chemical weathering?
Objective- Explain how Earth’s surface is worn away by
chemical weathering.
Types of Chemical weathering;
In chemical weathering, substances in water cause
substances in rock to dissolve.
*Chemical changes in rock occurs when minerals are
broken down into new substances.
*Chemical weathering is usually caused by reactions
with; oxygen, water, or acids.
Chemical Weathering
Oxidation- chemical change that occurs when oxygen
reacts with another substance.
New substances called oxides form.
*Rocks containing ferromagnetic minerals combine
with oxygen forming rust. The rock is weakened and
crumbles as a result of this process.
2Fe2SiO4 + 2H2O + O2 = 2Fe2O3.H2O + SiO2
Chemical Weathering
Hydration- chemical reaction that occurs when minerals
with little water content react with water.
*Most chemical weathering is caused by water.
When feldspar reacts with water it turns to clay.
Na-feldspar and K-feldspar undergo hydrolysis to form kaolinite (clay) and Na+ and K+ ions.
Chemical Weathering
Carbonation- chemical reaction that occurs when carbonic
acid reacts with certain minerals.
*Carbon dioxide can dissolve in rain to form carbonic
acid.
When the carbonic acid comes into contact with
certain minerals a chemical reaction occurs called
carbonation. The mineral calcite reacts with carbonic
acid.
Chemical Weathering
Carbonation
Chemical Weathering
Acids and weathering
*Plants produce weak acids which can react with minerals
weakening a rock and dissolve those minerals.
Factors that affect the rate of weathering.
Objective- Identify three factors that affect the rate of
weathering.
#1 Climate
* moisture speeds up chemical weathering.
* weathering occurs fastest in hot, wet climates.
• In very cold, dry areas, there is little weathering.
#2 Surface area
* Weathering occurs on exposed surface areas of rocks
and minerals.
* The more surface area a rock has, the faster it will
weather.
Factors that affect weathering
#3 Rock composition
* Slow weathering minerals; Quartz
* Fast weathering minerals; feldspar
* Weathering by carbonation; Calcium (limestone)
* Weathering by Oxidation; Iron
Factors that affect rate of weathering
#4 Chemical reactions
* Carbonic acid weathers calcite (limestone/marble)
• Natural weathering through carbonation is slow.
• Anthropomorphic (human activity); factories produce carbon
dioxide, sulfur and nitrogen. When combined with rainwater
they produce acids or acid rain.
• Acid rain- rain containing acids produced by water chemically
combining with certain gases.
How does soil form?
Objective- explain how soil is a product of weathering and
organic processes.
Formation of soil
Bedrock- solid rock that lies beneath the soil.
• Bedrock is the parent material of soil. Weathering breaks
bedrock into soil.
Soil formation
Living things and soil
Humus- decaying remains of plants and animals.
* Water helps speed up the breakdown of rock.
Soil formation
Soil- mixture that includes silt, sand and clay.
• Weathered pieces of rocks, minerals and humus are also
in soil.
• Soil that is rich in humus is very dark.
Importance of soil
* Soil is important to plants. Potassium, phosphorous and
nitrogen are important nutrinets.