DENUDATION Erosion and Weathering Introduction DENUDATION refers to

DENUDATION: Erosion and Weathering

Introduction DENUDATION refers to the wearing down and stripping and leveling of the earths surface. n They are also gradational because they grade/level the earth’s surface. n 2 processes: weathering and erosion. n Weathering is the breakdown of rock and minerals. n Erosion is the movement of these weathered materials. n

Erosion The removal of weathered sediment or rock by the forces of wind, water and ice. n This is a two-fold process: Transportation which is the movement of sediment or weathered material away from its source to another location. n - Deposition which is dropping or settling of sediments.

Weathering n Weathering is the breakdown of rocks and minerals by physical pressures and chemical reactions. n There are two types : physical and chemical.

Physical Weathering n Physical weathering is the breakdown of rock and minerals by mechanical stresses. n 4 types to be discussed… n Physical weathering prevails in: n cold and wet climates n high altitudes and high latitudes n hot/dry regions

1. Physical Weathering - Frost fracture water gets into the cracks of rocks, freezes and expands causing rocks to crack.

2. Physical Weathering – Heat or Thermal Expansion n Repeated daily heating and cooling of rock results in expansion during heating and contraction during cooling. n Different materials expand contract at different rates, resulting in stresses along mineral boundaries.

Heat or Thermal Expansion

3. Physical Weathering - Exfoliation is the breaking off of rocks in curved sheets or slabs along joints that are parallel to the ground surface. n Most commonly the release of stress upon a rock occurs when overlying rock is eroded away. n

Exfoliation

4. Physical Weathering – Plants and animals Expansion due to root growth. Animals that burrow in the ground. ROOTS grown into the rock Could be considered Biological weathering!!!!

Chemical Weathering n Chemical weathering is the breakdown of rocks and minerals by chemical reactions and usually involves the action of rainwater. n This involves three processes:

1. Chemical Weathering – Solution/Dissolution q The formation of solutions as rainwater absorbs CO 2 , SO 2, and other chemicals from the atmosphere along with organic acids from the soil q Which then reacts with rock and minerals causing some to dissolve and move away.

2. Chemical Weathering – Hydrolysis Ø Hydrolysis like the first process involves the minerals in solution. Ø In this case, carbonic acid reacts with silicates in some rocks leaving a soft clay from which potassium, sodium and magnesium are subsequently leached.

3. Chemical Weathering – Oxidation § Oxidation is the reaction of metallic minerals to oxygen (mainly in water. § This results in the formation of oxides, which tend to be softer than the original mineral. § For example, rust on iron.

Relate environmental conditions & rate of physical & chemical weathering • Freezing temperatures and moisture? • Frost Fractures • Variation/fluctuations in H/C temperatures? • Thermal Expansion • Presence of vegetation? • Roots expanding cracks • Heavy precipitation? • Accelerates dissolving of rocks/minerals

Relate environmental conditions & rate of physical & chemical weathering n n n CO 2 and SO 2 in the humid air? n Creates solutions that dissolve some rock and minerals O 2, Moisture and metallic minerals? n Chemical reaction-oxidation, ie. rust Carbonic Acid? n Hydrolysis, transform rock into soft claylike. . leach away High Temperatures? n Accelerates oxidation Oceans and Salt? n Accelerates oxidation

Practice Figure 2. 5, Text n Page 25 n Please complete the handout. n