Exogenic Processes and Weathering

Exogenic Processes

• Exogenic processes are the processes that shape Earth's surface.
• These processes include weathering and erosion.
• Weathering breaks down rocks into smaller pieces.
• Erosion carries away the weathered materials.
• Weathering and erosion are important for soil formation.

Learning Objectives

• Students will learn how rocks weather.
• Students will identify factors that cause erosion.
• Students will explain how the eroded materials are deposited.

Introduction

• Earth's surface is made up of water and landmasses.
• Rocks and minerals on the solid portion can undergo physical or chemical changes.
• Weathered materials are transported by factors like water, wind and ice.
• These progressions are called exogenic processes.

Weathering

• Weathering is the process of breaking down rocks into smaller particles.
• Two types of weathering are mechanical and chemical.

Mechanical Weathering

• Mechanical weathering breaks down rocks into smaller pieces without changing the composition.
• Causes include pressure, temperature changes (like frost wedging), abrasion, organic activities (roots), and human activities (digging, quarrying).

Pressure (Mechanical Weathering)

• Tectonic forces can lift rocks to high elevations.
• As the overlying rocks erode, pressure decreases.
• The decreasing pressure causes rock expansion.
• This can cause cracks and eventual breaking.

Temperature (Mechanical Weathering)

• Rocks expand when heated and contract when cooled.
• Repeated heating and cooling can weaken rocks, fracturing them.
• Frost wedging: Water seeps into cracks and freezes, expanding the crack, eventually breaking the rock.

Abrasion (Mechanical Weathering)

• Rocks collide with each other, wearing away edges.
• This occurs due to flowing water, wind, or waves.
• The rocks, sand, and silt result in sharp edges becoming rounded.

Organic Activities (Mechanical Weathering)

• Plant roots grow into cracks, widening them.
• The roots can push apart the rock by expanding as they grow.

Human Activities (Mechanical Weathering)

• Activities like digging, quarrying, or forest clearing can contribute to mechanical weathering.

Burrowing Animals (Mechanical Weathering)

• Animals like rats, rabbits, and squirrels make burrows, widening cracks and breaking rocks apart.

Chemical Weathering

• Chemical weathering changes the composition of rocks through chemical reactions.
• Dissolution, hydrolysis, and oxidation are examples.

Dissolution (Chemical Weathering)

• Minerals like Halite(NaCl) and Calcite (CaCO3) dissolve in water.
• Examples include caves formations (stalactites and stalagmites).

Hydrolysis (Chemical Weathering)

• Rock-forming minerals like amphibole, pyroxene, and feldspar react with water.
• The reactions change the composition of the minerals, eventually dissolving them into clay minerals.

Oxidation (Chemical Weathering)

• Oxygen reacts with minerals, altering their composition.
• Iron oxidation (rusting) is a common example.
• The reaction weakens the rock and causes decomposition.

Weathering (General Considerations)

• Weathering is crucial to soil formation.
• Soil is a mixture of grains, organic matter, water, and gases.
• Plants, animals, and humans also play roles in the process of erosion.

Erosion

• Erosion is the process of removing and transporting weathered materials.
• Water, wind, and glaciers are the primary agents.

Mass Wasting

• Mass wasting is the downslope movement of sediments under gravity.
• Common forms include falls, slides, avalanches, and flows.

Deposition

• Deposition is the process where eroded materials settle in new locations.
• It results in the creation of new landforms.
• Alluvial fans are an example of a resulting deposition feature.

Reflect Upon

• The presentation raises questions about animal and human impacts on erosion and the effects of soil erosion on communities.