WeatheringWeatheringChapter 10Chapter 10

Essential QuestionsEssential Questions

• What causes mechanical weathering?

• What causes chemical weathering?

• What factors determine how fast weathering occurs?

WeatheringWeathering

–The process that breaks down rock and other substances at Earth’s surface.

ErosionErosion

• The movement of rock particles by wind, water, ice, or gravity.

Weathering and erosion work together continuously to wear down and carry away the rocks at Earth’s surface.

Mechanical WeatheringMechanical Weathering

• The type of weathering in which rock is physically broken into smaller pieces.

• These smaller pieces of rock have the same composition as the rock they came from.

How it worksHow it works

• Mechanical weathering breaks rock into smaller pieces by freezing and thawing, release of pressure, growth of plants, actions of animals and abrasion.– Abrasion- the action of rocks and sediment

grinding against each other and wearing away exposed surfaces.

– Mechanical weathering works very slowly.

ABRASION

Contact of weathered and eroded particles with otherrock during erosion also leads to mechanicalbreakage due to ABRASION.

Types of Mechanical (Physical) Types of Mechanical (Physical) WeatheringWeathering

• Ice Wedging

• Animal action

• Plant growth

• Wind

• Water

• Gravity

ICE WEDGING

Water expands ~ 9% when frozen.Water trapped in the cracks, freezes and expands and actively fractures the rock.This works best where temperatures fluctuate above and below 0C (32F).When water melts, it seeps deeper into the crack and then refreezes.

ICE WEDGING

POTHOLES

GROWTH OF PLANTS – Root Wedging

Trees and plants grow in cracks in rocks and the force related to expansion with growth breaks the rocks.

ANIMAL ACTIONSAnimals mix up the soil exposing more material to the surface for weathering to occur. Burrowing into the ground contributes to weathering.

Chemical WeatheringChemical Weathering• The chemical breakdown of rocks into

new substances.

• Chemical weathering produces rock particles that have different mineral makeup from the rock they came from.

• The products of chemical weathered granite are sand and clay

How it worksHow it works• Chemical weathering creates holes or soft

spots in rocks, so the rock breaks apart more easily.– Chemical and mechanical weathering work

together– Agents involved with chemical weathering are:

water, oxygen, carbon dioxide, living organisms and acid precipitation (rain).

OXIDATION

Certain items react with Oxygen causing RUST.Water helps speed up the oxidation process.

OXIDATION

Copper reacts with Oxygen turning the copper a green color.

OXIDATION

Oxidation has the same result with iron-rich rocks and minerals. This affects olivine, pyroxenes, gabbros, and basalts. Georgia Clay!

LIVING ORGANISMSLiving organisms help with chemical weathering by decomposition.

Lichens are moss type organisms that grow on trees and rocks. They produce organic acids that slowly break down rock.

Rate of WeatheringRate of Weathering• The most important factors that determine

the rate of weathering are type of rock and climate.

• Some rock breaks down easier because it is permeable.– Means that the rock has tiny connected air

spaces that allow water to seep through it.

• Climate refers to the average weather conditions in an area.

• Elevation – the higher the elevation, the more exposure to wind, rain, and ice.

Differential WeatheringRelease of Pressure – Mechanical

ExfoliationWhen overlying mass of rock and sediment is released, pressure on the underlying rock is released. This allows the rock to expand. Expansion takes place outward from the exposed surface. Sheets of rock will fall off.

Stone Mountain goes through Differential WeatheringMechanical Exfoliation