Warm-up: What has occurred in Warm-up: What has occurred in these pictures? Please write a brief these pictures? Please write a brief

description.description.

WeatheringWeathering

Types of WeatheringTypes of Weathering

Mechanical or PhysicalMechanical or Physical ChemicalChemical

Weathering is the Weathering is the process that . . process that . .

________________________________________________________________________________________________________

__________

Mechanical Weathering Mechanical Weathering

Definition: Mechanical weathering breaks apart Definition: Mechanical weathering breaks apart rocks without changing the chemical structure. rocks without changing the chemical structure.

Types of Mechanical WeatheringTypes of Mechanical Weathering

1) Frost wedging1) Frost wedging

2) Exfoliation 2) Exfoliation

3) Thermal expansion3) Thermal expansion

Mechanical WeatheringMechanical Weathering

Expansion and Contractions Expansion and Contractions

water expands when it freezes and causes water expands when it freezes and causes rock to breakrock to break

Mechanical Weathering Mechanical Weathering

Freeze/thaw cycles break down rock as Freeze/thaw cycles break down rock as water enters cracks and widens themwater enters cracks and widens them

Mechanical Weathering: ExfoliationMechanical Weathering: Exfoliation

rock breaks off into sheets, which is caused by the rock breaks off into sheets, which is caused by the – Expansion of the rock due to erosion Expansion of the rock due to erosion

– Pressure from the earth’s surfacePressure from the earth’s surface

Mechanical Weathering: Thermal Mechanical Weathering: Thermal ExpansionExpansion

Chemical Weathering Types:Chemical Weathering Types:

Chemical weathering occurs when water, Chemical weathering occurs when water, air, and other substances react with air, and other substances react with minerals in the rocks and it’s chemically minerals in the rocks and it’s chemically changed. changed.

1) Dissolution 1) Dissolution

2) Oxidation 2) Oxidation

Chemical Weathering: Dissolution Chemical Weathering: Dissolution

– Can dissolve rock Can dissolve rock – Can form acids as they react with rocks and Can form acids as they react with rocks and

atmosphereatmosphere

– The gravestone shown The gravestone shown

here is chemically changedhere is chemically changed

from London’s pollution, vehicle from London’s pollution, vehicle

exhaust fumes that contain exhaust fumes that contain

sulfur and nitrogen. sulfur and nitrogen.

Chemical Weathering: OxidationChemical Weathering: Oxidation

– Oxygen combines with elements in the rock Oxygen combines with elements in the rock – Often rocks become discoloredOften rocks become discolored

Some types of rock are easily weathered by Some types of rock are easily weathered by chemicals. chemicals. – For example, limestone and chalk are made of a mineral For example, limestone and chalk are made of a mineral

called calcium carbonate. called calcium carbonate. – When acidic rainwater falls on limestone or chalk, a When acidic rainwater falls on limestone or chalk, a

chemical reaction happens. chemical reaction happens. – New substances are formed in the reaction. These are New substances are formed in the reaction. These are

washed away and the rock is weathered. washed away and the rock is weathered. – Chemical weathering can make caves form and cliffs fall Chemical weathering can make caves form and cliffs fall

away. away.

Chemical WeatheringChemical Weathering

– Carbon dioxide with water creates carbonic acid Carbon dioxide with water creates carbonic acid that eats away rock. Carbonic acid is the same that eats away rock. Carbonic acid is the same weak acid that makes soft drinks fizzy. weak acid that makes soft drinks fizzy.

Chemical WeatheringChemical Weathering

– Several caves around the world are examples Several caves around the world are examples of chemical weatheringof chemical weathering

What did we learn?What did we learn?

What is mechanical weathering?What is mechanical weathering? What is chemical weathering?What is chemical weathering? Do they work together? Do they work together? Now, let’s take a weathering walk and find Now, let’s take a weathering walk and find

what kind of weathering takes place in our what kind of weathering takes place in our backyard!!backyard!!