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WeatheringThis week we write it down if it’s in
ORANGE.
Photo: Grand Canyon, National Park Service
What do you think made the hole in this rock?
Wind blows sand and other sediment against rocks. Little by little, it wears away the rock!
This is an example of mechanical weathering.
What do you think made the notch where the waterfall starts?
Water from the river wears away the rock, over thousands of years.
This is another example of weathering.
Photo: Yosemite Falls, National Park Service webcam
Weathering is the process that breaks down rock and other substances on Earth’s surface.
Part 1: Mechanical Weathering
Mechanical WeatheringForce of Mechanical Weathering
How it Works
Abrasion
Plant Growth
Animal Actions
Freezing and Thawing
Release of Pressure
Abrasion: Sand and other rock particles carried by wind and water grind away rock like sandpaper on wood.
Here we go again with wind and rock particles sculpting rock!
Photo: Delicate Arch, Arches National Park, National Park Service.
Plant Growth: Roots of trees and other plants grow in the cracks of rocks and pry them apart.
Perhaps you have seen this on sidewalks?
Photo source: Morguefile.com
Animal Actions: Animals dig in the soil and loosen and break apart rocks.
Photo source: Morguefile.com
Ice Wedging: When water freezes it expands. Ice in the crack of a rock expands and makes the crack larger.
Perhaps you have seen a frozen bottle get cracked? Or cracks in the road? Why does that happen?
Whiteboard QuestionCHECK YOUR UNDERSTANDING!
Mechanical weathering in which rock is worn away by the grinding action of other rock particles is calledA. erosion.B. abrasion.C. ice wedging.
B. abrasion
Release of Pressure: When rocks reach Earth’s surface, reduced pressure can cause cracks and flakes in the rock.
Mechanical WeatheringForce of Mechanical Weathering
How it Works
Abrasion Sand and other rock particles carried by wind and water grind away rock like sandpaper on wood.
Plant Growth Roots of trees and other plants grow in the cracks of rocks and pry them apart.
Animal Actions Animals dig in the soil and loosen and break apart rocks.
Freezing and Thawing
When water freezes it expands. Ice in the crack of a rock expands and makes the crack larger.
Release of Pressure When rocks reach Earth’s surface, reduced pressure can cause cracks and flakes in the rock.
Your completed chart
should look like this!
Whiteboard QuestionCHECK YOUR UNDERSTANDING!
Ice wedging causes mechanical weathering of rock by means of:A. plant growth.B. animal actions.C. freezing and thawing of water.
C. freezing and thawing of water
Chemical Weathering
Write it down if it’s in ORANGE.
Chemical weathering is the process that slowly breaks down rock with chemical changes, including changes in the minerals.
This rusty color is caused by oxidation in a wet climate.
Whiteboard Question CHECK YOUR UNDERSTANDING!
What kind of weathering causes the mineral composition of rocks to change?A. Chemical weathering.B. Mechanical weathering.C. General weathering.
A. Chemical weathering
Part 2: Chemical Weathering
Chemical WeatheringChemical weathering is___________________________________________________________________________________________________________
Force of Chemical Weathering
How it Works
Water
Oxygen
Carbon Dioxide
Living Organisms
Acid Rain
Water: Water is the most important cause of chemical weathering. When a rock dissolves in water, it mixes completely with the water.
This limestone cave was created by water dissolving the stone.
Photo source: Morguefile.com
What made this old truck rusty?
Photo source: Morguefile.com
Oxygen: Iron combines with oxygen and water in a process called oxidation. The result is rust. Oxidation of a rock makes it soft, crumbly and red or brown.
Rust happens to old vehicles, and to rocks.
Photo source: Morguefile.com
Photo source: Morguefile.com
Carbon dioxide: Carbon dioxide in the air dissolves in rainwater, becoming a weak acid called carbolic acid. Acids weather rocks such as limestone and marble.
Limestone.
Living organisms: Plants, and other living organisms such as lichen, release weak acids that slowly dissolve rocks.
Lichen growing on a rock will weather it.
Photo source: Morguefile.com
Acid rain: Burning coal, oil, and gas for energy produces pollution. This pollution combines with air and water, to create acid rain, and fast chemical weathering.
Photo source: Morguefile.com
Whiteboard QuestionCHECK YOUR UNDERSTANDING!
A rock containing iron becomes soft and crumbly and reddish-brown in color. It probably has been weathered by:A. abrasionB. oxygen.C. acid rain.
B. oxygen
Chemical WeatheringChemical weathering is___________________________________________________________________________________________________________
Force of Chemical Weathering
How it Works
Water Water is the most important cause of chemical weathering. When a rock dissolves in water, it mixes completely with the water.
Oxygen A rock containing iron becomes soft and crumbly and reddish-brown in color. It probably has been weathered by
Carbon Dioxide Carbon dioxide in the air dissolves in rainwater, becoming a weak acid called carbolic acid. Acids weather rocks such as limestone and marble.
Living Organisms Plants, and other living organisms such as lichen, release weak acids that slowly dissolve rocks.
Acid Rain Burning coal, oil, and gas for energy produces pollution. This pollution combines with air and water, to create acid rain, and fast chemical weathering.
Your completed chart
should look like this!
Is it Chemical or Mechanical Weathering?
Final Whiteboard QuestionsAbrasion of a rock by blowing sand is an
example of __________________ weathering.Acid rain washing away the face of a statue
is an example of __________________ weathering.
True or False? Living things can cause both chemical and mechanical weathering.
A tree’s roots growing through cracks in a rock is an example of _________________ weathering.
mechanical
True
chemical
mechanical
Part 3: Rates of WeatheringWhat makes a rock weather fastest?
Photo source: Morguefile.com
The most important factors for the rate (speed) of weathering are1. rock type; and 2. climate.
Rate of Weathering
Photo source: Morguefile.com
Mechanical and Chemical Weathering Work Together
Mechanical weathering increases the surface area available for chemical weathering. Increased surface area usually results in faster chemical reactions (chemical weathering).
Photo source: Morguefile.comPhoto source: Morguefile.com
Mechanical and Chemical Weathering Work Together
A permeable rock weathers easily because it contains many small, connected air spaces
Which rock do you think will weather faster?
Whiteboard QuestionCHECK YOUR UNDERSTANDING!
A permeable rock weathers easily because it:A. is made up of small particles.B. contains many small, connected air
spaces.C. is made up of many minerals.
B. contains many small, connected air spaces.
Which of these places would have faster weathering of rock? Why?
How Does Weather Affect Weathering?
Photo source: Morguefile.comPhoto source: Morguefile.com
Photo source: Morguefile.com
Rainforests have warm, wet weather.
Wet climates with high temperatures speed up both mechanical and chemical weathering.
Photo source: Morguefile.com
Photo source: Morguefile.com
Whiteboard QuestionCHECK YOUR UNDERSTANDING!
Granite lasts a long time when it is used for building in areas where the climate:A. is cool.B. has lots of acid rain.C. is hot and rainy.
A. is cool
Whiteboard QuestionCHECK YOUR UNDERSTANDING!
The most important factors in determining the rate of weathering are:A. carbon dioxide and acid rain.B. animal actions and oxygen.C. rock type and climate.D. abrasion and acids from root plants.
C. rock type and climate