FIVE AGENTS OF MECHANICAL AND CHEMICAL WEATHERING

MECHANICAL WEATHERING

ANIMAL ACTIONS

• Animals that burrow in the ground loosen
• and break apart rocks in the soil.
• Including moles, gophers, prairie dogs, and insects

FREEZING AND THAWING

• The process of frost wedging also widens
• cracks in sidewalks and causes potholes in streets.
• When water freezes in a crack in a rock, it expands and
• makes the crack bigger.

PLANT GROWTH

• As roots grow, they force the cracks apart.
• After a while, the roots of even small plants can pry
• apart cracked rocks.

RELEASE OF PRESSURE

• As erosion removes material from the surface of a
• mass of rock, pressure on the rock is reduced.
• The release of pressure uses the outside of the rock
• to crack and flake off.

ABRASION

• Rock particles and sand are carried by wind,
• water, or ice can wear away exposed rock surfaces like
• sandpaper on wood

CHEMICAL WEATHERING

WATER

• Water weathers some rock by dissolving it.
• Water also carries other substances that
• dissolve or break down rock, including
• oxygen, carbon dioxide, and other chemical.

OXYGEN

• Iron combines with oxygen in the presence of water
• in a process called oxidation.
• The product of iron is rust, and rust makes rock
• soft and crumbly and gives it a red or brown color.

CARBON DIOXIDE

• Carbon dioxide also causes chemical weathering
• when it dissolve in water.
• Carbon acid easily weathers some kinda of rocks,
• such as marble and limestone.

LIVING ORGANISMS

• As a plants roots grow, they produce weak acids that
• slowly dissolve rock around the roots.
• Lichen- plantlike organisms that grow on rocks, also
• produce weak acids.

ACID RAIN

• Burning coal, oil, and gas for energy can pollute
• the air with sulfur, carbon and nitrogen compounds.
• Acid rain causes very rapid chemical weathering of rock.
• These compounds react with water vapor in clouds,
• making acids that are stronger than normal rainwater.

THE END