Unit 1 Lesson 2 Weathering
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Unit 1 Lesson 2 Weathering
Break It Down
What is weathering?
• Weathering is the breakdown of rock material by
physical and chemical processes.
• Two kinds of weathering are physical weathering
and chemical weathering.
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Unit 1 Lesson 2 Weathering
What causes physical weathering?
• Physical weathering is the process by which
rock is broken down into smaller pieces by
physical changes.
• The composition of the material does not change
during physical weathering.
• Agents of physical weathering include temperature
changes, pressure changes, plant and animal
actions, water, wind, and gravity.
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Unit 1 Lesson 2 Weathering
What causes physical weathering?
• Changes in temperature can cause a rock to break
apart by weakening the structure of the rock.
• Heat causes the rock to expand; cold causes it to
contract.
• Ice wedging, or frost wedging, causes cracks in
rocks to widen with repeated cycles of freezing
and thawing.
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Unit 1 Lesson 2 Weathering
What causes physical weathering?
• How can a small crack in a rock eventually split
the rock into two or more pieces?
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Unit 1 Lesson 2 Weathering
What causes physical weathering?
• Rocks that formed under pressure deep within
Earth can be exposed to the surface.
• As material is removed above the rock, the
pressure decreases and the rock expands.
• Exfoliation is the process by which the outer
layers of rock slowly peel away due to pressure
changes.
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Unit 1 Lesson 2 Weathering
What causes physical weathering?
• Animals can cause physical weathering by digging
burrows.
• New rocks, soils, and other materials become
exposed at the surface as a result of animal
actions.
• Materials exposed at the surface are more likely to
undergo weathering than those below.
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Unit 1 Lesson 2 Weathering
What causes physical weathering?
• Abrasion is the breaking down and wearing away
of rock material by the mechanical action of other
rocks.
• Three agents of physical weathering that can
cause abrasion are moving water, wind, and
gravity.
• Rocks suspended in a glacier can also cause
abrasion of other rocks on Earth’s surface.
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Unit 1 Lesson 2 Weathering
What causes physical weathering?
• Roots of plants start out as tiny strands that may
grow in small cracks in rocks.
• As the roots grow, they put more pressure on the
rock, causing the rock to expand and eventually
break apart.
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Unit 1 Lesson 2 Weathering
Chemical Weathering
What causes chemical weathering?
• Chemical weathering is the breakdown of rocks
by chemical reactions.
• Chemical weathering changes both the
composition and appearance of rocks.
• Agents of chemical weathering include oxygen in
the air and acids.
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Unit 1 Lesson 2 Weathering
What causes chemical weathering?
• Oxidation is the process by which chemicals in
rock combine with oxygen in the air or in water.
• Rock surfaces sometimes change color, indicating
that a chemical reaction may have occurred.
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Unit 1 Lesson 2 Weathering
What causes chemical weathering?
• Acids can cause chemical weathering by breaking
down minerals faster than water alone.
• Acids in the atmosphere are created when
chemicals combine with water in the air.
• Acid precipitation occurs when strong acids fall
to Earth as rain, sleet, or snow.
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Unit 1 Lesson 2 Weathering
What causes chemical weathering?
• Acids in groundwater can cause rock to dissolve.
• A small crack in the rock can result in the
formation of extensive cave systems carved out
over time.
• Rock material dissolved in groundwater can be
carried and deposited in new locations over time.
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Unit 1 Lesson 2 Weathering
What causes chemical weathering?
• Acids produced by living things can cause
chemical weathering.
• Chemical reactions occur as these acids move
through tiny spaces in rock material.
• As the acids seep deeper, cracks form. Eventually,
the rock can break apart.
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