Download Weathering - Holy Angels School

Module E: Unit 1, Lesson 2 – Weathering
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.
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.
• 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.
• 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.
• 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.
• 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.
• 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.
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.
• 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.
• Acids can cause chemical weathering by breaking down minerals faster than
water alone.
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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.
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.
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.