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Section 4.1 Notes
• Weathering is the process by
which natural forces break down
• There are 2 types of weathering:
1. Mechanical weathering
2. Chemical weathering
• Mechanical weathering is the
breaking up of rocks by physical
• There are 4 main types:
1. Ice wedging
2. Exfoliation
3. Plant root growth
4. Abrasion
• When water freezes, it expands.
When water freezes in the cracks
and pores of rocks, the force of its
expansion is strong enough to
split the rocks apart.
• The process in which layers or
sheets of rock gradually break off
due to the expansion of the rock
caused by a decrease in pressure.
• Trees, bushes, and
other plants may take
root in cracks of rocks.
As the roots of these
plants grow, they
wedge open the
• The process of wearing down
by friction, the rubbing of one
object or surface against
• The breakdown of rocks by
chemical reactions that change
the rocks’ makeup, or
• There are 2 main types:
1. Dissolving
2. Rusting
• Water is the main cause
of chemical weathering.
• Many more minerals
dissolve in water that is
slightly acidic – like
• The oxygen in air is also
involved in chemical
• Many common minerals
contain iron. When these
minerals dissolve in water,
oxygen in the air and the
water combines to produce
• Most weathering occurs over long
periods of time – hundreds,
thousands, or even millions of
• There are 3 Influential factors:
1. Surface area
2. Rock composition
3. Climate
• The more of a rock’s surface that is
exposed to air and water, the faster
the rock will break down.
• Different kinds of rock break down
at different rates.
• Chemical weathering occurs faster
in hot, wet regions than it does in
cold, dry regions.
• Mechanical weathering caused by
freezing and thawing occurs more
in cold regions than in hot regions.