Chapter 8 Section 8.1 Notes
How did these form??
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Weathering and Erosion!
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™ Weathering—the process that breaks down rock and
other substances at Earth’s surface
™ Erosion—the removal of rock particles by wind,
water, ice, or gravity
™ ***Together, weathering and erosion work to
continuously wear down and carry away the rocks at
Earth’s surface
Uniformitarianism
–
™ The weathering and erosion that geologists observe
today also shaped Earth’s surface millions of years
ago!
™ This is uniformitarianism, the principle that the
same processes that change and affect the Earth
today did so in the past (plate tectonics as well!)
Types of Weathering
–
Mechanical
™ When rock is physically
broken into smaller
pieces
Chemical
™ When rock is broken
down through chemical
processes
Mechanical Weathering
–
™ Forces of mechanical weathering
include:
–
–
–
–
–
Release of pressure
Animal actions
Freezing (ice wedging) and Thawing
Plant Growth
Abrasion
– Excellent pictures on p240-241
Chemical Weathering
–
™ Includes the action of:
™ Water
™ Oxygen
™ Carbon dioxide
™ Living organisms
™ Acid rain
Chemical Weathering
–
™ Water—weathers rock by dissolving it
™ Oxygen—oxygen in the atmosphere reacts with iron in
the presence of water which causes rust to form
(oxidation)
™ Carbon dioxide—dissolves in rainwater and creates
carbonic acid, which weathers rock
™ Living organisms—plant roots and microorganisms
release weak acids as by-products that weather rock
™ Acid rain—fuels that pollute the air react with water
vapor and form acids that mix with raindrops
Chemical Weathering
–
™ Remember:
™ Rock is made up of one or more minerals
™ Chemical weathering can produce new minerals as it
breaks down rock
™ Chemical weathering can also create holes or soft
spots in rock.
™ Hey…. That can lead to….
™ Erosion!!!
Rate of Weathering
–
™ The most important factors that determine the rate at
which weathering occurs are:
–  Type of rock
–  Climate
–  Human Activities
Rate of Weathering
–
™ Type of Rock
™ The minerals that make up rock determine how fast it
weathers
–  Minerals that are NOT easily dissolved in water will cause
rocks to weather slowly
–  Minerals that ARE easily dissolved in water will cause rocks
to weather quickly.
–  Rocks that are permeable have tiny air spaces where water
can seep into and increase the rate of weathering.
–  Practice—Analyzing Data p 244
Rate of Weathering:
Climate
–
™  Wet climates cause both
mechanical and chemical
weathering to speed up.
–  Chemical: Rainfall can help
cause chemical reactions to
produce weathering
–  Mechanical: Water freezes
and thaws causing the
rocks to condense and
expand.
™  Warm climates causes
chemical weathering to
occur even quicker
Rate of Weathering:
Human
Activities
™ Burning coal and
–
gasoline puts chemicals
in the air that create acid
rain, which increases
weathering
™ Damming rivers can
actually cause the water
on the other end to
absorb more sediment
from rocks so the water
causes more damage
from weathering.
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