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Transcript
Warm-up: What has occurred in
these pictures? Please write a brief
description.
Weathering
Types of Weathering
Mechanical or Physical
Chemical
Weathering is the
process that . .
__________________________
__________________________
_____
Mechanical Weathering
Definition: Mechanical weathering breaks apart
rocks without changing the chemical structure.
Types of Mechanical Weathering
1) Frost wedging
2) Exfoliation
3) Thermal expansion
Mechanical Weathering
 Expansion and Contractions
water expands when it freezes and causes
rock to break
Mechanical Weathering
 Freeze/thaw cycles break down rock as
water enters cracks and widens them
Mechanical Weathering: Exfoliation
 rock breaks off into sheets, which is caused by the
– Expansion of the rock due to erosion
– Pressure from the earth’s surface
Mechanical Weathering: Thermal
Expansion
Chemical Weathering Types:
 Chemical weathering occurs when water,
air, and other substances react with
minerals in the rocks and it’s chemically
changed.
1) Dissolution
2) Oxidation
Chemical Weathering: Dissolution
– Can dissolve rock
– Can form acids as they react with rocks and
atmosphere
– The gravestone shown
here is chemically changed
from London’s pollution, vehicle
exhaust fumes that contain
sulfur and nitrogen.
Chemical Weathering: Oxidation
– Oxygen combines with elements in the rock
– Often rocks become discolored
 Some types of rock are easily weathered by
chemicals.
– For example, limestone and chalk are made of a mineral
called calcium carbonate.
– When acidic rainwater falls on limestone or chalk, a
chemical reaction happens.
– New substances are formed in the reaction. These are
washed away and the rock is weathered.
– Chemical weathering can make caves form and cliffs fall
away.
Chemical Weathering
– Carbon dioxide with water creates carbonic acid
that eats away rock. Carbonic acid is the same
weak acid that makes soft drinks fizzy.
Chemical Weathering
– Several caves around the world are examples
of chemical weathering
What did we learn?




What is mechanical weathering?
What is chemical weathering?
Do they work together?
Now, let’s take a weathering walk and find
what kind of weathering takes place in our
backyard!!