Chapter 5 Weathering, Erosion and Mass Mov’t
Earth and Environmental Science
Weathering
Earth is continuously undergoing natural breaking down process –________________________
Weathering – the ______________________ of rocks and other materials on the Earth’s surface
 A __________________________________ process
 Affects __________________________ exposed to the __________________________
The effects are ____________________________________ due to how long weathering takes.
Two types of weathering - _______________________________________________________
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Mechanical Weathering
Forces of weathering break rocks into smaller pieces but
______________________________________ of the rock.
Strictly a ________________________________________________
Common agents of Mechanical weathering are
________________________________________________________________________
Like hitting a rock with a hammer and smashing it to pieces.
At the beginning of weathering, rock fragments are usually
___________________________________. As weathering continues they become
_____________________________________________________
Causes of Mechanical Weathering
1. __________________________________________
 Changes in temperature can cause rocks to break apart.
 The outside of the rock is _________________________________________ while
the inside of the rock remains cool and ___________________________________
expand. When the temperature drops, the outside of the rock
______________________________________.
 This cycle repeats every day and causes the particles to ________________________
 ______________________________________ – pieces break off in curved sheets or
slabs parallel to rock’s surface. Other agents also cause exfoliation.
2. __________________________________________________
 Water expands in ____________________________ by about ______________
when it freezes
 Repeated ____________________________________ of water
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 Water seeps into a small opening or ________________________ in a rock, the
temperature drops below freezing, the water freezes and
expand___________________________________________.
 The crack is made larger ________________________________________________
 Over time the cycle causes the rock to break into pieces.
 ________________________________ – large piles of broken rock
 ____________________________________ in roads and cement driveways are often
caused by frost action.
 Commonly occurs at high elevations and in climates where the temperature regularly
varies above and below freezing – _________________________________________
______________________________________
 _____________________________________________________________ causes it
to expand and allows slabs of outer rock to break off in layers in a process called
exfoliation.
_____________________________________________
 ________________________________________ - Roots of plants loosen rock
material by growing in a crack in a rock and make the crack larger as the plant’s roots
grow and spread out.
 ____________________________ of borrowing animals expose new rock surfaces to
weathering.
Gravity
 ______________________________________ - Pulls loosened rocks down
mountain cliffs
 Landslide – large movement of loose rocks and soil – As the rocks fall,
_______________________
___________________________________ and break into smaller pieces.
 A type of _____________________________
__________________________________
 The wearing away of rocks by solid particles carried by
_________________________________
 ______________________ - Sharp edges of sand particles scrape off small pieces of
exposed rock.
 ________________________________ causes abrasion by carrying along loose
rocks and other particles that scrape against each other and against the riverbed.
Causes the riverbed rocks to be
_____________________________________________
____________________________________________
 The __________________________ or mineral composition of the rocks is
___________________
 Chemical reactions take place between the minerals in the rock and
_____________________________________________________________________
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 Chemical reactions _________________________________________ of the original
mineral and lead to the _____________________________________________
 _____________________________________________________________________
__________ of the rock undergo changes.
 Minerals can be ________________________________________________
 Minerals can be broken down – ______________________________________
Causes of Chemical Weathering
1. Water – ______________________________
a. ______________________________________ when they react with water is
called hydrolysis
b. Causes most of chemical weathering with ________________________________
c. ___________________________________ most minerals that hold rocks together
d. ______________________________ – able to be dissolved in water
e. Water forms _________________________________________ in the atmosphere
f. Water can combine with a mineral to form a completely different mineral
i. Example – Water + Feldspar = Clay (called kaolin)
ii. Hydrogen ions from the water displace the elements potassium or calcium in
feldspar.
g. ____________________ – water carries dissolved minerals to lower layers of rock.
i. Bauxite (aluminum ore) form when leaching causes a mineral to concentrate
in a thin layer beneath the Earth’s surface.
2. Oxidation
a. _________________________ elements combine with ______________________
b. Often occurs in rocks with _____________________________ minerals
i. 4Fe + 3O2  2Fe2O3 (rust)
c. Occurs when oxygen chemically combines with another substance
d. Causes the ___________________ in a lot of the soil of the __________________
3. Carbonation
a. Carbonic acid forms when _____________________________________ – occurs
when carbon dioxide in the air combines with _____________________________
i. H2O + CO2  H2CO3
b. _____________________ – carbonic acid reacts chemically with other substances.
c. Carbonic acid is able to _____________________________________________
on or beneath the surface of the Earth
d. Carbonic acid is _______________________________________ to humans
e. Slowly decomposes _______________________________________
i. Carbonic Acid + Calcite (limestone)  Calcium Carbonate
ii. This dissolving action sometimes produces __________________________
4. Sulfuric Acid – _______________________________________________
a. ________________________________________ are in the air of polluted areas
b. A _______________________________________________ as a source of energy
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c. Sulfur dioxide ___________________________ to form ____________________
d. ______________________________ than carbonic acid.
e. Sulfuric acid _____________________________________________ very quickly
5. Plant Acids
a. Plants produce _______________________ that dissolve certain minerals in rocks
b. ________________________________________ produce acids
Rate of Weathering
Depends on:
1. Composition of rocks
a. Weather differently depending on the minerals that make up each rock
b. Stable rock – minerals in rock resist chemical weathering
i. Stability varies depending on the climate the rock is in
1. ex. Limestone (made with calcite) weathers very little in a dry,
warm climate. But, in a wet climate, moisture combines with
weak acids to dissolve limestone.
2. Granite is stable in cool, dry climates but in tropical climates it
decomposes quickly.
a. The moisture turns the feldspar in the granite to clay
which is not strong enough the hold the rock together.
ii. Igneous and metamorphic rocks weather more slowly
iii. Quartz is least affected by chemical weathering It is extremely hard
so it resists mechanical weathering and maintains it structure as grains
of sand.
iv. Shales and sandstones are not held together firmly and gradually
break into clay and sand particles. Conglomerates are strongly
cemented together by silicates may resist weathering even longer than
some igneous rocks.
v. The more moisture there is in an area, the faster the rocks will
weather.
2. Amount of time exposed on Earth’s surface.
a. The more time it is exposed, the greater the amount of weathering.
3. Amount of exposed surface are on the rock
a. Rocks broken down into small pieces (which exposes more surface area)
will weather more rapidly.
b. Cracks and joints in rocks also increase the amount of surface area exposed
to moisture and chemicals which causes more rapid weathering.
4. Climate
a. Rainfall and the freezing and thawing produced by alternating hot and cold
weather have the greatest effect on the rate of weathering.
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b. In hot, dry climates weathering takes place slowly.
c. Lack of water limits the rate of the many chemical and mechanical processes
like carbonation and ice wedging.
d. In warm and humid climates, chemical weathering takes place fairly rapid.
5. Topography
a. Elevation and slope of the surface where the rock is located.
b. Higher elevations have more ice wedging.
c. Steep slopes gravity pulls rock fragments downhill and or they are washed
away by heavy rains.
d. New surfaces of mountains are exposed more quickly to weathering.
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