Weathering is the breaking down of rocks and materials at the Earth's surface through mechanical and chemical processes. Mechanical weathering causes no chemical change and includes temperature fluctuations, frost action, root growth, and abrasion by water and wind. Chemical weathering alters the composition of minerals and includes dissolution by water and acids, oxidation, and hydrolysis. The rate of weathering depends on factors like composition, cracks/holes, climate, topography, air pollution, and exposure time. Both mechanical and chemical weathering work together to slowly break down rocks over very long periods of time.

1. Weathering

2. Weathering is the breaking down
of rocks and other materials on
the earth’s surface

3. TwoTwo Types of Weathering

4. No change in the rock’s chemical
composition.
Agents of mechanical weathering include:
 Temperature: causes repeated
expansion and contraction
1) Mechanical/physical
weathering

5. Ice wedging (frost action, freeze-thaw
cycle): when liquid water goes into
cracks and then freezes causing the
cracks to get wider
1) Mechanical/physical
weathering

7.  OrganicOrganic activityactivity (root-pry, burrowing
animals, human activities)

9.  GravityGravity: rocks falling and colliding
with other rocks

11.  AbrasionAbrasion: wearing away by solid
particles
Wind-blown Sand

12.  UnloadingUnloading: the expanding of high
pressure rock when exposed to a
lower pressure Classic sheeted granite
along the Tioga Road,
Yosemite National Park.
The granite is broken
into gently dipping plates
by unloading joints.
Unloading joints
probably form as the
rock is exposed by
erosion. These joints,
and others that are
more steeply oriented,
provide pathways for
water to enter the rock.

13. Exfoliation or unloading -
rock breaks off into leaves or sheets
along joints which parallel the ground
surface;
caused by expansion of rock due to uplift
and erosion; removal of pressure of deep
burial

15.  ContractionContraction due to crystallization
The surface pattern on this
pedestal rock is honeycomb
weathering, caused by salt
crystallisation. This example is
at Yehliu, Taiwan.
Salt
weathering
of building
stone on the
island of
Gozo, Malta

17. The altering of the composition of minerals
within a rock that results in a reduction in
size.
Agents of chemical weathering include:
 Water: Dissolves minerals out of rocks
making them weaker
2) Chemical weathering

18. Acid: Dissolves minerals in rocks (examples:
carbonic acid, acid rain, and plant acid)
Chemical weathering

19. Lichens such as
these growing on the
rocks in the picture
can produce weak
acids that react with
the rock.

21. 3000 year old Egyptian Obelisk
3000 year old Egyptian Obelisk
after 100 years in NY

22. The Parthenon in Greece shows
discoloration and chemical
weathering effects from air
pollution and acid rain.

23.  Oxidation: Oxygen combines with iron
minerals and sulfur minerals changing the
composition of the rock
Chemical weathering
Oxidation turned these rocks in
Nevada's Valley of Fire red.

24. Factors that determine
the rate of weathering:
o CompositionComposition
o Physical conditionsPhysical conditions of rock
 Cracks, holes, crevices – easier
weathering
 Solid, unbroken – more weather
resistant

26. ClimateClimate:
 ColdCold ClimatesClimates– mechanical
weathering breaks down rocks rapidly
 Warm, wet climatesWarm, wet climates – chemical
weathering breaks down rocks rapidly

27. o TopographyTopography: the position of the rock
o Air pollutionAir pollution
o Exposure timeExposure time
o Surface areaSurface area exposed
Mechanical and chemical
weathering work together

28. Weathering by BrainpopWeathering by Brainpop
1) How long does the weathering process take?
2) What is carbonic acid a mixture of?
3) What kind of rocks are formed by weathering?

29. • http://www.youtube.com/watch?
v=lyysL02ZvQ8