S6E5. Students will investigate the scientific view of how the earth’s surface is formed. d. Describe processes that change rocks and the surface of the earth.

1. Ch 10 – Weathering
Objectives
1.Contrast chemical and mechanical weathering.
2.List and describe the types of mechanical weathering.
3.List and describe the types of chemical weathering.
4.List the products resulting from the chemical
weathering of Igneous rocks.
5.List and discuss the factors that influence the type
and rate of rock weathering.

2. Read each slide then
fill in each blank
(underlined red
words) some slides
may be information
only!

4. Weathering
The breakdown of the materials on Earth’s
crust into smaller pieces.

5. Water causes weathering
What evidence of
weathering do you see
in this picture?

6. Wind causes weathering
What evidence of
weathering do you see
in this picture?
Why wasn’t this mass
of land weathered
away?

7. Ice causes weathering
Describe how ice
causes weathering?

8. Weathering
• Breakdown of rock
due to surface
processes
• 3 types of weathering
– Physical (Mechanical)
– Chemical
– Biological
http://www.geography.ndo.co.uk/animation
sweathering.htm#

9. Physical Weathering (Mechanical)
1. Abrasion – Means that the surface of the
rock is weathered due to the action of wind,
water & gravity
2. Frost wedging – Freezing–Thawing water
expands when it freezes
3. 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

10. Physical Weathering
(Mechanical)
4. Thermal expansion -
– repeated daily heating and cooling of rock;
– heat causes expansion; cooling
causes contraction.
– different minerals expand and contract at
different rates causing stresses along
mineral boundaries.
5. Plant Roots – break rocks apart as they grow
6. Animals – animals burrowing through the
soil-examples ants, molds, coyotes, worms,
mice

11. What type of physical weathering?

12. What type of physical
weathering?

13. What type of physical
weathering?

14. What type of physical
weathering?

15. What type of physical weathering?

16. What t ype of physical weathering?

17. What type of physical weathering?

18. What type of physical weathering?

19. Chemical Weathering
Rock reacts with water, gases and solutions
(may be acidic); will add or remove
elements from minerals.
1. Dissolution (or solution)
- also includes leaching
2. Oxidation
3. Hydrolysis
4. Biological Action/Acid in living thing

20. Dissolution
• Dissolution occurs when rocks and/or
minerals are dissolved by water.
The dissolved material is transported
away leaving a space in the rock. One
consequence of this process is the
formation of caves in limestone areas.
• Several common minerals dissolve in
water
– halite
– calcite
• Limestone and marble contain calcite
and are soluble in acidic water
• Marble tombstones and carvings are
particularly susceptible to chemical
weathering by dissolution.

21. Oxidation
• Oxygen, the second most
common element in the air we
breathe, reacts with iron in
minerals to form iron oxide
minerals, e.g. hematite (rust).
As many minerals contain iron,
it is not unusual to see red-
colored rocks
• Oxygen combines with iron-
bearing silicate minerals
causing "rusting"
• Iron oxides are red, orange, or
brown in color

22. Acid Precipitation
• 3. Acid Precipitation-Rain,
sleet, or snow, that contains a
high concentration of acids is
called acid precipitation.
Precipitation is naturally acidic.
However, acid precipitation
contains more acid than normal
precipitation.

23. Acid Rain
3. Acid Precipitation-Rain, sleet, or snow, that
contains a high concentration of acids is called acid
precipitation. Precipitation is naturally acidic. However,
acid precipitation contains more acid than normal
precipitation.

24. Acid in groundwater
Caves and caverns typically form
in limestone
• speleothems - cave formations;
made of calcite
• form a rock called travertine
–stalactites - from ceiling
–stalagmites - on ground

25. Karst topography forms on limestone
terrain and is characterized by:
• caves/caverns,
• sinkholes,
• disappearing streams,
• springs
More Dissolution

26. Acid Leaching

27. Hydrolysis – affected by H20
• Hydrolysis occurs when minerals react
with water to form other products.
Feldspar, the most common mineral in
rocks on the earth's surface, reacts with
water to form a secondary mineral
such as kaolinite (a type of clay) and
additional ions that are dissolved in
water. The weaker clay is readily worn
away by physical weathering.
• Feldspar alters to clay
– Feldspars = stable at high
temperatures and pressures
– Clays are stable under conditions at
the Earth's surface
• Quartz turns to sand

29. Biological Action
• Biological weathering is the actual molecular
breakdown of minerals. There are things
called lichens (combinations of fungi and
algae) which live on rocks. Lichens slowly eat
away at the surface of rocks.
• Lichens, fungi, and other micro-organisms
• Chemically and physically change rock

30. Mineral Content
Least stable
Olivine
Ca plagioclase feldspar
Pyroxene
Amphibole
Biotite
Na plagioclase feldspar
Potassium feldspar
Muscovite
Quartz
Most stable
Factors Affecting Weathering
*Surface Area
Texture
Temperature
Humidity
Topography
Time

31. Factors Affecting Weathering
Surface Area – Most
important
• Smaller particles,
more surface area
faster
• Examples
– Crushed ice cools
faster
– Granulated sugar
dissolves faster
– More exposed rocks
weather more

32. Temperature and Water
• The rate of chemical weathering is
faster in warm, humid climates

33. Weathering and Elevation
• Rocks at higher elevations, as on a
mountain, are exposed to more wind,
rain, and ice than the rocks at lower
elevations are. This increase in wind, rain,
and ice at higher elevations causes the
peaks of mountains to weather faster.

34. Gravity
• Gravity affects weathering, too. The
steepness of mountain slopes
increases the effects of mechanical and
chemical weathering. Steep slopes cause
rainwater to quickly run off the sides of
mountains.

35. Summary Types of Weathering
•Mechanical or Physical - the breakdown of rock material into smaller and
smaller pieces with no change in the chemical composition of the weathered
material.
•Chemical - the breakdown of rocks by chemical agents. Obviously the chief
chemical agent is water which carries dissociated carbonic acid.
•Mechanical Weathering Expansion and Contraction - the thermal heating
and cooling of rocks causing expansion and contraction.
•Frost Action - Water freezes at night and expands because the solid
occupies greater volume. Action wedges the rocks apart. Requires adequate
supply of moisture; moisture must be able to enter rock or soil; and
temperature must move back and forth over freezing point.
•Exfoliation - process in which curved plates of rock are stripped from a
larger rock mass. Example Half Dome. Exact mechanism uncertain but
probably due to unloading.
•Other types - Cracking of rocks by plant roots and burrowing animals.
•Chemical Weathering Factors which effect the rate of chemical weathering
are: Particle size - Smaller the particle size the greater the surface area and
hence the more rapid the weathering
•Climate