Weathering is the physical and chemical breakdown of rocks at Earth's surface. Physical weathering breaks rocks into smaller pieces through frost cracking, plant root growth, abrasion by water, ice or wind. Chemical weathering alters the composition of rocks through oxidation, hydrolysis and carbonation. The rate of weathering depends on climate, mineral composition, and surface area. Weathering produces sediments and soils through mechanical and chemical breakdown over time.

1. Weathering – the physical & chemical breakdown of rocks.Weathering – the physical & chemical breakdown of rocks.
Atmosphere (gas)Atmosphere (gas)
Lithosphere (solid)Lithosphere (solid)
Hydrosphere (liq.)Hydrosphere (liq.)
Involving an interactionInvolving an interaction
between the 3 spheresbetween the 3 spheres
of the earthof the earth..

2.  The rock surface of the continents of the
Earth, on which we are living, is
undergoing constant and continuous
destruction, a process called denudation.
Denudation is the process by which the
land areas are continually being reduced
and their shape modified by weathering
and erosion.

3. Rocks exposed at Earth’s surface are constantly being altered by
water, air, changing temperature and other environmental factors.
 The term weathering refers to the group of destructive processes that
change the physical and chemical character of rock at or near Earth’s
surface.
 The tightly bound crystals of any rock can be loosened and altered to
new minerals by weathering. It is important to distinguish between
weathering and erosion and between erosion and transportation.
Weathering breaks down rocks that are either stationary or moving.
Erosion is the picking up or physical removal of rock particles by an
agent such as streams or glaciers. Weathering helps break down a
solid rock into loose particles that are easily eroded.

4.  Transportation is the movement of eroded
particles by agents such as rivers, waves,
glaciers, or wind. Weathering processes
continue during transportation. A boulder
being transported by a stream can be
physically worn down and chemically
altered as it is carried along by the water.

5.  Types of weathering. These are three types
of weathering namely:-
 i) Mechanical weathering or disintegration.
ii) Chemical weathering or decomposition
iii) Biological weathering.

6.  Mechanical weathering or disintegration
This is the breakdown of rocks into small
particles by the action of temperature, by
impact from rain drops and by the abrasion
from mineral particles carried in the wind.
 Products of mechanical weathering The
products of mechanical weathering include
everything from huge boulders found
beneath the cliffs to the smallest silt.

7.  Chemical weathering.
 This is the breakdown of minerals into new
compounds by the action of chemical agents;
such as acid in the air, in rain and in river water;
although they act slowly, produce noticeable
effects especially in soluble rocks. The rate of
chemical weathering depends on temperature,
the surface area and the amount of water.
Chemical weathering causes the old minerals to
disintegrate and to form new minerals.

9. Weathering – the physical & chemical
breakdown of rocks.
I. Physical Weathering
- rocks break into pieces
- changing size and shape
- but not their composition.

10. AGENTS OF PHYSICAL WEATHERING
1.Frost Action -The freezing and thawing causes alternate
expansion and contraction of rocks eventually breaking them
apart.
Dominate in
mountain or polar
regions.
More likely to
occur in winter

11. Frost wedging & frost heaving
Buildings which are heated can be placed a little
above ground- level with a large air space beneath
them. Cold air in winter then circulates under the
building and contracts the heating effect from it.
Piped services to the buildings are also placed above
ground level to prevent their rupture by ground
movement

13. 2. Plant Action “Biological Action” - With plant growth the
root system will increase in volume and cause cracks in
the rock to expand.
Lichens are primary soil producers
creating conditions for larger plant growth.

15. 3. Abrasion- When ice, water, or wind causes sediments
to have collisions physical weathering results.
Wind abrasion is similar to
sandblasting and slowly
weathers the rock down.

16. Wind abrasion occurs
in arid environments
Note the lack of soil and
angular rock features.

17. Water abrasion occurs in moist and humid climates
Water produces rounded fragments as the sediments are
rolled and bounced along the stream bottom.

18. Glacial Abrasion occurs
when sediments are trapped
with in the ice and scrape
against the bedrock.
Forming Striations In the
Rock (Scratches)
Glaciers are found
in cold climates
high altitudes
latitudes

19. 4. Pressure Unloading / Exfoliation –
-The top rock layers are removed releasing pressure.
-The underlying rocks then crack and fall apart.

20. Chemical WeatheringChemical Weathering - when agents of weathering
chemically change the composition of a rock.
II. AGENTS OF CHEMICAL WEATHERINGII. AGENTS OF CHEMICAL WEATHERING
1. Oxidation – Oxygen combines with minerals to form oxides.
(iron + oxygen = Rust)
Oxidation weakens the bedrock making it softer.

21. 2. Hydration- minerals absorb water and chemically
change the composition of the material
Ex. granite contains mica.
Mica has a weak chemical
composition and absorb water.
Turns into clay

22. 3. Carbonation – When pollutants like Carbon Dioxide,
Nitrogen & Sulfuric Oxides mix with rain water creating
acid rain, which can dissolve limestone and harm the living
environment.
 Coal Burning For Electricity
 Fossil Fuel Consumption for Cars

23. 4. Water - Is unique and dissolves most minerals and
metals in our environment.
(universal solvent).

24. III. FACTORS AFFECTING The Rates of WEATHERING.
1. Climate Differences
Arid Climates are very dry and the rate of weathering is slow.
Humid Climates are moist and the rate of weathering is fairly fast.
 Usually in the presence of heat weathering rates will also increase.
 Different climates and temperatures produce more favorable
forms of weathering.

25. Arid and Humid Climates cause different rates of weathering.
ex, Cleopatra's Obelisk
Egypt New York

26. Cold and Humid -Physical weathering is dominate at high
latitudes altitudes, or in the winter.
-Frost Action and Glacial Abrasion
Hot and Humid - Chemical weathering is dominate near
the equator and in the summer.
-Oxidation, Hydration

27. Humid climates also favor
chemical weathering and
increase the rate in which
water will dissolve minerals.

28. Hot & humid climates can also
increase the rate of physical
weathering by biological action.

29. In the mountains and at the
poles physical weathering like
frost action and abrasion are
more likely.

30. 2.Particle Size and Shape as particle size decreases the
weathering rate increases
- When The Surface Area Increase
- More Sides Are Able To React
With The Elements

31. Angular Sediments have more surface area.
-weather at a faster rate.
Round sediments have less surface area
-weathering rate decreases.

32. 3. Mineral Composition - some rocks are resistant to
weathering because of their composition
Less Resistant
Soft Rocks have Weak
chemical compositions
More Resistant
Hard Rocks have Strong
Chemical Compositions

33. Limestone w/ weak chemical
composition (soft rock)
Granite w/ strong chemical
composition (hard rock)
Rocks will weather at different rates due to
their chemical compositions.

35. IV. Products of Weathering - sediments and soils
1. Sediment Types
a. Solids – Are clastic sediments
such as pebbles, sand, silt, or clay
b. Colloids – Are suspended clay size particles
c. Ionic Solutions – Are dissolved compounds in water

36. 2. Soil Types
a. Residual – Soils formed from the weathering of the local
bedrock and have the same mineral composition.
b. Transported - Soil that has been moved & the sediments
are not of the same composition as the local rock
Soil Horizons
A. Top layer rich in organics &
minerals from biologic activity.
B. Sediments with minerals
dissolved from above are found
here.
C. Mostly un-weathered bedrock.

37. Soil development from local bedrock.
Stage 1 Mostly un-weathered bedrock
Stage 2 Development of top soil by biologic activity
Stage 3 Mature thick and well developed soil horizons
Soil is non-renewable resource
1 inch is made for every 100 years in New York

38. Different climates produce different soil types
Form at different rates.