Weathering of rocks, types of weathering.ppt

weathering, physical and chemical weathering

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Weathering

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Positive or Negative?Positive or Negative?

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Split Apple Rock (New Zealand)
Kjeragbolten Cliff (Norway)
Wave Rock (Arizona, USA)
Painted Cliffs (Tasmania)

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Biri Rock Formations, Northern Samar
Sumaguing Cave in Mountain Province
Minalungao Cave,
General Tinio, Nueva Ecija

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MELC:MELC:
•Describe how rocks
undergo weathering
((S11Es-lla-22)

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Objectives:Objectives:
•1. describe how rocks undergo
weathering (S11Es-lla-22);
•2. differentiate the types of
weathering; and
•3. discuss how the different factors
affect the rate of weathering.

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1.What is Weathering?
2.What are the two types of weathering? weathering?
3.3.What are the different processes occurs during weathering?What are the different processes occurs during weathering?
4.4.What are the factors that affects weathering?What are the factors that affects weathering?

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WeatheringWeathering
•Weathering is the physical disintegration
and chemical decomposition by which
rocks change upon exposure to physical,
chemical and biological processes at or near
the Earth’s surface to produce an in-situ
mantle (in place) of the loosened or altered
material. It means that this reaction happens
on the surface or within the rock.

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Both physical and chemical
processes break down rock

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Types of WeatheringTypes of Weathering
•1. Physical weathering (or
mechanical weathering) disintegrates
rocks, breaking them into smaller
pieces. This kind of weathering
breaks apart the rock without
changing its chemical composition.

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1. Physical (Mechanical) Weathering
•A. Frost wedging
•when water gets inside the joints, alternate freezing and thawing episodes pry
the rock apart.
Split Apple Rock (New Zealand)

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•Physical (Mechanical) Weathering
•A. Frost wedging
ALTERNATE
FREEZE
AND THAW

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1. Physical (Mechanical) Weathering
•B. Salt crystal growth-
•force exerted by salt crystal that formed as water
evaporates from pore spaces or cracks in rocks
can cause the rock to fall apart
honeycombed stones (tafoni)
Utah

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1. Physical (Mechanical) Weathering
•C. Abrasion
•wearing away of rocks by constant collision of loose
particles
•Agents that move rock include Wind, Liquid water
(streams, rivers), Solid water (glaciers), Gravity alone
(along a cliff face)
Biri Rock Formations, Northern Samar

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•C. Abrasion
1. Physical (Mechanical) Weathering
Vermillio
n Cliff in
Arizona
USA

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D. EXFOLIATION
Rocks expand
and crack due to
unloading
(reduced
pressure at
earth’s surface)
or fluctuations
in temperature.
1. Physical (Mechanical) Weathering
Half Dome in California

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•decomposes rocks through chemical
reactions that change the original rock-
forming minerals.
•Weathering occurs as a response to the
low pressure, low temperature, and
water and oxygen rich nature of the
Earth’s surface.
2. Chemical Weathering

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•A. Dissolution-
•dissociation of molecules into ions;
common example includes dissolution of
calcite and salt.
2. Chemical Weathering
Minalungao Cave,
General Tinio, Nueva Ecija

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•B. Oxidation-
•reaction between minerals and oxygen
dissolved in water.
2. Chemical Weathering
Painted Cliffs (Tasmania)

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•C. Hydrolysis-
• occurs when water dissolves minerals in
a rock, producing new compounds. This
reaction is called hydrolysis.
2. Chemical Weathering
Feldspar crystals inside the granite react
chemically, forming clay minerals.

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•also called biotic weathering. This type
of weathering is the disintegration of
rocks caused by living organisms.
3. Biological Weathering

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Can be both mechanical and chemical
weathering.
3. Biological Weathering

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•A. Plants.
• help to cause physical and chemical weathering. Its root
continues to push through into the joints of rocks in searching
for moisture. As the plant grows, its roots grow larger and
thicker which causes the rocks to break. The larger and
thicker the roots, the more pressure it exerts on the rocks
which will result to break the rock.
•It also causes reactions to rock
minerals.
3. Biological Weathering

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PLANT ROOTS UPLIFT AND
FRACTURE ROCK
3. Biological Weathering

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•B. Animals
•such as ants, earthworms, rats, rabbits, and termites breakdown the rocks
through burrowing. These actions causes to breakdown rocks. The
disintegrated rocks will be easier to be exposed in other intense processes,
or to be eroded or removed by other agents. The chemical composition of
the rocks will change due to microbes. As a result of change in chemical
composition, the rocks will be more susceptible to weathering.
3. Biological Weathering

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•C. Humans act a significant role in weathering of rocks.
Human activities like agriculture, construction of houses and
buildings, development of roads, among others, demand a
large quantity of rocks to be broken down. Mining of ores and
minerals also contributes to breaking, weakening and
loosening of rocks. Furthermore, if there is an increase in
pollution, there will be also an increase amount of weathering
agents in soil, water and wind.
3. Biological Weathering
Banaue Rice Terraces

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•a. Climate-
•Areas that are cold and dry tend to have
slow rates of chemical weathering and
weathering is mostly physical; chemical
weathering is most active in areas with
high temperature and rainfall.
Factors that affect the type, extent, and rate
at which weathering takes place

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•b. Rock type
•The minerals that constitute rocks have
different susceptibilities to weathering. The
susceptibility of minerals (from high to low)
roughly follows the inverse of the order of
crystallization of minerals in the Bowen’s
reaction series.
Factors that affect the type, extent, and rate
at which weathering takes place

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•b. Rock type
•olivine which crystallizes first is the least
resistant whereas; quartz which crystallizes
last is the most resistant.
Factors that affect the type, extent, and rate
at which weathering takes place

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•c. Rock structure-
•Rate of weathering is affected by the presence
of joints, folds, faults, bedding planes through
which agents of weathering enter a rock mass.
•Highly jointed/ fractured rocks disintegrate
faster than a solid mass of rock of the same
dimension.
Factors that affect the type, extent, and rate
at which weathering takes place

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•d. Topography-
•Physical weathering occurs more quickly
on a steep slope than on a gentle one.
•On a gentle slope, water may stay longer
in contact with the rocks, hence chemical
weathering is enhanced.
Factors that affect the type, extent, and rate
at which weathering takes place

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•e. Time-
•Length of exposure to agents
of weather determines the
degree of weathering of a
rock.
Factors that affect the type, extent, and rate
at which weathering takes place

36. •Surface Area
•Greatly influences weathering rates
• weathering occurs at the surface of rock particles
Increasing Surface Area
Factors that affect the type, extent, and rate
at which weathering takes place

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38. Activity 2. Am I In or Am I Out?
Directions: Identify what kind of weathering is described below.
Write P if it is physical weathering and C, if it is chemical
weathering.
•1. repeated impact of running water
•2. grinding of rocks
•3. carbon dioxide deposition in rocks
•4. dissolution of rocks in water
•5. oxidation of iron in rocks
•6. eroding of sediments
•7. cracked beneath of rocks
•8. inclined slope of a river
•9. high rusting chains of rocks
•10. calcium carbonate gets dissolved in acidic soil found in bedrock
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39. Exfoliation 39
1.
Mechanical/
Physical
2.
Frost
wedging
3.
Abrasion Biological
Weathering
4.
5.
`Oxidation
II. You Complete Me! Illustrate a concept map by filling in the box below with
the words related to weathering to complete the diagram.

40. Exfoliation 40
1.
Weathering
2. Mechanical/
Physical
3.
Chemical
4. Frost
wedging
5. Salt
Crystal
Growth
6.
Abrasion
7.
Biological
Weathering
8.
Dissolution
9.
Hydrolysis
10.
Oxidation
II. You Complete Me! Illustrate a concept map by filling in the box below with
the words related to weathering to complete the diagram.