The earth's surface is an ever-changing entity. With the forces of weather and climate and tectonic variability, the rocks and minerals that make up the earth are always changing in size, shape and forms - a fascinating, ancient, never-ending process.

1. Rocks/
Weathering
AS Level Physical
Geography

2. Definitions
• Accretion: the process by which a substance grows
by the collection and clustering of different parts
• Geomorphology: The study of origin and evolution of
topographic and bathymetric features created by
physical, chemical and biological processes at or
near the earth surface.
• Silicates: Most common group of minerals – include
silicon and oxygen
• Magnetic Field: Area around and affected by a
magnet or charged particles

3. THE BEGINNING OF IT ALL
Introduction

4. Formation of Earth
• Collisions of objects in the galaxy – forming
protoplanets
• Soon the planets arrange into the 8 planets
• Asteroid belt between Mars and Jupiter (messed
up planet)

5. Formation of Earth
• Earth is formed
• Process of
differentiation
• Heavy elements
(NIFE) sink to
the core
• Lighter elements
(Silicates float to
surface)

6. Formation of Earth
• Another object collided with earth
• Some of earth’s materials knocked out
• Accreted and formed moon

7. Formation of earth
• Earth cools down at 3.8 – 4 billion years ago
• Water vapor condenses
• Torrential rain
• Ocean was formed then

8. Start of Life
• 3.8 Billion years ago
• Prokaryote first appears
• Start photosynthesizing
• Oxygen produced
• The reactivity of oxygen
caused Oxygen holocaust –
2.5 Billion – killed off a lot of
single cell organisms
• 1.7 Billion years ago -
Eukaryote

9. GEOLOGICALEPOCHS
GEOLOGICALEPOCHS

10. A PROFILE OF EARTH
INTRODUCTION
https://www.youtube.com/watch?v=zw-
z_iTnIdc&feature=iv&src_vid=PT7qhBUffvY&annotation_id=annota
tion_3093859399

11. Our Solar System

12. About Earth
• 3rd Planet from the Sun
• 150 million kilometers from the sun
• Diameter: 12,756 km
• 365.256 Days to orbit the sun
• 24.9345 hours to rotate once

13. Earth – and Life
• The only planet to harbor life
• Rapid Spin + NIFE (Nickel, Iron) core = large
magnetic field
• Atmosphere
• Both of the above shielded earth from radiation/
meteors

14. The Atmosphere

15. The Hydrosphere

16. The Lithosphere

17. Definition of Rocks and Minerals
• A mineral is an inorganic, naturally occurring
solid that has a definite chemical composition
and an atomic structure
• Inorganic: Not living, not composed of biological
• Definite chemical composition: Unique elemental
make-up
• Feldspar, Sulfur, Quartz
• Color, Hardness, Luster(metallic/non-metallic),
streak(color in particles), cleavage/fracture
• Building blocks of rocks

18. PLATE TECTONIC
Part 1

19. Earth’s Interior
• Scientists can determine earth’s inner core
through seismology/ nebular theory
• Seismo = Greek for shock

20. Seismic movement
• 4 categories of seismic waves
• Most waves are between: 3 – 15 km/s
• 2 types travelled along the surface in rolling swell
• Primary(compression)/ Secondary(shear) waves –
penetrates the earth’s interior
• Primary travels through rocks/ water
• Secondary cannot travel through rock
• Speed of waves reduce when in contact with hotter
matter
• These differences in seismology allow scientists to
identify the different properties of rocks underground

21. Earth’s Interior

22. Mechanical layer of the earth
• The topmost = crust
• Under the crust – the coolest top layer of the mantle –
Elements are different from the crust
• LITHOSPHERE 10 – 200 KM – 10 is unusual, usually
close to the hotspot
• Deeper you go… ASTHENOSPHER (Still act like solid –
jelly, puddy layer, the temperature semi - melted the rock
– the plates move on top of this [660 km deep])
• Next layer of the mantle (MESOSPHERE – don’t
confuse with the atmospheric Mesosphere) – still act like
solid
• OUTER CORE – The high temperature comes into effect
here – the temperature overrides the pressure – the
pressure can not affect the metal too much – liquid-like
(5100 KM)
• INNER CORE – Solid due to pressure – 1218 km

23. Chemical Structure
• The Denser element sunk to the center during
the formation of earth
• The core is almost entirely made up of heavy
metal

24. Earth is shaped from the inside out
• Transfer of heat
(hotspot, convection
current) or more
specifically energy –
determines the
landscape of the earth
• Causes plate tectonic
• Volcanic eruption
• Earthquake
• Seafloor spreading
• Orogeny (Mountain
building)

25. Inner Core
• A very hot, very dense
center of the planet
• Radius about 1218 km
• 1.7% of earth’s mass
• Inner core is solid
• Frozen with high pressure
• NIFE (Nickel, Iron)

26. Outer Core
• 30.8% of the earth’s mass
• 2200 km thick
• Liquid-like
• Composition: NiFe
• Conductive/ hot – site of violent convection
• Electrical current caused by churning of metals here
forms magnetic fields
• Still NIFE – however may contain Oxygen/ Sulfur
• Bullen discontinuity borders the core and the mantle
– the hottest

27. Mantle
• The most solid bulk of the earth’s interior (semi-
molten)
• 84% of the earth’s volume
• At 4.5 billion years ago, iron and nickel separate
from other minerals to form the core while other
molten materials formed the mantle.
• Mantle solidifies into molten state during outgassing
where water erupts with lava
• Materials: Silicate (oxygen+Silicon), Calcium,
Sodium, Aluminum, Iron, Magnesium oxide
• Mantle is more viscous near plate boundary and
magma plume

28. Oceanic Crust
• Formed at points of sea floor spreading center (Mid
Atlantic Ridge/ Pacific Rise)
• 0.99% of earth’s mass
• 200 million years old
• Dense – 3.0 g/cm3
• Thinner – 6 - 16 km
• New – new lands are formed here
• Basaltic Rock (Igneous) (SIMA) (MAFIC)
• Starts at mid ocean ridge – ends at subduction zone
• Edge can be stranded on land

29. Continental Crust
• Formed through arc volcanism and accretion
• 0.347% of the earth mass
• 4 billion years old
• Lighter – 2.6 g/cm3
• Made up of crystalline rock – with quartz and
feldspar
• Thicker – average up to 30 – 70 km in thickness

30. Difference between Basaltic/ Igneous
Rock
• Basaltic – extrusive igneous rock (Volcanic) –
Magma burst out through the earth surface and
cools down quickly – not much time for mineral
crystals
• Granitic – Intrusive igneous rock (Plutonic) –
crystals form due to the slow cooling in the earth
continent

31. Factors affecting the earth’s surface
• Movement of the plates
• Earthquake and seismic activities
• Volcanic activities
• Formation of fold mountains
• Chemical weathering
• Changes in temperature leading to wethering
• Erosion by wind
• Hydrology

32. The Plate Tectonic Theory – Key
Principles
• Outer layer of earth divided into Lithosphere and
Asthenosphere
• Asthenosphere has a convection current and an
almost adiabatic heat gradient
• The lighter lithosphere is divided into different
plates – riding on the more viscous and dense
asthenosphere
• 1 tectonic plate = lithospheric mantle with crustal
materials on top
• Points where 2 plates meet = plate boundaries

33. The Continental Drift Theory
• First introduced by Alfred Wegener
• A German meteorologist
• In 1911, he found the that similar organisms
could be found in different continents across the
Atlantic

34. The Continental Drift Theory
• The continents seemed to fit like jigsaws – the
eastern coast of South America and the Western
coast of Africa
• Some other scientists supported him with fossils
ideas as well as evidences of fold mountains
• However, Wegener couldn’t come up with a
mechanism to support the movement of plate

35. Mohorovicic Discontinuity
• If the earth was made of uniform mass (which it
isn’t) – the materials would get denser to the center
– the time taken for a wave to get to a distance
should be proportional to the distance (same
velocity)
• 1909 earthquake – Andrija Mohorovicic – at 200 km
from the earthquake – the wave began to accelerate
• He realized the wave must’ve been travelling
through a denser layer of the earth – it refracted to
the direction it was going – acceleration
• The boundary between mantle/ crust is now called
the Mohorovicic discontinuity

36. The Plate Tectonic Theory
• Since the 1950s – further exploration of the
theory supported Wegener’s claim
• Early 1960s – Hess and Dietz – discovery of the
Mid Atlantic Ridge and Sea Floor Spreading
• Discovery of paleomagnetism

37. Evidences supporting the theory

38. 1. The Fitting of the continents
The Shapes of the continents fit together very well – this was first noted by
Francis Bacon in the 16th century. The most visible fitting is between South
America and Africa

39. 2. Biological Fossil Evidenced
Various fossils found across the earth’s continents e.g. discovery of the
Mesosaurus fossil in both South America and India – discovery of plant fossil
like Glossopteris in the southern continents.

41. 3. Geological Evidence
Glacial depositions that seems connected between Antarctica and brazil.
Fold Mountains – e.g. The Swiss Alp
Later – The Appalachian mountain range was also used as an evidence for the
connection between the Eurasian and the North American Plate

42. 4. The Mid Atlantic Ridge
A distinct land form discovered in 1948 – found at divergent plate boundary -
showing that two plates are actually coming apart

43. 5. Seismic evidence/ Activity
Seismic, volcanic and geothermal activity found in connected network of lines
This includes the Mohorovicic Discontinuity

44. 6. Paleomagnetism
Magnetic anomaly existing in bands of rocks across the mid Atlantic ridge – also
symmetrical to between the 2 sides of the ridge: Best explanation is when the plate
diverges, the magma rises, as it cools and harden, it obtains the current magnetic
field of the earth which keeps on changing - hence the anomaly.

45. Mantle Convection
• The theory first put forth by Arthur Holmes in the
1930s
• The differences between temperature beneath
the lithosphere creates a convection current
which moves the plate
• There are many theories regarding how plates
move
• Debates are still going on regarding this

46. The Hotspot Theory
• The Hotspot theory states that the activities in
the core causes semi molten parts of the mantle
to rise
• The creates a plume of magma rising .
• As the viscous rocks reach the plate – the
magma might break through – causing rifts
• The magma flowing outward as they reach the
plate may create dragging forces
• However, the greatest hotspot of the world –
Hawaii – is not a plate boundary

47. The Dragging Theory
• His states that the colder edges of the plates are
colder and denser
• They therefore sink at points of subduction
• His sinking causes a dragging process

48. Plate boundary type1: Divergent
• 2 Plates moving apart – could be due to rising of hot
matters starting from the core (hotspot theory)
• Also called Constructive plate margin (constructs
new land)
• Magma creates a lump/ an arch in the lithosphere
• The arc becomes a crack in the lithosphere
• Magma rises up – filling in the gaps between the
plates
• The magma rises up due to lower density of the
asthenosphere.
• This also pushes the plates apart

49. Sea-floor spreading
• At Divergent plates boundary
• The crack appears at the ocean floor
• Heat from asthenosphere makes material hot and
less dense – these rises forming an elevated ocean
floor
• Crack widens – magma bubbles up and spill over
• The sea water cools down the magma – turns into
igneous rock (basaltic) – becomes a new earth crust

50. Mid Ocean Ridges
• The elevated ocean floors form large mountain
ranges e.g. Mid Atlantic Ridges or the East Pacific
Rise or the Southeast Indian Ridge
• Slow spreading ridges = tall narrow cliffs/ mountains
– because of smaller magma chamber =
discontinuous eruptions
• Fast spreading ridge = large magma chamber =
sheets of lava = gentler slopes
• As the oceanic crust moves away – it becomes
thicker
• The end of the plate sees a collision

51. Rift Valley
• Occur when two plates move apart
• Two plates moving apart – creates cracks
• The land in between the cracks begin to sink
• Leaving a valley
• Often found at Transform faults or triple junctions

52. Plate boundary type2: Convergent
• Two plates converge/ collide
• May be oceanic vs. Continental, oceanic vs.
oceanic or continental vs. continental
• Produce different landforms

53. Subduction Zone
• Elements:
1. Subduction Complex
2. Accretionary Prism/ wedge
3. Ocean trench
4. Fore-arc basin
5. Sedimentary arc
6. Volcanic Arc
7. Volcanic island
8. Back-arc basin

55. Fold Mountains
• When 2 plates collide
• Oceanic + continental – the heavier/ denser oceanic
sinks into the asthenosphere.
• One plate subducts beneath another
• This forces the continental plate to buckle and fold
inland
• The land rises into a mountain range e.g. The Andes
• In areas such as these – fore arc basins may
accrete to form a rising mountain
• Front island arcs may also be of causes
• Subduction zone – means volcanic arc may be
formed

57. Fold Mountains
• Continental crust + Continental crust
• Both are equally dense – they collide
• Sediments on both basins are folded and
buckled – forming a huge mountain range
• Generally – oceanic lithosphere is lost between
them
• These may cause some insignificant volcanic
activities

59. Ocean Trenches
• A deeper part of the ocean where subduction takes
place
• Where one plate is subducted right beneath the
other – there is an area where the ocean floor
deepens
• This point – can be quite hot – proximity to the
asthenosphere
• Trench outer rise – marking the point where the
plate is subducted
• Outer slope – gentle
• Inner slope - steep
• E.g. Mariana trench

61. Island Arcs
• Where oceanic lithospheres collide
• The denser one will sink beneath
• Destroyed at asthenosphere
• The water on the subducting sphere – cause melting
• This melted material rise
• Creating a bulge then breaking through
• Solidifies into an island
• The island arc runs along a boundary
• There may be volcanic feature
• Island arcs can also be formed at Hotspot points

63. Plate boundary type3: Transform
• When two plates move alongside each other
• There is no spreading or destroying of plates
here
• May be caused by diverging/ converging of
nearby boundaries
• Rift valleys may be formed
• Faults will be formed
• May offset nearby landforms
• San Andreas fault – best example

66. Earthquake
• Earthquakes may occur when there is a release
of pressure at plate boundaries

67. Earthquakes at Divergent boundary
• shallow earthquake at sea floor spreading
regions – there isn’t much friction or pressure
however

68. Earthquakes at Convergent plate
boundary
• Deep earthquake at the benioff zone (Wadati-
benioff zone – points angling at 30 – 45
degrees)
• Major earthquakes when plates sliding under
another plate – frictions are caused
• E.g. 2004 Tsunami – caused by Indo-Australian
plate subducting beneath the Eurasian plate

69. Transform plate boundary
• Release of pressure
• One plate may stop when friction is too great
• When this friction is overcame – a release of
pressure
• The 1906, 1989 earthquake in San Francisco

70. Tsunami
• Occurs near subducting plate margins
• A bulge in the ocean floor caused by the
accumulation of magma beneath the overlying
plate
• OR… the general bulging caused by the dipping
of the subducting plate
• This makes the ocean floor rise
• Water is pushed up some 15 m
• Causing huge Tsunami waves

72. Vulcanicity/ Volcanology
• All the processes by which solid, liquid or
gaseous materials are forced into the earth’s
crust or are ejected into the earth surface

73. Causes of Volcanic eruption
• Release of pressure at local points
• Due to folding, faulting, other movements
• Semi-molten magma becomes molten
• Reduction in density causes magma to rise
• Forces its way through weaknesses in the crust

74. Extrusive vs. Intrusive
• Extrusive Rocks
• Magma reaches the surface and cools quickly
• Not much crystal formed
• e.g. Basalt
• The Oceanic plates

75. Extrusive vs. Intrusive
• Magma doesn’t reach the surface
• Injected into the earth’s crust
• Cools, hardens slowly under the surface
• Exposed by removal of overlying rocks
• Large crystals

76. Extrusive Landforms

77. Lava
• The types of Extrusive landforms depends on:
• Viscosity of the lava
• Gaseousness of the lava

78. Basaltic Lava
• Upward movement of mantle materials
• At ocean ridges (Mid Atlantic)
• Hotspot points (Hawaii)
• Rift Valley (Ethiopia)

79. Andesitic Lava
• Result of the Subduction process
• Occurs as island arcs
• Volcanic eruptions
• E.g. Andes

80. Pyroclastic materials
• Materials ejected by
Volcanoes in fragments
1. Tephra
2. Ash
3. Lapilli (small stones)
4. Bombs
• Pyroclastic flow move
down the side as clouds
• Heavy rainfall

81. Basaltic vs. Andesitic
• Low viscosity, hotter
(1200oC)
• Lower silica content
• Longer time to cools,
flow at longer distance
• Extensive, gentle slope
landform
• Frequent, gentle
eruption
• Lava/ steam ejected
• High viscosity, less hot
(800oC)
• Higher silica content
• Shorter time to cool,
flow at shorter distance
• Steesides, local feature
• Less frequent eruption
but violent due to gas
build-up
• Pyroclastic materials
ejected

82. Different Types of Volcanoes
• Fissure eruptions e.g. Iceland
• Basic/ Shield e.g. Mauna Loa
• Acid/ Dome e.g. Karymsky
• Ash Volcano
• Composite Volcano e.g.. Vesuvius
• Caldera e.g. Andes

83. Minor Extrusive landforms
• Mud Volcanoes: Combination of hot mud/ water
• Sulfatara: Gas such as Sulphur released from
cracks
• Geysers: Water vapors heats up and rises,
pressure increases, steam exploding through at
points of weaknesses
• Fumeroles: Superheated water reaches the
surface, reduction in pressure casues it to turn to
steam

84. Nature of Explosions
1. Icelandic: Lava flow gently from a fissure
2. Hawaiian: lava emitted gently from a vent
3. Strombolian: Small but frequent eruption
4. Vesuvian: More violent, less frequent
5. Krakatoan: Explosions violent enough to
remove original cone
6. Pelean: Violent eruption with Pyroclastic flow
7. Plinian: Large amount of materials and lava are
ejected

86. Hydromagmatic
• Any eruptive processes where magma and lava
interacts with water
• Deep marine eruptions – pressure of water
suppresses lava to undergo cooling: forms pillow lava
• Lava flows into the sea
• Shallow marine eruption
• Crater lake eruption
• Subglacial e.g. Vatnajokull
• Magma comes into contact with groundwater

87. Intrusive Landforms

88. Intrusive Landforms
• Most of the magma do not reach surface
• Intruded into the crust – where it solidifies
• When overlying rocks worn away
• Landforms are revealed

89. Batholith

90. Dikes

91. Sill

92. The Pacific Ring of Fire
• An area of high volcanic and seismic activities
found along plate boundaries of the Pacific
islands
• These plates are generally subducting
• 90% of volcanic activities appear here
• 75% of the active volcanoes are here
• Course: Southern tip of South America – along
the coast of north America – across the Bering
strait – through Japan – into New Zealand

94. ROCKS AND WEATHERING
Part 2

95. The Rock Cycle
• The Rock Cycle is a model that describes the
formation, breakdown and reformation of rocks
into 3 main rock types
• Igneous
• Sedimentary
• Metamorphic

97. Igneous Rocks
• Rocks that are formed from the cooling and
solidifying of the lava
• Can be intrusive or extrusive
• Example: Granite

98. Sedimentary Rocks
• Rocks that are formed by sediments deposited
by erosion.
• Example: Limestone – Carboniferous and
Dolomites - sandstone

99. Metamorphic Rock
• Rocks that are formed from igneous and
sedimentary rocks under under high heat and
pressure
• Example: Gneiss, Slate, Marbles, Quartsize

100. Physical Weathering
• Freeze Thaw
• Exfoliation
• Crystallization
• Pressure Release

101. Freeze Thaw
Freeze Thaw weathering is when
rain water (precipitation- can be
snowmelt) enters the joints/
cracks on a rock surface. As the
temperature drops, the water
freezes causing it to expand by 9-
10%. This increases the pressure
exerted to about 14 kg/cm2. This
exceeds the resistance of most
rocks. When the temperature
increases, the water melts again.
By now the crack has widen and
deepen [Frost shattering], the
water enters deeper into the rock.
More rainwater fills in the gap.
The process repeats itself

102. Features supporting freeze Thaw
weathering
• Temperature fluctuating around 0oC – hence
freezing is involved.
• Places: Alpine regions, periglacial climate, polar
climate is less often (lack of freeze thaw cycle)
• Mountainous region
• North facing slope in the Northern hemisphere,
or a South facing slope in the Southern
hemisphere
• Precipitation required

103. Features supporting freeze Thaw
weathering
• Rocks may also be porous – eg. Sandstone
• Rock has to be EXPOSED – not covered in
vegetation
• Hence, too much precipitation will not be good –
as it leads to more vegetation

104. Results
• Frost shattering: materials broken down into
small angular fragments – clastic states e.g.
fragmented – at foot of mountains/ slopes
• Frost wedging: Block disintegration
• Frost spalling
• Frost susceptible soil – result in capillary actions
of water to move toward freezing front – hence
soil creep upward – may form terracettes.

105. Exfoliation
Direct heating ray from
insolation of the sun heats up
the rock. Rocks are poor
conductor of heat – hence only
the outer layer begins to
expand. At night, the temperate
becomes lower, causing the
rock to contract – once again,
this mainly affects the outer
layer. This cycle of expansion
and contraction combines with
the fact that different minerals in
the rocks expand at different
rates lead to the rocks having
lower stability. Finally, the outer
layer of the rock peels off like an
onion skin. This also leads into
pressure release…

106. Features affecting
• Wide ranging Diurnal temperature variation between
day and night – achieved in the arid regions.
• The lack of precipitation = less vegetation cover =
maximum insolation
• High insolation so lack of cloud cover
• Lack of cloud cover --- maximum out-radiation at
night – colder night temperature
• Griggs(1936) proved an idea that some moisture will
be needed for rocks to expand
• Rocks compositions
• Exposure of rock face

107. Results
• Divides rocks into sub-planar slabs
• As the outer layer peels away, the pressure is
released – causing the underlying rock to
expand and fracture parallel to the surface. –
pressure release
• Disintegration blocks/ screes can be found

108. Salt
Crystallization
1. Temperature rises
(26-28oC) – causing
Sodium sulphate
and Sodium
carbonate to expand
by 3 times. Once
again the pressure
forces the joints to
widen– or
destabilize the rock.
2. Water with salt
evaporates away –
leaving crystals.
These expand under
high temperature.

109. Feature affecting
• Rock may contain salt
• Rocks may be porous/ permeable
• Surface texture – speed of breakdown increase
over time with coarse materials
• Arid climate – the evaporation of water will leave
salt close to the surface
• Coastal area – sea water
• Salt from snowflake in Alpine regions

110. Results
• Most effective salts: Sodium sulphate,
Magnesium Sulphate, Calcium Chloride
• Produces the highest rate of break down
• When combined with freeze-thaw

111. Pressure
Release
When overlying rocks are
removed, the underlying
rocks experience release in
pressure that cause it to
expand – fracturing parallel
to the surface.
The removal of overlying
rocks can be the result of
exfoliation, erosions or rock
falls (if we are talking about
a cliff face)

112. PRESSURE RELEASE
• Rocks are usually formed under the surface
– under high pressure.
• The unloading of such pressure
• Cause cracks/ joints to form at right angle to
the unloading surface
• Hence at pseudo bedding planes – there are
cracks and joints right angled to the surface
• At cliff faces – the cracks are vertical along
the cliff face.

113. Chemical Weathering
• Oxidation
• Carbonation
• Hydration
• Hydrolysis

114. Carbonation
Rainfall – slightly acidic to the
pH of 5.6 – combines with CO2
to form Carbonic acid
Carbonic acid reacts with
Calcium Carbonate in rocks
(Carboniferous limestone for
example/ Chalk) to form
Calcium bicarbonate
H2CO3 + CaCO3 = Ca(HCO3)2

115. Features needed
• Rocks with Carbonate
• Precipitation is required – rain water
• Low vegetation cover, exposed rocks surfaces
• Cracks and joints that allow water to flow through
• Porosity but lack of permeability allow rocks to be
retained in joints
• Cooler climate – rainwater can hold more CO2 than
usual
• pH of water varies – and different rocks react
differently to acidity.

116. Oxidation
- Oxidation occurs with
metal – mostly Iron
(Fe) and Oxide
minerals
- These rocks have
distinctive blue black
colors
- Addition of oxygen
and water cause the
rocks to turn orange –
from Ferrous to Ferric
– AKA rusting
- Makes it easier to
crumble

117. Features supporting
• High oxygen area – hence usually happens in
rain forest e.g. the Amazon
• High amount of rainfall – wet rocks/ soil (usually
in areas of high runoff, precipitation and
humidity)
• Rocks should contain oxides or hydroxide
• CONTRAST: Reduction of ferric iron to ferrous in
marshy area may produce rocks with blue colors

118. Hydration
When minerals absorb
water, expand/change and
hence change the rock’s
composition
Mechanical stresses also
derive from exerting
pressure from expansion
E.g. Anhydrite – Gypsum
E.g. Shales - Mudstone

119. Hydrolysis
Hydrogen in rocks reacts
with minerals in clay
causing the breaking down
of rocks into rocks –
therefore water combines
with the mineral H+
combines with OH-
Occurs mostly on
Orthoclase feldspar –
Granite (Feldspar + mica+
Quartz)

120. Features supporting
• Depends heavily on the amount of hydrogen in
the atmosphere
• Hence, the amount of air in the water
• The presence of organic acid (humic acid)
• The activities of organisms
• TO produce H+

121. Results
• Formation of clay
• E.g. Feldspar --- Kaolin (China Clay)

122. Biological Weathering

123. Plants/ Animals
1. Roots of the trees growing – can exert pressure on
the rocks – creating cracks – leads to physical
disintegration
2. Chemical Weathering: Lichens and algae – can
cause microbial erosion. Fungi may release
organic acid that change the compositions of the
rock. This creates holes in the rock which cause
rocks to further break down.
3. Animals burrowing – cause lost of underlying
support – leads to mass movement
4. Animals burrowing – lead to loosening of soil and
rock particles

124. Property of Limestone
• Permeable – can hold a lot of water
• Soluble in rain water/ groundwater
• Consist of Calcium Carbonate
• Harder in strength
• Surface is dry: high permeability
• Carboniferous limestone – harder and less
permeable/porous – with more resistant to water
– landforms tend to shape more

125. Carboniferous limestone
• Massively jointed: Have distinct pattern of joints
and bedding planes – allow water to percolate
through and dissolve the rock
• Dissolving of rocks: Carbonation-solution of
base-rich rock
• Reversible process – limestone can be re-
deposited as speleotherms

126. System affecting Carboniferous Limestone
Carboniferous
Limestone
Carbonation
Freeze-thaw weathering
Glacial erosion
Water erosion
Mass movements
Precipitation/ Groundwater
Calcium bicarbonate in
water
Deposits as
Speleothems
Carbonation

127. The Water
• If water has high amount of Carbon dioxide =
more likely to weather limestone
• Water that is likely to weather – Aggressive
• If it reaches a saturation point – can’t dissolve
much limestone
• Non-aggressive due to over-saturation
• At which point limestone is likely to precipitate

128. The Water
• Colder water – can hold more Carbon dioxide –
hence Karst sceneries are found in temperate
areas
• Warmer water – will cause deposition of
limestone
• Turbulence of flow
• Meeting up with other streams – changing
chemical compositions
• The landform created by this process is called
Karst topography

129. Limestone Scenery
• Clint and grikes developed (Grikes are enlarged
joints)
GrikesClint

130. Limestone Scenery
• Clint and grikes developed (Grikes are enlarged
joints) – Clint are the large rocks separated by
grikes
• Processes: Carbonation-solution/ Freeze thaw/
ice action
Grikes
Clint

131. Limestone Scenery
• Karren/ lapies: Small-scale solution grooves (2-3
cm deep) – runoff/solution of limestone
• Swallow holes/ sinkholes: Caused by solution of
limestone, enlargement of grikes systems,
collapsed cavern
• Dolines: Large depressions – solution/ Collapse
of limestone – may be covered by glacial
deposits
• Uvalaas – 30 m in diameter

132. Formation of Dry Valley
• A collapsed cavern
• Climatic changes = less precipitation
• A valley that used to have a stream (limestone is
impermeable) – over a period of time the
limestone becomes permeable and allow
infiltration
• Limestones became temporarily impermeable
due to periglacial climate – permafrost.

133. Equifinality
• The idea that different processes can lead to the
dame landforms : E.g. The formation of the Dry
valley/ Granitic tor

134. Karst Topography
• A system of well-developed landforms features
on dry limestone – no surface drainage.
• Includes: Cave or underground tunnels –
carbonation-solution/ erosion of water
• Speleotherms: Cave deposits formed by
solutions containing Calcium carbonate

135. Karst Topography
1. Tufa: Precipitation of
CaCO3 near streams/
Springs/ around algae/
Mosses – Tufa dams,
Mounds/ waterfall curtains.
1. Stalactites: From the tope – dripping water slow –
causing precipitation of Calcium carbonate
2. Stalagmites: From the bottom – dripping water is
fast – accumulation of calcium bicarbonate
3. When top/ bottom combines - pillar

139. Granitic Tor
• Tors: Isolated granite rocks layered on top of a
mountain/ batholith
• There are 2 theories as to how Granite Tors form

140. Theory 1 – Linton 1955
• That Tors can be formed during the warm, humid
Tertiary era (Triassic, Jurassic, Cretaceous)
• Chemical weathering – caused the breakdown of
rocks other than granite which is more resistant
• Strongest weathering at close joints/ bedding planes
• Where joints are further away – the granite is left
standing
• Residues of weathering (growan) removed during
periglacial period
• Denudation

141. Theory 2 – Palmer and Neilson 1962
• Mention frost shattering from Freeze-thaw to be
the main process near joints/ bedding planes
• Evidences: The features are not round/ kaolin
not present – chemical weathering usually
produced these
• Removal of growan by solifluctions

143. SLOPE PROCESSES
Part 3

144. Slope
• A slope is inclined hill or surface/ an angle of
inclination
• Sub-aerial: Slopes that are exposed to the
atmosphere/ the elements
• Submarine: Slopes that are underwater
• Aggradation slopes: Inclination of earth surface
that are formed/caused by depositions of
materials
• Degradation slopes: Inclination of earth surface
caused/ formed by erosions/ weathering

146. The Slope as a system
• The slope is affected by various natural factors
• Climate/ Weather – differential
insolation/weathering of rocks
• Geology – different rocks have different
resistance to different types of weathering
• Hydrology – the presence of a river can increase
erosion or deposition
• Vegetation growth – increase biological
weathering/ increase weight on the slope
• Human activities

147. Slope as an open system
Slope’s shape/
stability
Climate
INSOLATION
Vegetation
RegolithGeology
Gradient
Ground water flows
from other aquifer
Mass movement
from other slopes
Seismic activities
Human activities

149. Slope System Control
1. Climate
2. Geology
3. Soil
4. Aspect
5. Vegetation

150. Climate
• The climate affects: Process of weathering/
presence of stream runoff/ amount of insolation
– hence the amount of vegetation present
• E.g. in arid climate – jagged slopes created by
physical weathering – screes at the bottom –
exfoliation domes
• In wet/humid climate – rounded slope created by
chemical weathering – organic weathering
favors soil – deep regolith- vegetation cover

151. Geological Structure
• Rock types – resistance/ susceptibility to
weathering
• E.g. Limestone produces flat surface – due to
erosions along the bedding planes
• Heterogeneous rock types – can lead to
differential weathering – destabilize a slope

152. Geological Structure
• Permeability/ porosity of rocks – allow water to
pass through
• Existence of joint/ bedding planes – affect the
rate of weathering – water entering may
destabilize the slope
• Risk of mass movements

153. Geological Structure
• Plate movements
• At subduction zones – fold mountains – how
steep depends on the angle of dip
• Rift valleys – steep sides
• Transform faults – see steep sides.

154. Soil/ Regolith
• Regolith: Superficial, unconsolidated materials
found at the earth’s surface (Soil, scree,
weathered bedrocks, organic materials,
deposited materials)
• Regolith – unconsolidated – large amount of
them destabilize the slope
• Composition: Clay holds more water – may be
more susceptible
• Deepness of soil

155. Aspects
• Influences insolation
• Insolated areas – more vegetation
• Insolated areas – more human settlements
• Both contributes to more weight
• Insolated areas – Freeze thaw weathering/
solifluctions

156. Vegetation Cover – Destabilizing
factors
• Increased weight to the slopes
• Increases chemical weathering
– oxygen in the air/ humic acid
for chelation
• Biological weathering – if the
vegetation is not abundant and if
the slope is not of soil
• Stops small landslide – causing
soil to absorb water and
increase in weight
• Prevents small landslide but
may induce large ones in long
term

157. Vegetation Cover – Stabilizing factors
• The Vegetation increases
interception of water –
stores water = less
surface runoff = less
possibilities for mass
movements (flows)
• The roots hold the soil
together – stabilizing the
slopes
• May block insolation –
reduces freeze thaw
cycles/ exfoliation

159. MASS MOVEMENT

160. Mass Movement
• Any large scale movements of the earth surface
not caused or accompanied by moving agents
such as water, wind, glacier and ocean wave.

161. Classifying Mass movement - 1
• Classifying by speed of movement
• Slow movement: Soil/Talus creep (heave),
Solifluction
• Fast movement: Landslide, mudslide, rock slide,
earthflow, mudflow, rock falls, avalanches

162. Classifying Mass Movement - 2
• By wetness
• Wet movement: Solifluction, Mudflow, mudslide,
Earthflow, avalanche
• Dry movement: Soil/ Talus creep (heave),
landslide, rockslide, rock fall

163. The Triangular graph

164. How do Mass Movement happen
• A slope is stabilized by a dynamic equilibrium
between shear strength and shear stress
• Shear strength: The internal resistance of the
slope
• Shear stress: The forces acting on the materials
on the slope that would cause them to move
downslope

165. How do Mass Movement happen
• Mass movement occurs when the shear stress
exceeds the shear strength
• Or
• When the shear strength falls below shear stress
due to internal destabilizing

166. How do Mass Movement happen
• Shear strength: Affected by geological structure
of the slope, type of soil and regolith, vegetation
cover, water content
• Shear stress: Affected by the gradient
(gravitational pull), surface water, the weight of
the forces acting on the slope, faults in the
slope, the way the slope is being ‘hit’

167. Factors affecting Shear Stress

168. The Weight acting on the slopes
• Heavier loading –
increases the stress
• Vegetation cover…
• Soil/regolith
• Water content
• Human activities…
houses… settlement

169. Lateral supports
• Steepening of slope – by
undercutting – causing
overhang to fall
• Increases the gradient
• Rivers erosion…
• Glacial erosions…
• Wave-cut platforms…
• Faulting (steepens an area)
• Rockfalls/ slides remove
lateral supports

170. Underlying supports removed
• Losing supports below can
cause slopes to fail –
places emphasize on the
weight acting on it
• Wave undercutting…
• River actions… at
waterfall…
• Underlying sediments
removed
• Human activities…

171. Lateral pressure
• Water in
cracks –
freeze thaw
• Swelling of
cracks
• Hydration
of clays
• Releases of
pressure

172. Transient stress
• Earthquake
• Volcanic activities
• Movement of trees in the wind

173. Factors affecting Shear Strength

174. Weathering
• Granular
disintegrations –
cause slopes to
destabilize (Freeze
thaw)
• Hydration of clay
• Solution of materials –
make the slope less
compact

175. Pore Pressure
• Water exerts
differentiating pressure
on the slopes
• Saturated materials –
becomes softer – more
unconsolidated after a
whiles

176. Changes in rock structure
• In shales –
fissures/ cracks
– reduce the
compact nature
of a slope
• Clays are
remould
• Sands are
remould

177. Organic effects
• Burrowing of animals
• Roots of plants

178. TYPES OF MASS MOVEMENTS

179. Soil Creep
• Slow movement of soil
• Result of heaving (soil particles moving up at
right angle from the surface due to freeze-thaw
cycle or expansion caused by water)
• After heaving the oil falls back but is now moved
slightly downslope
• More common in winter time

180. Solifluction
• Soil placed in the state of permafrost
• Warm weather thaws the layer of soil above –
leaves the underlying layer frozen as a
waterlogged zone
• Thaw soil moves downhill along the permafrost
layer

181. Rainsplash Erosion

182. Rainsplash Erosion

183. Falls

184. Mudflow

185. Earthflow

186. Landslides

187. Landslides

188. Rockslides

189. Mudslides

190. Avalanche

191. Avalanche

192. Sources and Websites
• http://www.ucmp.berkeley.edu/history/wegener.h
tml
• http://education.nationalgeographic.org/encyclop
edia/
• http://www.limestone-
pavements.org.uk/geology.html
• http://www4.uwsp.edu/geo/faculty/lemke/geomor
phology/lectures/06_weathering.html