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GEOGRAPHY FORM FIVE
TOPIC SEVEN NOTES
THE DYNAMIC-EARTH AND CONSEQUENCE
THE DYNAMIC-EARTH AND CONSEQUENCE
THEORIES
THEORY OF ISOSTASY
Denudation has been going on the continents where tons and tons of materials are removed from mountains and hills and get deposited in ocean; but the hill of mountains are not reduced to the sea level.
WHY THIS IS SO?
The phenomena can be explained by the theory of Isostasy.
Origin of the term is Greek; Made of 2 words meaning „Equal standing‟ is a state of equilibrium or balance in the earth‟s crust with equal mass underline equal surface area. Therefore there is a state of equilibrium. The theory suggest that the continents and their major features are maintained in a sort of equilibrium or are moving towards that equilibrium.
ISOSTATIC EQUILIBRIUM
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Isostatic equilibrium can be disturbed
How? Processes on the surface of the continents.
  1. Denudation
-Weathering/mass wasting, transportation, and erosion.e.g removal of material which lower the surface.
  1. Deposition -Building up process (rising of the land)
  2. Accumulation of ice masses and melting of ice masses.
For example
When denudation removes the material from mountains there is pressure released, uplift occurs where the material is removed and there is no Isostatic balance.
If the material is deposited on the sea bed there is compression which result in sinking (vertical movements) these vertical movements causes horizontal movements of simatic material from there is compression has taken place to where there was pressure release
In such process a state of equilibrium is restored.
EFFECT OF DISTURBANCE AT SURFACE AND READJUSTMENT OF ISOSTATIC EQUILIBRIUM
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EFFECTS OF DISTURBANCE OF ISOSTATIC EQUILIBRIUM
  1. Earth quakes- Earth movements (gradual)
  2. Subsidence +uplift (submerged coast /raised beaches)
  3. Faulting -Result to rift valleys or block mountains, lift blocks
  4. Fold- Fold Mountains
  5. Volcanic eruptions forming different volcanic feature (volcano)
  6. Displacement of lithosphere leading to plate tectonic
Evidences of Isostatic movements
  1. The depression of the crust in the northern part of America and Europe was due to the weight of ice sheets of vast thickness during the ice age.
  1. After the melting these ice sheets, the crust has been rising.
Slowly for example, there are numerous former beaches that occur around the coast of Scandinavia. They now lie between 8m-30m above the present day beaches. These old beaches have been raised because of the uplift of the land.
  1. The continental shelf around Antarctica is covered with water to a depth of about 750m compared with 180m around other continents.
  2. The presence of Rias and Estuaries between the coast lands of Gambia and Sierra Leone.
  3. The submergence of forests on the shores of Britain.
IMPORTANCE OF THE THEORY
  1. It provides the knowledge on the dynamic state of the earth‟s crust that is the earth‟s crust is not static but it is always dynamic as it tends to balance itself after some disturbances with the influence of the gravitational force.
  2. The analogy that the crust floats on the mantle, just like the iceberg floats on and the ocean or sea water, is so crucial in the understanding of the theories of plate tectonics and continental drift.
  3. The theory also helps in deciphering (understanding) how different landforms were formed.
  4. It also gives the basic for predicting the future of the crustal state at any particular place on the earth‟s surface.
  5. It can also help human being in taking some precautions depending on the nature of the phenomena that might have been observed in the course of time, like the occurrence of ice sheets and melting of ice.
2 THEORY OF CONTINENTAL DRIFT
There are 7 continents
Origin of these continents
Propounders
  • Francis Bacon (1620) Expanded earth – F .B Taylor
  • Alfred Wegener 1912.
According to his theory ,about 280 million years,the present day continents were united in a single block called Pangaea and sorrounded by ocean called Panthalassa.He believed that Pangaea was located near the South
pole.Later Pangaea split into two (2)Super-continental i.e Gondwanaland(south Pole) and Laurasia(along the equator in the northern hemisphere).
These two Super-Continents were separated by a narrow water body i.e Tethys sea.He assert that Laurasia split to
form present day N.America,Asia,Europe,and numerous landmasses found in northern Hemisphere-
Greenland,Iceland and United Kingdom.
Gondwanaland split to give present day Africa,S.America,Australia and Indian sub-continent,Antarctica and other islands in the southern Hemisphere.
Drift:
Since that time the continents have been drifting apart to occupy their present positions. And the drifting is a very sl
ow one about 2cm per year. The drifting is still in progress.
Evidence to support Wegeners theory of Continental Drift
  1. Structural evidence ( Jig saw fit)
If the continents were to be brought together it will form one single landmass called Pangaea. Hence proves that all the continents come from one land mass. For example S. America could fit into Africa, N. America into Europe, Antarctica, Australia, India and Malagarasy formed in a single landmass with S. America.
  1. Geological evidence :
Similar rock types in the coastal margin of the continents for example if you take the rocks of west Africa coastal margin and those of Eastern coast Brazil coastal margin the rocks will be the same (similar ) These rocks where one before the split. (Similar type, age, structure, formation)
  1. Biological evidence :
The study of earlier life in sedimentary rocks. That reveals life similar fossils of different time where found in different places. Similar animals, plants and e.g. .These fossils are found in all continents hence prove that they all come from one landmass
  1. Geomorphologic evidence:
Structure of mountains ( fold mountains) e.g. The Alps and Atlas have similar features and where also formed under similar conditions, type of rocks the mountain case, structure, alignment and were formed when Africa moved north wards ending up colliding with the European continent. This gives evidence that the drifting movement took place.
  1. Pale-climatic evidence:
The discovery of ancient is in the Congo basin where the climate is warm is used as evidence that the Africa continent drifted from parts which were cold to the current warm parts. For example, Africa has been shifting north wards from the south likewise coal deposit found beneath Antarctic ice caps and Greenland show that they were deposit when the continents had not drifted led to those places when the climate coast warm. This is because the organisms that led to the formation of those deposits cannot east in areas where there is very low temp.
  1. Paleo magnetism (palae-magnetic evidence
    ).
This is the most conclusive proof of the continental drift which was done through pale magnetic dating. When the rocks cooled they were magnetized in the same direction (magnetic North) but pale magnetic dating shows that rocks older than 200,000 years ago from different parts of the earth, have shifted their relative positions magnetic fields show new paths representing relative migration of the earth‟s materials
This is evidence that the continents have drifted or have been drifting.
  1. Ocean floor spreading.
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Weakness of Wegener / critiques of the theory
  1. He did not explain how the movement has occurred / the continental drift processes.
  2. He was not a geologist but meteorologist hence he was criticized to have involved in the field where he was probably less informed.
  3. Not all continents are able to fit exactly as argued in the jig-saw fit theory, but the theory does not account for this aspect.
  4. Other scientists argue that the plant remains might have been spread by aspects like wind, blowing from one continent to another.
  5. Wegner failed to explain the development of glacier in the hot arid Australia.
4.2 PLATE TECTONIC THEORY (Unifying theory)
It takes the combination of theory of theory of isostacy, continental drift and ocean floor spreading.
According to this theory,the earth has an outer shell(lithosphere) made up of several rigid piece called tectonic plates.
  1. Geometrical part – The crust is made up of segment called plates, which are of various sizes, Large and small plates. pacific, N. American, Nazca, S. American, Africa, Indian, Antarctica plates
  2. Moments– Movement of the plates. The plates are in motion. Either they are diverging or converging cause of movement – Convectional currents from the interior of the earth‟s especially aesthnosphere.
The movements can cause plates to collide or slide past one another. The rate of motion is very slow of the plates relative to one another 1cm to 2cm per year.
TYPES OF PLATE BOUNDARIES:
1) Divergent boundary – Is a boundary which is created when the plates are moving away from each other. This normally occurs in the ocean, where there are mid-oceanic ridges.
Example
  • Mid Atlantic ridges
  • Island Arcs ( volcanoes)
  • Rift. valley Graben
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    1. Convergent boundary – Is boundary where by the plates are moving towards one another
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  1. Neutral / trans current boundary- This occurs when plates are sliding past one another. Normally occur on the
Transform faults. (No uplift or submerge of the land (crust)
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MECHANISMS OF THE PLATE MOVEMENTS AND THE PLATE BOUNDARIES:
Plates are either continental or oceanic.
Oceanic plates are simatic (denser).
Continental Plates are Sialic (light).
CONVERGENT PLATE BOUNDARY
  1. Continental and continental – Both will go uplifted and result to folds and faults
  2. Oceanic and continental -The denser will down lift and lighter will uplift and may result to volcanic eruption and subduction result to trenches for the denser plate.
  3. Oceanic and oceanic – Convergent boundary ( subduction result to trenches both will move down) Plate Tectonic Theory states that “The lithosphere is made up of rigid segments called the plates and the plates are in constant state of motion relative to one another”
CAUSES OF MOVEMENTS:
    1. Convectional current – During mantle convection some materials rise due to the influence of radioactive heat generation and later moves laterally below the lithosphere. The lateral movements
drag the lithosphere leading to the plate tectonic movements. On cooling the materials sink down to the lower level of the mantle where they melt again due to the constant motion of the plates
      1. )Upwelling of magma in the lines of weakness for example in the mid-oceanic ridges where by the magma is pushed out of the surface through the weak lines of the crust, in order to form a new crust. This may result to the cause of movements
  1. Isostatic adjustment – May cause slight movement when trying to create balance.
  2. Cooling and heating of the crustal rocks -Expansion and contraction of rocks. The heat in the interior of the earth (mantle) causes rocks inside to expand and when the heat reduces, the rocks cool. This process causes the rocks to crack hence leads to the disturbance of the crust and causes movements.
EFFECTS OF PLATE MOVEMENT:
Changes on the plate boundaries which are lines of weakness and on these boundaries, major landforms of the earth‟s surface are going to be formed.
  1. Diverging plates
I) Oceanic
  • Mid oceanic ridges
  • Oceanic Islands
  • Rifts e.g. Red sea
II)Continental
-Volcanic mountain
  • Block mountains
-Rift valley
  1. Convergent plate boundary– Collision may lead to subduction and uplift.
  1. Oceanic – oceanic trends (Marianna trenches, Japan trenches )

  1. Oceanic and continental-Volcanic mountains on the coastal boundaries and also result into trenches.
  1. ( Continental )- Formation of Fold Mountains. Himalayas ( Indian and Russian plate formed)
c) Neutral / Trans current boundary – There is neither uplift nor seduction. There is lateral displacement of the plates. N. America, San Francisco – San Andrea‟s faults displacement of features of about 1000km.
The plate tectonic areas are areas of instabilities which results to earth quake, volcanoes.
The theory of plate tectonic can help to explain almost all of the landforms on the surface of the earth.
I. Deep sea Trenches: A sea trench is a long deep valley along an ocean floor.they form along a convergent destructive term of depth.the Mariana in the western Pacific with a depth of more than 36000ft.
II.Mid Oceanic Ridge: It refer to a giant undersea mountain range made up mostly basalt.It may be more than 80000km long and 1500 to 2500km wide and it may rise to 2.3km above the ocean floor.The feature is associated with a divergent plate boundary.As plate diverge,magma rises repeated and eventually cools to form the mid oceanic ridge.
Example: East Pacific as Nazea and Pacific diverges North Atlantic as North America diverges the Eurasian.
III.Island Arcs: Sometimes basalt eruption along the ridge or near may build up volcanoes that protrude above sea level to become Oceanic Island.They may vary in size.Example:Iceland,Japan,Hawaiian is lands, Mauna Loa,Easter Islands near the East Pacific ridge,west Indies.
  1. Magmatic Arc:It refers to island arcs at sea and belts of igneous activity on the edges of continents such as batholiths in mountain belts. Example:Aleutian Island.cascade volcanoes of the pacific North West,along Andes.
  2. Mountain Belts:At a convergent collision boundary,the sea floor is denser and will be subducted making the ocean thinner and narrower hence collision of the continents.Eventually the oceanic lithosphere breaks off leaving the continental crumple to form mountain ranges.
The thick sequences of sedimentary rocks that had built upon both continental margins are intensively.Example The Himalayas as India collided lided, Alps as African and Europe ,Atlas in Northern Africa.In addition to that at a convergent destructive boundary,young mountain like the Andes form due to the folding of the young sediments.
VI. Rifting and associated features:At a passive divergent plate boundary ,the continental crust is stretched and thinned producing faulty landforms like the great East Africa Rift Valley.The faults may be path associated volcanic landforms.This may explain the volcanic landforms in the rifted areas of East Africa.
Due to thermal expansion emanating from rising mantle plume,it causes uplift of landscape.
VII.New Oceanic Crust:This is associated with a divergent plate margin where the would be gap is filled with the up welled magma to form a new oceanic crust.
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4.3 MATERIALS OF THE EARTH’S CRUST
What is an element?
A substance which cannot be split into simple substances by physical or chemical means. Elements are made up of atoms. Atoms are made up of protons which are positive (+ve) charges, electron which have negative (-ve) charge and neutrons which do not have any charge
-Elements are about over 100 elements known so far
-About 90 elements exist naturally some elements exist naturally but they do not exist themselves they combine to form a compound (some exist independently which others are compound of more than one element.)
-Of the 90 element, 8 element are the most a bund and in the crystal rocks.
These are:
Element
1 .oxygen
  1. Silicon
  2. Aluminium
  3. Iron
  4. Calcium
  5. Sodium
  6. Potasium
  7. Magnesium
What is a mineral?
-Is composed of atoms arranged in a specific order which is 3 dimensional (crystalline) in structure.
OR
-Are naturally occurring inorganic substance made up of elements or compounds which is 3 dimensional
(crystalline) in structure.
Properties of Minerals
  • Definite shape (crystalline)
  • Is inorganic (naturally occurring substance)
  • Minerals must be solid
  • Made up of element or compound
N.B: Only minerals which are inorganic are minerals. Coal is not a mineral because it is not inorganic.
IDENTIFICATION OF MINERALS
In the field:
  1. Its colour-Minerals have different colours
  2. Luster -How a rock reflects the light. (Metallic luster they glitter and non-metallic luster are dull)
  3. Streak -Powder which is obtained by rubbing the rock with a harder substance
For example: Iron will remove a darker streak than the colour of the iron .But if it is not a non-mineral, the streak will be lighter than the substance.
  1. Cleavage -If break the rock it will split into definite shape (definite pattern) e.g. mica break into sheet pattern. 5) Crystalline – In 3 dimensional
    1. Specific gravity- All mineral have higher specific gravity than water. H2O is 1g/cm3
    2. Hardness -Minerals differ in hardness obtained through scratch test; there is a soft test & hardest test (Moh‟s scale hardness; 10 minerals starting from softest of hardest.)
WHAT IS A ROCK?
    • Is a more or less uniform mass made up of grains of one or more mineral which is found naturally on the earth crust.
    • Are aggregates of minerals.
ROCK CLASSIFICATION
They can be classified according to :-
(a)Mode of formation
(b)Geological Age
(c)Structure
A. ROCK CLASSIFICATION ACCORDING TO MODE OF FORMATION
According to mode of formation/origin , rock can be classified as Igneous, Sedimentary and Metamorphic.
1. IGNEOUS ROCKS:
These are crustal rocks formed by cooling either within or outside of the earth‟s crust. (Formed by cooling and solidification of molten materials from the interior of the earth)molten materials can solidify intrusively or extrusive (endogenically or exogenically)when molten material are still within the earth crust they are referred as magma, and when reach the surface they are called lava. Examples; basalt granite, Quartzite, Gabbro cools and solidifies to form volcanic rock
MECHANICALLY
FORMED
ORGANICALLY
FORMED
CHEMICALLY
FORMED
Shale
Lignite coal
Gypsum
Mudstone
Bituminous coal
Rock salt
Siltstone
Anthracite coal
Potash
Grit
Coral reef
Flint
Limestone
Trona
Chalk
Ironstone
TYPE
FORMED AT
RATE OF
COOLING
CRYSTALLINE NATURE
EXAMPLES
VOLCANIC
The surface
Fast
Small Crystals
Basalt
Rhyolite
Trachyte
Andesite
Shallow
Medium
Medium
Quartz
HYPABYSSAL

Depth
size Crystals
Porphyry
Dolerite
Great
Slow
Large
Granite
PLUTONIC
depth
Crystals
Syenite

Gabbro, diorite
Diorite
Original rock
Metamorphic rock
Granite becomes
Gneiss
Sandstone
Quartzite
Clay
Slate
Shale
Schist
Limestone

Marble
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Isotope
Half life
Daughter element
1. K – 40
1.3 billion years
Ar – 40
2. U 238
4.5 billion years
Pb – 206
3. Rb 87
49 billion of years
Sr – 87
4. C14
5730 billions of years
N – 14
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a) Primary (p) waves
Travel through the crust. There of two types
These are compression waves. These can be transmitted through solids, liquid s and gasses. They are transmitted to all.
Can be pass on the center of the earth and be felt on the other
They are fastest can travel 8km/sec.
b) Secondary (s) waves
Crustal rocks move back and forth in the direction of wave movements
These are shear waves. These can only pass through solids. They are slower, when they reach the mantle there reflect (bend). They speed is 4km, sec.
The crustal rock to move from side to side perpendicular, at right angle to the direction of wave movement.
ii) Surface waves
Produces shadow zone to the area which the secondary waves do not pass
These travel through the surface rocks and are of two types,
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    Run to open space iii. Build houses which are shock absolve.
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1. Lava Cones – A hill or type of a cone which is formed by lava (cumulo dome)
  1. Acidic Lava – This is viscous and will not flow very far from the vent but accumulates around the vent to form sleep sided cones. Viscous lava can form a spine (is a steep hill) has more silica.
Example: Mount Pelee Martinique West Indies.
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  1. Basic Lava Cone – Is very fluid, mobile. It spread far from the vent and it builds up gentle sloping cones.
Example: Mauna Loa – Hawaii.
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iii. Composite cone – This is formed by alternating layers of ash and lava
Note: These composite cones forms high composite peaks – (give highest peaks on the surface of the earth) e.g.
Mountain Cameroon, Mount Kilimanjaro, Mount Vesuvius.
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Iv. Plug Volcano (Volcanic neck) – They are cylinder like shaped it occupies the vent of a dormant or extinct volcano. It solidifies on the vest, and blocks the mountain forming dormant volcano.
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Caldera (Basal Wreck) – Is a large shallow cavity (depression) on the top of the volcano.
How formed
Formed by violent eruptions which remove the former top of the volcano.
NB: Water can accumulate in the caldera and form Caldera lakes e.g. Lake Toba in Sumatra (Indonesia) and Crater Lake in USA and Bosumtwi in Ghana
Caldera; Ngorongoro in Tanzania, Mount Meru in Tanzania, Longonot in the Eastern Rift S.W of Kenya.
Stages in the formation of a caldera
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  1. Lava Plateau – Result from fissure eruption. When lava is up welled then spreads to a wide area and when it solidifies forms lava plateau. (fairly high level lava plateau) (Basalt plateau which is acidic in nature). E.g. In Sahara, Algeria, Morocco and in S.S – Drakensberg Plateau, North America – Snake plateau, Deccan plateau in India.
  1. Other minor features associated with volcanism.
a) Hot spring – Natural outflow of hot H2O from the ground. E.g. In Mbeya, Arusha, Mara – Majimoto.
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FORMATION OF GEYSERS
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  1. Geysers – Superheated H2O and steam is drawn out with great force and sometimes explosively in comes periodically.
  2. Solfatara – Is a volcano which releases only steam and gas. The large % of gas is sulphur. c) Fumaroles – Emission of steam
d) Mofatte– Emission of carbon dioxide.
Stages / life cycle of Volcano.
  1. Active volcano – One which is definite / takes place periodically in recent time. Example oldonyo in Tanzania, Mufungiro in Uganda, Italy Vesuvius.
  2. Dormant Volcano (sleeping) – Has erupted before but has stayed dormant for a long while and not sure if it will erupt again or not. E.g. Mount Kilimanjaro, Mount Meru, it has signs of eruption
  3. Extinct (dead) Volcano – A volcano which has remained dormant and doesn‟t have any signs of eruption.
Global Distribution of Volcanoes and lava Plateau
Vulcanicity occurs in areas where the earth‟s crust disturbed. These are the areas where weaknesses in the crustal rocks provide an easy passage for volcanic materials to escape into the earth‟s crust or onto the surface of the earth. For this reason volcanic features and active volcanicity are associated with weaker parts of the crust. These include;
  • They are common along the zones of plate tectonic convergence mainly to oceanic and continental plate where the oceanic place subjected into aesthnosphere and get heated producing magma then rises through the line of weakness.
  • A long the zones of divergence where the crust spread apart giving to a line of weakness through which magma pass.
  • In regions of faulting like along the great East African rift valley.
  • In regions where folding as fractured the crustal rocks.
WORLD DISTRIBUTION OF VOLCANOES AND LAVE PLATEAUS
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Economic importance of Vulcanicity
Positive importance:
  1. Some lava out – Pouring have weathered to give fertile soils. These regions are of important agriculture value. E.g. Deccan plateau in India.
  2. Volcanic activity sometimes results in the formation of precious stones and minerals. These occur in some igneous and metamorphic rocks e.g. Diamonds of Kimberley, Copper deposits of U.S.A.
  3. Some hot springs are utilized for heating and supplying hot water to building in New Zealand and Iceland.
  4. Volcanic eruptions also provide geothermal power, which can be utilized for electric generation. Geothermal power is used in Kenya and Ethiopia
  5. Volcanic eruption can attract tourists and lead to the development of tourist industry in the country.
  6. The calderas resulting into lakes can be useful for fishing, irrigation.
  7. Volcanic activities result into the formation of different volcanic land forms such as Volcanic Mountains, which are attractive to tourists.
Negative significance
  1. Volcanism leads to migration of people from areas of volcanic activity.
  2. Leads to great loss of life
  3. Leads to destruction of property.
  4. Volcanic eruption causes environmental degradation
  5. Occurrence of earthquakes due to the movement of magma through the lines of weakness (fault lines)
  6. Some volcanic features create barriers, making construction of communication lines difficult and expensive e.g. In the Yalta Plateau.
  7. The rugged nature of some volcanic landscape discourages economic activities such as agriculture and the establishment of settlement.
4.6 DENUDATION AND
DEPOSITION
Denudation refers to all processes that involve the breaking, wearing away and lowering of the surface of the earth. Denudation involves several process such as weathering, Mass wasting, Erosion and Transport of materials.
Deposition:This is the laying down or release of the rock particles on the surface,It can be by:
1.Water producing features like flood plains.Natural Levees , alluvials fans,beaches etc.
2.By ice producing features like out wash plains ,clay plains,moraines ,eskers drumlins and kames.
3. By living organisms producing features like coral reefs.
4.By wind producing feature like loess plains and sand dunes(barchans and seifs)
5. By evaporation and precipitation producing features like salt deposits.
I. WEATHERING
– Is the physical disintegration and chemical decomposition/decay of rocks in situ / when exposed to weather.
Weathering does not involve transport, in weathering there is no large scale movement thus weathering doesn‟t involve transport.
In situ in the original or appropriate position.
Types of weathering
There are two types of weathering
i. Mechanical / Physical weathering
Is the breaking down of rocks into small particles / fragments without involving (undergoing) any chemical means / changes
Mechanism (How does it take place)
i) Temperature change: This is best noticed / occurs mostly in hot deserts / tropical deserts. (Dominant) where there is large diurnal range of temperature during the day, temperature is very high (450c). The rock surfaces are intensively heated which causes rapid expansion which causes cracks on the surface of the rock (Parallel cracks).
During the night, temperature falls rapidly (20C). Range is 430C. Rapid contraction on the rock surface which will increase cracks which are vertical / perpendicular to the surface.
  • This process takes a long time (100years) and results to the peeling of rocks on the surface “Onion Peeling”
The process is called EXFOLIATION.
  • A smooth mould which is called exfoliation dome remains after exfoliation has taken place
  • Exfoliation particles are called Screes. These are particles which collect on the foot of a hill / rock mass This happens on daily bases.
Why do we have diurnal range of temperature?
Because of absence of cloud cover. The incoming solar radiations reach at maximum and causes high temperature. And there is rapid cooling because the heat is not retained hence it removes.
EcoleBooks | GEOGRAPHY As LEVEL(FORM FIVE) NOTES THE DYNAMIC-EARTH AND CONSEQUENCE (1)
ii. Frost Action : – This is a process which is dominant in temperate regions and in high mountains
(mountainous regions)
  • The process occurs during summer where there melting and during winter there is freezing. It is a process which occurs seasonally.
  • When freezes it expands by 9% of its original volume this develops a crack. When the melts it will fill the crack and when the next winter reaches the water will freeze and will expand the crack. This is continuous action which happens seasonally and eventually will lead to the disintegration of the rock. EcoleBooks | GEOGRAPHY As LEVEL(FORM FIVE) NOTES THE DYNAMIC-EARTH AND CONSEQUENCE (1)
EcoleBooks | GEOGRAPHY As LEVEL(FORM FIVE) NOTES THE DYNAMIC-EARTH AND CONSEQUENCE (1)
iii. Action of living organisms: (biotic / biological).
a) Plants action – Root Penetration. As the plant grows the roots grow also and penetrate in the surface which causes cracks on the ground.
EcoleBooks | GEOGRAPHY As LEVEL(FORM FIVE) NOTES THE DYNAMIC-EARTH AND CONSEQUENCE (1)
b. Animal action.
  1. Micro-organism (barrowing animals i.e. roddents,rats):
These animals make some holes on the soil whereby their activities in t
he soil allow weathering to reach the bedrock. This makes the soil loose hence the rocks break down.
    1. Macro-organism (trampling animals and man i.e. cows, elephants) :
These animals encourage soil erosion also poor agricultural methods used by man and deforestation expose bed rock to weather.
  1. Alternating / alternate wetting and drying: –
This can be dominant in coastal areas. During high tides the rock is exposed to water which causes contraction to the rock and during low tides the rock expands because it is not exposed to water. This happens daily as a result it weakens the rock and hence it breaks (it is exposed to weathering).
  1. Salt Crystallization:
When salt water is in the rock, during dry time the water will evaporate and salt crystals will remain, these crystals are solid they will occupy space by expanding the rock and when the salt water returns the rock will contract. This continues and will hence develop a crack. vi. Pressure release or unloading
It always occurs in large scale than other processes discussed it resulted from the unloading rocks during exhumation. As the overlying materials are removed the consolidating pressure are released and the rock tends to rebound. The stresses created open up joints and bedding planes. Rarely the process result to direct disintegration but is seems to be a wide spread means by which rocks are weakened and make more susceptible to other weathering processes.
EcoleBooks | GEOGRAPHY As LEVEL(FORM FIVE) NOTES THE DYNAMIC-EARTH AND CONSEQUENCE (1)
EcoleBooks | GEOGRAPHY As LEVEL(FORM FIVE) NOTES THE DYNAMIC-EARTH AND CONSEQUENCE (1)
EcoleBooks | GEOGRAPHY As LEVEL(FORM FIVE) NOTES THE DYNAMIC-EARTH AND CONSEQUENCE (1)
ii) Chemical weathering
This is a process of decaying or decomposition of the rock when exposed to weather. In such process there is chemical change which weakens the rock, and makes it easily to break down by other forces / weathering agents.
Chemical weathering occurs under the following processes:
i. Oxidation ii. Carbonation iii. Hydration iv. Hydrolysis v. Solution
    1. OXIDATION:
Is the addition of Oxygen to the rock mineral. A process whereby certain mineral compounds takes additional oxygen. In that process it becomes weak and easily broken down. This is common in clay which contains iron compound when iron rusts it is oxidation.
EcoleBooks | GEOGRAPHY As LEVEL(FORM FIVE) NOTES THE DYNAMIC-EARTH AND CONSEQUENCE (1)
    1. CARBONATION – This process takes place where there is plenty of carbon dioxide and moisture.
Is a chemical process where weak carbonic acid reacts with calcium carbonate to form calcium bi carbonate which is soluble compound which is readily removed in solution by ground water.
O which will form weak carbonic acid, when reaches on EcoleBooks | GEOGRAPHY As LEVEL(FORM FIVE) NOTES THE DYNAMIC-EARTH AND CONSEQUENCE (1)
the ground will react with lime stone in the rock to form calcium bicarbonate. The solution will come out of the rock and make the rock weak.
iii. HYDRATION
Some rocks take in additional water molecules which causes stress to the rock / expansion and that expansion causes internal stress and fracture. In this case the rock becomes weak and easily broken down by other processes.
EcoleBooks | GEOGRAPHY As LEVEL(FORM FIVE) NOTES THE DYNAMIC-EARTH AND CONSEQUENCE (1)
iv. HYDROLYSIS:
This process involves hydrogen (in the water) combining with certain metal ions (in a mineral) that is the water and the mineral react chemically which gives rise to the formation of different chemical compounds.
H2O reacts with minerals rocks and carbon dioxide to form clay minerals, silica and potassium carbonate which is soluble and leaches out leaving the rock weak.
EcoleBooks | GEOGRAPHY As LEVEL(FORM FIVE) NOTES THE DYNAMIC-EARTH AND CONSEQUENCE (1) v. SOLUTION – Nacl + H2O = salt solution.
Where rock comes into contact with water and salt it disintegrates.
  1. BIOTIC WEATHERING –Associated by plant roots, where by root tips are secretes acid which react with rocks and they disintegrate
Decaying organs produce organic acids which when come into contact with rocks it disintegrates.
Organic acid of decaying vegetation – weathering of rock
FACTORS WHICH INFLUENCE THE RATE OF WEATHERING
  1. 1.THE NATURE OF THE ROCK – soft or hard
  1. Mineral composition. – This varies from one rock to another and hence affects its resistance some rocks tend to be stable, while others are unstable depending on their mineral composition. For example, rocks like granite with quartz are stable and very resistant to weathering hence weathering process will be slow which rocks which are unstable like basalt which have lower silica undergo weathering very fast. Iron minerals undergo oxidation very fast; rocky salt (sodium chloride) rocks dissolve quickly in water.
  2. Plane of weakness or rock structure – Through joints, weathering takes place very fast, since acids can penetrate easily into the rock and cause the rock to decay during chemical weathering. And frost action tends to be fast in the areas where the rocks have some cracks.

Color- rocks with dark minerals (olivine) heat faster than rocks with light minerals. Thus, the rate of weathering by temperature change is higher to rocks with dark minerals.




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EcoleBooks | GEOGRAPHY As LEVEL(FORM FIVE) NOTES THE DYNAMIC-EARTH AND CONSEQUENCE (1)

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3 Comments

  • EcoleBooks | GEOGRAPHY As LEVEL(FORM FIVE) NOTES THE DYNAMIC-EARTH AND CONSEQUENCE (1)

    Frank, May 2, 2024 @ 6:05 am Reply

    Understoodable and good notes

  • EcoleBooks | GEOGRAPHY As LEVEL(FORM FIVE) NOTES THE DYNAMIC-EARTH AND CONSEQUENCE (1)

    Baraka Thobias, April 13, 2024 @ 9:08 pm Reply

    Ipo saw

  • EcoleBooks | GEOGRAPHY As LEVEL(FORM FIVE) NOTES THE DYNAMIC-EARTH AND CONSEQUENCE (1)

    Abida, August 27, 2023 @ 6:36 pm Reply

    Good notes

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