GEOGRAPHY Form Five: PHYSICAL GEOGRAPHY

Physical Geography is a critical branch of geography that studies the natural processes and features of the Earth. In Form Five Geography for Tanzania, students explore various physical phenomena that shape the planet, providing insight into the forces behind the Earth’s structure and landscape formation. This set of notes covers nine important subtopics, each essential for understanding the physical dynamics of the Earth:

1. Isostacy Theory
2. Continental Drift Theory
3. Plate Tectonic Theory
4. Structure of the Earth
5. Internal and External Forces
6. Rivers
7. Waves
8. Wind
9. Glaciation

Through these notes, students will gain a deeper comprehension of how physical forces interact and create the environments we live in today.

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ISOSTACY THEORY

About the Theorist

Sir George Biddell Airy (1801-1892, Greenwich, London), English mathematician who was astronomer royal from 1835 to 1881. Airy graduated from Trinity College, Cambridge, in 1823. He became Lucasian professor of mathematics at Cambridge in 1826 and Plumian professor of astronomy and director of the Cambridge observatory in 1828. In 1835 he was appointed the seventh astronomer royal, i.e., director of the Royal Greenwich Observatory, a post he would hold for more than 45 years.

 Sir George Biddell Airy

The word isostacy is a Greek word means “equal standing”

The theory postulates that the continents and their major features are maintained in a sort of equilibrium; whereby the large portions of the Earth’s crust are floating on a denser underlying layer called mantle.

– Thus the areas of less dense rock rise topographically as continents and mountains, their movement is compensated for by a similar downwards penetration of this less dense rock into sima

– Hence the lithosphere has highland and lowland due to the variation in density of the materials and gravity, so lowland have denser materials than highland.

– Regardless the density variation, the Earth maintain its balance, any disturbance on the earth’s crust cause movement of the molten materials (Asthenosphere) in a mantle to different direction for the sake of bringing back equilibrium

The concept of Sir George Airy (hypothesis proposed in 1855)

– According to Airy, the inner parts of the mountains are not hollow; rather the excess weight is compensated by the lighter materials below.

– According to him the crust of relatively lighter material is floating in the substratum of dense material.

– Therefore, the continents which are made of lighter sial are floating over the sub-stratum which is built of the denser sima.

– Thus, Himalaya is also floating in the denser glassy magma.

– He suggested that the lighter sial of the Himalaya is floating over the denser material of sima lying underneath.

– Not only this, but the Himalaya is floating in the denser magma with their maximum portion sunk in magma in the same way as aboat floats in water with its maximum parts sunk in the water.

The movement are of two types;

 – Vertical and Lateral movement

– Vertical movement

involves upward and downward, hence it cause either uplift or sagging of the  earth’s  crust respectively.

– Highland are center of denudation while lowland is the center of aggregation.

– Thus when the highlands are worn down there occurs land uplift as a result of upward movement of mantle materials caused by reduction in weight on the earth’s surface.

– As well as when ice melt leads to crust uplift because of reduction in weight while Forming deposition  on lowland part of the continents.

Evidence of Isostatic movement

– 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.

– The slowly rising of crust due to ice sheet melting, in the former beaches that occur around the coast of Scandinavia. Now lie from 8m to 30m above the present day beaches.

– Submergence of forests on the shores of Britain.

The continental shelf around Antarctica is covered by water to a depth of about 750m compared with 180m around the continents.

– Presence of rias and estuaries between coastal lands of Gambia and Sierra-Leone.

A ria is a coastal inlet formed by the partial submergence of an unglaciated river valley. It is a drowned river valley that remains open to the sea. Typically, rias  have a dendritic, treelike outline although they can be straight and without significant branches.

Ria

Estuary

An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. 

 Estuary

Effects of Isostatic Movement

– Formation of faulting leading to the formation of Grabens, Horsts and tilted block.

– Creation of folding leading to the formation of various folds as well as fold mountain.

– Formation of Earthquakes with the associated effects like faulting subsidence and uplift.

– Volcanic eruption forming different volcanic features(volcanoes).

Critique/Challenges of the Theory

– The theory failed to explain the formation of depositional features which are seen to appear above the sea water level.

– The theory has more generalized that is it has over looked. It has not pointed out which mountains have roots

– Is it true that, all mountains maintain their heights in the same way as postulated by theory ? Consider the case of residual mountains which have been formed by denudation.

Importance of Isostacy Theory

– It provide an understanding on the dynamic state of the earth’s crust, that the Earth’s crust is not static it is dynamic as it tends to balance itself after some disturbance and the influence of gravitational force.

– It paves a way to understand theories such as plate tectonic and continental drift, through the idea that crust floats like ice berg on the ocean.

– It helps understanding of how various landforms were formed e.g fold mountain and garbens.

– It enhance human being to take precaution depending the nature of the phenomena at his localities. E.g volcano eruption.

– It gives basis for predicting the future of the crustal state at any particular place on the earth’s surface.

CONTINENTAL DRIFT THEORY

History of the Theory

Continental drift was first conceived by scholars and philosophers named Francis Bacon, George Buffon, and Alexander von Humboldt. As maps grew more accurate the landmasses began appeared as puzzle pieces. The continents once had fit together but had drifted apart after millions of years.

The continents now far apart showed similar sediment, rock formation, and vegetation supporting the theory that they were one landmass in the past. These men helped establish the idea of continental drift, but Alfred Wegener spent much time exploring and researching to prove this theory.

Alfred Wegener, in full Alfred Lothar Wegener, (1880 – 1930), German meteorologist and geophysicist who formulated the first complete statement of the continental drift hypothesis. He taught meteorology at Marburg and Hamburg and was a professor of meteorology and geophysics at the University of Graz from 1924 to 1930. 

 Alfred Wegener 

                                

The continental drift theory was advanced by Alfred Lothar Wegener in 1912

                          

According to his theory, about 280 million years, the present day continents were united in a single block called Pangaea and surrounded by ocean called Panthalassa. He believed that Pangaea was located near the South pole. Later Pangaea split into two (2) Super continents 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 North America, Asia, Europe, and numerous landmasses found in northern Hemisphere-Greenland, Iceland and United Kingdom.

Gondwanaland split to give present day Africa, South America, Australia and Indian sub-continent, Antarctica and other islands in the southern Hemisphere.

Continental Drifting

Drift:

Since that time the continents have been drifting apart to occupy their present positions. And the drifting is a very slow 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 South America could fit into Africa, North America into Europe, Antarctica, Australia and India formed in a single landmass with S. America.

2. 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)

3. 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 these fossils are found in all continents hence prove that they all come from one landmass

4. 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.

5. 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.

6. 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

Critiques of continental drift theory

1.Alfred Wegener meddled in the field of geology

– This was because Alfred Wegener was a meteorologist not a geologist, that means he had no enough knowledge to explain about geology as far as he was dealing with meteorology.

2. Misfit of some continents.

– Possibly not all continents fits exactly to each other if they could be brought together. but Wegener did not account on that aspect.

3. Wegener failed to explain the mechanism of drifting the continent; the forces that account for drifting the continent to be apart.

– However he presumed that tidal influence of the moon gave the continents a westward motion (a counter movement of the revolution of the earth)

– But according to Jeffrey’s, a physicist that tidal friction of such magnitude needed to displace the continents would bring the earth’s rotation to a halt in a matter up few years.

– The gravitational forces and centrifugal forces could not be such sufficient to cause the movements of the continents.

4. Existence of similar plant remains on both continents

– Some of the scientists argued that the existence of similar plant remains might have been brought by the aspect of wind blowing from one continent to another continent.

5. The development of glacier in the hot region of Australia

– Alfred lothar Wegener, failed to explain the existence and development of glaciers in the hot arid Australia.

Impacts of Continental Drift

– The theory led to the formation of continents, landforms like the rift valley, seas or ocean,mountains like Alps and Atlas.

– Occurrence of earthquakes and volcanic eruptions as a result of crustal deformation.

-Climatic changes, e.g some continents moved to the polar region and assumed very low temperatures such as Antarctica and Greenland.

-Also folding has led to the elevation of the surface leading to very low temperature on the Summit, for example Mount Kilimanjaro peak and Mount Everest summit; it is very cold

PLATE TECTONIC THEORY

History of Plate Tectonics

The concept of plate tectonics was formulated in the 1960’s. Plate tectonics is the modern version of continental drift, a theory first proposed by scientist Alfred Wegener in 1912. Wegener didn’t have an explanation for how continents could move around the planet, but researchers do now. Plate tectonics is the theory of geology, said Nicholas van der Elst, a seismologist at Columbia University in New York.

The theory also takes the combination of theory of theory of isostacy, continental drift and ocean floor spreading.

The Meaning of Plate Tectonics

Plate in geologic terms means a large slab of solid rock. “Tectonics” is a part of the Greek root for “to build” and together the terms define how the Earth’s surface is built up of moving plates. The theory of plate tectonics itself says that the Earth’s lithosphere is made up individual plates that are broken down into over a dozen large and small pieces of solid rock.

According to the theory, Earth has a rigid outer layer (shell), known as the lithosphere which is made up of several rigid piece called tectonic plates. The lithosphere (crust and upper mantle) is broken up into seven very large continental- and ocean-sized plates, six or seven medium-sized regional plates, and several small ones.

There are seven major tectonic plates (North America, South America, Eurasia, Africa, Indo-Australian, Pacific and Antarctica) as well as many smaller, microplates such as the Juan de Fuca plate near the United States’ state of Washington (map of plates).

These plates move relative to each other, typically at rates of 5 to 10 cm (2 to 4 inches) per year, and interact along their boundaries, where they converge, diverge, or slip past one another.

 Plate Tectonic Theory Plates and relative plate motion

Convection currents within the the Mantle

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.

TYPES OF PLATE BOUNDARIES

Plate boundaries can be categorized in three fundamental types:

(a) Divergent boundaries – This occurs when plates separate and move in opposite directions, allowing new lithosphere to form from upwelling magma. This either occurs at mid-ocean ridges (the so-called seafloor spreading) or at rifted continental margins.

– The space created can also fill with new crustal material sourced from molten magma that forms below. Divergent boundaries can form within continents but will eventually open up and become ocean basins.

1. i)On land
   Divergent boundaries within continents initially produce rifts, which produce rift valleys.

1. ii)Under the sea

The most active divergent plate boundaries are between oceanic plates and are often called mid-oceanic ridges.

(b) Convergent boundaries – This occurs where the plates move towards each other. One plate either sinks beneath the other along a subduction zone or plates collide because neither can be subducted.

– Subduction zones occur when one or both of the tectonic plates are composed of oceanic crust. The denser plate is subducted underneath the less dense plate. The plate being forced under is eventually melted and destroyed.

1. i) Where oceanic crust meets ocean crust

Island arcs and oceanic trenches occur when both of the plates are made of oceanic crust. Zones of active seafloor spreading can also occur behind the island arc, known as back-arc basins. These are often associated with submarine volcanoes.

1. ii) Where oceanic crust meets continental crust

The denser oceanic plate is subducted, often forming a mountain range on the continent. The Andes is an example of this type of collision.

iii) Where continental crust meets continental crust

Both continental crusts are too light to subduct so a continent-continent collision occurs, creating especially large mountain ranges. The most spectacular example of this is the Himalayas.

(c) Transform fault boundaries (Neutral / trans current boundary) – This occurs when plates move horizontally past each other.

– Natural or human-made structures that cross a transform boundary are offset-split into pieces and carried in opposite directions. Rocks that line the boundary are pulverized as the plates grind along, creating a linear fault valley or undersea canyon. Earthquakes are common along these faults. In contrast to convergent and divergent boundaries, crust is cracked and broken at transform margins, but is not created or destroyed.

Based on the three types of plate boundaries, a global network of approximately twelve major plates of irregular shape and size cover the Earth’s crust. Where one type of plate boundary is terminated it is transformed into a boundary of a different type.

CAUSES OF MOVEMENTS

1. i) 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. ii) 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

iii) Isostatic adjustment

May cause slight movement when trying to create balance.

1. iv) 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. a)Diverging plates

1. I) Oceanic

– Mid oceanic ridges

– Oceanic Islands

– Rifts e.g. Red sea

1. II) Continental

– Volcanic mountain

– Block mountains

– Rift valley

1. b)Convergent plate boundary– Collision may lead to subduction and uplift.
2. i) Oceanic – oceanic trends (Marianna trenches, Japan trenches)
3. ii) Oceanic and continental-Volcanic mountains on the coastal boundaries and also result into trenches.

iii) (Continental)- Formation of Fold Mountains. Himalayas ( Indian and Russian plate formed)

1. 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 1000 km.

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 36000 ft.

ii) Mid Oceanic Ridge: It refer to a giant undersea mountain range made up mostly basalt.It may be more than 80000 km long and 1500 to 2500 km wide and it may rise to 2.3 km 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. iv) 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.

1. v) 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.

1. 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.

 STRUCTURE OF THE EARTH

The Meaning of Earth

– Earth is the planet on which we live, the world

– Earth is the planet third in order from the sun, having an equatorial diameter of 7926 miles (12,755 km) and a polar diameter of 7900 miles (12,714 km), a mean distance from the sun of 92.9 million miles (149.6 million km), and a period of revolution of 365.26 days, and having one satellite.

– The earth is the land surface on which we live and move about.

 Earth

Structure of Earth

– The shape of the earth is an oblate spheroid, because it is slightly flattened at the poles and bulging at the equator.

– The earth is a system which is composed of outer and inner zones. The outer zones of the earth include the atmosphere, the hydrosphere and the barysphere. The inner zones of the earth include the crust, mantle and the core. 

 The Structure of the Earth showing Inner Zone and Outer Zone

CONCENTRIC ZONE OF THE EARTH

The inner zones of the earth constitute the internal structure of the earth. The inner zone / internal structure of the earth consists of three zones or layers which are:

1. Crust 
2. Mantle 
3. Core 
   
   The boundaries between these layers were discovered by seismographswhich showed the way vibrations bounced off the layers during earthquakes. Between the Earth’s crust and the mantle is a boundary called the moho. It was the first discovery of a major change in the Earth’s structure as one goes deeper.

1. CRUST

Is the outermost and thinnest zone of the earth which found between 8 – 50 km or 5 – 30 miles. It is known as Lithospere, It is largely composed of igneous rocks. Other types of rocks also exist as a result of changes on the earth’s surface. The rocks are crystalline, hard and brittle. Bacause of being brittle they tend to break when subjected to stress or forces especially the compressional forces. The crust also consist of two layers are sial and sima layers.

1. a) Sial

Is the outer layer of the crust which rich in silica and Aluminium minerals. The sial for the basis of the continent. The presence of silica and aluminium minerals collectively form SIAL layer.

1. a) Sima

Is the layer which found beneath the sial. It is the inner layer of the crust which separated from sial layer by the zone called Conrad discontinuity line. The sima layer is composed by silica and magnesium. It forms the basis of ocean floor. 

Note: Sial and sima layer together forms the crust.

2. MANTLE               

Mesosphere or mantle which found between the crust and core. It lies beneath the crust. It separated from the crust by the zone of separation called Mohorovic discontinuity or moho. It extends downward to about 2900 km (1800 miles) where the temperatures may reach about 5000⁰c. It consist of pale green minerals called Olivine (Ferromagnesium silicate) in form of ultra basic rock.It consists of lower and upper mantle. The upper mantle is rigid and crust to form a large layer called lithosphere.

The lower mantle is less rigid and forms the moltern layer within the earth’s interior called asthenosphere. Asthenosphere is the molten layer layer which responsible for the balancing movement of the earth’s material called isostatic readjustment. Asthenosphere has been investigated is found between 100 to 200 km below the upper surface.

3. CORE

The core is the innermost zone of the internal structure of the earth. It is also called barysphere or centrosphere. It has diameter of about 6900 km (4300 miles) density of about. The core is also classified into two parts i.e. the outer and inner core. It separated from the mantle by zone of separation called Gutenberg discontinuity.

1. The Outer Core

It is liquid in nature due to high temperature of up to 3700⁰c, and consist of nickel and iron (NIFE) . It is estimated to be 2100 km with density of about 10.5 gms/cc.

2. The Inner Coreis thought to be solid in nature because of high pressure exerted from different parts toward the center – It composed mainly by iron. It has diameter of about 2600 – 2700km. (1600 – 1700 miles)

EXTERNAL STRUCTURE OF THE EARTH

External structure of the earth consists of four main layers’. These are Atmosphere, Hydrosphere, Lithosphere / Land mass Biosphere, Biosphere

1. THE ATMOSPHERE

Is the thin layer of gases held on the earth by gravitation’ attraction. It composed by abiotic (nonliving matter) and biotic living organism. Non-living matter found in the atmosphere includes mixture of gases, water vapor and dust particles. The living organism include the smallest or microscopic organisms like bacteria

COMPOSITION OF ATMOSPHERE

Atmosphere is the outer zone or external structure of the earth composed by Abiotic and Biotic components.

1. Abiotic Components of Atmosphere. The abiotic components of the atmosphere include the following. Mixture of various gases These include Nitrogen (78%), oxygen (21%), argon (0.009%) and carbon dioxide (0.03%). Other gases include neon, helium, Krypton, xenon and other which are present in minite (small proportion) percentage. Water vapor Is the colorless and odorless (smell less) gas in the form of water which makes up a perfect mixture with other gases.

The degree to which water vapor is present in the atmosphere is called humidity. Humidity is very important to weather as condensed to form clouds and fog. Excess water vapor brings about precipitation in form of rain, hail, snow and sleet. Water vapor is capable of absorbing heat which penetrates into the atmosphere in the form of radiant energy from the sun to the earth. It is also act as a blanket which prevents the rapid escape of heat from the earth’s surface and therefore maintain heat budget. Dust particles.

The Dust Particles may Exposed to the Atmosphere Naturally or Artificially

1. a) Natural dust particles are those caused by natural phenomena like winds and volcanic eruptions.

1. b) Artificial dust particles are those derived from industrial pollutions such as soot and ashes. It includes the particles caused by other man’s activities like construction, mining and farming activities.

The function of dust particles serve as a nuclear or center around which water vapor

condenses to produce clouds.

2. Biota components of atmosphereincludes bacteria etc

STRUCTURE OF ATMOSPHERE

According to the temperature changes, atmosphere divided into two zones. These are Homosphere and Heterosphere

HOMOSPHERE

Homosphere is the layer which found between 0 – 80km above the sea level. This is the lowest part of the atmosphere which composed of uniform composition gas of uniform composition of gases and temperature. Homosphere consists of three layers, namely:

1. i) Troposphere

This layer extends by 0 – 15km above the sea level. Troposphere is the first layer of homosphere located nearest to the earth. It contains water vapor, gases and dust particles. It is the layer of atmosphere which support life on the earth due to the presence of plenty oxygen gas. All processes of rainfall formation take place in this layer and the temperature decreases as the altitude increases at the rate of per every 100 meters or per every 1000 meters.

Note: This situation where by temperature decreases as altitude increases is called lapse rate and because it occur near to the ground is called environmental Lapse rate. The upper limit of Troposphere which separates it to the next later is called Tropopause. Tropopause makes the upper limit of troposphere to the next layer called stratosphere.

1. ii) Stratosphere

Stratosphere exists between 15 – 48 km above the sea level. This is the second layer of homosphere which lies above the tropopause. It is also composed of water vapor, dust particles and various gases. It is the layer of atmosphere which characterized by high concentration of Ozonic gases. This gases form Ozone layer which found particularly at 20 –35 km in the stratosphere.

The Ozonosphere or ozone layer is the layer which form a shield or cover that prevent the earth’s surface from destroying by the sun rays. It prevents the direct incoming of harmful rays from the sun to fall direct on the earth’s surface. The temperature remains unchanged about between 20 – 35 km from the earth’s surface. Then temperature increases with height to about at the upper limit of stratosphere called stratopause. The increase in temperature with height is referred to as temperature invasion.

iii) Mesosphere

This layer extends between 48-80 kilometers above the sea level. Mesosphere is the third part of the homosphere where temperature decreases as the altitude increases. It separated from the stratosphere by the zone of separation called stratopause. The upper limit of mesosphere is called mesopause. Mesopause record minimum temperature of this zone that may fall to making this zone to be coldest. It is at this zone where strong upper air streams of wind like jet streams are experienced.

HETEROSPHERE

Is the second layer of atmosphere which extends from 80km towards the interplanetary space. Heterosphere divided into two layers which include Thermosphere and Exosphere

1. i)Thermosphere

Is the lower part of heterosphere where temperature increases as the altitude increases from i.e. temperature invasion. This is because there is no water vapor or dust particle in this zoneIonosphere consists of some ions which influence radio waves. This is because, ionosphere is electrically charged with free electrons that allow the passage of radio waves, television waves and telephone or mobile phone waves

1. ii) Exosphere

Is the part of heterosphere which found above the thermosphere. It has high temperature through it has little significance as it has not been greatly researched.

Note: Within the heterosphere, there is also a scientific significant layer called ionosphere. Ionosphere consists of some ions which influence radio waves. This is because, ionosphere is electrically charged with free electrons that allow the passage of radio waves, television waves and telephone or mobile phone waves.

 

Function of Atmosphere

1. Insulation Atmosphere is an insulator, it acts as a shield or blanket and therefore regulates temperature during the night and during the winter.

2. Filtration. The atmosphere is the filter, it filters solar insulation and percent ultra violet rays of certain length due to the presence of ozone layer in the stratosphere.

3. Scientific function. Atmosphere is the scientific field, it is the field through which the scientific experiments and observation carried out. Example ionosphere layer of atmosphere reflects some electromagnetic waves and ration signals back to the earth.

4. It supports much on hydrological cycle. The surface water, evaporation, condensation and precipitation formation take place in the atmosphere.

5. It support life some gases particularly oxygen is important for living organisms. Air has weight which contributes to the occurrence of atmospheric pressure variations without which breathing would be impossible. Wind movement and direction that balances temperature, humidity and precipitation also result from pressure variations.

2. THE HYDROSPHERE

Is the layer of water bodies of the earth including all oceans, rivers, precipitation and underground water.  It is estimated that 75% of the Earth’s surface is covered by water bodies.

3. THE LITHOSPHERE / LAND MASS

Is the whole solid body of the earth with various landforms such as mountains, valleys and plateaus. The lithosphere is also known as the crust. It includes all land masses. The major land mass is called continent and the minor land mass is called islands.

4. THE BIOSPHERE

Biosphere is the complex zone which comprises all living things. It includes a lower level of atmosphere and the upper level of lithosphere and hydrosphere. Biosphere receives substantial supply of energy from the sun which gives it condition necessary for life and does not occur in any part of the solar system. The living organisms that inhibit biosphere interact with each other and their environment. The sum of all these interaction components is called the ecological system or ecosystem. Biosphere comprises all living organism both macro and micro organisms living in water bodies, soils and on air.

MATERIALS OF THE EARTH’S CRUST

The earth’s crust is composed of different materials ranging from elements, minerals and rocks. These materials differ in their physical and chemical composition.

Elements

They refer to the smallest particles of matter which can not be split into different forms by any means. Examples of elements are magnesium, potassium, sodium, iron, aluminum and silicon.

Minerals

They are naturally occurring substances which have definite shape, colour and resistance formed due to combination of different elements. They are formed as a result of the combination of two or more elements. Some single elements like gold, silver and diamond may occur as minerals. Mineral Element Quartz Silicon and oxygen Feldspar Potassium, sodium, calcium and aluminum

ROCK OF THE EARTH’S CRUST

A rock is an aggregate of minerals in a solid state. On the other hand the term rock can include substances like clays, shells, sandstones and corals. Rocks which contain metallic compounds are called ores.

Types of Rocks on the Earth’s Crust

Rocks of the Earth’s crust can be classified according to their mode of formation and chemical composition. According to the mode of formation rocks can be classified as classified as igneous, sedimentary and metamorphic.

1. IGNEOUS ROCKS

Are rocks that formed when molten rock cools and solidifies within or outside the earth’s crust. The origin of igneous rocks is inside the earth where they are under great pressure. Igneous rocks do not occur in layers and they don‘t contain fossils. Igneous rocks solidify either within the earth‘s crust and form intrusive features or outside the earth‘s surface and form extrusive features.

Igneous rocks are formed when the molten magma is forced out from the upper mantle to the earth‘s surface, where it cools and solidifies due to low temperature. Crystals form on cooling and the rocks are called crystalline rocks. There are two main types of igneous rocks:

1. Plutonic: these have solidified deep in the crust and they are seen on the surface only after being exposed by prolonged erosion.

2. Volcanic: these have been poured on the earth‘s surface where they are called lavas.

Characteristics of Igneous Rocks

1. Igneous rocks reflect light.
2. They are not found in layers.

3. They do not contain fossils.
4. They are crystalline rocks.

5. They are formed through cooling and solidification of magma.
6. They can undergo metamorphic and weathering processes.

7. They contain different minerals like iron, magnesium etc.

In Tanzania igneous rocks are found in Dodoma, Iringa and in the shores of Lake Victoria (Mwanza). The main examples are granite, gabbro, basalt and diorite. Some are found in Kilimanjaro and Rungwe (Mbeya) such as basalt, pumice, diorite, gabbro, syenite and peridotite rocks.

Granite

Basalt rocks 

2. 
   SEDIMENTARY ROCKS

Sedimentary rocks are rocks formed through weathering processes when sediments are accumulated, compacted and cemented together. The sediments are compacted by compression to form sedimentary rocks. Sedimentary rocks are found in layers; they contain fossils and are very soft. These are weathered particles formed through deposition and lithification processes

Characteristics of Sedimentary Rocks

1. They are formed when particles or sediments are accumulated, compacted and cemented together.

2. They contain fossils.
3. They are found in layers (strata).

4. They do not reflect light.
5. They are non-crystalline rocks.

6. They can undergo metamorphic process.

Types of Sedimentary Rocks

1. Mechanically-Formed Sedimentary Rocks. These are formed through weathering process. When weathering agents erode and deposit rock particles, they are accumulated, compacted and cemented together to form sedimentary rocks. Examples of mechanically formed sedimentary rocks are clays, gravels and alluviums (all deposited by water), moraines, boulder clay and gravels (deposited by ice) and loess (deposited by wind); sandstones and shale.

Sandstone

Shale: Shale occurs in a wide range of colours that include: red, brown, green, grey, and black.

2. Chemically-Formed Sedimentary Rocks. These are formed through chemical precipitation process. They include carbonate (as it is in stalactite and stalagmite), sulphate, chloride, etc. The main examples are gypsum, rock salt, lignite, dolomite, flint, borax, limonite, haematite, etc.

 

Dolomite

3. Organically-Formed Sedimentary Rocks. These are formed through mineralization process of decaying and decomposition of dead organisms such as animals and plants. The remains of living organisms are accumulated, compacted and cemented together to form these sedimentary rocks. The main examples are chalk (limestone) and coral (formed from animals), and peat, coal and lignite (formed from plants).

Lignite rocks

Limestone

Chalk

Coal

Coral rocks

3. METAMORPHIC ROCKS

These are rocks which have changed from one type of rock to another due to the contact of heat, pressure or both. This process is referred to as metamorphism. Any rock can be changed into a metamorphic rock. Examples of metamorphic rocks are slate, marble and granite.

There are Three Kinds of Metamorphism

1. Dynamic metamorphism. This is influenced by pressure of the earth’s crust. Examples; Shale to Schist, Clay to Slate, Granite to Gneiss

2. Thermal or contact metamorphism. This is caused by intense heat. This can take place when the rock comes into contact with hot molten material like magma or lava. Examples: Lime stone to Marble, Sand stone to Quartzite

3. Thermal dynamic metamorphism This is the process that takes place as a result of a combination of heat and pressure. It is when the existing rocks are subjected to both pressure and heat to change their shape and appearance. Example Coal to Graphite

Characteristics of Metamorphic Rocks

1. They are very hard due to prolonged action of heat and pressure.
2. These rocks can change to another to another type of rocks.
3. They can undergo weathering process.

 

Slate

Gneiss

ROCK CYCLE

Rock cycle is a relationship in which rocks tend to change from one type of rock to another. This is the cycle in which rocks tend to change from one type to another. For instance igneous rocks may change to metamorphic rocks or sedimentary rocks; sedimentary rocks to metamorphic or igneous rocks, etc.

Necessary Conditions for Rock Cycle to Take Place or Process of Rock Cycle

1. First, the molten rocks erupt from the interior of the earth and then cool and solidify to formigneous rocks.

2. Secondly, the igneous rocks are subjected to denudation process to form sedimentary rocks.
3. Third, either igneous or sedimentary rocks undergo metamorphism, due to prolonged heat and pressure, to form metamorphic rocks.

4. Fourth, metamorphic or igneous rocks can undergo weathering process through erosion and transportation of sediments which are further deposited in layers in the ocean or lake floors where they are cemented and consolidated to form sedimentary rocks and vice versa.

5. Fifth, metamorphic or sedimentary rocks can be subjected to heat and pressure where melting take place and later cooling, due to low temperature, to form igneous rocks.

Rock Circle

Simplified Geological Time Scale

The geological time scale is a chart for dating the history of the earth including rock span. It tries to explain the age of rocks as far back as 600 million years ago.

 The simplified geological time scale

EraPeriodYears in millions before presentMajor geological events in AfricaMan and animals

Cenozoic	Quaternary	1	Glaciation of East Africa mountains.Formation of river terraces and raised beaches.	Age of man
	Tertiary	163	Formation of the Atlas mountains. Lava flows in Ethiopia.	Age of mammals.
Mesozoic	Cretaceous	135	Deposition of marine sediments in the Sahara and Southern Nigeria. Formation of Enugu coalfield.	Age of reptiles
	Jurassic	180	Break-up of Gondwanaland and Marine invasion of East Africa coastlands and separation of Malagasy Island from mainland.
	Triassic	230	Drakensburg lava and formation of upper Karro beds. Volcanic activity in West Africa.
Paleozoic	Permian	280	Formation of lower Karro beds. Formation of rich coal deposits in Tanzania and South Africa. Ice age in central and South Africa.	Age of amphibians
	Carboniferous	345	Cape fold formed.
	Devonian	405	Marine invasion of Libya, the Sahara and Western Sudan. Continental basins formed by crustal warping
	Silurian	425	Continental sedimentation in Zaire basin,Tanzania and South Africa, followed by intensive folding.
	Ordovician	500	Extensive deposition of sediments.Formation of sandstones in Guinea, Mali, Volta basin and North West Ethiopia	Age of marine invertebrates
	Cambrian	600	Marine invasion of Western Sahara and Kalahari basin.
Proterozoic	Pre Cambrian or Archarean		Glaciations of Africa South of Equator.Extensive metamorphism of oldest known fossilized, unicellular algae formed in Swaziland and Mali.	Algae

The Importance of Rocks

1. Rocks are very important in the formation of soils which can be used for agricultural production.

2. Rocks are used for building purposes: some rocks such as limestone, sandstone, gravels and sand are used for building houses, construction of roads, etc.

3. Some rocks are used as sources of energy or fuel such as coal and petroleum (mineral oil).

4. Limestone is widely used for cement manufacturing. In Tanzania, cement is produced at Tanga, Mbeya and Wazo Hill.

5. Salt extraction: salt usually originate from rock accruing strata, for instance, in Tunisia and Morocco there are large deposits of salt.

6. Manufacture of chemicals: some rocks contain nitrate or phosphate, while others have potash. This kind of rocks can be used for making dyes, fertilizers and medicines.

7. Mineral deposits: mineral ores occur in veins of some rocks such as igneous rocks. The minerals are formed when the magma coos down. Valuable minerals extracted from rocks include gold, lead, tin, silver, diamond, copper, zinc, aluminium, calcium and manganese.

8. Some rocks are so impressive such that they attract tourist to come and view them. In so doing, the country earns a lot of foreign exchange.

9. Some rocks are used for decoration of houses as ornaments or they are grinded to produce powder which is used for decoration.

FORCES THAT AFFECTS THE EARTH

Forces are the processes that operate (work) within or on the earth’s crust. There are different forces that affects the earth.

Internal Forces: These are forces which operate within the earth‘s crust. Internal forces include vulcanicity and earth movements, that is, horizontal (lateral) and vertical   movements. These forces may result into formation of several landform features.

External Forces: These are natural forces that operate on the earth’s surface. The force s mainly act on the earth’s crust or close the surface of the earth. Often the features produced by these forces are seen on the surface of the earth. They include mountains, volcanoes, moraines and valleys, just to mention a few.

INTERNAL FORCES

These are forces that operate within (inside) the earth’s crust OR These are forces which operate beneath (under) the earth’s surface. These forces are generally referred to as TECTONIC FORCES. The internal forces (tectonic forces) are divided into the following.

1. Earth movement (Diastrophism)
2. Vulcanism/ Vulcanicity/Volcanic erruptions

 

EARTH MOVEMENTS

Earth’s movement is the movement of the solid parts of the earth towards each other or away from one another or side way. These are also known as Diastrophism Types of Earth movement Earth movements are classified into two (2) main groups:

(i) Vertical or radial movements

(ii) Lateral or horizontal movements or tangential.

1. Vertical or Radial Movements

These are the upward and downwards movements or forces .These forces cause the uplift (epeirogenic) and the downward movement (cymatogenic). These forces which cause the vertical earth movements operate from the interior upward toward the surface or downward from the surface to the interior. The result of vertical movement

1. a) The crustal rock to fault. When faults develop produce feature like plateaus, basin, Block Mountain (host) and escapements.

1. b) Changes sea level because of the upward lift of the land or sinking of the land. NB: This changes in the sea level is not eustatic changes but is due to vertical forces. The eustatic change is the changes of the sea level due to ice melt during ice ages

2. Lateral/Horizontal Movements

Are the organic forces (movement) because they are on the process to build mountains. Orogenesis means the process of mountain building. There are two (2) types of lateral forces:

1) Compressional forces

2) Tensional forces.

Compressional Forces

Are forces which move towards each other i.e move against each other.  They tend to shorten the crust (the land) i.e. they squeeze the land. Compressional force causes the following.

(i) Folding of land hence fold mountains

(ii) Break the land to form faulting which may produce features like block mountains, rift valley and faults.

Tensional Forces

Are forces that tend to stretch the land i.e. the force move away from each other, they pull the land away. The forces cause faulting of the crust and produce features like faults, Block Mountains, and Features associated with earth movements

RIFT VALLEY

Rift valley is a trough or hollow which may result from both vertical and lateral movements of the earth’s crust. It is formed when two faults develop parallel to each other. It can develop either by tensional forces or compressional forces.

Formation of Rift Valley by Tensional Forces

This is formed when tensional forces move away from each other. These forces of tension produce faults and the block between two parallel faults subsides to form a rift valley.

Formation of the Rift Valley by Compressional Forces

This is formed when horizontal forces act towards each other. These forces of compression produce faults on the outside of the two parallel faults and the pieces of land on either side are lifted up above the general level of the ground to form a rift valley. Diagrammatically, formation of the Rift Valley occurs like this:

 Rift Valley

Examples of rift valleys include:

– East African rift valley – Africa

– Jordan rift valley – Asia

– Rhineland rift valley – Europe.

BLOCK MOUNTAIN (HORST)

A block mountain refers to a table-like mountain formed due to the influence of faulting that leads to rising of crustal rocks. It is nearly a flat surface. A block mountain can be formed by either tensional or compressional forces. This is when the earth’s movements cause parallel faults which results into uplifting of some parts. Examples of Block Mountains are: Usambara and Uluguru, in Tanzania, Ruwenzori, in Uganda, Vosges and Black Forest, in Europe; and Mount Sinai in Asia.

 Bock Mountain

PLATEAU

A plateau is a large, extensive uplifted part of the earth’s crust which is almost flat at the top. The top of the plateau is mostly a plain. Plateaus were formed during Mesozoic and Jurassic eras. It was due to uplifting of the earth’s crust. Such landforms are East African and Brazilian plateaus. High plateaus especially in tropical latitudes are used for agriculture and settlement.

BASIN

A basin is a large, extensive depression on the earth’s surface. Most basins are formed due to vertical movement of the earth. Examples of basins include: an inland drainage e.g. Congo basin, Chad basin; and Amazon basin.

VULCANISM / VULCANICITY

Vulcanicity or volcanism is the range of processes by which molten materials and gases are either intruded (injected) or extruded (ejected) into the earth’s crust or into the earth’s crust respective Vulcanicity is the formation of various feature due to the intrusion or extrusion of molten materials, and gases. The molten materials are called magma when found within the earth’s crust and magma when poured on the earth’s crust.

Vulcanicity therefore includes volcanic eruptions, which lead to the formation of volcanoes and lava plateaus and geysers, and the formation of volcanic features such as batholiths, sills and dykes, etc, in the earth‘s crust.

There are two types of vulcanicity namely:

1. a) Intrusive Vulcanicity 
2. b) Extrusive Vulcanicity

1. INTRUSIVE VOLCANIC FEATURES

This is when magma intruded within the earth’s interior. The features resulted due to the intrusive volcanic eruption is called intrusive features. The intrusive volcanic features are the features which are found within the earth’s interior. These include the following.

1. Dyke

This is a wall of rock which cuts across the bedding planes. It is formed when magma cools and solidifies vertically across bedding planes. Examples of dykes are Mwadui dyke in Tanzania, Gabbro dyke in Lesotho, and Tyolo dyke in Malawi.

 Dyke

2. 
   Sill

 This is a rock sheet formed when the magma solidifies horizontally along the bedding plane. It is concordant with the rock strata. Eg: Kinkon Falls found Fouta Djallon ranges in Guinea.

 Sill

3. 
   Laccolith

This is an intrusive feature which looks like a dome. It is formed when the magma cools and solidifies in anticline bedding plane. It looks like a mushroom. E.g: Morafanobe in Madagascar.

 Laccolith

4. 
   Lopolith

This is a saucer-shaped mass of rock formed in the geosyncline. The saucer-like shape may be due to the increased weight of the deposits. E.g: The Bushveld Basin in the Transvaal in South Africa.

 Lopolith

5. 
   Phacolith

It is a lens shaped strip of igneous rock formed when the magima solidies along the anticline or syncline. Eg: Cordon wills in U.K

 Phacolith

6. 
   Batholith

It is the large mass of solidified rock formed when magma cools plutonically at the great dept Eg: at the heart of the mountain ranges. Eg:- Chilu Batholic in Gabon

 Batholith

1. EXTRUSIVE VOLCANIC FEATURES

These are the features formed when the magma cools and solidifies on the earth’s surface. The following are landforms due to extrusive vulcanicity:

1. Ash and Cinder Cone(Scorio Cone)

It is a cone shaped accumulation of rock fragments around the vent. The slopes of the cone are always concave due to the spreading tendency of lava at the base of the cone. E.g: Busoka and Bitale in South West Uganda.

 Ash and Cinder Cone

2. Composite Cone(Strato Volcano)

It is a large cone with alternate layers of pyroclasts (fragments) i.e. ash and cinder on the other hand. E.g: Mount Kilimanjaro, Meru in Tanzania, and Virunga ranges in Uganda.

 Composite Cone

3. 
   Volcanic Plug(Plug Dome Volcano)

It is a rigid cylindrical plug formed when very viscous lava is forced out by very explosive eruptions. The plug is extruded amid clouds of hot blowing ash and cinders. E.g:Hoggar Mountains in Algeria.

 Volcanic Plug

4. Acid Lava Cone(Cumulo Dome Volcano)

It is a dome shaped volcano with convex slopes formed when acidic lava solidifies around the vent.. E.g: Ntumbi Dome located in East of Mbeya, Tanzania.

 Acid Lava Cone

5. Crater

It is a depression formed on the summit of the cone after the plug has been

 Crater

6. Caldera

It is a large crater (large rounded depression) formed when the upper par of the volcano is either bombarded away by violent eruptions or subsides into the crust or in the volcanic cone. E.g: Ngorongoro in Tanzania, and Eboga Crater in Cameroun.

 Caldera

Minor Volcanic Features

1. Geyser

 Geyser refers to the forceful emission of hot water and steam from the ground to a high level in the air. The ejected water contains fine materials such as volcano mud, which later form fertile soils. Geysers are found in Iceland, North Island and New Zealand.

2. Hot Spring

Hot spring refers to natural outflow of superheated water from the ground. It contains mineral substances in solution. Hot springs are found in Iceland, in Europe; and Kenya and Ethiopia, in Africa. Hot springs are also found in Manyara National Park, Songwe, in Mbeya and in Nigeria.

 Geyser and Hot Spring

Classification of Volcanic According to Activity

1. Active Volcano: is the volcano which erupts frequently. Eg:- Oldonyo Lengai in Tanzania and Mount

Cameroon.

2. Dormant Volcanois the one which has stopped erupting but not extinct and it is expected to erupt. The dormant volcano is also known as sleep volcano.

3. Extinct Volcano. Is the volcano which has stopped erupting for a very long time in history and is not expected to erupt. It is also known as

dead volcano.

Influences of Volcanic Eruption to Man and Environment

The following include the economic importance of volcanic eruptions to man.

1. Lava on weathering head to the formation of very fertile soil which support agriculture. The larva poured onto the earth‘s surface following vulcanicity forms a fertile soil upon weathering. This soil supports agriculture as well as forestry. Examples of fertile volcanic soils that resulted from volcanic activities are the rich acidic soils on the slopes of mounts Kilimanjaro, Kenya and Elgon, which supports the growth of coffee, banana, tea and other crops.

2. Volcanicity eruption lead to the formation of mineral deposits like copper deposits of butte in USA, diamond of kimberley in South Africa. Vulcanicity brings minerals from deep the earth‘s crust to close or onto the earth‘s surface. Various minerals and gemstones are mainly found in the volcanic regions. Diamond in Mwadui is mined from the volcanic plugs and dykes. Gold and silver are associated with the Nyanza batholith in Kenya.

3. Volcanic eruption provide geothermal power for electric generation. Geysers can be harnessed to generate geothermal electricity. Geothermal power is tapped from geysers in volcanic regions. In East Africa, geothermal power stations are established at Olkaria near Naivasha in Kenya.

4. Some hot springs utilized for heating homes in glaciated region. People use hot springs and pools of hot water as spas. They bathe in the water for the purpose of curing certain diseases. Hot water from hot springs is pumped into homes during winter to heat up homes. This is done in cold countries like Iceland and New Zealand.

5. Volcanic features attract tourist.  Spectacular features formed upon vulcanicity such as mountains, calderas, caldera lakes, cones, geysers and hot springs are interesting to look at. As such, they attract tourist and hence earn foreign currency to the country.

6. Construction activities. When the magma solidifies, it forms hard rocks that can be quarried and used to construct roads, bridges, houses and other infrastructures.

7. Some crater lakes are a source of salts and other minerals while others support fishing activities, for example Lake Chala. Some lakes are a source of fresh water for domestic and industrial uses.

8. Volcanic cones are the source of rivers.

EARTHQUAKE

Earthquakes refer to the sudden shaking or vibrations of the earth’s crust due to sudden and rapid displacement of tectonic plates along the line of weakness (faults). It occurs mainly in volcanic eruption zones. The point from which the earthquake originates is known as focus and the intensity of earthquakes can be measured by using an instrument called seismograph. The point on the surface vertically above the focus is called epicentre

Measurement of Earthquakes

The intensity and magnitude measure the strength of the earthquake. These are obtained by detecting the Seismic waves using instruments called seismograph or seismometer.

Intensity is a measure of how hard the earthquake shakes the ground. It is determined through the effects produced by the earthquake. Intensity varies from one place to another. While the intensity of a specific earthquake varies, its magnitude does not vary. So it is important not to confuse magnitude with intensity.

The scale that measures the intensity is called Mercalli scale. It ranges from undetectable, moderate, strong to major catastrophe. Magnitude refers to the total amount of energy released and it is given on the Ritcher scale. This scale ranges from 0 to 8.9.

 Earthquake

Causes of Earthquakes

1. Faulting of the lithosphere caused by tectonic movement where one plate slides over another plate.

2. Volcanism can cause occurrence of the earthquake. This is because the magma moves under the influence of intense pressure from within the earth’s interior.

3. Mass wasting like land slide and rock fall can cause occurrence of earthquake, but this is for local scale.

4. Falling objects from the atmosphere such as meteorites may lead to the shaking earth’s crust.

5. Man’s influence through his activities such as mining using explosives like dynamites and transport vessels like trains and heavy trucks.

Types of Shock Seismic Waves Generated during the Earthquake

Seismic waves can be categorized into broad groups as follows:

1. Body Waves. Are waves which travel through the crust and are of two types:

1. a) Primary Waves, which cause the crustal rock to move back and forth in the direction of wave movement

1. b) Secondary Waves. Are waves which cause the crustal rock to move side to side ie right angles to the direction of wave movement.

2. Surface Waves. These travel through the surface and are of two types:

1. a) Love Waves.Which cause the surface rock to move side to side of right angles to the direction of wave movement.

1. b) Rayleigh Waves. Wave which cause the surface waves to have a circular movement very similar to that of water wave movement.

Effects of Earthquakes

1. They can cause loss of life and property. An earthquake is a natural disaster. Whenever it occurs, it causes a lot of disturbances including loss of life and properties. For example, the earthquake that hit Toro in Uganda in 1966 killed 157 people, injured about 1300 people and destroyed about 6000 houses. The earthquake which occurred in California–Mexico border in 1975 caused damage running into millions of dollars and injured 100 people on both sides of the border where most of them suffered cuts from flying glass and debris.

2. They can displace parts of the earth’s crust vertically or laterally.

3. They can raise or lower parts of the sea floor. The Agadir earthquake in Morocco in 1960 raised the sea floor of the coast. In some areas the depth of the sea decreased from 400 m to 15 m after the earthquake.

4. They can raise or lower coastal rocks. In the Alaskan earthquake of 1899, some coastal rocks were raised by 16 m.

5. They can cause landslide and open up deep cracks in the surface rocks. The El Asnam earthquake in Algeria, in 1954, destroyed an area of radius 40 km and opened up deep cracks up to 3 m deep.

Precautionary Measures to Avoid high Damage from Earthquakes

1. Refraining from building high-rising structures on the land vulnerable to earthquake as well as strengthening buildings by using reinforced concrete, steel frames, deep foundations and light roofs.
   
   2. Geologists should detect epicentres and tell the people to evacuate the places likely to be affected by earthquakes.
   
   3. To avoid constructing very large water bodies like Kariba dam which can cause the earthquakes due to the weight of water and other materials.
   
   4. Discouraging the use of explosives like dynamites in breaking the rocks during mining and construction operations.

WEATHERING

Weathering refers to a processes where by rocks disintegrate into small particles due to the agents of weathering such as water, ice, wind, wave, etc. The process results from the forces of weather, that is, changes in temperature, frost action and rain action.

Types of Weathering

The main forms of weathering include:

1. Mechanical weathering;
2. Chemical weathering; and
3. Biological weathering.

1. MECHANICAL WEATHERING

This is also referred to as physical weathering. It is a type of weathering caused by changes in temperature. It is common in areas where there are extreme changes in temperature such as hot deserts, arid and semi arid regions. Mechanical weathering includes the following types:

1. Exfoliation

This process occurs due to temperature change. During the day time rocks expand due to high temperatures and contract during the night due to low temperatures. Alternate heating and cooling set up powerful internal stress in the top layer of the rocks. The stress produces fractures which cause the outer layer to pull away leading to the cracking and disintegration of rocks into small particles.

The rocks that remain standing as exfoliation takes place are called exfoliation domes. Exfoliation domes occur in desert, semi-desert and monsoon regions. There are many exfoliation domes in the Egyptian, Kalahari, Sahara and Sinai deserts.

 Exfoliation

2. Granular Disintegration. It is the breaking up the rock which consists of different minerals. These minerals expand and contract separately through temperature changes.

Granular Disintegration

                      

3. Block Disintegration. This takes place when the rock with homogeneous rock breaks into rectangular blocks due to changes in temperature. This is common when the rock is jointed . this process can be aided by chemical weathering.

Block Disintegration

4. Frost action

This is common in temperate regions where temperature falls up to freezing point. When temperature falls (freezing point) water collects in the rocks and it freezes, its volume increases causing the crack to deepen and widen. Usually it involves the freezing of water in the cracks during the night and thawing (melting) during the day in mountainous areas. This action of thawing (melting) and freezing of water in the cracks cause the rocks to shatter (break) into angular fragments.

 Frost Action

2. 
   CHEMICAL WEATHERING

Chemical weathering involves the decomposition of some of the minerals contained in a rock. Some rocks decompose when they come into contact with water (H₂O), or oxygen (O₂) and carbon dioxide (CO₂), two of the gases that make up air. Chemical weathering includes the following processes:

1. Oxidation– This happens when oxygen combines with a mineral. It takes place actively in rocks containing iron, when oxygen combines with iron to form iron oxides. This process is often preceded and accompanied by hydrolysis. The new minerals formed by oxidation are often easily attacked by other weathering processes.

2. Carbonation– This process occurs when hydrogen carbonate ions react with a mineral to give a soluble compound which can be carried away in solution. Hydrolysis often accompanies carbonation.

3. Solution –This refers to dissolution of a mineral with a chemical substance. Rain water combines with both atmospheric carbon dioxide and oxygen to form weak carbonic acid. CO₂(g) + H₂O(l) → H₂CO₃(aq).So when the rain reaches the ground it consists of a weak acid called weak carbonic acid. This acid helps to dissolve many insoluble minerals into minerals soluble in water, and which can be carried away in solution. 
   
   When rain containing weak carbonic acid falls in a limestone region, it reacts with limestone (calcium carbonate) and dissolves it into soluble calcium hydrogen carbonate, which can easily be carried away in solution.CaCO₃(s) +H₂CO₃(aq) → Ca(HCO₃)₂(aq). In limestone regions, the rocks are dissolved and produce features like grike andclint(trough and ridge).

3. Hydration – This is the process in which some minerals absorb water and swell up, causing internal stress and fracture of the rocks.
4. 
   Hydrolysis – This process involves the reaction of hydrogen (in the water) with certain mineral ions (in a mineral). This gives rise to the formation of different chemical compounds that can be easily weathered through other weathering processes.

NOTE: Usually two or more chemical weathering processes take place at the same time. Chemical weathering is most marked in hot wet regions.

3. 
   BIOLOGICAL WEATHERING

When plants grow on rocks, their roots penetrate into rock joints which later force the rocks to break apart. Also man contributes much to rock disintegration through farming activities, mining, quarrying and construction. Macro- and microorganisms also disintegrate rocks through burrowing and by mineralization process. Bacteria, for example, in the presence of air, break some minerals which are dissolved in the soil. Plants also absorb minerals from the soil by their roots. Decayed vegetation produce organic acid which remain in the soil. All of these actions help to weaken the rocks.

 Disintegration of Rocks caused by Plants

Factors Which Control the Rates of Weathering

1. Rock composition: There are certain elements which are included in rock composition. Some rocks will weather quickly and some slowly e.g. acidic rocks weather more quickly than basic ones.

2. Climate: It includes the meteorological elements effect on rocks such as moisture, temperature, and wind and air pressure. Climate determines whether physical or chemical weathering will be more active and speedy.

3. Topography and Vegetation: Topography directly effects weathering by exposing rocks to the temperature or sun and wind. The elevated areas will be affected more and low level areas will be affected less.

4. Vegetation: Surface covered by the vegetation are protected from weathering but bare surfaces are weathered to great extent.

– Thin root plants protects weathering

– Thick root plants accelerates weathering

5. Length of Exposure: The longer a rock is exposed to the agents of weathering, the greater the degree of alteration, dissolution and physical breakup. Lava flows that are quickly buried by subsequent lava flows are less likely to be weathered than a flow which remains exposed to the elements for long periods of time.

Disintegration of Rocks caused by Human Beings

The Significance of Weathering

1. Weathering leads to soil formation. Soil is formed through the process of weathering of rocks. Various forms of weathering lead to rock disintegration and hence formation of the soil. The soil is an aggregate of organic and inorganic particles formed by different processes of weathering.

2. Weathering may shape the rocks into attractive features whichcan attract tourists and hence earn the country and communities the much needed foreign exchange. An example of a feature that can attract tourists is the Bismarck Rock on the south shore of Lake Victoria.

3. The processes of weathering weaken the rocks such that they can be easily acted upon by agents of erosion. The process helps to shape the earth and produce various landforms. This, in turn, influences the type of human activities that can take place in an area. So the process is very important in supporting life.

4. When the rocks are weathered they become weak and hence easy to exploit, e.g. by quarrying. This process also helps to break up large rocks into small fragments such as sand, which is used for construction purposes.

5. Weathering serves as carbon sink. Any process that reduces the amount of carbon dioxide from the atmosphere is termed as carbon sink. Some processes of weathering involve absorption of carbon dioxide from the atmosphere. This helps to remove excess carbon dioxide from the atmosphere. Limestone and other carbon-based sedimentary rocks are important carbon sinks.

MASS WASTING

Mass wasting is the movement of the weathered materials downslope due to gravitational forces accompanied by rain action. Mass wasting also known as slope movement or mass movement

Types of Mass Wasting

Types of mass movement are distinguished based on how the soil, regolith or rock moves down the slope as a whole. Based on this factor, mass wasting can be categorized or grouped into two types. These are:

1. Slow Movement
2. Rapid Movemen,

Each with its own Characteristic Features

and taking place over timescales from seconds to years.

1. SLOW MASS MOVEMENT

This is the movement of soil at very slow speed, water acting as the lubricant. Slow mass wasting is categorized into several types.

These are as follows:

1. a)Soil Creep. Soil creep is the slow movement of the soil downhill after it gets soaked by water. This process is very slow and its evidence is provided by tilting of trees and falling of buildings and fences. Soil creep is activated by any process that loosens the soil, making it easy to move gradually down the slope.

Soil Creep

Factors Influence Soil Creep:

1. Alternate heating and cooling of the soil particles.
2. The freezing of water in the soil causing frost heaving.
3. Removal of the soil further down the slope.
4. Percolation of water into the soil, acting as a lubricant.
5. Ploughing of the soil, a fact which makes the soil loose and more mobile.

1. b) Talus Creep. It takes place due to the processes of thawing and freezing and is more pronounced in high latitude regions. It is very common on sides of mountains, scarps and valleys. This is also a very slow mass movement of screes. Rock creep It occurs commonly where individual rock blocks are lying over clay materials. In the presence of moisture, the clay surface becomes slightly slippery. The rock blocks may creep slowly down the slope under the influence of gravity. Individual rock blocks may move very slowly down a slope.

Talus Creep

1. c) Solifluction. This is the slow movement or flowing of weathered materials, especially when mixed with water and gravels. It is limited on highlands and cold regions.

Solifluction

2. RAPID MASS WASTING

This involves the movement of materials in form of mud flow, land slide, rock fall and earth flow.

1. a) Earth Flow. This type of movement occurs in humid regions. The materials on the earth’s surface gets so saturated with water that it gains much weight, and starts to move down the slope under the influence of gravity. This normally occurs on the slopes of the hills or mountains. The removed earth material leaves a shallow scar on its place of origin and it creates terraces or mounds in its destination.

  

 Earth Flow

1. c) Mudflow. Mudflow is the movement of a large mass of unconsolidated rocks down the slope when saturated with water. It flows in semi liquid state. It is common in desert slopes, which are not protected by a cover of vegetation. This occurs, for instance, during a torrential storm when more rain falls than the soil can absorb.

Mud Flow

1. d) Avalanches. It is a sudden and catastrophic movement of a wide variety of materials down slope associated with snow. The movement can take a flow or sliding or falling form.

Avalanche

1. e) Land Slide.This is the rapid movement of surface rocks and soil down a steep slope such as a cliff face. It includes slumping and sliding of materials. During the movement, the block tilts and leaves holes. It is common in well jointed limestone rocks, shale or clays. The common forms of landslides are slump, debris slide, rock slide, rock fall, debris fall and avalanche.

Land Slide

1. f) Rock Fall. This is the free-falling of a single mass of rock, common on steep slopes of mountains and along scarp slopes of the sea. This is the most rapid of all mass movements. If a rock fall occurs repeatedly, for a long time, the broken rocks collect at the bottom of the slope in a mound called talus.

Rock Fall

The Factors which Cause Mass Wasting

Mass wasting is caused by a number of factors which include the following:

1. Gradient or slope: When the gravitational force acting on a slope exceeds its resisting force, slope failure (mass wasting) occurs. Mass wasting is very common and severe in areas with steep lands as compared to flat or moderately flat lands.

2. Weathering: weathering processes weaken and loosen the rock, hence accelerating the process of mass wasting. For example, oxidation of metallic elements and hydration of the minerals in rocks create lines of fracture and, consequently, the onset of mass wasting.

3. Amount of water present in the rocks: Water can increase or decrease the stability of a slope depending on the amount present. Small amounts of water can strengthen soils because the surface tension of water increases soil cohesion. This allows the soil to resist erosion better than if it were dry. If too much water is present the water acts as lubricating agent, reducing friction, and accelerating the erosion process, resulting in different types of mass wasting (i.e. mudflows, landslides, etc.)

4. Vegetation: The roots of plants help bind the soil particles together making the soil resistant to agents of erosion and weathering. This makes the soil hard to break and hence resistant. Mass wasting processes, such as soil creep, cannot occur easily in soils well-covered with vegetation. Also the mass of vegetation cover blocks and prevents movement of the eroded material. Plants remove water from the ground through absorption. There for absence of vegetation accelerates mass

wasting.

5. The nature or type of the rock materials: Clay soil is compact and resistant to various types of soil erosion agents and mass wasting as compared to sandy soil, which is normally loose and easy to remove and transport by water, gravity, wind, etc. Thus, mass wasting may be more severe on sandy soil than its counterpart clay soil under similar prevailing conditions.

6. Overloading: When the soil accumulates in one location as a heavy mass of the rock material, it can be moved either by action of gravitational force or application of just a little force. Landslides occur as a result of the soil accumulated on a sloping land to an extent of exceeding the resistant force of gravity. Movement occurs when the gravitational force exceeds the resistant force of soil material.

7. Earthquakes: Earthquakes cause sections of the mountains and hills to break off and slide down. Earthquake tremors tend to loosen the soil material and make it easy to be removed and transported. It can accelerate rock falls, landslides and soil creeps.

8. Human activities: The activities of man such as cultivation, burning, mining, transportation, animal grazing, etc, removes the soil cover or leads to shaking of the soil.

9. Climate: Climate has a great influence on mass wasting. Areas that receive heavy rains often experience mass movements, such as landslides and soil creep, more often compared to dry areas. On the other hand, a little amount of rainfall does not wet the soil and so cannot cause the soil to move. In cold regions, alternate freezing and thawing triggers mass wasting.

10. Vulcanicity: Volcanic activity often causes huge mudflows when the icy cover of a volcano melts and mixes with the soil to form mud as the magma in the volcano stirs preceding an eruption.

Mass Wasting caused by Erupting Volcano

The Effects of Mass Wasting to the Environment

1. Formation of scars and bare land: When a large mass of soil moves, such as it occurs in landslide, the process leaves behind a large portion of eroded, bare and unproductive land. This land is often not easily colonized by plants, a fact which stimulates further erosion on the bare scar. Scars are very common on slopes of mountains such as mounts Kilimanjaro, Kenya and Rwenzori.

2. Soil erosion: When mass movement takes place, the load often removes almost all the vegetation on its way. This exposes the land to agents of erosion such as wind, animals, water, ice, waves, etc. Also the place from which the material has been removed forms a scar upon which water, ice and other agents of erosion can act and remove the soil, further leading to gullies, depressions and gorges.

3. Formation of new landforms: The materials removed and transported to a distant location may form hills at their destination and form scars and depressions at the place of origin.

4. Formation of lakes: Materials of landslide can block ariver bedand valley, preventing downward movement of water. The blocked water accumulates on the upper side of a river valley to form a lake. Examples of such lakes include Lake Bujukuin theRwenzori Mountains, Nyabihoho in Uganda and Funduziin South Africa. Lake San Cristobal in Colorado, USA, was formed when mudflow dammed (blocked) a river in the San Juan Mountains.

5. Diversion of a river course: The landslide material can block the natural river bed, forcing the river to divert and form a new route. This makes the river leave its usual flowing course, and form a new course. The direction of flow of the river is thus changed. This happened in the Rif Atlas Mountains of Morocco in 1963 when a mudflow pushed the course of RiverRhesana100 metres to the east.

6. Formation of a fertile soil: If the removed material comes from a fertile land, it can form a fertile soil at the place of destination, where fertile soil never existed, and encourage agricultural activities to take place.

7. Damage to property: Different categories of landslides may cause various damages to property and can adversely affect other resources. The effects of landslide are dangerous because they destroy everything in their path. Roads are blocked, hampering traffic flow. Homes, buildings and other infrastructures are destroyed. The water mains, sewers and power transmission lines are disrupted. Oil and gas production and transportation facilities are ruined. Farms are also destroyed by various forms of mass wasting.

8. Loss of life: The more populations expand and occupy more and more of the land surface, mass movement processes become more likely to affect humans.

RIVER AND RIVER SYSTEMS

River refers to a mass of water flowing through a definite channel over a landscape from river source to river mouth. River source is the place where a river starts. It may be in the melt water from glacier e.g. river Rhome (France), a lake, e.g. Lake Victoria, the source of river Nile, a spring e.g. Thames (England) or it can be formed following steady rainfall e.g. river Congo. River mouth can be anywhere a river pours its water, e.g. a lake, ocean or sea. 

 River

How Agents of Erosion and Deposition Operate on the Landscape

The river has three functions as it flows through its channel. These are river erosion, transportation and deposition.

1. RIVER EROSION

Erosion of a river operates in three ways, that is, head ward, vertical and lateral erosions.

1. a) Head ward erosion – this is the cutting back of the river at its source. It is through this erosion that a river increases its length.

1. b) Vertical erosion – this is erosion by which a river deepens its channel.

1. c) Lateral erosion – This is the wearing away of the sides of a river by water and its load. It is responsible for widening of a river valley.

River erosion involves four related processes. These are abrasion (corrasion), attrition, corrosion (solution) and hydraulic action.

1. Hydraulic Action: This is the process whereby the force of moving water plucks and sweeps away loose materials, such as silt, gravel and pebbles. Materials plucked by hydraulic action are responsible for bank caving and slumping.

2. Corrasion(abrasion): This is when the load of the river rubs against the bed and sides of the river channel. This causes wearing away of the sides and bed of the river. The amount of load determines the nature of erosive power and rate of erosion. This is a source of pot holes in the river bed.

3. Attrition: This is when the rock fragments in a river’s load are broken into small fragments due to collision against one another as the load is carried downstream along the river channel. As the river moves along its course, its fragments get progressively smaller because of disintegration and wearing away.

4. Corrosion(solution): River water dissolves certain minerals leading to dissolution and disappearance of some rocks, e.g. limestone, rock salt and chalk.

River Erosion

2. 
   RIVER TRANSPORT

This is the process which involves carrying away of the weathered and eroded, loose materials from one place to another. The materials carried out by river is called load. River transports its load in four ways:

1. Saltation – this is the process in which small pieces of the rock fragments are carried by a river while bouncing on the river bed.

2. Traction – this is the dragging or rolling of large boulder such as pebbles along its river bed.

3. Suspension – This involves transport of fine or light materials like silt and mud, which are carried in suspension forms. This is common when the river flow is too strong.

4. Solution – this involves moving some materials that dissolve in water, which are carried away in solution form. A river transports its load until it has insufficient energy to transport it any further.When this happens, the load is deposited.

River Transport

3. 
   RIVER DEPOSITION

A river deposits its load when its volume and speed decrease.

1. a) A river volume decreases when:
2. It enters an arid region especially a hot desert;
3. it crosses a region composed of a porous rocks e.g. sand and limestone; and
4. During the dry seasons or in a period of drought.

1. b) A river speed decreases when:
2. it enters a lake or sea; or
3. when it enters flat or gently slopping plain such as a valley bottom.

Deposition takes place when the river has insufficient energy to carry its entire load. The first part of the load that is dropped consists of boulders and pebbles. The last part to be dropped is the fine sediment, called silt. Deposition takes place at any point in a river’s course.

 River Deposition

THE LONG PROFILE OF A RIVER

The long profile of a river is the line following the course of a river from its source to its mouth. Three courses or sections of a river can be distinguished.

These are:

1. The upper course.
2. The middle course.
3. The lower course.

Long Profile of the River

1. THE UPPER COURSE

This is the first stage of a river. It is sometimes called the youth or torrent course.

Its characteristics are as follows:

1. It is the river source.
2. The speed of a river is high.
3. Most of the works of the river include vertical erosion.
4. The cross-section of a river valley in this section of a river is V–shaped.
5. The slope of a profile is very steep.
6. It is sometimes utilized for hydroelectric power (H.E.P) generation. Erosional and

Upper Course of the River

Depositional Features for Each Agent

The main features of the upper section are deep and narrow, V-shaped valley; a steep gradient; pot holes on the river bed; interlocking spurs and waterfalls and rapids, often with plunge pools.

1. V–shaped valley: this is a deep, narrow valley at youth/first stage of a river.

2. Pot holes: These are circular depressions on the river bed. They are formed when pebbles carried by the swirling water cut circular depressions in the river’s bed.

3. Interlocking spurs: An interlocking spur, also known as an overlapping spur, is one of any of a number of projecting ridges that extend alternately from the opposite sides of the wall of a young, V-shaped valley down which a river with a winding course flows.

Each of these spurs extends laterally into a concave bend of the river such that when viewed either upstream or from overhead, the projecting ridges, which are called spurs, appear to “interlock” or “overlap” in a staggered formation like the teeth of a zipper. As the river erodes the landscape in the upper course, it winds and bends to avoid areas of hard rock. This creates interlocking spurs. Waterfalls and rapids:

4. Waterfall: A waterfall is a place where water flows over a vertical drop in the course of a stream or river. A waterfall is formed when there is sudden change or drop in the bed of a river. Although waterfalls can occur in almost any part of a river’s course, they are most common in the upper course. Examples of waterfalls are Owen Falls in Uganda, Victoria Falls in Zimbabwe and The Livingstone

5. Rapids: These are sections of a river where the river bed has a relatively steep gradient, causing an increase in water velocity and turbulence. Rapids are characterised by the river becoming shallower with some rocks exposed above the flow surface. As flowing water splashes over and around the rocks, air bubbles become mixed in with it and portions of the surface acquire a white colour, forming what is called “whitewater”. Rapids occur where the bed material is highly resistant to the erosive power of the stream in comparison with the bed downstream. Very young streams flowing across solid rock may be rapids for much of their length.

6. Plunge Pool: This is a large depression formed at the base of a waterfall.

7. Gorge: It is a steep, narrow and elongated valley. A gorge often is formed when a waterfall retreats upstream, e.g. a gorge found in Victoria Falls.

Upper Course of the River

2. THE MIDDLE / MATURITY STAGE

This is the second stage of a river. The main features of this section are bluffs and waterfalls and rapids.

The Characteristics Features of the Middle Course of a River Valley

1. The speed of a river is fairly low.
2. Most of the work of a river is transportation.
3. The cross–section of a valley in this section is an open V.
4. The slope of a relief is gentle
5. The volume of a river increases.
6. Lateral erosion predominates.

Middle Course of the River

Features Associated with the Middle course of a River Valley

1. Bluffs: These are steep slopes of the truncated spurs in middle course where interlocking spurs turn into bluffs.

2. Waterfalls and rapids: Waterfalls and rapids can also be found in the middle stage of the river valley. This is mainly caused by river rejuvenation which increases erosive activity and transportation, hence development of waterfalls.

3. 
   THE OLD /LOWER STAGE

Third is the third stage of a river. The main features of the lower section of a river valley are a flood plain; braided river; ox-bow lake; levee and deferred tributary and delta.

Characteristics of Lower Stage

1. It is the river mouth.
2. Always there are gradient falls or slope falls.

3. The main work of a river is deposition.
4. The cross–section of a valley is a U–shaped valley.

5. The speed of a river is decreased.
6. The river valley is very wide.

Lower Course of the River

The Importance of Erosional and Depositional Features to Human Beings

1. Loess form very fertile soil in desert land,
2. Water falls attract tourists; headlands in coastal areas are natural ports.
3. Coastal features form breeding places for fish,
4. Coral reefs are used as building materials and for settlement.

ARTIFICIAL FORCES

These are forces that are caused by human beings through their activities such as farming, mining,

setting up settlements,  

road construction, transport, etc.

Man can influence in destruction or removal of some parts of the earth’s surface.

This shows that man can modify natural landforms and, therefore, acts as the agent of weathering,

mass wasting,

erosion,

transportation and

deposition on the earth’s surface.

Human modification of the land helps loosen large chunks of earth and cause them to slide downhill.

Man Produces Forces that Affect the Earth through the following Activities:

1. Removing vegetation: A slope with lots of vegetation is less susceptible to mass movement than a bare slope. Bare, exposed soil is very easily eroded, and can contribute to mass movement activity.

Vegetation: helps hold soil, loose rock, and regolith together by its roots; reduces the direct erosive impact of rainfall and other precipitation; actively reduces ground moisture by using it to contribute to plant growth; and produces litter and organic products (leaves, twigs, grasses, fruits) that help stabilize the soil.

2. Mining: In the course of mining, man uses machines to dig the soil and blast rocks. These activities results to earth tremors which loosen the soil particles making then vulnerable to removal by agents of weathering and denudation. Blasting also causes fractures in rocks, a fact which makes them less stable and resistant to shear and stress. If this happens, especially on steep slopes, the probability of occurring landslide is very high.

3. Farming activities: Farming involves digging the soil by using farm implements such as hoes, tractors, harrows, spades, etc. These activities involves breaking up the soil and rocks by the implements. In this way, crop cultivation directly leads to weathering and erosion.

Overstocking – (keeping many animals in just a small piece of land) also leads to soil erosion. This is because overstocking is usually accompanied with overgrazing, an act which removes the vegetation cover. This triggers soil erosion and other weathering processes.

4. Building and construction: Breaking up the soil for construction of houses and other

infrastructures can dramatically increase the potential of mass movement. These processes involve tearing rocks to get room for setting up infrastructures such as roads, railways, airports, seaports, etc. This leads to destruction of the soil, hence triggering mass movement, weathering and erosion.

5. Fishing: Fishermen in less developed countries sometimes use weapons such as dynamites to kill and catch fish. Tremors produced by these illegal fishing tools can cause fracturing of the coastal rocks. This causes both weathering and erosion.

6. Navigation: In some few cases, marine vessels accidentally crush onto stones in water, peeling or breaking then into pieces. This leads to rock disintegration, a typical form of weathering.

7. Transport: Vibrations from machinery, traffic, weight loading, stockpiling of rock or ore from waste piles and from buildings and other structures loosen the soil and make it prone to soil erosion and weathering.

9. Construction of dams and canals: Construction of dams, such as the Mtera dam in Tanzania and canals such as the Suez Canal in Egypt, involves removing a large junk of rock. This breaks up the soil, leading to weathering and soil erosion.
10. Warfare: The use of atomic bombs and other heavy weapons in war leads to destruction of the soil. During times of war, heavy and destructive weapons such as atomic bombs, shells, rockets and grenades are dropped or fired towards the enemy. When these weapons fall on land, they detonate and blow up a large mass of the earth, causing weathering and erosion. Military equipment such as tanks, heavy trucks and caterpillars break up rocks over which they pass. At the same time, they loosen the soil and carry away some of it as they move along.

 

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Mastering Biology Notes for Form Four is crucial for students who want to perform well in their exams and build a strong foundation for further studies in biological sciences. These topics provide essential knowledge for understanding the diversity of life and addressing global challenges such as health, the environment, and genetics. Whether you’re preparing for exams or considering a future in a biology-related field, these notes will provide valuable insights and information to guide your studies.