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CLIMATES

Average weather conditions of a given place over a long period of time usually 30-35 years.

Factors Influencing Climate Latitude

  • It influences temperature whereby low latitudes have high temperature and high latitudes have low temperature due to the angle at which the sun rays strike the earth and the distance travelled by the suns rays.
  • It also influences rainfall whereby places in the equator receive rainfall in two seasons when the sun is overhead there while northern and southern tropical areas receive rainfall when the position of the sun is overhead in those areas.

Inter-Tropical Convergence Zone

It’s a low pressure belt around equator where trade winds converge. It influences rainfall in the following ways:

  • Places further from equator experience one rainy season when the sun is overhead and a long dry season when the sun is in the S. hemisphere.
  • Regions near equator have 2 seasons of heavy rainfall because they experience passage of ITCZ twice.

Altitude

  • It influences temperature whereby at low altitude temperature is high while at high altitude its lower due to the thickness of atmosphere determining the number of particles to store heat and distance from space where terrestrial radiation is lost.
  • It also influences rainfall whereby mountains on the path of rain winds receive Orographic rainfall and the windward slopes receive heavier rainfall than leeward slopes.

Distance from the Sea

  • It influences temperature whereby places in temperate regions near the sea experience low temperature during summer onshore winds blowing over cold ocean water and taking the cooling influence on adjacent land because the water is heated at a slower rate than land.
  • Places near the sea also experience higher temperatures during the winter or cool season due to sea breezes carrying warmer air to the land because water loses heat at a slower rate than land.
  • Temperatures in the interior of continents tend to be high in summer and very low in winter due to lack of marine influence.
  • It also influences rainfall whereby coastal regions receive a lot of rain when the winds are onshore and the continental interiors receive less rain mainly in summer because onshore winds will have dropped most of moisture along the way.

Ocean Currents

  • It influences temperature whereby coasts which are washed by warm ocean currents are warmer while those washed by cold ocean currents are cooler due to the onshore winds being either warmed or cooled and then taking the warmth or coolness to the land.
  • It influences rainfall whereby coasts washed by warm ocean currents experience heavy rainfall when moist onshore winds are warmed by the current and made to hold on to moisture which they release on reaching the land.
  • The coasts washed by cold ocean currents on the other hand experience low rainfall as a result of moist winds being cooled and moisture in them condensed resulting in rain falling over the ocean thereby bringing little or no rain to the coastal areas. This is the cause of western margin deserts e.g. Kalahari and Namib deserts.

Aspect

Direction of slope in relation to sunlight and the rain bearing winds. Its effect on temperature is more pronounced in the northern and southern hemisphere.

  • In the N and S hemispheres the slopes facing sun are warmer while those facing away are cooler.
  • The slopes in the direction of rain winds i.e. the windward slopes receive heavier relief rainfall than the leeward side.

Winds and Air Masses

Wind blowing from a warm region warms the region its passing over and if blowing from a cool region cools the region it’s passing over since wind is a medium of transfer of heat.

  • Sea breezes take cooling influence on land during hot afternoons.
  • Katabatic winds cause low night temperatures on valleys and foot of mountains.
  • Fohn and Chinook which are descending dry winds take dryness to the leeward sides of Alps and Rockies.

Winds influence rainfall in the following ways:

  • Anabatic winds cause afternoon showers on mountainous regions.
  • Moisture laden winds cause heavy rainfall.
  • Persistent dry winds cause desert like conditions in the area they pass over e.g. Harmattan winds from Sahara which blow over W. Africa.
  • Regions around large water bodies experience high rainfall because of the effect of land breezes.

Configuration of Coastline

Coastal regions across the path of moisture laden winds receive higher rainfall because winds deposit moisture on land e.g. Mombasa while those lying parallel to the path of those winds receive less rainfall because moisture is deposited on the sea e.g. Lamu.

Forests

Forested areas experience a micro climate whereby:

  • Temperature is lower due to shades of trees reducing solar insolation reaching the ground.
  • Rainfall is heavier due to high rate of evapotranspiration and friction between trees and rain bearing winds.

Human Activities

  • Man has caused deforestation in the process of creating room for settlement and agriculture which has caused drop in rainfall amounts leading to semi-arid conditions.
  • Man has constructed dams across rivers and done afforestation which has caused semi-arid regions to become wetland.
  • Gases especially co2 emitted from burning fossil fuels and chlorofluorocarbons layer cause global warming through the green house effect and destruction of ozone layer respectively.

Modified Equatorial Climate

Experienced along the coast and along the coast from Somali-Tanzanian border and L. Victoria basin regions around the lake.

Along the Coast

Characteristics

  • High temperatures throughout the year mean annual about 27◦c.
  • Small mean annual range of temperature about 4◦c.
  • Hottest months are December and January.
  • Experiences rainfall throughout the year/ no real dry season.
  • Double maxima rainfall regime (2 rain seasons) in May and October.
  • High humidity due to high temperature causing high rates of evaporation and nearness to the sea.
  1. Victoria Basin

Characteristics

  • Temperature is lower than the truly equatorial climate due to modifying influence of the lake (mean annual range between 22-26◦c).
  • There are no real dry months.
  • Heavy rainfall ranging from 1000-600mm.
  • Double maxima rainfall regime.
  • Receives convectional type of rainfall which falls mainly in the afternoons.
  • High relative humidity due to high temperature and nearness to the lake which is a source of moisture.

Modified Tropical Climate

Experienced in central highlands E and W of R. Valley.

Characteristics

  • Mean annual temperatures averages between 17-24◦c.
  • Lower warmer slopes and cooler higher slopes due to modification by altitude.
  • Receives rainfall throughout the year (1000-2000mm).
  • Receives Orographic rainfall caused by S.E Trade Winds.
  • Double maxima rainfall regime in eastern highlands and single maximum in the W. highlands.
  • Humidity is moderate.

Tropical Continental/desert Climate

Experienced in about ½ of Kenya in most of N, N.E, most of E and S Kenya.

Characteristics

  • High temperatures throughout the year with mean between22 and 27◦c.
  • Generally dry with less than 500mm of unreliable rainfall.
  • Large diurnal range of temperature.
  • The skies are generally clear.
  • Low humidity.
  • Temperature has been modified by relief in some areas e.g. Voi-25◦c and Garissa -28.5◦c.

Tropical Climate

Experienced in Narok, S. Taita and Kwale region.

Characteristics

  • High temperatures (mean annual temp-16.5◦c).
  • Temperature is modified by relief in some areas e.g. Loita, Taita and Narok which has made the place suitable for human habitation.
  • Generally low rainfall amounts.
  • Rain falls in one season.
  • A long dry season lasting up to 6 months.

Tropical Northern Climate

experienced in a small area in the N. W part of Kenya bordering Uganda.

Characteristics 

  • High average temperatures.
  • Temperatures are modified in some places by altitude.
  • Low mean annual rainfall of about 850mm.
  • Rain falls mainly in June and September.
  • Experiences a long dry season of up to 6 months.

Desert Climate

Experienced in central northern Kenya where there are pure deserts such as Chalbi, Karoli and Kaisut deserts.

Characteristics

  • Temperatures are very high throughout the year averaging 30◦c due to cloudless skies.
  • Very low rainfall of less than 250mm per year.
  • Characterised by diverging or descending winds which don’t bring any rain.
  • Night temperatures are extremely low.
  • Humidity is low.
  • Sandstorms are common occurrences.

World Climatic Regions Classifications

  1. Hot climates
  2. Warm climates
  3. Cool climates
  4. very cold climates
  5. Mountain climates
  6. micro/local climates

Hot/Tropical Climates

Experienced within the tropical latitudes.

Subdivided into:

  • Equatorial climate
  • Tropical monsoon climate
  • Savannah climate/Sudan type
  • Tropical desert climate
  • Tropical marine climate

Equatorial climate 

Experienced in the following areas:

  • Amazon basin in S. America.
  • Along west coast of Africa from guinea to Cote d’ Ivoire.
  • Southern part of Nigeria through Cameroon, Gabon, Central African Republic, Congo to Zaire.
  • E Asia in Malaysia, Indonesia and a stretch between Burma and Vietnam.

Characteristics

  • High temperatures throughout the year (between 24-27◦c).
  • Temperature neither rises nor drops too low due to thick cloud cover all year round.
  • Heavy rainfall throughout the year (mean annual of about 2000mm).
  • Double maxima rainfall regime.
  • Experiences convectional rainfall in low lands and relief rainfall in areas of high relief.
  • High relative humidity of over 80% due to convergence of moist air masses and high evapotranspiration rates.
  • Low pressure all year round.
  • There are no seasons.

Tropical Monsoon Climate

It’s found in the following areas:

  • E Asia in parts of Pakistan, India, Bangladesh, S. china and Philippines.
  • Along the northern coastal region of Australia.

Characteristics

  • High mean annual temperatures of about 28◦c.
  • Seasonal reversal of winds.
  • Heavy rainfall when monsoon winds are onshore (600-1300mm) climate.
  • Rain falls in a few months and the rest of the year is dry due to influence of latitude.
  • Low pressure in summer when winds blow onshore.
  • High pressure in summer when winds blow offshore.
  • Cloudy skies in summer and clear skies in winter.

Tropical Marine Climate

It’s found on windward slopes of islands and coastal areas on the east of continents under the influence of S.E Trade Winds in the following areas:

  • America in S. Mexico through Guatemala, Nikaragua and Panama.
  • coast of S. America.
  • Caribbean islands of Cuba, Haiti and Jamaica.
  • Coastlands of E. Africa from Kenya, Tanzania through Mozambique and E. Malagasy.

Characteristics

  • Summer temperatures are very high approximately 30◦c.
  • High rainfall totals in summer when winds are onshore (10002000mm).
  • Orographic and convectional rainfall in summer.
  • Dry winters due to winds being offshore.
  • High humidity due to coastal location.
  • Experiences tropical cyclones towards end of hot season.
  • Winters are cool (about 21◦c).

Tropical Continental/Savanna/ Sudan type

The largest natural climatic region in Africa.

It’s found in the following areas:

  • In Africa it extends from Senegal through E. Africa to the northern part of s. Africa.
  • Western Madagascar.
  • A broad belt in N. Australia.
  • W and S.E of Amazon Basin called Llanos and Campos.

Characteristics

  • Higher temperatures of up to 32◦in hot season.
  • Large diurnal range of temperature in dry season.
  • Convectional rainfall in summer averaging 765mm annually.
  • High humidity during the hot wet season.
  • Low humidity in cooler drier months.
  • Prevailing winds are mainly trade winds.

Types of deserts 

Erg – Sandy deserts with large amounts of deposited sand.

Hamada – Rocky deserts made of bare surfaces.

  • Reg – Rocky deserts covered with angular pebbles, gravels and boulders.
  • Hot continental interior deserts found on the interior of continents on the leeward sides of high mountains e.g. Sahara and Arabian Desert. o Coastal deserts of western margins characterised by offshore trade winds and cold ocean currents e.g. Atacama of S. America, Namib in Namibia and Arizona in U.S.A. o Mid latitude deserts of continental interiors with high summer and low winter like Gobi in C. Asia.

Ice and snow deserts of polar lands like Greenland and Antarctica desert.

Tropical Desert Climate

Found on the western coasts of continents washed by cold ocean currents.

They are the following:

  • Arabian Desert of the middle East
  • Sahara, Kalahari and Namib deserts in Africa.
  • Atacama Desert in S. America.

Mohave and Colorado deserts of U.S.A. and Mexican deserts in N and C America.

  • Jordan, Syria, Iran, Iraq, Saudi Arabia, Israel and Afghanistan.
  • The great Australian desert in the greater western part of the continent.

Characteristics

  • High temperatures during the day and very low temperatures during the night due to high terrestrial radiation. o Large diurnal range of temperature. o Clear/ cloudless skies. o Receives less than 250mm of rainfall annually.
  • Rainfall is localised, short and torrential and accompanied by storms which cause flash floods.
  • Rain falls for a short period and the rest of the year or even several years are dry.
  • High wind velocity due to little frictional force. o Some areas experience temperatures below zero in winter with ice forming on the oasis.
  • Humidity is low and evaporation rate is high. o Sand storms are very common i.e. sand being blown through the air by the wind.

Warm Climates

They border tropical climates and they experience moderate temperatures lower than of tropical climates.

They are situated in the zone of divergence of trade winds and westeries (subtropical high pressure belt).

Subdivided into:

  1. Warm temperate Western margin/Mediterranean Climate.
  2. Warm Temperate Interior/continental Climate.
  3. Warm temperate Eastern marginal Climate.
  4. Warm temperate Deserts.

Warm Temperate Western Margin -Also known as Mediterranean Climate.

Found on the western margin or sides of continents in the following areas.

  • Southern Europe and N. Africa in the lands bordering Mediterranean Sea.
  • W tip of Africa around Cape Town.
  • Central Chile in S America.
  • W and S Australia.

Characteristics

  • Hot summers with temperatures of about 21◦c.
  • Mild winters with temperatures of about 10◦c.
  • Characterised by hot and cold local winds called Mistral and Sirocco.
  • There is high sunshine duration and intensity in summer.
  • Experiences cyclonic rainfall in winter when westeries are onshore.
  • Rainfall decreases inland.
  • Summers are dry due to trade winds blowing offshore.
  • There are distinct seasons i.e. summer, autumn, winter and spring.

Warm temperate Interior Climate

Also called Steppe Type.

It’s found in the interior of continents in the following areas (grasslands):

  • Steppe Land of U.S.S.R.
  • Veldt of S Africa.
  • Prairie lands of Canada and U.S.A.
  • Pampas lands of Argentina.
  • Downs of Australia.

Characteristics

  • Warm short temperatures between 18-21◦c.
  • Long winters with extremely low temperatures due to continentality which can fall up to -20◦c.
  • Precipitation is received all the year round.
  • Most rainfall is received in summer and snow precipitation in winter.
  • Rainfall is moderate with annual mean of 500mm.
  • Summer rainfall is caused by convection and depressions.
  • There is high humidity in summer.

Warm temperate Eastern Margin climate

Also known as China Type.

It’s experienced on the eastern margins of continents in the following areas.

  • S.E China and S. Japan.
  • E Australia.
  • S and S.E states of U.S.A.
  • America in S. Brazil, Uruguay, E. Paraguay and coast of Argentina.

Characteristics

  • Hot summers with a mean annual of about 26◦c.
  • Mild to cool winters due to marine influence and local winds (4- 13◦c).
  • Receives rainfall throughout the year (about 1000mm).experiences hurricanes and typhoons.
  • Convectional rainfall is common in summer.
  • Rainfall is moderate between 760 and1500mm.

Warm Temperate Deserts -Also known as Mid-Latitude Desert climate.

It’s experienced in the following areas:

  1. Nevada and Utah states of U.S.A.
  2. Pentagonia in S. America.
  3. Gobi Desert extensive desert area of southern Mongolia and northern China and the largest desert in Asia.
  4. Turkey, Turkmenistan, Uzbekistan and Kazakhstan.

Characteristics

  • High summer temperatures (27-37◦c).
  • Cold winters as low as -7◦c.
  • Very large diurnal and annual ranges of temperature.
  • Low and unreliable rainfall due to great distance from the sea about 250 mm annually.
  • Most rainfall falls in late winter or early spring.

Cool Climates

They differ from warm climates by having definite seasonal variations in temperature. Subdivided into:

  1. Cool Temperate Western Margin
  2. Cool Temperate Continental Interior
  3. Cool Temperate Eastern Margin

Cool Temperate Western Margin Climate

Also known as British Type. It’s under coastal influence.

Found in the following areas:

  • British Isles (Island)
  • Central and N.W Europe
  • W U.S.A. and British Columbia in Canada.
  • Chile
  • Tasmania in Australia

Characteristics

  • Warm summers (13-15◦c).
  • Cool winters (2-7◦c).
  • Small temperature range.
  • Well distributed rainfall throughout the year (760-2000mm).
  • Cyclonic rainfall in the coastal lands and relief rainfall in mountainous areas.
  • High humidity in winters.
  • Long summer days with irregular thunderstorms.
  • Convergence of sub-tropical and polar air masses.
  • Onshore westerly winds are dominant.

Cool Temperate Continental Interior Climate

Also called Siberian type.

Found in the following areas:

  • Alaska and most of Canada
  • Eurasia covering Sweden, Finland, Poland, Germany, across former U.S.S.R. up to Kamchatka Peninsular in the east.

Characteristics

  • Warm summers with temperatures of about 18◦c.
  •  Generally short summers.
  • Extremely cold winter temperatures which go below 20◦c.
  • Long winters with long nights.
  • Precipitation is mainly in form of snow during winter (annual precipitation 400-500mm).
  • Convectional rainfall in summer is accompanied by thunderstorms. Cool Temperate Western Margin Climate It’s also known as Laurentian Type. Areas:
  • U.S.A. and S Canada.
  • Argentina.
  • N & S Korea, N. China, C and N Japan and E. Siberia.

Characteristics

Long warm summers with temperatures of about 18◦c.

Cold winters (-40-0◦c).

Precipitation all year round (600-1000mm).

Snow precipitation in winter.

High humidity in summer.

Cold Climates

Also known as Polar Desert Climates or Arctic and Antarctic Climates.

Found beyond Arctic Circle i.e. 66 ½◦N and S of equator. -Classified into Tundra and Polar Climates.

Tundra Climate Areas:

  • Coast of N. America bordering Arctic Ocean.
  • N part of America from Alaska through Canada to Greenland.
  • From N coast of Scandinavia to the N.E of Russia.
  • Baffin Island.

Characteristics

  • Short cool summers with average temperatures of about 10◦c.  Long cold winters (-29 – -40◦c).
  • Continuous days in winter and summer for several days.
  • Low annual precipitation of about 250mm.
  • Precipitation in form of rain and snow in winter.

Polar Climate

experienced at the poles in the interior of Iceland, Green land and Antarctica.

Characteristics

Temperature is permanently below freezing point.

There is permanent snow cover and ice on the ground (permafrost).

Snow storms (blizzards) are common.

  • Continuous winter nights and summer days with exception of equinox when sun rises above horizon.

Mountain Climates

Experienced on high mountain ranges of the world.

Areas:

  1. Kenya (5199)
  2. Ruwenzori (5109)
  3. Kilimanjaro (5895)
  4. Everest (8848)
  5. Atlas mountains in Africa
  6. Rockies of N. America
  7. Alps of Europe
  8. Himalayas in Asia

Characteristics

  • Temperature decreases with increasing altitude.
  • Temperature ranges from cool to cold.
  • Experiences Orographic rainfall.
  • Rainfall increases with altitude up to 3000mm and starts to decrease because air is cold and hence has poor capacity to hold moisture.
  • Windward slopes are wetter than leeward slopes.
  • Atmospheric pressure decreases with increasing altitude.
  • Local winds are common and blow up the slope during the day and down slope at night.
  • In temperate regions slopes facing the equator are warmer than those facing the poles.
  • Atlas mountains in Africa
  • Rockies of N. America
  • Alps of Europe
  • Himalayas in Asia

Local/Micro Climates

Climate experienced within a small area which is slightly different compared to the general climate of the area.

It occurs on the immediate surroundings and within some phenomenon on the earth’s surface.

Micro-climates can be found in the following areas:

Within and around a forest

  • Experience low temperatures due to trees preventing solar insolation from reaching the ground.
  • Experiences high rainfall due to high rates of evapotranspiration.

Urban areas

  • Higher temperatures due to green house effect (situation where atmospheric gases absorb heat that is given off by the earth (terrestrial radiation) before its sent back to space causing the temperature of the lower atmosphere to increase.

Around man made lakes

  • Experience high convectional rainfall due to high moisture content.
  • Around natural lakes experiences land breezes which cause early morning showers and sea breezes which lower temperatures during the hot season.

Aridity and Desertification

Aridity-state of land being deficient of moisture leading to little or no vegetation.

Desertification-process in which desert like conditions slowly and steadily encroach on formerly productive agricultural land.

Causes of Aridity and Desertification

  1. Low and unreliable rainfall below 250mm per annum causing little or no vegetation and absence of animal and biological life causing soil forming processes to be incomplete.
  2. High temperatures which cause high rates of evaporation which exceed evaporation or low temperatures which reduces air capacity to hold moisture causing a place to receive little or no rain..
  3. Where a place is washed by ocean currents causing moist onshore winds to cool and then drop moisture over the sea and reach the land as dry winds e.g. Kalahari when onshore westeries cross the cold Benguela Current.
  4. Where relief barriers such as hills or mountains cause some areas to lie on the rain shadow hence rain winds drop most of their moisture on the windward side and they drop on the leeward side, are warmed and hold onto moisture causing dry conditions e.g. Kalahari and Namib on the rain shadow of Drakensberg mountains.
  5. Location of some places very far from the sea causing them to be far removed from wet onshore winds e.g. Gobi Desert.
  6. Where hot dry winds blow over a region causing drying effect on land e.g. Harmattan over West Africa.
  7. Where cool air descends causing no rain because cool air has to rise before condensation takes place.

Human Activities

  • When people clear forests which causes runoff to exceed infiltration which interferes with the water cycle.
  • Keeping large number of animals which exceed the carrying capacity of land they eat vegetation leaving the land bear exposing the land to soil erosion.
  • Poor agricultural practices such as overcultivation, monoculture and slashing and burning which lead to soil erosion.
  • Industrialisation which releases green house gases such as co2 to the atmosphere which absorb more heat making the earths temperature to rise.
  • Reclamation of water logged areas which lowers the water table causing arid conditions to set in plants when plants can’t access ground water.
  • Poor irrigation methods when evaporation takes place and salt from below are brought to the surface and are deposited on the top soil making the soil salty and hence unable to support plants.

Effects of Aridity and Desertification

  1. Infertile soils which support little or no vegetation.
  2. Low agricultural production due to insufficient rainfall leading to famine.
  3. Shortage of water for domestic and industrial use which may also lead to shutting down of my sons.
  4. Migration of people from areas affected by aridity and desertification leading to population pressure and eventually conflicts.
  5. Destruction of vegetation which exposes land to soil erosion.
  6. Can lead to extinction of some plants and animal species causing loss of biodiversity.

Solutions to Aridity and Desertification

  1. Afforestation and reafforestation because trees protect soil from erosion, increase run off and release moisture to the atmosphere leading to increased rainfall.
  2. Adopting soil conservation measures such as terracing, contour ploughing, planting cover crops etc.
  3. Rearing a number of animals which is proportional to the carrying capacity of land.
  4. Irrigating dry lands.
  5. Introduction of energy saving stoves to reduce demand for wood fuel which will reduce deforestation.
  6. Use of alternative sources of energy which don’t pollute the environment e.g. solar and water.
  7. Introducing drought resistant crops in the arid areas.
  8. Controlling industrialisation by setting laws governing pollution.

Climate Change -Establishment of a new climatic state.

Continuous changes in climatic states such as temperature and precipitation over time.

Causes of Climate Change

Natural Causes

  1. Variations in the Earths Orbital Characteristics

Changing or earths orbital characteristics within 1000 years from elliptical (aphelion) to nearly circular (perihelion) when the earth is nearest to the sun and  receives maximum solar energy and back to elliptical when the earth is farthest from the sun and receives least solar energy.

  1. Variation in the Atmospheric Carbon Dioxide -When natural rise in temperature cause carbon dioxide held up in cold ocean waters to be released to the atmosphere after oceans warmed.
  2. Volcanic Eruptions
  • When large quantities of volcanic ash and dust thrown out of the ground block some of the solar insolation from reaching the earths surface causing temperatures on the earths surface to drop for a short period.
  • When sulphur dioxide given off during volcanic eruptions reacts with water vapour forming a bright layer within stratosphere reducing the amount of solar radiation reaching the surface by reflecting some of it back which also lowers temperatures on the surface.

4. Variation in Solar Output

changes in the amount of solar energy given off by the sun whereby at times its less causing drop of temperature on the earths surface and at others its gives off more causing rise in temperature on the surface.

Human Causes

  1. Burning of fossil fuels in industries, transportation, electricity generation etc. which contributes 65% of additional co2 in the atmosphere which is the main green house gas.
  2. Burning of vegetation e.g. in shifting cultivation and forest fires which also adds co2 in the atmosphere.
  3. Clearing large tracts of forests foe agriculture, settlement etc. which reduces the main deposal system for co2 from the atmosphere by photosynthesis.
  4. industrial developments which add gases like methane, nitrous oxide and those containing chlorine and chlorofluorocarbons which damages ozone layer which filters a greater percentage of ultra violet radiation given off by the sun which causes the average temperatures on the earth to rise.

Consequences of Climate Change

  1. Global warming due to green house effect by gases added in to the atmosphere and destruction of ozone layer.
  2. Increased rainfall as a result of high temperatures causing high rates of evaporation causing wet areas to become wetter and dry areas to become drier.
  3. Effect on agriculture by causing crop growing areas to shift to cooler altitudes and latitudes e.g. wheat growing areas of Canada shifting to the poles and causing dropping or failure of crop yields in area where temperatures have increased.
  4. Water shortage when climate becomes drier causing less water to infiltrate underground and hence less water to feed rivers.
  5. Submergence of coastal areas causing flooding when Antarctic and Arctic glaciers melt and water is added to the oceans.
  6. Heat waves due to increased temperature which leads to death of people.
  7. Receding and disappearance of ice caps on mountains e.g. Mt. Ruwenzori.
  8. Abnormal growth of plants due to increased amounts of co2 causing increased rate of photosynthesis which may lead to increased yields of major crops, poor soils due to soils having to sustain high rates of plant growth.
  9. increased levels of ultra violet radiation which causes human diseases such as skin cancer, lowering crop production by slowing photosynthesis and germination, lowering fish population by damaging plankton which fish eats and degradation of paint and plastics.

Solution to Climate Change

  • Afforestation and reafforestation.
  • Use of energy saving stoves to reduce the rate of deforestation.
  • Use of alternative sources of energy which are environmentally friendly e.g. solar and water instead of fossil fuels.
  • Proper maintenance of vehicle to reduce emissions from their exhausts.
  • Use of public transport to reduce the amount of fossil fuel used and hence the amount of co2 added into the atmosphere.
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PHOTOGRAPH WORK

A photograph is an image of an object, person or scene recorded by a camera on a light sensitive film or paper.

Types of Photographs 

1. Ground Photographs -Taken from the ground.

They are of 2 types:

Ground Horizontals- taken with the camera at the same level as the object. They are of 2 types.

Ground close ups/particular view photographs-taken from the ground with a camera focused on one particular object.

Ground General View Photographs-taken from the ground with camera focused on general scenery.

Ground Obliques-taken from the ground with a camera slanting/held at an angle.

2. Aerial Photographs

Taken from the air e.g. from aircrafts, balloons or satellites. They are of 2 types:

Aerial Obliques-taken from the air with camera tilted towards the ground.

Vertical Aerial Photographs-taken from the air with the camera directly above the object or scenery.

Uses of Photographs

Used in learning geography because they bring unfamiliar features in the classroom enabling the students to understand them better.

Photographs showing vegetation and human activities can be used to deduce the climate of an area.

Aerial photographs show vital information on land use.

Photographs showing land forming processes help us to understand those processes.

Limitations in the Use of Photographs

Coloured photographs are generally expensive to produce.

Black and white photographs don’t show the real colours of objects or scenery e.g. it’s difficult to distinguish ripe coffee berries from green ones.

Some aerial photographs have objects which are far away and hence unclear which may lead to the wrong interpretation.

Vertical aerial photographs are difficult to interpret without special instruments like stereoscopes.

Photographs are difficult to interpret if they are brulled because it’s difficult to distinguish objects which look similar e.g. wheat and barley.

Interpretation of Photographs

Means to explain the meaning of the objects or features on a photograph. It involves the following:

Determining the Title

Photographs show human activities, physical features, natural catastrophes etc e.g. nomadic pastoralism, drought, flooding, etc. when determining the title  examine the photograph carefully and apply the knowledge you have learnt in geography.

Estimating Time

In the tropics the shadows are short at noon and longest in the morning and afternoon.

If the camera is facing south and the shadow is cast to the right it’s in the morning and if cast to the left it’s in the afternoon.

Estimating Season

Dry season

Bright clear skies

Dry vegetation harvesting

Light clothes e.g. shirts and T-shirts since temperature is high (also an indication of high temperature.

Rainy season

Rain clouds

Luxuriant vegetation

Young crops

Flowering plants

Weeding

Heavy clothing e.g. pullovers or jackets since temps are low (also an indication of cool season).

Determining Compass Direction

It it’s in the morning and the shadow of flag pole is cast to the left the photographer is facing north and if cast to the right he was facing south.

It it’s in the morning and the shadow is facing towards you the photographer was facing east and it taken in the afternoon and the shadow is facing towards you the photographer was facing west.

Interpretation of Physical Features on Photographs Relief

Flat land

  • Rice crop
  • Irrigation
  • Combine harvesters
  • Swamps
  • Meanders
  • Oxbow lakes
  • Inselbergs (isolated hills)

Hilly/Mountainous landscape/Highland Area

Steep slopes

Terraced landscape

Tea, wheat crops which grow at high altitude rapids

Water falls Interlocking spurs

Drainage

Youthful Stage

Rapids

Waterfalls  

Interlocking spurs

Middle Stage

meanders

oxbow lakes

Lower Stage

  • deltas
  • distributaries
  • meanders and oxbow lakes
  • flood plain

Vegetation

Natural

  • Indigenous species
  • Dense undergrowth
  • Trees grow haphazardly
  • Different species of trees
  • Not of the same height

Planted

  • Exotic species
  • In rows
  • Little undergrowth
  • Same species
  • Same heights

Tropical Rain Forests

  • Trees
  • Broad leaves
  • Umbrella shaped

Marshes

  • swamps

Savannah Grassland

  • Grass and short trees (woodland).

Desert Vegetation

  • Thorny leaves
  • Baobab and acacia
  • Scrub-land covered with shrubs and underdeveloped trees (shrubs).

Climate

High Temperatures and low rainfall

  • Sugar cane
  • Grass
  • Sisal
  • Scrub and bush land vegetation
  • Dense forests
  • Light clothes

Cool Temperature and High rainfall (Sufficient, Reliable and well distributed)

  • Tea
  • Coffee
  • Wheat
  • Dairy farming

Soils

Acidic and Volcanic Soils

  • Coffee
  • Tea

Clay Soils

  • Rice

Black Cotton Soils

  • Cotton
  • Rice

Loamy Soil

  • Horticultural crops

Human Activities and evidence

Settlement

Group of dwellings where people live.

Rural Settlements

  • Semi permanent houses
  • Farming or fishing activity
  • Uneven distribution of settlements
  • Presence of villages

Urban Settlements

  • Permanent buildings
  • Storied buildings
  • Heavy traffic presence
  • Regular street patterns

Agriculture/Farming

Subsistence Farming

  • Temporary and permanent houses
  • Small pieces of land
  • Mixed cropping
  • Simple implements
  • Local and exotic breeds of livestock

Crop farming

  • Crops
  • People preparing land or weeding or Harvesting

Commercial Crop Farming

  • cash crops
  • machinery
  • feeder routes
  • processing factories

Plantation Farming

  • Single crop on extensive piece of land e.g. tea, coffee, etc.
  • Many labourers
  • Nucleated settlement within farms

Livestock Rearing

Nomadic Pastoralism

  • Cattle grazing in a grassland or semi-arid region

Daily Farming

  • Zero grazing
  • Cattle with big udders

Ranching

  • Paddocks
  • Wind mills

Mining

  • Quarry
  • Large open pits
  • Large excavators
  • Lorries carrying loads of rocks

Industrial Manufacturing

  • Buildings with large chimneys
  • People engaged in a processing activity such as Jua kali artisans.

Lumbering

  • People cutting trees using power saws
  • People loading timber into lorries
  • Logs pilled near a saw mill
  • Forests with stumps
  • Logs floating on a river

Transport

Motor transport

  • Vehicles on roads

Railway Transport

  • Railway line
  • Trains

Air Transport

  • Flat tarmacked piece of land
  • Aircraft

Water Transport

  • Boats
  • Ships
  • Ferries

Communication

  • Telephone lines
  • Telephone booths
  • Post office
  • Satellite masts
  • V and radio stations

Sketching Diagrams from Photographs

  • Draw a rectangle the same size as the photograph.
  • Divide it into squares using faint lines.
  • Subdivide the photograph into 9 sections.
  • Insert the features in their exact positions using simple lines being guided by the squares.
  • Label the important features e.g. vegetation, land use, prominent buildings, transport, and communication.
  • Give the sketch a suitable title.

Graphs

2 dimensional drawings which show relationships between 2 types of data representing two items also called variables. These are dependent variable which is affected by the other e.g. temperature (on y axis) and independent variable whose change is not affected by the other e.g. altitude (on x axis).

Steps

Draw x and y axis.

  • Choose suitable scale to accommodate the highest and lowest value.
  • Plot the values accurately using faint dots.
  • Join the dots using curved line. If it’s a bar graph the dots should be at the middle of the top line. Years should also be at the middle. You should have also decided on the width of the bars.
  • In data without continuity e.g. crop production there should be gaps between bars and for one with continuity e.g. rainfall bars should not have gaps.
  • Draw vertical lines on either side of the dot then draw horizontal line to join them with the dot.
  • Shade uniformly if they are representing only one type of data and differently if representing one type of data.
  • In combined line and bar graph temperature figures are plotted on the right hand side of y-axis while rainfall on the left
  • Don’t start exactly at zero.
  • Include temperature and rainfall scales.
  • Start where the longest bar ends.

What a Well Drawn Graph Should Have

  • Title
  • Scale/scales
  • Labelled and marked x and y axis starting at zero.
  • Key if required e.g. in comparative bar graph.
  • Accurately plotted and lines, curves or bars properly drawn.

Simple Line graph Advantages

  • Easy to construct
  • Easy to interpret
  • Easy to read/estimate exact values.
  • Shows trend or movement overtime.

Disadvantages

  • Doesn’t give a clear impression on the quantity of data.
  • May give false impression on the quantity especially when there was no production.
  • Poor choice of vertical scale may exaggerate fluctuations in values.
  • Difficult to find exact values by interpolation.

Simple Bar Graph/histogram

Advantages

  • Easy to construct.
  • Easy to interpret.
  • Easy to read.
  • Gives a clear visual impression on the quantity of data.

Disadvantages

  • Poor choice of vertical scale may cause exaggeration of bars.
  • Doesn’t show continuity/ variation of data overtime.
  • Unsuitable technique when values exist in continuity.
  • Not possible to obtain intermediate values from the graph.

Combined Line and bar Graph

Advantages

Easy to construct.

Easy to read.

It shows relationship between two sets of data.

Disadvantages

  • Difficult to choose suitable scale when values of variables differ by great magnitude.
  • Considerable variation of data represented by the line may cause the line the bars thus obscuring the relationship.
  • Doesn’t show relationship between the same sets of data of more than one place.

Analysis and Interpretation

  • The month with heaviest rainfall is May.
  • The month with lowest rainfall is July.
  • The hottest month was January and February.

The months with lowest temperature were June and July.

Crop Production in Kenya in the Years 2001 and 2002

If the data has large figures e.g. 195262 plot in 1000s=195, 184,988=185.

You can draw comparative/group/multiple line and bar graphs from the data.

Comparative/Group/Multiple Line Graph

Advantages

  • Simple to construct
  • Suitable when comparing trends or movements
  • Comparison of items is easy because the graphs are drawn using common axis
  • Its easy to read exact values from each graph

Disadvantages

  • Number of items which can be represented are limited
  • Crossing of lines may make interpretation and comparison difficult and confusing.
  • Total amount of variable cant be established at a glance.

Comparative Bar Graph Advantages

  • Easy to construct
  • Easy to read and interpret
  • Easy to compare similar components within different bars.
  • Gives a good impression of totality.
  • Individual contribution made by each component is clearly seen.
  • Differences in quantity of components are clearly seen.

Disadvantages

  • Doesn’t show trend of components over time.
  • Not easy to compare components where bars are many
  • Not suitable for many components.

Look for a convenient scale say 1cm rep 100000 visitors

  • Draw a divided rectangle 10 cm long to represent the data.
  • Show your calculations.

It should have the following:

  • Title
  • Different shades
  • Key
  • Width of 2cm

Analysis and Interpretation

To get the meaning of

  • Factory leading in sugar production is Mumias.
  • The 2nd leading is Muhoroni.
  • Factory with the lowest production of sugar is Sony.
  • Calculation of %s.

Advantages

  • Easy to construct
  • Easy to compare components because they are arranged in ascending or descending order.
  • Takes less space than when the data is presented using graphs.
  • Each component proportion to the total can easily be seen at a glance.

Disadvantages

  • Can’t be used for a large data.
  • Only one unit of measurement can be used.
  • Difficult to asses values of individual component
  • The visual impression isn’t as good as pie charts.
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MAP WORK

Map – representation of the whole or part of the earth’s surface drawn to scale.

  • Shows outline of objects on the ground
  • Drawn as if the drawer was above the ground
  • It shows details
  • Most of the features are indicated by symbols. Picture: image of a real object.
  • Gives details in their visible shapes and sizes
  • Can be inform of free hand, drawing, painting or a photograph
  • Not drawn to scale

Plan: outline of something drawn to scale.

  • Also drawn as if a person was directly above the ground
  • It represents a very small place
  • The scale is large to show details e.g. house plan
  • Gives specific information

Types of Maps

Classified according to the purpose for which each map is drawn.

Topographical Maps: This shows selected natural physical features on a small portion of a country.

Atlas maps: this is a collection of maps in one volume.

Sketch maps: maps which are roughly drawn. A good sketch map should have the following characteristics:

  1. neat and clear
  2. title
  3. frame
  4. key
  5. compass direction

Uses of Maps

  1. Sketch maps are used to summarise information for easy reference.
  2. Used for locating other countries.
  3. Used for comparing sizes of countries.
  4. For locating climatic regions of different parts of the world.
  5. Give information on distribution of geographical phenomena e.g. vegetation on the earth’s surface.
  6. Help travellers to find their way.
  7. Used to calculate distance of a certain place.
  8. Used to locate physical features like landforms.

Marginal Information Information contained in the area surrounding the map.

  1. Map name e.g. Yimbo.
  2. Sheet title e.g. East Africa 1:50000 (Kenya).
  3. grid system numbers
  4. latitudes and longitudes
  5. Compass direction with grid, true and magnetic north.
  6. scales
  7. key
  8. publisher and copyright
  9. Map identification

Map series

Sheet number or sheet index

Map Scales

A scale is a ratio of a distance on a map to a corresponding distance on the ground.

Types of Scales

Statement scale –expressed in words e.g. 1cm represents 1km, 1cm to 1km.

Representative Fraction (RF)-expressed as a fraction or ratio e.g. 1/200,000 or 1:200,000.

Linear scale-shown by a line which is subdivided into smaller units.

Conversion of Scales Statement scale into RF

1cm rep 1km to RF

Multiply the number of kilometres by 100,000 (1km=100,000cm) i.e.

1×100000=100,000.

Statement scale is 1/100,000 or 1:100,000.

2cm rep 1km

Divide both sides by two to get 1cm rep ½ kilometres.

Multiply ½ by 100,000 to get 50,000.

RF is 1/50,000 or 1:50,000.

RF to Statement Scale

Divide the denominator by 100,000.

Write the scale in statement form.

Linear Scale to Statement Scale

  • Measure a unit distance off a linear scale e.g.

The distance is 4-3=1km which is represented by 2cm. Use the methods in (1) and (2) above.

  1. Given that the ground distance is 200km while the distance on map is 20cm calculate the scale.

Sizes of Scales

  1. Small scales- show a large area of land on a small size of paper. They show limited details e.g. 1:250,000, 1:500,000, 1:1,000,000.
  2. Medium scales- used to represent a relatively smaller area on a given size of paper e.g. 1:50,000, 1:100,000, 1:125,000.
  3. Large scales-used to represent a small area of land on a given piece of paper. They show a lot of details e.g. 1:2,500, 1:10,000, 1:25000

Arranging Scales in Order

Ascending Order-smallest to largest

Descending Order-largest to smallest

(1)1/500,000

(3)1:25,000

(4)1/10,000

(2)1cm rep 500m

Uses of Scales

  1. Estimating distances on maps
  2. Measuring distances accurately-use dividers and ruler, piece of string or thread for curved distances or straight edge of paper.

E.g. calculate actual distance of a line 8.5cm long on a map using the following scales.

  • 2cm rep 1km
  • 1:100,000
  1. Calculation of areas-no. of full grid squares+ number of ½grid squares/2 or use of rectangles (l×b) or triangles (½ b×h).

Direction

Course upon which something is pointing to.

Methods of Showing Direction Traditional Methods

1. Use of Stars

E.g. use of groups of stars called plough to find northern direction by locating the pole star and use of Southern Cross by using the brightest star which is over South Pole to find northern direction.

2. Use of Shadows

E.g. morning, shadow of flag pole cast to your left you are facing north, etc.

  1. Land Marks

Using conspicuous features such as hills, buildings even roads to get direction.

Modern Methods

1. Land Marks

2. Compass Direction.

Use of magnetic compass which has a needle which always points north.

It has 16 cardinal points and 4 are basic.

Bearing –Expression of direction in degrees of an angle.

It’s measured from north in a clockwise direction.

Calculation of Bearing

Draw N-S line through observation point. Join the two points. If it’s a feature the line should end at the centre of that feature.

Using a protractor measure the angle between the N-S line and the line joining the 2 points in a clockwise direction.

Bearing is expressed in degrees, minutes and seconds. 1◦=60’(min), 1 min=60” (sec)

The degrees are always expressed in 3 figures e.g. 030◦

Types of Norths

  1. True North

-Position on the globe where all longitudes meet or the direction of N. Pole.

  1. Grid North

-Point where Eastings meet at the N. Pole.

3. Magnetic North

-Point which the magnetic needle rests when left to swing freely.

Types of Bearing

1. Grid Bearing

Bearing calculated from Grid North.

  • Join the two points on the topographical map using a line.
  • Measure the angle where the Eastings intersect the line joining the two points e.g. 030◦.

True Bearing

Bearing calculated from True North. Its calculated when the type of bearing isn’t specified.

E.g. from our compass diagram true bearing will be 30◦-1’=29◦59’

Magnetic Bearing

Bearing calculated from Magnetic North.

Position of Magnetic North changes slightly every year.

Steps

  • Years which have elapsed × Annual change. (No need if annual change is negligible). E.g. from our compass diagram annual change =(20091991)×4.8’=18×4.8’’=86.4’’=1◦26.4’
  • Add to the angle between the grid and magnetic bearing 1.e. 1◦26.4’+2◦30’=3◦56.4’
  • Add to the Grid bearing (if change is towards E) or Subtract (if change is towards W). 30◦ +3◦ 56.4’=3356.4’ Location of Places

Showing of position of a place or feature on a topographical map.

Methods

Use of Place Names -Locating a feature by using the name of the place it’s at e.g. a river in Kisumu, Nakuru, etc or if it isn’t at a named place locate by the nearest name place e.g. a meander near Garissa town.

Use of Direction, Bearing and Distance This is from a stated position e.g. Locate Nakuru from Nairobi.

Nakuru is 157km N.W of Nairobi.

Latitudes and Longitudes

The main longitudes are I.D.L and Greenwich /Prime Meridian. The main lines of latitudes:

  • The equator/Great Circle (0◦) which is the longest.
  • Tropic of Cancer (23½◦N) of equator.
  • Tropic of Capricorn (23½◦) south of equator.
  • The Arctic Circle (66½◦N).
  • Antarctic Circle (66 ½ ◦ S).

They are marked at the margins. Latitude is stated first (N or S) and longitude later (E or W) e.g. X◦N Y◦E

  • Identify a place.
  • Identify the nearest numbered latitude and longitude.
  • Estimate to the nearest 1◦.

Grid Reference

Grid lines: network of lines on topographical maps.

Numbered in small and large numbers and the large ones are used.

Eastings: N-S grid lines called so because they are numbered eastwards.

Northings: W-E grid lines called so because they are numbered northwards. Grid reference is given in 4 figures or six figures. In 4 figure the nearest grid line is stated while the 6 figure is estimated in fractions by dividing the space between grid line into 10 equal parts.

Easting is stated first followed by northing.

In the example below the 4 figure grid references are:

  • A-6856
  • B-6856
  • C-6857

6 figure grid references are:

  • A-675555
  • B-680560

C-682568

Methods of Representing Relief on Topographical maps

Relief is the nature of landscape e.g. plain, plateau, valleys, hills, etc.

Spot Heights

Points on map whose positions and heights have been determined by surveyors.

They are shown by a dot and a figure e.g. (.1827).

  • Advantage-show actual heights
  • Disadvantage-can’t be used to identify landforms.

Trigonometrical Stations/Points

Carefully chosen points carefully chosen and their altitude determined which –Are used as a basis for surveying an area.

They are marked on the ground by concrete pillar or slab.

They are indicated on topographical maps by:

Isohypes/Contours and Form Lines

A contour is a line on a map joining all points of the same height above sea level. They are browner in colour and have heights written on them.

Form lines are lines drawn on a map joining places of approximately the same height above sea level. They are less brown than contours and not all have values written on them.

Both contours and form lines are referred to as contours.

Contour/Vertical interval is the difference in height between any two successive contours.

Advantages of contours:

  • They show actual heights.
  • Can be used to identify land forms.

Pictorials

-Showing relief by drawing landforms at approximate positions where they are found e.g. mountains, hills, valleys, etc. Disadvantages:

  • They obscure details behind them.
  • Don’t give height above sea level.
  • Limited variety of landforms can be accommodated.

Short lines drawn to represent direction of slope.

On steep land they are thick and close together.

On gentle slopes they are thin and wide apart.

Their disadvantage is that they can’t be drawn on flat land.

Hill Shading

Showing relief by shading to show shadows where by steepest slopes  which are list lit have darker shade while hill tops, surfaces of plateaus and plains and valley bottoms are well lit have lighter shade. 

Layer Tinting

Colouring or shading land within a certain range of altitude or using a single colour with varying tones where the colour gets darker with increasing altitude.

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VULCANICITY

Process in which solid, liquid or gaseous materials are forced out of the interior of the earth into the earth’s crust or onto the earth’s surface. These materials are magma, lava, gases, dust, ash and cinder.

Causes of Vulcanicity

  • Magma under high temperature and pressure moving through lines of weakness or faults.
  • When tectonic plates move away from each other and boundaries give way to magma.
  • Underground water coming into contact with hot materials hence changing into gaseous form.

There are 2 types of Vulcanicity:

Extrusive Vulcanicity (volcanic): in which materials intrude crustal rocks and don’t reach the earth’s surface. Magma is the molten material while it’s underground.

Intrusive Vulcanicity (plutonic): in which materials reach the earth’s surface.

Lava is the molten material after it reaches the surface.

There are two types of lava and magma, acidic and basic. Acidic lava is viscous and solidifies quickly and doesn’t spread far but accumulates around the vent. Basic lava is more fluid or less viscous and takes longer before cooling and spreads for great distances before doing so. Other materials emitted are gases, ashes, dust and cinder. The solid materials are called pyroclasts. Materials come out through a hole/vent (vent eruption) or crack/fissure (fissure eruption).

Features Resulting From Vulcanicity -Divided into intrusive and extrusive features or landforms.

Intrusive/Plutonic Features

Features formed by intrusive Vulcanicity when materials intrude the earth’s crust.

Sill

An igneous intrusion which lies along a bending plane of rock strata. -Formed when magma forces its way between rock layers then cools and solidifies.

It forms ridge like escarpments when exposed by erosion e.g. Fouta Djalon highland of Guinea and 3 sisters of S. Africa.

Dyke

A wall-like igneous intrusion which lies across the bedding plane of rock strata. -Formed when magma intrudes cracks or faults cutting across bedding planes of rocks then cools and solidifies.

Can be vertical or inclined.

When exposed it forms ridges e.g. Kaap Valley in Transvaal S. Africa and Jos Plateau in Nigeria.

Laccolith

A mushroom-shaped igneous intrusion lying between bending planes of a country rock.

Formed when viscous magma pushes its way through a vent and accumulates around the vent before reaching the earth’s surface pushing the overlying rock into a dome shape.

Its so high that land is turned into mountains e.g. El Koub Hill in Algeria, Henry Mountains in Utah U.S.A and Fonjay Massif in Madagascar.

Batholiths

Largest igneous intrusion formed underground formed when very hot magma intrudes bedding planes of rocks and replaces or metamorphoses it e.g. Chaila Massif in Gabon, Ikhonga-Murwe in Kakamega and the largest is in British Columbia.

Lopolith

a large saucer shaped igneous intrusion formed when viscous magma intrudes into bedding planes of a country rock. They form shallow depressions on the earths surface of the earth e.g. Bushveld complex in S. Africa and Duluth Gabbro mass in U.S.A.

Phacolith

A lens shaped igneous intrusion which forms in the crest or trough of an   anticline e.g. Corndon Hill in England.

Extrusive/Volcanic Features

Formed when magma reaches the earth’s surface through vents or fissures.

Volcanoes

A volcano is a cone shaped hill formed when volcanic materials flow out and accumulate around a vent. Volcanoes are classified into three groups:

  1. Active volcano- which is known to have erupted in recent times e.g. OL donyo Lengai in Tanzania and Mt. Cameroon, and Mauna Loa in Hawaii.
  2. Dormant volcano-not known to have erupted in the recent past but show signs of volcanic activity such as presence of hot springs, geysers and fumaroles e.g. Mt. Kilimanjaro, Longonot and Menengai.
  3. Extinct volcano-which has not shown signs of possible future eruptions e.g. Mountains Kenya and Elgon.

Types of Volcanoes

Acidic Lava Domes

A steep dome shaped volcanic hill made of acidic lava.

Viscous lava flows out through a vent.

  • It accumulates around the vent because it’s viscous.
  • Eruptions occur later and lava flows out covering the layers below.
  • A steep sided dome shaped mound of volcano is formed e.g. Itasy Massif of Madagascar, Mt. Kenya and Kilimanjaro.

Characteristics

    • Its dome-shaped
    • Has steep slopes
    • Made of acidic lava
    • Has lava layers
    • Has steep slopes
    • Has a narrow base

Basic Lava Domes/Shield Volcanoes

A low lying volcanic hill made of basic lava.

  • Basic magma flows out to the surface through a vent.
  • The lava flows far before solidifying because its fluid.
  • Eruptions occur later and lava spreads over the old lava.
  • A shield shaped mound of volcano is formed e.g. Canary Islands, Cape Verde and Sao Tome which are volcanic Islands in the Indian Ocean.

Characteristics

  • Dome/shield shaped
  • Has gentle slopes
  • Made of basic lava
  • Has lava layers
  • Has a broad base

Ash and Cinder Cones

A volcano built from ash and cinder or small fragments of lava.

  • Violent vent eruption occurs.
  • Ash and pyroclasts are emitted and thrown high.
  • Some materials fall and settle around the vent forming a hill.
  • Light materials are blown by wind to the leeward side e.g. Chyulu Hills, Teleki and Likaiyu near L. Turkana.

Characteristics

  • Made of pyroclasts
  • Asymmetrical about the axis
  • Cone shaped
  • Has smooth slopes

Has steep windward slope and gentle leeward slope

Composite /Complex/Stratified Volcanoes

A volcano made of alternating layers of lava and pyroclasts and conelets.

  • The first eruption throws out pyroclasts.
  • Then viscous lava flows out and solidifies on them.
  • Eruption occurs later blowing the rocks sealing the vent.
  • The pieces of rock settle on earlier solidified lava.
  • Another mass of lava flows out and spreads over pyroclasts and solidifies.
  • The process is repeated causing the volcano to build upwards
  • The conelets are formed when magma is unable to overcome the plug and finds its way through weak lines at the sides and then pyroclasts and lava accumulate around the side vent e.g. Mountains Kenya, Longonot, Elgon and Kilimanjaro.

Characteristics

  • Cone shaped
  • Stratified (made of alternating layers of lava and pyroclasts.
  • It has conelets (parasitic cones).
  • It has steep slopes.
  • Made of acidic lava

 Plug Dome/volcano/Spine

A column of very viscous lava which sticks above the ground.

  • A column of very viscous magma flows out of the ground.
  • It cools and hardens rapidly as it rises vertically.
  • Pieces of rock break from the plug and accumulate on the sides e.g. Mont Pelee in West Indies, Hyrax and Fischer’s Tower at Hells gate in Naivasha and Devils Tower in U.S.A.

Characteristics

  • Made of very viscous lava.
  • It is dome shaped like a mushroom germinating out of the ground. (c) Has debris on its sides.
    • Has very steep sides
    • Cylindrical in shape
    • Disintegrates fast due to rocks undergoing rapid cooling.

Volcanic Plug

Stump of rock formed when magma which solidified inside a vent (plug) is exposed by denudation.

  • A volcano is first formed.
  • Lava on the sides of the volcano is eroded fast due to cooling fast.
  • The lava in the vent which is hard due to slow cooling is exposed forming a stump of rock e.g. Peaks of Mt. Kenya, Rangwa Hill and Tororo Rock.

Characteristics

  • It resembles a stump of a tree.
  • Its dome shaped.
  • Very steep at the top and less steep at the bottom
  •  Made of hard/resistant rock

Lava Plains and Plateaus

Lava plain: fairly level lowland below 500m above sea level covered by thin lava layers.

Lava plateau: fairly level highland/upland above 500m above sea level covered by thick layers.

Formed by fissure eruption.

  • Magma of low viscosity comes out of the ground through a fissure.
  • It flows for a long distance before cooling and solidifying filling depressions and valleys forming a plain.
  • Eruption occurs later and lava flows out through lines of weakness on crustal rock and solidified lava.
  • The new lava spreads on top of the old lava forming a new layer.
  • The process is repeated and a plateau is formed e.g. Mwea, Nandi and Laikipia Plains and Yatta and Uasin Gishu Plateaus.

Craters

A funnel shaped depression found on top of a volcano.

Modes of Formation Cooling and Contraction of Magma

  • Eruption occurs and a volcano is formed.
  • Magma in the vent cools and contracts.
  • It withdraws into the vent leaving a depression at the vents mouth e.g. Ngorongoro and Menengai craters.
  • Rain water or water from melting snow may collect into craters to form crater lakes e.g. L. Paradise on Mt. Marsabit, L. Magadi on Ngorongoro Crater and L. Chala on Kenyan Tanzanian border.

Explosion

  • Gases underground expand due to heat from magma.
  • They force their way out through a weak line in the crustal rocks.
  • An explosion occurs leaving a hole in the ground called a ring craterg. Ghama and Dobot craters in Tanzania and Hora craters inEthiopia.
  • Water from underground or rivers may accumulate into ring craters to form lakes called maarsg. Lakes Katwe and Nyungu in Uganda. 

Falling of a Meteorite

  • A meteorite falls on the earth’s surface.
  • It sinks into the rocks leaving a depression.
  • Water may collect into the depression forming a lake e.g. L. Bosumtwi in Ghana.

Calderas/Basal Wreck

A very large basin-shaped depression on the summit of a volcano.

Modes of Formation

Violent Explosion

  • Gases and water heated by magma expand.
  • They force their way through a vent.
  • The rocks at the top of the volcano are blown off forming a large depression e.g. Nyirarongo Caldera in DRC and Sabiro Caldera in Uganda.

Block Subsidence/Cauldron

  • Eruption occurs to form a volcano.
  • An empty space (cauldron) is left in the magma reservoir in the mantle.
  • The rocks forming the middle of volcano are pulled inwards by gravity.
  • The middle of the volcano collapses forming a large depression at the top e.g. Menengai Caldera near Nakuru and Ngorongoro caldera which is the largest in E. Africa and 6th largest in the world.
  • Water from rain or underground may fill calderas to form lakes e.g. L. Magadi in the Ngorongoro caldera and L. Ngozi in Tanzania.

Outward Collapsing

  • Ash and pyroclasts volcano grows high.
  • Materials on top exert pressure on those below.
  • Materials at the base begin to spread outwards.
  • The top of volcano collapses inwards forming a collapse caldera e.g. Napak Caldera in Uganda.

A vent in a volcano which emits gases. 

Fumaroles

The gases come from chemical reactions in crustal rocks when heated by magma or when minerals in rocks come into contact with hot air and steam underground.

They are of two types:

Mofette: fumarole which emits carbon dioxide.

Solfatara: fumarole which emits gases with sulphurous compounds.

Hot Springs and Geysers

Hot spring is a place where hot water is emitted from the ground quietly e.g. at the shores of Lakes Magadi and Bogoria.

A geyser is a jet of water and steam which are violently ejected from the ground e.g. at Olkaria and western shores of L. Bogoria.

How They Are Formed

  • Percolating water is heated by hot rocks or magma.
  • Some collect into chambers called sumps where it develops pressure causing it to be superheated super heated.
  • The pressure forces the steam outwards towards the earths surface through holes and cracks in rocks.
  • The steam comes out of the ground which reduces pressure in sumps causing the water to expand/boil and come to the surface.
  • The steam comes out with a whistling sound accompanied by water forming a geyser.
  • The escaping steam heats ground water in surrounding rock.
  • The heated water may find its way to the surface where it quietly comes out of the ground forming a hot spring.

Pools of Boiling Water

Small area of still water which appears to be boiling.

  • Actual heating of pool water by gases and steam causing the water to boil.
  • Gases and steam coming out below the pool of water causing the pool to bubble and appear as if it’s boiling.

World Distribution of Volcanoes (

  • Regions of faulting e.g. the Great Rift Valley of E. Africa.
  • Mid-Atlantic ocean ridge.
  • The western coast of America.
  • Zones of recent mountain building e.g. fold mountains of S.E Asia.

Significance of Vulcanicity Positive

  • Volcanic rocks weather to form fertile agriculturally productive soils e.g. basalt.
  • Geysers are sources of geothermal electricity e.g. at Olkaria.
  • Hot springs water is pumped into houses for heating during winter e.g. Iceland.
  • Volcanic features are a tourist attraction e.g. hot springs, geysers and snow capped Mt. Kenya.
  • Igneous rocks e.g. phonolites are crushed to make ballast for building roads, bridges, etc.
  • Crater lakes are a source of fish e.g. L. Katwe in Uganda, sources of minerals e.g. L. Magadi and sources of water for domestic use.
  • Volcanic mountains are catchment areas, sources of rivers and habitats for wildlife.
  • Pumice a volcanic rock is used as a scrubbing stone.
  • Vulcanicity is useful for production of gases e.g. carbon dioxide used in soft drinks manufacture.

Negative

  • Volcanic eruptions cause of life and destruction of property e.g. sulphur dioxide, ash, cinder and lava may bury houses and farm land.
  • Volcanic mountains are barrier to transport and communication.
  • Volcanic mountains on the path of rain winds cause leeward slopes to receive little rainfall by preventing rain bearing winds from reaching there.
  • Volcanic eruptions cause environmental pollution from dust, ash and sulphur dioxide.

Sudden and rapid movement of the earths crust.

areas prone to them are called seismic zones and those not prone are called aseismic zones.

It’s caused by shock waves.

There are 3 types of earthquake waves namely:

  1. Primary waves-which travel fastest and cause the rock particles to vibrate in a push and pull manner and can pass through gases, liquids and solids.

2. Secondary waves-which cause rock particles to vibrate at right angles to the direction of wave movement.

3. Surface longitudinal waves-which cause surface rocks to shake sometimes causing buildings to collapse.

Rayleigh waves-Which cause surface rocks to move in elliptical orbits.

Love waves-which cause rock particles to move in a horizontal manner at right angle to the direction of wave

Earth quake originates from a point known as seismic focus/origin. The part of the earth vertically above the seismic focus and where the shock waves are first experienced is called epicentre.

Causes of Earthquakes

Natural Causes

  • Tectonic movements e.g. movement of tectonic plates. They cause tectonic earthquakes.
  • Vulcanicity when magma movement displaces rocks suddenly shaking and shuttering them.
  • Gravitative force when crustal rocks collapse into cauldron due to gravity.
  • Energy release in the mantle when radioactivity takes place in mantle releasing explosive energy which sends shock waves outwards.
  • Isostatic adjustment when the continental masses rise to restore the upset state of balance between sial and sima layers.

Human Causes

  • Exploding nuclear bombs underground which causes shock waves which spread outwards and are felt in the neighbourhood.
  • When a train rolls on its rails causing the ground to vibrate.
  • Explosion of explosives used in mining and quarrying which cause vibrations to be felt in the neighbourhood.
  • When large reservoirs are constructed and the heavy weight of water reactivate dormant faults causing tremors.

Measurement of Earthquakes

Seismograph is a pendulum based instrument used to measure earthquakes. It records seismic impulses on a graph-like record called seismogram mounted on it.

Earthquakes are measured by their intensity and magnitude.

Intensity

Measure of how strong/hard the quake shakes the ground.

It’s seen from the effects the earthquake has on people, buildings and other structures.

It’s measured on the Mercalli Scale which uses a scale running from Roman ixiii e.g.

  • I- description -imperceptible
  • V-rather strong-sleepers are awakened and there is swinging of objects.
  • VIII-destructive-gaping cracks in walls some brought down.
  • XII- major catastrophe-every building destroyed.

Magnitude

Measure of amount of energy given off by an earthquake.

It’s measured on Ritcher Scale which ranges from 0-8.9.

Intensity values depend on how far a place is from epicentre. The higher the scale the more severe the earthquake is.

  • Intensity I-magnitude 2
  • Intensity VIII-magnitude 6
  • Intensity XII-magnitude 8.5.

World Distribution of Earthquakes

  • Within the zones of major faulting e.g. Rift Valley.
  • In areas of Vulcanicity e.g. Oldonyo Lengai in Tanzania.
  • Along boundaries of tectonic plates e.g. Japan, Philippines, East Indies and west coast of north and South America.

Effects of Earthquakes

  • Can cause loss of life and property when buildings collapse burying people.
  • Disrupt transport and communication by vertically and laterally displacing land which disconnects pipelines, electricity lines, roads and railways.
  • Causes landslides which also cause loss of life and property and disrupts communication.
  • Causes raising and lowering of the sea floor and the coastal regions.
  • Cause huge sea waves called Tsunami which may flood the neighbouring coastal areas.
  • Trigger folding, Vulcanicity and fires.
  • Give off a lot of explosive energy more than an atomic bomb.
  • Cause fear and panic.
  • Hinder settlement as it is restricted to aseismic areas.
  • Cause violent motions of the earth’s surface.
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FAULTING

Faulting is the cracking/fracturing of the brittle crustal rocks due to tectonic forces.

Faults are fractures or cracks that develop in the crust.

  • When tensional forces cause crustal rocks to stretch and fracture at the region of maximum tension.
  • When compressional causes squeezing of crustal rocks to fracture at the areas where they are intensely squeezed.
  • When vertical movements exert pressure on rocks leading to fracturing.
  • When shear forces cause crustal rocks to tear.

  1. Upthrow-part of the land displaced upwards.
  2. Down-throw-part of the land displaced downwards.
  3. Throw-vertical displacement.
  4. Heave-horizontal displacement
  5. Hade-inclination of fault to vertical plane
  6. Fault line-fault path
  7. Fault plane-separation of land created by the fault

Types of Faults

Normal Faults

Type formed by tensional forces in which one block slides downwards in relation to the other.

Rocks are subjected to tensional forces

  • A normal fault develops

  • One block slides downwards.

Reverse Fault

Type formed by compressional forces in which one block of land is pushed upwards in relation to the other.

  • Rocks are subjected to compressional forces.

Type formed by shear forces in which adjacent blocks of land slide past one another. If a shear fault occurs between continents it’s called a Transform fault e.g. San Andrean fault of California and great glen fault of Scotland.

Type formed when very strong compressional forces cause almost horizontal faults to develop and one block of land is pushed over the other.

Type formed when anticlines are compressed further and cracks form on the crest.

Steep line of slopes formed by vertical movement of earth along a fault e.g.

Mau, Nguruman, Nyandarua and Nandi.

 

Are exposed parts of a fault plane.

It may be formed due to normal faulting or reverse faulting when overhanging blocks are eroded.

Fault Steps

Land resembling the staircase or steps of a house with a series of fault scarps at different levels.

  • Parallel vertical faults develop.
  • Land between the faults is unequally displaced downwards.
  • A series of fault scarps at different levels is formed. -E.g. Keiyo escarpment and at Kijabe.

Blocks of land raised above the surrounding land.

  • Where tectonic forces cause faulting and land on one side of the fault get raised or sink along the fault planes.

Examples of fault blocks are Aberdare/Nyandarua ranges, Mau escarpment and Nandi Hills.

  • Where Blocks of land bordered by normal faults which are almost parallel to each other sink leaving the middle block standing. Examples of horsts are Ruwenzori of W. Uganda and Usambara and Pare mountains of Tanzania.

Tilt Blocks -Fault blocks which are inclined on one side.

  • Occurs when the fault block, horst or fault steps have greater uplift on one side and as a result they are not flat at the top but tilted. The resultant features are tilted fault blocks, tilted horst and tilt fault steps which form ridges and fault guided valleys.

Along narrow trough with steep escarpments on both sides.

Theories of Formation

Tensional Theory 

Rocks are subjected to tensional forces.

Compressional Theory

Rocks are subjected to compressional forces.

  • Overhanging blocks are worn out by denudation to form escarpments

Suggests the rift valley was formed by Anticlinal arching.

  • Upward forces pushed sedimentary rock strata upwards.
  • The rock layers bent into a big arch.
  • A gaping/huge crack developed at the crest of the arch due to tension forming the rift valley.

The Great Rift Valley/The Great E.A Rift Valley

The world’s biggest rift valley.

It starts in Syria and ends in Mozambique.

It’s divided into 4 parts.

  1. Ethiopian Rift system-starts from Afar in Ethiopia to the Kenyan border around L. Stephanie.
  2. Gregory Rift system-Starts from the northern border of Kenya with Ethiopia to Tanzania. It has a small N.E-S.W branches:
    • Kano Rift valley in Kenya
    • Eyasi Rift Valley in Tanzania
  3. Western Rift valley-Starts at Sudan border to south of L. Rukwa. Features which are here are Ruwenzori Mountain and Lakes Albert, Edward, Kivu, Tanganyika and Rukwa.
  4. Malawi Rift valley-a continuation of Gregory Rift system to Zambezi River in Mozambique. It has a small N.E-S.W branch called Luangwa valley.

The Gregory Rift Valley

Named after a geologist called Gregory J.W who carried out extensive studies in this area.

It’s where the Rift Valley features are more pronounced.

Features associated with it

  • Fault blocksAberdare range, Mau, Nandi and Cherangani hills.
  • Step faults-Kijabe and Tambach
  • Tilt blocks-Aberdare range uplifted and tilted eastwards and Mau escarpment uplifted and tilted westwards.
  • Lava flows and volcanic cones e.g. Menengai and Ngorongoro crater.
  • Rift Valley lakes formed when unequal sinking created faults which were later filled with water. The lakes are deep and elongated. Examples are Lakes Naivasha, Nakuru, Elementaita, Baringo, Bogoria, Ol Bolossat and Turkana. Most of the lakes are salty with exception of L. Naivasha which has fresh water.

Why Most Rift Valley Lakes Are Salty

  • Lack of outlets to drain away salts contained in them.
  • Lack of enough water to dilute salinity due to little rainfall and lack of rivers flowing in them.
  • High rates of evaporation causing increased accumulation of salts.
  • Lake’s water being in contact with rocks with mineral salts which it directly dissolves.
  • Washing into the lake of mineral rich soils by surface runoff.

 Why L. Naivasha Has Fresh Water

  • It has underground drainage to the Indian Ocean.
  • There is inflow of fresh water from rivers and rain.
  • The latest volcanic eruption covered the bed rock with lava.

Major Faulted Areas of the World

  • The Great Rift Valley from Syria to Mozambique.
  • Northern England and the Great Glen Fault of Scotland.
  • The Central Massif of Europe.
  • The middle Rhine Rift Valley region.

Significance of Faulting

To Human Activities

  1. Rift valley lakes are important for fishing, irrigation and domestic use.
  2. The Rift Valley and associated features are a tourist attraction which earns foreign exchange.
  3. Hot springs and geysers formed during faulting can be harnessed for geothermal power.
  4. Block Mountains are water catchment areas and sources of rivers due to the heavy rainfall they receive on the windward side.
  5. Faulting results in the exposure of minerals such as diatomite in Gilgil and Fluorspar in Kerio Valley.
  6. Fault scarps may expose underground water resulting in the formation of scarp springs.
  7. Unequal subsidence caused by faulting may cause formation of depressions which may form lakes which useful for fishing, transport and mining e.g. L. Naivasha.

Negative

  1. Faulting disrupts transport and communication by disjointing land.
  2. Faulting may lead to loss of life and property by causing land to sink.
  3. Faulting may cause a river to disappear or change its course and flow along the fault line.
  4. Steep scarp slopes formed by faulting are prone to soil erosion.
  5. Faulting has given rise to semi-desert conditions in some areas when Block Mountains on the path of rain winds cause leeward sides to receive little rainfall.
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FOLDING

Process in which crustal rocks are distorted by compressional forces by being caused to bend upwards and downwards.

It occurs on fairly young sedimentary rocks.

  • Anticlines (upfolds)-parts of the earths surface which bend upwards when folding occurs.
  • Synclines (down folds)-Parts of the earths surface which bend downwards when folding occurs.
  • Crest-upper most part of Anticline.
  • Trough-lowest part of a syncline
  • Limp-rock layers sloping on both sides of a fold
  • Axis-imaginary line drawn vertically through the centre of the anticline.  

Which are symmetrical about the anticline.

Formed by 2 compressional forces of equal magnitude.

2.Asymmetrical Folds

Which are asymmetrical about the anticlines axis or in which one limp is steeper than the other.

Formed by two compressional forces of unequal magnitude in which one is stronger than the other.

In which anticline of one fold is pushed over the limp of the other.

                                            4.Isoclinal Folds

Which are packed closely together and with limps almost parallel to each other.

Vertical Isoclinal folds are formed by compressional forces of equal magnitude while inclined Isoclinal folds are formed by forces of unequal magnitude.

Which lie in a horizontal manner.

Formed by two compressional forces one of which is very strong.

In which one limp is pushed over the other limp.

The forces are very strong and they cause a fracture/fault to develop.

Folds characterised by minor upfolds and minor downfolds.

  • Land is first subjected to weak compressional forces resulting into minor folds.
  • Later the land is subjected to much greater compressional forces resulting into new upfolds with minor folds (Anticlinorium) and new down folds with minor folds (Synclinorium).

Resultant Features Due To Folding

1.Fold Mountains and Their Distribution

-Worlds highest and most impressive mountains and the most conspicuous feature of folding.

  • Himalayas-Asia
  • Rockies-W.N. America
  • Everest-Nepal-Tibet border-
  • Atlas-N.W. Africa.  highest point.
  • Appalachian-E.N. America
  • Andes-Peru in S. America
  • Alps-South Central Europe

 Theories of Origin of Fold Mountains

1.Contraction Theory

During the earth’s formation surface rocks cooled faster and wrinkled to form Fold Mountains.

2.Convectional Currents Theory

  • Horizontal convectional currents in the mantle exerted frictional pull on crustal rocks.
  • Continental crusts were pulled towards each other.
  • Sediments between them were squeezed into folds.

3.Continental Drift Theory

  • During break of Gondwanaland India drifted northwards and collided with Eurasia.
  • Sediments between were squeezed to form fold mountains e.g. Himalayas and Everest.

4.Plate Tectonics Theory

  • When an oceanic plate meets another or it meets a continental plate the sediments under the sea are compressed to form Fold Mountains.
  • When two continental plates meet the sial layer is compressed to form fold mountains

-E.g. Alps was formed when Africa plate pushed against the rigid European plate.

A relatively continuous line of steep slopes facing the same direction. Formed one compressional force causes folding resulting in one steep limp of the anticline which forms the escarpment.

Formed when not very strong forces cause folding causing some parts of the earths surface to form synclines forming basins.

When folding occurs anticlines form uplands/ridges/hills while synclines form valleys.

Plains which appear to rise and roll.

Formed when plains are acted upon by weak compressional forces resulting into gently sloping anticlines and very wide synclines.

A high fairly level land between mountains.

Formed when rocks at the edges of a region become intensely folded and the middle parts resist folding resulting into mountains which enclose a high fairly level land.

7.Inter-montane basins

-Formed when some parts of inter-montane plateau sink more to form basins.

Significance of Folding

To Human Activities/Economic significance

Positive/advantages

  1. Fold Mountains are a tourist attraction which brings foreign exchange.
  2. Fold Mountains are water catchment areas and sources of rivers.
  3. Some fold mountains have valuable mineral deposits such as coal and petroleum.
  4. Fold Mountains act as protective barriers during war.
  5. Some fold mountains on the path of rain bearing rainfall influence rainfall causing the windward slopes to receive heavier rainfall.
  6. Folding can lead to formation of valuable minerals due to metamorphism.
  7. Folding brings valuable minerals to the surface making them easily available.

Negative/disadvantages

  1. Fold Mountains on the path of rain winds cause the leeward slopes to receive less rainfall.
  2. Fold Mountains discourage settlement due to cold temperatures and rugged terrain
  3. Folding can lead to burying of minerals.
  4. Fold Mountains are a barrier to road and railway where there are no passes and where there are passes they may be covered by snow.

Orographic fog hinders pilot’s visibility.

To Physical Environment

  1. Folding can result in submerged coastal zones which are used as harbours.
  2. Can lead to metamorphism of rocks changing their original state and making them more resistant to erosion.
  3. Depressions formed by folding turn into wet land important for water purification.
  4. Folding leads to faulting and magma may escape through faults leading to Vulcanicity and earth quakes.
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INTERNAL LAND FORMING PROCESSES

Processes operating in the interior of the earth resulting in the formation of natural physical features or landforms.

They are caused by earth movements.

Examples of these processes are folding, faulting and Vulcanicity.

Formation of land forms by internal land forming processes is determined by:

  • Nature and age of earth materials
  • Type of movement involved
  • Intensity and scale of movement involved

Crustal Earth Movements

Displacement of the earth’s crustal rocks.

They are brought about by tectonic forces which originate and operate in the interior of the earth e.g. tensional forces (which operate along horizontal plane moving away from each other), compressional forces (which operate along horizontal plane moving towards each other), shear forces (which move past each other with unequal strength) and gravitational forces (which attracts things to the earths centre).

Earth movements are of 2 types:

  1. Horizontal/lateral/orogenic movements
  2. Vertical/epeirogenic movements

Horizontal Earth Movements

Movements which act along a horizontal plane within crustal rocks.

They are caused by tensional and compressional and shear forces.

Effects

They cause:

  • Strain and stretching of crustal rocks due to stretching caused by tensional forces which cause formation of cracks or faults.
  • Squeezing and shortening of crustal by compressional forces rocks which cause them which also cause formation of faults.
  • Crustal rocks to shear by slipping past each other or by dividing into layers which is caused by shear forces.

Results of Horizontal Earth Movements

results in the formation of the following features:

  1. Faults Escarpments
  2. Rift valleys Basins
  3. fold mountains Tilt blocks
  4. Block mountains

 Vertical Earth Movements

Movements which occur along the earth’s radius or towards the earth’s surface or towards its centre.

Effects Causes:

  • Subsiding/sinking/downwarping or pulling of crustal rocks downwards.
  • Uplifting/upwarping or pushing of crustal rocks upwards
  • Tilting of crustal rocks or shearing in vertical direction due to grater uplift on one side.

Results of Vertical Earth Movements

  1. Raised cliffs Plateaus
  2. Tilt blocks basins
  3. Rift valleys
  4. Fault scarps/escarpments

Causes of Earth Movements

  •  Magma movement within the earths crust.
  • Gravitational force
  • Convectional currents in the mantle
  • Isostatic adjustment

1. Magma Movement within the Earths Crust

  • When magma moves with force pushing crustal rocks horizontally or vertically.
  • When magma moves from reservoir and leaves empty spaces onto which crustal rocks are pulled inwards.

2. Gravitational Force

 When the attractive force of the earth pulls crustal rocks into empty spaces left after magma escaping from the reservoir.

When convectional currents in magma in mantle drug crustal rocks by friction. Horizontal movement of currents cause horizontal movements while vertical cause vertical movements. 

Isostatic Adjustment

Rising of continental masses to restore the upset state of balance between sial and sima layers.

Isostacy is the state of balance between sial and sima layers.

It can be disturbed by erosion on continents and melting of continental ice sheets.

The reduced weight causes continental masses to rise.

Theories Explaining the Earths Movements

A theory is reasoned ideas intended to explain facts or ideas. There are 2 theories which explain the earth’s movements namely the Continental Drift Theory and the Plate tectonics theory.

Theory of Continental Drift

Its proponent was A. Wegener.

It explains the origin of 6 continents.

It states:

  • The earth was a single sialic land mass called Pangaea surrounded by a huge ocean called Panthalasa whose floor was a mass of sima.
  • Pangaea broke into two parts called Laurasia (N. Hemisphere) which lay around equator and Gondwanaland (S. Hemisphere) which lay around south pole which were separated by a narrow ocean called Tethys (the present Mediterranean Sea).
  • Laurasia broke into Laurentian Shield and Fennoscandia (Europe, Asia and N. America) and moved northwards to their present positions.
  • Gondwanaland broke into Africa, Australia, S. America and Antarctica and India subcontinent.
  • Africa and India drifted northwards.

Evidences Supporting the Theory

  1. Fitting of western coast of Africa and S. America into a jigsaw.
  2. Discovery of coal 40◦N and 55◦N which was formed by burying of tropical vegetation.
  3. Considerable displacement of rocks along some faults e.g. along the Great Glen Fault of Scotland.
  4. Cape and Buenos Aires folds resemble one another by having east west trend.
  5. Red sea shores show evidence of having undergone lateral displacement an indication that it was formed by movement of the earth’s crust.
  6. Evidence of ancient Glaciation to the south of equator in Africa in Madagascar and India where there is presence of ancient glacial deposits suggesting these areas were once around south pole.

 

 Plate Tectonics Theory

It states that:

The earths crust is made of blocks called plates.

7 Large Ones

  1. Eurasian plate N. American plate
  2. Australian plate S. American plate
  3. Africa plate Pacific plate
  4. Antarctic plate

Smaller Ones

  1. Indian
  2. Arabian
  3. Caribbean Nazca
  4. Cocos Philippine
  5. Somali plates Scotia
  6. Juan de Fuca
  • These plates are two types : tectonic plates:
    1. Oceanic plates which form major areas of the ocean floor including coastal lowland.
    2. Continental plates which form the bulk of the continental land mass.
  • The plates float on molten mantle layer called
  • The plates move relative to each other due to convectional currents in the mantle.
  • They move away from each other forming extension or constructive boundary called so because magma fills the space between.

  • They move towards each other forming compressional or destructive boundary called so because materials between are crushed. The movements of those two types of plates have the following effects:

  • There is subduction and the ocean floor is pulled inwards forming a trench e.g. Java Trench .
  • Subduction is the passing of edge of one plate beneath the edge of another.
  • Sediments on the sea floor in the region of subduction are compressed to form Fold Mountains.

When an oceanic plate meets a continental plate the edge of the oceanic plate slides beneath the continental plate in a movement called subduction.

  • Sediments on the sea floor in the region of subduction are compressed to form Fold Mountains.
  • Fold Mountains are also formed at the edge of the continent when the sial layer is compressed.
  • The edge of the oceanic plate bends into the mantle forming a trench.

When two continental plates collide the sial layer is folded into mountains.

  • They move past each other forming transform or conservative boundary called so because there is neither construction nor destruction which occurs where the plates are separated by a major fault.

Significance of Plate Movements

  1. Are sources of earthquakes and Vulcanicity.
  2. Causes formation of land forms such as Fold Mountains and ocean trenches.
  3. Spectacular landscapes formed are a tourist attraction.
  4. Eruption of magma can result in formation of valuable minerals.
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MINING

Process of extracting valuable minerals from the earths surface.

Formations in Which Minerals Occur

1. Veins and Lodes

Occurrence of minerals in crevices, cracks or faults in igneous rocks.

  • They are said to occur in veins if they occur there in small quantities.
  • Said to occur in lodes if they occur there in large quantities e.g. zinc, copper and silver.

2. Reefs

Veins and lodes which are exposed on the surface.

3. Seams/Layers/Beds

Occurrence of minerals as sedimentary or as a result of compression of accumulated organic or inorganic material e.g. coal and halite.

4. Alluvial Deposits

Occurrence of miner  als while mixed with materials such as sand, gravel, silt, etc. These were minerals which were detached from the veins by weathering and carried away by streams and rivers and got deposited e.g. gold, diamond and platinum.

5. Weathering Products

Minerals formed by deep weathering of rocks then leaching carried minerals from the top to lower layers where they accumulated e.g. aluminium, nickel, iron and manganese.

6. Oil pools/Wells

Occurrence of minerals in pools or wells in sedimentary rocks e.g. petroleum and natural gas.

  1. Presence of fossils or organic remains
  2. Presence of sedimentary rocks for burying organic remains.
  3. Presence of pressure to compress organic remains to cook the oil and natural gas out of organic matter.
  4. Presence of a porous reservoir rock to store and transmit petroleum to the oil pools e.g. limestone and sandstone.
  5. Presence of a trap like a syncline to hold petroleum in a reservoir to prevent its escape.
  6. Presence of impermeable rocks below the trap or syncline to prevent petroleum from percolating further underground.

Factors Influencing Exploitation of Minerals

1. Value of Mineral

Minerals of high value will be mined even if they occur in small quantities because one sold it will be possible to offset mining costs and make a profit and vice versa.

2. Quality of Ore

Mining can be done if the mineral deposits have high mineral content because they are economical to work on but deposits with low mineral content are rarely worked on except if the mineral in them is rare e.g. uranium.

3. Size of Deposit

Minerals which aren’t of high value have to occur in large quantities for them to be mined so that it will be a possible to recover mining costs and make a profit.

4. Capital

Lack of capital causes developing countries not to exploit minerals and leave it to international companies because a lot of money is needed for exploration, infrastructure, salaries, energy etc e.g. titanium mining at Kwale is being done by Tiomin company from Canada.

5. Method of Mining

A mineral requiring open cast mining will be mined even if the mineral deposit is large but one requiring underground mining will be extracted if its in large deposit or if its of high value or rare.

6. Transport costs

Minerals occurring in remote areas far from the markets are not likely to be exploited if the transport system is poorly developed since mineral ore is heavy and bulky and transporting it by road and railway is expensive.

7. Market for the Mineral

Mining can be done if the mineral is in demand and if the prices are reasonable so that mining costs are offset and a profit is realised.

8. Political Influence

Mineral deposits at the borders of two countries may not be exploited as a dispute may arise concerning whom mine it e.g. dispute between Iraq and Kuwait over Rumaila should oil field.

9. Labour

Exploitation of some minerals require skilled workers and if they lack it may not be done as is the case in developing countries because expatriates have to be engaged and are very expensive to pay which may reduces the profits accruing from mining.

Methods of Mining

1. Open Cast Mining

Method of extracting minerals which are near the earth’s surface.

Types

1. Stripping

-Stripping off of the unwanted material lying on top of the mineral deposit and then digging to remove the mineral bearing rock if it’s soft or if it’s hard explosives may be used to loosen it and then huge power shovels are employed to dig up the mineral deposits.

2. Hill-slope Boring

Using boring instruments known as augers to drill out mineral deposit and bring it to the surface.

3. underground Mining

Method employed when the mineral lies very deep below the surface and the overburden is too thick to be removed by mechanical means.

Types

Shaft Method

Method employed when the mineral bearing rock doesn’t out crop.

How it’s carried Out

  • Vertical shafts are sunk into the earth’s crust to reach the layer with the mineral.
  • Horizontal tunnels are dug from the vertical shaft to reach the mineral.
  • Props are erected to support the roof to prevent it from collapsing.
  • The mineral bearing rock is blasted loose by explosives.
  • The deposit is transported on light rail or conveyor belt to the bottom of the shaft.
  • It is then brought to the surface in a crane or a lift called cage.

Drift/Adit Mining

Method employed when the mineral deposit can be reached from the valley sides.

  • Horizontal tunnels (adits) are constructed from the side of the hill.
  • Railway line is constructed into the mine to bring out the mineral e.g. mining of copper at Kilembe in Uganda.

 Solution Method

Method used in mining soluble minerals such as sulphur, salt, potash, etc.

  • Superheated water is ejected into salt deposits.
  • The mineral dissolves or melts.
  • The solution is then pumped into the surface.

Drilling 

Method employed in exploitation of petroleum.

  • Wells (oil derricks) are drilled.
  • Oil and natural gas are brought to the surface under their own pressure or by pumping.

Alluvial/Placer Mining

Method used to extract minerals occurring in alluvial deposits e.g. gold, tin, diamonds and platinum.

 Types

1. Panning

It involves:

  • Digging a mixture of sand, gravel and mineral from the river bed.
  • Putting it in a pan and rotating the pan while tilted.
  • The lighter sand or gravel is washed on the side leaving the heavier mineral at the bottom of the pan e.g. gold mining in Migori and R. Morun Beds in W. Pokot.

2. Dredging

  • A dredger scoops water logged alluvium from the bed of a lake.
  • The alluvium is passed over sloping channels with series of traps.
  • Wastes are washed away and denser materials are left at the bottom of the trap e.g. mining of soda ash at L. Magadi.

3. Hydraulic Mining -Method used when alluvial deposit occurs on a valley side.

  • A powerful jet of water is directed at the deposit.
  • Gravel and mineral collect at the valley because of the great pressure.
  • The mineral grains are recovered and washed out.

4. Sub-marine Mining

Method employed in extracting minerals in alluvial deposits lying deep down the ocean floor.

  • A sub-marine dredger goes down the ocean floor.
  • It scoops mineral deposit and rises to the surface.
  • The alluvium is passed over sloping channels with series of traps.
  • Wastes are washed away and denser materials are left at the bottom of the trap.

Significance of Minerals/Mining in Kenya

  1. Kenya earns foreign exchange from exportation of minerals which is used to import goods and services and fund development projects.
  2. Mining is a source of employment to people such as those who work in mines, in cement factories, in transport sector, etc.
  3. Mining has led to development of industries by providing raw materials used in those industries e.g. limestone used in cement factories, coal used in iron and steel industries, soda ash used in glass industry, etc.
  4. Mining has led to development of transport system to make mining areas accessible e.g. Magadi soda mine is connected to the main Mombasa-Nairobi railway line.
  5. Mining has led to development of settlements e.g. Magadi town which originated from the mining of soda ash.
  6. Mining is a source of market for goods and services e.g. there are shops and markets, banking and insurance services offered to people working in mines and related industries.
  7. Has led to development of social amenities by providing social facilities such as housing, health, electricity, water and education alongside infrastructure.

Distribution of Minerals in E. Africa

Phosphates used in the manufacture of fertiliser-Tororo in Uganda and Majingu Hill in Tanzania.

Limestone used in cement manufacturing-Hima in N.W Uganda, Tanga in Tanzania, Athi River and Bamburi in Kenya.

Fluorspar a source of fluorine used in chemical industries-Kerio Valley in Kenya.

Common salt used for consumption-Kilifi and Magadi in Kenya and L. Kitwe in Uganda.

Diatomite used in making insulators –Kariandusi near Gilgil and Gicheru in Nyandarua.

Stones in Machakos, Mutonga and Mbeere.

Carbon dioxide used in making dry ice and in beer and soft drinks industry- Esagari in Baringo and Kagwe in Kiambu.

Diamond used to make ornaments, glass cutters and drills-Mwadui in Tanzania.

Titanium used in the manufacture of insulators for aircraft- Kwale district.

Gemstones near Voi and Mwatate.

Soapstone used for sculpture-Tabaka in Kisii.

Copper used to make electrical wires and coins-Kilembe in Uganda.

Gold used to make medals and jewellery and as a basis of world currency-Musoma in Tanzania, Kakamega and Migori in Kenya.

coal used in smelting of iron and generation of thermal electricityin Ruvuma River Basin and Kivira Songwe in Tanzania.

Problems Facing Mining Industry in Kenya

  1. Inadequate capital making Kenya not to benefit from mineral resources because mining is left to multinational companies who pocket all the money to recover mining cost.
  2. Areas where mineral deposits are inaccessible due to poor transport and infrastructure which makes prospecting and mining difficult.
  3. Insufficient skilled personnel causing dependence on expatriates who are expensive to pay which reduces profits accruing from mining.
  4. Most of mining is controlled by foreign companies so most of the mineral revenue ends up to them as salaries and dividends.
  5. Occurrence of minerals in very small deposits which are not economically viable.
  6. Lack of power supply especially in remote areas with minerals.
  7. Land use conflicts which affect mining e.g. in Kwale between Tiomin and the local people due to inadequate compensation.

Effect of mining on the Environment

  1. Renders land useless for other economic activities such as agriculture (dereliction) due to open pits left on land and heaps of rock waste litter dumped on land.
  2. Pollutes the environment e.g. atmospheric pollution from dust and smoke from tractors and trucks, water pollution from spilling of oil from offshore oil drilling and soil pollution from chemicals and explosives used in mining.
  3. Leads to loss of bio-diversity due to destruction vegetation which also destroys habitats of various animals leading to their destruction also.
  4. Causes soil degradation e.g. by loosening the soil which makes it vulnerable to agents of erosion like wind and water, tractors and trucks compact the soil making water infiltration difficult and chemicals used interfering with soil chemical composition making it unsuitable for agriculture.
  5. Causes mass wasting when explosives and heavy equipment used in mining shake the ground making weathered materials to move faster down slope under the influence of gravity.

Trona mining on L. Magadi Location

L.Magadi is 120km S.W of Nairobi on the floor of the Great Rift Valley.

Occurrence

Trona deposits occur as a solution of sodium salts the main ones being sodium sequicarbonate and sodium chloride.

Mode of Formation

  • Rain water dissolves soda salts in volcanic rocks.
  • The solution percolates through the rocks and soil and gets beneath the basin.
  • The accumulated solution is heated by the hot rocks beneath.
  • Pressure builds up and the heated solution is pushed to the surface.
  • It comes out of the ground inform of hot springs below or on the sides of the lake.
  • Due to high temperature water evaporates leaving behind crystals of trona.

Extraction and Processing

  • A dredger scoops trona out of the lake.
  • It crushes it into smaller pieces and separates it from rock debris.
  • The material is mixed with water to form slurry and transported to factory on the lake’s shore.
  • In the factory the slurry is mixed with water to wash out impurities such as mud and salt and dried.
  • It is sent to desiccators and heated to remove moisture and hydrogen to form soda ash.
  • Soda ash is cooled and ground into powder and sieved.
  • It’s packed into paper bags, weighed and transported to the market.

Uses of Soda ash Used in the:

  1. Glass industry in the manufacture of glasses and bottles.
  2. Manufacture of soaps and detergents.
  3. Softening water in paper making.
  4. In textile industry.
  5. In oil refining.

Benefits to the Economy

  1. Has led to growth of Magadi town ship.
  2. Has led to development of social amenities such as hospitals and schools and water from Oloibortoto River which has benefited the local people.
  3. Has led to development of infrastructure e.g. railway line from Konza to L. Magadi.
  4. The Magadi Soda Company employs many Kenyans including the nomadic Maasai.
  5. Exports of soda ash earn Kenya a substantial amount of foreign exchange.

 Problems

  1. Stiff competition from developed countries with large soda deposits e.g. U.S.A and Israel.
  2. Low value of salt is insufficient to meet its production cost.
  3. High labour costs due to incentives given so that workers agree to work in the hostile environment of L. Magadi.

Gold in S. Africa

Gold occurs as small grains in a hard rock.

It’s mined by shaft mining since its bearing rocks are deep below the surface. The main mining area is the Witwatersrand and others are Ogendaalrus and lydenburg.

Processing 

  • Ore is crushed to a fine powdery dust.
  • Mixed with water until it is fluid mud.
  • Cyanide is added to dissolve gold.
  • The fluid is runoff with gold dissolved leaving behind waste salts.
  • Zinc dust is added to filter gold for solidification.
  • Gold sinks as it is denser.
  • Gold is smelted and cast into ingots.

Significance to the Economy of S. Africa

  1. Earns the country foreign exchange used for paying foreign debts.
  2. Offers employment to many people raising their living standards.
  3. Has led to widespread urbanisation contributing to formation of Witwatersrand conurbation.
  4. Has formed a broad market for other industries e.g. engineering, foot wear, electrical and construction industries.
  5. Has led to improvement of infrastructure and social amenities e.g. roads, schools, hospitals, etc.
  6. Led to development of agriculture.

Problems Facing Gold mining

  1. Expensive to mine for lying deeply.
  2. Large capital is required to start mines.
  3. Complication of mining by folds and faults in the crust.
  4. Low gold content in the ore.
  5. Problem of removal of underground water.
  6. Lack of adequate supply of fresh water on the surface in mining areas.
  7. Accidents resulting from collapsing of mine roofs.

Diamond Mining in S. Africa Diamond is the hardest known substance.

Mined in Kimberly, Bloemfontein and Alexander Bay. -Mined by underground mining or alluvial mining.

Processing

  • Diamond bearing kimberlite is crushed
  • Crushed rock is mixed with water
  • Diamond sinks to the bottom as it’s denser
  • Water and less dense residue are drained off
  • Remaining material is put on heavily greased trays and washed
  • Diamond repels water so it sticks to grease while remnants are drained off
  • Diamonds are then sorted out and graded into gem diamonds and industrial type (for cutting purposes).

Contribution to the Economy

  1. Provides employment to thousands of people
  2. Earns the country substantial foreign exchange
  3. Has led to growth of urban centres e.g. Pretoria and Kimberly.
  4. Has contributed to development of infrastructure

Problems Facing Diamond Mining

  1. Fluctuation in the world market prices
  2. High cost of mining and processing diamond
  3. depletion of mines
  4. Low mineral in the ore making mining expensive
  5. labour competition with other sectors e.g. manufacturing and gold mining

Petroleum in the Middle East

Oil is a thick black sticky liquid called crude oil

  • It was formed from small creatures that lived in shallow lagoons about 100200m ago.
  • Decaying remains of those creatures mixed with mud at the bottom as sediments
  • The sediments piled on each other and slowly transformed into sedimentary rocks
  • Gradually the remains were converted into oil and gas.

Major oil producers in the Middle East are Saudi Arabia with the largest reserves, Iraq, Kuwait and United Arab Emirates.

Middle East accounts for 64% of world oil reserves.

There are several giant oil fields in Ghawar in Saudi Arabia and Kirkuk in Iraq.

Processing

Crude oil is processed by refining using a technique called fractional distillation.

The process takes place near as possible to the market as it’s cheaper to transport crude oil than the different refined products.

It’s processed into secondary products such as petrol, paraffin, lubricating oils, dyes, fertilisers and plastics.

  • Impurities are removed from the crude oil
  • Crude oil is heated before entering fluctionating column
  • It’s turned into vapour or gas
  • Different ingredients turn back to liquid at different temperatures.
  • Ingredients gradually cool, condense and collect in various trays and allowed to overflow until they reach an outlet.

Contribution to the Economies

  1. Arab’s investments overseas have increased due to oil reserves.
  2. High income per capita due to oil profits.
  3. Has led to development of cities e.g. Tripoli in Libya.
  4. Investment of oil money in other sectors e.g. power stations, cement factories and exploitation of other minerals.
  5. Earns the countries substantial foreign exchange 6. Increased political and military power.
  6. Artesian water is made available for domestic and irrigation purposes e.g. in Libya.
  7. Oil companies help in fixing down the sand dunes and planting trees in the deserts.
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MINERAL AND ROCKS

Inorganic substances occurring naturally at or below the earth’s surface.

Characteristics of Minerals

  1. Different degrees of hardness e.g. some are very hard e.g. diamond while others are very soft e.g. talc.
  2. Some have atoms arranged in an orderly manner to form crystals e.g. quartz form a 6- sided prism.
  3. Varying number of elements e.g. gold has one (Av) while quartz has 2 (SiO2).
  4. Different abilities to allow light to pass through e.g. some are transparent, opaque or translucent.
  5. Specific colours e.g. gold is shiny yellow while copper is brown.
  6. Have specific surface appearance (lustre) when they reflect light i.e. metallic (shiny) or non-metallic (glass like).
  7. Definite chemical composition or constant ratio of elements e.g. quartz has one atom of silicon and two atoms of oxygen.
  8. Tendency to break along certain lines or cleavage) e.g. flint has cleavage like that of glass.
  9. Different densities e.g. some are very heavy e.g. lead while others are light e.g. silicate minerals.
  10. Some minerals conduct electricity while others don’t e.g. copper conducts while diamond doesn’t.
  11. Some can be pressed into different shapes while others can’t e.g. copper is malleable while flint isn’t.

Types of Minerals Metallic minerals

Ferrous Minerals-limonite, magnetite, siderite and haematite.

Non-ferrous Minerals-copper, aluminium, gold, lead, etc.

Non-metallic Minerals-graphite, diamond, asbestos, coal, etc.

Energy minerals-petroleum, coal and uranium.

Rocks A consolidated material composed of grains of one or more minerals.

Classification of Rocks

1. Igneous Rocks

Rocks formed when molten material from the earth’s interior cools and solidifies on or beneath the earth’s surface.

Types of Igneous Rocks

1. Intrusive Igneous Rocks

Rocks formed when magma cools and solidifies below the earth’s surface e.g. granite, diorite, gabbro, peridotite.

Have coarse texture as a result of slow cooling giving minerals more time to form large crystals.

Are classified further into two:

  • Hypabyssal rocks- intrusive igneous rocks which are near the earth’s surface.
  • Plutonic rocks-intrusive igneous rocks which are deep below the surface.

2. Extrusive Igneous Rocks –Rocks formed when lava solidifies on the earth’s surface.

Have fine texture due to fast cooling giving minerals less time to collect together to form larger crystals.

They are of two types namely:

Volcanic Ejecta -Extrusive igneous rocks formed in the following ways:

  • When ash and lava ejected from underground as they fall on the earth’s surface e.g. pumice.
  • When dust and ash ejected settle on the ground and get compressed to form a rock e.g. tuff.

Lava Flows

Extrusive igneous rocks formed when basic lava flows over a considerable distance then cools and solidifies e.g. basalt and obsidian.

3. Sedimentary Rocks

Rocks formed when particles of other rocks are laid down and compressed into layers or when plant and animal remains are buried and compressed and compacted.

  • When they are laid down a layer is formed.
  • As deposition continues additional layers are formed which compress the lower layers into a hard mass.

Types of Sedimentary Rocks

  1. Mechanically Formed Sedimentary Rocks -Sedimentary rocks formed when weathered igneous or metamorphic rocks are deposited and compacted e.g. sandstone and shale.
  2. Organically formed Sedimentary Rocks -Sedimentary rocks formed when animal and plant or animal remains are buried, compressed and compacted.

Classification of Organically Formed Sedimentary Rocks

Calcareous rocks-rich in calcium carbonate e.g. chalk and limestone. Coral rocks are formed from remains of sea polyps which extract lime from the sea, build shells for protection, attach themselves to each other and rocks to live in colonies, then die and shells to form coral rocks.   

  • Ferruginous Rocks-rich in iron e.g. ironstone.
  • Siliceous Rocks-rich in silica e.g. diatomite.
  • Carbonaceous Rocks-rich in carbon e.g. coal.

Chemically formed Sedimentary Rocks -Sedimentary rocks formed when materials dissolved in water chemically react forming new substances then water evaporated leaving layers of those salts.

Classification of Chemically Formed Sedimentary Rocks

  • Carbonates g. trona and dolomite
  • Sulphates-sulphate compounds
  • Chloridesg. halite (iv) Silicates e.g. flint

Iron stones e.g. haematite and limonite.

4. Metamorphic Rocks

Rocks which have changed their physical appearance and chemical properties as a result of subjection to great heat and pressure e.g.

  • Gneiss from granite
  • Slate from clay
  • Marble from limestone
  • Quartzite from sandstones

Distribution of Major Rocks in Kenya Eastern Kenya region

  • The major rocks are metamorphic rocks e.g. marble in parts of Machakos and schist and gneiss in parts of Kitui.
  • Volcanic rocks in Yatta plateau and Kapiti plans.
  • Sedimentary rocks e.g. limestone rocks used in Bamburi for cement manufacturing.

Coastal Region

  • Major rocks are sedimentary rocks e.g. limestone used in Bamburi for cement manufacture.
  • There are volcanic rocks in Tsavo rich in ground water resources.

Northern and N.E Region

  • Dominated by sedimentary sands.
  • There are volcanic rocks in Mt. Marsabit and around Rift Valley.

Rift Valley and Kenya Highlands

  • Dominated by volcanic rocks
  • There are metamorphic rocks which have resulted from changing of igneous rocks.

L. Victoria Basin

  • Granite and gneiss dominate Western Kenya where they form high rocky hills called granitic tors common in Kisii, Maragoli and Bunyore areas.
  • Sedimentary rocks deposited by rivers e.g. Nyando, Nzoia, Yala and Sondu.

Significance of Rocks

  1. Rocks weather to form soil which is important in agriculture.
  2. Form aquifers which store ground water which forms springs which form rivers and wells which provide water for domestic and industrial use.
  3. Some rocks are sources of building materials e.g. igneous rocks are used to make ballast and limestone rocks are used as building blocks and raw material in cement manufacturing.
  4. Phosphate and nitrate rocks are used to make fertiliser used in agriculture.
  5. Granitic tors of W. Kenya and high volcanic peaks such as those of Mt. Kenya are a tourist attraction which brings foreign exchange.
  6. Pumice is used as a scrubbing stone.
  7. A rock such as coal is used as fuel for heating, smelting of iron and thermal electricity generation.
  8. Source of minerals e.g. oil and coal is associated with sedimentary rocks.