‘The earth can be affected by two forces which may result into various Yandforms, Forces that at on the earth ean be grouped into intemal and extemal forees.

Forces Causing Earth Movements

The Forces Which Cause Earth Movement and their Origin Explain the forces which cause earth movement and their origin INTERNAL FORCES: These are forces which operate within the earth's erus, Internal forces include vulcanicity and earth movements, that is, horizontal (lateral) and vertical movements.

These forces may result into formation of several landform features EXTERNAL FORCES: These ate natural forces that operate on the earth's surface. The forces mainly act on the earth's erust or clase the surface of the earth. Often the features produced by these forces ate seen on the surface of the earth, They include mountains, voleances, moraines and valleys, just to mention a few

Radial/ Vertical Movement

The Vertical/Radical Movement

Describe the vertical/radical movement The earth is in constant motion and this movement results 10 a number of features such as mountains, plateaus and plains. Such features are due to both lateral and vertical movements These movements exert great force of tension and compression wihich later results 1o very impressive Features, Farh movements ate either vertical or lara ‘The Resulting Features from the Vertical Movement

Ident the resulting features from the vertical movement Vertical earth movements: These are up and down movements which cause the crustal rocks to fault, These movements result to a number of landforms such as plateaus, block mountains, rift valleys, basins, ete

Lateral or Horizontal Movement

How Horizontal Movements Take Place

Explain how horizontal movements take place Lateral carth movements: These are sideways movements of the earth’s crust which cause the cenustal rocks either to fold, fault or form joints, Features which are produced due to this movement are such as fold mountains, rift valleys, block mountains, ete

Different Features Produced by Horizontal Forces

Identify different features produced by horizontal forces Features associated with earth movements

Rift Valley

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

Formation of til valley by tensional forees

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

• Movement of tensional forces
• Submergence (subsidence) of the central block between the forces

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• Uplifting of the land on the outside of the two faults

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• Rift valley formed

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Examples of rift valleys include

• ast ASfican it valley — Aiea;
• Jordan ft valley ~ Asia

Block mountain hors) A block mountain refers to a table-like mountain formed due to the influence of faulting that leads to rising of crustal rocks. I is nearly a flat surice. A block mountain ean be formed by either tensional o¢ compressional forces. This is when the earth's movements cause parallel faults which results into uplifting of some pars.

uplifted part Co CE} block mountain a fault

Examples of block mountains are

• Usumbara and Ulugura, in Tanzani
• Ruwenzoni im Uganda:
• Vosges and Black Forest, in Europe; and

© Mount Sinai in Asia Plateau A plateau is a large, extensive uplifted part of the earth's crust which is almost Mat atthe 1p, The top ofthe plateau is mostly a plan, Plateaus were formed during Mesozoic and Jurassic ers It was due to uplifting of the earth's crust. Such landforms include those of East Aftican and Brazilian plateaus, High plateaus especially in topical latitudes are used for agriculture and settlement

Basin A basin is a large, extensive depression on the earth's surface. Most basin are formed due to vertical movement ofthe earth

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Examples of basin include

• aninland drainage e g, Congo basin;
• Chad basin; and
• Amazon basin

Vulcanicity

Difference between Vulcanicity and Voleanicity

earth's erust and onto its surface. Vulcanicity therefore includes voleanic eruptions, which lead features such as batholits, sill and dykes, et, inthe earth's crust.

Causes of Voleanicity and Resulting Features

Explain causes of volcanicity and resulting features Intrusive (internal) vulcanicity This oceurs when the magia cools, solidifies and forms features within the earths erst before it reaches the earth's surface. The features (landforms) formed by this process are sometimes vermed as intrusive (internal) Features Dyke processes

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Examples of dykes are Mwadui dyke in Tanzania, Gabbro dyke in Lesotho, and Tyolo dyke in

Malawi Sill This is an intrusive feature which lies horizontally along the bedding planes. I is formed when a a small-scale intrusive feature Bedding planes x Laccolith Kin i Batholith r ‘ Phacolith This is a lens-shaped mass of igneous rock. It is formed when magma cools and solidifies at anticline and syneline in folded rocks

Phacolith Anticline

Synelin Limb. ‘An example of a phacolith is The Gordon Hill in UK. Features Resulting from the Processes of Volcanicity Classify feanures resulting from the processes of volcanteity Eruption of magma, either intrusive or exirusive, results in the formation of features. Intrusive features are the result of cooling and solidification of magma inside the crust. The features formod includes dyke, sill, laceolith and batholith, Extrusive features include the formation of

volcanoes, domes, craters and calderas. Distribution of Major Volcanic Zones in the World Locate the diswrbusion of major volcanic zones in the world Extrusive (external) yuleanicity ‘This is the type of vuleanicity that occurs when molten rocks teach the surface of the earth When magma emerges at the surface it is called lava. This forms features called extrusive features of vulcanieity. The following are landforms due to extrusive vuleanicity

Acidic lava cone This is a cone made of viscous lava. Normally lava cones have high heights and break into small Fragments. The acidic lava always cools faster than basic lava because is it viscous, bey HEE ie SS — Pipe Kenya found in Kenya ast Africa) Mount Fuji found in Japan Mount Vesuvius found i aly Pipe Koes ae + Basic lava cone

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near to Lake Kivu in DRC This 15 a cone made up of ashes and stones that rupted from beneath (interior) the earth to form ee ak 6 the er and ud up acne Ash and

Cinder ; Pipe

Vent Teleki (both cinder cones), and Nabuyatom (ash cone) Other examples of cinder cones outside Crater Volcanic plug This is a big rock which plugs or blocks the top of the pipe, Its formed when lava solidifies quickly to block the pipe. Examples of volcanie plugs are Mount Palace in France and Hoggar mountains in Algeria.

plug (neck) volcano oe : java cone Composite cone This type of a cone is formed of alternate layers of ash and lava. The voleano begins each eruption with great violence forming @ layer of ash, As the eruption proceeds, the violence esases and lava pours out forming a layer on top ofthe ash keeed composite ates cones tin. 33 SEN S55 i BMS oh 5 SSS ash laver Ne Be sera lava layer

Examples of composite cones are Mount Kilimanjaro, in Tanzania and Mount Cameroon. Other

examples outside Affica are Vesuvius, Fina and Stromboli, all of which are in Italy

Caldera This is large depression on top of a voleanic cone. It is formed when a composite voleano explodes so violently that its top is blown off and disintegrates into a mass of rocks and ashes, leaving the eraier greatly enlarged. This huge erater-like depression is what we call 2 caldera Sometimes a caldera can be filed with water to form a caldera lake. Lake Shala, in Ethiopia, is the largest caldera lake in the world

Examples of calderas are

• Ebogar caldera, in Cameroon; and
• Longonot caldera, in Kenya, which lics in the Eastern Rift Valley, about 140 km south of

Mount Kenya

The stages in the formation of a caldera First stage:Magma cannot escape to the surface and collects under the lower crust. Lower crust

Mantie Pipe

Second stage-An ‘uplifted bulge’ begins to form under the lower crust as the magma chamber enlarges. ‘Lower crust Magma chamber

Mantie Pipe

Third stage:Cracks appear on the surface. Gas and ash erupt from the magma chamber through these cracks, Lower crust ‘Magma chamber

Mantie Pipe

Fourth stage: The magma chamber collapses and a depression is formed. This is called a caldera, Caldera Lower crust Magma chamber

Mantie Pipe

Geysers and hot springs

• A geyser refers to the forceful emission of hot water and steam from the ground to a high

level inthe ai. The ejected water contains fine materials such as voleano mud, which later form fertile soils. Geysers are found in Iceland, North Island and New Zealand, 2, Arhot spring refers to natural outflow of superheated water ftom the ground. It contains mineral substances in solution, Hot springs are found in Iceland, in Europe; and Kenya and

Ethiopia, in Africa

ese Geyser or hot spring 84 fy Hot springs are also found in Manyara National Park, Songwe, in Mbeya and in Nigeria. Lava plateau This is an extensive and flat landform which is formed when molten magma flows onto the earth's crust through fissure, Examples are found in Ethiopia highland, Bui plateau in Nigeria and Dacean plateau in India.

ch ~ fissure Distribution of major volcanic zones inthe world continents bordering the Paifie Ocean, an area refered to as Ring of Fire. The Ring of Fire is the name for the area around the Pacific Ocean where so many of the world's volcanoes are found. Besides volcanoes, there ace also more earthquakes in Ring of Fire than the rest of the sword Many island, ike the Hawaian Islnd, ae fred frm volcanoes.

Ring of Fire

eS : . wu SOS. Se eaee _—s ‘The Economic Importance of Volcanoes Assess the economic importance of voleances Vuleanicity results to features that are of economic value to man as outlined below.

1, The larva poured onto the earth's surface following vuleanicity forms a fertile soil upon weathering. This soil supports agriculture as well as forestry. Examples of fertile voleanic soils that resulted from volcanic activities are the rich acidic soils on the slopes of mounts Kilimanjaro, Kenya and Elgon, which supports the growth of cofiée, banana, tea and other crops.

2 When the magma solidifies, it forms hard rocks that ean be quarried and used to construct roads, bridges, houses and other infrastructures

• Speetacular features formed upon vuleanicity such as mountains, calderas, caldera lakes,

‘cones, geysers and hot springs are interesting to Took at. As such, they attract tourist and hence eam foreign currency to the county. 4, Vuleanicity brings minerals from deep the earth's crust to close or onto the earth's surface. Various minerals and gemstones are mainly found in the voleanie regions. Diamond in Mowadui is mined from the volcanic plugs and dykes. Gold and silver are associated with the Nyanza batholith in Kenya

• Geysers can be harnessed to generate geothermal electricity. Geothermal power is tapped

fom geysers in voleanie regions. In East Affica, geothermal power stations are established at Olkaria near Naivasha in Kenya.

• Hot water from hot springs is pumped into homes during winter to heat up homes. This is

done in cold countries like Iceland and New Zealand,

• People use hot springs and pools of hot water as spas. ‘They bathe in the water for the

purpose of curing certain diseases 8 Some erater lakes are a souree of salts and other minerals while others support fishing activities, for example Lake Chala. Some lakes are a source of fiesh water for domestic and industrial uses, Earth-quakes

Earthquake, Epicenter and Focus

Define earthquake, epicenter and focus Earthquakes refer to the sudden shaking or vibrations of the earth’s crust due to sudden and rapid displacement of tectonie plates along the line of weakness (fouls). It occurs mainly in volcanic ‘eruption zones (see 2 map of volcanic zones above) The point fom which the earthquake originates is known as focus and the intensity of earthquakes can be measured by using an instrument called seismograph The point on the surface vertically above the focus is called

epicentre How Earthquake can be Detected Describe how earthquake can be detected The intensity and magnitude measure the stwength of the earthquake, These are obtained by detecting the Seismic waves using instruments called seismograph or seismometer Intensity is a measure of how hard the earthquake shakes the ground, It is determined through the

effects produced by the earthquake, Intensity varies from one place 1 another, While the

intensity of a specific earthquake varies its magnitude does not vary. So it is important not to confuse mageitude with intensity The scale which measures the mtensity is called Mercalli scale. It ranges from undetectable, moderate, strong to major catastrophe. Magnitude refers to the total amount of energy released and itis given on the Ritcher scale, This scale ranges from 0 to 8.9.

The Causes and Effects of Earthquake Explain the causes and effects of earthquake

Causes of earthquakes

• Faulting of the lithosphere caused by tectonic movement where one plate slides over

another plate

• Vuleanism can cause occurrence of the earthquake. This is due tothe fact that the magma

moves under the inuence of intense pressure from within the earth's interior.

• Mass wasting like Tand slide and rock fill can cause occurrence of earthquake, but this is

for loeal scale

• Falling objects from the etmosphere such as meteorites may lead to the shaking earth's
• Man's influence through his activities such as mining using explosives like dynamites

and transport vessels like trains and heavy trucks.

Effects of earthquakes

occurs, it causes a lot of disturbances including loss of life and properties. For example, the earthquake that hit Toro in Uganda in 1966 killed 157 people, injured about 1300 people and destroyed about 6000 houses. The earthquake which occurred in Califomia-Mexico border in 1975 caused damage running into millions of dalla and injured 100 people on both sides ofthe border whore most of them suffered cus from flying gloss and debris. And the earthquake that

occurred in Northridge in the San Femando Valley in California in January 1994 Killed 61 people and caused damage estimsted at ten to thirty billion dollars. This damage includes the flyover to ruins.

• ‘They can displace parts of the earth’s crust vertically or laterally.
• They can raise or lower parts ofthe sea floor. The Agadir earthquake in Morocco in 1960

raised the sea flour off the coast. In some creas the depth of the sea dereased from 400 m to 15 matter the earthquake.

• They can raise or lower coastal rocks. In the Alaskan earthquake of 1899, some coastal

rocks were raised by 16 m.

• They can cause landslide and open up deep cracks in the surface rocks. The El Asnam

earthquake in Algeria, in 1954, destroyed an area of radius 40 km and opened up deep cracks up to 3m deep The possible Areas where Earthquake is likely to Occur on the World Map Locate the possible areas where earthquake is likely to occur on the world map Precautionary measures to avoid high damage from earthquakes

• Refining from building high-rising structures on the land vulnerable to earthquake as

well as strengthening buildings by using reinforced concrete, steel frames, deep foundations and light roofs

• Geologists should detect epicentres and tell the people to evacuate the places likely to be

affected by earthquakes

• To avoid constructing very large water bodies like Kariba dam which ean cause the

‘earthquakes due to the weight of water and other materials

• Discouraging the use of explosives like dynamites in breaking the rocks during mining

and construction operations

External Forces

These are natural forces that operate on the earth’s surface. The forces mainly act on the earth's est or close the surface ofthe earth, Often the features produced by these forces are seen om the surface of the earth, They include mountains, volcanoes, moraines and valleys, just to mention @ few

Mass Wasting

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

Types of Mass Wasting

Identify types of mass wasting

Types of mass movement are distinguished based on how the soil, regolith ar rock moves down

the slope asa whole, Based on this factor, mass wasting can be categorized or grouped into two types. These are slow and rapid mass movements, each with iis own characteristic features, and taking place over timescales from seconds to years.

Slow mass movement This is the inbvement of coil web slow apes, wter acta the Riricant. Stow mass soil ete Very slow andi evidene i provided by iting OF Woes and aling of buildings and Feces, aia ne ee Ty Qos down the sidpe. The following fio itluenc sll cee a -Aeuate ea andl cog tthe si patie, €—_etiovel oF htt arteritis Percolation of water into the soil, acting as a lubricant.

€ —_Ploughing of the soil, a factwhichmakes the soil loose and more mobile.

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This is also a very slow mass movement of screes. It is very common on sides of mountains, scare and valleys, I takes place due ta the processes of thawing and freezing end is more Rock ereep Individual rock blocks may move very slowly down a slope. It occurs commonly. where individual rock blocks are lying over clay materials. Inthe presence of moisture, the clay surface becomes slighily slippery. The rock blocks may creep slowly down the slope under the influence

of gravity. Solifluction This is the slow movement or flowing of weathered materials, especially when mixed with water and gravels, It is limited on highlands and cold regions. Rapid mass wasting This involves the movement of materials in form of wudflow land slide, rock fall and earth flow Earth flow This type of movernent occurs in humid regions. The materials on the earth's surface gets so saturated with water that it gains much weight, and starts to move down the slope under the

influence of gravity. This normally occurs on the slopes of the hills or mountains, The removed carth material leaves a shallow scar on its place of origin and it creates terraces or mounds in its destination Mudflow Mudflow is the movement of a large mass of unconsolidated rocks down the slope when saturated with water. It lows in semi liquid state. It is common in desert slopes, which are not protected by a cover of vegetation. This oceurs, for instance, during a torrential storm when more

rain falls than the soil cam absorb Land slide This is the rapid movement of surface rocks and soil down a steep slope such as a cliff face. includes slumping and sliding of materials. During the movement, the block tilts and leaves holes, It is common inwell jointedlimestone socks, shale or clays. The common forms of landslides are slump, debris slide, rock slide, rock fall, debris fall and avalanche.

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The Factors which Cause Mass Wasting

1 Gradient or slope:When the gravitational force acting on a slope exceeds its resisting ical fi (nan wating) ore nas ntng vey commen vere tee Wahaus GC oui Cat Hagia MA ae ua ln vaste died on minivan: tceoumcss ie ar onion slope depending on the amount present. Small amounts of water can strengthen soils because the iF were dry. Iftoo much water is present the water acts as lubricating agent, reducing friction, and accelerating the erosion process, resulting in different types of mass wasting (i.e. mudflows,

landslides, ete). Water also increases the mass of the soil, this is important because an increase in mass means that there will be an increase in velocity and mass wasting is triggered. This is due to the fact that water lowers resistance of the soil material to gravitational forces and this, facilitates movement, 4 Vegetation: The roots of plants help bind the soil particles together making the soil resistant to agents of erosion and weathering, A compact soil cannot be eroded easily by running

water, animals, wind or other agents of erosion. This makes the soil hard to break and hence resistant erode. Mass wasting processes, such as soil creep, cannot oceur easily in soilswel coveredwith vegetation. Also the mass of vegetation cover blocks and prevents movement of the eroded material Plants remove water from the ground via absorption. This reduces the amount of water in the soil and hence the bulkiness and weight of the soil. By so doing, they reduce the

‘quantity of water in the soil. And because water lubricates the soil particles, enabling them to move, reducing this water means minimizing mass wasting The sliding of bedding planes over each other is also reduced.

• The nature or type of the rock materials:Clay soil is compact and resistant to various

types of soil erosion agents and mass wasting as compared to sandy soil, which is normally loose

and easy to remove and transport by water, gravity, wind, ete. Thus, mass wasting may be more severe on sandy soil than its counterpart clay soil under similar prevailing conditions.

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

• arthquakes:Earthquakes cause sections of the mountains and hills to break off and

slide down. Earthquake tremors tend to loosen the soil material and make it easy to be removed and transported. It can accelerate rock falls, landslides and soil creeps. 8 Human activities:Theactivities of man such as. cultivation, burning, mining, transportation, animal grazing, ete, removesthe soil cover or leads to shaking of the soil. These activities leads to loosening of the soil particles and hence making it ease to remove and carry

away. Quarrying by undercutting the slope creates a vacuum underneath the soil. This accelerates the earth movement in the form of landslide, soil ereep and mudflow, especially when accompanied by tremors eause by earthquake or heavy vehicles passing nearby.

• Climate:Climate has a great influence on mass wasting. Areas that receive heavy rains

ofien experience mass movements, such as landslides and soil creep, more often compared to dry areas. On the other hand, a little amount of rainfall does not wet the soil and 50 cannot eause the soil 10 move In cold regions, alternate freezing and thawing triggers mass wasting. When the water in the soll freezes it expands. This causes the soil to be lifted up. In the due course, the rock particles are split apart of broken down. This entire process causes movement of the soil

material down the slope,

• Vuleanicity:Volcanic activity often causes huge nmdflows when the icy cover of a

volcano melts snd mixes with the soil to form mud as the magma in the voleano stirs preceding an eruption The Effects of Mass Wasting to the Environment Assess the effects of mass wasting to the environment Mass wasting has significant effects to the environment. ‘The following are some of the effects of mass wasting to the environment 1 Formation of scars and bare land:When a large mass of soil moves, such as it occurs in

landslide, the process leaves behind a large portion of eroded, bare and unproductive land. This land is often not easily colonized by plants, a fact which stimulates further erosion on the bare sear. Sears are very common on slopes of mountains such as mounts Kilimanjaro, Kenya andRwenzori 2 Soil erosion: When mass movement takes place, the load often removes almost all the vegetation on its way. This exposes the land to agents of erosion such as wind, animals, water,

ice, waves, ete. Also the place from which the material has been removed forms a scar upon which water, ice and other agents of erosion can act and remove the soil, further leading to aullies, depressions and gorges,

• Formation of new landforms:The materials removed and transported to a distant

location may form hills at their destination and form scars and depressions atthe place of origin 4 Formation of lakes:Materials of landslide can block ariver bedand valley, preventing downward movement of water. The blocked water accumulates on the upper side of a river valley to form a Take. Examples of such lakes. include LakeBujukuin theRwenzoriMountains.Nyabihohoin Uganda andFunduziin South Africa, Lake San Cristobal in

Colorado, USA, was formed when mudflow dammed (blocked) a river in the San Juan Mountains,

• Diversion of river course:The landslide material can block the naturatriver bed,

forcing the river to divert and form @ new route. This makes the river leave its usual flowing course, and form a new course. The direction of flow of the river is thus changed. This happened in the Rif Atlas Mountains of Morocco in 1963 when a mudflow pushed the course of RiverRhesana] 00 metres to the east

• Formation of a fertile sol:If the removed material comes from a fertile Land, it ean form

a fertile soil at the place of destination, where fertile soil never existed, and encourage agricultural activities to take place.

• Damage to property:Different categories of landslides may cause various damages to

property and can adversely affect other resources. The effects of landslide are dangerous because they destroy everything in their path Roads ate blocked, hampering traffic flow. Homes, buildings and other infrastructures are destroyed. The water mains, sewers and power transmission Tines are disrupted Oil and gas production and transportation facilities are ruined.Farms are also destroyed by various forms of mass wasting,

• Loss of lifesAs human populations expand and occupy more and more of the land

surface, mass movement processes beeome more likely to affect humans. The table below shows the impact of mass movement processes on human life over the last century

Year Location ‘Tyne Fataigfs

1916 Hialy, Austria Landslide 0.00] 1920 China Farthquake tiggered landstie 200,00 1945 Japan ood triggered landslide 1200 1919 USSR Earthquake triggered lndstie 12,000}, 1984 Austria Landslide 200 1962 Pe Landslide 4,000.40 1963 aly Landslide 2,000 1970 Pew Earthquake related debris avalanche 7,000 19S Columbia Mudow related to voleanc eruption 23,00 1987 Keundor Earthquake related lndside 1,000 1998 Nicaragua Debris avalanche and mudlTow triggered by heavy rins during Hurcane Mish ~2,000

2001 Salvador Karthguake-induced landslide 585 2006 Philippines Rain triggered debris avalanche >1100 2009 Taiwan Typhoon arakotrggered landstide 27 2010 Gansu, China Rai triggered muctiows 17 2013 Nontcmn Inia Heavy rin iggeted landslides 5700 Weathering Weathering Weathering refersto a processeswhere by rocks disintegrate into small particles due to the agents that i, changes in tempersture, Fost action and rain action,

‘Types of Weathering ‘The main forms of weathering include: © Mechanical weathering; Mechanical weathering Mechanical weathering include the following types: The peeled off rock fragments fall to the bottom of the standing rocks and are subjected to fragments collect at the base of the standing rocks to form mounds of steeply sloping rock produced by the action of frost. ‘The rocks that remain standing as exfoliation takes place are

‘There are many exfoliation domes in the Egyptian, Kalahan, Sahara and Sinai deserts. Lemperatue falls (freezing point) water collects inthe rocks and it freezes, its volume increases ‘causing the crack to deepen and widen. Usually it involves the freezing of water in the cracks daring the night and thawing (melting) during the day in mountainous areas. This aston of angular faginents wiich form cress and tls. Afr thawing the cracks deepen futher,

‘eerebs a Altes wetigatliying This usully occurs in tropical regions. These areas have seasonal rainfall and they get rin disintegrate

Differences between Weathering Processes

Differentiate weathering processes Chemical weathering Sime rocks decompose when they come into contact with water (H,0), or oxygen (O;) and carbon dioxide (COs), two of the gases that make up airChemical weathering includes the following processes 1 Oxidation This happens when oxygen combines with a mineral I takes place actively in rocks containing iron, when oxygen combines with iron to form iron oxides. This process is

often preceded and accompanied by hydrolysis The new minerals formed by oxidation ate often easily attacked by other weathering processes. 2 Carbonation- This process occurs when hydrogencatbonate ions react with a mineral to ive a solublecompound whichean be earried away in solution. Hydrolysis often accompanies carbonation,

• Solution-This refers to dissolution of a mineral with a chemical substance Rain

watercombines with both atmospheric carbon dioxide and oxygen to form weak carbonic acid COAg) + H0() + H;COs{aq).So when the rain reaches the ground it consists of a weak acid called weak carbonic acid. This acid helps to dissolve many insoluble minerals into minerals soluble in water, and which can be earried away in solution. When rain containing weak earbonie acid falls in a Timestone region, it reacts with limestone (calcium carbonate) and dissolves it into

soluble ealeium hydrogen carbonate, which can easily be carried away in solution CaCOs(s) #COsfaq) —r Ca(H1COs)x(aq)in limestone regions, the rocks are dissolved and produce features, like grike andelint{trough and ridge) 4 Hydration This is the process in which some minerals absorb water and swell up, ‘causing intemal stress and fracture ofthe rocks.

• Hydrolysis~ This process involves the reaction of hydrogen (in the water) with certain

mineral ions (in a mineral). This gives rise to the formation of different chemical compounds that can be easily weathered through other weathering processes NOTE: Usually two or more chemical weatherimg processes take place at the same time.

Chemical weathering is most marked in hot wet regions Biological weathering: When plants grow on rocks, their roots penetrate into rockjoints whichlater force the rocks to break apart. Also man contributes much to rock disintegration through farming activities, mining, quarrying and construction. Macro- and microorganisms also disintegrate rocks through burrowing and by mineralization process. Bacteria, for example, in the

presence of air, break someminerals whichare dissolved in the soil. Plants also absorb minerals from the soil by their roots. Decayed vegetation produce organicacid whichremain in the soil. All of these actions help to weaken the rocks.

The Significance of Weathering

Assess the significance of weathering Weathering is important to man in the following ways:

• Weathering leads to soil formation. Soil is formed through the process of weathering of

rocks. Various forms of weathering lead to rock disintegration and hence formation of the sol. The soil is an aggregate of organic and inorganic particles formed by different processes of weathering 2, Weathering may shape the rocks into attractivefeatures whichcan attract tourists and hence carn the country and communities the much needed forcign exchange. An example of a feature that can attract tourists isthe Bismarck Rock on the south shore of Lake Victoria

3, The procesces of weathering weaken the rocks such thatthey can be easily acted upon by agents of erosion. The process helps to shape the earth and produce various landforms. This, in tum, influences the type of human activities that can take place in an area, So the process is very important in supporting life 4, When the rocks are weathered they become weak and hence easy 10 exploit, eg. by ‘quarrying. This process also helps to break up large rocks into small fagments such as sand,

Which is used for construction purposes.

• Weathering serves as carbon sink Any process that reduces the amount of carbon dioxide

from the atmosphere is termed ascarbon sink, Some processes of weathering involve absorption ‘of carbon dioxide from the atmosphere, This helps to remove excess carbon dioxide from the atmosphere, Limestone and other carbon-based sedimentary rocks are important carbon sinks, Erosion and Deposition by Running Water, Ice, Wind and Wave Action

The Concept of Erosion and Deposition

Define the concept of eroston and deposition River refers to a mass of water flowing through a definite channel over a landscape fiom river source to river mouth. River source is the place where a river starts It may be in the melt water from glacier @g. river Rhome (France), a lake, eg Lake Vietoria, the source of river Nile, a spring eg. Thames (England) or it can be formed following, steady rainfall eg river Congo

River mouth ean be anywhere a river pours its water, ¢.g, 2 lake, ocean or sea, How Agents of Erosion and Deposition Operate on the Landscape Examine how agents of erosion and deposition operate on the landscape The river has three fimetions as it flows through its channel. These are river erosion, transportation and deposition River erosion Erosion of a river operates in three ways, that is, head ward, vertical and lateral erosions.

• Heard ward erosion- this is the cutting back of the river at its source. It is through this

erosion that a river increases its length

• Vertical erosion this is erosion by which a river deepens its channel
• Lateral erosion This isthe wearing away of the sides of a river by water and its toad. I

is responsible for widening of a river valley River erosion involves four related processes. These are abrasion (cortasion), attrition, corrosion (solution) and hydraulic action

• Hydraulic action-This is the process whereby the force of moving water plucks and

sweeps away loose materials, such as silt, gravel and pebbles. Materials plucked by hydraulic action are responsible for bank caving and slumping,

• Corrasion (abrasion):This is when the load of the river cubs against the bed and sides of

the river channel. This causes wearing away of the sides and bed of the river. The amount of load determines the nature of erosive power and rate of erosion. This 1s a source ofpot holesin the river bed

• Attrition:Vhis is when the tock fragments in a river's load are broken into small

fragments due to collision against one smother as the load is carried downstream along the river channel. As the river moves along its course, its fragments get progressively smaller because of disintegration and wearing away.

• Corrosion (solution):River water dissolves certain mincrals leading to dissolution and

disappearance of some rocks, ¢.g. limestone, rock salt and chalk, River transport This is the process which involves carrying away of the weathered and eroded, loose materials from one place to another. The materials carried out by river is called Toad, River transports its load in four ways. These ways ate as follows

• Salrarion- this isthe process in which small pieces of the rock fragments are carried by a

river while bouncing on theriver bed. 2 Traction~ this is the dragging or rolling of large boulder such as pebbles along itsriver bed.

• Suspension This involves transport of fine or Hight materials lke silt and mud, which are

carried in suspension forms. This is common when the river flow is 100 strong.

• Solution this involves moving some materials that dissolve in water, which are carried

away in solution form, AA river transports its load until i¢ has insufficient energy to transport it any further, When this happens, the load is deposited. River deposition A river deposits its load when its volume and speed decrease. A river volume decreases when: 1, itenters an arid region especially hot desert;

• iterosses a region composed of a porous rocks e.g. sand and limestone; and
• duringthe dry seasons or in a period of drought.

A river speed decreases when: 1 itenters a lake or sea: or 2 whenit enters flat or gently slopping plain such 2s a valley bottom. Deposition takes place when the river has insufficient energy to carry its entire load. The first part of the load that is dropped consists of boulders and pebbles. The last part to be dropped is the fine sediment, calledsilt. Deposition takes place at any point in a river's course

THE LONG PROFILE OF A RIVER

• It is sometimes utilized for hydroelectric power (IHEP) generation,

Erosional and Depositional Features for each Agent pot holes on the river bed; interlocking spurs and waterfalls and rapids, often with plunge pools.

• Pot holes:These ate circular depressions on theriver bed. They are Formed when pebbles

carried by the swirling water cut circular depressions in the river's bed.

• Interlocking spury:Aninterlocking spur, also known as anoverlapping spur, is one of

any of a number of projecting ridges that extend altemately from the opposite sides of the wall of 4 young, V-shaped valleydown which a river with a winding course flows. Fach of these spurs extends laterally into a concave bend of the river such that when viewed either upstream or from ‘overhead, the projecting ridges, which are calledspurs, appear to "interlock" or "overlap" in a staggered formation like the teeth of a zipper.As the river erodes the landscape in the upper

course, it winds and bends to avoid ateas of hard rwek This ereatesintertocking spurs.

• Waterfalls and ropids-Waterfall-Awaterfallis a place where water flows over a vertical

drop in the course of a stream or river. A waterfall is formed when there is sudden change o drop in the bed of a river. Although waterfalls can occur in almost any part of river's course, they are most common in the upper course. Examples of waterfalls are Owen Falls in Uganda, Victoria Falls in Zimbabwe and The Livingstone

The Yosemite Falls in USA

• Rapids-These are sections of a river where theriver bedhas a relatively steep gradient,

causing an increase in water velocity and turbulence.Rapids are characterised by the river becoming shallower with some rocks exposed above the flow surface. As flowing water splashes ‘over and around the rocks, air bubbles become mixed in with it and portions of the surface acquire a white colour, forming what is called "whitewater" Rapids occur where the bed material is highly resistant to the erosive power of the stream in comparison with the bed downstream.

Very young streams flowing aeross solid rock may be rapids for much of their length. a at t < PheepociTt unary deci fil alba of a wml The middle/maturity stage/section rapids. ‘The characteristics features of the middle course of a river valley 1 ‘The speed of a river is fairly low.

• Most of the work of a river is transportation
• The cross-section of a valley in this section is an open V

4 The slope of a relietis gentle

• The volume of a river increases.
• Lateral erosion predominates,

Features associated with the middle course of « river valley

• Bluffs: These are steep slopes of the truncated spurs in middle course where interlocking

spurs tara into iu,

• Waterfalls and rapids: Waterfalls and rapids can also be found in the middle stage of the

river valley, This is mainly caused by riverrejuvenation which inereases erosive activity and transportation, hencedevelopment of waterfalls. The old/lower stag Third is the third stage of a nver. ‘The main features of the lower section of a river valley are @ food plain; braided river; ox-bow lake; levee and deferred tributary and delta.

lis characteristics areas follows

• Itisthe river mouth,
• Always there are gradient falls or slope falls.
• The main work of a nver is deposition
• ‘The cross-section of a valley is a U-shaped valley.
• ‘The speed of a river is decreased

6 The river valley is very wide The Importance of Erosional and Depositional Features to Human Beings Assess the importance of erosional and depositional features to human beings Some feaiures resulting from erosion and deposition are very important to human beings in the following ways: Loess form very fertile soil in desert land, water falls attract tourists, headlands in coastal areas are natural ports. Coastal features form breeding places for fish, coral reefs are

used as building materials and for settlement.

Artificial Forces

‘The Meaning of Artificial Forces that cause Earth Movements Explain the meaning of artificial forces that cawye earth movements These are forces that are caused by human beings through their activities such as farming, mining, setting up setilements, road construction, transport, etc. In the previous sections we learned about the natural forces that affect the earth. We saw that the forees act on and within the earth, These forces occur naturally with Tittle rn human intervention

In this section, we shall deal with forces that occur as a result of human actions, hence called artificial or man-made forces. Man is considered as an agent of denudation, that is, he takes part in destruction or removal of some parts of the earth's surface. This shows that man can modify natural landforms and, therefore, acts as the agent of weathering, mass wasting, erosion, transportation and deposition on the earth's surface.

Human modification of the land helps loosen large chunks of earth and cause them to slide downhill. Man produces forces that affect the carth through the following activites:

• Removing vegetation: slope with lots of vegetation is less susceptible to mass

movement than a bare slope Bare, exposed soil is very easily eroded, and can contribute to mass movement activity. Vegetation: helpshold soil, loose rock, andregolithtogether by its roots reducesthe direct erosive impact of rainfall and other precipitation; activelyreduces ground moisture by using it to contribute to plant growth; and produceslitter and organic products (leaves, twigs, grasses, fits) that help stabilize the soil

• Mining:In the course of mining, man uses machines to dig the soil and blast 1ocks. These

activities results to earthtremors whichloosen the soil particles making then vulnerable to removal by agents of weathering and denudation. Blasting also causes fractures in rocks, a Fact which makes them less stable and resistant to shear and stress. If this happens, especially on steep slopes, the probability of occurring landslide is very high

• Farming netivities:Farming involves digging the soil by using farm implements such as

hoes, traciors, hartows, spades, ete. These activities involvesbreaking up the soil and rocks by the implements. In this way, crop cultivation directly leads to weathering and erosion, Overstocking (keeping many animals in just a small piece of land) also leads to soil erosion. This is because overstocking is usually accompanied with overgrazing, an act which removes the vegetation cover. This triggers sol erosion and other weathering processes

• Building and construetion:Breaking up the soil for construction of houses and other

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

• Fishing:Fishermnen in less developed countries sometimes use weapons. such as

dynamites to kill and cateh fish, Tremors produced by these illegal fishing tools can eause Fracturing of the coastal rocks. This causes both weathering and erosion,

• Navigation:in some few cases, marine vessels accidentally crush onto stones in water,

peeling or breaking then into pieces This leads to rock disintegration, a typical form of weathering.

• Transport:Vibrations from machinery. traffic, weight loading, stockpiling of rock or ore

from waste piles and from buildings and other structures loosen the soil and make it prone to soil ‘erosion and weathering

• Construction of dams and eanals:Construction of dams, such as theMteradam in

‘Tanzania and canals such as the Suez Canal in Egypt, involves removing @ large junk of tock This breaks up the soil, leading to weathering and soil erosion,

• Warfare:The use of atomic bombs and other heavy weapons in war leads to destruction

of the soil. During times of war, heavy and destructive weapons such as atomic bombs, shells, rockets and grenades are dropped or fired towards the enemy. When these weapons fall on fand, they detonate and blow up a large mass of the earth, causing weathering and erosion Military equipment such as tanks, heavy trucks and caterpillars break up rocks over which they pass. At the same time, they loosen the soil and carry away some of it as they move along,

The Causes and Effects of Artificial Forces Describe causes and effects of artificial forces Apart from the effects caused by natural forces that affect the earth, man-made (artificial) forces have an effect of creating artificial landforms and features on the earth's surface. These include the following features

• Man-made lakes such as LakeCahoraBassain Mozambique, Lake Volta in Ghana,

LakeKaribain Zambia (the world’s largest artificial lake and reservoir by volume) and Lake Nasser in Egypt. 2, Man-made rivers in the form of canals such as Suez and Panama Canals,

• Wells and boreholes
• Roads, harbours, railways, airports, bridges, ete