◄UNIT 2 :THE ORIGIN AND DISTRIBUTION OF THE CONTINENTSUNIT 4 : WAVE EROSION AND DEPOSITION►

UNIT 3:EXTERNAL LANDFORM PROCESSES AND RELATED FEATURES

  • UNIT 3:EXTERNAL LANDFORM PROCESSES AND RELATED FEATURES

    Key Unit competence:
    By the end of this unit, I should be able to demonstrate an understanding of 

     different landforms resulting from the external processes.

     Introductory activity
    Observe the photographs below and explain the processes that affected 

    the rocks that appear on them.

    3.1. Definition, types and process of weathering

     Learning activity 3.1

     1. Differentiate physical weathering from chemical weathering

     2. Outline the processes of chemical weathering

     3.1.1. Definition of weathering

     Weathering refers to the process of disintegration and decomposition of rocks 

    into small particles by the action of weather and living organisms.

     Agents of weathering include the temperature, rainfall (water), wind, animals 

    and plants (vegetation).

     3.1.2. Types of weathering and processes
     There are three types of weathering namely physical or mechanical 
    weathering, chemical weathering and biological weathering which cuts 
    across each of the physical and chemical weathering.

    i) Physical weathering
     Physical weathering refers to the breaking down or disintegration of rocks, 
    without any change in the chemical or mineral composition of the rock being 
    weathered. Rocks disintegrate into smaller particles but maintain their previous 
    chemical characteristics. Only the physical size and shape change. Physical 
    weathering is mostly influenced by temperature changes.

    Processes of physical weathering include:
    1) Thermal expansion or insolation weathering:
     This process is caused by the changing of temperature ranges which 
    causes differential heating of minerals forming the rock. When heated 
    dark minerals expand, faster than others resulting in cracking and 

    fragmentation of the rock

     2) Exfoliation
     Exfoliation occurs when there is expansion of rocks during the day and 
    contraction of rocks during the night due to repeated temperature changes. 
    This process is common in arid and semi-arid regions. This results into rocks 
    of a few centimeters thick to start peeling off (breaking away) leaving behind 

    exfoliation domes.

     3) Freeze thaw
     This process also called frost weathering (or frost shuttering) occurs due to 
    water that enters into the cracks of the rocks; this water freezes and expands 
    exerting pressure within cracks. Water from rain or melting snow and ice is 
    trapped in a crack or joint in the rock. 

    If the air temperature falls below freezing point, the water freezes and expands. 
    As a result, the rock becomes weak and breaks. This process is common in cold 
    regions, especially glacial, periglacial and high mountainous zones. The figure 
    below shows steps from infiltration of water into the rock to the condensation 

    within rock fissure which result in the fragmentation. 

     4) Pressure release 
    The process of pressure release known as the unloading or dilatation 
    weathering occurs when materials on top are removed by erosion. This releases 
    (decreases) pressure, which causes the materials below to expand and crack 

    parallel to the surface.

     5) Salt crystallization
     The process of salt crystallization weathering illustrated on the figure below 
    occurs when saline water (or water carrying salts in solution) passes through 
    cracks and joints in rocks. As it evaporates, the dissolved salts change into salt 
    crystals. These crystals expand within cracks as they are heated up and apply 

    pressure on the rock leading to its breaking up. 

    6) Shrinkage weathering
    Some clay rocks expand after absorbing water. For instance, there are some 
    clays which swell when they absorb water during rainy seasons. This results 
    in increase in their volume. During dry seasons, they massively lose this water 
    through evaporation and they contract. This process of alternation of expansion 
    of these rocks during the wet season and contraction of clay during the dry 
    season is known as shrinkage. This creates stresses and weakness of rocks 
    causing cracks within the rock.

    7) Granular disintegration
    This takes place almost in the same way as exfoliation except that in this type, 
    rocks disintegrate into small particles called granules. It is produced either by 
    differences in thermal expansion and contraction, or through the frost heaving 
    process (congeliturbation).

    ii) Chemical weathering
     This is a type of weathering which involves a complete change in the chemical 
    and mineralogical composition of the rock resulting into the disintegration of 
    rocks. It is common in areas which experience alternating wet and dry seasons.

    The following are the chemical reactions that take place during weathering: 
    1) Oxidation: oxidation is one of the varieties of chemical weathering 
    in which oxygen dissolved in water reacts with certain rock minerals, 

    especially iron, to form oxides.

    2) Carbonation: This is the process through which rain water dissolves the 
    atmospheric gases of carbon dioxide (CO2 ) to form a weak carbonic acid 
    which reacts rocks to wear (weather) them away especially in limestone 
    areas. After reaction, new compounds are produced as it is shown by the 

    following equation:

     3) Dissolution: Dissolution is one of the less important forms of chemical 
    weathering, in which solid rocks are dissolved by water. When water (e.g. 
    rainwater) mixes with carbon dioxide gas in the air or in air pockets in soil, 
    a weak acid solution, called carbonic acid, is produced. When carbonic 
    acid flows through the cracks of some rocks, it chemically reacts with 

    the rock causing some of it to dissolve.

    4) Hydrolysis: Hydrolysis involves water combining with rock minerals to 
    form an insoluble precipitate like clay mineral. Compared to hydration
    - a physical process in which water is simply absorbed, the hydrolysis 
    process involves active participation of water in chemical reactions to 

    produce different minerals.

    5) Hydration: Hydration is one of the major processes of mechanical 
    weathering, involving the addition of water to a mineral, causing it to 
    expand and thereby initiate stress within the rock. For example the 
    conversion of hematite to limonite. Once minerals have experienced 
    hydration, they become more susceptible to the effects of chemical 

    weathering, especially those of carbonation and oxidation.

    6) Solution: is a process in which the minerals in the rock directly dissolve 
    in water without their chemical and mineralogical composition being 
    altered. e. g. olivine, Rock salt (calcium chloride) and calcium bicarbonate 
    are easily weathered in solution.

     e.g. NaCl + H2O → Na+, Cl- (dissolved ions with water).

     7) Chelation: Chelation is a form of chemical weathering by plants. It is a 
    complex organic process by which metallic cations are incorporated into 
    hydrocarbon molecules. In fact, the word chelate means a coordination 
    compound in which a central metallic ion is attached to an organic 

    molecule at two or more positions. 

     iii) Biological weathering
     Biological weathering is a process of rock disintegration (decay) due to the 
    influence of living organisms both growing plants and animals. The diversity of 
    life in soil includes plants, algae, fungi, earthworms, flatworms, roundworms, 
    insects, spiders and mites, bacteria, and burrowing animals.

    Plants wear away the rocks by their roots which widen the rock joints hence 
    allowing in other weathering agents like water to disintegrate the rocks. Some 
    plant roots also have chemicals at the tips of their roots which are acidic and 
    hence cause rock weathering.

    Tree roots find their way into cracks or joints in the rocks. As they grow, they 
    cause the joints to become bigger. The end result is that the rocks break into 

    smaller pieces at some points.

     Burrowing animals like rodents and moles, warthogs (wild pigs) and wild animals 
    in game parks like the chimpanzee, excavate the rocks and as such, they break 
    up the rocks hence weathering them. Man also disintegrates rocks through his 

    activities.

    Man’s activities such as mining, construction, quarrying, agriculture, etc. result 

    in such a fast rate of disintegration of rocks.

     Application activity 3.1
    Use your local environment to identify the evidences of biological weathering.

    3.2. Factors influencing weathering and interdependence 
    of physical and chemical weathering
     Learning activity 3.2
    Using the diagram below, explain how these elements influence the rate of 

    weathering in your local area.

    A number of factors are required for weathering to occur in any environment. 
    The major factors of weathering include relief, living organisms, time, climate 

    and rock (parent material),

    i) Relief
    The term relief refers to the nature of landscape or topography. It influences 
    significantly the weathering process because it controls the flowing of run
    off and infiltration of water through slope exposition, steepness and length. In 
    mountainous regions, the windward slopes receive heavy rainfall which may 
    speed up chemical weathering, whereas the leeward sides receiving little 
    amount of rain becoming arid. This favors physical weathering to dominate on 

    the leeward part.

     ii) Living organisms 
    Living organisms include plants and animals. They both contribute to weathering 
    in a number of ways. Growing roots of trees widen and deepen into the ground 
    and open up joints. Animals ranging from the big to small, including man affect 
    the rate of weathering both mechanically and chemically. Animals and micro
    organisms mix soils as they form burrows and pores, allowing moisture and 

    gases to move about.

     iii) Time
    The longer a rock is exposed to agents of weathering, the more weathered it is 
    likely to be and vice-versa. Young rocks such as solidified volcanic rock after a 
    fresh volcanic eruption are likely to be less weathered than rocks formed long  ago.  

    iv) Climate
     The key components of climate in weathering are moisture and temperature. 
    The type and amount of precipitation influence soil formation by affecting the 
    movement of ions and particles through the soil, and aid in the development 
    of different soil profiles. High temperatures and heavy rainfall increase the rate 
    of chemical weathering. Arid and semi-arid areas are associated with physical 
    weathering since there is low rainfall and high temperature. As the rocks 
    expand during a period of high temperature and contract during a period of 
    low temperature, they develop cracks. In addition, equatorial regions with high 

    rainfall and high temperature experience fast and deep chemical weathering.

    v) Nature of rocks
    Nature of the rock determines the rate at which it may break down. Their nature 
    depends on rock forming minerals. Some minerals are easily soluble. Also 
    environmental condition such as organic acids and temperature may increase 
    the rate of weathering of rocks. Soft rocks, for example, break down more easily 
    than hard rocks. Similarly, jointed rocks (rocks with cracks) break down faster 
    than rock substances without joints.

    vi) The interdependence of physical and chemical weathering 
    There is interdependence between mechanical and chemical weathering. 
    Chemical weathering to occur needs first mechanical process which provides 
    fragmented pieces of rocks. These rock fragments are then attacked by the 
    chemical process of weathering. Many reasons can be advanced to justify their 
    interdependence:
     • The joints and crack found in a rock as a result of physical weathering 
    allow deeper penetration of water which leads to chemical weathering.
     • Some rocks are dissolved in water and weathered away in solution. 
    The solutions formed may later undergo precipitation leading to the 
    formation of crystal. These crystals will exert a lot of pressure that will 
    disintegrate the rocks physically.
     • Hydration (chemical process) results in a high rate of absorbing water 
    by rocks .e.g.: hematite, limonite which makes these rocks to peel off in 
    a physical process called spheroidal weathering.
     • The physical process of frost shattering opens up cracks in the rock 
    and when these cracks are occupied by water, chemical weathering 
    process takes place. e.g. carbonation.
     • Roots of plants which expand within bedding planes of rocks and 
    burrowing animals which drill holes in rocks allow water entry into these 

    rocks which accelerates chemical weathering.

    Application activity 3.2
    Visit your local environment and explain how relief and climate have influenced 

    the rate of weathering.

     3.3. Landforms associated with weathering and their 
    importance
     Learning activity  3.3
     1. Identify the features associated to weathering
     2. Analyse the importance of the following weathering features
    a) Cave
    b) Oasis

    Landforms processes may be similar of different depending on whether rocks 
    have the same or different mineralogical compositions.  The major landforms in 

    different geological structures are briefly presented in the following paragraphs.

     3.3.1. Landforms associated to weathering in limestone regions

    Limestone is a sedimentary rock in which calcite (calcium carbonate: CaCO    3 ) 
    is the predominant mineral, and with varying minor amounts of other minerals 
    and clay. Limestone rocks are very sensitive to organic acids derived from the 
    decomposition of living organisms.

    The major landforms associated with weathering in limestone regions are Karsts 
    landforms that include: caverns, stalagmites, stalactites, pillar, dolines, limestone 

    pavements (uvalas), poljes.

     1) Caverns
     Caverns or caves are also one of the important characteristic features of 
    groundwater in limestone regions. Caverns are formed in several different 
    ways. The rocks in which most caverns occur are salt, gypsum, dolomite and 

    limestone, with the latter by far the most important.

    2) Doline
    Doline also called Dolina is a round or elliptical hollow on the surface of a 
    limestone region which is formed when several small hollows merge. The small 
    hollows are formed when water starts acting on the points of convergence of 

    joints on the surface.

    3) Uvala
    Uvala is a large surface depression (several km in diameter) in limestone terrain 
    (karst region). It is formed by the coalescence of adjoining dolines and has an 

    irregular floor which is not as smooth as that of Polje.

    4) Polje
    Polje is a large depression in a karst region with steep sides and flat floor. If it is 

    drained by surface water sources, it is termed as open Polje. 

    5) Stalactites
    Stalactites are protrusions on top of limestone cave formed as results of water 

    dissolving some rocks which form a solution that leaks from the roof.

    6) Stalagmites
    Stalagmites are formed like a columnar concretion ascending from the floor 
    of a cave. It is formed from the re-precipitation of carbonate in calcite form 
    perpendicularly beneath a constant source of groundwater that drips off the 
    lower tip of a stalactite or percolates through the roof of a cave in a karst 

    environment. It may eventually combine with a stalactite to form a pillar.

    7) Pillars
    Pillars are formed within the weathered limestone cave after the joining together
    of stalactites from up and stalagmites from down. The two may finally meet 

    forming a pillar.

    For karst land forms to be formed the following conditions must be in place:
    – Precipitation: the major types of precipitation which contribute to 
    groundwater are rainfall and snowfall.
    – Slope: infiltration is greater on flat areas since water is likely to remain 
    in one place for a long time given that other factors are favorable. On 
    steep slopes, a lot of water is lost through surface run-off with little 
    infiltrating in the ground.
    – Nature of the rock    : For groundwater to percolate and accumulate 
    there must be spaces within the rocks for it to pass through as well as 
    to occupy further beneath.
    – Vegetation cover:     the presence of vegetation increases the rate of 
    infiltration.
    – Level of saturation of the ground:     The rate of water infiltration is 
    high when the ground is very dry and the soil is dry; all the air spaces 

    in it are wide open.

    3.3.2. Landforms associated with weathering in arid regions 
    The features formed in these regions as a result of weathering are both erosion

    al and depositional. 

    a) Erosional features
    1) Inselbergs
    An inselberg (island hill or mountain in German) called Monadnock in the 
    United States, is an isolated hill, knob, ridge, or small mountain that rises 
    abruptly from a gently sloping or virtually level surrounding plain.  These forms 
    are characterized by their separation from the surrounding terrain and frequently 

    by their independence of the regional drainage network.

    2) Bornhardts
     These are dome-shaped and steep-sided rocks that rise up to 30 meters. They 
    are massive rock, commonly granite comprised of bare rock that stretches 
    several hundred meters. They take many shapes such as oranges. A good 

    example of where Bornhardts are found is Central Australia.

     3) Tor
     A tor is a pile like hill of rocks or rock peak. It is a product of massive weathering 

    and comes in all manner of shapes

     4) Pediment
    This is a rock that is gently inclined at an angle of 0.5 to 7 degrees. It is concave 
    in shape and is found at the base of hills where rainfall is heavy and falls over a 

    short period of time.

    5) Deflation basins
     Deflation is the process whereby loose or non-cohesive sediment are blown by 
    the wind. Depressions formed in the deserts due to removal of sand through the 
    process of deflation are called Deflation Basins.  They are also called blow
    outs     or deserts hollows. The depth of deflation is determined by groundwater 

    table. 

    6) Mushroom rock
    The rocks having broad upper part and narrow base resembling an umbrella 
    or mushroom are called mushroom rocks or pedestal rocks. These undercut, 

    mushroom-shaped pedestal rocks are formed due to abrasive works of wind.

     7) Demoiselles
     Demoiselles represent rock pillars having relatively resistant rocks at the top 
    and soft rocks below. These features are formed due to differential erosion of 
    hard rocks (less erosion) and soft rocks (more erosion). The demoiselles are 

    maintained so long as the resistant cap rocks are seated at the top of the pillars.

    8) Zeugen
    Rock masses of tabular form resembling a capped inkpot standing on softer 
    rock pedestal of shale, mudstone is called Zeugen. The bases of such features 

    are broader than their tops. 

    9) Yardangs
    These are formed always in the same way as Zeugens except that yardangs 
    only develop on landscapes which have alternating rock layers with different 
    resistance to erosion parallel to the direction of prevailing winds. Winds enter 
    and scour up rock particles from the soft bands, thus digging depressions within 
    the soft bands. The resistant hard bands therefore remain standing high up as 

    raised ridges.

    10) Reg
    Reg is a desert surface covered with a pebble layer, resulting from long continued 
    deflation; found in the Sahara Desert of North Africa. Often the winds blow off 
    all the smaller fragments, and leave the bigger size pebbles and gravels over an 

    extensive area.

    11) Oases
    These are depressions that have water in deserts. These are created by strong 
    winds which remove rock particles from a particular place until a depression is 

    excavated (created).

    b) Depositional features in desert
    1) Dunes
     Dunes are mounds or ridges of wind-blown sand. They are depositional features 
    of the sandy deserts and are generally mobile. They vary in size and structure. 
    The main types of sand dunes are Barchan, Transverse Dunes, and Seifs.

    – Barkhans
     Also called Barchans, these are typical crescent shaped sand dunes. The 
    windward slope of barchans is gentle and convex, and the leeward slope is 
    steep and concave. Barchans move slowly, at a rate of meters per year in the 

    direction of the prevailing winds.

    – Seifs
     These are long and narrow sand ridge which grow parallel to the direction of the 

    prevailing or dominant wind.

    – Transverse dune
     Transverse dune is an alongated dune lying at right angles to the prevailling 
    wind direction. They have a gentle sloping windward side and a steep sloping 

    leeward side, they are commmon in areas with enough sand and poor vegetation.

    2) Loess
     Loess is a wind-blown deposit of fine silt and dust. It is unstratified, calcareous, 

    permeable, homogenous and generally yellowish in colour. 

     3) Erg 
    Erg is also called sand sea or Dune Sea. It is a large, relatively flat area of desert 

    covered with wind-swept sand with little or no vegetative cover.

     3.3.3. Importance of landforms resulting from weathering
    – This soil supports poor scrub vegetation as well as some shrubs and 
    grasses.
    – Chalk landscapes are characterized by undulating topography.
    – The surface and underground landforms of karsts appearance are 
    beautiful to attract tourists.
    – Limestone blocks are used for building houses.
    – They are also raw materials for cement manufacturing.
    – Weathering results into soil formation.
    – It produces a number of landforms which modify the nature of landscape
    – It produces lateritic soils, which are important in road construction.
    – It helps to expose mineral rock on the surface.

    – It produces clay which is important in pottery industry

    Application activity 3.3
     1. Examine the contribution of weathering on human activities

     2. Humid tropical regions are the most affected by weathering. Discuss

     3.4. Mass wasting
     3.4.1. Definition and types of mass wasting
     Learning activity  3.4
     Study the photograph below taken in northern part of Rwanda and describe 

    the cause of the phenomena which happened. 

    i) Mass wasting
     Mass wasting, also called mass movement, is defined as the creeping, 
    flowing, sliding or falling of rocks and weathered materials down slope under 
    gravity. It is different from erosion in a sense that, in erosion water physically 
    transports away the soil particles, in mass wasting water does not wash away 
    but assists the rock to slide down under the influence of gravity. 
    ii) Types of mass wasting
     Mass wasting is classified into two major categories: Slow movement and 

    rapid movement.

     1) Slow movement
     Also called creep movements, they are very slow in their motion and they may 
    occur without being noticed. These slow movements include: 
    • Soil creep: This is the most common and the most widely spread 
    type, because it is found in both tropical and temperate climates. The 
    movement of materials is so slow that they may move a few centimeters 
    per day. It can be detected by leaning of trees, electric poles and 

    fencing poles in the direction of the slope. 

     • Solifluction: This is limited to glaciated mountainous regions and 
    cold climatic areas where thawing causes the saturated surface layer 

    to creep as a mass over underlying frozen ground.

     • Talus creep: This is a down slope movement of mainly screes that are 
    relatively dry. It occurs almost in the same way as soil creep and it also 
    occurs under tropical and temperate climate.
     • Rock glacier creep: This is a slow process of slope failure in which 
    individual rock boulders with very little soil but with some ice embedded 
    within them slowly move down slope confined within a channel.
     • Rock creep: This is the movement of individual rock boulders slowly 
    down slope
     2) Rapid movement
     • Earth flows: These are the rapid down ward movements of clayish or 
    silty soils along a steep slope.
     • Mud flows:  These are similar to earth flows but they are muddy and 
    occur on slopes that receive heavy rainfall. They are very fast. In Rwanda 

    they are common in the Northern and Western-provinces.

     • Debris avalanches: This is the most form of rapid flowage due to the 
    fact that slopes are very steep and there is enough rain to soak slopes. 
    It occurs on very steep slopes that occur in humid climate. 
    • Slumping: This is the downward slipping of one or several units of 
    rock debris, usually with a backward rotation with respect to the slope 
    over which movement takes place. Undercutting of slopes by streams 
    and man are the main causes of slumping. The surface of the slumped 
    mass has a number of step-like terraces. 
    • Rock slide: This is the type of sliding in which individual rock masses 
    fall from vertical cliffs or faces of slopes or jointed cliffs.

    • Rock fall: Here, individual boulders fall freely from a steep rock face.

    Landslides: These are also called landslips. They are down-slope gravitational 
    movements of a body of rock or earth as a unit. It may be induced by natural 
    agencies (like heavy rain, earthquake) or it may be caused by human interference 

    with the slope stability.

     3.4.2. Causes of mass wasting
     The following are the major causes of mass wasting:
    – The degree of slope: The steeper the slope, the higher are the 
    chances of material movement. Mass wasting is almost nil in gentle and 
    flat areas.
    – The structure and lithology of rocks: Alternating hard and soft rock 
    layers on a slope can be a cause of slope fall. For example, a layer of 
    clay on top of limestone layer can easily slide down. 
    – The degree of lubrication: Most mass wasting processes occur 
    after a heavy down pour. Water assists to lubricate rock particles and 
    the layers of rock on top of a slope. Therefore, water provides a medium 
    of sliding because it reduces internal friction between rock particles 
    and layers.
    – The amount of load on a slope: Slopes which are light rarely fall 
    compared to those which are heavy. Therefore, additional load on a 
    slope increase chances of slope fall.  
     – Tectonic movements: Earthquake and Volcanic eruptions cause 
    vibrations of the earth which often trigger off widespread movements 
    of materials such as landslides.
    – Climate: The amount and nature of rainfall received in an area 
    determines the kind of movement that occurs. 
    – Grazing: The grazing of cattle, movement of elephants and other 
    animals can cause some tremors on slopes hence making them fall.
    – Nature of soil: soils which are infertile and therefore unable to support 
    vegetation in enough quantities, are more susceptible to mass wasting 
    compared to soils, which are fertile and therefore able to support dense 
    vegetation.
    – Influence of vegetation:     Vegetation help to hold rock materials 
    together thus reducing their movement on the surface.
    – The work of animals: Animals and micro-organisms facilitate deep 
    weathering which results into the reduced cohesion of the rock particles 
    on slopes. This therefore leads to easy movement. 
    – Vulcanicity: Volcanic eruption on the ice capped highlands cause ice 
    to melt and therefore soak the slopes. This lubrication greatly increases 

    the chances of slope movement.

     Application activity  3.4
     1. Examine the major causes of mass wasting

     2. Using diagrams distinguish between slumping to rock fall

     3.5.  Effects and control measures for mass wasting
     Learning activity  3.5
     Observe the photograph below showing the effects of mass wasting and 

    answer questions:

     1. Analyse the effects of mass wasting.

     2. Suggest any three measures to control mass wasting.

    3.5.1. Effects of mass wasting
     The following are some of the effects of mass wasting:
    – Threat to life and property:     There are several serious incidents 
    of landslides and rock slides every year. They cause loss of life and 
    property. In a minor incident they may block only one line of a road, but 
    in severe cases entire blocks of buildings collapse.
    – Loss of vegetation    : Mass wasting and soil erosion result in the loss 
    of surface topsoil which is essential for vegetation. As a result, more 
    areas become barren.
    – Scars and Gullies: I    n areas where topsoil and vegetation are removed, 
    bare spots form scars in the landscape. Gullies form on weathered 
    slopes through rain action and mass wasting in areas with little or no 
    vegetation. Intense gully cuts up the landscape into large-scale gullies 
    and ridges and destroys the area. Gullying is common in the bare, 
    granitic areas.
    – Pollution of water:     large amounts of geologic materials enter streams 
    as sediments as a result of this landslide and erosion activity, thus 
    reducing the potability of the water and quality of habitat for fish and 
    wildlife.
    – Wildlife destruction:     Although most kinds of wildlife are able to 
    retreat fast enough to avoid direct injury from all but the fastest-moving 

    landslides, often are subject to habitat damage by landslides.

     3.5.2. Control measures for mass wasting
     Mass wasting, especially landslides, has severe impacts on humans and 
    environments. For this reason, measures have to be taken for preventing or 
    mitigating them. Some of the measures are highlighted below:
    – Gradients of steeper slopes could be reduced by constructing terraces. 
    – Retaining walls can be built to stabilize the slope. 
    – Steep slopes should be inspected regularly, especially during periods 
    of intense or prolonged rainfall to identify areas prone to mass wasting 
    for preventive measures. 
    – More surface drainage channels and ditches can be constructed to 
    reduce overflowing discharge
    – Legislation can restrict development and building in zones prone to 
    mass wasting. 
    – Trees can be planted on steeper slopes to stabilize the soil and the slope. 
    – Appropriate instruments can be installed to monitor slope stability, 
    providing early warning in areas of concern. 

    – Mass education of people

    Application activity 3.5
    Make a field trip to observe different areas affected by mass wasting. 
    Analyse the causes of mass wasting and propose the sustainable measures 

    to control it.

     Skills Lab
    Identify any area mostly affected by mass wasting, examine how the 

    Community Work / Umuganda may help you to fight against it.

     End unit assessment
     1. Give the reasons why highlands are the most affected by mass wasting. 
    2. How have topography and parent rock influenced the rate of 
    weathering in your area? 
    3. Explain how the weathering landforms identified in your area affect 

    positively and negatively human activities.

    ◄UNIT 2 :THE ORIGIN AND DISTRIBUTION OF THE CONTINENTSUNIT 4 : WAVE EROSION AND DEPOSITION►