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This work looks at the various dimensions of slope processes and how these process in turn result in the development of land forms in Idanre area of Ondo state.

          The work also exposes the triggering mechanisms for the processes to manifest. These include rainfall, temperature and other physical characteristics of the rocks.

          The study also focuses attention on the strength and capacity of material components and their relative resistivity to climate condition and weathering process at large.

          A critical review of the topographic structure of the Idanre are of ondo state gives one an impression of which agricultural practice tales place. In this connection, the general landscape structure is viewed with the hope of showing areas where agriculture is practiced within the locality. This is obtained through cross-sectional profiling of the area.

          Generally, the nature, structure and the lithological composition of the area is reviewed to see how these result in landform development in Idanre area of ondo state. 



Geomorphologists the world over would probably agree that the form and origin of hillside slopes pose certain fundamental problems in landform study.

          The physical landscape is an assemblage of slope, the appearance and dimensions of which give an area its essential morphological character. More so, slope study, though slope study, though essential to geomorphology, have until recent times, been somewhat neglected. This neglect is nevertheless not unconnected with the immense difficulties encountered in the attempt to determine the nature, rate of operation and precise effects of the various processes working or acting upon slope form.

          Despite the shortcomings envisaged in the neglect of slope study in the past years, evidence now has it that the trend has changed tremendously in recent years, and there is growing concentration of study on the mechanisms and rates of operation of basic slope processes such as weathering, soil creep and rain-wash.

          These various processes are undoubtable altering the form of the slopes and creating other micro-forms which had in general, posed problems to man curiously in search of comfort.

          Places where slopes are profound in number, the result of the work of the various processes, had coursed extra burden to civil engineers and the like construction companies; and as well modified the settlement pattern of the areas. The agricultural pattern as well as the types of crops cultivated have been conditioned to the nature of the general landscape structure.

          There is also an association influence of the topography to the climate and vegetation of the area which consequently has influence on the rainfall distribution. The life-style of the people is also wholly influenced by such factors as landscape structure topography and climate variation.

          Among the numerous processes of slope, landslide has assumed a dramatic expression of force overcoming resistance. Landscape is more of a generic term embracing other sub-processes. Same as the study of slope and remained neglected in the past, is also that of landslide. But in recent times, the problem has been identified as a result of re-newed movement in previously unorganised land slipped areas. This neglect as well as the undue unawareness is however connected with the nature of deposited resulting from slope processes slope study in its forms, nature and evolution have been done by many geomorphologies notably Davis, Penck, King and others who have assigned different approaches to slope evolution. These approaches are however discussion in subsequent chapters. But it is noteworthy at this juncture to mention that two prominent geomorphologies, W.M Davis and W. Penck, have views slope evolution through the propounding of theories: the parallel retreat of slope evolution through the propounding of theories: the parallel retreat of slope and the slope decline. Suffice it to say that other geomorphologies have either agreed with the Davisian and Penchkian theories or deduced new theories to replace the later.

In recent times mathematical models have been deduced to fully appreciate slope formation. However, it si not enough to appreciate these variously deduced models without asserting their degree of connection with present-day slope forms.


The objective of this study is to gain an insight into the reality and mechanisms of the dual processes as shall be seen in the main body of this study seek to examine and give room for answers to certain geomorphological questions with regard slope study. Precise among such questions with regard slope study. Precisely among such questions are

  • What is the precise relationship between slope form and the various denudation processes operating on slope?
  • What is or are the various form(s) slope assume?
  • Are slopes, like rivers, able to attain or even approach a state of equilibrium? And
  • What is the influence of geologic structure and rock type on slope form and steepness? These ate however few among the numerous questions that abound in slope study.

The study also aims at focussing attention on the influence of climate and vegetation cover on slope forms and patterns and as these ie climate and vegetation, later turn out to effect the general characteristics of the slopes.

         It is within the above framework that the format of the study has been divided into various sections for precision and comprehension. Chapter 1 is dedicated to the review of the introduction of the study, statement of the objective and rationale of study, statement of problem in which case, the different processes of slope and their impacts on the general landscape of the indanre area is received. The morphological description of the area is also attempted in this chapter. This is done to expose the different types of slopes found within the area: those covered with the earth but assume an inclined angular differences with surrounding areas and those that bare rocky surfaces that assume steel angular differences and otherwise.

         The methodology employed in carrying out the study is also stated. The methodology exposes the precise and exact methods, instruments and sources of data, employed in carrying out the study. Here field measurements and observations are prominent; literature review however concludes the chapter. The literature review attempts to look at the work of early writers on the subject.

Chapter ii is principally devoted to the theoretical framework whereas, topics like slope forms, process and form analysis, slope failure analysis among others will be revealed.

         Chapter iii is essentially field study work. This is further divided into sub-sections: slope profiling and survey, soil characteristic of the area, texture and catena. Within this chapter, the influence of the climate and hence vegetation is also taken into consideration rock type and characteristics are also examined to ascertain the actual proficiency of the various denudation activities of slope.

         Chapter iv is devoted to data evaluation: This entails the correlation of data obtained from the field and those (data) obtained from secondary sources. This chapter also examines the relationship between landslides and the processes of slope. Conclusion and recommendation are also contained in this chapter.

         In as much as mathematical application hence qualification is attaining higher grounds in geomorphological studies, attempt is made to employ this in places where such is applicable. This is done to effect precision and clear definition.


It is undoubtedly an exclusive fact that the various processes of slope and the general structure of slopes do pose problems to people in and around Idanre and this manifests in

  • Distortion of agricultural activities around the surrounding areas.
  • Susceptibility to erosional features which demises the soil nutrients rapidly.
  • Distortion of civil construction and difficult in construction work due to hard resistant rocks.
  • Additional cost in construction work on the part of the government due to the nature of the topography.
  • No room for expand as the whole town (Idanre) is enclosed by ringed complexes.
  • Deformation of the landscape structure by the effects of erosion and
  • Modification of the people’s mode of life pattern.

Idanre is one of the major cocoa producing areas of ondo state. The town is located between latitude 705’N and longitude 50E of the Greenwich Meridian. It (Idanre) could also be located geographically 16km south west of Akure, the state capital.

          The Idanre area is generally and characteristically hilly and the new town, Odode is walled round by ringed complexes. These ringed complexes assumed different patterns and heights which have allowed settlement on top of few hills, notably oke Idnare, where the paramount ruler, the owa of idanre lives. Settlement pattern in the area could be said to be linear following the pattern of distribution of the   ringed complexes, which restrict4ed expansion to areas where the slopes are not so steel for human habitation. More so, houses are built in line with the structure of the topography. That is where the terrain is sloppy, houses are constructed to meet a unit of elevation with slopes.

          The agricultural systems also follow the nature of the topography where different systems of agricultural practices are employed. Specifically, the terrace farming system and contour ploughing are pre-dominant in the area. Erosional feature have remarkable influence on the agricultural practices of the people. Deep gullies are created by the action of running water, and have caused devastation to the soil vis-à-vis cultivated crops. This has constrained the people to the cultivation of tone major cash crop (cocoa) at the foot of the slopes.

          Apart from the major structural features of the town-Idanre, beyond the are, that is the outskirt, deep gullies have been formed and consequent upon this, rivulets emanate from the foot hills which disengage their contents into bigger rivers: the rivers are ipelu, Owena, Apomu, Arun to mention but a few. Within the Idanre ringed complexes, the major river that drains the area is the opa river which subsequently empties into the owena River.

          Like earlier established, the general feature wh ich distinguishes the are from other areas within the state is the residual alignment. (Fariran & Ojo 1980). These are characteristically bare-faced rocks but with little soil and vegetation cover. These have been subjected to weather conditions typified by scars produced on the rocks. On the bare rocks, plane features, granular fracturing, and rock disintegration are also noticed.

           However, the nature, pattern and structure of alignment for the rocks of the area make the area distinct in varying degrees to adjoining areas.


This study employed a number of sources in gathering information: Primary sources were based on field measurements and observations; while secondary data based on data obtained from various materials such as text books, journals and metrological data. The work strictly deals with ‘’processes and forms’’ of the Idanre landscape. No questionnaires were employed.


A hillslope could be defined as any inclined element on the earth surface to the horizontal plain. The inclination element therefore introduced the concept of graduation giving it orientation and or direction in space. (Finlayson and strathan 1980)

          It is however empirically obvious that many land surfaces are inclined at particular angles and at varying degrees of inclination. Recognizing that land surfaces are inclined, then presupposes the extend of rainfall devastation on the land surfaces through the work of erosion within the soil or over them and hence contribute to the movement of participles      of rocks, soil and dissolved materials. This then provides room for the operation of the mechanism of denudation that ultimately module the landscape. (dury 1976, Bloom 1978) slope therefore is a surface inclined at a gradient less that 40% (King 1975)

          Slope evolution theory essentially entails tracing of historical development of the slopes from their initiation to their present-day forms. It also involves predicting future slope forms hence contingent upon time or time independent.

          Basically there are two major approaches to slope evolution study. One of the approaches to slope evolution study. One of the approaches- that by Divis 1899 and Penck 1924, is by means of general descriptive, explanatory and inductive methods applied to examples studied in the field, sometimes illuminated by flashes or inspiration. (Monk house 1981). The second, more modern approach, involves the application of geometrical methods, both inductive deductive, which attempt to erect a hypothetical sequence of development of a given slope under carefully specified conditions. Davis (1902) has argued the view that slopes tend to decline in steepness as the cycle of erosion proceeds toward the old age stage. Thus steel slopes are designated as ‘’youthful’’ and gentle slopes as ‘’old’’ the erosion cycle of David is essentially an inductive study of slope evolution and emphasises the pull of gravity on weathered materials as a mechanism to feed streams with sediments.

It is also encompasses the vertical decrease of land slopes. Principally by soil creep as opposes to back wearing postulated by L.C. king (1953).

          The Davisian erosion theory was principally demonstrative as well as imaginative of the initial form of mass of land uplifted from beneath the sea by earth movements. He assumed that the uplifted land mass took place very rapidly, so that the processes of denudation were able to act almost from the start on what was, in effect, a stable mass.

          In general, Davis demonstrated that as varied stream action continues to act on the landmass at various stages ie. The youth, maturity and old age, that the landmass is subjected to down cutting leaving hard resistant faces bare, and hence the mergences of hills. Below is a diagrammatic section of the Davisian cycle of erosion.

          Soon after the publication of Davis work, the study had received critical criticisms from various other geomorphologies notably walter  pench, Lester king among others, according to walter pench (1924) Davis misconceptions particular, stemmed from his (Davis) basic tenant that the cycle of erosion is initiated by a very rapid uplift and thereafter occurs a period of structural stability dur9ing which erosion can proceed without hindrance. Penk’s basic thesis was that slopes do not necessarily change form, in an evolutionary manner, with the passage of time as deduced by David-slope decline, rather, that slope forms are determined by one overriding control, ie the rate of downward erosion of the rivers flowing at their bases.

          However, penck‘s approach to slope evolution, not wholly incompatible with that of Davis, is essentially deductive by making certain assumptions about the initial form and role of slope processes. Penck’s basic assumptions are that:

  1. The form of a denudation slope is not influenced directly by the processes at work on the slope and
  2. The rate of retreat is determined by its gradient.  Thus, that a steep slope will undergo more rapid weathering and removal than a gentle slope. And that a steep slope beneath a gentle one will weather back rapidly that later in the process, the upper slope will be destroyed and that steeper ones (slopes) one either side of a divided will destroy themselves by rapid retreat. Hence the concept of slope replacement is now seen as one of the most fundamentals of penk’s contributions to slope study (small 1980).
  3. All slopes are regarded as occupying a number of rectilinear section or slope units.
  4. These slope units are usually initiated at the base of the slope as whole. Meaning that most river side valley slopes will not exist but for vertical corrosion.

in fig. 2, it is an admittedly theoretical situation that the unit would under-go parallel retreat, owing to weathering, removal, and in a given interval of time would retreat from position A and B. not all the weathered materials can be evacuated, for some must remain at the foot of the unit to provide a ‘’slope of transport’’ down to the non-eroding river. Subsequent stages of development are indicated by position C, D, E and F of the main slope unit. It is be observed that, as slope retreat proceeds, the length of the original unit will be progressively reduced, and a new basal unit, of ever increasing dimensions, will be formed.

          L. C. king (1953) expounded the pen planation theory which to him was of a characteristics in semi-arid climatic zones, but argues that the basic elements of hill slopes are present in all environments in varying degrees. He argues that differences in environmental effect are not geomorphological significant. Also, he maintains that scarp retreat, resulting in the generation and formation of piedments is the standard mode of cycle landscape formation. He maintained further that hill-slopes are assumed to retreat more or less parallel to one another reducing uplands and leaving hard resistant rocks at a reduced or lower elevation.

          King (1953) concluded that modes of slope retreat vary with rock-type, taking into consideration the mechanical effect of resistivity of the rock components as well as other factors. That the end products or points of the cycle is a surface composed of coalesced piedments or pediplane through the overall process of pediplanation.

          The claim to world-wide applicability of this theory has been questioned by several geomorphologies who observed that slope4 forms and their associated processes are so complex in character that it would be fool hardly to hold rigid views as to any unique manner of slope development in any area. (Faniran & Jeje 1983). In the humid tropics, as elsewhere, parallel retreat has been found to occur under several conditions, more especially where slope evolution is under strong structural and lithological control especially on hard and resistant basement complex rocks example those found in Nigeria.

          The observed modes of slope evolution in the humid tropics show clearly that within a single climatic regime, some slopes and their associated processes are so motivate in character that is no longer possible to hold rigid views as to any unique of slope development even in a given region of uniform structure, lithology and climate. (Charley 1964).

          M.F. Thomas (1965) also noted the development of landforms but with particular interest in the humid tropics. This restrictive tendency of Thomas to the humid tropics contrasts with earlier theories of land-form development which had taken generalized patterns. The concept of etcplanation was then deduced by Thomas. The model among others, consider that the twin processes of rock weathering and removal have proceeded paripassau. This assumption is understandable in semi-arid areas, as well as in cold temperate regions, where the rate of chemical weathering is very slow, perhaps slower than the rate of removal in the humid tropic where thick layers of waste mantle have accumulated on top of the fresh unweather rock in many places. The above limited spatial slope development these further accentuate and solidly vaunt the pre-conditional materials which decondense earlier assertions by Davis and King’s models with reference to inselbergs landscapes.

          According to Thomas (1965), the most fruitful way or tool to study the landforms in the humid tropical regions is to consider them in terms of periods of deep weathering followed by periods of stripping or etching. This goes to further strengthen the dual episodes to consider: the deep weathering episode when rocks are weathered to great and variable depths, resulting in an irregular basal surface; and the etching episode when parts of the weathered mantle are removed, exposing when parts of the weathered mantle are remove, exposing parts of the basal surfaces as hills-called bornhardts or inselbergs. This stripping episodes according to fall of the basal level or climate change.

          The major deviation from king’s thesis is the location and occurance of hills. Whereas, according to around the major interfluves, the insel bergs of many humid regions tend to occur everywhere, depending upon the nature of the country rock (jeje 1973, faniran 1974).

          Generally, it is agreed that these different thesis of peneplanation, pediplantion and etchplanation use the cyclic model.

          Geometric studies of slope development is one other aspect which reveals the literature of slope evolution. The geometric studies is attributed to several people slope developoemtn in a vertical rock face under the influence of weathering. With this third method of slope studies, it tends to disprove the earlier assertion that there are two major approaches to slope studies as depicted by small (1980). But according to Sparks (1972), there are three major approaches to slope study. However the geometric studies, which focuses on inferential statistics is based on possible controlling factors which are measured or obtained from maps. The second and third approaches have been dealt with. (Davis 1909 & Penck 1924).

          Wood (1942) identified certain features which are of predominating importance to slope development. According to wood (1942) weathering of vertical face called the free face, causes debris to accumulate as scree or talus at the foot of the slopes. Gradually the talus grows until finally the free face buried and the whole slope consist of talus.

 FIG 3:

          Wood (1942) argued on that at the early stage of the area of the free face, available to weathering is much longer than that of the surface of the talus, and consequently the talus grows upward rapidly. By and large, wood’s treatment of slopes is quantitative, although the ideas are expressed in wards rather than figures. The later development of slopes from talus accumulation is a far more complex process, the effects of which can only be stated in general terms (Sparks, 1972).

FIG $:

In recent times, attempts have been made by M.J. Kirkby (in Brusden 1971) to provide mathematical treatment to slope developoemtn based fundamentally on analysis of the transport rates of debris, data obtained from the field by measurement of processes such as soil creep and wash. This attempts differs from the foregoing geometrical methods so far as it depends on field estimates of transport rates rather than the theoretical scree development.


          A.E. scheidepper (1959) postulated slope evolution with special references to work of people who had earlier written on the topic. Lehmann (1933) deduced a mathematical model for the decay of the Alphine cliffs thus that a steep slope angle is bounded by two horizontal planes which have vertical distance in apart. That each individual amount weathering off the slope will pile up at the bottom, and the surface of the pile will form scree angle. Some of the materials may get lost during transfer so that         = 1-C – – – -(1)

         Where VR  is the slope material removed and VD the corresponding volume of debris pilling up at the bottom. The scree building up protects the slope underneath from further weathering so that each infinitiestimal amount of slope recession =


dy = h cot B + (cot     – c cot      – cot B ) y – – – – – -(2)

where y = vertical and x = horizontal coordinate of slope cross section.


The dynamic equilibrium concept is cyclic time-dependent models of landscape development which provides an alternative to Hack (1960) and thus proposed a time-dependent model. This is purely the dynamic equilibrium concept which is based on earlier works Gilbert (1909).

         According to Hack (1960), the concept states that every slope and channel in an erosional system is and erosional energy remains the same, all elements of the topography are down-wasting at the same rate. Differences in relief and form may not be explained in terms of an evolutionary development through time. Also, that when erosional energy changes over equilibrium, form will be established rapidly whenever changes over time and space, topographic equally adjust.

         According to Ritter (1978), the model and others, logically represent end members of a spectrum of geomorphic possibilities ranging from complete dependence to total independence of time. However, in order to resolve the divergent opinions about time strength in geomorphology in general and slope development in particular, schumm of Lichty (1965) agreed that time could be could be considered on three levels of magnitude (cyclic, graded and steady time levels) in which time may or may not be considered a significant factor in slope or landscape development. At the level of cyclic time, it is significant in explaining the development of landscape hence the relevance of the Davision Cycle concepts. Nonetheless, at relatively short graded time period in which geomorphic forms are balanced with the operating processes, landform may exist in a state of equilibrium as suggested by Hack (1960). The interpretation of slope development will greatly depend on time scale under consideration.

Despite the inductive approach attached to the dynamic equilibra theories which rely heavily on multivariate statistical models because little has be4en done on the application of the theory to hill slope forms, although the criteria for open system equilibrate.

Carson & Kirky (1972). Basically, the theory is founded on knowledge of the fundamental principles of earth sciences particularly the physical sciences. As regards the latest development in physics and related sciences. As sciences, the earth and many of its features can be linked to open system in which there is constant exchange of energy and materials. In general, the dynamic equilibrium model of landscape development has been most successful in river studies at micro or meso scale predicting overall long profiles.


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