Geomorphology and Soil Geography Lecture Notes
DEPARTMENT OF GEOGRAPHY AND SUSTAINABILITY STUDIES
# FACULTY OF EARTH SCIENCES AND SUSTAINABILITY STUDIES
# COLLEGE OF COMPUTING, ENGINEERING AND SCIENCE
# KADUNA STATE UNIVERSITY
# KASU-GEO201: INTRODUCTION TO GEOMORPHOLOGY AND SOIL GEOGRAPHY
# COURSE CONTENTS
Meaning and Scope of Geomorphology
Rock types, their Origin and Characteristics
Nature and origin of 2nd Order Relief forms of the continents
Structural Landforms
Landform Classification
The meaning and scope of soil geography
Factors of soil formation
Classification of soils: Zonal Soils, Azonal Soils and Intrazonal soils.
Laboratory classes are essential in order for students to get acquainted with soil composition and properties
UNIT 1.0 Meaning and Scope of Geomorphology
Geomorphology is concerned with the nature, evolution, and origin of the earth's surface features (i.e., different structure of landforms).
It involves the study of the form (shape) and development (process) of the earth’s surface features with special reference to landforms.
1.2a Nature
Geomorphology is concerned with the:
i. Internal geologic process of the earth crust such as tectonic activities:
The geologic or geomorphic processes are all those physical and chemical changes which enhance a modification of the earth surface form aided by geomorphic agents that secure and transport the materials.
Tectonic plate movements under earth can create landforms by pushing up mountains and hills, synclines and anticlines, fault mountains, block mountains are product of tectonic movements
ii. Volcanism that construct new landforms:
Two processes operating in the lithosphere are the endogenetic or energy operating within earth. E.g. folding, faulting, earthquake, metamorphism and volcanism
iii. Externally driven forces of wind, water, waves and ice (glaciers) which modifies such landforms:
Exogenic processes are energy operating outside the earth surface e.g. the gradational and degradational or denudational processes.
1.2b. Scope of Geomorphology
There are three major aspects of the study of geomorphology:
a. Study of the relationship between landforms and the underlying rocks i.e. geological geomorphology
b. Evolution of landscapes (denudation chronology) which looked at the pictures of relief at different times
c. The aspect of geomorphology which study the actual process of erosion that gives rise to landforms
1.3. Rock Types, Origin and Characteristics
Rocks are the solid part of the earth made up of aggregate of minerals, and these minerals vary in proportion from rock type to another.
For example, the common mineral element in rocks is iron oxide, calcium, dolomite, clay mineral, quartzite among others base on texture, structure, color, permeability, and degree of resistance to activity of denudation.
Generally, all rocks are group into three main types’ igneous, sedimentary and metamorphic rocks.
About 75% of the total earth surface consists of sedimentary rocks, while 25% remaining consist of igneous and metamorphic rocks.
a). Igneous rocks
Are formed by the cooling and solidification of molten magma from within the earth crust or above the earth crust to form both internal and external landforms.
Molten magma is a semi liquid that contains about 8 silicate minerals.
Molten magma that gets to the earth’s surface is no more known as magma, it is known as lava.
Types of igneous rocks
i. Plutonic
Plutonic rocks formed as a result of slow cooling and solidification of magma in great depths and high pressure within the earth crust and have large crystal of over 1.25mm long e.g., granites, gabbro, diorite.
ii. hyperbyssal
Hyperbyssal rocks are rocks that have cooled near the surface within the cracks along the tectonic plates of the earth crust. They contain medium sized crystals or large crystals. However, it may be exposed to the surface by the activities of denudation.
iii. Volcanic rocks
The volcanic rocks on the other hand poured out of lava into the surface. They solidify quickly on exposure due to temperature variation.
This mode of cooling promotes the presence of small crystals. Colombia snake Plateau in USA and the Cameroon Mountain are good example of the type of igneous rocks.
Characteristic of Igneous rocks
Igneous rocks are crystalline in nature.
Do not occur in strata, or layer.
Do not contain fossil of animals or microbes but they are rich in heavy minerals.
On the basis of mineral composition, they can be classified into acid, intermediate or basic rocks.
They are usually hard and impervious.
Igneous rocks contain aggregate of minerals such as silica, basic oxides of NA, Ca, MN, Fe; Andesite, Augite etc. Zubain selbergh hill, Zaria inselbergh hill, Kagoro hills Plateau of Jose.t.c. are examples of igneous rocks in Nigeria. These rock can be used for road making, polished as monuments etc.
b. Sedimentary rocks
Result from the accumulated and compartment of eroded sediments usually over a long period of time underwater.
The constituents comprise mainly of deposited mineral and fragments produced by both mechanical and chemical weathering of formal rock masses or by organic action.
Types of sedimentary rocks
i. Mechanically formed sedimentary rock
Originated from the accumulation of materials derived from other rocks, cemented together.
However, the texture, composition and colour of these rocks vary tremendously due to the nature and constituent of the parent materials.
Mechanically formed rocks are sandstones, clay, shale, and gravel (Lake Chad and Sokoto). Examples of the mechanically rocks are common in the North Western Nigeria, Southern Niger Republic and Senegambia.
ii. Organically formed sedimentary rocks
Derived from the remains including corals and shellfish whose fleshy parts have been decompose leaving behind the hard shells.
The calcareous rock such as limestone or chalk is in these categories of sedimentary rocks. Bituminous and Migmitite rocks are forms of carbonaceous rocks.
Carboneous rocks form from vegetative matter includes peat, lignite (Asaba), or coal (Enugu).
Examples of calcareous and carbonaceous rocks are common in the regions of the Peninsular, equally present in Nigeria, part of Senegal, Southwest of Ghana. While calcareous rock is common in Enugu.
iii. Chemically formed sedimentary rocks
Originated from the chemical precipitate or evaporation of salt solution.
Rock salt is derived from strata which once formed from sea or lakes.
Gypsum or calcium sulphate is obtained from evaporate of salt such as the Dead Sea.
Potash and Nitrate are also form by the evaporation of lakes and seas containing them in high quantities.
Characteristic of Sedimentary rocks
Strata formation.
Non-crystalline in nature.
Contains fossils of animals’ microbes and plants.
May be coarse or fine depending on the nature of materials
They are pervious and easily percolated by water except clay.
The general texture of sedimentary rock depends on the circumstances under which they were laid down. They are sandstones, coal, limestone (Kogi), chalk, lignite, crude oil, potash, gypsum and dolomite, shale, clay, breccia etc.
c). Metamorphic rocks
Results from the alteration, transformation in the physical or chemical properties of any mass of rocks i.e. all rock types whether igneous or sedimentary may become metamorphic or changed rock under intense heat or pressure. The transformation process is called metamorphism.
There are two types of metamorphism, thermo metamorphism (due to heat or high temperature) and thermodynamic metamorphism (alteration cause by high pressure during earth movement. There are three agents of metamorphism 9 heat, fluids chemical active, and pressure
Although, the original appearance on rocks may be greatly alter e.g.
Shale changes to schist
Limestone changes to marbles
Igneous to granites
Granites to gneiss
Clay changes to slates
Sandstones to quartzite
Coal to graphite among others.
1.4. The types of landforms
The landforms are physical features or structures found on the earth surface that has shape and form. They can be grouped into 4 categories: Structural landforms, weathering landforms, erosional landforms and depositional landforms.
i. Structural landforms
Are landforms that are created by the solidification of large quantities of magma or by massive movements of rock due to plate tectonics. This includes landforms like; shield, fold mountains, rift valleys, and volcanoes
Structural landforms can be divided into three main orders, these are mainly;
a. First order structural landform
First order landforms are considered on the global scale.
In this regard, effort have been made to identify which categories of landforms i.e., highland areas or lowland areas can be found anywhere in the World. They include large pieces of plates.
The first order of relief is represented by continents and ocean basins. This mode of discussion does not give room for a detail understanding of any category of landforms. This is because the effort focus on all landform especially as they exist all over the World.
b. Second order structural landforms
These considers the description of landforms on continental bases i.e., landforms that exist north and South of the country Africa, etc.
Essentially, these approaches assist a fairly detail understanding of landforms on continental bases. In addition, the categories of landform as they exist on continental basis can be so identified and these can possibly assist in making comparison on the bases of the existences of landform in each continent.
The second order includes mountain ranges, plains, continental shelf, continental rise, and the abyssal plains (flat areas of the ocean floor water 3000-6000m down.
c. Third order structural landforms
This mode relate to a situation in which landforms are study on the bases of country.
In this effort, very detail description of land forms in terms of the decomposition of such landform, the area occupancy, the degree of denudational activities affecting it in each location relative to other landform can be considered.
Generally, third order structural landforms demonstrate a detail understanding of landform. e.g., the chad basin, the Kalahari sand stone among others.
The third order by the landscape features such as individual hills, mountains, and valleys. Kagoro hills, Jos Plateaux, Mambilla, Plateaux, Obudu, Idanre Hills etc.
ii. Weathering Landforms
Chemical weathering dissolves large portions of limestone or other rock on the surface of the earth to form a landscape called karst.
In these areas, the surface rock is pockmarked with holes, sinkholes, and caves.
iii. Erosional landforms
Wind erosion can lead to formation of pediplains, desert playas, cliffs, wave cut platforms, arches, stacks, headlands and bays are landforms associated with coastal erosion. Erosional landforms also include valleys, potholes, entrenched meanders and river terraces
iv. Depositional landforms
Includes beaches, sand dunes, spits, and bars, alluvial fans, deltas braided channels. Similarly, we have glacial depositional landform to include drumlins, erratic, moraines, outwash plain, esker among others
1.5 Landform classification
On the basis of some major characteristics, various methods of landform classification existed e.g., Strahler A.N. divided landforms into the main groups of initial form and sequential forms.
i. The initial form of landforms
Indicates that the original feature produce by tectonic force have been maintain. Volcanic and tectonic processes bring fresh rock to the planet's surface. We call these endogenic processes because they work from within the Earth. They produce initial landforms.
ii. The sequential form
Relate to pronounce modification and whether the initial may have been destroyed virtually beyond recognition retaining the newest vestiges of these classification. Exogenic processes that work at the Earth's surface to produce sequential form.
iii. Other form of classifications is based on the actual relief form.
These are: High Mountain, Mountain and basin, hilly upland and plateau, Hamadan, Intermountain basin, Low Mountain, and Ice cover are abasin these according to Preston and James recognized a physical background from the regional surface dividing the land surface of each continent into 9 categories of planes..
iv. -The classification that follows is essentially a compromise between initial tectonic cause, method and degree of external modification and present relief forms, the four major groups are; Mountain, Plateau, Plain and valley, and Basin.
UNIT TWO
2.0. The Meaning and Scope of Soil Geography
2.1. Meaning of Soil Geography
Soil geography is a branch of soil science that studies the pattern of the distribution of soils on the earth’s surface for the purpose of soil-geographic regionalization.
2.2. Scope of Soil Geography
There is general and regional soil geography: general soil geography studies the factors that influence soil formation, geomorphic distribution of soils, types of soils and structure on the micro or meso-scale. While regional soil geography, is concerned with regions and the description of the soils in the individual regions. These can be use in the classification of soils and making of soil maps.
2.3. General Introduction and concept of Soil
Soil has been of a particular interest to man since the beginning of organized agriculture thousand years ago. An understanding of the fundamental principles of soil science, which is the pedology is of immense importance to a geographer.
Soil constitutes an important environmental factor because of their contribution to the human population. Man derives his food, shelter and clothes as well as other products useful to him from soil. Soil is also a dynamic layer in which many complex chemical, physical and biological activities are continuously in place. Therefore, soil is changing and a developing body.
The concept of soil has had different meanings to different people.
i. The most popular concept of soil is that of a medium of plants crop growth.
ii. The other viewpoint of soil is that of the chemist
Who considers soil either as in chemical laboratory where various chemical processes and reaction takes place, a situation where a test tube is provided and plant nutrient can be introduce for the benefit of plants.
iii. To the physicists or geologist
Soil is a collection of matter in form of solid, liquid and gas. Having the recognizable mechanical properties associated with the rock of what it was formed.
iv. To the Engineer
Soil is either a material (or civil engineering construction-roads, bridges) in terms of its suitability for a particular type of foundation.
v. But to the soil geographer and a pedologist
Soil is a natural body which differs from the underlying material according to the process of formation.
vi. Against this background therefore, a soil may be defined as the uppermost layer of the solid earth crust i.e. the lithosphere consisting of decomposed and chemically altered rock and biotic materials thereby having both mineral and organic materials or substances.
These substances exist in form of matter i.e. the solid, liquid and gas.
These have to be in balance form or a better quality of soil for it to support plants growth.
The solid portion is both organic and inorganic particles which gives soil its volume and weight.
These are rock material in form of gravel, sand to colloidal particles. The organic component includes death or decayed living organisms, plants and animal material. The liquid portion is the soil solution, i.e., Chemicals dissolve in water while the gaseous part is the air contain in the open pore spaces or voids.
2.3.1 Soil Characteristics and Properties
There are two groups of characteristics of soil. There are the physical characteristics regarded as morphological properties, and the chemical characteristics also known as analytical properties.
A. Physical characteristic
The physical characteristics include soil texture, soil structure, soil porosity, color, consistency and soil temperature.
i. Soil Texture
This is the relative proportion of different sizes of particles that make up the soil. The common sizes are sand, silt, and clay.
Texture is important because it largely determines water retention and transmission in soil or mobility in soil.
ii. Soil Structure
Soil Structure refers to the way in which soil particles are grouped together into large pieces or aggregates. These particles are held together by colloids otherwise known as sediment.
There are structures such a blocky (nut like), these have regular pieces with sharp corners and edges. Granular and crumb structure, these are spherical in shape, columnar and prismatic; they are made up of vertical prism and columns. There is the platy structure, they are in the form of plate and most at time are in horizontal layer form. Generally, soil structure influences the rate of which water is absorbed by soil. It also influences the susceptibility of the soil been eroded or to erosion, and of course the ease of cultivation.
iii. Soil Porosity
Refers to the pore’s spaces or void of soils which may contain either air and or water. These may vary in proportion with the weightiness and dryness of the soil. Usually, air occupies the larger pores while water the smaller ones. Soil porosity is determined by the structure of the soil.
iv. Soil Colour
This is the physical character of the soil recognizable at first glance. Soil color can help indicate how a soil was formed and what its contents are. Soil color is highly associated with organic matter content of the soil.
In general terms, soil color range from white through brown to black as a result of an increasing contents of humus in which case the darker soil the more the humus contents and of course the better the soil.
v. Soil Temperature
This is the relatively coolness or hotness of the soil. This is normally determined by the water and the climatic condition of the area.
Soil temperature influences plant growth and development. It determines the planting period of most crops. It also determines the length of growing seasons. Warm soil temperature enhances bacteria activities and mechanical weathering. It also influences the chemical contents of soils.
vi. Soil Consistency
This describes the several aspects of feel between fingers. There are four properties associated with soil consistency these are; stickiness when the soils are wet, plasticity when the soil is also wet, friable (firm) when the soil is moist and soft or hard when dry, gritty and pricky.
vii. Soil Profile
This is the vertical arrangement of the soil pedon when looked from the top downward.
Basically, there are three parts to the soil profiles. These are Horizon A, B, C. Horizon A and B represents the true soil which is regarded as solute. While horizon C is the subsoil.
This subsoil is the weathered parent material, below this subsoil is the parent material; or the bedrock or even the underlying rock. This is designated as the horizon D. There could be subdivisions of these horizons depending on the climatic region.
B. Chemical characteristics (Analytical properties) –
There are many chemical characteristics of soils, however, the most common characteristics are three namely: Soil Humus, Soil reaction (pH) and Soil nutrients, others are Cation exchange capacity and Total exchangeable bases
i. Soil Humus
Is the final product of decaying organic matter. This organic matter refers to plants and animals remains in the soil which are acted upon by soil organisms especially bacteria and fungi giving rise to the dark sticky material called humus.
In the process mineral compound are available to plants in form of nutrients.
Humus binds the particles of soils and together and encourages the formation of crumb structure, humus also gives soil a good texture, and it helps in development of loamy soils, and also slows soil drainage.
ii. Soil reaction (pH)
This is a term used to denote the concentration of hydrogen ion and soil solution. It can be measured using pH meter. Based on this measurement, soil can either be acidic, alkaline, or neutral. These are considered to be extreme conditions for soil reactions.
Soil pH values range from 1.0 to 14.0 while the soil with pH > 0 is considered to be neutral. Soils with pH values with less than 7.0 are acidic while those with pH values greater than 7.0 are considered to be alkaline.
According to Yong (1976) the following variation in the soil pH can be noted. Less than 4.0 very strongly acid, 4.0-5.0 strong acid, 5.0-6.0 moderately acid, 6.0-7.0 weakly acid, 6.5-7.5 neutral, 7.0-8.0 weakly alkaline, 8.0-9.0 strongly alkaline, 9.0-10.0 very strongly alkaline 0r >9.0 very strongly alkaline.
It must be noted however that soils rarely have pH value less than 3.0 or greater than 10.0
iii. Soil Nutrient:
These are elements in the soil, essential to plant growth and development. Broadly, these are elements divided into two groups; the macro elements and the micro elements. The macro nutrients are those required by pants in large or moderate quantities, while the microelements are also referred to as traced elements and are required by plants in smaller quantities.
The macro elements include Nitrogen, Phosphorus, and Potassium, referred to as primary nutrients. Others are Calcium, Magnesium and Sulphur also referred to as secondary nutrients and is required in moderate quantities.
The micro nutrients include iron, Manganese, Zinc, Copper, Boron, Chlorine, and Molybdenum. Other elements required by Oxygen, hydrogen and carbon.
iv. Cation Exchange Capacity (CEC)
This is a measure of the negatively charged sites on the surface of clay and humus particles. It is expressed as milligram equivalent per thousand gram of soil (Meg Kg-1) others are.
v. Total Exchangeable Base (TEB)
This is the sum of exchangeable Calcium ions, Magnesium, Calcium and Sodium absorbed into these (clay, humus surfaces).
2.3.2. Soil Constituents
There are four soil constituents, these are mineral materials derives from bedrock or underlying rock, organic matter derives from dead and or decaying living organisms, water from underground water, surface water, or atmospheric water and the air is derive from the atmosphere
Mineral Materials
The soil contain about 45% of the mineral matter. These include all the material in the soil derive either from the soil parent materials or from inorganic sources through the process of mineralization. The soil mineral according to the major texture groups are sand made up of basically mineral quartz (SiO3). This is the most resistant of the entire mineral. Silt consists essentially of silica.
The important of these two is connected with their influence on soil structure and pore space distribution. Clay is the most important constituent of the soil fraction because it consists entirely of chemically active secondary minerals formed by the decomposition of primary rock minerals. The mineral element here can be divided into three categories:
(i). the Silicate mineral which includes Silicon, Iron, Aluminum etc. (ii). The Metallic Cation which includes Calcium, Magnesium and Potassium (iii). Non-metallic Cations which include Phosphorus, Sodium and Sulphur. He others are considers to be trace element in the soil e.g., Manganese, Molybdenum, Titanium, Copper, Zinc, Lead and Vanadium
Organic Matter:
These include the living and dead plant and animal matter in and on the soil is made up of 5%. The plant matter concentrates on the upper layer (A horizon) and the upper part of the B horizon the animal matter can be found in any part of the profile. When the plant and animal matter die, they are decomposed by micro-organism to form humus through the process of humification.
Organic matter is a storehouse for nutrients. It contains 90-95% of soil nitrogen, about 50% of phosphorus and up to 80% of Sulphur
Soil Air
This constitutes the soil atmosphere form which soil and plant organisms obtain oxygen for their metabolism and dispose of carbon dioxide and other gases. This is contained in the pore spaces of the soil.
Soil water
This is derived from precipitation and others sources are on the ground and surface water. There are three types of soil water. Gravitational, capillary and hygroscopic water. The gravitational water is responsible for leaching and eluviation. Capillary is that which is available to plants while hygroscopic water because it is non liquid state; it is not available to plant. Soil water helps in the formation of soil solutions and other processes in the soil.
The mineral materials and organic matter determine the nutrients content of the soil while soil air and water determine their availability of nutrients to the plant.
3.0 Soil Formation
3.1. Introduction:
Before a soil is form, the raw material must be available. The preparation of these raw materials which is mostly from the parent rock is referred to as weathering.
Weathering is the disintegration and decomposition of rocks into regolith, Saprolith of sediment materials or minerals. These materials are either develop in Situ or transported and redeposit elsewhere by agent of denudation including rivers, ice, wind or sea.
The term regolith refers to weathered rock in situ. The materials have not undergone any appreciable movement. Saprolith is use to describe between dirt and regolith for the entire weathering profile from the surface to the heart of weathered rock.
While sediments or drift materials is considered to be similar to regolith and Saprolith except that it has undergone transportation over a fairly long distance by either river, wind, ice or sea.
The sediment materials or rock debris carried from the valleys sides are called Colluvium (colluvial materials) while those carried in suspension along the channel are called Alluvium (alluvial materials). Those carried by wind are called Aeolian deposits or sand dunes. Those carried by ice are called glacial material (moraine). Those carried by sea are considered as lacustrine deposits.
3.1.1. Types/Process of Rock Weathering
The process of rock weathering may be divided into three:
a. Physical or mechanical weathering
This is merely the broken down of rock into smaller fragment or particles without changing their composition. This is more or less the process of rock disintegration.
There are two types of physical weathering namely thermal and mechanical weathering. Whereas thermal weathering has to do with the internal movement of materials that makes up the rock, the mechanical weathering is due to the external forces or agents.
The physical weathering process comprise essentially of exfoliation or peeling of rock layer in form of onion, expansion and contraction due to temperature fluctuation, block disintegration shattering. The major agent of physical weathering is heat others are wind which causes (corrosion) water and ice.
b. Chemical weathering
Chemical weathering process involves both physical breakdown and chemical alteration of the rock to varying extent depending on the intensity of the activity. This alteration is more than disintegration but lead to decomposition. Chemical weathering is a more important process because it aids the breaking down further the material produce by physical weathering. The agents of chemical weathering are water, gases, and organic acid. The following simple processes are common in chemical weathering.
(i). Solution:
This is the process in which soluble rock-salts dissolve in soil water or acid to form a solution which can be remove either partially or completely from the soil.
(ii). Hydration:
Is a Simple chemical reaction involving the absorption of water by rock materials or substances
(iii). Hydrolysis:
This is a reaction between hydrogen ions and hydroxyl and the element or ions on the rock. The rock reaction is more intense in the feldspars and other rock forming silicate. It is similar but more intense than hydration and can lead to complete decomposition of some materials.
(iv). Oxidation:
Is the addition of Oxygen to rock materials with water as the oxidizing agent. This is very common with ions base rocks. In the process oxygen is absorb and hydrogen removed.
(v). Reduction:
Is an opposite reaction to oxidation and operate under saturated condition i.e., the drainage condition of the soil. Here oxygen is removed with the introduction of hydrogen. This also operates with the native metals like ions and silicates.
(vi). Carbonation:
This is the process by which carbonates and bi-carbonate combine with a rock element to dissolve it. The important agent here is the carbon dioxide gas which dissolves both in air and rainwater to form a weak acid which is called carbonic acid. This can dissolve carbonate rock. E.g. limestone can be dissolve very easily.
Other chemical processes that lead to rock weathering are leaching, aggregation, dispersion and precipitation.
c. Biological weathering
Biological weathering is carried out by both physical and chemical means. Through the presence of plants around, while physical means is because plant roots can penetrate rock crevasses or cracks thereby expanding them to and extend that they can break by chemical means because of the activity of organic acid originating from decomposition. Animals through their activities can lead to weakening and eventual decomposition of rocks.
4.0 Factors of Soil Formation
Dokucheav, the famous soil scientist observed that soils do not occur by chance but as a result of the interplay of the five factors which can be group into two: passive and active factors.
Passive factors include parent materials, topography and time while active factors are climate and organic matter. The passive factors were considered thus because they do not generate any energy of their own to effect soil formation while the active factors were considered so because they are responsible directly for the formation of soil by the action of the energy they supply in various forms.
(i). Parent Materials:
This is the product of weathering in situ or residual of overburden of materials of regolith or Saprolith or transported and deposited matter. E.g., an ordinary weathered rock, beach sand, river sand, newly deposited glacial tilt, fresh sand dune or Aeolian deposit.
It provides the soil mineral matter which made up to 50% the soil body by volume and enough more by weight. It also decides to a large extend a number of important properties of the soil including texture, structure and in some cases color or pH.
(ii). Topography:
This also has an indirect effect. It influences both climate and vegetation. E.g., Jos Plateau x type of climate. It controls the rate and nature of rock weathering. Removal and deposition of the soil parent materials (distribution).
The most important aspect of topography is slope, angle and length, altitude, aspect and site. Aspect is the locational along the valleys site or slope and has to do with the direction of the sun. The relationship to soil erosion is that it is rapid on the steep slope and less on the gentle slope. Thus, it affects the profile depth as well as the maturity of soil.
Profile depth increases with decreases slope angle. Leaching is more pronounce on upper slope areas and the soil tends to be well drain. While on down slope areas, is fairly reduced. Soil tends to be poorly drained. Altitude tends to lower temperature and increases temperature particularly on the sun facing direction and vice versa on the shadow sight. Therefore, there is a different in soil type along a slope in a catena sequence.
(iii). Time:
This is associated with the age of the bedrock of sedimentary soils. It is also associated with the duration of the operation of soil formation which leads to it maturity. However, the duration is not purely a determining factor for soil maturity. Certain soil may take 20 year or less year to mature. Others may take up to a thousand or more years.
(iv). Climate:
This is the most important factor of soil formation. Its plays both direct and indirect role to soil formation. Direct in the sense that it produces soil, water and warm which are important agent of soil formation.
Indirectly because it act through vegetation and other forms of organic life. The most important climatic element of soil formation is therefore temperature and precipitation. Temperature directly increases the rate of chemical and bacterial activity.
It directly affects the rate of evaporation and movement of soil water. Temperature also favors vegetation growth which enhances a supply of organic matter and its composition. It also causes the expansion and contraction of rock. Precipitation is the main source of soil moisture and solution. Directly the moisture is a carrier of substances in solution. Colloidal stage or even in solid state within the profile by the processes of leaching. Eluviation, illuviation or capillary translocation. Precipitation aids chemical reaction leading to the decomposition of rock. Therefore, it promotes indirectly the physical disintegration of rock.
(v). Organic Matter:
This constitutes about 5% of an average soil by volume. It provides life for the living soil. Organic matter produces organic acids which intensify pedogenic processes.
The soil fauna such as bacteria, earthworm, termites or even man contribute in several ways to soil formation. Soil flora also contributes through root penetration and the presence of plants remains. Process of soil formations such as nitrification, Denitrification, humification and even leaching, eluviation etc. has a do with living matter in the soil.
5.0 Processes of Soil Formation
The activities that take place to produce soil from dead mineral matter and soil parent materials that is weathered rock can be group into two: simple processes and complex processes.
The simple processes include leaching, eluviation, illuviation, mineralization, and humification.
(i). Leaching:
This involves the removal by water of constituents from the soil vertically downward. The mineral involves are those that are readily soluble in soil water, e.g., salt/carbonate. The leaching process may be complete or total if the mineral is removed from the profile completely. It may also be partial if the mineral is removed from one part of the profile to another e.g., from the A-horizon to the B-horizon. An example is the removal of clays sesquioxides and decomposed organic matter from the A-horizon and deposited in the B-horizon below.
(ii). Eluviation:
This is the movement of soil materials particularly colloids in solution or in suspension from one place to another within the soil. This may be vertically i.e., upward or downward or lateral/sideward depending on direction of movement of soil water.
(iii). Illuviation:
This is the deposition of eluviated materials or substances in another location. Both eluviation and Illuviation normally take place in the vertical direction due to gravitational pull of water. The horizon that loses the material is considered the eluvial zone while the one that receive is considered the illuvial zone. Most often eluviation takes place in the A-horizon and Illuviation in the B-horizon.
(iv). Humification:
This is the process by which organic matter is decomposed to form humus in other words humus formation. The process of humification is enhanced or promoted by the two- active factor of soil formation.