EROSION AND
DEPOSITION
1.
Erosion involves acquisition and transportation
of rock debris. When massive rocks break into smaller fragments
2.
Through weathering and any other process, erosional
geomorphic agents like running water, groundwater, glaciers, wind and waves
remove and transport it to other places
3.
Depending upon the dynamics of each of these
agents.
4.
Abrasion by rock debris carried by these
geomorphic agents also aids greatly in erosion.
5.
By erosion, relief degrades, i.e., the landscape
is worn down.
6.
Weathering, mass-wasting and erosion are
degradational processes.
7.
It is erosion that is largely responsible for
continuous changes that the earth’s surface is undergoing.
8.
Denudational processes like erosion and
transportation are controlled by kinetic energy
9.
The erosion and transportation of earth materials
is brought about by wind, running water, glaciers, waves and ground water.
Wind, running
water, glaciers represent three states of matter gaseous (wind), liquid
(running water) and solid (glacier) respectively
1.
The erosion can be defined as “application of the
kinetic energy associated with the agent to the surface of the land along which
it moves
2.
Kinetic energy is computed as KE = 1 / 2 mv2
where ‘m’ is the mass and ‘v’ is the velocity
3.
Hence the energy available to perform work will
depend on the mass of the material and the velocity with which it is moving.
4.
In case of waves it is the location along the
interface of litho and hydro sphere — coastal region — that will determine the
work of waves,
5.
Work of ground water is determined more by the
lithological character of the region
6.
If the rocks are permeable and soluble and water
is available only then karst topography develops
7.
Deposition is a consequence of erosion
8.
The erosional agents lose their velocity and
hence energy on gentler slopes and the materials carried by them start to
settle themselves.
9.
Deposition is not actually the work of any agent
the coarser materials get deposited first and finer ones later
10.
By deposition depressions get filled up.
11.
Running water, glaciers, wind, waves and
groundwater act as aggradational or depositional agents also.
SOIL
Soil and Soil
Contents
1.
Pedologist who studies soils defines soil as a
collection of natural bodies on the earth’s surface containing living matter
and supporting or capable of supporting plants.
2.
Soil is a dynamic medium in which many chemical,
physical and biological activities go on constantly.
3.
Soil is a result of decay, it is also the medium
for growth
4.
It is a changing and developing body.
5.
It has many characteristics that fluctuate with
the seasons.
6.
Biological activity is slowed or stopped if the
soil becomes too cold or too dry
7.
Organic matter increases when leaves fall or
grasses die.
8.
The soil chemistry, the amount of organic matter,
the soil flora and fauna, the temperature and the moisture, all change with the
seasons
9.
Soil becomes adjusted to conditions of climate,
landform and vegetation and will change internally when these controlling
conditions change.
Process of Soil Formation
1.
Soil formation or paedogenesis depends first on
weathering
2.
First, the weathered material or transported
deposits are colonised by bacteria and other inferior plant bodies like mosses
and lichens.
3.
Several minor organisms may take shelter within
the mantle and deposits.
4.
The dead remains of organisms and plants help in
humus accumulation.
5.
Minor grasses and ferns may grow; later, bushes
and trees will start growing through seeds brought in by birds and wind.
6.
Plant roots penetrate down, burrowing animals
bring up particles, mass of material becomes porous and sponge like with a
capacity to retain water and to permit the passage of air
7.
Finally a mature soil, a complex mixture of
mineral and organic products forms.
Soil-forming
Factors
·
Five basic factors control the formation of soils
o
Parent material
o
Topography
o
Climate
o
Biological activity
o
Time
Parent Material
1.
Parent material is a passive control factor in
soil formation.
2.
Parent materials can be any insitu or on-site
weathered rock debris (residual soils) or transported deposits (transported
soils).
3.
Soil formation depends upon the texture (sizes of
debris) and structure (disposition of individual grains/particles of debris) as
well as the mineral and chemical composition of the rock debris/deposits.
4.
Nature and rate of weathering and depth of
weathering mantle are important consideration under parent materials.
5.
There may be differences in soil over similar
bedrock and dissimilar bedrocks may have similar soils above them.
6.
Young soils show strong links with the type of
parent rock.
Topography
1.
Topography like parent materials is another
passive control factor.
2.
The influence of topography is felt through the
amount of exposure of a surface covered by parent materials to sunlight
3.
The amount of surface and sub-surface drainage
over and through the parent materials.
4.
Soils will be thin on steep slopes and thick over
flat upland areas.
5.
Over gentle slopes where erosion is slow and
percolation of water is good, soil formation is very favourable.
6.
Soils over flat areas may develop a thick layer
of clay with good accumulation of organic matter giving the soil dark colour.
7.
In middle latitudes, the south facing slopes
exposed to sunlight have different conditions of vegetation and soils
8.
the north facing slopes with cool, moist
conditions have some other soils and vegetation.
Climate
1.
Climate is an important active factor in soil
formation.
2.
The climatic elements involved in soil
development are
(i)
Moisture in terms of its intensity, frequency and
duration of precipitation - evaporation and humidity
(ii)
Temperature in terms of seasonal and diurnal
variations
3.
Precipitation gives soil its moisture content
which makes the chemical and biological activities possible.
4.
Excess of water helps in the downward
transportation of soil components through the soil (eluviation) and deposits
the same down below (illuviation).
5.
In climates like wet equatorial rainy areas with
high rainfall, not only calcium, sodium, magnesium, potassium etc. but also a
major part of silica is removed from the soil
6.
Removal of silica from the soil is known as
desilication
7.
In dry climates, because of high temperature,
evaporation exceeds precipitation and hence ground water is brought up to the
surface by capillary action
8.
In the process the water evaporates leaving
behind salts in the soil. Such salts form into a crust in the soil known as
hardpans
9.
In tropical climates and in areas with
intermediate precipitation conditions, calcium carbonate nodules (kanker) are
formed.
10.
Temperature acts in two ways
11.
Increasing or reducing chemical and biological
activity
12.
Chemical activity is increased in higher
temperatures,
13.
Reduced in cooler temperatures (with an exception
of carbonation) and stops in freezing conditions.
14.
Tropical soils with higher temperatures show
deeper profiles
15.
In the frozen tundra regions soils contain
largely mechanically broken materials.
Biological Activity
1.
The vegetative cover and organisms that occupy
the parent materials from the beginning and also at later stages help in adding
organic matter, moisture retention, nitrogen etc.
2.
Dead plants provide humus, the finely divided
organic matter of the soil.
3.
Some organic acids which form during humification
aid in decomposing the minerals of the soil parent materials.
4.
Intensity of bacterial activity shows up
differences between soils of cold and warm climates.
5.
Humus accumulates in cold climates as bacterial
growth is slow.
6.
With undecomposed organic matter because of low
bacterial activity, layers of peat develop in sub-arctic and tundra climates.
7.
In humid tropical and equatorial climates,
bacterial growth and action is intense and dead vegetation is rapidly oxidised
leaving very low humus content in the soil.
8.
Bacteria and other soil organisms take gaseous
nitrogen from the air and convert it into a chemical form that can be used by
plants.
9.
This process is known as nitrogen fixation
10.
Rhizobium, a type of bacteria, lives in the root
nodules of leguminous plants and fixes nitrogen beneficial to the host plant.
11.
The influence of large animals like ants,
termites, earthworms, rodents etc., is mechanical, but, it is nevertheless
important in soil formation as they rework the soil up and down.
12.
In case of earthworms, as they feed on soil, the
texture and chemistry of the soil that comes out of their body changes.
Time
1.
Time is the third important controlling factor in
soil formation.
2.
The length of time the soil forming processes
operate, determine maturation of soils and profile development
3.
A soil becomes mature when all soil-forming processes
act for a sufficiently long time developing a profile.
4.
Soils developing from recently deposited alluvium
or glacial till are considered young and they exhibit no horizons or only
poorly developed horizons
5.
No specific length of time in absolute terms can
be fixed for soils to develop and mature.
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