WEATHERING,
PROCESSES AND AGENTS SIMPLIFIED
Weathering
is the physical disintegration of the earth material and change in its chemical
properties due to the action of Air, Water and Organisms at a particular place
without distant removal of its products. It is a continuously occurring process
both on exposed surface of earth and beneath the ground within the rock strata.
Various weathering agents are classified into two major classes.
WEATHERING
PROCESSES OR TYPES
MECHANICAL WEATHERING
It
is also called physical weathering. The process of weathering that occur due to
imposition of certain stresses occurring by some physical means such as
freezing and thawing, expansion of salt crystals, rainfall and temperature.
FACTORS RESPONSIBLE FOR MECHANICAL WEATHERING
Following
factors are responsible
Frost Action
Ice
has a great damaging capacity as the volume of water increases by 9% upon ice
formation. So upon freezing the water in the cracks, joints or pores in the
rocks expand by 9%, as a result the material on both sides of the cracks
experiences huge pressure resulting in the wear and tear of those rocks
Salt Wedging
In
deserts salt play same role as ice. The saline water in small pores and cracks
evaporates leaving behind the deposits of salt crystals that result in cracks
in the rocks. When this process is helped by wind the weathering may occur
Temperature Changes
The
rocks are made up of different mineral grains that have different physical and
chemical properties and different expansion rates on basis of temperature
changes. If continuous temperature changes occur borders between these mineral
grains may be loosened resulting in weathering of rocks.
Rainfall
When
the rain water drops on temperature heated rocks in dry areas, the rocks
develop cracks and are broken
Removal of Overburden
Many
rocks are formed under pressure below the earth crust. When the upper material
is eroded off those underlying rocks are exposed and the pressure is released.
As a result the cracks may occur in these rocks and result in weathering.
Gravity
Many
rocks having large cracks may be disintegrated on the basis of gravity. However
its effect is minute and time taking.
CHEMICAL WEATHERING
The
rocks are made up of mineral particles so the disintegration of these mineral particles
due to chemical action results in the breakdown of the whole rock. This type of
weathering is called Chemical Weathering. Various agents or processes of
chemical weathering are:
Hydrolysis
We
know that hydrolysis is breakdown of material due to water acting as a chemical
agent. When the water present in the rock material comes in contact with
certain minerals of the rock hydrolysis is initiated and during this process
expansion of the rocks occur due to the formation of certain new products. As a
result cracks appear in the rocks and ultimately wear and tear of rocks occur
Oxidation
Chemical
reaction of Oxygen present in the air with any element is called Oxidation. It
is a dominant weathering agent in the tropics. Oxidation process is easy to
judge because when oxygen chemically react with rock minerals it produces Iron
or Aluminum product that show a distinct red color e.g. “Grand Canon”.
Carbonation
Under
various conditions the H2O might be converted into a mild acid solution and its
effectiveness as a weathering agent is increased. For instance when water
combines with CO2 it forms a highly reactive acid known as Carbonic acid. It
reacts readily with Limestone and Dolomite and result in weathering of rocks.
This process is known as Carbonation. It is a prominent process in the humid
areas.
Solution
Some
minerals such as Rock Salt and Gypsum may be Dissolved by water and then
removed in solution resulting in weathering of rocks.
BIOLOGICAL WEATHERING
The
disintegration of rock minerals through the biological agents is known as
biological weathering. For instance Earthworms and plant roots are important in
the development of the soils; Lichens contribute to the breakdown of rocks and
human also play various roles in the disintegration of rocks. It may be
classified as:
Weathering by Animals and Human
An
important aspect of this type is the mixing of soil by the burrowing animals
and the earth worms, Rats, Rabbits and Termites etc. they burrow the soil for
food and shelter and thus soften it and cause its weathering. Similarly hoved
animals or grazers also soften the upper layer of soil with their hoves and
make it soft. Human also contribute a lot to the weathering process through
activities like mining, roads, dams, tunnels and other construction processes.
The harmful chemicals released by industry and Auto-mobiles also act as
weathering agents.
Weathering due to Vegetation
The
trees and shrubs grow in a thin layer of fertile soil on the Rocks and
mountains. Their roots may percolate deep into the rocks and on growth these
produce cracks in the rocks causing the weathering of the rocks. Similarly
Lichens (combination of Algae and Fungi) living on bare rocks by drawing minerals
from the rock material trough ion exchange method. The swelling and contraction
of lichens as they alternatively get wet and dry may cause small particles of
rock to fall off.
FACTORS AFFECTING WEATHERING
PROCESS
· Nature of rock is an important factor,
if rock is soft it will weather easily and if it is hard process will be slow
· If slope is less there will be less
weathering as compared to sharp slopes
· The rocks with joints are easily
weathered by factors such as temperature variation, Gravity etc.
· Vegetative cover protects rocks. Those
without vegetative cover or having less vegetative cover are more exposed to
weathering process
· Climate is an important factor, humid
climates promote Chemical Weathering whereas dry climate promote Mechanical
Weathering.
IMPORTANCE
OF WEATHERING
It is a significant process in a
way that
· New land forms are produced as a result
of Weathering
· Weathering produces sediments that are
then transported by transporting agent such as Wind and then come under
pressure and converted into Sedimentary Rocks
· Weathered minerals are when transported
to Agricultural zones through agents such as River floods they increase the
fertility of the soils.