Landforms- Geography Notes-01

Landforms- Geography Notes-01

A landform is any natural formation of rock and dirt, found on the

Earth. A landform can be as large as a mountain range or as small as a

hill. Landforms are natural features of the landscape, natural physical

features of the earth’s surface. eg., Valleys, Plateaus, Mountains, Plains,

Hills, Loess Plains etc.,

The major landforms of the Earth are 

i) Mountains 

ii) Plateaus and

iii) Plains. 

The minor landforms include hills, ridges, valleys, basins etc.,

According to Geo-scientists the landforms are formed by the forces acting

from the interior and on the surface of the Earth.

GEOMORPHIC PROCESSES:

The surface of the Earth is facing continuous changes because of the

influnce of some natural agents. The agents that influence on the surface

of the Earth are called External agents or Exogenic agents, while the agents

which bring the change inside the Earth are called Internal agents or

Endogenic agents. The processes carried out by Endogenic and Exogenic

forces are called Geomorphic processes.

Endogenic Forces: 

The internal forces are also known as Endogenic

forces. These are mainly the land building forces. Diastrophism includes

all these processes that move, elevate or build portions of the Earth’s

Crust. 

It includes Orogenic or Mountain building processes and Epeirogenic

or Continental building processes. Volcanoes and Earthquakes are the

most important internal forces which involve in the Crustal disturbances Exogenic Forces: The external forces are also known as Exogenic

forces. These forces are found on the surface of the Earth, which bring changes through degradation and aggradation processes. The important external forces are river, glacier, wind, sea waves etc.,

Mass Movements

Mass movements are directly under the influence of gravity. Transfer of one mass of rock debris down the slopes is the regular activity of mass movement or mass wasting. The term includes a variety of gravity induced movements of slope material, but excludes transportation by running water, wind, glacier etc.,

The processes of mass wasting and the landforms they produce are extremely varied and tend to grade one into another. The mass movements usually depends on: a) kinds of earth materials involved b) kinds of motion that occur and c) physical properties of those materials. The most important forms of mass movements or wasting are Rockfall, Talus, Earthflows, Mudflows, Landslides, Rockslides etc.,

The external and internal forces of the Earth play a major role in changing the face of the Earth. Geomorphic processes are building mountains, continents and other landforms. The shaping, sculpturing and carving of the surface of the Earth is the outcome of geomorphic processes. The end result of this process is formation of relief features, soils, and its influence on land use, vegetation, biomes and biodiversity.

WEATHERING:

The process of disintegration and decomposition of rocks is known as "Weathering". Factors like temperature, pressure, rainfall, frost, wind, plants, animals, and human beings are responsible for weathering.

The character of the rock, its chemical composition, hardness, texture, joints & permeability play an important role in weathering.

Types of Weathering:

- There are three types of Weathering processes:

i) Mechanical weathering

ii) Chemical weathering

iii) Biological weathering

I. MECHANICAL WEATHERING:

The disintegration of rocks by mechanical way and without any chemical changes is called "Mechanical weathering". It is also called "Physical weathering". Mechanical weathering is mainly influenced by temperature, frost, wind and sea waves. The agents of mechanical weathering are:

a) Temperature: 

High temperature leads the rocks to expand and low temperature makes them to contract. During the day the rocks expand due to high temperature and at night contraction takes place due to reduction in temperature. This continuous process leads to breaking or disintegration of rocks.

b) Frost: 

In the cold and frigid regions during night time, due to low temperature water solidifies into ice (freezing) and in the day ice melts (thawing). Continuous freezing and thawing leads to expansion and contraction of rocks, resulting in the disintegration of rocks.

c) Wind: 

In the desert, wind carries sand materials from one region to another and causes friction of particles on the rock surface. This results in scratching and breaking of rocks.

d ) Gravitation: 

The gravity of the Earth makes the huge rocks to roll towards the slope. Rolling rocks strike against each other and break up into pieces.

e) Sea waves: 

Sea waves brush against the coastal rocks of the Sea and cause breaking of rocks.

The process of Mechanical weathering is in various forms, depending on the type of rock. They are:

1. Block disintegration: Due to temperature variation, there is continuous expansion and contraction in the rocks causing tension and stress. Later these rocks disintegrate into blocks known as "Block Disintegration".

2. Granular disintegration: 

Rocks consist of several types of minerals and these minerals react differently to heat. As a result, the rocks break into different mineral grains known as "Granular Disintegration".

3. Exfoliation: 

Due to the heat of the Sun, outer surface of rocks gets heated up, but inside it remains almost cool. This makes the rock to expand and crack. The thin layer of rocks peel off, like the peeling of an onion. This process is called "Exfoliation".

II. CHEMICAL WEATHERING: Disintegration and Decomposition of rocks by chemical processes is called "Chemical Weathering".

In this process secondary or new minerals are developed from the original minerals of the rocks. The rain water and atmospheric gases are the main agents of chemical weathering. It is very common in humid regions.

Types of Chemical weathering

There are four types of chemical weathering processes. They are:

a) Oxidation 

b) Carbonation 

c) Hydration and

d) Solution

a) Oxidation: 

The rain water with oxygen, reacts on rocks containing iron and produce oxides. This chemical reaction is known as "Oxidation". The common process of rusting of iron is an example of oxidation.

b) Carbonation: 

The rain water with carbon-di-oxide, becomes a weak carbonic acid and it reacts with calcium carbonate or limestone to form calcium bicarbonate, which dissolves easily. This process is called "Carbonation". It is very active in limestone regions.

c) Hydration: 

The rock minerals take up water, the increased volume creates physical stress within the rock. As a result certain minerals like feldspar and gypsum are reduced into powder. This process is called "Hydration".