WBBSE Chapter 4 Geomorphic Process And Landforms Of The Earth’s Introduction
The processes that build various new landforms and deform the shapes of landforms are called geomorphic processes or land-building processes
Geomorphic processes are of two types. These are- the terrestrial process and 2 extra-terrestrial processes.
Terrestrial processes are of two types- endogenic or endogenetic processes and 2 exogenic or exogenetic processes.
Endogenic processes are further divided into two divisions- diastrophism movement and 2 sudden movements.
The diastrophic process acts slowly over a long period, It can be of three types- geotectonic movement,2 isostatic movements,s, and 3 eustatic movements.
Geotectonic movements are further subdivided into two groups- Orogenic movement: This movement works almost horizontally or tangentially with the surface. Epeirogenic movement: This movement works vertically with the surface or along the radius of the Earth.
The word ‘petrogenic’ has been derived from the Greek word ‘repairs’ meaning continent and the word ‘orogeny’ has been derived from the Greek word ‘oros’ meaning mountain.
Read and Learn Also WBBSE Class 9 Geography And Environment Notes
The process of worldwide simultaneous change of water-holding capacity of the ocean basin due to the rise or fall of the sea level is called eustatic movement.
The tectonic process that helps to maintain elevational balance among various landforms is called isostatic movement.
Sudden movements occur very rapidly due to sudden endogenic forces that originate within the Earth’s interior. Examples of sudden movements are volcanic eruptions and earthquakes.
Processes that operate on the Earth’s surface are known as exogenetic processes. These processes are divided into three divisions- degradation, aggradation, and mass wasting.
The process which is involved with the decrease of elevation of landforms by erosion is called degradation.
The process which is involved with the upliftment or increase of elevation of landforms by deposition is called aggradation.
Gradation is a process of reaching the equilibrium of altitude differences (i.e. level land) through the process of degradation and aggradation.
Without any medium of erosion disintegrated or loose rock materials move downward along the slope of any sloping land due to gravitational force. This process is known as mass wasting.
Extraterrestrial materials are those which originate in outér space. When extraterrestrial materials like comets and meteors strike the Earth’s surface, it causes a change in the shape of the Earth’s surface. This process is known as the extraterrestrial process.
According to the order of relief, landforms can be divided into three types. The first order of relief continent is the ocean. O Second order of relief-mountain, plateau, plain. Third order of relief-erosional and depositional landforms.
Based on the origin, landforms are divided into three groups-mountain, 2 plateaus, and 3 plains.
Rocky regions that extend over vast areas, with an average height of more than 1000 m above sea level, and have peaks are called mountains.
Fold mountains are mainly composed of sedimentary rocks.
WBBSE Class 9 Geography Chapter 4 Geomorphic Processes Notes
The highest mountain in the Himalayas; the Longest mountain in the world; the Oldest mountain in the world of India, the Ural of Russia, the Great Dividing Range of Australia, the Appalachian mountain of the USA, the Caledonian mountain, etc.
The term ‘plate’ was first used by Canadian geophysicist J Tuzo Wilson.
French scientist Xavier Le Pichon (1968) is called the ‘Father of Plate Tectonic Theory’.
According to the plate tectonic theory, fold mountains are developed along the convergent plate boundary.
Fold mountains are formed by the collision of two plates- The formation of the Himalayan mountain by the collision of Eurasian and Indian plates, and 2 Formation of the Alps mountain by the collision of Eurasian and African plates. Formation of Rocky Mountain by the collision of the North American plate and Pacific Ocean plate. Formation of Andes mountain by the collision of Nazca plate and South American plate.
A cordillera is an extensive chain of mountains or mountain ranges. A belt or group of parallel mountain ranges is known as a cordillera. Example-Rockies, Andes.
- Barren is the only active volcano in India and Narcondam is a dormant volcano of India.
- The highest volcano in the world is Mauna Loa Volcano (9,750 m) on Hawaii Island.
- The Katmai Volcano of Alaska is known as the Valley of Ten Thousand Smokes.
- Fujiyama of Japan and Krakatoa of Indonesia are examples of dormant volcanoes.
- Popa of Myanmar is an extinct volcano.
- In certain places in the mantle, the temperature remains relatively higher than normal conditions due to the presence of radioactive materials and convection currents. These are called hotspots. Tibesti Mountain is located on the top of such a hotspot.
- Due to excessive heat, an upwelling current of magma originates from the hotspots. It is known as a plume.
- Most of the world’s active volcanoes are situated along the margin of the Pacific Oceanic Plate; thus together these volcanoes are called the Pacific Ring of Fire.
- When a block of the landmass is uplifted along a fault as a result of epeirogenic movement, it forms a flat-topped hill called block mountain.
When a block of landmass subsides along two faults as a result of epeirogenic movements, it forms a subsided block known as a rift valley or graben.
- The longest rift valley in the world is the Great Rift Valley (4800 km long) in East Africa.
- Another name for the residual mountain is a relict mountain.
- The residual mountains of India are Aravalli, Mahakal, Mahadev, etc.
- Table like landform which lies around 300 meters above sea level and has an almost flat top with a steep slope, is called a plateau.
- The highest plateau of India is the Ladakh plateau.
- Largest plateau of India is Deccan plateau.
- The continental plateau is also called the shield plateau.
- The stable interior portion of the Earth’s surface is called a craton.
Some important continental plateaus are the Colorado Plateau of the USA, the Africa Plateau, the Canadian Shield, the Greenland Plateau, the Australian Plateau, etc.
- The largest intermontane plateau in the world is the Tibetan Plateau.
- The highest plateau in the world is Pamir. It is also known as the Roof of the Earth.
- Examples of dissected plateaus of India are the Chota Nagpur, Bundelkhand, and Baghelkhand Plateau.
- The Deccan Plateau is an example of a lava plateau. It is composed of alkaline rock like basalt.
- A large expanse of land, having gentle undulations, at sea level or a slightly higher altitude (less than 300 m), is called a plain.
- The largest plain of India is the North Indian Plain which has been formed by the silt of the Ganga-Brahmaputra-Indus River.
- Turan lowland is an example of a subdued plain.
- Siberian Plain is the largest plain in the world.
- The delta plain between the Ganga and the Brahmaputra is the largest deltaic plain in the world.
- The flat plains formed over the eroded uneven topography by the continental ice sheets are called glacial plains.