Landforms of the Earth

Orogenic movements

Reason — Fold mountains are formed by orogenic movements, which are mountain-building forces caused by the compression and collision of tectonic plates. These forces fold rock layers to form mountain ranges such as the Himalayas.

Epeirogenic movements

Reason — Epeirogenic movements are continent-building forces that cause large-scale uplift or subsidence of land through vertical movements within the Earth.

Diastrophic forces

Reason — Orogenic and epeirogenic movements together form diastrophic forces, which act horizontally and vertically to create landforms such as mountains, plateaus, plains, lakes, and faults.

Exogenic forces

Reason — Exogenic forces act on the Earth's surface and shape landforms through weathering and erosion. They are also known as destructive forces.

A: Anticline B: Syncline

Reason — During folding, the upfold rock strata in arch-like shape are called anticlines or crest, marked as A in the figure, while the down folded structures are known as synclines or troughs, marked as B in the figure.

Ridges

Reason — Oceanic trenches, formed by the same tectonic forces as fold mountains, combine with volcanic systems to create ridges, such as the Mid-Atlantic Ridge.

Young fold mountains

Reason — Volcanic activities are common in young fold mountains, such as the Himalayas, Andes, Alps and Rockies.

A is true but R is false.

Explanation — The external forces or Exogenic forces are described as Destructive Forces because they cause widespread destruction through weathering and erosion of existing landforms.
Diastrophic Forces (originating deep inside the earth) are responsible for producing reliefs such as mountains, plateaus, plains, lakes and big faults.

Both A and R are true and R is the correct explanation of A.

Explanation — Residual mountains are also called mountains of denudation. This is because denudation and erosion by natural agents such as winds, water, snow, etc., cause the mountains to be lowered. However, some resistant areas may remain and form residual mountains.

Old fold mountains

Reason — Old fold mountains, such as the Appalachians, the Urals and the Aravallis, are highly eroded by the agents of gradation. As a result, they have gentler slopes, rounded tops and sculptured domes.

Relict mountains

Reason — Relict mountains are formed when weathering and erosion wear down mountains over time, leaving behind hard, resistant rock masses.

All of the above

Reason — All the pairs are correctly matched. The Himalayas and Alps are examples of young fold mountains, the Urals and Aravallis are examples of old fold mountains, and the Nilgiri and Rajmahal Hills are examples of residual mountains.

Both A and R are true but R does not explain A.

Explanation — The Assertion (A) is true because block mountains are formed by faulting (epeirogenic movements), where a block of land is uplifted between faults. The Reason (R) is also true, as block mountains are often separated by grabens (rift valleys). However, the presence of grabens does not explain the formation of block mountains.

Subsidence, deposition

Reason — The Coromandel plains in India are the result of mild subsidence followed by sedimentation (deposition). Thus, the forces of structural development as well as deposition were active in the formation of these plains.

Depositional plain

Reason — The plains that are formed by the deposition of materials which have been brought by various agents of transportation, such as rivers, wind and the sea, are called depositional plains.

existence of sand dunes and hallows.

Reason — Depositional plains formed by wind deposition, such as the Sahara and Thar Desert, have irregular, undulating surfaces with sand dunes and hollows.

Polder

Reason — A polder is a piece of land reclaimed from the sea or lake. The submerged land is surrounded by an embankment (dyke) and drained by pumping water into canals.

Structural plains

Reason — Structural plains are formed by the uplift or subsidence of land due to diastrophic forces, often involving the emergence or submergence of coastal areas.

Marine Deposition Plains : Western Coastal Plains (India)

Reason — The Western Coastal Plains are not marine deposition plains; in India, marine deposition plains occur mainly along the east coast.

All of the above.

Reason — All the statements are true. Block mountains which have flattened summits are called horst mountains, block mountains are often separated by intervening basins called graben, and the Vosges in France is an example of a block mountain.

Intermontane Plateaus

Reason — The plateaus that are surrounded by hills and mountains on all sides are called intermontane plateaus. They are formed along with fold mountains. For example, the Tibetan plateau, which is the world's highest and most extensive intermontane plateau.

Both A and R are true and R is the correct explanation of A.

Explanation — The fact that they were submerged under water is responsible for the existence of many lakes in the vast lowland.

A landform is a natural feature on the surface of the earth. For example- mountains, plateaus.

Fold mountains are formed by compressional forces that fold the Earth's crust due to large-scale tectonic movements. Hence, these mountains are called fold mountains.

Two chief characteristics of the fold mountains are-

1. The fold mountain system has parallel ranges.
2. A fold mountain region is also a region of sudden forces such as of volcanoes and earthquakes.

(a) Young fold mountain - The Himalayas
(b) Old fold mountain - The Aravallis

An example of residual mountain - Nilgiri mountains
An example of depositional plain - Northern plains of India

The Great Plains of the USA were formed due to uplift of land submerged under water. The fact that they were submerged under water is responsible for the existence of many lakes in the vast lowland. The Great Plains of the USA are examples of Structural plains.

If there are two parallel faults, the valley floor may sink and a rift valley is formed. For example- African Rift Valley.

Plateau is defined as an area of high ground, 500 feet above the ground level. Plateaus have steep slope on one side. The upper part is generally flat and is called tableland.

The plateaus surrounded by hills and mountains on all sides are called intermontane plateaus. For example- Tibetan plateau.

The importance of landforms are-

1. The mountain ranges of the world are the abode of snow and glaciers. They are thus the source of perennial rivers.
2. Mountains, plateaus, plains and valleys are beautiful sculptures of nature on the surface of the earth. They add to the beauty of the earth.

Landforms are formed on the surface of the earth due to the following natural processes-

1. Plate Tectonics — The tectonic plates push, collide and slide past each other due to which sedimentary rocks are compressed. This causes folding of the rocks and forms fold mountains.

2. Uplift and Submergence — A set of forces operates inside the earth's centre to the surface and is characterized by large scale uplift and subsidence of land area. These forces result in the formation of block mountains, basins, rift valleys, plateaus, plains, lakes and big faults.

3. Exogenic Forces — These forces cause widespread destruction through weathering and erosion of existing landforms and form new landforms through both erosion and deposition.

A mountain is a very steep land or hill rising to great heights above the land surrounding it. Mountains are classified into three types based on the forces that have formed them.

1. Fold mountains — Fold mountains are the result of large-scale earth movements caused by stresses in the earth’s crust. Such stresses may be caused by weight of the overlying rocks, movements in the mantle, the expansion or contraction of some part of the earth, etc. These stresses subject the rocks to compressive forces, producing wrinkling or folding along the lines of weakness. For example- the Himalayas in India.

2. Residual Mountains — Mountains which are subjected to weathering and erosion for a longtime, are lowered down and called residual or relict mountains. Denudation and erosion by natural agents like winds, water, snow etc., cause the mountains to be lowered but some resistant areas may remain and form residual mountains. They may also be formed on plateaus that are dissected by rivers. For example- Nilgiri in India.

3. Block Mountains — It is an uplifted land mass situated between two adjacent faults. The central block is upthrown or land on the outer-sides of the faults is downthrown so that the central mass appears like a highland. Its surface is like a plateau, but it has steep edges. For example- Vosges in Europe.

(i) The internal heat of the earth doesn't travel to the surface because rocks are bad conductors of heat. The internal heat of the earth melts the rocks and keeps the asthenosphere in a semi-molten state.

(ii) Exogenic forces are also called destructive forces because they cause widespread destruction through weathering and erosion of existing landforms.

(iii) Residual mountains are also called mountains of denudation as they are formed due to denudation and erosion by natural agents such as winds, water, snow etc.

The characteristics of Intermontane plateau are-

1. These plateaus are surrounded by hills and mountains on all sides.
2. They are formed along with fold mountains.
   For example- the Tibetan plateau.

The characteristics of Volcanic plateaus are-

1. They are formed by numerous volcanic eruptions that slowly build up over time, forming a plateau.
   For example- the Peninsular Plateau of India.

The characteristics of structural plains are-

1. These plains are formed due to uplift or subsidence of land.
2. Diastrophic forces may cause uplift of a portion of land beneath the ocean water or may cause submergence of coastal land under ocean water.
3. For example- The Great Plains of USA were formed due to the uplift of land submerged under water while the Coromandal plains in India are a result of mild submergence followed by sedimentation.

(i) There are different types of plain based on the way they are formed. While some have been formed due to depositional activities of rivers and winds, some are formed due to the upliftment and submergence of lands.

(ii) Alluvial plains are regarded as the granaries of the world because they are formed by the deposition of rivers. So, the soil in these plains is very fertile and supports agriculture.

(iii) The landforms on the surface of the earth are symbols of the energy of the earth as they are basically a result of enormous heat generated inside the earth and climate factors operating on the surface of the earth.

Depositional plains are formed by the deposition of materials which have been brought by various agents of transportation. Depositional plains are of three types-

1. River Deposition — The most widespread of these are alluvial plains like the Northern Plains of India; the flood plains like the Mississippi Plains in the USA, deltaic plains in Egypt and India.

2. Wind Deposition — Most such plains are sandy deserts like the Sahara in Africa and the Thar desert in India. They have irregular and undulating surface made by existence of sand dunes and hallows. Loess plains in China are formed from deserts.

3. Marine Deposition — These plains are found in coastal regions. Examples are the east coast of India, the estuarine banks in the Netherlands, coast of Germany and Denmark.

My state is in Northern India. It is home to a variety of landforms that have been shaped by both natural and human processes. These include the vast alluvial plain of the Indo-Gangetic region, the Himalayan foothills, and the valleys, deltas, and floodplains formed by major rivers such as the Ganges, Yamuna, and Ghaghara.

These landforms have been shaped by erosion, sedimentation, and tectonic activity over millions of years, while human activities such as deforestation, agriculture, and urbanization have caused changes to the landscape over time.

If the energy generated by tectonic movements, earthquakes, and volcanoes remained trapped inside the Earth, it would cause a continuous buildup of pressure, leading to catastrophic consequences.

1. Excess pressure inside a volcano could trigger a violent eruption, releasing lava, ash, and toxic gases. For example, the 1815 eruption of Mount Tambora in Indonesia was one of the most powerful eruptions in recorded history.
2. Similarly, pressure accumulating along tectonic plate boundaries could result in powerful earthquakes, causing widespread destruction of life and property.
3. Volcanic activity also releases gases such as carbon dioxide, sulphur dioxide, and water vapour, which influence the Earth's atmosphere and climate. If this energy were not released, it could disrupt the climate, ecosystems, agriculture, and wildlife.