Landforms of the Earth

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The Earth’s surface displays a remarkable variety of landforms, from towering mountains to vast plains and elevated plateaus. These features are not fixed but are constantly molded by powerful forces originating both inside and on the Earth’s surface. Internal (endogenic) forces, driven by the Earth’s core, cause significant vertical and horizontal movements. These forces are responsible for folding, which creates magnificent Fold Mountains like the Himalayas, and faulting, leading to the formation of uplifted Block Mountains and sunken Rift Valleys. Furthermore, volcanism and earthquakes are internal processes that contribute significantly to the development of unique topographical features, such as volcanic mountains and expansive volcanic plateaus.

In contrast, external (exogenic) forces continually reshape the Earth’s surface through the actions of water, wind, and ice. These forces primarily operate through weathering (the breakdown of rocks), erosion (the transport of weathered material), and deposition (the laying down of eroded material). While often seen as destructive because they wear down existing landforms, these forces are also constructive, building new features through the accumulation of sediment. Major landforms shaped by these combined forces include mountains (classified as fold, residual, or block), plateaus (elevated flatlands such as the intermontane Tibetan Plateau or the volcanic Deccan Plateau), and extensive plains, which are often fertile and densely populated, especially those formed by river deposits.

Ultimately, the chapter highlights the profound influence of these diverse landforms on our planet’s systems and human existence. They are critical in shaping regional climates, impacting the availability of natural resources like minerals and water, and determining patterns of human settlement and economic development. A grasp of the dynamic interaction between these internal and external forces is essential for understanding the Earth’s ever-changing surface and its complex connection to life.

Exercises

I. Short answer questions.

Question 1.
What is meant by a landform ?
Ans:

The Earth’s diverse surface, from towering peaks to expansive plains, is shaped by a constant interplay of internal and external forces.

Internal (Endogenic) Forces act as the Earth’s architects. Driven by processes deep within the planet, such as tectonic plate movement, these forces build major landforms. They are responsible for the dramatic uplift of mountain ranges, the formation of high plateaus, and the creation of rift valleys. Volcanic activity further contributes to this by forming new landforms and modifying existing ones through eruptions.

Conversely, External (Exogenic) Forces act as the Earth’s sculptors, constantly modifying its surface. Agents like flowing water, wind, and glacial ice wear down existing features and create new ones. Water carves valleys and builds deltas, wind shapes deserts with dunes, and glaciers grind out valleys. These forces operate through the continuous processes of weathering (breaking down rocks), erosion (transporting material), and deposition (settling material), collectively creating the ever-evolving mosaic of Earth’s landforms.

Question 2.

Why are the fold mountains called so ?

Ans:

Fold mountains are named for the way they are formed: when two or more of Earth’s tectonic plates collide, the immense compressive forces between them cause the layers of rock in the Earth’s crust to buckle, bend, and wrinkle into wave-like structures, much like pushing a rug against a wall causes it to fold. These bends in the rock layers are precisely what geologists refer to as “folds,” hence the name.

Question 3.

Give two chief characteristics of the fold mountains.

Ans:

Here are two chief characteristics of fold mountains, presented uniquely and concisely:

  1. Undulating Topography: Fold mountains are characterized by a series of waves or folds, leading to a landscape of alternating peaks (anticlines) and valleys (synclines). This gives them a distinct, often rugged, and undulating appearance.
  2. Formation by Compression: They are formed when tectonic plates collide, causing immense compressive forces that buckle and crumple the Earth’s crust. This process results in the uplift of large rock masses into elevated mountain ranges.

Question 4.
Give one example of each :

(a) Young fold mountains;
(b) Old fold mountain. Why they are called so

Ans:

Here’s a concise and unique explanation of young and old fold mountains:

(a) Young Fold Mountains:

  • Example: The Himalayas
  • Why they are called so: They are geologically “young” because they formed relatively recently (within the last 50-70 million years). Due to their recent formation, they are still actively rising, have sharp, jagged peaks, and are characterized by deep, narrow valleys. The erosional forces of wind, water, and ice have not had enough time to significantly wear down their rugged features.

(b) Old Fold Mountains:

  • Example: The Aravalli Range (in India)
  • Why they are called so: They are geologically “old,” having formed hundreds of millions of years ago. Over vast periods, these mountains have been subjected to extensive weathering and erosion by natural agents. This prolonged erosion has worn down their original sharp peaks, giving them a much lower elevation, rounded tops, and gentler slopes compared to young fold mountains. They represent the roots of much higher mountains that existed in the distant past.

Question 5.

Give an example of residual mountains.

Ans:

Examples of residual mountains include:

  • Aravalli Range (India): These are considered one of the oldest fold mountains in the world, now significantly denuded and appearing as residual mountains.
  • Appalachian Mountains (USA): While originally fold mountains, extensive erosion over millions of years has reduced them to residual mountains with rounded peaks.
  • Highlands of Scotland (UK): These too are ancient mountain ranges that have been extensively worn down by various agents of erosion.

These mountains are formed when pre-existing mountain ranges are subjected to prolonged weathering and erosion by agents like wind, water, and ice. Over vast geological timescales, the softer rocks are eroded away, leaving behind the more resistant, harder rocks as the remnants, or “residuals,” of the original larger mountain system.

Question 6.

How is a rift valley formed ? Give one example of a rift valley.

Ans:

This “pulling apart” or extensional force causes the Earth’s crust to stretch and thin. As it stretches, parallel cracks or faults develop. The central block of land between these faults then subsides or drops down, creating the characteristic elongated depression known as a rift valley. This process is often accompanied by volcanic activity and earthquakes.

One prominent example of a rift valley is the East African Rift Valley.

Question 7.

Give a brief definition of a plateau.

Ans:

A plateau is an expansive, elevated stretch of land distinguished by its notably level summit, which ascends considerably higher than the adjacent landscape. It typically features one or more abruptly sloped boundaries, commonly referred to as escarpments.

Question 8.
Give one example of each :

(a) Intermontane plateau
(b) Volcanic plateau and
(c) Piedmont plateau

Ans:

(a) Intermontane Plateau: This expansive high-altitude plateau is cradled by the towering peaks of the Andes Mountains on both its eastern and western flanks, making it one of the most significant intermontane regions globally, second only to the Tibetan Plateau in size.

(b) Volcanic Plateau: Consider the Deccan Plateau in peninsular India as a compelling instance of a volcanic plateau. This vast elevated landmass was predominantly forged from successive flows of basaltic lava, which solidified into extensive sheets over millions of years, giving rise to its characteristic step-like topography and rich, dark soils.

(c) Piedmont Plateau: The Piedmont Plateau in the eastern United States serves as an excellent example of this plateau type. Situated at the base of the Appalachian Mountains, it gently descends eastward towards the Atlantic Coastal Plain, acting as a transitional zone between the rugged highlands and the flatter coastal lowlands.

Question 9.

Give two points of importance of landforms.

Ans:

Impact on Climate and Water Availability

Landforms are pivotal in shaping climatic patterns and water resources. Tall mountain ranges, for example, force moist winds upward, leading to heavy rainfall on one side (orographic precipitation) and dry conditions on the other (rain shadow effect). Beyond this, mountains are crucial as they are often the source of major rivers, fed by melting snow and glaciers. This water is essential for agriculture, drinking water, and hydroelectric power in lower regions.

Influence on Human Life and Economy

Landforms largely dictate human settlement patterns and economic activities. Flat, fertile plains are ideal for large populations and extensive agriculture due to easy farming and development. In contrast, challenging mountainous areas may have fewer inhabitants and specialized economies like mining, forestry, or tourism, despite their mineral and hydroelectric potential. Plateaus can support particular types of farming, animal rearing, or provide access to rich mineral deposits, depending on their characteristics.

Question 10.

What are known as epeirogenic movements ?

Ans:

Epeirogenic movements are slow, large-scale, vertical movements of the Earth’s continental crust, typically involving uplift or subsidence. Unlike mountain-building (orogenic) movements which cause intense folding and faulting along narrow belts, epeirogenic movements affect broad, stable parts of continents and result in gentle warping or broad undulations with little to no folding.

These movements are often caused by forces acting along the Earth’s radius, like isostatic adjustments (crustal response to changes in load, such as glaciers melting) or mantle convection. They play a significant role in creating vast plains, plateaus, and basins, and can also lead to changes in sea level relative to the land.

Question 11.

Name two landforms created by epeirogenic movements.

Ans:

Epeirogenic movements are broad, large-scale uplifting or subsiding movements of the Earth’s crust that affect continents or large parts of them, resulting in changes in sea level relative to the land. They are generally very slow and do not involve intense folding or faulting.

Here are two landforms created by epeirogenic movements:

  1. Continental Plateaus: These vast, relatively flat, and elevated landmasses can be formed when large sections of the continental crust are slowly uplifted due to epeirogenic forces. A prime example is the Colorado Plateau in the United States, which has been uplifted as a block over millions of years.
  2. Coastal Plains/Emergent Coastlines: When epeirogenic uplift occurs along a coastline, the former seabed can be exposed, creating new land in the form of a coastal plain. Conversely, if epeirogenic subsidence occurs, it can lead to submergent coastlines. An example of an emergent coastline formed by epeirogenic uplift is seen in parts of Scandinavia, where the land is still rebounding after the melting of glacial ice.

Question 12.

Why are the sudden forces described as ‘Constructive forces ?

Ans:

Sudden forces, primarily internal (endogenic) forces like volcanism, folding, and faulting, are termed ‘constructive’ because they are responsible for building up and creating major relief features on the Earth’s surface.

For instance:

  • Volcanic eruptions form new land, islands, and volcanic mountains/plateaus.
  • Folding leads to the creation of vast mountain ranges (e.g., Himalayas).
  • Faulting results in block mountains and rift valleys.

These processes uplift, deform, and add material to the crust, thus “constructing” new landforms, in contrast to external forces that wear them down.

Question 13.

What are called endogenic forces ?

Ans:

Endogenic forces are geological forces that originate and act within the Earth’s interior. Driven primarily by the Earth’s internal heat (generated by radioactivity, primordial heat, and rotational/tidal friction), these forces cause movements and deformations of the Earth’s crust.

They are responsible for creating major landforms and significant geological events, including:

  • Folding: Leading to the formation of fold mountains (e.g., Himalayas).
  • Faulting: Creating block mountains and rift valleys.
  • Volcanism: Resulting in volcanic mountains, plateaus, and eruptions.
  • Earthquakes: Sudden tremors caused by the release of accumulated stress in the Earth’s crust.
  • Plate Tectonics: The large-scale movement of the Earth’s lithospheric plates, which underpins many of the above phenomena.

Question 14.

Name four relief features on the surface of the earth.

Ans:

Major Relief Features of the Earth’s Surface

The Earth’s diverse landscape is shaped by a variety of relief features, each with distinct characteristics. These features are broadly categorized into:

Mountains: They are defined by their steep slopes and often culminate in high peaks. Mountains can be formed through various geological processes, including the collision of tectonic plates (fold mountains), volcanic activity (volcanic mountains), or erosion of softer rock (residual mountains).

Plateaus: Representing a different kind of elevated landscape, plateaus are essentially flat-topped landmasses that stand high above the neighboring areas. They typically feature at least one, and often several, sides that drop off sharply, creating a distinct boundary with lower elevations.

Plains: In stark contrast to mountains and plateaus, plains are characterized by their extensive, flat, or gently undulating low-lying topography. These vast stretches of land are often fertile and conducive to agriculture and human settlement, making them among the most densely populated regions on Earth. Plains commonly form through the deposition of sediments by rivers, wind, or glaciers.

Valleys: These are depressed, elongated areas on the Earth’s surface, typically found nestled between higher landforms such as hills or mountains. The formation of valleys is predominantly attributed to the erosive power of flowing water (rivers) or the grinding action of glaciers. Over long periods, these natural agents carve out the distinctive U-shaped or V-shaped cross-sections characteristic of valleys.

Question 15.

What are known as exogenic forces ?

Ans:

Exogenic forces, also known as external forces, are natural processes that originate from or operate on the Earth’s surface and within its atmosphere. These forces are primarily driven by energy from the sun and gravity.

Their main characteristic is their role in wearing down or denuding the Earth’s surface. They are often referred to as “destructive forces” because they cause the breakdown, removal, and reshaping of existing landforms.

Key processes associated with exogenic forces include:

  • Weathering: The disintegration (physical or mechanical weathering) and decomposition (chemical weathering) of rocks and minerals in situ (without significant movement).
  • Erosion: The process of acquiring and transporting weathered material from one location to another by various agents.
  • Transportation: The movement of eroded material.
  • Deposition: The laying down of transported material in new locations, which can then lead to the formation of new landforms (e.g., deltas, dunes).

The primary agents responsible for exogenic processes are:

  • Running water (rivers and streams): Carves valleys, erodes riverbeds, and deposits sediments to form floodplains and deltas.
  • Wind: Dominant in arid and semi-arid regions, causing erosion (e.g., abrasion) and deposition (e.g., sand dunes).
  • Sea waves: Shape coastlines through erosion (e.g., cliffs, caves) and deposition (e.g., beaches, sandbars).
  • Gravity: Directly responsible for mass wasting and plays a role in all erosional processes by influencing the movement of materials downslope.

Question 16.

Name the two land forms produced by exogenic forces.

Ans:

The two landforms produced by exogenic forces are Plains and Valleys.

Here’s why and how they are formed:

  1. Plains: Exogenic forces, primarily erosion and deposition by agents like rivers, wind, and glaciers, are responsible for creating plains. For example, Alluvial Plains are formed by the deposition of silt, sand, and clay carried by rivers over long periods. As rivers flow from higher elevations, they erode material and then deposit it in flatter areas, building up vast, fertile plains.
  2. Valleys: While some valleys can be influenced by endogenic (internal) forces (like rift valleys), the classic River Valleys or Glacial Valleys are primarily shaped by exogenic forces.
    • River Valleys: Rivers erode the landscape as they flow, cutting into the land and carving out V-shaped valleys over time. The continuous flow of water deepens and widens the valley.
    • Glacial Valleys: Glaciers, as they move, exert immense erosional power, carving out distinctive U-shaped valleys. They scour the land, transport large amounts of debris, and reshape mountainous terrain into these characteristic forms.

Question 17.

Give one chief characteristic of the fold mountains.

Ans:

A chief characteristic of fold mountains is their undulating or wave-like appearance, formed by the intense buckling and compression of the Earth’s crust.

Question 18.

Give one example of volcanic mountains.

Ans:

Mount Fuji

Question 19.

How is a rift valley formed ? Give one example.

Ans:

A rift valley is a distinctive type of lowland, characterized by a linear shape and often bordered by steep sides, or escarpments. It forms as a direct result of extensional tectonic forces acting on the Earth’s lithosphere (the rigid outermost layer, including the crust and uppermost mantle).

Here’s a breakdown of its formation:

  1. Divergent Plate Boundary: Rift valleys typically occur at divergent plate boundaries, where two tectonic plates are slowly moving away from each other.
  2. Stretching and Thinning: As the plates pull apart, the Earth’s crust in that region undergoes tremendous stress, causing it to stretch and thin. This process is known as extensional tectonics.
  3. Faulting: The stretched and thinned crust eventually fractures along parallel sets of normal faults. A normal fault is a type of fault where the hanging wall (the block of crust above the fault plane) moves downward relative to the footwall (the block below the fault plane).
  4. Subsidence (Graben Formation): Due to the pulling apart and the resulting normal faulting, the central block of land between these parallel faults sinks downwards. This subsided block is called a graben. The linear depression formed by this sinking of the graben creates the rift valley.
  5. Erosion and Volcanism: Over long geological periods, the rift valley can be further widened and deepened by erosion (from wind, water, and ice). Additionally, the thinning of the crust can lead to volcanic activity along the rift, as magma from the mantle rises closer to the surface, contributing to the landscape of the rift valley.

Essentially, a rift valley is a crack in the Earth’s crust where a section of land has dropped down between two parallel faults as the crust pulls apart.

Example:

This massive geological feature stretches for thousands of kilometers through Eastern Africa, showcasing numerous active volcanoes, deep lakes (like Lake Tanganyika and Lake Malawi), and distinct escarpments. It is an active zone where the African plate is slowly splitting into two new plates.

Question 20.

Give a brief definition of a plateau.

Ans:

A plateau is an expansive, elevated stretch of land with a relatively flat top, which rises abruptly from the surrounding lower terrain. Often referred to as a “tableland” due to its characteristic shape, it can be formed by various geological processes, including volcanic activity, erosional forces, or the uplift of the Earth’s crust.

Question 21.
Give one example of each

(a) Intermontane plateau
(b) Piedmont plateau
(c) Volcanic plateau.

Ans:

Here is one example for each type of plateau:

(a) Intermontane Plateau: * Example: The Tibetan Plateau in Central Asia. It is bordered by the Himalayas to the south, the Kunlun Mountains to the north, and other mountain ranges, making it a high-altitude plateau surrounded by mountains.

(b) Piedmont Plateau: * Example: The Piedmont Plateau in the eastern United States. This plateau lies at the foot of the Appalachian Mountains, extending eastward to the coastal plain. 

(c) Volcanic Plateau: * Example: The Deccan Plateau in India. This large plateau was formed by extensive flood basalt eruptions that occurred millions of years ago, resulting in a vast, elevated landform composed primarily of volcanic rocks.

Question 22.

How are erosional plains formed ?

Ans:

Erosional plains are extensive, relatively flat landforms that are formed over long periods through the wearing down of higher land features by various agents of erosion. Unlike depositional plains (which are built up by accumulated sediments) or structural plains (which result from crustal movements), erosional plains are essentially residual landforms left behind after the removal of vast amounts of overlying or surrounding material.

Here’s a breakdown of how they are formed:

  1. Starting Point: Elevated Landforms: The process begins with existing elevated landforms such as mountains, plateaus, or other rugged terrain. These areas are subject to various natural processes that constantly work to break down and transport their material.
  2. Agents of Erosion (Denudation): The primary sculptors of erosional plains are external forces, also known as agents of denudation. These include:
    • Running Water (Rivers): Rivers are incredibly powerful agents of erosion. Over millions of years, they continuously erode their valleys through processes like hydraulic action (the force of water), abrasion (grinding by sediment), and corrosion (chemical dissolution). This lateral and vertical erosion widens valleys and reduces the height of interfluves (areas between rivers). As a river reaches its mature and old stages, its gradient decreases, and its primary action shifts from downcutting to lateral erosion, leading to the formation of wide, almost flat floodplains and ultimately, contributing to vast plains.
    • Glaciers: In cold regions, massive sheets of ice (glaciers) move slowly over the landscape, carving out U-shaped valleys and grinding down bedrock. As glaciers recede or melt, they can leave behind vast, relatively flat areas that were previously scoured by the ice. The Canadian Shield is a prime example of a region heavily impacted by glacial erosion.
    • Wind: In arid and semi-arid regions, wind acts as a significant erosional agent. It picks up and carries away loose particles (deflation) and abrades rock surfaces with entrained sand (abrasion). Over extended periods, this action can wear down elevated areas, leaving behind flat, stony plains known as pediplains (if formed solely by wind action and associated processes like sheetwash).
    • Weathering: While not an erosional agent in itself, weathering (physical and chemical breakdown of rocks) weakens the bedrock, making it more susceptible to removal by the agents of erosion mentioned above.
  3. Long-Term Process of Gradation: The formation of erosional plains is a testament to the immense power of sustained geological processes. It involves the gradual and continuous wearing away of rock and soil, transporting the eroded material to lower elevations, and eventually depositing it elsewhere (often forming depositional plains). This long-term process of levelling down the land is known as gradation.
  4. Resulting Landforms:
    • Peneplains (Almost Plains): These are the most common type of erosional plain, formed primarily by the combined action of rivers and other sub-aerial agents of erosion (excluding wind as the dominant force). They are characterized by gently undulating surfaces, often with scattered isolated hills (monadnocks or inselbergs) of more resistant rock that have withstood the erosion.
    • Pediplains: As mentioned, these are extensive plains formed in arid and semi-arid environments primarily by wind erosion and other associated processes that erode the base of mountains, causing them to retreat parallel to their original slope.

Question 23.

Give two points of importance of landforms.

Ans:

Here are two points highlighting the importance of landforms, keeping in mind uniqueness and avoiding plagiarism:

  1. Influence on Climate and Weather Patterns: Landforms significantly shape regional climates. High mountain ranges, for instance, act as barriers to winds and moisture, leading to orographic rainfall on their windward side and rain shadows (dry areas) on their leeward side. Plains, on the other hand, allow for the free movement of air masses, often resulting in more extreme temperature variations. This direct influence on precipitation, temperature, and wind patterns dictates the type of vegetation, agricultural practices, and overall habitability of a region.
  2. Resource Distribution and Economic Activities: Landforms are intrinsically linked to the distribution of natural resources. Mountains are often rich sources of minerals (e.g., coal, metallic ores) due to geological processes, and their slopes provide sites for hydroelectric power generation. Plains, particularly riverine plains, are exceptionally fertile due to alluvial deposits, making them ideal for agriculture and supporting dense populations. Plateaus can also hold significant mineral deposits and offer suitable conditions for certain types of farming or pasturage, thus directly influencing the primary economic activities and development potential of a region.

II. Distinguish between each of the following 

  1. Fold Mountain and Block Mountain.
  2. Intermontane plateau and Volcanic plateau.
  3. Structural plain and Depositional plains.
  4. Tectonic mountain and Volcanic mountain.

Ans:

1. Fold Mountains vs. Block Mountains

  • Fold Mountains: Formed by the intense compression and buckling of the Earth’s crust due to tectonic plate collisions, creating wavelike ridges and valleys (e.g., Himalayas). Imagine a crumpled rug.
  • Block Mountains: Result from the fracturing of the crust along faults, where sections of land are either uplifted (horsts) or down-dropped (grabens), leading to steep, linear slopes (e.g., Vosges Mountains). Think of shifting dominoes.

2. Intermontane Plateau vs. Volcanic Plateau

  • Intermontane Plateau: An elevated, relatively flat landmass entirely surrounded by mountains, often formed by the same uplifting forces as the adjacent ranges (e.g., Tibetan Plateau). Like a table within a room of furniture.
  • Volcanic Plateau: Created by the widespread accumulation of solidified lava flows from multiple eruptions, forming extensive, flat, elevated regions made of igneous rock (e.g., Deccan Traps). Picture layers of pancake batter building up.

3. Structural Plain vs. Depositional Plains

  • Structural Plain: A flat or gently sloping area that primarily reflects the horizontal layers of underlying sedimentary rock, formed by minimal crustal disturbance (e.g., Great Plains). Similar to a gently lifted, undisturbed layer cake.
  • Depositional Plains: Low-lying, often fertile areas built up by the accumulation of sediments transported and deposited by external agents like rivers, glaciers, or wind (e.g., Indo-Gangetic Plain). Analogous to a sandbox filling with material.

4. Tectonic Mountain vs. Volcanic Mountain

  • Tectonic Mountain: A broad category encompassing mountains formed by large-scale crustal deformation due to plate tectonics, including both folding and faulting (e.g., Andes, Basin and Range Province). A complex sculpture shaped by immense, slow forces.
  • Volcanic Mountain: Mountains built directly from the successive eruptions and accumulation of lava, ash, and other volcanic materials, often forming conical shapes around a vent (e.g., Mount Fuji). Like a sandcastle built layer by layer from a central point.

III. Give one technical term for each of the following 

Question 1.
Block mountains with flattened summits.
Ans:

Here’s a concise, unique explanation of block mountains with flattened summits:

Block mountains typically form when large blocks of the Earth’s crust are uplifted between faults. If these mountains have been subjected to prolonged erosion, their peaks can become worn down and flattened, resulting in horst structures (the uplifted blocks) that exhibit broad, level summits rather than sharp, pointed peaks. This flattening occurs as erosional agents, over geological timescales, abrade the higher, more exposed parts of the uplifted blocks.

Question 2.

Plateaus surrounded by hills and mountains on all sides.

Ans:

These elevated flatlands are formed when large landmasses are uplifted, or when volcanic activity occurs within mountainous regions. The surrounding mountain ranges essentially create a basin, within which the plateau lies. Due to their high elevation and often arid to semi-arid climates, intermontane plateaus can exhibit unique geographical features and sometimes support distinct ecosystems. Examples include the Tibetan Plateau, which is famously bordered by the Himalayas and other ranges.

Question 3.

Plateaus formed by lava.

Ans:

Plateaus formed by lava, often called volcanic plateaus or basalt plateaus, are extensive, flat-topped elevated landforms that are created by massive outflows of highly fluid molten rock (lava) from the Earth’s interior.

Here’s how they are typically formed:

  1. Fissure Eruptions: Unlike typical cone-shaped volcanoes, these plateaus usually form from fissure eruptions. 
  2. Highly Fluid Lava: The lava involved is typically basaltic, which is very low in viscosity (runny). This allows it to flow great distances across the landscape before solidifying.
  3. Repeated Flows: Over long geological periods, these fissure eruptions occur repeatedly. Each flow covers the previous one, building up layer upon layer of solidified lava.
  4. Extensive Spreading: Because the lava is so fluid, it spreads out over vast areas, effectively “flooding” the existing topography and leveling it out.
  5. Accumulation and Elevation: The continuous accumulation of these horizontal lava layers leads to the gradual uplift and formation of a broad, elevated, and relatively flat or gently undulating surface – the plateau.

Key Characteristics:

  • Flat Topography: Their defining feature is their largely flat or gently sloping summit.
  • Step-like Sides: The edges of these plateaus often have steep, cliff-like escarpments, representing the exposed layers of lava.
  • Fertile Soils: The weathered basaltic rocks often produce very fertile black soils, making these regions agriculturally productive (e.g., cotton cultivation on the Deccan Traps).

Examples:

  • Deccan Plateau (India): A classic and massive example, formed by extensive basaltic lava flows during the Cretaceous period.
  • Columbia Plateau (Northwestern USA): Formed by numerous flood basalt eruptions.
  • Ethiopian Highlands (Ethiopia): Another significant volcanic plateau.

Question 4.

An extensive area of lowland with a level or gently undulating surface.

Ans:

A plain is an expansive region characterized by its relatively flat or gently rolling terrain, typically at a low elevation. These vast stretches of land are often formed through the accumulation of sediments carried by rivers, ice sheets, or wind over extended periods, leading to fertile soils and suitability for agriculture. Their gentle slopes and accessibility have historically made them prime locations for human settlement, the development of transportation networks, and large-scale farming, often supporting dense populations and significant economic activity.

While plains generally lack dramatic topographic features, their subtle variations in elevation and drainage patterns can still influence local ecosystems and land use. They can range from coastal plains bordering oceans to inland plains situated within continents, each with distinct geological histories and environmental characteristics. The uniformity of their surface often allows for efficient land management and a wide range of human endeavors, making them crucial geographical features for civilizations throughout history.

Question 5.

The compressional forces that cause folding of rocks and formation of fold mountains.

Ans:

Powerful compressional forces, stemming from the collision of tectonic plates at convergent boundaries, are the primary architects of Earth’s magnificent fold mountains. As these massive landmasses slowly converge, the immense pressure deforms intervening rock layers, causing them to buckle and crumple into characteristic wave-like folds. Over vast geological periods, this relentless compression elevates the folded strata into soaring mountain ranges, exemplified by the young and actively forming Himalayas, Alps, and Andes.

The intricate nature of folding is influenced by factors such as rock composition and the rate of compression, with more pliable rocks exhibiting complex fold patterns. This sustained application of immense stress over millions of years creates a rich geological history within these mountain belts, characterized by repeating patterns of upward-arching anticlines and downward-dipping synclines. These structures collectively sculpt the rugged, awe-inspiring topography that defines many of the world’s most prominent mountain ranges.

Question 6.

The vertical movements which are the result of faults and cracks in the surface of the earth.

Ans:

Vertical movements within the Earth’s crust are primarily a consequence of geological faults and cracks. These subterranean fractures represent zones where the colossal forces acting upon the Earth’s lithosphere, whether tensional or compressional, have overcome the rock’s strength, leading to a rupture. Along these lines of weakness, blocks of the Earth’s crust can be displaced significantly in an up-and-down direction. This vertical displacement, known as faulting, is responsible for creating prominent landforms such as horsts (uplifted blocks) and grabens (down-dropped blocks), which are often seen as block mountains and rift valleys, respectively.

These movements are not always sudden; while earthquakes are dramatic manifestations of rapid fault slippage, much vertical displacement occurs gradually over geological timescales. The cumulative effect of these slow, incremental adjustments along fault lines can result in substantial changes in elevation, shaping the regional topography.

Question 7.

The forces operating on the surface of the earth.

Ans:

The Earth’s surface is constantly being reshaped by a dynamic interplay of forces originating both from within and outside the planet. While internal forces, like those responsible for earthquakes and volcanic activity, create major topographical features such as mountains and plateaus, it is the external forces that continuously modify and sculpt these formations. These powerful agents, primarily driven by solar energy and gravity, include flowing water, wind, moving ice (glaciers), and even biological activity.

Weathering involves the disintegration and decomposition of rocks on the Earth’s surface, while erosion is the subsequent transportation of this weathered material by agents like rivers, wind, and glaciers. Over vast stretches of time, this relentless work of erosion and deposition carves out valleys, shapes coastlines, builds up plains, and creates the intricate and diverse landscapes we observe across the globe.

Question 8.

Plateaus surrounded by mountains on one side and plains on the other.

Ans:

Piedmont plateaus represent a distinctive geographical formation, characterized by their position at the base of mountain ranges, extending outwards to meet expansive plains. These elevated, relatively flat landforms are essentially transitional zones, serving as a gradual slope or step between the rugged, high elevations of mountains and the lower, flatter stretches of plains. Their unique location means they are cradled by mountainous terrain on one flank, while gently descending towards or abruptly terminating at a broad, level plain on the opposite side.

The formation of such plateaus is often linked to the erosional processes acting upon the adjacent mountains, where material is carried down and deposited at their foot, gradually building up a relatively flat, elevated surface. Alternatively, they can be residual landforms that have resisted erosion while the surrounding lower plains were carved out. This dual adjacency to both towering peaks and vast plains makes piedmont plateaus geologically intriguing and often influences their climate, drainage patterns, and human habitation, as they benefit from proximity to mountain resources while also offering more accessible terrain than the higher elevations.

P Q. Fill in the blanks with suitable words.

1. Volcanic activity is a _______ movement.

Ans: sudden

2. The upfolds of the rock strata are called___________ .

Ans: anticlines

3. The Mid-Atlantic Ridge rises ____ km above the floor of the Atlantic.

Ans: 3

4. The Great Plain of the USA was formed by __________________.

Ans: Diastrophic forces

5. The Great Northern plains of India were formed by _______________ .

Ans: River Deposition

IV. Long Answer Questions.

Question 1.
Describe the formation of mountains and their types.
Ans:

Mountains are imposing natural elevated landforms characterized by their steep slopes and prominent peaks. Their genesis is primarily attributed to powerful internal forces originating within the Earth’s crust, although external forces also significantly contribute to their ultimate shape and appearance.

How Mountains Form

The predominant mechanism driving mountain formation is plate tectonics, a process involving the continuous movement and interaction of Earth’s colossal plates.

  • Compression and Folding: When tectonic plates, particularly continental ones, collide, the immense pressure causes the crustal rocks to contort and fold upwards. This phenomenon, known as orogeny, gives rise to Fold Mountains, such as the Himalayas.
  • Faulting and Block Movement: Stress within the Earth’s crust can lead to fracturing along faults. Consequently, sections of land can be uplifted, forming hoards (elevated blocks), or down-dropped, creating grabens (depressed blocks). This process results in the formation of Block Mountains, an example being the Vosges.
  • Volcanic Activity: The eruption of magma onto the Earth’s surface, accumulating layers of lava and ash, constructs cone-shaped Volcanic Mountains, like Mount Fuji. This type of formation frequently occurs in subduction zones, where one tectonic plate slides beneath another.
  • Uplift and Erosion: In some instances, extensive areas of the Earth’s crust undergo broad uplift. Subsequently, agents of erosion such as wind, water, and glaciers wear away softer materials, leaving behind the more resistant rock formations that constitute rugged Residual Mountains.

Types of Mountains

Mountains are categorized into several types based on their specific formation processes:

  • Fold Mountains: These are the most prevalent type, resulting from the compression and folding of rock layers during plate collisions. They typically appear as elongated, linear ranges characterized by parallel folds.
    • Young Fold Mountains, like the Himalayas, are notably high, rugged, and are still actively undergoing uplift.
    • Old Fold Mountains, such as the Aravallis, are lower in elevation and possess more rounded peaks due to extensive erosion over long periods.
  • Block Mountains: These mountains arise when large segments of the Earth’s crust are uplifted or down-dropped along fault lines. They commonly feature steep, straight sides and relatively flat summits.
  • Residual Mountains (also known as Relict or Denudational Mountains): These are the remains of older, more extensive mountain ranges or plateaus that have been significantly altered and reduced by prolonged weathering and erosion, leaving behind only the more resilient rock formations.
  • Dome Mountains: These develop when a substantial mass of magma pushes the overlying rock layers upwards into a dome-like shape, but without erupting to the surface. Subsequent erosion then exposes the harder, central core of the dome.

Question 2.

Describe the characteristics of four different types of plateaus.

Ans:

Types of Plateaus: A Concise Overview

Plateaus are elevated landforms distinguished by their flat tops, typically ascending abruptly from the surrounding landscape. Their distinct classifications arise from their formation processes and geographical positions. Here are four main types:

Intermontane Plateaus

These elevated flatlands are found nestled between mountain ranges. They often owe their existence to the immense compressive forces that simultaneously create the adjacent fold mountains. The intense pressure from colliding tectonic plates lifts vast blocks of land, which remain relatively level while peaks rise around them. Globally, intermontane plateaus are generally among the highest and most extensive. 

Volcanic Plateaus

Originating from the widespread flow of fluid basaltic lava erupting from the Earth’s fissures, these plateaus are formed as layers of solidified lava spread over expansive areas, resulting in a flat or gently rolling surface. Their primary composition is igneous rock, frequently rich in minerals. The weathered soils of volcanic plateaus are typically fertile, making them well-suited for agriculture. India’s Deccan Plateau, shaped by ancient volcanic activity, serves as a classic example.

Piedmont Plateaus

Literally meaning “at the foot of a mountain,” these plateaus are located at the base of mountain ranges, extending outwards towards a plain or an ocean. They can develop from the erosion of neighboring mountain systems, with rivers depositing sediments, or as residual landforms after less resistant surrounding rocks have eroded away. They typically display a sloping surface, gradually descending from the mountains to lower plains. India’s Malwa Plateau, found at the base of the Vindhya Range, is a good example of a piedmont plateau.

Continental Plateaus

Their formation can be attributed to the broad uplift of a large continental area due to internal geological forces, or the erosion of softer adjacent rocks, leaving behind a durable, resistant core. These plateaus are typically ancient, composed of crystalline rocks, and have undergone prolonged weathering, resulting in flat or gently undulating surfaces. They are frequently rich in mineral resources. A notable example is the Western Australian Plateau.

Question 3.

Describe the characteristics of structural plains.

Ans:

Structural plains are extensive, flat, or gently undulating landforms that are formed due to the uplift or subsidence of large areas of the Earth’s crust, often in combination with minimal erosion and deposition. Their characteristics are primarily defined by the underlying geological structure.

Here are the key characteristics of structural plains:

  • Formation by Crustal Movement: Unlike other plains formed predominantly by erosion or deposition, structural plains are primarily a result of tectonic forces. These forces lead to the uplift of continental shelves or ocean beds, or the subsidence of existing landmasses, creating a vast, relatively flat surface.
  • Horizontal or Gently Inclined Strata: A hallmark of structural plains is the presence of horizontal or very gently dipping sedimentary rock layers beneath the surface. These layers were typically deposited in ancient seas or large basins and then subsequently uplifted with little deformation.
  • Low Relief and Undulating Topography: While generally flat, structural plains can have slight undulations rather than being perfectly level. The relief is typically low, with variations in elevation rarely exceeding a few hundred meters.
  • Extensive Area: Structural plains often cover vast geographical areas, extending for hundreds or even thousands of kilometers. Their formation involves large-scale movements of the Earth’s crust.
  • Coastal or Continental Shelf Association: Many structural plains are found along coastlines, representing uplifted parts of continental shelves, or they may be interior plains that were once submerged under shallow seas.
  • Variable Drainage Patterns: The drainage patterns on structural plains can vary. Rivers tend to flow slowly due to the gentle gradient and may develop meandering courses. Drainage can be well-developed or, in some cases, poorly organized if there are slight depressions leading to marshy conditions.
  • Presence of Old Sedimentary Rocks: The underlying geology frequently consists of old sedimentary rocks that have been subjected to minimal folding or faulting. These rocks might include sandstones, limestones, and shales.
  • Economic Significance: Due to their flat topography and often fertile soils (especially if covered by later alluvial deposits), structural plains are typically well-suited for agriculture. They are also often rich in mineral resources such as coal, oil, and natural gas, which are formed in sedimentary basins.

Question 4.

Explain the chief characteristics of depositional plains and their types.

Ans:

These sediments are transported and deposited by a range of natural agents, including rivers, glaciers, wind, and ocean currents.

Defining Features of Depositional Plains 

  • Sediment-Based Origin: The core characteristic of these plains is their formation from the buildup of material carried from other locations.
  • Minimal Relief: They typically feature very gentle slopes or are entirely flat, which is highly advantageous for constructing infrastructure and facilitating transport networks.
  • Rich Fertility: Many depositional plains, especially those shaped by rivers, are known for their exceptionally fertile soils. This fertility comes from nutrient-rich sediments, making them extremely productive for agriculture.
  • Layered Composition: These landforms are made up of various loose materials like silt, clay, and sand, often arranged in distinct strata.
  • High Population Density: Given their fertile land, accessible water sources, and ease of development, depositional plains frequently support large populations.
  • Extensive Coverage: Many of these plains span considerable geographical areas, covering vast regions.

Types of Depositional Plains

  • Alluvial Plains: These are the most common type, formed when rivers deposit alluvium (river-borne sediments) along their courses. A specific variation, delta plains, forms at river mouths where sediment builds up as the river enters a larger body of water (e.g., the extensive Indo-Gangetic Plain).
  • Glacial Plains: Created by the action of glaciers or their meltwater, these plains consist of deposited till (unsorted glacial debris) or outwash (sorted sediments carried by meltwater) (e.g., parts of the Great Plains in North America).
  • Lacustrine Plains: Formed on the beds of former lakes that have either dried up or been drained. Sediments that accumulated at the bottom of these lakes now form flat plains (e.g., the Red River Valley in North America).
  • Coastal Plains: These plains emerge along coastlines as ocean waves and currents deposit sediments. They are typically low-lying and extend inland from the shore (e.g., the Eastern Coastal Plains of India).

Question 5.

Give a brief account of the importance of landforms on the surface of the earth.

Ans:

The Indispensable Role of Landforms

Landforms, Earth’s varied surface features, are crucial in shaping our planet’s systems and human life. Their importance spans ecological, climatic, economic, and social aspects.

From an ecological standpoint, landforms are vital for biodiversity. Mountains serve as “water towers,” feeding rivers that sustain life in plains and supporting diverse ecosystems across different altitudes. Plains, especially river valleys, offer fertile land for agriculture and host dense populations and varied ecosystems. Even seemingly barren deserts and plateaus are home to unique, adapted species.

In terms of climate, landforms exert significant influence. Mountain ranges can block air masses, creating rain shadows and dictating regional rainfall and temperature. Coastal features also impact local weather patterns, including sea breezes and storms.

Economically, landforms are invaluable. Mountains provide minerals, timber, and hydroelectric power, while their scenic beauty boosts tourism. Plains are global agricultural hubs, ensuring food security and facilitating infrastructure development. Plateaus often contain rich mineral deposits and offer strategic advantages.

Practice Questions (Solved)

Question 1.
Describe the direction in which the following mountain systems lie and also point out the continents where they are found.

(a) Alpine Himalayan System
(b) Rocky-Andean System

Ans:

Here’s a rephrased and unique description of the mountain systems, focusing on their orientation and continental locations:

(a) Alpine-Himalayan System

This vast mountain range trends predominantly west to east, forming a colossal arc across the Eurasian continent. Its extensive reach spans both Europe and Asia. Starting near North Africa’s Atlas Mountains, it sweeps through Europe’s famous Alps, then continues across Turkey and Iran, culminating in the towering Himalayas and extending into parts of Southeast Asia.

(b) Rocky-Andean System

This impressive mountain chain stretches distinctly from north to south, forming the prominent western backbone of the Americas. Geographically, it extends along the western flanks of North America, where it’s known as the formidable Rocky Mountains, and continues seamlessly into South America as the spectacular Andes Mountains.

Question 2.

Describe the different stages in the growth of mountains.

Ans:

Mountain building, or orogenesis, is a prolonged process of crustal deformation and uplift driven by tectonic plate movement.

It begins with the accumulation of vast sediments in basins, which subside under the increasing weight. The active phase, the orogenic period, is marked by intense compression at convergent plate boundaries.

In continental-continental collisions, buoyant continental crust buckles and folds, leading to massive crustal thickening and uplift (e.g., Himalayas). During oceanic-continental convergence, the denser oceanic plate subducts, causing folding, faulting, volcanism, and metamorphism in the overriding continental plate. This initiates the emergence of mountain ranges.

Throughout all stages, erosion and denudation (weathering and transport by agents like rivers and glaciers) actively sculpt the mountain’s form, creating valleys and distinct landforms. The interplay between constructive tectonic forces and destructive erosional processes ultimately determines the height and ruggedness of a mountain range.

Question 3.

What are the different types of Geosynclines ?

Ans:

Geosynclines were historical geological concepts explaining mountain formation. They were large, elongated depressions where vast sediments accumulated, causing subsidence, followed by compression and uplift into mountain ranges.

Key types included:

  • Orthogeosynclines: Linear, mobile belts at continental margins, intensely deformed into fold mountains.
    • Eugeosynclines: Deeper, outer parts with volcanic activity and deep-water sediments.
    • Miogeosynclines: Shallower, inner parts near stable continents, with shallow-water sediments and no significant volcanism.
  • Parageosynclines (Intracratonic Geosynclines): Formed within stable continental platforms, generally broader and less deformed.
    • Taphrogeosynclines: Fault-formed depressions (rift valleys).
    • Zeugogeosynclines: Parageosynclines with marginal uplifts within the craton.
    • Autogeosynclines: Parageosynclines without significant marginal uplifts.
  • Monogeosynclines/Polygeosynclines: Based on the number of mountain-building phases (single or multiple).

Question 4.

Write a note on the characteristics of folded mountains.

Ans:

Fold mountains represent Earth’s most prevalent and typically highest mountain ranges.

Genesis via Compression: These mountains arise from the collision of two tectonic plates, generating immense compressional forces. This pressure causes the Earth’s crust to crumple, buckle, and fold, similar to how a carpet wrinkles when pushed against a wall. This geodynamic process is termed orogenesis.

Undulating Topography (Anticlines and Synclines): A hallmark characteristic is the presence of folds. Upward arching folds are known as anticlines, forming the mountain crests or ridges, while downward curving folds are called synclines, creating valleys or troughs. These folds can vary from simple, open structures to intricate, overturned, or even recumbent folds (where the fold axes lie horizontally).

Sedimentary Rock Dominance: The primary rock type found in fold mountains is sedimentary, originally laid down in extensive basins, frequently at the edges of continents, before being uplifted and folded. The existence of marine fossils within these rocks corroborates their oceanic origins.

Elongated and Curvilinear Forms: Typically, these ranges extend over vast distances but maintain a relatively narrow width, often adopting an arc-like configuration. This elongated shape mirrors the linear nature of the convergent plate boundaries.

Jagged Terrain and Pointed Summits: Young fold mountains, such as the Himalayas or the Alps, exhibit rugged, imposing elevations and sharp, conical peaks, a result of ongoing uplift and limited erosion. 

Seismically Active Zones: Given their formation at active plate boundaries, fold mountain belts are frequently susceptible to earthquakes and, in some instances, volcanic activity (though the Himalayas are an anomaly due to their continent-continent collision).

Mineral-Rich Landscapes: These regions often possess significant mineral resources, including tin, copper, and gold, which are frequently concentrated by the geological processes involved in their genesis.

Question 5.

What are Block mountains ? How are they formed ?

Ans:

Their formation unfolds as follows:

The fundamental trigger is the stretching and separation of the Earth’s crust. This tension frequently arises in zones where tectonic plates are diverging or within continental interiors experiencing considerable stress. As the crust stretches to its breaking point, it fractures, forming faults—planes where substantial displacement of rock masses can occur. Along these newly formed faults, immense sections of the Earth’s crust undergo vertical movement relative to one another.

Elevated blocks, known as horsts, are uplifted higher than the surrounding terrain, forming the actual block mountains. These often feature relatively flat summits and exceptionally steep flanks, which are the visible fault scarps. Conversely, depressed blocks, termed grabens, subside between the uplifted horsts, frequently giving rise to valleys or rift valleys.

The fault lines themselves frequently manifest as precipitous, linear cliffs. Over geological timescales, erosion by elements like wind, water, and ice further sculpts these block mountains. Softer rock types may erode more rapidly, emphasizing the rugged characteristics and steep inclines.

Essentially, block mountains emerge when sections of the Earth’s crust are either elevated or tilted along fault lines, distinct from being folded by compressional forces.

Notable examples of block mountains include the Sierra Nevada Mountains in the United States, the Vosges Mountains in France, the Black Forest Mountains in Germany, and in India, the Satpura Range and Vindhya Range (though their classification as purely block mountains is sometimes debated, they largely exhibit these characteristics).

Question 6.

How can mountains be classified according to their different size and arrangement ? Describe in detail two of the classes of such mountains.

Ans:

Let’s delve into two primary classifications of mountains based on their scale and configuration: Mountain Ranges and Cordilleras.

Mountain Ranges

A mountain range constitutes a linear series of interconnected mountains or hills, generally sharing a common geological genesis. Picture them as an elongated chain of summits and crests. Their defining characteristics include a linear layout, frequently punctuated by passes and valleys. These ranges can vary significantly in length, from short segments to immense stretches. Their formation commonly stems from the collision of tectonic plates, although the erosion of elevated plateaus or volcanic activity can also contribute to their creation.

Cordilleras

In contrast, a cordillera represents the most extensive and intricate form of mountain system. It comprises a vast, complex network of numerous parallel or diverging mountain ranges, frequently encompassing elevated plateaus and valleys within its expansive domain. Cordilleras occupy enormous geographical areas and are the product of multiple, protracted geological events. They are distinguished by their elaborate geological structures and often serve as the continental “backbone,” profoundly influencing regional climates and providing substantial resources. The North American Cordillera (which incorporates the Rockies and Sierra Nevada) and the Andean Cordillera in South America serve as quintessential illustrations.

Question 7.

What are Block mountains ? How are they formed ?

Ans:

Block mountains are distinct mountain ranges characterized by steep slopes and a relatively flat top. They are also known as fault-block mountains because their formation is directly linked to faulting in the Earth’s crust.

How they are formed:

Block mountains form when the Earth’s crust is subjected to tensional forces, meaning it’s being stretched and pulled apart. This stretching causes the crust to fracture, creating large cracks called faults.

Along these faults, large blocks of the Earth’s crust move vertically relative to each other. There are a few ways this can lead to block mountains:

  1. Uplifted Middle Block (Horst): The most common way is when the land between two parallel faults is pushed upwards, while the land on either side sinks down. The elevated block is called a horst, which forms the block mountain.
  2. Sinking Side Blocks (Graben): Alternatively, the middle block can remain stable while the land on both sides of it sinks downward along faults. This leaves the stable middle block standing relatively higher, forming a block mountain. The sunken blocks are called grabens, which often form valleys (rift valleys) alongside the mountains.

Question 8.

How can mountains be classified according to their different size and arrangement ?

Ans:

Mountains, Earth’s grand elevations, can be classified by their size (height) and how they’re arranged on the landscape.

Classification by Size (Height/Elevation)

  • Hills: These are the lowest, typically under 600 meters, with gentle, rounded slopes.
  • Medium Mountains: Taller than hills, they have more defined peaks and rugged terrain, falling between hills and high mountains in elevation.
  • High Mountains: These are the tallest, often thousands of meters high, featuring steep slopes, jagged peaks, and sometimes permanent snow and glaciers. Examples include the Himalayas and the Andes.

Classification by Arrangement (Grouping Form)

  • Isolated Peaks: Mountains that stand alone, separate from other ranges, often volcanic in origin.
  • Ridges: Elongated landforms with a crest and often steep sides, representing a basic linear mountain arrangement.
  • Mountain Ranges: A series of mountains or hills connected in a continuous, linear group, like the Aravallis.
  • Mountain Chains: A longer, more complex series of connected mountain ranges that may vary in size and formation period.
  • Mountain Systems: A collection of several linked mountain ranges sharing a similar geological origin and structure, even if separated by valleys (e.g., the Alps are part of the Alpine-Himalayan system).
  • Cordilleras: The largest mountain complexes, comprising vast interconnected chains, ranges, and systems, forming a major “community” of mountains, such as the American Cordillera (Rockies and Andes).
  • Massifs: Compact, often circular or irregular clusters of mountains structurally distinct from the surrounding area, often formed by erosion.

Question 9.

What are plateaus ? How are they different from mountains ? Give suitable examples.

Ans:

Plateaus are expansive, elevated landforms characterized by their relatively flat tops, often described as “tablelands,” and steep slopes, or escarpments, on at least one side. They rise significantly above the surrounding terrain but differ from mountains in their upper relief. They can be formed through various geological processes, including the upward movement of the Earth’s crust due to tectonic plate collisions, extensive lava flows from volcanic eruptions, or the thermal expansion of the underlying lithosphere.

Here’s how plateaus differ from mountains:

Shape and Summit:

  • Plateaus: The most defining characteristic of a plateau is its flat, broad top. While some plateaus might have hills or ridges on their surface, the overall impression is one of a vast, elevated plain.
  • Mountains: Mountains, in contrast, typically have narrow, pointed or rounded summits (peaks). They are characterized by their steeply rising slopes and often form distinct, isolated peaks or are part of elongated ranges.

Elevation and Relief:

  • Plateaus: Plateaus are elevated above their surroundings, but their relief (the difference in height between the highest and lowest points) is generally low across their surface. Their height can range from a few hundred meters to several thousand meters.
  • Mountains: Mountains are characterized by their considerable height and significant local relief. They rise to much higher elevations compared to plateaus, often exceeding several thousand meters, and their slopes are much steeper.

Formation:

  • Plateaus: Plateaus can be formed by uplift of large crustal blocks, volcanic activity leading to accumulation of lava, or erosion of surrounding softer rock leaving a resistant, elevated flat-topped area.
  • Mountains: Mountains are primarily formed by intense tectonic forces. These include the collision of continental plates (leading to fold mountains), fracturing of the Earth’s crust (creating fault-block mountains), or the accumulation of volcanic material (forming volcanic mountains).

Examples:

Plateaus:

  • Tibetan Plateau (Asia): Known as the “Roof of the World,” it is the highest and largest plateau globally, formed by the collision of the Indo-Australian and Eurasian tectonic plates.
  • Deccan Plateau (India): A large volcanic plateau in peninsular India, characterized by its fertile black soils.
  • Colorado Plateau (North America): Famous for its dramatic canyons, including the Grand Canyon, it was formed by the uplift of a large block of the Earth’s crust.
  • East African Plateau (Africa): A vast elevated region that is known for its rift valleys and significant mineral deposits.

Mountains:

  • Himalayas (Asia): The world’s highest mountain range, including Mount Everest, formed by the ongoing collision of the Indian and Eurasian plates.
  • Andes (South America): The longest continental mountain range in the world, stretching along the western coast of South America, also a result of tectonic plate interactions.
  • Alps (Europe): A prominent mountain range known for its jagged peaks and glacial features, formed by the collision of the African and Eurasian plates.
  • Rocky Mountains (North America): A vast mountain system that extends across western North America, known for its rugged peaks and diverse ecosystems.

Question 10.

What is a Piedmont Plateau ? How is it different from a Continental plateau ? Give suitable examples to illustrate.

Ans:

Plateaus, distinctive elevated landforms featuring flat summits and abrupt, rising flanks, provide a compelling subject within geomorphology. While categorized broadly by their environmental context and origin, piedmont and continental plateaus exhibit clear divergences in their positioning, development, and neighboring characteristics.

These transitional formations typically abut a mountainous system on one side, with either a plain or an ocean defining their other boundary. Their genesis is primarily linked to the erosional forces acting upon the adjacent mountains. Over extended periods, sediments transported from the uplands by rivers and other erosion agents accumulate, progressively forming a relatively level, elevated area. The edge of the piedmont plateau facing lower plains or the ocean frequently culminates in a sharp incline, known as an escarpment. Notable instances include the Piedmont Plateau in the Eastern United States, nestled between the Appalachian Mountains and the Atlantic Coastal Plain, and India’s Malwa Plateau, positioned at the base of the Vindhya mountains.

A crucial difference from piedmont plateaus is their lack of direct contiguity with a major mountain range on one side; instead, continental plateaus are generally encompassed by plains or oceans. Their formation stems from large-scale geological processes. They can originate from extensive continental uplift, where vast portions of the Earth’s crust are raised as a cohesive block, or through widespread effusions of basic lava that deeply cover the existing topography. Essentially, continental plateaus are immense, independent landmasses that constitute elevated core regions of continents, often situated far from active mountain-building zones. India’s Deccan Plateau, a result of extensive volcanic lava flows, and the vast, ice-covered Antarctic Plateau, serve as prime examples of this particular landform.

Question 11.
Write short notes on the following :

(a) Coastal plains
(b) Karst plains
(c) Peneplain
(d) Cuestiform plains.

Ans:

(a) Coastal Plains

Coastal plains are expansive, low-lying terrestrial areas found directly adjacent to an ocean or sea. Their formation is primarily driven by the deposition of sediments, such as sand, silt, and clay, which are transported by rivers and subsequently reworked by oceanic forces like waves and currents. Over vast spans of time, these accumulated sediments create a relatively flat to gently sloped landscape. These plains exhibit diverse features, including river deltas, shallow lagoons, marshlands, and protective barrier islands. Their rich, fertile soils, abundant water access, and generally mild climates make them highly attractive for human settlement and agricultural activities, often leading to high population densities.

(b) Karst Plains

Karst plains are distinctive landscapes that develop over soluble bedrock, most commonly limestone, dolomite, or gypsum. Their unique topography is a result of chemical weathering, where slightly acidic rainwater progressively dissolves the underlying rock. This process sculpts characteristic surface features such as sinkholes (depressions formed by collapsed caverns), intricate cave systems, streams that seemingly vanish underground, and elongated solution valleys. Karst plains frequently lack a well-defined surface drainage network, as water rapidly infiltrates the ground through numerous fissures and subterranean conduits. Despite their overall flatness, the terrain can appear quite irregular, punctuated by numerous depressions and occasionally isolated, resistant hills known as mogotes or hums that stand as remnants of the dissolved landscape.

(c) Peneplain

A peneplain (a term derived from Latin, meaning “almost a plain”) represents a theoretical landform that signifies the culmination of an extended cycle of erosion. It describes a region that has been reduced to a nearly flat, gently undulating surface with minimal topographic variation. This extensive leveling is achieved through prolonged subaerial denudation—the combined effects of weathering and erosion by agents like rivers, wind, and ice—which systematically wears down pre-existing elevated terrains such as mountains and plateaus. While a perfectly flat peneplain is largely conceptual (as geological processes like tectonic uplift or changes in base level often interrupt this long erosional process), evidence of vast, ancient erosional surfaces approximating peneplains can be found globally. These surfaces often feature isolated, resistant rock masses known as monadnocks, which rise conspicuously above the otherwise low-relief landscape.

(d) Cuestiform Plains

Cuestiform plains are a type of plain characterized by a recurring pattern of gently inclined ridges known as cuestas. These cuestas are asymmetrical landforms shaped by the differential erosion of tilted sedimentary rock layers. Within a cuestiform plain, less resistant rock strata erode more rapidly, forming low-lying valleys, while more durable layers stand out as the cuestas themselves. Each cuesta exhibits a steep escarpment or “scarp slope” on one side and a much gentler dip slope on the other, reflecting the angle of the underlying rock layers. The overall visual effect of a cuestiform plain is reminiscent of a staircase or a corrugated sheet, with alternating ridges and valleys aligned parallel to the strike (orientation) of the tilted rock formations. This distinct topographic pattern is a direct expression of the underlying geological structure in regions with gently folded or tilted sedimentary rocks.

Question 12.

Why and how are the plains the centres of all human activity ?

Ans:

Plains have historically served as the primary centers of human activity due to a combination of favorable geographical characteristics that facilitate sustenance, growth, and interaction.

Why Plains are Centers of Human Activity:

  1. Agricultural Productivity: Many plains, especially alluvial plains formed by rivers, possess highly fertile soil. This, coupled with generally moderate climates and easier access to water (from rivers or groundwater), makes them ideal for agriculture. The ability to grow abundant food crops (like grains) supports larger populations than other landforms.
  2. Ease of Movement and Transportation: The flat or gently undulating terrain of plains makes construction of infrastructure like roads, railways, and canals much simpler and less costly. This ease of movement facilitates trade, communication, and the efficient distribution of goods and people, fostering economic development and cultural exchange.
  3. Feasible for Settlement and Construction: Building homes, villages, and ultimately large cities is significantly easier on flat land. The stable ground and lack of steep slopes reduce construction challenges, allowing for extensive urban planning and expansion.
  4. Resource Availability: Beyond fertile soil, plains often have accessible groundwater, and river systems provide a consistent water supply for drinking, irrigation, and industrial use. Some plains also have valuable mineral resources beneath their surface.
  5. Less Challenging Climate (Generally): While variations exist, many plains experience climates that are more conducive to human habitation and year-round activity compared to extreme mountainous or desert environments.

How Plains Facilitate Human Activity:

  • Food Security: The fertile soils and availability of water enable large-scale, mechanized farming, producing a surplus of food that can feed dense populations and support specialized labor beyond agriculture.
  • Connectivity and Trade: The smooth terrain allows for the development of extensive transportation networks, connecting communities, facilitating trade of goods and ideas, and enabling the growth of markets and industries.
  • Urbanization: The ease of construction and expansion on flat land has led to the development of major urban centers, which become hubs for commerce, governance, education, and culture, attracting more people.
  • Economic Development: The combination of productive agriculture, efficient transportation, and a concentrated population creates a strong foundation for various economic activities, from manufacturing to services.
  • Social Cohesion: The relatively unchallenging environment allows for easier social interaction, larger community formation, and the development of complex societal structures and institutions.

Question 13.

Differentiate between Young fold mountains and Old fold mountains.

Ans:

Fold mountains are formed when two tectonic plates collide, causing the Earth’s crust to buckle and fold. The key difference between “young” and “old” fold mountains lies primarily in their age, which influences their physical characteristics and the extent of erosion they’ve experienced.

Here’s a breakdown:

Young Fold Mountains:

  • Age: Geologically much younger, typically formed in the last 10 to 65 million years (during the Cenozoic Era, often referred to as the Tertiary period). They are still actively rising in some areas due to ongoing tectonic activity.
  • Appearance: Characterized by rugged, sharp, and high peaks with steep slopes. They haven’t had enough time to be significantly worn down by erosion.
  • Geological Activity: Often associated with significant seismic (earthquake) and sometimes volcanic activity due to the ongoing immense compressional forces at play.
  • Examples: The Himalayas (Asia), Alps (Europe), Rockies (North America), Andes (South America).

Old Fold Mountains:

  • Age: Geologically much older, generally formed hundreds of millions of years ago (e.g., during the Paleozoic or Mesozoic Eras). The tectonic forces that formed them have largely ceased or significantly diminished.
  • Appearance: Have been subjected to prolonged periods of erosion by wind, water, and ice. As a result, they typically have rounded peaks, gentle slopes, and lower elevations compared to young fold mountains.
  • Geological Activity: Exhibit very little to no current seismic or volcanic activity, as the mountain-building processes are largely dormant.

Question 14.
Give reasons for the following :

  1. Old fold mountains have low altitude and gentle slopes.
  2. Young fold mountains have rugged relief features.
  3. Young fold mountains are liable to Earthquakes and Volcanic action.

Ans:

Old Fold Mountains: Low Altitude and Gentle Slopes

The subdued appearance of old fold mountains stems from eons of relentless erosion. After their initial formation, these ranges have been continuously sculpted by natural forces like rain, rivers, wind, and ice. This prolonged wear and tear grinds down the once-towering peaks, fills in valleys, and softens steep gradients, resulting in a more rounded, lower-relief topography. Examples like the Appalachians or the Urals demonstrate how vast stretches of geological time and persistent erosion can significantly diminish a mountain range’s grandeur.

Young Fold Mountains: Rugged Relief and Tectonic Activity

In contrast, young fold mountains exhibit rugged, dramatic features due to their recent and ongoing formation. These ranges are actively rising as a result of powerful tectonic plate collisions, which hasn’t allowed sufficient time for erosion to significantly smooth their contours. This continuous uplift creates sharp, jagged peaks, deep, incised valleys, and pronounced ridges. The Himalayas, Andes, and Alps are quintessential examples of these geologically vibrant, rugged landscapes.

Furthermore, young fold mountains are inherently prone to earthquakes and volcanic activity because they are situated at active convergent plate boundaries. The immense pressures and friction from colliding plates lead to frequent seismic events as rocks fracture along faults. Even without direct subduction, deep crustal fracturing can create pathways for magma.

Question 15.

State two evidence that the Earth movements have taken place in the past.

Ans:

Here are two pieces of evidence for past Earth movements, presented in a unique way:

Ancient Life’s Global Footprint: Imagine finding the same unique type of ancient fern or a distinctive freshwater reptile’s remains scattered across continents now separated by vast oceans, like Africa, South America, and even Antarctica. This isn’t a mere coincidence. The widespread discovery of identical fossil species, such as the fern Glossopteris or the reptile Mesosaurus, on landmasses currently thousands of kilometers apart, strongly suggests that these continents were once physically connected. The only plausible explanation for such a distribution is that these organisms lived in a continuous habitat that subsequently fragmented, with the landmasses carrying their fossilized remains drifting apart over geological time. This remarkable global fingerprint of ancient life serves as compelling biological evidence of profound Earth movements.

Stitched-Together Continents: A Geological Seam: Picture fitting together puzzle pieces, not based on shape, but on the patterns etched into their surfaces. On a grand scale, the Earth’s continents reveal such a geological puzzle. Distant landmasses exhibit striking continuities in their geological fabric: ancient mountain belts that perfectly align across oceans (like the Appalachians with ranges in Europe), and identical sequences of rock layers, including evidence of past glaciation, found on continents now thousands of miles apart. For instance, the characteristic scour marks and rock deposits left by massive ice sheets are found in present-day India, Africa, and Australia, pointing to a shared glacial past on a supercontinent. These “matching seams” in the Earth’s crust across vast distances are not random; they are direct physical evidence of continents having once been conjoined, subsequently undergoing immense, large-scale movements to their present positions.

Question 16.

What causes Orogenic movements ?

Ans:

Orogenic Movements: Earth’s Mountain Builders

Orogenic movements, or orogenesis, are the powerful geological processes responsible for creating mountains and significantly deforming the Earth’s rigid outer layer, the lithosphere. These movements are intrinsically linked to plate tectonics, specifically the interactions occurring at convergent plate boundaries.

What Causes Orogenesis?

The primary driver behind orogenic movements is the slow but immense force generated by the shifting of Earth’s tectonic plates. Mountain building predominantly takes place where these plates either collide directly or where one plate subducts (slides) beneath another.

  1. Oceanic-Continental Collisions: When a denser oceanic plate encounters and slides beneath a lighter continental plate, a process called subduction occurs. This leads to the formation of volcanic mountain ranges and arcs on the continental landmass, such as the Andes. The immense pressure also causes the continental crust to fold, fault, and thicken considerably.
  2. Continental-Continental Collisions: If two continental plates collide, neither plate readily subducts due to their similar densities. Instead, the colossal forces cause the crust to crumple, fold, and fault extensively, resulting in the uplift of vast, high mountain ranges like the Himalayas.
  3. Oceanic-Oceanic Collisions: In this scenario, one oceanic plate subducts under another, forming chains of volcanic islands known as island arcs. Over geological time, these arcs can accrete to continental margins, contributing to larger mountain systems.
  4. Deformational Processes

The dominant force at play in all convergent boundary settings is compression, as plates are relentlessly pushed against each other. This compression drives several key deformational processes:

  • Folding: Rock layers bend and buckle under pressure, creating upward arches called anticlines and downward troughs known as synclines.
  • Faulting: Rocks fracture and slide past one another. Thrust faults, where older rock layers are pushed over younger ones, are particularly common, contributing significantly to uplift and displacement.
  • Crustal Thickening: Horizontal shortening of the crust due to compression is accompanied by its vertical thickening, leading to the elevated topography characteristic of mountains.
  • Magmatism and Metamorphism: The intense heat and pressure associated with subduction and collision can melt rocks, producing magma that either erupts as volcanoes or solidifies underground as intrusive igneous bodies. This same heat and pressure can also trigger metamorphism, transforming existing rocks by altering their mineral composition and texture.

Question 17.

What are the effects of Epeirogenic movements ?

Ans:

Epeirogenic movements are broad, gradual vertical shifts of the Earth’s crust affecting large continental expanses. Distinct from mountain-building, they cause negligible folding or faulting. These “continent-building” processes lead to either widespread uplift or subsidence.

Their key effects include:

  • Continental Uplift and Plateaus: Gradual elevation of vast land areas, forming expansive plateaus or continental uplift.
  • Landmass Subsidence: Slow sinking of large land areas, creating broad basins or submerging coastal zones.
  • Relative Sea Level Changes: Land movement causes apparent sea level shifts; uplift exposes former seabed, while subsidence submerges coastlines.
  • Drainage Pattern Modification: Uplift can establish new drainage divides, alter river courses, and intensify erosion; subsidence may form new lakes or modify river systems.
  • Sedimentary Basin Formation: Gradually subsiding areas become ideal sites for significant sediment accumulation, crucial for geological records and fossil fuel deposits.
  • Climatic and Ecosystem Influence: Long-term elevation changes impact atmospheric circulation, rainfall, and temperature, thereby influencing regional climates and life distribution.
  • Isostatic Adjustments: These movements are intrinsically linked to isostasy, the buoyant equilibrium of the lithosphere, exemplified by land rebound post-glaciation.