Landforms of the Earth

1. Introduction to Landforms

• The Earth consists of concentric rock layers: crust, mantle, and core.
• Intense internal heat melts rocks, keeping the asthenosphere (beneath the crust) in a semi-molten state, which leads to landform development.
• A landform is defined as a natural feature of the earth's surface.

2. Causes of Landform Development

• Plate Tectonics (Orogenic Movements): The lithosphere is broken into plates that float on the semi-molten asthenosphere. Their horizontal movement (colliding, pushing, sliding) compresses sedimentary rocks, causing them to fold. These mountain-building forces act at a tangent to the surface.
• Uplift and Submergence (Epeirogenic Movements): Vertical movements acting along the Earth's radius cause large-scale uplift or subsidence of land (continent-building). This leads to faulting, block mountains, basins, and rift valleys.
• Note: Orogenic and Epeirogenic forces originate deep inside the earth and are together called Diastrophic Forces.
• Exogenic Forces: External forces operating on the surface. They are called "Destructive Forces" because they cause widespread weathering and erosion, creating new landforms through erosion and deposition.

3. Major Landforms: Mountains

A mountain is a steep land or hill rising to great heights above the surrounding land. They are classified into three types based on formation:

A. Fold Mountains

• Formed by lateral compression and stresses in the earth's crust, producing wrinkles or folds along lines of weakness.
• They form irregular wave-like formations: upfolded arch-like shapes are anticlines (crests), and down-folded structures are synclines (troughs).
• Most are constituted of sedimentary rocks formed in shallow oceans (e.g., the Tethys Sea for the Himalayas).
• They are the highest and most extensive ranges, generally found on continental margins, facing oceans, and associated with volcanic activity.
• Old Fold Mountains: Formed long ago, highly eroded, gentle slopes, rounded tops (e.g., Appalachians, Urals, Aravallis).
• Young Fold Mountains: Formed later, much higher with steep slopes, deep valleys, and sharp snow-covered peaks (e.g., Himalayas, Andes, Alps, Rockies).

B. Residual Mountains

• Also known as relict mountains or mountains of denudation.
• Formed when existing mountains or plateaus are subjected to weathering and erosion by winds, water, and snow over a long time, wearing them down.
• Examples: Nilgiri, Parasnath, and Rajmahal Hills (India), Catskill range (USA).

C. Block Mountains

• Formed due to tensional forces causing cracks or faults in the crust.
• When land between parallel faults subsides, it forms a rift valley (e.g., African Rift Valley). When a block rises, it forms a horst or block mountain.
• Often have flattened summits or tilted summits (one side steep, the other gentle). They are separated by intervening basins called graben.
• Examples: Vosges (France), Black Forest (Europe), Salt Range (Pakistan), Sierra Nevada (USA).

4. Major Landforms: Plateaus

A plateau is an area of high ground (500 feet above ground level) with a steep slope on one side and a generally flat upper part called a tableland.

• Intermontane Plateaus: The highest and most extensive types, surrounded by hills and mountains on all sides. Formed along with fold mountains. Examples: Tibetan Plateau (world's highest), Columbian, Bolivian, Peruvian.
• Volcanic Plateaus: Formed by numerous volcanic eruptions that slowly build up over time. Examples: Peninsular India (northwestern Deccan lava plateau), South African, Ethiopian, Columbian plateaus.

5. Major Landforms: Plains

Plains are extensive areas of lowland with a level or gently undulating surface.

• Structural Plains: Formed due to diastrophic forces causing uplift or subsidence of land. Examples: Great Plains of the USA (uplift of submerged land) and Coromandel plains in India (mild subsidence followed by sedimentation).
• Depositional Plains: Formed by the deposition of materials brought by various agents:
  • River Deposition: Alluvial plains (Northern Plains of India), flood plains (Mississippi), deltaic plains (Egypt), and Piedmont plains at mountain foothills.
  • Wind Deposition: Sandy deserts (Sahara, Thar) with undulating sand dunes, and Loess plains (China).
  • Marine Deposition: Coastal regions, estuarine banks, and reclaimed land from the sea called polders (e.g., in the Netherlands and Denmark).

6. Importance of Landforms

• They are beautiful natural sculptures that add to the earth's aesthetic value.
• They impact climate, wind direction, and precipitation (e.g., the Himalayas act as a climatic divide).
• Mountains covered with snow and glaciers are vital sources of perennial rivers.
• Mountain slopes, hills, and plateaus support diverse forests, contributing heavily to Earth's biodiversity.
• Coastal landforms and island groups serve as ideal fishing sites.
• The interior disturbances that create major landforms bring valuable mineral and fossil fuels closer to the earth's surface.