Factors controlling landform development

I. Structure of the Earth

A. ROCKS

FEATURES

• Physical: Rocks are mechanical aggregates of mixtures with no consistent physical or chemical properties.
• Landforms: Landforms are made up of rocks, which are composed of minerals.
• Minerals: Minerals are made up of elements and there are 5-6 types of dominant minerals. Examples include silicates, oxides, sulfates, sulphide, carbonates, and native elements.
• Silicates: Silicates are abundant in the upper layer of the Earth. Examples include non-ferromagnetic silicates (NFMS) like quartz, alkali feldspar, plagioclase, and muscovite (mica), as well as transition metal silicates like biotite, and ferromagnetic silicates (FMS) like amphibole, pyroxene, and olivine.
• Types: There are three types of rocks: igneous, sedimentary, and metamorphic.

IGNEOUS

• Features: Igneous rocks are also called primary rocks or fire rocks. They are formed by the solidification of molten magma or lava. They are unfossiliferous, very hot, and azoic. Igneous rocks are unstratified and do not have layers. Examples include granite and basalt.
• Classification: Igneous rocks can be classified based on the composition of minerals or the size of crystals.
• Based on Silica Content:
  • Acidic Igneous: Also known as felsic rocks, they have silica content greater than 65%. Examples include extrusive rocks like rhyolite and intrusive rocks like granites.
  • Intermediate Igneous: These rocks have silica content ranging from 65% to 55%. Examples include extrusive rocks like andesite and intrusive rocks like diorite.
  • Basic Igneous: Also known as mafic rocks, they have silica content ranging from 55% to 45%. Examples include extrusive rocks like basalt and intrusive rocks like gabbro.
  • Ultra Basic: These rocks have silica content less than 40%. Examples include extrusive rocks like komatite (very rare, found only in mantle) and intrusive rocks like peridotite.
• Based on Size of Crystals:
  • Pegmatite Igneous Rocks: These rocks have very large crystals. An example is granite.
  • Phanerite Igneous Rocks: These rocks have large crystals.
  • Aphanite Igneous Rocks: These rocks have very fine crystals.
  • Glassy Igneous Rocks: These rocks have fine crystals.
  • Porphyritic Igneous Rocks: These rocks have a mix of small and large crystals.
• Based on Location of Solidification:
  • Intrusive Igneous Rocks: Also called Plutonic rocks, they have relatively bigger crystals. Examples include granite.
  • Extrusive Igneous Rocks: These rocks are formed outside and have small crystals. Examples include basalt.

SEDIMENTARY

• Features: Sedimentary rocks are also called secondary rocks. They are formed from sediments derived from the weathering and erosion of rocks. Sedimentary rocks are layered, stratified, and softer compared to igneous rocks. They are more vulnerable to erosion and weathering. They can be fossiliferous. Examples include limestone, shale rocks, and mudstone.
• Classification: Sedimentary rocks can be classified based on the nature of sediments or the transporting agents.
• Based on Nature of Sediments: Mechanically Formed / Clastic Rocks: These rocks are formed from mechanically derived sediments. Examples include sandstones, conglomerates, clay rocks, shale, and loess.
  • Chemically Formed: These rocks are formed through chemical processes. Examples include gypsum and salt rocks.
  • Organically Formed: These rocks are formed through organic processes. Examples include limestone, dolomites, coals, and pearls.
• Based on Transporting Agents:
  • Argillaceous/Aqueous Rocks: These rocks are formed in marine, lacustrine, or riverine environments.
  • Aeolian Rocks: These rocks are formed through wind processes. An example is loess.
  • Glacial Rocks: These rocks are formed by glaciers. Examples include till and moraines.

METAMORPHIC

• Features: Metamorphic rocks are also called tertiary rocks. They are formed through the drastic changes in properties of igneous or sedimentary rocks due to intense heat and pressure. Examples include slate, schist, and marble.
• Metamorphism: Metamorphism occurs due to intense heat or pressure.
• Types of Metamorphism:
  • Thermal Metamorphism: Change in rock forms due to high temperature.
  • Dynamic Metamorphism: Change in rock form due to high pressure.
  • Hydro-Metamorphism: Change in rock form due to hydrological factors, such as chemical weathering.
  • Hydro-Thermal Metamorphism: Minor change in rock composition due to the weight and pressure of water mass, as well as chemically active hot gases and water vapor.
• Based on Place/Area:
  • Contact Metamorphism: Mineral composition changes due to intense heat from intruding magma.
  • Regional Metamorphism: Rocks are altered in their forms over an extensive area.
• Examples: Examples of metamorphic rocks include granite-gneiss, limestone-marble, and shale-schist.
• Himalayas: The Himalayas have an abundance of schist and phyllites, and metamorphic rocks are abundant on the Peninsular plateau.

B. MOUNTAIN

Fold Mountain

• Features:
• True mountains composed of sedimentary rocks of marine origin.
• Unique to Earth and help in understanding the origin and evolution of Earth’s crust.
• Formed at specific locations through specific geological processes.
• Always part of a mountain range system.
• Examples:
• Himalayan ranges, Andes Ranges, Rockies Ranges, Great Dividing Range, Atlas mountain range, South European range, Apennine (Italy), Jura mountain, Pyrenees mountain.

Block Mountain

• Features:
• Also known as Horst mountains.
• Associated with rifting, faulting, and vertical displacement of blocks.
• Formed due to compressive and tensile forces acting along the axial line, as well as shear forces.
• Formation:
• Fault theory: Rise of the middle block, downward movement of side blocks, or downward movement of the middle block.
• Examples:
• Sierra Nevada (USA) in the Rockies fold mountain system, Hartz mountain in North Germany, Vosges mountain range in France (N-E), Satpura, Western Ghats (Sahyadri).

Volcanic Mountain

• Features:
• Accumulation of volcanic matter, including water, gases, molten rocks, burnt rocks, and fragmented material (pyroclasts).
• Classification:
• Based on the mode of eruption:
  • Central/Explosive eruption type: Eruption through a central pipe due to violent explosive gases accumulated deep within the Earth. Rapid and violent eruption. Subtypes include Hawaiian, Strombolian, Vulcanian, Peleean, and Vesuvius types.
  • Fissure/Quiet eruption type: Eruption along a long fracture, fault, or fissure.
• Based on periodicity of eruption:
  • Active volcanoes: Constantly eject volcanic lavas, gases, ashes, and fragmented material. Mostly found along mid-oceanic ridges representing divergent plate margins. Examples include Stromboli volcano.
  • Dormant volcanoes: Became quiet after eruption for some time with no indication of future eruption. Example: Vesuvius volcano.
  • Extinct volcanoes: No indication of future eruption.

Residual Mountain

• Remnants of some mountains associated with mountains of denudation.
• Not a separate category of mountains.
• Most of them are escarpment residuals or fold mountain residuals.
• Examples: Aravallis, Eastern Ghats.

C. PLATEAUX

Plateau

• Definition: A flat-topped table land.
• Features:
  • Covers about one-third of Earth’s land.
  • One of the four major landforms.
  • Can be old or new.
  • Often contains rich mineral deposits.

Tectonic Plateaux

• Formed from processes that create mountain ranges.
• Processes include:
  • Volcanism (e.g., Deccan plateau).
  • Crustal shortening (e.g., Tibet).
  • Thermal expansion (e.g., Ethiopian highlands).
• Examples: Deccan plateau.

Volcanic Plateaux

• Features:
  • Formed due to cracks and volcanic fissures.
  • Composed of mafic lava, such as basaltic lava.
• Examples:
  • Deccan lava plateau.
  • Colombia-Snake River plateau.
  • Kimberley plateau.
  • Parts of Patagonia plateau (Argentina).

Plateau Types

• Dissected Plateau:
  • Formation involves upward movement in the Earth’s crust.
  • Caused by the slow collision of tectonic plates.
  • Examples:
    • Colorado plateau.
    • Tibetan plateau.
• Volcanic Plateau:
  • Formed by numerous small volcanic eruptions over time.
  • Examples:
    • Columbia Plateau.
    • Deccan plateau.
    • (Figure: Volcanic plateau)
• Intermontane Plateau:
  • Highest in the world.
  • Bordered by mountains.
  • Examples:
    • Tibetan plateau.
• Continental Plateau:
  • Bordered on all sides by plains or seas.
  • Formed away from mountains.

D. PLAINS

• Definition:
  • Area of lowland.
  • Often referred to as the best land of a country.
  • Heavily cultivated and populated.
• Examples:
  • Indo-Gangetic plains.
  • Mississippi plains.

Types:

Structural Plains

• Features:
  • Structurally depressed areas of the world.
  • Most extensive natural lowlands on Earth’s surface.
  • Formed by horizontally bedded rocks.
• Examples:
  • Great Plains of USA.
  • Central lowlands of Australia.

Depositional Plains

• Features:
  • Formed by the deposition of materials brought by transportational agents.
  • Depositional work of alluvial rivers, flood plains, and deltaic plains.
• Examples:
  • Gangetic plains (for rice and jute).
  • Nile delta of Egypt (for rice and cotton).
  • Hwang ho plain in China.
• Glacial Depositional Plains:
  • Deposited by glaciers and ice sheets.
  • Deposits include fluvio-glacial sands and gravels in outwash plains, as well as boulder clay that forms till plains and drift plains.
• Aeolian Depositional Plains:
  • Deposited by winds, often consisting of very fine particles known as loess.
  • Loess plains form upon hills, valleys, and plateaus, helping in leveling the undulating plain by filling up grooves and depressions.
• Examples:
  • Pampas in Argentina.

Erosional Plains

• Features:
  • Carved by agents of erosion such as rain, rivers, ice, and wind.
  • Described as peneplains (almost plains) in glaciated regions influenced by glaciers and ice scours.
  • In arid and semiarid regions, they can be found as reg in Africa, pediplane/pediments, and remaining steep hills known as inselbergs.

II. CLIMATE

• Definition:
  • Atmospheric conditions of an area over a long period of time.
• Influences:
  • Rate of weathering in a particular direction.
    • Example: Chemical weathering mostly occurs in warm, moist climates, while frost action is prominent in cold regions with repeated freezing and thawing.
  • Vegetation cover, which influences the effectiveness of the erosion process.

Types:

Direct

• Temperature:
  • Diurnal freeze (during night).
  • Thaw cycle (during the day).
• Precipitation.
• Humidity.

Indirect

• Vegetation.
• Soil cover.

III. STAGES

• Characterized by:
  • Energy:
    • Rate of work done in carving out a characteristic landform and imprinting its type.
    • Landforms are the product of various processes driven by internal and external energy.
  • Depends upon:
    • Intensity.
    • Magnitude.

IV. MINERAL COMPOSITION

• Rock Minerals:
  • Affects the rate of weathering.
  • Examples:
    • Calcite in limestone dissolves in water.
    • Quartz is unaffected by chemical weathering.

V. GEOLOGICAL PROCESSES

Definition:

• Activity of various surface processes.
• Examples: Alluvial fan and delta, involving both erosional and depositional conditions.

Denudation:

• Weathering:
  • Gradual disintegration of rocks in-situ.
  • Chemical weathering:
    • Solution:
      • Dissolution of soluble particles and minerals from rocks with the help of water.
      • Solution of rocks depends on the nature and solubility of rocks, as well as the ratio between volumes of solute and solvent.
    • Oxidation:
      • Reaction of atmospheric oxygen to form oxides.
      • Oxidation of minerals in rocks when oxygen is dissolved in water.
    • Hydration:
      • Absorption of water by minerals in wet areas due to continuous wetting and drying, leading to the breakdown of rocks under stress.
    • Chelation:
      • Release of chelating agents resulting in the breakdown of rocks.
    • Hydrolysis:
      • Chemical reaction between minerals and water.
      • Example: Hydrolysis of potassium feldspar with carbonic acid.
  • Physical or Mechanical weathering:
    • Block disintegration due to repeated temperature changes, wetting and drying, frost action, and biotic factors.
  • Biotic weathering:
    • Weathering caused by plants, animals, biological factors, and anthropogenic activities.
  • Biochemical weathering:
    • Decomposition and disintegration of rocks due to organic materials from fauna and flora.
• Mass Movement:
  • Movement of weathered material due to gravitational forces.
  • Examples:
    • Soil creep: Gradual but continuous movement of soil down the hill.
    • Soil flow (solifluction): Saturated soil acting like a liquid, known as “bog-bursts” in Ireland.
    • Landslides (Slumping or Sliding): Sudden fall of a large mass of soil or rock, often triggered by earthquakes or volcanic disturbances.
• Transportation:
  • Removal of eroded debris to new positions.
• Deposition:
  • Accumulation of dumped debris that forms new rocks.

VI. RELIEF FEATURES

Definition:

• Relief of a place refers to the difference in elevations between the highest and lowest points in an area.
• Examples: Himalayas, characterized by greater height, steeper slopes, high erosion rate, and high deposition.

Influenced by:

• Action of waves, tides, and currents.
• Glaciers.
• Running water.

VII. TIME

• Landscape:
  • Function of time and space.
  • Examples:
    • Volcanic mountain: Rapid formation.
    • Block mountain.
    • Fold mountain: Late formation.
    • Plains.

VIII. SLOPE

Definition:

• Angular inclination of the terrain between hilltops (crests) and valley bottoms.

Types:

• Steep.
  • Example: Himalayas.
• Moderate.
  • Example: Western Aravallis.