Landforms

Learning Outcomes:

1. Understand the formation and characteristics of various folding structures.
2. Comprehend the processes involved in faulting and its resulting landforms.
3. Identify types of volcanic activities and their impacts on landforms.
4. Recognize the nature and classification of earthquakes and their global distribution.
5. Explore exogenetic forces and their influence on weathering and erosion.

Folding Structures

Folding results from the compression of the Earth’s crust, creating various structural formations:

1. Isoclinal Fold: Arises from continued lateral compression on an overturned fold, resulting in both limbs dipping at equal angles in the same direction.
2. Recumbent Fold: A fold lying horizontally due to continued pressure, where both limbs and the axial plane lay roughly flat.
3. Nappe: Occurs when immense pressure on a recumbent fold causes it to tear from its roots and thrust forward. Notable examples include the Himalayas, Atlas Mountains, Rockies, and Andes.

Important Note: Folding structures are present on every continent, illustrating the pervasive impact of tectonic movements globally.

Faulting

Faults form through compressional and tensional forces affecting the Earth’s crust, leading to various landforms:

1. Horsts and Grabens: Result from crustal block movements, forming features like the Great Rift Valley in Africa. Horsts are raised blocks, while grabens are depressions.
2. Normal Faults: Caused by stress; rock blocks displace in opposite directions, with one moving downward and the surface stretching.
3. Reverse (Thrust) Faults: Created by compressional forces, where rock blocks move towards each other, leading to one block overriding another and compressing the faulted area.
4. Tear (Strike-Slip) Faults: Occur due to lateral movement of crust, where blocks move horizontally rather than vertically. Example: San Andreas Fault in California.

Volcanism

Volcanism involves the movement of molten material from Earth’s interior to its surface, resulting in volcanic landforms:

1. Magma Composition: A molten mix of silica, water, gases, and minerals. Silica content and gases like CO₂ determine magma’s explosiveness and mobility.
2. Lava Types: Basic lava is hot, fluid, and flows quietly, forming shield volcanoes. Acidic lava is viscous, explosive, and forms composite or volcanic mountains.
3. Hot Springs and Geysers: Heated groundwater surfaces as hot springs or erupts intermittently as geysers (e.g., Old Faithful Geyser in the USA).
4. Volcano Classification:

• Active Volcanoes: Erupt frequently (e.g., Mount Etna).
• Dormant Volcanoes: Have erupted in the past and may erupt again (e.g., Mount Vesuvius).
• Extinct Volcanoes: Show no signs of future eruptions.

Concept: Dormant volcanoes are unpredictable and often more dangerous due to their latent eruptive potential.

Types of Volcanoes

1. Shield Volcanoes: Formed by fluid basaltic lava flows, these large, gently sloping landforms include examples like Hawaiian shields.
2. Cinder Cone: Special shield volcanoes where lava erupts as fountains, forming a cone around the vent (e.g., Parícutin, Mexico).
3. Composite Volcanoes: Feature explosive eruptions with viscous lava and pyroclastic material, forming layered structures (e.g., Mount Fuji, Japan).
4. Caldera: Highly explosive volcanoes that collapse into their vent post-eruption, creating a large depression.
5. Flood Basalt Provinces: Extensive basaltic lava flows covering large areas, forming distinct layers (e.g., Deccan Traps, India).
6. Mid-Oceanic Volcanoes: Occur along mid-ocean ridges, characterized by frequent eruptions forming peaks taller than Mount Everest.

Earthquakes

Earthquakes are vibrations of the Earth’s surface resulting from the adjustment of rocks beneath:

1. Types:

• Tectonic: Caused by rock sliding along fault planes.
• Volcanic: Confined to volcanic areas.
• Reservoir-Induced: Occur near large water reservoirs.

1. Measurement:

• Richter Scale: Measures magnitude on a logarithmic scale (0 to 10).
• Mercalli Scale: Measures intensity based on visible damage (1 to 12).

1. Seismic Waves:

• P-Waves: Fastest, travel through solids, liquids, and gases.
• S-Waves: Medium velocity, cannot pass through liquids.
• L-Waves: Slowest, travel along the Earth’s surface and cause maximum destruction.

1. Shadow Zones: Areas where seismic waves are not recorded, indicating the Earth’s interior properties.

Important Note: The shadow zone of S-waves covers more than 40% of Earth’s surface, highlighting variations in seismic activity globally.

Earthquake and Volcano Distribution

Exogenetic Forces

External forces that shape the Earth’s surface, continuously altering landforms:

1. Wind Action (Aeolian): Predominant in arid regions; includes deflation, abrasion, and attrition.
2. River Action (Fluvial): Erodes land through processes like corrosion, abrasion, hydraulic action, and attrition.
3. Glacial Action: Erosive action of glaciers, creating features in highlands and lowlands.
4. Weathering: The mechanical disintegration and chemical decomposition of rocks influenced by temperature, water, organisms, and climate.

Concept: Exogenetic forces play a gradual role in leveling the landforms shaped by endogenetic processes.

Weathering

Weathering breaks down rocks through physical, chemical, or biological means:

1. Chemical Weathering: Involves alteration of rock’s mineralogical composition, including:

• Solution: Dissolves minerals in water.
• Hydrolysis: Reacts minerals with water, changing composition.
• Oxidation and Reduction: Interaction with oxygen alters mineral structure.

1. Physical Weathering: Mechanical breakdown by thermal expansion, pressure release, or freezing and thawing.
2. Biological Weathering: Root growth and organism activity lead to rock fragmentation.

Erosion

Erosion transports weathered materials, influenced by agents like water, wind, and glaciers:

1. Abrasion: Friction between rock surfaces due to erosional agents.
2. Attrition: Mutual friction reduces particle size.
3. Corrosion: Chemical solution of minerals in water.
4. Deflation: Wind removes loose material, altering landforms.

Cycle of Erosion: Landforms undergo a sequential transformation from uplift to erosion, leveling into a peneplain over time.

Comparative Overview

Concept: Different landforms result from varying interactions between endogenic (internal) and exogenetic (external) processes.

MCQ: Which seismic wave cannot pass through liquid layers?

1. P-Waves
2. S-Waves
3. L-Waves
4. Surface Waves
   Correct Answer: 2. S-Waves

This comprehensive overview integrates structural formations, volcanic processes, earthquake dynamics, and external forces, highlighting their collective impact on Earth’s landforms.