Chapter 3: Earth Movements and Major Landforms
This chapter explores the internal (endogenic) forces that shape the earth’s surface, focusing on how mountains, plateaus, and plains are created through folding, faulting, and volcanic activity.
1. Earth Movements
The earth’s crust is constantly subjected to forces that cause physical changes to the landscape.
- Tectonic Movements: These are divided into two main types:
- Orogenic (Mountain Building): Horizontal forces that cause the crust to bend (folding) or crack (faulting).
- Epeirogenic (Continental Building): Vertical forces that cause large-scale uplift or subsidence of the crust.
2. Fold Mountains
Formed by the wrinkling of the earth’s crust due to horizontal compressional forces.
- The upfold of a fold mountain is called an Anticline, and the downfold is a Syncline.
- Young Fold Mountains: High, rugged, and pointed peaks (e.g., Himalayas, Alps, Rockies, and Andes).
- Old Fold Mountains: Lower peaks due to millions of years of erosion (e.g., Urals and Appalachians).
3. Block Mountains (Horsts)
Formed when the earth’s crust cracks due to tensional or compressional forces, causing parts of the crust to be raised or sunken.
- Horst: An uplifted block between two faults (e.g., The Vosges in France and the Black Forest in Germany).
- Graben / Rift Valley: A sunken block between two faults (e.g., the East African Rift Valley and the Rhine Rift Valley).
4. Plateaus
Plateaus are elevated uplands with a flat top and steep sides, often called “Tablelands.”
- Intermontane Plateaus: Enclosed by fold mountains (e.g., the Tibetan Plateau, the highest in the world).
- Piedmont Plateaus: Located at the foot of mountains (e.g., the Patagonian Plateau).
- Continental Plateaus: Large, stable blocks often formed by ancient rocks (e.g., the Deccan Plateau in India).
5. Plains
Low-lying, relatively flat areas that are the most populated regions of the world.
- Structural Plains: Formed by the uplift of a part of the sea floor (e.g., Great Plains of USA).
- Depositional Plains: Formed by the deposition of materials by agents like rivers (e.g., Indo-Gangetic Plain), wind (e.g., Loess in China), or ice.
- Erosional Plains: Formed when highlands are worn down over time by erosion (e.g., Canadian Shield).
6. Volcanism
The process where molten rock (magma) from the mantle reaches the surface as lava.
- Intrusive Landforms: Magma that cools inside the crust (e.g., Sills, Dykes, and Laccoliths).
- Extrusive Landforms: Lava that cools on the surface, forming Volcanic Cones or Lava Plateaus.
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Summary Fact: Most of the world’s major relief features are formed by the interaction of folding (compression) and faulting (tension), with water and wind acting later to smooth them out.
