Syllabus: General Studies Paper 1(World Geography)
While the earth’s crust is undergoing constructive changes to create new relief, external forces of nature are working vigorously to level this down”. Explain. (250 words)
The Earth’s crust is subject to change due to a variety of forces. Endogenic (internal) forces which create new relief features. Exogenic (external) forces are working vigorously to wear away the surface. External forces that bring about changes in the Earth’s crust include erosion, weathering, deposition, human activity.
Forces that is responsible for constructive changes to create new relief.
The various internal forces help in formation of various landforms like mountain, plains, plateaus, valleys and hills. Internal forces compress, tear, shatter, tilt, twist, fracture and dislocate the earth crust in many ways. These forces might be horizontal or vertical. Horizontal forces are either tensional forces when they pull apart, or compression forces, when they pull towards each other. The forces disfigure the earth crust in many ways:
- is the process of building new mountain ranges by the convergence of tectonic plates.
- This takes place by ocean-continent collision(e.g., the Andes), continent-continent collision (the Alps and the Himalayas), or island arc-continent collision (e.g., New Guinea).
- All these tectonic processes create sedimentary basins of various types.
- Compression forces: give rise to folding or wrinkling of the rocks
- Folding: A fold can be defined as a bend in rock that is the response to compressional forces.
- Folds are most visible in rocks that contain layering. It causes uplift of particular area. The simplest type of fold is called a monocline.
- This fold involves a slight bend in otherwise parallel layers of rock. An anticlineis a convex up fold in rock that resembles an arch like structure with the rock beds (or limbs) dipping way from the center of the structure.
- Most of the great mountain chains of the world like the Himalayas, the Rockies (N. America), the Andes (S. America), the Alps (Europe) etc are formed in this manner.
- Causes depression of particular areas.
- These faults are named according to the type of stress that acts on the rock and by the nature of the movement of the rock blocks either side of the fault plane.
- Normal faults occur when tensional forces act in opposite directions and cause one slab of the rock to be displaced up and the other slab down.
- Reverse faults develop when compression forces exist. Compression causes one block to be pushed up and over the other block.
- A graben faultis produced when tensional stresses result in the subsidence of a block of rock.
- On a large scale these features are known as Rift Valleys. A horst faultis the development of two reverse faults causing a block of rock to be pushed up.
- Faulting results in the formation of well-known relief features such as RiftValleys and Block Mountains. (E.g. Vindhya and Satpura Mountains)
- A rift valley is formed by sinking of rock strata lying between two almost parallel faults. (E.g. Valley of Nile, Rift valley of Narmada and Tapti )
- Volcanic disturbances
- Vertical forces sometimes push molten rocks called magma midway or all the way to the surface in a process called volcanicity or cause the earth crust to tremble in earthquakes.
The various external forces that working against constructive forces
The action of Exogenic forces results in wearing down and hence they are considered as land wearing forces. Once the internal forces produce the landforms, external forces start to modify or reshape their surface immediately.
- Forces of erosion:
- Causes pieces of rocks to decay or weather and tear off from their parent rock.
- The active wearing away of the earth’s surface by moving agents like running water, wind, ice and waves.
- Example: formation of waterfalls, rapids, sea caves, sprayholes.
- Forces of transportation:
- The removal of the eroded debris to new positions. Various types include mass movements like Soil Creep, Landslides.
- Example: Formation of Sand dunes in deserts, Barchans etc.
- Forces of deposition:
- Cause the materials to be deposited in the new location.
- The dumping of the debris in certain parts of the earth, where it may accumulate to form new rocks.
- Example: Beaches
- The gradual disintegration of rocks by atmospheric or weathering forces. They are of two kinds
- Chemical Weathering: basic process by which denudation occurs. Extremely slow and gradual decomposition of rocks due to exposure to air and water. Solution, Oxidation and Decomposition by Organic Acids are few processes.
- Physical or Mechanical weathering: physical disintegration of a rock by the actual prising apart of separate particles. Repeated temperature changes, Repeated wetting and drying, Frost action and Biotic factors are processes.
- Human activities leading to destruction: Man has a profound effect on the land, in many ways, and has done so for.
- With the advent Agriculture. This in itself has a marked influence on land through several mediums, land clearing, leading to deforestation on a global scale.
- Grazing leading to increased greenhouse gasses and large tracts of land made suitable for livestock grazing.
- Deforestation is still happening today on a massive scale endangering the very ecosystem which increases the pace of erosion.
- We use open cast and other mining methods, transforming landscapes as we go.
- Divert river courses and create dams flooding thousands of miles around the globe.
- Our emissions induce global warming which in turn has caused sea levels to rise, which are due to rise further, devastating coast lines and possibly changing the landscape forever.
Earth’s crust is undergoing geological changes caused by the internal processes (earth movements, earthquakes, volcanoes, etc.), which create new relief features, such as mountains, plateaus and plains. Meanwhile, there are external processes that are working vigorously to wear away the surface. The interaction of the internal and external processes gives rise to the great diversity of present-day landforms.
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